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Old 06-01-2014, 04:17 PM   #1
Niels Abildgaard
 
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Default Future small aircraft engines.Which way?

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.


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Old 06-03-2014, 12:51 PM   #2
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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.

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Old 06-03-2014, 02:41 PM   #3
Niels Abildgaard
 
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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.
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Old 06-03-2014, 05:07 PM   #4
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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.


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Originally Posted by Niels Abildgaard View Post
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.
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Old 06-04-2014, 03:11 AM   #5
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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.

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Old 06-05-2014, 03:58 PM   #6
Niels Abildgaard
 
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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.
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Old 06-07-2014, 04:24 PM   #7
Niels Abildgaard
 
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Default Inverted V2 two stroke.A usefull Harley technology user.

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.
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Old 06-07-2014, 06:27 PM   #8
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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.

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Old 06-07-2014, 07:15 PM   #9
Niels Abildgaard
 
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Default Noise,vibration and harshness

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.
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Old 06-07-2014, 07:41 PM   #10
Niels Abildgaard
 
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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..._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


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