747 leading edge slats?
Discussion
When did this become a thing???
https://youtu.be/149TJ9nxxRU
Leading edge "flap" "retraction" at the 4.20minute mark. Or more accurately flat panel fold away. When did aircraft start using that method rather than the fixed slat/slot? Looks massively draggy.
(Came about watching KLM747 landing by a passenger inside, and the retraction on landing looked a good way to massively increase drag).
https://youtu.be/149TJ9nxxRU
Leading edge "flap" "retraction" at the 4.20minute mark. Or more accurately flat panel fold away. When did aircraft start using that method rather than the fixed slat/slot? Looks massively draggy.
(Came about watching KLM747 landing by a passenger inside, and the retraction on landing looked a good way to massively increase drag).
Just be grateful they generally stay where they're supposed to stay, until commanded otherwise.
A mate was flying a 747 departing Johannesburg, must be nearly 10 years ago now, when a fault that had lain buried in the 747-400 control systems for years manifested itself and the leading edge devices retracted as soon as they had rotated. What followed was a prolonged edge-of-stall incident until they managed to resolve the situation, and they were fortunate not to deliver the aircraft into a populated area. As it happens, my mate's wife, also an airline pilot, was sitting in the First Class compartment directly underneath the flight deck and could hear the stick-shaker going off above. Not good.
Had the same happened to that St Maarten flight they would almost certainly not have made it over the hills.
IanH755 said:
It was used on the 707-320B variant I worked on and they were early 60's build (1st flight 1962) so around early/mid 50's design?
Ah interesting, - I honestly had no idea large aircraft used krueger over slotted/slats. I feel today will be lost looking into this in more depth... Unlike a multiple screwjack operated slotted slats which move the slats as a single item, the "panel" style each have their own separate jack, meaning they don't deploy/retract as one single surface but each one of the 6 per side (I think) 4-8ft section moves at its own pace within certain limits.
The timing was for all slats to be at deployed within 2 seconds IIRC but each panel would hit the end stop at slightly different times with upto a maxmum of 1/2 second allowed between 1st to last panel fully extending, which means during the travel phase the individual panels can be out of sync by quite a lot which I always thought would effect the aerodynamics but no pilots ever complained of any unauthorised roll moments during slat deployment/retraction so I'm guessing I thought too much about it
The timing was for all slats to be at deployed within 2 seconds IIRC but each panel would hit the end stop at slightly different times with upto a maxmum of 1/2 second allowed between 1st to last panel fully extending, which means during the travel phase the individual panels can be out of sync by quite a lot which I always thought would effect the aerodynamics but no pilots ever complained of any unauthorised roll moments during slat deployment/retraction so I'm guessing I thought too much about it
Brother D said:
IanH755 said:
It was used on the 707-320B variant I worked on and they were early 60's build (1st flight 1962) so around early/mid 50's design?
Ah interesting, - I honestly had no idea large aircraft used krueger over slotted/slats. I feel today will be lost looking into this in more depth... Also, I think all variants of the 747 retract the leading edge devices either side of engines 2 and 3 on landing when the engines are in reverse thrust mode. Not to increase drag, but to reduce the effect of foreign bodies getting blown up into the flap mechanisms.
Separate, slightly connected question:
As the engines are throttled up prior to roll, they always feel / sound like they are at about 70% thrust, then pretty much as soon as the aircraft actually starts moving, say about 5m/s, then the engines are noticeably throttled right up to 'full' power. Is that second throttle up pilot commanded, or just a result on the intake becoming sub critical as the dynamic airflow into the fan increases the upstream pressure? (and the FADEC automatically adding more fuel to account for the increase in core mdot / secondary shaft speed drop)
(or i wondered if the max stationary a/c throttle setting might also be limited to less than 100% n1 in order to prevent the brakes/tyres being overwhelmed in case of a low all up weight / slippy r/way, and hence the pilots only apply full throttle after brake release and enough speed for reasonable flight control authority (rudder i guess primarily) has been gained)
As the engines are throttled up prior to roll, they always feel / sound like they are at about 70% thrust, then pretty much as soon as the aircraft actually starts moving, say about 5m/s, then the engines are noticeably throttled right up to 'full' power. Is that second throttle up pilot commanded, or just a result on the intake becoming sub critical as the dynamic airflow into the fan increases the upstream pressure? (and the FADEC automatically adding more fuel to account for the increase in core mdot / secondary shaft speed drop)
(or i wondered if the max stationary a/c throttle setting might also be limited to less than 100% n1 in order to prevent the brakes/tyres being overwhelmed in case of a low all up weight / slippy r/way, and hence the pilots only apply full throttle after brake release and enough speed for reasonable flight control authority (rudder i guess primarily) has been gained)
Composite Guru said:
jamieduff1981 said:
They're called Kruger Flaps. 
Beat me to it. https://en.m.wikipedia.org/wiki/Krueger_flap
Max_Torque said:
Separate, slightly connected question:
As the engines are throttled up prior to roll, they always feel / sound like they are at about 70% thrust, then pretty much as soon as the aircraft actually starts moving, say about 5m/s, then the engines are noticeably throttled right up to 'full' power. Is that second throttle up pilot commanded, or just a result on the intake becoming sub critical as the dynamic airflow into the fan increases the upstream pressure? (and the FADEC automatically adding more fuel to account for the increase in core mdot / secondary shaft speed drop)
(or i wondered if the max stationary a/c throttle setting might also be limited to less than 100% n1 in order to prevent the brakes/tyres being overwhelmed in case of a low all up weight / slippy r/way, and hence the pilots only apply full throttle after brake release and enough speed for reasonable flight control authority (rudder i guess primarily) has been gained)
On most aircraft you’d set a middle power setting and make sure all the engines are working and producing the same power before advancing them to take off power. As the engines are throttled up prior to roll, they always feel / sound like they are at about 70% thrust, then pretty much as soon as the aircraft actually starts moving, say about 5m/s, then the engines are noticeably throttled right up to 'full' power. Is that second throttle up pilot commanded, or just a result on the intake becoming sub critical as the dynamic airflow into the fan increases the upstream pressure? (and the FADEC automatically adding more fuel to account for the increase in core mdot / secondary shaft speed drop)
(or i wondered if the max stationary a/c throttle setting might also be limited to less than 100% n1 in order to prevent the brakes/tyres being overwhelmed in case of a low all up weight / slippy r/way, and hence the pilots only apply full throttle after brake release and enough speed for reasonable flight control authority (rudder i guess primarily) has been gained)
If on a big twin engine jet you shoved the thrust levers all the way forward and one engine was slow to accelerate or worse failed, you’d be off the runway pretty quick due to the thrust asymmetry. It’s worse at low speeds as the rudder isn’t having much affect due to the lack of air passing over it.
As an aside, take off power is usually reduced from full power to save the engines. Airlines use fixed de rates (reduced percentage of maximum power) and assumed temperatures (telling the aircraft it’s warmer than it is) or a combination of both to extend engine life. You’d only really use full power if there was a problem with the aircraft or a very short runway or maybe some dodgy winds around.
Edited by anonymous-user on Tuesday 19th September 16:49
Condi said:
Must feel good for the pilots when they get the opportunity to really wind them up.
Sometimes you ferry an empty aircraft somewhere that has a issue that requires a full power take off, they can be a bit of a handful In a previous type I flew, if you did a go around at some light weights it would reduce power as it was going up so fast. That’s very disconcerting, seeing the autothrottle going back when you’re climbing near the ground.
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