EGT over limit
 

Guys,
I'm a F/O of A320 family. I was asked why during the engine start sequence, if we enconter strong tail wind, the EGT over limit may occur. Can anyone help me to find the answer? coz I have gone through the FCOM and FCTM, i found nothing there.

Cheers.

just a guess but I would assume that it if the tailwind was strong enough it would prevent exhaust gases from easily exiting the tail pipe at relatively slow exhaust gas speeds, resulting in increased EGT.

A tailwind means that the starter can't spin up the engine as quickly as is normally scheduled.

This means that the EEC commands the FCU to pump more fuel into the engine to maintain the scheduled engine acceleration.

More fuel = higher EGT.

Yes and it also depends on how good the APU bleed pressure is.
Be careful with low duct pressure on a tired old APU starting with a tail wind.
The Engine may hang or over temp.

( naturally the EEC/FADEC will take care of it but it will still happen, some little forethought will help prevent it )

Used to be an issue with the 744 manual starts with older APU's starting with a strong tailwind. You needed to get max motoring before introducing fuel to give it the best chance of accelerating correctly.

Also applies to starting using ground air. ( a lot of ground carts are crap )

There's obviously no problem with training standards around the place is there..... :ugh:

Wow. It is pretty basic really. :rolleyes:

How about that hole in the front sucking in what's coming out the hole at the back.

Check out FCOM Supplementary Procedures- Powerplant- Manual Engine Start.

And these guys are starting to whinge about getting ICUS for a command hahahaha

Hahahhaha

Hahahahahhahahaha

Happy landings!

Wind Up :ugh:

HA!!! Very good Beached az....

Wind up or Wind up!!!

VB

Less RPM = less compression which means less expansion of the gasses thus higher EGT. Similar to why a TC piston engine has higher EGT than a TN/NA piston engine due to the lower compression ratio.

PV=nRT

https://en.wikipedia.org/wiki/PV%3DnRT

Please let this be a wind up
 

Jabawocky,


I'm with you on your intention to bail up the crew as per the Virgin thread.

What was happening in Gas Turbine theory?


Next time I get on a Kerosene burner I am going to ask the pilots if they did their time in GA or not.

What?:confused:

Got nothing to do with whether they flew pistons, hey probably did but. Never saw an EGT gauge let alone understood what it did.

Physics, the laws of physics apply to all things equally, including turbines on A320's.

I wish I understood your post. :confused:

General Knowledge
 

An FO on an a 320 who needs to ask about turning a turbine into wind strikes me as someone who did a cadetshup and landed in the right hand seat rather than someone who rose up through the ranks and went to the school of hard knocks. Even so Gas Turbine Theory should have instilled the knowledge, maybe they don't go into it that deeply with pilots, certainly got drummed into me in engineering.

You were criticised in the virgin emergency thread because you wanted to ask about fuel load. I think its a valid question. Put the fuel gauges on the inflight foxtel with the airspeed I say! I am simply reflecting that I would ask similar questions about pilots who had gone straight to the right hand seat, rather than worked their way through the ranks. AF 447 comes to mind, missing the basics, power and attitude

Turbine into wind promotes flow through the engine, pretty simple really. You should see the look on an ag pilots face after he has just cooked a PT6

Gotcha :ok:

'Jaba dabba do' yr too clever for us buddy:E:ok:

All combustion donks don't enjoy excessive heat especially during the start phase & a T/W strong enuf on a fan donk can actually turn the big fan up front backwards, not a good start to a start. As long as N2 is rotating/motoring max rpm & the big fan is going the right way then all things being = a good start should result:-)
All good answers here from those in the know but remember guys rather than bag the guy how about we all help, now wouldn't that be a novelty for pilots:ok:
None of us where born with any answers to any Q's, we learn & not just from the text books either:)


Wmk2

Jabbs, the Ideal Gas Law doesn't tell the whole story as there is additional heat energy when the Jet A1 burns. It's been a while since I studied chemistry but my impression was that Avogadro's Law P1V1/T1=P2V2/T2 was only true for a closed system.

Anyway...

Turbocharging an engine doesn't change the compression ratio. The compression ration is the ratio of cylinder volume at bottom of stoke to volume at top of stroke, is it not? Turbo or supercharging does increase total pressure in the cylinder, is that what you meant?

I always thought that turbocharging increases the mass flow of air (oxygen) through the cylinder which allows more fuel to be converted to mechanical energy.

Using iPad so this will be brief. As I said above it is like a TC Vs. TN or NA, it is the lower compression ratio. It has nothing to do with the turbo itself. A TN has the same turbo lets say, but the TC aircraft have lower compression ratios say 7.5:1 compared to 8.5:1 and thus due to less expansion of the end gasses at any given fuel flow if there is less expansion there is higher egt.

Simple thought experiment. Take your BBQ gas bottle, full and lots of pressure....open valve and get LOTS of expansion. Now get another bottle but at a much lower pressure, but same volume. Which one freezes up the most?

The one that does the most expanding of the gas has the lower temp. Same with everything else. Bigger delta P bigger temp drop.

Back to the turbine on the A320, same deal with the lower speed will be less compression, therefore less expansion, so the fuel burns and the gasses have to be a higher egt. They can't not be.

According to Wally who in his old age :} must have started a few, it's a bad thing.....so young pups like us should listen and learn :p


PS anthill, consider the exhaust gases only, immediately after the combustion, the laws then work fine, just like they do on the intake side. You need to examine each component of the process one bit at a time.

:\ my head hurts now, this stuff was too long ago, and I never use it daily, probably got it wrong anyway, and the iPad keyboard and auto spell is doing me in.

Brief?? I'd hate to see lengthy!:}:ok: Bet that took a while to bang out on an iPad!! V informative though :ok:

Thats why the V2500 spins for 30 seconds before the big bang.

It's built for the lowest commen denominator who fly them. I've seen them start with horrific tailwinds and never miss a beat. Usually the big fan is turning the right way long before the gas goes in....

Basic stuff really. FADEC has saved a lot of engines from the ignoramus types out there :)