Download Hummel Bird build manual Build manual

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Hummelbird Kit
Name: _________________________
Kit / planholder # ________________
Start Date: ______________________
First Flight: _____________________
Purpose of this Publication
While this instruction manual has been provided with your plans/kit to assist you in
building your Hummelbird, it does not provide all information necessary to complete the
project. It is assumed that the builder will have some previous knowledge (or will assume
responsibility for obtaining that knowledge) of basic aluminum aircraft construction. This
manual should not be viewed as a complete step by step set of instructions.
Builder Support
You are encouraged to call Hummel Aviation with any technical questions you may have.
You are also encouraged to use the technical assistance resources available through the
EAA (reading material, technical advisors, etc).
Finally, support from peers/other builders can be invaluable. Seek out others in your area
who have experience building either a Hummelbird or similar project and introduce
yourself. There are also groups on the internet that share information, tips and lessons
learned, including the forums on www.flyhummel.com.
Updates to Manual
Updates to this manual will be posted on the Hummel Aviation website. It is the builder’s
responsibility to periodically check for updates. If access to the internet is not available,
builders are encouraged to periodically call Hummel Aviation to request info on updates.
Contact Info:
Hummel Aviation
16288 Co Rd D, Bryan Ohio 43506
phone: 419-636-6700 fax: 419-636-4522
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INTRODUCTION
This manual is to be used along with a set of Hummel Bird plans and grants the purchaser the
right to construct and use one aircraft for his or her personal experimental use.
The Hummel Bird was designed as a sport aircraft; not intended for any aerobatics. This is a
"minimum" airplane which will provide its owner with years of fun and service for a relatively
small outlay of resources. Deviation from the plans is not recommended unless approved by the
designer since performance and structural integrity may be jeopardized.
Now just a word about the plans. The Hummel Bird in it's original form was a taildragger and
previous versions of these plans were for the taildragger only. Such was the interest in a trigear
version, that it was decided to develop, build, and test the trigear configuration and now, it is
offered here as an option. It is realized that a taildragger is not everyone's "cup of tea". Also, if
you've had no prior experience and no way of getting formal taildragger instruction, then your
preferences may turn toward the trigear configuration. The purpose of this option is to allow
both types of pilots to enjoy the simplicity and low costs of this airplane without compromising
skills.
The original plane was built with the narrow fuselage but again, general preferences tended
toward the wider version. Even though the writer has found the narrower version to be
completely adequate, the plans are now based upon the wide fuselage version only.
The wing-tip extensions were not part of the original plane but they have proved to be such a
performance enhancement that they are included in the plans. Please note however, that the
design limit of +/- 6g applies only to the basic wing, without wingtip extensions. If you do install
the wingtip extensions, the design limit then becomes +/- 5g. When you consider that most of
the commercial light planes, like Cessna and Piper, have design limits well below this, then it is a
small concession to pay for an increase of 100 fpm in climb, 3-5 mph lower stall, and a 33%
improvement in glide ratio.
The two cylinder V. W. engine is the only engine recommended. Other engines such as
Rotax etc., have had limited application in this plane but such a small track record exists that
virtually nothing can be said regarding their use. The 1/2 V. W. engine on the other hand, has
demonstrated reliability and fuel economy. If you build your own engine, it will be far cheaper
than anything you can buy. Besides, building your own engine removes that mystique about
factory engines which often scares owners away when it comes to thoroughly inspecting and
evaluating the engine. Let it be said right now that a reliable, aircraft-quality engine can be built
by anyone who is careful and meticulous. Experience is a plus but not a requirement. Of
course, you can purchase an engine from Hummel Engines (www.hummelengines.com).
The 1/2 VW engine can be built as a basic 30 HP motor and this is definitely the least expensive
way to go. Or for a few hundred dollars more, you can get horsepowers up to 37 HP. Morry
Hummel and myself have been using the 30 HP version almost exclusively in this plane and
have found it to have adequate horsepower for most situations. Having said this, if you intend to
fly from airports where density-altitude is a consideration, then the larger (37 hp) will no doubt
perform better. A few years ago, Mosler Motors and Global manufactured engines that were
basically equivalent to the 1/2 V.W. and these would be entirely suitable if you can pick one up
second-hand but watch out—that perception of building an inexpensive airplane will begin to
evaporate.
Before starting your project, be sure to register with the FAA or MOT and advise them of your
intent to build. They will then send you all the necessary forms that must be completed as the
project matures. Also, they will send information regarding what stage of progress inspections
are required. Be sure to join your local EAA chapter for the encouragement and wealth of
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information available. As you encounter problems during the course of your project, you will
have someone to call upon for help. You can also find peer-to-peer help on the forums on
Hummel Aviations website (www.flyhummel.com/forums).
Remember also, that before your newly completed plane can fly, it must carry the proper
registration, identification, and posses a valid weight and balance form.
Tools you will need:
-
Hacksaw
Sheet metal ships; one left cutting, one right cutting for short,
sharp curves; and one long blade set for straight cuts
Files; assorted fine cutting fine metal files
Hammer; plastic tipped for bending aluminum flanges
Electric drill; variable speed with an assortment of small
drills. A numbered and lettered drill set is best
Cleco pliers and clecos; 50 - 3/32", & 50 - 1/8"
Rivet gun and bucking bars; more about this later
Pop-rivet gun
Access to a sheet metal brake at least 3' long
Stop-countersink tool for countersinking rivet holes (optional)
Home made water-hose level; made from 8', 3/8" dia.
clear tubing filled with coloured water.
90 degree, angle drill attachment would be useful.
Saber saw (to cut form blocks)
One advantage of belonging to an EAA chapter is that you will probably be able to borrow some
of the tools necessary from other members.
The use of solid rivets (AN) wherever possible is strongly recommended even if you have never
used this equipment before. Such was the case of the writer and even after borrowing a rivet
gun, an air compressor was still needed. That was solved by salvaging a compressor from a
discarded refrigerator and then hooking it up to a throwaway freon bottle. There it was; a quiet
running air compressor capable of 100 psi for next to nothing. The main wing spar was riveted
first as a learning exercise since it was easy to drill out poorly set rivets and to replace them. It
did not take long to get the hang of it. The bucking bar can be any chunk of steel with a smooth
surface to set the rivets, but it should weigh at least 3 pounds and more if possible.
For this project, riveting can be a one-man job; that is, one person can quite comfortably hold the
rivet gun in one hand while supporting the bucking bar with the other. Riveting information is
available from EAA publications and more exotic bars for those hard-to-reach places can be
welded up to get the desired shape. 1/8" dia. rivets AN470AD (dome head) or AN426AD
(countersunk) can be used throughout; however, 3/32" AN426AD solid rivets, which are easier
to use, can be used for the wing and tail skins (if you choose this option), and to secure
nutplates. Some pull-type rivets are needed, especially for the top of the wing skins. The
recommended pull rivets are:
AVEX Cat# 1682-0412 (previous p/n was 1604-0412) (thickness range up to ¼” thick)
AVEX Cat# 1661-0414 (thickness range ¼” – ½” thick)
These rivets are 1/8" dia., but the #1682-0412 are countersunk rivets. For use in noncountersinking applications, your rivet gun will need to be modified. The nose of the mandrel
which is normally flat, must be countersunk using a 1/4" drill to allow the head of the rivet to be
pulled up into the mandrel as the rivet is being set. This will force the head to fold over slightly
leaving a nicely formed crown. You may have to experiment a bit as you drill the end of your
mandrel to get the proper countersunk depth. This method will give you a finished rivet with a
lower profile head than could be obtained with conventional dome-head rivets.
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LIST OF MATERIALS
If you live near a major city, most of the materials should be available locally. Check your
"Yellow Pages" for aluminum and aircraft part suppliers. There are some excellent mail-order
suppliers that have established a good track record and if you write to them for a catalogue, they
will oblige for a nominal fee of a dollar or two for postage. Often, it will be cheaper to obtain your
parts through the mail even paying the shipping costs, duties, etc. The following mail order firms
are suggested:
Hummel Aviation
Bryan, Ohio 43506
www.flyhummel.com
419-636-6700
Aircraft Tool Supply
www.aircraft-tool.com
P.O. Box 370
Oscoda, MI 48750
800-248-0638
International Customers call 1-989-739-1447
Great Plains Supply Co. Inc.
http://www.greatplainsas.com/
P.O. Box 545
Boystown, NE 68010
1-800-922-6507
Rand Robinson Engineering
15641 Product Lane Suite A-5
Huntington Beach, CA 92649
714-898-3811
Aircraft Spruce
www.aircraftspruce.com
Order Dept. 877-477-7823
M & K Aviation, Inc., (AN hardware)
5412 Hwy. 62,
Jeffersonville IN 47130 Phone
(812) 282 5493
Air Parts, Inc. (aluminum and 4130 steel)
2400 Merriam Lane
Kansas City, KS 66106
www.airpartsinc.com
800-800-3229
Wicks Aircraft Supply
410 Pine St.
Highland, IL 62249
www.wicksaircraft.com
800-221-9425
Dillsburg Aero Plane Works
114 Sawmill Rd.
Dillsburg, PA 17019
717-432-4589
Engines:
Hummel Engines
16777 County Rd. D
Wauseon, Oh 43567
(419) 335-2147
humeng@fulton-net.com
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Some people prefer to order all parts and to have them on hand before starting the project and
this is fine if you choose this option. Others, like myself, prefer to ease into the project by buying
only the parts needed for the tasks at hand. It doesn't seem to hurt as much this way since the
cost can be distributed over a longer period of time. For those of this latter persuasion, here's
what I recommend: from the complete parts list, buy these parts first:
-
the sheet of .040",
1 sheet of .020",
the sheet of .025",
12' of the 1/8" angle,
and the 8' of 3/16" angle.
With an outlay of $400 or so, you will now have all the aluminum to build the fuselage and to
make a few wing ribs.
Now just a word on the aluminum to be use for skins, ribs, and bulkheads. The material called
out for these items is aluminum grade 2024-T3 which is great if you plan to keep your plane
polished instead of painting it. If you opt to paint your plane, then aluminum grade 6061-T6
(which is cheaper) may be substituted and even though it has about 80% the strength of 2024T3, the overall structural integrity of the plane will not be compromised. Note from Morry: Those
who want to prime or paint their airplane, use PPG Part # DX1791 & DX1792. This is the least cost,
easiest to use and best you can buy—spray or brush on.
ALUMINUM
- 1- sheet 4'x12', .040" 2024-T3 Alclad (bulkheads, spar webs, etc)
- 3- sheets 4'x12', .020" 2024-T3 Alclad (skins, ribs)
- 2- sheets 4'x12', .016" 2024-T3 Alclad (skins, ribs, T/D)
- sheet 4'x6', .016" 2024-T3 Alclad (for wingtip extensions)y
- sheet 4'x6', .025" 2024-T3 Alclad (skins, ribs)
- 84', 1 1/2"x1 1/2"x1/8" angle 6061-T6 (spar caps, side rails)
- 8', 1 1/2"x1 1/2"x3/16" angle 6061-T6 (firewall backup, misc struc)
- 24', 1/2"x1/2"x.065" square tubing 6061-T6 or 6063-T6 (W/S & T/D Bows)
- 12', 3/4"x.049" tubing 6061-T6 (push rods)
- 12', 1/2"x.035" tubing 6061-T6 (push rods)
- 3', 5/8"x.049" tubing 6061-T6 (push rod)
- 3', 1/2"x.049" tubing 6061-T6 (push rod)
- 12"x6"x1/8" plate 6061-T6 (blkhd "E" reinforcement)
- 12'x1 1/2" wide x1/8" thick bar 6061-T6 (wing pnl spars, spar att.)
STEEL
- 2', 1 1/2"x.058" tubing 4130N
- 4', 1 3/8"x.058" tubing 4130N
- 2', 1 1/4" x .058" tube (req'd only for main gear suspension)
- 1', 7/8"x.058" tubing 4130N
- 12', 3/4"x.035" tubing 4130N
- 1', 9/16"x.058" tubing 4130N
- 2', 3/4"x.090" tubing 4130N (axles)
- 2', 1/2"x.035" tubing 4130N
- 1'x1'x.125" plate 4130N
- 1'x2'x.090" plate 4130N
- 1'x2'x.065" plate 4130N
- 2'x2'x.020" stainless steel or galvanized for bulkhead "A"
(Galvanized is cheaper & easier to work with.)
- Additional requirements for Trigear version only
- 1' - 1 1/2" x .058" tube
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-
2' - 1 3/8" x .058" tube
4' - 1" x .065" tube
1' - 5/8" x .090" tube
HINGES
- 10 - pieces 6" long, 1 1/2" wide, extruded aluminum MS20001-P4 (Ailerons & elevators)
- 1 - piece 14" long, 1 1/2" wide, extruded aluminum MS20001-P4 (Canopy)
ROD END BEARINGS
- 14 - 1/4" bore, 1/4-28 shank; Heim HM-4M (Airparts Inc. sells similar units for ≈ $4.20)
- 4 - Same as above for rudder pedal option
-
- Additional for trigear version
3 - 1/4" bore x 1/4-28 shank. Order from Airparts Inc.
NYLON BEARINGS (These are BOSTON GEAR products can be obtained from
a bearing supplier)
- 8 - 3/16" bore with flange; Boston Gear, cat.# NF35-2 1/2
- 2 - 1/4" bore with flange; Boston Gear, cat.# NF46-3
ENGINE CONTROLS
- Throttle: Push-pull type with friction lock - Cessna 150 type
- Carb heat: Automotive choke cable
- Mixture: Vernier type - Cessna 150
- Magneto kill switch: Heavy duty toggle switch - contacts close to stop engine
INSTRUMENTS
- Air speed 0-140 or 0-160 MPH
- Sensitive altimeter
- Aircraft compass
- Engine oil pressure - Automotive, mechanical type
- Engine oil temperature - Auto coolant temp, mechanical type
- Tachometer: 0-3500 or 0-5000 RPM electric type powered from
magneto. GREAT PLAINS 90-2AT3-2 or 90-2AT5-2. If this is
used with a Fairbanks Morse magneto, the positive
terminal is grounded and the negative terminal
connects to the magneto's kill post via a 1/4 amp.
fuse.
Note: A better tach. is available from:
Microflight Products, Inc., 16141-6 Pine Ridge Rd.
Fort Meyers, FL. 33908. Phone (813) 454 6464.
It is a digital unit, part # TA010, and has a
built in hourmeter, installs in minutes, accurate
to the nearest `tens' of RPM.
PROP SPINNER 10" or 12” diameter complete with bulkhead and backplate; (Great Plains
Aircraft)
SEAT BELT
Aircraft shoulder harness, see Wag Aero catalog.
WHEELS
 11" overall diameter complete with 5” aluminum wheels mechanical brakes and tires and
tubes listed below. These are the same as used on the Sonerai 2, and are available
from Great Plains Aircraft Supply Co. Inc., (Wheel and brake kits are also available directly
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from Hummel Aviation.)
- 11-400 x 5 tire, cat# J1285
- 11-400 x 5 tube, cat# J1310
Notes:
 340x 300 x 5 (10.5” KR) tire kit must be used it if using Morry’s fairings or Hummel Aviation’s
prefab nosegear.
 For the trigear version, you will need to buy 3 wheels (2 with mechanical brakes)
AN HARDWARE LIST
- Bolts: Includes extras for trigear version
QTY
SIZE
QTY
18
AN3-4A
2
14
AN3-5A
9
7
AN3-6A
8
10
AN3-7A
17
9
AN3-10A
2
6
AN3-11A
7
7
AN3-12A
2
4
AN3-13A
22
1
AN3-14A
4
1
AN3-15A
2
3
AN3-16A
2
1
AN3-17A
2
1
AN3-21A
2
1
AN3-22A
4
2
AN3-60A
2
2
1
AN5-10A tail spring
4
2
4
AN8-13 wing attach
4
SIZE
AN4-4A
AN4-5A
AN4-6A
AN4-7A
AN4-H7
AN4-10A
AN4-10
AN4-11A
AN4-12A
AN4-13A
AN4-14A
AN4-15A
AN4-16A
AN4-17A
AN4-20A
AN2-25A
AN6-26 eng mount
AN6-35A lndg gear
AN6-42 (hole in shank)
- Screws: Qty- 100, AN526-632 (6-32, 3/8" long )
- Nuts:
QTY
SIZE
90
AN365-1032 (3/16" Self locking)
110
AN365-428 (1/4" Self locking)
2
AN310-428 (1/4" Castle Nut )
2
AN365-624 (3/8" Self locking)
4
AN310-624 (3/8" Castle )
4
AN310-820 (1/2" Castle )
2
AN310-1018 (5/8" Castle )
- Washers:
- Nutplates:
QTY
SIZE
QTY
SIZE
100
AN960-10 (3/16)
3
AN366F-1032 (3/16”)
100
AN960-416 (1/4")
16
AN366F-428 (1/4")
10
AN960-616 (3/8")
1
AN366F-524 (5/16")
4
AN960-816 (1/2")
50
#6 Two-lug fibrelok for 6-32
screws -- buy from Airparts
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SOLID RIVETS (to be used instead of pull-rivets)
QTY
SIZE
QTY
SIZE
2 oz
AN470AD4-4
2 oz
AN426AD4-4
1 oz
AN470AD4-5
1 oz
AN426AD4-5
4 oz
AN470AD4-6
4 oz
AN426AD4-6
2 oz
AN470AD4-7
1 oz
AN426AD4-7
9 oz
AN470AD4-8
4 oz
AN426AD4-8
1 oz
AN470AD4-9
3 oz
AN426AD3-4 (for wing
& tail skins - optional)
PULL RIVETS
For those of you who do not wish to use the solid (bucked) rivets, a quantity of 4000 Avex
#1682-0412 and 300 Avex #1661-0414 will be needed.
For those hardy souls who decide to use as many bucked rivets as possible, you will still need
about 1000 Avex #1682-0412.
SUSPENSION SPRINGS
Note: If you opt for the suspension-type gear, you'll need 2 for the taildragger or 3 for the trigear.
These springs are Die (as in "tool and die") springs, 1 1/4" OD, 4 1/2" free length. Spring
constant = 160 lbs. per inch. They are blue in color and are made by PRODUCTO, cat # MP-59.
Check your yellow pages for a local supplier or go to a tool and die maker where you may be
able to get used springs for nothing. By no means are you limited to this type of spring since
valve springs for a diesel engine have even been used. Whatever spring you decide upon,
check it's spring constant by compressing it with a known weight and measuring the deflection of
the spring. Springs are also available from Hummel Aviation.
NOTE: Hummel Aviation has many prefabricated parts available. See the website for photos, pricing, etc.
www.flyhummel.com
GENERAL CONSTRUCTION NOTES
When bending aluminum tabs, flanges, angles, etc., bend slowly and take your time. Always drill
and deburr the 3/16" stress relief holes first. Observe proper bending radius which is .06" for
.016" & .020" 2024-T3, .09" for .025"2024-T3, .16" for .040" 2024-T3, and .56" for 1/8" 6061-T6.
Bending with a sharper radius than these will severely compromise the integrity of the finished
part.
When cutting or sawing aluminum, file all edges smooth and use emery cloth for the final finish.
Inspect the edges for cracks or nicks.
Take care when drilling holes for bolts or rivets that they are not drilled oversize. Any hole drilled
in aluminum will result in burred edges. Remove these with a larger size drill turning it by hand
or at a very low speed to prevent countersinking the hole. Make sure all the chips are cleaned
away before assembling.
All interior aluminum surfaces should be given a light coat of zinc chromate primer for corrosion
protection. A light coat is emphasized here since heavier coats tend to flake off. Just give the
surface a light spray; no need to cover the surface evenly. Coat overlapping surfaces before
bolting or riveting them as well. Zinc chromate primer is available at auto supply stores. Another
product that can be used to protect against corrosion is a "wash primer" used in aircraft finishing.
It can be purchased from most aircraft supply stores and is cheaper and more durable than zinc
PAGE 9
chromate. Morry recommends PPG Part # DX1791 & DX1792, he says this is the least cost, easiest to
use and best you can buy—spray or brush on.
The procedure for assembling skin panels and parts is to fit it in place, holding it there with tape
or clamps; drill and cleco as many holes possible, remove the panel and deburr all holes, prime,
then reassemble with clecos and rivet or bolt in place.
Allow a distance of at least 1½ times the diameter of the hole from a bend when drilling and 2½
times the diameter from an edge.
Make drill guides for rivet holes from thin strips of metal when installing the wing skins. Measure
out the required rivet spacing to miss the rib flutes and drill undersize holes. Then with the
proper sized drill, enlarge the holes as required. Drill guides are available from Hummel Aviation.
ONE FINAL ADMONISHMENT
Before you begin construction, let it be stressed that the final success and performance of your
plane will be more or less determined by how well you stick to the plans. Resist the temptation
to "improve" the design by adding parts or beefing-up here and there. The end result will
generally be a heavier plane and/or a weaker structure. Resist the temptation to make this
plane into something that was never intended. Additions tend to be compounding such as
adding IFR electrical equipment (believe me, it's been tried). Where will you get the power to
drive all this stuff? You'll then have to add a generator or a battery and on it goes. The weight
goes up and the performance and safety margin go down. You would not believe how a few
(seemingly insignificant) ounces added here and there will end up as pounds of overweight.
This is a strong plane, overbuilt perhaps, in some areas. Accept it as it is and don't let your
dreams and fantasies get carried away. Adopt a "KEEP IT LIGHT" mentality and become a
fanatic throughout the project. Now let’s get on with it.
BUILDING THE HUMMEL BIRD
FUSELAGE CONSTRUCTION - SHEETS 2, 3, 4, 5, 6
Begin using the general sequence outlined on sheet 2. Make forming blocks for the bulkheads
from 3/4" plywood using the inside line of the full-scale patterns in the prints. Use a coarse file to
smooth the forming block and round the edges to a radius of at least 3/16" to give an acceptable
bending radius for bending the bulkhead tabs. Trace the outside line of the pattern, the
centerlines, cut-lines & bend-lines for the flanges, and the notch lines for the tabs on aluminum
and cut out the blank. Drill and deburr the 3/16" stress relief holes at the appointed spots and
cut the notches where shown. Clamp the blank between the forming block and another piece of
plywood and place in a vise. Gently bend over the tabs with a soft faced mallet about 20
degrees at a time until they are all bent over. Cut out the center of the bulkhead, drill the 3/16"
holes and bend over the flanges in a similar fashion.
After all bulkheads are formed, construct the alignment beam and mark the center lines top and
both sides. Assemble the bulkheads "E", & "C" in their appropriate spots and secure them with
scraps of wood nailed or screw-nailed to the beam. Bulkhead "D" should be in it's approximate
position but may need to be shifted to ensure a straight line top & bottom and both sides. Make
sure both center lines line up with those on the beam and that the bulkhead “E” & “C” is
positioned at the correct angle. Fit the fuselage stringers top and bottom between the bulkheads
and clamp the bent-over end of the stringer to the bulkheads. Sight down the top and bottom
stringer to ensure that each is straight and adjust the position and angle of "D" to eliminate any
PAGE 10
unevenness. Now, fasten "D" to the beam via wood and screws and rivet the ends of the
stringers to the bulkheads. Also, keep in mind that no permanent riveting is to be done on "E" at
this time. This will enable "E" to be removed after the skin is installed, so that the vertical
stabilizer spar can be hard riveted to it.
For the skin from "E" to "D", measure the outside circumference of the bulkheads and add about
3/4" for overlap. If you are brave, draw the skin layout on aluminum and cut it out. If not, make a
cardboard pattern first, trim to fit and then transfer that pattern to the aluminum. Wrap the skin
around "E" & "D" with the overlap on the bottom and secure with fiberglass tape. The skin
should be wrapped as tightly as possible using large diameter screw clamps or nylon tiedowns
around the bulkheads with pieces of carpet in between to protect the skin surface. When you
are satisfied with the fit, use a felt-tipped pen and tape measure to mark the rivet hole locations
around bulkheads "D" & "E", along the bottom seam and along the top where the stringer will be
secured. Drill and cleco all holes. Remove the skin, deburr, prime, reposition & cleco. Rivet
bottom seam and stringer and rivet top skin to top stringer. Using 6 or 8 pull-rivets, temporarily
rivet skin to bulkhead "D" and file the rivet heads as flush as possible.
Measure and cut skin "D"-"C" allowing a 3/4" overlap at the bottom seam, 3/4" overlap at "D",
and a 5/8" overlap ahead of "C" for the installation of the turtledeck bow. If skin "D"-"C" is made
from two pieces, be sure to allow a 3/4" overlap where they meet at the top. Fit the skin in
position and tighten using the large screw clamps. Bend the tabs on bulkhead "C" below the
siderails so that they are in line with bulkhead "B" and notch the skin so that it will fit tightly
against the tabs without any bulges. Drill & cleco. Drill from the inside out (back-drill) at
bulkhead "D" using the rivet holes previously drilled. Remove the skin and drill out the temporary
rivets in "D". Replace the skin and back-drill the 6 or 8 remaining holes in the skin previously
blocked by the temporary rivets. Remove the skin, deburr, and prime then replace and cleco in
position. Rivet skin to bulkhead "D", bottom stringers, and top of bulkhead "C" above siderails.
Use 5 or 6 temporary rivets to secure skin to "C" below the siderails. Install the shoulder harness
support and rivet to the top skin and top stringer. Rivet the remaining holes in the skin to the top
stringer. At this time, remove bulkhead "E" and set it aside until the installation of the tail group.
Install bulkheads "B" and "A" on the alignment beam. Fit the siderails in place and cut out
clearances in bulkheads "C" & "B" to accommodate. Install the 3/16" angles and motor mount
supports in position on bulkhead "A" then bolt to the siderails. Install the bottom skins and rivet
to the bulkheads. Temporarily rivet the sides of the skins to the siderails with 3 or 4 rivets per
side and file the heads flush. Install lower motor mount supports and braces. Remove alignment
beam and support fuselage on sawhorses either side.
RIB CONSTRUCTION - SHEET 7
Using the inner line, trace the full-size outline of the wing rib on two pieces of 3/4" plywood.
Round the edges slightly with a coarse file and sand smooth. Using a 1/2" round file, make
grooves 1/4" deep along the edge of one of the formers to accommodate the forming of the
flutes as the flange of the rib is bent over. Make sure that the flutes will be located between the
rivet hole positions used when installing the skins. Cut the rib blanks from the appropriate
aluminum using the outer line of the outline as a guide. Note that the nose ribs and rear rib
portions are formed separately. Cut all blanks, stack together and drill the 1/4" guide holes
through the complete stack. Bolt the blanks one by one between the wood formers and secure
with the 1/4" bolts through the guide holes in the former. Gently bend the flange over all around.
Then take a steel rod 3/8" diameter, and hold it above the flange over one of the grooves in the
wood former. Force it into the groove with a few sharp blows of a hammer and repeat for the
rest of the flutes. This will then produce a rib with nicely formed flanges. Further hand fluting
may be required to straighten the rib.
Cut the lightening holes where indicated and flange the edges with a flanging tool or a
PAGE 11
male/female plug made from wood. Add the 3/4"x3/4"x3 1/2" angles used to make the rib more
rigid; see sheet 7.
Identify each rib with a felt-tipped marker. Install the rib-attach brackets to the rear rib portions.
The nose ribs attach to the spar by bending over the flange at the end.
AILERON BELLCRANK - SHEET 7
The bellcrank is mounted on the inside face of the first wing panel rib (ribs 7L & 7R) as shown
on sheet 7. Before this can be done, the rib web must first be beefed up with extra material so
that there will be no flexing whenever the aileron control is actuated. The bellcrank is offset
about 15º to the vertical so that the pushrod to the aileron control horn operates in a straight line.
Mount the bellcrank to the rib before attaching it to the spar. Make sure that it moves freely and
there is no play in the pivot point. Also, make sure that the short arm of the bellcrank is the one
that connects to the aileron.
The bellcrank is completely accessible for maintenance and inspections through the gap
underneath the wings where the wing panels attach. When a wing panel is removed, the aileron
control rod to the cockpit is disconnected from the bellcrank.
SPAR CONSTRUCTION - SHEET 8
Before drilling any holes in the spars, make sure you have chosen the proper rivet size and rivet
pitch as detailed on sheet 8. It is recommended that you use the hard or "bucked" rivets when
fastening the spar caps to the .040" thick web. You have a couple of options here and if you
select the AN470AD-5xx (5/32") rivets, less of them will be needed to achieve the same strength
as the AN470AD-4xx (1/8") rivets. The decision is yours and if your rivet gun can handle the
larger ones, use them. Pull rivets (Avex) can be used but you will need almost twice as many to
equal the strength of the AN470AD-4xx.
Start by making the spar caps from 1 1/2"x1 1/2"x1/8" 6061-T6 angle. Note that the angles
required for the center section are 72" long which means that you can buy a standard length
(12') of angle and get 2 caps out of it. Check with your supplier and you may find that the
standard length exceeds 12' by a few inches. Cut the spar webs from the .040 sheet. Build the
spar assembly box from wood, fit and clamp spar caps and web for the center section in place.
Make sure that the outer corner of the inner angle is rounded as well as the edges of the web to
ensure a good fit. Mark rivet holes and bolt holes evenly and accurately also marking the rib
positions. Drill and cleco as shown. Remove all pieces and deburr. Reassemble and drill the
holes for the 8 bolts at each end of the spar. Drill them out to say 15/64" (undersize) for now
and bring them up to size later as needed. Be sure to clamp the 1 1/2"x5 7/8"x1/8" filler plates in
place before drilling. It would be a good idea to drill 1/8" holes for 3 or 4 rivets to secure each of
these pieces since the bolts will not be installed till later. Deburr all holes and prime web & spar
caps.
Again, reassemble with clecos and begin riveting with AN470AD rivets. Do not rivet the holes
used to attach the ribs at this time. Start riveting at the center of the spar working outward and
rivet every 8th hole. When you get to the end, repeat beginning at the center working outward
riveting every 4th hole and so on. This is necessary to keep the spar straight because it could
have a tendency to curve. Check this often as you rivet.
Make the spars for the outer wing panels in a similar fashion but before riveting, make sure to fit
the wing attach brackets and drill the 1/4" holes. As you rivet, the tendency for the spar to curve
PAGE 12
will be more severe. Take your time and check it often to prevent this. The 1/8" holes on top
and bottom surfaces of the spar caps spaced 1" apart, can be drilled after riveting since they can
easily be deburred. Cut the lightening holes in the web with a hole saw or fly-cutter but do not
attempt to flange them. You may find it helpful to use a few small nuts and bolts located in say,
every 4'th rivet hole to help keep the spar straight as you rivet it.
If you find that your spar has warped slightly during the riveting process, it can be straightened
by placing it on two blocks of wood on the floor. Use a hydraulic jack (2-ton capacity) between
the top of the spar at the center of the span and say, the support beam of your house to apply a
downward force. Be careful, make small corrections then check for straightness each time. Try
to get your spars within 1/16" of a perfect line.
Fit all spars together and shape the edges with a file to give the proper dihedral. Assemble the
wing attach brackets to the outer spars with 1/4" bolts and clamp them securely to the center
section. Again, check for proper dihedral. Now locate the 1/2" holes for the wing attach bolts.
Start drilling and as you get close to size, grind the flutes of a 1/2" drill slightly undersized and
use a 1/2" reamer to accurately fit the bolts. The fit should be snug but not so tight that a
hammer is necessary to get the bolts in or out.
CENTER WING CONSTRUCTION - SHEETS 2 & 7
The following steps may seem to be very complex and even confusing. Please bear in mind that
the sequence in which the various steps are done is very important. It is best to read through
the steps a few times until you get a feel for what's going on.
Cut the holes in the side of the fuselage behind bulkhead "C" and install the rear spar. Clamp it
in position to the horizontal flange of "C" and bend the flange as necessary to align the spar.
Measure the distance from the siderail to the bottom of the spar keeping it in mind when
installing the main spar. Using one of the rear ribs as a guide, mark the side of the fuselage to
be cut out for the main spar.
Assemble the main spar in fuselage noting the alignment required. Forward spacing from the
rear spar is determined by clamping ribs 6L & 6R in position. Secure the spar as outlined on
sheet 4 and check it's alignment often. Install front and back spar side covers. Go back now to
the rear spar, recheck the alignment and bolt it to the bulkhead flange. Install the flange stiffener
strip and the seat belt brackets.
Clamp all ribs in place per sheet 7. Rivet ribs to the main spar only at this time. Be sure to
install 1/8" filler strips between the spar face and rib attach brackets on all nose ribs and rear-rib
portions. To help in locating rivet holes later on, take a felt-tip marker (red) and draw a line down
the center of all rib flanges.
Cut and fit the leading edge skin clamping it to the spar in position. Check wing alignment. Mark
a straight line along the top & bottom edges where it will be fastened to the spar caps and
measure off 1" spacing to correspond to the rivet holes to be drilled. Drill 3/32" holes through
the skin and the spar caps.
Fit the landing gear at this time ensuring proper alignment then set aside until the skins have
been installed.
Bend bottom skin and fit into position. Secure the front edge with 3 or 4 clecos into the bottom
spar cap. Clamp the rear tab of the ribs to the trailing edge ensuring that the vertical portion of
the bottom skin is sandwiched in position per section A-A, sheet 7. Alignment of the bottom
PAGE 13
wing surface is paramount and must be checked often with a level spanning the chord from main
spar to rear spar, at the wing root and at the outer end on both sides of the fuselage. The level
must show consistent readings in all positions to eliminate any twist in the wing. Drill and cleco
the rear flange of the ribs to the rear spar. Use a felt-tipped marker to mark off the rivet hole
positions on the skin that will be used to secure the bottom flange of the rib to the skin. As you
drill the rivet holes in the skin to fasten the bottom rib flanges, keep a light touch on the drill so
that you don't drill through the material below. Look through the hole for the red line on the rib
flange then drill through it as well. You may have to shift the rib sideways slightly to get it to line
up. Use the rivet spacing shown on the rib outline on sheet 7. Drill & cleco for 3/32" rivets.
Also mark the rivet hole positions on the flanged portion of the skin that fastens to the rear spar
then drill with a 1/8" drill.
Reinstall the leading edge and use a 3/32"drill to drill holes through the bottom skin using the
holes in the leading edge as a guide. Enlarge with a 1/8" drill and cleco. Remove leading edge
skin. Mark a straight line down the center of the top & bottom flanges of the nose ribs. The 3/32"
rivet holes are marked out on the leading edge skin and drilled first. When the leading edge is
installed, the ribs can be shifted with a piece of wire to place the line on the rib flange right under
the hole in the skin. Replace the leading edge and drill the rivet holes in the rib flanges.
Remove leading edge & bottom skins, deburr & prime. Countersink (if AN426AD rivets are
going to be used) the holes in the lower spar cap of the main spar and in the rear spar using a
countersink tool or a 1/4" drill specially ground to an angle of 100 degrees. Replace both skins,
cleco and check wing alignment. Dimple the skins over the countersunk holes per step 40,
sheet 2 and rivet the ribs to the bottom skin with AN470AD (or AN426AD) rivets, and the leading
edge & bottom skins to the main spar only, using AN426AD rivets. Do not rivet skin to rear spar
at this time. Install the landing gear through cutouts in the leading edge.
Cut and fit top skin and clamp in position. Drill 3/32" holes through the front edge using the
holes in the leading edge skin as a guide then open up the holes with a 1/8" drill. Again check
for correct wing alignment and twist. Use the same method used for the bottom skin, to drill the
rivet holes that will fasten the top skin to the top rib flange. Back drill through the previouslydrilled holes in the rear spar to make the holes in the rear edge of the top skin. Remove top
skin, deburr & prime. Countersink the holes in the top spar cap and in the rear spar then open
up with a #30 drill. Reinstall the top skin and dimple it together with the leading edge skin over
the countersunk holes in the top spar cap. Rivet with AN426AD rivets. Next, rivet the skin to the
nose-ribs starting at the front working backwards using pull-rivets. Do not rivet the trailing edge
to the rear spar at this time. This will be done later when the trailing edge piece is installed. As a
general rule, use 1/8" diameter rivets to secure the skins to the main spar caps and to the rear
spar. 1/8" or if you prefer, 3/32" rivets can be used to secure the rib flanges.
MAIN GEAR - SHEETS 11 & 12
There are two ways you can go with the main gear suspension: with or without. The drawings
show the taildragger gear without suspension on sheet 11 and the trigear with suspension on
sheet 12. It was done this way for demonstration purposes only and is not to be regarded as an
endorsement for either configuration. Experience has shown that main gear without suspension
is totally satisfactory even when the plane is flown from a sod field. Certainly, construction of the
solid gear is far simpler and the finished product is lighter. If you are undecided as to which type
you'd want, then it is suggested you build the solid gear first. If you change your mind down the
road, then suspension can be added without too much trouble.
You'll notice that the suspended gear (sheet 12) consists of an upper portion, lower portion, and
suspension details. To retrofit a solid gear, the upper part is virtually the same for both types.
Just eliminate the lower portion (beyond 16" as measured from the top) and build it according to
the details in the plans.
PAGE 14
After the clips have been welded at the bottom of the 1 3/8" tube for the scissor link, it will be
necessary to ream the I/D in that spot to allow the 1 1/4" O/D inner tube to slide freely. It's best
to borrow a proper reamer if you can, rather than using a file since you want to keep the I/D as
round as possible.
For the taildragger, mount the gear to the front face of the spar as shown, using the 3/8" bolt at
the top and check that it is perpendicular. The landing gear bracket is bolted to the bottom spar
cap but before drilling any holes, make sure that the centerline of the axle is 9 1/2 " ahead of the
front face of the spar. Clamp in place then drill the holes. A 1 1/2" x 1 1/2" x 3/16" 6061-T6
angle must be bolted on the rear of the spar, right behind the landing gear so that no new holes
are required. This is necessary to reinforce the spar at this point.
For the trigear, mount the upper portions on the rear face of the center wing spar making sure
that they are fitted perpendicularly to the spar. Again, before drilling the holes to attach the
landing gear bracket to the lower spar cap, check to ensure that the axle center line will be 6 1/2"
rear of the spar front face. The 1 1/2" x 1 1/2" x 3/16" angle must be bolted to the front face of
the spar to maintain rigidity. No new holes in the spar are required for this since it can utilize
existing holes.
Weld up the pieces for the lower portion and use the suggested jigs on sheet 12 to keep
everything aligned. Again, some reaming will be required to mate the axle to the assembly. The
axle is held in position with an AN3 bolt that will require a fairly long nutdriver (inside the 1 1/4"
tube) to tighten it.
The scissor links are made as shown. Bend the .063" 4160 steel cold maintaining a generous
bending radius. Heat it afterwards to cherry red and allow to cool in still air to relieve any internal
stresses. Weld the bushings in position making sure that their bores are parallel lengthways and
vertically. The best way to keep the bushings parallel during welding is to make a jig with two
1/4" dia. pins spaced the required distance apart. Then place the bushings over these pins,
mount the scissor link and weld. Weld the steel pads in place. The purpose of these are to
provide a surface perpendicular to the AN3-60A bolt to prevent it from bending when it is under
load.
The success of your efforts will depend greatly on how well you make your jigs for welding
especially for the scissors links. Accuracy here, is very important in order to achieve proper
wheel alignment. While on that subject, align both wheels so that there is no toe-in or toe-out.
This holds true for both the taildragger and trigear configuration. If, after you've done the
welding, you discover that there is a problem with alignment, you can always make minor
adjustments by heating the part to cherry red and gently bend till you get the desired results.
After welding and any adjustments made, then bead-blast (like sand blast except glass beads
are used in place of sand) all parts, prime with a red oxide primer, then paint.
Assemble everything and lubricate the sliding surfaces well. The 1 1/4" tube should slide freely
inside the 1 3/8" tube. When assembling the scissor links, use washers as spacers to make
minor alignment adjustments. That long AN3-60A bolt at the front of the scissor links is to keep
the whole assembly together and the rubber pads act as rebound bumpers. The length of the
wood dowels should be such to allow the spring to be pre-loaded by 1/4" during the assembly.
You may have to add some 1 1/4" O/D washers if the dowels are too short. The large AN3 bolts
in the scissor links can be adjusted accordingly to set the maximum extended length of the lower
gear assembly (3 1/2" from bottom of 1 3/8" tube to axle centerline). Before the dowels are
inserted inside the tubes, drill a 3/16" hole about 1 1/2" deep, in the end. This, along with a large
wood screw, can be used to extract them later if need be. That 5/8" dia tube inside the spring is
important because it prevents the spring from being over-compressed.
PAGE 15
NOSE GEAR (trigear only) - SHEET 13
Even if you are building the trigear without main gear suspension, the nose gear should be
constructed as shown. Lay out the yoke assembly (1" and 1 1/2" dia. tubes) on a flat surface
such as a table or an old door on saw horses. Mark the positions of the holes on the firewall and
all reference lines. Cut and bend the tubing as required and position it in place on the flat
surface use clamps or whatever, to hold it all in place. Tack weld the pieces then weld them
completely. Weld the .090" x 1" wide supports in place. Fit the bushings in place as close as
possible to the firewall hole marks, then tack/weld. Fit the steering bellcrank supports and weld
in position.
Now, clamp the yoke in position on the firewall, make sure the 1 1/2" tube is at right angles to
the main spar (or fuselage siderails) and back drill through the bushing holes to attach it. In this
way, the 3/8" firewall holes will be accurate and the alignment of the yoke will be correct. Weld
the upper saddle (that strip of .090" x 1" wide) to the 1 1/2" tube. Make sure there is at least
3/16" space between the strip and the tube on both sides. This is to ensure that the piece of
hose (end stop cushion) will slide over the end as shown on the drawing. Ream the I/D of the 1
1/2" tube to 1 3/8" then check that the 1 3/8" tube slides freely inside.
Lay out the nose wheel fork and 1 3/8" tube on the same flat surface again, having drawn the
necessary reference lines. Tack and weld as before then recheck with the reference lines to
ensure proper alignment. Minor corrections can be made by heating the fork and bending as
needed. The ends of the fork can be flattened by heating to cherry red then squeezing them in a
vise. After you get the desired results, weld the ends shut and stress relieve the ends by heating
cherry red and cooling in still air.
Bead blast all parts, prime and paint.
Make the steering arm collar and wood dowels as shown and fit everything in place. Cut a 1/4" x
2 1/2" slot in the upper dowel which allows up/down movement of the bolt that secures the
steering arm collar. That 1 1/4" piece of hose serves as a bumper when the gear is fully
extended and when everything is together, the spring should have a pre-load of 1/8" to 1/4".
Lubricate all sliding parts.
Make the steering linkage as shown. The purpose of the springs in the steering link is to allow
some rudder movement should the nose wheel be restricted from turning. A direct link made
from two rod end bearings could be used if desired. At any rate, make sure that the linkage is
free from binding through the vertical travel range of the nose gear. Also, ensure that the
bellcrank moves freely without vertical movement or twisting.
The rudder bar will need an extra piece to allow steering so follow the details on sheet 13.
WING PANELS - SHEETS 2 & 7
Before proceeding to this step, invert the fuselage on it's saw horse stand. Bolt the wing panel
spar to main spar and bolt the rear spar-attach in place. Rivet the ribs in position along the spar
and double check to make sure that the rear flange of all ribs are in line. Use a straight edge to
simulate the rear spar to ensure the line-up and check the face of the wing panel spar (along it's
length) with a vertical level to ensure that no twist has been introduced. It may be necessary to
drill out the rib-attach-bracket rivets to reposition the rib properly. Assemble the bell cranks, control stick and pushrods. It may be necessary to open up the lightening holes in the ribs of the
center section wing to eliminate any pushrod interference for all positions of the control stick.
PAGE 16
Fit the leading edge skin in position securing it with clamps and making sure it lines up with the
centre-section leading edge. Adjust and trim the inner edge for a close fit with the center wing
section at the wing-attach point. Use a chalk line to check that the outer wing spar is in a
straight line with the center-section wing spar. Same for the leading edge. Mark off the rivet
holes then drill the leading edge skin along top and bottom of the spar with a 3/32" drill, & cleco.
Drill the 3/32" rivet holes in the leading edge to secure the nose ribs. Remove the skin, deburr &
prime.
Cut and fit the bottom skin using tape to secure the front edge to the spar cap. Use a
carpenter's square to mark off the rear rib position and clamp the rib's rear flange to the rear
spar (actually, the previously bent portion of the bottom skin). At rib #7, place a 1/8" shim
between the rear spar-attach and the bottom skin to enable you to clamp the rear flange of this
particular rib. Support the outer wing section with a stand and as before, use a level to ensure
no twist.
Now secure the front edge of the bottom skin to the spar by drilling about 6 holes, 3/32" dia.,
along the length of the bottom spar cap picking up the previously drilled holes then use clecos to
temporarily hold the front edge of the skin. Drill and cleco the skin along the bottom flange of
each rib. Do the same for the rear flange (except rib #7 which will be done later).
For a final check, make sure that outer wing panel spar is in a straight line with the centersection spar, you'll have to loosen the clamp at rib #7 if adjustment is needed. Tighten the
clamp again and drill through the rear spar-attach, 1/8" spacer, bottom skin, and rear flange of
rib #7. Drill and cleco the rear spar-attach at remaining places along it's length to finish the job.
Reinstall the leading edge and drill the remaining holes through the front edge of the bottom skin
then remove both skins, deburr and prime. Drill out the 3/32" holes along the bottom spar cap
with a #30 drill and countersink for flush rivets. Mount the bottom skin only, at this time. Again,
check for wing twist and rivet bottom skin to rib flanges with AN470AD or with AN426AD. The
front edge is not riveted at this time.
Remove the wing panel from the aircraft and finish skinning on a flat surface. Use a level to
ensure flatness. Cut and fit top skin. Drill & cleco the leading edge & top skins to the top of the
spar. Drill & cleco top skin to rib flanges. Trim the trailing edge and fit the wing hinge doublers &
trailing edge filler strips and clamp at several spots along the trailing edge. Mark a straight line
and drill 3/32" rivet holes on 1" centers & cleco. Remove top skin, deburr & prime. Countersink
holes on top of spar and holes in the wing hinge doublers & filler strips. Reassemble top skin
and dimple holes at the spar and trailing edge. Rivet first, the top of the spar with AN426AD
rivets, rivet top skin to rib flanges with pull-rivets, then rivet trailing edge, except those holes that
attach the aileron hinges, with AN426AD rivets.
Mount wing panel back on the aircraft, sight along the leading edge, and position it until it lines
up with the center-section leading edge. Drill and rivet the rear spar-attach and the 1/8" spacers
in place.
Make the ailerons on a flat table with the top surface of the aileron facing down. Attach the
hinges to the trailing edge of the wing first. Then use tape to secure the other half of the hinge
to the aileron. When every thing is lined up, pull the hinge pins to remove the aileron and rivet
the hinge in place. Mount the aileron and lockwire the hingepins.
CENTER WING-SECTION, TRAILING EDGE PIECE - SHEET 7
Mount the wing panel on the aircraft again. Make the center-section trailing edge and fit it in
place to form a straight line with the trailing edge of the aileron. Drill & cleco, remove, deburr
PAGE 17
prime and replace. Dimple the holes in the top and rivet to the center-section trailing edge with
AN426AD rivets. You will have to be imaginative with the shape of the bucking bar used but
persevere; it is possible. Use pull-rivets to rivet the bottom to the bottom skin. Make and install
an end cap similar in shape to the aileron root end cap but without the control arm.
TAIL GROUP - SHEETS 2, 9, 10
Install the horizontal stabilizer supports (sheet 6) at the rear of the fuselage. Locate the 1/4"
horiz. stab. mounting holes on either side of the fuselage. Be sure to locate these accurately
using a hose-style level if necessary. Install the 1/4" nutplates inside. Install also at this time, the
tailspring support plates & support doubler (sheet 6). Also install the 5/16" nutplate used to
fasten the tailspring.
Refit bulkhead "E", cut out the top and bottom flange and bolt on the vertical stabilizer spar.
When properly aligned, drill and cleco. Remove the bulkhead, mount & fasten all hardware
including vert. stab. spar with AN470AD rivets, etc. Now replace the bulkhead and cleco in
place, and check the alignment. Fit the vert stab lower end cap in position on top of the rear
fuselage and it should butt up to the front face of the vert stab spar. Drill the rivet holes and the
two 3/16" bolt holes. Remove blkhd "E" and rivet the end cap in place with AN470AD rivets.
Now, reinstall "E" for the final time and very carefully align it so that the vert stab spar is at true
vertical. Cleco (or use a few pull rivets) to hold in place while you rivet with AD470AD rivets.
Install vert. stab. skin and align properly. Drill & cleco, remove & deburr, prime and rivet in place
with AN426AD rivets.
Make the horiz. stab. mounting brackets and bolt in place. Make horiz. stab. rear spar and
mount in position with proper alignment. Flush-rivet the two gussets (called "brace" in the prints)
in the corners. Mount front spars to the mounting brackets and make temporary ribs to secure
it's outer end to the rear spar. Cleco these ribs so that they can be removed after the horiz. stab.
skins have been installed.
Before the leading edge of the horiz. stab. skin is formed, use a sheet metal brake to make the
bends for the trailing edge. After bending the leading edge, place the skin on a flat surface and
use clamps to hold both trailing edges together. Now, measure the distance from the nose of
the leading edge to the flat surface at each end of the skin. Loosen the clamps and slide the
trailing edges sideways to make both distances the same. Tighten the clamps and mark with felt
tip pen to allow you to return to that position after the skin is placed on the spars. These last
steps may be difficult to visualize at first, but they are necessary to ensure that the skin will be
flat and not twisted when installed. Take your time and double check everything; accuracy here
will pay off later.
Make the filler strips for the top surface of the rear spar and hold in place with masking tape.
Install the elevator hinge stiffeners and filler strips in the trailing edge and clamp together. Mark
& drill all rivet holes. Remove skin, deburr & prime. Countersink the hinge stiffeners and the filler
strips. Reassemble & cleco, then dimple the trailing edge over the countersunk holes. Install
elevator hinges & drill rivet holes. Clamp the trailing edge together and rivet with AN426AD
rivets. Use pull-rivets elsewhere.
Make the elevators as shown, but use a sheet metal brake to form the bends on both ends of
the sheet first, before you make the bend in the middle for the trailing edge. Place on a flat
surface and before drilling and riveting it together, make sure the top surface faces down.
Measure the distances from the nose of the trailing edge to the flat surface to eliminate any twist
(just as you did for the horiz. stab. skins).
Use tape to secure the other half of the hinge (one half should already be riveted in place on the
PAGE 18
rear edge of the horiz. stab.) to the elevator skin. Place the elevator in position at the rear of the
horiz. stabilizer and insert the hinge pins. When you are satisfied that the elevator surface
mates properly with the horiz. stab., take the hinge pins out to remove the elevator and rivet that
half of the hinge to the elevator with pull-rivets. Be sure to secure the hinge pins with lockwire
when you re-assemble. Install elevator coupler.
Install rudder and controls. If applicable, install tailwheel, spring, and steering details per sheet
10.
ADJUSTABLE TRIM TAB - SHEET 9
Make the cutout in the right elevator as shown. Leave enough material so that the top and
bottom skins can be bent over and rivetted to provide a surface to attach the trim tab hinge. Add
a rib to the elevator at the place shown. This is necessary to beef up the elevator surface.
Make sure that you install the rib keeping the elevator on a flat surface in ensure that no twist or
curvature is introduced to the elevator. Form the trim tab using .016" 2024-T3, in a manner
similar to the elevators and add end caps to each end. Attach a length of hinge 5 1/2" long, to
the elevator and then to the trim tab. Make the control horn as shown and rivet it in place.
The control is .063" O/D spring-steel wire and can be obtained from any place that manufactures
springs. You'll need at least 8' of this wire. The outer casing is from the brake cable of a 10speed bike and may have to be spliced as detailed in the brake lever description. Note how it is
routed over the elevator hinge line and how it is secured at the end.
FIREWALL & INSTRUMENT PANEL COVERS - SHEET 15
Install the engine firewall & instrument panel covers with AN426AD rivets. Be sure to install the
pieces underneath, used later to fasten gas tank cover.
GASOLINE TANK & COVER - SHEET 15
See Sheet 15 for instructions of building the tank and cover.
NOTE: A six gallon welded aluminum tank is available from Hummel Aviation, as well as a separate
fitting package for that tank. See the website for more details and pricing.
CANOPY & WINDSHIELD - SHEET 12
Install the windshield bow by riveting nutplates inside the 1/2" square tubing. This will take
patience working in a tight area but work each nutplate down the tube until it reaches the 9/64"
hole drilled previously. Hold the nutplate through the hole with a 6-32 screw and drill the rivet
holes to secure it. Rivet in place with countersunk pull-rivets.
Use the full-size pattern for the windshield and frame to make an aluminum template from .032",
3003-1/2 hard aluminum or soft, Utility-grade aluminum (it is possible to use .032", 2024-T3 but
is harder to work with). Clamp to the windshield bow and form the edges where it meets the
fuselage using a hardwood block with a 1/2" deep sawcut in one end. Measure back 1 1/2" from
the formed edge and cut. This cutout portion becomes the windshield frame.
A forming jig will be required to drape-form the plexiglass in an oven heated to 270º- 290º F.
PAGE 19
Place the sheet over the jig and put into the oven for about 20 minutes. When withdrawn from
the oven, hold the plexiglass down until it cools sufficiently to hold it's form. Trim to size and
secure to the windshield bow with the hold-down clamp (sheet 16) and to the windshield frame
with joggle strips. Install to the fuselage with nutplates and 6-32 screws.
Install the turtledeck bow and turtledeck as shown on sheet 14. Form the edges with the
hardwood block made earlier. A nylon block with a sharp edge can be used to finish off the
edges by rubbing it back and forth after the turtledeck is installed. Rivet with pull-rivets. Fit and
install dorsal fin.
The canopy frame details are shown on sheet 14. The plexiglass canopy is difficult to make but
entirely possible with patience, availability of a walk-in furnace, and some extra help. It is well
advised to purchase the canopy and windshield from Hummel Aviation and the canopy
you get will be optically perfect. For those adventurous, sometimes called `thrifty' souls, these
are the basic steps for "rolling" you own. First make a canopy mold. This is done by
constructing in-place, a wooden frame. Cut from 1/4" plywood the contour of the canopy top and
fasten to the frame. Cut about 6 more of these plywood shapes (the same as the first) and
space them on either side of the first one. What you have now will be the skeleton for the mold
and the plywood shapes will act as ribs. Cover all of this with metal screening such as used on a
screen door. Apply an automotive type of body filler to the mold than shape it until it blends in
with the turtledeck and windshield lines. Make sure that the surface is smooth and that all
curves are continuous (no depressions or bumps). Place a piece of flannel over the shell and
stretch it tightly around. It can be stapled in place along the edges. The flannel will protect the
plexiglass from scratches when it is being formed.
Make a blank approximately 33"x44" from acrylic plexiglass FF , heat it up and drape over the
mold. Install wood strips along the bottom edges of the plexiglass with clamps to provide a
means of stretching the plexiglass down over the mold. Place all this in the oven at 290º F. for
20 minutes. Withdraw quickly and with the help of a friend, apply downward pressure on the
wood strips. You will have to repeat this step 3 or 4 times until the canopy is formed. After the
first "pull-down", hang weights of 30 - 40 lbs. on the wood strips at each end of the canopy then
place back into the oven. The newly formed canopy will need to be buffed vigorously after it has
cooled. Trim and fit to frame.
ENGINE MOUNT SHEETS 13 & 15
The main difference between the engine mount for the trigear and that for the taildragger is the
distance of the engine from the firewall. In the trigear configuration, that distance is 8 1/2", 1"
less than that for the taildragger. Note too, that the engine mount uses the same holes in the
firewall as the nose gear yoke.
To make the engine mount, use a jig similar to the one shown on sheet 15. Take the nose gear
yoke which by now, should have been fitted to the firewall and mark the mounting holes on a
piece of 1/4" steel plate. Bolt the engine mount bushings to this plate and fasten this plate to the
second steel plate (the one with the bolt pattern for the engine). Check alignment for proper
crankshaft position. Some people recommend that the engine be offset to the left to counter
slipstream effects but the author has found that it really isn't necessary.
The engine rubber shock mounts shown on sheet 15 are quite easy to make. Make the outer
casings as shown and attach them to the second steel plate. Cut, fit, and weld the tubing pieces
in place.
Even by using a jig to make the motor mount, you may still find some mis-alignment when it
comes time to install it. Usually 3 of the holes will line up but the fourth will tend to be off. If this
is your case, then install it using as many holes as you can. Heat the 3/4" tubing around the misaligned bushing and gently bend it till the hole lines up; bend to fit.
PAGE 20
ENGINE COWLING
Make the bulkhead and top engine cover shown on sheet 16. It is best to make a cardboard
template of the bottom cover then trace it on .016", 2024-T3 later. Make the cutouts around the
front corners of the engine crankcase to allow a tighter fit. Install a ram air cover on the bottom
to enclose the carburettor and carb-heat box. The whole bottom cover will probably end up
being made of 4 or 5 pieces of aluminum riveted together. Note that no part of the cowling must
touch the engine. It must be entirely supported by it's attachment to the firewall.
BRAKE LEVERS SHEET 12
The system shown on sheet 12 has been in use now on both the author's Hummel Birds and
has proven to be satisfactory. The hand-operated levers are effective and easy to make. Use
only 1/16" aircraft cable for brakes. The outer casing is from a 10-speed bicycle rear brake cable
and if more length is needed, make a splice use a 2" long piece of aluminum tubing with an I/D
compatible with the O/D of the casing. Gently crimp the aluminum splice to secure both ends of
the casing. Be sure to grease the 1/16" cable well, before feeding it into the casing.
That piece of teflon or nylon used to anchor the casing was chosen for convenience. A similar
piece of aluminum could also be used.
Before you install the skin on the center wing section, route the brake casings through
grommeted holes in the fuselage and through the nose ribs in the center wing panel section.
Avoid sharp bends of any kind and the rule here is to keep the bends as large as practical.
Secure the outer end of the casing on the landing gear with a small clamp and ensure that the
up-down travel of the suspension does not cause the casing to bind or to get caught on a
structural part. When attaching the cable to the brake control arm, you could slide a small spring
over the cable itself which would help to retract the cable when the brake lever is released.
This whole discussion deals entirely with a mechanically operated brake system. Hydraulic
brakes would be superior but would require a whole new arrangement. If you feel that this is
within your capabilities to do so, then by all means proceed. Otherwise, the mechanical brakes
are satisfactory and probably cheaper.
WEIGHT AND BALANCE REPORT
This must be done before a flight permit can be issued. Level the plane using a level on the
bottom surface of the wing and sufficient blocking under the tailwheel. Be sure to block up the
wheels depending on the scales used, to ensure that level attitude is maintained throughout the
exercise. A set of digital (strain gauge type) bathroom scales can be used because these have
sufficient accuracy for a meaningful report.
Three sets of scale readings at least, are necessary to establish the C.G. for each load item.
First, weigh the plane empty, weigh again with the pilot in place (make sure that the plane is still
level), then fill up the gas tank and weigh again for the third time. If you plan to have a baggage
compartment, then fill it up and weigh the plane once more. This may seem to be overly
laborious but really it's the only way to get accurate and reliable results. The object of all this is
to obtain the C.G. for these load items so that you can figure out min's and max's of the various
weight combinations while staying within the C.G. envelope. Use the enclosed weight and
balance forms as a guide.
The C of G forward limit is 1" forward of the vertical front of the main wing spar and the
rearward limit is 2" behind the front of the spar. The C of G must fall within this 3" range for all
combinations of pilot weight, gasoline on board, and baggage. The upper limit for pilot weight is
about 190 lbs.
PAGE 21
ALLOWABLE AIRFRAME MODIFICATIONS
For taller pilots, you can raise the turtle deck by 2" and the windshield bow by the same amount.
This should allow a 6', 2" pilot sufficient headroom.
Heavier pilots will require more horsepower and the 1/2 VW type engines offered from Hummel
Engines or Great Plains are rated at higher outputs than the 900 cc 1/2 V.W. engine normally
recommended for this plane. Hummel Engines has kits available to increase the output of a
converted 1/2 VW engine. See Hummel Engines website for more information
(www.hummelengines.com).
INITIAL TESTING
The sequence of events presented here are extremely important and require a disciplined
approach to carry them out systematically and completely. Your plane may now look ready to go
but until each check has been completed, you have no business trying to get it into the air. Your
well-being and that of your plane is at stake. For that matter, the reputation of amateur-built
aircraft is at stake. We don't need any more negative statistics just because some "gung-ho"
pilot couldn't wait to get his bird upward without first ensuring that it would stay up. Please
accept this discourse with all the sincerity that can be mustered and now that you are so close to
flying your long-awaited dream, DON'T BLOW IT !!!!!
Fuel flow test: remove the gas line from the carburetor and route it into an empty can, and fill
the gas tank with gas. Open the shutoff valve and measure how long it takes to empty the tank.
Calculate the gallons per hour that you measured and compare it with the rated fuel
consumption of the engine. Your calculation should be at least 7 times greater.
Full throttle test: dig a hole in the ground if you must, but get the tailwheel about 1 foot lower
than the main wheels to simulate the aircraft's climbing attitude. The gas tank should be nearly
empty with no more than 1/2 gallon fuel. Start the engine and run at full throttle for at least 5
minutes to ensure that during a climbout, your engine will not experience fuel starvation.
Taxi test and liftoff: If you have never flown a taildragger or have had limited experience, then
by all means find a place where you can get some instruction. A taildragger is a different animal
on the ground and requires teaching and lots of practice to get on to it. Make no mistake about
it; as you first begin to taxi, you'll swear something is wrong with the plane unless you've had
taildragger experience. It is recommended that you get someone else to make your test flight,
someone who is current on short-coupled taildraggers. These are just words of wisdom that
were learned the hard, painful way and are intended to prevent others from making the same
mistake.
PAGE 22
THE HUMMEL BIRD
PREPARATION FOR FLIGHT
Having had the experience of test flying both of my Hummel Birds, this article will formalize the
steps required to systematically check out your plane before the first flight. The purpose of such
a program is to eliminate as many "surprises" as possible and to protect the pilot and his brand
new plane from unnecessary trauma.
By no means is this article intended to be an exhaustive list of tests. To do such would be
delving into the realm of certification tests for a C. of A. Obviously, this is not required for
Amateur-built planes but it is a good idea to perform the tests listed just to get to know your
plane better and to develop a formal flight manual for your new aircraft. After all, this is what
safe flying is about - safety for man and machine.
It is presumed that at this stage:
- 1. All inspections have been completed.
- 2. All noted snags have been corrected.
- 3. The proper documents are in hand to allow legal flight
(flight permit, current pilot's license, and insurance).
Note that if someone else will be test flying your plane, his license must be current as well. In
short, your plane, outside of the following tests, is ready to fly. Keep in mind that these tests, all
of them, take more importance because you are dealing with the least desirable of situations,
that of an unproven airframe with an unproven engine.
To help even up the odds with this combination, you've got to ensure yourself that the engine will
hold up while you're busy trying to see if the plane has any bad habits. These are the following
checks to make before you get into serious taxi tests:
1. Fuel flow test: Lower the tail to raise the nose to climbing attitude then disconnect the fuel line
at the carburettor. With minimum fuel in the tank, open the fuel shutoff valve and use a
stopwatch to determine how long it takes to fill a measured container. Convert the data to get the
flow rate into Imperial or US gals per hour. Your flow rate should be 7 to 10 times that of the
engine's fuel burn rate. For my planes, the rates were 7.8 : 1 and 9.4 : 1 respectively.
2. Calibration of engine gauges: Check the oil temp gauge by immersing the bulb in hot water
along with a thermometer of known accuracy. Check the oil pressure gauge by disconnecting
the oil line at the engine and blowing compressed air into it. Check the air pressure first with a
tire pressure gauge then compare that with what oil pressure gauge reads. It goes without
saying that any discrepancy of more than 7 - 10% should result in a new gauge.
TAXI TESTS:
By now, your engine should have an hour or so running time and running consistently at all
speeds. You are about to embark on the next phase of tests. If yours is the taildragger version
and you have never had taildragger experience then stop right now! Get some dual instruction
on a taildragger until you've developed the responses necessary to control these animals. This
is the voice of bitter, painful experience talking. Without this skill, I defy you to keep the plane in
straight line even at slow ground speeds. If you are a fairly seasoned taildragger pilot, then you'll
need to spend a couple of hours taxiing up and down the runway adjusting your skills and
reflexes to the shorter coupling of this aircraft.
PAGE 23
A side benefit of this extra work is that you will be breaking-in the engine even more. You will be
able to see if the oil pressure and temperature stay within range.
For the trigear version, spend at least an hour taxiing, feeling out the ground handling
characteristics and noting the engine performance.
Now that your first real flight is imminent, it's imperative to check the plane over thoroughly.
1. Take the cowling off and look for oil leaks.
2. Check the engine mounts and all accessories for any loose bolts.
3. Check the prop, prop bolts and spinner.
4. Check the landing gear for cracks, deformation, and tire pressure.
5. Check the controls for any loose parts or damage.
6. Check oil level and make sure you have lots of fuel.
THE FIRST FLIGHT:
For the first flight, plan on doing just one complete circuit and no more. Remember, the engine
has still not proven itself for sustained high power output yet. The winds should be light and
right down the runway; cross-wind experience can wait. Now, with your plane facing the wind,
give her pedal to the metal and allow it to lift off. Your climb out should be fairly shallow at 60
mph indicated. Your first turn should be done by gently pushing the stick sideways to establish a
bank. Although my planes don't exhibit any signs of adverse yaw, be prepared to feed in a little
rudder to coordinate the turn. Throughout the flight especially note the following:
1. The engine oil pressure - normal range is 25 to 50 psi.
2. The engine oil temperature - should be well below 190 F.
3. The aircraft trim in level flight - adjust horiz. stab.
4. Feel out the ailerons, noting sensitivity and how much is required for normal turns.
If you have to use excessive elevator control to lift off or to maintain level flight, then the angle of
incidence of the horizontal stabilizer may need some adjustment. Normally, the setting given in
the plans is just about right-on and you should ensure before any taxi tests that it is set up that
way.
On final, reduce engine power to idle and set up the glide for an approach speed of 60 mph.
Flare as you would with any light aircraft and allow it to settle to touch down. If it bounces more
than a foot or so, better give it power and go around again. This plane, like most other planes, is
susceptible to PIO (pilot induced oscillation) and you really don't want to ruin your day do you?
At this stage, provided that there was nothing unusual during the first flight, the plane and engine
have proven themselves airworthy and dependable for 5 to 10 minutes of sustained flight. Why
not check things out under the cowling again, just to give you peace of mind that all is in order.
Now you're ready to repeat the exercise. It is important to stay in the circuit for the next half hour
or so doing touch and goes. Aw! That's boring, you say. Maybe it is but it allows you to gain a
feel for the plane and to hone your landing skills. And should a problem occur (saints preserve
us!), you're close enough to the runway to make a "quick" landing. It's important to realize that
the plane needs time to prove itself and to give you a confidence level to go on to larger and
better things. Don't worry about getting the numbers for stall speed, rate of climb, and max. and
cruise speeds just yet. The only question to be answered now is "Will this machine hold
together for any length of time?"
PAGE 24
Words Of Wisdom From Morry On Taxi Testing And First Flight
Before your first flight, check the weight and balance in all possible conditions, such as full and
low fuel. Be sure fuel flow test is satisfactory and that engine runs smoothly through all RPM
ranges with no hesitations. Have some help available in case of an off airport landing. Also
have a fire extinguisher handy and first aid supplies.
Even though the FAA has looked your new plane over, it is wise to have an EAA technical
counsellor look at your new bird. Don’t be too proud to do this, it could be to your advantage.
These counsellors have more experience and have seen many planes. Make sure you have
experience in the landing gear type. If you are not current, get some dual time or have a
qualified, experienced pilot make your test hop.
The Hummel Bird roll rate is fast, but elevator and rudder are more like general aviation
aircraft. It will handle 25 mph cross winds by putting the wing down into the wind and steer
with the rudder. Its really groovey and easy to fly, but more responsive than Cubs and Champs.
Do not do any high speed taxi tests, as this type of test has damaged many home builts.
However, you should taxi below lift off speeds to check steering, brakes and controls.
“Checking yourself out in single place planes” Be prepared to fly for at least a ½ hour to 45
minutes. Wind down runway, long enough to abort take-off.
Take-off—do not raise the tail wheel. The trigear is a pussy cat. Lift off over 50 mph in a
shallow climb, this will help cool the engine. Go to 2500 AGL, feel the control’s responsiveness
and note oil pressure and temperature. When comfortable, do some slow flight turns.
Stalls— With power off, slowly bring the stick back. It will not really stall, it just porpoises and
ailerons are still responsive; but if a wing should go down respond with rudder, as aileron will
induce a spin.
Feel it out, see what it will and will not do. Slow flight will prepare you for a perfect landing. In
windy, gusty weather the wheel landing gives better control than a stalled landing.
You will find the Hummel Bird to be a pure joy to fly. It will do 3 mph per HP, this is great
economy. It’s a low drag aircraft, and approach speed should be 55-60 mph. Also, the glide
ratio is better at that speed.
In slow flight, note the nose position relative to the horizon. If power is lost, immediately lower
nose to a safe gliding speed. This should be a habit and done automatically upon reduction of
power or power loss.
Builders who have built their Hummel Birds to the plans and didn’t try to change anything are
enjoying their planes and say its great just the way it is. If you change anything in it or put in a
different engine, please don’t call it a Hummel Bird.
Inspections—see the form on the next page for inspection checklists.
PAGE 25
First Flight and Annual Inspection
ENGINE
TAIL WHEEL AREA
Spinner retention screws
Torque prop bolts
Engine mount bolts safetied
Throttle arm bolt secured
Choke arm bolt secured
Magneto attach bolts tight
Firewall pass-thru fittings
Fuel hose secure
Remove tail cone
Steering arm attach secure
Tail wheel wear left
Tail wheel free to spin
Elevator arm bolt secure
Rudder arm bolt secure
Bearings free*
Install tail cone
MAIN LANDING GEAR
Tire wear and inflation
Brake pads useable
Wheel cotter secure
Brake cables secure
Reverse tires on their rims
L R CONTROLS
Cockpit
Remove cover
Stick mount secure
Aileron push rod secure
Elevator push rod secure
After push rods secure*
Reinstall cover
FORWARD COCKPIT
Chock mount secure
Rudder bar bolts tight
Brake pedals secure
Pitot/static lines secure
Instrument attach nuts tight
AFT COCKPIT
Throttle mount secure
Mag switch tight
Seat support
Canopy latches secure
Seat belt attach secure
Shoulder harness attach secure
Ailerons
Bellcrank attach secure
Push rod to aileron secure*
Hinge pins secure
Ailerons free and undamaged
Wing attach bolts secure
Rudder
Attach bolts cottered
Rudder undamaged
Stab Elevator
Stab attach bolts secure
Hinge pins secured
*REPACK ALL BEARINGS
Fuel Tank
Remove tank cover
Inspect all fittings & hoses
Replace tank cover
Run in and adjusting Zenith carb, starting and first run up
 Tie tail to some immovable object for safety.
 Set idle air on top rear of carb to 5/8 -3/4 turn open.
 Set main jest at rear lower three full turns open.
L R
PAGE 26
Fuel flow test—See Bill Spring’s instructions for fuel flow test on page 23. Use automotive ¼” fuel line.
Only 10w30 oil is used and no high volume oil pumps, as they will cause oil pressure gauge fluctuations.
Starting—have competent person in cockpit with fuel turned on, mag off, and throttle closed. Prime
engine by pulling through four blades, or in cold weather use choke. If carb is dripping fuel, it’s ready to
go. Standing behind prop on left side of ship, mag on, it should start on first pull. Gradually open
throttle, noting oil pressure.
Run full throttle for five minutes. During this time turn main needle in until RPM drop. Open needle
valve to the highest RPM, then 1/8 turn more. Always prime and start with throttle closed.
After running full throttle for five minutes slowly reduce power and set idle screw on the throttle arm to
1100 RPM. Stop and let cool. Do this three times for fifteen minutes total. Check idle RPM and top
RPM. It should static at 3100 RPM with the right prop. The piston rings are now seated.
The two most used displacements are 92mm bore and 69mm crank 916 cc 32 HP at 3000 RPM using a
Tennessee or Prince 46 x 34 prop, and the 92mm x 78mm stroke 1050 cc engine 37 HP at 3000 RPM
using a Tennessee 46 x 36 prop. Hummel Engines has these props in stock for quick service.
The valve clearance should be checked before your first flight. The clearance should be .005” on intake
and .007” on exhaust. Change oil after 2-3 hours and then every 20 hours after initial run-in.
Morry Hummel
FLIGHT TESTING:
This is where you start gathering all that flight envelope data that allows you to brag (or to keep
quiet) about how great your machine is. Keep your eye on the engine gauges at all times to
make sure that everything is well within limits.
1. First and foremost, you must calibrate your airspeed indicator. This is done by flying
over two landmarks with a known distance apart such as two concession roads. Set up for level
flight at a given airspeed and at some determined heading say, 180º. Use a stopwatch to record
the time it takes to fly between landmarks and divide it into the distance to come up with an
actual speed; (V=3600*D/T) V=mph, D=mi, T=sec. Change your heading to 360º and repeat.
Average the two speeds and compare this to the indicated speed and it should be within 5%. If
the error is greater than this, your airspeed indicator and/or pitot system needs attention and
should be fixed before proceeding.
2. Now for the power-off stall. Climb to 2500 ft agl and reduce power to idle. Keep the
ailerons neutral and the nose just slightly high and allow airspeed to bleed off. At stall, the nose
will break downward slightly and bob back up again and so on without moving the stick forward.
If the plane tends to roll off toward one side at the stall, then it could mean that differences in
wing construction or rigging causes one to stall slightly before the other. Anyway, practice this a
few times and note the airspeed. This is your power-off stall speed and should be close to 40
mph.
3. Climb and glide tests: The purpose here is to establish such parameters as max climb rate,
best climb angle, glide ratio, and best glide angle. To do this, you'll need a stopwatch and pen
and paper to record your findings. For the climbing tests, begin them at 500' or so, agl, set the
plane up at full power and at 60 mph IAS. Record the time it takes to climb 500 ft of altitude.
Repeat at speeds of 55, 50, 45, and one speed lower if stall speed permits. Convert your data
to `horizontal distance travelled for 500 ft gain in altitude' and draw a graph with this on the "Y"
axis versus speed in mph on the "X"axis. The resulting curve will be "U" shaped and the speed
at which the bottom of the "U" occurs will be the best angle of climb (typically 44 mph). Now
draw another graph but this time, mark off the "Y" axis in `seconds to gain 500 ft altitude' versus
speed in mph on the "X" axis. Again, the resulting curve will be "U" shaped and the speed at
which the bottom occurs will be that for the best rate of climb and the max. climb rate, which
occurs here, can be found by dividing 500 ft by the time converted to minutes. Typically, this
figure should be around 700 fpm at an IAS of 47 mph.
PAGE 27
CLIMB TEST CURVES
Horiz dist travelled in time (t)
= (t x IAS x 5280)/3600 ft.
t = seconds to gain 500' altitude
IAS = mph
HORIZ
DIST
│TIME
│
│
│
* BEST ANGLE
**
*
*
*
*+*
*
│
l
* + * BEST RATE
│__________l_____l__________
MPH
44
47
The glide tests are similarly done by recording the time taken to lose 500 ft of altitude. Tests
should begin at 1000 ft agl and at successive of speeds of 60, 55, 50, 45, and lower if possible.
convert the data to `horizontal distance travelled for 500 ft loss in altitude' and plot on the "Y"
axis versus speed in mph along the "X" axis. The resulting curve will be an upside-down "U".
The speed corresponding to the peak of the curve is that for the best glide angle. The glide
ratio, which is greatest at this speed, is found by dividing the distance travelled at this speed, by
500. Typical value: glide ratio of 10:1 occurring at a speed of 50 mph.
GLIDE TEST CURVES
Horiz dist travelled in time (t)
= (t x IAS x 5280)/3600 ft
t = seconds to lose 500' altitude
IAS = mph
│
─ ─ ─ ─*|*─ BEST ANGLE
│
* | *
HORIZ│
* | *
DIST │
* | *
│
*
|
*
└──────|────────
MPH
5. Cruise tests: The max. RPM for a 1/2 VW engine is from 3400-3500 RPM. Set the plane up
for level flight and let her tear. when the IAS has stabilized, note the engine RPM. Keep an eye
on those engine gauges especially the temperature. The next bench mark cruise speeds occur
at 75% and 65% power settings. The engine RPM for these settings is 91% and 87% of max.
RPM respectively. Set up for level flight at each of these RPM and note the airspeed.
6. Stability tests: The two most common are stick-fixed neutral and stick-free neutral and these
determine the longitudinal stability of the aircraft. Since these tests are beyond the scope of this
article, it is suggested that the pilot read an article on how these are performed before trying
them out on his plane. By now, you should already know or have some idea of how stable the
plane is; the stability tests will only serve to confirm this. Even if the tests showed poor stability,
there really is not too much you can do about anyway. Stability problems are related to the C. of
G. and are more pronounced when the aft C.G. goes beyond its limits.
7. Spin tests: I have not performed this on either of my planes nor do I intend to do so. I don't
feel qualified. If you are qualified or know of someone who is, then by all means go for it.
AFTERTHOUGHTS:
Now that you have determined your stall speed and best climb and glide rates you can adjust
your flying techniques to suit your plane. My preferences are:
climb out speed after takeoff - 55 mph
approach speed on final
- 55 mph
cruise
- 3200
I have no problem getting "greased-on", 3-wheel landings with my taildragger. With my trigear, I
land nose high and hold it off for as long as possible.
Both planes sideslip beautifully and will lose altitude like a manhole cover on it's edge if so
desired. I find that the best IAS for sideslipping is 60 mph. Just lower a wing and feed in
opposite rudder and adjust as required to hold the attitude. Keep the IAS at 60 mph by adjusting
the elevator. The engine is, of course, at idle.
PAGE 28
CHECK LISTS:
Preflight inspections involve:
- 1. Checking the control surfaces, hinge points, and control horns.
- 2. Check the landing gear for cracks, deformation and tire inflation
- 3. Check the engine for oil, sparkplug wires, and fuel.
- 4. Check the gascolator for water contamination.
- 5. Do the usual cockpit checks when inside.
- 6. When taxiing, check the brakes.
Pre-take-off checks involve:
- Engine RPM drop when carb heat is applied - typical 50 RPM at 2500 RPM.
- Engine oil press and temp.
- Note the RPM as soon as full throttle has been applied during
the take-off roll - should be greater than 2900 RPM.
Pre-landing checks involve:
- Application of carb heat if weather conditions merit it.
- Fuel mixture full rich.
- Safety harness properly adjusted.
- Check fuel quantity.
Pre-shutdown procedure:
- Check mag switch by turn off and on quickly.
- Shut fuel off.
- When engine quits, shut mag switch off.
Now to complete your very own flight manual for your airplane, you should record the findings of
all of the tests and insert a copy in the airframe and engine logbooks. Should you ever sell your
plane, the information becomes invaluable to the new owner.
PAGE 29
HUMMEL BIRD CENTER OF
GRAVITY CALCULATIONS
The calculations below, are to
be regarded as typical. Your
situation may produce slightly
different figures.
Aircraft is level (bottom of wing)
for scale readings which are
taken under each wheel.
TAILDRAGGER
TRIGEAR
EMPTY WEIGHT: - 2 litres of oil, no gasoline, no pilot.
Scale (lbs)
Arm (ins)
Left = 144
Right = 142
Tail = 13
Dm= -5
Dm= -5
Dt= 107.5
Total = 299
Moment
(in-lbs)
-72
-71
1397.5
Scale (lbs)
Arm (ins)
Left = 110.5
Right = 107.6
Nose = 92.3
Dm= 14.5
Dm= 14.5
Dt= -22.6
1254.5
Total = 310.4
T/D Empty C of G = 1254.5/299 = 4.2"
rear of datum
Moment
(in-lbs)
1602.3
1560.2
-2076.8
1085.7
Trigear empty C of G = 1085.7/310.4 = 3.5"
rear of datum
PILOT C of G: - 2 litres of oil, no gasoline, 168 lb pilot
Scale (lbs)
Arm (ins)
Left = 209
Right = 209
Tail = 49
Dm= -5
Dm= -5
Dt= 107.5
Moment
(in-lbs)
-104.5
-104.5
5267.5
Total = 467
5058.5
Pilot C of G =
(5058.5-1254.5)/(467-299)= 22.6"
rear of datum
Scale (lbs)
Arm (ins)
Left = 213
Right = 215
Nose = 54.4
Dm= 14.5
Dm= 14.5
Dt= -22.6
Moment
(in-lbs)
3088.5
3117.5
-1224
Total = 482.4
4982
Pilot C of G =
(4982-1085.7)/(482.4-310.4)= 22.65"
rear of datum
PAGE 30
GASOLINE C of G: - 2 litres of oil, 15 lbs (approx) gas, no pilot
Scale (lbs)
Arm (ins)
Left = 151
Right = 151
Tail = 12
Dm= -5
Dm= -5
Dt= 107.5
Total = 314
Moment
(in-lbs)
-125.5
-125.5
1290
Scale (lbs)
Arm (ins)
Left = 113.5
Right = 111.5
Nose = 101.5
Dm= 14.5
Dm= 14.5
Dt= -22.5
1139
Total = 326.8
Gasoline C of G =
(1139-1254.5)/(314-299) = -7.7"
Note: forward of datum
3950.3
983.1
Gasoline C of G =
(983.1-1085.7)/(326.8-310.4) = -6.26"
Note: forward of datum
EXTREME C of G CALCULATIONS
C of G limits: Extreme Forward = 8.25" rear of datum
Extreme Rear = 11.25" rear of datum
Max Gross Weight = 530 lbs, Max Fuel Capacity = 6 imp gal or 43.2 lbs
Weight (lbs)
Arm (ins) Moment
Scale (lbs)
(in-lbs)
A/C empty=299
4.2
1254.4
A/C empty=310.4
Pilot = 134
22.6
3083.4
Pilot = 146
Fuel = 43.2
-7.7
-332.6
Fuel = 43.2
Total = 476.2
Moment
(in-lbs)
1650.1
1616.75
-2283.75
Total = 499.6
Arm (ins) Moment
(in-lbs)
3.5
1085.7
22.65
3307.3
-6.25
-270
4123
Extreme forward C of G = 3950/476.2
= 8.3" rear of datum.
With a full tank of gas, minimum
pilot wt is 134 lbs .
Weight (lbs)
Arm (ins) Moment
(in-lbs)
A/C empty=299
4.2
1254.4
Pilot = 185
22.6
4181
Fuel = 0
-7.7
0
Extreme forward C of G = 4123/499.6
= 8.26" rear of datum.
With a full tank of gas, minimum
pilot wt is 146 lbs.
Scale (lbs)
Arm (ins) Moment
(in-lbs)
A/C empty=310.4
3.5
1085.7
Pilot = 210
22.65
4756.5
Fuel = 0
-6.25
0
Total = 484
Total = 520.4
5435.5
5842.2
Extreme rear C of G = 5435/484
= 11.23" rear of datum
With no gas, the max pilot wt = 185
Weight (lbs)
Arm (ins) Moment
(in-lbs)
A/C empty=299
4.2
1254.4
Pilot = 210
22.6
4746
Fuel = 21
-7.7
-161.7
Extreme rear C of G = 5842.2/520.4
= 11.23" rear of datum.
With no gas, the max pilot wt = 210
Scale (lbs)
Arm (ins) Moment
(in-lbs)
A/C empty=310.4
3.5
1085.7
Pilot = 210
22.65
4530
Fuel = 19.6
-6.25
-122.8
Total = 530
5838.8
C of G at Gross wt = 5838.8/530 =
11.02" rear of datum (safe).
Total = 530
5492.9
C of G at gross wt. = 5492.9/530 =
10.4" rear of datum (safe)