2 stroke thread (with occasional F1 relevance!)

[Brake Horse Power]

Hello all

This array (from the Youtube video of Big_Tea post):

https://www.pattakon.com/tempman/Achates_BSFC.png

"talks" for 1 to 1,000 (or so) oil to fuel ratio for the Achates Power 2-stroke engine(s).

(~0.2gr/kWh Brake Spec. Oil Consumption divided by ~200gr/kWh Brake Spec. Fuel Consumption)

Do I (or they) miss something?

Is there a 4-stroke that achieves such figures?

Thanks
Manolis Pattakos

Quite high NOx?

[manolis]

And this oil is scraped by the piston rings and passes over the “hot” open holes pof the exhaust port.
This simply says that you can’t avoid oil from escaping (total loss).

Yes.

The same with the opposite piston that slides over the open intake (transfer) ports.

No.
Surely it will end up back in the cylinder carried by the fresh charge of air.

It would be great, but it happens the other way around, and it is the worse problem of the 2-strokes.

The oil entering the cylinder with the fresh air is partly burned during the combustion, and is partly lost unburned through the exhaust.
In both cases it is a total loss.

Unless the Detroit Diesels (or "Oilers"), which are rid of exhaust ports, have not extremely hight specific oil consumption.

Thanks
Manolis Pattakos

[manolis]

Hello all.

Here is another application of the OPRE Tilting engine:



The (single) OPRE Tilting engine has on its casing two “arms” whereon a holed pipe (yellow) is secured.

The one crankshaft drives, by means of a reduction gearing (comprising a pair of sprockets and a “short” toothed belt (not shown)), a propeller which is rotatably mounted on the holed pipe at the one side of the engine,
the other counter-rotating crankshaft drives, in a similar way, another propeller which is also rotatably mounted on the (yellow) holed pipe, but at the other side of the engine.
The two propellers are contra-rotating.



Through the holed pipe they pass the fuel and the control (like: the gas cable, a cable for the release of a parachute, etc).

Here is the engine with the arms whereon the holed pipe is to be secured; at right is the synchronizing gearing and the transmission to the one propeller.



The diameter of the propellers is as large as desirable.
The basis of the engine (say, the flange or the pipe whereon the engine is secured) is rid of gyroscopic rigidity, of vibrations and of reaction-torque.


The flange at the end of the (yellow) pipe can be secured on the frame at the back of a parachuter replacing the conventional propulsion unit.


If the flange at the end of the holed pipe is secured on the nose of an ultra-light or of a small airplane, it is a complete propulsion unit having significant advantages.


If the holed pipe is substantialy extended, then a simple Portable Flyer (say, a "Witch’s Broom" Portable Flyer) is made:



For safety,
a second OPRE Tilting engine with its own pair of contra-rotating propellers can be secured higher on the holed pipe.

Thanks
Manolis Pattakos

[Rodak]

Have you ever stood on a disc, as illustrated? I have; the c.g. is such that body weight tips the base forward and you end up being supported by your arms which tire very quickly. Just look at the picture and visualize where the c.g. is and what will happen. Even sitting on a disc like that is tiring as the same thing happens. Again, as with your other flier, I do not see how this could be controlled as there is no means of shifting body weight.

[manolis]

Hello Rodak.

Quote from Mayman’s interview with New Atlas’ Loz Blain (https://newatlas.com/david-mayman-inter ... der/58822/ ) :

“Jetpack Aviation's David Mayman on his upcoming Speeder flying motorcycle
. . .

Loz:

Indeed, he's become one of the four superhero horsemen of a new personal flight revolution. Mayman, with his calm, methodical aviator's approach and multi-turbine jetpack, plays Buck Rogers. On the other end of the scale is Frenchman Franky Zapata, an extreme sports nut and former jet-ski champion whose turbine-powered Flyboard Air has been seen thundering across air and water throughout Europe and the US. Zapata makes a natural Green Goblin.
Then there's Richard Browning, a British martial arts master with a multi-turbine jet suit and a company called Gravity. Browning's suit places jets not only on his back, but on his arms, making him a shoo-in for Iron Man. And standing slightly apart from them all is ex-Swiss military pilot Yves Rossi, whose extraordinary Jetwing literally lets him dance with aeroplanes in the sky. It needs to be launched out of a plane, though, so while it certainly looks like an incredible experience to fly, it can't lift straight off the ground like the others.


. . .

Mayman:

But the pilot has to be on top. So the thing is literally dynamically unstable. Inherently unstable. And it has to be flown by computer. So that's what we're building. And the prototype is exactly that. The engines are clustered together, we purposely put the weight above that, and then we try to fly it.”

End of Quote.


In the specifications of the Speeder of Mayman, while the take-off weight is unknown, the price is US700,000$.

Thanks
Manolis Pattakos

[Tommy Cookers]

.... another application of the OPRE Tilting engine:
The diameter of the propellers is as large as desirable.
The basis of the engine (say, the flange or the pipe whereon the engine is secured) is rid of gyroscopic rigidity, of vibrations and of reaction-torque.
The flange at the end of the (yellow) pipe can be secured on the frame at the back of a parachuter replacing the conventional propulsion unit.
.... on the nose of an ultra-light or of a small airplane, it is a complete propulsion unit having significant advantages

in a slow-flying application .....
for the same thrust ......
relative to a single prop ....
2 coaxial props means accelerating half as much air to more than twice the velocity

is this concept right eg for a paramotor ? (or even for an ultralight/microlight or class whatever they're called)
it may be better as a retractable auxiliary unit on a glider

[manolis]

Hello Tommy Cookers

You write:
“in a slow-flying application .....
for the same thrust ......
relative to a single prop ....
2 coaxial props means accelerating half as much air to more than twice the velocity”

Not necessarily.

On one hand a single propeller creating some thrust needs a secondary “reaction” propeller located at some eccentricity (the big main rotor in a conventional helicopter creates the thrust while a power consuming tail rotor (it consumes more than 10% of the available power and adds nothing to the thrust) provides a reaction torque that prevents the helicopter from spinning).

On the other hand, the two coaxial (contra-rotating) propellers need not be smaller in diameter than the “single” one; instead they can be of the same diameter with the “single” propeller, and rotate slower. This improves the efficiency (defined as the ratio of the thrust to the power consumed) in two ways: because a reaction propeller (and the power it consumes) is eliminated, and because the same diameter contra-rotating propellers rotate at slower revs.

The human powered helicopter that won the Sikorsky prize had four propellers:






You also write:
“is this concept right eg for a paramotor ? (or even for an ultralight/microlight or class whatever they're called)
it may be better as a retractable auxiliary unit on a glider”

Yes and yes.

Nice application. Not only for gliders, but also for small airplanes: a backup OPRE Tilting located somewhere in the airplane (say, at its back) can provide the required thrust for a safe landing in case of a stall / malfunction of the main engine / propeller.
With a total weight of less than 25lb (10Kg) it seems a solution.

For air applications, what counts the most is the thrust (or power) to weight ratio.

Thanks
Manolis Pattakos

[PlatinumZealot]

Hello all.

Here is a slide from the Achates_Power Opposed Piston youtube video (posted a few posts ago by Big Tea):

https://www.pattakon.com/tempman/Achates_OP_Thrust.jpg

A is the exhaust port.
B is the piston skirt.
C is the piston pin.

The piston skirt B abutting / sliding on the cylinder liner (not shown) transmits a thrust force F from the piston to the casing (the inclination of the connecting rod causes this thrust load F); F times the eccentricity of the piston pin from the crankshaft rotation axis makes the instant torque provided by the engine (more correctly: by the specific cylinder of the engine).

To take the heavy thrust loads without wear, it is necessary a thick oil film between the piston skirt and the cylinder liner, no matter where the oil rings (if any) are located.

The piston rings need a substantially thinner oil film on the cylinder liner to avoid scuffing.

So, you need adequate oil above the exhaust port A.
And this oil is scraped by the piston rings and passes over the “hot” open holes pof the exhaust port.
This simply says that you can’t avoid oil from escaping (total loss).

The same with the opposite piston that slides over the open intake (transfer) ports.


Unless they use some “smart” / magic oil that avoids falling into the open holes (i.e. the ports) of the cylinder, the specific oil consumption for this 2-stroke engine of Achates Power can’t be real / true.

The Junker Opposed Piston engines, the “famous” Ecomotors OPOC, the Detroit Diesels of GM had exactly the same problem.


Thanks
Manolis Pattakos

That problem can be reduced greatly by tapering away (increasing the bore diameter) in a spiral (imagine a spiral groove) as you get near the exhaust ports. OR even better just creating pockets to "trap" oil until the pistons return on the compression stroke. Note that the piston has a high crown, and the piston skirt itself has a ring pack, I assume these give stability to the piston as it comes down, ensuring contact at all times, even if you add the "oil traps" near the ports. I have a feeling they are doing something like this.

[OO7]

The following is an interesting design from INNengine, which they're calling a 1 stroke cycle engine. It appears to operate like a "Big Bang" or "Screamer" engine, with two cylinders mirroring a cycle, e.g firing simultaneously.:


http://innengine.com/
http://innengine.com/home/

[manolis]

Hello PlatinumZealot

You write:

“That problem can be reduced greatly by tapering away (increasing the bore diameter) in a spiral (imagine a spiral groove) as you get near the exhaust ports. OR even better just creating pockets to "trap" oil until the pistons return on the compression stroke. Note that the piston has a high crown, and the piston skirt itself has a ring pack, I assume these give stability to the piston as it comes down, ensuring contact at all times, even if you add the "oil traps" near the ports. I have a feeling they are doing something like this.”


We talk for a wide band of revs and of loads engine.

It doesn’t fit to use taper cylinder liners, pass heavy inertia and combustion loads through the “contact” between the liner and the piston skirt, and expect longevity / reliability.

It doesn’t also fit to have pockets of lubricant and expect the “based on the inertia of the oil droplets” lubrication to work efficiently from below 1,000 to above 5,000rpm.

The original engine design Achates Power started with, was a “crosshead” design wherein each piston was connected to a pair of “symmetrically” (about the cylinder axis) arranged counter-rotating crankshafts through at least two “straight of bent” connecting rods (this was the basic design of Lemke).



The above would be a great design if the materials where absolutely inflexible and the construction accuracy perfect.


The EcoMotors OPOC had similar issues never addressed.
Initially the OPOC engine presented as the perfect engine for cars motorcycles etc, then it was limited for use in trucks, then it was limited for use in electric generator sets (and other constant revs applications) and finally, after raising some US100M $, they shut the business down.


Unless I am wrong, this video (end 2018):



is, so far, the only case wherein a “Junkers-Jumo”-like Opposed Piston engine of Achates Power was “demonstrated” on the road. Unless I miss something.

Thanks
Manolis Pattakos

[manolis]

Hello 007

A crucial problem of the design is the overloading of the “line” (if it is “line” and not “point”) contact between the track roller bearings and the “waving surfaces”.

The Bourke engine:



had the same issue .

The Revetec engine (with its true “line” contact between its track rollers and its cam lobes) didn’t worked reliably.

Theoretically the rollers keep contact with the waving surfaces all the time; but in practice they strike and rebound digging the ramps.


A far better design in this class (track-roller-bearings rolling on cam-lobes to replace the conventional “crankshaft – connecting rod – piston mechanism) is the following one:





Thanks
Manolis Pattakos

[gruntguru]

Mayman:

But the pilot has to be on top. So the thing is literally dynamically unstable. Inherently unstable. And it has to be flown by computer. So that's what we're building. And the prototype is exactly that. The engines are clustered together, we purposely put the weight above that, and then we try to fly it.”

This is nonsense. In a hover situation with an axial thruster, the stability is the same no matter how low or high the CG might be relative to the thruster. An axial thruster always exerts its force along the same axis as that axis tilts. Although somewhat non-intuitive the situation is not the same as a parachute where the thrust remains upwards as the system tilts. (A parachute needs to be above the CG)

[manolis]

Hello Gruntguru.

Mayman:
“But the pilot has to be on top. So the thing is literally dynamically unstable. Inherently unstable. And it has to be flown by computer.”

Gruntguru:
“Nonsense. . . Although somewhat non intuitive the situation. . .”.


For most people the situation is “heavily non-intuitive”.

Despite his long flying (and manufacturing) experience, Mayman can’t get it.

So let me help with a drawing:



It is the “Broom Flyer” of a previous post modified by adding another OPRE Tilting propulsion unit at the bottom of the (yellow) pipe.

Suppose for a moment that the pilot is aerodynamically “transparent”.

Case 1: upper engine running, lower engine stopped.
Case 2: lower engine running, upper engine stopped.
In either case the pilot feels the same, and controls his flight the same way.

The force from the spinning propellers is along the yellow pipe in both cases.
In the one case the power unit is above the pilot, in the other case the power unit is below the pilot.


But the pilot is not aerodynamically “transparent”, which brings a significant difference of the two cases.

With the running engine above the pilot (i.e. with the pilot inside the downstream of the propellers), he has not only “weight displacement control”, but he has also aerodynamic control over his flight: his head and limbs act as flaps / ailerons / fins: deflecting a part of the downwash, they receiving reaction forces which give full control over the flight (yaw, pitch and roll).

With the running engine under the pilot (say, as in Zapata’s Jetpack) the pilot at take-off, at landing, at hovering and at low / medium speeds is based exclusively on “weight displacement” to control his flight. And this is not a full control.



Hello Rodak

This photo shows a windsurfer:



From Wikipedia:

“In 1948, 20-year-old Newman Darby was the first to conceive the idea of using a handheld sail and rig mounted on a universal joint so that he could control his small catamaran—the first rudderless sailboard ever built that allowed a person to steer by shifting his or her weight in order to tilt the sail fore and aft.”

Doesn’t it remind the way the pilot of the Broom_Flyer controls his flight?

Thanks
Manolis Pattakos

[Dr. Acula]

This is nonsense. In a hover situation with an axial thruster, the stability is the same no matter how low or high the CG might be relative to the thruster. An axial thruster always exerts its force along the same axis as that axis tilts. Although somewhat non-intuitive the situation is not the same as a parachute where the thrust remains upwards as the system tilts. (A parachute needs to be above the CG)

True. the main problem with this "hover bike" is that the thrusters are bundled togheter, no so much that the CG is above the center of lift or thrust in this case. Anyway. It's certainly true that it will be quite delicate to handle and a fully fledged FBW could certainly help to keep the thing stable.

Doesn’t it remind the way the pilot of the Broom_Flyer controls his flight?

Honestly? No not at all. First of all the surfer can only "hang in there" so much because of the forces the wind applies on the sail. Now look at the size and especially the surface area of the sail compared to the size and surface area of a human. Even if we aren't "aerodynamical transparent", we generally aren't very efficient in redirecting an airstream with our body.That's also why we're utter crap at gliding without a wingsuit or a wing on the back.
Secondly the water gives the whole thing a huge amount of stability. The surf board will not simply "slip away" sideways because the water generates a lot of resistance against that. Air on the other hand doesn't.

[joshuagore]

I've spent years being educated by this thread, but I can't help but wonder, now that you have this compact power unit, why not use the easiest method available to prove flight, then move to the harder ones? If your goal is personal travel or individual flight, wouldn't it be easier to design around the STOL trend in an ultra lightweight winged package? You can always move to providing lift in more novel ways, and even maybe to the existing package, while still keeping some of the effeciencies of winged flight.

I worked on a plane recently which is being built to hit ultralight(250lb) standard which is EDF powered, certainly seems your engine package could be competitive with a longer flight time in this package. That being said, there seems to be reasons 99% of aircraft or anyone dealing with flight chooses painfully known engines and technologies despite their sometimes obvious inefficiencies. People were very skeptical when we were doing the demo with a 25kw edf, that skepticism will be hard to avoid among experimental pilots. But I wish you the best of luck, I learned a lot about engines from this thread so I hope it continues to progress.

https://joshgoreworks.com/portfolio/ody ... -aircraft/