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Need some help in diagnosing an odd noise in flight

moespeeds

Well Known Member
Friend
I have an RV8 with about 400 hours on it. I am not the builder, but have put approximately 25 hours on it in the last few months.

I have an IO-360 and Whirlwind RV200 prop that I had rebuilt by whirlwind when I first bought the aircraft.

On a flight last week, we had just done a touch and go and were climbing back into the downwind. Just at the top of the climb at 24"/2500, the pilot-passenger and I noticed a sound that I can only describe as having a turboprop flying somewhere close in our vicinity. I felt it was coming from up front by the prop, the passenger who is also a pilot felt is was coming from below us. The sound remained with MP and RPM changes, and did not change much in pitch or volume. By the time we returned to our home airport 15 miles away, it was gone. It was not loud, or scary, and I couldn't perceive any associated vibration. Only the sound.

On the ground we theorized that it could be a panel vibrating that I recently attached a cupholder to.

Yesterday, we went up again to test, and through all different power and climb/cruise configurations, we could not get it to come back. When returning to the airport, we initiated a decent of about 1500 fpm at around 15"/2400 rpm and the sound came back. I added MP and began to climb so we could spend some time diagnosing, and it immediately went away. We could not get it to come back.

My passenger was quick enough to push on the panel the cupholder was on, and verified that it was not the problem.

I never heard this in the previous 22 hours I put on the aircraft.

I have checked the following between the first flight and yesterday:

-I checked the entire exhaust system
-Looked at everything with the cowling off
-Spinner is tight, true, no rubbing
-Prop blades are tight, clean, and tapping the entire length, both blades sound the same
-Wheel pants are tight
-We did not notice any flutter or vibration through any controls
-Wing root rubber strip is secure
-All panels and fairings are tight and secure

Any thoughts on how I can diagnose this? It might be nothing, it might be something. Intermittent problems are the worst!
 
A friend's RV-8 makes what could be a similar noise when the rear vent on the passenger's floor is open. Goes away when closed. Or vice versa, cant remember exactly.
 
I’d go with seals…..aircraft can make quite odd noises relating to leaks, door seals, vibrations (you want to hear a seat belt caught in the door in flight!)…..I’d check over your canopy seals too.
 
I had a similar noise for the first time last weekend when it was in the 90's here in PA. Afterwards I realized that since it was so hot it was the first time I've flown the airplane with both panel vents fully open (first flight was last December) so I'm thinking the noise was somehow due to vent air escaping under the skirt.

I flew it on Monday night when it was much cooler, with the vents closed, and I didn't notice the noise.

I have a roll of felt on order and am planning to put a strip of it along the inner bottom edge of the skirt to help with the noise and sealing.
 
Check your wheel bearing preload.

On the Rv-10 I have had the nose wheel bearing get loose enough that the wheel started turning due to air slip-stream under the wheel fairing.

The wheel was not quite in balance so it creates a vibration. That vibration changed with air speed although somewhat delayed. The engine/prop vibration changes with RPM. When the 2 vibrations get very close to synchronizing you will hear the in and out of phase pulsed noise that gets your attention. Took a lot of troubleshooting to find it.


May not be your problem but may be worth jacking the plane and blow the front of the wheel fairing with a leaf blower. See if the wheel spins and shakes.
 
Noise

Moe,

I had a weird nose issue in my -8 when I got it. Took me a while to figure it out, sounded like metal to metal rattling. Figured out it was the sheet metal pockets built into the cockpit side of the canopy making the noise. I ended up getting various sizes of the foam pipe wrap in the plumbing section of box stores. Found one that seemed to fit and shoved it down into the bottom of the pocket.

It didn’t do it all the time, just a real irritating intermittent problem. That was 3 years ago and haven't heard a thing since. I can send pics of these pockets and the foam pipe wrap I used if you want.
 
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I would go with the skirt seal as others said. If you don’t have enough dampening on the back skirt via its seal you can get that noise. The appearance and exact sound depends somewhat on the pressure in and outside the cockpit so sometimes open/closing vents, changing airspeed, changing density altitude, different temp or air pressure can make it appear or disappear. Permanent fix is to seal the skirt properly.

Oliver
 
Another item to check. Remove upper gear leg fairing & check if the gear leg mount cover plate is loose. Can produce a fairly high buzzing sound if screws are loose or missing, seems influenced by angle of attack.
 
I had a similar problem 150 flight hours RV8 Lycoming IO-360 (without counterweights), propeller 150 hours hartzel HC-C2K 1BF
Blade:F7666A-4

Never lubricated by me, I put grease on it and it never bothered me again.
 
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