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RV-9A cruise speed reality check

Paul Eastham

Paul Eastham

Well Known Member
Hi,
I am curious what you all are getting for your 75% cruise speed. I'm coming up a few knots short of the book value, though I have not spent much time debugging it yet. I'm hoping some tweaking of my heavy wing and/or leg fairings will resolve it.

Don't forget to post your equipment installed with your speed.

My airplane: RV-9A, O-320, one lightspeed ignition. Van's recommended sensenich prop, nothing else fancy, and all fairings installed including intersections.

At 75%, I get about 156 KTAS / 180 mph. That's at 8000 DA, 2530 RPM, 22.1 MAP. 9.5-10 GPH.

Van's publishes 75% cruise at solo weight as: 187 mph = 162.5 knots
 
Pretty close to book

Hi Paul,

I get pretty close to book, I have a ECI O-320/Hartzell/carb/Dual EI. If I run ROP@8000DA - I am at ~22" 2300RPM and 162kts or so. I haven't done this in a while - I'll check it next flight.

I usually cruise at 55% ~150kts and ~6gph 22/2200/LOP. Saves a bunch of gas.

Flat out, down low, it will do 165kts.
 
I get in the neighborhood of 158 KTAS at 75% at 8000 DA. O-320, dual p-mag, Hartzell CS prop, with lots of toys (heavy 1109#). I know I have a slight trim "issue" in one of my flaps.
 
Paul,

My setup is closer to yours than Pete's. I have O-320, two mags, Sensenich FP ordered through Van's. According to my record (1/2007) TWO at 8,500 I have 2550 rpm and 161 kts. Keep in mind that there are measurement errors. I am not 100% sure about my TAS calibration. The %power calculation is also not very reliable. Try throttle wide open at 8,500 and see what you get (that should be 75%). Most of the time I also feel that my performance is not as good as the factory numbers.

You may find my numbers at the end of the following page:

http://tc1234c.googlepages.com/phaseiflighttest


Ted
 
At 8900 p.a., 21.4" MAP, 2590 RPM and OAT of 63F:

I see 120.1 HP (75%) and 160-161 ktas. Slightly faster than Van's spec, and calibrated using Doug Gray's spreadsheet.

Engine is an O-320 A1AC2 (roller lifters). ECI cylinders, Superior crankcase, Lycoming crank. Solo weight, half fuel.

I've always had to fly higher because I see about a 1" MAP boost over expected values (ram air?).

At lower altitudes I will redline the Sensenich prop (2600 rpm and have to throttle back). I usually plan on 11000' density altitude for wide open throttle operation.

In side by side flight tests against an RV-6A with an O-320/160, I was faster and climbed better. My gracious oponent was so humiliated that he build a 7A with an O-360.
 
My setup is O-320 w/one mag, one E-mag and a Catto three blade. I was fairly light at 1054 empty. With me and half fuel I see 185 mph at 8000 DA WOT. My normal cruise is 155-160 mph at around 6 gph LOP with carb heat. Speed is from three way GPS ground speed, so it is pretty close. I have never opened it up down low. At least not for measured speed runs!!

Bob Kelly

P.S. Changing to the E-mag didn't add any speed but did cut the fuel burn about 1 gph.
 
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speeds

Here is where the difference between a 160 HP and a 180 Hp 9A can maybe be seen. N42P with the Titan 0-360, Hartzel CP blended airfoil, EW 1100# using 120 HP which is 66% power does about the same as the 160HP versions at 75%, ie 160kts TAS at 8000' at a fuel burn of 7.6 GPH, But does 173 using 135HP, or 75% at 8.7GPH. All at approx 1650#. At 1000' it will, depending on throttle, just like the 160's get high into the yellow, so one must be vigilant. I believe that I might get to the 8K a bit quicker. I am happy with my decision to go 180HP especially at my mile high airport, but at the same time understand the reasoning given by the proponents for using 160HP. It's all good, right?


Karl N942P RV 9A
 
Feel free to correct me but for 75% you need 8000 DA, wide open throttle and 2700 RPM. I think your 2530 RPM is producing less then 75% regardless of what you engine monitor might say. I?m serious about correcting me, this is as much a question as a statement.

Russ
 
Yes, you are correct That is what the Piper manual says. Fixed pitch and leaned.
2530 is 68% on the Piper chart for fixed pitch prop.
 
Last edited:
gasman said:
Yes, you are correct That is what the Piper manual says. Fixed pitch and leaned.
2530 is 68% on the Piper chart for fixed pitch prop.
Click to expand...
If you have a fixed pitch prop, you can't compare power at an rpm against another aircraft. The manifold pressure you need to produce a given rpm will vary depending on the prop pitch and the aircraft drag. This changes the relationship between rpm and power.
 
Too rich

Hi Paul,
I agree that your mixture at 9.5 GPH + is still on the rich side, costing you horsepower. That's what my 0-360 burns at 75%. If you're fixed pitch, as I am, 75% is WOT and 2700 RPM for me. I then exceed Van's numbers by several MPH at over 202 MPH.

Regards,
 
Guys,
I cannot run 2700 rpm, my prop is limited to 2600.

I don't think I'm that far from 75% -- I did run the power calculations using that crazy chart in the O-320 manual but didn't correct for DA. It's been warmer than standard recently -- I ran the calculations for 6500 DA, and have been flying at 6500 MSL / 7500 DA. That gave me 2530/22.1" = 75% at 6500. So I guess I should be at a slightly lower MAP for 75%? I think I've been seeing 21.8" to get that rpm recently.

Paul
 
So how are you measuring FF? Is it accurate?

What does the book say for O-320 @ 75%? 9.5-10gph sounds very high to me.. (for comparison, O-360 is listed at 9.6gph at 75% power)... especially since you say that's leaned out to "just rich of rough"... assuming same BSFC (at 75%) you should be somewhere around 8.6 gph..
 
hours and cracks

dan said:
Karl, how many hours and how many cracks in your tail skins?
Click to expand...

230 hrs TT and no cracks yet. All hours except for a few, say less then 5hrs total, have been operated at 5000' or higher. I live and operate the plane in a high desert area and probably do not pull more than 85% of rated HP at any time, which equates to about 160 HP from the 0-360.The engine starts, stops, and runs quite smooth for a 360 and I do not expect cracks. Am I mistaken here?
 
Paul Eastham said:
Hi,
I am curious what you all are getting for your 75% cruise speed. I'm coming up a few knots short of the book value, though I have not spent much time debugging it yet. I'm hoping some tweaking of my heavy wing and/or leg fairings will resolve it.

Don't forget to post your equipment installed with your speed.

My airplane: RV-9A, O-320, one lightspeed ignition. Van's recommended sensenich prop, nothing else fancy, and all fairings installed including intersections.

At 75%, I get about 156 KTAS / 180 mph. That's at 8000 DA, 2530 RPM, 22.1 MAP. 9.5-10 GPH.

Van's publishes 75% cruise at solo weight as: 187 mph = 162.5 knots
Click to expand...
You might be closer than you think. I don't know which engine model you have (the different O-320 models have slightly different power charts), but if you have an O-320-D series (or equivalent clone), then the rpm and MP you quote is pretty close to 75% power. I strongly suspect that Van's 75% at 8,000 ft perf data is actually at full throttle at max rpm. This might yield 75% on lessor aircraft, but on an RV, with its very efficient, low loss air box, and the ram air pressure rise from the high cruise speed, full throttle at 2700 rpm at 8,000 ft will be closer to 85% power than 75% power. If you don't believe me, compare actual reported MPs against the Lycoming power charts. The data in the CAFE Foundation reports is worth studying. They don't say exactly what the altitude is, as they only report density altitude, but if you put their data for 8000 ft or 8500 ft in the Lycoming power charts you'll get much more than 75% power.

If Van's data is really at 85% power, and yours is at 75% power, you need to subtract about 3% from Van's numbers before you compare them to yours.

What speed, rpm and MP do you get at full throttle at 8,000 ft? If you can't use full throttle without exceeding 2600 rpm at 8000 ft, then maybe your prop needs a bit more pitch.
 
vlittle said:
At 8900 p.a., 21.4" MAP, 2590 RPM and OAT of 63F:

I see 120.1 HP (75%) and 160-161 ktas. Slightly faster than Van's spec, and calibrated using Doug Gray's spreadsheet.

Engine is an O-320 A1AC2 (roller lifters). ECI cylinders, Superior crankcase, Lycoming crank. Solo weight, half fuel.

I've always had to fly higher because I see about a 1" MAP boost over expected values (ram air?).

At lower altitudes I will redline the Sensenich prop (2600 rpm and have to throttle back). I usually plan on 11000' density altitude for wide open throttle operation.

In side by side flight tests against an RV-6A with an O-320/160, I was faster and climbed better. My gracious oponent was so humiliated that he build a 7A with an O-360.
Click to expand...

Update: My buddy's RV-7A/O360 is officially faster than my RV-9A/O320. He asked me to post this on the VAF forums. I am now humbled. Just wait until I build a Rocket!
 
Thanks for the data, Vern. Since we have similar airplanes, I will try a run at those same values to see how we compare.

What sort of fuel flow do you see during that run?

As for my own fuel flow, someone asked how I measure it. It is a Floscan unit read by a Dynon EMS. I have not calibrated it in any exacting fashion, but every time I've compared the totalizer to the bill at the fuel island, it's been pretty close.

Paul
 
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