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#1
09-08-2006, 03:55 AM
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Bridge effect
Ken posted a picture of a bridge in my "crops changing colors" thread and got me to thinking.
We all know that ground effect makes our gyrocopters...or any aircraft more efficient due to less drag. What would happen if you were flying just under a high bridge...being in a new term I am inventing..."bridge effect"? I would think that the gryocopter or airplane would not get as much lift due to the air being restricted before it gets downwashed. I am talking about flying just under a flat ceiling of a bridge that is high enough to be out of ground effect. Any aeronautical experts want to liven up the forum with their input on this topic? Stan with a downwashed mind.... 
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PPSEL airplane/helicopter Helicopters turn air into their runway. Got kerosene? www.stansstairways.com 
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#2
09-08-2006, 04:45 AM
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Is this all you have to think about at 3:45?
The wife must be out of town.
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David G. Holmes, Brundidge, Alabama THE MOST IMPORTANT THING IS THAT WE BE READY TO MEET OUR MAKER ANYTIME!
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#3
09-08-2006, 05:45 AM
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Stan, I'll steal one of Chuck Beaty's favorite images. When you block off the hose of a vacuum cleaner with your palm, the motor speeds up. Without a supply of air to accelerate, the motor isn't working hard anymore and unloads.
A rotor or prop works the same way. It acts continually upon a fresh supply of air, accelerating the molecules and spitting them out. The lift or thrust is the recoil from this process, just like a gun recoil. If the rotor or prop's air supply is cut off, it won't do its work, just as the vacuum cleaner doesn't. So, in theory, flying right under a large ceiling will reduce lift, in that the rotor cannot "breathe" air from above. In fact, a great deal of the air acted upon by a gyro rotor in forward flight comes from in front/below rather than from above, so I doubt that the effect would be that strong. It would be more noticeable in a hovering helo, with its straight-down flow.
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#4
09-08-2006, 07:57 AM
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Say WHAT??????
I know this or any question is food for thought,
It Seems like every time someone gets to flying REALLY WELL.... they go to "THINKIN" way way "TOO MUCH" Hey,,,,, "FLY THE DAMNED THING" MURPHY is workin on all of us.... and he can and will bite Ya square in the ass.. I ONLY say this because " I've Been There, Done That.." YALL Watch Ya selves steve Last edited by Steve McGowan; 09-08-2006 at 08:00 AM.
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#5
09-08-2006, 08:30 AM
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I agree with Doug
limiting the air above the rotor will affect its ability to feed the upwash, downwash and subsequent pressure less pressure is less lift this regardless of whats happening below the suction side has a more powerfull effect that pressure side
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I couldnt believe it, this frisbee seemed to be hanging in the air and was getting bigger.........then it hit me... Last edited by Ga6riel; 09-08-2006 at 08:34 AM.
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#6
09-08-2006, 09:26 AM
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Oops,
 I was lead to believe the drag benefits gained "in ground effect " were from disruption of tip vortices,which would work above or below a wing.
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best to be silent and thought a fool than to open my mouth and remove all doubt James PRA member#40152
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#7
09-08-2006, 10:15 AM
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You have been taught correctly James. I have been waiting for someone other than me to see and correct this. 1/2 the length of the wing will allow the wing to compress the air between the wing (rotor) and the ground.(Ground effect)
Thom
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Thom  I think I am addicted to gyros. I fly a RAF N5127C Sonerai IILT N 42HL AOPA member PRA Chapter 6 Last edited by dragonflyerthom; 09-08-2006 at 10:36 AM.
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#8
09-08-2006, 10:37 AM
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I have to agree with Steve. If pilot's didn't think, you wouldn't need controllers to sort out the mess.
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Cody McCormick **************** I often question my sanity. It never answers.
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#9
09-08-2006, 11:14 AM
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...and if you have AIG insurance, make sure Cody doesn't catch you testing this hypothesis!
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#11
09-08-2006, 12:14 PM
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Paul, I have eyes and spys everywhere!! Pilots and bikers have one thing in common: They like having pictures of themselves doing dumb things so they can post them on the internet.
James, I was nice. Well, to the guys with guns. AH-64s and A-10s don't like to hold.
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Cody McCormick **************** I often question my sanity. It never answers. Last edited by Cobra Doc; 09-08-2006 at 12:24 PM.
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#12
09-08-2006, 12:18 PM
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when you go under the bridge close your mouth. bugs will fly in to it. and they tast really bad.
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#13
09-08-2006, 12:48 PM
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Thom, James: If your method of reducing vortex action still allows the lifting surface to draw in UNaccelerated air from the appropriate direction, then, yes, blocking off the vortices is good. "Appropriate direction" in the case of a lifting device is from ahead and above, since the net flow must be down-and-back in order to make lift.
A vertical vortex "fence" such as the typical winglet or wing cuff still allows the wing to receive air from ahead and above. The ground does, too. OTOH, if the blockage is a horizontal plane above the wing (i.e. on the low-pressure side of the lifting surface), its air supply will be disrupted.
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#14
09-08-2006, 12:55 PM
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 Time to say I agree. Sure wouldn't want to be sucked up into the bridge Thom
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Thom I think I am addicted to gyros. I fly a RAF N5127C Sonerai IILT N 42HL AOPA member PRA Chapter 6
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