2 stroke thread (with occasional F1 relevance!)

[manolis]

Hello Uniflow

You write for the advantages of the liquid cooling.

The air cooling has its own advantages.

The Rotax 914 is a turbo-charged, four-stroke, four-cylinder, horizontally opposed aircraft engine with air-cooled cylinders and water-cooled cylinder heads.



The cooling system of the ROTAX 912 is designed for liquid cooling of the cylinder heads and ram-air cooling of the cylinders.

Using liquid cooling allows a smaller engine package. This is mostly due to the fact that air cooling fins make the cylinder head larger, when the head is larger the crankshaft must be larger, this means the crankcase must be larger and so on…
Liquid cooling also allows tighter tolerances of the engine components by controlling the temperature extremes.
This allows reduced weight and increased power.

Some Porsche Boxer engines (for cars and airplanes) use similar cooling: liquid cooling for the cylinder heads, air cooling for the cylinders.

The ULpower uses air cooling for the cylinders and the cylinder heads.

So, there are decent / expensive / reliable aero-engines using air colled cylinders.


OPRE TILTING

The OPRE Tilting engines of the Portable Flyer have no cylinder heads, only cylinders.



The flow of cool air from the propellers on the cylinders is more than adequate at all conditions.

The thrust loads are taken away from the red hot exhaust ports (i.e. from where the scuffing of the conventional two-strokes typically starts).

The inner cooling on the back-side of the piston crown is better than in the typical 2-strokes.

The hottest area of the cylinder is around the exhaust port.
But in the OPRE the combustion completes substantially sooner (the increased dwell of the pistons at their Combustion Dead Centers, due to the pulling rod architecture, leaves less energy into the exhaust gas (i.e. the exhaust gas temperature is lower), which in turn lowers the exhaust ports temperature).

As for the increased power concentration (kW/Kg) of the water cooled 2-strokes, the OPRE Tilting is so lightweight (due to its architecture) that there is no such issue. Its power cencentration is expected extreme because, among others, it is extremely lightweight.

I asked you what is the weight and the capacity of your liquid-cooled two-stroke. I wanted to compare it with the air cooled OPRE Tilting.

I also asked you for the reasoning behind using ethanol as fuel in your autogyro.
I know it is your right to use any fuel you like.
But when someone (who knows that the ethanol is too heavy for its energy content) hears that a guy uses ethanol in his Flying Device, he can’t help thinking “do I miss something?”.

Thanks
Manolis Pattakos

[manolis]

Hello NatanE / Rodak / Nzjrs


From your posts it seems that the mathematical analysis / the calculations / the simulations and the similar, is “piece of cake” for you.
For any system; with the Portable Flyer included.

I, on the other hand, think that the analysis of the motion / control of, say, the air-dancer that flies controllably in the wing tunnel is so complicated that it is currently impossible to be done (not even by NASA).

I may be wrong. Right or wrong, I admit I cannot do such calculations / analysis.

But as you claim repeatedly, you can.


So I propose you (together? each alone? your business) to do what I consider impossible, i.e. to do the calculations / analysis and present the results in this forum.

The next step would be to add the engines/propellers on the back-torso of the air-dancer and run once more your “program”.


PS.
If the flying dancer (that in the video) is too much, start with the analysis of the slow walking of an old person.

Thanks
Manolis Pattakos

[nzjrs]

Hello NatanE / Rodak / Nzjrs


From your posts it seems that the mathematical analysis / the calculations / the simulations and the similar, is “piece of cake” for you.
For any system; with the Portable Flyer included.

I, on the other hand, think that the analysis of the motion / control of, say, the air-dancer that flies controllably in the wing tunnel is so complicated that it is currently impossible to be done (not even by NASA).

I may be wrong. Right or wrong, I admit I cannot do such calculations / analysis.

But as you claim repeatedly, you can.


So I propose you (together? each alone? your business) to do what I consider impossible, i.e. to do the calculations / analysis and present the results in this forum.

The next step would be to add the engines/propellers on the back-torso of the air-dancer and run once more your “program”.


PS.
If the flying dancer (that in the video) is too much, start with the analysis of the slow walking of an old person.

Thanks
Manolis Pattakos

It's not a piece of cake, but its also not impossible. Let not perfect be the enemy of good.

From your behavior and explanations here you agree that it is better to do some 'analysis' - like you do when you compare your PF to other flyers, animals, babies etc, than doing no analysis. So it is also in modelling, it is better to do some quantitative modelling than it is do do none (if one knows the limits of the model).

It's not worth analysing the gait and walking of humans, that is already well studied (I posted some of this earlier). If you want to know about the behavior of your PF it's best to just stay as near as possible to the PF - modeling Rossy and then assuming it corresponds to the PF would be silly.

So, I will go an look again at the H4 paper (http://www-personal.umich.edu/~punsingh ... genh4.html). I would expect you would need to also measure many of the same things in that paper requires. You assume the flyer is rigidly attached to your torso so that makes some things easier for you to measure I guess.

As a collective analysis project we would need you to measure/provide (from memory, I should refer to the papers again)

• rotor diameter, mass, rpm and thrust
• your centre of mass with knees up, and in superman pose (knees pushed back as far as possible). Maybe we could also derive this via FBD from seeing how your hangining position changes as you hang from the shoulders and tuck you knees up and extend your feet back superman style. If you take a photo during the neutral, knee-up and knee-back pose that might be sufficient
• moments of inertia for the body, I guess depending on how flexible you are in your knee poses would determing how much something like http://article.sapub.org/10.5923.j.spor ... 06.08.html could be simplified in the direction of you being a couple of cylinder masses
• it would be overkill to estimate the forces/torques from you moving your feet in the airstream via CFD, and tbh is too many more unknowns, so It's going to be easiest if you just measure these. I mean here for yaw correction, like a stride motion I guess with some arms out, and also for roll correction. I would recommend just mounting the PF and rotors on a rigid stand and then you can just use either a manakin human model with a crude scale/force measurement arangement, or perhaps you could just hang from a non-rigid rope below the propwash and just perform the motions in front of a video camera. From the videos of your change in position/ motion about the appropriate axes, and some knowledge about your mass, we could derive the aerodynamic forces/torques you wish to use for control of the PF.

It sounds like measuring some of these might be quite hard, hanging from a rigid frame, bending forwards, backwards, extending your limbs into the airstream, but its probbably good training for the actual flight.

@Others, It's been about 10 years since I did one of these. What have I forgotten to measure? (I'm ignoring rotor dynamics like the H4 paper had a whole section on, for reference)

[NathanE]

30 years for me I'm afraid, so I'm not any use but to be fair, I also didn't claim to be.

Manolis, don't take it as an insult, I was careful to flag that many people make and innovate without having a clue about the maths/physics behind what they do.

I'm now a luthier, and couldn't model soundwave propogation in the body of the mandolins I build (sadly once upon a time I could have but that's what getting old and crusty does to you) but I can make them sound good. I can't/don't do maths to do that, but I do build and test, listen and refine as I go rather than watching videos of birds singing.

I also (on other things) make engineered products using vacuum formed fibre reinforced composites. Material property modelling of this stuff is possible, but so much of the material performance of the finished product is down to manufacturing accuracy - which frankly I'm average at - that I just build and test using ndt or full on hit it till it breaks analysis to make sure it's OK!

I must admit though if I was going to put my life on the line I'd probably take a different approach.

[uniflow]

manolis, comparing my standard technolagy twostroke to your engine is not possible, mine is flying, yours is not even in flyable hardwear yet. No comparision. Mine works, yours is still just theory.
My 700cc twin is rated at 80Hp, it could be re tuned to approx 140 HP according to EngMod tuning softwear. But I would not want to fly it at that, too close to the edge. Weighed it at 38kg originaly, more likely 40kg now. At 80 HP / 40kg, its not short if performance.
You do remember I built an OP twostroke, crank case pumped, fitted to an autogyro. But it only ran ground tests, I was not willing to fly such an engine, even under autorotation. Pity as some video of ground hops would have been valuable. It ran up to 9500 rpm. I ceased development 25 years ago, there was no intetest. But Im back into development now, as I said with a far better approach, I will show the external hardwear but not its internals.
Ethanol, as I said manolis, its not all black and white, is it. Im not telling seeing as you poo pooed me for running it. .

[Rodak]

I'm not ready to commit to a major project like that without more information and probably not then. This is harvest time in the wine business and I'm pretty busy.

But for starters manolis, you could provide some basic information like a dimensioned power unit drawing with weight and center of mass location, etc. Where is the fuel going to be stored and how much is there? I hope the pilot is sitting in a parachute or rock climbing harness type thing and not just strapped to the frame; is that the case? Where are the attach points/how is the motor unit attached to the pilot? What is the horsepower and propeller rpm range? What is the pitch of the propeller(s)? I assume a drawing will show prop diameter. How do the controls work and what do they control? Are there gauges, etc. and how are they presented to the pilot? What basic calculations have you done? When is a power unit going to run? Do you have any test data with an operating propeller set re thrust, etc? Have you done any experiments with the human body configuration re lift, center of pressure, etc? If so can you provide that data? Are there any pilot safety systems, such as the ability to (somehow) bail? What do you envision as a test program? Is it legal to fly something like this where you are?

Basically, if you want help we need to know where you are with this thing, and I don't mean youtube videos or word salads.

Uniflow, interesting stuff.

[manolis]

Hello Uniflow.

Thanks for the information about your 700cc two-stroke engine.

Nearer to 700cc is the single crankshaft PatOP opposed-piston “uniflow” Diesel engine:



Its capacity is 635cc (64+64=128mm stroke, 79.5mm bore) and weighs (without starter and flywheel) less than 20Kg.
Its compression ratio is 17:1.
Its built-in scavenge pump capacity is 850cc (1.34 scavenging ratio; it uses two pairs of reed valves to control the air).
Its height is 500mm.

It has “four-stroke-like” lubrication (no premixed, no lubricant in the combustion chamber).

With the fuel directly injected (at high pressure) into the combustion chamber (near the end of the compression, i.e. way after all ports are closed), the unburned fuel in the exhaust is no more than in the 4-stroke Diesels.
Without oil in the combustion chamber, and without unburned fuel in the exhaust, it can be greener than the 4-strokes.



As a Diesel, its exhaust gas temperature is way lower than the exhaust gas temperature of the conventional spark-ignition 2-strokes (actually, the exhaust gas temperature is lower than the exhaust gas temperature of the Diesels, too, because it completes the combustion earlier, milking more energy from the fuel).
This means substantially lower temperatures around the exhaust ports (i.e. wherein typically the scuffing starts).
This also means that the air cooling is more than adequate (at partial loads it actually needs not external cooling, at all, because the air that passes through the cylinder makes the job).

And with its 30%+ longer piston dwell at the combustion center, its revving limit – for efficient combustion of the Diesel fuel – is 30%+ higher (and similarly its power output).

According the theory, its BTE (brake thermal efficiency) is higher than the conventional Diesels and way higher than the spark ignition 2-strokes, reducing substantially the required quantity of fuel for a specific range of an Autogyro or a smal airplane.


The PatOP is a highly unconventional engine.


Only one prototype has been made.

The casing is from billet aluminum 7000 (we started with 54Kg to end up with less than 10Kg), the crankshaft and the connecting rods are from Orvar Supreme steel.



Excluding:
1. the high pressure fuel pump and the injector (they are from a cheap Chinese electric power generator set),
2. the piston rings (they are from a VW TDi),
3. the plain bearings of the con-rods big-ends (they are from a BMW 1600cc),
everything else is handmade.


It seems the theory behind the PatOP project was so good / correct, that everything worked fine in practice from the beginning.

Thanks
Manolis Pattakos

[uniflow]

So this engine is flying? how many hours? what HP, sustained. Runs a particle filter? As all diesels must now.
What rpm. Dyno curves? Do you have a video of this one flying?
I would very much like to see it under sustained full load for, say an hour. At what output? Come on, some real, independent numbers please. What BMEP,

I don't consider my developments a success until they are out in the real world, doing the bussiness, I make no claims until then.
Difference is I'm not selling something I guess.

[manolis]

Hello Uniflow.


You have manufactured a conventional two-stroke engine:



that has, so far, 15 hours trouble-free-operation (http://rg500delta.com/fantastic_project ... togyro.pdf) .

Congratulations. I mean it. Only few people are skilled enough to complete such a project.

The reasoning behind your project: “build and fly your own engine”.



The PatOP project is different.

It is a completely unconventional engine that brings several innovations, like:

• more time for efficient combustion,
  connecting rods loaded in tension,
  short crosshead architecture,
  built in piston-type scavenge-ump,
  four-stroke-like lubrication,
  full vibration free,
  thrust loads away from the cylinder liner ports.

The reasoning behind the PatOP prototype was to demonstrate all these new characteristics, not to “built and run an engine”



As for its reliability,
what makes you think that it can’t complete 15 hours of trouble-free heavy-load operation?

Thanks
Manolis Pattakos

[Rodak]

I am not convinced manolis' reverse attitude for deceleration is possible. but if that attitude could be achieved during high forward speed I wonder if the helicopter phenomenon 'vortex ring state' might occur. The conditions of flight look very similar.
https://www.thehelicopterstudyguide.com ... ing-state/

A vortex ring state is when the helicopter’s downwash recirculates into the induced flow and the helicopter descends while under power.
A vortex ring state is a very dangerous situation but can be avoided. The condition occurs when the vortices from the blade tips recirculate into the induced flow of the rotor. For this to occur, there are several conditions that must be present:

1) The helicopter must be under power, generating lift
2) The helicopter must be descending at least 300 feet per minute
3) The helicopter must be below effective translational lift (ETL)

[uniflow]

well then manolis, fire it up, lets see it run 15 hours under flying load.
I dont see a reply with actual HP, rpm, BMEP yet.

[uniflow]

Any old bugger can cast their own at home. Foundry by Heath and Robinson, but good enough. Cast in LM13, thermally stable and nikasil sticks real well to its surface.

[uniflow]

Once again, seen here earlier, an OP Uniflow scavenge technolagy demonstrator but this one actualy did many hours under full load.
Loads of new fearures internally. I don't crow about theoreticly how well this engine might perform, I demonstrate it.

[uniflow]

Out in the real world, first and second time under load. Full throttle at approx 5,30 min, timing and jetting only estimated at this point. As I said earlier with no actual outside interest I went on to other projects, TPI for example, a whole another story.

[uniflow]

I know Im repeating myself here but I am trying to make a point.
My new uniflow engine is fitted into a YZ250F frame, it will be out doing trail rides, or if not, its a failure. These days I even have an engine dyno so I can show real outputs, power revs, fuel burn amongst other stuff.