Bush Plane Design

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Bush Plane Design

Postby Exosock » Tue Nov 12, 2013 5:07 pm

Good afternoon everyone!

As part of a final year project I'm running at university, I need to produce a basic design for a light cargo aircraft. My tutor (who introduced me to the LAA in the first place) initially expressed an interest in keeping the weight somewhere near a C172, though he'd be perfectly happy if I scaled this down.

Due to my own interests and a very broad project scope, I was hoping I could drive this towards being a bush plane (obviously the weight of a C172 would give this design less aggressive performance than a Carbon Cub or CH701). My current thinking is a high-wing, V-tailed, twin-seater aircraft with a taildragger configuration.

Does anyone know of any similar designs I could compare against? Or any sources that could point me in the right direction for designing my aircraft?
And can anyone tell me why V-tails are so much more common on model aircraft than full-scale machines? I understand V-tails have a somewhat mixed reuptation when you stick a human in the cockpit, but I never understood why (apart from the obvious point of models being more chunkily built).

Thanks in advance for the help!
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Re: Bush Plane Design

Postby TRAZZELL » Tue Nov 12, 2013 8:55 pm

Dan Raymer's book on preliminary light aircraft design is a very good start, for more in depth stuff try Hiscocks (both available from the LAA bookshop). I don't know anything about V tails -is there a reason why you are looking at a V instead of conventional?

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Re: Bush Plane Design

Postby ROB THOMASSON » Wed Nov 13, 2013 12:06 pm

You might look at the Escapade Microlight as it's quite close to your requirements. Lots of good ideas there and used in the USA for all sorts of bush flying I gather. The wings will take 12 G for a start!
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Re: Bush Plane Design

Postby Exosock » Wed Nov 13, 2013 9:54 pm

Thanks for the direction!

But 12G? I know these machines need to be tough... but why... how could that kind of loading occur without extreme aerobatics?

V-tails... well, I think it's largely a personal thing, though the technical reasons for their implementation make sense. I learned to fly RC aircraft on a Firebird Commander (V-tail design hooked up to the servos with what looked like fishing line), which I absolutely loved to bits. There's also an element of crossover, as I wanted to use a V-tail on a micro indoor design for another module to increase the Reynolds flow, by combining fin and tailplane surfaces into two larger surfaces. And gain bonus originality points. Maximising Re flow on a bush plane seems like a good plan of action. The biggest disadvantages I can think of would be the torsional loads imposed on the fuselage (which would need to be reinforced to support a tailwheel anyway), and the potentially nasty effects of sudden crosswinds acting on the tail, which could push the nose down at unwelcome moments. Also increased complexity required for mixing.
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Re: Bush Plane Design

Postby Ed Parkin » Thu Nov 14, 2013 2:48 pm

Hi Matthew,

Bush planes are massive in the states and there are plenty of designs to get ideas from. It appears that one of the ultimate lightweight rotax powered designs currently in favour is the 'Just Aircraft Superstol' an updated Highlander with some amazing landing gear for the rough stuff, have a bit of a Google and check out some of the landings on YouTube that this aircraft can do, most impressive! It will give you a bit of an idea what is available at the extreme bush plane end of the market, regrettable its not approved (yet?) in the UK.

The Groppo Trail is anther one to give you some inspiration, again rotax engine and folding wings, have fun with your designing,

Ed
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Re: Bush Plane Design

Postby Exosock » Thu Nov 14, 2013 11:12 pm

Thanks Ed. I got the impression that very light aircraft were popular in the USA, but I wasn't sure whether it was just a small percentage of the population living in remote areas. I... don't suppose you could point me towards sources that could give me a figure on bush plane use?
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Re: Bush Plane Design

Postby Ian Melville » Sat Nov 23, 2013 9:35 am

Murphy range of aircraft are close to what you are looking for. IIRC the Maverick is already approved by the LAA. There are others.

http://www.murphyair.com

Not wishing to complete your project for you, I would spend some time looking at the Pros and Cons of the 'V' tail before deciding on that configuration.
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Re: Bush Plane Design

Postby Exosock » Sat Nov 23, 2013 1:01 pm

Jackpot! That was just the kind of design I was hoping I could compare mine against. Thanks for the link. Also appreciate your concern. I'll take another look and see if I've missed anything.
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Re: Bush Plane Design

Postby GuyGratton » Mon Dec 02, 2013 12:32 am

The Escapade is a great aeroplane but "only" a 6g wing, not 12.

Have a look also at the MXP740 Savannah, Zenair CH701 and CH801.

Raymer's introductory book is good but steer clear of his more advanced books which seldom lead to a half secent design. Rather go to Stinton and if you need to go beyond that, Roskam.

The control blending complexity and interlinking of pitch and yaw that go with a V-tail are seldom worth the small mass gains. That's why so few designers ever go down that route successfully.

G
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Re: Bush Plane Design

Postby Nigel Hitchman » Mon Dec 02, 2013 8:21 pm

Yes I guess the complexity of the controls from the stick/rudders to the V tail is the problem for a "real" aeroplane, which perhaps isn't at all a problem on a model with electric wires to servos on the controls.
Maybe if you had a fly-by wire aircraft it would be a lot easier!

Only V tail aircraft Ive flown much is a Robin ATL, did about 30 hours and 60 or 70 flights, inc 50 plus rides at the PFA rally back in 92! It flew nicely in the air, but I felt you ran out of rudder for crosswind landings when you started to flare.
That aircraft went out of production in the 90s, maybe some info around, but to look at a modern V tail aircraft have a look at the Sonnex, not a bushplane though!
The ultimate bushplane is of course the Super Cub. Another modern copy is the Zlin Savage, which I believe was originally a bit of a Rans S7 copy, but has become more Cub like with evolutions and the later models real bushplanes. As for the Murphy aircraft I understand the larger Murphy Moose had some problems with the rear fuselage area strength.

good luck with the project!
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