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First flights unknown noise

Ron B.

Well Known Member
My friend's RV-14 has about 7 hours on it. Today he said he was trying to figure out what is causing a noise that sounds to be coming from down by his feet. It is only noticeable or occurring when he reduces the throttle for landing. Today he said he made some slow flights and while reducing the throttle no noise was heard. He says he has been running the engine hard ( more than I would, I broke mine in at 25 squared and I'm not burning any amount of oil, normal 1 quart in 8 to 10 hours). I'm wandering if he's not running the EXP239 very hard and reducing power too fast . He thinks it's perhaps backfiring when he is reducing power. I'm thinking of having him reduce power overhead tomorrow so I can see if I hear anything from the ground.
Thanks
 
If he doesn’t have any carpet the floor resonance is pronounced at certain power settings.
 
I changed the short metal hangars to belting and it got rid of a lot of sound and vibration in the floor area
 
I used to hear a funny noise coming from the right side of the Boeing, then I realized it was the co pilot!
Grin....

G.
 
My friend tried not bringing the engine to an idle position on landing approach as if I recall correctly was Mike Seager’s instructions. A few flights today seamed to reduce the backfire considerably.
 
Backfiring on throttle reduction / idle or close to, is pretty normal in these beasts. You can gentle the reduction to minimize it but I usually get some popping when reducing power for landing regardless of technique.
 
Could it be…

…after-fire? In my -14 w/an IO390X I would get what was termed after-fire if I brought the throttle rapidly to idle. It also happened at idle at an airspeed above 80KIAS. That made glide testing disconcerting cause gliding at idle at best glide would cause the event. Adjusting idle mixture seemed to help.
 
Back fire

What is not to like about that back fire in the pattern pulling the power back from say 18 to 10" in order to slow down?:)
If I keep the mixture lean for the descent and pull back the power in the pattern, I do not get the backfire. Anecdotal.
Is "after fire" a better term as suggested when we refer to backfire?
 
pretty normal backfiring

This scared the poop out of me when it first happened. I thought something was broken, but a search of VAF let me know that it was normal. It doesn't happen all the time. Actually it happened to me only once. I was coming in to the pattern super hot and cut the throttle very quickly. For some reason I was flying like a fighter pilot that day (the performance of theRV7A can bring that out of me) IO360 FP Prop.
I heard lots of terrible popping as soon as I cut the throttle. Hasn't happened since, though I am more gradual on the throttle these days.
 
6 cyl Pitts, stock, do that. One of my favorite sounds. Sounds good inside and out of the plane, Merlinesque.

Must be the fabric and exhaust outlet location.

Just don't do it with the smoke pump on, using diesel as smoke oil;)
 
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