12-03-2006 Ask Mike! Archive
Ram air question

Hi Mike

Do you have any experience with the Atlantic Aero mod? Specifically, they claim that the engine retains horsepower with altitude because of some sort of ram effect from the altered nose bowl. I would be grateful for any expert thoughts you may have, especially, as here in Australia, no one has seen the system.

Kind regards
Peter


Hello, Peter;

No, I do not have experience with that modification.

That said, let's theorize for a moment... Mooney successfully brought ram-air into general aviation in the early 60's. Beech's turn came in '64 when the S35 was developed. On the S (and subsequent 520 powered, normally aspirated Bonanzas), the diameter of the induction forward of the throttle valve was found 5 inches behind the air filter, on P and previous 35's, it was about 2 inches. A very much more gradual means of "stuffing" the air down the hole. Of course, Mooney's variation by-passed the air filter also, but the air took a bend - not very efficient. Both net results about 1 inch MAP.

Atlantic Aero eliminated a separate inlet in the cowling for induction air; the air filter draws air from the top of the engine, from cooling air. If what the engineers tell us is true, you need 10 square inches of inlet air for every 100 horsepower, with triple the outlet area. Atlantic Aero's mod inlets are quite small. Provided a reasonably well sealed baffle system, and considering that cabin heat air is also drawn from the cooling air provisions, I would say there would be very little, if any, ram-air effect from this design.

But, I'm not an engineer...

Gear Green,
Mike