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Old 10-22-2012, 02:11 AM   #1
npowell28
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Default How does the position of the horizontal stab affect a model/

Hi,

I'm trying to establish how, when designing a model, how the position of the horizontal stabilizer affects flight. e.g. level with the wing, higher than the wing etc etc.

I did once find a site that gave basic rules but i can't find it now.

Cheers all
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Old 10-22-2012, 09:08 AM   #2
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Originally Posted by npowell28 View Post
Hi,

I'm trying to establish how, when designing a model, how the position of the horizontal stabilizer affects flight. e.g. level with the wing, higher than the wing etc etc.

I did once find a site that gave basic rules but i can't find it now.

Cheers all
http://avstop.com/ac/flighttrainghan...stability.html

http://en.wikipedia.org/wiki/T-tail

hope that helps, Chellie

I may be getting Older, But I Refuse to grow Up I am Having to much Fun to Grow Up LOL
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Old 10-22-2012, 10:11 AM   #3
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It's complicated.
T tails are used to put the tail up out of the way of the wake that comes from the wing, this means the tail operates in 'clean' air and so is more efficient. You will see t tails used on some sailplanes for this reason but T tails have their problems because that are hard to do from a structural point of view and the added weight to make the tail strong enough usually counteracts and aerodynamic advantage.

On many full size planes the tail position is set so that the elevators don't not get buffeted by the wake off the wing. This is mainly to prevent vibration through to the control column and possibly structural fatigue issues. These things don't really matter on an RC model so tail position for buffet is less of an issue.

On aerobatic models the tail position on the fuselage can be used to fine tune knife edge flight (yaw to pitch coupling to be precise).Tails that are high on the fus tend to cause the model to tuck toward it's landing gear in knife edge. Tails that are low on the fus might cause the model to pull toward the canopy in knife edge. If you look at many of the RC versions of real aerobatic planes, like the Edges, Extras, MXS's etc made by 3DHS and Extreme Flight and others you will see that the tails are generally mounted lower on the fuselage than the real plane. This is to improve knife edge flight (reduce yaw to pitch coupling)

As an example look at the tail heaight on the real MXS in the photo attached and compare it to the RC version of the same plane. Notice how much lower the tail is set on the RC model:
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Old 10-22-2012, 11:58 AM   #4
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There is also another factor to consider additional to height above ./ below main wing.

The distance between wing and stab. Take a Pitts - its short. Take a Cessna - it's long.
Why ? Longer is smoother and generally more docile. The moment arm is such that more movement is needed to effect change of model attitude.

There are exceptions to the rule .. of course.

Various full-size aircraft over the years have suffered blanketing of tail surfaces ... buffeting ..... lack of authority ... usually because the format has been taken out of it's designed envelope. High mount stabs, all moving tails etc.

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Old 10-22-2012, 05:29 PM   #5
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Originally Posted by CHELLIE View Post
Nice link Chellie. Very interesting reading.

Long Island Silent Flyers
www.lisf.org
Eastern Soaring League
www.flyesl.org
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