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Old Oct 21, 2012, 04:23 PM
scratch-built
Jim Lee's Avatar
United States, WA, Port Orchard
Joined Apr 2007
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Here's a artical that was published in March of this year, Concerning aileron differential. Maybe it will clear up the mystery.

J


http://www.modelairplanenews.com/blo...-to-set-it-up/
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Old Oct 21, 2012, 04:53 PM
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Joined Jan 2007
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Hmm. That article is the old down going makes more drag. That may be slightly true on the initial roll input, and would require differential opposite what Jim originally suggested I think?

There is a second effect once the roll rate is stable, which happens very quickly after the initial aileron deflection. The down going wing has it's lift vector rotated forward because of the local velocity it sees, and the up going wing has it's lift vector rotated backwards by it's local velocity. This results in a yaw away from the direction of roll also. Dr. Drela explains it better than I can:

http://www.rcgroups.com/forums/showp...0&postcount=31

It seems to me that increasing the down going aileron deflection is going to add to these two effects, and increase the yaw away from roll direction, if it does anything at all.

Kevin
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Old Oct 26, 2012, 10:29 PM
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United States, CA, Long Beach
Joined Sep 2011
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Hmmm what is wrong with this photo of the wing? Don't worry the other wing is the same...

Robert
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Old Oct 26, 2012, 11:28 PM
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Quote:
Originally Posted by kingconsulting View Post
Hmmm what is wrong with this photo of the wing? Don't worry the other wing is the same...

Robert
Wrong hole for the aileron serve. It's right above whats been already cut out.
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Old Oct 26, 2012, 11:34 PM
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United States, CA, Petaluma
Joined Mar 2011
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Quote:
Originally Posted by Carl Petersen View Post
Wrong hole for the aileron serve. It's right above whats been already cut out.
That is what the AJ stickers are for, to cover those holes up
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Old Oct 26, 2012, 11:45 PM
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Hey good idea! Saves me from buying two rolls of ultra cote.

Quote:
Originally Posted by Inverted-I-Fly View Post
That is what the AJ stickers are for, to cover those holes up
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Old Oct 26, 2012, 11:45 PM
inverted-i-fly
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I did the exact same thing
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Old Oct 27, 2012, 08:28 AM
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I should have known too. All the other openings were hard to find and see. Held the wing up to the light and wow piece of cake! Then I tried fitting my servo in and it wouldn't fit. Ruh Ro.

So it looks ok with it on? At least it's on the bottom.

Robert
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Old Oct 27, 2012, 09:17 AM
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Missouri
Joined May 2010
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Hi guys,
Great discussion of adverse yaw and aileron differential.
A couple of quick things that helped me. 1) In the 62" Osiris build video from Higher Plane Productions, AJ shows he uses 11degrees up and 11.5 degrees down deflection for aileron differential. I used this differential on my 47" and my 62" Osiris and was very happy with the results.

2) I am also including Peter Goldsmith's article and trim chart about trimming a plane. Goldsmith is an IMAC pilot but the principles have helped me trim my pattern planes.
Step 5 covers aileron differential. Goldsmith says to start at step 1. I recommend reading the attached article about his experience with trimming a planes for competition

By following Jesky's and Goldsmith's tips both of my Osiris' fly even better.

Gadget
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Old Oct 27, 2012, 07:58 PM
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Gadget,

Thanks, those are interesting.

I wonder if the 45 degree up-line roll tests for differential are actually looking for a pitch effect, not classic adverse yaw? If the net camber of the wing increases with aileron deflection, you would get a pitch up of the nose. For the first 180 degrees of a right roll, this would move the airplane to the right.

For a right roll, they are saying if the airplane "walks" to the right, you have too much down aileron on the left side. If you decrease the down aileron travel on the left side, you are effectively reducing the average camber of the whole wing. This will reduce any pitch-up effect of the ailerons, which will reduce movement to the right. And the reverse.

Classic adverse yaw, where the nose moves to the left during right roll should cause the airplane to track left intially during a roll. The very small changes in differential they are suggesting would have no effect on the pure adverse yaw, but could have a fairly large effect on the pitch change from overall wing camber. I think adverse yaw still occurs even after the trimming suggested, but by changing the pitch motion of the airplane from aileron inputs, the airplane is trimmed to fly a straight path during at least an up-line roll.

It would be very interesting to have some video of a yaw string on a canopy during rolling manoeuvres, like would be used on a full size airplane to indicate adverse yaw.

I have an aeronautics background, and some of the trimming methods used don't seem to make a lot of sense aerodynamically at first glance. The level of trimming on pattern airplanes is compensating for some pretty esoteric effects that aren't always obvious. I like to try and understand the aerodynamics, but it doesn't seem to help my flying much!

To have something on-topic in this post, I am having good success with the addition of a T-flap to the trailing edge of the rudder of my Osiris. My stall turns with the Osiris have been a hit and miss affair. I'm sure that is my lack of skill and bad timing usually, but I was having better luck with another airplane. I added a 5mm high each side (about 2% chord) T-flap, and I now have much more rudder power at low speeds. It is just a strip of red polyethylene from a snow slider, CA'd to the TE of the fin. It has definitely helped my stall turns.

I have some good papers on Gurney flaps and T-flaps if anyone is interested.

Kevin
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Old Oct 27, 2012, 10:15 PM
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Marietta GA.
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Thx Gadget, for the trim list...My problem is the guy looking at the plane to trim it, is me.. I`m not sure what I`m seeing all the time is correct..It has gotten windy in Atlanta and thats not helping. Anybody here? These things don`t need the CG set like a 3D plane correct? I keep trying to roll upside down and keep moving the battery back...I`m not so sure it flys better...How much down should it be inverted? a touch? I know enough too know I need help with that first...thx..J
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Old Oct 28, 2012, 01:05 AM
scratch-built
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United States, WA, Port Orchard
Joined Apr 2007
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Mazjag,

I like to set my C/G to where I have to push a little down Elevator when inverted. If you fly with exponential, I like to set less exponential on down Elevator. I adjust it until I get the same feel, Both upright and inverted. I fly on low rates and only use high rates when doing snaps and knife edge loops.

Of course it's much easier to set trim when there's little to no wind. If you try to trim when it's windy, You usually just end up chasing your tail.

If you change anything on the plane after you get your C/G set, You should check your C/G again to make sure it's still where you want it.

My 47" Osiris didn't require very much trimming, Once I had the C/G set. I have so little pull either way in knife-edge flight that I didn't need to use any mix. It also tracks and rolls true. I did laterally balance it as I do all of my planes.

Don't give up on trimming the Osiris, Once you get it set-up. It will be a joy to fly.

J
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Old Oct 28, 2012, 09:32 AM
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Marietta GA.
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Thx Jim, I need to just play around with it some more.. Jason
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Old Oct 28, 2012, 09:36 AM
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Missouri
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edited
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Last edited by Gadget99; Oct 28, 2012 at 09:38 AM. Reason: add quote
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Old Oct 28, 2012, 09:38 AM
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Missouri
Joined May 2010
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Quote:
Originally Posted by kcaldwel View Post
Gadget,

Thanks, those are interesting.

I wonder if the 45 degree up-line roll tests for differential are actually looking for a pitch effect, not classic adverse yaw? If the net camber of the wing increases with aileron deflection, you would get a pitch up of the nose. For the first 180 degrees of a right roll, this would move the airplane to the right.

For a right roll, they are saying if the airplane "walks" to the right, you have too much down aileron on the left side. If you decrease the down aileron travel on the left side, you are effectively reducing the average camber of the whole wing. This will reduce any pitch-up effect of the ailerons, which will reduce movement to the right. And the reverse.

Classic adverse yaw, where the nose moves to the left during right roll should cause the airplane to track left intially during a roll. The very small changes in differential they are suggesting would have no effect on the pure adverse yaw, but could have a fairly large effect on the pitch change from overall wing camber. I think adverse yaw still occurs even after the trimming suggested, but by changing the pitch motion of the airplane from aileron inputs, the airplane is trimmed to fly a straight path during at least an up-line roll.

It would be very interesting to have some video of a yaw string on a canopy during rolling manoeuvres, like would be used on a full size airplane to indicate adverse yaw.

I have an aeronautics background, and some of the trimming methods used don't seem to make a lot of sense aerodynamically at first glance. The level of trimming on pattern airplanes is compensating for some pretty esoteric effects that aren't always obvious. I like to try and understand the aerodynamics, but it doesn't seem to help my flying much!

To have something on-topic in this post, I am having good success with the addition of a T-flap to the trailing edge of the rudder of my Osiris. My stall turns with the Osiris have been a hit and miss affair. I'm sure that is my lack of skill and bad timing usually, but I was having better luck with another airplane. I added a 5mm high each side (about 2% chord) T-flap, and I now have much more rudder power at low speeds. It is just a strip of red polyethylene from a snow slider, CA'd to the TE of the fin. It has definitely helped my stall turns.

I have some good papers on Gurney flaps and T-flaps if anyone is interested.

Kevin
Yes, I would love to read the articles. I have been considering adding to the trailing edge of the rudder on my 62" Osiris but don't know where to start.
I love this hobby because fellow hobbyists are willing to share their expertise.

Thanks

Gadget
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