jjconstant
Well Known Member
I have finally gotten my static port location/shape/airspeed calibration testing done. My CAS is 3 knots slower than IAS and is linear from fast cruise all the way down to 75 knots indicated. I stall heavy and clean at 57kts IAS and dirty at 55kts IAS. Stall technique can be improved but those are the numbers I'll be using for now.
So I went out to check my real 8000'DA speeds and to see at what RPM my C/S Whirlwind 200RV prop is most efficient. My test plan was to fly WOT for everything. First vary rpm by 100 rpm from 2700 down to 2300, FULL RICH. Then pick a couple of "sweet spot" rpm's and test those with differing mixtures.
It was a hot day and 8000'DA was found at 5,500'. Here was my first surprise...I was at Wide Open Throttle and was getting 25"MP at 8K'DA. Shouldn't it have been around 22"? My problem was that I had always been using the "rule of 48" to guesstimate 75% power and wasn't comfortable leaning aggressively at this higher combined RPM/MP. But, I was at 8000'DA which is supposed to be 75% power with everything pushed forward, right? Full throttle, full rpm, full mixture. Have I screwed this up somewhere?
What I found was that at 25" and both 2200 and 2300rpm, I was uncomfortable as I approached finding peak egt and never allowed myself to get there. No way was I going to lean much at all at 25" and 2700rpm At 1420 egt on the hottest the CHTs were all above 400 and the engine didn't seem happy. At lower MP on previous tests peak EGT was typically found around 1450, 2300rpm, 23'MP and about 7.5gph.
Procedure Question: How do you establish 50 or 100 degrees rich of peak if you don't know where peak is and you're running too much power to lean to peak I know to look at take off egt and you're O.K. to lean to that in the climb. Beyond that I'm in the dark. Maybe I need to Re re re-read Deakins. Again.
Could I get some fuel flow vs. rpm/MP combinations from some of you who have been there before? I know this is in the engine books in theory, but I'm pretty sure that those numbers are out the window with higher compression ration pistons and electronic ignition. 9:1 pistons and dual PMags on the conservative curve.
BTW: it seems that the WW200RV has a sweet spot at around 2500rpm in terms of speed/fuel flow. Anyone else test this? I'm not sure if I'm going to cruise there or at the lower rpms (23 to 2400) I've been using, but I might test it on extended trips just to see how much a difference it makes vs. the higher pitched noise. I had the prop dynamically balanced using 2200 and 2400 test points.
Thanks for any help/observations/hints/tips!
Jeremy Constant
RV7A 120hrs
So I went out to check my real 8000'DA speeds and to see at what RPM my C/S Whirlwind 200RV prop is most efficient. My test plan was to fly WOT for everything. First vary rpm by 100 rpm from 2700 down to 2300, FULL RICH. Then pick a couple of "sweet spot" rpm's and test those with differing mixtures.
It was a hot day and 8000'DA was found at 5,500'. Here was my first surprise...I was at Wide Open Throttle and was getting 25"MP at 8K'DA. Shouldn't it have been around 22"? My problem was that I had always been using the "rule of 48" to guesstimate 75% power and wasn't comfortable leaning aggressively at this higher combined RPM/MP. But, I was at 8000'DA which is supposed to be 75% power with everything pushed forward, right? Full throttle, full rpm, full mixture. Have I screwed this up somewhere?
What I found was that at 25" and both 2200 and 2300rpm, I was uncomfortable as I approached finding peak egt and never allowed myself to get there. No way was I going to lean much at all at 25" and 2700rpm At 1420 egt on the hottest the CHTs were all above 400 and the engine didn't seem happy. At lower MP on previous tests peak EGT was typically found around 1450, 2300rpm, 23'MP and about 7.5gph.
Procedure Question: How do you establish 50 or 100 degrees rich of peak if you don't know where peak is and you're running too much power to lean to peak I know to look at take off egt and you're O.K. to lean to that in the climb. Beyond that I'm in the dark. Maybe I need to Re re re-read Deakins. Again.
Could I get some fuel flow vs. rpm/MP combinations from some of you who have been there before? I know this is in the engine books in theory, but I'm pretty sure that those numbers are out the window with higher compression ration pistons and electronic ignition. 9:1 pistons and dual PMags on the conservative curve.
BTW: it seems that the WW200RV has a sweet spot at around 2500rpm in terms of speed/fuel flow. Anyone else test this? I'm not sure if I'm going to cruise there or at the lower rpms (23 to 2400) I've been using, but I might test it on extended trips just to see how much a difference it makes vs. the higher pitched noise. I had the prop dynamically balanced using 2200 and 2400 test points.
Thanks for any help/observations/hints/tips!
Jeremy Constant
RV7A 120hrs