I don't know how to describe this problem in short, I will try.

 

In default state PMDG 737-800 NGX is loaded about 67% of MTOW, with 100% fuel. I place it on LSZH (Zurich) runway, set flaps to 5, push the throttle to 96 or 98 N1, and rotate on 150kts, first at 12 degrees than 15. About 300ft I retract the gears, and in that moment NGX is going around 160kts. The problem is aircraft won't increase the airspeed when climbing above 1500ft/m, staying at 160-165kts not allowing me to set flaps to 1 at above 180kts and then off above 200kts. When I retract the flaps to 1 at 160kts (not safe in RL) the speed will increase slowly at the above climb rate. So that is a practically a derated takeoff at 96/98 N1, and with that almost heavy payload (67%) I think the throttle must be at TO/GA to perform as expected. But in that case what to do when payload is 80-90%? In that scenario even TO/GA will not help. This airplane is very underpowered. What if the airplane is departing from airport located at much higher altitude? Is there something I've missed?

Hmm..I don't have that problem.  When you lift off, you climb out at v2+10 or so until you reach acceleration height.  Once there, you lower the nose to start gaining speed.  Using VNAV (or LVL CHG with the speed bug at 250) should do that for you.  Vertical speed isn't that important while speeding up as long as it stays positive and you don't have obstacles in your way (which is another matter).

 

Also, make sure you are not de-rating the climb thrust too much for the climb out.

The aircraft will not exceed the speed of the flaps in AP.  Manually yes.  You also have to watch your vertical speed.  If you manually take off (which is proper) and pull the joystick back to say 2500 to 3000 fpm, then you will lose speed and you will have to manually change the vs.

 

Best regards,

Hmm..I don't have that problem.  When you lift off, you climb out at v2+10 or so until you reach acceleration height.  Once there, you lower the nose to start gaining speed.  Using VNAV (or LVL CHG with the speed bug at 250) should do that for you.  Vertical speed isn't that important while speeding up as long as it stays positive and you don't have obstacles in your way (which is another matter).

 

Also, make sure you are not de-rating the climb thrust too much for the climb out.

 

Oops, my mistake that I didn't lowered the nose at acceleration height.  :ph34r: In contrary I continued to climb at the same rate not allowing the plane to gain any speed as far as I can see.

 

The aircraft will not exceed the speed of the flaps in AP.  Manually yes.  You also have to watch your vertical speed.  If you manually take off (which is proper) and pull the joystick back to say 2500 to 3000 fpm, then you will lose speed and you will have to manually change the vs.

 

Best regards,

 

I forgot to say that I do this take off practice fully manual, without AP, FMC and other mumbo jumbo. Jsut simple take off routine practice and a pattern around the airport just for fun.

 

 

So the shortest answer is - pull the yoke, climb at 2000-3000fpm, retract the gears, reach acceleration height, lower the nose to reach 180 then 200 kts to retract the flaps, and go for a climb out?

 

 

I forgot to say that I do this take off practice fully manual, without AP, FMC and other mumbo jumbo. Jsut simple take off routine practice and a pattern around the airport just for fun.
 
 
So the shortest answer is - pull the yoke, climb at 2000-3000fpm, retract the gears, reach acceleration height, lower the nose to reach 180 then 200 kts to retract the flaps, and go for a climb out?

 

FPM is less relevant that establishing a pitch angle that achieves a steady IAS around V2+10 and holding it. Make pitch adjustments as required. At acceleration height lower the nose, set climb thrust and carry on.

 

While your desire to not use the automation is admirable, it's all there for a reason, and it would benefit you to use it to learn how to fly a jet takeoff profile before you go fully manual and 'use the force'. Of course, it's a sim at the end of the day, and you can do what you want! 

Same what Devin said.  If you enabled AP, your flight management system would do all the figuring out for you (when properly configured).  I enable AP as soon as I retract the gear.  I may or may not bring the flaps up and, if I do not, it will not speed up until I do.  I like to keep the speed down a little while the aircraft is going through the SID waypoints.

 

Best regards,