Direct Lift Control
Joined: Mar 2000
Posts: 8,571
Likes: 3
From: Arizona USA
The well known secret to reliable TriStar maintenance (in my personal opinion, anyway) was the mandated used (by the respective airline concerned) of the FIRM manual.
With this method of fault isolation and reporting, snags could well be easily fixed, with minimal ground time.
I worked for one small carrier whose director of maintenance thought the FIRM idea was hogwash...and quite predictably, they had a huge dispatch reliability problem.
They also had missing serviceable tags in many cases, and obtained quite critical inspection by aviation authorities as a result.
Obi, the flare maneuver in the TriStar resulted in a deck angle change of about three degrees.
The approach however, was quite a constant angle, thanks to DLC.
It really does work as advertised.
With this method of fault isolation and reporting, snags could well be easily fixed, with minimal ground time.
I worked for one small carrier whose director of maintenance thought the FIRM idea was hogwash...and quite predictably, they had a huge dispatch reliability problem.
They also had missing serviceable tags in many cases, and obtained quite critical inspection by aviation authorities as a result.
Obi, the flare maneuver in the TriStar resulted in a deck angle change of about three degrees.
The approach however, was quite a constant angle, thanks to DLC.
It really does work as advertised.
Joined: Jul 2006
Posts: 71
Likes: 0
From: London
Originally Posted by 411A
Obi, the flare maneuver in the TriStar resulted in a deck angle change of about three degrees.
The approach however, was quite a constant angle, thanks to DLC.
It really does work as advertised.
The approach however, was quite a constant angle, thanks to DLC.
It really does work as advertised.
Obi
Joined: Jun 2004
Posts: 25
Likes: 1
From: Durham, NC, USA
Originally Posted by 411A
.
The approach however, was quite a constant angle, thanks to DLC.
It really does work as advertised.
The approach however, was quite a constant angle, thanks to DLC.
It really does work as advertised.
Joined: Mar 2000
Posts: 8,571
Likes: 3
From: Arizona USA
Yes, it is the control column, uniuniunium, and the exact details I can't remember at the moment.
But I'm sure glhcarl will chime in here as he has the technical details, and has probably forgotten more than I ever knew about the inner workings of the 'ole Lockheed tri-motor.
But I'm sure glhcarl will chime in here as he has the technical details, and has probably forgotten more than I ever knew about the inner workings of the 'ole Lockheed tri-motor.
Joined: Jan 2006
Posts: 454
Likes: 3
From: Georgia, USA
Thanks for the kind words 411A, the problem is that I forget more everyday, However:
Activation of DLC is fully automatic and controled by logic circuitry in the Flight Control Electronics System (FCES) computer. The FCES computer looks for the following:
1. DLC servo is pressuried
2. 2 of 3 Throttle Handles in less then full power.
3. Flap position greater than 30 degrees.
4. Stall warning not detected.
5. Go around not commanded
If the above conditions are met Spoilers 1 - 4 are activated to a new null point of +7 degrees (+9 degrees on -500's). 777AV8R's description a few posts earlier provided an excellent discription of what happens after DLC activation.
The above critera is followed in Autoland and Manual approches.
Activation of DLC is fully automatic and controled by logic circuitry in the Flight Control Electronics System (FCES) computer. The FCES computer looks for the following:
1. DLC servo is pressuried
2. 2 of 3 Throttle Handles in less then full power.
3. Flap position greater than 30 degrees.
4. Stall warning not detected.
5. Go around not commanded
If the above conditions are met Spoilers 1 - 4 are activated to a new null point of +7 degrees (+9 degrees on -500's). 777AV8R's description a few posts earlier provided an excellent discription of what happens after DLC activation.
The above critera is followed in Autoland and Manual approches.
Joined: Jan 2005
Posts: 280
Likes: 0
From: uk
To answer a previous question: yes, the L1011 did have a conventional flare, you did not 'fly it on' like a carrier landing. DLC could not sense ground proximity, it was purely a pilot input.
The rearward movement of the control column at flare initiation stowed the DLC spoilers from the null postion and gave extra lift into the flare. The secret of a smooth landing was to keep the back pressure on, right through to touchdown. Any relaxation could result in a very firm jolt at touchdown as the DLC redeployed back to null ( or more ) and reduced the lift.
The rearward movement of the control column at flare initiation stowed the DLC spoilers from the null postion and gave extra lift into the flare. The secret of a smooth landing was to keep the back pressure on, right through to touchdown. Any relaxation could result in a very firm jolt at touchdown as the DLC redeployed back to null ( or more ) and reduced the lift.
Joined: Jan 2002
Posts: 297
Likes: 0
From: The Far Side
L1011.
Agree with 411A, with minor mod.
At 50' radalt start gradual flare for additional 3 degrees noseup. The rate of radalt decrease to be proportional to the flare rate. If radalt moving rapidly, a bit of an undignified tug required to avoid a thud.
Great aeroplane, wish I could still fly one.
Agree with 411A, with minor mod.
At 50' radalt start gradual flare for additional 3 degrees noseup. The rate of radalt decrease to be proportional to the flare rate. If radalt moving rapidly, a bit of an undignified tug required to avoid a thud.
Great aeroplane, wish I could still fly one.
Joined: Jul 2006
Posts: 71
Likes: 0
From: London
Hmmmm.Considering the pilots pitch inputs control spoiler deflection, I wonder what occurs during the flare that causes an increased deck angle, as this change in angle doesn't present itself during approach.
Perhaps the usual input to execute a flare, results in a greater change of vertical velocity that during approach, or perhaps ground effect plays a part?.
Obi
Joined: Mar 2000
Posts: 8,571
Likes: 3
From: Arizona USA
Well, as usual, it depends.
Large pitch (control column) inputs during approach will definitely change the pitch (deck) angle, small ones will not.
During the flare maneuver, larger than normal column inputs reduce the spoiler extension, while at the same time increases the pitch angle.
Also contributing to the outstanding handling of the TriStar is the all-flying horizontal stabilizer.
Relaxing the backpressure during the flare maneuver however (as has been pointed out already) many times results in a 'thumper'.
Hmmm, a few Boeing guys try 'the push' and then promptly find out it ain't a good idea.
'Tis a good thing the folks at Palmdale installed the wing bolts really tight.
Large pitch (control column) inputs during approach will definitely change the pitch (deck) angle, small ones will not.
During the flare maneuver, larger than normal column inputs reduce the spoiler extension, while at the same time increases the pitch angle.
Also contributing to the outstanding handling of the TriStar is the all-flying horizontal stabilizer.
Relaxing the backpressure during the flare maneuver however (as has been pointed out already) many times results in a 'thumper'.
Hmmm, a few Boeing guys try 'the push' and then promptly find out it ain't a good idea.
'Tis a good thing the folks at Palmdale installed the wing bolts really tight.
Joined: Jan 2006
Posts: 454
Likes: 3
From: Georgia, USA
Originally Posted by 411A
Well, as usual, it depends.
Large pitch (control column) inputs during approach will definitely change the pitch (deck) angle, small ones will not.
During the flare maneuver, larger than normal column inputs reduce the spoiler extension, while at the same time increases the pitch angle.
Also contributing to the outstanding handling of the TriStar is the all-flying horizontal stabilizer.
Relaxing the backpressure during the flare maneuver however (as has been pointed out already) many times results in a 'thumper'.
Hmmm, a few Boeing guys try 'the push' and then promptly find out it ain't a good idea.
'Tis a good thing the folks at Palmdale installed the wing bolts really tight.
Large pitch (control column) inputs during approach will definitely change the pitch (deck) angle, small ones will not.
During the flare maneuver, larger than normal column inputs reduce the spoiler extension, while at the same time increases the pitch angle.
Also contributing to the outstanding handling of the TriStar is the all-flying horizontal stabilizer.
Relaxing the backpressure during the flare maneuver however (as has been pointed out already) many times results in a 'thumper'.
Hmmm, a few Boeing guys try 'the push' and then promptly find out it ain't a good idea.
'Tis a good thing the folks at Palmdale installed the wing bolts really tight.
Joined: Jul 2006
Posts: 71
Likes: 0
From: London
Ok, so moderate longitudinal control inputs with DLC active, would result in a constant pitch angle but a change in vertical velocity, as the spoilers control the velocity vector. Here the pilot has direct control of the spoilers, but the stabilators are positioned to maintain a constant pitch angle and their positioning is accomplish completely through FCS feedback logic.
As well as direct spoiler control, longitudinal control inputs with DLC active above an FCES defined threshold, would also add or subtract pilot commanded stabilator inputs to blend with the FCS commanded stabilator input.
Is this how the system works?.
Thanks
Obi
As well as direct spoiler control, longitudinal control inputs with DLC active above an FCES defined threshold, would also add or subtract pilot commanded stabilator inputs to blend with the FCS commanded stabilator input.
Is this how the system works?.
Thanks
Obi
Last edited by Obi Offiah; 5th August 2006 at 03:52.
Joined: Jan 2006
Posts: 454
Likes: 3
From: Georgia, USA
Obi Offiah,
I am not a pilot (I was a Tech Rep) but the way I have been told the DLC should work is: The stabilizer is used to establish the angle of attack, approxmately 9 degrees nose up. The spoilers, which are controlled by the FCES, and the throttles control the sink rate. If all works, the pitch angle should not change during approch.
I am not a pilot (I was a Tech Rep) but the way I have been told the DLC should work is: The stabilizer is used to establish the angle of attack, approxmately 9 degrees nose up. The spoilers, which are controlled by the FCES, and the throttles control the sink rate. If all works, the pitch angle should not change during approch.
Joined: Mar 2000
Posts: 8,571
Likes: 3
From: Arizona USA
All correct, except that the normal deck (pitch) angle on approach is approximately 7.5 degrees.
Upon landing, the pitch angle is nine to ten degrees.
IF ten degrees is exceeded during landing, care needs to be exercised, as the tail skid (long body aircraft) will contact the runway surface at approximately 13.5 degrees.
Does this happen?
Yes, IF the aircraft is mishandled.
On a slightly different slant, the geometry of the L1011 (standard, long body model) is such that during crosswind manual landings, the wing tip will contact the runway surface, before the engine pod does.
A very good, and reliable design.
Appreciated by those that have extensive experience in same.
Upon landing, the pitch angle is nine to ten degrees.
IF ten degrees is exceeded during landing, care needs to be exercised, as the tail skid (long body aircraft) will contact the runway surface at approximately 13.5 degrees.
Does this happen?
Yes, IF the aircraft is mishandled.
On a slightly different slant, the geometry of the L1011 (standard, long body model) is such that during crosswind manual landings, the wing tip will contact the runway surface, before the engine pod does.
A very good, and reliable design.
Appreciated by those that have extensive experience in same.
Joined: Jan 1999
Posts: 187
Likes: 1
From: hongkong
Was told of an interesting technique used by Pan-Am drivers when they were flying the -500s. Not sure if it was offically approved though!
In the flare they would push the GA button thus stowing the DLC and creating a nice load of lift just when it was needed.
Seemed to me that this was OK as long as there wasn't a very large back stick input which would have stowed them in the first place!!
In the flare they would push the GA button thus stowing the DLC and creating a nice load of lift just when it was needed.
Seemed to me that this was OK as long as there wasn't a very large back stick input which would have stowed them in the first place!!
