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Old Aug 19, 2003, 04:03 AM
Registered User
Stockholm Bromma, Sweden
Joined Mar 2000
141 Posts
How to make a model roll better

My KZ II sport (a 1938 Klemm-like two-holer) is a nice flyer but is hard to roll. I might have the Center of Gravity to near the nose. I know there is a "Diving test" to check the CG on a model but I cannot find how to do it now.

Please advice.

Christer Lagerstedt
Haninge MFC, Sweden
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Old Aug 19, 2003, 05:29 AM
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Goodychrischild's Avatar
Bristol, UK
Joined Oct 2002
630 Posts
Hi Christer,

Nice looking plane!

The following was posted in one of my threads and I think it is what you are refering to:

"If you can, get some alltitude, fly straight and level at cruise speed, then push the nose down into a 45 degree dive and let go of the stick. If she pulls up sharply, it`s nose heavy. This effect should minimize as you move your pack further back to a more balanced CG (weight towards tail end)."

You can also read further discussions on the subject within the thread (pages 5 & 6) here:

http://www.rcgroups.com/forums/showt...4&pagenumber=5

Chris
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Old Aug 19, 2003, 05:58 AM
Registered User
Stockholm Bromma, Sweden
Joined Mar 2000
141 Posts
Thank You, Just what I was looking for.

Christer
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Old Aug 19, 2003, 09:41 AM
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Captain Ed's Avatar
Florida Keys
Joined May 2003
146 Posts
An important factor in roll rate is aileron travel. The "up" aileron is the primary roll control. The "down" aileron, even though it contributes to the roll can cause the plane to resist rolling by creating too much drag on the opposite side from the "up" aileron. For good roll response the controls should be set up so the "up" aileron travel is greater than the "down" aileron.
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Old Aug 19, 2003, 12:00 PM
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feathermerchant's Avatar
USA, TX, Euless
Joined Aug 2003
9,343 Posts
I've had success mixing a little rudder with the aileon.
If your radio won't do it you can use your left thumb.
Right rudder with right aileron, etc.
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Old Aug 19, 2003, 01:46 PM
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Paul Willenborg's Avatar
Little Rock,AR,USA
Joined Jun 1999
801 Posts
Uhm, actually the last two reponses will give you better turning response, but may hurt rolling ability. Both aileron differential and mixed rudder will cause the plane to yaw in the same direction as the roll- good for turning, bad for rolling. For best rolls you'd like no yaw whatsoever from the ailerons.

If you've got a lot of aileron differential try reducing it. Seal aileron/wing gaps if there are any. Moving the CG back does more to help pitch authority but can't hurt within reason. No need to dive at 45 degrees to test! A shallow, sustained dive is just as good.

Paul
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Old Aug 19, 2003, 02:17 PM
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DanSavage's Avatar
Trabuco Canyon, CA
Joined Nov 2000
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Re: How to make a model roll better

Quote:
Originally posted by Christer Lagerstedt
My KZ II sport (a 1938 Klemm-like two-holer) is a nice flyer but is hard to roll. I might have the Center of Gravity to near the nose. I know there is a "Diving test" to check the CG on a model but I cannot find how to do it now.
Beautiful model, Christer.

Keep in mind that roll rate is a directly related to how effective the ailerons are and that there will be some cases where you will not be able to increase the roll rate beyond a certain speed.

Since this is a trainer, I would expect that the roll control would be slower than an aerobatic design.

I personally don't think that CG is going to have any effect on roll rate, but I've been wrong before.

Dan
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Old Aug 19, 2003, 02:24 PM
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Tomball, Texas
Joined Nov 2002
29 Posts
Can't see them in the pic, but if you have any gap at the aileron hinges, try sealing it with tape. Some planes benefit greatly from this simple fix.
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Old Aug 20, 2003, 01:40 AM
Registered User
Stockholm Bromma, Sweden
Joined Mar 2000
141 Posts
Thank you all.

I usually fly CAR (coupled aileron and rudder) but always disconnect it for rolling maneuvers. My ailerons are sealed and I use around 2 to 1 differential. Will try other settings.

If I remember correctly the model was nose heavy when first built. I think I added a lump of lead under the elevator, have to check.

I was flying in a scale competition last Sunday and my rolls were quite bad. Halfrolls like in Immelmanns and Split-s are usually OK.
Have to do a series of test flights.

Christer
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Old Aug 20, 2003, 02:34 AM
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Gordon's Avatar
Joined Aug 2000
3,919 Posts
Hi Christer

Beautiful model you have there.

If the KZ is like the Klemm, it will have long-span wings. Such high-aspect ratio wings naturally roll more slowly than fighter-type low aspect ratio ones. It's very likely that the real KZ II and Klemms rolled very poorly.

Recognising that you've applied just about every practical fix to get the model rolling better, I'd guess that the only other thing left is to increase the airflow over the ailerons. In other words, precede the roll manoeuvre with a long shallow dive to build up the airspeed, level off, and then roll.

What's puzzling me, however, is that the model seems to roll from erect to to inverted OK (Split-S) and also to roll from inverted to erect (Immelmann) as well. Somehow, it's not doing a joined-up roll

Best regards

Gordon
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