powerandpassionGreat information that ties a few observations together. Certainly Watts fixed pitch wood props were fitted to Hart biplanes, eg Australian Demon and other interwar aircraft. The Hart biplanes generally had RH tractor RR Kestrels, and so did the HP Heyford, but the Watts prop numbers and props are different in these applications. Mind you the RR Kestrel had different reduction gear ratios/supercharging depending on application, eg Flying Boat versus fighter, and the fixed pitch blades would have to be different too. The Hector, a Hart biplane, also has a different Watts prop, also being LH tractor. My understanding is that different blade designs had different Watts numbers, being different designs. For Christmas, I would love to get data on Watts prop designs, sufficient to be able to reconstruct a blade design model, and compare these with other blade designs. Was the Hector blade just a Demon blade in reverse? Was the LH tractor Hector blade just a LH tractor Bristol Mercury blade ? SBAC had different ‘standard’ prop hubs, not sure if the interwar biplane hubs on Kestrels transmitted to new fangled Merlins on Hurricane I’s. A gent here had half an original Hurricane Watts fixed pitch prop, I was half minded about it, offered him half the price he wanted and was called a half wit.
powerandpassionFantastic !
powerandpassionA US politician, by virtue of the engagement of the United States in both world wars, and the postwar US consensus around the global investment of US taxpayer dollars and power, is not just a local representative. The whole world takes its cues from the United States. There have been a whole generation of US politicians that were formed or informed by the Depression, World War 2 and the Cold War who are fading out. Understanding that US power was purchased on the beaches of Omaha or Iwo Jima, or even Vietnam, gave some insight and balance to this generation. Understanding suffering gave a maturity to their words, thoughts and conduct. It is this that is fearful in the passing of this generation, of which McCain, for all his faults, was an exemplar. Now we are entering an age of a less poised, less tactful,less assured America. Mistaking noise for substance, careless of old friends, thinking the world is just a game of cards where you can push every hand as a Royal Flush. There was something bigger than John McCain in the United States, and when you looked at it, it was a whole lot of John McCains. Vale.
powerandpassionpowerandpassionThis is what I mean about ‘piggy backed’ 4 blades, with narrow waists fitting into the same hub as a single fixed pitch blade. This is a Viastra of West Australian Airways, fitted with LH tractor Bristol Jupiters. In order to equalise thrust, depending on the pitch of the airscrew setups, one engine may have had to be run at a different RPM on this Viastra. A pathway between LH tractor Dagger engined Hectors straining to tow gliders are LH tractor Pegasus engined Swordfishes straining to lift torpedoes. Maybe piggy backed Swordfish experiments allowed the Hectors to be ‘salvage’ equipped with piggy back blades when Swordfish went to variable pitch. Viastra photo stolen from Geoff Goodalls excellent website.
powerandpassionInteresting 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.
powerandpassionOK, OK, stop your whining ! I will buy but don’t overcharge for postage!
powerandpassionMate I would but not in pink ! Very interesting jobbie. Are you 3D printing ‘chunks’ that are then stuck together?
powerandpassionWONZ Show, always a very good visit, thanks for putting these together. Always interesting to hear all the stories of the other 98%, who weren’t flying Spitfires. Construction brigades did an amazing job. Love to get some Rosie the rivetter stories on the Show, shine some light on how much flying metal was shaped under painted fingernails.
powerandpassionComing together. Once you start laser cutting you cannot stop. I think I have been fascinated with laser since James Bond was strapped to a table while a sinister laser beam tracked towards his goolies…anyway a poor man’s ‘buck’ of a Merlin and Kestrel were laser cut and assembled, to provide a lightweight shape for another fairing forming job, but we can fit these to the engine stand and see if it all works.
powerandpassionBrake bladder
An old brake bladder was sectioned to show a thick layer of ‘insulating’ rubber adjacent to the brake segments. A postwar NOS brake bladder showed a different evolution, being a reinforced fabric (asbestos?) layer close to the surface, machined down to a tolerance. A NOS brake segment from a postwar brake unit showed Mintex and a friction material product code, for what inevitably would be an asbestos containing material.
Does anybody know if rubber brake bladders are still made? I cannot see a 50 year old NOS brake bladder being suitable where original rubber components were given a 5 year shelf life…
Are there any modern materials used in this application? Eaton Air Flex?
Does anybody recognise the Mintex product code and have technical information on its characteristics? What modern, non asbestos containing friction materials are used in current aerospace braking applications?
The Dunlop product catalogue for a mainwheel for Bristol 170 had an original inspection period for mainwheels on every 150 landings. This was amended to ‘upon every brake inspection’. The section on brake inspection said ‘generally on 150 landings but depends on frequency of landings and severity of use’. Probably reflecting on RNZAF supply trips into Vietnam. So a good guideline derived from the OEM for the inspection of Mosquito magnesium mainwheels would be 150 landings for a thorough inspection. All modern fleet trucks and some historic aircraft are equipped with inertia loggers that can indicate rough use. So probably an inspection after any hard landing event, if you have a pilot called Captain Schettino.
powerandpassionThe brake units are light. Too light. Magnesium? A little bit was cut off from a ‘goner’ and the oxy torch confirmed magnesium. As you do, water was thrown on burning magnesium to see if it would cause a more intense flame. It did. A lovely hydrogen smell emitted, reminding me of the hydrogen gas I used to generate reacting hydrochloric acid with steel wool as a 10 year old, to make flaming, exploding garbage bag Zeppelins, while all this was still considered unremarkable childhood play, not the mandatory 25 year jail sentence of today…
A little research in the Moorabbin Air Museum archives unearthered a Dunlop technical manual which confirmed the brake unit body was magnesium. I figure you have to add magnesium brake units to your magnesium component inspection list. These brake units do not form part of the support geometry of the wheel. If a crack were to develop in a brake unit the rolling function of the wheel would not be impaired. But flaking bits of magnesium brake unit casing could get trapped between the unit and the drum during braking, building up heat before igniting, causing an out of control, flaming wheel Mosquito to career into a tractor towing a trailer of corn cobs, causing a conflagration of pop corn sending flaming, expanding corn kernels into the eyes of gathering crowds pouring out from a nearby legal convention.
powerandpassionBrakes
Doing a few brake units, after immersing them in water to keep the asbestos dust sticking in my hair. The brake segments are on a metal backing retained by a clip, retained by a spring. Each segment is relatively easy to remove, revealing the rubber brake ‘bladder’ underneath. In operation, compressed air is directed into the bladder, pushing the segments outward to bear against the brake drum. When the air is released, the brake segments re-seat under the force of the springs drawing them back. It is a simple design. The only negative is if the ‘parking brake’ is activated while drums are still hot, causing too much heat transfer to the rubber bladder over time.
powerandpassionNow 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.
powerandpassionJust 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.
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