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Thread: Mosquito throttle materials

  1. #1
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    Mosquito throttle materials

    Here is a picture of a recently acquired Australian PR41 Mosquito throttle that needs some tidying up. I would be grateful if anybody could advise on materials available today to attend to the following :

    Click image for larger version. 

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    1) Yellow friction damper knob for prop speed control.
    Based on its lack of oxidation and feel I think this is bakelite. Are there any modern engineering plastics or even bakelite rod supplies that could allow the machining of a new knob, or does anybody have one they are willing to part with?

    2) Top handles for prop speed control levers. These are missing and I am looking for one to pattern off. I have seen these coloured black and white and yellow, is there any logic behind the colour schemes? I would assume it would be coloured yellow, to be consistent with the friction damper knob.

    3) Electronic push button on starboard engine control.
    There are two wires running to the tip of the starboard engine control and the remains of what I assume to be a push button. I cannot find in any of the wiring diagrams a role for this push button - does anybody know anything about this?

    4) Knobs for mixture control levers and engine controls.
    The PR41 had two mixture control levers linked to the Packard Merlin 69 or V1650-7. Both these mixture control levers and the engine controls had 'plastic' tips which are badly oxidized, swollen and have a 'rubbery' feel to them. I am wondering if these were a rubber product and if anyone knows anything about them.

    5) Crackle finish.
    The casing has a typical matt crackle finish. I understand this was originally stoving enamel, but was the crackle achieved by placing the object in a very hot oven or air stream or was this achieved by adding a chemical compound to the standard stoving enamel? I am familiar with the use of stoving enamel on steel objects which results in a smooth finish, based on long stoving at moderate temperature and the slow uptake of heat into steel. Aluminium transfers heat rapidly so I would assume that a coated aluminium object placed in a very hot oven might result in the crackle finish as the volatiles are rapidly evaporated, perhaps an almost accidental discovery in the past when somebody 'ruined' a stove baking job by rushing it into a too hot oven. Has anybody done any research on this?

    6) Labels.
    The throttle control is missing the labels for propeller speed control, mixture control, supercharger switch. Does anybody have images of these that I can scale off to create new labels.

    7) Supercharger switch.
    From looking at other throttles this switch looks like the standard AM toggle switch but the opening allowed for it in this throttle implies a narrower switch. Does anybody have an idea of what switch could fit?

    So many questions!
    Thank you,
    Ed

  2. #2
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    Hi Ed,
    I believe that you can buy 'crackle finish' paint that crackles by itself.
    Paul

  3. #3
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    Yup, you can get it as spray paint.

  4. #4
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    Be aware that 'crackle finish' and 'wrinkle finish' are totally different in appearance. I believe we are looking at 'wrinkle finish' here, as used on a lot of US radio equipment and vintage motor car dashboards.
    A potential supplier is http://www.frost.co.uk/automotive-pa...roplating.html
    Andy

  5. #5
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    Yes you're right Andy, wrinkle finish it is.

  6. #6
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    Thank you ozjag & AndyY, followed the link to Frost and it looks like the stuff. They must have a clear coat too that the fairies spray on my face each night...
    I think we are getting as close to the divide as you can when she buys 'anti ageing creme'- a waste of money- and you buy wrinkle finish - a sound, practical investment!

  7. #7
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    Used this on the dash of my MGB. Does exactly what it says on the tin... but do follow the instructions precisely.

  8. #8
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    Quote Originally Posted by powerandpassion View Post
    2) Top handles for prop speed control levers. These are missing and I am looking for one to pattern off.
    The bakelite radio world has a lot of information on replicating knobs, basically using a sound piece to make a casting mold, then using acrylic resin to liquid cast a copy. I would suspect that acrylic would be brittle, good for an old radio, but perhaps not for a flying control. In each casting step there is shrinkage, shrinkage in the mold, then shrinkage in copy, and this may add up to a 5% reduction in size of the copy, perhaps annoying.

    One good, practical suggestion is to machine the knobs out of aluminium and paint, certainly no strength issues. I was ready to run with this, when a quiet bell went off in the dim recesses, something about a prewar study on lightning strikes. Now what would happen if you had one hand on the metal control column, and one hand on a metal throttle control? The throttle was string wrapped, but there was enough bare metal in brake levers, and sweaty hands or leather are a good conductor. Rubber soled boots on the rudder pedals would probably isolate well. Certainly, between metal throttles and control column, your body might become a pathway in a lightning strike, or, less spectacular but annoying, static electricity. I know this sounds a bit 'far out' but losses of largely timber aircraft to lightening strikes in the prewar were a significant concern. This no longer mattered as much when stressed skin metal aircraft became the order of the day, which would allow lightning to easily travel through and out of an airframe, but deHavillands laid dozens of metres of copper strip through the timber Mosquito airframe only because of lightning strike. All Mosquito electrics were doubled up, in other words two cables were provided, one positive supply and one negative return, the copper strip was never a negative return. Only the Australian PR41 had heavy duty copper strip laid as a negative return, in addition to the strip for lightning strike. Things in the Mosquito were always deeply thought out, and lightning was a clear danger in a timber aircraft. I have to think the choice of bakelite throttle controls was purposeful, as bakelite has remarkable insulating properties, evidenced by its use in magneto distributor caps, where very high voltage was involved.

    So maybe we have to make new bakelite knobs. We do have access to a bakelite press. We do have bakelite powder. The job of CNC'g an aluminium knob would be no more expensive than CNC'g a metal bakelite press tool, which would allow a number of knobs to be pressed out to original specification. But we need the missing prop control knob to CAD up an accurate CNC file. Does anybody have one prop speed knob I can borrow for a week, please ?

  9. #9
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    Look similar to this my dear chap?
    https://www.shapeways.com/product/9N...ionId=55941542
    "If the C.O. ask's you to be Tail End Charlie...just shoot him!!!....A Piece of Cake.
    http://spitfirea58-27.blogspot.com.au/

  10. #10
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    Close but no cigar !
    The prop speed handles are the yellow, rectangular 'caterpillar' pieces standing upright on the outer two arms and the throttle handles are the black lollipops on the inner two arms standing upright in this photo :

    Click image for larger version. 

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    I am after a black lollipop and a yellow caterpillar (or original drawings of the same) to CAD up.
    The black lollipop closest to the pilot has a brown, inset push button which is the mystery push button I would love to find out about.

  11. #11
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    How did this project go??

  12. #12
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    Ausflyboy,
    Found another throttle box with complete bakelite to pattern off so that part sorted. Found an original drawing with complete labeling arrangements. That's about as far as it's got so far. Did discover the box case is cast magnesium, adding to all the other magnesium bits on the Mosquito, lots of magnesium.

  13. #13
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    We have a spare starboard throttle lever top, which is available for swapsies. The FBVI has the RP fire button on this side, which may explain why there is a redundant push button on yours.
    Alex Liggett
    DH98 Mosquito HR 339 Restoration - Ferrymead Aeronautical Society - Christchurch NZ
    https://www.facebook.com/NZMosquito/

  14. #14
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    There's a surprising variety of throttle box details used on the many Mosquito Marks.

    The button on the starboard throttle lever was also a "P-T-T" button on some variants.

    This is from the TR33 but I would hazard a guess that the majority of Mosquitos did not have this feature at all:-
    Attached Images Attached Images  
    The garage that keeps on giving.

  15. #15
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    "The button on the starboard throttle lever was also a "P-T-T" button on some variants."

    Air Ministry, brilliant, that explains it. Even the string holding the power cable to the lever arm is the same ! Now I have a new question ! On the unarmed PR41 there is the standard stick top, which in an armed FB features an inset press button for the MG trigger. Do you have any information on what this press button may have been used for on a recon Mosquito? Camera control?

  16. #16
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    "We have a spare starboard throttle lever top, which is available for swapsies. The FBVI has the RP fire button on this side, which may explain why there is a redundant push button on yours."

    Alex, it looks like this button was adopted on different variants for different purposes, thanks for the RP insight. Kind of makes sense if you want to let a salvo go on the Tirpitz while raking the decks, you only have two hands....

    Yes, I would be interested in swapsies, but we need to come up with a more tough guy term like 'targeted drop'! Swapsies is what Smurfs and Dora the Explorer do!

  17. #17
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    Well Ed, I'm really more akin to Dora than to Leonard Cheshire, but I'll drop you a line with a few targets of interest. Cheers A

  18. #18
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    Camera control?
    I doubt it, although my knowledge of Aussie versions is almost zero.

    My understanding is that the PR41 is a conversion of the FB40 which would have had the stick you describe. So, probably just a left-over from the conversion process.

    Another possibility is that whereas the BXVI was a dedicated bomber, it could carry a suite of cameras similar to the PRXVI. Likewise, the PRXVI could carry bombs if necessary.

    Perhaps there was an element of conversion back to FB if necessary in their thinking?
    The garage that keeps on giving.

  19. #19
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    Thanks AM and Alex

  20. #20
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    A52-319

    I was just taking general photos at the time... here are some details of photos of the AWM aircraft while still at HdH. The throttle box was on the edge of the prints.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Let your soul stand cool and composed before a million universes – Walt Whitman
    http://vhjet.com

  21. #21
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    You've got to love a good Mosquito throttle box discussion.

    I tend to do more digital collecting than the real thing these days so here's a few from my collection:-

    BIV, representing an early style of box, with Merlin 21 engines:-
    Attached Images Attached Images  
    The garage that keeps on giving.

  22. #22
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    The BXX, although based on the BIV, had slight differences, presumably due to the use of Packard Merlin 33:-
    Attached Images Attached Images  
    The garage that keeps on giving.

  23. #23
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    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 !

  24. #24
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    We can all thank Jimmy Woods!
    Let your soul stand cool and composed before a million universes – Walt Whitman
    http://vhjet.com

  25. #25
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    Thanks Jimbo !

  26. #26
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    Playing around with my 3D printer.Click image for larger version. 

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    "If the C.O. ask's you to be Tail End Charlie...just shoot him!!!....A Piece of Cake.
    http://spitfirea58-27.blogspot.com.au/

  27. #27
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    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 !!
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  28. #28
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    Soda blast and a very weak rust converter followed by a sealer primer.Dont use acid or it will fizzzzzzzzzz.
    "If the C.O. ask's you to be Tail End Charlie...just shoot him!!!....A Piece of Cake.
    http://spitfirea58-27.blogspot.com.au/

  29. #29
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    Yes, having learnt from bitter experience, I would agree with that!

  30. #30
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    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.
    "If the C.O. ask's you to be Tail End Charlie...just shoot him!!!....A Piece of Cake.
    http://spitfirea58-27.blogspot.com.au/

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