mlsrar
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Direct Lift Control

Thu Nov 06, 2003 12:09 am

Having just read some interesting information about the Tristar's ability to take off with an essentially null AOA, I was also informed about the Direct-Lift-Control system. (It isn't too fresh at the moment, but I do believe that was the name of the system)

Does anyone have any information on whether or not this was a true asset to the technology of the Tristar, and, if so, was it incorporated into modern aircraft design?

Regards,

Mike
I mean, for the right price I’ll fight a lion. - Mike Tyson
 
tito
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RE: Direct Lift Control

Thu Nov 06, 2003 3:19 am

I had an instructor who was a retired Tristar captain, and used to say in reference to flying airplanes, "when you push forward the nose goes down, when you pull back the nose comes up... except on the L-1011 that is..." He said it took some getting used to moving the yoke on approach and not effecting a pitch change but rather vertical rate.

this guy has a description:

http://flytristar.tripod.com/page/feature.html

-Tito
 
mlsrar
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RE: Direct Lift Control

Thu Nov 06, 2003 4:48 am

Thanks Tito-

I was also wondering if the automated design was incorporated into modern design?
I mean, for the right price I’ll fight a lion. - Mike Tyson
 
9VSIO
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RE: Direct Lift Control

Mon Jun 22, 2009 12:10 pm

Hi y'all, sorry to dig up such an old thread, but is DLC still used on modern aircraft?
Me: (Lining up on final) I shall now select an aiming point. || Instructor: Well, I hope it's the runway...
 
OldAeroGuy
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RE: Direct Lift Control

Mon Jun 22, 2009 2:07 pm



Quoting 9VSIO (Reply 3):
Hi y'all, sorry to dig up such an old thread, but is DLC still used on modern aircraft?

No, it is not. The L1011 was designed when noise regulation was just beginning.

The emphasis on noise reduction in today's environment makes it unwise to fly the approach with spoilers partially deflected. The additional drag means engine thrust (and noise) will be increased.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
474218
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RE: Direct Lift Control

Mon Jun 22, 2009 4:18 pm



Quoting OldAeroGuy (Reply 4):
No, it is not. The L1011 was designed when noise regulation was just beginning.

The emphasis on noise reduction in today's environment makes it unwise to fly the approach with spoilers partially deflected. The additional drag means engine thrust (and noise) will be increased.

DLC has nothing to do with noise control. Its purpose is to allow vertical corrections to the glide slope to be accomplished without use of pitch control. When the flaps are lowered beyond 30 degrees the four inboard spoilers on each wing assume a new null point. Excursion above or below the glide slope will cause the spoilers to extend or retract bring the aircraft back to the glide slope. This is accomplish automatically through the Flight Controls Electronics Computer (FCES) and works in both autopilot and manual modes.

As for noise requirements: The L-1011 was designed to meet FAR Part 36 noise requirements. Those requirements were: Take off, Sideline and Approach were 106.2, 107.3 and 107.3 Decibels (EPNdB). The L-1011 was certified at 98.1, 97.8 and 102.4 respectively.
 
411A
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RE: Direct Lift Control

Mon Jun 22, 2009 8:07 pm

I would only add....

The L1011 was FAR 36 certified at all weights, unlike it other wide body competition.

DLC has operated without fail, just as advertised, in my nearly 30 years of flying this truly remarkable design.
 
9VSIO
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RE: Direct Lift Control

Thu Jun 25, 2009 11:59 am

I only ask because I swore I saw minute deflections on the 773ER spoilers (without any noticeable roll change) while coming down on finals.

When I first read about DLC a while ago, I thought it was one of the most ingenious methods of adjusting the GP!
Me: (Lining up on final) I shall now select an aiming point. || Instructor: Well, I hope it's the runway...
 
411A
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RE: Direct Lift Control

Thu Jun 25, 2009 1:16 pm



Quoting 9VSIO (Reply 7):
I thought it was one of the most ingenious methods of adjusting the GP!

It still is...and a Lockheed exclusive in the wide-body civil airliner world.
 
twal1011727
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RE: Direct Lift Control

Thu Jun 25, 2009 9:32 pm



Quoting 474218 (Reply 5):
DLC has nothing to do with noise control. Its purpose is to allow vertical corrections to the glide slope to be accomplished without use of pitch control. When the flaps are lowered beyond 30 degrees the four inboard spoilers on each wing assume a new null point. Excursion above or below the glide slope will cause the spoilers to extend or retract bring the aircraft back to the glide slope. This is accomplish automatically through the Flight Controls Electronics Computer (FCES) and works in both autopilot and manual modes.

If I remember my dad (TWA L10 Capt) explaining it to me.
with the spoiler change came a slight pitch change.
To keep the deck angle constant through out the approach - pitch trim was also adjusted.

The L1011 was way ahead of its time. Too bad Rolls-Royce had troubles financially
and the L1011 was delayed ; otherwise, Douglas aircraft might have been forced out of
commercial aviation and not Lockheed

KD
 
474218
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RE: Direct Lift Control

Thu Jun 25, 2009 10:56 pm



Quoting TWAL1011727 (Reply 9):
If I remember my dad (TWA L10 Capt) explaining it to me.
with the spoiler change came a slight pitch change.
To keep the deck angle constant through out the approach - pitch trim was also adjusted.

What TWA L10 Capt told you is partly true, but its the other way around. The horizontal stabilizer and DLC spoilers work together. When the DLC is armed (flaps lower than 30 degrees) any input to the horizontal stabilizer will cause the DLC spoilers to raise or lower to counteract this input.

If the aircraft is above the glide slope and either the automatic systems or the pilot attempts lower the aircraft nose, to bring the aircraft down to the glide slope, the DLC spoilers raise to counter this, keeping the pitch angle constant and lowering the aircraft to the glide slope. So while there is stabilizer movement is kept to a minimum.
 
2H4
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RE: Direct Lift Control

Thu Jun 25, 2009 11:03 pm

Is it true that the L-1011 is the only aircraft to have ever used DLC?

2H4
Intentionally Left Blank
 
KevinL1011
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RE: Direct Lift Control

Fri Jun 26, 2009 5:24 am



Quoting 2H4 (Reply 11):
Is it true that the L-1011 is the only aircraft to have ever used DLC?

AFAIK it is. Lockheed referred to it as the "Flying Stabilizer". It was developed along with the CAT III auto-land system, another Tri-Star first.

Quoting 474218 (Reply 5):
When the flaps are lowered beyond 30 degrees the four inboard spoilers on each wing assume a new null point.

I believe it's 8 deg.

The 500 model was equipped with a Recovery Speed Brake (RSB) which deployed the spoilers at high speeds (Mach .85 plus) to improve stability as the 500 was a bit shorter with an extended wingspan.

The Tri-Star also introduced an Active Control System (ACS) which modified the outer aileron null point to compensate for wing flex.

Coincidentally, the first scheduled AFCS flight occurred on June 25th,1972, almost exactly 37 years ago. It was a TWA L-1011 flight from STL to LAX.

I dearly miss flying on Tri-Stars.
474218, Carl, You will be missed.
 
474218
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RE: Direct Lift Control

Fri Jun 26, 2009 3:01 pm



Quoting KevinL1011 (Reply 12):
I believe it's 8 deg.

To activate DLC the flaps must be in the landing configuration ie: greater then 30 degrees.

Quoting KevinL1011 (Reply 12):
The 500 model was equipped with a Recovery Speed Brake (RSB) which deployed the spoilers at high speeds (Mach .85 plus) to improve stability as the 500 was a bit shorter with an extended wingspan.

Recovery Speed Brakes are only found of CAA certified L-1011-500's, British Airways -200's and aircraft modified by Service Bulletin 093-27-181 the Rapid Decent Modification.
 
tdscanuck
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RE: Direct Lift Control

Fri Jun 26, 2009 3:16 pm



Quoting 2H4 (Reply 11):
Is it true that the L-1011 is the only aircraft to have ever used DLC?

It might be true that the L-1011 is the only commercial jet to use it, but it's not the only aircraft. The C-17 uses this too. I'm not sure if it's used to hold glideslope in the C-17, but it's used as part of the "flareless landing", I believe.

Tom.
 
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keesje
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RE: Direct Lift Control

Fri Jun 26, 2009 4:31 pm

I introduced DLC on a sketch aircraft named Turboliner some time ago.

http://i191.photobucket.com/albums/z...Turboliner28april.jpg?t=1246033147

IMO it could offer steeper more controlled, more comfortable approaches to places like London City.

http://www.youtube.com/watch?v=8hce7A4mluw

Maybe F14 had it too.
"Never mistake motion for action." Ernest Hemingway
 
9VSIO
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RE: Direct Lift Control

Fri Jun 26, 2009 5:13 pm



Quoting 474218 (Reply 13):
Quoting KevinL1011 (Reply 12):
I believe it's 8 deg.

To activate DLC the flaps must be in the landing configuration ie: greater then 30 degrees.

I think he meant the null point for the spoilers?
Me: (Lining up on final) I shall now select an aiming point. || Instructor: Well, I hope it's the runway...
 
474218
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RE: Direct Lift Control

Fri Jun 26, 2009 5:36 pm



Quoting 9VSIO (Reply 16):
I think he meant the null point for the spoilers?

He was still wrong: the null point is 7 degrees for all L-1011's except for the -500's which is 9 degrees.
 
KevinL1011
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RE: Direct Lift Control

Fri Jun 26, 2009 8:22 pm



Quoting 9VSIO (Reply 16):
I think he meant the null point for the spoilers?

Yes.

Quoting 474218 (Reply 13):
To activate DLC the flaps must be in the landing configuration ie: greater then 30 degrees.

And 2 of the 3 engines must be less than TO thrust or Auto Land.

Quoting 474218 (Reply 17):
the -500's which is 9 degrees.

I stand corrected.
474218, Carl, You will be missed.
 
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DL_Mech
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RE: Direct Lift Control

Sat Jun 27, 2009 3:48 am

DLC can be seen in this video, beginning at 3:51.

http://www.youtube.com/watch?v=Vf2nFYHKGuU
This plane is built to withstand anything... except a bad pilot.
 
OldAeroGuy
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RE: Direct Lift Control

Sat Jun 27, 2009 4:06 pm



Quoting 474218 (Reply 5):
As for noise requirements: The L-1011 was designed to meet FAR Part 36 noise requirements. Those requirements were: Take off, Sideline and Approach were 106.2, 107.3 and 107.3 Decibels (EPNdB). The L-1011 was certified at 98.1, 97.8 and 102.4 respectively.

The approach noise of the L-1011 was excellent when certified, but compare it to a 772LR today. At MLW, the 772LR is almost 3 EPNdB quieter (99.6 vs 102.4) while weighing 33% more (492,000 lb vs 368,000 lb).

Given that EPNdB is a log scale, a reduction of 3 dB equates to a halfing of the noise level.

While much of the noise reduction over the past 40 or so years has come from engine technology improvements such as higher bypass ratios and better acoustic treatments, airframe improvements have also played a role.

Wing aspect ratios have been increased and high lift systems have been simplified to reduce approach drag. Reduced approach drag means lower engine thrust and less engine noise. At the same time, high lift system improvments mean less airframe noise due to fewer flap edges and discontinuities.

Quoting 474218 (Reply 17):
the null point is 7 degrees for all L-1011's except for the -500's which is 9 degrees

Deflecting the spoilers by 7 to 9 degrees will increase approach noise due to increased drag (higher approach thrust) and higher airframe noise. This is why DLC is not commonly used on commercial airplanes today even though it's a great idea for tracking the glide slope.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
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dash500
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RE: Direct Lift Control

Mon Jul 06, 2009 10:35 pm



Quoting OldAeroGuy (Reply 20):
Deflecting the spoilers by 7 to 9 degrees will increase approach noise due to increased drag (higher approach thrust) and higher airframe noise. This is why DLC is not commonly used on commercial airplanes today even though it's a great idea for tracking the glide slope.

Nevertheless, even with DLC inducing more drag, the L-1011 was quieter than its rival  Smile
Flying all Across the World
 
OldAeroGuy
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RE: Direct Lift Control

Tue Jul 07, 2009 5:41 am



Quoting Dash500 (Reply 21):
Nevertheless, even with DLC inducing more drag, the L-1011 was quieter than its rival



Quoting Mlsrar (Thread starter):
Does anyone have any information on whether or not this was a true asset to the technology of the Tristar, and, if so, was it incorporated into modern aircraft design?

But what commercial airplane uses DLC today? That appears to one of the questions Mlsrar is asking. The answer is none and Approach noise is a primary reason for the lack of DLC airplanes.

The blow-in nacelle doors used on the 747-100 are not seen today either. Noise is a primary reason for this as well.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
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Starlionblue
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RE: Direct Lift Control

Tue Jul 07, 2009 10:56 am



Quoting OldAeroGuy (Reply 22):

The blow-in nacelle doors used on the 747-100 are not seen today either. Noise is a primary reason for this as well

Isn't there also the fact that intakes have more modern designs and don't need those doors?
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
OldAeroGuy
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RE: Direct Lift Control

Tue Jul 07, 2009 3:15 pm



Quoting Starlionblue (Reply 23):
Isn't there also the fact that intakes have more modern designs and don't need those doors?

If blow-in doors were used, nacelle drag could be reduced for the cruising flight as the inlet lip could be made thinner. This is true even with today's engines.

A primary reason that blow-in doors are no longer used is the acoustic treatment that is applied in the nacelle inlet. Blow-in doors would preclude the use of this noise reducing material.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
474218
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RE: Direct Lift Control

Tue Jul 07, 2009 4:47 pm



Quoting OldAeroGuy (Reply 22):
But what commercial airplane uses DLC today?

DLC will not function correctly without the flying stabilizer as the DLC spoilers and the stabilizer work unison's. Since no other airlines uses the flying stabilizer they don't have DLC.

The L-1011's DLC system provided, more rapid response, reduced attitude changes, better speed control, lower flare height, better control in variable winds and reduced the vertical and longitudinal scatter at touchdown. Additionally, it provided a smoother ride for the passengers.

Quoting OldAeroGuy (Reply 22):
Approach noise is a primary reason for the lack of DLC airplanes

For some reason you seem to be obsessed with noise. The L-1011 was quieter than all its contemporary airliners and a few of the 'modern' airlines. It was not just a marketing slogan when Eastern named them "Whisperliners".

Lockheed has always been innovator and if the other manufacture choose not to follow it, does not mean Lockheed was wrong just first.
 
OldAeroGuy
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RE: Direct Lift Control

Wed Jul 08, 2009 9:21 am



Quoting 474218 (Reply 25):
DLC will not function correctly without the flying stabilizer as the DLC spoilers and the stabilizer work unison's. Since no other airlines uses the flying stabilizer they don't have DLC

Elevators will accommodate DLC quite well, particularly with FBW. You don't need a flying stab.

Quoting 474218 (Reply 25):
Quoting OldAeroGuy (Reply 22):
Approach noise is a primary reason for the lack of DLC airplanes

For some reason you seem to be obsessed with noise.

Read up on the A380 development history with respect to QC levels at LHR and see if I have a noise obsession compared to the design changes Airbus was required to make.

Any airliner development is a series of trade-offs. Approach noise is a greater concern now than when the L-1011 was developed. In the trade between approach noise and DLC in today's environment, DLC doesn't make the cut despite its other virtues.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
phollingsworth
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RE: Direct Lift Control

Wed Jul 08, 2009 10:18 am



Quoting OldAeroGuy (Reply 26):
Read up on the A380 development history with respect to QC levels at LHR and see if I have a noise obsession compared to the design changes Airbus was required to make.

The killer with QC is that it puts weight back in the equation by using absolute certification levels as the basis for the quota count. You can tell how important LHR is/was to the economic case for the A380. The funny thing is that while LHR is potentially QC limited (most of the other UK airports have QCs limits that are far above their movement limit), it has not yet moved to base it charges and fees on an aircrafts QC rating. The noise charges are still based on certification margin. I still cannot figure why airlines were so worried about the QC level for the A380 as it has led to a fairly sever SFC penalty.

Quoting OldAeroGuy (Reply 26):
Any airliner development is a series of trade-offs. Approach noise is a greater concern now than when the L-1011 was developed. In the trade between approach noise and DLC in today's environment, DLC doesn't make the cut despite its other virtues.

The reason DLC makes sense is that you cannot adjust the pitch of the rotors on modern jet engines, this leads to spool lag. So instead of changing thrust you change drag and lift. Of course this increases noise. With a 3 degree glide slope the trade is unacceptable. However, while there were some reasonable reasons to use 3 degrees in the past, we can probably be smarter going forward, in which case DLC might make more sense. If nothing else we need to start thinking about the trade in noise and fuelburn on the terminal approach. Let's just say that 3 degrees is often not particularly efficient.
 
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dash500
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RE: Direct Lift Control

Wed Jul 08, 2009 2:53 pm



Quoting OldAeroGuy (Reply 26):
Any airliner development is a series of trade-offs. Approach noise is a greater concern now than when the L-1011 was developed. In the trade between approach noise and DLC in today's environment, DLC doesn't make the cut despite its other virtues.

I still don't get why you insist with this.

L-1011 has DLC. B747-100/B747-200 and DC-10 don't. However the L-1011 was still quieter. It certainly was by some means a cleaner and more clever design. And certainly you can compare L-1011-1 with DC-10-10, very similar designs.

On the other hand, maybe DLC induced more drag. But you had a better stabilized approach and perhaps no need of big throttle corrections wich can also make noise  Smile
Flying all Across the World
 
OldAeroGuy
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RE: Direct Lift Control

Wed Jul 08, 2009 4:32 pm



Quoting Dash500 (Reply 28):
Quoting OldAeroGuy (Reply 26):
Any airliner development is a series of trade-offs. Approach noise is a greater concern now than when the L-1011 was developed. In the trade between approach noise and DLC in today's environment, DLC doesn't make the cut despite its other virtues.

I still don't get why you insist with this.

Because it's an accurate assessment of why no modern airliners use DLC?

If you don't think so, please explain why modern airliners don't use DLC. Implementation of DLC would be quite simple for FBW airplanes.

The relationship of the L-1011 to its contemporaries is not relevant to designing a Stage 4 compliant and QC1 Approach (or lower) compatible airplane today.

Please recall this Reply.

Quoting OldAeroGuy (Reply 20):
The approach noise of the L-1011 was excellent when certified, but compare it to a 772LR today. At MLW, the 772LR is almost 3 EPNdB quieter (99.6 vs 102.4) while weighing 33% more (492,000 lb vs 368,000 lb).

Given that EPNdB is a log scale, a reduction of 3 dB equates to a halfing of the noise level.

While much of the noise reduction over the past 40 or so years has come from engine technology improvements such as higher bypass ratios and better acoustic treatments, airframe improvements have also played a role.



Quoting Dash500 (Reply 28):
On the other hand, maybe DLC induced more drag. But you had a better stabilized approach and perhaps no need of big throttle corrections wich can also make noise

Throttle corrections don't play a part in noise certification. Certification noise levels are established using steady state, stabilized flights over the mircophones. An airplane configuration that has higher drag will require more thrust and produce higher noise levels.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
474218
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RE: Direct Lift Control

Wed Jul 08, 2009 5:31 pm



Quoting OldAeroGuy (Reply 26):
In the trade between approach noise and DLC in today's environment, DLC doesn't make the cut despite its other virtues.

I suggest you read FAA Advisory Curricular No. 36-1H, which lists the noise levels for all FAA certified aircraft. On page 45 it lists all models the L-1011 and their certified noise levels. In every case the L-1011 approach noise level is higher without DLC than with DLC.

Since the L-1011 certified approach noise levels are higher without DLC than with DLC your entire argument against DLC has been debunked.
 
411A
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RE: Direct Lift Control

Thu Jul 09, 2009 5:43 pm

Quite correct, 474218.
I find it rather strange that a few folks who normally wouldn't know an L1011 from the back end of a bus...seem to 'know' so much about it.

This is generally called....'don't confuse us with the facts, our minds are made up already'.

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