Slow Takeoffs

[Fabo 213]

Happy to help Dan, takeoff performance seems to be one of those areas where simmers have some deeply rooted misconceptions so I always try and make sure to add something - its nice to see I'm not doing it wrong and someone actually benefits.

 

FWIW Boeing has a very nice CBT that explains performance, though for obvious reasons I cannot share it...

[NEXTGENERIC 1]

What are your flaps configured to? If you haven't set them, you're going to have a problem.

[jetsflier 87]

Were you given your V1/VR/V2 speeds from the FMC? If they were never given, that means the aircraft knows it is unsafe to use that runway for departure. 

 

There was someone who a little while ago had this issue at Chicago, and they were able to get off the ground, but barely in time. They found out that no V speeds were given, which just proves that the takeoff was unsafe.

[cannonplug 126]

This discussion raises an interesting question for me, particularly because just yesterday I saw the "Air Disasters" episode about the crash of the Yak in which almost all the members of a Russian hockey team lost their lives.

 

The conclusion was that the FO was riding the brakes during the takeoff roll, which of course kept the airplane from reaching proper speeds in time (among several other issues). The investigators spoke of the importance of properly calculating V1 and how not having done so led in part to the crash. it seems, however, that the issue was not a wrong calculation, but simply the fact that they reached V1 much too late.

 

So, my question is whether there's an objective way for the crew to know at which point down the runway they're supposed to have reached V1 so that they can abort the takeoff if they haven't.

[77west 139]

 

 

Topcat does not provide data for the 300er yet, only for the lr/f which has different engines...

Just to be picky, they are actually exactly the same engine, some operators on the -200LR and F did choose the slightly (4.8%) more powerful rating of the -115B, (standard on the -300ER) and with no TOPCAT -300ER profile, the 77F profile get use as close as we can. I realize it is technically "wrong" but so far for me has resulted in numbers within a few kt of the manuals. Best we can do for now...

[aerhead1 5]

Thanks everyone for the tips. The runways in question were 25R at VHHH, 7R at LAX, and 14L at O'Hare. All pretty long runways. I probably did need to check the MTOW. I'll have to keep that in mind for the next flight.

[hopskip 253]

What flap setting?

The 777-300ER, being heavier than the 777-200LR, often needs more flap in my experience.

I used to fly some shorter hops (YSSY - YMML, 1.5hr type distance) in the 777-200LR and deploy flap 5 for a VR of around 135 - 145 knots.

 

To get the same kind of VR on the same distance with the -300ER I'm usually needing to deploy flap 15, because flap 5 gives VR of 155+kts.

 

Havn't flown anything longer than KLAX - EGLL in the -300ER yet, but I was seriously considering flap 20 already by then.

[pcubine 143]

My first attempt was Hong Kong to Chicago. I don't remember the weight cause the flight was yesterday.

Do you remember the number of pax and cargo weight. If I can get any kind of weight I can have PFPX and TOPCAT do their thing and see what they come up with.

[Morvious 43]

I have done some ULH flights and had the same issue once or twice. Although V-speeds were fine it just didn't get there in time.

 

Problem was that TopCat gave me a derated takeoff and the 300 didn't like it. On all my TO1 or TO2 takeoffs the 300 felt sluggish.

 

When this happened I always knew before hitting 80 kts. It takes already ages to get to it so I aborted, resetted takeoff performance page with an higher rating and took off without an issue.

 

Untill TopCat can provide me with a 300ER profile I have learnt that the 200F profile isn't going to do it on these type of flights

[Fabo 213]

 

 

Just to be picky, they are actually exactly the same engine, some operators on the -200LR and F did choose the slightly (4.8%) more powerful rating of the -115B, (standard on the -300ER) and with no TOPCAT -300ER profile, the 77F profile get use as close as we can. I realize it is technically "wrong" but so far for me has resulted in numbers within a few kt of the manuals. Best we can do for now...

 

They are a different airframe though. Overall length changing leads to several important differences in takeoff behaviour, one of which is lowering of minimum control speeds due to longer arm on rudder, another would be higher minimum unstick speed due to lower AoA before tailstrike.

 

I would say doing the TOPCAT as a sanity check only and keeping the FMC values would be better - best I can offer is do the full balanced field calculation by QRH / FCOM v1.  It will be somewhat more limiting than using TOPCAT and a lot slower, but you'll have the nice feeling of comfort in that you are safe and legal.

[77west 139]

They are a different airframe though. Overall length changing leads to several important differences in takeoff behaviour, one of which is lowering of minimum control speeds due to longer arm on rudder, another would be higher minimum unstick speed due to lower AoA before tailstrike.

 

I would say doing the TOPCAT as a sanity check only and keeping the FMC values would be better - best I can offer is do the full balanced field calculation by QRH / FCOM v1.  It will be somewhat more limiting than using TOPCAT and a lot slower, but you'll have the nice feeling of comfort in that you are safe and legal.

Touche. I should mention I ONLY use the derate figures provided by topcat - not the V-speeds. I use the FMC v-speeds. I do realize they are different airframes and the length has seen me rotating a lot more carefully than in the -200.

 

I have done the FCOM calcs but after a long day at work and only time for a quick flight, I figured topcat was better than nothing...

[Fabo 213]

 

 

Touche. I should mention I ONLY use the derate figures provided by topcat - not the V-speeds. I use the FMC v-speeds. I do realize they are different airframes and the length has seen me rotating a lot more carefully than in the -200.
 
I have done the FCOM calcs but after a long day at work and only time for a quick flight, I figured topcat was better than nothing...

 

If you take it with a grain of salt - as you seem to do - then you should be OK.

[3-2-1-Now 126]

If you don't need the best second segment climb performance the aircraft is capable of, then try a higher flap setting (instead of flap 5, try flap 20).

 

Best regards,

Robin.

[Jmg22511 0]

My Takeoff Roll is so slow it’s unusable. Light plane full thrust 10000 ft runway I’m only at 120 kts at the end

[Budbud 227]

Hi,

I can see three possibilities but there is a big lack of info in your post:

_ Takeoff thrust too low > What was your thrust?

_ Brakes not fully released (most likely) > Check the temperature of the brakes on the gear page and recalibrate your hardware. Also if you use fsuipc, it may be worth creating a brand new profile from scratch

_ Issue with friction > What sim do you use and do you use any friction script with fsuipc?

Also, be informed that PMDG requires that you sign your posts with full names.

Edited February 25, 2018 by Budbud