REFLECTOR: Nose Cooler Pressure Study

[Al Gietzen]

Before we go too far down this path; I'm going to throw in another factor. I
agree that getting sufficient flow is about getting sufficient pressure drop
across the core. Sufficient flow is the first priority; the second is
minimum drag.  For that you'd like to have maximum pressure recovery in the
duct before the core (conversion of dynamic pressure to static pressure); to
take the drop across the core; and have pressure (energy) left to accelerate
the air in a converging duct to have it exit at some reasonable velocity
closer to free stream.  The expansion due to the heating helps out.  

 

So 0 pressure at the aft face of the cooler is not the ideal (and we need to
distinguish between static and dynamic pressure - depends how you measure
it) Zero, or better yet, negative static in the region outside the exit is a
good thing.

 

Of course having good flow and low drag would likely require a substantial
rework of the stock ducting - perhaps beyond where you'd like to go. And I
fully agree that some pressure measurements can certainly help in
understanding what's going on.

 

Al

 

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Brent Bourgeois
Sent: Saturday, October 10, 2009 7:14 PM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Nose Cooler Pressure Study

 


Jon,

I have the arm pit scoops.  Probably slightly smaller than the plans call
for. Built them big before understanding what I was doing.  Lots of testing
and I have CHT probes under the cylinder and under the top plugs for
measurment. IO 360-A1A

Brent 

N61VB

Std RG

--- On Sat, 10/10/09, Bachman, Jonathan <Jonathan.Bachman at mtsi-va.com>
wrote:


From: Bachman, Jonathan <Jonathan.Bachman at mtsi-va.com>
Subject: Re: REFLECTOR: Nose Cooler Pressure Study
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Date: Saturday, October 10, 2009, 9:15 PM

Brent,

 

What kind of engine cooling inlets do you have?  I have under wing (not arm
pit type) and think they are not very efficient.

 

Jon

N956DR

1992 Std RG

 

  _____  

From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Brent Bourgeois
Sent: Saturday, October 10, 2009 6:59 PM
To: Velocity Aircraft Owners and Builders list
Subject: REFLECTOR: Nose Cooler Pressure Study

 


Scott,

I have spent a lot of time getting my oil cooler working properly. Before
cutting anything, please do a basic pressure study to understand what is
going on. All you need is a plastic tube about 1 inch in front of the cooler
and one in the exit duct. Route them inside and use a airspeed indicator to
get an inlet press and an outlet press. The key is to maximize the
differential.  

I have pages of data that prove (at least on my plane ) that the problem is
positively not getting the air in, but getting it out. 

One example is : 155mph on the pitot, 88mph on the cooler face and 10 mph in
the exit duct. I was eventually able to get the exit duct to 0. This 88mph
proved to be the max oil cooler inlet speed all the way past 220 pitot
speed. 

I think that once the inlet pressures up, the air stops entering and flows
on by. Once I got max vacuum possible behind the cooler I was able to block
off some of the (weird NACA type)  inlet and not raise the oil temp.

I believe the trick is to find a reverse scoop or lip arrangement that
maximizes the air extraction

I had thermocouples on the cooler inlet and outlet lines. The front cooler
is worth 15 to 20 degrees in oil temp.

I also found this method very useful at maximizing engine cooling while
making the air inlets smaller. 

Let me know if I can help.

 

Brent 

N61VB

Std RG

 

 

 

 

 

 


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