Future small aircraft engines.Wich way?

[Niels Abildgaard]

The Pipistrel aircraft from Slovenia with a 80 hp Rotax 912 engine did very well in a CAFE test some Years ago.
Propeller was 1.6 m diameter and turned 40 rev per second giving a tip speed of 200 m per second.This gives an acceptable flyover noise.
American engines/props/aircrafts run 270 meter per second .Noise is not acceptable and is the reason/excuse why most hobby airports in Europe are closing.
I have been dreaming of an opposed piston twin prop scheme since 1988 and still believe it is the rigth way,but a single prop driven by an inverted V2 two stroke is maybe smarter,and at least much more acceptable to old know it alls.Me for one.Let us play that You had some money and wanted to invest it in the shining future of personal aircrafts.
We have already lost ground contact here.
The twin scheme can be seen to a certain extent here

http://archive.today/zHnXJ
and http://archive.today/s7gTY

and the picture shows a V2 twostroke with a 1.6 meter prop superimposed on a twin 1.2 meter prop scheme.
Both will do the same job as the Rotax 912 and be ligther and more fuel efficient.
Noise will be the same.

 

[lohring]

There is a world of two stroke enthusiasts mostly centered on motorcycle and kart racing with a few outboard and jet ski racers as well. A modern two stroke is being developed by Eco Motors. For high output you probably need to gear down the propeller and use water cooling. Even so, the power of most road engines would need to be seriously reduced for reliability. Aftermarket cylinders are available through CP Industries and have been used to power a V4 fan engine. Rotax already makes a two cylinder two stroke aircraft engine. Starting from scratch is going to be very hard. Marco also from Slovenia is a dedicated two stroke enthusiast who might be able to help. He casts his own cylinders, builds pipes, and generally knows his way around two strokes.

Lohring Miller

 

[Niels Abildgaard]

My guiding philosophy is that small aircraft engines shall have few and non geared cylinders.Teledyne Continental and Porsche tried to market six-cylinder geared aviation engines and fell flatt on their nose.The first real succesfull geared four-cylinder is Rotax 912 so this will be my yardstick.

My east german MZ bike ran nearly 1000 hours at a mean effective pressure of 6 to 7 bar until wife got ill and me to old.It could probably have done 1000 more.Maybe two new crankshaft seals.
One spark plug and no decarbonisation.
Modern two stroke oils are miracles.

Two 1.2 meter props 0.85 meter apart doing 40 rps will make much less noise than a standard Rotax 1.6meter installation. and we accept that for first experiment.

The Junkers single cylinder ,twin prop scheme shall have a 105 mm cylinder and two pistons doing 160 mm strokes.The mental process has to start somewhere and this is the dimensions of the JuMo 205 engine.

2.8 littre two stroke engine making 80 horsepower at 40 rps work at a mean effective pressure of 5.4 bar and a mean piston speed of 12.8 m per second.
An eternity machine.

The BMW IIIa engine of WW1 was 15 kg per littre mass,ran at a higher mean effective pressure and used 185 gram gas per horsepowerhour.

If I found such an engine and could be cruel enough,I could make three Junkers engines and still throw cylinderheads,valves and camshaft away to save weigth.

It is therefore not unrealistic to say that my 2014 Junkers 80 horsepowerscheme will be under 50 kg.Beat that Rotax.

 

[Till]

This is a pipe dream. It will be expensive to develop and to purchase because of the small lot size. Plus engines with hot exhaust gasses passing hot, well lubricated parts such as piston rings will never meet emission standards.

If there’s is any future for new small aircraft in the current hellfire of American court decisions, it belongs to rather smallish, liquid cooled, turbo-charged fourstroke engines with low compression ratio and high boost derived cost efficiently from new European-style automotive engines to drive geared props.
Driven by upcoming European CO2 regulations, this type of engine has evolved very quickly over the recent years, having archived very high standards one couldn’t even imagine 20 years ago.
Just wait a few more years and well proven engines from mass production will be available in large scale at very competitive pricing. The key is to adapt one of these with keping as many parts from mass production as possible.

My guiding philosophy is that small aircraft engines shall have few and non geared cylinders.Teledyne Continental and Porsche tried to market six-cylinder geared aviation engines and fell flatt on their nose.

Well from today's point of view these came straight from the dark ages of knowledge, manufacturing techniques and materials.

 

[lohring]

The last really serious two stroke aircraft engine development effort was the Rolls Royce Crecy. An interesting account of its development is in Harry Ricardo's The High Speed Internal Combustion Engine. (Get the reprint at a reasonable cost.) The Napier Nomad was a too ambitious last gasp at combining piston engines and turbines for aircraft. Both failed as soon as pure gas turbines advanced. I thought in my college days that a small three cylinder version of the Crecy design might make a good substitute for the flat six four strokes in the day's (1961) private planes. That market is very small and never supported much new engine development after the 1950s. Except for kit planes it's dead today. Automobile engines are now the most advanced small piston engines. BRP is about the only manufacturer pursuing advanced two strokes bigger than scooter engines.

Lohring Miller

 

[Niels Abildgaard]

Hello Till and Lohring

My hope is of course that someone here will want to make useless models of possible future aircraft engines rather than useless small fourstroke engines that was obsolete even then way back in time.
It is only a pipe dream.
Where environmentalist/lawyers rule ,small aircrafts have no place ,and that is the future scene in USA.
There are a lot of other places where small personal aircrafts with modern electronics is way smarter than cars.
Africa,Australia and Iceland spring to mind.
Uncatalysed two strokes are not dirtyer than fourstrokes if fuel injected and that is a must thing to get range.
The idea of using cheap car engines and propellor gears have a long and unhonorable track record.
Future downsized turboed car engines will be two and three cylindered and they will need a lot of flywhell mass on crankshaft to avoid torsional vibrations.
If aircraft flyover noise shall be reduced, propeller tip speed has to be lowered further than the ca 200 meter per second Rotaxed aircrafts run to day.
If we keep the prop rpm and reduce prop diameter propulsive efficiency go down.If we reduce prop rpm,reaction torque goes up and is already unpleasant and downright dangerous on Cessna 172 as is.
How do I know?
That is the reason the Wrigth brothers,smart as they were,used two opposite turning props.
It will be very beneficial to have a sparkplug central in the oilcooled exhaust side piston and I do not have a good scheme for that.

 

[Niels Abildgaard]

The picture shows my fall back option if the Junkers thing is no good.
The german Argus 10C engine was 15 kg per litre and ran at 8.5 bar mean effective pressure.My Rotax 912 Erzatz will be 2 (92 mm bore and 150 stroke) litre and run at 7.5 bar and a mean piston speed of 12 m per second.Engine mass can thus be less than 30 kg plus turbo and cooler.Not much.
Four cylinder fourstrokes has a reaction torque variation dominated by the second order composant and is basicly the difference You feel between a six and a fourcylinder engine.It is zero in a V2-90 degree two stroke.

 

[lohring]

I think a turbocharged two stroke would make a great small aircraft engine. Two strokes don't mind back pressure like a four stroke and have a low exhaust temperature due to the excess air needed for scavenging. The snow mobile racers have built some really impressive turbocharged engines, but a much simpler solution would be better for your purposes. See the picture below of an 800 hp nitrous injection turbocharged four cylinder engine. The Eco Motors engines are the latest versions of the Junkers uniflow system. See the second picture. They have an electric turbocharger that's probably their most interesting innovation.

The simple crankcase scavenged V twin would have enough of a crankcase pump for starting while the turbocharger would provide the air for cruising. The variable inlet vane turbochargers would provide the variable boost needed to compensate for altitude as well as extra power for takeoff. There are lots of air cooled motorcycle cylinders available to attach to a custom crankshaft and crankcase. You would need 3000 to 4000 cc for 100 hp at 2400 rpm, though. It would take a lot of detail development.

An alternative would be one of the water cooled V-6 outboard power heads. The latest of those are direct injection with sophisticated engine management computers. Reprogramming it to account for a turbocharger would be a relatively easy way to develop a fairly powerful 2,400 rpm, 100 hp (derated from the advertised power) engine. The water cooling would be a negative factor, though.

Neels van Niekerk's latest version of his two stroke simulation program accommodates turbochargers. I've used this for tuned pipe development and it's a great version of Gordon Blair's simulation work. This is the low cost place to start engine development. For hardware testing you need some kind of brake (a propeller and a tach) or a brake type dyno. There are old Stuska water brakes that show up from time to time. I have a lot of experience testing engines with an inertial dyno, but a brake dyno would work better for the constant load testing you would need.

lohring Miller

 

[Niels Abildgaard]

I gave my flying licence back many years ago and harbour no wish any longer to be rich and famous.
Much to old and tired for that.
What still interest me is which of these two schemes will be best for future two seat aircrafts.
I was not impressed by the engines of Cessna 152 aircrafts.
Vibrating and had to be treated with care to avoid cylinder damage at shock cooling etc.The lead solution as fuel is downrigth criminal to my view.
I have tried to make parts for a pair of very conventional pressed up two stroke crankshafts and could not.They wobled wildly.
It is not really nessecary to make running combustion engines for finding the answer to my question.
A Junkers and a V2 airdriven models,let us say 20 mm bore and 30 mm stroke,is possible for me maybe.
They can be put on the end of a stick with a handle on the other end.A spherical bearing on midle of stick will make it safe to have hands on expirience and this is OK for me.

 

[Niels Abildgaard]

Hello Lohring
Thank You for the pictures.
I like the 800 hp snowmobile very much .
The ECO thing less so.
It is constructed to be a replacement for normal car-engines and for turning generators.
The car driving thing is very difficult where environmentalists rule ,using engines that have holes in the cylinder walls.
For making special case electricity my solution with an AC generator on each shaft is much smarter .

http://chevy57.free.fr/FORUM/junkers_two-stroke_crosshead.gif


Thank You also for the suggestion of using V4 or V6 outboard crankshaft cutoffs for making functional models of V2 engines.I had not thougth of that

 

[lohring]

Even though a friend of mine works for Eco Motors, I agree that it's a complicated solution. The simple Schnurle scavenged, crankcase pump two stroke with a tuned exhaust system puts out remarkable power in a very simple, light package. Walter Kaaden at [FONT=&quot]MZ (Motorradwerk Zschopau) [/FONT] managed to get 200 hp per liter from that type of engine in 1961 and by 2007 Aprilia was getting twice that from their 125 cc engine. These are racing engines with high rpm and short lives. A three cylinder engine can use the 120 degree piston spacing to get tuned effects without the bulky tuned pipe. The advantage aircraft engines have is constant rpm. That heavily favors intake and exhaust tuning. The simulation I mentioned above is great for studying those effects. If you add a turbocharger like the snowmobile engine above, you have a potential high power aircraft engine, even without reduction gearing.

It will still take a huge amount of development to make it viable. Orbital's injection system is successful on 50 cc scooter engines and along with the Etec system is a place to start with engine management. You also need to include oil injection in the engine management system. BRP has shown that its possible to have lower oil consumption than a four stroke. The mechanical layout is simple and has been done by model aircraft engine builders for a long time. You just take commercial cylinders and add them to a custom crankcase like this 100 cc engine that develops 100 hp per liter without a tuned exhaust. Motorcycle engine builders have the fixtures to build crankshafts. It just takes money. The mechanical solutions are well explored. The development needs to be in electronic engine management. Unfortunately, the market is too small to make it worthwhile, even for companies with an ongoing two stroke program.

Lohring Miller

 

[Niels Abildgaard]

The present idea for a Junkers Rotax 912 erzatz look like first picture.
I am not sure that bevel gears are nessecary.
Worlds best diesel engines (Danish design by the way) have chain drive between crank and cam.
The Wrigth brothers used two chains,straigthforward and crossed between motor and props and maybe a single crossed chain is best solution.
To try I have started to make next picture and third is a close up.
http://www.homemodelenginemachinist...ngle-cylinder-engines-machined-pressed-22522/
is a picture of first crank

Hope You like it and it will be a honnor to answer eventual questions.

 

[makoman1860]

Though I never try to discourage anyone in their ambitions, I see some things I would call serious flaws in your design. The first two are in the crankshaft area. The larger of the 2 main bearings is much to large in diameter to be able to spin any kind of RPM. Second the crankshaft is so short I would be concerned about the gyroscopic loading. The whole concept seems to defeat any kind of streamlining and just looks awkward. I do not discount the 2-stroke potential, especially an air assist DI system. However that is not something that is easily undertaken, few in the world know how to actually design and calibrate such a system.

 

[lohring]

I have no experience in full size engine design,however, I tend to agree that the large diameter bearing on the crankshaft is the wrong solution. In models with overhung crankshafts we use a large bearing next to the crankshaft with a smaller bearing spaced well down the crankshaft. Scale effects keep this arrangement stiff and reasonably light for small engines. I think it could be used for even 30cc size engines. The inexpensive weedeaters use overhung crankshafts, but these break when we modify them for twice their designed power. No one runs overhung crankshafts in larger engines. It just takes serious precision to build them.

What are you going to use to scavenge your engine? You can use both crankcases as a combined pump like ordinary crankcase scavenged engines. The volume is too low, though. An enlarged piston base or auxillary piston pump can solve this. DKW used a vane pump, but I like Eco Motors electric turbocharger the best. Again, I know how much work it took to develop that system.

An explanation of the advantages of the opposed piston engine (Eco Motors again) is here. Some DKW engine pictures below.

Lohring Miller

 

[Niels Abildgaard]

The 105 times 160 times 2 engine will need a turbocharger to supercharge the left hand roller bearing crankcase.Turbos are magnificent exhaust and intake noise reducers.
Crankcase pumping alone will enable start and idle.
The big diameter roller bearings are not very different from what two row radials have in middle and ceramic rollers allow three times more speed than needed.
The strange looking 40 times 60 times 2 single bearing crank is meant to be a non flying ,wiser getting engine.
It will be possible to try electrical , bevel gears or crossed chain synchronisation.

 

[makoman1860]

The 105 times 160 times 2 engine will need a turbocharger to supercharge the left hand roller bearing crankcase.Turbos are magnificent exhaust and intake noise reducers.
Crankcase pumping alone will enable start and idle.
The big diameter roller bearings are not very different from what two row radials have in middle and ceramic rollers allow three times more speed than needed.
The strange looking 40 times 60 times 2 single bearing crank is meant to be a non flying ,wiser getting engine.
It will be possible to try electrical , bevel gears or crossed chain synchronisation.

Crossed chain I feel is a bad idea, even a direct coupled system with gears will be difficult with the torsional harmonics. The crankpin design gives me worry as well. Getting an engine to run is one thing, getting it to live in a car or motorcycle is another. Getting it to live with an aviation or marine duty cycle is much much more difficult. Unfortunately with an opposed piston design, direct injection is pretty much out of the picture. Without direct injection, multi fuel capability is gone. Personally an inverted NA 60 deg V6 2-stroke with DI that is multi fuel capable with a rugged PSRU would be a much more viable option.

 

[Niels Abildgaard]

Jumo 205 diesel aircraft engines were direct injection and Fairbank Morse OP engines also.Diesel aircraft engines have up til now been dead ends.The 10 to 20 gram fuel advantage per horsepower hour is nullified by the greater engine mass unless flying more than ten hour missions.
Luftwaffe found one diesel advantage.Less burning when chrashing.

 

[makoman1860]

Jumo 205 diesel aircraft engines were direct injection and Fairbank Morse OP engines also.Diesel aircraft engines have up til now been dead ends.The 10 to 20 gram fuel advantage per horsepower hour is nullified by the greater engine mass unless flying more than ten hour missions.
Luftwaffe found one diesel advantage.Less burning when chrashing.

CI and DI/SI engines have completely different needs combustion chamber wise. I was speaking of DI spark ignition multi fuel engines, not CI "diesel".

 

[Niels Abildgaard]

CI and DI/SI engines have completely different needs combustion chamber wise. I was speaking of DI spark ignition multi fuel engines, not CI "diesel".

That is why it will be nice to have a spark plug central in each piston.
On the other hand Fairbank Morse engines run very well as DI/SI gas engines.
I do not really see the advantage of multifuel capability.

 

[lohring]

Your drawings show ball bearings on the crankshaft. I assume they will take thrust loads as well as radial loads, Your post mentions ceramic rollers. I'm not aware of ceramic roller bearing manufacturers. You will need a thrust bearing with them. All aircraft engines I know of use ball bearings for the thrust load.

Somewhere I have a drawing of a small Eco Motors engine that used a piston compressor on the base of the outer pistons. It had reed valves and they were troublesome. The Bernard Hooper engine uses stepped pistons. They might be a good solution for your engine as well, but you would need valving for a two cylinder version like your drawings. Turbochargers are the best solution especially for an aircraft engine. In Junkers' day they weren't as well developed and inexpensive or they would have used them. Larger diesel engines today are nearly all turbocharged. That gives big advantages in fuel consumption and power to weight,

Lohring Miller