powerandpassionHere are a few pics of rolling Merlin stands that I’ve found. Tom.
Tom, thank you for the selection of pictures, very informative. It seems that everybody goes for a ‘universal’ type stand that can handle truck diesels, which makes sense. A lot of air space is left for reduction gearbox and supercharger removal. The RR stand is a bit of a stradivarius in comparison, but allows you to ‘get in’ to the engine from all angles. In thinking about how you would do a RR stand today, you could laser cut the ring and arms connecting to the engine feet, with the outer diameter being standard. That way, you could have different rings for different v12s, but use the same base. The ‘knuckle’ engaging with the engine feet need be no more than a flat plate with a suitable number of holes in it. Hmmm…
powerandpassionI am licensed you know and hold 6.3 ( ALL piston engines) :p
Never too late to teach a young dog old tricks, and an old dog, new tricks:p
May need to ask you about screwing barrels in to develop variable compression ratios in Cheetahs…apparently there was a Mother Country compression ratio and India and Colonies compression ratio, based on ambient atmosphere.
One thing that I am mulling over is fuels, how different crudes ( Persian, East Indies etc) made different fuels, and how 87 octane fuel in the 1930’s might be different to 87 octane fuel today, certainly no lead. I would dearly like to find a Cheetah engine test chart from the 1930’s, to see what all the parameters were.
powerandpassionyou manufacture new ones
I guess this is the cost problem. I have been quoted the equivalent of GBP15,000 to machine a V12 style crankshaft from billet. Indeed high performance car racing crankshafts are machined from billet from vacuum remelted aerospace billet but you need a brave certifying engineer to risk her professional indemnity insurance to certify a machined billet crankshaft as replacement for the original forged and machined aircraft crankshaft. Let alone the cost of a nickel chromium alloy billet, let alone the incredible task of machining out throws and journals and line boring hollow journals. Just horrific cost. How much cheaper to just ‘recoat’ a crankshaft worn beyond limits with HVOF? If it’s a once off, rare crankshaft that would never support an investment in forge tooling that might be amortized across a range of users, which is in anyway conditional on someone with patient, risk capital to spare? I think HVOF offers a relatively affordable pathway to keeping rare, once off engines going in the long term. Just have to demonstrate it on some 1930’s British metallurgy. I find, from metallurgical analysis, that the 1930’s alloys are of exceedingly high quality, made from the finest Swedish iron and always over salted the alloys. Only when war erupted and resources were stretched, did metallurgy get shandied down. The 1930’s material has ‘good bones’, just need to find a way to keep it going. For access to cores, cannabilising of spares, affordability and 1930’s metallurgy, the Cheetah is the standout proposition to develop an understanding of the possibilities of HVOF on hardened and non hardened steel engine components subject to wear.
powerandpassionTony, I apologize for my Ramsayesque outbursts. I have been watching a few episodes and Mr Ramsay is a lurid exponent of that art what used to get your mouth washed out with soap. I lost my cool and the dignity of the forum has suffered for it. The forum is not a kitchen !
powerandpassionTell Siggi that I have some DB spanners that went to Russia and he can have them if he can help educate me about DB engines. Mainly interested in the Kawaskai licenced Ha140 DB 601 derivative and understanding why it coughed so much.
powerandpassionGordon waxes
Now you got me fired up!
On the front engine you will notice no exhaust gear. How it came. Corks where the exhaust rocker arms came out. Apparently they were used in the 60’s as air compressors on diesel locomotives. Diesel accessory drive connected to prop shaft, so the Cheetah was driven through its own shaft. All accessories stripped of back of Cheetah, air inducted through carb, into inlet, out to exhaust manifold which had a one way valve on the end. Some inefficiency, but if you follow the Otto Cycle and firing order it worked, obviously better than the original air compressor on the loco. Lots of swept air, cheap war surplus engine. So I did not feck this engine, it was fully fecked over last century. I will try and unfeck it. Most of these engines come out of paddocks where they have been shet upon by birds and used by farmers for shotgun practice. They are junk already. As Gordon Ramsay would say, get fecking real!
powerandpassionI still cannot get over why you would choose to possibly screw up what are getting rare engines, why do you not simply find a knackered lycoming and use that, their cylinders are nitrided, which incidentally you cannot renitride, however you can chrome plate them to restore them, you just need to make sure you get the right rings for it as the standard ones will strip it..
Lycoming will run different metaullurgy and crank pressures are different and many 1930’s cranks are not nitrided. I can only half stuff up because one engine will run stock as Control.
So I wish to demonstrate that a 2016 process, not within the OEMs 1930’s repair scheme, that will work with 1930’s British metallurgy on a crankshaft subject to X pressure.
if it works, THEN I might try the process on an excruciatingly rare crankshaft that is worn beyond limits, like a Napier Dagger or Bristol Jupiter crankshaft trawled out of the sea.
I guess I want to create a scientific dataset to engage in a conversation with a regulator using pertinent data to find a pathway over the next decade for keeping rare aeroplanes flying.
So, once your rare Cheetah crankshaft is worn beyond limits, beyond plating, what do you do? I think ALL of these engines were worn back then anyway. No mint Cheetahs laying around. The real problem is that some of the beautiful vintage stuff flying today can’t in the rapidly approaching future, unless some modern techniques are introduced to keep them safely flying for decades to come.
Stop grumbling and rebuild an Anson airframe and wings, and I might show you how to keep the engines going for 50 years. Might have to cast some new pots though, and the magneto coils have probably turned to chewing gum too. Few bits of silicon aluminium in there turning back into bauxite as well. Hoffman roller bearings unavailable. Maybe you are right ! Leave it alone ! Too hard. Siddeley was a grumpy old coot! It wasn’t a fabulous engine. Why invest? To learn.
powerandpassionAnd you have not mentioned the cooling or viscosity effect of the oil………maybe that will come with the castor oil research?
Keith
I thought the introduction of the term wibble-wobble into rheological discourse was enough for one day.
I am sure temperature and related viscosity are great influences. I seem to recall stories of groundcrew heating oil over a gas burner in winter to allow a quick fill and start for scrambles. I think the Soviets just lit fires under their engines.
What is proposed is test and control – one Standard engine and one with a HVOF crankshaft, run simultaneously with identical oil and fuel, identical atmosphere and identical operator incompetence. What I would love to find is an original AS engine test chart for Cheetahs, to understand duration, revs, fuels and oils used in original acceptance tests. Run the same test, can’t argue with that.
powerandpassionA tale of tailwheels
Here we go with tailwheel casting pattern, all magnesium.
The pattern maker said that according to the drawings the machining would pop the side of the magnesium barrel. Surely not! Not the chaps from Salisbury Hall! Poor design, hurrumph! But sure enough, when you look at the original casting, the original machining does pop through the surface, highlighted in the blue texta. The chaps put in a steel liner insert, that fixed it ! A steel liner in a magnesium body was never meant to last electrolytically…it would certainly help as a splint if you got a crack in the magnesium.
When you think about the risk of a tailwheel, right at the end of the hydraulic run, failing to lock down, you understand why the tailwheel was sometimes isolated from the hydraulic circuit and left down at all times in service, according to some old pilots. The little hydraulic ram that lifts the tailwheel unit has to do a lot of work to lift it, which is why they probably went for lighter magnesium for a massive assembly.
Now if you told the chaps that the tailwheel would never need to retract in service, and you wanted the tailwheel assembly to last for 50 years, might they have chosen aluminium for the casting……luckily the shrinkage factors for magnesium and aluminium are pretty close, so maybe you could do both materials out of the same pattern…
The pattern maker has original plans, but draws the logic of the pattern out on a piece of wood : how the pattern breaks apart and how the foundry man will set up his sand molds. So the piece of plywood drawing goes off to the foundry as well. But you can’t email the piece of wood, you have to hold it in your hands as you ride your horse to the foundry.
powerandpassionHere we go, some sacrificial lambs lined up. Cheetah Fits and Clearances courtesy of ANAM Archives Moorabbin.
Found a local HVOF aerospace workshop, so, in theory, it’s all possible. Just have to get engines dug up from paddocks working.
Been reading books and thinking – what is supposed to supply the ideal surface for the lubricant : the bearing or the crank journal (surely not?)
Don’t you want the sacrificial bearing to wear some nice grooves rather than the journal? Reading something about the theory of white metal bearings where the more resistant parts of the matrix stand up like goosebumps while the softer metal wears away, allowing the oil to do its sinewy dance through the bearing metal and around the journal.
Or do we want pickup on both surfaces ?
Why do journals wear anyway? Surely the bearing is the softer metal? Bits of aluminium crankcase have to be softer than the journal. Is it dirt in the oil? I get the sands of Libya being ingested through open carbs. If it’s little bits of hardened steel from wearing roller bearings why don’t aircraft engines have magnetic sump plugs or traps?
There’s a bloke I know that hand pumps oil before start until he gets a pressure reading off the crank before starting. Never blown an engine. Then there’s another bloke I heard about that paid big bucks for a Merlin, got his mates around, opened some beers and kicked the thing over to full revs, soon laying a leg outside the block. Most damaged bearings and journals seem to be oil starved rather than anything else, dirty oil, poor pressure, blocked orifices, too much beer.
I think the journal, subject to the oscillating pressure via the conrod, wibble-wobbles through the clearance between bearing and journal, while retained by the bearing cap. There is more pressure in the middle of a V12 crankshaft and less at the front and back, but better oil supply at the end it is fed in. For a radial main bearing, the wibble wobble must be more extreme. The V12 middle journal does more work than the outer ones, more wibble-wobble. I imagine oil is squeezed around rather than oil pump pressure fed around a journal : the pump gets it there but the squeeze comes via the conrod and the wibble wobble. The journal is a kind of lobe in a lobe pump, but the lobe is imperceptible unless you shrink to ant size and get sucked into the oil pump and carry a bright torch. I am thinking out loud here, and drinking absinthe….
So smooth journal or not? I am thinking the original journal was very smooth.
Merlins took DTD109 in 1940, what has happened to aero engine oil since then that gives better Merlin engine life? Crikey, I had better look up Cheetah oil, maybe they were designed around castor oil…
powerandpassionok, found some pics.
ZRX61, thanks for the pics and info. Everybody needs a pickup truck to get their Merlin bits around !
powerandpassionPowerandPassion
You probably know this… but let me know if pictures would help.Tom.
Tom, I know nuffink, as Sergeant Schultz would say! Pictures always help. I wonder what happened to the orgiginal RR Merlin assembly stands, surely one or two must have crept out, even from field repair shops. I wonder what Packard supplied for field repair? I have found a Merlin Mosquito ‘power egg’ static stand here in Australia, turned upside down and used as a bench in a farmer’s shed.
What I am wondering is :
a) there must of been a ‘knuckle’ that connected to the engine feet, that then allowed top or bottom ring to connect via the knuckle to the engine. I note one ring is, say 210 degrees and one is, say 150 degrees. Both rings have gussets that reach out to the knuckle.
b) I figure the rings were rolled from mild steel channel, assembled as a ring, low temperature stress relieved, machined to perfect round, then disassembled. I figure if you dropped the ring on the ground too often it would not work. I wonder if the actual rings were cast steel. I can’t get enough resolution from the photos to figure it out.
c) Is there some friction damper that prevented auto rotation once you had it in the desired position, eg for bank A or B when lowering the banks.
powerandpassionAs for roll over stands see
https://www.thesamba.com/vw/forum/viewtopic.php?t=175412
Thanks Tony, great article. Rollover for cars and fuselages is a fantastic idea, some set ups very elegant.
powerandpassionI have seen this version in several photos here and there from several restorations. It seems simplified and would be easier to construct, and allows full rotation. Maybe split the hoops to remove half for more access when needed.
[ATTACH=CONFIG]251084[/ATTACH]
DNF, thank you for that, yes, looks like a modern version, non splitting, most likely relies on its strength via being a unit. Your engine? I have some factory issue DB-600 spanners that came out with a migrant to Australia in the 50’s, very light, well designed, expensive alloy. Who are the DB600 rebuilders out there?
powerandpassionGreat book! ANAM Moorabbin Archives has a similar copy, so it looks like more than one was generated, unless one refers to radial engine configuration….will have to compare !
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