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RPRIEVER

Takeoff flaps...when not to use other than 5

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Greetings all..A question about the proper flap settings for takeoff. I usually read that the normal setting is 5. I'm have the 737-600/700, and recently bought the 800/900, but I would assume this question could refer to the 747's as well. When would you use a different flap setting? Is it directly related to take-off speed, or does airport altitude/weather/aircraft weight also factor into the equation?Ron

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Ron,it all comes down to how much runway you have and how much you need. A higher flaps setting basically gives you lower take-off speeds.Now there are numerous factors to consider for how much runway you need: Take-Off weight, Temperature, Wind, Runway surface contamination, etc.But as you said most aircraft have a standard flap setting. For the B744 it is 10 or 20 when heavy, the FBW Airbusses have Flaps 2, MD-11 anything from 15 to 25 depending on company.So with these standard settings the question is not really what flap setting to use but more importantly how much derated thrust to use, if any. Most of the time you just go with the standard flap setting and then look in the tables if a derated thrust is possible. I intentially say most of the time, there are many things to consider with all these factors influencing the take-off performance.Regards,Markus

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Good question (I've wondered the same thing). I notice in the TAKEOFF PERFORMANCE section that V-speeds are a function of weight and flaps, but there is no guidance on which flap setting to employ.I don't understand what the Required Takeoff Field Length Tables are based on. Seems to me that the length of runway required to liftoff wouldn't have anything to do with the length of available runway but that is what the table seems to convey.I'm not a jet jock, most my time is in a piston twin where runway length depends on weight, density altitude and wind component. The simulation adds to the complexity of the problem by introducing variable thrust options and flap setting. The PMDG documentation is lacking in this regard.I think the question of how much flaps to use is a trade-off between speed and distance. The more flaps you use, the lower the V-speeds but I'd expect acceleration and therefore runway distance to increase due to the additional drag caused by higher flap settings. Lower V-speed verses longer time required to reach V-speeds. There's no reference data to go by. I'm sure there's also a consideration to single engine performance and the need to have enough excess thrust available for successful climbout in the event of an engine failure.I hope to hear from the experts too.

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The runway length tables are used to check you have enough runway length available for the gross weight you plan. If not you either have to reduce your gross weight or choose a longer runway. These days the Electronic Flight Bag takes care of these look-ups and calculations, hopefully someone will come up with the PC equivalent for use with this sim.Flaps 20 means a shorter takeoff run (extra drag is more than compensated for by lower V-speeds), but slower climb out and longer time to accelerate and clean up. It is often a matter of company policy and pilot preference more than anything else.Hope this helpsKevin

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>the FBW Airbusses have Flaps 2, MD-11 anything from 15 to 25>depending on companyNot really relevant here, but Airbuses can use anything from Flap 1 to Flap 3 for takeoff. The MD-11 has a variable flap detent for takeoff, which is set from takeoff data via the dial-a-flap system. I really hope the forthcoming PMDG MD-11 has this simulated. No flightsim addon for a McDonnell Douglas aircraft has had it incorporated so far.Some aircraft, such as the Fokker F.28 and Fokker 100/70 can takeoff with no flaps. So there is no such thing as a standard flap setting in reality.Kevin

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Thank you, Kevin. I still wish we had something in the aircraft data that provided takeoff distance verses weight, thrust, flaps and density altitude. I googled this subject for awhile and found some tables for the -300. Also found an accident report for a 737-200 that failed to lift off after rotation due to aircrew error, the aborted takeoff overran the runway and did some damage. It was many years ago. But there's a lesson here.I also found that the flap configuration affects takeoff attitude, where tailstrikes are more likely with less flap, everything else equal.I'm amazed that this bird has enough thrust that acceleration rates are less significant than V-speeds. Is it true then that more flaps is better up to a limit as long as climbout isn't an issue?

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