[Kyle Boatright]

I was looking at the yellowed plans for my RV-6 the other day and was reminded by the 3-view that the RV6 prototype had updraft cooling. There was a funky (ugly?) scoop on the underside of the cowl and there were no intakes located next to the spinner.

Anyway, a couple of questions:

1) Why did Van's abandon the concept? In theory, a properly developed updraft cooling system should be more efficient than the traditional downdraft system. Why? A) Natural convection (heat rises) and B) The underslung intake is in a higher pressure airstream, particularly during climb, where cooling is most critical.

2) Where was the air exit for the prototype RV6 with the funky cowl?

 

[gmcjetpilot]

Not really

99% sure it did not have up draft, but it did have an annular scoop around the spinner vs. two straddling the side. I flew it in the mid late 80's with Van the man. Van is a very smart guy, and the planes he has designed where not by accident. No doubt he was experimenting with reducing cooling drag. But if you look the air still exits below the firewall. It is not really ugly, just differnt. There are several reasons it did not work, not the least was engine temps. The area immediately next to the spinner is dirty air, due to the shape of the props blunt shaped blades, near the hub. He never sold that cowling. It was only on the prototype.

The problem with updraft is the exit by the way. The area in front of the windscreen is major high pressure. The NAVION tried it but most use down draft. I think some Long-EZ's are updraft.


George

PS I bought a tail kit right after my ride with Van.

 

[Guy Prevost]

In theory, a properly developed updraft cooling system should be more efficient than the traditional downdraft system. Why? A) Natural convection (heat rises)

It's been a while since my heat transfer courses, but I'm pretty sure that counterflow convection is more efficient. In other words, you can more effectively transfer heat to the cooling air if it is moving down through the fins than you can when it is moving up through them.

 

[osxuser]

I wanted to tweak around with this idea initially when I thought about buying a RV kit, but mine was based off of greed, not efficiency. What I wanted to do was use a crossflow cylinder off a Chieftain, with a high compression piston, to produce a higher HP crossflow IO-360. Of course in this application, the exhaust comes of the top, so downdraft cooling would have been... interesting. I toyed with this idea for awhile, but when the IO-390 came out, I kinda gave it up. It would be interesting to find out if a 390 barrel could be fitted to the crossflow head.

 

[Mel]

The Globe Swift had updraft cooling for years. It is not normally very efficient, partially because the cooling air has to come in horizontally, make a 90 degree turn to go up through the cylinders, then another 90 degree turn to go aft, then another 90 degree turn to go down to the exit. It worked ok on the Swift, but the baffle system had to be kept in very good condition, and the cooling drag was tremendous.
Mel...DAR

 

[Allen Barrett]

cross flow 390

Without re-inventing the cross flow head, it couldn't happen. With the 390 barrel being bigger than the cross flow barrel, the thread diameter too is bigger.

 

[tin man]

updraft cooling

Pretty sure Rutans Voyager had updraft cooling on the front engine. Kinda apples and oranges I know but still interesting.
Tom

 

[N941WR]

Pretty sure Rutans Voyager had updraft cooling on the front engine. Kinda apples and oranges I know but still interesting.
Tom

I knew one of the engines was water cooled but it was the rear engine.

The following is from: http://www.nasm.edu/research/aero/aircraft/rutanvoy.htm

engines, one at each end of the fuselage, powered the aircraft. The highly efficient 110-hp, liquid-cooled rear engine, a Teledyne Continental IOL-200, ran during the entire flight except for four minutes when a fuel problem caused a temporary shutdown. The 130-hp, air-cooled front engine, a Teledyne Continental 0-240, was used for a total of 70 hours and 8 minutes during the initial, heavyweight stage of the flight, and also while climbing over weather and at other critical times. Voyager was equipped with Hartzell constant-speed, variable-pitch aluminum propellers that proved to be a critical factor in stretching the aircraft's range enough to bring it home. These propellers were designed, built, and delivered in only 17 days after one of the original propellers failed.

That should start that entire water vs. air cooled and FP vs. CS prop thing all over again.

 

[Ola]

That should start that entire water vs. air cooled and FP vs. CS prop thing all over again.

Air cooled propellers are far superior to liquid cooled ones!