D and X
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D and X
Is anybody familiar with the "D" and "X" method of take-off performance prediction and if so can you explain what the "D and X" values actually represent?
I understand that it is a reasonably old method of take off prediction not widely used nowadays but I have failed to find any references either on the web or in text books. I am happy with using the method to predict the take-off performance but I don't have a physical understanding of what the parameters D and X actually represent.
A quick summary (or some useful references) would be much appreciated
Thanks
I understand that it is a reasonably old method of take off prediction not widely used nowadays but I have failed to find any references either on the web or in text books. I am happy with using the method to predict the take-off performance but I don't have a physical understanding of what the parameters D and X actually represent.
A quick summary (or some useful references) would be much appreciated
Thanks
D& X
D77, going back a bit, and you may get more answers on Tech Log, but here goes; taken from the Brize Norton `Aeroplane scheduled performance ` notes, which I believe were based on the VC-10, operated to `Perf `A`.
`D` represents the equivalent balanced field length, taking account of wind, slope ,etc.
`X` represents a correction to the respective deviation from the balanced field power failure speed ratio.
Values of `x` are ratios of V1 and Vr for a balanced field, but the value of 100 is equiv. to the balanced field length.
Thus `x` is 100 when `toda` and `emda` are equal in still air, no slope. thus a `toda` and an `emda` of 6000ft, `d` would be 6000, and `x` is 100.
Graphs are for `d` and `x` for toda and emda,,`d and x` for `tora ` and emda; `d` for `toda- all engines operating`; `tow ` for a given value of `d`; PFSR` for a given value of `x`; limitation on `pfsr( brake energy considerations).
If you want the notes , send me a pm. Syc
`D` represents the equivalent balanced field length, taking account of wind, slope ,etc.
`X` represents a correction to the respective deviation from the balanced field power failure speed ratio.
Values of `x` are ratios of V1 and Vr for a balanced field, but the value of 100 is equiv. to the balanced field length.
Thus `x` is 100 when `toda` and `emda` are equal in still air, no slope. thus a `toda` and an `emda` of 6000ft, `d` would be 6000, and `x` is 100.
Graphs are for `d` and `x` for toda and emda,,`d and x` for `tora ` and emda; `d` for `toda- all engines operating`; `tow ` for a given value of `d`; PFSR` for a given value of `x`; limitation on `pfsr( brake energy considerations).
If you want the notes , send me a pm. Syc
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D and X
Sounds pretty much like the HS125 data also. A quaint English way of performance calculation methinks?
We certainly have the 'D' value charts, yet rarely have to resort to them. For the vast majority of performance planning a quick reference table gives us a value for required runway length without concern for the effect of clearway, stopway, slope, wind etc. This gives us a runway length more than adequate with lots spare room. After all most runways are more than long enough, certainly for us.
But if we need to make more accurate calculations using all the TODA TORA clearway stopway information then we go into the 'D' calcs using all the data available.
Quick reference table might give 5500', using 'D' charts could bring it down closer to 4500'.
Sycamore has put given you an academic answer, mine is just to add that indeed they are still a consideration for take off calculations should we be performance limited.
Hope this helps.
Sounds pretty much like the HS125 data also. A quaint English way of performance calculation methinks?
We certainly have the 'D' value charts, yet rarely have to resort to them. For the vast majority of performance planning a quick reference table gives us a value for required runway length without concern for the effect of clearway, stopway, slope, wind etc. This gives us a runway length more than adequate with lots spare room. After all most runways are more than long enough, certainly for us.
But if we need to make more accurate calculations using all the TODA TORA clearway stopway information then we go into the 'D' calcs using all the data available.
Quick reference table might give 5500', using 'D' charts could bring it down closer to 4500'.
Sycamore has put given you an academic answer, mine is just to add that indeed they are still a consideration for take off calculations should we be performance limited.
Hope this helps.
