Cowl flap advice

[Bicyclops]

When I put an upper gear leg fairing on our 6A, closing the slot in the lower cowl better, temps went down and the plane got faster. My take on that was that air was entering through the slot reducing differential pressure.

Ed Holyoke



If Dan or anyone else has these missing fotobucket pictures , I?d very much like to see them. I?m fighting high temps and have done the basics of plugging holes in baffling. I have resorted to leaving the close out panel for the nose gear off in order to get enough air through the cowl. I need to do more and was about to resort to a cowl flap.
Thanks,
Eric

[BruceW]

Drove me crazy having to fly my high performance RV-7 like a fat lazy Cessna 172 to keep the jugs cool on a hot day. What is the point of having performance for a continuous 1500 fpm climb, yet slog along at 300-400 fpm to keep the jugs cool?

Put in two antisplat cowl flaps that solved it good. (not crazy anymore).
(yes, I did all the cowling, baffle things to no avail)

[Guyfly47]

Ed,
I already had the slot well closed out. So, I built a manometer system to have some facts about the pressure differential between the upper deck and the lower deck and discovered I didn?t have the inches of water pressure differential for cooling that Lycoming required. When I removed the slot close out, the pressure differential got better. Good enough to climb to pattern altitude before having to reduce power to control engine CHT temps. Thanks for the suggestion anyway. I?m still hoping to see DanH?s fotos.

Eric Schlanser

Originally Posted by Bicyclops

When I put an upper gear leg fairing on our 6A, closing the slot in the lower cowl better, temps went down and the plane got faster. My take on that was that air was entering through the slot reducing differential pressure.

Ed Holyoke



If Dan or anyone else has these missing fotobucket pictures , I?d very much like to see them. I?m fighting high temps and have done the basics of plugging holes in baffling. I have resorted to leaving the close out panel for the nose gear off in order to get enough air through the cowl. I need to do more and was about to resort to a cowl flap.
Thanks,
Eric

[Michaelpk3]

I recently installed Antisplat cowl flaps (2 of them) and even on the hottest Florida day, the CHT's will not ride over 390. It even helps keep my oil temp down when wiating for IFR release...

[Bicyclops]

Howdy Eric,

I just started doing some manometer testing too. It looks like I've got about 9" differential. How about yours? I built some cowl flaps into mine and I can raise the differential by 5 or 6 more inches.

Ed Holyoke

Originally Posted by Guyfly47

Ed,
I already had the slot well closed out. So, I built a manometer system to have some facts about the pressure differential between the upper deck and the lower deck and discovered I didn?t have the inches of water pressure differential for cooling that Lycoming required. When I removed the slot close out, the pressure differential got better. Good enough to climb to pattern altitude before having to reduce power to control engine CHT temps. Thanks for the suggestion anyway. I?m still hoping to see DanH?s fotos.

Eric Schlanser

[DanH]

Originally Posted by Bicyclops

I just started doing some manometer testing too. It looks like I've got about 9" differential. How about yours? I built some cowl flaps into mine and I can raise the differential by 5 or 6 more inches.

No comparison can be made without comparable altitude and airspeed.

To record cowl pressure information which can actually be compared to others, all participants fly the same altitude (current small database was taken at 3500PA), and record cowl pressures on one leg of NTPS-style TAS triangle. Fly it at 100, 125, 150, and 175 indicated, then plot the data with true airspeed (from the triangle) on the X-axis and pressures on the Y.

[Guyfly47]

Sorry Ed, but I?m away from my test records. The Lycoming number for my O320 is 5.5 inches at sea level in standard atmosphere conditions at 105 mph. I just tried with each test to duplicate the conditions I had on the day I did the test. Probably at 3-4000ft msl at a range of speeds and power. I think it started with about 2 inches and got up to 4 inches with very limited testing. It is enough to fly in cool (<70 deg) conditions or with reduced power in warm (>70 deg) conditions. But not enough to climb above pattern altitude at full power at Vy.
Eric

[Bicyclops]

Howdy Eric,

As warm as you are running, gotta ask if you've looked at timing and fuel flow and sealed everything up. At first blush, your cowl pressure numbers look low which kinda jibes with your temp control issues, but might not be all of it.

Like Dan, I've got a modified inlet to exit area cowl, so my numbers are going to be different. I've only done a couple of tests, one at 8K and a very brief look at 3500'. I haven't done any testing at lower airspeeds. The low altitude run was at about 165kt TAS and I saw about 9". I couldn't spare much time to be scientific. I was talking to approach, getting ATIS, and looking for traffic. Both at high and low altitudes I was able to increase the pressure differential substantially by deploying cowl flaps. Once again, I didn't really get a lot of data, just enough to see that it really works.

I always used to cruise climb at about 130 - 140kts groundspeed with our fixed pitch O-320 powered 6A. I was able to get more RPM (power) that way while packing more air into the cowl. She would still climb at about 700 - 800fpm and cooled a lot better. When your temps are marginal, lower nose is better. Just have to be sure of obstacle clearance.

I've got the cowl flaps on my new airplane, but hardly ever use them and I still mostly cruise climb. It's a habit, I guess. When the winds and fires let up around here I'll try and get some more accurate data.

Ed Holyoke

[simatos]

has anyone opened the cowl flap at cruise speeds? Not just in the climb??

[alpinelakespilot2000]

Originally Posted by simatos

has anyone opened the cowl flap at cruise speeds? Not just in the climb??

Don't need to, but yes. Seems like I lose maybe 2-3 knots at most and it will drop temps significantly. Don't really need to adjust trim either.