737 spoiler mixer / ratio changer question.

jetmech · 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.

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?

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.

A few more pictures / diagrams of the device.

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

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

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

Regards, JetMech

Avatar2go · 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.

jetmech · 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 · 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...

jetmech · 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 · 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.

jetmech · 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

737 spoiler mixer / ratio changer question.

737 spoiler mixer / ratio changer question.

Re: 737 spoiler mixer / ratio changer question.

Re: 737 spoiler mixer / ratio changer question.

Re: 737 spoiler mixer / ratio changer question.

Re: 737 spoiler mixer / ratio changer question.

Re: 737 spoiler mixer / ratio changer question.

Re: 737 spoiler mixer / ratio changer question.

Who is online

Popular Searches On Airliners.net