REFLECTOR: Induction scoop

[Al Gietzen]

Scott:

Yeah, what Keith said.  I sized mine for 120 Kts (~135 mph), plus maybe 10 -
15% for scoop inefficiencies - so at 200 mph cruise it is likely spilling
some air a making a small amount of drag.  Assuming your 460 cfm (and my
math); I calculate the scoop entrance area of about 5.5 sq. in. 

You'll want to expand that as much as feasible to slow the air before the
filter - even then the filter will likely eat up much of the ram pressure
the scoop generates. Not likely you could follow the 7 degree guideline; and
I think here the static recovery is not the issue it is if your pushing air
through a heat exchanger.
Al

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Scott Derrick
Sent: Monday, July 06, 2009 8:25 PM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Induction scoop

I was going to make the scoop large enough to hold the air filter but
that would seem quite a bit larger than your saying...

Maybe I need to reduce its cross section even more?

I'm trying to get my head around 406 cubic ft per minute, flowing at 200
mph and how large an opening that is accounting for filter and turning loss?

Using this nifty calculator

http://www.comairrotron.com/airflow_calc.shtml

it looks like your saying an optimal(no restrictions) circular scoop
would have an opening of 2" diameter at 200 mph?  Thats
amazingly small!

Scott

Al Gietzen wrote:
> Scott;
>
> Not to worry; the most pressure you would ever see in the scoop is about
0.5
> psi.; well, unless you get a serious back-fire - that might be worse.
>
> Just a reminder that on an induction scoop the edge at the entrance should
> be very rounded; like 0.25 radius or so.  When the plane is moving very
> slowly; like beginning the takeoff roll, the air is being drawn from all
> directions, and the rounded entrance will reduce the pressure drop.  For
max
> ram pressure at speed you'll want to size the entrance for flow velocity
> just a bit less than the aircraft speed for the expected engine rpm and
> displacement.  But then you probably knew that.
>
> Best,
>
> Al
>
>
> -----Original Message-----
> From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
> Behalf Of Scott Derrick
> Sent: Monday, July 06, 2009 12:00 PM
> To: Velocity Aircraft Owners and Builders list
> Subject: REFLECTOR: Induction scoop
>
>
> I'm reshaping the induction scoop(P51 style) and was wondering if I need
> to do anything  about pressure  building up in it?
>
> Unlike a cooling scoop that always has flow through it, I can pull the
> engine to idle, which is shutting down the flow.
>
> Think I could blow up the scoop at high speeds? 
>
> Should I put a spring  loaded  door  on it to  open at  high pressures?
>
> this is the original scoop, before shrinking and putting a new flange on
it.
>
> http://www.eharwood.com/catalog/product.php?productID=344
>
> Scott
>
>
>
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