Post by LOU on Jul 9th, 2012 at 6:40pm
We were limited to 30 degrees bank for passenger comfort. The 727 had an interesting quirk, the selection of spoilers from the cockpit went through a device called the aileron mixer spoiler ratio changer . This was a complicated device that mixed the ailerons and spoilers to obtain a rapid roll rate during various phases of flight. With the spoiler handle full down or full up the roll of the 727 was fairly snappy but controllable. If you placed the spoiler handle in something less than full up or full down the roll rate was VERY fast and not considered controllable. The only time in any procedure that the spoiler handle was used in a mid position was during landing with one main not extended. The idea was that the enhanced roll rate would help to keep the wing without the gear off the runway a bit longer. Never had to try it in real life, only in the simulator. However, since the activation of the spoilers was manual, the speed of the movement of the handle was critical. If you moved the handle slowly from down to up during landing and any aileron input happened it was a pretty wild ride and could result in a scraping of the wing tip or flap. Later planes (747, 767, 757) did not have this problem.
As you bank the plane, lift generated by the wing is used to turn the plane.
Here, have a look...
With the plane in level flight the lift is perpendicular to the wing and all is balanced.
As you bank the wing, the lift generated by the wing remains perpendicular to the wing and is used to move the wing sideways. The lift loss needs to be made up or the plane will loose altitude. This is why you need to increase the angle of attack as the bank is increased to make up for the loss of lift in the turn.
If you have the speed brakes/spoilers extended you are loading the wing and the stall speed will increase. If you are at high altitude and heavy weight and either increase the wing load by a steep bank (remember, 60 degree bank turn produces 2 G's) or make a quick level off which also increases the G load you could induce buffet and a stall. The autopilot authority could be exceeded with such a maneuver and may not be able to control the plane and could trip-off. Remember the operating space between stall buffet and Mach buffet at high altitude and heavy weight is very narrow. It is called "coffin's corner" where if you slow down just a bit you stall and if you speed up a bit you are into Mach buffet.
The result of either is not good! :o
Pilots were very careful making abrupt maneuvers or loading the wing at high altitude in the 727 since it had fairly high wing loading. The 707 had a bit more in the way of wing and was a little bit less critical. That is why it was iffy to try to climb over a CB (cumulus build-up) since the higher you go the narrower the operating range is, and a few knots either way results in buffet. In turbulence at high altitude it was recommended to turn OFF the altitude hold and accept a slight loss or gain of altitude since increasing the G load would result in buffet and stall.
Lou
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As you bank the plane, lift generated by the wing is used to turn the plane.
Here, have a look...
With the plane in level flight the lift is perpendicular to the wing and all is balanced.
As you bank the wing, the lift generated by the wing remains perpendicular to the wing and is used to move the wing sideways. The lift loss needs to be made up or the plane will loose altitude. This is why you need to increase the angle of attack as the bank is increased to make up for the loss of lift in the turn.
If you have the speed brakes/spoilers extended you are loading the wing and the stall speed will increase. If you are at high altitude and heavy weight and either increase the wing load by a steep bank (remember, 60 degree bank turn produces 2 G's) or make a quick level off which also increases the G load you could induce buffet and a stall. The autopilot authority could be exceeded with such a maneuver and may not be able to control the plane and could trip-off. Remember the operating space between stall buffet and Mach buffet at high altitude and heavy weight is very narrow. It is called "coffin's corner" where if you slow down just a bit you stall and if you speed up a bit you are into Mach buffet.
The result of either is not good! :o
Pilots were very careful making abrupt maneuvers or loading the wing at high altitude in the 727 since it had fairly high wing loading. The 707 had a bit more in the way of wing and was a little bit less critical. That is why it was iffy to try to climb over a CB (cumulus build-up) since the higher you go the narrower the operating range is, and a few knots either way results in buffet. In turbulence at high altitude it was recommended to turn OFF the altitude hold and accept a slight loss or gain of altitude since increasing the G load would result in buffet and stall.
Lou
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