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Old 13th Aug 2018, 16:13
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FCeng84
 
Join Date: Feb 2009
Location: Seattle
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I agree with eckhard's thinking about approach and flair pitch attitude, flight path angle, and resulting AOA. I question the data presented above by scifi. Pitch attitude during 777 landing rarely exceeds 5 degrees. Tail strike would occur at about 10 degrees depending on which minor model is involved. With flight path angle close to zero at touchdown, AOA is approximately equal to (no more than one degree higher than) touchdown pitch attitude. 777 touchdown AOA is much closer to 5 or 6 degrees than the 10+ degrees scifi suggests.

Another issue I take with scifi's data is stall AOA for 777 in landing configuration. With flaps out to 30 and slats fully gapped (position commanded with flap lever at 30) the stall AOA is much higher than 13 degrees. Stall AOA for this configuration is 20 degrees or higher.

Commercial aircraft are not and should not be operated near stall during any part of a normal mission. A key performance parameter is the ability to execute a prompt go-around if one is needed at any time during the landing sequence. This means having the ability to pull up with as much as 0.3g incremental (total of 1.3g) from the approach or even during flair. In order to maintain this performance margin, AOA cannot be allowed during normal operation to get so high as to not allow for a 30% increase in lift without risk of stalling. Because the zero lift AOA is actually quite a bit below zero with flaps extended, approach AOA cannot be allowed to get to much more than 2/3rd of stall AOA.
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