150 HP RV-6 breaks the 200 mph barrier!

[elippse]

Jim Smith has just sent me some TAS numbers which he obtained after making and installing a streamlined cowl outlet as shown by Vetterman. Jim has a 150 HP Lycoming RV-6 running on auto gas. He originally changed his two-blade Aymar DeMuth prop for a three-blade Elippse prop, then added triangular wingtips, then reduced the cooling inlet area, added a single LSE ignition, and finally added this fairing on the outlet. He also recently installed an altitude-hold which gives him very consistent TAS numbers within 1 mph. His latest TAS numbers: 203 mph, 2745 rpm, 6000' dalt; 202 mph TAS, 2734 rpm, 8000' dalt; and 199 mph TAS, 2680 rpm, 10,000' dalt. How's that for only 150 HP!!!!He finally broke the 200 mph barrier!

[chrispratt]

Originally Posted by elippse

Jim Smith has ... finally broke the 200 mph barrier!

Tell Jim to "Pull Up" before it's too late

Chris

[Mike S]

Photos please....

[petehowell]

Originally Posted by elippse

His latest TAS numbers: 203 mph, 2745 rpm, 6000' dalt; 202 mph TAS, 2734 rpm, 8000' dalt; and 199 mph TAS, 2680 rpm, 10,000' dalt. How's that for only 150 HP!!!!He finally broke the 200 mph barrier!

Any reports on fuel flow at each of those sets of #'s? - pretty impressive!

[Bob Axsom]

I would like to see Jim's exhaust fairing installation. I raced with him at Wichita a few years ago. I talked to him and looked at his plane there and I read about him and the airplane in the very last issue of Sportsman Pilot before Jack Cox died and publication ceased. Jim was very easy to talk to and seemed like a nice honest guy. I have seen photographs of two Larry Vetterman installations one with the exhaust pipes displaced outboard and one with them in a more standard position. His was basically a boat tail design with louvers on the lower surface. He made speed claims for the earlier design but I never saw any on the second. Even before Larry Vetterman came out with his first version I had been thinking about something in this area but I have done nothing but think. Alan Carroll tried something on his fast RV-8 I believe and reported no increase in speed. Someone reported a guy installed part of an old bonanza wingtip there and got an increase in speed. I understand the concept but I feel something dynamic is required to get adequate cooling at low speed and maximum speed from the mod at the other end of the operation. I am currently unable to work on my plane because of more important responsibilities here at home but looking ahead I have several ideas cooking for more speed and a photo of Jim's cooling air exhaust fairing installation would add to my knowledge.

Bob Axsom

[pierre smith]

Originally Posted by Mike S

Photos please....

I'm with Mike....pleeeease?

Thanks,

[Geico266]

Would not a 2 blade prop be faster than a 3 blade?

[elippse]

Originally Posted by Geico266

Would not a 2 blade prop be faster than a 3 blade?

Sorry, Larry, but that's one of the well-known facts that is totally wrong and should have been eliminated long ago. The reason on a CS prop that a three-blade will be slower is that it usually has such draggy hub-shapes that the plane's total drag is much higher. Let's look at Tom Aberle's "Phantom" biplane racer. In 2003 at Reno it qualified at 220 mph with a two-blade prop. In 2004 it qualified at 240 mph with a three-blade at 7.5% less power. Then with a four-blade it did 260.805 mph last year. 'Still believe that tale?

[Flyfalcons]

How different were the biplane's prop designs?

[hevansrv7a]

Originally Posted by elippse

Jim Smith has just sent me some TAS numbers which he obtained after making and installing a streamlined cowl outlet as shown by Vetterman. Jim has a 150 HP Lycoming RV-6 running on auto gas. He originally changed his two-blade Aymar DeMuth prop for a three-blade Elippse prop, then added triangular wingtips, then reduced the cooling inlet area, added a single LSE ignition, and finally added this fairing on the outlet. He also recently installed an altitude-hold which gives him very consistent TAS numbers within 1 mph. His latest TAS numbers: 203 mph, 2745 rpm, 6000' dalt; 202 mph TAS, 2734 rpm, 8000' dalt; and 199 mph TAS, 2680 rpm, 10,000' dalt. How's that for only 150 HP!!!!He finally broke the 200 mph barrier!

Paul, going back to the report of last spring when it was 193.4 mph at 8000', I re-worked my analysis because the old one was C**P (my bad) and came up with the stuff below. Please tell me/us if this is close. If it is, then it can be used to evaluate the additional changes.
http://www.vansairforce.com/communit...4&postcount=28
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193.4 mph at 8000' on a nominal 150 HP engine, 1440 pounds.
New max L/D speed: 92.8 vs. CAFE 6A at 106.
New glide ratio with "transparent prop": 14.0 vs CAFE 6A at 12.245.
Minimum Drag: 102.6 pounds at 1440 pounds aircraft vs. CAFE's 128.5 corrected for weight and nosewheel.
THP at 193.4 mph: 98.1 vs CAFE 6A would be 103.85.
Total reduction in drag at 8000' and 194 mph is about 7 pounds.
Reduction in induced drag approx. 37%.
This set of data is for 193.4 mph vs. 189.5 for Van's as corrected for weight and nosewheel, using factors derived from CAFE 6A. A difference of about 4 mph. I think your original posting said the gain from tips was greater than that, so a lower starting point?
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If the above is assumed correct, then:
Estimated 81% BHP available at 8000' (no, not 75%!) is 121.11.
Kevin Horton's spreadsheet suggests that 81% is a better estimate.
If BHP is correct, then net prop efficiency would be 80.75% at that speed.
If BHP is assumed 75% at 8000', then prop is 87.2%.
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To move that airplane from 193.4 mph to 202 mph would take an additional 15.2 BHP. Therefor the changes since the wingtips would have that value, total of increased HP and reduced drag.

That's about 12.5%. Not too shabby! And that's above the previous 4 mph for the tips.