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Theory, Theory quite too leery,
Quoth the Maven, only lore.
Applied science requires live experimentation. To wit:
A certain Lancair 320 has a smooth 3.5 inch diameter air intake ultimately
necked down to the front mounted throttle body intake size. There is a
fiberglass flange bolted to the throttle body with a 2 inch diameter (maybe
2.25) rubber plumber's sleeve pipe-clamped to the flange. This rubber sleeve
fits tightly over the ram air intake. The inside of this 10 inch air route
is relatively smooth (unlike scat tube) without the benefit or interference
of a filter.
Using insturments such as a sensitive altimeter, a Rocky Mountain
Micro-Encoder air data computer and the EPI 800 Digital engine
instrumentation, the following was observed:
On the ground -
MP=29.1, When the altimeter was set to zero(Sea Level), the pressure reading
was 29.35. The outside air temp was 85F, 27C and the Baro setting was 30.12.
After engine start -
RPM MP
700 12.7
1000 12.5
1500 14.1
1750 16.5
Take off: 2710 RPM, 90 Kts, 29.6 MP
@6000 feet AGL--
AutoPilot and Alt Hold on, Leaned in the best power range, full throttle,
2600 RPM, 22C (18C True Air Temp), 174 Kts IAS, 197 Kts TAS, 24.6 MP
29.1 ground MP - 6 (approx 1 inch per 1000 ft below 10000 ft) = 23.1 ambient
24.6 MP - 23.1 ambient = 1.5 inch ram air rise as measured at the MP tap. If
I round up, thats' two inches! :) If I round down (like my accountant)
thats' 1 inch! :(
Note that my ram induction system is not sealed -- that is, the throttle body
input flange is only 3 layers of glass and is fastened at each corner -- hi
pressure air can leak under the flange. The plumbers sleeve is not fastened
at the cowling with a hose clamp and can leak hi pressure air around the the
rubber and into the lower cowling plenum. The next test flight, I will try
to plug these leaks and report the results.
Any Comments?
BTW, I believe Tom Giddings concept of a pressure plenum is the right way
rather than deal with friction losses and pressure fronts from hi velocity
air. The same is true for cooling air ( it is best to have a 5-9 psi
pressure differential between the upper intake plenum and lower exit plenum
for 'slow speed' air flow).
Scott Krueger
N92EX
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LML homepage: http://www.olsusa.com/Users/Mkaye/maillist.html
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