Building A Replica Aircraft

Part Four

Construction Details

Firewall Forward

• “If anything is worth trying at all, it's worth trying at least 10 times.” Art Linkletter, radio and TV personality

Brief Review

• After obtaining a partially complete Graham Lee 7/8 scale Nieuport 11 project – I decided to reconfigure it to resemble a 1929 Boeing F4B-2 US Navy Fighter.

• Boeing developed the F4B in mid 1928 at company expense as a small light weight fighter for the US Navy.

• The -1 and -2’s had a unique structure as the fuselage was bolted/gusseted aluminum tubing. Wings were all wood (in fact the last of the wooden wing fighters in the Navy).

F4B-2

Objectives

• Utilize as much of the original project as possible.

• All modification must not compromise structural integrity.

• Keep as light as possible – don’t go “overboard” on detailing!

• Maintain the look of the Boeing with out becoming “anal”.

• Have some fun!!

Firewall Forward

• From the start I was aware the whole look of the aircraft would hinge on the look of the front end.

• Since a radial engine would not be readily available in size, horsepower or affordability a Continental A-65 was located and procured.

• This presented problems in being able to properly cowl a flat engine to look like a round one.

Initial Weight and Balance

• Early on I knew I would have to achieve the proper CG with the placement of the engine. With that in mind the Fuselage, Wings and Empennage were completed and covered.

• The aircraft was assembled with the engine mounted on a standard Continental mount of unknown origin.

• The aircraft was then weighted to determine what would be needed to obtain a proper CG range.

Initial Weight and Balance

April 2014 = 455 lbs

CG Determination

• With the initial weights and location of various variables (Seating, Fuel, Engine, etc.) the fun begins.

• While I had the CG range for the Graham Lee Nieuport 11 ,which this project began life as, many changes affecting the CG were made (top wing rake, increase of lower wing chord, moving the cockpit aft one bay).

CG Determination

• Research was done on the Internet, documents on hand and various examples of where a CG should be located on a biplane.

• I found that the CG location is based on calculations that involve the areas of the top wing, bottom wing and stagger to determine the Mean Aerodynamic Chord (MAC).

• Using this information and I was able to determine the CG range of the GL Ni 11 in percentages of the MAC. (13.5% - 20%)

CG Determination

• Since the GL plans do not give any information of the airfoil used, I used (13.5% - 20%) for my preliminary determination of the “Boeing’s” CG range.

• Using a spreadsheet I plugged in all the “Boeing’s” numbers and translated that in to a graphical presentation.

• Further research led me to information on calculating tail volume to determine safe rear cg limits. Using all that information I have set the initial CG limits at 15 to 27%. Which falls within the range of 3 other like biplanes which I had information (Hatz, GL Ni11 and Boredom Fighter).

Motor Mount

• All of this and working various W&B variations led me to determine that the motor mount needed to be extended 7 inches. Due to that extended length I chose heavier than normal tubing (5/8 x .12 wall 4130).

Note: The motor mount has 5 degrees of down and right thrust.

“Boot” Cowl • With the mount done I could proceed with

constructing a “boot” cowl. First was to fabricate a bulkhead from .032” 6061-T6

“Boot” Cowl

• Once the bulkhead was formed. Patterns for top, side and bottom panels were developed.

“Boot” Cowl

• Meanwhile since the side and bottom panels have Louvers a hard wood die was fabricated Amazing what you can find on the Internet!

“Boot” Cowl

• Step one: cut slot length of louver with Dremel tool .

• Step two: position die and press (pound) die.

Note: 3003 Aluminum for Louvered sections

“Boot” Cowl

“Boot” Cowl July 2014

“Boot” Cowl (Revised)

When I assembled the “Boot” cowl and mounted the engine, something didn’t look right. It just did not look like what the cowling looks like behind a radial engine. It needed a “Dishpan”. Originally I procured a spun nose piece for the Ni11 cowling intending to use it for the basis of the “Boeing’s” ring cowl, but it was going to be too small. It was however the right size for the “Dishpan”.

“Boot” Cowl (Revised)

Bulkhead mounts between engine mount and engine with the engines accessories protruding through the bulkhead.

“Boot” Cowl (Revised)

Yes – all new top, bottom and side panels!

November 2014

Ring Cowl

With the “Boot Cowl” in place I began to consider the Ring Cowl. The proper name being Townend Ring and is described as a narrow chord cowling fitted to radial engines to reduce drag and increase speed (aka “Speed Ring”).

The cowl scaled out to be 40 inches in diameter.

Ring Cowl Leading and Trailing edge bent from ½” 5052 tubing

18 Ribs formed from .016 6061 T6

Ring Cowl

Ring Cowl

• Now that we have the Ring Cowl structure fabricated – How do we mount this thing?

• The F4-B ring cowl attached to the top of the cylinder heads with brackets. That’s won’t work with the A-65 – just not enough cylinders in the wrong place.

• After much thought I decide to incorporate a base (shelf) for the cowl to rest on into the engine cooling baffles.

Engine Baffling

• Since the wasn’t any really good way to make the ring cowl into a pressure cowling I settled into a “Cub” type “Scoop”.

• I started with an end plate attached to the cylinder heads and incorporated a braced “Shelf” for the cowling halves to rest on.

Engine Baffling

The baffles, shelf and supports are .032 6061-T6.

Top and back of the “Scoops” are attached to the end plates with hinge stock. The “Scoops” added much rigidity to the end plate/shelf assembly.

Ring Cowl With the base established I could trial mount the cowl for position. Ok - problem here cowl is sitting too high!

First solution drop the shelf with an extension. Cowl is position better but now the engine is not centered in the cowl – grrr!

Dec. 2014

Ring Cowl

• Ok as they say back to the drawing board! Many measurements were taken and a layout drawing was produced.

• Two problems were addressed which actually were correlated. - The engine is mounted with down thrust, the “shelf” needed to be offset to align the center of the cowling with the centerline of the airframe. - With that determination I was able to establish that the engine needed to be lowered 4” from it’s current position.

Motor Mount (Revised)

Bite the bullet! New material ordered – new fixture fabricated , tubing fitted and welded!!

“Boot” Cowl (Revised Again)

Falling Dominoes! With the engine moving down the opening in the “Boot” cowl bulkhead needed to move as well. Old hole was plated over with .032 6061-T6 and a new clearance hole was cut. Luckily none of the side panels were affected.

Ring Cowl

• With the modifications to the Motor Mount, Baffle/Shelf combination and Bulkhead made the engine was remounted and the cowl was positioned for fabrication of the actual support structure.

• Normally you do not attach cowlings to engines as it causes problems when the engine moves on the mounting bushings. However, since the ring cowl does not touch the airframe that is what has to happen.

Ring Cowl

With the cowling halves positioned to the “shelf” it became possible to measure/fabricate and mount “N” struts from ½‘” aluminum tubing. The result rigidly amassed me and all that have “inspected” it.

Brackets were fabricated that mount to the engine, engine mount bolts and cowling ribs.

Ring Cowl

• With all the support structure determined and fabricated the cowl structure could now be skinned. In keeping with my original objectives of not going overboard on detailing and not being any more “anal” than I am. I decided to keep the fabrication as simple as I could and not involve any “new” fabrication techniques.

• So the cowl was divided into 16 sections and each section has a flat wrapped panel.

Ring Cowl

Panels were fabricated from .020” 3003

Aluminum – which is soft and easily formed.

Conversely it is soft and easily deformed!

Ring Cowl

With the lower cowl clecoed it was time for a trial fit – not really sure about this something just doesn't look right.

Ring Cowl (Revised)

• Now this is getting a little old! I actually riveted the lower cowl panels and started to form the panels for the upper cowl, but I kept coming back to the previous picture. I finally came to the decision that the cowl looked to big and massive. The diameter was Ok but the depth and thickness looked off.

• So I drilled out all the rivets in the lower cowl and proceed to redo everything.

Ring Cowl (Revised)

• After disassembling everything I was able to salvage the leading and trailing edges, mounting brackets and @80% of the panel skins.

• First step was to fabricate 18 new ribs 4” shorter in chord and ½” less in height.

Old

New

Ring Cowl (Revised)

• Repeat skinning the cowl

Better – I think I can live with this! Special Thanks to Ted Callahan for the fuselage markings.

April 2015

The “Pan”

In order to partially close the huge gaping maw in the cowling opening normally occupied by a big round engine, a simulated shutter assembly the real F4B-2 incorporated was fabricated.

Loose Ends

• With all the firewall forward fabrication done all the sheet metal and tubular items were powder coated to match the fuselage pieces.

• Instrument wiring and fuel system components have been fabricated and installed.

• Next steps – assemble, weight, system checks, engine run, etc., etc.

Testing

• Fuel Flow test preformed, 2 gallons in tank resulted in an 25.9 gals/hr flow for an engine requiring 5.5 gals/hr.

Note : In this attitude one gallon was required before fuel started to flow.

Testing

• First engine run 10/9/15

Surprise!! Started on first flip! Wow

Ok – the plane is not equipped for IFR and neither am I – I’m setting on the bottom of the seat – flight cushions not installed!

Troubleshooting

• Following the Fuel flow test the fuel line was reconnected a fuel leak at the carb. was experienced; traced to a cracked Aeroquip fitting which was replaced. Accomplished before first engine run.

• At engine start up the Oil Pressure gauge and Tachometer were dead. After the normal troubleshooting process both units were replaced.

• Oil Pressure issue proved to be a lack of prime in the oil pump not the gauge/sender.

• Surely more to come!

Final Assembly

• Finally was able to assemble the wings to the fuselage and get a true look at my labor!

Weight and Balance

Weight (lbs.) Arm (in.) Moment (in lb.)

Left Wheel 244 5.5 1,342.00 Right Wheel 268 5.5 1,474.00

Tail 5.5 159.5 877.25

Totals 517.5 3,693.25

Empty CG 17.4 inches

Minimum Pilot Weight = 104 lbs Maximum Pilot Weight = 190 lbs Original Empty Weight Goal was 500 lbs. (missed by 3.5%) CG range = 15.3 to 19.9 inches

Weight & Balance

100 120 150 170 180 185 190 200

1 15.0 16.3 18.0 19.1 19.6 19.9 20.2 20.6

2 15.0 16.3 18.0 19.1 19.6 19.9 20.1 20.6

3 15.0 16.2 18.0 19.0 19.6 19.8 20.1 20.5

4 15.0 16.2 17.9 19.0 19.5 19.8 20.0 20.5

5 15.0 16.2 17.9 19.0 19.5 19.7 20.0 20.4

6 15.0 16.2 17.9 18.9 19.4 19.7 19.9 20.4

7 15.0 16.2 17.9 18.9 19.4 19.6 19.9 20.4

8 15.0 16.2 17.8 18.9 19.4 19.6 19.8 20.3

9 15.0 16.1 17.8 18.8 19.3 19.6 19.8 20.3

10 15.0 16.1 17.8 18.8 19.3 19.5 19.7 20.2

condition exceeds CG Limits

Gross Weight of 750 lbs (Utility Cat. 4.4/-2.1 g's)

Gross Weight of 800 lbs (Normal Cat. 4.1/-1.9 g's)

Recommended Fuel Reserve

Pilot WeightF

uel

(Gall

on

s)

& 3

qts

Oil

CG envelope 15.3 - 19.9 inches

Next Steps

• Get all the required paperwork in order

• Contact FAA/DAR for Aircraft Inspection/Certification

• (A) Shoot a bunch of landings in the KR in preparation (B) Draft a Test Pilot

• Wait for a clear/calm weather Tuesday for 1st Flight

To be Continued !

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