Inward-opening oil door?

[jarvis]

I think someay'all are looking for this-- http://www.vansairforce.net/builderm...essdoormod.htm
If the link doesn't work, it's in the "Builder Modifications" on VAF homepage.

[mburch]

I really wanted to do this on my airplane, but when I finally got the cowl fitted I discovered that there was no way it would work without hitting the dipstick. Maybe other airplanes are different, but I don't see how you could make it work without some kind of super-low dipstick. If I'm wrong, I'd love to find out the secret!

mcb

[pierre smith]

On the 4 cylinder engines, the oil filler is behind the rear baffle where there shouldn't be much pressure, and it makes me wonder what keeps it shut, if not for a spring or magnets. Lift on the cowl curvature perhaps?

On the 6 cylinder engines, the filler is within the confines of the baffling and positively has pressure to hold it closed. The filler is just about in the middle of the engine. Besides, on my -10, the oil filler cap is only 2 inches below the oil door, which is 6 inches wide, so it wouldn't work anyway.

Best,

[DanH]

Originally Posted by pierre smith

On the 4 cylinder engines, the oil filler is behind the rear baffle where there shouldn't be much pressure, and it makes me wonder what keeps it shut, if not for a spring or magnets. Lift on the cowl curvature perhaps?

Measured ballpark about 0.2 psi minimum...roughly 5 lbs of closing pressure on a 5" x 5" door, or 7 lbs for a 6' x 6".

Why do you think a stock door bows up in flight?

[pierre smith]

Originally Posted by DanH

Measured ballpark about 0.2 psi minimum...roughly 5 lbs of closing pressure on a 5" x 5" door, or 7 lbs for a 6' x 6".

Why do you think a stock door bows up in flight?

Dan, you measured that much pressure back there, under the oil door? It just seems contrary to my intuition but I can't argue with your measurements but I still wonder where that pressure comes from.

With your "shrinking exit", I can see where the buildup of pressure might happen...more air coming in than can escape, pressurizing the entire lower engine compartment, and the area behind the engine, no?

Thanks,

[roee]

Originally Posted by pierre smith

Dan, you measured that much pressure back there, under the oil door? It just seems contrary to my intuition but I can't argue with your measurements but I still wonder where that pressure comes from.

Pierre,

As intuition suggests, there is obviously a pressure drop from the "high pressure" area to the "low pressure" area in the cowl. But perhaps less obvious, the "low pressure" area in the cowl still has higher pressure than outside the cowl, and it must. If that wasn't the case, no air would flow out of the cowl exit, and there would be no air flow through the cowl.

Originally Posted by pierre smith

With your "shrinking exit", I can see where the buildup of pressure might happen...more air coming in than can escape, pressurizing the entire lower engine compartment, and the area behind the engine, no?

Thanks,

Nope. Regardless of the shapes and sizes of the inlets and exits, the mass air flow in and the mass air flow out are always equal in the steady state. They must be.

To correct your intuition on this, do the following thought experiment. Consider what would happen if you were actually somehow taking more air in than you were letting out. You would be trapping more and more air molecules with every passing second. And so, given that the volume of the cowl is fixed, the pressure would have to climb and climb continuously toward infinity.

[6 Gun]

Pierre dont belive anything you read and only half of what you see.
Bob

[pierre smith]

Fluid/aero dynamics are always fascinating. I walked all over Rare Bear at Reno and had built a Cassutt F-1 racer back in the '70's.

The cowl work that Bill Falck (sp?) had done was simply gorgeous and really fast airplanes, so all this talk is very interesting to me.

I've closely followed Ross's work with the Subie cooling scoop and exit setup...a masterpiece!

Best,