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Elevator Pulsing/Hunting
Hi All,
Looking for some thoughts from the VAF brain trust. I have put my 14A through it's paces and have about 230 hrs on it now . I'm puzzled by a "problem" I keep experiencing in flight. It appears that when the trim tab is in the neutral position, or close to neutral, the control stick "pulses" back and forth at about 1-2hz. I've spoken to Van's about it in the past and they believe the elevator is "hunting" when the elevator and the trim tab align just right. There is advice is to "trim it out", which does work, just seems like a bit of a cop out. For the past year I have been testing various theories as to why this might be happening, some theories related to the trim tab and others not. Below is a summary of what I've tried so far
Couple of questions:
Thanks, |
Does the pitch change with the hunting, or does it stay stable and the elevator assembly is "floating" as in moving but not making any pitch change? I know back in my R/C days we would make the trailing edges thick like the 14 has to make the sensitivity less so at neutral like you describe. I never noticed this on my 14A but will try to pay close attention to replicate what you describe.
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Interesting to hear this.
Obviously I don't have nearly as many hours on my 14A as you do but so far, twice I have noticed a very short "vibration/pulsing" in my stick just right after rotating (during take off) that last about 1sec to 1.5 second. I have not noticed it in the air at all. I do believe the pulsing during rotation is related to where exactly my trim tab is which I set it to neutral position but It is not a precise setting. I have, likewise, checked for any 'play' in the control surfaces and can say there is about 1/32" (as best as I can measure it) of play in my trim tab but zero on my elevators in relation to one another and I did balance my elevators each individually. |
Jared, could you fasten something like a rubber strap, temporarily with tape, to keep the trim tab always against one side of whatever small slop might be in the system? Some way to preload it to one direction. Seems it could be related to that. Putting a small amount of trim in and the putting a small pressure on the stick does a similar thing.
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Here's an experiment: Try putting a 30-40 lb weight in the baggage compartment. See if you get an improvement when you fly.
If so, you may have to adjust the incidence of the HS. V |
No pitch change
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No perceptible pitch change. I've asked passengers while it's happening and they can't feel it. It would appear to be "floating". Thanks, |
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The trim tab has 0 slop. I machined SS bushing sleeves that go over the clevis pins to remove all slop. Thanks, |
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Good idea. Easy to do. I'll give it a shot! Thanks, |
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This is not something that has been common with RV-14's so there is no "yea we have heard that a bunch of times.... just do this...." Regardless, in the interest of trying to help you out, please explain what you mean by "trimming it out does work". (to stop the pulsing?) |
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Think of the poor guy that said "look at that ugly rivet for a static port; I can make something much better" and proceeded to make a nice flat one that looks just like the expensive certified planes then wondered why his airspeed readings were so far off. Larry |
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