RV-7A Speed Information

jtppalmer050390 · #1 05-11-2015, 01:26 PM

I have an RV-7A with 0-320 160 hp lycoming. I am using a wood fixed pitch prop. I am getting about 140 knots at 2450 rpm. Anyone else with a 6A or 7A with 160 hp mind sharing their speeds?

JohnInReno · #2 05-11-2015, 02:25 PM

If you want to compare speeds, make sure you are talking about the same speeds. The best method of determining True Air Speed from GPS info is found by following the links in this thread to the gps-pec spread sheet.

http://www.vansairforce.com/communit...ad.php?t=94314

The TAS numbers for my RV9A IO320 CS are:

155 @ 7.0 gals/hour (30 LOP)

165.5 @ 8.7 gals/hour (100 ROP)

These tests were done at 8,000 indicated with the barometer set to 29.92. My indicated airspeed is generally around 140 knots so we may be in the same ball park.

krw5927 · #3 05-11-2015, 02:32 PM

Are all gear leg fairings and wheel pants installed? These have a significant effect on speed.

jtppalmer050390 · #4 05-11-2015, 03:07 PM

Yes. I have all the wheel pants and fairings on the plane. I was just wondering about others with 160 hp RV7A with wood props. Just general idea of how fast they are cruising in general. There are several RV 6A and 7A at my airport, but none that have a wood prop on a 160 hp Lycoming. Closest thing I can compare to at my airport is a RV 7 180 hp with wood prop. Obviously, he is faster.

N941WR · #5 05-11-2015, 04:38 PM

Remember, the speed runs are typically done at 8,000' DA.

With a FP prop, to get 75% power you need to spin the prop at the redline.

Don't worry, our engines are designed to run at that RPM until TBO. Anything less, and you won't see the speeds advertised by Van's.

jtppalmer050390 · #6 05-13-2015, 09:43 PM

Flew with DA of 7900 today. At 2500rpm and 8gph, I was getting 170-172mph TAS. I guess that is about what I should get with my configuration which is RV 7A with 160hp and fixed pitch wood prop.

rvbuilder2002 · #7 05-13-2015, 11:24 PM

Quote:

Originally Posted by jtppalmer050390

Flew with DA of 7900 today. At 2500rpm and 8gph, I was getting 170-172mph TAS. I guess that is about what I should get with my configuration which is RV 7A with 160hp and fixed pitch wood prop.

Actually it is 15-20 MPH slow from what it should do, but since you didn't provide what throttle setting / manifold pressure you were at, it could be that you aren't really at 75% power.
Your airplane at 75% power should be able to hit about 190 MPH TAS if you have a prop that will allow you to get to 75% power (you would need to turn it a bit faster at 8000 DA to do that).

WA85 · #8 05-14-2015, 06:26 AM

I have an RV-8 with 160 HP IO-320 and a 2 blade Catto prop. At 8000 feet, full throttle (max MAP available), leaned to best power, RPM 2750 to 2800, I consistently get 170 KTAS. Fuel flow is 10.8 to 11.2 GPH.

Economy cruise setting at 8000 ft, 22.5 MAP, 2450 RPM, 7.5 to 8.0 GPH depending on leaning, consistently getting 145 KTAS.

LOP - 6.0 GPH, 138 KTAS.

jtppalmer050390 · #9 05-14-2015, 07:22 AM

Thanks for all the info. I do not have a manifold pressure sensor wired so I am not sure of manifold pressure. Prop will definitely turn more RPM than 25. I think I can turn 2650 or 2700 at 8000 DA. Didn't think you were suppose to lean much at that power setting so I just kept it at 2500. Is there any value in knowing manifold pressure with a fixed pitch prop??

rvbuilder2002 · #10 05-14-2015, 08:55 AM

Quote:

Originally Posted by jtppalmer050390

Thanks for all the info. I do not have a manifold pressure sensor wired so I am not sure of manifold pressure. Prop will definitely turn more RPM than 25. I think I can turn 2650 or 2700 at 8000 DA. Didn't think you were suppose to lean much at that power setting so I just kept it at 2500. Is there any value in knowing manifold pressure with a fixed pitch prop??

As a general rule you can lean at any power setting that produces 75% or less power.

As Bill already mentioned, with a fixed pitch prop you will have to turn it at higher speeds than you are used too, but as long as the MP is in line with the RPM it is not a problem.
If you weren't at full throttle when doing your speed test, you certainly weren't at 75% power which explains your slower speed. To have 75% power at that DA you would need to be able to use full throttle and turn about 2500 RPM. Most fixed pitch props that are a good match on RV's will not allow full throttle at 8000 DA without exceeding 2700 RPM. Try doing a test at an altitude where you can use full throttle and have the RPM at about 2650 (likely somewhere between 10500 and 12000) and see what speed you get. My guess is the TAS will be much higher than the 170 MPH you have measured so far.

The value of MP on a fixed pitch airplane is it allows you to estimate the % power being produced. A secondary benefit is a one time setting of the throttle for cruise. You don't have to keep fiddling with the throttle as RPM keeps increasing with speed. You can just set the MP that you know (after some experience) is what you want for a cruise setting at that altitude and when you finally come up to full cruise speed your RPM will be just what you want.
My personal airplane has a fixed pitch prop. I make all power settings using MP. The only time I really look at the tach is during run-up.