Take off performance
 

Hello,

I have heard of 'first principle' and 'second principle' calculations for take off performance analysis.
I have no idea of what it means. Can someone help?

Thanks

Macadam

.. probably makes quite a few of us who have no idea what it means ... ?

First segment, second segment et al, perhaps? :confused:

The initial method used for calculating takeoff performance was based on model tables, a takeoff program looked up the answer on the appropriate model table. It worked quite quickly but was a tad conservative.

Enter Airbus with the A340, they decided that they could get better answers by calculating the takeoff performance rather than using model tables. This became known as the "First Principle Method". The calculation is quite slow but the resulting takeoff performance is usually worth the wait!

For example, B747-400 from J'burg will get approximately 8000 kgs more takeoff weight when the calculation is based on the first principle method.

Mutt.

Mutt ... no problems with "(from) first principle(s) calculation" as is the obvious reference ..

... but whence the "second principle" ?

That's what tossed OzEx et moi, I suspect ....


.. no prizes for guessing I flew Boeing velocipedes and not Airbus.

Boeing talk about 1st principles nowadays with the BLT.

If you have ever used it I reckon it is an unfriendly little program that is best suited to being used by the blokes that wrote it rather than performance engineers or pilots.

Obviously NO operational input was sought in the design of the program

Shame really, because it could have been very good.

J_T,

The term "second principle" is used to describe the old model table calculation method :)


unfriendly little program

What dont you like about it? I've seen various versions since the initial prototype and actually find it quite easy to use !

Mutt.

... is there any logic to that, Mutt ? .. or am I just a bit slow this morning ?

Mutt,

I don't like the fact that things like 30-45m runways are tied to the aircraft performance model tables that the program uses rather than the airfield data file.

This means that if you have an airport that has 30 and 45 m runways such as Brisbane (and others) you have to use a different aircraft configuration for each runway - ie you can't select 14/32 and have it automatically use the narrow runway data, and then select 01/19 and have it use the 45m data.

From a management perspective it means that you have to have double the aircraft tables (normal and narrow runway) - which is a pain, but it also means that you have to break up your airfield data so that people don't have access to the narrow runways when using the normal runway data.

From a user perspective the same dramas apply - you have to leave and re-start the program to switch between narrow and normal runways - confusing for those of us less comfortable with computers.

There are a couple of other issues with it as well, but I can't off the top of my head think of them - its been a few months since I used it.

It has its good points, don't get me wrong, but with some operational input at the beginning (and I don't mean the guys that fly at Boeing - but real airline users) it could have been significantly better.

Can one download this program?

No,

It is Boeing proprietory software, much like BPS and others.

You get it when you pay the dollars (and lots of them) to Boeing

Doh! Can't afford big dollars on my salary! :{

Cheers

J_T,

It isnt logical nor correct, however thats the way it is! I think that i would call it an adopted name rather than a proper term!

Dehavillanddriver.

Extremely interesting comments, can you tell me what part of the takeoff performance calculation changes due to the runway width? Is there a real need to enter that parameter?

BLT was designed for BBJ operators so there wasnt a design working group involving airlines, however, they were soliciting comments by handing out the initial version in Tukwila prior to its release.

Cost Index.

The program itself isnt that expensive, or at least in our case it was free, however you must supply $50 million liability insurance to be allowed use it!

Mutt.

Mutt,

Pending DHD's response ... the most likely width effect, at least in Oz where there is a certification implication, is at the low weight end. The Vmcg-limited V1 may go up as a result of the runway width test program for a particular type as part of the approval to operate from less that the normal geometry-limited minimum runway "standards".

This requirement was introduced years ago as part of an ICAO recommendation ... appears Oz was the only country to take the thing seriously ... I have a number of test videos showing quite alarming centreline deviations under test conditions ... all very interesting and I experienced a rapid change from non-believer to convert ...


Quite astounding re the 1st and 2nd principle nonsense ...

Thanks a lot guys....it is now clear !!!

JT got it in one!

Boeing had to provide us with a AFM supplement for narrow runway operations, with everything narrower than 45m being narrow.

It called for amongst other things, no unservicabilities associated with things like thrust reversers, anti skid, nosewheel steering etc.

BLT has separate datasets for narrow runways.

Very interesting... you guys certainly have an interesting way of doing things :):)

45m runways are our norm but on occasion we have gone to narrower runways without any restrictions imposed by the FAR's.

Mutt.

That's the interesting thing, Mutt ... Oz is the only State (so far as I know) to have implemented demonstrated runway width capabilities .... the penalties arise due to the conservative nature of the approach to the test problem .. at the low speed end ... but, make no mistake about it ... my preoccupation, from time to time, in threads on Vmcg and crosswind .. derives directly from seeing the sort of centreline deviations during runway width test programs ....

Guess that the other States figure that the risk of a failure under critical conditions is a fair risk ... but have that failure and you should expect to roll the wheels in the mud off the side of the runway.

J_T,

You are right, but remember that it doesnt snow in the land of FAR's :(:( So you dont have much chance of getting them to admit that narrow runways exist!

Mutt.

Fair comment .. the Oz test requirements are based on critical conditions .. ie NWS disabled (if feasible) to cover low/zero nosewheel cornering force capability. However, the birds do jump to the side quite forcefully. If you don't have enough bitumen then it's the dirt and grass ...