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Why does the Lockheed Martin U-2 spy plane need a car behind it during landing? Is that to help the pilot in case of excursion off the runway?

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    $\begingroup$ From L.A. Times: “U-2 pilots drive the chase cars and assist the landing pilots through radio calls.” Also: popularmechanics.com/military/a7818/… : “We rode along with the pilots who hop in muscle cars to tail a U-2 during the landing, radioing the spy plane's pilot to guide him or her through the delicate operation.” $\endgroup$ – PerlDuck Jan 8 '17 at 15:37
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    $\begingroup$ There are a number of videos on YouTube from inside U-2 chase cars. They're pretty fun to watch and will give you an idea of what they do. $\endgroup$ – Zach Lipton Jan 8 '17 at 20:02
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It is to help the pilot land the aircraft (the chase cars are also used during takeoff). The U2 is considered notoriously difficult to fly in low altitudes- a tradeoff in an aircraft optimized for very high altitude flight:

Because the U-2 was so specialized, it was amazingly difficult to fly. ... the lower the U-2 flew, the heavier its unassisted controls got, to the point where pilots literally had to brute-force the plane around during take-off and landing.

... landings were the biggest problem. The replacement for Johnson's cart-and-skid ground system was a compact setup — two centrally located landing gear in the fuselage and one detachable "pogo" gear on each wing — that turned the U-2 into little more than a 30,000-pound bicycle. Because of the high-lift wings, pilots didn't so much land the plane as fly it really close to the ground (usually about two feet), stall it, and then fall out of the sky.

The decreased visibility of the pilots, combined with the highly efficient wings and bicycle landing gear meant that unassisted landings are difficult (but certainly possible, as has been demonstrated)- thus the chase cars.

On of the chase car drivers (themselves U2 pilots) describes the drill:

... the objective is ensuring that the pilot safely landing the aircraft... calling him down to two feet... holding them off there and then the plane will just kind of settle down on the ground.

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    $\begingroup$ Note that the wing gears are only for takeoff - landing is done as a bicycle, falling over on the titanium wingtips at the end. $\endgroup$ – Sanchises Jan 8 '17 at 20:39
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    $\begingroup$ Does the U2 not have a radar altimeter? $\endgroup$ – TomMcW Jan 8 '17 at 20:43
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    $\begingroup$ @TomMcW: It wouldn't surprise me. a) it was designed in 1953, b) the underside of a spy plane is prime real estate. If you can squeeze an additional camera, a larger sensor, a larger lense in by getting rid of an instrument that is only used for about 10 seconds on every flight, you will, c) it's essentially a glider, weight is a prime factor, again, the radar altimeter would only be used for a couple of seconds, and the chase car solution works just fine. Remember: this is a plane that even throws away its landing gear! (The original design actually took off from a sled and landed on its … $\endgroup$ – Jörg W Mittag Jan 8 '17 at 22:51
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    $\begingroup$ … belly, it didn't even have the bicycle gear of the production version.) $\endgroup$ – Jörg W Mittag Jan 8 '17 at 22:51
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    $\begingroup$ "pilots didn't so much land the plane as fly it really close to the ground (usually about two feet), stall it, and then fall out of the sky." This is exactly how gliders land. Fly half a meter from the ground and then stall it. Of course, gliders fly somewhat slower and are somewhat lighter. But for a further glider comparison, it would be interesting to know when you are fully committed to landing the U2. I guess aborting the landing and making a go-around is not really easy with a U2. Landing as a bicycle and then falling over on the wingtip is also typical for gliders. :) $\endgroup$ – vsz Jan 8 '17 at 23:54

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