Re[2]: REFLECTOR:Engine ram air

[steve]

Hi Jim,

Thursday, August 21, 2003, 8:53:31 AM, you wrote:

JA> The air intake should not be less in square inches than the
JA> area of the fuel controller intake.  If the controller
JA> intake is 3" then the area is a little more than 7 Sq. In..

JA> Jim

 
JA> --- KeithHallsten <KeithHallsten@quiknet.com> wrote:
>> Rene',
>> 
>> I have no particular expertise on this subject to share
>> with you, but this month's Sport Aviation has an article
>> on engine cooling that may have some principles you can
>> put to work.
>> 
>> Keith
>>  
>>   ----- Original Message ----- 
>>   From: Rene Dugas 
>>   To: reflector@tvbf.org 
>>   Sent: Wednesday, August 20, 2003 10:18 AM
>>   Subject: REFLECTOR:Engine ram air
>> 
>> 
>>   I've asked this before but did not get an answer.  I am
>> no engineer either.  How big should the opening be on a
>> ram air scoop feeding air to the engine on an IO 540 at
>> 2300 rpm's?  I understand it is best to not have the
>> scoop any bigger than necessary because of the overflow
>> forms a slow mushroom of backed up air pushed ahead of
>> the scoop.  Any takers?  Mine is about 2.5 by 2.75"
>> expanding into an airbox with a K& N filter then into the
>> 3 inch orifice under the engine.
>> 
>>   Rene'
>> 


JA> =====
JA> James F. Agnew
JA> Jim_Agnew_2@Yahoo.Com
JA> Tampa, FL
JA> Velocity 173 Elite Aircraft Completed
JA> _______________________________________________
JA> To change your email address, visit http://www.tvbf.org/mailman/listinfo/reflector

JA> Visit the gallery!  tvbf:jamaicangoose

To optimise the intake size for the cruise...

lets see... 540 cubic inches for every *two* rpm (because only 3 of your
cylinders open their intake valves on one revolution and the other 3 do it on
the next revolution)at 2300rpm a 540 ci displacement engine needs 621,000 cubic
inches per minute.  (540/2 * 2300)

lets say the cruise speed is 180kts.  Thats 3 naut/miles/minute or  ( 3 * 6000 *
12 inches per minute) Air speed = 216,000 inches per minute.

If your intake opening was say 1 sq inch, at 180 kts in a perfect world the
intake would pass 216,000 cubic inches of air every minute. But your IO 540
needs about 3 times that much air .... so make the cross sectional area of your
intake 3 square inches ( not the same as 3" square).

If your intake is NOT in an area of clean airflow, or is affected by the
boundary area etc... then the 'scoop' probably needs to be bigger. If your
cruise is higher than 180kts then the intake may need to be slightly smaller. Of
course you now *need* to consider take-off and climb.... full power (or maybe
2500 rpm in the climb) but lower forward air speed

eg. say 2700 rpm and 100kts, plug these numbers into the above equation ...
engine needs 729,000 cu inches of air every minute. At 100 kts (120,000 inches
per minute) the intake needs to be about 6 Sq inches. I would say that your
intake is approx 1 sq inch too big for the climb and lots too big for the cruise
... answer adjustable intake ????

I'm not an engineer either so you would be well advised to check both my numbers
and my methodology....... hope this is of help

btw... a good simple test that I use every month to check for intake performance
or partially blocked filter. Record manifold pressure BEFORE engine start, look
at manifold pressure during the takeoff roll at about 60 kts and it *should* be
within about 1.5" of the first reading prior to eng start. If over time it
becomes 2" - 2.5"  suspect the air filter.

--  Best regards,  steve
mailto:steve_beilby@yahoo.com.au