Cruise engine RPM's for FP prop

I have a 9A that flew on Saturday for the first time. It has a 160hp o320 and a 79" Sensenich prop. There are no gear leg or wheel fairings.

I'm not too sure about the engine speeds I'm getting. The static RPM is 2100 rpm and climbs out at 2200 rpm. While cruising at 3000 feet I was only getting 2450 rpm at WOT and and an IAS of 145-155 mph. I have a Grand Rapids EIS with the tach coming off the mag so I think the engine speeds are correct. The manifold pressure at WOT is 28.7. I thought I would have to be throttling back at low altitudes with this prop. I'm a little worried about the engine power output. I'll check compression tomorrow.

So any of you guys that are flying with a Sensenich prop have any numbers like this?

Thanks
Cam

Your cruise RPM sounds about right. You will find that your RPM will have dramatic swings with airpspeed changes. If you don't have a manifold pressure guage, I would recommend getting one. It eliminates chasing the tach all over the board trying to get cruise set up. My RV-6 has a 0-320 and a fixed pitch prop. When I level off for cruise, I leave it at full throttle till the plane accelerates to just above cruise speed, then bring the power back to about 22.5" MP and let the rpm fall where it will. It's generally somewhere around 2500 RPM. No wind, the GPS says 153-156 kts

I apologize for not reading your post more thoroughly. You do have a manifold pressure instrument. Appearently one of the electric ones. A friend has one of those in his RV-6A. When we are flying right together his MP reads 24" hg and mine reads 21" hg. Mine is an old direct reading manifold pressure guage. We have the same hp engines. At full throttle, there isn't one mph difference between the two planes.

I have been doing some of the test flying for a friend who recently finished an RV9A configured as yours except WITH fairings.

1. The numbers sound about right to me. I think they are the same static and remember you have a lot of drag that will go away when you put the fairings on.
2. There is plenty evidence that the fairings make a BIG difference on RVs, so your plane should be slicker and faster with the same MP pressure and the RPMs should go up.
3. I would do little but get the fairings on and then check the numbers.
4. With them on, I would expect you to see 150-155 KTS at that power setting and faster at WOT.

James

p.s. I am doing performance testing now but have not done enough runs to feel good posting repeatable data. I am willing to share data with you later.

N916K said:

I have a 9A that flew on Saturday for the first time. It has a 160hp o320 and a 79" Sensenich prop. There are no gear leg or wheel fairings.

I'm not too sure about the engine speeds I'm getting. The static RPM is 2100 rpm and climbs out at 2200 rpm. While cruising at 3000 feet I was only getting 2450 rpm at WOT and and an IAS of 145-155 mph. I have a Grand Rapids EIS with the tach coming off the mag so I think the engine speeds are correct. The manifold pressure at WOT is 28.7. I thought I would have to be throttling back at low altitudes with this prop. I'm a little worried about the engine power output. I'll check compression tomorrow.

So any of you guys that are flying with a Sensenich prop have any numbers like this?

Thanks
Cam

Click to expand...

Fairings make a big difference

I have the same engine and prop on my 9A and I can't get up to 2600RPM with the fairings off but can easily with them on. There's over a 10kt difference in airspeed with and without.

I recently took all the fairings off to work on the fiberglass after flying with them on for 150 hours and it is like a different airplane. I had to watch the speed on final or it would get too slow. Wait till you add those fairings... I'll bet your first few landings are go-arounds!


Also, calibrate your tach with a hand held optical tach just to make sure your EIS is reading correctly.

-Clay

Sensenich thinks I'm down 100 rpm

I talked to Sensenich this morning and it sounds like I'm about 100 rpm down on my static rpm. I'm pretty sure that the Tach is correct, I was flying next to an RV4 with a slightly higher pitched prop and same egine and he was going about 150 rpm less than me to match my speed. I will check it with an optical tach.

I'm doing a compression check and retime the mag and EI this afternoon, maybe that will show something.

Cam

25 mph from leg fairings ???

I've been thinking I had a engine problem for the last couple of weeks. I could only get 2450rpm and 150 mph at WOT at sea level. I installed the gear fairings and main wheel pants and now run 2600 rpm and 175 mph at WOT at sea level. I was told maybe 15 mph from the gear fairings, but 25 mph sure seems like alot. Maybe I'll get anouther 5 or 10 mph from the nose wheel fairing and intersection fairings. 185 mph would be nice.

Thanks to everyone that helped.

Cam

Good news

Cam: I was following your thread on this and was glad to read your last post. I just posted my first flight numbers yesterday and what I recorded was close to yours. I know builders like to hear good news on flight numbers so here's some more. On my second flight I paid more attention to the ASI and with 1/2 fuel and me (240 lbs.) I was climbing at 1700 fpm. At cruise and 3500 ft. I was at 150 mph. This is without any gear fairings. So with your new report, the others who have checked in and Vans published numbers, I think the 9/9A is truely a 180+ mph cruising machine. This is NOT a wimpy trainer. It just doesn't go upside down, and it's easier to land than it's aerobatic brothers and sisters. (I know they are easy to land, too.) Can't wait to get back in the airplane. Jack N489JE 1.2 hours. flying.

This is good news!

From what Cam and Build9A are both saying it might just be possible to get a 175 mph cruise out of my O-290 powered -9, just like Van's web site states.

Keep posting numbers guys, they keep me pounding rivets!

(Just about finished putting my engine back together so it's back to the fuselage for me.)

Last summer I flew coast to coast in my 9a. Wide open, 10.5K ft, 2550 RPM, 180MPH TAS for 35 hours of flying... All on 8GPH.

numbers prior/post installing fairings

Here's the numbers on my airplane. I was really disappointed initially and called Van's several times looking for reasons mine didn't meet the expectations that I had. Simply, as the fairings went on and the thing got cleaner and slipped through the air easier the speeds came up. Don't worry, your planes will meet the published numbers easily.

Here is the entry that the test pilot who flew my first flight wrote in my aircraft log. He was really amazing with his approach and the way he carried out flight testing my plane that first day.

Aircraft first flight. Climb 1800fpm @ 100mph. Cruise 145 mph 24mp/2500rpm, oil temp max 240 degree, rolls slightly left, yaw 0, pitch 0. Stall power off flap's 0 degree 55mph, stall full flaps 50mph. Approach 80mph, land 3/4 flaps. Test flight satisfactory.

We looked at the oil temp and found that I had left the ramps off of the cowl top. Installed them and the oil temps came down to about 190.

I agree completely with Clay and Andy. Don't worry about a thing. As Andy said about his coast to coast flight, the 9A will do a steady 180mph at 8gph. On the power setting above (test flight) mine will easily do 180mph true which is a huge gain over the early flights. When I first put on the wheel pants and gear leg fairings the most it would give me was about 168-170mph true. The intersection fairings helped then also. Now the plane is in the paint shop and I'm waiting to see if it makes a difference in cruise speed. The Cherokee I used to have was faster by about 5 knots after waxing it, but the folks at Van's said there should be no noticable difference after paint. Oh well, I'm still hoping.

Bryan