Strange noise

[Sideshowbob]

Flying my long ez back the other day I had a strange noise like a high pitched hum only occurs above 125kts and depends on angle of attack, doesnt seem engine related, any ideas? Im going to check the obvious canopy seal, prop torque and  tracking etc..... The aircraft is fitted with a lycoming 235l2c

Cheers

[Waiter]

Bob;  Look at everything carefully. Its talking to you! If able, Look at the ailerons and rudders carefully in flight, to see if they are fluttering.

Also look at the wheel pants, I had these do some funning vibrations until I secured the outside to the axel.

I do not wish to alarm you , but here is my experience with a sudden strange buzzing sound!  Goto my web site:

www.iflyez.com

Look under PHOTOS - Cracked Flange.

I was very, very, lucky, but I also listened to my plane.

Waiter

[Dan Patch]

Bob,  I agree with Waiter - listen to the plane when it talks!  New words mean something's different.  

Airspeed related noise implies that it' something being excited by the airstream - Waiter covered the obvious candidates.  I'd also carefully check the cowl for some type of dynamic contact, since the cowl will deform under air loads, depending on airspeed.  The cowl can be a surprisingly elusive source of wierd noises.

The only experience that I have had that relates to your question was getting a humming noise when I had an open tank with the gas cap hanging off on its tether.  It made the tank 'organ pipe' at certain speeds and AOAs.  Guaranteed to get your attention once you've heard it and know what it is!  So look for 'openings to airframe cavities' (e.g., at the cowl-wing intersection, etc.).  

Another, albeit, quite unlikely candidate would be a piece of tape or the like.  These puppies will really scream if they start to come off, as I discovered coming back from Mexico in the rain with 'press-apply' N-numbers.  (They don't like rain!)  Also know a well-known racer who aborted in the middle of a RACE event from a very scary noise that turned out to be a piece of joint seal tape coming off.  

So good luck, look carefully, and let us know when you figure it out.

[rglos]

Excellent Advice from Waiter and Dan.

Something is reaching natural frequency at these speeds. Possibly due to air motion, engine motion, loose part motion or any combination. Things that move in the airstream, wings, rudder, canard etc look for changes.

Things that are removed from the airstream (closer to the cowling ) may reach or are induced into a resonance by something innoculous like worn bushings on the engine mounts, the baffling chaffing the cowls etc.

The engine is a natural source of vibration that can also induce other vibrations.

Higher or lower frequencies of the noises should also offer clues. Hi pitched noise generally means lighter items vibrating real fast. This is opposed to lower frequencies and bigger parts but this is not a hard fast rule.

Borrow a set of ANR headsets and see if the frequency changes or disappears altogether might be another idea. if you're already using an ANR set, change the batteries. This may sound strange but I endured a flight back to the airport with a low frequency "thumping" all the way back.
When I shut down the radios and the engine, the thumping was still there. It was coming from some  feed back loop caused by low batteries.

[Drew]

Related to what Deltapop said, do you have anything taped up like the canard or wing joints?  If you did not clean the area real good where you want to stick on glider tape-----and/or you mix high speed with rain---the front edge of the tape can lift up and make a real loud high pitch squeal.  It will also change frequency with AoA.  For me, when the tape finally gave way, it scared the crap out of me as it flew past the left side of the canopy (didn't know what it was at first----just saw a shape fly by real close).  It then stuck on the strake----and proceeded to "thump" the strake with the rest of the tape that would not stick.

Another funny sound----more of a rattle than a squeal---can be the canopy safety beating on the canopy locking rod.

[Anonymous]

Flying my long ez back the other day I had a strange noise like a high pitched hum only occurs above 125kts and depends on angle of attack, doesnt seem engine related, any ideas? Im going to check the obvious canopy seal, prop torque and  tracking etc..... The aircraft is fitted with a lycoming 235l2c

Cheers

My first suspect in a case like this, check what you have just worked on. If that doesn't work and after a very thorough preflight.  Just ease her into and out of 125 knots and keep your eyeballs and senses on high alert.

Couple of times after liftoff, I have left the speed brake down and encounter some different wind noise and the canopy lifting a tad. My SOP is keep the speed brake down at all times on the tarmac until 40 knots and the airspeed comes alive on takeoff.

Good luck;

Jack

[Anonymous]

Guys and gals
 
Thanks for all your help and ideas, i have had a piece of tape covering the wing access for the bolts seperate half off  and this could be the culprit, however i am checking everything thoroughly that has been suggested. Any other ideas welcome and I will let you know how it goes and what it is.

Best Regards

Sideshowbob

[Anonymous]

GREAT,  Glad to hear that it wasn't something serious, and the only thing that got rattled, was the nerves.

Waiter

[niceez]

Had tape do that on a few occasions and it really gets your attention!  Feel kinda silly though once you figure oue what it was.

Coyote

[sideshowbob]

hello again just an up date i checked everything suggested noise has been stopped flown 10 hours with no repeat noises a big thanks for all the advice! cheers!