Numbers

With a little over 35 hours now on the ship, I believe I have some firm numbers. I have a Vetterman's exhaust with mufflers and the thinking was the mufflers were taking up too much room by the cowl exit and making the temps run high. I had them send me straight pipes and took the mufflers off and just used the straight exhaust. I really couldn't tell the difference in noise level between the two. We used a pressure differential test by putting one end at the back of cylinder 4 facing towards the middle of the engine (so as not to get ram air) and ran the tube through the back of the baffling where we have the vent for the mag cooling, then back into the cabin through the heater vent, into the measuring board back out the vent into the bottom of the cowl by the oil cooler. We were getting between 6-10" of change, depending on the speed and altitude, all really good.



Once we knew the pressure was good, we landed and removed all of the testing equipment. Now it was time to log the aerobatics. A good friend of mine has a RV-6 with thousands of hours and hundreds doing aerobatics. I let him do them, while I watched from the ground. All were done, including Lazy 8, Aileron Roll (R&L), Barrel Roll (R&L), Loop, Cuban 8, Reverse Cuban 8, Split S, Vertical Roll (R&L) and Immelmann. All were performed with +G and did not exceed 3.25Gs. He also did Spins (R&L). Having spun his 6 numerous times, he said the spins were very gentle compared to his 6.

The next day I took the plane on a short cross country, 1.25 hrs each way and the temps were great. Averaging 169kts at 63% in cruise @ 8500', oil temp was 193?, CHTs 321-353?, running about 50? LOP and burning 9.6GPH. Ground temps at takeoff around 90? and at altitude OAT was 53?.

Are you saying that the temps were better with the straight pipes? IOW, the mufflers probably WERE blocking too much of the exit flow?

Stoney,

The image from your G3x Touch looks like a screen grab. Does the G3x have a screen grab function?

Your data looks great. Have you used the percent of power calcs in the G3x?

n982sx said:

Stoney,

The image from your G3x Touch looks like a screen grab. Does the G3x have a screen grab function?

Your data looks great. Have you used the percent of power calcs in the G3x?

Click to expand...

Yes, the G3X does have a screen grab, hold down the menu key. I love that function. I haven't used the calculations, the G3X does it for you. You can see the 63% to the left and below the MP. My friend tells me that the G3X is a guesstimate and not accurate, that my % of power was closer to 75%, but I am going to have to check with Garmin to see if it needs to be calibrated.

SabreFlyr said:

Are you saying that the temps were better with the straight pipes? IOW, the mufflers probably WERE blocking too much of the exit flow?

Click to expand...

I can't say 100% that was the problem. We probably should have done the pressure test with the mufflers on, then without. It is possible that my engine could have reached the break in period right as I exchanged the pipes, I'm not sure.

Heavy Wing

You will also notice at the bottom to the right of the oil temp is the aileron trim indicator and it is all the way to the right. I have a heavy wing, left wing and I need full right deflection and I try to burn gas from the left wing to keep it level. That's the next issue to resolve.

jswareiv said:

The next day I took the plane on a short cross country, 1.25 hrs each way and the temps were great. Averaging 169kts at 63% in cruise @ 8500', oil temp was 193?, CHTs 321-353?, running about 50? LOP and burning 9.6GPH. Ground temps at takeoff around 90? and at altitude OAT was 53?.

Click to expand...

Stoney, thanks for posting the numbers. Did you notice what your peak CHTs were during climbout? Most of the O-360 powered RVs will easily hit 400F during initial climb on a 90 F day, so I'm curious how your 390 compares in this regard.

Thanks for posting this, very interesting. A couple of stupid questions but were you WOT at 8500 feet? Surprised to see a RPM at 2400, thought maybe 2300 a better RPM that would give a few more knots?

I'm having my G3x Touch system harness built by Stein right now and have just started going over all the manuals in some detail. I had not noticed the screen capture feature, that's a nice to have.

I have read about the % of power calcs and was wondering how accurate they may be. Hoping that they can be calibrated fairly close.

I did notice the aileron trim and was wondering about that. Just the next problem on the list. Keep up the work on the gremlins and let us know how you are doing.

Real world data is always nice to have.

stevep said:

Thanks for posting this, very interesting. A couple of stupid questions but were you WOT at 8500 feet? Surprised to see a RPM at 2400, thought maybe 2300 a better RPM that would give a few more knots?

Click to expand...

Yes it was WOT, I'll have to reduce RPM next time to see what I can get. Thanks.

HP%

n982sx said:

I'm having my G3x Touch system harness built by Stein right now and have just started going over all the manuals in some detail. I had not noticed the screen capture feature, that's a nice to have.

I have read about the % of power calcs and was wondering how accurate they may be. Hoping that they can be calibrated fairly close.

I did notice the aileron trim and was wondering about that. Just the next problem on the list. Keep up the work on the gremlins and let us know how you are doing.

Real world data is always nice to have.

Click to expand...

I spoke to Garmin about the % and they believe it is correct since 24 square is 75% of power and I was 21.8/24. They also calculate in Fuel Flow and OAT to come up with the %, so that number should be pretty close.

Thanks for the post

Stoney - keep the posts coming - great motivation for 14 builders.

Stoney Said: " We probably should have done the pressure test with the mufflers on, then without."

Might be easier to temporarily slip something over the exhaust that would occlude the exit same as the mufflers.

See if you can achieve 5.5" H2O Delta P (top/bottom of baffles) at about 100 mph (100-105) with the exits blocked down.

mjb

Think i may have been wrong about lower RPM equals more TAS. All a function of altitude, drag and power. Found this on an earlier thread.

Hartzell Two Blade HC-C2YK-ABF/F7666A-4 on an RV-6A from http://www.lessdrag.com/lycomingpropeller.html

RPM 2700 2500 2400 2300
2500' 205 205 198 193 Equal at 2700 & 2500
5000' 201 202 200 198 Slower at 2700 than 2500
7500' 200 197 196 194 Faster at 2700 than 2500
10000' 194 196 194 193 NO FASTER THAN AT 2400
12500' 185 191 190 187 NOT AS FAST AS 2300

Marc Bourget said:

See if you can achieve 5.5" H2O Delta P (top/bottom of baffles) at about 100 mph (100-105) with the exits blocked down.

Click to expand...

Standard day maximum available dynamic pressure is 4.79" H2O at 1000 feet and 87 KTAS (100 MPH true). In rough terms, multiply by 0.8~0.85 for a good upper cowl static pressure rise, 0.6 being more like a GA average (see NASA 3405). So, about 4" delta would be a maximum if the lower cowl volume was at freestream static....which it may not be with the exit blocked. A delta of 5.5" would probably need 110~115 KTAS.

A detail; upper cowl pressure rise increases as the system exit is reduced, so the delta pressure change with a change of exit area, although significant, may not be as large as one might assume at first glance.

To add a bit to Dan's post, I feel the key is Lyc's cooling specification, which I believe is 5.5" H2O for an 0-360. (from memory). You won't get that at lift-off, but it is the target for cooling at full power.

FWIW