Why do you use engine anti-ice ?
 

Why do you think you use engine anti-ice ? Lets keep the answers relevant to modern jet-liners if posible.

hey hey vnav i,ll give you all the answers you need to all the questions i will email them to you. In answer to this question though. I believe it is two-fold

1.) To prevent large supercooled droplets forming on the engine intakes i.e formong clear ice which can disrupt airflow into the intakes. Hence icing conditions exist at TAT +10.
2.) and I think more importantly the heat created at the intakes warms the moist intake air so it does not cause icing on the fan blades which can obviously lead to disrupted airflow, compressor stalling, and vibration. I hope others can clarify these points somewhat.

On the 757 RB211s and 767 CF-6s, only the cowl ring is anti-iced. The 211's have a small rubber tip (US technical nomenclature "dohicky", UK technical nomenclature "thingy") that supposidy sheds ice.

Other times A/I should be used is when encountering volcanic ash and in severe turb - A/I increases the stall margin of the engine.

[ 09 August 2001: Message edited by: Roadtrip ]

and following a hot start
:cool:

Thanks for the responses thus far, Nads you seem to have thought this over hey !

Any further comments or theories ?

Roadtrip:- That little rubber "Thingy" is called the "Bullet"! As ice builds up on it, it becomes unbalanced. The rubber flexes and the ice vibrates.This causes the ice to be shed through the engine. :)
Eff Oh. :D

...and then on some RR RB.211 powered aircraft, the fan hub is de-iced....all the time with bleed air.

Why is it that it is TAT that is determining? I mean it must be the temperature of the drops that is the factor here. Anyone?

Because the engine cowl (the part that is anti-iced) is much like any other forward facing surface on the aircraft and heated by the ram effect. Therefore -2c oat can be +12C on the leading edge of the cowl - hence ice will not form.

So are we more concerened about disturbed airflow entering the engine or damage to engine components leading to disturbed airflow ? You know what I mean ?

So you don't ice-up your engine parameter sensors and end up spudding your 737 into a frozen river because you didn't have correct EPR readings, amongst other things. (Like the Air Florida 737 on Jan 13th 1982.)

We are more concerned about disturbed airflow, meaning more nasty vibration, decreased power, surges and stalls. We stick it on below +10 TAT when there's visible moisture or standing water. Although some people get extremely hung up about the difference between 10 and 11 degrees...

[ 16 August 2001: Message edited by: Checkboard ]

Criticalmass I had a similar discussion about that 737 with a workmate last night. Not a nice story at all.

malteser - lol, how true!

vnavspeed,

For detailed treatment of that accident, "Air Disaster" Vol 2, Macarthur Job, pp 83-95, ISBN 1-875671-19-6 (still in print) makes fascinating (and disturbing) reading.

Why do I use engine anti-ice?

To prevent icing of the nose cowl, guide vanes, etc., and to keep chunks from breaking lose and getting ingested.

A few other abnormal situtions may be helped by opening the bleeds as well, like hung starts, unscheduled surge bleed openings, etc. But those are "desperation" measures. Is that what you're looking for?

: :eek: You know what I think?I think the reason you need engine antice on on take-off is that you do not want ice in your engines. It's solid.
It's not that complicated.Or is it?

Yep!as the name Anti Ice implies its to prevent ice build up.

vnavspeed - although you may not expect ice to form at +10c TAT, this figure is commonly used due to adiabatic expansion causing temperature reduction.

Just beware of that bloodey TAT gage guys! Make sure its reading what it should read. Ive had erroneous TAT indicating +17 at FL290 at M.75! ALWAYS keep an eye on the underside of your windscreen wiper as a backup, and a reasonable knowledge of expected TAT at various levels at your usual flying speeds. If in doubt throw open the valves and be done with it. Most modern engines can handle engine thermal anti-icing up to a very high ambient temp (+38C in 737 CFMs) so its not like youll burn anything.