On Thu, 25 Dec 2003 12:15:46 -0600, RR Urban wrote:



that is most curious bob. my aircraft has a brackett foam airfilter
(replaced annually) on the air inlet and none on the carby heat. the
reasoning is that carby heat is only applied when well off the ground
and the risk of contamination is small.

the problem is not bugs imho the problem is grains of sand.

you sure the builder didnt rig it up backwards? Stealth Pilot
+++++++++++++++++++++++

It is neither curious nor backwards.

The few RAM AIR designs I have encountered, ALL do WITHOUT the filter
for max ram effect - even the certified Mooney. However, Mooney does
have a mode that employs a filter when RAM AIR MODE is not desired. In
effect, I do the equivalent with carb heat mode.

FWIW....
Loss through the filter appears to be unacceptable to those engineers
that care to max performance with RAM AIR designs. Perhaps those more
knowledgeable will add their 2 cents???

P.S.
The RAM AIR topic has been addressed here in the past. I'm surprised you
are not somewhat familiar with the topic.


Barnyard BOb --

I'm not sure how much manifold pressure is lost going through a well
designed filter. But, for the sake of argument, if we assume a loss of
0.5" HG manifold pressure, my O-360 power spreadsheet tells me that would
be about a 4 hp loss at a 75% cruise condition at 7500 ft, or about 3% of
the power. A 3% power loss would give about a 1% speed loss. If you want
to compensate for the loss in power by increasing the rpm, you need about
a 150 rpm increase to get the same power you would have had with no air
filter losses.

These numbers are specific to the Lycoming O-360A series engines, but I
would expect similar percent power losses for the same MP loss for any
normally aspirated engine. The power loss would be roughly linear to the
amount of MP loss.

--
Kevin Horton RV-8 (finishing kit)
Ottawa, Canada
http://go.phpwebhosting.com/~khorton/rv8/
e-mail: khorton02(_at_)rogers(_dot_)com