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Old Jan 02, 2009, 04:55 AM
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Rudder question ...

Need help from you all.

How big a rudder should be ? and .....How much a big rudder will affect the flight of a plane ?

T.I.A.

Franky
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Old Jan 02, 2009, 05:36 AM
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Any particular model in mind?

I rarely use the rudder when flying, but when I do it's effect depends on the layout of the model. If the model has significant dihedral in the wing, the rudder simply banks it and turns it just like the ailerons do (some elevator needed also). With some other models the rudder simply makes the plane sideslip.
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Old Jan 02, 2009, 06:07 AM
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Hello Abenn,

I will recycle some meat trays, this is my aim.

Any rule of thumb to follow ?

Franky
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Old Jan 02, 2009, 06:51 AM
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Average rudder/fin area should be about 8% of wing area for an aileron plane according to Andy Lennon. He has a great book if you like to do your own designs. The TLAR method works well. To small and you may run into Dutch roll where the tail wags back and forth like a fish tail. To big and you may run into spiral instability. A short tail requires more area. The opposite for a long tail moment arm.
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Old Jan 02, 2009, 08:11 AM
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Build in confidence.

It really really comes down to control in a breeze during the speeds on landing and takeoff. Too little control areas, there are all kinds of weird & different types of crashes.

Too much areas, in my overdoing it, just make the SCALE SPEED planes twitchy. But I do not lose control suddenly as I get near the stall speeds.
All my scratch blue foams & GWS foams are well under 1 pound per sq ft wing loadings. That alone makes any plane much easier to control. Anyone running flat out, can pass them during landings.

I use a flat bottomed Clark Y in all scratch built foams. It starts to noticeably lower the nose & pick up speed as I glide too slow. Sort of a built in auto pilot condition. At height, it makes people wonder. Why is it doing that very slow, lower the nose & raise the nose?

Rich
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Old Jan 02, 2009, 10:52 AM
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Is is to your benefit to learn to use the rudder along with the elevator and ailerons. Once you start using the rudder, you will feel lost when flying a plane without rudder control. There is so much more you can do when you control pitch, roll and YAW rather than just pitch and roll axis.
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Old Jan 02, 2009, 11:26 AM
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Landings in a side wind.

Are less exciting with a oversized rudder.
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Old Jan 02, 2009, 12:16 PM
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Thank you all.
I found few design parameter on the web, but not much clear about the tail area distribution for the stabilizer/elevator & fin/rudder.

Quote:
Originally Posted by flypaper 2
Average rudder/fin area should be about 8% of wing area for an aileron plane according to Andy Lennon. He has a great book if you like to do your own designs. The TLAR method works well. To small and you may run into Dutch roll where the tail wags back and forth like a fish tail. To big and you may run into spiral instability. A short tail requires more area. The opposite for a long tail moment arm.
Flypaper can you clarify what you say about the rudder/fin area ratio.
That mean the total area (fin + rudder) must be equal to 8% of the total wing area. Correct ?
If so, how to distribute that value between the fin and the rudder ?

Franky
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Old Jan 02, 2009, 12:27 PM
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Hi Franky:
Yes, it's the total area of the fin and rudder. For 3D and aerobatics you would want a higher % of rudder area. For a trainer type maybe 1/2 or 1/4 of the area for rudder so the fledglings don't get into deep doo doo. For the plane you showed, more or less a sport plane, probably 50% would be fine.
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Old Jan 02, 2009, 12:37 PM
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frankyfly: The plane you wish to build uses ailerons and an elevator for banked turns. No rudder is used on it.
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Old Jan 02, 2009, 12:40 PM
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Area distribution.

Quote:
Originally Posted by flypaper 2
Hi Franky:
Yes, it's the total area of the fin and rudder. For 3D and aerobatics you would want a higher % of rudder area. For a trainer type maybe 1/2 or 1/4 of the area for rudder so the fledglings don't get into deep doo doo. For the plane you showed, more or less a sport plane, probably 50% would be fine.

Let me see if I understood what you say ....

Example : If I have a total of 200 square/cm fin/rudder area, the fin area should be 100 sq/cm end 100 sq/cm for the rudder. Is it right ?

Franky
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Old Jan 02, 2009, 12:43 PM
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^Yes, from what he is saying. However, with a plane like that, if the total rudder size is 3" long, about a 1" rudder would be sufficient. It's all really experimentation, and seeing what size of a control surface you prefer. Some like biger, more responsive controls, and some prefer softer and smaller controls.
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Old Jan 02, 2009, 01:19 PM
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Quote:
Originally Posted by Xpress..
^Yes, from what he is saying. However, with a plane like that, if the total rudder size is 3" long, about a 1" rudder would be sufficient. It's all really experimentation, and seeing what size of a control surface you prefer. Some like biger, more responsive controls, and some prefer softer and smaller controls.
Thank you EX. I got it.

Can you help me a bit more to understand and interpret the following pictures.

Franky
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Old Jan 02, 2009, 01:37 PM
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V-stab and H-stab mean vertical stabiliser and horizontal stabiliser respectively. The vertical stabiliser is the "tail fin", and the horizontal stabiliser is ... the horizontal thing

So, your diagrams are showing you how big the V-stab and H-stab should be as a percentage of the wing area (similar to flypaper 2's reply), and it's then showing you how big the moving surfaces (rudder and elevators) should be as a proportion of the total V-stab and H-stab.
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Old Jan 02, 2009, 07:47 PM
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Here's a little diagram of the aircraft parts.
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