Vapour....trails that is

[FluffyMcDeath]

JaXanim wrote:
@blobrana

Yes, that's the transient precipitation I talked about earlier. The car didn't leave a trail right around the track did it.  If the right conditions were to prevail, it might happen, but that's highly unlikely.

So, what is it about flying that's different from the F1 scenario?

JaX

On a cold day, my car leaves a vapour trail, even when it's moving slowly. The vapour tends to drift upwards though.

Now, that's just the water from burning petrol at the rate of approx. 3 ltr/hr.

A 747 (according to this has a mac fuel capacity of 173 tonnes, for a range of 13.000 km and a cruising speed 0of 930kph.

That's a burn rate of 12.4 tonnes of fuel per hour.

Aviation jet fuels are C8-C16 hydrocarbons. As a stab in the dark say that the average is round about C about 12 and H around 22.

That works out to be about 15 tonnes of water produced per hour. It doesn't seem unreasonable to suspect that if the upper atmosphere is cold and saturated, then that amount of condensate would be visible.

[FluffyMcDeath]

QuikSanz wrote:
Hi, Actually blobrana is right you don't need an engine. Living in southern California I have been privlaged to see the shuttle come in.when high up with the heavy wing loading it creates an extreame low pressure and if the humidity is not too high the vapor freazes and hangs for a while.

Show me a commercial jet liner that does Mach 9.

Yes, if you look out of the window when you're going through cloud you can often see condensation in the air coming off the wingtip. But this is not the mechanism that causes contrails in high altitude commercial flight.

Get a pair of binoculars and take a look next time you see a jet making a contrail. The trail starts well back from the wing and not in line with the wing tip but with the engine.

The trails that form from shocked air cling to the edge that creates them generally. Far back from the wing they just don't spring into existance.

[FluffyMcDeath]

JaXanim wrote:
@QuikSanz

Maybe this will refine as more data comes in on aviation fuel.

JaX

Maybe best to just buy some jet fuel and do an empirical test. :-o

[FluffyMcDeath]

Here's a nice little shot of the Shuttle coming in for a landing, with a nice little trail.

[FluffyMcDeath]

JaXanim wrote:

@blobrana

Aviation kerosene is mainly a C10-C12 hydrocarbon mixture, but that doesn't have any significant effect on water volume.

Think those were my numbers your refering to. As to the hydrogen content, I was just guestimating what the average H would roughly be for such a mix of hydrocarbons.

[FluffyMcDeath]

JaXanim wrote:
@Fluffy...

Assuming kerosene is a saturated hydrocarbon fraction, its empirical formula will be C(n)H(2n+2). The carbon number(and therefore the hydrogen content) makes relatively little difference to the weight of water created on combustion.

Cheers,  

JaX

When I was looking up jet fuel all I found was the weights of fractions expressed in terms of C. IN addition to the saturated hydrocarbons, jet fuel also has such stuff as napthalene (C10H8), so I jogged the H down a bit.