×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Contrails everywhere

Contrails everywhere

Contrails everywhere

(OP)
Why do people call a rocket's exhaust plume a "contrail".  Contrail is derived from condesation trail formed by condensation of water drops or ice within an aircraft's exhaust at particular weather conditions.  Rockets don't have condensation trails (or at least it is not a significant portion of its plume).  What you see coming out of the tail of a rocket is the actual exhaust itself, not water condensing within it.  So, what's that about?

Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group

RE: Contrails everywhere

i'd be willing to bet (not much tho') that there is a bunch of condensation going on ... the rocket exhaust is pretty hot, and the surrounding atmosphere is pretty cold and quite full of water vapour.

RE: Contrails everywhere

Isn't that the wrong way around though?

- Steve

RE: Contrails everywhere

I've never heard someone call a rocket's plume a contrail.  I have heard a few nutters call an airplane's leavings a chemtrail...  I was actually hoping this would be one of THOSE threads (Fri morning laugh).

RE: Contrails everywhere

And growing up, we always called contrails 'vapour trails', even though we knew that it wasn't vapour, it was condensation.

Even Joni Mitchell did:

I was driving across the burning desert
When I spotted six jet planes
Leaving six white vapour trails
Across the bleak terrain
It was the hexagram of the heavens
It was the strings of my guitar
Amelia, it was just a false alarm

RE: Contrails everywhere

Most rocket fuels have some hydrogen in them, and usually some oxygen-containing oxidizer, which produces water when reacted, thus condensation when it cools.  Even if the combination was something exotic like hydrogen and chlorine, the reactant HCl vapor would condense if at high enough altitude, leaving a visible condensation trail.

RE: Contrails everywhere

Doesn't the shuttle main engines use hydrogen and oxygen, so I'd guess that there'd be a lot of condensation there.

KENAT, probably the least qualified checker you'll ever meet...

RE: Contrails everywhere

Seriously, folks, how many lay persons could even follow the terms in this thread, let alone know where the word "contrail" came from?  They've heard the puffs produced by aiplanes called contrails, so when they see a streak of "smoke" in the sky, they'll call it a contrail, regardless of what machine caused it.  I'm pretty sure the answer to the OP is as simple as that...



If you "heard" it on the internet, it's guilty until proven innocent. - DCS

RE: Contrails everywhere

In the same way that steam pouring from cooling towers is always potrayed as pollution on the TV (i.e. smoke to the lay person).

- Steve

RE: Contrails everywhere

Yep, ignorance may be a slightly harsh term but that's probably the answer.

KENAT, probably the least qualified checker you'll ever meet...

RE: Contrails everywhere

(OP)
This came up cuz I had a conversation with someone awhile back that called the rocket exhaust of a military missile a contrail.  It was high atmosphere, it glowed green and although I forget the mixture, I know it didn't produce water as a by-product, and it wasn't visiable because of any condesation in the upper atmosphere.  By contrast, the shuttle does produce exhaust which is water, so I guess it could technically it is a contrail of a sort, but not the produced by the same method from which the term is derived (condesation of water within the exhaust vs. chemically producing water as a component of the exhaust).

Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group

RE: Contrails everywhere

(condesation of water within the exhaust vs. chemically producing water as a component of the exhaust)

um, don't jet planes chemically produce water as a component of the exhaust (as a major biproduct of the combustion of hydrocarbon-based fuel)?

RE: Contrails everywhere

"...I know it didn't produce water as a by-product..."

I'd be willing to bet (a lot) that it did.  And even if it didn't, that some condensation of some chemical species was ocurring in order to create a visible plume.

"don't jet planes chemically produce water as a component of the exhaust "

Yes.  Which is why gliders generally don't produce contrails...excepting when they are on fire...

RE: Contrails everywhere

Contrails can be formed without any combustion process at all.

Look out the window the next time you are in a plane.  If conditions are correct, there can be lots of mini contrails formed - vortex generators at various places on the wing, the wing end vortex, at the end of flaps and ailerons.

Race cars with wings can also form contrails in the wing vortex.

And, the white stuff coming out of the top of a cooling tower isn't steam, it's also condensation.

RE: Contrails everywhere

To follow on from Mint, I saw a very cool video of a Tomcat doing a fly by past a carrier at low level.

It went supersonic and you could see the shock patterns, as condensation.

It was way cool.

(Sorry, that sounded a bit too spotter ish didn't it)

KENAT, probably the least qualified checker you'll ever meet...

RE: Contrails everywhere

So thinking about it some more it may not have actually gone supersonic but it was in the transonic region and there is some impressive condensation.  It doesn't have sound but it's the most impressive visually that I've seen.

http://vids.myspace.com/index.cfm?fuseaction=vids.individual&VideoID=1099821

KENAT, probably the least qualified checker you'll ever meet...

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources