How to build the P-39 Airacobra

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This plan is reduced in size! The plan is split up into 4 TIF-files, that you can take into a suitable graphics editor and print out.
I suggest you use Paintshop Pro, and print it using original proportions and full sheet printing.
Then you must scale the printouts up to proper size, and fit them together.
On the plan you have a kind of ruler, consisting of filled squares. Each square is 1cm long. (5cm=2inches).
Using the ruler to adjust the upscaled plan, you should succeed in getting a proper plan to build from.
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Please note that the P39 design is about 25mm (=1inch) too long in the fuselage, according to the aircombat rules. If you wish to compete at a higher level, you should adjust this.
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About the design: The P-39 is a 1/12 scale fighter, and should be built quickly to get up in the air as fast as possible. The finish is not that important on this kind of model, instead it is important that the radio-installation and certain things of the model are properly built. It is an advantage using CA-glue during the building, but also other types may be used, for example to assemble the wing-sheeting, which must be adjusted for proper fitting. 
	Be aware that these things are built correctly: Engine direction and fin direction. Wing and stabiliser alpha. Washout must be done, and be the same on both wing-tips. Centre of gravity must be measured and be on or in front of where it is marked on the plan.

The fuselage: You build the fuselage upside down. Take a 5mm sheet of balsa. Draw a centreline on to it, which you will use to assemble 5-7 according to. You do not have to draw this line in the centre of your 5mm sheet of balsa, instead you should draw it so that you use the sheet at a maximum. Prepare 5-7 for attachment.
	5 is built up by three parts, which are glued together to accommodate most strength at minimum weight. The 5mm balsa is covered on both sides by 1,5mm plywood. Use epoxy for this.
	5 must have a hole for engine mount, engine push-rod and fuel-lines. Attach the engine mount with blind-nuts. You may then easily change engine-mount if it is broken. 
	Onto 6 a reinforcement should be assembled, for wing-mounting. Do this properly, because it must cope with heavy landings.
	You can make 6 in two ways. Either you do it according to the plan and make a hole in it to be able to reach the fuel-tank. You might also let 6 be whole, and let the fuel-tank be built in. If you should need to get to the fuel-tank, you could always cut a hole afterwards. 
	Make sure you have a good fuel-tank if you choose the last alternative. A hint is changing the long fuel-line inside the fuel-tank against a piece of copper tube. Attach the tube with two small fuel-lines to the tank-tube and the clunk. In this way, you eliminate problems with a clunk that goes into the front of the fuel-tank, thus cutting the fuel supply.
	Glue 11 and 12 to 7. Make a hole for the elevator push-rod in 7. 
	Pin 1 to the building-table. Glue 5-7 to 1. Make sure that 5 is in the proper direction.  The engine should be pointed down and to the right. Because you are building upside down, you should point 5 to the left and up, approximately 2-3 degrees. This is important! 6-7 are to be assembled in 90 degrees angle to 1 and the centreline. Then assemble 4 to 1 and 5.
	Glue one 3 to each of the 2s. Note that you should have two different 2s, one right and one left side! The right side should stop at 5, because the engine will be in front of 5. Sand the rear part of the 2s, so that they fit when bent together. 
	Assemble 2 to 1 and 5-7. The most important is that the 3s attach to 1, because you will sand the fuselage to a round shape later. Bend the 2s together in the rear. Make sure you get a straight fuselage!
	Now you have a halfway finished fuselage. Install elevator push-rod, fuel-tank and engine push-rod, before you cover the bottom of the fuselage.
	Assemble 8 and 9 to the fuselage. Assemble 10 to the fuselage. Sand to proper shape first when the wing is ready.
	Assemble 15 to the fuselage. Glue 14 together. If you are planning to cover the model with iron on film or tex, then you must cover 16 now. Adjust 16 to the slot in 14. Thereafter you can glue 14 to the body, with 16 in place. Don't forget this, because 16 can not be fitted afterwards!
	Sand 31 into descent shape. Sand 29 according to the side-view. Glue 29 and 31 to place. 
	You now have a ready fuselage. Sand the top fuselage to even rounding. Shape 29 according to the original. Note that it is easy to make 29 too high in profile. At painting, you also use a bit of the fuselage side to make a cabin, so 29 until then makes an illusion of being too small.
	
Balsa-wing: There are two wings in this design. We start with the balsa wing. Note that the wing that is showed on the plan, is showed without top sheeting!
	Glue two 1,5mm sheets and two 2,0mm sheets to two broad sheets. You do this by putting tape above the line where the two sheets meet. Bend the two sheets apart, put glue between them, and put it together. Let the glue dry under pressure.
	Cut out 17 and 18 out of the sheets you just made. Note that 17 and 18 stretches to the leading edge of  19! Make 17-18 a little bit too big. 19 is then glued on top of 17. Thereafter you assemble 20-23 to 17. Do the same thing to the other wing half. 
	Glue the two wing-halves together, with 24 as assistance. You automatically get the proper dihedral out of 24, so be careful when you cut it out!
	Sand 19 according to the top surface of the ribs. 
	Pin the wing down at the wing root, and put something under the rear of the wing-tip, so that it is lifted 8mm. Be sure that the front of the wing-tip is pinned down. This is to get the proper washout. Then cover the wing half with 18. Note that 18 should stretch over 19, and later be sanded down to proper rounding. Do the same with the other wing-half.
	Assemble 26 to the wing-tips. Glue two 27s to the bottom sheeting. Then assemble 28 to 27. Be careful here, because the model will land on this part!
	Adjust 30 to the fuselage, and then assemble it to the wing. It is important that this part fits! Cut and sand the 25s.

Foam-wing: Cut out wing profiles according to the plan. Mark the profiles with lines to assist you in making your wing-halves. Saw two foam-blocks, to the size the wing top view shows. Draw a centreline to the two blocks. Attach the inner profile according to the centreline. Attach the outer wing profile with its rear 5mm above the centreline, to automatically give washout. 
	Start cutting with your thermal saw. It takes two persons to do this. Cut the top surface first. Cut in even tempo according to the lines drawn to the wing-profiles. It gets easier if you place weights on top of the block, so that it can not move. Then cut the bottom surface. Save the scrap that is left over from the cutting. You will use this when covering the wing. Now do the same thing to the other foam block, but be sure to make a left and a right wing half!
	Glue four 1,0mm balsa sheets into two broad sheets. Se "Balsa wing" on how to do this. Cut out these into an approximate bottom and top sheeting. Make them a little bit bigger. 
	Place the bottom sheeting in the bottom part that was left over when you cut the wing. Place glue, polyurethane or something the like, on the sheeting. Put the wing half on top. Place PU-glue onto the leading-edge ((5mm birch spar), and place it in front of the wing half, and on top of the bottom sheeting. Be sure that the leading edge really touches the wing half and the sheeting. 
	Place glue on the top sheeting, and put it on top of the wing half. On top of this you put the top part that was left over when you cut the wing. Place weights on top of everything, and let it dry for several hours. Do the same thing with the other wing half.
	Sand the wing middle parts to the proper shape, that gives the proper dihedral. The dihedral should be 12cm, measured at one wing-tip. Glue the two wing halves together, with the proper dihedral and without any errors. Use PU-glue for this.
	Assemble 33 to the trailing edge of the wing, and 26 to the wing-tips. Reinforce the wing middle with glass-fibre cloth and epoxy. Glue 27 and 28 to the bottom sheeting. 27 must be adjusted to the rounded surface.

Installation: The engine is installed in a nylon engine mount, in 45 degrees angle. The carburettor then comes in a proper height, to the fuel-tank. At the same time the muffler gets outside of the fuselage.
	Assemble a standard nylon elevator horn to the elevator. Assemble standard aileron horns to the ailerons. The aileron horns runs through 7. Therefore, you must cut holes into it, to make the aileron horns run smoothly. Make the holes big! Otherwise, you might loose aileron control if the wing is fitted wrongly.
	Assemble elevator and ailerons with hinges. You may use thin plastics for this, to make things easy. 
	The elevator push rod is most easily made out of a (5mm birch spar. Drill holes in it and assemble linkages with glue. The engine push-rod is most easily made with Ny-Rod type push rods.
	You should not get any space problems when installing this model. The P-39 has a lot of space for radio equipment, compared to most other 1/12 scale fighters. Although, you might get a problem having the centre of gravity too far in front of the place that is marked on the plan. This should not give any problems, as long as you have a little nose up trimming on your radio. Be aware though! The centre of gravity should not be in front of the wing!
	The wing is attached with rubber bands, that are drawn down from 11 out of the fuselage and forward round 27-28. In this way you get a wing mounting that can cope with rough landings without breaking anything. 
	Control-throws in this kind of model are most individual. An experienced fighter pilot has most certainly very big throws, to accommodate fast manoeuvrability. The beginner should of course have a little lesser throws. You might start with 5mm throws in each direction, both on ailerons and on elevator. If you have dual-rate on your radio, you can lesser the throws if you think they are too big.
	
Finish: You can do as you like with finish on this model. A hint is using coloured iron-on tex or film. My models are covered with olive drab Solartex, which is painted with a thin, thin layer of clear paint. The underside is painted with white paint. Try to have different colours on the underside and over-side! The model will be much easier to see in the air in this way.
	The cabin is supposed to be painted. Use either dark or light paint, and try to paint it like the original cabin.
	There are a lot of original painting schemes to take from, unless you want to do your own fighter. The P-39 can be painted in US, USSR or British markings. The Russian are the simplest, containing of only red stars. Also add small texts and stuff, to make it look like the real thing.

Premiere flight: Be sure to trim a little up on the elevator. Have an assistant to help you throw the aircraft. Make the engine run perfect. Let your assistant throw the aircraft with a strong push straight forward. If you have the opportunity, try to make these first starts over high grass, to ease up bad landings. 
	Trim the aircraft so that it flies straight forward. Make a few manoeuvres to feel how it flies. If you are unfamiliar with fast aeroplanes, then you should adjust the throttle to slow things up a little. A usual mistake is flying at maximum speed in panic, which most often ends in an unnecessary crash. 
	Take it easy when landing. Keep up speed, and land in high grass if available. The P-39 is normally easy to land.

Common mistakes: If you forgot to give your wing a washout, it will stall as soon as you try to turn a little harder. The result is half a quick roll, ending in a turn the opposite way around!
	Another classic mistake is having the centre of gravity too far aft. This will result in a model that spins as soon as you press it. This will probably not happen with your P-39.
	A common mistake with the P-39 is having the centre of gravity to far to the front. This leads to a model that manoeuvres slow, and loops very widely. It might also result in a model that "falls through" in landings, and needs a lot of speed to land normally. Try to move the centre of gravity more to the aft. If you have to, place the batteries behind 7. 
	Something that might happen when you have not pointed your engine downwards, is that you stall the model on the premiere flight. This is most common with the balsa wing.

Some tips: In a rough landing 30 might be pulled off the wing. If you can not glue it in place again, just draw rubber-bands around the leading edge of the wing and up over the fuselage (I have myself made a "kill" with the wing mounted this way).
	In a rough landing, 7 might be pushed loose. This is no problem - just take 7, and glue it to its place again!
	In a crash, 5-7 might be pushed loose. This is also no problem, because the fuselage is held together by 1. Just glue 5-7 to its proper places again.

Numbered parts:

1. Fuselage top covering		5mm balsa
2. Fuselage sides					3mm balsa
3. Wedged balsa					10x10 balsa
4. Wedged balsa					10x10 balsa
5. Bulkhead 1					1,5mm ply + 5mm balsa + 1,5mm ply
6. Bulkhead 2					5mm balsa
7. Bulkhead 3					5mm balsa
8. Forward, bottom covering	3mm balsa
9. Rear, bottom covering		1,5mm balsa
10. Wing saddle					3mm balsa
11. Rubber band pin				(5mm birch
12. Reinforcement, pin			5mm balsa
13. Fin, fillet						3mm balsa
14. Fin							3mm balsa
15. Stabiliser						3mm balsa
16. Elevator						3mm balsa
17. Wing, bottom sheeting		2mm balsa
18. Wing, top sheeting			1,5mm balsa
19. Leading edge					8x8 balsa spar
20. Rib 1							3mm balsa
21. Rib 2							3mm balsa
22. Rib 3							3mm balsa
23. Rib 4							3mm balsa
24. Wing dihedral spar			5mm balsa
25. Ailerons						4x30 wedged balsa
26. Wing-tip						20mm balsa (2x10)
27. Throw hold					3mm balsa
28. Throw hold, sheeting		3mm balsa
29. Cabin							Foam or balsa
30. Wing mount piece			3mm ply (2x1,5mm)
31. Air-intake					10x15 scrap balsa
32. Leading edge, foam-wing	(5mm birch
33. Trailing edge, foam-wing	3x6 balsa spar
34. Inner wing profile			Ply
35. Outer wing profile			Ply

Note that some materials can be replaced by others. For instance 2x10 in wing-tip can be built out of 4x5 etc.

Materials:

2pcs		1,5x100x1000 balsa
2pcs		2,0x100x1000 balsa
3pcs		3,0x100x1000 balsa
1pc		5,0x100x1000 balsa
1pc		1,5x100x1000 plywood
1pc		8x8 balsa spar
1pc		4x30x1000 wedged balsa
2pcs 		10x10x1000 wedged balsa
1pc		(5mm birch
1pc		foam
1pc 		engine mount, .10-.15 size
1pc		fuel-tank, 100-150cc
1pc		spinner, 40-50mm
(4pc		1,0x100x1000 balsa)
(1pc		foam block)
(1pc		(5mm birch)
(1pc		3x6 balsa spar)

Materials within paranthesis are for the foam-wing.
