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An aircraft at high altitude passed by faster and higher than normal, about 50% faster when compared to others in this recording. 2 mins later it appeared that half of the contrail developed right angle pulses evenly spaced along the contrail. It took about 7 minutes to clear. Is this normal? I have complete video. 2 pics attached.

Pulses begin to appear

Aircraft passing

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    $\begingroup$ A contrail is a cloud-like stream behind a high altitude jet aircraft, a con trail is what police dogs follow to capture an escaped prisoner. $\endgroup$ Jul 17 at 15:13
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    $\begingroup$ But... What if the prisoner has hijacked a high altitude jet? Eh? Think about that one? Ha! $\endgroup$
    – John K
    Jul 17 at 16:24
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    $\begingroup$ I know I know, High Altitude Jet Tracking Dogs... $\endgroup$
    – John K
    Jul 17 at 16:25
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    $\begingroup$ Clearly one of the mind-control-chemical sprayers had a partially clogged nozzle. 😎 $\endgroup$ Jul 17 at 17:00
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    $\begingroup$ it's the lizard people sending coded messages $\endgroup$
    – RedSonja
    Jul 18 at 6:55

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This phenomenon--which is not all uncommon-- is 100% meteorological. On a day when conditions favor this, you'll notice this happening in most or all of the contrails visible, or at least in most or all of the contrails in a given altitude range.

You shouldn't assume that just because the phenomenon appears to involve only one side of the contrail, that one of the (presumably two total) engines is operating differently than the other. If there is a wind shear, then parts of the contrail that ascend or descend will also move laterally relative to the main body of the contrail. In the photo, the "puffs" appear to be descending relative to the main body of the contrail. I believe I've also seen cases where the puffs appeared to be ascending, but would have to check old notes or photos to be sure.

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    $\begingroup$ Sounds reasonable, but how do you know this? $\endgroup$
    – 757toga
    Jul 17 at 18:22
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    $\begingroup$ Inferred due to fact that on days when it happens, it appears to involve nearly all the contrails that are visible. $\endgroup$ Jul 17 at 18:25
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In 1992, Aviation Week reported on sightings of unusual contrails which were called "donuts on a rope" because they had evenly spaced puffs along a central line. The article speculated that they are the result of a "pulsed detonation wave engine", a propulsion technology which offers high efficiency at hypersonic speed.

Since then, there have been many sightings of such contrails and in many cases they were caused by conventional airplanes. The "donuts on a rope" speculation has been discredited as exactly this.

If you google for "donuts on a rope", you will find many more pictures and sometimes even a breathless comment that someone has spotted the airplane behind the black "Aurora" program. However, I am at a loss to explain how those contrails are made.

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  • $\begingroup$ @RobertDiGiovanni I prefer not to engage in speculation because I have no detail knowledge here. $\endgroup$ Jul 19 at 7:56
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    $\begingroup$ Good references, thanks. $\endgroup$ Jul 19 at 9:28
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Contrails are the same as the steam that comes out of you car's exhaust on a cold morning. It's condensed or crystallized water as a byproduct of burning gasoline or kerosene.

Therefore, I would say it's some kind of fuel control or airflow issue with one of the engines. The contrails are ice crystals from moisture in the engine exhaust. Certain temperatures and exhaust moisture levels will produce the contrail - drop below a threshold, and the contrail stops.

The puffs suggest that one of the engines has some oscillation in fuel flow or mass airflow, and the oscillation is taking the moisture level in the exhaust above and below the contrail formation threshold with each cycle. It may or may not be noticeable to the crew, and may not even be a problem, as in engine malfunction, just a phenomenon that occurs when conditions hit a sweet spot.

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    $\begingroup$ Took the words righ out of my keyboard. $\endgroup$
    – Jpe61
    Jul 19 at 11:43
  • $\begingroup$ It’s quite possible that this kind of ‘standing wave’ or more accurately resonant airflow isn’t established until some distance behind the aircraft and so would be undetectable on the aircraft (and unlikely to be observed in a wind tunnel). $\endgroup$
    – Frog
    Jul 22 at 22:05
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I’m going to speculate that the hot exhaust gases quickly cool and the water content freezes into small ice crystals. Steam turning into ice contracts significantly and so clumps of water vapour may be pulled together into blobs that are visible from the ground, under certain conditions. Under other conditions the ice crystals may remain more or less amorphous, although I can’t immediately say what conditions would favour the one over the other.

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  • $\begingroup$ This is very plausible. $\endgroup$
    – Jpe61
    Jul 22 at 11:57
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Looking at the exhaust of the high supersonic turbo/ram Pratt&Whitney J58 jet engine we can see definite shockwave pressure pulse "diamonds" in the exhaust stream, which under the right conditions, may cause pulsed contrails (variable pressure is more favorable to form a "doughnut").

We can rule out a high bypass turbo fan as it would leave behind a better mixed "swirl". So, we may have a lower bypass military jet here, perhaps in afterburner, especially based on the "higher, faster" observation.

A pulse detonation engine is a candidate to produce this type of contrail, but may not be the only doughnut maker out there.

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  • $\begingroup$ A busy airways goes over my summer cottage. I can assure you this phenomenon happens on your garden variety high bypass jet engines also. $\endgroup$
    – Jpe61
    Jul 19 at 11:41
  • $\begingroup$ @jpe61 the second photo, yes, the first one that looks like a millipede, not as common. I'm still going with an afterburner run, especially since it took so long to dissipate. $\endgroup$ Jul 19 at 15:15
  • $\begingroup$ As for the mach diamonds: they are stationary w/r to the plane, how can they leave a pulsed contrail (maybe provide source)? $\endgroup$
    – Jpe61
    Jul 19 at 16:53
  • $\begingroup$ @jpe61 the diamonds may leave a trail of variable pressure behind them, while a hi bypass fan may leave a stable vortex. In a high dew point atmosphere + the water from combustion it seems the lower bypass (especially with afterburner) has more of a chance to "doughnut". Also evident is the robustness of the contrail and the "higher and faster" observation. What would be really interesting is to study any contributions from the airframe to contrails, subsonicly or supersonicly. $\endgroup$ Jul 19 at 17:51

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