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Asymmetric Timing in the Two-Stroke engines


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#51 Kelpiecross

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Posted 01 August 2014 - 04:17


Interesting stuff.
Are there actually any examples of the valved "loop-scavenged conventional two-stroke" in production or being proposed?

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#52 manolis

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Posted 01 August 2014 - 09:29

Interesting stuff.
Are there actually any examples of the valved "loop-scavenged conventional two-stroke" in production or being proposed?

Hello Kelpiecross.

Almost every company (Ricardo, Toyota, AVL, Denso etc) has proposed such a "loop-scavenged conventional two-stroke" (some proposed switchable 2/4 strokes versions).

However none of the proposals is in production.

It seems that instead of combining the advantages of the two-strokes (power density, lightweight, simplicity) and of the four-strokes (clean exhaust, low specific lube consumption, low specific fuel consumption, scuffing resistance etc), the "loop-scavenged conventional two-stroke" combines their disadvantages, too.

A big problem is the small valve time-area when all valves are on the cylinder head.

Take a look at the PatrPortLess uniflow two-stroke engine:

PatPortLess_Opposed_Cylinder.jpg

at http://www.pattakon....PatPortLess.htm

Compare the valve time-area of the PatPortLess to the valve time-area of the "loop-scavenged conventional two-stroke"

Take also a look at the PatMar:

PatMar.gif

that can replace the conventional giant marine two strokes keeping their top thermal efficiency (more than 50%), reducing substantially the specific lube consumption and the emissions, and increasing substantially the scuffing resistance / reliability.

Thanks
Manolis Pattakos

Edited by manolis, 01 August 2014 - 09:33.


#53 ray b

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Posted 01 August 2014 - 16:46

yes but can it run backwards ?



#54 manolis

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Posted 01 August 2014 - 18:11

yes but can it run backwards ?


Hello Ray B.

If you mean if the PatMar can run backwards, yes it can.

Think that in the simplest case the intake valve on the piston of the PatMar opens and closes symmetrically with reference to the BDC, i.e. exactly as the intake ports of the conventional marine two-stroke.

In a more sophisticated version, with a system like the HyDesmo (at http://www.pattakon....akonHyDesmo.htm ) actuating the intake valve on the piston of the PatMar, the control over the engine operation / efficiency / emissions is better; for instance, at "slow steaming" the closing of the intake valve near (or at) the BDC increases the effective compression ratio (not possible in the current designs with the intake ports at the lower end of the cylinder liner)."

Thanks
Manolis Pattakos

#55 manolis

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Posted 05 August 2014 - 18:03

Hello.

You may like to think (or dream) about this application of the PatATi:

PatATi_OP_props.gif

PatATi_half_OP.gif

It is an Opposed-Piston PatATi Portable Flyer having

80mm bore,

80+80=160mm stroke,

800cc,

540mm crankshaft axis to crankshaft axis distance (two directly-driven counter-rotating propellers, 1m diameter each),

perfectly "vibration free" and "reaction free" structure,

total weight less than 15Kp (33lb).


The second GIF is the one half of the Opposed Piston PatATi engine and shows the "internals".

The narrowing at the center of the cylinder of the OP PatATi engine enables a compact combustion chamber without spoiling the - loop - scavenging. The spark plugs (not shown) are located more centrally. The narrowing causes the required squeeze during the combustion.

Without phase difference between the two crankshafts (yet, with asymmetric transfer and intake) and with the same instant pressure acting on the two piston crowns (common combustion chamber), the synchronizing mechanism (not shown) between the two crankshafts runs unloaded, so it can be lightweight and reliable, causing minimum power loss.

The two counter-rotating propellers act as the flywheels of the engine.

With the two oppositely moving pistons counterbalancing each other, the balance webs on the crankshafts have to balance only the mass of the crankpin and of the rotating part of the mass of the connecting rods (lightweight and compact crankshafts).

At 5,000rpm the speed of the blade tip of the 1m diameter propellers is 260m/sec.
With 0.5Kg reciprocating mass per piston (it includes the mass of the piston, of the wrist pin and of the "reciprocating part - typically 1/3 - of the connecting rod) the resulting maximum inertia force is 700Kp at the TDC (at the BDC the inertia force drops to 400Kp; con-rod to stroke ratio: 2). In comparison, with only 20 bar pressure inside the cylinder (20 bar is the BMEP - brake mean effective pressure - in the typical marine two-stroke supercharged engine), the resulting pressure force on each piston is 1,000Kp.

PatATi_OP_flyer.gif


Application:

Imagine a pilot / rider wearing a wingsuit and having secured on his shoulders this Portable Flyer, flying only 2m above the sea (for safety), from island to island.

The pilot / rider can take off vertically, like a helicopter, and then he can progressively turn to horizontal fly, like an airplane, to cover the distance quickly and fuel efficiently (fast and cheap).
At landing he returns to "helicopter" mode to land vertically.

Thoughts?

Thanks
Manolis Pattakos

Edited by manolis, 06 August 2014 - 06:34.


#56 manolis

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Posted 14 August 2014 - 04:12

Hello.

As I wrote in the last post, the PatATi Portable Flyer is a:

perfectly "vibration free" and "reaction free" structure.


It seems (from other forums) that only a few people understand the meaning of these terms, so let me further explain them.


The Wankel engine can be, "inertially", a perfectly balanced engine, however it cannot be a "perfectly vibration free" engine / structure.

Consider the case wherein your airplane (or your Electric Car Range Extender Module REM) is having a Wankel rotary engine driving a propeller (or an electric generator).
At each combustion / expansion the propeller (or the generator) accelerates and the rest structure inevitably receives a reaction torque pulse.
The NVH (Noise Vibration Harshness) of a Wankel REM cannot be as good as of an Opposed Piston REM (like the OPRE, for instance).
And this is not just theory: think what can happen in a light airplane at a sudden opening or closing of the throttle.


Consider now that your airplane (or your REM) is having a PatATi Opposed Piston engine driving two counter-rotating symmetrical propellers (or two counter-rotating electric generators).
As happens with the Wankel rotary, the PatATi OP is, “inertially”, a perfectly balanced engine.
But it is also a "perfectly vibration free" structure.
During a combustion/expansion, each piston, through the respective connecting rod and crankshaft, accelerates its own propeller (or its own electric generator). The casing receives a "reaction" torque in order to accelerate the one propeller (or the one electric generator) and an equal and opposite reaction torque in order to accelerate the other propeller (or the other electric generator). The two reaction torques cancel each other inside the casing of the engine. This way the basis of the engine remains perfectly rid of inertia and of combustion vibrations (common combustion chamber, same instant pressure acting on both piston crowns, zero phase difference between the two crankshaft).

The sudden opening or closing of the throttle cannot de-stabilize the structure any longer.



Consider now the PatATi Opposed Piston Portable Flyer.

With the two propellers (and flywheels) rotating at opposite directions (like two symmetrical gyroscopes), the structure has, according the theory (I can further explain if there is interest) and the experiments:
“no gyroscopic stabilization (acts just as if the gyroscopes were not spinning, ie., the gyroscopes fall over exactly as when they are not spinning - zero net angular momentum)” (quote from Physics Forums at http://www.physicsfo...ad.php?t=173215 )

So, either the two big propellers (1m diameter each) rotate at 5,000rpm, or at 2,000rpm, or they are slow revving or they are completely stopped, the pilot / rider “sees” the same difficulty in order to change the direction of the Portable Flyer (and, so, the direction of the thrust force).

And this is quite important for a stable flight.

Worth mentioning that at high revs the sudden change of direction of the PatATi Portable Flyer causes significant loads on the bearings of the two propellers / crankshafts and on the engine casing, however these loads cancel each other internally, with the rider / pilot feeling nothing.

Thanks
Manolis Pattakos

Edited by manolis, 14 August 2014 - 04:18.


#57 Kelpiecross

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Posted 15 August 2014 - 05:34

I have no particular argument with your OP engine - but - I think your "backpack" portable helicopter (if you are actually serious)is a bit of a disaster. Mainly; two unducted (or even ducted) 1 metre diam. propellers could never lift anybody off the ground no matter what rpm or HP - the propeller disc efficiency is just too low. There have been many attempts at backpack helicopters - but, essentially none have worked - certainly not with 1 metre propellers. There was an interesting episode of Mythbusters where they built a backpack helicopter using two ducted fans of about 4 feet diam. and using 80+ HP - it didn't leave the ground.
Apart from this it would be fiendishly dangerous (for many reasons) both to the pilot and any bystanders.

#58 manolis

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Posted 15 August 2014 - 14:54

I have no particular argument with your OP engine - but - I think your "backpack" portable helicopter (if you are actually serious)is a bit of a disaster. Mainly; two unducted (or even ducted) 1 metre diam. propellers could never lift anybody off the ground no matter what rpm or HP - the propeller disc efficiency is just too low. There have been many attempts at backpack helicopters - but, essentially none have worked - certainly not with 1 metre propellers. There was an interesting episode of Mythbusters where they built a backpack helicopter using two ducted fans of about 4 feet diam. and using 80+ HP - it didn't leave the ground.
Apart from this it would be fiendishly dangerous (for many reasons) both to the pilot and any bystanders.



Hello Kelpiecross.

What makes you think that it's not possible to lift a man with two 1m diameter propellers?


Take the MartinJetPack.

Its maximum weight at take-off is 330Kp (733lb).
It has a 2lt, 200bhp, V-4, two-stroke engine (some 60Kp heavy).
It has two ducted propellers of only 520mm diameter each.
And, the most important, it flies (see the several videos in the Internet).


Think about it a little deeper: the mission is a 70-75Kp man to vertically take-off, then to fly horizontally from a first point to a second point (fast if possible) and finally to vertically land.

Martin’s approach starts by increasing a few times the weight (the worst enemy when you try to fly).
The birds, bats and bugs fly because their weight relative to the power their body can provide is small.


Now take the PatATi Portable Flyer.

The total weight at take-off can be less than 100Kp (220lb): 70-75Kp the rider / pilot, 15Kp the complete Flyer and 10Kp the fuel (for a long range).

At 5,000 rpm the blade tip speed is well below the sound velocity, and the propellers near to their optimum efficiency.

The mission of the PatATi Portable Flyer is to lift the rider / pilot like a helicopter and then to allow him fly like an airplane (at high speed, fuel efficiently).


Wearing a wing-suit and falling at a 1:3 fall rate, you can fly with over than 150 Km/h.

Calculate the power:

The 75kp (750Nt) total weight lowers by (150Km/h)/3=13.8m/sec, which gives a power of 750Nt*13.8m/sec=10.4kW or 14bhp.

Imagine wearing a wing-suit and having the PatATi Portable Flyer above your helmet.
If the Portable Flyer provides this power (just 14 bhp), you can fly horizontally with 150Km/h for as long as the fuel tank has fuel.
With more power, you can go much faster.



Safety.

You can put a (removable) safety ring around the propellers for the take-off and landing (like those used in the paragliders). When you fly at high speed, say above 150-200Km/h, this ring should be removed (to avoid its aerodynamic resistance).


So, think again what (and why) is impossible and what not.

Much more important is to think how much the world can change with such a Portable Flyer.

Thanks
Manolis Pattakos

#59 Kelpiecross

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Posted 17 August 2014 - 05:50


I remain unconvinced - two one metre (unducted) propellers will never lift anything useful.
The Martin device is interesting - but - 200hp? - a Robinson R22 is only 124hp - and has 2 seats, useful endurance etc. - and the Martin weighs almost as much as an R22 (hardly a walk-around backpack).
The backpack helicopter is an attractive idea - you can walk around, perform various tasks etc. - and then fly off into the distance. In reality this "anti-gravity suit" approach has no great advantages (unless you do have a genuine AG suit).
Some sort of very lightweight micro-helicopter is probably far better and more practical - and could even have 2 seats maybe.
It does make me wonder however if something with a layout like the Martin could be an idea. But with a proper weatherproof sit-down capsule (maybe for two) and with two decent-sized ducted fans (5-6 feet diam?) could be usefully practical. It would have the advantage (compared to R22 for example) of not having a giant whirling rotor whizzing around - so it would able to land in a much more confined space (like your own backyard) compared to an R22.
(But you would want to have a very effective ballistic parachute in case of problems).
An R/C electric-powered model could be interesting.

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#60 manolis

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Posted 17 August 2014 - 18:08

Hello Kelpiecross.

First consider the case of MartinJetPack:
a pair or ducted fans of 520mm diameter each,
a 2,000cc, 200 bhp engine,
a maximum take-off weight of 330Kp,
a fuel capacity of 45 lt,
a range of 30Km,
a maximum airspeed of 74Km/h,
and a cruise speed of 56Km/h.

Now consider the case of the Ossprey (Bell Boeing V-22):
a pair of counter-rotating propellers of 11.6m diameter each,
a pair of engines providing 6,150 bhp each,
a maximum take-off weight of 27,400Kp,
a range of 1,627Km,
a maximum speed of 509Km/h.

Now consider the case of the Chinook (Boeing CH-47):
a pair of counter-rotating propellers of 18.3m diameter each,
a pair of engines providing 4,733 bhp each,
a maximum take-off weight of 22,680Kp,
a range of 741Km,
a maximum speed of 315Km/h.

And here is the estimation for the PatATi Portable Flyer:
a pair of counter-rotating propellers of 1m diameter each,
an 800cc PatATi Opposed Piston engine,
a take-off weight of 100Kp,
a range of 300Km,
a maximum speed above 200Km/h.

Consider the disk loading (weight to propeller area at take-off) for the three cases:
MartinJetPack: 330Kp/0.43m2 = 776Kp/m2
Ossprey: 27,400Kp/211.4m2 = 129.6Kp/m2
Chinook: 22,680Kp/526m2 = 43Kp/m2
PatATi Portable Flyer: 100Kp/1.57m2 = 63.7Kp/m2

The "disk loading" in the case of the PatATi is 50% more than Chinook's, but it is also half of the "disk loading" of the Ossprey and a dozen times lower than the "disk loading" of MartinJetPack.

If you still think that a pair of 1m diameter non-ducted propellers cannot lift a man, please explain your reasonig.


By the way, from the specifications you can see a serious problem of the JetPacks: their ducted fans and architecture may be good for hovering but not for cruising (power to cruising speed ratio); as for the fuel efficiency (lt/Km), the 45lt for covering 30Km is not good at all.


While its disk loading is closer to Chinook's, think of the PatATi Portable Flyer as a "small scale" Ossprey (it is capable for vertical take-off / landing and very good for covering long distances at high speed / low fuel consumption) wherein the sensors and the controls over the flight is the rider / pilot himself.

**********

Assuming the same “disk loading” with the Ossprey, the maximum weight of the PatATi Portable Flyer at take-off would be: (129.6 / 63.7)*100 = 203Kp (i.e. it lifts two heavyweight persons).

Simplifying things further by assuming the necessary engine power is proportional to the maximum weight at take-off, the power required by the 800cc PatATi engine in case of 203Kp total weight would be: (2*6,150*(203/ 27,400)) = 91bhp, while in case of 100Kp total weight at take-off it would be only: (2*6150*(100/27,400)) = 45bhp.

Thanks
Manolis Pattakos

Edited by manolis, 18 August 2014 - 02:44.


#61 manolis

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Posted 14 September 2014 - 03:00

Hello.

The following youtube video ( https://m.youtube.co...h?v=bzbVwiIeM0M ) demonstrates the gyroscopic rigidity (or stabilization) of a set of "parallel" not coaxial flywheels in case they spin at the same direction and in case they spin at opposite directions:

bzbVwiIeM0M

According maths and physics (or, simply, according the above video) the pattakon Portable Flyers (at http://www.pattakon....pattakonFly.htm ) are rid of "gyroscopic rigidity": with the symmetric counter-rotating propellers (and crankshafts), the total gyroscopic rigidity is zero, i.e. the rider / pilot can "instantly" (as instantly as with the propellers stopped) vector the thrust to the desirable direction:

As aerodynamic "controls" the rider / pilot can use his feet, hands, head and body just like the wing-suiters do.

A wing-suit fits with the Portable Flyer, especially for long flights and "fast acrobatics".

Imagine a guy having a Portable Flyer on his shoulders and wearing a wing-suit competing in the Red Bull Air Race.

Flyers.gif

The birds and the bats and the bugs can fly only because their bodies can provide enough power for their weight.
The weight of a man cannot be decreased. In order to fly, a man needs more power than what his / her body can provide.

When I want to fly, what I need is neither a vehicle, nor sensors, nor transmission shafts, nor gearboxes, nor differentials, nor servomechanisms, not even a seat.
What I do need is more power provided in a perfectly "neutral" way.
My body is the vehicle and the sensors, and the servomechanisms and the landing system, just like the bodies of the birds, bats and bugs.


Objections?


Thanks
Manolis Pattakos

Edited by manolis, 14 September 2014 - 03:04.


#62 Kelpiecross

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Posted 15 September 2014 - 07:35


Don't know about air races - the propeller pitch for static lift and fast forward flight are very different.

#63 gruntguru

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Posted 15 September 2014 - 16:49

Aerobatics in a powered wing suit would be pretty tame. The L/D and max G would both be quite low.


Edited by gruntguru, 15 September 2014 - 16:50.


#64 manolis

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Posted 16 September 2014 - 03:43

Don't know about air races - the propeller pitch for static lift and fast forward flight are very different.


Hello Kelpiecross.

It is a matter of optimization and of available power.

If you want the Portable Flyer for hovering (say as a "toy", for demos etc) a low pitch provides the necessary lift (static lift) requiring substantially fewer power by the engine (and consuming substantially less fuel per hour of hovering). The drawback is the limited cruise speed and range.

But if you want the Portable Flyer as transportation means, the high pitch optimizes the cruising (the fuel consumed per Km covered lowers, the cruising speed gets high, say more than 250Km/h; think of the small front area / aerodynamic resistance when the pilot / rider flies horizontal, think also how fast a motorcycle with similar power can go).
As for the static lift with the high pitch propellers: during the hovering, the required by the engine power increases substantially as compared to the case wherein the pitch is small; however the static lift / hovering (i.e. the take-off and the landing) is a very small part of the flight.

For specific uses (say for rescues of injured people / of near-drowning swimmers / of fire-trapped people etc) the variable pitch propellers are preferable for the Portable Flyer in order to get faster (at high pitch) to the incident and then to lift (at low pitch) a lot of weight.

Thanks
Manolis Pattakos

#65 manolis

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Posted 16 September 2014 - 04:30

Aerobatics in a powered wing suit would be pretty tame. The L/D and max G would both be quite low.


Hello Gruntguru.

When a non-powered wingsuiter falls constantly at a 3:1 ratio flying with 150Km/h, the power consumed is about 15bhp (weight lowering).
This indicates a good L/D ratio.

And it seems that with a Portable Flyer providing more than, say, 70bhp, the top speed gets higher than what a wingsuiter - or a rider / pilot without a wingswuit - can stand for long.

Yet, more power is still useful during the accelerations ( G ) wherein both help: the redirection of the Portable Flyer (its gyroscopic rigidity is eliminated, so the thrust force can be redirected “instantly”) and the “aerodynamic controls” (the hands / feet of the rider wearing the wing-suit).

The precision at which the wingsuiters pass near rocks and though narrow openings (there are many videos in the Internet) indicates that the wingsuiters can, even without a power-unit, keep excellent control over their flight.

I think that seeing a guy taking-off and flying fast and controllably as a bird / helicopter / airplane will be, at first at least, spectacular.

Thanks
Manolis Pattakos