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machine2035

Guide/Tutorial: Takeoff Performance in the 777

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Thank you. Very interesting read.

You're welcome.

 

If anyone has any other questions regarding understanding some of the data presented in the Performance Dispatch/Inflight sections of the FCOM, please ask away!


Regards,
James White

 

Aerosoft (Airbus X Extended/Twin Otter Extended/PFPX) & Majestic Q400 Beta Team
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This guide is so useful.

 

I think FMC calculates V-speeds automatically, can you confirm that?

 

BTW, why you don't calculate takeoff distance from the charts provided in FPPM than tables? Wouldn't that be easier?

 

Now what we need is a source for a complete set of these tables! The PMDG NGX has many, but not all, of these and I fear the 777 may be similar.

FCOM has some of these tables. You can still calculate takeoff distance, but only with one flaps setting. (e.g. only the tables for flaps 15 is included, not flaps 5 or 20)

David Chen

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The FMC for the PMDG 737NGX series does calculate Vspeeds, so I think it is safe to assume the 777 will.  If I understand correctly, the FMC's do actually have the Vspeed data stored, but 1) pilots should verify this and 2) SOPs can dictate using different sources such as runway specific tables to accommodate obstacle clearance.

 

This guide is so useful. 

 

I think FMC calculates V-speeds automatically, can you confirm that? 


FCOM has some of these charts. You can still calculate takeoff distance, but only with one flaps setting. (e.g. only the chart for flaps 15 is included, not flaps 5 or 20)

 

Again, based on the NGX (which may or may not be similar), we get the everything but the TO1/2 to TO weight adjustment chart and the assumed temperature chart.  Unfortunately, these are both critical in determining the proper derate.


Can anyone elaborate on what climb, obstacle, tire speed and brake energy refers to on these the TO1 adjusted weight chart?  Obviously certain conditions, but I'm not clear exactly what?


Eric Szczesniak

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Can anyone elaborate on what climb, obstacle, tire speed and brake energy refers to on these the TO1 adjusted weight chart? Obviously certain conditions, but I'm not clear exactly what?

Currently at work on my iPad, but when I finish in a few hours ill explain it all - unless someone beats me to it :-).


Regards,
James White

 

Aerosoft (Airbus X Extended/Twin Otter Extended/PFPX) & Majestic Q400 Beta Team
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Can anyone elaborate on what climb, obstacle, tire speed and brake energy refers to on these the TO1 adjusted weight chart?  Obviously certain conditions, but I'm not clear exactly what?

 

 

Okay. So basically, the purpose of the 'TO1 Takeoff Weights' table is to be able to convert the figures calculated by the 'Takeoff Charts' into ones that take-into account the 10% less thurst available

 

For example, you find, after plotting your lines on your 'Obstacle Limit' chart, that your obstacle limit weight is 280t. If you look at the TO Takeoff Weight table, you can see that corresponds to 251.9t. So therefore, using a TO-1 derate, due 10% less thrust, your now limited to a MTOW of 251.9t. On a OPT or similar tool in real life, usually the MTOW is follow by a letter. A number followed by S, usually means structural MTOW (so what the plane is designed to go to), or a L which means limit (due to obstacles, brake energy etc.)

 

I have only ever seen a few cases were MTOW are limited by brake energy or tire speed, but there are a few airports where obstacles play into the game. It all just depends where you are flying out of.

 

Hope this helps a bit.


Regards,
James White

 

Aerosoft (Airbus X Extended/Twin Otter Extended/PFPX) & Majestic Q400 Beta Team
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James,

 

Many thanks for your explanations.

 

I am still unsure how the calculations that you have demonstrated may differ from those calculated by the FMC. If they are the same, then we may not require TOPCAT.

 

However, I believe that they are not the same, mainly because of meteo conditions and obstacle heights/distances. Therefore, is it true to say that we are dependent on TOPCAT supporting the T7 if we are using PFPX?

 

Cheers, Richard


Cheers, Richard

Intel Core i7-7700K @ 4.2 GHz, 16 GB memory, 1 TB SSD, GTX 1080 Ti, 28" 4K display

Win10-64, P3Dv5, PMDG 748 & 777, Milviz KA350i, ASP3D, vPilot, Navigraph, PFPX, ChasePlane, Orbx 

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James,

 

Many thanks for your explanations.

 

I am still unsure how the calculations that you have demonstrated may differ from those calculated by the FMC. If they are the same, then we may not require TOPCAT.

 

However, I believe that they are not the same, mainly because of meteo conditions and obstacle heights/distances. Therefore, is it true to say that we are dependent on TOPCAT supporting the T7 if we are using PFPX?

 

Cheers, Richard

Hi Richard,

 

The FMC is only able to calculate V-Speeds. As mentioned by some others, it is unable to calculate using the ATM (Assumed temperature method) for an assumed temperature and associated de-rate rating. Usually if the figures in the FMC are conservative compared to what we calculated, we will use them anyway (but keep the assumed temp/de-rate that was calculated).

 

In regards to your TOPCAT/PFPX question, I am not too sure what you are asking. TOPCAT is not needed at all to use PFPX for it's main purpose - to generate/build a flightplan and hence release an Operational Flight Plan.

 

On aircraft which are supported by TOPCAT (not the 777 at this stage), the only advantage of having TOPCAT with PFPX is that you can incorporate the TO DATA directly into the OFP release rather than calculating it at a later stage individually with TOPCAT application.

 

I assume we will see another 3rd party dev such as Aurasim or that bloke that made the freeware NGX take-off data calculator some time in the near future... I just hope those which would like to have some primitive performance method prior to these such tools being released.


Regards,
James White

 

Aerosoft (Airbus X Extended/Twin Otter Extended/PFPX) & Majestic Q400 Beta Team
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If you want accurate non balanced Vspeeds you will definitely need TOPCAT, the FMC and above method only gives you balanced v speeds.


Rob Prest

 

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If you want accurate non balanced Vspeeds you will definitely need TOPCAT, the FMC and above method only gives you balanced v speeds.

There are also charts/tables which will calculate the neccesary reductions required to your v-speeds to provide a selected margin.

 

Therefore the speeds can be un-balanced (For those unfamiliar, a balanced v speed means stop distance = take off distance required).

 

Remember, that airlines and software developers all get their data from somewhere in the first place - Every thing is able to be calculated manually... It is just very time consuming, and for most of the general public, such manuals/info from the manufacturer is not available (I am just fortunate I have it).

 

I agree TOPCAT would make it a tonne easier, hoping Christian can create a profile sometime in the future once PFPX settles down.


Regards,
James White

 

Aerosoft (Airbus X Extended/Twin Otter Extended/PFPX) & Majestic Q400 Beta Team
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Yep, understood. Was trying to clarify that TOPCAT is the best tool for simmers that want accurate Vspeeds that are calculated by the onboard laptops or EFB.

 

I also have access to the runway specific charts and as you say it can be a hassle performing the calculations, I still know of one Gulf carrier that refuse to supply crew with onboard laptops.


Rob Prest

 

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I also have access to the runway specific charts and as you say it can be a hassle performing the calculations, I still know of one Gulf carrier that refuse to supply crew with onboard laptops.

Does it begin with S...

 

I have a sneaking suspicion (damn thats alot of alliteration) :lol: :P


Regards,
James White

 

Aerosoft (Airbus X Extended/Twin Otter Extended/PFPX) & Majestic Q400 Beta Team
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James and Rob,

Many thanks for your replies. I think that I now understand.

Cheers, R


Cheers, Richard

Intel Core i7-7700K @ 4.2 GHz, 16 GB memory, 1 TB SSD, GTX 1080 Ti, 28" 4K display

Win10-64, P3Dv5, PMDG 748 & 777, Milviz KA350i, ASP3D, vPilot, Navigraph, PFPX, ChasePlane, Orbx 

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On aircraft which are supported by TOPCAT (not the 777 at this stage), the only advantage of having TOPCAT with PFPX is that you can incorporate the TO DATA directly into the OFP release rather than calculating it at a later stage individually with TOPCAT application.

 

There's a lot of confusion on this in the PFPX forums, so to clarify.  OFP's do not include takeoff Vspeeds and derated takeoff data.  If included, the only takeoff performance data is in relation to maximum takeoff rate for the runway in use for current meteorlogic conditions.  PFPX simulates this in the OFP.  No Vspeeds or derate are included.  This function is all done without "opening" TOPCAT.  However, after the OFP is generated, PFPX can send the payload/fuel data from the OFP to TOPCAT (which is actually opened at this point) and you can then make your loadsheet and takeoff/landing report as you normally would.


Eric Szczesniak

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I'm looking at these data more and more.  I anticipate that it may be a while until we have a TOPCAT profile.  What I am seeing with these tables here is that I think as a community we could maybe make a excel spreadsheet that can do a lot of these lookup values and serve as a close proxy.  In fact, some of these data are easily reduce to mathematical functions (TO1 to TO weight adjustment...I checked) that negate the need for the table even.

 

Now here's the problem.  I'm not a computer programmer, but I'm ok with excel and good with math, so I can figure that stuff out.  I don't have access to these data though.  From this thread alone, we can do flaps 15 TO and TO1 with assumed temperatures though.  Does anyone think that as a community we could get enough information together to cover at least TO2 as well and then maybe flaps 5 also?

 

I would certainly simplify this some, such as considering wet and dry conditions only rather than break, obstacle or tire speed weight limits.  But I think this could be feasible.  The most work would actually be entering the data in to an excel spreadsheet.  The math/lookup tables can be pretty quick work.


Eric Szczesniak

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Further to the question on what the FMC can do.;. it can spit out V-speeds for you, but before you're allowed to take-off (in real life), you have to draw lines on hard to read charts to make sure that you're going to get off the ground! Not something the FMC can do. Obviously software like TOPCAT replaces the need to manually plot your take-off solution.


David Zhong

 

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