View Full Version : 737 performance
Tapshi
24th Nov 2012, 09:29
I was going through the FPPM the other day. Seeing the graph for calculating the climb limit weight, it struck me that winds were not being considered. Whereas winds are taken into account for calculation of obstacle limit weight.
Any ideas as to why this is so? As per my understanding, winds will affect the climb performance. Have I got it wrong somewhere or did i miss out on something?:ugh:
CLW' or 'WAT' limit is to do with engine performance, nothing else. It matters not which way you are pointing or what is 'in the way'..
For a Perf 'A' twin jet WAT limit will be the lowest to achieve:
For the 1st segment climb - a positive rate
" " 2nd segment - 2.4% one engine inop or 5.2% all engines
" " 3rd segment - 1.2% one engine inop
" " 4th segment - 1.2% one engine inop or 4.0% all engines
(I think! Perf A was a few decades agohttp://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/smile.gif)
Looking at your posts, I ask what your interest is? Your profile is blank. Have you studied any performance stuff? It might help us to answer your questions..
Tapshi
24th Nov 2012, 16:18
For the question, I kind of still don't get it. I figured out that climb limit weight depends only on engine performance. But any specific reason as to why?
Practically climb will be affected by other factors too, wouldn't it?
As far as I go, I had never seen that there was an option for personal information too:p
I updated it now:ok:
I'm pretty new and learning stuff. I intend to know about the 737 as much as I can:O
For the question, I kind of still don't get it. I figured out that climb limit weight depends only on engine performance. But any specific reason as to why?- because it is, by definition!
As an 'F/O' flying on 737s, you MUST have studied performance, surely, even in India? Where did you do your CPL licence training? Which airline are you flying with?
Why not tell us how you calculate the maximum weight that you can take-off with in your airline?
Denti
24th Nov 2012, 17:07
Oh, but BOAC, you must surely realize that knowing how to calculate isn't all that important anymore. After all its just entering all the values into boeings program and press the big button CALCULATE upon which one gets all the answers.
john_tullamarine
25th Nov 2012, 10:58
BOAC .. you might have a rethink about your numbers ?
The basic thing about WAT limit is to make sure that the aircraft doesn't head off without a (very) modest climb capability if one of the noise sources goes quiet. No particular intent to achieve anything other than that.
Keep in mind that determining RTOW involves going through a whole bunch of sums to check a variety of limits .. one of which is the various WAT cases.
JammedStab
25th Nov 2012, 11:05
CLW' or 'WAT' limit is to do with engine performance, nothing else. It matters not which way you are pointing or what is 'in the way'..
Quick questions. Don't the A and T in WAT stand for altitude and temperature and if so.....assuming an engine were able to maintain the same thrust, won't higher altitude and temperature still have a detrimental effect on aircraft climb performance in ways other than affecting engine performance?
BOAC .. you might have a rethink about your numbers ?(I think! Perf A was a few decades ago:)) - I found those figures elsewhere- is that ("a (very) modest climb capability if one of the noise sources goes quiet") not what they are providing? I will freely admit I do not carry them in a flight bag so happy to be corrected.:)
assuming an engine were able to maintain the same thrust - I think that is where you came off the rails.:)
Any sign of Tapshi?
JammedStab
25th Nov 2012, 15:56
- - I think that is where you came off the rails.:)
I guess my question more clearly is.....Is the reduction in aircraft performance due to altitude and/or temperature increases only because of reduced engine thrust(as posted earlier) or are their aerodynamic reasons as well.
Getting a little esoteric here and my aero eng quals are distinctly 'historic'. One for the theorists, I feel. For we simple 'drivers, airframe', suffice it to say the donk is not so good at 2000'AMSL as at 0.
It doesn't really matter to us, since clever folk like JT give us numbers we look at. When/if Tapshi returns, he/she can explain what system the airline uses to establish MTOW.
john_tullamarine
25th Nov 2012, 21:10
BOAC - apologies. I noted your reference to 2.4 and, as I am always thinking net rather than gross .. mea culpa.
Regarding WAT which I put as maximum limiting Weight for Altiude and Temperature, one generally sees a reduction in the WAT limit as Hp and/or OAT increase.
The interest is not so much engine performance as overall aircraft performance. The aim is to give the pilot a small chance of keeping on going up in the event of failure rather than going down.
Not a problem, John. As I said it is reliable people like you and others who work out whether it is gross or net and just give us pilots the limiting numbers - the detail does not bother us and nor do we care really which factors influence - as long as our ambient conditions are inside your tables:)