# Why did the USAF keep the U2 and ditch the SR-71 Blackbird? **URL:** \ **Category:** Factual Questions\ **Created:** [October 6, 2001, 11:58pm UTC](https://boards.straightdope.com/t/why-did-the-usaf-keep-the-u2-and-ditch-the-sr-71-blackbird/85852 "2001-10-06T23:58:16Z")\ **Posts on this page:** 14\ **Page:** 2
**Author:** ![Popup](https://avatars.discourse-cdn.com/v4/letter/p/94ad74/32.png) [@Popup](https://boards.straightdope.com/u/Popup)\ **Post date:** [October 8, 2001, 7:45am UTC](https://boards.straightdope.com/t/why-did-the-usaf-keep-the-u2-and-ditch-the-sr-71-blackbird/85852/21 "2001-10-08T07:45:05Z")
> [@](#): > > \*Originally posted by Country Squire \* > **For the record, the SR-71 was a long-range strategic reconnaissance aircraft officially capable of flying at over Mach 3.2 and 85,000 feet, but insiders said it went faster and higher.** Is that true? Let’s for the moment ignore any current conflicts, and look at the speed records. I thought that the only one to have acieved **mach 3** was **Gillette**. According to [this site](http://hypertextbook.com/facts/AvivaLaurenti.shtml) the (airplane speed) record is still held by the SR-71: > [@](#): > > … an SR-71 set two world records for its class: an absolute speed record of 2,193.167 miles per hour If Mach1=741.4mph (as [this site](http://shahrazad.bd.psu.edu/Baxter/classes/phys215/215sept081997.html) claims), that works out as Mach 2.96. Beaten by a razor! 🙂 ---
**Author:** ![Santos\_L\_Halper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/santos_l_halper/32/1_2.png) [@Santos\_L\_Halper](https://boards.straightdope.com/u/Santos_L_Halper)\ **Post date:** [October 8, 2001, 8:29am UTC](https://boards.straightdope.com/t/why-did-the-usaf-keep-the-u2-and-ditch-the-sr-71-blackbird/85852/22 "2001-10-08T08:29:02Z")
The speed of sound isn’t a fixed number. It varies base on various factors, especially altitude. Here’s a site that can calculate it based on various factors: [http://aero.stanford.edu/StdAtm.html](http://aero.stanford.edu/StdAtm.html) Eric ---
**Author:** ![pulykamell](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pulykamell/32/3166_2.png) [@pulykamell](https://boards.straightdope.com/u/pulykamell)\ **Post date:** [October 8, 2001, 11:44am UTC](https://boards.straightdope.com/t/why-did-the-usaf-keep-the-u2-and-ditch-the-sr-71-blackbird/85852/23 "2001-10-08T11:44:38Z")
The speed of sound at 35,000 - 60,000 feet is about 660 miles per hour. (Speed of sound is dependent on temperature. Hence, higher altitude=lower temp=slower sound.) Calculating, we get Mach 3.23 for the world record, which is consistent with County Squire’s assertion. ---
**Author:** ![ElvisL1ves](https://avatars.discourse-cdn.com/v4/letter/e/5daacb/32.png) [@ElvisL1ves](https://boards.straightdope.com/u/ElvisL1ves)\ **Post date:** [October 8, 2001, 1:27pm UTC](https://boards.straightdope.com/t/why-did-the-usaf-keep-the-u2-and-ditch-the-sr-71-blackbird/85852/24 "2001-10-08T13:27:17Z")
In more comprehensible terms, the SR-71 the Smithsonian has set a record on its last flight by getting from Los Angeles to Washington in 64 minutes and 2 seconds. ---
**Author:** ![Popup](https://avatars.discourse-cdn.com/v4/letter/p/94ad74/32.png) [@Popup](https://boards.straightdope.com/u/Popup)\ **Post date:** [October 8, 2001, 1:55pm UTC](https://boards.straightdope.com/t/why-did-the-usaf-keep-the-u2-and-ditch-the-sr-71-blackbird/85852/25 "2001-10-08T13:55:59Z")
> [@](#): > > \*Originally posted by ElvisL1ves \* > \*\*In more comprehensible terms, the SR-71 the Smithsonian has set a record on its last flight by getting from Los Angeles to Washington in 64 minutes and 2 seconds. \*\* OK, that’s faster than my razor. Point taken. Hijack over. Now, back to the actual specs, economics and politic considerations of the OP. ---
**Author:** ![Enola\_Straight](https://avatars.discourse-cdn.com/v4/letter/e/dec6dc/32.png) [@Enola\_Straight](https://boards.straightdope.com/u/Enola_Straight)\ **Post date:** [October 8, 2001, 6:24pm UTC](https://boards.straightdope.com/t/why-did-the-usaf-keep-the-u2-and-ditch-the-sr-71-blackbird/85852/26 "2001-10-08T18:24:10Z")
Country Squire, I thought “Aurora”…aka “Darkstar” was a real plane. It would make sense: the SR-71 and the U-2 were both designed in the 50s and tested in the 60s, the stealth bomber and stealth fighter designed in the 70s and tested in the 80s. What are they designing and testing today? The Aurora/Darkstar was supposed to fly at mach3-5, using a hupersonic version of the pulse jet, first used by the Germans in WW2 in their V-1 buzz-bombs. The fuel would be some combination of liquid hydrogen and liquid methane. Also a form of external combustion technology would be used for propulsion. Instead of fuel being burned in a combustion chamber and blown out the jet nozzle, raw fuel would simply be squirted through the rear of the plane; the supersonic shock-wave and the plane’s fuselage becoming the rocket nozzle. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [October 8, 2001, 6:57pm UTC](https://boards.straightdope.com/t/why-did-the-usaf-keep-the-u2-and-ditch-the-sr-71-blackbird/85852/27 "2001-10-08T18:57:46Z")
> [@](#): > > \*Originally posted by Enola Straight \* > \*\*What are they designing and testing today? > > The Aurora/Darkstar was supposed to fly at mach3-5, using a hupersonic version of the pulse jet, first used by the Germans in WW2 in their V-1 buzz-bombs. The fuel would be some combination of liquid hydrogen and liquid methane. > > Also a form of external combustion technology would be used for propulsion.\*\* I saw some show on TV that showed video of a vapor trail left by some kind of plane. No one saw the plane but the vapor trail was very unique. Instead of just a straight line of vapor there were ‘balls’ of vapor along the line akin to a string with knots tied along its length. The show could only speculate what made those but their experts said that they would expect a pulse jet to create such a thing. Obviously not proof of anything but interesting nonetheless. I don’t know if it is real or not but it would I’d bet that they have _something_ up their sleeve. As an aside I didn’t think making engines to move planes quickly was a problem. I thought the real problem lied in the heat generated by flying so fast. As **Johnny L.A.** mentioned the SR-71 leaked like crazy while on the ground till external heat from friction sealed up the tanks. Pulse jets/RAM Jets/SCRAM jets/etc., are all well and good but you still have major friction problems unless you fly near or in space (at which point you’re probably better off with a cheaper satellite anyway). ---
**Author:** ![ski](https://avatars.discourse-cdn.com/v4/letter/s/bbe5ce/32.png) [@ski](https://boards.straightdope.com/u/ski)\ **Post date:** [October 8, 2001, 7:09pm UTC](https://boards.straightdope.com/t/why-did-the-usaf-keep-the-u2-and-ditch-the-sr-71-blackbird/85852/28 "2001-10-08T19:09:17Z")
**Enola Straight** - Aurora and Darkstar are most certainly NOT the same plane. But Darkstar IS most certainly a REAL plane, or rather, I guess, WAS a real plane (because the program’s been canceled). They were testing it for a while when I was at Edwards AFB. It was a stealthy UAV with a high-aspect wing with a top speed on the order of 150 knots, not Mach 3+. There used to be a large dark spot next to the runway where it crashed on takeoff. Too bad I missed that! We started calling Darkstar “Darkspot” or “Darksplat”. I have no information on the existence of Aurora. ---
**Author:** ![tsunamisurfer](https://avatars.discourse-cdn.com/v4/letter/t/a698b9/32.png) [@tsunamisurfer](https://boards.straightdope.com/u/tsunamisurfer)\ **Post date:** [October 8, 2001, 9:06pm UTC](https://boards.straightdope.com/t/why-did-the-usaf-keep-the-u2-and-ditch-the-sr-71-blackbird/85852/29 "2001-10-08T21:06:03Z")
> [@](#): > > **I saw some show on TV that showed video of a vapor trail left by some kind of plane. No one saw the plane but the vapor trail was very unique.** There have been numerous reported sightings of futuristic aircraft that supposedly emitted a strange pulsing sound and traveled at incredible velocity. One such sighting was from an oil rig on the North Sea sometime in the 1990s. Several workers claim to have seen something quite different from the SR-71/U2 and said it moved faster than they thought possible. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [October 8, 2001, 9:27pm UTC](https://boards.straightdope.com/t/why-did-the-usaf-keep-the-u2-and-ditch-the-sr-71-blackbird/85852/30 "2001-10-08T21:27:40Z")
> [@](#): > > Darkstar IS most certainly a REAL plane, or rather, I guess, WAS a real plane (because the program’s been canceled). They were testing it for a while when I was at Edwards AFB. It was a stealthy UAV with a high-aspect wing with a top speed on the order of 150 knots, not Mach 3+. [Information on Darkstar RQ-3A Tier III Minus](http://www.fas.org/irp/program/collect/darkstar.htm). ---
**Author:** ![geepee](https://avatars.discourse-cdn.com/v4/letter/g/ebca7d/32.png) [@geepee](https://boards.straightdope.com/u/geepee)\ **Post date:** [October 8, 2001, 10:13pm UTC](https://boards.straightdope.com/t/why-did-the-usaf-keep-the-u2-and-ditch-the-sr-71-blackbird/85852/31 "2001-10-08T22:13:02Z")
hey a Mig25R can do over Mach 3 , Eygpt used to use them to spy on Israel as it could out run any SAM system at the time oh and the U-2 probably could be defeated by the S-300 russian SAM these days ---
**Author:** ![robby](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robby/32/11048_2.png) [@robby](https://boards.straightdope.com/u/robby)\ **Post date:** [October 9, 2001, 12:29am UTC](https://boards.straightdope.com/t/why-did-the-usaf-keep-the-u2-and-ditch-the-sr-71-blackbird/85852/32 "2001-10-09T00:29:15Z")
> [@](#): > > \*Originally posted by geepee \* > hey a Mig25R can do over Mach 3 , Eygpt used to use them to spy on Israel as it could out run any SAM system at the time Cite, please? (I’ve never heard that the MiG-25 could go that fast.) ---
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [October 9, 2001, 12:49am UTC](https://boards.straightdope.com/t/why-did-the-usaf-keep-the-u2-and-ditch-the-sr-71-blackbird/85852/33 "2001-10-09T00:49:22Z")
I heard that the MIG-25 can do Mach 3 _ **once** _, after which it’s engines are burnt out. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [October 9, 2001, 12:50am UTC](https://boards.straightdope.com/t/why-did-the-usaf-keep-the-u2-and-ditch-the-sr-71-blackbird/85852/34 "2001-10-09T00:50:10Z")
> [@](#): > > Cite, please? I remember hearing about the MiG-25 when I was a kid, and distinctly remember hearing that it would do mach 3. But just to make sure, I entered the following into google: “mig-25” “foxbat” “performance” “mach”. I didn’t read the pages, but I could see from the search that maximum speeds quoted ranged from 2.35 to mach 3+. From what I remember the MiG-25 was extremely fast, but very heavy and handled poorly compared to U.S. aircraft. It was designed to combat the B-70, which never saw production. I’d say it was a huge waste of money on the part of the U.S.S.R. Still, it was quite the bogeyman until a pilot defected with one to Japan. [Previous page](https://boards.straightdope.com/t/why-did-the-usaf-keep-the-u2-and-ditch-the-sr-71-blackbird/85852.md?page=1)