U2

[Tom_D]

I was at the Beal Air Force Base open house and air show (http://www.beale.af.mil/2009bealeairshow/index.asp) yesterday and fascinated by the U2.

This photo is of a U2 at 70,000 feet flying just above stall speed at about 500 mph. (Sigma 50-500, 500mm, f/8, 1/600)

http://gallery.thomasdowdphotography.com/img/v5/p587431806-3.jpg

There was another U2 on display and we got to see the one in the photo above take off and land.

More U2 photos from yesterday are here. (http://gallery.thomasdowdphotography.com/2009/beal/u2)

[bazzaboeing]

Unless there are two U2s flying in close formation or they have found a way of attaching the engine/engines on to the wings now, this is not a shot of a U2. The U2 has only one center mounted engine.

Cheers Bazza

[FlyingPhotog]

I dunno if it is or if it ain't but...
How long did it take to get to FL700?

Hope you packed a lunch and dinner to consume while waiting... ;)

[Tom_D]

This was at the Beal AFB air show. Beal is the home of the 9th Reconnaissance Wing and flying the U2 is what they do.

The U2 took off at about 11:00, the fly over was at noon and the plane landed at 1:00. The photos are here (http://gallery.thomasdowdphotography.com/2009/beal/u2). The fly over sequence starts with the plane taxiing by, taking off, fly over and then landing.

There was lots of commentary as all this was going on and especially during the fly over. A big deal was made of the U2 flying at just above the stall speed for that altitude - about 500 mph.

My guess is that if the U2 as a mater of course left a trail like that all the time the usefulness of the plane would be diminished and they (the Air Force) did something to make it visible for the air show.

I am not a plane person. You point to the sky and say, "Look, there goes a U2" and I'm not going to argue with you. There were LOTS of folks at the air show, many of who know all about these planes and a few that had flown them all. I guess they could all be in on the scam but I would rather believe that it was a U2, THE U2 we saw take off and land, and continue to be impressed with the plane.

[PGAero]

A couple of things... Nice shot of the U2 with the Sutter Buttes in the background. Nice composition.

When I was last at Beal (close to 20 years ago) the U2s landed with chase cars to catch the wings. is that still the case? Are those out-riggers permanent, or just for taking off?

Next, engines don't make the vapor trails, do they? It's the disturbance of the air caused by the wings (2 of them) that cause the vapor to condense out of the air and show up as white. Although engines can lead to this disturbance, they are not required, right?

[PGAero]

One more thing. Stall speed would mean that the wing is using as much pressure differential as possible, which would make vapor trails very likely. I suspect that at higher speeds, the flaps can be "flattened" and the plane can go a bit more inconspicuously. Can anyone confirm or dispute this?

[Ruakituri]

PG Aero, totally correct in everything you say, engines have minimal affect with regard to creation of contrails. Also the more flap, the greater air disturbance, therefore better vapourtrails....

[Tom_D]

Thanks for the comments.

They still use chase cars when the U2 lands but not so much to catch the wings but to guide the pilot in. They were explaining it all as I was try to get photos so I missed a bit of it but one of the statements was that the pressure suit/space suit "reduces IQ by 20 points" and the limited visibility out of the plane and helmet make the chase cars a help in the pilot knowing where he is.

There is now a skid plate on the end of the wings but they made a point of mentioning how long the plane taxied without the wings touching the ground.

The chase cars also pick up the wheels when they fall off at takeoff.

I like your theory about the low speed causing the vapor trails. The made a big deal out of the high stall speed at 70,000 feet and that the plane was barely above it. That may have been what they were doing to make the plane visible.

Thanks again for your comments and I hope someone who knows this plane a bit better can answer more of your questions.

[FlyingPhotog]

A couple of things... Nice shot of the U2 with the Sutter Buttes in the background. Nice composition.

When I was last at Beal (close to 20 years ago) the U2s landed with chase cars to catch the wings. is that still the case? Are those out-riggers permanent, or just for taking off?

Next, engines don't make the vapor trails, do they? It's the disturbance of the air caused by the wings (2 of them) that cause the vapor to condense out of the air and show up as white. Although engines can lead to this disturbance, they are not required, right?

It's almost entirely dependant upon meterological conditions...predominantly moisture and temperture.

In WWII, one of the most important functions of the "Weather Shack" was determining where the contrail level was and how to avoid it. B-17s and B-24s were totally capable of leaving enormous contrails and yes, it was as much due to the engines and their exhaust as anything else.

Remember that a jet engine basically works via the four-step process of:
Suck
Squeeze
Bang
Blow

AFAIK, the key is "Squeeze" and how it relates to Temp/Dew Point spreads. The closer the spread, the more chance of making contrails.

[Moppie]

Don't forget that one of the by products of combustion is water.
And there is LOTs of combustion going on in a jet engine :)

[kilr95ss]

Not a plane expert either, but just looking at Bazza's avatar of the single engine F16 with a contrail off of both wings, why couldnt this be a U2.

[ChunkyDA]

At that altitude, the contrails would be produced from the engine(s). Pretty good information and pictures here: http://www.mdbsite.com/skies/contrails/intro.htm
And other photos here:
http://photography-on-the.net/forum/showpost.php?p=6955402&postcount=1
http://photography-on-the.net/forum/showpost.php?p=4889480&postcount=1


The F-16 in Bazza's avatar pulls the vapor from the air not by burning but by reducing the pressure in high speed, high-G flight. There are planty of cool examples of this type on POTN, fighters and the prop-tip corkscrews make some really dramatic images. More so at the warm, humid airports or during or after a rainshower.
http://photography-on-the.net/forum/showthread.php?t=590340

Perhaps Tom_D could pixel peep for us.:D

[Jeff]

It's all about squeezing water out of the air. Engines, wings, props, high G turns, etc can all do it given the right conditions. You can see it from the shuttle once its gliding in the atmosphere.

[jungle]

Nice shot, but it isn't a U2, more likely an airliner. A U2 would leave a single contrail from it's engine, but not likely at 70,000 feet.

All jet and piston engines will produce a contrail from the exit of water produced by combustion in subfreezing air. The typical temperature aloft for contrail formation is around minus 50 degrees C, but relative humidity aloft also plays a role.

This is different than condensation or vapor trails caused by high lift on wings, prop blades or other surfaces at low altitude. High differential pressure tends to condense water out of the atmosphere in the low pressure region.

As an aircraft climbs into the very high levels the engine contrail may be much less apparent because the ice or frozen water vapor sublimates rapidly at extremely low humidity.

" Schmidt in Germany (1941) and Appleman in the United States (1953) independently developed the currently accepted theory of contrail formation. Their theory showed that the threshold temperature depended on the ambient pressure, temperature and humidity outside of the aircraft, and on the ratio of water vapor and heat released into the atmosphere by the aircraft exhaust. From this theory, Appleman developed a graphical method to determine when an aircraft would or would not form a contrail. Until recently, this graphical technique formed the basis of the contrail-forecasting algorithm used by the United States Air Force. "

A more complex predictive algorithm is now used.

See also:http://en.wikipedia.org/wiki/Contrail

Short article on flying the U2:http://67rts.org/flightofthedragonlady.htm