Does anybody know what happened with the 125cc RCV (rotary cylinder valve, PGO Scooters of Taiwan)?
Thanks
Manolis Pattakos
Hi Manolis, it appears the 4T RCV did not offer the performance/durability factor required,
likely perhaps due to - valve pressure sealing issues - esp' within cheap basic transport usage.
Although PGO hasn't expressed openly, just why it was not proceeded with as a production item.
But PGO do AFAIR now 'feature' a fairly basic type of low-maintenance 4T DOHC 4V direct-follower
hydraulic-bucket set-up, similar to those commonly used in sporty-ish cars, ~30 years ago.
Here's a link to an upcoming 2T DFI conference, which may be of some topical interest here, also:
With both engines running at 9,000rpm, the upwards acceleration....
The props are geared from the cranks at a ratio of 2.74:1. So 9000rpm at the crank is as @gruntguru says at the props.
The gearing is in the same paragraph as the 9000 rpm @manolis highlights.
Hope that helps.
Re: 2 stroke thread (with occasional F1 relevance!)
Posted: 04 Jan 2020, 07:47
by manolis
Hello J.A.W.
You write:
“Included in this fairly recent conference on 2T technical matters is an interesting presentation of the potential for existing Rotax 2T snowcraft engines - to meet stringent Euro-emissions regulations - while powering a road-legal motorcycle.”
At page 7,
the “modified” to Range Extender Rotax 600 HO (GDI: Gasoline Direct Injection) appears having at its best point(?) a BSFC (Brake Specific Fuel Consumption) of 305gr/kWh (~27% BTE: Brake Thermal Efficiency)), which is not good enough. Besides complying with the euro emission standards, the reduction of CO2 footprint is another important requirement.
For instance, with 200gr/kWh BSFC (~40% BTE, attainable with a Diesel or an HCCI gasoline) the average CO2 emission would be some 50% less.
For an electric car (wherein the absence of vibrations, noise etc is a must), the twin in-line 2-stroke is not a good solution.
A dozen, or so, years ago AVL and FEV proposed Wankel rotary Range Extenders for electric cars. Their main advantage / key-point was their superior NVH (compare it to the 2-cylinder REM, green line):
Even if the exhaust gas is treated to comply with the strictest emission regulations, the CO2 footprint of a Wankel cannot help being large.
In the same study (beginning of 2018), the direct injection Rotax 600 HO appears as a promising solution for powering motorcycles:
“The purpose of this project: to demonstrate the potential of using an adapted DI production 2-stroke engine for a 100 hp motorcycle application.
Its main issue: to meet the most stringent Euro 4 & Euro 5 NOx
emissions limits.”
Better than in a study:
In practice the KTM EXC models, those with the cheap "non-Direct Injection" TPI (Transfer Port Injection), were already euro-4 compliant in 2018; reasonably these KTM-EXC models must be now euro-5 compliant (are they?).
The question was, and still is, why KTM never put these green 2-stroke engines on street motorcycles or scooters.
Thanks
Manolis Pattakos
Re: 2 stroke thread (with occasional F1 relevance!)
Posted: 04 Jan 2020, 08:21
by manolis
Hello Rodak.
Here is the transmission of the Portable Flyer:
With the green toothed belts (there are four, two long and two short ones) each crankshaft drives its "own" propeller at a transmission ratio of 2.4:1 (when the engine is revving at 9,000rpm, its propellers are revving at 9,000/2.4=3,750rpm which gives a propeller tip speed of 195m/sec, which is less than 60% of sound velocity).
The two upper counter-rotating intermeshed propellers are driven by the left OPRE_Tilting engine,
while the two lower propellers are driven by the right OPRE_Tilting engine.
The toothed belt transmission smooth out / dampers the torque from the engine.
This architecture provides two completely independent propulsion units.
The malfunction of the one does not affect the other, enabling a safe landing even at an engine stall, even when a propeller is fall apart.
In comparison, the Osprey V22:
cannot complete successfully a vertical take-off or landing if one of its propellers is damaged, or if its central transmission fails.
Thanks
Manolis Pattakos
Re: 2 stroke thread (with occasional F1 relevance!)
Posted: 04 Jan 2020, 09:47
by J.A.W.
Hi Manolis.
AFAIR, the only KTM scooters I've seen have been electric, but since 2T dirtbike sales
(& racing) are much more of a sales focus for them, it does seem a natural priority at this point.
As for the BRP/Rotax 2T 600 design, its parallel twin architecture is predicated by packaging
convenience as a snowcraft engine - rather than as an ultimate performance motorcycle mill,
which would most likely be a V-twin (or triple) - but they do feature amelioration of NVH,
(like resilient mountings, something you could find in a Norton Commando ~1/2 a century ago).
Of course, fuel economy is never a primary concern for a sports motorcycle vs power, & 4T units
too are less than optimally fuel efficient in order to pass their own emissions issues, of which
they inherently suffer from certain emissions-parameter problems, worse than 2T engines do.
What effort have you put into quelling the potentially noxious emissions (noise/fumes, etc)
from your flyer, in terms of customer convenience/safety - not least, as well as per EU regs?
Will you have to run an annular safety ring around the perimeter of your prop-blades also,
on safety grounds, & if so, will that assist or hinder, any useful pitch control methodology?
Re: 2 stroke thread (with occasional F1 relevance!)
With the green toothed belts (there are four, two long and two short ones) each crankshaft drives its "own" propeller at a transmission ratio of 2.4:1 (when the engine is revving at 9,000rpm, its propellers are revving at 9,000/2.4=3,750rpm which gives a propeller tip speed of 195m/sec, which is less than 60% of sound velocity).
Just a question.
Do you plan to incapsulate the transmission setup in any way? Because i see a serious issue their. The gear setup you plan to use to syncronize the pistons, (the yellow gears) they aren't lubricated in any way, are they? Generally speaking gearwheels will not live very long if you transmit proper loads through them without any lubrication.
Re: 2 stroke thread (with occasional F1 relevance!)
Hello Tommy Cookers.
You write: “if the wingsuiter's glide angle is 30 deg (having a L/D ratio of 1.7) .....
how does your mannequin have the PF in level flight at an apparent AoA of only 11 deg ?”
The angle of attack is a different thing than the glide angle.
The 30 degrees glide angle (from horizontal) is the angle of a line L along which the wingsuiter moves / flies / falls.
Relative to this line L (and not relative to the horizon) is the angle of attack of the wingsuiter.
Thus, an 11 degrees angle of attack of the unpowered wingsuiter (who’s glide angle is 30 degrees) means that his long axis is at an angle of 30-11=19 degrees from horizontal.
If I am not clear, please let me know to make a drawing.
yes I should like to see a drawing .... additionally ....
to me L/D = 1.7 is optimistic (the PF isn't a Rossy-type wingsuit)
yes the PF actual L/D isn't a show-stopper
re others' comment about the PF exposed gears and proprotor 'pitch control metholodogy' ....
sintered gears to hold liquid-based lubricant ?
proprotors if cfc-based could be rather self-adjusting for pitch (as much as useful) without moving parts
Re: 2 stroke thread (with occasional F1 relevance!)
That works for sealed off bearings, but not in this scenario. The centrifugal forces would sling the oil all over the place, eventually letting the gearwheels dry up and as you probably know, scatter oil all over the environment is big nogo today.
In my opinion, if he wan't a "dry" transmission, he needs to go with timing belts for everything.
Re: 2 stroke thread (with occasional F1 relevance!)
The two upper counter-rotating intermeshed propellers are driven by the left OPRE_Tilting engine,
while the two lower propellers are driven by the right OPRE_Tilting engine.
Of course with intermeshing propellers, the failure of a belt takes out both propellers. Can you see any benefit in staggering the propellers enough to avoid such a clash? This would leave 3 propellers and 2 power units functional in the event of such a failure. It would also eliminate the cost and debris created by clashing propellers.
Torque is one obvious problem with a 3 propeller system.
Re: 2 stroke thread (with occasional F1 relevance!)
That works for sealed off bearings, but not in this scenario. The centrifugal forces would sling the oil all over the place, eventually letting the gearwheels dry up and as you probably know, scatter oil all over the environment is big nogo today.
In my opinion, if he wan't a "dry" transmission, he needs to go with timing belts for everything.
Or phased electromagnetic 'gears' (mag-lev style) sans mechanical mesh, perhaps?
It could do double duty as a starter motor, as well.
Re: 2 stroke thread (with occasional F1 relevance!)
Posted: 05 Jan 2020, 09:05
by manolis
Hello J.A.W.
You write: “AFAIR, the only KTM scooters I've seen have been electric, but since 2T dirtbike sales (& racing) are much more of a sales focus for them, it does seem a natural priority at this point.”
When you have the only euro4 compliant (and euro5?) 2-stroke engine in the market, to leave it “useless” and produce – as every other maker can - electric scooters seems as not a good choice, unless you know some problems or issues (say, like “intellectual property rights”) of your 2-stroke technology.
This is why I keep asking the same question: “why KTM is not making / selling 2-stroke street legal motorcycles and scooters?”
You also write: “As for the BRP/Rotax 2T 600 design . . . but they do feature amelioration of NVH, (like resilient mountings, something you could find in a Norton Commando ~1/2 a century ago)."
For an electric car the “resilient mountings” is not adequate: when the internal combustion engine operates to charge the battery, the NVH inside the car will be worse than in a conventional car powered by a 4-in-line engine (which also uses resilient mountings).
This is why AVL (and FEV) offered Wankel Rotary REM (Range Extender Module) for the electric car manufacturers.
You also write: “What effort have you put into quelling the potentially noxious emissions (noise/fumes, etc) from your flyer, in terms of customer convenience/safety - not least, as well as per EU regs?”
First priority of the Portable Flyer is to fly.
The emissions and the noise are future issues.
On the other hand, the existing “Flyers” / JetPacks of Rossy, Zapata, Mayman and Browning have more than 50 (fifty) times lower mileage (about 1mpg) and unaffordable noise (supersonic velocity of the gas existing from the jet exits).
But even compared to the conventional reciprocating piston engines, the architecture of the Portable Flyer engines brings new “solutions” for better BTE (Brake Thermal Efficiency), cleaner exhaust, lower lubricant consumption, lower noise and lower vibrations:
The Pulling-Rod architecture of the OPRE engine gives some 35% longer piston dwell around the CDC (Combustion Dead Center), which means that almost all the fuel is burnt during the first portion of the expansion stroke (this is what Mazda claims with its SkyActivX (controlled HCCI) technology that brings to the gasoline engines similar to di Diesels fuel efficiency without the emission problems of the di Diesels).
The same Pulling Rod architecture offers lower specific lube consumption, too, because the trust loads are taken at the cool side of the cylinder, away of ports and especially of “red hot” ports (i.e. wherein the scuffing of the conventional 2-stroke engines begins).
The same Pulling Rod architecture lowers the noise, too, because when the exhaust port opens, the pressure inside the cylinder is substantially lower: the more energy you milk from the fuel during the expansion stroke, the less energy remains in the exhaust gas to make noise.
Here it sounds and looks like HCCI:
The Tilting Valves of the Portable Flyer engine make “positive” the first half part of the scavenging (positive as, say, the way a desmodromic valve train closes the valves): at the opening of the transfer port the pressure inside the transfer passageway is high enough to push a lot of fresh charge in the cylinder; then the scavenging continues “positively” (back side of the piston, closed tilting valve, small “scavenge pump dead volume”) till about the BDC; then the scavenging continues and completes inertially (open tilting valve, communication of the scavenge pump space with the “crankcase” that communicates freely – though the open inlet ports - with the intake).
With direct injection (or TPI?) the OPRE Tilting seems capable of being greener than any conventional gasoline 2-stroke.
As for the vibrations: each OPRE Tilting is as perfectly balanced as the best V-12 engine. The two crankshafts counter-rotate in synchronization at zero phase difference (the tilting valves allows this symmetry, without sacrificing the breathing).
You also write: “Will you have to run an annular safety ring around the perimeter of your prop-blades also, on safety grounds, & if so, will that assist or hinder, any useful pitch control methodology?”
The purpose of the Portable Flyer is to cover distances flying over 95% of the time at its “optimum” cruise speed, wherein the propellers are at their “optimum”.
For the rest of the flight (take off, landing, hovering) the propellers will not be at their optimum.
The drones also need variable pitch propellers.
Hopefully self-adjusting lightweight propellers will soon be available.
Thanks
Manolis Pattakos
Re: 2 stroke thread (with occasional F1 relevance!)
Posted: 05 Jan 2020, 09:34
by manolis
Hello Dr.Acula
You write:
“Just a question.
Do you plan to incapsulate the transmission setup in any way? Because i see a serious issue their. The gear setup you plan to use to syncronize the pistons, (the yellow gears) they aren't lubricated in any way, are they? Generally speaking gearwheels will not live very long if you transmit proper loads through them without any lubrication.”
The synchronizing gears need not lubrication.
The common instant pressure on the two opposed pistons of the OPRE Tilting engine, the zero phase difference between the two crankshafts:
and the fully symmetrical load on the two crankshafts eliminates the loading of (and the frictional losses in) the synchronizing gearing.
The two synchronising gearwheels are loaded only during the cranking (just like the gearwheel around the flywheel of a car and the gearwheel of the starter, which are loaded only at cranking and run without lubrication).
Thanks
Manolis Pattakos
Re: 2 stroke thread (with occasional F1 relevance!)
Posted: 05 Jan 2020, 09:54
by manolis
Hello Gruntguru
You write: “Of course with intermeshing propellers, the failure of a belt takes out both propellers. Can you see any benefit in staggering the propellers enough to avoid such a clash? This would leave 3 propellers and 2 power units functional in the event of such a failure. It would also eliminate the cost and debris created by clashing propellers."
Torque is one obvious problem with a 3 propeller system.”
In the drawing with the propellers (this page, a few posts ago) the propellers are shown staggering: the blue propeller hub is longer than the red propeller hub. This prevents the propellers from collision in case of a broken toothed belt. It also allows somewhat longer blades.
In case of a broken belt or propeller, the respective engine has to shut down because otherwise the unbalanced reaction torque will spin the pilot about his/her long axis.
With the one only engine running, the pilot has to land safely as soon as possible.
