Designing an airplane?

[fly300s]

Ok guys. I want to desing an airplane, where do I start? What do I do? Lets take this from the begining step by step.

Thanks,
Ryan

[Sparky Paul]

First, steal a chicken... no, that's the recipe for Gypsy Chicken Soup.
.
First, what KIND of airplane?
2nd, what is it to do?
3rd, your knowledge of how to get #2 into #1.
4th, your experience building..
Then it gets complicated...

[fly300s]

I want an aerobatic biplane.

It should be aerobatic.

I have lots of building experiance, first time designer.

[fly300s]

It should be anyewhere from 60 sized and up

[Ollie]

You begin by desiding what type of flight characteristics you want the plane to have. Then you try to quantify and prioritize those characteristics. This data then becomes a standard against which you can judge the virtue of the many design decisions to resolve conflicting objectives that are involved. You can start with the characteriatics of the model that the equipment came from. Calculate its performance and deside how you want to modify it for "improvement." The process goes something like this: analyze, modify, reanalyze, judge results and consider new modifications. With sufficient iterations, the process should converge on your objectives.

Nature evolves its designs by a slow process of random variations and natural selection. You can evolve your designs so very much faster by insiteful variations.

Equations analyze. Design decisions synthesize.

It should be aerobatic.
Weight ~ low
Thrust ~ big
Drag ~ big
Controls ~ big
Slow ~ low
Fat airfoil ~ symmetrical
AR ~ low

[vintage1]

I'l add, for precision aerobatics,

(i) make it relatively symmetrical in all axes - i.e. as much fin above the thrustline as below.

(ii) As much wing above the thrustline as below

(iii) little or no dihedral

(iv) plenty of fuselage side area to allow knife edging and reduce sideslpip under yaw.

For slow speed control authority all control surfaces at least partially in the prop wash. Otherwise you will have no roll control when hovering for example with outboard ailerons..

I would think that big control surfaces moving a little, are better than little ones moving a lot, but this does mena big forces on the servos at high speeds. Hence many peoples use of tail/wing mounted servos with very short and stiff pushrods.

Its probably also betst to concentarte the weiht around the CG if you can, to reduce the moment of intertia, and rely on BIG flying surfaces to keep the thing stable rather than the aircraft mass. This has the downside of making the model twitchy in turbulence, so a compromise is on - pattern planes benefit from a bit of intertia, 3D planes need less.

[DLC]

I recommend that for your first design effort you not try to completely re-invent the wheel. Find a plane that has the general characteristics you want and use it as a starting/reference point.

[omega blood]

http://www.amazon.com/exec/obidos/tg/detail/-/0911295402/qid=1094029751/sr=1-1/ref=sr_1_1/002-3207610-5244802?v=glance&s=books

get this book.

[Buzz_Man]

I have lots of building experiance, first time designer.Same here - I'm almost finished building my first self-designed plane from scratch.

How many times have I thought to myself "You really should've just bought something - you'd have been in the air weeks ago and it would've WORKED!" (especially as I'm just getting back into r/c after being out for over two years).

I'm still several hours away from the maiden and I have no idea if this thing is going to end up being a great flying model or just a heap of busted foam. I'm guessing the latter is more realistic in my particular case. :(

I've learned the hard way that I don't have much talent at scratch building. I wish I could say it's been fun so far - more frustrating than anything else. Creating problems is my gift - solving them aint my forte.

But, don't let this discourage you - good luck,

Buzz

[fly300s]

well, I'v scratch built alot before. I just never put any thought into the designing part. So, the planes have never flown/never flown very well. How about some calculations. What should the wing area be? Tail area? Distance between tail and wing? and so on. Are there any formulas or anything besides gussing?

Ryan

[Sparky Paul]

Areas, lengths, moments... look at what is already out there..
These are the specificiations you will use to design your own.
Decide what you like and dislike about that stuff..