REFLECTOR: Front Vibration revisited

Rene Dugas dugasd at bellsouth.net
Mon Nov 15 13:03:55 CST 2004


Thanks Ronnie,

I spoke with a 30 yr builder and he feels like the ailerons may still be
vibrating and I can’t feel it because of the push pull cables.  My
cables have approx. 1/8th inch of slack caused by the 90 Degree bend.  I
also found a little slack in the torsion tube in the keel where it is
spliced.  When balancing the ailerons, my ailerons are bonded and
riveted to the aluminum tube. According to the manual the chord line
should be slightly down back to front.  I am rebalancing and trying to
get the slop that has developed in this system out in annual now.  I am
replacing my cables.  Still looking.

I down loaded the program.

Rene’

 

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Ronnie Brown
Sent: Saturday, November 13, 2004 5:34 AM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Front Vibration revisited

 

Rene,

 

Since it sounds like you have exhausted everything else, try this:

 

There is a program on the internet at
http://www.tunelab-world.com/rpmsound.html which is an audio spectrum
analyzer.

 

It actually works - I have checked RPM's on aircraft engines, even from
several video tapes that I had from cross country trips.  You can use
this to try to determine what frequencies are occurring in your plane.
It has high and low rpm settings (to trap unwanted harmonics), harmonic
settings, etc to help trap these frequencies.

 

You can run it on your laptop while you are flying.  Perhaps a better
way would be to record the sounds using a high quality audio recorder or
a analog cam corder with stereo hi fi capability.  You could attach two
good quality remote mikes - taped to the areas that may be generating
the vibrations.  Then analyze these at home.  You should be able to
isolate engine rpms, prop pulses, and in your case, perhaps the randomly
generated air pressure pulses - or what ever - then using the
frequencies found, figure out what the source of your vibration might
be.

 

Happy Hunting!!!!

Ronnie Brown

 

 

----- Original Message ----- 

From: Rene Dugas <mailto:dugasd at bellsouth.net>  

To: reflector at tvbf.org 

Sent: Monday, November 08, 2004 7:38 PM

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


  _____  


_______________________________________________
To change your email address, visit
http://www.tvbf.org/mailman/listinfo/reflector

Visit the gallery!  www.tvbf.org/gallery
user:pw = tvbf:jamaicangoose
Check new archives: www.tvbf.org/pipermail
Check old archives: http://www.tvbf.org/archives/velocity/maillist.html

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.tvbf.org/mailman/private/reflector/attachments/20041115/9e3ef560/attachment.html


More information about the Reflector mailing list