N62588 Phase 1 Flight Testing

[svyolo]

Yeah I have a 1.5" lip set at 30 degrees.

[Steve W]

IMG_1952.jpg LoopIMG_1948.jpg You might need 2.5-3” lip and more angle.
And check your timing. If it’s at 25*, maybe back it off to 20*. I know that was a fix for some of the angle valve engines in some airframes

[svyolo]

Angle valves are normally set at 20, but it might also work on mine. I have EFI/EI and can adjust the timing per rpm and MP. I may try dropping the high MP down to 20. I heard it makes little difference in power at very high power.

[Bcone1381]

The Patrol has been down a month due to service and work. The two issues wer of course hot cowl, but also starter kick back.

I have a lot to write, but just thought I'd share real quick some data. I flew yesterday and learned that the air temp under the floor is warm. The tunnel heats it up. I measure the bulkhead temp as my air temp indicator. It reached 107F. The fuel line temp entering the "basement" was ~ 83f and it exited ~96f rise thru this area was 13f @ about 9 gph and rises to 15F @5 gph.

I'll be insulating those lines and the Gascolator today.

I also got Cowl Pressure data with my unmodified cowl. Now I can make changes and see the change.

[rodsmith]

The Patrol has been down a month due to service and work. The two issues wer of course hot cowl, but also starter kick back.

I have a lot to write, but just thought I'd share real quick some data. I flew yesterday and learned that the air temp under the floor is warm. The tunnel heats it up. I measure the bulkhead temp as my air temp indicator. It reached 107F. The fuel line temp entering the "basement" was ~ 83f and it exited ~96f rise thru this area was 13f @ about 9 gph and rises to 15F @5 gph.

I'll be insulating those lines and the Gascolator today.

I also got Cowl Pressure data with my unmodified cowl. Now I can make changes and see the change.

I insulated the top and sides of the tunnel area with the same 5/8" closed cell foam I used on the inside of the firewall. I didn't want the heat radiating up through the floor, didn't consider the fuel line traversing that area.

[Bcone1381]

Fuel Temp As my fuel wandered thru the fuel system I saw the temp was increasing under the floor of the cabin 13f due to a hot tunnel I suppose. So I insulated 80% of the fuel lines and the gascolator and now have fuel increasing 3F under the floor. I place the temp sensors on fuel tee above the floor before the fuel enters the "basement", a sensor on a line as it exits the basement, one on the bulkhead forward of the gascolator as an air temp indicator, and a sensor on the gascolator itself.

Cowl Lip and Piccolo Tubes. I installed a 1.75" wide lip angled at 45 degrees at my cowl exit. My exit area is 90 sq inches. (Sven's DA-40 w/ a 180 hp IO-360 in a nearby hanger seems to have an exit area of about 80 sq in.) I installed piccolo tubes in my cowl. Two tubes were installed above the cylinders, and two below. the procedure has me connecting hose from them to an airspeed indicator to measure the pressure change, then I use a table to convert the indication to inches of water pressure.

Cowl Pressure: At 100 KIAS my cowl pressure went from 5.67 in h20 to 7.62 in h20. That is an increase of 34% pressure differential across the cylinders and oil cooler.

Oil Temp: My oil temp with a big oil cooler went from 200-205f (with an OAT of 65 to 80f) down to about 182f with an OAT of 86f on the ground.

When I taxi to the hangar after I land my engine would stumble and miss and burp due to hot fuel in the system. Last month I was hearing it do that in the traffic pattern when I reduced power abeam of the numbers at 70 F OAT. Yesterday it was about 80 F and it ran smooth during the taxi in. I never thought I'd get the fuel that cool.

[Nev]

Good work Brooks - a differential of over 7" at 100 kts is excellent. I'd be interested to see a photo of your lower cowling exit lip.

[Viking]

Hey Brooks, I’m getting ready to start my baffling installation on my patrol, and I’m curious about your larger oil cooler installation. Is your 13 row cooler mounted behind the #4 cylinder on the baffling? If so, how is the figment compared to the 7 row? Do you have any pictures of your cooler installation you could share?

[jaredyates]

Great news Brooks, how did the differential cowl pressure reflect in the CHTs?

[Bcone1381]

Great news Brooks, how did the differential cowl pressure reflect in the CHTs?

Good Question. I dont have apples to apples data but we can get close. I'll keep it quick, but the school house might offer some argument. Call it 30 F decrease. At 24"/2400 rpm I saw 380 F before and 360 F but since I can lean it now without getting into vaporization of fuel I can run it leaner which mask the results. SO its fair in my laboratory to call it 30 F not 20 F.

Photo shows the Minimally Viable cowl exit lip version 1. 1.750" lip at 45 degrees. Yes, that is Gorilla Tape.
Screenshot 2025-06-21 at 8.22.52 PM.png Screenshot 2025-06-21 at 8.23.01 PM.png

I am still experimenting. I want more. I have an idea that if the lip can introduce vorticies at flying speed then when it mixes with the exit air it will draw more out. Since the deflector is proven I copies it for Version 1.

Version 2 has a saw tooth edge. The B787 and B747-8 inspired this idea. We'll see. It might fail to produce. It might work. I'll keep you updated. I'm also curious about a saw tooth trailing edge of the cowl without the 45 degree angle.

Screenshot 2025-06-21 at 8.23.16 PM.png

[Bcone1381]

Can you see all three photos?

[Bissetg]

Brooks, this is an interesting concept and I’m following closely! Please keep the info coming on this one.

[Bcone1381]

This is my response to Viking's comment in post 35.2

Viking;

My 13 row cooler install is a minimally viable installation. Its packaging is an after thought and not an industry best practice and I don't recommend you follow my installation. There were numerous workaround space issues that I dealt with. The Packaging of the install at your stage was hard for me to get my head. Then making changes we learn that we wished we packaged it differently.

You must attach that environment to this 13row cooler installation. Here is a Question I’m now asking... with my improved pressure differential do I need a 13 row cooler now? Would the origonal 7 row cooler work, or a 9 row? The 13 row choice was made with this attitiude "Go big to know the issue is resolved." The O-540 often uses the 13 row cooler.

I like this placement of an oil cooler.

https://bearhawkforums.com/forum/bearhawk-lsa-quickbuild/95635-north-carolina-lsa-kit-build-underway

(in that install, one might Consider a device to allow the air flow to gently transition from the SCAT to the cooler, but I like this placement/packaging)

Screenshot 2025-06-22 at 6.47.47 AM.png Screenshot 2025-06-22 at 6.48.01 AM.png
IMG_3701.jpg
Air enters thru the baffle behind #4 cylinder where I had my 7 row cooler attached. Baffle seal material is attached to what you see so that it seals the area when my L cowl door is closed. I was able to use the same oil lines that served my 7 row cooler. Its a pain to remove and install but I'm flying.

[gregc]

When trying to decide whether or not to have a cowl lip on my airplane and if so, how big and at what angle, I wondered why there is so little consensus on this issue. This paper by John Thorp helped me understand the basic issues:

https://www.scribd.com/document/536076050/Cowling-and-Cooling-of-Light-Aircraft-Engines-J-Thorp

Thorp was not fan of a large stalled flap on the outlet and pointed out that separated airflow is largely unpredictable (or at least was for folks in 1963 without digital modeling systems and still is for most of us) and that it may well create an area of high pressure just where the pressure needs to be low. I suspect this is why something that works on one cowl design does not work on another even though it appears similar.

The other key point in his presentation is that cooling drag is a big deal and that even well designed systems require 8-12% of available engine power for cooling so there is plenty of opportunity to make things worse!

In the end I concluded that there is no "right" answer. Perhaps over time we can accumulate a set of configurations that have worked experimentally but I would not be surprised to find that they differ for each Bearhawk model.

[Bcone1381]

Here is the feedback on the Cowl Lip....

The standard cowl lip (Version 1 viewd in post #37) had better performance than the Saw Tooth lip. At 100 kts, the Pressure differential dropped from 7.38" to 6.56" with the Saw Tooth.