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NACA cockpit cooling vents

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Vince Frazier

Joined: 10 Jan 2006
Posts: 132

Posted: Wed Feb 22, 2006 7:46 am Post subject: NACA cockpit cooling vents

James,



I can't tell you where the best spot is, but I can tell you where it

doesn't work on my airplane

http://vincesrocket.com/2003-10-20/finished%20cowl%20paint%201.jpg



I have a NACA scoop on each side of the fuselage for the front seat and

a scoop under the wing (placement like an RV-8)which supplies the rear

seat.



If I hold my hand in front of the air blast from the front outlet and

the rear outlet at the same time, I can feel a HUGE temperature

difference between the two.  The rear seat outlet (from under the wing)

is at least 20 F cooler than the front outlet.



I can only speculate as to why this is.  I tried taping over the cowl

seam on the assumption that hot air was leaking out of the cowl seam.

No change.  Maybe hot air is spilling back out of the engine inlets?  My

engine temps are very good so I'm not about to fiddle with them. 



I know that simply going fast will heat the air, something like 7 degree

F.  But that doesn't explain why the front and rear outlet temps are so

different.  And the temps stay different at all speeds.



I'd like for someone who really knows to post it to the list.



All I know for certain is that I'm changing the spot where my cockpit

cooling air comes from before summer arrives. Probably take it from

under the wing like the rear vent.  Thank goodness that my firewall is

well insulated on both sides!



Vince



--

_________________
Vince Frazier
3965 Caborn Road
Mount Vernon, IN 47620
812-464-1839 work
812-985-7309 home
F-1H Rocket, N540VF
http://vincesrocket.com/

n395v

Joined: 10 Jan 2006
Posts: 450

Posted: Thu Feb 23, 2006 6:31 am Post subject: Re: NACA cockpit cooling vents

Vince,



I have 1 Naca scoop under the left wing for the rear seat and one on the right side of the Fuselage in the same exact location as yours for the front. I have no discernible difference in air temps from either (based on feel).



Have you opened up your louvers and tried it?

My best guess is it is (as you also suspect) it may be air spilling out of the inlets.



After adding louvers my CHTs dropped on average 15 degrees and, subjectively, I think I picked up a little speed.



Never paid any attention to air temp from the vents before I put the louvers in.

_________________
Milt

CalBru(at)aol.com
Guest

Posted: Thu Feb 23, 2006 7:27 am Post subject: NACA cockpit cooling vents

Milt,

 

I'd like to see pictures of your louvers...

 

Cal Brubaker

n395v

Joined: 10 Jan 2006
Posts: 450

Posted: Thu Feb 23, 2006 3:19 pm Post subject: Re: NACA cockpit cooling vents

The following is a series of attachments if you view the bulletin board.



If they are stripped from your e mail version let me know an I will e mail them to you.  



#1

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_________________
Milt

n395v

Joined: 10 Jan 2006
Posts: 450

Posted: Thu Feb 23, 2006 3:21 pm Post subject: Re: NACA cockpit cooling vents

#2 if you need more flow just cut out some of the cross bridges.

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_________________
Milt

Last edited by n395v on Thu Feb 23, 2006 3:30 pm; edited 1 time in total

n395v

Joined: 10 Jan 2006
Posts: 450

Posted: Thu Feb 23, 2006 3:22 pm Post subject: Re: NACA cockpit cooling vents

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_________________
Milt

Last edited by n395v on Thu Feb 23, 2006 3:29 pm; edited 1 time in total

n395v

Joined: 10 Jan 2006
Posts: 450

Posted: Thu Feb 23, 2006 3:24 pm Post subject: Re: NACA cockpit cooling vents

#5



The finished product

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_________________
Milt

James Baldwin

Joined: 16 Jan 2006
Posts: 23

Posted: Fri Feb 24, 2006 2:29 pm Post subject: NACA cockpit cooling vents

Not sure I actually believe the temps on Vince's machine are REALLY 

different without an actual measurement, but also not sure what either 

of you mean by "air spilling out of the inlets."  Surely you don't mean 

the pressure side of the cowl inlets where it has been noted that vented 

air tapped from the rear baffle provides a cool source.  Please 

enlighten me as I have no machine to go fly yet.  Skin surfaces exposed 

to sunlight might add energy in comparison to a source underneath the 

airplane.  I doubt any energy difference at these speeds due to 

compressibility in a low pressure inlet,  a.k.a. a NACA duct.   I sure 

would like to know the numerical values of the air temp coming out of 

the two sources.  I don't want to cut holes in the wrong place.  JBB

N395V wrote:



 	  Quote: 	
		  



Vince,



I have 1 Naca scoop under the left wing for the rear seat and one on the right side of the Fuselage in the same exact location as yours for the front. I have no discernible difference in air temps from either (based on feel).



Have you opened up your louvers and tried it?

My best guess is it is (as you also suspect) it may be air spilling out of the inlets.



After adding louvers my CHTs dropped on average 15 degrees and, subjectively, I think I picked up a little speed.



Never paid any attention to air temp from the vents before I put the louvers in.



--------

Milt

N395V

F1 Rocket





Read this topic online here:



http://forums.matronics.com/viewtopic.php?p=14325#14325

fairlea(at)amtelecom.net
Guest

Posted: Fri Feb 24, 2006 7:11 pm Post subject: NACA cockpit cooling vents

This air inlet provides gobs of fresh cool air.  



Tom Martin

Vince Frazier

Joined: 10 Jan 2006
Posts: 132

Posted: Mon Feb 27, 2006 10:49 am Post subject: NACA cockpit cooling vents

James,



Yesterday when it was 32 degrees outside (on the ground), the front NACA

inlet was providing relatively warm air.  My OAT probe happens to be in

the front inlet and read 56 degrees at 3500'    As you can see,

something doesn't add up since I should have been getting about 30

degree (or less) air coming in those inlets.



I don't have a temp gauge in the rear seat vent path, but I did put my

hand in front of the eyeball airstream and it was freezing cold, and

certainly NOT the 56 degree air that I had coming out of the front NACA

vent.



I don't have an explanation for why it does it, but it's not from the

sun warming the side of the fuselage. 



All I can say for certain is that I will not put my next airplane's NACA

vents on the side of the fuselage. 



When the wx gets warmer, I'll figure this out and post any findings.



If you don't know about air spilling back out of an inlet then study the

early P-80 jet intake structure.  The gills were a fix to prevent

exactly what we're talking about.



Vince

*************************************

SNIP

Not sure I actually believe the temps on Vince's machine are REALLY

different without an actual measurement, but also not sure what either

of you mean by "air spilling out of the inlets."  Surely you don't mean

the pressure side of the cowl inlets where it has been noted that vented

air tapped from the rear baffle provides a cool source.  Please

enlighten me as I have no machine to go fly yet.  Skin surfaces exposed

to sunlight might add energy in comparison to a source underneath the

airplane.  I doubt any energy difference at these speeds due to

compressibility in a low pressure inlet,  a.k.a. a NACA duct.   I sure

would like to know the numerical values of the air temp coming out of

the two sources.  I don't want to cut holes in the wrong place.  JBB

SNIP

_________________
Vince Frazier
3965 Caborn Road
Mount Vernon, IN 47620
812-464-1839 work
812-985-7309 home
F-1H Rocket, N540VF
http://vincesrocket.com/

James Baldwin

Joined: 16 Jan 2006
Posts: 23

Posted: Mon Feb 27, 2006 8:06 pm Post subject: NACA cockpit cooling vents

Vince -

Good temp "data." That's close enough for me, and I'm not sure why you 

are seeing warm air from the front vent location either.   Obviously a 

logical place to put the vent, too bad it doesn't work. 

My  comment on "air spilling"  was in regard to at least one 

installation I know of where the vent source is from the rear baffle of 

the pressure side of the cowl inlet.  No complaints of outlet 

temperature and you would think the air would be warmed as it passed by 

the cylinder fins.  

At the least, I know where I won't put my vents.  JBB

Frazier, Vincent A wrote:



 	  Quote: 	
		  



James,



Yesterday when it was 32 degrees outside (on the ground), the front NACA

inlet was providing relatively warm air.  My OAT probe happens to be in

the front inlet and read 56 degrees at 3500'    As you can see,

something doesn't add up since I should have been getting about 30

degree (or less) air coming in those inlets.



I don't have a temp gauge in the rear seat vent path, but I did put my

hand in front of the eyeball airstream and it was freezing cold, and

certainly NOT the 56 degree air that I had coming out of the front NACA

vent.



I don't have an explanation for why it does it, but it's not from the

sun warming the side of the fuselage. 



All I can say for certain is that I will not put my next airplane's NACA

vents on the side of the fuselage. 



When the wx gets warmer, I'll figure this out and post any findings.



If you don't know about air spilling back out of an inlet then study the

early P-80 jet intake structure.  The gills were a fix to prevent

exactly what we're talking about.



Vince

*************************************

SNIP

Not sure I actually believe the temps on Vince's machine are REALLY

different without an actual measurement, but also not sure what either

of you mean by "air spilling out of the inlets."  Surely you don't mean

the pressure side of the cowl inlets where it has been noted that vented

air tapped from the rear baffle provides a cool source.  Please

enlighten me as I have no machine to go fly yet.  Skin surfaces exposed

to sunlight might add energy in comparison to a source underneath the

airplane.  I doubt any energy difference at these speeds due to

compressibility in a low pressure inlet,  a.k.a. a NACA duct.   I sure

would like to know the numerical values of the air temp coming out of

the two sources.  I don't want to cut holes in the wrong place.  JBB

SNIP

n395v

Joined: 10 Jan 2006
Posts: 450

Posted: Mon May 29, 2006 5:51 am Post subject: Re: NACA cockpit cooling vents

Vince,



Pulled this off the VAF website and thought about this thread when I read it.



Walter tufted the inside of a cowl and fillmed what went on.



Bet dollars to doughnuts that  this is what is going on with your rocket.



Have you opened up the louvers yet and tried it?



How about an update.



 	  Quote: 	
		  The first thing we learned is that what we learned in A&P school was just, flat, wrong. The air does NOT come in, go to the back plate, pressurize the cowl and go down through the fins. Nothing could be farther from the truth.



The BASIC airflow is that the air enters the cowl openning at the outboard edges of the openning. It passes along the outboard edges of the cylinders until it gets to the back plate whereupon it turns inboard and meets the air that came in the other side right over the spine of the engine. This results in the air moving forward along the spine of the engine case toward the spinner where it exits the cowl and goes over the windscreen aft! That's why you get oil spots on the windscreen when you have an oil leak!



Yep, about 70% of the air that comes in a cowl goes right back out the FRONT! That's why smaller opennings, limiting the air IN and baffles blocking the front are very helpful. If one tufts the cowl openning you will be surprised to see about half of those tufts pointing straight forward TOWARD the prop when in flight. That's the air going OUT forward.



The biggest advantage in cooling is created by slowing the air down on top and creating a large deltaP with the lower deck. That allows more air to work it's way through the fins and allow engine heat to move into the air. It is essentially impossible to make intelligent changes in cowl and baffle design unless you can WATCH the airflow with the changes. They can be very counter-intuitive.



We've fixed several problems that have existed for decades and we've run up on some to which the solutions remain elusive. One in particular really has me frustrated and downright chapped--dozens of brilliant ideas and sure-fire solutions have failed over many months of efforts. 



Walter Atkinson

Advanced Pilot Seminars

_________________
Milt

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