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Your three cylinder engine:
Are you going to use a balance shaft?
Without a counter-rotating balance shaft, the vibrations will be "comparable" to those of your unbalanced twin.
Uniflow, could you please give an overview of the design?
Bore x stroke?
Single plane or 120 degree crank?
Reeds or disc valves?
Carburettor size?
Estimated power?
It looks great, like a Rotax skidoo motor, did you follow an existing pattern or start with clean sheet?
The three cylinder engine?
All my own, actually cast two of these cases but realised I couldn't afford to fill it with all the hardware needed. So I cut one down to a two cylinder, the original engine in my gyro, the one I ended up using as a counter balancer test.
New cases for the gyro now with internal counterweights.
This one three cylinder case was to go in my two seat gyro but nothing has happened yet, money and time deficient.
Cylinder spacing in not compromised like the skidoo engines, room for big sweaping transfer ports. Engine was to run two up one down firing not 120 degress, easier to balance.
Case reed, bore and stroke not so good at 80 bore 70 stroke, thats 1050cc .
Was planing on not running carburetors, TPI, there is room just and it would be my new mk2 system.
Your three cylinder engine:
Are you going to use a balance shaft?
Without a counter-rotating balance shaft, the vibrations will be "comparable" to those of your unbalanced twin.
Thanks
Manolis Pattakos
Hi Manolis, per my experience of inline 180` twin & 120` triple 2-strokes, (sans balance shafts)
I'd reckon that vibration-wise (even if/when quelled by resilient rubber mounts) they do 'feel'
quite different,with the triple layout giving a lower subjectively received vibration sensation,
(being not so objectional in high-frequency 'buzzing'), so is it a matter of closer-firing/sinuous
torque-impulses compensating for the longer crankshaft's 'rocking couple' imbalance, perhaps?
Perhaps you & Uniflow may also be interested in a review of the inherent advantages of
the even-firing (120 degree) 2-stroke triple layout, by notable 2T engineer Olav Aaen:
Ed Hilary on being 1st to top Mt Everest,
(& 1st to do a surface traverse across Antarctica,
in good Kiwi style - riding a Massey Ferguson farm
tractor - with a few extemporised mod's to hack the task).
All of these engines are great, and I want to see and learn more, but I want something for a ground vehicle. Has anyone tested their engines on the ground to expediate use case testing or in search of alternate application, or what about boats? I only really fly things when the ground or water induces lift, but I really want to pilot one of these unique engines somehow.
Uniflow writes: “Engine was to run two up one down firing not 120 degrees, easier to balance.”
With “two up one down” (crankpins at 0, 180 and 0 degrees):
the two cylinders fire together (big bang), the other alone,
while the free inertia moment of the conventional triple is eliminated (so you don’t need any longer an external balance shaft), the arrangement creates a heavy unbalanced inertia force that needs a pair of counter-rotating balance shafts to be cancelled out (say, as in the big single cylinders).
Alternatively:
To correct this problem, you should double the weight of the central piston and of the central connecting rod; this will give a balancing similar to the inertia balancing of the conventional 4-stroke even-firing straight-four (those used in most cars).
To exploit the need for a much heavier central piston and cure the uneven power pulses, you can increase the central cylinder bore 1.4 times (1.4*1.4=2, i.e. from 80mm to 112mm): this way you have the balancing of the 4-stroke even-firing straight-four, you have also equal power pulses at equal time intervals, i.e. the 2-stroke triple becomes quite similar (in vibration quality and power delivery) to the 4-stroke even-firing straight-four.
It has been done (more or less) by Illmore in their "5-stroke" three-cylinder engine:
An alternative solution is to use the “T” crankshaft of Triumph.
This Tiger 900’s “T-Plane” crankshaft places crankpins one and three 180 degrees apart, with the number-two crankpin 90 degrees from the others, defining a “T.”
. . .
But in the case of this Triumph, engineers increased the firing interval on two cylinders to 270 degrees by closing up the third interval to 180—not a big change, 12-1/2 percent. Yet without testing the result ourselves, who can say how much this change improves “feel”?
Ah, but doesn’t such a change require a balance shaft?
Even-firing inline-triples already need a balance shaft to cancel what would otherwise be a substantial side-to-side rocking motion, so the only change needed is to reangle the eccentric weights on the already-existing shaft.
End of quote.
The last paragraph of Kevin Cameron is wrong.
Because if you just reangle the eccentric weights on the already-existing shaft, you can’t have the same vibration-free quality as you have in the even firing triple (that with the crankpins at 0, 120 and 240 degrees); the architecture of the latter cancels out all inertia forces while the architecture of the first leaves unbalanced heavy inertia forces of first order and of second order.
You can think of it differently: the T-plane triple is actually your twin (with their cylinder axes at double distance) plus a central cylinder at 90 degrees phase difference. The first order balance shaft can cancel out the inertia moment of the pair of the external cylinders (leaving only a second order unbalanced inertia force) but it can't do much with the central piston.
So,
the even firing triple (crankpins 120 degrees apart from each other) is, by far, the best solution, especially for a lightweight vehicle like an autogyro.
But if you run it without a counter-rotating balance shaft, its vibrations would be more than those in your unbalanced twin (which was like day and night after adding the balance shaft).
In simple words: your best choice for your autogyro is the even-firing triple with an external balance shaft.
Having said that,
when it comes to extra lightweight vehicles (say like the Portable Flyer) a better solution appears the Opposed Piston engine: simpler, more lightweight, more fuel efficient (elimination of cylinder heads, lower thermal loss etc) and top as regards its vibration-free-quality (allowing the direct support of the engine on pilot's body).
The single cylinder 635cc PatOP Diesel (no balance-webs at all, not even on the crankshaft) stands free on the desk:
This single cylinder OPRE Tilting that stands free on the floor needs not external balance shafts. A fast “static balancing” was applied (if it was a correct dynamic balancing, it would stay completely immovable on the floor).
You write: “Hi Manolis, per my experience of inline 180` twin & 120` triple 2-strokes, (sans balance shafts)
I'd reckon that vibration-wise (even if/when quelled by resilient rubber mounts) they do 'feel'
quite different,with the triple layout giving a lower subjectively received vibration sensation,
(being not so objectional in high-frequency 'buzzing'), so is it a matter of closer-firing/sinuous
torque-impulses compensating for the longer crankshaft's 'rocking couple' imbalance, perhaps?”
The even firing triple, besides having weaker and more frequent power pulses, it is also having a substantially weaker inertia torque that gives “a sense of turbine”.
The VFR of Honda and the R1 of Yamaha give the same sense of turbine.
In comparison, the even firing two-stroke twin is having 50% stronger power pulses happening at 50% longer time intervals from each other (same rpm), it is also having a strong inertia torque; this inertia torque is what the Yamaha YZF-R1 and the newer TDM cancel out (in expense of uneven firing), giving a much better sense to the rider for what the rear tire is doing.
is doing in the even firing straight four 4-stroke, in the even firing twin etc : it reduces the vibrations (actually the inertia torque) passing from the engine to the transmission line.
That is, basic advantages of the even firing triple (two-stroke or four stroke) is the elimination of the free inertia forces and the significant reduction of the inertia torque. The inertia moment of the even firing triple is a problem (and requires a counter-rotating balance shaft to be solved).
You also write: “Perhaps you & Uniflow may also be interested in a review of the inherent advantages of
the even-firing (120 degree) 2-stroke triple layout, by notable 2T engineer Olav Aaen: https://amsnow.com/how-to-tech/2007/12/ ... s-comeback “
Useful and explanatory the article of Olav Aaen. Thanks.
Quote from it:
"You will never see a big triple again," said one U.S. OEM product manager confidently. "The triples with triple pipes are just too large, heavy and bulky to package in today's sleds," he continued, "and with all the new EPA requirements, the 2-cylinders are easier to work with."
. . .
The larger the twins get, the rougher they run and the harder they are on clutches. The twins hit hard and are rough on an engine. Every time a 500cc cylinder fires through a long 80mm stroke and rattles clutch components and strains belts, you are taking life off parts.
You can counterbalance the piston vibrations with balancer shafts, but that doesn't dampen the torque reaction of each power stroke. More inertia through heavier flywheels will dampen torque reaction, but this means slower acceleration and increased weight.
. . .
Triple emissions
When it comes to controlling emissions, the triples with single exhaust have an advantage. This system works differently than regular expansion chambers. The three-into-one manifold offers its own "plugging pulse" due to the 120-degree spacing of exhaust pulses, and it is therefore not dependent on an expansion chamber to push the extra fresh gases from scavenging flow back into the cylinder again.
The expansion chamber, part of the three-into-one system, does not resonate at engine speed like the single pipe per cylinder. Instead, this short and stubby chamber must resonate at three times the engine speed to reinforce the plugging pulses. The small chamber reinforces power at top rpm, the result being a wide power band that could compete with a 4-stroke for torque.
Since the three-into-one "log" manifold always offers a plugging pulse every 120 degrees, no matter what the engine speed, it means this system is more efficient in pushing unburned fuel into the cylinder again at lower engine speeds where an expansion chamber exhaust system is "out of tune."
Emissions at lower engine speeds are therefore easier to control with a triple "log" manifold.
End of quote.
If something makes the triple two-stroke better than the twins two-stroke, it is its even firing (crankpins 120 degrees apart from each other) and the advantages this even firing brings.
If you cancel it (say, by using T-plane crankshaft, or flat crankshaft etc) . . .
.... this inertia torque is what the Yamaha YZF-R1 and the newer TDM cancel out (in expense of uneven firing), giving a much better sense to the rider for what the rear tire is doing.
.... This is also what the PatVRA is doing in the even firing straight four 4-stroke, in the even firing twin etc : it reduces the vibrations (actually the inertia torque) passing from the engine to the transmission line.
all of that is wrong ....
(except for riding in Moto GPs etc - btw how come GP Suzuki and other inlines are 'flat' crank ?)
in the lower 90% of the rpm range the torque events from combustion are far greater than the inertia torque events
ie the conventional even-firing inline four is better at this than is the R1, the TDM, or the conventional triple
'the rider's sense of what the rear tyre is doing' remains (PR-conveniently) unsubstantiated
anyway what matters to the buying public is a traction-control sensor's sense of what the rear tyre is doing
re. the Triumph 'T' crankshaft ......
doesn't the 90 deg piston cancel some of the secondary vibration force sum (EDIT as 1990s Yamaha twins and the R1) ??
secondaries are greatly underappreciated as resonant vibration sources with solid-mounted engines
RETRO-EDIT Triumph talked of such secondaries benefits when introducing the '270 deg' version of their twin
re. the flat-crank 3 - Laverda made such for years before going to rubber-mounted 3-plane crank engines
regarding the gyrocopter ......
remember that the engine receives from the propeller vibrations of mechanical and of aerodynamic origin
Last edited by Tommy Cookers on 03 Oct 2020, 12:33, edited 2 times in total.
