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rickofudall
Joined: 19 Sep 2009
Posts: 1392
Location: Udall, KS, USA
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 Posted: Sun Dec 04, 2011 5:29 pm Post subject: Perplexed |
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After reading, and rereading Jack Hart's response to my last post about the IIIX I'm trying to fix, I decided to try changing the thrust line as a way of either ameliorating, or eliminating the right yawing tendency of the aircraft. We had a pretty good winter rain storm starting on Friday so while my grandson played with his new Wii, I loaded up the engine mount drawing into DraftSight and started dinking around. After a bit I figured I could twist the thrust line 3 degrees left without having to redo radiator mounting or lines again (this would have made the 4th time). About an hour after that I had all the holes drilled in a piece of plate and was ready to saw it out and finish. Yesterday, I moved the hoist over the engine and installed it and today, with clear skies and warm weather, by December standards, anyway, I flew it. On take off it was obvious that the change hadn't eliminated the yaw, but it wasn't causing my left leg to cramp either so I climbed up to 3,000 feet to check it fully. Once I leveled out and adjusted power to cruise, I took my feet off the rudder peddles. To my surprise, the aircraft didn't yaw less, it yawed more, quite a bit more. Enough more that the airplane would not fly level without aileron input to hold up the right wing.
Obviously the old motor mount plate goes back on in the morning, and I have to look elsewhere for the source of the excessive yaw.
Rick Girard
--
Zulu Delta
Mk IIIC
Thanks, Homer GBYM
It isn't necessary to have relatives in Kansas City in order to be unhappy.
- Groucho Marx
[quote][b]
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John Hauck
Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)
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| Posted: Sun Dec 04, 2011 5:52 pm Post subject: Perplexed |
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After reading, and rereading Jack Hart's response to my last post about the IIIX I'm trying to fix, I decided to try changing the thrust line as a way of either ameliorating, or eliminating the right yawing tendency of the aircraft.
Rick Girard
Rick G:
I experimented with changing thrust lines 25 years ago on my Firestar. I tried changing left, right, up and down. Flew better just like Homer designed it.
When I build the MKIII 20 years ago, I decided changing thrust line was not going to help it. What tweaking I had to do I did with adjustable leading edge of the horizontal stabilizers and rudder trim tab.
I did experiment with offsetting the leading edge of the upper vertical stabilizer. After three or four progressively more offsets, I put her back where Homer said put it in his plans, centered.
What I share about my experimentations with my three Kolbs may not work for you, but it works for me.
john h
mkIII
Titus, Alabama
[quote] [b]
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John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama |
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jbhart(at)onlyinternet.ne
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| Posted: Mon Dec 05, 2011 4:53 am Post subject: Perplexed |
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Date: Sun, 4 Dec 2011 19:27:11 -0600
From: Richard Girard <aslsa.rng(at)gmail.com>
| Quote: | After reading, and rereading Jack Hart's response to my last post about the
IIIX I'm trying to fix, I decided to try changing the thrust line as a way
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of either ameliorating, or eliminating the right yawing tendency of the
aircraft.
| Quote: | ......................
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Rick,
Since you have done all this work to make a new plate, can you flip it over
and use it again to rotate the engine to the opposite side?
One of the problems with rotating the engine on a pusher is that the
vertical center of the engine may be behind the cg and the moment arm is
much smaller than on a tractor setup. If you can flip the plate and use it
again, the results may be better.
I tried wallowing out the mounting plate holes for the 447 to try swiveling
the engine and I did not have much luck. Due to the fact that you were able
to make it much worse is encouraging. I did not try it with the Victor 1+
because I could off set the thrust line by rotating the reduction unit.
Jack B. Hart FF004
Winchester, IN
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rickofudall
Joined: 19 Sep 2009
Posts: 1392
Location: Udall, KS, USA
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| Posted: Mon Dec 05, 2011 9:20 am Post subject: Perplexed |
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Jack, I was feeling pretty low when I wrote last night, and I must have really worked it over in my sleep as I awoke with a "dope slap" moment. I was thinking direction of prop blast when I should have been thinking of its center. I moved the blast left and got more right yaw. Doh! So, yeah, flip the motor mount plate and move the blast to the right. Off to the hangar. Thank goodness the wind is from the north so I won't be in it while I work. With wind chill it's 21 out there. I guess winter has come to Kansas.
Ya'll stay warm out there.
Rick
On Mon, Dec 5, 2011 at 6:57 AM, Jack B. Hart <jbhart(at)onlyinternet.net (jbhart(at)onlyinternet.net)> wrote:
| Quote: | --> Kolb-List message posted by: "Jack B. Hart" <jbhart(at)onlyinternet.net (jbhart(at)onlyinternet.net)>
Date: Sun, 4 Dec 2011 19:27:11 -0600
From: Richard Girard <aslsa.rng(at)gmail.com (aslsa.rng(at)gmail.com)>
>After reading, and rereading Jack Hart's response to my last post about the
IIIX I'm trying to fix, I decided to try changing the thrust line as a way
of either ameliorating, or eliminating the right yawing tendency of the
aircraft.
>......................
Rick,
Since you have done all this work to make a new plate, can you flip it over
and use it again to rotate the engine to the opposite side?
One of the problems with rotating the engine on a pusher is that the
vertical center of the engine may be behind the cg and the moment arm is
much smaller than on a tractor setup. If you can flip the plate and use it
again, the results may be better.
I tried wallowing out the mounting plate holes for the 447 to try swiveling
the engine and I did not have much luck. Due to the fact that you were able
to make it much worse is encouraging. I did not try it with the Victor 1+
because I could off set the thrust line by rotating the reduction unit.
Jack B. Hart FF004
Winchester, IN
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--
Zulu Delta
Mk IIIC
Thanks, Homer GBYM
It isn't necessary to have relatives in Kansas City in order to be unhappy.
- Groucho Marx
[quote][b]
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