Inflight Question

[ardypilot]

Rightnow I am 30,000 feet above the Tasman enroute from YSCB to NZWN and I have a problem. Ever since I reached my cruising altitude, white plumes of smoke have been trailing out both of my ifdg a320 engines! I have tried climbing and desending, slowing down from my crusing speed of mach 0.74 and even shutting down my lefthand engine in mid flight. Once the engine stopped, so did the plume of smoke but I had to restart the engine quickly and thus the smoke returned. can someone tell me how to get rid of it please??? it is different from the smokesystem I see when I hit 'I', so that is not the problem. I am 833nm out and still have 1.47 hours of flight time left, so an answer would be good sometime soon cheers!

[toprob]

This is a vapour trail which kicks in at 30,000.

[ardypilot]

So it is normal then? I never remember it happening before on any of my Trans Tasman flights, many of which have been in iFDG a320's, just not this Freedom Air version which I am in now. Would it be a special feature of a particual model, or is this effect changable in the fs9 display settings somewhere?

[flynz]

I believe it is standard on all jet aircraft. I think in fs9 it actually works on the outside temperature and kicks in at around -17 degrees or something which is usually somewhere around 30,000ft. makes for great fun if you are sitting on the ground and change the weather so that the temperature on the ground is less than that so you get vapour trails while taxiing on the ground.

[Jimmy]

Why are you only at FL300 for transtasman in a 320? Isn't FL350 a better and more economical alt and itd make the trip a bit faster too

I remember once I took of from nzwn in a posky 763 and from striaht after takeoff untill shut down I had red sparks flying from my engins! I have no idea why but i certainly wasn't gana take any screenies on that flight

[flynz]

Its pretty nasty weather out there. maybe theres like 5000ft seas out there that would make him 30,000ft above the tasman as he said and 35,000ft above average sea level

I got that on a posky 744 going from boing field to paris CDG. i think it was because I kinda overran the runway on takeoff and i couldnt be botherd starting again as i knew that the flight was gonna take ages as it was. i also didnt take any screenshots from that flight.

[ardypilot]

Well I made it down (just), the approach to Wellington with real world weather was tricky, but I managed it with ILS B)

Just as you said, the trails disappeared as I descended down and I lost them at about FL270.

To see a collection of screenshots (56k friendly), look here: http://z11.invisionfree.com/nzff/index. ... wtopic=915

By the way, I thought the vapour trails came from the wingtips? I have seen many-a-plane overhead my house with these trails, but in the sim, they clearly came from the engines, and disappeared when I shutdown the engines in mid air. How do you explain that?

[Zöltuger]

becuase they don't come from the wings? they just look like that because its happening 30,000ft away

[Alex]

Wingtips when you are operating ailerons and flaps etc, or when you are dumping fuel. Engines when they are running and it is cold enough. Basically the air is very cold and dry, warm air holds moisture better than cold air, and what do you have coming out the back of your engines? So, the moisture is wicked from the cooler air into the warmer air, at least thats my very basic understanding of it.

Alex

[ardypilot]

Thanks for clearning that up for me Alex.

[Alex]

No problem Trolly, like I tried to say, its a very basic explanation, but I've found it does the trick.

Alex

[deaneb]

One result of combustion is a small percentage of water. This is minimal and not noticed normally, but at the higher altitudes, where the outside air temp is -30 degrees or more, this moisture will condenese and form ice crystals, thus forming the vapour trail or jet trail we see high in the sky.

Vapour trail at high altitude

At lower altitudes you may also see vapour from aircraft even down to see level. This occurs where the air is very humid. In these cases low pressure areas around the aircraft ( lower pressure also means lower temp) will cause the moist air to condense and form water vapour. This is noticable from wing tips and flaps, propeller tips, jet engine intakes and sometimes over the top surface of wings. All areas where a pressure drop (and thus temp drop) are experienced.

Lots of vapour !!

When an aircraft approaches high speeds (just below speed of sound) in humid conditions a pressure drop also ocurrs across the pressure wave which builds up.

B-1 high speed

For more pics - search www.airliners.net using vapour as a keyword.
Lesson 101 over for today !!

Deane

[Ian Warren]

Great Lesson Deane - Vapour/compression wave over the wing ,
People plane spotters go out to the airport on a cloudy/humid day with a good pair of high power Binoculars ! u can see even effect as each control surface works . during the approach !