REFLECTOR: Front Vibration revisited
Scott Derrick
scott at tnstaafl.net
Thu Nov 11 18:19:07 CST 2004
Being that it was not there for 200 hours, I'd be very suspicious of what I
did at 200 hours.... 90% of the problems I have with my plane turn out to
be pilot error.
Problems usually don't just appear, unless its something like the prop
running out of grease as somebody suggested...
Scott
At 01:04 PM 11/11/2004, you wrote:
>Thanks,
>Vibration is similar to the one caused if one pushes down on the canard
>tip and releases it. Don’t know the frequency. This vibration is
>new. It did not do this for the first 200 hours. My scoops are NACA left
>and right front and two top. I talked with the Factory about vortex and
>they state the vortex does transfer from below to above near that airspeed
>but they are unaware of a plane in which it can be detected. I plan to
>attach yarn strips to try to determine this weekend. Fairly constant in
>amplitude speeding up slightly with speed up to 200 knots.
>
>Can rotate prop 120 degrees but since prop is balanced I will wait on this
>‘till other suggestions exhausted. It does not change based on prop or
>engine speed or power.
>
>Thanks and keep them coming.
>Rene’
>
>-----Original Message-----
>From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
>Behalf Of Al Gietzen
>Sent: Thursday, November 11, 2004 1:10 AM
>To: 'Velocity Aircraft Owners and Builders list'
>Subject: RE: REFLECTOR: Front Vibration revisited
>
>Rene;
>
>Since you have pretty much checked everything mechanical/structural it
>seems that it must be an aerodynamic phenomenon. Is there anything
>different about your air inlets – NACA scoops or engine air scoop, than on
>other Velocitys? What would be your guess of the frequency of the vibe,
>and is it constant with the amplitude varying with speed?
>
>Not sure where I’m going with this, but some kind of vortex shedding comes
>to mind; you know the old Von Karmen thing.
>
>Al
>
>-----Original Message-----
>From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
>Behalf Of Rene Dugas
>Sent: Wednesday, November 10, 2004 11:14 AM
>To: amillin at sbcglobal.net; 'Velocity Aircraft Owners and Builders list'
>Subject: RE: REFLECTOR: Front Vibration revisited
>
>Thanks Andy, Scott and Herb,
>I will be taking the plane down for annual next month for a more thorough
>shake down(pun intended). Propeller tips are within 1/16” and prop
>balanced 6 weeks ago. What kind of sensor are you proposing Andy? I have
>hade three pilots feel around in the plane but not with the rear bulkhead
>removed. They could not localize it. The rear compartment cover has a
>window and the retracted gear brackets are not moving. Front gear is
>solid after retraction. I have removed the cowl and plenum examined the
>nose cone and interior areas. I have removed the wing bolt covers and
>find nothing loose. I do not have any KNOWN tools missing that have been
>left anywhere in the plane. My next attempt will be to forward weight the
>elevators a little since the elevator is the only control surface that
>changes significantly as speed increases. I agree that control surfaces
>seem to not be involved but my gut tells me it is the canard somehow
>vibrating. It may even be some harmonic. Tightening the elevator hinges
>before helped a little. I do have a front oil cooler that is snug. Only
>my engine air scoop is hanging out in the air. It is tight. My cowl and
>engine plenum touch but they have since new over the #1 cylinder. I do
>have foam caulk under my canard and along the outer body to lower the cold
>air entering but removing it did not decrease the vibration and changing
>it to another type had no effect. Nose door and “dog house” are tight.
>
>-----Original Message-----
>From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
>Behalf Of Andy Millin
>Sent: Tuesday, November 09, 2004 11:05 AM
>To: 'Velocity Aircraft Owners and Builders list'
>Subject: RE: REFLECTOR: Front Vibration revisited
>
>Rene',
>
>Just thinking.
>
>No change with engine and prop rpm ... must be airframe
>No change with controls and no vibration felt in the controls ... not the
>controls
>Nothing loose on the airframe ... not the cowl or gear doors
>
>Sounds like an aerodynamic issue. Harder to find.
>
>Now the challenge seems to be to find a clever way to locate the affected
>area.
>
>Alex Balic might have an idea on how to measure vibration. Every time I
>try to figure out what his background is he comes up with a new tale of
>experience in a different discipline.
>
>It would be helpful if we could place a sensor or sensors on the airframe
>and measure vibration.
>
>You have looked at the obvious things. We still need to find out just
>what is vibrating. Then we might find out what is making it vibrate.
>
>FWIW,
>
>Andy
>
>Just an afterthought. Could you take up a passenger and while the
>vibration is going have them feel around the plane. Check the center
>spar, gear legs, firewall, windows, etc. Might give a direction...
>-----Original Message-----
>From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
>Behalf Of Rene Dugas
>Sent: Monday, November 08, 2004 7:38 PM
>To: reflector at tvbf.org
>Subject: REFLECTOR: Front Vibration revisited
>Folks,
>Five weeks ago I began chasing a vibration in my XL that only occurs over
>160 knots. Some helpful suggestions have been received and pursued to no
>avail. I spoke with the factory today and they don’t know what it could
>be but suggested I keep looking. This symptom is a shimmy that starts at
>over 160 kts and gets slightly worse all the way to 200 knots. It is not
>uncomfortable but VERY annoying. It does not change with pull ups or ½ g
>unweighting or turns. Prop speed or engine RPMs eo not affect the
>shimmy. No vibration can be felt in the stick ( I have 230 hrs of
>experience in this plane and this is new.) No visible shake is noted in
>the canard winglets or wings. Slight pressure on the rudders does not
>change it and no vibration is transmitted to my feet. No increase
>vibration is felt in the torque tubes to the elevators or in the canard
>with my feet or hands. Back seat passengers can feel the vibration.
>I have
>Removed the wings and confirmed incidence and tight bolts.
>Removed the canard and confirmed bulkhead is ok and bolts are tight.
>Elevator matched and balanced and hinges snug.
>Elevators adjusted up 1/8th inch and then down 3/8th inch no changes.
>Front gear doors tightened –Very snug.
>Main gear doors adjusted x five no change
>Main Gear doors removed no change
>Doors confirmed snug and vibration the same as entire plane
>Cowl removed and realigned x five
>Left wing incidence increased 0.2 degrees no change
>Discussed canard vortex hitting wing – Why a change and factory states a
>non problem.
>No glass cracks found. Fuselage and wings and canard all very solid.
>No fuel leaks.
>Spinner tight rotates very centered.
>Prop balanced.
>Windows not loose.
>Heated Pitot tube snug no slack.
>Door handles not moving.
> Same problem solo or with slightly over gross wt.
>Only external scoop is ram air to engine just behind the firewall very
>stable. Unable to move on the ----ground at all.
>Not expecting cures but ideas?
>
>Rene’ Dugas
>
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