2 stroke thread (with occasional F1 relevance!)

[autogyro]

Here is an example of a current flight certified 2-stroke.. http://www.hirth-motoren.de/en/engine-3702.html

~1 litre triple, weighs 45kg, torque 121 Nm @ 4850rpm , 1000hour TBO.. ..not too shabby..

So you are telling me that I can use this engine in a certified airframe and receive a FULL certificate of aviation?

[uniflow]

AG, you telling us that your one off, home brewed two cylinder was certified by CAA?

[J.A.W.]

A-G, why do you imagine that anyone here would be interested in a discussion of CAA rules & regs for the UK?
If you read Hirth's attached technical data - they make their liability position on that issue plain..

I have however - posted an example which demonstrates what is currently commercially available, 2-stroke wise..
& quite evidently - it is designed & manufactured with the intention of powering practicable flying machines..

It shows a pretty workman-like torque curve on the supplied dyno chart,
& is evidently satisfactorily robust for doing rigorous duty..

[manolis]

Hello J.A.W.

The Hirth 3702 E/V 2-stroke you mention has 939cc capacity and provides, according the data sheet, 84H at 4,950rpm and 121Nm or torque at 4,850 (carbureted or injected).

In analogy, the PatATi Opposed Piston 800cc engine of the Portable Flyer can provide:
121Nm*(800/935) = 103.5Nm of torque.
With 103.5Nm torque at 4,750rpm you get 70HP.

The mean piston speed of the triple Hirth, at peak power revs, is:
0.069*2*4,950/60 = 11.4m/sec
The mean piston speed of the PatATi Opposed Piston, at 4,750rpm, is:
0.08*2*4,750/60 = 12.7m/sec (11% higher, but still low).

It seems the PatATi OP 800cc can provide reliably 70HP of power.
You don’t need more than 70HP on your shoulder in order to take-off.
You don’t need more than 70HP in order to fly horizontally at, say, 250Km/h (150mph).

In a Portable Flyer you need more than plenty of power. You need "a true neutral propulsion unit", like the PatATi: neither vibrations, nor reaction torque, nor gyroscopic rigidity; only a force that can "instantly" and effortlessly be vectored towards the desirable direction.

In comparison the power to weight ratio of the Hirth 3702 E/V 2-stroke is not good enough. The Hirth triple is also anything but a “neutral propulsion unit”.

Thanks
Manolis Pattakos

[manolis]

Hello Uniflow

If it is not secret, what kind of injection and control you use in your YZ250 and Kawasaki 350 engines?

Thanks
Manolis Pattakos

[manolis]

Hello Autogyro

It is wrong to compare everything with your “great”, but secret, project.
Think why.

It would also be better to have specific technical objections / arguments to specific claims. For instance, what is – according your calculations - the minimum required power in order, with a pair of 1m diameter counter-rotating propellers, to take-off vertically 100Kp (220lb).



This rotary engine:



(we call it PatRE rotary engine, more details at http://www.pattakon.com/pattakonRotary.htm )

is a true four-stroke as regards its breathing (just like the Wankel rotary engine),

it is also a two-stroke as regards its lubrication (just like the Wankel rotary), so it fits with the title of this thread.


Quote from http://www.pattakon.com/pattakonKeyAdv.htm#rotary

“The Wankel rotary engine features the freest breathing, being rid of camshafts, valves, springs etc. The PatRE rotary engine features as free breathing as the Wankel rotary engine, being also rid of camshafts, valves, springs etc.

The attenuated combustion chamber and the poor sealing have been, and still are, Wankel's Achilles' heel, causing way lower thermal efficiency than conventional. This rotary engine has not the sealing problems of the Wankel rotary: its "piston rings" - more than one if desirable - keep "surface contact" with the toroidal "cylinder", while Wankel's rotor apex seals - inevitably one only per rotor apex - keep poor "line contact" with the epitrochoid. It is also the shape of the combustion chamber of the PatRE rotary engine: it is as compact as the combustion chamber of the conventional reciprocating engine. The good sealing, the compact combustion chamber and the low friction enable comparable to the conventional, if not better, thermal efficiency.

The two-rotor Wankel rotary engine completes two combustions per power shaft rotation, while the PatRE rotary engine completes four combustions per power shaft rotation (one per chamber).

The Wankel rotary engine needs a pair of gear wheels to synchronize the motion of the rotor with the power shaft, it also needs counterbalancing weights on the power shaft. The PatRE rotary engine needs neither gear wheels nor counterbalancing webs.

For equal "expansion cycle" (or power stroke) duration (i.e. time in seconds), the power shaft of the Wankel rotates three times faster, while the crankshaft of the conventional rotates two times faster than the power shaft of the PatRE rotary engine.
This built-in revs reduction is beneficial in many applications. For instance when a propeller of an airplane is driven directly by the power shaft.”

Thanks
Manolis Pattakos

[uniflow]

Hello Uniflow

If it is not secret, what kind of injection and control you use in your YZ250 and Kawasaki 350 engines?

Thanks
Manolis Pattakos

No secrets, I use the New Zealand made Link Electro Systems ECU. I am using the ATOM at the moment but will need to upgrade to the EXTREEM for the next project. Excelant service, resonable pricing.

Finally, an elegent design Manolis. I too have an intermeshing prop like you show, designed to run off the front of my Uniflow engine but for propulsion not lift. Each two blade prop is 12 degrees inclined awway from the centre and at 90 degrees rotation to each other ( like an Kaman helicopter ). The uniflow needs gears to join the cranks so I thought I would have two idler gears angled appart. No torque reation and a more efficent bite on the air. But it's not made sadly, just an idea ( and a pattern ).

[J.A.W.]

Manolis, I was by no means intending to compare/show your pioneering designs as being conceptually
inferior to current commercially available 2-stroke designs - as available for flight applications.

It is a matter for which you are due significant kudos, by any reasonable standards..
& the same applies to Uniflow too, of course..

FYI though, that Hirth triple previously posted is a de-rated unit, there is a 100hp version available too.
& if you don't like triples..

(.. albeit -they do offer smooth inertia torque/even firing characteristics,
& the inherent rocking couple issue - is quite mild in such softly tuned/low rpm examples..)

Hirth do also have a 100hp/42kg H-4..

[manolis]

Hello

J.A.W, the link for the Hirth 3702 was quite useful, thanks: it allowed some simple calculations regarding the PatATi power and torque.

Besides, the 1,000 hours recommended TBO at 75% load show that the Hirth 3702 is oriented to reliability and not to performance.
Am I wrong to suppose that the reed valves are replaced every 1,000 hours?
And that there is a lot of noise from the reed valves?

In comparison, for the state-of-the-art 4-stroke Rotax-912 it is recommended 2,000 hours TBO.


Regarding the PatRE rotary engine (GIF animation in previous post):

Suppose it is a 500cc engine.
This means that the capacity of every chamber is 125cc.
PatRE’s expected weight is, reasonably, no more than 10Kp (22lb) for 500cc.
If each propeller has 1m diameter, then at 5,000 rpm the propeller tip speed is M0.76, still not big.

Here are a few calculations about the expected power of the PatRE 500cc.

At 5,000 rpm there are 4*5,000 combustions, each one being related with 125cc of air at atmospheric pressure, i.e. the PatRE “burns” per minute 4*5,000*0.125*0.00128 = 3.2Kg (7lb) of air (and 215gr of gasoline if it runs stoichiometric).

In comparison, in a conventional four-cylinder 4-stroke 1,000cc engine, at 5,000 rpm there are 2*5,000 combustions, with each combustion related with 250cc of air at atmospheric pressure, i.e. the 1,000cc conventional engine “burns” per minute 2*5,000*0,250*0.00128 = 3.2 Kg(7lb) of air (and 215gr of gasoline if it runs stoichiometric).

That is, a 500cc PatRE and a conventional four-stroke 1,000cc give the same power at the same revs.

For a free breathing 1,000cc 4-stroke, a reasonable torque is 10mKp (98Nm, 72lb*ft). This makes the expected power provided by the 500cc PatRE at 5,000rpm, 70bhp.

Do I miss something?

Thanks
Manolis Pattakos

[J.A.W.]

TBO is generally governed by specific output/tune parameters Manolis..
I 'd reckon the 4-stroke Rotax is subject to this rule too..
Labouring under 4-stroke mass & BMEP power density issues, & trading off lazy output for longer TBO..
Current 4-stroke MX mills are much more highly stressed & accordingly - TBO limited.

Reed valves actually reduce sound levels from the induction tract,
since they are 'soft' responding, unlike sharp snappy disc valve & reversion
prone piston port gas column pulses..

Here Kevin Cameron considers TBO factors..
http://www.cycleworld.com/2014/05/23/en ... n-cameron/

[autogyro]

AG, you telling us that your one off, home brewed two cylinder was certified by CAA?

Yes, the original W116 was the ONLY light autogyro ever to be awarded a full C of A by the old Ministry of Aviation and even that was subject to engine type.

As far as I am aware NO light autogyro has a full C of A currently in the UK.
Ken Wallis suggested that all such aircraft be grounded until the CAA produced a definition of autogyro flight which currently does not exist at the CAA.

Modern light autogyros fly on 'permits to fly' which is one stage removed from untried prototype.
This will remain the case unless the CAA decides it is of benefit to them to find out how an autogyro works.

So you see NO engine can be fully flight certified in the UK for light autogyro use.

[autogyro]

...

I only deal with VTOL as a side issue to flight Manolis.
Autogyros do not need to take off vertically in their standard flight configuration.
ANY system designed for VTOL and sustained powered rotary winged flight, using small diameter props or turbines will require a level of power that will not result in a worthwhile or safe tasking capability for the machine so fitted.
It is not possible to sustain 'safe' autorotation, either for main flight dynamics or for safety requirements using small diameter powered props/rotors for lift.
The Osprey has a compromise on rotor diameter but is still a potential 'death trap' in most mechanical failures as is the Chinook to a lesser degree because of the less complex gearing.
The F35B Lockheed cash cow can only operate 9 times using VTOL because of the need to replace the front turbine after this number. The front turbine is under huge load because it drives the forward lift fan mechanically.
The chances of failure are much much higher than for the Harrier which was way lighter and simpler in concept.
Expect a number of fatal crashes from the type if it ever enters service.

Manolis, I see you have worked out that the maximum usable direct shaft rpm for a small prop drive is 4000.
Less is even better check out the reduction drives on WW2 fighter aircraft with larger and slower tip speed props.
Of course small props will work at higher revs but not very well.
The problem with reduction gearing for high revving engines used in aviation is the vibration problems at low (tick over) rpm. If just gearing is used the unit will shake itself to pieces.
It is of course possible to fit balance and shock systems in the gear train similar to those used by Cosworth on the DFV and later engines for the cam problems. However this results in over complexity and unacceptable increases in weight.
I have found horizontally opposed four strokes the best for direct drive (below 4000 rpm) use.
We have tried Wankel engines, Norton gave us two and various engines made specifically for our use from companies like Weslake and Hewland. The aviation modified VW flat four and the Porsche variants work well but are far to heavy.
The best engine tried was the Subaru flat four with modified cams for low rpm and turbo charging, direct drive.
Many modern kit aircraft use this engine with a reduction box which I disagree with.

Non of the above is a comparison with any 'secret' project I may be involved in.
Electric motors driving props have an advantage because they can be configured to deliver high torque to the prop at low rpm. This allows for a better design of prop with a higher performance.
Just a little hint at my 'great' project.

http://books.google.co.uk/books?id=dk47 ... pt&f=false

Worth a read.
The Wallis W116 was part of this development program at both Hayes and Boscombe Down.
Hardly a backyard built kit eh J.A.W

[J.A.W.]

Indeed, A-G & sadly - the Rotodyne was..
.. yet another case in the sorry litany of British defeats snatched from the jaws of victory..

Here's a bit about what kinds of things contributed.. http://www.cycleworld.com/2011/07/21/ask-cw-anything/

& back to topic, here is another recent re-look at sleeve valve type operation for 2-strokes..

http://www.wolfhartindustries.com/engine.htm

[gruntguru]

ANY system designed for VTOL and sustained powered rotary winged flight, using small diameter props or turbines will require a level of power that will not result in a worthwhile or safe tasking capability for the machine so fitted.

This describes every personal VTOL machine whether rocket or fan in principle. Perhaps you should advise the US Army, Bell, NASA, Martin etc that the function they are seeking is not worthwhile.

[manolis]

Hello Autogyro.

For a couple of minutes forget the gyroplanes and enjoy this



youtube video at https://m.youtube.com/watch?v=E81KQ7u3-7s .

It shows the most impressive – and the most useless at the same time – flying machine.



Quote from the Internet for the peroxide JetPack (or Bell Rocket Belt):

“The pack with its fuel weighed 125 lb (57 kg).”

“On 17 February 1961, the pack veered sharply, reaching the end of the safety tether, which then broke, causing the Moore (remark: he is the inventor of the JetPack) to fall approximately 2.5 meters, breaking his kneecap. He could no longer fly. Engineer Harold Graham took over as test pilot and testing resumed on 1 March. He then carried out 36 more tethered tests which enabled them to achieve stable control of the pack”

“On June 8, 1961, Harold Graham demonstrated Bell's "portable Army rocket" for the first time to an incredulous public. The flight saw Graham fly over a truck at a height of 15 feet landing 150 feet away after 14 seconds of air time. Nevertheless, the "ear-splitting" flight was described by the New York Times as "short but spectacular." By December 1961 Bell's 100-pound rocket belt would carry a man as high as 35 feet or a distance of 368 feet when barely skimming the ground.”



“In the course of testing maximums of duration and distance were achieved: duration 21 seconds; range 120 m; height 10 m; speed, 55 km/h.”

“Before the flight the timer is set for 21 seconds. When the pilot turns the handle for the takeoff, the timer begins counting and will give second-by-second signals to a buzzer in the pilot's helmet. In 15 seconds the signal becomes continuous, telling the pilot that it is time to land.”

“The pack's pilot wears protective overalls made of thermal resistant material, since the exhaust jet and the engine's pipes are very hot.”

“However, the army was disappointed. The maximum duration of flight of the rocket pack was 21 seconds, with a range of only 120 m. A large contingent of service personnel needed to accompany the rocket pack. During flight 5 U.S. gallons (19 liters) of hydrogen peroxide was expended.
In the opinion of the military, the "Bell Rocket Belt" was more a spectacular toy than an effective means of transport.”

End of quote


Think how much the world could change if the peroxide JetPack was capable to fly for two hours on cheap fuel, even if it was too noisy (as it is), even if it had no autorotation.


And now think again of the PatATi Portable Flyer as the evolution of the JetPack.

Both are:
vibration-free,
“reaction torque” free,
rid of gyroscopic rigidity,
based on a force that can "instantly" and effortlessly be vectored towards the desirable direction,
based on a pure manual control wherein the eyes, the brain and the body of the rider are the sensing and controlling mechanisms.

On the other hand the PatATi Portable Flyer:
has a several times smaller weight than the JetPack, making it true portable,
can fly for hours, while a JetPack can fly at most for less than half a minute,
etc.


Now imagine a wingsuiter:



with the PatATi Portable Flyer secured on his shoulders, flying horizontally at 250Km/h (150mph), or making acrobatics on the air, or participating in the Red Bull Air Race.

Thanks
Manolis Pattakos