Performance

[Duchess_Driver]

...discussing perf with a student this morning and the subject of take off distance calcs arose.

I seem to remember a picture being banded about recently of an IL86/96 taking off and being 'a tad low' over the lights. It's been on A.Net but a quick trawl couldn't pick it out...

Anybody got the url for it please.


MTIA.

DD

['India-Mike]

This is it, I think

http://www.airliners.net/open.file/0995911/L/

Cheers

[Duchess_Driver]

Twill Do.

Not sure if this is the one I was thinking of, but it illustrates my point.

Thanks

[eyeinthesky]

On the pictured example, would it be correct to assume that V1 (the speed above which the take off run could not be aborted and stop within the EDA) would be considerably less than Vr?

[londonmet]

eyeinthesky,

Just thinking about your question....

V1 is an IAS at which you correctly state is a stop/go speed (loosely put). However, in a Hot and High airfield the ground speed associated with a V1 would be higher than the IAS. So the V1 could be limited to perhaps V MBE. In essence, the V1 is limited at the lower end by Vmcg and at the upper limit by Vmbe, Vtire and Vr. If you reduce V1 you reduce the stop distance required and increase the go distance. In addition to this if you have a lower V1 then in cases where you're hot and high it might have ben selected low as it would be deemed safer to GO and to STOP - at that high G/S eg Vmbe and Vtire etc etc.

A V1 speed could be low for a number of reasons, eg field limited (short runway) or as per CDL ie no reverse thrust available therefore stopping action reduced.

In the pictured example I would guess the stopping action of this a/c would be the brakes, spoilers and reverse thrust. I am guessing reverse thrust would be most effected by being at a hot and high airfield. The brakes would be probably the most effective retardation device, however, as stated before the G/S would be high to they'd work bloody hard!

L Met

[john_tullamarine]

Two points ..

(a) the pix is with a long lens which distorts the story somewhat .. hard to tell how high the bird is at the time

(b) probably scheduled with a maximum use of clearway over the water .. not an uncommon sort of result for this scenario ..

[Duchess_Driver]

I'd have thought that any distortion would also have applied to the fence at the end of the runway - whichever way you twist it, it still looks extremely close!

[john_tullamarine]

Problem with a big lens is that the image suffers from major foreshortening .. ie everything looks closer than it is .. the pix looks a bit alarming but I suspect that the reality is a little less so ..

Having said that, the ADL 722 operation in years gone by blew the odd airport worker over (or frightened him mightily at the very least ..) if he didn't keep a wary eye on the takeoff sequences ...

Same situation ... significant use of clearway with no after takeoff obstructions to upset the effect ... depends, too, on what is the limiting calculation for the takeoff .. either way .. not at all strange to see things a bit like the URL pix.