Venturi on Belly

[Grant S. Bailey]

Anyone have any experience with a venturi mounted on the belly of the airplane rather than the fuselage side?

I want to install a 4" venturi to drive a directional gyro but would prefer a belly installation. Is the slipstream okay for a venturi in the area of the fuselage bottom metal fairing ahead of the gear?

[jrzangger]

Venturi

The belly locations are usually not used due to the possibility of oil contamination. If yours is like mine, you wouldn't want it there! The "correct" or most productive side would be on the same side as the descending blade. Be sure to mount it low enough to avoid a conflict with the cabin door!

[captjon]

Grant:

I agree with Jim on the oil issue. Also you may get some turbulent air disrupting good flow down there due to the slight flare of the rear edge of the bottom cowling.

If you need a nicely refurbished venturi, I have one that I was going to put on Tami T-Craft. The new panel got filled before I had a space for the heading gyro.......no, actually it was going to make the panel look assymmetrical so I decided to go without it.

See, Jim.......I was planning on making it more complex.......and decided against it!

Oh, the gyro will be available too if you are interested.

They will be posted shortly on my web site at http://T-Restore.biz

Have fun. Good seeing you this summer!

Cheers,

[David Price]

The "correct" or most productive side would be on the same side as the descending blade.

Jim,
How is the venturi effected by the blade, "descending" or "ascending"? Is it not, still a push from the prop to the port, either up or down? What am I not seeing here?

"LOVE AIR"

[jrzangger]

Jim,
How is the venturi effected by the blade, "descending" or "ascending"? Is it not, still a push from the prop to the port, either up or down? What am I not seeing here?

"LOVE AIR"


__________________
David Price
N96045 #8245
T-Foundation #558
Molt Taylor Field
Kelso,WA,

I don't know anything about a push from the prop to the port, but the descending blade produces more thrust than the ascending blade during a climb. The aircraft's angle of attack is increased which increases the pitch of the descending blade accordingly and decreases the pitch on the ascending blade. If you mounted a venturi on the side of the descending blade you would have a difficult time achieving the rated suction during a climb. I don't have any exact numbers but wouldn't be surprised if it would be an inch less or so. Not enough to keep an attitude gyro fully erected anyway. Review "P factor" in an aerodynamics book.

[Richard Boyer]

My venturi is on the left side. I don't think I ever had any trouble with the gyro spinning up..... While climbing, aren't you doing about 60mph anyways? Wouldn't that be going through the venturi?

curiously yours,

Richard Boyer
N95791

[jrzangger]

Now you're going to put me on the spot aren't you?!! Yes, you would have the relative wind or forward airspeed of the plane in a climb, cruise or descent, but in the climb, with power, there is significantly more relative wind on the side of the descending blade. There are many aircraft with venturi's mounted on the ascending side, but that could be from a lack of understanding (I was going to say ignorance but changed my mind!) and not knowing about "P factor". If you've got one on the left I wouldn't relocate it. Just given the choice, the most correct side would be on the side of the descending blade! If all you're running is a turn & bank it probably isn't an issue. If you are trying to run a turn & bank, an attitude gyro, and a gyro compass, you need them on the side of the descending blade. Just don't mount it so high that the door would hit it! I don't have any of this fancy stuff on my Taylorcraft so it isn't an issue on my plane!

[David Price]

Jim,
Thanks for taking the time to explain and answer my question.
I shall not wonder anymore, why I see them on one side, on one plane and the other, on another.
And yes, mine is on the left side.

"LOVE AIR"

[Grant S. Bailey]

Well this has been interesting and as always helpful. I guess I will mount the venturi on the side of the descending blade!! I don't know that it really matters as I had a 4" venturi on the left side of my Cessna 140 and it pulled plenty of vacumn, almost to the point where I needed a regulator. But obviously the belly mount isn't the best idea.

[yerich109]

Originally posted by jrzangger
Not enough to keep an attitude gyro fully erected anyway.

Boy, where's Storman when you need him???? I can't believe he let this one slide. Must be less attentive to details in his old age. I'll bet he could fill the internet with smart remarks about keeping the ag erected during flight. C'mon let's see what you got...


Blue Skies,

[taylorcraft078]

There was a belly mounted venturi on a Taylorcraft last night on A Plane is Born on Discovery Wings. I didn't write down the tail number but maybe our British correspondent knows of it. It was Blue/White.

The "is Born" series of shows are fun to watch. The guy has built a plane, a helicopter, and a trike bike, rebuilt a Jaguar and couple of other bikes on the ones that I have seen.

Dave
N36078 '41 BC-12-65

[Dick]

Venturi

There was a belly mounted venturi on a Taylorcraft last night on A Plane is Born on Discovery Wings. I didn't write down the tail number but maybe our British correspondent knows of it. It was Blue/White.

My BC12D has the venturi mounted on the belly and in spite of the oil I have had no problems with it runing the directional gyro.