Building and designing a rc plane frm scratch

[kevjcarvalho]

heyy guys
i am participating in an aero competition in which the problem stmt is to design an acrobatic hand launched rc plane of wingspan 3 ft max which can perform stunts like a vertical loop, sharp turns and 360 roll...can you please tell me how to begin designing this aircraft...i have elementary knowledge in aerodynamics and flight mechanics..the wt of the aircraft is approx 700g.

 

[Danger]

I'm not sure exactly what you mean by 'begin'. Do you mean a concept, or a technique? Everything that I design begins with a pencil, paper, and an open mind.

 

[kevjcarvalho]

begin in the sense how to i get chord length, fuselage length, type of airfoil,etc...im just assuming them ...is that right??...or is there some way to start frm..i just know the wt -700g, the wing span-3ft and the max velocity-36kmph...all the rest is unknown...technique in a nutshell

 

[Topher925]

You should look over other plane designs that already exists and study the characteristics each design type has.

 

[FredGarvin]

Have you done any research yourself? Perhaps what kits are out there right now, ...you know...the basics?

 

[kevjcarvalho]

i have done the basics...i have chosen a NACA 2415 airfoil assuming a chord of 15cm using profili-2.24 software...the aerodynamic data is fine...i am using carbon fibre rods 4mm diameter to form the skeleton of the fuselageand the skeleton of the wings...the wing is a built up balsa sections with ribs to from an i-section at the point of maximum thickness of the airfoil and two ribs one at the leading and the other at the trailing edge...what would be the best configuration of the carbon rods to make the fuselage structurally strong...i am using a motor cum propeller generating 1kg of thrust approximately...i am using a Li-polymer battery which weighs 193g...the length of the fuselage is 66 cm

 

[FredGarvin]

OK. You seem to have a good start. Now what EXACTLY do you need help with? Saying "I need help with designing an aircraft" is too broad of a question.

 

[kevjcarvalho]

i need to design the skeleton of the fuselage...like trusses or something like that...can you please suggest a design ...should i use carbon fibre or do you suggest something else?

 

[Topher925]

Fiberglass is often use for aerobatic gliders. Carbon fiber might be a bit overkill but you could use it. Carbon spar reinforced foam might not be a bad idea either.

 

[herpamad]

Hi

I can't help much here, but i hope some-one here can fill the blanks in as i can't find the URL or even name of the scheme.

MIT and a few other universities, thing all usa ones, do a competition where they design, build and fly a RC aircraft.

There was a website that had all the documents from each uni, it was the organisers one i think, but not 100% sure.

I think it was sponsered by AutoDesk and Boeing and a few others, but can't really remember and i have lost the link.

Any ideas? i too could use the info they had on the site, but searching for it has not come up trumps...

 

[kevjcarvalho]

can you please get me that link...it would really help me..thanks

 

[kevjcarvalho]

can someone send me stuff on landing gear for rc planes

 

[redargon]

have you done any mechanics courses or do you have knowledge of trusses and bending moments and shears and things? I think that in general, you should probably use existing designs as much as possible for the wing structures, working them out by hand could posssibly save you weight and help pick an appropriate material, but will take a long, long time.

 

[kevjcarvalho]

done this stuff...but in an odd sort of way...done analysis not design....thanks all the same though...

 

[mugaliens]

Check the library for back issues of RC Modeler. About once every five years they come out with a three-part series on airfoil design. As for the horizontal stabilizer, it's about 1/10th the surface area of the wing. The vert stab's about 1/25th. The fuselage for an acrobatic plane can be either plywood sheeted balsa, or box. As for the engine, for full acro you'll want an engine/prop combo that'll provide a static thrust of about 1.5 times the finished weight of the aircraft.

 

[Cyrus]

Check the library for back issues of RC Modeler. About once every five years they come out with a three-part series on airfoil design. As for the horizontal stabilizer, it's about 1/10th the surface area of the wing. The vert stab's about 1/25th. The fuselage for an acrobatic plane can be either plywood sheeted balsa, or box. As for the engine, for full acro you'll want an engine/prop combo that'll provide a static thrust of about 1.5 times the finished weight of the aircraft.

I'm curious as to where you got these rules of thumb from!

 

[FredGarvin]

Check the library for back issues of RC Modeler. About once every five years they come out with a three-part series on airfoil design. As for the horizontal stabilizer, it's about 1/10th the surface area of the wing. The vert stab's about 1/25th. The fuselage for an acrobatic plane can be either plywood sheeted balsa, or box. As for the engine, for full acro you'll want an engine/prop combo that'll provide a static thrust of about 1.5 times the finished weight of the aircraft.

Ugh. I have read those "airfoils for dummys" articles. They are horrible. Pretty pictures and graphs without a whole lot of substance.

 

[kevjcarvalho]

thanks a million...that was really helpful

 

[mugaliens]

Ugh. I have read those "airfoils for dummys" articles. They are horrible. Pretty pictures and graphs without a whole lot of substance.

I wouldn't design a full-scale, human-rated airplane using them, naturally! But they work just fine for scale-model balsa R/C's.

Also, it may interest you to know that I ran the dimensions of a B-52 (weight, sweep, chord, airfoils, etc.) through those "horrible" models, and the results in terms of stall speed were only 3 knots off actual. I did the same for several full-scale aircraft and achieved similar results.

So while the graphs aren't "pretty," they're pretty accurate, and certainly good enough for R/C model use.

ETA: Yes, I adjusted for the different Reynold's regimes.

AND:

I'm curious as to where you got these rules of thumb from!

WAG! My favorite flying aircraft was a Falcon 56 I built with the lower dihedryl option. That's about what it's ratios were, perhaps 1:20 for the vert stab.

Going back to the old RC modeler articles, they included formulas for calculating all of that based on overall weights, wing moments (CP vs CG, also airfoil moments), etc. Good resources - I have yet to find anything as good out there on there Internet!