748 Takeoff Dynamics

[HighFlyer310 21]

Hello all -

I've noticed a difference in takeoff dynamics with regard to pitch in the -8. I understand that there are differences in the wing & air frame design so it makes sense.

In the -400 series.. upon reaching Vr.. i'll start a smooth pitch up at the standard rate & the mains will leave the ground right at or above v2 for a nice climb out.  In the -8.. I use the same procedure however it seems very sluggish to get airborne & achieve v2+.  There seems to be more back pressure required to sort of "pull it off" the runway as opposed to letting it fly off.  Acceleration through v2 is also slightly delayed.  I understand there are several factors that come into play here.  I've done testing at different weights / thrust settings & get same results.  It could be a controller issue (sensitivity set to max & zero null calibrated through P3D).  It could be a non issue & this is just how the -8 behaves.  I'm certainly no expert but just wanted to start a topic to see if I might be having a problem or using incorrect procedure. 

Tom

Edited February 16, 2019 by HighFlyer310

[downscc 1,327]

It took me awhile to adjust to the -8 as well.  The FCTM recommended procedure for normal rotation is to rotate to 9 deg nose up at a rate of  2.5 deg per second to achieve liftoff about 5 sec after Vr and by 35 ft AGL attitude is 11-14 deg nose up, which occurs about 8 sec after Vr.  Don't stop rotating at 9 deg, keep adding the pitch up for V2+10.

Vr calculation includes tail strike protection but do not over rotate, and of course under rotating will use much more runway.

Edited February 16, 2019 by downscc

[vc10man 732]

This absolutely fascinating aircraft is becoming more and more a real Study Level aircraft all things considered. Good thing there are very clever guys like you, Dan, here to augment thoughts.

[berts 97]

21 hours ago, downscc said:

It took me awhile to adjust to the -8 as well.  The FCTM recommended procedure for normal rotation is to rotate to 9 deg nose up at a rate of  2.5 deg per second to achieve liftoff about 5 sec after Vr and by 35 ft AGL attitude is 11-14 deg nose up, which occurs about 8 sec after Vr.  Don't stop rotating at 9 deg, keep adding the pitch up for V2+10.

Vr calculation includes tail strike protection but do not over rotate, and of course under rotating will use much more runway.

Apart from the initial target attitude there isn't really that much difference in technique between the 747-400 and the 747-8 in order to carry out the rotation and establish the initial climb.  Even setting the Flaps to 10 or 20 makes very little difference, if any, to the liftoff attitude in these two aircraft types (approx 10degs and 9 degs respectively). 

A typical initial target attitude of 15 degs in the 400 will take around 6 - 7 seconds after VR to achieve and, as Dan has said, in the -8 it is between 11 -14 degs and will take a second or so longer.  As the aircraft leaves the runway you might notice a slight 'hesitation', so It is important to keep the rotation rate going by keeping a constant back pressure and aim for the target attitude commanded by the F/D.  At very light weights the pitch attitude might be higher than normal, but in all cases the most important point is to rotate at the correct speed and rate and aim for an intitial climb speed of V2+10kts or the achieved, up to a maximum of V2+25kts.

[HighFlyer310 21]

On 2/16/2019 at 2:14 PM, downscc said:

It took me awhile to adjust to the -8 as well.  The FCTM recommended procedure for normal rotation is to rotate to 9 deg nose up at a rate of  2.5 deg per second to achieve liftoff about 5 sec after Vr and by 35 ft AGL attitude is 11-14 deg nose up, which occurs about 8 sec after Vr.  Don't stop rotating at 9 deg, keep adding the pitch up for V2+10.

Vr calculation includes tail strike protection but do not over rotate, and of course under rotating will use much more runway.

 

On 2/17/2019 at 11:56 AM, berts said:

Apart from the initial target attitude there isn't really that much difference in technique between the 747-400 and the 747-8 in order to carry out the rotation and establish the initial climb.  Even setting the Flaps to 10 or 20 makes very little difference, if any, to the liftoff attitude in these two aircraft types (approx 10degs and 9 degs respectively). 

A typical initial target attitude of 15 degs in the 400 will take around 6 - 7 seconds after VR to achieve and, as Dan has said, in the -8 it is between 11 -14 degs and will take a second or so longer.  As the aircraft leaves the runway you might notice a slight 'hesitation', so It is important to keep the rotation rate going by keeping a constant back pressure and aim for the target attitude commanded by the F/D.  At very light weights the pitch attitude might be higher than normal, but in all cases the most important point is to rotate at the correct speed and rate and aim for an intitial climb speed of V2+10kts or the achieved, up to a maximum of V2+25kts.

This is great stuff guys! Thanks for the input!  It really is amazing how meticulously designed these products are down to subtle differences likes this.  Hats off to PMDG for putting us in the driver's seats of these magnificent machines!

Edited February 20, 2019 by HighFlyer310