Takeoff config policy?

[FreightDog]

Having watched the WAR Polar DVD some operational questions have arisen.

On the 744, they always took off using full thrust and flaps 10.

So the question is whether there is a common policy with regards to flex temps, TO1 or TO2 and flap settings under normal circumstances? For instance, do the RW guys use full thrust even for shorter flights with an almost empty plane?

Thanks!

p.s. I have adjusted the weights in the load manager, aircraft cfg and the fsbuild aircraft profile according to the official weights published by Boeing for the GE engines, the one modeled by PMDG (as there are 3 different models) . By doing so I get the correct weights, correct ZFW etc. in KG's. Should anyone need them, just answer and I'll post the settings.

[1691]

It really depends on the situation. The great thing about reduced thrust/assumed temperature takeoffs (they are 2 different things) is not only does it save wear and tear on the engines, but it saves fuel. If youre ferrying out of somewhere empty, theres no reason to use full thrust. The length of the flight isnt really that big of a deal, as much as the weight at takeoff.

[nwadc10]

Usually airlines will want you to flex as much as possible for the reasons Allen mentioned. What the flex takeoff does is allow you to takeoff with a lower thrust setting and still meet certain performance requirements in the event of an engine failure. In other words, at full thrust, the takeoff exceeds the performance requirement, with a flex thrust takeoff the performance requirements are met but doesn't exceed (to put it simply).

With regards to flaps settings, sometimes you have to adjust what flap setting is used to allow a flex thrust takeoff. In scenario 1, flaps 20 takeoff, you may not meet the required performance but if you takeoff at flaps 10 the requirements are met. In this case, if you want to flex, you must use flaps 10. In general, flaps 10 will give you better climb performance (in case your flex is restricted by climb performance) whereas flaps 20 will give you better runway "performance", i.e. shorter takeoff roll and lower V1 and Vr.

If there's an obstruction in the departure path then you will be most likely climb restricted. If your runway isn't huge then you may be runway restricted.

How do you know if you can flex or not, or even if you can takeoff at all at your weight? The minimum performance requirement is expressed in gross weight. In the real world, the crew will get a maximum weight for takeoff (XTOG). There are several different limitations that can cause a lower MTOW that's less than the structural MTOW (the max takeoff weight noted in the manuals).

First we have RTOG (Regulatory Takeoff Weight) which is actually a combination of a few max weights: Runway Limit, Climb Limit, and Structural Limit. The runway limit takes into consideration accelerate stop, accelerate go, obstruction clearance, brake energy (V1mbe), and tire speed. The RTOG becomes the most restrictive weight of the three above. Next, the landing limit is considered. Take the structural landing limit and add the planned fuel burn and that's your XTOG, landing limited. Max Zero Fuel Weight usually isn't a concern for takeoff but is for leaving the gate and beginning a taxi. Exceeding MZFW and moving under your own power will cause a gate return and mx inspection. Taking all of that into consideration, XTOG is the most restrictive.

As you can see, there is a lot that goes into takeoff planning. If your actual takeoff weight is well below XTOG you will most likely be able to flex at which point you will get a flex temp and flex weight (your new XTOG using flex thrust).

How do we apply this to FS? So far the only way I know of is to use the TOPCAT program which works for the 744 and 763 while the Takeoff Calculator that comes with RFP will give you a flex temp but not a flex XTOG I believe.

I am planning to add this feature to GCFM for all of our aircraft types but I can't gaurentee it because it's a pretty big task.

[Mike Schmitt]

I am starting to get really interested in this product TOPCAT (http://www.topcatsim.com/ )and I have couple of questions. Am I reading this program right you can load passengers and/or freight into PMDG directly out of this software and plan your flight minus fuel? Or can it actually plan you fuel load too?

[Joe Clark]

Has anyone created an aircraft database file of all the Polar Aircraft for TOPCAT? Since we have all the r/w info for all of the fleet, it would make it even more realistic so we can calculate proper thrust and such with TOPCAT

[FreightDog]

Usually airlines will want you to flex as much as possible for the reasons Allen mentioned. What the flex takeoff does is allow you to takeoff with a lower thrust setting and still meet certain performance requirements in the event of an engine failure. In other words, at full thrust, the takeoff exceeds the performance requirement, with a flex thrust takeoff the performance requirements are met but doesn't exceed (to put it simply).

With regards to flaps settings, sometimes you have to adjust what flap setting is used to allow a flex thrust takeoff. In scenario 1, flaps 20 takeoff, you may not meet the required performance but if you takeoff at flaps 10 the requirements are met. In this case, if you want to flex, you must use flaps 10. In general, flaps 10 will give you better climb performance (in case your flex is restricted by climb performance) whereas flaps 20 will give you better runway "performance", i.e. shorter takeoff roll and lower V1 and Vr.

If there's an obstruction in the departure path then you will be most likely climb restricted. If your runway isn't huge then you may be runway restricted.

How do you know if you can flex or not, or even if you can takeoff at all at your weight? The minimum performance requirement is expressed in gross weight. In the real world, the crew will get a maximum weight for takeoff (XTOG). There are several different limitations that can cause a lower MTOW that's less than the structural MTOW (the max takeoff weight noted in the manuals).

First we have RTOG (Regulatory Takeoff Weight) which is actually a combination of a few max weights: Runway Limit, Climb Limit, and Structural Limit. The runway limit takes into consideration accelerate stop, accelerate go, obstruction clearance, brake energy (V1mbe), and tire speed. The RTOG becomes the most restrictive weight of the three above. Next, the landing limit is considered. Take the structural landing limit and add the planned fuel burn and that's your XTOG, landing limited. Max Zero Fuel Weight usually isn't a concern for takeoff but is for leaving the gate and beginning a taxi. Exceeding MZFW and moving under your own power will cause a gate return and mx inspection. Taking all of that into consideration, XTOG is the most restrictive.

As you can see, there is a lot that goes into takeoff planning. If your actual takeoff weight is well below XTOG you will most likely be able to flex at which point you will get a flex temp and flex weight (your new XTOG using flex thrust).

How do we apply this to FS? So far the only way I know of is to use the TOPCAT program which works for the 744 and 763 while the Takeoff Calculator that comes with RFP will give you a flex temp but not a flex XTOG I believe.

I am planning to add this feature to GCFM for all of our aircraft types but I can't gaurentee it because it's a pretty big task.

Thanks for the info. I was aware of these things, I also use TOPCAT and am familiar with it. I really enjoy such high levels of realism.

The only reason I asked the question is still the same I wrote in my first post: watching the Polar DVD, they always used flaps 10 and full t/o thrust, regardless from where they were actually departing. Maybe just short runways and high TOWs, windshear reported etc.

Again, thank you.

[1691]

It could be that the runway config charts they had were for full thrust takeoffs only. I can recall a time when I worked at PO departing BOS empty at full thrust in a -400 because we only had the full thrust takeoff charts on board.