2 stroke thread (with occasional F1 relevance!)

[J.A.W.]

Hello J.A.W.

You write:
“Did you read this 2T research : http://cdn.intechopen.com/pdfs-wm/43662.pdf”


The RD350LC was an important engine in the 2-stroke history.
Great engine at its time, not competitive today.


The basic design/philosophy of the two-strokes needs fundamental changes/modifications to make them again competitive.
Isn't it obvious?

Thanks
Manolis Pattakos

Hi Manolis,

No argument that it must be galling to see funds lavished on the 'OPOC' with all its faults,
but that research article also dismissed uniflow with poppet valves as uncompetitive due to
cost/complexity/port-time-area issues for small automotive/ low boost, car-type use.

Just as Toyota rejected its 4T-based DOHC 4V conversion to an externally scavenged SI 2T..

As for the YPVS Yamaha 350 design, sure, it is out of production, but entirely due to 'marketing' reasons,
as can be seen by the Jawa comparison, & in fact, the Yamaha's nearly 180 rwhp/litre @ <10,000 rpm
some thirty years ago - & from a light, simple, inexpensive, compact unit, is still very "competitive"
- as a tractable, reliable motorcycle output.

A modern RDLC equivalent with the advances in ECU power inc' fuel injection shown by other recreational 2Ts noted here previously, would offer a much more efficient & capable machine yet, maybe like a 130Kg/180hp KTM 900/3 road bike - based on their well proven 300cc cylinder ( & under much less stress as a three).

If the makers had the gumption to do it..

Ironically enough, the high 'current market value' of 2T machines such as the RDLC Yamaha & H2 Kawasaki
& the ready aftermarket support for parts & services, really ought to have the makers re-think the deal..

See here: http://sso-bikes.de/shop

[Tommy Cookers]

@ Manolis
since you ask for thoughts and/or objections .....

your 'short stroke' In-Line Four illustrated in your post at 4.44 yesterday .......
would to me apparently generate extremely large vibrations at engine frequency
(unless equipped with some unusually capable counterbalance shaft/s that you didn't show)


and with your Cross Radial PatATeco .....
again, I wonder, have you evaluated the likely detriment to crankshaft/propellor shaft torsional vibration when driving a propellor or rotor ?
complicated by and strongly related to reduction gearing factors (if reduction gearing is used)

there are very many precedents of crankshaft redesign due to this, not all conveniently in the distant past
eg the RR 1970s development of Continental's flat 4 (direct drive of course) to 130 hp for the Aerobat version of the French-built Cessna 150
had fatigue failures in service and was effectively banned, without iirc compensation to customers
the props were disappearing in flight
many other efforts by lesser organisations have similarly failed since


I hope that you can follow these attempted suggestions of mine better than a previous one
(when you seemed to think I said the TZ 750 jackshaft is or should be driven only about 1 or 2% slower than the crankshaft)

[J.A.W.]

I said the TZ 750 jackshaft is or should be driven only about 1 or 2% slower than the crankshaft)

T-C that is correct, & so would be unsuitable for double-duty as a basic counter balance shaft.
The necessary 1-1 ignition timing drive was driven by another shaft in train, via corrective gearing.

The Yamaha racing engineers were obviously going for simplicity/reliability/low-cost/parts-sharing,
while their production colleagues were running into difficulties with their 'Omni-phase balanced' big twin 4T.

Ironically, the TZ inline 4 was initially shown as a production road bike ( the GL 750, with FI! )
since as F750 racing rules then required - engines raced, were to be derived from production bikes.

Yamaha got around this stipulation by building hundreds of TZ/4 racers for sale,
& unlike the other 2 big Nippon 2T bike makers, never did sell a 2T 750 roadbike,

[manolis]

Hello Tommy Cookers.

You write:
“your 'short stroke' In-Line Four illustrated in your post at 4.44 yesterday .......
would to me apparently generate extremely large vibrations at engine frequency
(unless equipped with some unusually capable counterbalance shaft/s that you didn't show)”

You are right.

The I-4 with the crankpins arranged at 0, 90, 90 and 0 degrees around the crankshaft rotation axis (i.e. the PatRoVa in the animation) has an unbalanced inertia force (1st order, rotating).

Similarly the I-4 with the crankpins arranged at 0, 90, 270 and 180 degrees around the crankshaft rotation axis (i.e. the Yamaha M1 and R1) has an unbalanced inertia moment (1st order, rotating).

I know Yamaha R1 does use a balance shaft (counter-rotating at crankshaft speed) having two balance webs arranges 180 degrees from each other.

Does anybody know if Yamaha M1 (the racing engine in MotoGP) uses a counter-rotating balance shaft?
Or Yamaha prefers the vibrations from adding a balance shaft, and the synchronization gearing it requires, in a racing engine?

The PatRoVa I-4 of the animation requires either a counter-rotating balance web at the middle of the crankshaft, or a pair of balance webs symmetrically located relative to the center of the crankshaft. For normal use.
For racing use the need of external balance webs is questionable.


In order to avoid the external balance webs (of the Yamaha crossplane-crankshaft I-4 and of the I-4 PatRoVa of the animation), a better choice is the V-4 arrangement with the crankpins arranged at 0, 0, 90 and 90 degrees:



(used by some Ducati V-4 in the moto-GP).



You also write:
“and with your Cross Radial PatATeco .....
again, I wonder, have you evaluated the likely detriment to crankshaft/propellor shaft torsional vibration when driving a propellor or rotor ?
complicated by and strongly related to reduction gearing factors (if reduction gearing is used)

there are very many precedents of crankshaft redesign due to this, not all conveniently in the distant past
eg the RR 1970s development of Continental's flat 4 (direct drive of course) to 130 hp for the Aerobat version of the French-built Cessna 150
had fatigue failures in service and was effectively banned, without iirc compensation to customers
the props were disappearing in flight
many other efforts by lesser organisations have similarly failed since”


Here is a UL-power crankshaft for a flat four aircraft engine:



Single piece, big diameter of journals / crankpins. It seems strong.

And here it is shown the crankshaft of a Hercules 14-cylinder double-row Radial:



The crankshaft is “a built-up three-piece unit which allows the use of solid master connecting rods”. It seems not adequately strong, however it deals with several times more power than the crankshaft of the flat-4.

In a flat-4 engine, all the four pistons stop together (at BDC and TDC), which means zero kinetic energy. And 90 degrees later (middle stroke) they all move at high speed, which means they, as a set, have a big amount of kinetic energy. As in all even firing 4-stroke four-cylinder engines, the heavy second-order inertia torque requires strong / heavy crankshaft structure.
If a heavy propeller is secured at the one end of the crankshaft, then the propeller has to accelerate / decelerate twice per crankshaft rotation in order to absorb and then give back the kinetic energy required by the set of the four pistons.

In the PatATeco Cross-Radial of the animation, the total kinetic energy of the four pistons is constant (about zero inertia torque). The propeller can be secured on the crankshaft without any issue.
Things are better than in the conventional Radials because the motion of all pistons is the same and because there is no master rod (you can read more at http://www.pattakon.com/pattakonPatAT.htm ).
It is hard to believe, however a four-cylinder PatATeco is better balanced than the double row 18-cylinder Centaurus Sleeve-Valve Radial of Bristol.

Another advantage of the PatATeco Cross-Radial is that it is a two-stroke engine.
A combustion happens every 90 crank degrees.
The successive power pulses overlap as in the even firing V-8 (smooth delivery of power).
The pistons around their TDC run always under heavy pressure (compare to the pistons of the four-strokes when they pass from their combustion-TDC, and when, 360 crank degrees later, they pass from their overlap-TDC).

When I compare the PatATeco Cross-Radial with a flat-four airplane engine (like, say, the Rotax 912 or the UL-260i of UL-power) what I see is a more reliable engine (no valves, no valve springs, no camshafts, no push-rods, no rocker-arms etc), a way more lightweight engine (one crankpin serves all the four pistons), a better cooled engine (air-cooled; read at UL-Power how proud they are for their aircooling, even if the two cylinders are necessarily arranged behind the other two cylinders), an engine with better fuel efficiency (less friction, better shape of combustion chamber), etc.


So, take another look at the PatATeco and let me know where you see problems.

Thanks
Manolis Pattakos

[manolis]

Hello Tommy Cookers.

You write:
“hope that you can follow these attempted suggestions of mine better than a previous one
(when you seemed to think I said the TZ 750 jackshaft is or should be driven only about 1 or 2% slower than the crankshaft)”


What I write is that even if the jackshaft is driven at 1 or 2% slower (or faster, it doesn’t matter) speed than the crankshaft, even then the engine balance cannot improve (actually it gets substantially worse).

What is required is exactly 1:1 transmission ratio between the crankshaft and the jackshaft.

In case wherein balance webs are secured to the jackshaft (we talk for a TZ750 with crossplane crankshaft) to counterbalance the unbalanced inertia moment of the engine, any other than 1:1 transmission ratio between crankshaft – jackshaft (from, say, 0.001% slower to 99.999% slower, or from 0.001% faster to 1000% faster) is a disaster for the balancing.

Do you agree?

Do I miss something?

Thanks
Manolis Pattakos

[Tommy Cookers]

.....In case wherein balance webs are secured to the jackshaft (we talk for a TZ750 with crossplane crankshaft) to counterbalance the unbalanced inertia moment of the engine, any other than 1:1 transmission ratio between crankshaft – jackshaft (from, say, 0.001% slower to 99.999% slower, or from 0.001% faster to 1000% faster) is a disaster for the balancing.
Do you agree? Do I miss something?
Thanks - Manolis Pattakos

at that time I was guessing that the jackshaft ran at about (but not exactly) half crankshaft speed
eg if half, jackshaft counterweighting when out of phase reduces/cancels the unbalanced inertia moment (and when in phase adds to/doubles it)
ie roughly equivalent to vibration of doubled amplitude but halved frequency
as I said before

rider perception of vibration is a high rpm problem, in amplitude the sum of forced vibration and vibration amplification by resonance
because some parts of the motorcycle eg frame, footrests, and handlebars will to some extent enter the resonant range at high rpm
(true, this novel crankshaft gives notionally none of the usual vibration (at twice engine rpm), all vibration being at engine rpm)

imo also, subjectively, at any given amplitude the higher the frequency the more problematic is the vibration to the rider

in my suggestion the forced vibration is double but the amplification is near-zero, and the perceived vibration frequency is halved
so there should or could be a benefit to the rider
a bit like fitting an engine of the same power but double the capacity and half the rpm

so, no, I don't agree with your statement I quoted above
yes of course a 1:1 jackshaft ratio is the only perfect ratio, we all knew that from the start

[J.A.W.]

T-C, in fact the TZ/4 jackshaft arrangement does not run 1-1, ( didn't you note a 'hunting tooth' - as a norm?)

It was likely done as an economy measure to utilize a pair of crankshafts from the twin, with central PTO.
As Kevin Cameron points out in his review, the strong rocking couple resultant from the twin-fire 180`
set-up caused crankcase stress fatigue with cracking, pressure loss & structural failure.

To be fair, Yamaha likely had not envisioned the number of duty cycles that customer machines would
put up - over the many years that they provided a competitive power-unit.

Here KC gives consideration to the nebulous 'big bang' firing order deal.
http://www.cycleworld.com/why-single-an ... od-in-dirt

[manolis]

Hello Tommy Cookers.

Sorry, but you are wrong.

But this is not bad: it is a good opportunity to be clarified a couple of things about vibrations.


The high frequency has an important advantage: it gives less time to the free inertia force, or moment, to displace (linearly or angularly) the engine and the frame / vehicle / passengers.

The unbalanced inertia force or inertia moment causes the linear or angular acceleration of the engine (and of the structure whereon the engine is supported / mounted).

For instance, the displacement (i.e. the amplitude of the oscillation) caused by a 10,000Nt (1ton) free inertia force having 200Hz frequency is four times smaller than the displacement (i.e. the amplitude of the oscillation, i.e. the vibrations) caused by the same 1ton free inertia force having 100Hz (i.e. half) frequency.

This is so because the time during which the engine accelerates at each direction doubles.


For simplicity, forget the rest vehicle and take the engine alone.
Suppose the engine mass is 100Kg.

The acceleration acting on the engine due to the 10,000Nt free inertia force is:
a = 10,000Nt/100Kg = 100m/sec^2 (or 10*g, where g is the gravity acceleration).

The relation between the displacement d of a body and the acceleration applied on it is:
d = 0.5 * a * t^2
where t is the time.

With t=0.5*(1/200)=0.0025sec (200 comes from the 200Hz frequency), the displacement d is: 0.3mm (i.e. +/- 0.15mm from its central position)

This is not away from what happens in a normal size In-Line-Four engine running at 6,000rpm (the unbalanced inertia force is of 2nd order, i.e. it has 200Hz frequency).


With half frequency, the time the free inertia force acts on the engine doubles, which means the overall displacement (amplitude of vibrations) of the engine becomes four time longer (some +/- 0.6mm from its central position).


If it is not yet clear, take it to the limit.


Suppose the 1ton free inertia force acting on the 100Kg engine has a frequency of only 5Hz (which means: during one tenth of a second the 1ton force pushes the engine at one direction, during the next tenth of a second the 1ton force pushes the engine at the opposite direction, and so on).

In a first approach, the amplitude of the oscillation is calculated at:
d = 0.5 * 100m/sec^2 * 0.1 sec^2 = 5m

This means that if the engine were free on the frame of the vehicle, it would move / vibrate 2.5m away its central position.
This also means that if the total mass of the motorcycle – rider – engine is, say, 250Kg and the engine and the rider were secured on the frame, the amplitude of the vibrations would be +/-1m (meter, not millimeter) about the central position.

The free inertia force has a sinusoidal waveform and not a square waveform as in the above calculations; this means a somewhat smaller amplitude of the oscillations. It is easy to make the calculations.


All the previous are similarly applied in the case of the free inertia moment. The only that changes is that the linear displacement turns to angular displacement.


Differently speaking:

At lower revs the unbalanced inertia forces and moments decrease with rpm square. The time increases proportionally with rpm. So the displacement of the engine around its central position (in case it is free to move) remains the same.


From a different viewpoint:

Think: what is the meaning of the inertia vibrations?

There is a body (a running engine) inside which some parts (the pistons, the connecting rods, the crankshaft etc) move away from their previous positions.
Without external support, the center of gravity of the body (i.e. of the running engine) should remain immovable (or keep moving at constant speed).
The casing of the engine has to oscillate / vibrate in order to compensate the motion for the inner moving masses and keep the total center of gravity “standstill”.


From another, different viewpoint:

The Fourier analysis of the free inertia forces and moments of an engine is a useful tool.
You can’t play with frequencies (i.e. with different “orders”).
If you want to cancel out a first order moment, the only you can do is to apply a first order opposite moment. Any mix of other “orders” is useless. It may balance the unbalanced moment at some instances, in expense of substantially heavier vibrations at other instances.
For instance, suppose the jackshaft of the TZ750 with the “crossplane” crankshaft rotates one millionth times slower than the crankshaft (i.e. the jackshaft speed is 99.9999% of the speed of the crankshaft) . If the set of the balance webs secured on the crankshaft and on the jackshaft counterbalances now the free inertia moment, after half a million turns of the crankshaft (if the engine runs at 5,000rpm, this means after 500,000/5,000 = 100min, i.e. after one hour and 40 minutes) the vibrations will be extreme. After another 100 minutes the engine will be again perfect (zero inertia vibrations). It is funny (imagine the case). But it is not a solution.

Thanks
Manolis Pattakos

[Tommy Cookers]

The high frequency has an important advantage: it gives less time to the free inertia force, or moment, to displace (linearly or angularly) the engine and the frame / vehicle / passengers.
....... For instance, the displacement (i.e. the amplitude of the oscillation) caused by a 10,000Nt (1ton) free inertia force having 200Hz frequency is four times smaller than the displacement (i.e. the amplitude of the oscillation, i.e. the vibrations) caused by the same 1ton free inertia force having 100Hz (i.e. half) frequency.
...... Differently speaking:
At lower revs the unbalanced inertia forces and moments decrease with rpm square. The time increases proportionally with rpm. So the displacement of the engine around its central position (in case it is free to move) remains the same......

the example quoted above is totally unrealistic
high frequency is a disadvantage in most vehicles that have solid-mounted engines eg motorcycles, aircraft, and single-seat race cars

what happens for any given engine is that the vibrating force (or moment) from the engine increases with the square of the rpm and ...
because the amplitude of the vibration for a given force (or moment) decreases with the square of the rpm ......
the amplitude of the vibration is constant for any rpm .... but .....

the acceleration of the vibratory motion increases greatly with rpm (it's proportionate to the square of the rpm)

the greater this acceleration the greater is the distress (even damage) to the rider (or chainsaw operator etc wrt 'white finger' etc)

and usually the acceleration increases even more at high rpm due to some level of structural resonance effect ie between the engine and the rider

[manolis]

Hello Tommoy Cookers.

You write:
“the acceleration of the vibratory motion increases greatly with rpm (it's proportionate to the square of the rpm)
the greater this acceleration the greater is the distress (even damage) to the rider (or chainsaw operator etc wrt 'white finger' etc)
and usually the acceleration increases even more at high rpm due to some level of structural resonance effect ie between the engine and the rider”


The distress / damage has to do with both, the acceleration and the amplitude of the resulting vibrations. It has also to do with the structure whereon the engine is mounted (or supported) and the mounts used.


A chainsaw operator suffers mainly from first order vibrations (the crankshaft balance webs can cancel out only half of the first order free force, leaving the 2nd order force unbalanced).
The resulting free inertia force comprises a 1st order rotating force and a second order force along the cylinder axis (which is a little more than half of the first order unbalanced rotating force).
The amplitude of the vibrations from the first order rotating force is about seven times bigger than the amplitude of the vibrations from the second order unbalanced force (the 2nd order force is about half than the 1st order force, the time before it changes direction is half; that is how the “7” results).
If less vibrations is the requirement, the first order constituent is the real problem.
This is why in the single cylinder motorcycles engines (and in most twins) the added balance shaft(s) deal only with the 1st order free force.


The acceleration of the vibratory motion caused by the 2nd order unbalance force is comparable in size (more than half) with the acceleration caused by the 1st order unbalance force.
But its higher frequency makes the amplitude of the resulting 2nd order vibrations several times (about 7 for normal “piston stroke to connecting rod” ratio) smaller than the amplitude of the vibrations caused by the 1st order rotating unbalanced force.
Despite their higher frequency, nobody cares about these 2nd order vibrations.


So, the problem is not the acceleration but the vibrations caused by the acceleration. The higher the frequency, the smaller the vibrations for a given maximum acceleration.



I hope that from the analysis in the previous post it became clear that trying to cancel out the free inertia moment of a TZ-750 cross-plane by securing balance webs on the jackshaft that counter-rotates at half crankshaft speed, is not a solution.

Suppose the jackshaft really cancels out the unbalanced first order inertia moment at some instance. After 360 degrees of crankshaft rotation (i.e. 180 degrees of jackshaft rotation) the unbalanced inertia moment doubles as compared to the case without balance webs on the jackshaft.

But it is even worse: due to the half frequency of the jackshaft, the amplitude of the vibrations becomes 5 times bigger than the amplitude of the vibrations of the engine without balance webs on the jackshaft (if it is not clear how, let me know to explain).

So, every other crankshaft rotation the rider almost falls from the motorcycle due to the vibrations of the engine.


I think the previous is a good example that we cannot play with different frequencies.
We cannot mix / “cook” other frequencies to cancel out the vibrations of a specific frequency. It does not work this way.

The Fourier analysis is a great tool because it analyzes the problem in different orders (frequencies); i.e. in independent simpler problems.
If you deal with a specific order (1st, 2nd, 3rd etc), forget all the rest orders and deal exclusively with the specific one.


The balance program at http://www.pattakon.com/pattakonEduc.htm (it is written in Quick Basic several years ago and requires Windows / DOS to tun) makes the Fourier Analysis and resynthesis of the inertia force / moment and torque of any engine arrangement

Thanks
Manolis Pattakos

[manolis]

Hello J.A.W.

You write:
“Here KC gives consideration to the nebulous 'big bang' firing order deal.
http://www.cycleworld.com/why-single-an ... od-in-dirt”


Later they discovered the inertia torque:

In an even firing 4-stroke In-Line-Four, at high revs, the rear tire receives besides the combustion torque, a strong inertia torque (all the four pistons stop together (zero kinetic energy) at TDC-BDC, 90 degrees later (middle stroke) all the four pistons move at high speed (having lots of kinetic energy)) which loads unnecessarily the rear tire and confuses the rider about what is happening in the contact between the tire and the road.
The inertia torque gets so high near the red line that the useful (the working) torque (from the combustion in the cylinders) passes like “noise” in the dominat inertia torque.
The inertia torque just reciprocates doing nothing useful; it only adds friction and stressing on the various parts.


The same for the in-line-even-firing twins, like the initial TDM of Yamaha.

Later Yamaha turned the even-firing TDM (crankpins at 0 and 0 degrees) to the uneven-firing TDM (crankpins at 0 and 270 degrees) and had a big gain in feeling and driver friendly behavior.

Later Yamaha changed the plane crankshaft of their older four-in-line to the crossplane crankshaft in the M1 – R1 (which eliminates the inertia torque, leaving the rear tire deal only with the useful combustion torque).
With the elimination of the inertia torque, the feeling of the M1 – R1 is the same with the feeling of the V-4 at 90 degrees with crankpins at 0 and 180 degrees. Some tester wrote about it: “it is like a turbine”.

With the third gear in the gearbox, the clutch engaged and the engine revving near its red line, the Yamaha R1 (cross plane crankshaft) behaves substantially different than a similar Yamaha In-Line-4 having plane crankshaft.
For instance, if the throttle is closed, the R1 leaves alone the contact between the rear tire and the road to work for the required side forces, while the other Yamaha loads unnecessarily the contact between the rear tire and the road with inertia forces, reducing its side loading capacity.

Thanks
Manolis Pattakos

[J.A.W.]

Actually Manolis, inertia torque effects were known by some - & long since... ~80 years ago at least..

Napier provided for its 24 cylinder (superimposed flat 12/180` V-12 units) 'Sabre' aero-engine to be phased
- so that each 12 cylinder unit was timed to fire 180`degrees apart, & no two cylinders fired together.

Rolls-Royce, when they built their version of an H-24 'Eagle 22' - thought that by running the two cranks
in opposite rotation, but with two cylinders firing simultaneously & geared together though a simple spur,
together with 'reactive' crank counter balance weights - they could avoid the sophisticated balanced coupling used by the Sabre..

R-R were wrong, & the resultant harmonic vibration periods caused catastrophic fatigue failures in the ignition drive shaft..

By contrast, the Sabre was found to be so well balanced, that the original 12-counterweight cranks were found
needless, & were accordingly replaced with a 6-counterweight set-up.

[Tommy Cookers]

....Later they discovered the inertia torque:
In an even firing 4-stroke In-Line-Four, at high revs, the rear tire receives besides the combustion torque, a strong inertia torque (all the four pistons stop together (zero kinetic energy) at TDC-BDC, 90 degrees later (middle stroke) all the four pistons move at high speed (having lots of kinetic energy)) which loads unnecessarily the rear tire and confuses the rider about what is happening in the contact between the tire and the road.
The inertia torque gets so high near the red line that the useful (the working) torque (from the combustion in the cylinders) passes like “noise” in the dominat inertia torque.
The inertia torque just reciprocates doing nothing useful; it only adds friction and stressing on the various parts.

Later Yamaha changed the plane crankshaft of their older four-in-line to the crossplane crankshaft in the M1 – R1 (which eliminates the inertia torque, leaving the rear tire deal only with the useful combustion torque).
With the third gear in the gearbox, the clutch engaged and the engine revving near its red line, the Yamaha R1 (cross plane crankshaft) behaves substantially different than a similar Yamaha In-Line-4 having plane crankshaft.
For instance, if the throttle is closed, the R1 leaves alone the contact between the rear tire and the road to work for the required side forces, while the other Yamaha loads unnecessarily the contact between the rear tire and the road with inertia forces, reducing its side loading capacity.
Thanks
Manolis Pattakos

this is nonsense - just Yamaha advertising hype

mostly because the inertia torque cannot and does not reach the rear tyre

at very high rpm the reciprocational inertias are very large
they give a substantial positive-rotational, then negative-rotational, impulse twice per rev to the crankshaft
these impulses are almost completely opposing, so the net effect over the whole rev is only small, and actually a power loss from friction

all reciprocation does this whether the pistons reach tdc/bdc together as conventional or at intervals as do the Yamaha's
strain energy is stored and released, the true loss from this is about 1 part per 1000 ie 0.1 - 0.2 hp
(this dynamic hysteresis loss is far lower than the conventional/basic 'benchtop' hysteresis values because these don't conserve heat)

the power-producing impulses are similarly large and also twice per rev, and lightly opposed by frictional and pumping losses
so their net effect is large, and the total effect over the whole rev is what we call the power output

so the crankshaft briefly experiences over each rev rotational impulses, some useful and others essentially useless but harmless
at eg 12000 rpm there's 200 revs/sec and each impulse type happens 400 times/sec (and each impulse lasts 1 or 2 millisec)
crankshaft etc inertia largely impedes the impulses propagation, rotational energy being accumulated and released

such impulses happening 400 times per second cannot propagate beyond the transmission shock absorber (usually it's in the clutch)
this works by attenuating and killing any torque variation faster than equivalent to above about 2 or 3 times per second
that's what shock absorbtion is

also nowhere near 400 Hz can propagate through the gearbox (since metal is not infinitely rigid)
and particularly not along a chain and sprocket transmission (especially as the chain is not positively constrained as in a CVT)

and even if the transmission shock absorber is removed etc etc ......
the pneumatic tyre won't transmit torque variations at more than a few Hz

actually chain and sprocket transmission will generate an inherent 'velocity ripple' impulse effect which in use amounts to a torque ripple
that's why powered devices don't use sprockets smaller than maybe 13 or 14 teeth
some bicycles use maybe 10t and the ripple can be felt, particularly if there's no derailleur jockey to cushion this
and anyone could produce a rear wheel torque ripple simply by using eg a slightly eccentric sprocket - you don't need a Yamaha


Yamaha has manufactured a new 'urban' myth
in conflict with the established belief/myth that a low frequency 'torque ripple' eg from a big single gives greater tyre grip

yes, there's benefit in the crossplane 4 cyl crank at very high rpm, from its even spacing of inertial torques (outweighing the uneven power strokes)
high crankshaft natural frequencies required for the rpm are reachable using a lighter/smaller crank, smaller bearings saving about 1 hp in friction
and free from 2nd order vibrations, it saves 5hp iirc that eg John McGuiness' Honda potentially wasted if retaining its 2nd order counterbalance shafts

the disadvantage is in manufacturing cost and inferior low-speed 'traffic' behaviour (as the firing intervals are uneven)
the power curve might be a bit different (suffering at the top end ??) because of competition between the overlapping induction periods

[Tommy Cookers]

@ Manolis
ok the PatATeco has a rather constant inertial torques .... but.....
the inertial torques will in a non-race eg aero engine be quite small relative to the combustion torques (4 stroke anyway)
but your engine still has combustion torque impulses, though these are more frequent and smaller than in a comparable 4 stroke

ok this might allow the necessary crankshaft torsional etc frequencies to be met with quite a slender crankshaft - if the load had relatively little inertia
but the load has great inertia (particularly so relative to the slender crankshaft)
and is worse than purely inertial because the (propellor) blades will oscillate in use at a natural frequency
and there will be cyclic bending loads of aerodynamic origin with eg 2 and 4 ? bladed props

aero engines generally have increased crankshaft and bearing dimensions because of these factors
and typically have tuned dampers eg 41/2th and 6th order
yours might suffer more than most in this regard
and reduction drive or only direct drive capability is likely to be a big factor for consideration in this regard

btw
a clear idea of the market is helpful eg because of crankshaft issues there's only 2 or 3 engines certified for aerobatics
an acquaintance turned down a flight in a plane fitted with a new super crankshaft made by a well-known crankshaft expert
the plane then crashed, killing its owner and the expert (no parachutes)
because the crankshaft broke and the new cg position sans propellor caused or allowed an unrecoverable spin

[Tommy Cookers]

Hello J.A.W. You write:
“Here KC gives consideration to the nebulous 'big bang' firing order deal.
http://www.cycleworld.com/why-single-an ... od-in-dirt”

Later Yamaha turned the even-firing TDM (crankpins at 0 and 0 degrees) to the uneven-firing TDM (crankpins at 0 and 270 degrees) and had a big gain in feeling and driver friendly behavior.

KC seems to think the so-called 'big bang' Honda NSR500 was a success and an improvement
actually that Doohan fellow disliked it and won most races on the so-called 'even-firing' 'screamer'
saying the bb had too much engine braking and too sudden a response on picking-up the throttle

the 0/270 TDM would without counterbalance shafts have far less primary imbalance (and no secondary imbalance) than the 0/0 in the same state
so the 0/270 needs less counterbalance, hence this is smaller, has less friction, and is compact so placed closer to the ideal position
ok the crank is made with less inertia (because the more even recip inertias help here) so both up and down response is improved

(and, yes this also applies to the R1, but remember faster downturn is another way of saying more engine braking)