Bearhawk O-540 engine cooling

[svyolo]

A lot of big engined BH's have cooling issues, despite the inlets in the kitset nosebowls being plenty large. Battson and Nev did their cowl inlets a bit different, which I copied as best I could. Aerotango in Quebec tried to emulate Vans. Both worked. Any Comments on either technique.?

[Nev]

I think it comes down to personal preference. I've done mine without cowl flaps to try and avoid the complexity. So far I'm happy with it, having come through one summer and one winter of flying. After getting mine "close enough" during the test flying with regard to the exit area and cowl lip, I then turned to flow matching the injectors. It initially seemed like another small incremental improvement, yet it had a disproportionate effect on cooling. Adding a butterfly valve to the oil cooler also made a decent difference. It has a simple summer/winter setting on it and allows the oil to stay warmer in the winter. Also if flying lots of circuits (or stalls where the airspeed is low and AOA high), I keep it open. In practice I can takeoff from a valley airstrip and climb over an 8000ft mountain range, then descend on the other side in summer or winter, with no issues. Usually for the descent I would keep some power on, RPM at say 2000, and increase the mixture toward peak.

[John Bickham]

I'll offer a few OPINIONS :

I avoided cowl flaps cause I am a weight freak! I now have three "cowl exit lips" for seasonal OAT changes. I think your OAT swings and density altitudes will define that. Right now in New Mexico it is 28°F. A month ago it was 70°F. If I were still in Louisiana I'm pretty sure I would only need one. This morning I have long johns on and will shed them just after lunch. I'd rather take a 30 minute labor hit , three times a year, than carry weight and complexity all year.

I copied Battson's closed tunnel inlet transition to the front wall of Van's baffle system. That first 8-10 inches and the transition to top surface of the cowl doors is important. The RV builders have figured this out. A lot of baffle installations loose cooling air around the nose of the engine. There are some theories about the transition to the cowl roof and reducing turbulent flow there will help with cooling.

Location of oil cooler outlet can make a difference. Locating lower and closer to cowl exit can make a difference in the pressure differential.

Ignition system choice is a consideration. I have learned as I am in a transition from Bendix magneto system to E-mags.
There is a bit of step change increase of CHT's with the ability to run leaner/hotter mixtures with electronic timing advance. I think I wouldn't need the third summer cowl exit lip if I was still with dual magneto ignition.

hope helpful

[TimTall]

I also used Battson's cowl inlet transition as inspiration when i built my cowl and baffles. I did my best to smooth out the airflow as it entered the nose bowl. In the photos below you can see aluminum and silicon baffle material that tucks in behind the nose bowl all the way around the inlet.

I also did my best to completely isolate the area behind the spinner from both the high and low pressure area of the cowl using a combination of aluminum and silicon. I tried to minimize the spinner gap as much as I could but some air will always get in there. From what i've read, keeping air from getting into, and out of, the pressure chambers around the spinner is important apparently.

I installed the rounded fairing to the bottom of the firewall at the tunnel transition.

My oil cooler is on the right side of the engine at the front so it's easy to get lots of air to it. In cooler weather i can put a piece of aluminum duct tape on it to warm it up.

I did install cowl flaps. The added weight was only a few pounds and they aren't very complex to build. By adding cowl flaps I completely eliminated the cooling lip.

No temperatures issues at all. Even in the hottest summer weather that we get (mid 30'sC)

I can't say which of the above worked, or if they were all necessary, but in combination they work well together.

IMG_5994.jpgIMG_5995.jpgIMG_6002.jpgIMG_6019.jpg

[sherrre]

Thanks. Are you using a -470 or a -520? I went back and read your first flight report (I now see where you reported flying behind a Continental) but I didn’t see engine size.

[TimTall]

It's an IO-470. 260hp. It made the build a bit more complicated than using a more typical Lycoming but its a strong engine with a good reputation. They're less typical in the homebuilt world so they're easier, and cheaper, to find.

[Daniel]

Hey Tim, any chance you could share some details/pictures on how you built your cowl flap actuation method? I've seen a few different ways to go about it. Thanks

[svyolo]

I built something very similar, was trying to figure out how to seal the nosebowl inlets. The later RV's use something called Airseal and attach it to the inside of the nosebowl and it sits flat against the inlet ramps. The top of the ramp I was going to attach the seal to the ramp and have the rubber seal against the upper part of the nosebowl.

Thanks for the info.