Catto up from 2690 to 2800 rpm!

David-aviator · #1 06-01-2009, 08:27 PM

Today was the first time I had a chance to climb to 8500' and let the airplane run out at WOT since the cowl finish job. Last month the engine wound up to 2690 rpm which I felt was a bit anemic, TAS also seemed a bit slow, like 163 knots as I recall. Today was quite different. The engine wound up to 2800 at 12.2 gph and as near as I can tell, the TAS was 172 knots (or in marketing terms, 198 mph). Van's advertises 203 mph for the 7A at 8000' with a CS 2 blade prop so this machine is in the same ball park, finally.

After the WOT run, I reset 8 gph, my usual cross country planning number and was pleased to see 152 KTAS (or 175 mph). RPM was 2540, MP 19.8, CHT 386, EGT 1436, OT 170 and OP 71. Power is about 52% with very reasonable numbers. The engine should run forever.

I am not about to suggest the cowl is in laminar flow, but it sure is less drag than when it was about half raw unfinished fiber glass. Smooth paint really makes a difference. Another item is ram air into the FM200 AFP fuel controller. It boosts MP from 19.3 to 19.8 at 8500 and rpm goes up from 2510 to 2540 burning 8 gph. It is becoming habit to open ram air when climbing through 1500', the engine does perform better, and closing it when the boost pump is turned on for landing. (MP at WOT was 23 inches)

The EIS 4000 fuel flow calibration is also about right . Calculated add was 21.3 and actual was 20.6. That .7 gallons can be accounted for with the purge valve by-pass feature. If anyone is interested - the Flocal number in this set up is 170.

Pierre suggested using 1900 rpm on down wind to get this pony under control for landing and 1400 turning final. I tried it today at 3 airports and it works quite well, at least better than driving in at 2500 rpm and 140 IAS. You can not do a slam dunk with this machine as was routine with the Subby and MT. Max final airspeed for me is 70 KTAS, if you go into the flare at 90, the machine will float 3000' in a calm wind.

flytoboat · #2 06-01-2009, 09:20 PM

Congrats on your new powerplant. Keep up the good work.

pierre smith · #3 06-02-2009, 05:23 AM

Negative. 1400 RPM abeam (across from) the touchdown point while you're on downwind.

Regards,

sprucemoose · #4 06-02-2009, 06:47 AM

Quote:

Originally Posted by David-aviator

If anyone is interested - the Flocal number in this set up is 170.

I'm very interested. I've been using 170 for that setting since very early on. The recommended range is 190-210, but through extensive testing I found 170 to be the right number. It has served me well for the past 500 hours as it's always within a gallon at fillup.

I've never known anyone else who used 170 so yours is a good data point.

hevansrv7a · #5 06-02-2009, 06:58 AM

Quote:

Originally Posted by David-aviator

Today was the first time I had a chance to climb to 8500' and let the airplane run out at WOT since the cowl finish job. Last month the engine wound up to 2690 rpm which I felt was a bit anemic, TAS also seemed a bit slow, like 163 knots as I recall. Today was quite different. The engine wound up to 2800 at 12.2 gph and as near as I can tell, the TAS was 172 knots (or in marketing terms, 198 mph). Van's advertises 203 mph for the 7A at 8000' with a CS 2 blade prop so this machine is in the same ball park, finally....

Van's is only claiming 198 mph at 8000' for the 180 HP 7A, solo weight. For 200 HP it's 205 mph.

Just as a data point, at 8800 D-Alt, best power, full throttle I was burning 12.0, so your number looks very good although my RPM was 2620 (FP prop). Also, FWIW, I think that at 8000' DAlt we are getting much more than 75%.

I'm curious why you want to go beyond 2700 rpm?

David-aviator · #6 06-02-2009, 08:42 PM

Quote:

Originally Posted by hevansrv7a

Van's is only claiming 198 mph at 8000' for the 180 HP 7A, solo weight. For 200 HP it's 205 mph.

Just as a data point, at 8800 D-Alt, best power, full throttle I was burning 12.0, so your number looks very good although my RPM was 2620 (FP prop). Also, FWIW, I think that at 8000' DAlt we are getting much more than 75%.

I'm curious why you want to go beyond 2700 rpm?

Actually, I don't (and won't) operate beyond 2700, I was just pointing out that drag seems to be down so rpm, power and speed are up.

Another item, which may be a factor, is this engine came in at 187 HP on the Barrett dyno. Could be now that the airplane is closer to stock with regard to drag, that extra power is showing up by turning a prop that is designed for 180 HP a bit faster than 2700. Craig Catto has done many of these props and he knows what is appropriate for the 180 HP engine. The fact that it is turning up 2800 says something about the engine, not the prop.

Don't get me wrong, I am NOT complaining. I am most pleased to be seeing Van's numbers in a RV-7A like most everyone else.

roadrunner20 · #7 06-02-2009, 09:03 PM

David,
You may have posted this already but, are you running the 66x76?
This is what I'm running and I've never seen 2800.
I am getting your speeds but turning about 2700.

David-aviator · #8 06-03-2009, 06:08 AM

Quote:

Originally Posted by DanLandry

David,
You may have posted this already but, are you running the 66x76?
This is what I'm running and I've never seen 2800.
I am getting your speeds but turning about 2700.

It is a 66x74, Dan.

roadrunner20 · #9 06-03-2009, 06:48 AM

Quote:

Originally Posted by David-aviator

It is a 66x74, Dan.

That makes sense. I was one of the first to use this prop with forward induction. I felt early on I may have been overpitched slightly as I could not get the rpms until the airframe was cleaned up and engine broken in.

Any 66x75 out there?