Mosquito throttle materials

Interesting observation about ‘excess’ bonding tabs. I tend to start from a point where nothing on any historical structure is accidental or seemingly thoughtless. In a timber aircraft EVERYTHING metal must be connected to the bonding system, so excess tabs might have been provided to allow additional equipment, installed later or in service, to be easily bonded in. There were so many changes to navigation, radio, radar, armament setups in service that it would help to have a few spare tabs in the vicinity to bond to. I have an extra dooby-wacky washer to post for the bracket mounting that is flat on one side, concave on the other for fitting the bracket to the tube, so no need to whittle one out of old, crusty chewing gum.

The timber Mosquito is W/T, Wired Throughout, that is copper bonding strips join EVERY metal component within the aircraft so that there cannot be any arcing to ignite petrol fumes, interfere with radio radio transmissions or, in the case of lightning strike, cause massive voltage to carbonize the pilot or disintergrate the airframe. The pilot’s seat and armour backplate is bonded, every piece of metal is bonded.

Ed, just as an aside have you come across enough original bits of structure to have noticed how many ‘spare’ bonding tabs there are? While as you say all metal components are bonded, often the bods at Standard Motors seems to have been in doubt as to exactly how many tabs were needed on a given component, and so have generously sprinkled extras around, which aren’t connected to anything. Mind you, they might just have been short of washers. In a lot of places in the cockpit of NZ2328 star washers have been used in place of penny washers, which is a bit funky. C’est la guerre.

Thanks Ferrymead

No trouble old chap. I had been meaning to email to let you know that your latest parcel arrived safe and sound, and is off for corrosion treatment and painting.

Cheers
A

OK, OK, stop your whining ! I will buy but don’t overcharge for postage!

Free?I have a family to feed,cat to entertain and a dog to deflea along with other adulty duties to perform.:dev2: Buy a model and copy it for your own eeeevil expirements Bwahahahahahahaha
For originality Bakelite would be the go if you can scour the Salvos for all their old saucepan and pot handles to grind down into powder.

Now QldSpitty here’s a pitch :

I am absolutely convinced that the use of Bakelite control knobs is a purposeful design feature meant to electrically isolate a RAAF pilot in shorts and sweaty shirt from the aircraft. The timber Mosquito is W/T, Wired Throughout, that is copper bonding strips join EVERY metal component within the aircraft so that there cannot be any arcing to ignite petrol fumes, interfere with radio radio transmissions or, in the case of lightning strike, cause massive voltage to carbonize the pilot or disintergrate the airframe. The pilot’s seat and armour backplate is bonded, every piece of metal is bonded.

Accordingly, Bakelite knobs, (or a Rubber composition similar to WW2 cable sheathing on later throttle knobs), with their magnificent diaelectric, insulating, properties are featured on the throttle box. The control column is wrapped in string, that I betchya was insulating. The stirrups of the rudder pedals had a bakelite liner. The earpieces of the headphones were bakelite. All this to prevent electrical current flowing through the brain or across the chest of a pilot manipulating the throttles on takeoff.

So I think new knobs should be bakelite, not 3D printed bumper bar plastic, if the intent is to offer up a throttle box that can survive a lightning strike or pulsed energy blast from a Tie Fighter that has travelled through a vortex in time and has an angry, confused replicant at the controls.

A bakelite press exists and you can get bakelite powder. The problem is the cost of tooling to make 3 knobs, where conventionally you would machine out a female clam shell form in steel, load it up with bakelite powder, clamp and heat. Machining this tooling would be kind of expensive.

Now the latest 3D printing guff is metal powder suspended in a substrate. You print your ****e using this mix, then stick it in an oven. The substrate evaporates away and the particles of metal coalesce and you are left with a metal thing, albeit shrunk 15-22%.

So if you take your accurate CAD knob drawing, increase it be 15-22%, CAD up the reverse in the ‘tooling form’ , it might be possible to output some bakelite tooling. I have no idea what the tooling finish would be. Probably need to machine finish, but only clean up 2% of the surface rather than great gobs in the conventional sense.

So if you would give me, FREE, an unlimited licence to use your CAD knob drawing, I will report on the outcome of this experiment here, and give you a big bakelite knob, if it works out. I already know that the tooling will probably cost as much as if it was made conventionally, going up and down the stairs of various 3D playpens thirty eight times, I just want to fool around with this new technology. I do Solidworks. I can redraw the knob myself, but the opportunity cost is not sitting on a deckchair and drinking beer.

Just for the dishonest sake of showing off two throttle boxes together and the honest sake of preserving engineering data, throttle boxes shown for single stage Merlin and double stage Merlin Reconaissance Mosquitos (RAAF PR41).

The main differences are the PR41 are the use of more functional mixture controls for leaning out the engines to maximise range. In this case a teleflex control (later used in Meteors for High Power and Low Power management) is incorporated into the throttle box with a longer slot cut in.

The PR41 also has longer bakelite knobs on the throttles, incorporating a Rocket Projectile firing switch (thanks Ferrymead!). Accordingly, the steel release levers are longer.

The single stage throttle box has a Mixture Control with a shorter travel and slot, but the Mixture lever engages via a cam arrangement with the Throttle Levers. In other words you cannot Lean the Mixture without having or pushing the Throttles forward, or with Throttles back for landing or starting you are at Rich Mixture. Accordingly the levers within the box are different for single and double stage Merlin, or certainly the throttle box controlling Packard Merlin 69 – V1650-3/7’s used on the PR41. (and RAAF Mustangs).

The Throttle Box casting is Magnesium and the Levers are Magnesium, as many components on the Mosquito are. In this case pushing the throttles forward on takeoff, and having 80 year old magnesium levers suddenly snapping off with the tail just rising, may make it difficult to simultaneously hold a can of coke between the knees without some spilling. Control could be maintained through nomex gloves by gripping the the control rods that run back and under the throttle box, or modern Risk Assessment paperwork could call for a midget to be carried behind the pilot’s seat to effect the same, but this could all be distracting. I am thinking of some casting patterns for new levers, with some NASA HACCP around magnesium components in flight control systems.

I’ve had good results using WD40, a wire brush and some good old fashioned arm muscle. Just means you take your time but without the worry of getting it horribly wrong.
Each to their own!

Rob

I would be tempted not to blast that, you might find nothing left, you could try if you can get some, Chromic acid.

https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_43-4a_.pdf

https://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/amt_handbook/media/FAA-8083-30_Ch06.pdf

Just a headsup Ive designed up the Airscrew Lever handles and Friction Wheel and Lock wheel and uploaded them.
https://www.shapeways.com/shops/spit?section=Mosquito&s=0

Ooohhhh nice… 🙂

They do get quite crusty!

This one is of the type used in the NF30. As recovered approx. 35 years ago. Requires a few spares too!

Ill pattern what Ive got here and manufacture some spares if anyone is interested.I have the handles on file so only take a coupla hours to print one off.

Yes, having learnt from bitter experience, I would agree with that!

Soda blast and a very weak rust converter followed by a sealer primer.Dont use acid or it will fizzzzzzzzzz.

Found in a yard today. Is there a way to prevent or stabilize the magnesium corrosion or is this unit too far gone.
All I need now are the internals !!

Playing around with my 3D printer.[ATTACH=CONFIG]255718[/ATTACH]

Thanks Jimbo !

We can all thank Jimmy Woods!

AM, great images and yes indeed, a Mosquito throttle box conversation is always a good meal, particularly with a pint ! Nicko, your photos are brilliant, because they show the unique, twin lever mixture controls/ cutoff used only on the Australian built PR41. These are a feature of the Packard Merlin V1650-3-7 (renamed Merlin 69 when fitted with a SBAC instead of SAE prop shaft). These run from 9 o’clock to 12 o’clock on the throttle box, while every other type runs through a shorter distance, if there is a mixture control at all. Your photo is the end of a journey that started with finding these twin teleflex type controls in the bottom of a box of scrap, stamped with a 98 part number but absolutely no literature anywhere to show what they were. It took years to find out what they were, and all this time your photo was there ! The same teleflex control is used for High Power-Low Power control on the Meteor, so the Australian built PR41 was the duck’s nuts in latest available technology ! There were about 8 of these controls in the bottom of the box, which I finally learnt had been pulled out in Tocumwal in 1957, probably in anticipation of farmers wanting a tractor control. Tocumwal is where the last of the Australian Mosquitos, all PR41’s from 87 Survey Squadron, were retired to in 1953 and finally scrapped and burnt in 1957. So what we have here is in fact 8 PR41 Mosquito projects for rebuilding !