Engine Anti-Ice/Engine inlet

[FlatBread]

Hi,

I've a question about engine anti-ice. I understand you're supposed to use it at TAT +10 C or below (and vissible moisture). This is because of the temperature drop at the engine inlet.

However, are the inlets of those engines not designed to rise the pressure to an optimal value before it enters the compressor. And if the pressure rises, would the temperature not rise aswell?

Where I'm missing something?

FB

[BOAC]

Engine anti-ice is there to take care of the intake lips, front compresser/fan spinner and any IGVs there may be. The temp rise you mention has not taken effect at these points.

[FlatBread]

So it has all to do with the intake of the inlet. Which is on it self a convergent duct, so there the temperature will decrease?

There after the inlet is a divergent duct, so pressure and temperature rise.

Would there be another reason why you can expect engine icing at temperatures up to 10 deg C?

[411A]

FlatBread,
The greatest concern with engine anti-icing is many times on the ground, just before takeoff.
Takeoff thrust applied with little forward movement can result in rapid intake icing...clearly not good.
Engine anti-icing is used to prevent this problem.
Once airbourne, the +10C number (some designs use +5C) is used to be sure that anti-icing is switched on well ahead, to preclude intake icing.

[lomapaseo]

the +10C number (some designs use +5C) is used to be sure that anti-icing is switched on well ahead, to preclude intake icing.

The problem with two different manual temp call outs is that both were intended to make up for subjective judgement of crews deciding on whether to turn on the anti-ice based on visible conditions at their windscreen and wipers.

However having two dfferent temp recommendation between manuals only leads to more confusion among crews. Thus the intent was to go through all manuals among different aircraft and make them the same. I was assured by Boeing and Airbus that this had happened..

[BOAC]

Flatbread - I did an Aeronautics degree in the 60's, and have NO wish to get into convergent/divergent ducts and the like (brain fade!). My advice?....stick to the Flight manual, don't try to work it out for yourself. The 10 deg is VERY conservative, but after all, it does not use THAT much fuel, does it?, so stick it on.

[alatriste]

FLATBREAD, you can also check about this topic in a thread called
COLD WEATHER PROCEDURES B737 NG. Started by FLAREARMED 2 on the 9th of OCTOBER.

REGARDS