Due to the ultra-rarified altitude of the U-2 spyplane, there is only appox. ten knot difference between stall-out and mach1…at which point the wings would get ripped off.
Is it possible to make a U-2 with swept back wings?
My WAG:
Lower-altitude performance would suffer too much.
I suppose you could then look at a swing-wing, but that is such a massive modification and you might as well design a new aircraft.
Besides, being able to break Mach 1 and a little over isn’t going to really give much of a benfit anyhow. To go appreciably faster, say 2+ you’d need a whole different aircraft (Such as the A-12/SR-71). The Dragonlady has done her job quite well being that is about 40 years old 
BTW - There is more required for supersonic flight than just the wings for the shockwave
Can you give a reference for where you read this ES? I would have been under the impression that the corner of the flight envelope at those conditions would have involved not Mach 1 but rather critical Mach for the airplane. Critical mach is that airspeed where shock waves start to develop on the airframe, usually first on the wings and would probably involve loss of lift and/or control problems before structural failure. But I’ve been wrong before.
The phenomenon of getting “cozy” in the upper right hand corner of the flight envelope is common to a lot of sub-sonic, high-flying aircraft. Your average airliner at FL 410 (41,000 feet or so) is doing the same thing.
While I have you all here…
Why did they drop the SR-71 and keep the U-2?
Remember that from the program “Wings” on the Discovery Channel.
Sorry, can’t cite, but I saw a news program the other day and they said the SR71 didn’t have the range of the U2 and was much pickier about takeoff & landing locations to the point that it almost always landed & took off in the US. It also required a big support effort with the mid-air refueling needs, etc.
The U2, on the other hand, was able to take-off and land in much rougher conditions making it a good choice for deployment in many different areas. Electronically, the U2 has been kept up-to-date, too.
Costs were the real biggie.
from a still active thread: http://boards.straightdope.com/sdmb/showthread.php?threadid=164316
The U2 doesn’t require nearly as much specialized support as the SR did, and hence a whole lot cheaper to operate.
In the end, the USAF just didn’t really have a need for the SR. The U2 in conjunction with Satellites are very effective.
I think that they have another plane that is much more stealthy, faster, and rugged than the SR-71. The plane just disappeared “too easily.” What about those rumors of the aurora project, blue prjects, and miscellaneous documented sonic booms over california that people talk about every once in a while?
I will dig up some sites and get back
Here is one link, I am naturally suspicious of anything on the internet, but I think these guys have their heads, more or less, in the center of their shoulders
Given those two answers, maybe the SR-71 has been secretly replaced but the U-2 was too cheap, versitle and easy to not keep around.
Cool. Thanks.
Can we have a cite that the U-2 is still used for its initial purpose (that is to say, spying)? I know that NASA has one or two that they use for atmospheric research (the ozone layer comes to mind), but does the CIA or any other intelligence agency still use them?
I think that the U-2 is useful as a beard – a convenient excuse to explain intelligence that some other asset truly delivered. Not that it doesn’t return some good info on it’s own, but I think it is more redundant than essential.
They are going to overfly Iraq for weapons checks.
Not exactly. Be it a U-2 or a Predator, the benefit of a “spy plane” is the unpredictability. Satellites follow a fairly regular pattern. Just as we generally know where the “bad guy’s” satellites are, they know our patterns as well. A spy plane can not be predicted.
And for the sake of argument, when it comes to intelligence, redundancy, IMO, is absolutely essential when possible. If a second and closer look can help confirm something good and/or prevent a disaster, how is that really a bad thing?
I just noticed that the Global Hawk unmanned aircraft has very similar specs to the U2 - i.e. they are both subsonic aircraft designed for >65,000 ft altitude reconnaissance flights. So there must still be a big demand for this type of flight.
And I believe that NASA still gets to fly a couple of SR-71’s as research vehicles. They don’t have to bear the burden of worldwide infrastructure that has been mentioned pointedly above.
Nasa only has 2 SR-71s and they are flown quite rarely. They don’t go out on 3000 mile spy flights, either. Regardless, the pair of them require far less infrastructure than a wing of them. I don’t even know if Nasa has any KC-135Qs.
When the SR’s were re-activated in 94, the DoD had to re-aquire large amounts of certain items just to make them flight worthy again. 3M and Dow chemical just wouldn’t make enough of a particular item for say, 1 years worth of usage for 4 airframes so they had to do full production runs for several of the items. The fuel sealent alone was a biggie. It took over $1,000,000 just to buy that product alone. Result: Nasa has enough of most of the rarer items to keep their 2 aircraft flying for a while.
Regardless, they are still a very expensive aircraft to maintain and fly. Even for Nasa.
From what I understand, an SR-71 fuel tanks are sealed up tight only when the air friction of Mach3+ velocities heat up the fuselage enough for thermal expansion to tighten things up.
A cold SR-71 sitting on the tarmac leaks fuel like a sieve.