737 speedbrake conversion

[paulnd]

Hello,

The conversion of my OEM 737 TQ is almost complete, the only part that I am having difficulties with is the speedbrake.

I see that some have used a sail arm servo, others DC motors or windscreen wiper motors. I've tested a 12v DC motor but it hasn't provided consistent results yet, my very rusty physics memory suggests that a longer arm will increase the torque?

I'll be grateful for any advice please before I go out buying a servo or 2nd hand windscreen wiper motor. Plans or diagrams of brackets and/or mounts will be most helpful.

thanks

Paul

[mickc]

Everyone has different methods and opinions on how to do this, the most problems I see with this are from those using servos.

I used an OEM Speed brake actuator and a friction clutch arrangement. There are 2 arms that replace the existing arm that the speedbrake lever rod attaches to.
the thicker arm has a friction clutch inside it, and the thinner one that attaches to the actuator has a captive bolt that is set-screwed to the inside of the clutch.

That setup gives the following functions:
The clutch allows the actuator to operate from any handle position
If the speedbrake lever is down & locked and the actuator triggers, the clutch prevents any damage to the mechanism
The clutch allows the setting of the correct handle resistance (quite heavy on the NG, around 20lb / 9Kg)
The Prosim autodeploy and autorestow functions trigger relays to operate the actuator, and Normal deployment on landing, retraction on throttle movement and RTO functions all work correctly.

You could substitute the OEM actuator for a high speed linear actuator, but it wouldn't sound the same as the real one

Here is a pic of the lever setup:




http://imgur.com/a/NKpgT


The actuator mount to the rod end at the bottom of the inner arm.
im still assembling this after the conversion so I dont have a fully assembled pic, but here is a video of it operating that i took back in the pre-conversion testing era of the TQ build.

https://www.youtube.com/watch?v=RJAE2eOWtnE

A few details have changed in the final build, but it still works pretty much the same.

[paulnd]

Thanks Mick, very helpful. Using 2 arms is something that I never thought of. Do you have any suggestions on specs for a linear actuator as it's unlikely that I'll be able to get an OEM actuator?

I unfortunately get an error message on the YouTube link: "This video is unavailable"

Paul

[mickc]

Hi mate,  video should work now!

you only need about 8 - 10"  of travel for the actuator, but it has to be a high speed one.  You want the whole travel to be completed in under 2 seconds.

[paulnd]

the OEM actuator is quite a monster but has a beautiful sound, thanks for the video!

[mickc]

Yeah, its not small!  Its actually off a 747-400, not a 737.  It all fits into CDU bay so its not a problem, although it does pull 6.5 amps when it runs, so there is a dedicated 28v 10A power supply for it in the pedestal. (also runs the fire panel)

[bernard S]

nice next thurst reversers ?

[FredK]

I am using a combination of a servo with a slide potentiometer. Works flawlessly.

It took a bit of time to get the two lever arms to work in sync without binding through the full length of travel.  So that involved a bit of bending and trial and error.  A very simple solution otherwise.

Click on this video link to see Speed Brake in operation:
https://www.youtube.com/watch?v=d6DtCHm1MMI

Fred K

[paulnd]

thank you Fred, much appreciated.