powerandpassionMore spark
One last thing is the application of the hand starting spark in the cylinder. Both the Jupiter and the Mercury fired at 29 degrees BTDC and the Kestrel at 40 degrees BTDC. The hand starting magneto spark traveled to the main magneto and was distributed via a trailing contact on the rotor to all the cylinders. When you take off the distributor cap from a 12 cylinder
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or 9 cylinder BTH magneto
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you can see the trailing contact at 30 odd degrees behind the main contact in the direction of travel. So as the cold engine was hand cranked into life, the first standard spark would try and suggest the fuel to ignite, then 30 degrees later the biggest, continent splitting stream of sparks would explode into the cylinder, smashing the fuel out of existence. I should make a movie, “ The Brief and Savage Life of the Hand Starting Magneto Spark.”
Of course once the ground crew or pilot stopped hand cranking the hand starter magneto it would fizz into silence, brooding for its next explosion.
powerandpassionPut some spark in your life!
If you take engine magneto drive at 9/8 crankshaft speed or 1.125 crankshaft speed it all falls into place, with a serendipitous 9 sparks coming from the four lobed cam driving the breaker points ! See the whiteboard which lays out the full cycles below. Finding this exquisite organization of affairs always reinforces the fact that the old timers always went for absolute perfection with their engineering, there was never any fudging. Understanding this relationship, it is possible to understand how the 10 cylinder Armstrong Siddely Serval would have been arranged out of the same magneto body, if it had a four lobe cam driving the points. Say 10 sparks are needed per 2 revolutions of the crankshaft (full cycle) and one revolution of the rotor (full cycle). Therefore 10 sparks/4 lobes equals 2.5 revolutions of the engine to magneto drive gear during two revolutions (full cycle) of the crankshaft, or 1.25 revolutions per single revolution of the crankshaft, therefore a 1:1.25 gear running off the crankshaft. :applause:
Then the rotor, running off the 2.5 revolutions of the engine to magneto drive gear, would need to be slowed down to 1 revolution of rotor, so we gear down 2.5:1. Say we use the same rotor cog as the v12 at 75 teeth, we would need a 30 tooth drive.:applause:
I could not let this go without trying to figure out how the hand starting magneto worked within this system ! The default starting method seemed to be hand cranking in the 30’s. RAAF Bulldogs and Demons had Hucks starter clutches on the prop but I have never seen photographic evidence of Huck’s starters in Australian use. There is a lot of photographic evidence of hand cranking.
I was never sure where the hand starting magneto was on Australian Demons. No Demon or Hart family aircraft have hand starting magnetos in the cockpit. APs refer to a chain driven hand starting magneto in the engine bay, but photographic evidence of this eluded me until now. This photo of RAAF Demon A1-4 from the RAAF, via the South Australian Aviation Museum, finally showed its position of the starboard side clearly.
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Frustratingly, I have found no technical details on the chain gearing of this arrangement, until ebay offered this BTH AS magento with sprocket.
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It has twelve teeth, and by reference to the photo of A1-4, 48 teeth are counted on the drive socket linked to the hand cranking shaft. So the starting magneto was driven 4:1 from the engine hand cranking shaft. BTH seemed to be ubiquitous in service aircraft hand starting magnetos. Not only the RAAF Demon but the Bristol Bulldog featured them. In the Bulldog the hand starting magneto was fixed in the cockpit panel, with a handle protruding for the pilot to spin as the engine was started.
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The BTH magneto manual of the day for hand starter magnetos describes “ the average speed the handle can be turned is 80 RPM”. This is reasonable, as I am sure you can open a window winder at 80 RPM too ! The hand starting spindle is geared to the armature 5: 1, so the armature, on this basis, is doing 400 RPM. In simple terms, it is sending out a constant stream of sparks. Many of these hand starting magnetos were preserved on the benches of gas welders to fire up oxy acetylene torches, while I am sure a few sophisticates may have used them to light cigars.
Back to the ground crew hand cranking the engine, and starter magneto, to life. How fast could they do this ? Delightfully, the following preserved films give a fair indication.
https://www.youtube.com/watch?v=wIuQyKhSys4
In the first, at 1:15 secs elapsed, a Hawker Hart Kestrel engine is brought to life in 6 turns in 3 secs, two turns per second, or 120 RPM for a briefly sustainable human effort.
If the hand crank runs at 120 RPM then the 4:1 chain gearing runs the hand starting magneto spindle at 480 RPM, more than adequate according to the manufacturers recommendations. The actual armature, at 5:1, will spin at the dizzying speed of 2,320 RPM, the same speed as a standard industrial electrical motor. So it would be sending out a plasma stream of electrical sparks which would remove all doubt about ignition. It amazes me how quickly the engine starts in the footage, and no doubt trial and error found out that such a cascade of sparking was essential for prompt and reliable starting, particularly in the worst case backstop of prop spinning.
Delightfully again, the following film of SAAF Gladiators with Bristol Mercury engines, at 1:20 secs elapsed, shows a similar ratio of 5 turns over 2-3 seconds, akin to 120 RPM.
https://www.youtube.com/watch?v=oG8wQicz6tc
I do not know whether, like the Bulldog, the hand starter magneto was hand cranked in the cockpit, or enjoyed a chain drive arrangement like the Hart family aircraft.
By reference to another earlier post, the Kestrel hand cranking ratio was 13 : 1 of the crankshaft. On the whiteboard the following information could be added to precede the 2 crankshaft revolutions of one full Otto cycle for Kestrel V12 :
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Starting Handle – 26 revolutions
Hand starting Magneto at 4:1 – 104 revolutions
Hand staring magneto armature at 5: 1 – 520 revolutions
Crankshaft – 2 revolutions.
Considering that the ground crew started the Hart Kestrel with 6 cranks, the engine crankshaft would have only done 6/26 or 0.23 of a revolution. By referring back to the whiteboard, it can be seen that the distributor rotor would have traversed only 12 sparks X 0.23 = 2.76 sparks/distributor points/cylinders out of the 12, so the engine started from the firing of only 2 cylinders out of 12. For a brief 2-3 seconds of human effort, these ratios resulted in the engine crankshaft turning a fifth of a revolution, while the armature of the hand starting magneto spewed a plasma stream of over a thousand high tension sparks.
Sometimes you see today’s ground runners linked to electric starters that turn and turn and turn and you wonder if the old ground fitters would be turning the same way in their graves ! Getting a V12 to fire on 2 cylinders would mean a nice, tight, well loved and understood engine. It is interesting when you read about the sand of the Middle East campaigns getting into the engines and they started to loose compression, becoming “harder to start”. Certainly if you were hand cranking !
powerandpassionTough material, tough question
Asking the impossible – but why not!
Former E of the Lancaster sits between the nose section and the front centre section. While there are some other parts, the former is in two sections, both closed hoops joined top & bottom with short angle & channel parts. The front hoop is an angle section and is part of the nose. The rear hoop is an extruded channel section and is part of the front centre section. The two hoops are bolted together to join the nose & front centre sections together.
A good mate of mine wants to build this former but is in fearful trouble over the extruded channel. As he works the ally channel into shape, it becomes brittle and breaks.
Could this be avoided by a special ally alloy?Unfortunately the original Avro drawings for the extruded channel itself are no longer on Earth. But I do have an Avro component drawing which suggests the material is SS.3075.
If this is the material code and a modern equivalent exists without costing the earth, then perhaps we are ok.Is there the slightest chance you or anyone can help us with this.
Which top shelf brand do you like the best?
All the best
Mike
Mike, these are tough and easy questions. Easy : for brand I like Coopers, made in South Australia, served on a hot day by a smiling woman in a bikini, surely not too much to ask ?
Most of the metallurgical effort here is focused on historical steel, as aluminium is still a ‘current’ material, and there would be many more practicing engineers on this forum that could give you a practical response, if you shut the door on their coat tails fast enough !
If your friend is trying to make something fly then I cannot provide any advice.
If it is a static then I can only guess, in the absence of drawings and contextual information, some responses which I don’t feel too much faith in their usefulness :
1. If this is construction/glazing extruded channel bought in a hardware store it is supplied in the hardened condition. Any manipulation would cause the failure you describe. Talk to a heat treating shop about softening options, but you would need to understand the alloy you are working with.
2. Extrusion dies are fairly simple to make and for an economical sum you may find that an extrusion facility can make you any profile you like in any alloy for static purposes. If they are sufficiently engaged they may be able to help select an alloy and assist in forming. I assume you are trying to form the channel into the cross section of the cockpit shape, a big bending ask.
3. I do not know the Avro alloy you have specified, perhaps it is a proprietory specification, typically aluminium alloys of the day are British Standard L1, L3 etc or a DTD spec. The cockpit to fuselage joining channels would have to be very, very strong members, formed in the softened state and age hardened. This would be a high performance alloy and any modern equivalent would no doubt cost a bit.
4. If, like me, you are in your underpants in the back yard holding a piece of glazing channel that your partner has given you three hours permission to form into a Lancaster, then I can only suggest the following :
a) get someone with a tig welder to tack weld a flat to the channel to form a closed section, later removable. You might try tack welding both channels to kiss each other for same affect, do both sections at the same time if the profile allows it.
b) fill the closed section with sand
c) make up a bending mandrel or former, being the inside dimension of the bend, out of strong timber or a pieces of steel.
d) experiment with a blow torch on the channel while bending
e) Clamp one end and work the bend around, allowing 3 or 4 feet of extra length to allow you to lever the shape around.
If all else fails at least you can feel confident that you could participate in that schlocking film where they rebuild a crashed aeroplane to fly out of the desert, I can’t even remember its name…
powerandpassionSkysport
When the RAF museum Bulldog was rebuilt did they re-manufacture this tubing? Or did they create a simpler ‘look-alike’ structure where the original structure was too damaged for repair?
Tony, I do not know, but a forumite familiar with the excellent restoration undertaken by Skysport may be able to answer. From the display of the aircraft there is a diagram which shows original aircraft material and replacement material from other Bulldogs. From this I understand much of the structure is original, with sections from other remnants ‘spliced in.’
I would love to see if anyone has film footage in their attic from this Bulldog flying in the 1960’s
powerandpassionI find this quite interesting.Thanks for posting. Look forward to your findings. Andy Scott
Thanks Andy for your interest. Any leads on strip steel remnants for testing are always appreciated !
Ed
powerandpassionThank you
Ed,
There’s no better description than that given in AP1095 dated 1935. I’ve copied the relevant paragraphs from a PDF I have into a Word document, but at 1.1Mb it’s too big to attach. If you PM me your email address I’ll send it.
Andy
Andy, fantastic, thank you, PM sent, Ed
powerandpassionBulldog
Below are images of Bristol Bulldog fuselage section, probably the ultimate development of the strip steel construction technique. The structural engineering genius behind Bristol aircraft design in the late 20’s and 30’s was HJ Pollard, who pushed the art and science of strip steel construction to its limit. The longerons pictured were made of ultra thin DTD 99 (= British Standard S87 1936) strip steel in two sections with the lips locked over each other. Only the friction of the lips held the section together, they were not held together by rivets in a structural sense.
HJ Pollard was a visible contributor in the literature of the day. There were others in the battle of ideas whose concepts were iterated in aircraft designs but were not fond of arguing their points in print. Fred Sigrist of Hawkers was a titan and competitor in these design battles but it is extremely hard to find him sharing his mind in print. Pollard, with all his mathematics and surety, would have been a hard man to challenge, not in his personality, but in the dread of being embarrassed by a confident and invariably correct return from him. How much British aircraft design was retarded by the omnipresence and omnipotence of it’s titans is hard to judge; but the French and Germans had nothing but morbid curiosity and astonishment for the British preoccupation with strip steel construction, while forging ahead with aluminium and monocoque, stressed skin designs.
There is a wobble in 1935 when Pollard, on the basis of improved strength values for aluminium, concedes that the monocoque aluminium structure is the way of the future. The Bristol Aeroplane Company then constructs the Britain First, a moncoque aluminium design that spawns the Blenheim, and strip steel construction is utterly abandoned. So Pollard, in print at least, becomes the father of strip steel construction, presenting the astonishing structure of the Bulldog to the world, then as Abraham with the knife quivering over the body of his son, hears the word in 1935 that things have changed.
In the Bulldog, why not just use a simple tube ? In the first instance the art of cold forming thin walled tubes was in its infancy in the 1920’s, when the Bulldog was designed. It was not possible to secure ultra thin walled tubes with a predictable wall thickness, so the designer had to over specify tube wall thickness to cover this deficiency. Rolled strip, on the other hand, could be provided in an exact and measurable thickness, so a roll formed tube section could be reliably provided with ultra thin walls. The tube folk resented this disparaging of their product, and argued that the provision of extra material in the lips negated weight savings. But it was many years until they could refine their cold formed tube to be a more predictable product and earn the ubiquity that tube material enjoys today.
Even the wing spars of the Bulldog were made of strip steel sections friction fitted together without rivets. It’s hard to get your head around this, but a lot of effort and research went into proving this technique, and the Bulldog had a remarkably light, strong and flexible structure that worked. You cannot use SAE 4130 to replicate the performance of the original material.
For anybody that expects a Bulldog could ever fly using original eighty five year old corroded strip steel sections that range from a fifth of a mm thick, get very good life insurance !
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powerandpassionHurricane spar
With thanks to forum members samples of material are coming in for analysis. As testing results come through I will post them here and on http://www.silverbiplanes.com
Pictured is a centre section spar remnant of a Canadian Hawker Hurricane, showing the adaptation of the late 20’s Hawker design concept of octagonal spars for biplanes to faster, more highly stressed monoplanes. Both spars use BS S88c in original British specification, but I wonder if North American production relied on a material called SAE 8630. Testing will tell.
Below the Hurricane section from the 1940’s is the 1930’s Hawker Demon spar section, with additional web and bottom octagonal boom, for size comparison. The use of internal spar liners in the Hurricane design becomes clear as a simple and effective development of the concept that carried through from 1925 to Typhoons in 1945.
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powerandpassionGoing nuts
I realise that the A16 series for nuts has been superseded, but does anyone have a copy of the spec sheet for A16 nuts that they could post or send to me? Thanks.
CK,
I don’t have BS A16 ” Hexhagonal Steel Nuts (Ordinary, Thin, Slotted and Castle)” but this may be purchased from British Standards at significant cost. Sometimes I find, after assisting the balance of payments issue for Her Majesty’s Government, that the purchase of the Standard does not actually answer all the questions that would allow you to make any informed engineering decision, because the document is couched in terms that assume you have or know other documents of the period.
So here is A16 GS pieced together from a range of documents :
“RAAF Publication 434 1944 Correlation & Interchangebility Tables” giving A16Y -GS as 5/16 BSF , MS, slotted, RH with Standards Association of Australia and Commonwealth Aircraft Corporation equivalents.
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Then we go to “RAAF Publication 314 Aeronautical Engineering Handbook 1944” giving pitch and dimensions
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Then I checked this against “BS 916 : 1946 Black Bolts and Nuts” which is not the aerospace standard BS A16 but gives pitch and dimensions to show nuts are nuts:
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None of these give metallurgical information so I looked at DAP Beaufort Division inspectors notes which give pitch, dimensions and metallurgy as BS S1, which you may purchase at cost from British Standards :
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Or alternatively trust to contemporary RR material specs for nut metallurgy :
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All this for one slotted nut ! You owe me a beer !
Ed
powerandpassionI’m looking for a copy of Air Publication 1641E. Does anyone have a copy that they’d be willing to share?
Thanks
Can you tell me the title, might ring a bell…
powerandpassionShow me a photo of Gilman
p&p
Are current Merlins fitted with Gilman bearings ? Does this explain the engines apparent reliability?
No and yes and ‘don’t know’!
Steel backed shell bearings were a Gilman patent in 1938 but RR went for silver indium as an alternate to copper lead and didn’t have to pay royalties. I figure there was much cross pollination/theft of IP in the 30’s.
It’s hard to ascribe the successful interplay of many components moving at 2500 RPM to one singular design aspect or one single innovator, though the driving force of individuals such as Gilman at Allisons, Fedden at Bristols and the wandering ghost of Royce tended to create a great result.
Gilman is that most unAmerican contributor. This is no self promoter. I cannot find a photo of him anywhere and even the history of the Allison engine coy does not have one and provides a sense that he was a secondary figure. In terms of reliability the Allison of WW2 was very reliable. I figure a designer in California or New York understood an engine failure meant a three week trip on horseback to bring in a replacement for a busted valve spring, so things were sturdy. Things were easier to get to in Europe so a premium was placed on lightweighting and performance. This cannot be proven but you get to wonder when you look at an RR conrod that feels like a bone in a bird’s wing and then an Allison cylinder liner that could probably double as a mortar tube. Probably Russian engines are the same, same three week trip on horseback to change a spring.
I do not think an honest RR development engineer in 1938 would have had much confidence in the developing Merlin. Coolant leakage around cylinder liners was one issue. In the end, of course, a remarkable powerplant.
I have a BBC recording of a Mosquito doing a flypast during WW2 and it doesn’t sound like a Mosquito. I have seen KA 114 fly in NZ and that is a Mosquito ! A loud thing. But the BBC recording sounds like the 1908 Tunguska Meteorite impact meshed with the sound of 15 freight trains running over the foot of Godzilla ! Literally a bunch of 20 something pilots with a smile on their faces and the throttle full forward flogging the chicken crate across the sky. Good chance of punching a conrod out the side. I know I will never see something like that ever in my life. For good reason warbirds are run the way modern children are introduced to swimming, blue faced, anxious parents blowing up inflatable devices to keep them dog paddling in the shallow end. Merlins today have more medical imaging and cosseting than the entire heath budget of sub Saharan Africa in aggregate. The poor things don’t get a chance to be unreliable !
Stop asking questions that get me off topic ! No more questions requiring rambling answers unless you open your wallet and put some top shelf liquor on the table ! 😉
powerandpassion..”bile from other sources…”
I’m ready to donate.
:p I am already self powering the thing ! Thank you for your offer and good humour !
powerandpassionAP1275 1930 “General Instrument Equipment for Aircraft” Sect 1, Chap 1 :
“Mark VI Revolution Indicator
As the dimensions of aircraft increased, it was found that standard types of revolution indicated(sic) needed exceptionally long flexible drives, more particularly in the case of multi engined aeroplanes whose engines were carried in nacelles on the wings at some distance from the pilots cockpit..trouble was experienced when the flexible drive exceeded 30 ft..there arose a demand for dials for the use of the engineer..led accordingly to the development of a large dial indicator.
The MkVI has a dial of 5 inch diameter, graduated 600 – 2600 RPM, movable lubber mark, weight 3lbs 12 ozs.”
3500 RPM is associated with V12 engines, contemporary Hawker Hinds with Kestrels had 3000 – 3400 RPM Mk IX indicators, which AP 1275 1937 shows came after the Mk VI. As aircraftclocks has pointed out, perhaps this was a Mk VI special order.
If the guts of the dial stayed the same as a 2600 RPM unit and only the dial face changed, you would only have to alter the engine output ratio for the needle to traverse approximately 300 degrees around the dial, which is a product of the engine gearing ratio for output to the flexible drive. So what apart from the V12s output this ratio to the RPM indicator ? Armstrong Siddeley Serval ? Saro Cloud flying boat ?
I wonder if this is an early thirties gauge from multi engined type using RR Kestrel, HP Heyford, Short Singapore, Supermarine Southhampton ?
Nice gauge.:)
powerandpassionC’est ne pas possible !
Last post, I promise ! (on this topic 😉 )What I like the most about instant answers are instant new questions. Here is a Gilman bearing from a RR Kestrel that comes up with an astonishing value for Silicon in the steel shell component. I would not believe that so much silicon could be in a steel alloy, surely making it so hard it would snap. After the Lab V XRF test, I have to believe that I am not being taken for an XRF ride. Ferro silicon alloys are used in electrical transformers and are those thin steel wafers you see laminated together and are used for their unique characteristic of absorbing magnetism.
Until the Gilman bearing patent came along RR had lots of trouble making their R and F engines of the thirties to work, the increased HP chewing out the white metal conrod bearings. Then Mr Gilman of the Allison engine company invented a bearing that RR took and paid a royalty for, that made the Kestrel and ultimately the Merlin workable. Chas Lindburgh achieved fame in 1928 for crossing the Atlantic because the engines of the day were certain to fail on such an epic voyage, but he used Gilman bearings and made it.
http://forum.keypublishing.com/showthread.php?128767-RR-Kestrel-Gilman-bearings&highlight=
Now is it possible that the secret behind the Gilman bearing was an ultra hard silicon alloy steel bearing case, connecting to a 5% Nickel conrod shaft ? A metallurgist is as likely to put 13% silicon in a steel as you are to put bourbon on your cornflakes, but perhaps the best discoveries start from an unusual breakfast. Now XRF is my trusty companion on new voyages of re discovery.
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powerandpassionLab V XRF
Back to business ! So the ultimate test for XRF is to compare the cuppa soup, 9 seconds to get result, XRF LCD display with conventional spectroscopy via a lab, which took two weeks to arrive, cost a lot of money, needed me to destroy the original piece by cutting off a slice and get a paper cut slipping the test piece into an envelope…
The test piece is Hawker Australian Demon spar, albeit two different locations on the same piece. % Results are :
LAB V XRF :
Mn 0.56 Mn 0.625
Ni 4.56 Ni 4.91
Cr 1.20 Cr 1.04
Mo 0.09 Mo 0.023
V 0.15 V 0.167
So I am pretty happy with XRF to give me PMI as good as the lab in 9 seconds at $5 per result, given that I will hire the unit for one day and do many, many tests. I did not clean the corrosion off the test piece either.
So XRF will lower costs, increase safety and make historic aircraft restoration more effective.
It will not do to leave this on such a positive note, given the zen of the forum, so I must unhappily report that XRF is powered by extracts from the bile ducts of caged baby pandas, though efforts are being made to replace this with bile from other sources, grumpy old goats being a promising line of inquiry.;)
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