Alternate Engine Cooling Outlet?

[David Paule]

Looks as if you could develop some interesting oil cooler and cooling air exits by making an annular exit duct between the back of the cowl at the cheeks and the cheek fairings.

You'd have to make the fairings sized just for this with rounded fronts, and you'd have to seal the cowling bottom except for the exhaust pipes.

There would be a chance that you could get some energy recovery, read that as "thrust," with the heated outlet air being directed aft.

What do you folks think?

Dave

 

[Bruce]

David,

Maybe F1 Boss will get on here, but he tried it on his rocket.
Don't think it worked very well and had to rework several time.

Sound and looks good in theory.

My .05

 

[Ironflight]

The RV-1 has "open" back ends on the cowl cheek extensions - and Van did not carry that design detail foward into the RV-3....might tell you something...

Paul

 

[Tom Martin]

I think the idea has merit and would likely work on the RV4 as well. There was not room in cowl area of my rocket to internally duct the oil cooler to the lower opening and so I dumped it out the side of the cowling. I fabricated numerous "bluff body" extractors until I came up with a shape and outlet size that worked. The extractor is just a bump on the side of the cowling forward of the outlet. Supposedly it helps to create a bit of negative air to help improve the efficiency without adding a lot of drag. It worked in my installation.
The cowling cheeks would be a natural to create a nicely shaped internal duct.
I would keep the exhaust pipes on the bottom of the aircraft but you would be able to close the lower cooling air outlet, perhaps considerably. It would be a fun, and interesting experiment.

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[F1Boss]

Why not?

Hey Dave:

I think your idea has merit. Your best plan would be to allow for several changes to the outlet size while installing your 1st version. I used about 1.2:1 outlet to inlet ratio. This ratio is not 'outlet flow optimized', of course.

Caveat: keep in mind that the exhaust air is very warm (150F+), and the side of your airplane is made from aluminum, which conducts heat very efficiently. This translates into a large dose of cockpit heat on a continual basis. Very comfortable at higher altitudes and colder ambient temps; not so much in Texas in July. Early flight testing on my version led to the Dynon going grey scale, which I think it does at 140F? So, if the panel was 140F, what temp do you think the cockpit was? 'Time to land and re-think this mess' is about how I would describe it.

On the upside, you can experience what it's like to fly a WW2 fighter, as these ships had similar heating characteristics. So, I've got that going for me...

Summary: Since I am well along with this experiment, I will follow thru with changing the engine exhaust to exit out the bottom so I can get equal flow from the right and left cooling outlets (the current exhaust exits out thru the rt exit, above the wing, which confuses the flow on that side), but I still doubt if the interior heating issue can be solved without rebuilding the fuselage from composite, or installing some kind of shielding on the outside of the fuselage. I doubt I will carry the experiment that far, and will likely end up with a bottom outlet for both exhaust and cooling: it's easier to insulate the lower skin to reduce cockpit heating.

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You can see the outlets are actually easily changeable panels, and the rt outlet has the exh tailpipe in a less than optimal place. I will build up a new exh system to move the outlet to the bottom, seal it as well as possible, and then proceed with tweaking the bluff body outlets. It is possible that by balancing the two outlets, the cockpit heat will subside?
We shall see!

Cowl flaps: didn't work either, again due to the exh pipe changing the rt side flap size (about 60% of the left side), which allowed the rt side to be an INLET when the cowl flaps were deployed. 20/20 hindsight!


Carry on!
Mark

 

[RVjim]

Cheek cowl outlets

The RV-1 has "open" back ends on the cowl cheek extensions - and Van did not carry that design detail foward into the RV-3....might tell you something...

Paul

Actually, the original RV-3 had cheek cowl outlets and the bottom tunel.

Van's brother, Jerry, was overcooling his Lyc. 320 engine and put a plug in the side cheek cowl exhausts. By Jerry's data, he gained 5 mph and still had more than adequate cooling, by just having the cowl fairings.

Van included Jerry's cheek cowl fairing concept for the "standard" RV-3.

Jim Ayers

 

[Ironflight]

Actually, the original RV-3 had cheek cowl outlets and the bottom tunel.

Van's brother, Jerry, was overcooling his Lyc. 320 engine and put a plug in the side cheek cowl exhausts. By Jerry's data, he gained 5 mph and still had more than adequate cooling, by just having the cowl fairings.

Van included Jerry's cheek cowl fairing concept for the "standard" RV-3.

Jim Ayers

Now THAT is cool info Jim - thanks for not letting it get lost "to the mists of time..."

I got a note from Van last week that the original RV-3 cowl was made from his RV-1 cowl mold (with a slit and an added "gore" down the middle of the lower cowl to make it match the fuselage). Cool stuff that gets added to these archives....

Paul