DaveD

iTrader: (2)

The weight of the bird is laid down in the specification of the airworthiness authorities - although the engine could cope with a slightly more weighty bird, it would be pointless to use one for the cirtification test just to prove a point.....the test isn't cheap, especially if the engine doesn't pass!

Therefore the ducks are specially bred, and several are chosen for being the correct weight. They are then x-rayed (apparently they like to eat the odd stone to help thier digestion!) before being used for the test. There are two separate tests - large bird and small flocking bird.

The objective of each test is that the engine should maintian full thrust following the simulated bird strike. I think the engine then does a simulated aborted landing (another bout of full thrust) and landing.

The test may seem to be artificial, but no two birds are the same, so this is accepted as being representative of a typical strike.

Sonic'

Just got back from NY this afternoon (should have been this morning but flight delayed for 3 hours whilst they cleared the runways withthe snow ploughs and had to join a queue for the De-Icing park prior to take off

Here are a couple of pics of the plane when we wandered down towards Battery Park









Pretty scarey stuff, and happened the our first morning there, probably less than a mile from our hotel too

J4CKO

iTrader: (1)

Cheers for that Dave, makes sense now, very interesting to know the background, cheers !

Snazy

Good snaps Sonic

What were your feelings about getting back on a plane after that?
Not trying to be sarcastic, just wondered what its like to see whats left after a plane crash, then get on one.

LG John

Class, what a life! Specifically bred to one day be chucked into an engine and minced up - ha ha ha!!

LG John

Sonic I'm amazed you were allowed to get that close to it!

J4CKO

iTrader: (1)

This is not just Duck, this is Specially Selected, Flash Fried, Guaranteed Stone Free Pratt and Whitney Duck in an Jet A1 "Jus"

Sonic'

It didnt bother me at all getting back on a plane after that

It was Donna's first time ever on a plane, so to be confronted by that the day after we landed she really wasn't keen on getting back on a plane

The wing of the plane was under the concrete we stood on, as the water goes right underneath the main walk area

We managed to get talking to a nice NYPD officer, and we had gone there late in the day when most people had gone

Leslie

If you get a large bird into a jet engine which has damaged the compressor, then the engine is very likely to suffer a surge which leads to air flow reversal in the engine. At that moment the fuel suppy to the engine is too much for the air being supplied and that will lead to the above surge. The effect of that is a pretty loud bang as was reported.

This surge could also be caused by a fault in the fuel supply engine system which can lead to the same effects. I have heard a few of those without a bird strike being the cause.

If there was such a fault it is most likely to be to only one of the engines which would not have led to the necessity for a ditching from 2800 feet which is where the aircraft was reported to be. Very unlikely to be both engines so the most likely cause is the geese in the engines as first reported.

We shall see what comes out of the investigation anyway.

Les

ALi-B

iTrader: (1)

Leslie, just a question:

Would you know if wake turbulence (or any other turbulence at that) may cause an engine surge?

Myself not being sure of exactly how modern(ish) turbofans measure the amount of airflow into the engine (hot wire/film MAF sensors? With their troublesome reliability on car engines, I hope not ), I presume there must be an automated method of controlling fuel mixture should for whatever reason the airflow through the engine not be what is expected at that particular speed/altitude/RPM etc.

DaveD

iTrader: (2)

The answer to this question could be quite long and boring, so I'll try to keep it short!
In theory, yes, wake turbulance could cause an engine to surge. The sudden drop in inlet pressure will mean that there is insufficient air being drawn through the compressors, and instead of air being drawn into the combustor, it will be coughed back out the front of the engine.
However, that would probably require a fairly large disturbance.

Modern jet engines use Full Authority Digital Engine Control (FADEC) controllers to operate the engine. This basically means that all the fuelling, operation of various bleed valves etc, is controlled by software. The software has many routines built into it to cope with most expected events - engine surge being one of them. The sudden drop in pressure from the compressors would be detected by the controller, and it would instantly all but cut the fuel supply to the engine to allow things to settle down and recover. The pilot would not have to do anything.

Jet engines don't use MAF sensors - they work out the fuelling to maintain an EPR pressure ratio (or TPR on the most recent, very high bypass engines) which is basically equivalent to thrust (what the pilot and passengers are really intersted in!). The mass flow is calculated during development testing by measuring temperature and the depression at the inlet to the engine - a production engine fitted to an aircraft doesn't really need to know the actual mass flow, but does calculate an approximation from inlet pressure & temperature, fan speed and altitude.

HTH

Leslie

Thank you DaveD, saved me having to explain.

Les

Sonic'

A quick question for you guys, but at approx 30,000 feet what is the slowest speed (ground speed) that a plane can fly at (eg a 757-200)

speedking

Faster than a goose

J4CKO

iTrader: (1)

Yes, I bet that engine was a right mess, have you seen all the fat when you cook a Goose, our oven ends up in a right state

Sonic'

Cheers for that but Crikey, that doesnt half take some working out

Whilst flying to the US we went as low at 350mph (ground speed) at 33,000 feet with a 200mph head wind

Coming back we hit 667mph (ground speed) with an 85mph tail wind at 33,000 feet

LG John

If that was the case would the plane not be able to stay in the air even if ground speed = 0mph. Surely if the engines produced enough thrust to prevent the plane being swept along with the wind then the 200mph win acting over the wings would keep her up?

TopBanana

Why wouldn't it?

bugeyeandy

Yes it would stay aloft.
IAS is the key not groundspeed, hence the IAS is one of the primary instruments on any aircraft.

bugeyeandy

Thats a different question, you still need thrust from the engines or the aircraft will just be blown backwards.

ALi-B

iTrader: (1)

...well, at one point it nearly went backwards:

YouTube - Husky Short Field Landing and Take-off

Diesel

I just got back from Cuba. Twin engined A300 (I think). Was doing 450 knots outbound and took 10hrs. But had 190 tailwind coming back and it was doing almost 700knots and did it in 7 hours - barely time for a kip!!!

So. MY question is, at what mph does the world rotate?

D

Sonic'

Is the ground speed (once airbourne) including the relevant head or tail wind, as the book states that the maximum cruising speed for a 757-200 is approx 560mph IIRC

Now add / subtract the tail / head winds to the max cruising speed and you get the figures shown on the TV screen during flight

bugeyeandy

At the equator approx 1000mph but as the atmosphere is rotating with it (fortunately for us) then it makes no difference.