-8 nose pitching up on the takeoff roll

[downscc 1,327]

53 minutes ago, Sekkha said:

I experienced the same behaviour with the 744, never saw that before the recent major update..

TOW was around 856000 (payload set by RANDOM function) / Flaps 20 /  TO 1 derate / CG 22,6 / Trim settings 6,7 and Vspeeds as suggested by FMC (and except for V1 identical to those suggested by topcat) :  Vr = 170

Aircraft startet rotating on its own some knots before reaching Vr.....

 

Check your controller calibration maybe?

I just gave this a try... I only use derated for things like contaminated runways so I thought it was worth giving ti a trial.  In the B747-400 PW TOW 856 klbs F20 TO-1 CG 22 Trim 6.7 Vr 171.  Watched real close above V1 and never saw any nose up pitch moment.  Sure, there was quite a bit of bouncing but that pretty much smoothed out above 120 kts.

I am using a Thrustmaster Warthog HOTAS stick and throttle, axis assigned and calibrated in P3Dv4.3.

When you say " Aircraft startet rotating on its own some knots before reaching Vr.....  " can you be more specific?  At what speed did it start rotation and how much did it rotate before you intervened?

In many many B747 QOTSII sessions I've never experienced this problem.  None of my fellow beta testers have.  I cannot imagine it is anything other than a controller issue or maybe I guess the bouncing was a surprise and you thought it was rotating? Looking for answers.

Edited October 8, 2018 by downscc

[VHOJT 172]

3 hours ago, downscc said:

Check your controller calibration maybe?

I just gave this a try... I only use derated for things like contaminated runways so I thought it was worth giving ti a trial.  In the B747-400 PW TOW 856 klbs F20 TO-1 CG 22 Trim 6.7 Vr 171.  Watched real close above V1 and never saw any nose up pitch moment.  Sure, there was quite a bit of bouncing but that pretty much smoothed out above 120 kts.

I am using a Thrustmaster Warthog HOTAS stick and throttle, axis assigned and calibrated in P3Dv4.3.

When you say " Aircraft startet rotating on its own some knots before reaching Vr.....  " can you be more specific?  At what speed did it start rotation and how much did it rotate before you intervened?

In many many B747 QOTSII sessions I've never experienced this problem.  None of my fellow beta testers have.  I cannot imagine it is anything other than a controller issue or maybe I guess the bouncing was a surprise and you thought it was rotating? Looking for answers.

I have checked my controller calibration - it is fine, and flight controls show centred when they should.

Trust me, I have done lots of flights with the 747 too, and I have never seen this before two flights recently.

The common factor - both were a high TOW with fuel in stab tank.  I haven't had this happen on my last two flights (SIN-SYD, SYD-SIN) with lower weights.  I have only had the problem twice on the SIN-LHR and LHR-SIN flights.

Look I'll do some testing on my end to see if I can get it to reproduce...

Edited October 9, 2018 by VHOJT

[Sekkha 15]

9 hours ago, downscc said:

Check your controller calibration maybe?  "

My calibration is definiteley fine, I always calibrate controls before each flight

9 hours ago, downscc said:

When you say " Aircraft startet rotating on its own some knots before reaching Vr.....  " can you be more specific?  At what speed did it start rotation and how much did it rotate before you intervened?

 It rotated until liftoff,  I allowed  it to do so in order to see what happened (it was a nice rotation rate just as if I had done it manually :) ....NO BOUNCING.. its was ROTATING

cant remember nor define the exact speed, maybe 2-3 knots before...

 

5 hours ago, VHOJT said:

The common factor - both were a high TOW with fuel in stab tank.

exactly this

 

 

Never had this behaviour before the update. And I did quite a lot of flights, believe me :)

 

Edited October 9, 2018 by Sekkha

[Sekkha 15]

To ammend that:

I just tried the scenario again. Same result. Rotation started  1-2 knots before VR without any intervention

ZFW was 518.6

FUEL LOAD (set by directly entering the amount , not by ground operations):

TOTAL 338,0 --> Center 81,4 / Main 2+3  83,5 / Main 1+4 29,3 /  Res 2+3  8,9 /  Stab 13,2

PAX GE variant

[downscc 1,327]

I guess this is going to be a tricky one to figure out.  I still cannot reproduce.

I just tried with your ZFW 518.6 klbs (always use units pls) Fuel 338.0 klbs distributed by FMS as you annotated with 13.2 klbs in the stab tank in the PMDG 747-400 GE taking off from KIAD rwy 30 Flaps 20 TO power V1 155 Vr 169 V2 180.  I watch the PFD very closely to see if their was any nose up pitch in case I missed a subtle rise from the windshield view and I didn't see any.  Pitch on the HSI remained at zero until I rotated at 170.

This is in P3Dv4.3 with weather set to clear all.

 

[Ephedrin 418]

A few things come to my mind. I have only GA SEP experience, C172, DR400 and HK36. But all of them do the same at „Vr“. (Yeah, you don‘t calculate the speed :D) 

All of them behave just like an airplane behaves as they gain speed: they fly. The C172 gets lighter and at some point it simply flies. Now the B747 has 4 powerful engines below the CG. That‘s why you fly manually on approach with autothrottle off, same with the 737. when the stab trim is set for T/O, it basically neutralizes the weight of the nose at Vr. In my understanding this means that the engines move around the CG and lift the nose as long as you don‘t hold it down manually. Drag mostly takes effect above the engines and above the CG. In a very light airplane you will notice that a lot more than in a heavy sluggish airplane. 

So in my understanding at least that‘s nothing but torque.

[Sekkha 15]

58 minutes ago, downscc said:

I guess this is going to be a tricky one to figure out.  I still cannot reproduce.

I just tried with your ZFW 518.6 klbs (always use units pls) Fuel 338.0 klbs distributed by FMS as you annotated with 13.2 klbs in the stab tank in the PMDG 747-400 GE taking off from KIAD rwy 30 Flaps 20 TO power V1 155 Vr 169 V2 180.  I watch the PFD very closely to see if their was any nose up pitch in case I missed a subtle rise from the windshield view and I didn't see any.  Pitch on the HSI remained at zero until I rotated at 170.

This is in P3Dv4.3 with weather set to clear all.

 

Dan,  if you dont intervene at all,  will it start rotating allone anytime after Vr? If yes, at which speed?

Would be interesting to know  if its just a matter of some knots or if it doesnt rotate allone until quite highr speeds...

 

also PD3v4.3 btw

Edited October 9, 2018 by Sekkha

[downscc 1,327]

34 minutes ago, Sekkha said:

Dan,  if you dont intervene at all,  will it start rotating allone anytime after Vr? If yes, at which speed?

Would be interesting to know  if its just a matter of some knots or if it doesnt rotate allone until quite highr speeds...

 

also PD3v4.3 btw

I don't have enough runway for that test.  I'd have to lighten here a lot and then we'd be comparing apples and oranges.  Let me see if I can find a suitable test runway.

Using the 15000 one at KEDW Edwards AFB with 744 set up as before I find the nose lifts on it's own without control input at V2... 180 kts.  That is 10 kts above Vr in this case.

Edited October 9, 2018 by downscc

[Sekkha 15]

47 minutes ago, downscc said:

Using the 15000 one at KEDW Edwards AFB with 744 set up as before I find the nose lifts on it's own without control input at V2... 180 kts.  That is 10 kts above Vr in this case.

Thanks Dan...so that is about 12 knots above what I have experienced...quite some difference actually....very strange

 

I will try some more scenarios and also how much I would have to trim down to get the same result as you did....

Edited October 9, 2018 by Sekkha

[Bob Scott 7,720]

With the 747-8F, ZFW set at 634.6 via the FMS payload page and 80K lbs of fuel also set thru the FMC, and stab at 6.3 as per the FMC computer, I got an unambiguous uncommanded rotation that required a significant amount of forward yoke to correct at about 20 knots below V1 departing KMEM rwy 18R.  I don't believe that's normal.  Power was set at at the takeoff-1 derate.

Regards

 

[scandinavian13 5,192]

If this is something that you all assert we should look into, please submit tickets with exact steps to reproduce.

[VHOJT 172]

3 hours ago, scandinavian13 said:

If this is something that you all assert we should look into, please submit tickets with exact steps to reproduce.

Will try and find you a way to! 🙂

[Sekkha 15]

12 hours ago, scandinavian13 said:

, please submit tickets with exact steps to reproduce.

Ok, will do that later