Generative Designed Crankshaft

[Tommy Cookers]

Compare to Lycoming:

most Lycomings etc these last 50 years have bolt-on counterweights
and in aerobatic version crankshafts integral counterweights

[Tommy Cookers]

Do pistons not transfer their inertia to the block via the crank in absence of a similar counter force?

yes they do (did anything say otherwise ?)
they make engines with 2 or more pistons etc so typically the sum of the engine-frequency inertia forces always zero
any summing not done in the crankshaft is done in the block

[Tommy Cookers]

Well T-C, at least in the case of the Napier Lion, C.F. Taylor must've been relying a bit too much
on theory, as he came up short on empirical experience, unlike the U.S. engineers who actually
tested a Lion, (with a highly critical eye),& they remarked on its smooth running characteristics,
despite being rigidly fixed on their test stand, rather than by typical resilient airframe mounts.
As for the Napier Sabre, rather than "too much bearing area", it was likely the robust crankcase
which contributed, in marked contrast to the Allison V-1710 V12 engine, which required revision
to a fully counterweighted crank in its later increased output series, due to what a Roy Fedden
analysis described as deficiencies in design per cylinder block/crankcase fixation methodology.
Likewise, the R/R Griffon received a full suite of crankshaft vibration/harmonics palliatives...

with 29% less vibrating force and c.twice the weight (of a Wright/Hispano 90 deg flat crank V8) it was less rough
no resilient mounts in 1918
the V12's so-called palliatives supported unprecedented power increases eg Allison's steady progress to even 3400 rpm
a very small price to pay
the Sabre architecture (that prevented it ever having a superior power:weight ratio) was irremediable
the so-called 2000hp class engines weren't required to have a superior power:weight ratio - just to have more power
bomber engines at best
the deletion of Sabre counterweights was logical but a negligible benefit in performance terms

[vorticism]

Compare to Lycoming:

most Lycomings etc these last 50 years have bolt-on counterweights
and in aerobatic version crankshafts integral counterweights

Yes, which may be what the flanges are for in the OP. On the Lycoming they were spaced between the 3&4 cylinders iirc, for whatever reason, not on the end, though. Any idea why?

Do pistons not transfer their inertia to the block via the crank in absence of a similar counter force?

yes they do (did anything say otherwise ?)
they make engines with 2 or more pistons etc so typically the sum of the engine-frequency inertia forces always zero
any summing not done in the crankshaft is done in the block

"sum" yes, roughly speaking (the second order force is asymmetrical). A single cylinder will also sum to zero while it's jumping up and down on the test stand if it's not bolted down. Multicylinders sum to zero only after rotating about their mass center through one refrence frame duration (1 revolution of the crankshaft). Some try to quell that with counterweights. That's why I asked the question.

[Tommy Cookers]

what Lycoming call counterweights are also pendulum torsional dampers
at the firewall end not the prop end
Ly seem to want to plant fear and confusion

now that everybody has a CS prop the over-rev (which would throw a bolt-on) is rarer
the Pitts started in the late 1940s

https://vansairforce.net/community/show ... hp?t=17377

showthread ?
once there was a 'Showcat'
apparently still in 2020

[vorticism]

Why place such a device internally and not at either end of the engine? I'm used to seeing harmonic dampers f.e. on the front crankshaft snout.

once there was a 'Showcat'

Did it win?

[Tommy Cookers]

the prop dominates the torsionals - unlike cars boats etc where the load is isolated from the crank via compliant stuff

btw the air load on a 2 blade prop winds/unwinds the prop shaft etc every rev as our Mr Handley Page predicted in 1911

[J.A.W.]

Well T-C, at least in the case of the Napier Lion, C.F. Taylor must've been relying a bit too much
on theory, as he came up short on empirical experience, unlike the U.S. engineers who actually
tested a Lion, (with a highly critical eye),& they remarked on its smooth running characteristics,
despite being rigidly fixed on their test stand, rather than by typical resilient airframe mounts.
As for the Napier Sabre, rather than "too much bearing area", it was likely the robust crankcase
which contributed, in marked contrast to the Allison V-1710 V12 engine, which required revision
to a fully counterweighted crank in its later increased output series, due to what a Roy Fedden
analysis described as deficiencies in design per cylinder block/crankcase fixation methodology.
Likewise, the R/R Griffon received a full suite of crankshaft vibration/harmonics palliatives...

with 29% less vibrating force and c.twice the weight (of a Wright/Hispano 90 deg flat crank V8) it was less rough
no resilient mounts in 1918
the V12's so-called palliatives supported unprecedented power increases eg Allison's steady progress to even 3400 rpm
a very small price to pay
the Sabre architecture (that prevented it ever having a superior power:weight ratio) was irremediable
the so-called 2000hp class engines weren't required to have a superior power:weight ratio - just to have more power
bomber engines at best
the deletion of Sabre counterweights was logical but a negligible benefit in performance terms

Airframes themselves were fairly 'resilient' a century ago T-C, however 'bench tests' noted that
an equivalent mounting was desirable for accurate assessment of N.V.H. issues. In regard to 'fuzzy',
I am still unsure if you are suggesting the 'broad arrow' 120 degree triple bank 12cyl architecture
was inherently smoother than the 90 degree V8, or vice-versa...

As for the Napier Sabre being inferior in power-to-weight, I'd suggest you revise your view by doing
a bit of fact checking, since a perusal of official figures published by Wilkinson duly notes that the
Sabre was ~equivalent to the V12 Griffon from early marks (0.48kg/hp vs 0.49kg/hp respectively)
yet widened that margin as development progressed so that by final series (Mk VII vs Griffon 130)
the Sabre offered 0.33kg/hp vs 0.41kg/hp...

& as you are aware, with regard to the sole 'bomber' type to test multiple Sabre-power,
viz: Vickers Warwick - well, by displacing its P & W R-2800s it was found to not only improve
performance from marginal to nearly excessive (capable of over-reaching Vne by Vmax!)
- & besting them by power-to-weight (including installed weight/coolant etc) as well.

[J.A.W.]

the prop dominates the torsionals - unlike cars boats etc where the load is isolated from the crank via compliant stuff

btw the air load on a 2 blade prop winds/unwinds the prop shaft etc every rev as our Mr Handley Page predicted in 1911

True enough, and it has been found to overwhelm the crankshaft catastrophically in Subaru engines
used in homebuilt planes, indicative of the need for torsional palliatives to be applied in that case...

[Tommy Cookers]

with 29% less vibrating force and c.twice the weight (of a Wright/Hispano 90 deg flat crank V8) it was less rough
the Sabre architecture (that prevented it ever having a superior power:weight ratio) was irremediable

Airframes themselves were fairly 'resilient' a century ago
I am still unsure if you are suggesting the 'broad arrow' 120 degree triple bank 12cyl architecture
was inherently smoother than the 90 degree V8, or vice-versa...
As for the Napier Sabre being inferior in power-to-weight....
official figures published by Wilkinson duly notes .... Mk VII

the Lion was somewhat smoother than 90 deg flat-crank V8s or a flat-crank straight 8s (which are bad vibrationwise)
the Lion was rougher than 90 deg crossplane-crank V8s or crossplane straight 8s (which are good vibrationwise)
the Lion '120 deg arrow' angle gives even firing intervals but is vibrationwise not some 'magic angle'
(similarly so 18 cylinder broad arrows use 80 deg - also for even firing)
WW1 8s were essentially a kind of crossplane straight 8s
Kalb's paper 'Engine Types Adapted to Car Trends' (in the 1935 Journal of the SAE) is the CFT book's source

as you can see if you look I have not said that the Lion had an inferior power:weight ratio
your Sabre VII was a hypothetical and so unofficial engine - and nothing to do with any Tempest that existed
the best power:weight ratio comes from low-altitude versions of engines ie the Sabre variants that existed not the VII

[J.A.W.]

with 29% less vibrating force and c.twice the weight (of a Wright/Hispano 90 deg flat crank V8) it was less rough
the Sabre architecture (that prevented it ever having a superior power:weight ratio) was irremediable

Airframes themselves were fairly 'resilient' a century ago
I am still unsure if you are suggesting the 'broad arrow' 120 degree triple bank 12cyl architecture
was inherently smoother than the 90 degree V8, or vice-versa...
As for the Napier Sabre being inferior in power-to-weight....
official figures published by Wilkinson duly notes .... Mk VII

the Lion was somewhat smoother than 90 deg flat-crank V8s or a flat-crank straight 8s (which are bad vibrationwise)
the Lion was rougher than 90 deg crossplane-crank V8s or crossplane straight 8s (which are good vibrationwise)
the Lion '120 deg arrow' angle gives even firing intervals but is vibrationwise not some 'magic angle'
(similarly so 18 cylinder broad arrows use 80 deg - also for even firing)
WW1 8s were essentially a kind of crossplane straight 8s
Kalb's paper 'Engine Types Adapted to Car Trends' (in the 1935 Journal of the SAE) is the CFT book's source

as you can see if you look I have not said that the Lion had an inferior power:weight ratio
your Sabre VII was a hypothetical and so unofficial engine - and nothing to do with any Tempest that existed
the best power:weight ratio comes from low-altitude versions of engines ie the Sabre variants that existed not the VII

Both Sabre Mk VII & Griffon 130 were officially type tested & flown, (inc' the former - in a Tempest),
& interestingly both Sabre & Griffon (plus Centaurus, too) were flown in the Hawker Fury prototypes, flight testing showed that Sabre power provided the most impressive performance figures.

Wilkinson's listing of the type-test data refutes your assertion regarding power-to-weight, T-C...

[Tommy Cookers]

I count two big counterweights and 2 small ones. 3 mains 4 big ends, I wonder if we'll go back to that for fuel consumption? Not being a bearingologist I wonder if you get more friction from 3 big mains or 5 smaller ones?

wouldn't such a counterweight arrangement produce a vibration (orbital) at primary frequency ?
(though it could be beneficial stresswise)
as I suggested of the counterweighted 2 main bearing Austin 7 and MG J2 crankshafts


------------------------------------ 4 MAIN BEARINGS - for less friction --------------------------------

Stewart Tresilian advocated and patented inline fours with 4 main bearings

and so? the designers of the first (2 litre F2) and second (2.3 litre for F1) Vanwall engine then used 4 mains
http://8w.forix.com/vanwall-grand-prix- ... ngine.html
and part2
all the subsequent (2.5/2.6 litre) Vanwalls used the conventional 5 mains
(btw Vanwall tried 3 and 4 valves but always raced 2 valves)
OR TRY THIS https://primotipo.com/tag/vanwall
SCROLL THROUGH - ITS BRILL and you can find their red link to Capps's site about vanwalls YES IT WORKS

Tresilian sold to Connaught (F1) a design - but that seems to have used 5 mains
see c.p23 https://www.grandprixengines.co.uk/CONN ... ONS(8).pdf

Tresilian worked for BRM and produced a 4 main 2.5 litre design the BRM P25 - their F1 entry until the 1958 season
Berthon changed it to 5 mains for 1958 (Rudd said this cost 19hp in oil cooling - of course the 58 Avgas fuel ran hotter)
Nye says for 1959 Rudd reverted to 4 mains (other sources seem to think that 5 mains continued)
https://www.autosport.com/f1/news/autos ... 6/4982576/

I haven't found a drawing of a 4 mains engine ... but accounts mention a single very large counterweight (at the centre)
wouldn't these arrangements engines also produce an orbital vibration at primary frequency (etc etc) ?

[Greg Locock]

You don't need what we call counterweights for 1E balance, that is any rigid shape can be 1 and 2 plane balanced for one axis.

Counterweights are there to reduce the local bearing loads and stop the crank from breaking, and to react the inertial forces of the pistons and rods. To give you some idea on that typically they react about 50% of the piston and rod inertia, and that number hasn't changed in 120 years.

In the mid eighties we were having a big push on engine noise quality, and for our straight six I identified that one cause of poor sound quality was that our crank torsional and bending frequencies were too close, and the crank was too floppy and we were getting excessive vibration in some of the mains. So we wandered off to the experts and they came back with a recommendation to treat our crank as if it was 6 one cylinder engines, giving rise to the 12 counterweight crank. It weighed a couple of kg more than the standard 8 counterweight crank, but because the forces were locally resolved it was bulletproof, and is consequently much favored by the engine modders. The improvement in noise QUALITY was indisputable to the musically inclined, but the change in noise LEVEL was tiny - that had not been our objective. So it went into production and 2 years later they changed back to the original lighter cheaper crank.

[johnny comelately]

You don't need what we call counterweights for 1E balance, that is any rigid shape can be 1 and 2 plane balanced for one axis.

Counterweights are there to reduce the local bearing loads and stop the crank from breaking, and to react the inertial forces of the pistons and rods. To give you some idea on that typically they react about 50% of the piston and rod inertia, and that number hasn't changed in 120 years.

In the mid eighties we were having a big push on engine noise quality, and for our straight six I identified that one cause of poor sound quality was that our crank torsional and bending frequencies were too close, and the crank was too floppy and we were getting excessive vibration in some of the mains. So we wandered off to the experts and they came back with a recommendation to treat our crank as if it was 6 one cylinder engines, giving rise to the 12 counterweight crank. It weighed a couple of kg more than the standard 8 counterweight crank, but because the forces were locally resolved it was bulletproof, and is consequently much favored by the engine modders. The improvement in noise QUALITY was indisputable to the musically inclined, but the change in noise LEVEL was tiny - that had not been our objective. So it went into production and 2 years later they changed back to the original lighter cheaper crank.

Not being a crankshaft person but if you are talking about the balance factor when mentioning the 50%, it is different for every engine and that is more typical for the garden variety V8 american engines
A lot of engines are 60% -68% , and often varied by 1%
Sometimes this varied according to engine mounts , chassis design etc
There is one partic vee engine that I cannot bring myself to say that was 63% but could go to 68% depending on the model of frame, but nothing really mattered becaause it would vibrate anyway.
There is a prize to guess who that manufacturer is

[vorticism]

Here's one that has four main bearings and no counterweights. Although it is a triple. A rather large triple.