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What determines...

Old 01-03-2004, 10:11 PM
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boss_blueangels
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Default What determines...

What determines the thickness of an airfoil, the chord/span, and how do you determine approximate location of wing on fuselage? Is there some kind of mathematical formula to calculate area/weight of balsa wood or something? I assume you could get an approximate location by simply looking at the placement of other models with respect to fuselage length. But that's not really scientific enough for me. I've been joting down a few ideas for a design and was curious about this. Sometime in the next several weeks I'll see if I can't try putting this idea into the computer with a cheap CAD program.
Old 01-03-2004, 11:35 PM
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Tall Paul
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Default RE: What determines...

The placement of -anything- on a plane is dictated by the requirements for that plane.
That's why planes for similar missions look like every other plane for that mission.
For example, real world...
P-51, Bf-109, Spitfire... fighters, liquid cooled motors;..P-47, FW-190, F6F...fighters, air cooled motors.. etc...
Personal choice alters these as deemed proper.
For specific missions, there's sets of generic specs that will result in a flyable airplane, if followed without deviation.
In addition, there's TLAR... That Look About Right... which also dictates shapes and sizes.
Old 01-04-2004, 02:29 AM
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Default RE: What determines...

Yeah, I understand why they all have the similarities, I was just wondering what specific aerodynamic factors MUST go into consideration, I know a thinner airfoil won't produce as much lift as a thick one at lower speeds, but at high speeds does better... and washout, and tapering all help improve different flight characteristics... it'd be fun to have an RC plane that has, maybe just 5 degrees of washout, just for the fact its possible. I want the design process to be as "real" as I can make it is all. Anyway, the research continues. And thank you for the response.
Old 01-04-2004, 03:12 AM
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Default RE: What determines...

Like the porridge in the 3 Bear's home it's also best to have the "just right" amount of things in the aerodynamic world. It's not really wise to try to stretch a charactaristic just because it's possible.

I suppose it is possible to actually do a proper material list with volumes and densities on it to determine nose lengths and such but it's a lot easier to study other similar designs and use those as a meter to gauge your own designing. Later, when you have a good grounding in what's hot and what's not, you can step out of the rut and use some educated guesses to make something that is truly unique.

The best advice I can offer for any budding designer is to study plans in the magazines and now on the internet for any and all types of models. Not just pattern ships or racers but small and large models of ALL types, forms and categories. Control line stunt models can often teach you about structural aspecs that may find a home later in an F3A pattern model. Free flight models can offer much about light design for RC parkflyers. The list goes on. Never turn your nose up at an opportunity to learn from a plan. Study the wing spars, the wood sizes, equipment installs, motor mounts, wing mounts, wing stab and motor angles and artistic cues for what makes a good looking design.
Old 01-04-2004, 11:06 PM
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phread59
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Default RE: What determines...

do a search of Rc planes designing. I found a web site that has a listing of general rules of thumb. It is a series of proportions. All based off wing span and chord. Search and you will find it. There is a thread going here IN RCU right now on this topic. Just give a look around and you will find it.

Mark Shuman
Old 01-05-2004, 02:34 PM
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Patrick Underwo
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Default RE: What determines...

There are some books on the subject, Martin Simons has one called "Model Aerodynamics" or some such.

Andy Lennon also has a book on design, even though much of it is filled up with his interesting lift-enhancing doodads.

And at home I have a nice little book which might be just what you're looking for, an old self-published one bound in plastic coil, I'll see if I can find it.

Patrick
Old 01-05-2004, 03:01 PM
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Flypaper 2
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Default RE: What determines...

might be Design & Build your own R/C Aircraft by Kenneth L Smith Edmonton Alberta. I'll see if I can find an email address. A very good little book for the scratch builder.
Old 01-05-2004, 03:50 PM
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Flypaper 2
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Default RE: What determines...

In search type in Robson House Hobby Supplies They are the publisher of this book. I think you'll find everything you need.
Old 01-05-2004, 09:07 PM
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boss_blueangels
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Default RE: What determines...

Hey, thanks for all the resources and advice everyone! It's always been a goal of mine to design, build (and ultimately fly!) a design completely on my own. I was thinking of making maybe a 1/3 or 1/4 scale version first... to at least see if the thing is buildable. But in the meantime, as I'm learning how to use my CAD program... I'll definately check out as many of those resources as possible!

Thanks again!!
Old 01-06-2004, 12:04 AM
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Default RE: What determines...

You might want to start with something a bit smaller for a 25 to 40 engine. Less to loose if it all goes wrong and the wing parts company with the fuselage. There's a lot to learn. Not just the aerodynamic layout but the structural details. Starting right off the bat with a big model is kind of stacking the deck against yourself.

A simple trainer or sport type is a great way to get the feel of all this.
Old 01-06-2004, 05:52 PM
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Patrick Underwo
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Default Flypaper that's it.

Yeah, I think that's it. Very no-nonsense.

Patrick

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