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Yaw oscillation, 701

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mileski(at)sonalysts.com
Guest

Posted: Sat Jul 08, 2006 6:39 am Post subject: Yaw oscillation, 701

Hi all,

  

 I just sort of solved an odd problem I was having with my CH701 currently under flight test with 14 hours on it, and hope this may serve someone else at some point.

  

 At every take-off I was getting an oscillation in the yaw axis, a few seconds after liftoff, for anywhwere from 2 to 5 seconds, which went away if  a) I continued climb normally, b) I dropped from 5450 rpm (max) to 5200 or lower. It is felt in the whole airframe, and the cowl looked like it was visibly displacing a half inch as the aircraft "wobbled" in yaw at approximately 3 or 4 cycles per sec.  Airspeed is accelerating between 50 and 60 mph at this time. The oscillation is mild, more annoying than concerning.

  

 It could not be stopped by pitching up or down slightly, or changing rudder position slightly.  No perceptible vibration is felt in the pedals.  My rudder cable tension seems possibly slightly on the high side, and I also tried pressing on both pedals during climb, with no change.

  

 After adding another pair of dzus fittings at the cowling at the bottom of the firewall, verifying blade pitch and minimum vibration, without any change, it occurred to me that the main gear might be out of balance, and the wheels are spinning down from a 40+mph rpm during this time. Although I don't feel any out-of-roundness or vibration from the gear during the takeoff run, I tried pressing the brakes immediately after liftoff.

  

 I made four takeoffs today pressing the brakes after liftoff, and got none of the oscillation, which has been very consistent prior to today.

  

 So either the wheels and tires spinning down were the culprit, or I am wrong about my rudder tension, and by braking I'm adding more rudder cable tension (through slop and flexure of the nose-wheel steering hardware) than I did before when trying this by pushing only on the pedals (no brakes). I'll try more with pedal pressure without brakes again, too, to see if I can figure out what's happening.  But at least it's under control for now.

  

 Sorry for the longwinded explanation, but it seemed like there was a lot to explain for anyone interested.

  

 Bill Mileski

 N701MW

 Ledyard, CT

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Tommy Walker

Joined: 12 Jan 2006
Posts: 442
Location: Anniston, AL 36207

Posted: Sat Jul 08, 2006 1:56 pm Post subject: Yaw oscillation, 701

Bill,

  

 Thanks, that  is one for me to file in my list of things to know about.  I had not  considered that happening........

  

 Boy, that  first lift off is going to be exciting.......

  

 Tommy Walker  in Alabama

 Do Not  Archive

  

 [quote]   --

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_________________
Tommy Walker
N25A - Anniston, AL

raymondj(at)frontiernet.n
Guest

Posted: Sat Jul 08, 2006 2:09 pm Post subject: Yaw oscillation, 701

William,  

  

     I had a similar experience in a 172 I did some training in. It  only seemed to happen when I would do touch-n-gos.Too much speed on the runway  before "going" again.   When I asked the CFI about the vibration he knew  exactly what it was and put on the brakes. I guess he was so used to it he  didn't notice it any more. In my case it was only a vibration and didn't really  have any impact on flight characteristics.

  

 Raymond  Julian

 Kettle River,  MN

 Corvair core  acquired.

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ch701builder

Joined: 07 Feb 2006
Posts: 119
Location: N38.9947,W105.1305,ALT. 9,100'

Posted: Sat Jul 08, 2006 3:08 pm Post subject: Yaw oscillation, 701

All, I guess I thought everybody was taught that way. That was one of the first things I learned when I was flying, was to tap the brakes to stop the tires from spinning.



Keith

CH701 8% scratch -- no engine decision yet, it keeps down on the negative e-mails:)

N 38.9947

W 105.1305

Alt. 9,100'

*************************************************************************



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Rick Roberts

Joined: 10 Jan 2006
Posts: 28
Location: Orlando, FL

Posted: Sun Jul 09, 2006 4:48 am Post subject: Yaw oscillation, 701

Thanks Bill...EXCELLENT report...definitely IN my archives!

   

  DO NOT ARCHIVE



Tommy Walker <twalker(at)cableone.net> wrote:

  [quote]  BODY {   FONT: 10pt Tahoma, Verdana, sans-serif  }        Bill,

   

  Thanks, that is one for me to file in my list of things to know about.  I had not considered that happening........

   

  Boy, that  first lift off is going to be exciting.......

   

  Tommy Walker in Alabama

  Do Not Archive

   

  [quote]  --

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_________________
Low & Slow,
Rick
Orlando, FL. USA
www.n701rr.com

dredmoody(at)cox.net
Guest

Posted: Sun Jul 09, 2006 5:45 am Post subject: Yaw oscillation, 701

Now if we could just balance the nose wheel, we'd have  this problem on the ropes. That's probably why taildragger pilots can't be lured  to tricycle gear.

  

 Ed Moody II

 Rayne, LA

 601XL / right wing complete!

  

 Do Not Archive

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