# Is there a relationship between length and wingspan?

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The originals have a rather attractive curved wing where the derivatives have one bent in a couple of places. They are designed to be simple to fly and won't spin. or spiral which caused most prangs at the time. Late 20's early 30's. You tilt the mainplane and move the rudder. That's it. Nev

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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

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.

I am building a Savannah S. It works out as follows:

Savannah XL or S: L = 6.6 m; W/span = 9.0 m; W/L = 1.36.

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I think that this rough rule of thumb could be greatly influenced by the airfoil profile, which I think some have alluded to with technical words.

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I think that this rough rule of thumb could be greatly influenced by the airfoil profile, which I think some have alluded to with technical words.

A well known engineer uses a "tailplane volume" formula in his design courses. The area and arm of the tailplane is directly related to the wing area.

I will see if I can dig out the formula.

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I will see if I can dig out the formula.

Looking forward to seeing that. I always prefer a formula.

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Older stuff like Kingsford Smith's Fokkers had long tail moment arms with small volume tailfeathers. Speed planes had minimum area tail volumes for less drag. This gives a more critical CofG allowable range. The area of the fin and rudder depend on other keel surface effects which all affect directional stability. (Weather cocking).Nev

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Found this on an RC Groups thread

For more or less "normal" looking designs the stabilizer and elevators together should be between 15 to 20% of the wing area. The fin and rudder together should be around 12 to 15%. From there it all depends on how long the tail is, the wing's aspect ratio and a bunch of other things. There's no one perfect size to any of this stuff unless you're making a very specific model to fly in a very specific manner. Even then there is still an acceptable range but the range is tighter.

The portion of the tail surfaces you use for controlling the model will depend on a lot of things but generally if you make the elevators about 1/8 to 1/4 the width of the horizontal tail and the rudder from 1/5 to 1/2 that's fine. The 1/2 being more for gliders or very slow flying models that do not have ailerons.

This is a really rough approximation so take it for that.

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M61A1. I am guessing that you are referring to bill Whitney.

His formula is gross tailplane area, that is horiz stab plus elevator area multiplied by distance from wing mean aerodynamic chord to 20% of tail chord point. Divided by gross wing area multiplied by wing mean aerodynamic chord.

His example was for the CT4.

29.1sq ft tail area multiplied by 12.4 ft =360.84, divided by ((129 sq ft multiplied by 5.24 MAC) 675.96) = 0.5335.

Bill Whitney noted that he considered this high and recommended the following.

Low performance planes aim for 0.35 which is a Lightwing.

Medium performance 0.45 Jabiru.

High performance 0.55 Lancair.

He emphasises that these are minima and can be increased by 0.1.

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M61A1. I am guessing that you are referring to bill Whitney.

His formula is gross tailplane area, that is horiz stab plus elevator area multiplied by distance from wing mean aerodynamic chord to 20% of tail chord point. Divided by gross wing area multiplied by wing mean aerodynamic chord.

His example was for the CT4.

29.1sq ft tail area multiplied by 12.4 ft =360.84, divided by ((129 sq ft multiplied by 5.24 MAC) 675.96) = 0.5335.

Bill Whitney noted that he considered this high and recommended the following.

Low performance planes aim for 0.35 which is a Lightwing.

Medium performance 0.45 Jabiru.

High performance 0.55 Lancair.

He emphasises that these are minima and can be increased by 0.1.

That’s the one. Saves me looking for it. ?

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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?

Are you talking about the blue/silver 503 powered Flying Flea at the Oaks, or my Stollite, seen here flying (with it's latest motor, a BMW R100 conversion), over Taree...

Oh yes, I finally repainted it.

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Hiho Arthur, can you give some details on your BM conversion? Howiz it go? What sort of revs are you cruising with?

Sorry to say I liked the Stollite yellow, it sort of looked military somehow

How high you flying in that piccie?

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Hey there, don't want to derail this thread, so go over to;

Just Bragging and I'll try to get back into more regular posting there.

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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.

Flying Flea after departure from the runway at The Oaks. Can't remember what year.

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Seeking a relationship between length and wing span is a question many a duck has asked of a drake

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Tandems like the flying flea don't come into this. Flying wings and canards ditto.

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NOW you tell us.. Nev

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• 2 weeks later...

Length of the fuse and wingspan have absolutely no relationship with each other.

There's a rule of thumb that states that the wing quarter cord point and the horizontal stabilizer quarter cord point should be at least four times the cord of the wing apart. Mainly to keep the tail out of the downwash. However the length of the fuse is mire dependant on the size of the tailplane to ensure enough elevator and rudder authority.

Wing Span and Aspect Ratio are dependant on Induced Drag, Cruise Speed, and Stall Speed. Kitplanes magazine contributer Barnaby Wainfarn has a current series about the process of designing aeroplanes, called Design Process. He's up to wing design. The upcoming July 2020 issue will feature, Span and Aspect Ratio. It's very interesting. Read it if you can.

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Snoopy. I think you may have a few knowledgable people who disagree with you. Could you explain why they have no relationship?

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'Length and span have no relationship'

As in my earlier post, this technically is true, flying wing has no fuse ratio, F104 is way out the other side.

The technical design ratio is wing chord to fuse length, although arbitrarily stating 4:1 is a little bold.

Back in my day of designing control line stunt models, 2.5~3:1 gave a nice balance, but in real aircraft it can vary widely.

A Piper Cherokee would be around 2.5:1, a 737 might be around 4:1 and a performance sailplane would be up near 7:1 for the reasons I mentioned earlier.

It comes down to design goal criteria.