Catto 68x74

[Jamie Aust]

I would like anyone with the same prop as mine to reply with your TAS at 8K.
I have been reading all catto posts and have not found anyone with the same prop as me.



All leg and wheel pants etc are on. Only 1 com and 1 Txpdr antenna. 2 steps.
0360A1A, Plenum, 1 mag, 1 plasma II. Prop balance only a few weeks ago.

If the weather is better on the weekend, I will post the new findings of a gps box run at @8K WOT.

I dont seem to be able to get over 150kts just now. Im also going to go over my static system to see if that could be a problem.

[lostpilot28]

Hi Jamie,
Going by the date on your prop's sticker, I am a little confused. I thought Craig stopped making the 68" prop about a year before yours was manufactured. I may be misremembering, but I thought his latest design was "more efficient" and it was a 66x74.

Whether I'm misremembering or not, I recall a conversation with Craig when I ordered my prop where he said the new design gave the same performance, if not 1 mph faster.

I've had my RV-7A up to 187 knots TAS. I'm guessing your static or pitot lines are leaking. Have you compared your airspeed with a GPS going 3 different directions (to compensate for wind)?

[Jamie Aust]

Thanks Sonny,

Im going to look over my static / pitot system, then do some more box gps runs. I hope its just a leak in the system.

ok, if 66x74 is the new style prop, anyone with that combo please tell me your TAS.

[NDrv8r]

I Received my prop April 2011.
It is on a IO360-A1B6 200hp.

At a DA of 8080 WOT I'm getting 176Kt 2780rpm.

at 2700rpm I'm getting 170kt tas

I need to do some work on the snorkel, I think I'm losing about an inch of manifold pressure. On the ground engine off, I'm showing 28.2 inches hg.

full throttle on the ground 27.4. I took off and stayed just above the runway and it moved up to about 27.6.

I plan to paint in a couple weeks, and plan pull the prop and send it back to craig for re-pitch to bring the rpm down 100 RPM.

[NDrv8r]

Originally Posted by lostpilot28

Hi Jamie,
I've had my RV-7A up to 187 knots TAS. I'm guessing your static or pitot lines are leaking. Have you compared your airspeed with a GPS going 3 different directions (to compensate for wind)?

Can you tell me a bit more about your engine configuration? About the max I have seen is 178kt and the engine is taching over 2800rpm.

thinking I was slow, I did multiple gps runs and confirmed the tas was about 3kt lower than actual.

I did some static ports tweaking and now my SV D1000 TAS is a knot or so faster than actual.

[lostpilot28]

Hi Larry,
I have an ECI O-360, 180 hp engine. Dual P-mags, 8.5:1 compression. I have the Sam James cowl and plenum setup, which seem to be faster, but the cooling is worse. I had all the wheelpants on, airplane was painted and clean...and I think the aircraft's loaded weight was around 1650, so this wasn't at gross weight. Also, I think I was flying at about 5,500 ft density altitude that day.

Truth be told, I think it would've gone 1 or 2 mph faster...but I got tired of waiting for it to claw it's way up there...the air wasn't smooth enough!

[Jamie Aust]

I also did some static ports tweaking. This is what we found yesterday. All in KTS.

Max static on the ground 2240 rpm, Max at alt was 2740 rpm, on climb out just after takeoff 2440 rpm,

GPS box RUN 1 @ 2500 ft OAT 22 C Full fuel WOT, TAS 169

N 176
E 154
S 160
W 181

RUN 2 @ 3000 ft OAT 17c WOT 2450 rpm 34 ltrs ph TAS 145

N 155
E 137
S 140
W 157

[sbarger24]

Originally Posted by Jamie Aust

I also did some static ports tweaking. This is what we found yesterday. All in KTS.

Max static on the ground 2240 rpm, Max at alt was 2740 rpm, on climb out just after takeoff 2440 rpm,

GPS box RUN 1 @ 2500 ft OAT 22 C Full fuel WOT, TAS 169

N 176
E 154
S 160
W 181

RUN 2 @ 3000 ft OAT 17c WOT 2450 rpm 34 ltrs ph TAS 145

N 155
E 137
S 140
W 157

Jamie,

I have the same prop same pitch, and an O-360. Your max static and max WOT RPMs at altitude are right in line with mine. I'm seeing at 8000 density altitude WOT, a True airspeed of 205 mph. That was before paint, but with all of the fairings installed. We are pretty close in numbers other than your at 2500 ft, so I would check your static system.

[lostpilot28]

Originally Posted by sbarger24

Jamie,

I have the same prop same pitch, and an O-360. Your max static and max WOT RPMs at altitude are right in line with mine. I'm seeing at 8000 density altitude WOT, a True airspeed of 205 mph. That was before paint, but with all of the fairings installed. We are pretty close in numbers other than your at 2500 ft, so I would check your static system.

I don't know, Steve...you're 11 kts faster...that's not very close! Because Jamie is indicating close to the same RPM at WOT as me, I'm guessing he still has a pitot or static leak, or his instrument is out of calibration. 25 kts between my RV and his is pretty big, and I'd guess that if his airplane was draggy he wouldn't be generating the same RPMs. I think I was turning 2780 or so when I did 187 kts.

I guess my point is, wouldn't his engine be lugging more than that if he was going that much slower? Also, are you sure your prop is pitched the same as his? I thought you and I had 66x74.

[RV10inOz]

Steve,

Jamie's static is now correct. Or should I say the calculated TAS based on the EFIS, compared to the GPS box data is within 1 to 2 knots.

I think realistically it will do around 200MPH or 172 knots when leaned for best power at altitude.

Doing a GPS box and comparing the result to your calculated TAS based on instruments is a very important task. If at around 150 knots +/- 30 you are within 2 knots, I would say all is good. Your altimetry and encoder will be within say 25 feet. If you are out by say 9-10 knots, your altimetry is well over 120 feet out And depending on where you are in the world that makes you out of tolerence before you start!.

Read up on Kevin Hortons posts.... he is the guru