Lockheed Polecat has 2 engines, but I thought that it had been shelved...

http://www.flightglobal.com/assets/g...x?ItemID=13837

Twin engine contrails so all the single engine drones are out.

No they aren't. Contrails are formed by wingtip vortices, not a function of number of engines.

My money is on an X47B

Condensation trails can be caused either by pressure reduction, for example in wing tip vortices or by engine exhausts.

If you ever saw a Buccaneer flying a blown overshoot on a damp day, you'd see a plethora of such pressure reduction trails.

Contrails formed by pressure drop are short lived. Trails formed by engine exhaust are usually longer lived, depending on atmospheric conditions. The ones in the photo are definitely exhaust generated.

Vapor trails that are formed by wingtip vortices never persist because the low pressure area disappears as the vortex quickly dies, whereas those formed by engines persist because of the water vapor added by the combustion process in the engines. Index finger to glasses, glasses adjust...

DITY, if we're talking about high level contrails, they are caused by the jet exhaust, specifically the water content, being mixed by wingtip vortices. Hempy, if you were to take another picture 30 secs later you'd see two contrails. Beagle, what you say about pressure drop is true but doesn't much help identify our mystery machine; we're talking tens of thousands of feet over Texas not Honington on a drizzly morning.

Shot- you would either have to have the jet under G or have lift devices deployed for what you are referring to and as has been mentioned are short lived and are not present at the altitudes this aircraft was flying. The photo shows engine contrails emitting from the aircraft. What the vortices do afterwards is irrelevant.

Doncha just love amateur hour

Read my post in the context of the question being answered, Bob. It's simply not possible to state how many engines this aircraft had just by looking at the contrail.

Jet engines eh?

So all those Flying Fortresses I saw during the war were running on jets after all.

So the USA invented the jet engine and flew it before Germany or GB?

Real education this thread.

I think they scrapped all the X/YB-35s...

So all this is telling me is high altitude stealth is a bit pointless if your in the contrail layer?

The only airframe(s);) I know of that has fewer contrails than engines is because 40% of the engines fitted where shut down for most of the flight.

Bloody hell. All that time watching the VC10's contrails and apparently the exhausts were mixing with the wing tip vortices!!

I don't know why it's all such a mystery?

Surely it was just one of these on test:

Sea Vixen?


I'll get my coat!!

Here's an interesting video

Yes they were, Roland. Are you postulating that contrails from aircraft with tail mounted engines behave fundamentally differently from others? I'd challenge you to tell those of, say, an MD80 and a 737 apart a minute after they'd passed.

That said, I feel the contrail debate is a red herring; my money is still on the (single engined)X47B for the much more basic reason that the planform looks like it. This isn't the 50's with dozens of exciting projects. Even if some new mega plane had somehow been funded and built in super-secrecy, would it reallly be cruising over Texas in broad daylight?

http://anandgreenwell.com/wp-content...40916_std1.jpg

This one is for Shot. If you're telling me that the vortices mix the contrails, fair enough. However, that is not what your post said "Contrails are formed by wingtip vortices". This is also why, in order to ID the number of engines, that you would look very close to the aircraft itself. However, given the video and the similar contrail pattern from the original picture may very well show a UAV.