[NSRCA-discussion] cooling area

[Dean Pappas]

Bad arithmetic ... that's less than 20% expansion or 1.2 rear-facing square inches out for every square inch in.
 

Dean Pappas 
Sr. Design Engineer 
Kodeos Communications 
111 Corporate Blvd. 
South Plainfield, N.J. 07080 
(908) 222-7817 phone 
(908) 222-2392 fax 
d.pappas at kodeos.com 

-----Original Message-----
From: nsrca-discussion-bounces at lists.nsrca.org [mailto:nsrca-discussion-bounces at lists.nsrca.org]On Behalf Of Dean Pappas
Sent: Tuesday, December 05, 2006 10:19 AM
To: NSRCA Mailing List
Subject: Re: [NSRCA-discussion] cooling area


Hi All,
I'll go one step further: measuring the exit area by looking at the bottom of the airplane is wrong. Do you want the air shooting vertically out the bottom of the ship? Of course not.
The expansion of air in our cooling setups is practically negligible. Let's say that the air heats up a whole 100 degrees F as it goes through the system. There is no way that it heats up even half of that. On a normal day, the air is at at roughly 535 degrees absolute, so a 100 degree warmup will make the air expand less than 10%.
 
If you take a square inch of air into the front of the airplane at 80 MPH, you want 1.1 square inches of exit ... as viewed from directly behind the aircraft!
Now if you cut a hole in the bottom of the plane, you have to ask how the air is coming out. Is the hole really aft of the fuselage bottom "high point"?
Is it really on the flat bottom? Then air is going to exit the plane at some shallow angle, and the effective area is going to be much smaller than what you see looking at the bottom of the plane.
Unless the exit hole is huge, this means that the system is outlet choked, when flying at speed, and adding drag to boot.
 
We really should build aft-facing exit scoops like some older Pattern designs, or the slick trick used on the aft end of the belly pan of the Zeque.
Later,
Dean
 

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