powerandpassionFastest Bulldog
Here is the Bulldog-T188 in modernist magazine pose, that is before post modernism came into vogue and it became evil to manufacture these sorts of things in the UK, pictures of rampaging jets no longer suitable reading material for youth, who instead of reading about boldly injecting unburnt fuel into the stratosphere were forced to eat celery and read Catcher in the Rye, turning them into the miscreants of today scratching graffiti onto trains. As I was saying here it is :
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A close up of test pilot Godfrey Auty, who nosed over the Bulldog in 1962, and might have unscrewed a few T188 panels and given them to the apprentices to fix up the damage.
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powerandpassionWulfie,
Sidestrand brochure strapped to leg of pigeon winging its way over to you – you have PM
powerandpassionThankyer kindly
Cornovii, wonderful, thank you, does it for me very well. Here’s a set of well worn Mosquito rudder pedals with a bracket coming off the shaft that would readily connect with the arm on the ‘square one’. There just seems to be no detail within the usual Vol I Mosquito APs for this sort of thing, I figure that this was a ‘standard setup’ for pneumatic brake control across a number of types, self evident and not worthy of detailed description.
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powerandpassionFantastic ! Thank you comrades for the detail and information. By reference to the photos and plans of the pneumatic unit, and in the absence of taking the unit apart or seeing an AP cross section :
The rudder linkage is connected to an articulated, joint set of levers, bearing against a return spring.
The geometry of the linkages means Port rudder ‘pulls down’ port valve, opening an internal valve directing air flow to Port brake, while reducing airflow to Starboard.
The volume of air is controlled by the handgrip, running to a valve in the centre of the unit. No handgrip input, no air to brakes, irrespective of rudder position.
The default position of ‘centred rudder’ would allow equal airflow to both Port and Starboard, if the handgrip was actuated.
What sort of aircraft were fitted with the vee design of valve?
What sort of aircraft, with pneumatic brakes, were fitted with the later ‘block’ design of valve?
Does anybody have any images of the linkage setup on the Mosquito, which had pendulum type rudders?
I wonder if a statistical link can be drawn between left handed pilots and nose overs with pneumatic brakes, in that the ‘natural’ left hand was typically on the throttle, while the less coordinated right hand was ‘on the brake’.
powerandpassionHow did pneumatic systems compare with hydraulic? I can see the no-freeze advantage, but was the response to input adequate?
And what was the pump used at what pressure? Thanks
FP, My understanding of original 1930’s hydraulic fluid was that it was castor oil, which did not freeze. In fact the later Mosquito, designed for high altitude recon, had a castor oil (Lockheed Red) based hydraulic system from the outset for this purpose, with natural rubber seals. More aircraft of WW2 used mineral based hydraulic fluids (Lockheed Blue) with synthetic seals. So freezing was not the problem that determined selection of hydraulic over pneumatic.
In a recent conversation with a pilot in respect of Shuttleworth Hawker Hind with pneumatic brakes and Hawker Demon G-BTVE with hydraulic brakes the reflection re brakes was that the hydraulic system was sluggish, with much foot pressure and raised eyebrows as expensive machinery hurtled towards the hedge, while pneumatics fitted in the Hind were much more effective.
The next reflection is how many prewar Hawker biplane photos you see with the aeroplane on its back and a sheepish trainee pilot posing near it. By the late thirties, I would suspect that the preference from experienced pilots for pneumatics and the development of engine mounted compressors would have moved constructors to pneumatics. This then met the influx of novices as the Air Force grew from 1938, less capable of dealing with the bite of pneumatics. So sluggish hydraulics were good for preventing training aircraft from nosing over, while pneumatics were better at the serious end of things.
Cars still run hydraulic braking, but with vacuum assist. It is always frightening to try and stop a car rolling down a hill with no engine running, just relying on hydraulics. Then you see articulated trucks which just run pneumatic brakes. Generally drivers dial up the hydraulic pressure delivered to the trailer when it is loaded, but then the careless ones forget to dial it down once unloaded, and you see the back wheels lock up at traffic lights. Feck the boss’ tyres, eh!!
In conversations with a Mosquito pilot he said it was ‘tricky’ to master the pneumatic brakes, some pilots ‘got it’ and some never did. A gentle ‘pip’ of the brake on one wheel could correct a tendency to swing on takeoff and I suspect with not enough airflow over the rudder you could find a ‘sweet spot’ with the rudder pedals in the crucial seconds before the tail lifted that came with practice.
I think each aeroplane is different. There may be too much mass to stop and not enough brake friction area for some designs that would make them sluggish whatever the transmission means. I have had the pleasure of taking apart a wheel brake assembly for a Boeing 737 which is astonishing for its compactness of design in comparison to friction area, and which is hydraulic, but I guess servo assisted. If this hydraulic design was put into a Hawker Hind then the pilot and engine would no doubt end up in the cafeteria while the aeroplane stayed a long way back on the grass.
powerandpassionKnee bone connected to the thigh bone…
Thank you for all your replies.
What I would really like to find out is the ‘typical’ physical connection between the rudder pedals and the brake unit, of which the earlier (Anson, Hurricane 1 etc) is shown on left and later (Mosquito – Canberra) units are shown below :
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Some rudder pedal assemblies are like the steering of a childhood ‘billy cart’ while others are pendulum type jobs, so the constructor would have to devise some means of transferring the movement of the pedal to the pictured brake unit. Does anybody have photos of these types of connections, or an AP dealing with the servicing of the actual brake unit ?
powerandpassionThank you for posting this. I have to reflect that we live in a good paradigm where something like this, whether fact, disputed fact or opinion, can be published. A post such as this in too many places, unfortunately even today, could cost you your life, or perhaps 25 years cutting timber or digging coal in the permafrost. Thank God for participatory Democracy, the free vote, the free press and long life to the Key Forum, comrades! Today my father turns 99 and he spent 2 years cutting timber for Stalin between 1940 – 42. There is no greater pleasure than listening to the chuckle of an old man when he reflects on outliving Hitler and Stalin, Mein Kampf and Das Kapital, and all the cruelty that flowed from it. I do hope that you keep digging into the P38 pilot. A single person’s story is often the only way of comprehending a cruel time, so gigantic that it blocks out the entire sky.
powerandpassionI would concur that this is Meteor HP & LP control, you can see it in cockpit views if you google.
powerandpassionDo you know if these were originally cast?
It’s a very good question, but these wheels were cast. The evidence for this is in the marks left by foundry core tooling. In the photo below you can see X’s in the guts of the wheel which may have been used by the original foundry to align core tooling in production. These types of marks would be inconsistent with forging.
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The spokes of the wheel have webs which also cannot be accomplished by forging because the webs of the spokes on the opposite side directly oppose each other. It would be possible to accomplish this only if the design was split then the two halves later bolted together, which some wheel designs are. I appreciate that forged wheels would be superior to cast wheels but we are dealing with a product of its time and circumstance, and the journey, for me, is about understanding an ‘antique’ process as much as making a sound product.
In looking at the wheels today, there is a lot of metal in the design, particularly in comparison to some of the contemporary Bendix magnesium wheels of the day, which seem far more optimised. Today, as you idle at the traffic lights lost in thought about mortgages, kid soccer transport etc and some young punk sidles up next to you in a fully optioned, lowered, fully speakered, four cylinder sheetbox and you look down at the painfully thin spokes of some alloy wheel held on by four oriental suggestions of a bolt you wonder the things don’t shatter when they drift through shopping centre carparks at midnight. The Mosquito wheels could, by comparison, almost go on a tank.
I have taken some samples of the wheel for chemical analysis to identify the composition of the magnesium. As Canadian wheels the punt is that either Dow Metal or American Magnesium supplied the metal. In the UK it was Elektron and a common specification was AZ91. There is a 1944 chart of Magnesium compositions and mechanical attributes for casting and forging that I can reference by manufacturer and also British DTD specifications, so this will help to confirm that it is a casting composition that was used. I have two Kelsey wheels date stamped 1943 and 1944 that cover this timeline. Often US made Bendix wheels have a plethora of information cast and stamped on the spokes which make identification easy. This P-38 wheel below has both a casting number and a Dow metal material identification on it, showing Heat Treated Dow H magnesium was used, making life easy. It is interesting that only in the last few years have leading automotive manufacturers included this type of information on automobile components to facilitate end of life recycling.
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In Australia many magnesium wheels that persisted after the war were scrapped in the 1960’s, and one theory is that they were used to support the production of VW engine and gearbox cases, which started in the country at that time.
Magnesium is a ‘German’ material more readily embraced in the designs of the Luftwaffe, particularly the engine bearers of various designs using the DB engine. I don’t know what folk do to replace these members, which look like they might be forged. It was fascinating to find, on this forum, that later Lancasters, and I can now confirm Lincolns, used large magnesium members in the interface between landing gear and wings, which probably deserve careful thought in respect of time in service.
powerandpassionBoulton & Paul did sell their technology to other companies, both Saro and Blackburn used their system. In fact B & P built the Bluebird IV wings and the London flying boat wings. They also received royalty payments covering some of their metal patents. Hawker paid them royalties, early on, for some of their spar patents.
I retract my statement that B&P ‘”did not sell their technology to other constructors”, I am wrong ! I do not know much about B&P as a company and their strip steel work, from leading the field in the late 20’s, seemed to become overshadowed by Hawkers with their Hart biplanes and Bristols with the Bulldog. Were the royalties paid by Hawkers in relation to the concept of the system of standard spar elements being combined into different sizes of spar ? Do you have any pictures or information on the Bluebird and London wings and the era of strip steel construction at B&P that you can share? Do you know of any other remnants of B&P strip steel construction anywhere ? Thank you, Ed
powerandpassionThe small piece, about 5 in. long, slightly bent, I cut off this ragged end for the new display, left the rusty remainder, about 7 in. of broken spar. You can have this in exchange for the Sidestrand brochure to go with our display.
Wulfie, happy to send the brochure for your Museum display, please PM your postal details. In the spar remnant, I am after enough material to sample the boom and flange, the ultra thin web in the middle and the large rivet that goes through the centre. Each sample does not have to be big, but if those elements can be salvaged from the 7 inch piece that will do. Can you post up some photos of the larger pieces of spar, this would be fascinating to see. No doubt the farmer would of had some nice roof beams – is there any history in relation to the aircraft they came from?
powerandpassionNow for some absolute butchery. The bearing is retained by a threaded cap, retained by a grub screw. After 70 years the grub screw was reluctant. The United Nations came in with diplomacy in the form of one of those clever counter threaded bits that you can drill to remove stuck studs and screws, but nothing budged, only bits of rusty gunk were thrown back in derision by the grub screw. So Shock and Awe was visited upon it with a drill and the grub screw became collateral damage. Now the cap didn’t really want to move either. I guess that 70 years ago a special spanner engaged with slots on the threaded cap and the thing was opened. I figured this was not a difficult part to machine and replace and a day of soaking in lubricant did not change things so the cold chisel came out. Smash, crash, bang.
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The cap has a removable oil seal which is a press fit. Underneath, exposed to sunlight for the first time in decades, is the bearing, a SKF unit, Made in the USA, so Kelsey of Canada used US made bearings.
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SKF USA famous of course, for selling lots of bearings to SKF South America that were re exported to SKF Germany, so the Luftwaffe could keep it’s wheels turning. No doubt with transfer pricing the units were sold to South America at modest profit to avoid US wartime excess profits tax, then sold to Germany at a princely risk premium in a low tax Latin environment. These are the types of angry thoughts that come when you are trying to remove corroded bits of metal from each other, like trying in consternation to stop a mongrel street dog rutting your poodle as you go for a walk.
The bearing was a press fit, but behind it’s seating was a section that would allow a small piece of metal to be placed across the inner race. The perfect size of this metal is about a half inch larger, both sides, the diameter of the steel axle tube that goes into the inner race.
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Once the steel piece is in the Goldilock’s zone it can be slipped in the veterinary sense past the inner race, flipped then laid on the inside of the inner race. The steel pipe and persuader is then used to pop the bearing out.
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Once the bearing is out all the necessary dimensions are accessible to the pattern maker. What remains as a press fit is the cast iron brake liner, held by easily accessible Simmonds type nuts and a press fit. This brake liner is not meant to be removed, and the pattern maker had what he needed, so I proceeded no further. Once I get the wheel back I will give removing the brake liner a go, just out of curiosity.
Is it possible to 3D scan the wheel and generate a casting pattern ? Yes and no. There are internal features which cannot readily be captured by a scan on one plane, and a lot of work would be necessary to fix the partial shape generated by the scan. As a regular shape, it would almost be easier to recreate the wheel as a CAD model, but finding a 20 something CAD jockey with the patience to accurately measure and reproduce the wheel would be difficult. It is almost faster for the practiced hand of the pattern maker to recreate an accurate timber pattern and when you compare the cost of a stumbling CAD jockey and the amount of resin and size of machine required to output a casting pattern then the pattern maker will be economic.
Mostly the pattern maker understands how things are cast, so can output a sequence of patterns that allow a practical sand mold to be made in a casting shop. This wizard craft no 20 something can know, so a 3D printed pattern is probably wasted, in this case.
Anybody want some new sand cast magnesium Mosquito wheels in 2016?
powerandpassionThe spindle is an interference fit on the steel axle tube which is held by the bearings inside the wheel. In order to remove the axle tube one of the spindles needs to come off. A quick ‘bridging tool’ was made out of a piece of steel with two threaded rods connecting this to the bolting flange, normally connecting the brake assembly, of the spindle.
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This allows a piece of pipe to be passed through the wheel from the other side and the use of the persuader to drive the spindle off.
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Once one of the spindles is off the steel axle tube, with the other spindle still connected, can be driven off using a suitable drift.
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powerandpassionThe Bride stripped bare
In order to prepare a wheel for patterning it needed to be stripped down so the internal dimensions, housing the bearing, could be measured. Nothing in any AP or training document I have seen describes changing over the bearings, so I assume this was basic knowledge taken for granted. But there are always little taps with the hammer in just the right spot that make a job easy, and this practical experience goes to the grave, so I will try and document an approach here, that also deals with the ‘new art’ of prying apart 70 year old parts that are combinations of dissimilar metals that adhere via corrosion in ways that the fitter of 1945 did not have to deal with.
The first challenge was to remove the aluminium caps on the aluminium spindles that support the compression legs. These caps are normally held together by a length of threaded rod passing through the centre of the wheel. Once the threaded rod is removed it would seem that the caps would come out, but they are pressed in with interference. The lips of these caps are cracked, testament to some historical fitter prying them off with a screwdriver, but I had very little luck following this path.
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If I persisted it seemed the lips would crack off entirely. The solution was to get a suitable length and diameter of rod or allthread that could pass through to the other side, then tilt it so it did not pass through entirely. A few taps with the persuader and manipulation of the rod around and the cap popped out on the ground side.
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The cap itself is nearly 20mm of solid aluminium with a thin retaining lip. It will cope with a pounding on the backside but a plastic tip on the rod will prevent marking as you pound away.
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Once the cap was removed on one side it was straightforward to turn the wheel around, drop a little timber ‘coin’ down to prevent marking and follow it with a length of pipe and more persuasion. Caps off.
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powerandpassionIt has the identical section to the drawing of the Bulldog spar, and illustrates how Boulton & Paul sold their steel strip system to other companies
To be fair to the immense effort from late WW1 to 1935 to evolve aeroplanes of strip steel construction the ferment of design thought should be put in perspective. Different constructors, personified in the names of driving individuals like Pollard at Bristols, came up with very different approaches and products, though on parallel pathways. Today, these products, from a cursory glance, look all the same, but it is unfair to accept that thought. My first impression was to see these spar designs as florid and curious adventures in steel rollforming, almost as something Liberace would make a candlestick out of ! It is not until you get into the mind of the designers does it all start to line up as a cool logic developed from reams of calculus. These sections pushed the attributes of metal to its ultimate limit, and these ‘Liberace’ box spars resulted in high strength, ultra thin structural sections that are unequaled today. Were any budding designer interested in the problem of tethering cables that ran from the surface of the earth into orbit, allowing the science fiction of ‘earth elevators’, they would do well to study Boulton Paul spars from 1925 as well as spider silk, to conjure the low cost, self supporting structure that the concept requires to be real
The principle of corrugating for strength, familiar in turning paper into a cardboard box that you can sit on, is illustrated in this diagram, showing an increase in functional strength with an increase in corrugation :
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There is the basic constraint in that as you increase the size of the corrugation the width of the strip to make the shape increases, adding weight. So the challenge is to chose the radius of curve and disposition of curves relative to the other with the least increase of weight. There were many different combinations tried, based, at first, on theoretical calculus, then ultimately tested. You could try to experiment with the top section, the flange and then the side section the web, in limitless combination, all requiring dozens of pages of calculus to prove. What would the designer of the day give to be able to use CAD and predictive software to evolve their ideas in hours instead of years ! But to make a set of experimental rolls to form metal was expensive, and rollforming was a new technology. To be a designer in 1925 trying to convince the Board to buy a new rollforming machine and commission coils of barely obtainable strip steel made from exotic new alloys such as Nickel Chromium would require brave and patient promotion. This patent of 1924, lodged by Pollard of Bristol’s, goes into painstaking detail, to describe the nature and disposition of the curves in the metal, ultimately part of the Bulldog design, five patient years later, in 1929:
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When you line these box spars up next to each other, and compare flange to flange, and web to web, they are each utterly different :
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Boulton Paul technology was not sold to other constructors, each, in the heat of competition, evolved their own designs, where each curve was the product of a roomful of mathematicians plotting every fingernail width feature with reason and precision. This art was defeated in 1935 by the more apparent simplicity of monocoque aluminium design and the conjuring of metallurgists to develop aluminium alloys of greater strength. What would be interesting today would be to use materials such as titanium and some of these old designs to create structural members of immense performance, a great gift across the years, where I hope your display of a rusty relic might light a fire in at least one tender mind of an upcoming generation.
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