Its a long time ago that we had regular L1011s here in Hamburg (late 90s!) but I can remember that they had very high Angle of Attack on approach and also when landing, this looked pretty awesome. Does anybody know why the TriStars had such a high angle of attack?



Heres a Video in Atlanta:

https://youtu.be/2xuxwWnUKT4?t=13m52s

Short answer : Direct Lift Control (DLC).

DLC allowed for the aircraft to maintain a constant pitch angle on approach while using spoilers to correct for glide path variations.

A pretty good explanation here:
https://www.airliners.net/forum/viewtopic.php?t=99463

You can see DLC in action in this video. When the flaps are deployed from 22 to 33, the spoilers assume their new neutral at 3:53. After that point, when the pilot pushes forward on the yoke the spoilers retract. When he pulls back, they deploy further.

http://www.youtube.com/watch?v=Vf2nFYHKGuU

DL_Mech wrote:

You can see DLC in action in this video. When the flaps are deployed from 22 to 33, the spoilers assume their new neutral at 3:53. After that point, when the pilot pushes forward on the yoke the spoilers retract. When he pulls back, they deploy further.

http://www.youtube.com/watch?v=Vf2nFYHKGuU

Sorry, I mixed up the spoiler operation. When the pilot pushes forward on the yoke, the spoilers deploy further (killing lift). When he pulls back, they retract (providing lift).

DLHAM wrote:

Its a long time ago that we had regular L1011s here in Hamburg (late 90s!) but I can remember that they had very high Angle of Attack on approach and also when landing, this looked pretty awesome. Does anybody know why the TriStars had such a high angle of attack?

Heres a Video in Atlanta:

https://youtu.be/2xuxwWnUKT4?t=13m52s

That's pitch angle, not angle of attack. Pitch angle is the angle between the longitudinal axis and the horizontal. Angle of attack is the angle between the mean chord line of the wing and the relative airflow. Pitch angle and angle of attack are related but not directly. You can have a very high pitch angle with a very low angle of attack, for example.

You can't tell the angle of attack from just looking at footage or pictures.

Starlionblue wrote:

DLHAM wrote:

Its a long time ago that we had regular L1011s here in Hamburg (late 90s!) but I can remember that they had very high Angle of Attack on approach and also when landing, this looked pretty awesome. Does anybody know why the TriStars had such a high angle of attack?

Heres a Video in Atlanta:

https://youtu.be/2xuxwWnUKT4?t=13m52s

That's pitch angle, not angle of attack. Pitch angle is the angle between the longitudinal axis and the horizontal. Angle of attack is the angle between the mean chord line of the wing and the relative airflow. Pitch angle and angle of attack are related but not directly. You can have a very high pitch angle with a very low angle of attack, for example.

You can't tell the angle of attack from just looking at footage or pictures.

You are right, thank you. I mean Pitch Angle, L1011s have a very high Pitch on approach and landing.

The short answer to the original question is aerodynamics, airfoil shape and type, leading and trailing edge lift devices. You get a rough idea of the angle of attack when you consider the attitude combined with the flight path. On a normal ILS, the flight path is -3 degrees.

DL_Mech wrote:

DLC allowed for the aircraft to maintain a constant pitch angle on approach while using spoilers to correct for glide path variations.

Did the tailplane have any involvement when DLC was in operation?

Regards, JetMech

jetmech wrote:

DL_Mech wrote:

DLC allowed for the aircraft to maintain a constant pitch angle on approach while using spoilers to correct for glide path variations.

Did the tailplane have any involvement when DLC was in operation?

Regards, JetMech

Yes, the flying stabilizer operated normally with the control yoke, there was no lockout. The elevators were mechanically linked & operated with stabilizer motion and designed only to assist in the nose up direction at (near) full travel.

Imitation being the sincerest form of flattery, the Steep Approach System of the Embraer 170/190 uses the same concept as Lockheed’s DLC, albeit controlled by FBW.

https://youtu.be/IcmETxca2Zg?t=151

You’ll notice that the aircraft has a relatively nose-up attitude, despite the 5.5 degree glide slope, and the symmetrical modulation of the spoiler panels on both wings controlling the rate of descent. With minimal change in pitch. There are further occasional spoiler movements, but these are as roll spoilers.

But basically Embraer used the DLC concept from the TriStar as their Steep Approach System. And very effective it is too.

Regards
CROSSWIND

That is a much higher neutral point than the L-1011. I’m glad that the system was finally used on another airplane.

Is there a steep approach switch in the cockpit? The L-1011 used a 30 degree flap switch to activate DLC.

DL_Mech wrote:

That is a much higher neutral point than the L-1011. I’m glad that the system was finally used on another airplane.

Is there a steep approach switch in the cockpit? The L-1011 used a 30 degree flap switch to activate DLC.

I suppose the higher neutral point is due to the steep 5.5 degree glide requiring a steeper approach than the TriStar would ever have ever made.

There is a push button switch on the Flight Deck to arm the mode… which becomes active once Flap Full is achieved.

Spoilers seen to good effect in this photo

Starlionblue wrote:

You can't tell the angle of attack from just looking at footage or pictures.

i would guess with very high resolution cameras these days sometimes you can if you (can) zoom in enough.

best regards
Thomas

tommy1808 wrote:

Starlionblue wrote:

You can't tell the angle of attack from just looking at footage or pictures.

i would guess with very high resolution cameras these days sometimes you can if you (can) zoom in enough.

best regards
Thomas

I think Starlionblue's point was that angle of attack is also a function of direction of travel as well as perceived pitch angle, which can be difficult to judge from some angles.

tommy1808 wrote:

Starlionblue wrote:

You can't tell the angle of attack from just looking at footage or pictures.

i would guess with very high resolution cameras these days sometimes you can if you (can) zoom in enough.

best regards
Thomas

Resolution doesn't really help you. As DH106 says, direction of travel and pitch angle are both factors in AoA. Unless you have verified references, such as the horizon, and probably some angle maths, you can't tell just by looking from the outside.

Telling approximate pitch angle is not a big challenge, I suppose. AoA is another story.

Starlionblue wrote:

you can't tell just by looking from the outside.

Sure you can...if you can discern the attitude of the AOA sensor, you get a good idea of the aircraft's AOA.

fr8mech wrote:

Starlionblue wrote:

you can't tell just by looking from the outside.

Sure you can...if you can discern the attitude of the AOA sensor, you get a good idea of the aircraft's AOA.

Haha ok fair.