Jburry
Posts: 552
Joined: 7/12/2006
From: Cape Spencer,
NB, CANADA
Status: offline
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We only recorded audio, and I don't know how to upload that for you.... The actual doppler numbers I got were:
HSE Dopplers
9 14 = 84mph, 85.5mph, 21850rpm 85 avg
34 43 = 85.8mph, 84.7, 84.3, 21810rpm 85 avg
106 116 = 93mph, 88mph, 91mph, 22270rpm 90 avg
142 150 = 89.9mph, 92.7mph, 91.9mph, 22220rpm 92 avg
Mustang Dopplers
27 35 = 121.5, 17240; 122.1, 17299; 119.9, 17347; 123.5, 17363 121.75 avg
55 104 = 117.8, 17213; 115.6, 17194; 118.1, 17174 117.17 avg
123 132 = 109.2, 17047; 109.7, 17080; 108.1, 17048; 108.7, 17015 108.925 avg
There are 4 runs from the little red electric plane there on top, and 3 runs of the mustang below. The different numbers (2 3 or 4 measurements per pass) were done on each of the octaves that displayed clearly between 200 and 2000 hz.
The HSE dopplers are from the little red electric plane. That plane's RPMs seemed very, very consistant coming towards the speed trap, and leaving it, so we consider them to be OK.
Now, I gotta qualify those Mustang numbers. They are not believable (well, the third run is actually), and I think I know why. I was flying essentially standard orbits of our field, flying the downwind leg about 200m or more away, at 300' or so. I'd turn "base and final" in an almost knife edge attitude, allowing the nose to drop and plane to accelerate as it climbed thru the turn. Very little control input needed keeps the plane clean thru the dive. I'd end up on the C/L of the runway, between 1 and 200m from the threshold, at about 30-50', and do my best to keep her straight and level for at least a few seconds before and after the plane passed our pilot station. Beautiful roar. I think, though, for the entire straight run, RPM's are bleeding off slowly, sinking from a high of about 17.6 to a low at the far end of the run about a 1000 below that. Falling RPM's will falsely exaggerate the doppler numbers.
On each progressive run of the 3 the 'stang flew here, I made my approach longer and longer, so the third represents the least inflation. The mustang was clearly quicker than the HSE, but not by the 30mph these numbers would seem to indicate. more like 10mph, thus my best speed estimate of 100-105mph in the straights. I don't want to think about what it momentarily achieves in the dive.
Clearly I need a radar gun.
I've read about exceeding pitch speed by upto about 10% before too. The 'stang is a pretty slippery ship, but it does have fixed gear and the cylinder head is in the wind. Other than that, I did my best to keep it clean. The muffler is partially buried in the fuse too.
It really was the HUGE unloading and almost pipe-like performance of the lovely OS46AX that took me by surprise, though. I know some aren't big fans of the ax series for speed planes, but I couldn't be happier with my .46. Perhaps it's a little exceptional in the AX line with repect to achievable RPM's.
If you want the .wav (which includes one last dive/pullout pass at the end that dopplers at 146 mph or so, but was flown just for fun, not for doppler. It's simply nowhere near reality), let me know how I can get it to you. Email comes to mind 
J
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.46AX behavior without baffle - 
