Windshear and takeoff flaps settings
Thread Starter
Join Date: Aug 2008
Location: 6554N
Posts: 147
Likes: 0
Received 0 Likes
on
0 Posts
Windshear and takeoff flaps settings
In a twin engine jet aircraft with flap 7 or 15 setting configuration option. How does either flaps 7 or flaps 15 setting affect wind shear escape maneuver?
Bottums Up
In practical terms, I don't think it does. The procedure on the Douglas/Boeing 717 is pitch to the PLI (Pitch Limit Indicator - onset of stickshaker), max power, emergency max power if required, and, DO NOT RECONFIGURE until clear of shear.
In real terms, it is most likely that Flap 7 (I assume you means degrees?) will provide better climb performance than flap 15, assuming all other variables are constant but the manoeuvre would be flown the same way for either flap setting.
In real terms, it is most likely that Flap 7 (I assume you means degrees?) will provide better climb performance than flap 15, assuming all other variables are constant but the manoeuvre would be flown the same way for either flap setting.
Bottums Up
does this have any relationship to second segment climb performance?
Whereas my understanding of windshear escape is that all segments go out the window, and one uses all available power, and the highest AoA possible - without stalling of course to out climb a severe downdraught. Fortunately my experience to date is limited to simulator models, and I hope it stays that way.
Join Date: May 2000
Location: Seattle
Posts: 3,197
Likes: 0
Received 0 Likes
on
0 Posts
In practical terms, flap setting DOES have a bearing on performance!
In the 747, the choice of using Flaps 10 or 20 for takeoff has to balance takeoff roll performance (better at Flaps 20) with climb performance (better at Flaps 10). While the 744 usually has plenty of excess thrust available, it is not the case with the 747 Classic. I have been in a situation where Flaps 20 was needed for runway limitations, but the airplane would not climb above 2000' until the flaps were retracted to 10. If you add windshear to that situation, it is clear that Flaps 20 would significantly detract from climb ability, possibly making recovery impossible.
The obvious answer is to not attempt takeoff when there is known low-level windshear. Also, do not attempt takeoff in marginal conditions when windshear is suspected or forecast. If you decide to risk it, optimize for climb performance, because that is where it will be most needed.
In the 747, the choice of using Flaps 10 or 20 for takeoff has to balance takeoff roll performance (better at Flaps 20) with climb performance (better at Flaps 10). While the 744 usually has plenty of excess thrust available, it is not the case with the 747 Classic. I have been in a situation where Flaps 20 was needed for runway limitations, but the airplane would not climb above 2000' until the flaps were retracted to 10. If you add windshear to that situation, it is clear that Flaps 20 would significantly detract from climb ability, possibly making recovery impossible.
The obvious answer is to not attempt takeoff when there is known low-level windshear. Also, do not attempt takeoff in marginal conditions when windshear is suspected or forecast. If you decide to risk it, optimize for climb performance, because that is where it will be most needed.
Join Date: Jun 2001
Location: UTC +8
Posts: 2,626
Likes: 0
Received 0 Likes
on
0 Posts
Practical reality suggests that if you can get off the pavement at flaps 10, then there is no need to use flaps 20 . . . because once you're airborne, flaps 20 is unnecessary drag during climb, and especially in case of an engine failure. 
Thread Starter
Join Date: Aug 2008
Location: 6554N
Posts: 147
Likes: 0
Received 0 Likes
on
0 Posts
Good points, so the lowest takeoff flaps setting is the best setting in the event of a low level windshear encounter immediately after takeoff. Though we never depart with windshear reported in the vicinity of the airport. Thanks Ladies and Gennts.
