REFLECTOR: ram air

[steve korney]

Hi Pat...

    I won't run my engine at full throttle on the ground, not even on 
take-off until I get moving about 20 mph...
So, I use my ambient MP gauge reading with engine off, against my dynamic MP 
gauge reading at 220 kts. ias WOT... If I were to add in the loss of any 
restrictions in my induction system, then I would be getting more then 2 
inches of Ram Air MP increase.  This way I eliminate any error in the gauge 
and any losses through the system and only show net gain...I have a forward 
facing intake system on my Glasair... Straight through the Airflow 
Performance FM-200 into the intake manifold... No Filter on Ram Air...The 
difference between filtered air and ram air is about 2.5 inches of MP at any 
speed... That shows how bad my filtered air is working as far as performance 
goes, but does a good job of keeping junk out of my engine.   I can live 
with 28 MP inches of filtered air for take-off most places...  If I'm at Big 
Bear on a hot day, I just open the ram air butterfly and I have an extra 2.5 
inches for take-off..


Best... Steve



----Original Message Follows----
From: Pat Shea <xl340hp at yahoo.com>
Reply-To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
Subject: Re: REFLECTOR: ram air
Date: Sat, 8 Jul 2006 01:18:26 -0700 (PDT)

Okay Steve,

So assuming you didn't go out on a standard day, what
reference did you use to determine your 2" of ram?

The local barometer reading?

Your ambient MP gauge reading?

I'm running a filtered induction. Here's a realistic
scenario: The local baro setting is 30.0". With my
engine off the MP on my Vision Microsystems gauge
reads 29.0". In the run-up area at WOT the gauge reads
28.0". I think that means I have a pressure loss of 1"
across my plumbing/filter. Now, during a high speed
pass down that runway at WOT my MP gauge reads 29.0".
That means I'm getting 1" of ram pressure right - just
enough to offset my plumbing/filter losses?

It seems to me that comparing your static WOT MP
reading to your MP reading during a high speed low
pass at WOT down that runway would be the most
accurate way to determine your true ram. This way you
eliminate any errors in you MP gauge calibration and
account for any restrictions in your induction system.


What's funny is that I hear a lot of people talk about
ram but not how they derive it. I suspect that it's
being derived lots of different ways and therefore not
easy to compare and contrast.

Pat

--- steve korney <s_korney at hotmail.com> wrote:

 > This little chart assumes std. day  :   sea level,
 > 29.92, and 59 f.
 > It's what the front of the airplane is up against at
 > different speeds...
 >
 > In my Glasair, I see up to 2 inches of ram pressure
 > on the manifold pressure
 > gauge at sea level @ 220 kts. ias....  ie. 32 inches
 > of manifold pressure on
 > a std. day...
 >
 > Best... Steve
 >
 >




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