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Slow Rolls

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Old 12-31-2002, 06:21 PM
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Default Slow Rolls

What factors would contribute to an airplane having a slow roll rate? I have been reading reviews of the DynaFlite Chipmunk and they all have said that it rolls very slow and that the ailerons are not very effective at slow speeds, such as landing speeds.

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-Bob George
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Old 12-31-2002, 06:32 PM
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CONTROL THROW AND OR SIZE OF AILERONS
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Old 12-31-2002, 06:43 PM
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Default Slow Rolls

And SEAL THOSE GAPS!
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Old 12-31-2002, 06:53 PM
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Default Slow Rolls

Some general thoughts, I am not sure if they help:

I do not know what the ailerons look like on the Dynaflite Chipmunk, but I would guess that ailerons all along the span would be more effective at low speed compared to barn door ailerons near the wing tips due to increased airflow over the wing behind the propeller.

Maybe the geometry of the wing could have some impact too. I remember reading that the clipped wing Spitfires rolled much faster than those with the standard wings.


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Old 12-31-2002, 06:54 PM
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Default Slow Rolls

How about dihedral? Would that have any effect?

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-Bob George
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Old 12-31-2002, 07:00 PM
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Default Slow Rolls

Generally, dihedral won't do much to slow your roll rate. If you have a high wing trainer with a high amount of dihedral, then the CG is much lower than the wing which will hinder the roll rate. On the Chipmunk I don't think it is as much of an issue. Scale 'Barn Door' ailerons don't do as well at low speed because they rely on airflow over the outer wing to be effective. With full-span ailerons, you get some prop wash over the inner ailerons which helps, but on Barn Door style you end up in a tough spot.
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Old 12-31-2002, 09:43 PM
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Here is why I ask. I ahve a DynaFlite Chipmunk kit and I want to build it as a Super Chipmunk. This will involve clipping a bay off each wingtip. The ailerons will stay the same size and move inboard, which means the flaps will be smaller.

So, do you think the reduced span while retaining the same size ailerons will improve the roll rate over building it per the instructions?

Thanks again,
-Bob George
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Old 12-31-2002, 10:04 PM
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Default Slow Rolls

My guess is that the roll rate would improve over all. There would be less wing to move with the same aileron.

What you seem to be describing sounds pretty much like what Supermarine did to some versions of the Spitfire in WW2, which I mentioned briefly in an earlier posting. They basically clipped the wingtips just outside the ailerons. Their intention was improved speed I think, but I read somewhere the biggest difference it did was more or less doubling the roll rate!

You would probably still find the ailerons to be less responsive at low speed than at high speed though, as that would be due to the airflow. Otherwise, it ought to make the Chipmunk roll faster.

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