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Old Mar 09, 2003, 09:19 AM
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Why don't we get vapor trails?


Why don't RC plane get vapor trails off the wing tips and other condensation like the big planes?
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Old Mar 09, 2003, 09:31 AM
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Vaspor trails are caused by the steam in jet exhaust condensing and form a cloud. The happens primarily at high altitude where the temp is sub-zero (or at least below freezing). Electrics lack the ability to put out a steam plume.

For the stuff you see forming off the wing tips and other surfaces, again, the air conditions must be right for condensation, and these bigger airplanes have huge wing loading compared to models. When they fly, they apply lots of pressure (both high and low) and energy to the air. These pressure changes cause the condensation, and our planes just don't have the energy it takes.
Old Mar 09, 2003, 09:34 AM
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It would be cool if we did!
Old Mar 09, 2003, 09:46 AM
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Typical tempuratures in the altitudes the jets operate are anywhere from -25 to -50 deg. C. VERY COLD. Condesation of jet exaust is instantaneous, but does require the right conditions. There are many days where there are no condesation trails left behind. As for the wingtip vortices one sees, they are generated by every aircraft. It is always neat to see an airshow, with lots of smoke,( ie the warbirds demos with explosions) and see all the types fly through the smoke. Wing tip vorices are almost always visible for a short time. If the wind were calm enough, and the smoke was there, one could fly a model through, and generate a small vortice that could be seen, all be it briefly.(seen it happen, and it was cool!)

Darryl
Old Mar 09, 2003, 09:56 AM
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So it's mainly the pressure for wing tip votecies then? This Sea Fury was low and it never really gets cold here.
Old Mar 09, 2003, 10:52 AM
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Lets see, in Australia wing tip vortices would rotate counter clockwise, so that can't be it.

Perhaps P- tube exhaust.
Old Mar 09, 2003, 12:17 PM
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Quote:
Originally posted by R2800
Lets see, in Australia wing tip vortices would rotate counter clockwise, so that can't be it.
Don't the vortices rotate up and over the wing then inwards, in opposite directions?
Old Mar 09, 2003, 12:28 PM
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Quote:
Originally posted by propfan
Don't the vortices rotate up and over the wing then inwards, in opposite directions?
.
Yup!
Old Mar 09, 2003, 12:44 PM
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Air temperature at 10.000 meter (cruising altitude for comersial airliners) and higher is -56 deg C
Old Mar 09, 2003, 12:50 PM
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Quote:
Originally posted by R2800
Lets see, in Australia wing tip vortices would rotate counter clockwise, so that can't be it.

Perhaps P- tube exhaust.

Errrrrrrrr,ummmm its a joke.
Old Mar 09, 2003, 02:28 PM
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I imagine that if the humidity were high enough and the model fast enough it would produce vapor trails. You can see vapor trails coming from the rear wings of Formula 1 cars on the right days.
Old Mar 09, 2003, 02:33 PM
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The way they taught us in aviation school, is that the aiflow not only travels fore to aft on a wing, but also in board to out board slightly, refered to as spanwise flow. When it gets to the wing tip, the flow comes off the bottom and around the tip, spiraling to the top. This creates the wing tip vortices. Every wing produces them, and they are worse the heavier the airplane is, and the slower the speeds. It is a very uncomfortable and sometimes dangerous situation to fly behind and in someone elses wing tip vortices. The problem is, you know they are there, but just cant see them(normally, the right atmospheric conditons must exist for them to appear, ie proper humidity, etc.) or when you fly through dense smoke. Wake turbulence is the common term when one does encounter this.

Darryl
Old Mar 09, 2003, 04:05 PM
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I'm talking about the wing tip contrails like on the Sea Fury.

There is great vortex action in teh movie Pearl Harbor wehn the planes fly out of the smoke.
Old Mar 09, 2003, 04:36 PM
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Quote:
Originally posted by R2800
Errrrrrrrr,ummmm its a joke.
Joke not detected. Restarting sense of humor.

There must be something other than humidity. I have flown (but not for long!) in the summer when the humidity is 100% or close to it and have never seen any interesting condensation.

I wonder if a propeller on an engine/motor running on the ground would do the same thing? (in the air it would probably be invisible) You could mess with the AOA and speed of the blades quite a bit. I'm not sure where exactly the trail would go but you should be able to see something at least.
Old Mar 09, 2003, 06:25 PM
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In reguard to condesation trails, read this:
http://www.madsci.org/posts/archives...7897.Ph.r.html

as for wake voritces, see this site,
http://nasaui.ited.uidaho.edu/nasasp...ic/thrust.html

Darryl,


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