The induction port for the ram air on the m20J bypasses the air filter
as well, so we typically observe about a half inch improvement in MP.
That's in line with some of the other numbers offered here.

I guess there's no free lunch. There is no way we want to have an
IO540 pull the airplane along, nor do we want the fuss with turbo
charging. The payback for our typical for real flight mission is just
not there. My thought was and is that if it was something pretty
obvious someone would have done it on a homebuilt. Actually, knowing
some of those guys, it does not have to be obvious at all, they are
really creative designers.

I had better stick with my day job.








with some On Jun 1, 12:28 pm, "Ken S. Tucker"
wrote:
On Jun 1, 3:35 am, Tina wrote:



The Mooney 201 has a ram air port, a half a foot under the prop
spinner. The POH tells us it can be opened at altitude for a very
modest increase in MP and we find maybe a half inch increase in
pressure. The idea of the thing is, if the port is looking right at
the air being thrust toward it by the prop (it can't be more than 6
inches or so behind it) as well as the air impact from the airplane's
motion the air being 'rammed' into it should effectively lower the
altitude the engine thinks it's at. Well, a half inch of Hg is about
500 feet or so. The question is, though, wouldn't you think there
would be a way to capture a great deal more of the ram air effect and
really boost the engine performance? Who wouldn't like to fly at 24
square at 12000 feet without a turbo charger?

What makes me wonder about it is, even at 60 mph holding your hand out
of the window of a car subjects it to a significant backward pressure,
so the energy must be there.

Good thinking, but physics prevails.
For example we just built a building with sides 10'x20',http://www.flickr.com/photos/dynamics/
and the load computation of a wind at 60 mph is 1 ton
on a 200 sq ft surface, being a shear force on the
foundation, which is 10#/sq ft. That might sound like
alot but in terms of pressure per sq. inch it's,
Per sq. inch, divide 10# by 144 = lbs/ sq. inch,
~ .07# / sq. inch.
By comparision, sea level pressure is 15#/sq.inch,
which is convertible to Hg units.

Ramming air increases pressure with speed squared
so at 120 mph, pressure is 40#/sq. ft etc.
So at 420 mph, ram pressure is up to 3.5 #/sq in.
which is about a low as is practical, as in a V-1
buzz bomb.
Cheers
Ken