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Is there a relationship between length and wingspan?


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For something to do, I decided to build an RC plane to fly in the park next door. Nothing fancy. Probably only rudder and elevator and a brushed motor. I did the usual Internet search for free plans and downloaded some for a simple high wing one that I can put together from corflute.

 

However, the plans did not show the wingspan. For some time now, while looking at aircraft specs, I've thought that wingspan and overall length might be related. There must be some ratio that fulfills the adage, "If it looks right, is probably is right. So I had a look at some common high winged aircraft to see what came up. Here are the results:

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As a rule of thumb, perhaps one could say that for a slow flying aircraft the ratio of overall length to wingspan is roughly 1.5:1.

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Yep I remember that old saying from my R/C days, and it's probably true.

 

The other thing I remember is HT span is about 1/3 of wingspan and CG approx. 25% of chord.

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It is pretty much a 'if it looks right' kind of thing.

The two primary things that generally relate to wingspan are; wing chord, which will give you aspect ratio, and; moment arm ratio, which boils down to the leverage that the tail has on the wing to control pitching moment and overall elevator authority.

Oddly, the 1.5:1 span/length ratio is probably pretty close with most gliders as well, but because the wing is narrow chord, the moment arm ratio is much higher, which then allows the use of much smaller (read less drag) tailplanes.

Shorter the moment arm ratio, the larger the tail to wing percentage needs to be...

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Interesting thought to which I don’t know the answer, however, if you look at an F104 and then look at a U2, then maybe the answer is no?

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well said pylon. There was a glider ( the speed astir ) where they did a redesign with a longer fuse and a smaller tailplane to get some more performance.

On our planes, I reckon the thatcher looks better than the corby because it is longer.

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This might apply to RC gliders, but the power to weight ration with powered RC aircraft is massively greater than full size aircraft and you can make a lot of odd shapes fly that would be a disaster full size. There are park flyer RC models available - slow and easy to turn in and out of trees., but if in doubt, a slightly more powerful engine is your friend.

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It was a full-size glider turbs. The speed astir came late on the scene for 15m class, and it was promoted as a world-beater. It had an Eppler wing section, and later Eppler said that the factory didn't make the wing accurately enough. The glider suffered in the climb from turbulence-induced higher drag for some of the time.

There is at least one in Australia. Grob no longer make any gliders.

The basic thing about tailplane size though is simple. A given pitching moment is the tailplane downforce times the moment arm. Doubling the moment arm means you need half the force and therefore have less induced drag from the tailplane.

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No real hard and fast rule toy planes are in a world of their own. Scale toy planes are only in looks/size but nothing else so you can get pretty much anything to fly, given a if gee gee's?

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you can make a lot of odd shapes fly that would be a disaster full size.

The Flying Flea.

Now I'm not sure if I countered the comment, or agreed with it?

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if you look at an F104 and then look at a U2, then maybe the answer is no

 

Those are a different kettle of fish. I'm talking about the things we fly.

Foxbat: Length 6.3; W/Span 10.1; W/L 1.6

J230: Length 6.55; W/Span 9.55; W/L 1.45

 

There are park flyer RC models available

 

Yeah, costing over $150, RTF. I've got the radios and servos from wayback, I just needed a something to put them in. Don't forget that I'm trying to teach myself how to fly, so I need something cheap, but flyable.

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Yeah, costing over $150, RTF. I've got the radios and servos from wayback, I just needed a something to put them in. Don't forget that I'm trying to teach myself how to fly, so I need something cheap, but flyable.

The key factor in a Park Flyer design is that you're probably going to have to throw stones at it to get it out of a tree, or make up 2 metre lengths of 25 mm plastic pipe to make an extension, so it has a short life.

 

I've seen them made of a skeletal fuse covered in doped fabric, wire or balsa rod wing frame, and with doped fabric (no curved top), and they'll fly just on power from the engine and force to the underside of the wing, or a couple of flat balsa sheets glued edge to edge.

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Foxbat: Length 6.3; W/Span 10.1; W/L 1.6

Foxbat w/s 9.55m...... 1.51 ratio.... (Don't believe everything on wiki...lol)

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The Flying Flea.Now I'm not sure if I countered the comment, or agreed with it?

 

They do fly!

 

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On our planes, I reckon the thatcher looks better than the corby because it is longer.

Caution Bruce! Could be treading on a lot of toes.

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I don't care which looks better, just having one to fly is great.

The length to span ratio can be varied, but the area of wing to area of tailplane needs to be kept to closer proportions. If you increase the length, you can reduce the area of tailplane, but you have to get enough strength in the fuselage to carry the loads, reduce the length and you increase the tailplane area, you can go to ridiculous proportions like the old racer planes and because the length between centre of pressure of wing and tail becomes so short, the plane gets very twitchy.

The Corby is fairly short, but I have never found it twitchy. I have never dissected the design numbers to see how it compares, maybe I should do that.

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Don't forget that I'm trying to teach myself how to fly, so I need something cheap,

Get yourself an RC flight sim. It will save you money in the long run. They are worth very penny.

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Get yourself an RC flight sim.

 

But if I get one of those, I be spending my time with that and not regaling you all with my wit and wisdom here.

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My Jabiru SK has the short fuse too Yenn, and they made the fuse longer on later designs. But I too am happy just to have a plane to fly, and I like the way it flies.

The extreme thing is the flying wing, where the tailplane is attached to the trailing edge of the main wing. The flying wing has been given lots of chances but it just doesn't work well enough. Or maybe we are so fixed in our ideas that we reject the idea too quickly? Is there a flying wing among our planes at the moment?

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OME .Most persuasive argument I've seen in a while. We need our regular regaler.

Tail moment arm is just one factor in pitch response. Probably affects directional control in a T/W significantly too as does rudder shielding and a square V/s round fuselage section. In the models V/s true sized comparo ,Reynolds number(scale effect) makes a big difference. A jumbo sized bumblebee would not get off the ground. High subsonic and supersonic throw the rule book out the window. Nev

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Hard to see the point of that unless as a cheap trainer. The Flea can never be a good glider. Aerodynamic efficiency is not it's strong point. It was designed to not spin or spiral, primarily. and be easy for anyone to build cheaply out of readily available materials. Maybe one of the first true ultralight homebuilts? Nev

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But if I get one of those, I be spending my time with that and not regaling you all with my wit and wisdom here.

It's OK, just hit pause.....

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I saw a Flying Flea derivative many years ago at The Oaks. I don't know where it came from, maybe Wedderburn, but it seemed to do all that was asked of it.

That was around the time Pylon 500 had his little Stolite parked there.

 

OMG! just Googled it. That would have been 20 or 21 yrs ago Arthur. Is it still flying?

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