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Design => Stunt design => Topic started by: Steven Kientz on May 04, 2009, 02:44:58 PM
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Is there a specific ratio used when designing a model from scratch? I'm considering building a 50+" ws profile for sport flying. probably same size as Primary Force or Tutor II. I assume the Nose moment should be as short as possible, just enough room for engine and tank.
Would it be easier to take a known airframes numbers and just change the profile to what I like? I'm not looking to set the world on fire, just have something different to fly. I am currently flying a Tutor II, not sure if it will survive this summer or not( I have 5 teenage neices and nephews who would like to try control line this summer)
My other question is concerning engine and tank mounting on profiles. I would like some ideas how to make these (somewhat) adjustable so I can balance the model without adding as much weight.
Thanks
Steve
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Steve,
The easy was it to just mix and match fuselage, empanage and rudder shapes of other airplanes.
There is nothing set in stone on how much nose and tail moments to use. Just determine how much you need for the engine and tank your using and then estimate what the tail moment should be without making it tail heavy.
It's much easier to use tail weight than nose weight.
Jim Pollock, H^^
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Steve, the typical way to design a plane is to develop the wing layout and tail layout, including the tail moment, to get the kind of flight characteristics you want. Then balance it with the nose moment.
A really good example of this from full scale aviation is the jump from the FW 190 A3 to the D9 model. The original FW had a fairly heavy radial engine and a quite short nose. The D9 used a lighter liquid cooled in-line motor and had a longer nose and a longer tail moment(to improve stability and handling).
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So, If I know that I need 7"(minimum) for tank and engine then that gives me an idea where the LE should be. I' ve already figured 52" ws, 10"ribs with a tapered(3" root,1" tip) TE, and guessed at 14"tail moment.Does this sound about right?
One other question.
On a nonflapped model what tail volume percentage , I've seen where some had said 14% or even larger.I guess if it's to large you can always decrease it.
Thanks
Steve
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I can tell you that if the nose moment is too short, the plane looks silly.
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If its too short then you end up with a combat model. As of right now I'm thinking a 40" fuselage, still trying to get the look I want. Started with a jet look, but I could never get the fuse less than about 8" tall. It looked okay, just figured that was to much for the engine to haul around. I'm back to a two seat aerobatic style fuse, 6" tall at the canopy. Much better.
I'm starting to consider a ribset of an appropriate plane instead of trying to cut my own( then I could do something different than a constant chord). Was thinking that Brodaks probably had something. Any ideas?
Steve
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FYI-
Brodak sells rib sets for most of his profiles.
Roger V.
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One of the best tapered wing airfoils in Brodaks stable, is the Cardinal. It's a good wing, and a great wind and turbulence penetrating airfoil.
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Checked brodaks after posting, definitely think the cardinal ribset will work. Now if I can just finalize the fuselage I'll have a place to start. I've been drawing every morning before work(waiting for bldg to be opened)and at night after dinner. I have done at least 10 drawings of two different styles,but have yet to see the ONE. Oh well, maybe tomorrow.
Steve
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Steve,
If the airplane has flaps then the stab/elevator area combined should be between 23-27% of the wing area, including the flaps and wing tips. Without flaps you can go down on stab/elevator areas to about 18-20 percent since the stab/elevator won't have to overcome a negative pitching moment of the flaps. :P
Jim Pollock, H^^
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I can tell you that if the nose moment is too short, the plane looks silly.
Is that why my DoodleBug and the ex HumBug looked so strange? DOC Holliday
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Thanks to everyone for the info.I have given myself a deadline of 5/11/09 to finalize the fuse shape and then I get to start.
Steve
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I can tell you that if the nose moment is too short, the plane looks silly.
Maybe not.
Al
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That is one gorgeous looking Fury!!!! Is that your latest model? Looks fantastic. How does it fly?
Cheers Neville
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I was looking at the Cardinal ribset and I can't tell if it is a tapered or not. If it is, what is an inexpensive jig or way to jig this build?
Steve
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It is a tapered wing. A simple method of jigging is the one listed in the instruction book. Brodak calls it a levelling bar. Another would be a rod jig, also available from Brodak, as well as others.
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thanks for the info, John
Steve
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If you have not built a Brodak kit using his leveling set up it is different. The trailing edge is set with the leveling peice of wood. The spars are put in place with the tips elevated and shimmed to make them straight. Then the leading edge is checked to make sure it is straight/level with the building surface. Each one I have built of his kits has been straight when I lifted it from the building surface. His instructions are very thorough. DOC Holliday
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I might be using the wing from my Tutor II. The LG holes are worn out. I have repaired this problem once, not sure there is enough left to try again. Also the LE of the stab is broke on the outboard side. Easy repair, strip the covering, sister a piece on the inside and then cover stab with 1/32 ply before recovering.
The landing gear is another story. Not really sure where to start, short of filling old hole and drill a new one. I might try bushing this hole with delrin or some of my old RC car parts. Am really suprised how handy some of that old hardware is.
By the way if anyone is interested in a couple of straight axle carpet cars send me a pm.
Steve