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FT Commuter 140 % Build

#1
Hi, thought I'd just share the build process, comments (positive and constructive criticism both ok) welcome.

I started by using the free download Inkscape to convert the FT plans to 140 % PDF.

I felt that 140 was the perfect size for a few reasons. It gives it about exactly 1m wingspan which is just small enough to fly on a grass oval/large park, and not freak people out, and also land on grass without roughing up the landing gear. The other reason is that I am building with 6mm foamboard from Spotlight (probably the Australian version of your cheap craft warehouse) and so the slots etc per the plan didn't have to change, everything still fits per plan.

I've attached them.

Cheers
 

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#2
I then set about cutting as usual and as soon as the fuselage back end was up, I left the front open to make it easier to work on the other internals.

I expoxy'd a balsa plate and used music wire for the rear landing gear, attaching it with cotton and thin CA.

The front gear I decided on a bent 'question mark' going into a balsa former for strength. The shape is to allow room to move for a decent size 3s 1500 battery - not exactly knowing where the CG weight is going to be needed, I gave myself the option if it needs to go right forward. Also you'll note both landing gear formers lean at an angle per the FT/scale concept of raked-forward landing gear and I suspect this would help with supporting the plane better in landings by bracing against the direction of travel/impact more.

Servos were just your cheap 9g.

In an attempt to keep weight down as much as possible, I used balsa for the pushrods with wire at each end. This also makes the pushrod a lot stronger and stiffer to make for a much more responsive control than you get with wire, and this size also makes wire start to be a bit sloppy.
 

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#3
Another point of interest is that I went with an elastic band attachment for the wing and will also be trying this as the means to access the internal and put the battery in/out. What this lacks in convenience, in my opinion, is made up for by retaining the integrity of the bottom of the fuselage (no hatches) and from flying these things, that's where the wear and tear happens so I wanted to keep it clean and strong.

I used a thick BBQ skewer for the elastic band but there's a bit more to it. Internally, there is a balsa spar sitting directly on top of the skewer and it's designed just proud so that when you close down the fuselage top, it sandwiches the balsa, making for a stronger structure. You don't want the skewer pulling through the foamboard due to the tension and this seemed a lightweight solution.
 

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#4
I went with a very light motor mount system. I used the stock FT ply, mounted to two transverse spruce rails. They are tacked on to the internal of the fuse with CA. The strength however is borrowed from the FT skewer concept. They run through the external cowling like in the standard FT builds and then I've actually done tight cable ties to attach them internally to the spruce, seems pretty solid. For extra rigidity (which also helps the landing gear as well), there are two thin balsa piece between the landing gear former and the top spruce rail.

Don't forget the right thrust, this was part of the the initial positioning of the rails.

The motor is a Tomcat P4002 940kv running a 10 in prop. I don't know a great deal about volts, motors etc but seems powerful enough with the 3s and about the right weight and size for a plane like this. My guess is if you rev it and it's blowing your hair and the curtains around and all the stuff off your bench, then it should be able to get a <1 kg plane into the air. And at this stage it's on track for under 1kg, weighing in at 340 g as pictured here (no battery). I'm very happy with that.
 

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buzzbomb

I know nothing!
#5
Very nice build! You're really thinking this through. Once the model starts getting around the 36 inch wingspan mark, down and right thrust are much less critical, and perhaps not even desired. I would advise just straight on, except I'm not yet familiar with the Commuter model.
 
#7
Very nice build! You're really thinking this through. Once the model starts getting around the 36 inch wingspan mark, down and right thrust are much less critical, and perhaps not even desired. I would advise just straight on, except I'm not yet familiar with the Commuter model.
Cheers - good thoughts, I'll consider straightening the thrust up.
 
#9
I've had a few issues with the wing build. I wanted a balsa spar and to dispense with dihedral mainly because the centre join is always a weak point. (As for the changes to flying characteristics, no doubt we shall find out). The main issue is that the Mini is designed to fit with dihedral, so I've got to deal with gaps and so forth. I'll figure something out... But the wing feels nice and flexi like a real plane.
 

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#10
The bonnet (that's what I call it..) had to be re-made from scratch to work better with the way the bottom of the fuselage was already formed. The fit is ok, sort of :) - close enough for a drug-running Cessna, heh. I've dispensed with the FT foamboard windshield and gone with a lighter drink bottle plastic that is formed in the style of the fullsize 150. I've left it uncut at the top because I want to fit it around the leading edge when the wing it on. But, in a difficult day, this bit cheered me up.
 

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#13
Gosh, but it looks like a bug! Did you treat the foamboard in any way before painting?
Lol - ok. To be honest, I just hit it with spray, I am not aware of any 'treatment' process for foamboard but keen to hear of any. That said, the white is more or less an undercoat, as much of the fuselage will be red. But I'm keen to hear about any treatment given I want the wing to mainly be white.
 

buzzbomb

I know nothing!
#14
Lol - ok. To be honest, I just hit it with spray, I am not aware of any 'treatment' process for foamboard but keen to hear of any. That said, the white is more or less an undercoat, as much of the fuselage will be red. But I'm keen to hear about any treatment given I want the wing to mainly be white.
MinWax to seal the foamboard and help the paint adhere. @BATTLEAXE didn't invent it, but he's got a good video of the process on his "tips" thread.
 
#16
Things got interesting when I added the wing. The CG was a touch too heavy in the tail and so had to re-think the battery position. Going to have to try right up front (and vertical). So had to create an opening bonnet for that. CG now good. Second problem, still dragging on the tail, so have had to bend the rear landing gear back. A bunch of things left before we fly, but not far now.
 

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#17
Well, I'm back. Bunch of things not going quite right, but that's the hobby sometimes...

Managed to maiden her yesterday and yes, got her up in the air! Might need a bit of tweaking control wise as it didn't seem very responsive as it's mini counterpart. Tried a low dual rate of 60% but too sluggish.

Other issues included a left aileron servo that was 'twitching' (anyone know what causes that?) In the end I had to cut back into my lovely new wing to pull out the wiring. Replugged it, seems to be working ok so maybe a loose connection?

Beyond that, it's reallly just the newbie mug flying the bus, eh? Interested in any good posts on landing, there seems to be a lot of different info around and with a smaller plane like this landing on grass, it's only going to struggle to land if you float it in, as I discovered, and in the process broke part of the engine mount.

Sorry for the mixed post but I'm still optimistic that the right approach can make this plane a good flyer in the right hands.