From: "Scott Dahlgren" <spdahlgren@uswest.net>
To: "___Lancair list" <lancair.list@olsusa.com>
Subject: ram air
Date: Sun, 22 Aug 1999 10:38:02 -0600
Message-ID: <000001beecbc$b3d2dc60$0200000a@scottdah>
Importance: Normal
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John Spry,

The Questair Venture group did quite a bit of work with ram air as they were
trying to get more air into the engines of their high flying planes. They
had some luck by actually mounting thin (.032" thick?)sheet aluminum plates
onto their props, close to the spinner, about 2x the cord thickness (please
note I am not recommending any of this...). It looked like the AOA of the
plate was approximately the same as the cord from pictures I saw. The
tapered plate would sweep flush across the face of a large ram opening and
send a pressure pulse to the carb that matched the valve opening, the most
beneficial time to have pressurized air. they reported much success and
increases in altitude and ground speed. sort of a poor man's supercharger.

to get the prop firing timing right, required some interesting and
asymmetrical placement of the ram intake as I recall, and the prop had to be
clocked to the valve timing as well.

the dynamic pulse you receive putting the carb inlet close to the prop will
do you little to no good at cruise speed on the Lancair as the ratio of prop
wash velocity to ambient velocity is too close to unity to gain any
sustained pressure increase at the manifold. the pulse is also ~1/30th of
the total intake at Lancair's carb intake location. this is likely why the
Venture group mounted their ram openings close to the hub and made them big,
to get bigger pulses for a greater percentage of the valve open time.

You could get a lot of valuable information on these designs from the
Venture group. They may have perfected the art at this point and have all
the pros and cons for you and maybe have something for our group as well.

Let us know what you find out.

Scott

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