Blackbird From , joined Dec 1969, posts, RR: Posted (7 years 2 months 5 days 5 hours ago) and read 4373 times:
The DC-10 has two slat positions; one setting from flaps 0 (slats only) to anything less than 35-degrees to my knowledge which yields optimum Lift/Drag ratio, and the second setting from Flaps 35 to Flaps 50 (full-down) which while not yielding the best Lift/Drag ratio, gives the most lift of the two.
The L-1011 has a single slat position which from the minimum flap setting (Flaps 4 IIRC) all the way to Flaps 42 (Full-Down)
-Why doesn't the L-1011 use a similar set-up to the DC-10?
-Is the L-1011's slat set-up optimised for the highest Lift/Drag ratio, or a best-fit across the whole range of speeds which the flaps are down?
(BTW: This thread even though being about the L-1011 and DC-10 is not in anyway connected with the previous thread about the L-1011 and DC-10's wing positions)
DH106 From United Kingdom, joined Jun 2005, 626 posts, RR: 1
Reply 1, posted (7 years 2 months 5 days 1 hour ago) and read 4340 times:
I'm not sure your statement about the DC-10's first slat setting giving 'optimum' Lift/Drag is correct. I can't imagine ANY slat deployment increasing L/D above the optimised cruise value simply because although slats' improve lift considerably, there's bound to be flow seperation behind & under them. I think you'll find the first slat setting on any aircraft with multiple settings gives a better L/D than fully extended, but not as good as cruise. It's a compromise for takeoff.
As to your question, there are many possible reasons - a lot of these questions you're posing are really those that can only be properly answered by the design engineers from the companies concerned, and may at the end of the day have purely arbitary answers. At the time of design, the engineers didn't have the luxury of looking back as we're doing now and comparing two or more designs. But possible answers might be:
* The intermediate setting might not be absolutely necessary but something that Douglas added anyway to enhance performance.
* The L-1011 airfoil/slat setup might yield a higher L/D than the DC-10's fully extended, possibly making an intermediate slat setting unnecessary.
* Perhaps the L-1011 has a slightly higher thrust/weight ratio on takeoff making drag less important than lift
But clealy Lockheed didn't feel it was necessary through their test program or they'd have fitted a 2 posistion system. Retrofitting a slat system like this probably wouldn't be a major structural design change - so if required it would have been done.
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