Help) My 747 tends to take off too early and nose up.

[Rations 102]

I don't think it's correct to say Flap 20 should be used if heavy enough. Either 10 or 20 can be used as long as weight, runway length and obstacle clearance is fine. Some carriers standardise on 20, some on 10 and others leave it to the pilot's decision. Given the option, some pilots prefer 10, others 20.

But takeoff weight definitely affects takeoff distance depending on the flaps setting. While there is not a rule that says "above a certain weight, flaps 20 should be used, regardless of other conditions", my understanding is that flaps 20 shortens takeoff distance, the latter of which may become an issue in specific cases when the weight of the aircraft is very heavy, and maximum thrust does not result in safe or sufficient speed gain during takeoff roll.

 

I used to use flaps 10 for my short B747 flights, and was intrigued by how some carriers standardize flaps 20. My takeoff speeds were already very low with flaps 10, and rotation and climb were very rapid and responsive. I have since adopted the flaps 20 standardization, and I actually like seeing the extended flaps during replays.

[kevinh 409]

But takeoff weight definitely affects takeoff distance depending on the flaps setting. While there is not a rule that says "above a certain weight, flaps 20 should be used, regardless of other conditions", my understanding is that flaps 20 shortens takeoff distance, the latter of which may become an issue in specific cases when the weight of the aircraft is very heavy, and maximum thrust does not result in safe or sufficient speed gain during takeoff roll.

 

I used to use flaps 10 for my short B747 flights, and was intrigued by how some carriers standardize flaps 20. My takeoff speeds were already very low with flaps 10, and rotation and climb were very rapid and responsive. I have since adopted the flaps 20 standardization, and I actually like seeing the extended flaps during replays.

Yes, Flap 20 reduces the takeoff roll, but Flap 10 increases the climb gradient. If both settings are possible then it's a matter of preference or company SOP.

[joolsd 10]

Flap 20 or 10 are used, but it shouldn't cause the problem. The FMC should calculate the CG and trim setting regardless of the flap setting. If the PERF page is set up correctly.

[fstulm 4]

Julian,

 

No FMC in this world can calculate the CG! The trim GIVEN the CG yes, but not the CG. CG is the product of the load sheet where you better not lie.

 

To be able to compute the CG, the FMC would need extremely scale-like precision sensors at each wheel which no aircraft that I know of has.

 

Regards

Ionut "John" Micu

[joolsd 10]

But there's a cheat for the CG if I remember when I had the 747. On the scratch pad? I'm not saying the real one has sensors.

 

There is a right CG and trim setting for each weight and cargo., just making the flaps 10 or 20 won't make a difference, except a shorter take off roll. If there is a problem with the nose going up, it will be something else.

[yos233 1]

But there's a cheat for the CG if I remember when I had the 747. On the scratch pad? I'm not saying the real one has sensors.

 

PMDG does include with the 747 (and 737) an atomatic CG calculator. By pressing the CG button with nothing in the scratchpad, it will give you your current CG (and calculated trim),