What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Ram Air Measurements

cfiidon

Well Known Member
A few days ago I was on a return trip from SoCal to Norcal. I was IFR at 10,000 MSL and took some data:

MP 21.2
OAT 47F
DA 11530
PA 10,000
Altimeter 29.93
TAS 181kts

From this I used some on-line calculators to determine that the atmospheric pressure at 10,000 ft was 20.39.

So... that gives me a ram air boost of about 0.8 in/hg. Sound reasonable?

I subsequently verified that my MP pressure gauge is accurate (read 29.3 when my D180 altimeter set to zero feet MSL read 29.28). This was done on he ground. OAT read 58F in the hangar when AWOS reported 56F.

I am using a Sam James conical canister and K&N filter. The SJ cowl scoop is modified and adapted to my original updraft scoop lower cowling. The scoop feeds a horizontal cold air plenum. I am thinking this is probably only a little better than the Vans snorkel arrangement, probably owing to whatever added benefit I get from a larger filter area.

Comments?

Don
 
The Standard Day theoretical dynamic pressure for 10,000 ft and 181 TAS is 1.16 Hg. You can't capture all of it because the intake is not a closed end system like a pitot; 0.8 sounds pretty reasonable.
 
I experimented with this a few times in the past. I'm not sure if my approach was very scientific. I got the airplane as slow as I could, then went full throttle and noted my MP. As my airspeed increased, so did the MP. The MP rose 0.8" from minimum speed to maximum speed. I also noted my OAT rose 4 deg C due to aerodynamic heating.

Jerry Esquenazi
RV-8 N84JE
 
I have a home made forward induction, thru Airflow performance FM-150 injection servo and a Superior cold air sump. I use a K&N cone filter and get about the same ram air pressure using the technique Jerry describes. Not precise, but verifiable and repeatable.
 
Back
Top