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Old Oct 28, 2009, 12:02 PM
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Fus/wing ratio

Are there any rules of thumb for the ratio of fus length(tail) to wingspan?

Joe
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Old Oct 28, 2009, 02:49 PM
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No.
structural issues put an upper limit on it, and zero is the lower limit.
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Old Oct 28, 2009, 04:47 PM
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Originally Posted by vintage1 View Post
No.
structural issues put an upper limit on it, and zero is the lower limit.
LOLI like zero myself, Joe, but if you really want other numbers search for "tail volume".

--Norm
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Old Oct 28, 2009, 07:00 PM
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As the others have indicated there is a huge range and thare is no 'right length'. Generally structural issues and weight asside its more efficient to have a long tail boom, but weight and structural issues do have to be considered in the real world.

At the risk of being shot down in flames, i'll stick my neck out and say; 'Normal average looking' planes usually have the distance between the wing and the tail about equal to half of wing span.. But this is a horrible sweeping generalisation and there are many planes that are way outside this 'rule'.

Steve
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Old Nov 01, 2009, 06:57 AM
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a nother rule of thumb i catched up here:

measure the angle between wingtip, tail and wingtip.
if itś somewhere 90 it should be ok...
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Old Nov 01, 2009, 11:00 AM
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Originally Posted by HugePanic View Post
a nother rule of thumb i catched up here:

measure the angle between wingtip, tail and wingtip.
if itś somewhere 90 it should be ok...
Which is just another way of saying that the wing to tail length should be about half of wing span......
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Old Nov 01, 2009, 07:13 PM
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Originally Posted by JoeSantora View Post
Are there any rules of thumb for the ratio of fus length(tail) to wingspan? Joe
Don't let them fool you with their arrogant pseudo little science games (which are also factually wrong in many cases).
In praxis the ratio between fuselage length l and wing span b for single- engined tractor planes [ l/b ] is between 0.8 and 0.5. Usually the chord (or mean chord) of the wing [ c ] is the guiding parameter. One c in front of the wing and two c for the tail behind normally produce a balanced fuselage.
For modern gliders the ratio can be between 0.4 and 0.3. Because of the narrow chord one often ends up with two "c" in front of the wing and four for the tail.

W.
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Old Nov 02, 2009, 02:35 AM
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Originally Posted by Wendi Smol View Post
Don't let them fool you with their arrogant pseudo little science games (which are also factually wrong in many cases).
Wendi,
There is only one person arrogantly pedalling 'rough rules of thumb' as firm scientific theory in this thread....


Steve
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Old Nov 02, 2009, 10:12 PM
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I put my drawings on the wall and then stand back and squint. If it looks about right then that's close enough....

Seriously though there's no optimum length at all. However there's some pluses and minuses to either long or short depending on what you want to do with the model. It's also entirely possible and practical to make the tail extremely long or extremely short. We don't see many super long tails but there's lots of examples of super short tails that are still not actual flying wings. The Great Planes Slo Poke is one and the Clancy Lazy Bee is another. Scale models of racing planes from the 30's often have very long fuselages compared to the wingspan and do just fine as well.

It really comes down to aesthetics. To produce a design that is aesthetically pleasing that is based even loosely on full sized or other models study the plans or 3 views of such designs and blatantly copy them in terms of the tail length and overall fuselage length to span so you get the same overall planform appearance.

But just be aware that you still want to ensure you have either a decent horizontal tail volume coefficient or that you make some other choices in a suitable airfoil for those cases where you want to make the tail super short and still keep the stabilizer normal sized. In other words the more closely the model resembles a plank style flying wing the more important it is to have an airfoil that has a very low negative pitching moment, a neutral pitching moment or a positive pitching moment. The neutral or positive pitching moment choice being suitable for either an extremely short coupled model with a very small tail or a full on plank style flying wing.
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Old Nov 03, 2009, 05:16 AM
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contol line combat models ended up as wings with no fuselage partly because tails were vulnerable, but also because a wing without a fuselage tail is the fastest turner of all.

The longer the fuselage, the better relationship there is between wing and tail and the better overall L/D the model will have, so gliders tend to have long tails for efficiency.

In between is really arriving at a different sort of compromise. Pattern ships tend to have long tails because a long tail at a fixed sort of airspeed tends to be smoother in manoeuvring, and operating close to zero net up-force or down-force, will fly inverted as well as right way up with minimal trim changes.


More sporty models will tend to have shorter tails for greater nimbleness, and operate with net downforce on the tail. This makes them both a bit less neutral to fly, and a bit more responsive to large control input.


There is no one answer. Despite all these rules of thumb.
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