2 stroke thread (with occasional F1 relevance!)

[uniflow]

Manolis, you may be in for a surprise. EFI in a twostroke is not as straight forward as you might think. I would allow quite a bit of development time on this part of the project.

if it is injected in the cranks case should be more or less equivalent to an "electronic carburetor"

direct injection is whole nother kettle of fish ..

Have you tried it? There are many people that are trying to inject into the inlet / crank case but results are always less than perfect. I know why, I've done it, not just talked about it. There is a problem with fuel distribution. With a carb, every atom of air is mixed with the right amout of fuel ( approx ) but with EFI fuel mixture is by injector on time so at low rpm for example injector on time is very short, you get a pocket of fuel amoungst a crank case full of air. How do you guarantee that this pocket of fuel is going to enter the cylinder every cycle, it doesn't. What happens over a few cycles is the combustion chamber " sees " lean, lean, lean then rich, remember the crank case is not a 100% pump so doesn't completly full and empty every cycle. I have found the only way is to inject into the transfer ports at transfer but time becomes limited. There is the problem, depending on rpm required and tricky injector blending ( number of and type ).

[J.A.W.]

Quite right U, & there is also the matter of redesigning the cooling system to compensate for the absence
of latent heat of vapourisation cooling from carburettor fuel air mixture - in the crankcase..

[manolis]

Hello Uniflow.

We need the oil (premixed with the fuel) to lubricate the moving parts into the crankcase, i.e. we do not want to inject just before the transfer ports.

The thought is to inject against the incoming air, just after the intake ports.

The PatATi Opposed Piston for the Portable Flyer is not to work at low idling or at partial loads (and transient conditions).
It is to run between 3,500 and 5,000 rpm at heavy load.

Thanks
Manolis Pattakos

[uniflow]

Hello Uniflow.

We need the oil (premixed with the fuel) to lubricate the moving parts into the crankcase, i.e. we do not want to inject just before the transfer ports.

The thought is to inject against the incoming air, just after the intake ports.

The PatATi Opposed Piston for the Portable Flyer is not to work at low idling or at partial loads (and transient conditions).
It is to run between 3,500 and 5,000 rpm at heavy load.

Thanks
Manolis Pattakos

Have you seen my earlier post showing the YZ250 I fuel injected, see where the injectors are, see where they are pointing. I was worried about bigend oil too but ( oil is in the fuel ) the crank case stays oil moist and the bigend has been in for over two years now, still racing. My 350 Kawasaki is similar only it injects across the top of the crankshaft from the rear ( rotory disc valve engine, no reeds in the way ). The Kawasaki injects only at transfer time also, this engine has been running even longer, three years now, never had a bigend fail yet. No separate oiler. So there is more going on in the crank case than you might think, there is more to a twostroke than meets the eye.

[J.A.W.]

Usage does matter, as this production road-going Kawasaki - which was modified for F750 racing - shows..

http://www.3cyl.com/mraxl/manuals/h2r/h2rservice.pdf

Kawasaki retained the oil-pump - which meters oil to the crankshaft, but set it at a fixed rate rather than
via throttle opening controlled variable rate - as on the road machine.

Premix oil/fuel was also added with a rich pilot mixture & carb throttle slide cut-away - to prevent partial
piston seizure events on hot, closed throttle high-rpm down shifts - under race conditions.

It was still needful to run NGK sparkplugs up to 10.5 (cold) range in this air-cooled mill..

[autogyro]

3500 rpm to 5000 rpm is too high without reduction gearing to the props.
5000 rpm will exceed usable tip speed on such small props if driven directly.
On our three feet diameter props 4000 rpm is the maximum and the dual props on this device would be much smaller.
The power to achieve VTOL at this prop size will be very high and very noisy at all times in flight.

[J.A.W.]

A-G, d'ya reckon.. that Manolis might well've - done his sums/had 'em checked - on those matters - already?

[autogyro]

The Wallis W116 had four stroke engine of 60hp directly driving a three foot diameter prop at a maximum of 4000rpm.
Above 4000rpm the prop exceeded its usable tip speed.
This aircraft achieved a number of world records using this specification and was used in many roles in actual service.

I will let the readers draw their own conclusions J.A.W.

The main reason we did not like two stroke engines like the rotax was because they were too high revving and needed a reduction gear box adding weight, vibration and complexity.
It compared well to driving a car or bike stuck in low gear.
The best engine we used was the Subaru flat four water cooled unit.
This allowed for a heated pilot nacelle for flying at heights over 20,000 feet, less engine noise and better reliability.
Prodrive were prepared to help us build the ideal unit based on the group N rally car engine with suitable camshafts for turbocharging for altitude use and reversed heads for updraft intakes suitable for packaging in the airframe.
Subaru stopped the development.
An autonomous pilot less version of this aircraft would be superior to almost all current medium sized drones.

[manolis]

Hello Autogyro.

You write:
“3500 rpm to 5000 rpm is too high without reduction gearing to the props.
5000 rpm will exceed usable tip speed on such small props if driven directly.
On our three feet diameter props 4000 rpm is the maximum and the dual props on this device would be much smaller.
The power to achieve VTOL at this prop size will be very high and very noisy at all times in flight.”

With 1m diameter propellers (as in the PatATi Portable Flyer prototype), the tip speed at 5,000rpm is only:

pi*1*5000*60 = 942Km/h = M0,76

At such tip speed the propellers are near their optimum efficiency.

Besides, driving the propellers directly by the crankshafts, there is no transmission. The related with the transmission friction, weight, complication, cost are eliminated.


The power required to achieve VTOL with a pair of 1m diameter propellers is well below 50bhp in case of small pitch. The lower the pitch, the smaller the required power.

But what you really need is more than just VTOL.
After the take-off you need high pitch in order to fly horizontally at high speeds (like an airplane) and fuel efficiently.

So you have to compromise with the pitch (if it is not variable).
If the pitch is too big, you cannot VTOL (i.e. the static thrust cannot exceed the total weight of the Portable Flyer, including the pilot and the fuel)) with the available power of the engine,
if the pitch is too small, you cannot fly at high speeds.

So give another look at the PatATi Portable Flyer.
It is neither a gyroplane, nor a helicopter.
You can think of it as a scaled-down Osprey V22, i.e. as an airplane capable for VTOL.

Regarding the “capable for VTOL”, think:
If the high-speed horizontal flight covers the 99% of the total time, it doesn’t matter the efficiency and the noise at the remaining 1% of the time (i.e. during the vertical take-off and the vertical landing).

While it is not necessary, even if you had to operate the 1m propellers at 6,000 rpm (M0.92) for a few seconds at take-off, it would still be OK.

Thanks
Manolis Pattakos

[J.A.W.]

Manolis, the sound level may need to meet some municipal transport mechanical noise level limit..
..depending on which category - your flyer - is deemed to be subject to the provisions of..

& perhaps some air filtration system is needed - if/when operating in a foreign object (dusty) environment?

[gruntguru]

I am sure Manolis is concentrating on getting it off the ground first.

[J.A.W.]

He might have to get off the grass 1st.. ..in case he needs to turf it..

Has he done any flight control practice using a safely water launched/tethered water pump powered unit?

[uniflow]

The main reason we did not like two stroke engines like the rotax was because they were too high revving and needed a reduction gear box adding weight, vibration and complexity.

AG, Usually those who "bag" twostrokes are the same one's that don't know how they work.
Come on, the whole world is wrong and only you and Commander Wallis are right? You need to have a serious look at the modern world. Twostrokes have come a long way since YOU decided they where wrong to power aircraft.

I would say the best Fourstroke microlight avaiation engine would have to be the four cylinder Rotax, by far the most sold world wide and by the way they are geared drive. Not just me that says this, almost the whole homebuilt aviation industry. Not a lot of two cylinder direct drive fourstroke out there that would come close to a Rotax, two or fourstroke. Imagine the records Commander Wallis could have broken with a Rotax aviation engine.( I'm not a Rotax salesman by the way )

[autogyro]

The main reason we did not like two stroke engines like the rotax was because they were too high revving and needed a reduction gear box adding weight, vibration and complexity.

AG, Usually those who "bag" twostrokes are the same one's that don't know how they work.
Come on, the whole world is wrong and only you and Commander Wallis are right? You need to have a serious look at the modern world. Twostrokes have come a long way since YOU decided they where wrong to power aircraft.

I would say the best Fourstroke microlight avaiation engine would have to be the four cylinder Rotax, by far the most sold world wide and by the way they are geared drive. Not just me that says this, almost the whole homebuilt aviation industry. Not a lot of two cylinder direct drive fourstroke out there that would come close to a Rotax, two or fourstroke. Imagine the records Commander Wallis could have broken with a Rotax aviation engine.( I'm not a Rotax salesman by the way )

Two stroke performance engines like the rotax work OK in light fun flying machines and in some autonomous drones with a sacrifice in reliability.
The W116 was never a 'fun' aviation project.
It was and still is a fully proven and working aviation system.

The reason the rotax is chosen for most home build and fun aircraft is simply because there are no better engines available.
Most production light aircraft still use engine designs that originated in the late 1930s.
This is because the CAA and other regulating bodies make it hugely expensive to develop engines for light aircraft unless the type will be flown solely on a permit to fly and not a full C of A restricting sales and regulating use.
The main reason this problem still limits the development of modern light aircraft piston engines is because the car manufacturers dominate engines of this potential type and are not prepared to allow development of their engines for aircraft use, they will not risk their reputations in the event of accidents which are common in light home builds and fun aircraft.
I have attended a number of such fatal crashes with Ken Wallis who was the official crash investigator for autogyros.
Considering the CAAs demands for over four million for Ken to develop a definition for autogyros in the UK, somewhat of a hypocritical position to force him into by the CAA.

I do not say that a two stroke engine cannot be developed for 'proper' regulated light aviation, the rotax has come close and there are other engines with potential.
Manolis should look into the problems of high revs for practical flying use though, short hops in a strap on device does not really compare and neither do hang gliders and most light autogyro designs with little payload and restricted operational capability.
The W116 is fundamentally different to other types, not in the engine used, we have tried at least a dozen different types but in the airframe and flight system which I am NOT going to give details of.
Check out the world records on 60hp if you dont believe me.

[J.A.W.]

Here is an example of a current flight developed 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..

Edit: legal CAA -type "certification" is a fraught national issue AFAIK..