I understand that without TOPCAT support, we cannot know the recommended takeoff flap settings to be used for a flight, so we usually just default to flaps 5.

 

Has anyone had a takeoff where a takeoff flaps setting of greater than 5 has been necessary?

 

Cheers, Richard

i use flaps 15 when the ac is loaded more than 300 000kg and if i use a runway shorter than 3500m. and flaps 20 when the ac is close to his mx tow wivh is around 251 000 kg(-300er) and runway less than 3000m .

but as u mantioned, we cannot know exactly the optimum config with accurency.

In the -300ER I use flaps 15 under 90% of circumstances, due to higher gross weight, reduced tail clearance, etc. Only if the aircraft is incredibly light, with a TOW of less than around 240 tonnes, do I go for flaps 5.

 

Not very precise, I know, but it seems to work quite well.

 

Best regards.

I use full flaps for take off, but I don't fly my planes like mortals do, so please ignore me :smile:

I understand that without TOPCAT support, we cannot know the recommended takeoff flap settings to be used for a flight, so we usually just default to flaps 5.

 

Has anyone had a takeoff where a takeoff flaps setting of greater than 5 has been necessary?

 

Cheers, Richard

 

There's at least Beta support for the -200LR in the latest TOPCAT beta release...

 

It will occasionally have flaps 15/20 as optimal config when operating close to MTOW on "shorter" runways. I don't fly the -300ER, and there's no TOPCAT support for it beta or otherwise, so I can't speak to it.

I use an airline takeoff performance calculator which gives me both 5 and 15 in the 300er.

 

I don't think it's as straight forward as lighter = less flaps , the algorithm is a little more complex

 

Alex

 

 

I don't think it's as straight forward as lighter = less flaps , the algorithm is a little more complex

 

You have to take into account drag as a result of higher flap settings. Most of the time at heavy weights and a long runway, Flaps 5 is plenty. - At the same weight, Flaps 15 would only increase drag while reducing takeoff distance by a small amount. The increased drag would need to be offset with a higher thrust setting. 

Aircraft weight along with runway conditions etc etc seems to determine flap settings. FMC will compute V1 VR speeds, based on flap setting and TOW. Heavier you are ...use more flaps.....Have used F20 for an 11 hour flight, simply because lower VR speeds at higher flap setting with higher weight beacuse more fuel. Kinda makes sense.

Good topic.  FCTM 16.20 recommends F20 in windshear conditions; otherwise, FCTM 3.3 suggests using higher flap settings will result in less takeoff distance so this is where weight becomes a factor.  Note that tail clearance is constant regardless of flap setting because the Vr schedule is designed to provide this (also FCTM 3.3)

 

I prefer F5 unless there's reason to go higher just because acceleration performance is better and I love having a little excess thrust on takeoff. I have used F15 with there was an altitude constraint right after departure turn like many of the KDFW RNAV SIDs, in a heavy -300ER I also boost V2 a little to increase my climb angle but none of that is in TOPCAT... just guesswork.

 

 

Heavier you are ...use more flaps.

 

This is not accurate in many scenarios. You have to remember that these calculations take into account loosing an engine just at or after V1. 

 

If its hot, high, and your heavy, chances are, Flaps 15 or 20 will induce way too much drag for you to safely be able to loose an engine at V1 and still have enough thrust to overcome the drag forces in order to proceed with the liftoff and climb out. That is one of the critical factors for takeoff thrust calculations that many are likely forgetting.

 

Overall, in most cases, heavier does not = more flaps. 

I wonder how long we shall have to wait for TOPCAT to provide for B77W?

This is not accurate in many scenarios. You have to remember that these calculations take into account loosing an engine just at or after V1.

 

If its hot, high, and your heavy, chances are, Flaps 15 or 20 will induce way too much drag for you to safely be able to loose an engine at V1 and still have enough thrust to overcome the drag forces in order to proceed with the liftoff and climb out. That is one of the critical factors for takeoff thrust calculations that many are likely forgetting.

 

Overall, in most cases, heavier does not = more flaps.

Taking into acc RW length, lower flap settings at higher TOW will mean a higher VR speed, then imagine losing an engine, may have no runway left to safely rotate. Works both ways I imagine.

...and so far I haven't seen mention of climb performance yet.  Different flap settings affect initial climb performance as well (which TOPCAT also calculates...surprise).

 

Ever see a LIMIT: CLIMB message in the results box?

 Ever see a LIMIT: CLIMB message in the results box?

 

Yes I've seen this on a few occassions. What exactly does this mean?

Yes I've seen this on a few occassions. What exactly does this mean?

 

LIMIT: FIELD would be the length of the runway itself, given the parameters used.

LIMIT: CLIMB (or OBS) would be the need to clear an obstacle, or meet a minimum climb gradient, given the parameters used.

 

A lot of people forget that takeoff performance includes initial climb figures, too.  The CLIMB limit would be one of those times where TOPCAT is using a lower assumed temp or higher trust rating in order to meet climb performance requirements.