View Full Version : Direct Lift Controls

17th Feb 2000, 19:23
Does anyone have any information on Direct lift controls? Thanks again

17th Feb 2000, 20:59
Tristar thing.

Not much of an engineer

17th Feb 2000, 22:32
Great no pitch change during an ILS just goes up and down like an elevator using spoilers I took the DLC out of a L1011 b4 they cut it up very complicated :makes life tough for an engineer I'd think ?

gas path
18th Feb 2000, 03:13
Tristar 500 got even more complicated has MDLC (manoevering direct lift control) and RBS (recovery speedbrake) all automatic.!besides the ACS (active control system)

18th Feb 2000, 04:01
Okay, this is all great information fella's but I am still not sure of EXACTLY what a Direct Lift Control is?

Cornish Jack
18th Feb 2000, 20:54
Tristar DLC was, as has been said, PFM.
When flaps were selected into the Landing range, the spoilers popped up to a null point (on the early models) of 7 degrees. Thereafter when pitch inputs were made, the spoilers would deploy further - up to 14 degrees for pitch down inputs and down to zero for pitch up inputs. (those were MAXIMUM values and were applied pro rata to the amount of pitch input). The effect, therefore, was to provide vertical positional change with minimum pitch disturbance.
The null position was increased on the 500s to 9 degrees(if memory serves correctly) with a similar operating function. The other active controls bit was effectively using the ailerons to provide gust load alleviation by means of a clever piece of kit detecting gusts as soon as the aircraft felt it at the nose and providing an aileron droop to compensate immediately.
The Tablets of Stone are lurking at home somwhere if you need chapter and verse from the Tech Authors. :)

18th Feb 2000, 21:02
Should we say DLC is a passenger comfort enhancing feature on approach ?

Not much of an engineer

19th Feb 2000, 13:15
The DLC makes handflying a ILS easier by staying on glideslope with little pitch/power changes (sort of like an elevator effect).
Just remember that "rolling it on" on landing in a L-1011 makes for a a landing similar to extending the speedbrakes in the flare...

5th Feb 2001, 05:53
Smooth landings in the TriStar are NOT difficult once the technique is mastered. Have seen guys try the "Boeing push" with poor results ie: a real thumper.

8th Feb 2001, 10:21
Chatting to an ex-Lockheed L-1011 test FE, part of the reason for installing DLC on the L-1011 was it was fairly pitch unstable at landing flaps 33 and 42 ( if my mem serves me...?), so they wanted a smoother vertical rate control for auto-lands. If you look at the plan view of the a/c, you'll see that the tailplane/trailing edge of the wing are very close coupled.

I preferred landing it with the DLC un-latched, personally. Just to add to the tech description, the spoilers also operated in the roll mode through mixers, at the same time as operating in the DLC mode, leading to every check-airmans' favourite question:
" you're high on the approach into HKG and need to tighten, what happens to the positions of all the spoilers during the manouvre? Which hyd systems are powering which? What's their max deflection? 40 or 60, plus or minus the 14 degrees ?" Oh my God....I could have killed that flt-test FE, personally.....

The 747 is much nicer....but the TriMotor was well ahead of it's time, and built well.

John Farley
12th Feb 2001, 02:05

A direct lift control is one that enables the pilot (or autopilot) to vary the lift at constant pitch attitude. It has the advantage that the controls do not have to fight the pitch inertia to get an attitude change to make the AOA change. (A potentially big advantage with a high mass aircraft)

The normal way such systems are arranged is that they reduce lift by using a spoiler type of surface. If this system is partially deployed at the start of an approach then by waggling the spoilers a tad in and out from this mid position you control lift directly.

Or you could wave the ailerons (symmetrically of course) up and down together to get the same effect of a lift variation at constant AOA. The notion was much in favour before the likes of the 747 came along as designers worried about the difficulty of quickly changing pitch attitude on such “monsters”. In fact pilots did not find it too hard so long as they got the approach “stabilised” well out. (In other words did not have to vary the lift close in!)

Any help?


13th Feb 2001, 12:08
Interesting to note that "another aircraft" uses DLC, the Space Shuttle. The patent belongs to Lockheed.

FE Hoppy
18th Feb 2001, 02:44
L1011 DLC
"reduces longitudinal scatter" ie the a/c touches down in the same area on the runway when coupled to an apropriate ILS. as said the spoilers move to a null 9 degrees position and operate up and down from there. This results in a stable approach attitude with elevator inputs controling rate of descent. It works very well, having completed 3 auto lands this week all were on the centerline 1000' from the threshold with about 1-200fpm sink on touchdown. Very smooooth.

18th Feb 2001, 10:16
Ahhhh, Lockheed! Have flown the 1649A & 1329(in addition to the L1011) and they were surperb as well.