REFLECTOR: Induction scoop

Tue Jul 7 13:26:55 CDT 2009

The scoop size vs the filter size seem at odds with each other.

Per this engine air/flow site my io520 at 2700 RPM, assuming volumetric
efficiency is 100%(yeah right!) is 406 CFM(not 460)

http://www.stealth316.com/2-air-fuel-flow.htm

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Per this air flow calculator site for 406 CFM at 130 mph, would require
a scoop opening of a tad smaller than 1x6 inches or 6 sq inches.  With
that size opening, I'm dumping 350 CFM at 200 MPH which basically
translates to a flat plate resistance of 6 sq inches or the size of the
opening..

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

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Per K&N's filter size equation  Area = (CID X RPM)/20,839  says I will
need 65 sq inches of filter!

http://www.knfilters.com/filter_facts.htm#SELECT

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From a 6 sq inch scoop opening to a 65 sq inch filter area!   Wow!

If I shrink the scoop to a 6 sq inch opening,its going to be tough to
get a 65 sq inch filter into it as that was my plan.  Not imposable, but
tough.  I was planning on using a flat rectangular filter.  I'm sure the
T210's with TSIO520's that breath about 1/2 again as much air have a
flat filter about 3x10 or 30 sq inches.

My Bonanza with a io470, had a filter about 4x8, 32 sq inches..

Well, off to the airport to play with a 65 sq inch block of foam and the
scoop to see how much of an angle it will have to be mounted at to fit.

Scott

Al Gietzen wrote:
> 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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>
>
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