Xwind limit engine start A321

[Speedwinner]

HI folks,

Just no answer for that: we do have a 35kts crosswind limit for the 321 at engine startup. The engines are iae and I have no clue why!

Cheers

[FlightDetent]

The engines are iae That's why. :O I was told it is intake airflow related.

[Sokol]

Just no answer for that: we do have a 35kts crosswind limit for the 321 at engine startup. The engines are iae and I have no clue why!

Just think a bit about it, You´re starting the engines with bleed air...

Greetings,

[FlightDetent]

Well, Sokol, the CFMs are started in a similar fashion with no such limitation. On top of which, were you thinking tailwind perhaps?

[RAD_ALT_ALIVE]

I wouldn't compare IAE with CFM - the only similarity is that they hang off the same airframe.

The IAE has a smaller diameter intake, it has an extra spool (if memory serves correctly) and it needs to be cranked prior to light-off. I'm sure that all those factors have resulted in the crosswind capability comment.

Which leads me to this: is 35kts actually a limit? My company thinks not - nor do I. The wording in FCOM LIM is 'This engine is capable of starting in crosswinds up to 35 kt.' The bush-lawyers might say it IS a limitation, but I would argue that it would need to be worded similarly to the wind limitations in the 'Environmental Envelope' section.

If the the maximum crosswind for engine start was a limit, I suggest it would be written as, eg, 'Maximum crosswind for start...35 kt'.

I read '...is capable of...' in the same spirit as 'Maximum demonstrated crosswind...'. It's the maximum experienced in testing, but is no hard limit.

My two cents worth.

[Capt Quentin McHale]

Sokol,




"Just think a bit about it, You´re starting the engines with bleed air..." Yep, I've thought about it and you are correct, most turbine jet engines are started with bleed air..... from the apu or ground cart or x-bleed after another engine is started. I fail to see your point.


Speedwinner,


As RAD ALT pointed out re the smaller diameter inlet on the IAE, possibly the x-wind limit imposed is to prevent engine stall/surge/hot start on engine start up due air blowing past the inlet and the engine "choking" so to speak. In any strong x-wind it would surely be wise to start with aircraft into wind. Hope this helps.


McHale. :)

[TURIN]

The IAE has a smaller diameter intake, it has an extra spool (if memory serves correctly) and it needs to be cranked prior to light-off. I'm sure that all those factors have resulted in the crosswind capability comment.

IAE V2500 is a twin spool engine. As is the CFM 56.

[Sokol]

Well, Sokol, the CFMs are started in a similar fashion with no such limitation. On top of which, were you thinking tailwind perhaps?

No. It is the bypass ratio an the layout of the spools that makes the difference.

[...]engine "choking" so to speak.

The correct phrase is "Pumping".

Greetings,

[lomapaseo]

So is this "limitation" due to the inability to light off? or the inability to accel to idle? or the potential stability of the fan blades when their incidence angle gets badly mangled?

Did somebody ring up IAE and ask?

[Capt Quentin McHale]

Sokol,


"The correct phrase is "Pumping"." Very sorry for not using the"correct" phraseology, perhaps I should have said "surging". But I think we all get the idea.


Now could you please explain what you meant in your post#4 because as I said previously "I fail to see your point".


McHale. :)

[Sokol]

Now could you please explain what you meant in your post#4 because as I said previously "I fail to see your point".I meant it as complete, please. You´re starting the engines with bleed air, bleed air is for getting the compressor of one (mostly the high pressure) stage out of pumping(TURIN: Hunting) into an stable environment.
(and yes, we in Germany see a difference between a compressor that´s pumping(Hunting) and an compressor that´s working good)

Now the bypass ratio: Air won´t change its Direction on its own, if you ever built a turbine you know that. To manage a start with bleed air the compressor of the (high or low pressure)stage is often deactivated at the very beginning. When the compressor starts working it has to Pump enough air through its stages to provide the turbine with air and support the cooling system.
High bypass ratio guarantees higher massflow even at low speeds, so the air changes its direction properly. Low bpr has an lower massflow and an smaller diameter, anyhow the air will change its direction, but there is an danger that the air won´t get into the compressor properly. (Two possibilities:
-Compressor gets no air: Turbine stops working when bleed air is off
-Compressor wont get enough air: Posibilities of rotating stall, definetively not enough air in the cooling system, Danger of destroying turbine and compressor!)

Often the reason for such an limitation is: "We haven´t tested it in this environment" But you can ask how much a single turbine blade costs and then think about trying it even in a 1 in a million chance to fail.

Greetings,

[TURIN]

I think much of the above must be lost in translation as I can't understand a word of it.

The bleed air drives a motor. That drives the HP spool. It doesn't cool the turbine.
When you say the compressor is deactivated are you talking about SURGE bleed valves and VSVs?

The word 'pumping' that you are using. Do you mean a surge, compressor stall or are you talking about 'hunting' ? I.E. The rotor accelerating and then decelerating before reaching self sustaining speed?

[Capt Quentin McHale]

TURIN,


"I think much of the above must be lost in translation as I can't understand a word of it."


I could not agree more. WTF ???


McHale. :hmm::hmm::hmm:

[Sokol]

The bleed air drives a motor. That drives the HP spool. It doesn't cool the turbine.I didn´t say it does.

When you say the compressor is deactivated are you talking about SURGE bleed valves and VSVs?SURGE bleed open.

The word 'pumping' that you are using. Do you mean a surge, compressor stall or are you talking about 'hunting' ?Your word "hunting" describes the matter the best.

I.E. The rotor accelerating and then decelerating before reaching self sustaining speed?I don´t get that point.

I think much of the above must be lost in translation as I can't understand a word of it.Study it for 3 Years and then try to explain this topic without using "Grade of reaction" and "Smith diagramme". I am trying my best.

Greetings,

[MathFox]

I'll try a summary:
With a strong crosswind it is possible that the air flow into the compressor is disturbed and not enough air is getting into the hot part of the engine; this might cause damage.
I could be completely wrong...:}

[Sokol]

MathFox: Thats what i am trying to explain. Good point.

Greetings,

[Capt Quentin McHale]

MathFox,


"With a strong crosswind it is possible that the air flow into the compressor is disturbed and not enough air is getting into the hot part of the engine"



Correct, you have hit the nail on the head!!! Not enough airflow into the engine inlet on start can and will cause a surge or hot/hung start and/or possible internal damage to the engine.


Sokol, appreciate that you are trying, just a little confused.


McHale. :)

[barit1]

22 Jan 1970 - Pan Am operated its first revenue 747-100 flight JFK-LHR.

The aircraft was parked in a tailwind, and one JT9D-3 stalled and overtemped on starting. Fortunately a second 747 was on hand so it was called up as a replacement, and after some considerable delay, it successfully completed the flight.