View Full Version : Bridge effect
09-08-2006, 03:55 AM
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....:der:
09-08-2006, 04:45 AM
The wife must be out of town.
09-08-2006, 05:45 AM
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.
09-08-2006, 07:57 AM
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
09-08-2006, 08:30 AM
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
09-08-2006, 09:26 AM
Oops,:suspicious: 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.
09-08-2006, 10:15 AM
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)
09-08-2006, 10:37 AM
I have to agree with Steve. If pilot's didn't think, you wouldn't need controllers to sort out the mess.
09-08-2006, 11:14 AM
...and if you have AIG insurance, make sure Cody doesn't catch you testing this hypothesis!
09-08-2006, 11:57 AM
Yea go me
HEY CODY I even know some nice controllers:p
09-08-2006, 12:14 PM
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.
09-08-2006, 12:18 PM
when you go under the bridge close your mouth. bugs will fly in to it. and they tast really bad.
09-08-2006, 12:48 PM
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.
09-08-2006, 12:55 PM
:party: Time to say I agree. Sure wouldn't want to be sucked up into the bridge:help:
09-08-2006, 03:40 PM
yea but who warned the air we were coming ?:lol:
Cody's spies I bet:spy:
09-08-2006, 04:31 PM
09-08-2006, 06:02 PM
Aha! It has nothing to do with aerodynamics. Bridges just reach down and smack flying things!
09-09-2006, 02:37 AM
I have to agree with Cody! I think it's more Murphy than Aerodynamic...
As to the 'suction/vacuum' thing, I'm guessing this would only apply if there is no other source of airflow (such as in a tube), otherwise it seems your rotor blades would have to be awfully close (and parallel) to the bottom of the bridge.
I'm new to Gyro's (all fixed wing experience), and I have a question about Ga6riel's statement, "the suction side has a more powerfull effect that pressure side". Can someone explain this to me? I know much in aerodynamics is counter-intuitive, and I can't seem to wrap my head around this one.
09-09-2006, 12:02 PM
The following sites shall remain nameless...
Many years ago when I was into gyros for a few years...there was a WIDE river and several bridges spanning that river. There was quite a bit of river traffic, with some large and tall craft traversing the waterway.
Dependent on the normal water level, before the spring floods, I would guess the bridge height above the water to be 90 ft. plus.
I did fly under a bridge or two and I can't recall any anomaly whatsoever. I did fly about 10-20 ft. above the water level. Didn't want to get any higher.
09-09-2006, 05:49 PM
Anthony, I'm not sure I entirely agree with Ga6riel's statment. I think they have to more or less be equal. As for the bridge thing, I don't think the disk angle on a gyro is conducive to trying out the vaccuum theory. Now if somebody has a theory about the ability fo carbide rotortips to carve concrete... Never mind, that's a silly idea.
Luc De Keyser
09-10-2006, 11:18 AM
whatever we think it should if we were air ourselves ...
A few things come to mind when mulling about the "ceiling effect" vs "ground effect":
1. You can blow out a candle but not suck it out ...
2. ground effect is not about more pressure below, but altered air flow, mimicking longer and wider wings/rotors (different from extreme ground effect)
3. air does not "like" to go around sharp edges
I would bet ceiling effect is much less than ground effect ...
Anybody with a wind tunnel and a moving ceiling?
09-10-2006, 12:36 PM
1. I have a mustache, I won't even try that one.
2. What ever ground effect does exactly, the recent Kentucky crash is the first time ground-effect has been a contributing factor.
3. If anyone has one of those goofy r/c flying ring things, this should be easy to test: fly it near the ceiling. Not sure where sharp edges come in to the equation.
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