Don, are you sure you are not talking MPH instead of KNOTS? 150kts is 172-173MPH. If this is true then I am stunned at the difference in fuel burn compared to my 9a. In my 9A it will easily cruise at 172MPH but I am burning 8-8.5gph in doing so. No way I can get down to 5.9/1.2 = 4.92gph at that speed.I'd expect just a bit higher burn than 6 gph. Probably closer to 5.5 gph?but, I did a 1.2 hr flight with a tail wind, doing 150kts or a bit more, and I took 5.9 gallons of fuel when I arrived (4.9 gph). I have not duplicated those numbers and I tend to fly faster now. My memory is my IAS was just over 130.
Don, are you sure you are not talking MPH instead of KNOTS? 150kts is 172-173MPH. If this is true then I am stunned at the difference in fuel burn compared to my 9a. In my 9A it will easily cruise at 172MPH but I am burning 8-8.5gph in doing so. No way I can get down to 5.9/1.2 = 4.92gph at that speed.
Aw, Don, now that makes much more sense!I am positive its knots. Everything I have is calibrated in knots. The 150 kt figure is GS, not IAS, and I noted a tailwind in my post. I'm not positive but my memory is I had about a 20 knot tailwind, which sure helped. At 150 IAS I'd be burning around 8 gph?if I could get there.
FWIW, I regularly see fuel burns of less than 5.5 gph @ when I'm cruising around 130 knots IAS (2200-2250 RPM).
I agree the 5gph seems w-a-y low for the performance numbers. I would see a burn very similar what others said. Somewhere likely between 6 and 7. Is that fuel burn corroborated by both tank gauges and fuel flo totalizer?
Yep, brought the plane down on Monday. I'm at Pearland and will be out there on Saturday working on the plane. That is if the weather is nice. Check your PM's.Bill,
Are you still in Houston?
Would enjoy meeting you and seeing your plane. I am in Katy.
...
Bill,
Are you still in Houston?
Would enjoy meeting you and seeing your plane. I am in Katy.
Just so I do not hijack the thread, I have a Lycoming 150 hp O-320 swinging a Sensenich FP with 2600 max rpm blade. At 181 mph (that is all I can muster at 2600 rpm), I am burning 9.5 gph. At 2250 rpm, 152-155 mph am burning around 6 gph. I have to go to 2200 rpm to get to 5.5 gph.
Pat Garboden
RV9A N942PT
Katy, TX
Flying Phase I complete
2014 dues paid
Pete,
I appreciate your input but again I have not been able to see those numbers with my 9A. I routinely cruise at higher altitudes, 8000' or higher, on long cross country flights unless the winds are just not cooperating. There is absolutely no way I can burn less than 7.5 gph at the absolute leanest I can get LOP running anything faster than 143kts TAS. Yes, I always run LOP.
I can only surmise that if your numbers and others are accurate, my prop pitch is hurting me much more than I previously thought it was. I have been discussing my speed/economy performance situation with Craig Catto for 1.5 years now. I have been trying to see about getting a different pitch on my 3-blade prop. I have received a glimmer of hope from Catto's shop last week when they informed me they would ship me a new prop in about 3 weeks. Whenever I do get the new prop I will run some numbers and perhaps see what you are showing but I am most definitely not seeing it now.
For reference I am running a forward facing cold air induction, 4-straight pipe exhaust, fuel injected 180HP IO-340 with 68x72 Catto 3-blade.
Pete,
I appreciate your input but again I have not been able to see those numbers with my 9A. I routinely cruise at higher altitudes, 8000' or higher, on long cross country flights unless the winds are just not cooperating. There is absolutely no way I can burn less than 7.5 gph at the absolute leanest I can get LOP running anything faster than 143kts TAS. Yes, I always run LOP.
I can only surmise that if your numbers and others are accurate, my prop pitch is hurting me much more than I previously thought it was. I have been discussing my speed/economy performance situation with Craig Catto for 1.5 years now. I have been trying to see about getting a different pitch on my 3-blade prop. I have received a glimmer of hope from Catto's shop last week when they informed me they would ship me a new prop in about 3 weeks. Whenever I do get the new prop I will run some numbers and perhaps see what you are showing but I am most definitely not seeing it now.
For reference I am running a forward facing cold air induction, 4-straight pipe exhaust, fuel injected 180HP IO-340 with 68x72 Catto 3-blade.
not sure where any extra drag would be coming from. Other than the engine changes the airframe was built as a standard 9A.If you're relatively sure that your engine is making good power, and your prop is hooking it up (or getting changed and on it's way to hooking it up) then the only other variable to consider is drag. Start looking at what is causing drag on the airplane - it makes a lot more difference than you might think.
i am running a Slick mag with impulse coupling on the left. A Lightspeed Plasma III on the right. I have the IO-340 not the carbed O-340. Since no carb, no carb heat. I run LOP most every flight especially on X-country flights. Oh, and just to hit this topic, my CHT's are running within 10 deg of each other at all times. The engine is a smooth running machine.Steve,
What are you running for ignition? I have dual EI and I think it helps quite a bit.
I have done quite a few tests at various settings, I have done some side by side flight comparisons with friend's RV 7's with 180 hp engines to compare speeds, rpm, MP, fuel burns, etc. At comparable true air speeds I am spinning the prop approximately 200 rpm faster and MP approx. 2in more than they are.
I understand and agree. Now the difference in my friend's plane(s) and mine is basically 7 vs 9A, tail vs nose wheel, carbed 360 with standard Van's snout lower cowl on the 7 vs FI forward facing cold air induction with Van's smooth cowl and snorkel on the 9A, standard Vetterman cross-over exhaust for the 7 vs Vetterman 4-straight pipes clogging up the exit area with the nose gear on the 9A (most assuredly creating more drag that one day I am going to try to address). Maybe there are some rigging issues that could possibly be creating more drag but I do know my plane does not have any adverse flight characteristics.If you have a higher RPM and MP, you are producing more power than your friends. You must either have a less efficient prop or more drag/weight.
-Andy