Fly Electric!

'Chitty Chitty Bang Bang'

I'm sure Chitty is something that everyone will recognise. It's great to see it fly on calm sunny days even if Truly still refuses to come up with me! Started in January 2004 this has been my most difficult plane to design (can I call it that?). It flies pretty well now even if it did take 18 months with many crashes and changes. Caractacus must have been very determined (so must I!).

I realised when I started the project that the wing area would need to be larger than the original. However one of the major problems was that the car masks the tail surfaces. This meant that it pitched randomly up and down. Changing the CG had absolutely no effect. Well larger tail surfaces sorted this out.

I could not get the tiny pusher prop and heli blades to work so abandoned them in favour of a more traditional tractor prop. Initially this was with a GWS 'IPS' motor with 9.6:1 'D' ratio, 12x6 prop and 3 lithiums. This provided good thrust although I now use one of my CD-Rom motors with a 8x3.8 and 3 lithiums.

The wing was fun. The terms 'control reversal and 'adverse yaw' took on very special and personal meanings to me and my Chitty! For example, when flying indoors as you approach a corner of the hall it would always turn towards it when you banked the other way!!! Outdoors it would stick its nose up, stall and usually spiral into the deck. Some of the photos show an undercambered 3mm Depron wing with ailerons. The ailerons added no benefit. I changed to a thick built up wing made from EPP (without ailerons) and it still did the same. I then observed that when the plane banked the bottom of the inside wing was visible whereas the bottom of the outer panel was not. This is the same as having full opposite aileron which was probably why it rolled in the opposite direction to the intended turn. The dual skin wing allowed me to build in exagerated washout on the tips and this has cured the problem.

Well the plane flies well now and I fly it often when weather permits. Indoor is fine too but it takes up a fair amount of space and is faster than you might like. I seldom crash now but it can still catch you out from time to time, I guess mainly when you try to slow it down. 'Power and Push'; just like learning to prop hang!

As mentioned, the wing is now built up and has a 3mm spar inside braced at the join in the middle of the wing. Note that some of the photos show the original wing. The servos are now inside the wing and battery just behind the motor. The motor and tail are attached to 4 or 5mm carbon tube. The car is made of 2mm Depron; the photos mainly show thin polystyrene which is also OK but tends to suffer from manhandling. The tail surfaces are 3mm Depron. The wing is 38 inches and AUW is just under 8oz with two 6g servos. The single CDRom has adequate power and you would not want less. It flies best on three 450mAh lipos and 860's feel a bit heavy.

The wheels are built up from 6mm Depron, 1/64 ply inner rim and toothpicks. The balsa disc you see in one photo is to keep the wheels circular while building them. The black 'tyres' are Depron and were cut off the inner red Depron before painting (to make them easier to paint). I probably would not bother separating the black from the red next time. The wheel may look complex but in practice they don't take much effort and they add greatly to the authentic look.

Hopefully the pictures will help illustrate the construction but feel free to send me an email if you need help. Being a near scale replica of a real 'plane' make sure to search the web for photos of the prototype to get the detail right. Thanks to MGM for bringing us such a great movie. As usual you may build the model but may not profit from the design. Check your printer settings (don't 'fit to paper') to avoid distorting the size. Page 1 should print a reference line to check.

Format Free Plans
'PDF' A4 paper 117kb
'PDF' Letter paper 119kb

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