No Plan — No Clue — My FW-42

Recently Scott pointed me at ‘Printed Warbirds’ in that list was the Focke-Wulf FW-42.

A fantastic looking plane that looks like it is something out of the wacky races and I was a little surprised that  Scott hadn’t noticed and already started building it. So with a bit of persuasion I decided to have a go.

 

 

I couldn’t find any plans for the plane, but I did manage to find a sheet with the 3 views, front, top and side already blown up to a 48″ wing span. So I downloaded, printed and tiled it up on the dinning room table.

I thought the lovely square body lent itself perfectly to foamboard and flitetest’s method of folding fuselages rather than depron, and the main wing with the engines attached would need quite a lot of carbon reenforcing if made out of depron, but made into an aerofoil shape with foamboard could probably quite nicely support the weight and stress. Also the 2 motors should be able to give the model enough muscle to lift the heavier foamboard into the sky. And I’ve still got a few boards of foamboard left, so foamboard it is.

Unfortunately my tiled image is rather low resolution, so I put a piece of board under the plan and started by using a pencil to go round the outline of 1 wing, this produced a light dent in the foamboard which I then made into a better shaped wing, added the extra underside so it could  be folded into a aerofoil shape and cut it out. Because the plan was so low resolution if I did the same for the other wing they would never match so I flipped this wing over and made a new trace of it for the other wing. The spars were next. On the plan the wing is very tapered almost to a point, although I dont think I can quite get this, I did make a tapered spar to try to mirror this, but still leaving just enough room for the aileron servo in the wing void.

I didn’t want to glue this up yet because I am still not sure how this will go onto the fuselage, or how the engines will connect to it.

So the next step is the canard. Initially I was going to make this a KF step but thought that was a bit of a cop out after making the main wing as an aerofoil. So I decided to make this an aerofoil shape also. I also wanted to make this out of 1 piece so used a piece of paper to trace round the front canard on the plan with the intention of folding it and cutting it out to produce the full wing template.

Then after I added the underside of the wing I realised that because of the shape of the wing, and the direction of the folds (not perpendicular to the body centre line) the base of the wing would need to be in 1 piece and the top would need to be separated and come together when folded, so I cut this 1 sided paper template out and traced round it twice to create my front canard wing.

I also initially wanted to put the elevators on this canard but the placement of the servo and the connecting of the pushrods eluded me. I did want to put it out of the bottom of the plane since the base of the plane was such a nice square shape, putting a servo inside the body with a connecting rod to each side of the canard would be almost impossible to thread and connected. Putting 1 servo on 1 side with a bit of bent wire to make each elevator work together was an option but would create a rather lob sided look. The best option I could come up with is 2 servos, 1 either side each connected to each elevator, but this would mean there a 2 servos right at the front putting extra weight and extra complexity. So although the elevators are marked they are not cut and the plane for the moment is going to be going forwards with Elevons and the hope that I can get the plane balanced enough for these to give enough control. But that might change yet…

Next I turned to the engine mountings, These will need to fit over the wing and key into the wing for strength. So to try to make sure I get the right shapes, and location for keys to avoid the spar I made a little paper mock up

A bit of shaping and fitting and it fits to the wing nicely, perhaps needs shortening a bit so it fits just the flat underside of the wing and doesn’t trail onto the tailing angled edge of the top side

Marked up where the keys should go on the paper and then a quick check with the motor placed in front of it to see if they are somewhere about the right size pointing forwards from the wing. The sheet was traced from the main plans because it is easier to move a single A4 sheet than the whole big sheet.

It looks about the right length, maybe even a little bit short to the scale but not too bad.  I think that will do, I am still wary of putting too much weight too far forwards on this model. Once I transfer to foamboard I will try to bend up the underside to a nice curve by removing the inside paper and put a top on the box which will hopefully taper into the wing. Although this of course needs to happen after the wing has been pushed through the main body.

The main body is a nice simple shape, effectivly 2 boxes, a larger to the back and smaller to the front, although the plans do show that the body behind the main wing is narrower than the main body in front of the main wing. Since I dont have the plans of how this reduces I have discounted this and created a standard box for this section.

So now with all the pieces are cut we are ready to start assembly. The plans show the bottom of the canard wing is level with the baseline of the body, I am going to bring this up slightly so as to put a 5 degree inclination on it and add strength. The main wing also appears to come through the top of the main body, again this I think I will need to put so the main body remains in tact above it for strength.

More updates to follow…

Next update:

I’ve created the torque bar by bending up a single piece of wire with a loop in the middle to put a z bent piece to the servo, as suggested by Mr Mel. Here is the piece sat on the plane:

I did initially think of putting the wire in a hearing aid tube were it come through the bodywork so that it can be glued and not impede the movement of the elevators, but this didn’t work very well so I removed these tubes. Here is the canard, servo and mechanism all in place and working with the torque bar stuck to the elevators with epoxy glue.

I wanted to now fold up the engine nacelles and do a quick check of the receiver, speed controller and both motors to ensure that they reacted the way I expected. With the 2 speed controllers, 1 BEC had to be disabled by cutting the red wire from one of them. Everything checked out, both motors work fine, so I’m happy with that setup.

The next step was to put the wires through the main wing for the motors and the elevon servos, then join the 2 sides of the wing. To get a good fit I sanded these then hot glued them together. Passed it through the body, I used the plans to line up the wing and glued it into place

So the nacelles go onto the wing and the servos connected to the control surfaces

Now with the engines in place and held I could do a power test of the engines. The first prop I tried was a 6×4.5 triple blade prop (as shown above) this would be an ideal size since it clears the ground so the plane could belly land. On test these drew 11 amps each on a 3 cell battery, about 125watts each. This would give total power of 250watts. The weight of the model now was about 900grams, still with some work to do, so the estimated dry weight of the plane would be about 1kg (2 pounds) with an extra 500grams (1 pound) of batteries so 3 pounds all up weight, 250 watts would be a little under power. So I also had 2 triple blade 7×3.5 props. Surprisingly under test this developed even less power about 8 amps or 90 watts each definitely no good. So my triple blade 8×4.5 was next. This drew around 17amps, 180watts per motor this is still within the motors rating, but with a total power of 360watts this should give a reasonable power level for a 3 pound model, its not going to be acrobatic, but should lift it into the air nicely. So the 8×4.5 props it was. This did give another problem that the plane now could not be a belly lander, the prop does stick out rather too much and would be likely to do some damage to either the props or even the plane on landing. So I had to make some landing gear. The rear wheels where quite simple, making them in the same way as flitetest created the landing gear for the FT Cruiser attaching them to the engine nacelles. The front wheel was a little more of a problem, this was what I came up with

Hot gluing a piece of plywood on the bottom of the plane and bending a loop of wire through the wheel, retaining it with an elastic band to give it a little play. This now nicely lifts the whole plane up above the level of the propeller touching the ground. Although I haven’t yet put the vertical tail fin on, the COG is currently towards the front of the main wing, using this calculator online: http://adamone.rchomepage.com/cg_canard.htm it should be about half an inch in front of the main wing. So placing the batteries in the main body ahead of the wing should move this to the correct place. So I created a hatch in the top of the main body for this, put a bit of velcro in to stop the battery moving around and a magnetic catch to keep it closed.

The final step is to put the vertical tail fin and hook it up to the servo and receiver

All looking good and ready for its test flight, final dry weight is exactly 1Kg, with 2 1400mah batteries the all up weight is just under 1300 grams. This maiden may not be this week, although the ground is nice and soft it is supposed to be a little windy tomorrow. So I will need to upload details of the maiden when I pluck up courage to do it. You never know I might even decorate it….