Things That go Bump - in the Day (an unsolved mystery)

On the way home from Vetterman's wonderful fly-in Saturday (thanks Larry and Clint and all), we were around 1000' agl a couple miles from landing at Ortonville, MN, for gas. I had just finished slowing the plane to about 120 knots prior to landing. Then THWACK! A rather loud sound unlike anything I'd heard in 11 years in the plane. I instantly assumed a bird strike. My copilot thought perhaps it was a pop of some sort in the audio system, and he may indeed be correct. But, I had the distinct impression it was somewhere to my right and low. We both scanned the wings leading edges, and as much of the horizontal and vertical stabs as we could see. Controls felt fine, so I refocused on the landing (winds were gusting 28, but mostly down the runway). On inspection of the exterior, we were not able to see any sign of anything. So, explanations are slim, and it could indeed be an audio glitch. Or, had we hit a bird with a tire? Guess I may never know. I'll tell you this - it got our attention!

I hate sounds out of the norm. A couple weeks ago I had an exhaust hanger brake. Just the sound pitch change and vibrations from that little thing got me heart going.

Same Here

Hey Alex,

Glad you're OK! This is sorta like what happened to me in the RV10. Cruising along nice and slow a little more than pattern altitude, called the Class D airport for landing at 8 miles out, then....the silence was broken buy an E-X-P-L-O-S-I-O-N that sounded like both barrels of a double barrel shotgun, LITERALLY. The entire airframe shook from front to back and tip to tip and oil completely covered the windscreen and both doors/windows. All this in a nano-second. 11.5 months ago today and after almost being burned alive I am grateful for every breath that I take.

Again, glad yours worked out OK. I'd triple check everything. Tires are a good point....you might even look at the sidewalls real good...you could find some evidence to put your mind at rest. May also want to pull the cowls and look at the engine real good. Something could have entered your air inlet or something may have broke?

I have had things hit the baggage or passenger floor(uncarpeted) and get my attention. Yep, like Rick said I would do a real good inspection of my engine. Also look at all areas around flight controls. Look for any lost tools from prior work. Could it have been an afterfire? That will produce a loud thump on bottom skin. Do you leave mixture leaned from altitude until in the pattern and pull power off no more than 2" MAP at one time?

I pull my ANR's away from my head occasionally in flight, especially over those big hills to the South.

Possible bird strike

I just recently hit a bird, which if it wasn't for me having a polished wing, I would of never been able to see where it hit. With a white paint job, it would of been impossible to see since there was no damage.

http://www.vansairforce.com/community/showthread.php?t=90566&highlight=Bird+strike

Thanks for all the thoughts, all good. A few replies:

-Could be bird with no visible evidence, I recall the picture referred to in the previous post.
-Afterfiring - I have FI so I'm fairly familiar with that, not that type of sound at all.
-Baggage area full of junk and carpeted.
-Pipe mounts good.

Will look over again with good lighting.

Not that this could have anything to do with your sound, but there are times sounds from the ground can be focused just right... I flew over a regatta once years ago and for a brief second I KNEW I had been buzzed by a P-51, and close. I realized it was the very instant I was directly over an unlimited hydroplane. Yes, I duplicated it, just to be sure. Very scary. Since you were low, and probably throttled back, could it have been something similar?

Bob

I think I've solved it.
http://news.yahoo.com/stowaway-might-survived-international-flight-wheel-well-153026252.html?_esi=1