PWDE Contrail?

Hi, just found this while surfing the web.

The photo of the vapor trail, taken Nov. 10 by amateur meteorologist Bill Telzerow from his backyard, shows a distinctive "doughnuts-on-a-rope" shape.

Link

Image

is this contrail produced by one of those PWD (Pulse Wave Detonation?) engines?

It's a possibility. However, because we can only see a small portion of it we can't say for sure. The stream falters a bit on the left-side portion, and we'd need to see a more consistent pattern throughout the majority of the stream to give answers more accurately, but as it is, I think it's a possibility.

Most PDWE engines fire at 100-200 Hz, which would run the donuts close together even on a very fast aircraft.

Compressor surges on normal jet engines can leave donuts, you can also watch donut shapes form out of straight contrails if the wind's blowing right.

thanks guys!

i wonder if anyone somewhere has a pic of another "donuts on a rope contrail" so we can compare.

Your wish is occasionally my command.




Panoramic of the same picture. You can see the donuts without a problem. The stream is straight, and the donuts are quite close together. The rope part is a bit harder to see, but it's there if you look for it.

hey thanks Darkpr0 & everyone else for your replies.
sorry i wasn't able to post earlier, still getting the hang of this.

This topic is also being covered in the Military and Government Projects section.

While I usually get tired of those on this board who simply state "it is a PDE/scramjet/magic-carpet engine" with little to back them up, aside from a handful of pictures of some contrails blowing in the breeze. However, in this case it is not totally out of the realm of possibility. The Air Force Research Lab Propulsion Directorate (AFRL/PR) is HQ'd at WPAFB in Dayton, and they have been at the forefront of U.S. based PDE/PDC research from the beginning. The AFRL/PR also contracts out with some local technology firms, most notably ISSI (www.innssi.com...), which just happens to be located in Beavercreek, OH (Dayton suburb mentioned in article). I am unaware of any planned flights of their little 'PDE-dragster' as they call it, but I haven't been there for a year now and could easily have missed any announcements.
I highly doubt it's anything top-secret, since it was carried out during the day over a heavily populated area, instead of at night over a lake-bed out west. In any event, PDE's are by no means top-secret. There has been an enormous amount of white-world research done on them. Most of it is focused on replacing conventional constant-pressure combustors with pulse-detonation based pressure rise combustors. The idea being that a constant-volume process (PD-based) is inherently more efficient than a constant-pressure process (conventional). One of the primary concerns has been high-amplitude unsteady loads on a disk spinning at many thousands of rpm's in an environment well in excess of 2000F.
One mistake people tend to make when looking at these contrails is they immediately say the 'donuts' are too tightly or loosely spaced. Most PDE experiments being conducted these days are multitube experiments (those outside of the basic combustion phenomenon research done within the lab). Certainly any setup providing enough thrust (even a fraction of 'enough' thrust) would be a multi-tube setup. So if you don't know what tube setup was flying, trying to back-calculate the firing frequency is pointless. Sometimes they fire simultaneously and sometimes in sequence. The research community has not come to a consensus on what setup (if either) is best for whatever application.
All this being said, I too doubt it was a flying PDE test, simply on the fact that (to my knowledge) PDE's have not proven themselves all that reliable of a propulsion system, and as a result I would think any flight test would be conducted in the safe confines of Edwards AFB, not over a metro-area of a quarter-million people. Sadly, I do not have a counter-offer of what the apparent 'donuts' might be. The easy answer is 'some sort of aerodynamic phenomenon', but that's not really an answer at all, without being more specific. I'll have to defer to someone else's fluid mechanics knowledge on that.