Moderators: richierich, ua900, PanAm_DC10, hOMSaR

 
User avatar
jetmech
Topic Author
Posts: 2415
Joined: Wed Mar 29, 2006 2:14 am

737 spoiler mixer / ratio changer question.

Sat May 28, 2022 2:01 am

Hello All,

I've been reading up on the 737 spoiler mixer / ratio changer mechanism. It's an amazingly complex and clever device which takes some studying to understand.

The following picture is the mixer / ratio changer in the neutral control wheel, speed-brakes down configuration.

Image

What's interesting is the spoiler mixer / ratio changer operation when the control wheel is turned with the speed brake lever down. The following picture shows the configuration with a left control wheel input with the speed brake lever down.

The mixer / ratio changer commands the left wing flight spoilers up to assist the left aileron to drop the left wing, but interestingly - and according to the maintenance manual - a small down command is also sent to the right flight spoilers which are already stowed!

IIRC, the spoilers always receive hydraulic stow pressure in flight when the speed-brake lever is down to prevent spoiler float. As such, why would there be a need to send an additional stow command to the flight spoilers on the rising wing?

Image

The following picture shows the mixer / ratio changer configuration with speed-brake up commands and the control wheel neutral which will help in understanding how the mixer / ratio changer works.

Image

A few more pictures / diagrams of the device.

Image

https://www.sjap.nl/openmixer1.JPG

Image

https://www.sjap.nl/openmixer2.JPG

Image

https://ic.pics.livejournal.com/lx_phot ... iginal.jpg

Regards, JetMech
 
Avatar2go
Posts: 1053
Joined: Thu Apr 14, 2022 3:41 am

Re: 737 spoiler mixer / ratio changer question.

Sat May 28, 2022 3:56 am

Just speculating, but perhaps the changer doesn't care whether the spoilers are stowed by the speed-brake lever. It commands right spoiler drop for left wheel turn, in all cases. If the spoiler is stowed, then no impact. If not stowed, then the changer has the desired effect on the right spoiler.

The "don't care" state is common in control system design of complex interacting systems. In this case, the purpose of the changer is to enhance roll authority with spoilers in any position.

Unlike the ailerons, the spoilers can affect vertical flight in only one direction (raise above the wing but can't drop below). So that would seem to necessitate the "don't care" state for control inputs in the opposite direction.
 
User avatar
jetmech
Topic Author
Posts: 2415
Joined: Wed Mar 29, 2006 2:14 am

Re: 737 spoiler mixer / ratio changer question.

Sun May 29, 2022 5:20 am

Avatar2go wrote:
Just speculating, but perhaps the changer doesn't care whether the spoilers are stowed by the speed-brake lever. It commands right spoiler drop for left wheel turn, in all cases. If the spoiler is stowed, then no impact. If not stowed, then the changer has the desired effect on the right spoiler.

The "don't care" state is common in control system design of complex interacting systems. In this case, the purpose of the changer is to enhance roll authority with spoilers in any position.

Unlike the ailerons, the spoilers can affect vertical flight in only one direction (raise above the wing but can't drop below). So that would seem to necessitate the "don't care" state for control inputs in the opposite direction.

What you say makes total sense the more I think about it.

The aileron cam is designed to stow the deployed flight spoilers on the upgoing wing to assist the ailerons with roll. This just so happens to send an additional stow command to the flight spoilers when the speed-brake handle is down. I think I got thrown off when the maintenance manual mentioned it specifically and I assumed there was some specific, unexplained reason for it.

Regards, JetMech
 
kalvado
Posts: 3733
Joined: Wed Mar 01, 2006 4:29 am

Re: 737 spoiler mixer / ratio changer question.

Sun May 29, 2022 11:59 am

As for maintenance manual, this weak signal may be a good diagnostic metric for some reason. For example, weak can become zero if there is any problem with flow or alignment...
 
User avatar
jetmech
Topic Author
Posts: 2415
Joined: Wed Mar 29, 2006 2:14 am

Re: 737 spoiler mixer / ratio changer question.

Sun May 29, 2022 7:51 pm

kalvado wrote:
As for maintenance manual, this weak signal may be a good diagnostic metric for some reason. For example, weak can become zero if there is any problem with flow or alignment...

Definitely makes sense. No doubt it's a complex rigging / adjusting task when you change the mixer and / or ratio changer.

Regards, JetMech
 
milhaus
Posts: 135
Joined: Fri Dec 10, 2010 4:19 pm

Re: 737 spoiler mixer / ratio changer question.

Wed Jun 15, 2022 5:20 pm

Today i had possibility to check system behavoir on real aircraft, cables from mixer definitely move to both direction. Via quadrant they move valves inside actuator but spoiler remains in the same position, it is already at downstop. I think that valve inside actuator is fully open when spoliers are stored, there was no feeling that it gets more pressure from aileron signal.
 
User avatar
jetmech
Topic Author
Posts: 2415
Joined: Wed Mar 29, 2006 2:14 am

Re: 737 spoiler mixer / ratio changer question.

Thu Jun 16, 2022 12:53 pm

milhaus wrote:
Today i had possibility to check system behavoir on real aircraft, cables from mixer definitely move to both direction. Via quadrant they move valves inside actuator but spoiler remains in the same position, it is already at downstop. I think that valve inside actuator is fully open when spoliers are stored, there was no feeling that it gets more pressure from aileron signal.

Very interesting.

I recall that each of the spoiler input control quadrants has a spring relief mechanism as part of the quadrant. However, I believe this is to allow for the case where a spoiler input quadrant jams, so as not to restrict the movement of the remaining quadrants.

I wonder if it also plays a part in what you observed?

Regards, JetMech

Who is online

Users browsing this forum: dennypayne and 15 guests

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos