I had a bit of a eureka moment in the shower earlier (I think Archimedes had his in the bath!!).
Was not really looking forward to making the airbrakes as I remembered doing it before and how fiddly it was. One problem I had was that the operating arm holes were very slightly different dimensions and that was making the blades come up at an angle.
In the shower I remembered that I had a broken pair of airbrakes from the Multiplex ASW 22 that I got earlier this year
, I had tried to repair them but gave up and replaced them with a new set. I was determined to fix and use them.
The problem with the old brakes (and it's quite common apparently) is that a small plastic pin had broken off of the operating arm on one brake. This happens when the wings slide out on landing and the control rod to the fuselage mounted servo hits full extension, the only thing holding the wing on then is the little plastic pin and it doesn't like it!!
I tried all sorts of ways to fix it but gave up, I noticed though that all the operating arms have the pin moulded on, all I had to do was disassemble the brake and swap the arms around.
I thought that the pins were peened in but they're not (an interference fit in the plastic is what holds them in), I carefully tapped them out using a small screwdriver, swapped the arms round and bingo!!
Only other little job to do was scrape off the balsa and foam remnants where they had been glued in to the ASW 22 wings.
I think these Multiplex brakes are discontinued, they are slightly longer than the home-made ones shown on the plan and weigh 74 g (2.6 oz).