Airboat Cowling advice for o-235 in Airplane

Aircraft powered airboat discussion.
mcurcio1989
Southern Airboat Member
Posts: 7
Joined: Mon Feb 13, 2012 4:00 pm

Airboat Cowling advice for o-235 in Airplane

Postby mcurcio1989 » Fri Jan 27, 2017 10:19 am

Weird question for an airboat forum right? Let me explain. I built an Aventura 2 aircraft and flew about 65 hours on it last summer. This is a slow pusher engine, amphibious aircraft - it will do 90mph in a dive but 70mph is where it cruises. It will spend a lot of time on the water taxiing either at just above idle speed or on step which would mean about 50%power and 25mph. I had an auto conversion engine installed which I am removing due to a number of issues. The aerodynamics of this aircraft make it inherently slow and I am not going to put an aerodynamic cowl around the engine (it would do no good-just add weight) so just baffling. For an airplane like this the concerns for cooling are when it is idling either moving or not moving on the airport or more of a concern is on the water (need more power and get less speed as you all know) and when it is in a climb which will be 60mph at full power. In this regard I think when it comes to keeping the cylinders and oil cool I can gain a lot from your experience. Airboats are pushers that need to be able to make high power with less air velocity available for pushing through the cylinders, like a typical airplane baffling uses.

So two questions, first is easy:

- for those who have experience with an O-235 on an airboat (I know this would be a small airboat) can I get by (oil temps below ~225F) without an oil cooler? Every ounce matters! If there was no oil cooler where would oil temps be?

-I'm trying to study airboat baffles and the first picture below is probably the best I have seen that shows this. I believe this is a Rhodes Heat extractor. My original and current plan was to make a baffle basically like a turned around version of the piper cub baffle shown in the second pic this will have the baffles at the bottom of the jug to keep air from short circuiting. It looks like the baffle shown in the first pic has 2 key differences - air can flow through it and it has a sort of diffuser at each cylinder for pulling air through rather than ramming. My guess is that this design allows good air flow at low speeds as the air kind of just flows through and around like a typical air cooled motor with no baffles (motorcycle) then at higher speeds it pulls air through. Is this true and do you think the first picture below would be a good design approach for my baffling, given what I have described? Thanks!

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