PMDG MD -11 FLEX data finished.

[XWRed5 0]

Dear all,Bryan brought this thread to my attention, I'm not an expert in performance but I'll see if I can shed some light on some of the questions asked.And don't forget guys, UTOPIA is just a multi dimensional interpolation machine with a whole bunch of fudge factors for various variables, the fact it's providing derates anywhere near charts is a miracle.The maximum derate (minimum thrust) allowed for takeoff is controlled by a number of things. The main limitation we are seeing here is that take off thrust cannot be less than climb thrust. It would make no sense to take off, reach the acceleration altitude and then increase power to climb away. You can never take off with less than climb power set.I don't know how climb power is calculated but I do know that it increases with pressure altitude. i.e. the higher you go the more thrust climb power will produce.Therefore if the derate limit you are up against is climb power then as you place yourself at airports increasing in altitude then the maximum derate will go down (i.e. produce more thrust) so that at least climb power is always being produced on the take off roll.That is why the aircraft will not let you set a take off derate temperature that would equate to less than climb power.Hope this helps,Ian

[xkoote 57]

This aircraft really has the most ridicules but versatile flap/slat system, reminds a lot of the older generation up/down switch type flaps (-;Yahav lipinski

Our company flies MD-80's and always use the optmum flaps sytem above 61.000 GW. You thought the MD-11 is rediculous? The MD-80 can set any flap angle from 0.0

[yahavl 0]

Our company flies MD-80's and always use the optmum flaps sytem above 61.000 GW. You thought the MD-11 is rediculous? The MD-80 can set any flap angle from 0.0

[adamant365 28]

Hello All,I have a quick question about using these fantastic charts. I have a nomograph that can be used to determine airport density altitude from current pressure altitude. If I use that chart and get the actual density altitude of the airport, do I still need to apply the pressure correction based on a non-ISA ambient atmospheric pressure? I'm having trouble understanding how if your charts are based on the aerodrome's current density altitude, we would still have to do a correction for current atmospheric pressure. Thanks for any explanation you can give me. Adam

[E6BAV8R 88]

The maximum derate (minimum thrust) allowed for takeoff is controlled by a number of things. The main limitation we are seeing here is that take off thrust cannot be less than climb thrust. It would make no sense to take off, reach the acceleration altitude and then increase power to climb away. You can never take off with less than climb power set.I don't know how climb power is calculated but I do know that it increases with pressure altitude. i.e. the higher you go the more thrust climb power will produce.Therefore if the derate limit you are up against is climb power then as you place yourself at airports increasing in altitude then the maximum derate will go down (i.e. produce more thrust) so that at least climb power is always being produced on the take off roll.That is why the aircraft will not let you set a take off derate temperature that would equate to less than climb power.Hope this helps,Ian

Actually, yes you can. However, I am not sure of the MD-11. On the Boeing 737, 747, 75/767, your TO thrust can be below Climb thrust - and it is not uncommon.

[yahavl 0]

Hello All,I have a quick question about using these fantastic charts. I have a nomograph that can be used to determine airport density altitude from current pressure altitude. If I use that chart and get the actual density altitude of the airport, do I still need to apply the pressure correction based on a non-ISA ambient atmospheric pressure? I'm having trouble understanding how if your charts are based on the aerodrome's current density altitude, we would still have to do a correction for current atmospheric pressure. Thanks for any explanation you can give me. Adam

Hi Adam,Actually Bryan's charts like most aircraft performance charts are designed in a philosophy that all the charts represent the aircrafts performance at a standard atmospheric datum, this philosophy is derived from the way aircraft performance testing is standardized. This means the charts will give you the standard atmospheric performance DATAAnd the ways to correct for non standard conditions.I believe that the confusion is because Bryan has chosen to categories the charts indensity altitude in ISA conditions. This basically refers to pressure altitude as pressure altitude equals density altitude in ISA conditions Conventionally the altitude on the charts should be in PRESURE ALT.That being said, technically there is no conflict between the terms in Bryans charts(For standardization of a performance chart the density altitude with ISA conditions at a given altitude should be renamed to Pressure altitude as density altitude is just a performance term and does not represent elevation or actual altitude) Simply put the charts should be used as though they represent actual airport elevation with the options to correct for non standard atmospheric conditions.1. Aircraft altitude equals chart elevation (interpolation will be needed for accuracy)2. Aircraft performance equals chart corrected for atmospheric conditions.Hope this helped Yahav

[Tallguy 9]

Update on my auto take-off which wasn't planned :( Have flown multiple times since, used the charts and never ever had that same issue again. Must have been some user-error @ keyboard :( I can't recall. Anyway..all is well on the left seat.

[Saturn_V 0]

Hello All,I have a quick question about using these fantastic charts. I have a nomograph that can be used to determine airport density altitude from current pressure altitude. If I use that chart and get the actual density altitude of the airport, do I still need to apply the pressure correction based on a non-ISA ambient atmospheric pressure? I'm having trouble understanding how if your charts are based on the aerodrome's current density altitude, we would still have to do a correction for current atmospheric pressure. Thanks for any explanation you can give me. Adam

Hi Adam, I

[adamant365 28]

Bryan,Thank you for the detailed reply. So, just so I know this 100% straight: for the conditions in my example (assuming the density altitude was 2000ft as in my example from what I obtained from my other chart) I would use the 2000 chart and still make the correction for barometric pressure variance from 29.92in. This is correct, right? It's funny, but if I had gone with my gut and trusted your charts and the corrections, I would have been okay. My gut told me that the correction for non-standard pressure was there because as the air pressure changes, so too does the number of molecules available to move over the airfoil and generate lift. And now the big DUUUUH...the density altitude on your chart assumes a barometric pressure of 29.92 at that density altitude, regardless of how the density altitude was figured. That's the piece I was missing in my thoughts. Phew, now that I've got that straight...thank you so much for figuring this out and helping me to understand the physics. I'll have you know that I graduated with a bachelor's in science (in medical technology no less) and never had to take a physics course. My wife tells me I'd love physics with my enjoyment in the science behind the flight simulation. I tell her I would merely pull all my hair out. :( I love being right occasionally :( Adam

[Saturn_V 0]

Bryan,Thank you for the detailed reply. So, just so I know this 100% straight: for the conditions in my example (assuming the density altitude was 2000ft as in my example from what I obtained from my other chart) I would use the 2000 chart and still make the correction for barometric pressure variance from 29.92in. This is correct, right?

[adamant365 28]

[Saturn_V 0]

Okay, so no matter what, I would always use the "Sea Level" chart for an airport that sits on the earth between 0 and 2000 feet above sea level (elevation), regardless of what the current atmospheric air pressure and temperature is doing to my altimeter??

Yes.

I can just toss my "Density Altitude Calculation" nomograph out the window, right??

Um, yes, well, you don

[adamant365 28]

Bryan,Okay, I think I finally get it. Simply follow the instructions and I'll get what I need. One thing's for sure...I'll never need to ask another question about how to use these FLEX calculation charts again. On a side note, I'm know I'm not alone in my appreciation of this work you have done. It adds a tremendous amount of realism and nicely fills in a gap in the takeoff preparation portion of -11 flights. Thank you for the hard work.Thanks,AdamP.S. I didn't realize I had used "dense" in my attack of myself until after I posted it. Now THAT'S ironic....

[adamant365 28]

@Yahav,I didn't even see your post until just now. I must have glazed right over it...I gave it a read and now I also understand why Bryan's charts say "Density Altitude" at the top even though the altitude that an end user should start with when doing the FLEX determination is the airport's elevation. And here I thought that I knew something about aero science....Thanks you for that explanation. This information is very helpful for my understanding as well. Adam

[E6BAV8R 88]

By the way, the images for the FLEX data are no longer showing up.