What causes the slight "pause" at around 10 degrees during rotation in the 767 and 73
 

Appreciate any factual technical information on why does the 767 and 737 have a "pause" around 8-10 degrees nose up as the aircraft is rotated for take off? Do any of the FCOM or FCTM mention the reason for the pause?

One explanation is it happens as the tail goes down into ground effect and causes a stick force change. That theory is shot when one considers these aircraft have hydraulic controls with artificial feel. Another theory is the relative positions of the C of G and Centre of Pressure change during rotation, causing a nose down change of trim.

The third answer is that the "pause" is designed into these aircraft to minimise tail strike if the rotation is too fast?

I suspect ground effect considerations. A change in pitching moment is still going to require a change in pilot input regardless of what is between pilot and surface.

I think it is because that is when the aircraft unsticks- the center of rotaion then shifts from the bogies to the C of P.

Presume it's the same thing as what happens in the A319/320/321. More backstick is required around 10 degrees to continue the rotation

Maybe it is due to the stabilizer getting into the wing wake/downwash, which would reduce the stab AoA and the downward lift? Just a thought...

That's correct. It is called "dead band".

It may well be called that but it woud increase the stab alpha and increase it's lift.

Only really noticeable in the sim.

If that is correct, it suggests the fidelity of the simulators needs to be re-examined. The simulator is supposed to accurately replicate operation of the actual aircraft which is why the zero flight time concept was introduced all those years ago. Hands up all those who have never experienced this "pause" while rotation on the real 737,767 et al

To me, al least on the 73, is more noticeable in the plane than in the sim, I will keep an eye on it in the next opc anyway.

The tail going into ground effect is the reason given by our training department on the 737 which has always made sense to me as the tail is getting close to the ground (especially on the 800/900) and we need to keep the tail going 'down' whereas the result of ground effect is to stop that happening.
I don't understand why 'hydraulic controls' discredit this theory as all that needs to be done as one approaches the dead band is increase the elevator deflection.

Yes, and hence the slight pause in rotation....

I assume NT means Northern Territories and thus you're in Oz where everything is upside down.

But just think what happens when you increase horizontal stabiliser lift in the northern hemisphere where the the HS is the right way up ;)

Its because it is cool as hell to do it that way.

Not sure what you're getting at here?

If you increase stab alpa, the stab will want to go up. However at rotation what one wants it to do, is go down! Hence the pause at rotation!!!

Thanks Mono!::8

there are some ugly scratches on the tail when you pitch significantly higher with the mains still on the ground. :ooh:

Memory is that the 727 had the most noticeable lag. You'd rotate and it would sit there 'yeah, what do you want me to do now?' and then it would say 'ok, I'll fly'.

737 has it also. Guys ask what a 727 flew like - a 737NG with derated 22K. :ooh:

Don't recall it on the 767.

Like sevenstroke said - why's it do that? Because it's cool. ;)

What happens to the elevator when you pull back on the stick and what does that do to the stab alpha??

Even my girlfriend can understand it!

Disagree there, flew the B767-300ER for three years, thought the 'lag' was very noticeable. Can't say I ever noticed it on the B737-200, but that was a long time ago!