Aircraft Performance
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hope your day is better than mine
Hello all,
Yesterday I was rear ended by idiot paying more attention to her cell phone conversation than her driving. Will posgt answers and explanation plus answer the private messages fro, inbox when I feel better.
Jon
Yesterday I was rear ended by idiot paying more attention to her cell phone conversation than her driving. Will posgt answers and explanation plus answer the private messages fro, inbox when I feel better.
Jon
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Hello all! Holy cow muscle relaxants are wild!
Well since last post live for me has been wild...had to stop taking muscle relaxant doc prescribed because it really knocked me for a loop!
As promised here's some food for thought:
Sample questions and answer/explanation
1-Of the answers given D is correct. The second segment A is usually but not always most limiting.
2-Of the answers given D is correct. In addition to differences in allowable height of obstacles the other significant difference is STOPWAY must be able to support the weight of the aircraft during the stopping manuver.
Other Questions
3-B the least
4-D C is almost correct however as it, and none of the other possible answers, does not include obstacle data D is correct.
5-D more flaps will shorten take-off roll but also lessen climb gradient
6-B if you disagree I'd love to hear why
7-D Remember climb is determined by how much thrust is available in excess of that required to maintain level flight.
8-D I've seen this several times where parallel runways have different take-off weights for a given aircraft because of the difference in the obstacle sets.
9-A Although you do see this occassionally fom a strictly engineering perspective. Thanks to the Dry Check you should never see results that allow this to happen.
10-B Due to differences in how vendors select obstacle data to be reported and data sources there can be pronounced differences in data for the same airport from diffferent vendors.
11-A but perhaps not for the reason(s) you think. I've seen engineering analysis for the B757 (forgot engines used) where you could actually get better weights at reduced thrust off of a wet runway because with lower thrust there was a lower VMCG. But the dry check eliminated this from results sent to customer...but sure had us scratching our heads until we ran the problem with an engineering output!
12-C Most performance data testing is done around a range of V1s but regardless of the actual speed the aircraft (under FAR and most certification schemes) must be kept within 35 feet of the centerline without using nosewheel steering.
13-B Actually it depends upon the AFM you purchase. There are differences between all of the regulatory schemes which can result in different weights and speeds for the same aircraft/engine/brake combo.
14-A As several folks have commented, sometimes all you need is to pay more to get heavier weights!
Please feel free to comment on here or send me a personal e-mail. Hope this has stirred some thought!
Jon
As promised here's some food for thought:
Sample questions and answer/explanation
1-Of the answers given D is correct. The second segment A is usually but not always most limiting.
2-Of the answers given D is correct. In addition to differences in allowable height of obstacles the other significant difference is STOPWAY must be able to support the weight of the aircraft during the stopping manuver.
Other Questions
3-B the least
4-D C is almost correct however as it, and none of the other possible answers, does not include obstacle data D is correct.
5-D more flaps will shorten take-off roll but also lessen climb gradient
6-B if you disagree I'd love to hear why
7-D Remember climb is determined by how much thrust is available in excess of that required to maintain level flight.
8-D I've seen this several times where parallel runways have different take-off weights for a given aircraft because of the difference in the obstacle sets.
9-A Although you do see this occassionally fom a strictly engineering perspective. Thanks to the Dry Check you should never see results that allow this to happen.
10-B Due to differences in how vendors select obstacle data to be reported and data sources there can be pronounced differences in data for the same airport from diffferent vendors.
11-A but perhaps not for the reason(s) you think. I've seen engineering analysis for the B757 (forgot engines used) where you could actually get better weights at reduced thrust off of a wet runway because with lower thrust there was a lower VMCG. But the dry check eliminated this from results sent to customer...but sure had us scratching our heads until we ran the problem with an engineering output!
12-C Most performance data testing is done around a range of V1s but regardless of the actual speed the aircraft (under FAR and most certification schemes) must be kept within 35 feet of the centerline without using nosewheel steering.
13-B Actually it depends upon the AFM you purchase. There are differences between all of the regulatory schemes which can result in different weights and speeds for the same aircraft/engine/brake combo.
14-A As several folks have commented, sometimes all you need is to pay more to get heavier weights!
Please feel free to comment on here or send me a personal e-mail. Hope this has stirred some thought!
Jon
Join Date: Sep 1999
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Sorry to hear about the car crash..
Hope that you have recovered.
I believe that you will find that in your 757 example the increased weight was due to lower screen height and use of thrust reverser for stopping, not a different VMCG as you don’t have contaminated/dry VMCG’s.
If you compared different ratings, then you might get better contaminated weights with a lower thrust ratings depending on the runway length, we do this all the time to get out of JFK, the wet check just stops the benefits of the screen height/thrust reverser credits
Mutt
Hope that you have recovered.I believe that you will find that in your 757 example the increased weight was due to lower screen height and use of thrust reverser for stopping, not a different VMCG as you don’t have contaminated/dry VMCG’s.
If you compared different ratings, then you might get better contaminated weights with a lower thrust ratings depending on the runway length, we do this all the time to get out of JFK, the wet check just stops the benefits of the screen height/thrust reverser credits
Mutt
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Hi Mutt, thanks for your comments!
Hi Mutt,
Thanks for your comments! I hope this thread has been interesting and thought provoking, if not please let me know. If anyone has some questions send em!!
Actually the improved performance off of the wet runway with reduced thrust was due to a difference in VMCG. Until I saw it I would not have thought this would happen. However if you think about it what happens to VMC with lower thrust? Think about it, with less thrust you will encounter less yaw due to assymetric thrust. I wish that I had kept some copies of the runs we performed while working on this...but I didn't and don't have a way to duplicate them now.
Jon
Thanks for your comments! I hope this thread has been interesting and thought provoking, if not please let me know. If anyone has some questions send em!!
Actually the improved performance off of the wet runway with reduced thrust was due to a difference in VMCG. Until I saw it I would not have thought this would happen. However if you think about it what happens to VMC with lower thrust? Think about it, with less thrust you will encounter less yaw due to assymetric thrust. I wish that I had kept some copies of the runs we performed while working on this...but I didn't and don't have a way to duplicate them now.
Jon
Seejonfly, sorry I've been too tied up in personal matters to look at pprune,...I perfectly understand the stupidity of ground vehicle drivers
,..so I hope all is well get better
now back to business
---in my view many of these items have been discussed thoroughly on pprune in the context of various operational problems encountered by pilots regarding performance however in light of the teaching and performance engineering aspects [and I'm in 100% agreement that it needs further exploration in flight training curricula], I'm not saying it's not worth discussing again and again,...and the question you've submitted to pprune are exactly some of the issues that need to be explained much better and currently pilot texts fall hopelessly short ---even the 'official' FAA stuff---of approaching the subject correctly,
Mutt, Old Smokey, and John Tullamarine are all experienced performance engineers; who I'm sure share your concerns [I'm not but I'm no slouch with the subject
] and perhaps a search of Pprune will be highly enlightening as to the type of questions that pilots generally ask
but, also I'm sure that the aforementioned gentlemen would be glad to direct you to areas of this vast subject that tend to cause operational confusion
but from my experience and education gained from Pprune they mostly concern
1. the segmented takeoff wrt to runway geometry
2. obstacle clearance and OEI flight paths [engine failure charts/procedures]
3. the derivation and limitations and uses of operational speeds V1, VR, V2
4. derated and FLEX or ATM takeoff
5. wet and contaminated runways
6. the limitations of FMC derived speeds
7.the Unbalanced field [which relates to item 1]
again sorry for the delay, I hope the accident was comparatively minor, and of course feel free to PM me if you wish
PA
,..so I hope all is well get betternow back to business
---in my view many of these items have been discussed thoroughly on pprune in the context of various operational problems encountered by pilots regarding performance however in light of the teaching and performance engineering aspects [and I'm in 100% agreement that it needs further exploration in flight training curricula], I'm not saying it's not worth discussing again and again,...and the question you've submitted to pprune are exactly some of the issues that need to be explained much better and currently pilot texts fall hopelessly short ---even the 'official' FAA stuff---of approaching the subject correctly,
Mutt, Old Smokey, and John Tullamarine are all experienced performance engineers; who I'm sure share your concerns [I'm not but I'm no slouch with the subject
] and perhaps a search of Pprune will be highly enlightening as to the type of questions that pilots generally ask but, also I'm sure that the aforementioned gentlemen would be glad to direct you to areas of this vast subject that tend to cause operational confusion
but from my experience and education gained from Pprune they mostly concern
1. the segmented takeoff wrt to runway geometry
2. obstacle clearance and OEI flight paths [engine failure charts/procedures]
3. the derivation and limitations and uses of operational speeds V1, VR, V2
4. derated and FLEX or ATM takeoff
5. wet and contaminated runways
6. the limitations of FMC derived speeds
7.the Unbalanced field [which relates to item 1]
again sorry for the delay, I hope the accident was comparatively minor, and of course feel free to PM me if you wish
PA
