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I've always wondered how much the elevator actually needs to deflect in order to cause rotation on takeoff for a large airliner. On videos I can rarely see the elevator moving at all.

I'd really like to know what the degree required is for a 777, but if someone can provide this for another airliner that would be ok. I presume that it depends on takeoff speed, which is of course variable, but let's see what you can come up with.

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  • $\begingroup$ Degree measured from what? The elevatot doesn't have to deflect much because the whole stabilizer is already turned to an optimal setting for take-off. Even the angle of attack for the stabilizer would be hard to say since it depends on speed, weight and center of gravity. $\endgroup$ – Sami Jul 3 '15 at 14:47
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    $\begingroup$ @Sami The stabilator AoA might not be hard to see. On the EMB-145, e.g., it is almost always +8 degrees for takeoff and if you look closely (on ours at least) there is a scale painted on the tail to visually read the stabilator AoA. $\endgroup$ – casey Jul 3 '15 at 17:17
  • $\begingroup$ There's a scale on the tail of E190 also. I'm pretty sure it's not degrees though. Even if it was, I would still find it difficult to determine the elevator angle during takeoff. $\endgroup$ – Sami Jul 4 '15 at 11:55
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    $\begingroup$ Stabilator settings vary by CG, takeoff weight, and power setting. In Boeing 747 manuals they're in section 1-06-001. You can look at an example at terryliittschwager.com/WB/manuals/… starting at the 71st page of the pdf. I don't know how to convert from the stab units to degrees. $\endgroup$ – Terry Jul 4 '15 at 17:19
  • $\begingroup$ @casey Sorry, I was wrong. They are degrees. Just checked.. $\endgroup$ – Sami Jul 5 '15 at 13:38
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It depends. Mostly on two parameters:

  1. What is the position of the center of gravity? A more forward position would require a bigger downforce at the tail, so deflection angles would be bigger. On the 777-200, c.g. positions from 14% to 44% of MAC are allowed.
  2. What is the trim setting of the stabilizer? Depending on the setting, more or less deflection is needed to set the whole horizontal tail to the right downforce for rotation.

Further parameters are flap settings, take-off mass, rotation speed and desired rate of rotation, but the first two are the most important.

Since I do not have the official Pilot's Operating Handbook for the Boeing 777, the virtual version has to do. Sadly, it contains very little information. The more seedy corners of the internet have maybe more substantial content, but here you are on your own.

The Boeing 777 has a computer based weight and balance system, called Accuload, which will compute the proper take-off trim setting, therefore, no discrete values can be given. With the recommended trim setting, the pilot will apply forward pressure on the control column until roatation speed ($v_R$), relaxing control forces to neutral for smooth rotation.

If you would take off with the trim setting for cruise, the elevator would need to be deflected by approx. -10° (trailing edge up) in a simulation with typical parameters. Please note that this is not the regular take-off procedure, and the actual deflection angles are much smaller.

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