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Inward-opening oil door?

L

Loman

Well Known Member
I saw somewhere (probably here) that a builder had his oil door opening inward. You just pushed on it and the door hinged down into the cowl. I think it was hinged on the outboard side. He had inserted springs in the hinge to exert closing pressure while on the ground but air pressure kept it closed while flying. The advantages are lightness and smoothness - there is no latch and a piece of standard hinge with one or two springs inserted is all that is required. As the flange is molded onto the back of the door instead of around the opening, it stops the door from arching up in flight.The only disadvantage is that your sleeve is constantly rubbing the paint job on the outside of the door as you work inside.

Can anybody here provide a link to information on this set-up?

I would also be keen to hear opinions on whether this would still work with the SJ plenum I have bought. Maybe it is suction from low pressure over that area of the cowl that keeps it in place rather than high pressure from below?
 
I did that on my 6......

it works really well. Bought a European Cabinet hinge at Home Depot. Hinge pushes the door back in place. If you do this fiberglass a lip on the backside of the door, where the door can come only so far up to meet the lines of the cowl. Have 120 hours on the plane with no problem. Very clean. Door stays down when your checking the oil. Start it back up and it snaps in place. Sorry don't know how to post pictures here. No exterior fasteners.
 
Mine does

Mine opens inward, stopped flush by a lip around 3 sides. Sometimes it sags a little when not running, but plenty of pressure to keep it closed in flight. No latch mechanism, just a spring. BTW - SJ cowl and plenum.
 
How to avoid hitting the dip stick?

I can't believe it is almost two years since I originally posted this thread and I am only now getting to stage of actually cutting and fitting my oil door.

Now that I am working on it, I can't see any way of placing this door so that I avoid hitting the oil filler cap and tube while still being able to get my hand to it and withdraw the dip stick.

It seems that no matter how you place the door opening, the door itself will either hit the cap/tube which stops it from opening fully or the opening will be further outboard than usual so that the dip stick is under the cowl rather than the door and can't be withdrawn

If this really has been done, please prove it to me with a photo that shows how.
 
Reasons:

  • Smoother (The door can't arch up in flight and form a scoop)
  • Lighter (only a simple piece of piano hinge, plus spring, and no latching/fastening hardware)
  • Cheaper (no Hidden Hinge or fasteners to buy - though at a pinch you could use the 'Mickey Mouse ears' ones that come with the kit and leave the line of a standard hinge exposed - but to many eyes that looks ugly)
  • Simpler to use (nothing to unlock - just push) - as long as the door doesn't hit the oil filler tube that is. Hence the reason for my last question.

... and, since it's my plane - why not!
 
I think I would add cooler :cool: too. Smooth, clean, inventive.... Basically why people build airplanes.

It would certainly attract my attention when checking out a plane. The Mickey mouse ears do not add anything to the smooth factor of these airplanes that is for sure.

Mark
 
A friend did this on his 8, door is hinged about 1" from the outboard edge of the hole, held closed with a magnet, keep closed in flight by air pressure.

When opened the last inch is sticking up, gives him a way to close the door.
 
pierre smith said:
...and the big reason for doing this is??
Click to expand...

Wish I'd thought of it. The door could be totally sealed, no small thing as it produces drag in two ways...leakage creates a plume, and reduces lower cowl pressure thus reducing exit velocity.
 
I would have thought that you don't want high pressure inside the cowl where the oil filler is. Surely high pressure there would reduce the pressure differential for the cooling air.
 
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
 
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,
 
Last edited:
pierre smith said:
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?
Click to expand...

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?
 
DanH said:
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?
Click to expand...

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,
 
pierre smith said:
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.
Click to expand...

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.

pierre smith said:
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,
Click to expand...

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.
 
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,
 
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