Completed Bearhawks with High CHT’s

[Steve W]

Over the last while, Ive had a chance to look at several completed-flying Bearhawks. Most have been experiencing high running temps and when I see what the original builder did, I understood why the problem. Some have not extended the bottom engine cowl below the level of the bottom of the tunnel. They followed the contours of the firewall. The size of the exit was restricted to the tunnel size which not sufficient. Stuff the outlet with exhaust pipes and hose etc and no way is there enough exit area to cool the engine. And yes, by tucking up the bottom of the cowl like that, it looks so nice and slick but without cutting a large section forward of the firewall out of the cowl with a 3-4” lip, it won’t work. I think this is such a critical point that is often overlooked or not understood when it comes to constructing the cowl. Im putting this out there cause I know what a pain it is to re work the cowling. I had roughly the right exit size (1.5 times the inlet area) when I was on wheels and it was ok. Temps were high when I went to floats and I had to redo the bottom cowl. I’m probably at 2+ times the inlet area now. Just hoping to save someone the aggravation.

Steve P203

[svyolo]

Mine are fine at cruise, the whole left bank(especially #5) runs hot on full power climb, even at 90 kts. The whole right bank runs much cooler, #1 runs 80 deg F cooler. Still working on it.

[AKKen07]

Steve, have you found your solution to be adequate? I have floats for mine now but have several improvements to make before floats fly - including the cowling remodel. It would be great to have an opening size to shoot for.

[Steve W]

IMG_0346.jpg IMG_1952.jpg I don’t know what your building but if you make your lower cowl deeper rather than just tucking the bottom skin towards the bottom of the tunnel, you will have a larger exit area rather than cutting the cowl out forward of the firewall and relying on a large lip to create a low pressure area. Other than that, Id suggest a very large cowl flap system. Correct me if I’m wrong here because it’s been awhile, but the nose bowl supplied for the kits has about 75-80 square inches of intake area. So 1.5 times that suggests an outlet of roughly 5” by 25”. On floats I would think a minimum of 6-7” by 25” to give you at least 175” sq. When your flying on the water, you always want more HP and bigger floats and in this case, more airflow through the cowl.
I know Ive posted one of these pictures on other topics but it shows the before and after. Its the distance from the bottom of the firewall to the lower cowl skin that should be increased. I wish I had a picture of what I saw last week to show what was not adequate.
I just went out and measured the tunnel area on a 5 place and its 22” X 3” so thats about 66 sq in and was pretty close to what I saw on a 4 place with a 260 hp 540.

[svyolo]

Thanks for the pics.

[AKKen07]

Thanks Steve, great intel

[Steve W]

The 2nd owner of the 4 place I saw last week sent me the picture of what not to do 4179703544888385950.jpg

[Nev]

This is very good practical information thanks Steve.

[Bcone1381]

Steve, I took some screenshots in order to help the reader see what you have done. It looks to me like the second shot might have a wider deeper scoop at the rear, or maybe some material was removed and the lip shape changed.


Screenshot 2025-06-10 at 8.56.06 AM.png Screenshot 2025-06-10 at 8.56.46 AM.png

[TimTall]

AKKen07 if you're remodeling your cowl for floats consider cowl flaps. They're not that hard to build and they work really well for me. I've got a lot of outlet are when I need it but I can keep the engine warm when I don't. I only use them when it's hot out or when I'm heavy and have to get over something.

In cruise, LOP, with the flaps closed i run in the low 300's. If I open them in cruise, the top of my cowls gets sucked down so they definitely increase the vacuum on the upper side of the engine substantially.

I'm running a Continental IO-470. 260hp.

IMG_6018.jpg IMG_6017.jpg IMG_6015.jpg IMG_6014.jpg IMG_6016.jpg

[AKKen07]

Nice, they look great. I will definitely include cowl flaps in my revision. I actually have some now but they are not well located or sized (quite small). I already have a pretty enlarged lower cowl as well and am barely adequate regarding CHTs on (big) wheels. I have to pay attention to stay below 410 and on a hot day extended climb outs require level-offs for cooling. I never stay below 360, regardless of OAT. So, a larger lower cowl plus large cowl flaps are my plan. And probably increasing the intake area to boot.