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I took this photo when I saw a plane make a crazy 90 degree turn. What kind of aircraft could do this? I have a plane finder app for commercial aircraft and this plane did not show, which is the first time that's happened.

plane making sharp turn

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    $\begingroup$ Do you have any idea how long it took from starting to ending the course change? $\endgroup$ – Peter Kämpf Feb 18 '15 at 8:20
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    $\begingroup$ Although the contrail looks quite unbroken, it is very possible that strong winds aloft have pushed the lower section (at about 270 degrees) into a more right angled appearance. Contrails often do not show the path an aircraft actually took. What makes you think that what you saw is "crazy"? $\endgroup$ – Simon Feb 18 '15 at 8:46
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    $\begingroup$ @Simon: This could even be two independent contrails, stopping rsp. beginning at the boundary of two air masses. Only the air mass on the left side would make contrails stable. $\endgroup$ – Peter Kämpf Feb 18 '15 at 14:44
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    $\begingroup$ The perspective can be misleading. The turn was not more than perhaps 50° and at least 50 km away, so it did not even have to be particularly sharp. $\endgroup$ – Jan Hudec Feb 18 '15 at 15:16
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    $\begingroup$ Not on PlaneFinder suggests military. I don't think it's low, and your perception of it passing behind a mountain is just perspective since contrails don't usually form below about 20K feet. In your photo, it appears much higher to me. 4 contrails would then suggest a military heavy, e.g. KC135. Civil jets tend to make shallow turns, typically 30 degrees of bank or less, mainly for passenger comfort, but a KC135 is capable of much higher rates of roll, and therefore much tighter turn radii. It may also have been a training manoeuvre. $\endgroup$ – Simon Feb 18 '15 at 19:14
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It looks like a 90 degree turn, but it isn't. You're not looking vertically up at it; you're looking at a fairly shallow inclination, maybe only 20 degrees elevation at the corner of the turn. It means that the actual course change is probably only about 20 or 30 degrees, and just looks like more because of the optical effect of foreshortening. As for the aircraft, pretty much anything capable of flight at high altitude - probably 30,000 to 40,000 feet - any jet airliner or many business jets.

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We looked at how tight a turn a Boeing 747 can make in this question. The answer gave a radius of just 6.11 km.

Your contrail photo clearly shows that the airplane has either one or two fuselage-mounted engines. The 747 was assumed to have a limit of 1.5g for the 6 km turn, but if the aircraft in your photo has a higher buffet and airframe limit, much tighter turns would be possible.

The turn radius $R$ can be determined when airspeed $v$ and bank angle $\Phi$ rsp. load factor $n_z$ are known: $$R = \frac{v^2}{g\cdot tan\Phi} = \frac{v^2}{g\cdot \sqrt{n_z^2-1}}$$

If your airplane was traveling at Mach 0.7 in FL300, its speed would have been 212 m/s. Let's further assume it could pull 3g at this speed and altitude, and your turn radius becomes 1.624 km or just about one mile.

It is very hard to judge the radius of the contrail's turn section, but it is quite easy to list the characteristics which help to make the radius small:

  • Low wing loading
  • enough thrust to sustain high load factors
  • enough strength to allow for high load factors
  • enough lift capability to allow for high load factors

One could add the capacity to fly high enough to be able to form contrails, but this is already implicitly contained in the other conditions. We need something with big wings and a powerful engine - a lightly loaded fighter aircraft in other words.

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    $\begingroup$ How can you tell from looking at the picture where the engines are located? $\endgroup$ – user7241 Feb 18 '15 at 18:42
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    $\begingroup$ @jjack: If the engines are under the wings, you will see two or four distinct contrails, especially when the contrail is fresh. $\endgroup$ – Peter Kämpf Feb 18 '15 at 18:57
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As we do not know which airplane were you observing and neither the airspace it was moving in, one possibility, aside for military aircrafts, it could be that it was an acrobatic one, maybe training on specific maneuvers.

enter image description here

Such a turn from a long distance could look like it is seen in the photo you posted.

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    $\begingroup$ Wouldn't it be strange that it flew perfectly straight for most of the time? With smoke on? $\endgroup$ – Peter Kämpf Feb 18 '15 at 9:14
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    $\begingroup$ @PeterKämpf 1. it can be contrail, why assume it is smoke? 2. if it is training, you prepare, concentrate and do the maneuver in the cleanest possible way, thus flying straight most of the time $\endgroup$ – Federico Feb 18 '15 at 12:45
  • $\begingroup$ The first part of the contrail disappeared seconds later, as my next photo didn't show its initial flight direction. I was on a board, on the ocean when I took the photos. The plane made the turn & flew over me & behind a mountain , which is 1700 feet. So it wouldn't have been flying much higher than that. $\endgroup$ – user7351 Feb 18 '15 at 15:25
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As Federico said, there is definitely a possibility of an acrobatic or stunt aeroplane, and the first thing that came to my mind when I saw this picture was an Extra 300S. The contrail looks to me like more of a smoke trail (Extra 300 series planes are usually equipped with smoke generators), as towards the beginning of the line the trail seems to be 'bunched up', or wavering. Also, a couple hundred feet (at best guess) from the turn, the line shifts, possibly as a result of wind shear and/or turbulence.

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    $\begingroup$ Unlikely to be a sport/aerobatic aircraft - it's a high altitude contrail. Sport/aerobatic aircraft are unlikely to have a ceiling that high, and would have no reason to have smoke turned on. $\endgroup$ – Anthony X Nov 15 '17 at 1:15

protected by ymb1 May 12 '18 at 12:07

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