Posted for Villi Seemann <villi.seemann@nordea.com>:
Dear listers

It appears to me that something has slipped in the discussion about RAM-air
induction. A lister asked if the air would not speed up again when it
reached the carb/injector body.

Let us take a look at some figures. Let us initially assume we are flying in
a world with no losses, just to make it easyer.

Let us assume that I am running an (I)O-360 at 2700 RPM. If we had no vacuum
in the manifold (losses) it would ingest appx 486000 cu.in @ min (360 * 2700
/ 2) as each cylinder only inhales during half of its revs. It will not
inhale during the whole intake cycle and the manifold pressure is lower so
the air mass inhaled is less than the expected 486000 cu.in.

If we pretend we are flying at 180 kts, this equals 3 miles @ minute. This
means we are meeting the air with a velocity of appx 218740 inches @ min.

If we have a RAM air opening of 3 inch diameter, it has an area of appx 7
sq.in ( 1/2  *  3^2  *  PI ) . This means, if we did not have any inlet
losses, back pressure etc, the RAM air would enter our plenum chamber with a
volume of appx 14 mill cu.inches @ minute (speed * area ).

We know we have a lot of losses in this system otherwise, with the above
equations,  we should get more than 64 times the required mass of air pumped
into our engine. According to Mr Pitot the raw pressure increase is much
less, but according  to Mr. Bernoulli, we can realy increase the pressure a
lot, by slowing the incoming air velocity down.

What I want to say is, there is plenty of room for losses (and there will
be) in the induction system, if we are going for RAM boost, but will still
have a gain.

If anybody can tell me where my assumptions are wrong, I would love to be
enlighted. Please bear with my poor english.
  

Regards
Villi H. Seemann
Senior Engineer
Infrastructure Network
Phone  (+45) 3333 2101
FAX      (+45) 3333 1130
CellPhn (+45)2220 7690