# Future small aircraft engines.Wich way?



## Niels Abildgaard (Jun 1, 2014)

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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## lohring (Jun 3, 2014)

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


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## Niels Abildgaard (Jun 3, 2014)

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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## Till (Jun 3, 2014)

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.




Niels Abildgaard said:


> 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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## lohring (Jun 3, 2014)

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


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## Niels Abildgaard (Jun 5, 2014)

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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## Niels Abildgaard (Jun 7, 2014)

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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## lohring (Jun 7, 2014)

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


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## Niels Abildgaard (Jun 7, 2014)

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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## Niels Abildgaard (Jun 7, 2014)

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


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## lohring (Jun 8, 2014)

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


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## Niels Abildgaard (Jun 9, 2014)

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.


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## makoman1860 (Jun 9, 2014)

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.


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## lohring (Jun 10, 2014)

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


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## Niels Abildgaard (Jun 10, 2014)

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.


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## makoman1860 (Jun 10, 2014)

Niels Abildgaard said:


> 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.


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## Niels Abildgaard (Jun 10, 2014)

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.


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## makoman1860 (Jun 10, 2014)

Niels Abildgaard said:


> 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".


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## Niels Abildgaard (Jun 10, 2014)

makoman1860 said:


> 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.


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## lohring (Jun 11, 2014)

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


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## Niels Abildgaard (Jun 11, 2014)

Lohring

First picture is exhaust side.Very much car technology.Two slide bearings and divided conrod foot.Thrust bearing standard ball bearing.Lots of oil everywhere and some is cooling underside of piston.
Next picture is inlet side where crankcase pumping is part of scavenging system.Standard thrust ball bearing and a big roller bearing on crank disc.
Diameter 200 mm more or less and 2400 rpm gives a dn number of 480000.
Accepted value for steel rollers 600000 and 2000000 for ceramic rollers.


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## lohring (Jun 12, 2014)

Very nice.  An overhung crankshaft is a lot more tolerant of manufacturing imperfections and the all rolling element bearings don't need much oil.  Two of the overlooked advantages of crankcase scavenged engines are connecting rod big end and piston cooling.  High output engines need oil cooling of both without the fuel and oil flowing through the crankcase.  That often burns more oil than needed for lubrication. 

Even the small 26 cc engines I deal with are getting to the limits of their big end bearings.  Life is limited at over 20,000 rpm as I found out. The blue overheated rod end is the first sign of a problem.  The cage then fails allowing the needles to skew breaking the rod end.  One solution is a high strength cage with two needles in each slot to carry the high loads.

Lohring Miller


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## makoman1860 (Jun 12, 2014)

lohring said:


> Very nice. An overhung crankshaft is a lot more tolerant of manufacturing imperfections and the all rolling element bearings don't need much oil. Two of the overlooked advantages of crankcase scavenged engines are connecting rod big end and piston cooling. High output engines need oil cooling of both without the fuel and oil flowing through the crankcase. That often burns more oil than needed for lubrication.
> 
> Even the small 26 cc engines I deal with are getting to the limits of their big end bearings. Life is limited at over 20,000 rpm as I found out. The blue overheated rod end is the first sign of a problem. The cage then fails allowing the needles to skew breaking the rod end. One solution is a high strength cage with two needles in each slot to carry the high loads.
> 
> Lohring Miller



Lohring,
  We spent a lot of time on cage and roller design. There are so many tiny details of the design and manufacturing of that type of system if you want it to live. I personally would never use a cantilever type crankshaft, too flexible.


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## Niels Abildgaard (Jun 13, 2014)

A more conventional method of two stroke crank construction.

http://global.yamaha-motor.com/news/1999/0323/images/map1e.gif

It is same method as the two cylinder two stroke Trabant made in millions in DDR.

For my 105 160 mm version cold (inlet) side


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## makoman1860 (Jun 13, 2014)

That would seem much more reasonable of a design. If it were me I would eliminate the through hole in the crankpin if you plan on heat treating the crankshaft, unless you plan to hone/polish the hole. They tend to be sources of cracks. I may be a little confused by your drawing, how close is the main bearing to the crank cheek? It looks to be quite far away.


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## lohring (Jun 13, 2014)

makoman1860 said:


> Lohring,
> We spent a lot of time on cage and roller design. There are so many tiny details of the design and manufacturing of that type of system if you want it to live. I personally would never use a cantilever type crankshaft, too flexible.



I tend to agree especially as engines get larger.  However, bearings on both sides don't necessarily make the crankshaft stiff enough.  The crankshaft our race engines use comes from a weedeater engine that started out at around 2 hp 20 years ago.  Its design (and I believe materials) are unchanged even though it's now used in engines that develop over 8 hp at a lot higher rpm.  This crankshaft and a similar design used on a 35 cc engine we worked on flexes enough to cause flywheel strikes even with .015" (.4 mm) clearance to the magneto coil pickup.  The solution has been two bearings on at least the output side.  The crankshaft bearings need a lot of clearance to prevent  seizing from heat and heavy press fits.  In effect we are treating each half of the crankshaft as an overhung crankshaft.

A long time ago we souped up Homelite overhung crankshaft engines.  Both the rods and crankshafts of these engines are too light duty to stand much more than their design power and rpm.  However, they cost around 1/3 as much as the Zenoah engines we now use.

Lohring Miller


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## Till (Jun 13, 2014)

Niels, that crankshaft design will wobble unter load conditions because of the bearing layout. There will be lots of undesireble sideeffects, including periodic noise (and wear) of the bevel gears.

And I think that the amount of power supplied to each prop is not equivalent (at least with asymetric timing). You will need some kind of damper on the geared shaft to reduce torsional vibration.


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## makoman1860 (Jun 13, 2014)

lohring said:


> I tend to agree especially as engines get larger. However, bearings on both sides don't necessarily make the crankshaft stiff enough. The crankshaft our race engines use comes from a weedeater engine that started out at around 2 hp 20 years ago. Its design (and I believe materials) are unchanged even though it's now used in engines that develop over 8 hp at a lot higher rpm. This crankshaft and a similar design used on a 35 cc engine we worked on flexes enough to cause flywheel strikes even with .015" (.4 mm) clearance to the magneto coil pickup. The solution has been two bearings on at least the output side. The crankshaft bearings need a lot of clearance to prevent seizing from heat and heavy press fits. In effect we are treating each half of the crankshaft as an overhung crankshaft.
> 
> A long time ago we souped up Homelite overhung crankshaft engines. Both the rods and crankshafts of these engines are too light duty to stand much more than their design power and rpm. However, they cost around 1/3 as much as the Zenoah engines we now use.
> 
> Lohring Miller



 Hi Lohring,
  I get what you are saying. It seems that the root cause of the issues you have is the crankshaft design, not the general layout of a "full" crank. I am curious if your need for excessive clearance comes from the same issue. In effect you are bracing the crankshaft with the main bearing design as kind of a Band-Aid it seems. Are the rollers on the crankpin straight, or barrel? Is there enough room ( in the case and pocketbook) for a new crankshaft design with a larger crankpin?


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## lohring (Jun 13, 2014)

Motorcycle racers have the issue mostly under control with the exception of the rod bearings.  In both cases the secret is in the details, not the basic idea.  I'm sure another crankshaft design would be better, but how can you beat $55 for a crankshaft and connecting rod assembly?  

On a previous topic, I found the drawings of the OPOC (previous incarnation of Eco Motors) small engine with piston scavenging pumps.  It was a very clean design, but they never got the reed valves working well, even though they were a standard air compressor design.

Lohring Miller 






View attachment Reed_Valve_New_Concept 3-9-06.pdf


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## lohring (Jun 13, 2014)

makoman1860 said:


> Crossed chain I feel is a bad idea, even a direct coupled system with gears will be difficult with the torsional harmonics. ---



If you take power off both crankshafts, the connecting gears or chain should carry very little load since it's just being used to time the two cylinders.  This should be possible by staggering the propellers if their radius is less than the crankshaft center to center distance.

Lohring Miller


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## Niels Abildgaard (Jun 13, 2014)

Till said:


> And I think that the amount of power supplied to each prop is not equivalent (at least with asymetric timing). You will need some kind of damper on the geared shaft to reduce torsional vibration.



Torsional vibrations come in a very narrow rpm band .
If it cannot be engineered outside 1500 2400 rpm,I will counter it with the generator/starter fixed on one of the cranks.Modern electronics can easily do that.Asymmetric timing serves no purpose.The 800 horsepower snowmobile engine shown has symmetric timing.


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## makoman1860 (Jun 13, 2014)

There is always going to be asymmetric loading on an OP 2 stroke. The blowdown event is above one piston only which tends to set up a gas dynamic in the cylinder. OP engines are anything but simple, if they were, everyone would use them (if the application deemed it worthwhile), its not like its a new idea. Most engine companies have experimented with them and found that for most situations, there is not enough there worth developing. The gen 1 ecomotor suffered a lot of design flaws that made it impractical. Reeds are very very complex things to get to work well, especially stainless ones for long life. Most companies throw in the towel and go with a composite reed that has a short life but at least wont destroy the engine. I wish the fellows at EM well on their adventures, however I sadly see that venture slowly disappearing as they find nothing to gain in the design for light motive power.


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## Niels Abildgaard (Jun 14, 2014)

Many outboard engines use reed valves at 5000 to 6000 rpm and the proposed Junkers at 2400.
Are outboard reed valves a problem ? 
In that case I will opt for a rotating disc valve.


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## lohring (Jun 14, 2014)

Attached is a paper on some of the work Eco Motors founder did for his truck APU engine.  It's a preliminary copy of an SAE paper.  I have a more detailed paper on their truck engine, but it's too big for this forum.  Like any real engine development, there's lots involved. They had to address a lot of the issues mentioned in this thread. 

Car companies may change body styles every few years, but engine designs live on for decades due to the development needed even for a long proven basic design.  Large and medium size aircraft piston engines haven't been developed at all for at least 50 years because there's no market.  Two strokes really only dominate the smallest sizes and large marine two strokes  due to cost and low weight for the constant high load power (really, even at 100,000 hp).  The big BRP outboards are an example of what might be done in moderate sizes, but their development bankrupted OMC.

Lohring Miller 

View attachment 2005 SAE epc Paper 05P-669 Truck APU.pdf


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## Till (Jun 14, 2014)

lohring said:


> Attached is a paper on some of the work Eco Motors founder did for his truck APU engine.


 Well there are already small power plants established to supply trucks, especially for the refrigeration units (at least in Europe they are). So they clearly aimed at the military market.  Military? Funding comes from the taxpayer &#8594; if theres a problem, continue to throw money at it until it goes away or the project becomes obsolete Just take a look at the engine: Lots of new, unproven and expensive design = very little chance for commercial success.  





lohring said:


> Large and medium size aircraft piston engines haven't been developed at all for at least 50 years because there's no market.



There is a market but american jurisdiction makes it a highly dangerous minefield for potential investors.


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## makoman1860 (Jun 16, 2014)

Till said:


> Well there are already small power plants established to supply trucks, especially for the refrigeration units (at least in Europe they are). So they clearly aimed at the military market. Military? Funding comes from the taxpayer &#8594; if theres a problem, continue to throw money at it until it goes away or the project becomes obsolete Just take a look at the engine: Lots of new, unproven and expensive design = very little chance for commercial success.
> 
> There is a market but american jurisdiction makes it a highly dangerous minefield for potential investors.


 
 Niels,
  If long service life is what you are after, rotary might be a good path. Metal reeds are not an issue when designed and manufactured well. The scope of doing so is out of the realm of all but a couple companies in the world.

 There are new aviation engines every year, certified and experimental. The reason that you see little change in design is that if you had a clean sheet to start with, and all the functional requirements of the current engines, a new design would look pretty much like what we have now. Its not that there is a fear of change, there just isn't much to gain. Many people falsely assume that an automotive type engine is somehow better than an aviation engine. The reality is that application dictates design. Auto engines make poor aviation engine, and vise-versa. Honestly the fuel burn on an O-320 Lycoming at 150hp is amazing , and you will never find an automotive engine that weighs the same, with the same BSFC, and lifespan. Two different sets of needs, and requirements. Trying to "set the airplane engine world on fire" is nothing new. People have been trying for at least 70 years. A look back through aviation tech magazines from the 1930's on shows the same ideas we have now, experimenting with new engines. All have failed, i.e. you cant fix what is not broken.


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## Niels Abildgaard (Jun 16, 2014)

Hello Markoman.
I guess You are not investing in the future Junkers?
The O 320 makes awfull noise by turning a suitable prop at 45 rps.
If You reduce rps ,power goes down,and if You reduce prop diameter ,thrust efficiency goes down.
It yaws and rolls aeroplane,especially during start and aborted landing.
It uses/needs a criminal fuel and it rattles all the time.
Good engine?
You must be joking.
On the other hand I will be very interested in real measurements of fuel consumption for present day engines.


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## makoman1860 (Jun 16, 2014)

Niels Abildgaard said:


> Hello Markoman.
> I guess You are not investing in the future Junkers?
> The O 320 makes awfull noise by turning a suitable prop at 45 rps.
> If You reduce rps ,power goes down,and if You reduce prop diameter ,thrust efficiency goes down.
> ...



 Hi Niels,
  Haha no I'm not . Honestly the O-320 powered planes I am used to have little prop noise, but much of that is in the blade design. Yaws and rolls....well I guess to me that's just part of flying that I never gave a second thought to. Since when is premium auto fuel criminal? Rattles? Sure its not the smoothest being a big 4 cylinder, but I have felt worse. I am not saying that the O-320 is the best 150 horse out there by any means. The 6 cylinder Franklin and Continental are much smoother. I will give you this though, when you are flying over the mountains, there is no better feeling then knowing the engine will keep running, and that comes from a trusted design. I've worked in the engine design field for some 15 years now, and quite honestly the more I learn, the more I cringe at many of these "experimental" engines. The level of detail, development, and testing to get an engine into production is staggering. The work involved in understanding the control, tracking and processing of the components is mind boggling. This is why few have managed to survive. Jabiru is doing OK....but have had issues since they don't have the capability to do in house development, and I really wonder how long they will be around. They have this trouble building a pretty much "standard" engine. I really am not trying to be a wet-blanket here. If you make it work, all hats are off to you. 

 On the fuel consumption side, what engines are you interested in? Marine engines come the closest to the duty cycle of aviation.


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## Niels Abildgaard (Jun 16, 2014)

Hello Markoman.
It is a shame to let a mental game (Design a better mousetrap , aircraft engine etc ) degenerate into the usual (Old american iron is best).
Next step down is that someone tells me that Harley Davidson makes motorbikes.
What would interest me was if You had a fuel consumption map for a o 320?


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## makoman1860 (Jun 16, 2014)

Niels Abildgaard said:


> Hello Markoman.
> It is a shame to let a mental game (Design a better mousetrap , aircraft engine etc ) degenerate into the usual (Old american iron is best).
> Next step down is that someone tells me that Harley Davidson makes motorbikes.
> What would interest me was if You had a fuel consumption map for a o 320?



Hi Niels,
  Ha no I do not consider a Harley to be the best at anything (maybe marketing). Honestly I still believe a air assist DI "V" type 2-stroke would be a better road to travel down. If torque reaction is a big issue, then a concentric counter-rotating prop setup could be used. A traditional ( non OP type ) combustion chamber would allow you to run stratified up to almost 75% power. This is something the OP type design wont allow you to, its been tried and you just cant get the injector where you need it. Keep the power density down to about 60 hp/litre and it can be made to have a 3000hr TBO at 75% duty cycle without having to invent much. A V4 will be much easier to keep a gearbox on than a V2. An I3 would be good up to 100 horse and is excellent for pulse tuning ( as is a V6  as 2 I3's ). A good look at outboard engines will give some ideas. Both Mercury and BRP are the experts in this field (big 2 stroke, long life, high duty cycle, light).


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## Niels Abildgaard (Jun 16, 2014)

Hello Makoman

Glad You like the V2 aircraft scheme with central exhaust valve and stratified charge by moderate swirl.
Would You invest in that?


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## makoman1860 (Jun 16, 2014)

Niels Abildgaard said:


> Hello Makoman
> 
> Glad You like the V2 aircraft scheme with central exhaust valve and stratified charge by moderate swirl.
> Would You invest in that?



Invest? If you need design help I would be more than willing to assist with that. Send me a PM and I will give you my e-mail.


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## Niels Abildgaard (Jun 16, 2014)

Hello Makoman

As I wrote in the first letter this is just an mental game while we wait for another put put fourstroke design.
Future aircraft propulsion systems will not come from neither America or Europe,but we are still allowed to dream and argue.Let us enjoy that.


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## mu38&Bg# (Jun 16, 2014)

I've been following along here. What is the story with Delta Hawk? Are they viable? I would think that multi-fuel (at least the ability to use kerosene) is beneficial.

With the twin prop arrangement I would expect noise due to the proximity of the prop tips to the fuselage. Has this been tested or is tip speed low enough to minimize this?

Fuel consumption piqued my interest. I saw mention of the BMW IIIa at 180g/HP-hr (240g/kWh), but the published tests put it at 270g/kWh? O-320, O-360 is something like 255g/kWh.









It seems knock limited large bore low RPM engines are pretty well sorted. Where is the increased efficiency going to come from? There is an interesting reference to the turbo versions burning much more fuel here, at the bottom of the page. Bristol was working with mechanical direct injection of gasoline during WWII, did it ever become common? Germany also used it in some airplanes in production, I think.

Niels, have you read anything about this company? http://www.achatespower.com It seems they are investing a lot in the Junkers type.

I agree that everything in the engine world was done by WWII when turbines took over. There have been advances since then, but the cost is staggering for the gains. Besides, much of the automotive work won't apply. Which brings me to question how much might development of this engine cost?

Greg


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## makoman1860 (Jun 16, 2014)

dieselpilot said:


> I've been following along here. What is the story with Delta Hawk? Are they viable? I would think that multi-fuel (at least the ability to use kerosene) is beneficial.
> 
> With the twin prop arrangement I would expect noise due to the proximity of the prop tips to the fuselage. Has this been tested or is tip speed low enough to minimize this?
> 
> ...



Hi Greg,
  DeltaHawk is doing well, and not that far away from me. I think the cert process will finish up the summer on the 180 horse V4. Honestly that seems like a viable engine. They are fortunate to be in "engine country" here in Wisconsin and have many manufacturers local to pick brains and such. Time will tell how well it is executed. 

 Niels,
  If you are suggesting that a new engine will come from china.....I would be beyond shocked if that happened.


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## Niels Abildgaard (Jun 16, 2014)

Hello Greg

I have seen 185 gram per hph for BMWIIIa in a german book ISBN 3_7637-6107-1.
The firm of Hirth who makes two stroke ultraligth engines measured 160 gram gas/petrol on 313 ccm cylinders with mechanical injection ten years ago.
All german 1000hp engines or more after 1939 were mecanical directinjected.

Hello Makoman

The CAFE test some years ago were won by a Slovenian aircraft with an Austrian engine.
Solidly
Initiative is moving east.
Just as wired telephones were bypassed in Africa and parts of Asia by mobilephones,the same thing can happen with road vehicles and aircrafts.
80 to 100 horsepower (Rotax 912) is were the action and numbers are.


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## makoman1860 (Jun 16, 2014)

Niels Abildgaard said:


> Hello Greg
> 
> I have seen 185 gram per hph for BMWIIIa in a german book ISBN 3_7637-6107-1.
> The firm of Hirth who makes two stroke ultraligth engines measured 160 gram gas/petrol on 313 ccm cylinders with mechanical injection ten years ago.
> ...



Niels,
Honestly over here in the US, there is not as much interest in the CAFE "green" stuff anymore on a corporate level. The shift seems to have gone to total performance, not efficiency, even though they are intertwined. Just a different set of needs. Fuel is plentiful, noise is not an issue, and we have large distances to cover. The work here is going into racing it seems. That being said there are some really neat engines that have come out, and will come out in the near future, just not competitive to the little euro stuff. The rotax made a big splash here, but has been slowly drying up. The cost of ownership is higher than many thought. The Jabiru, Rotec, M-14P, and Lom type engines are very popular. Delta hawk will have their 180hp diesel out soon, with larger engines to follow. Not much on the smaller scale.

Where am I going with all of this. Just because a country is not doing something, does not mean they are not capable of it. With the light sport category we are seeing the popularity surge of "cub" type designs with little Cont O-200 base engines. It works, it sips auto fuel, is easy to work on, parts are everywhere, and taken care of they last forever. Whats not to love? Ever come to Oshkosh?


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## Niels Abildgaard (Jun 17, 2014)

Hello Makoman

Have been to Sun and fun and heard a Harvard and later an Antonov 2 full blast.The AN 2 has double power and less noise.More tipspeed means serious more noise


All You want is an O 200 (with Cub) to parafrase Beatles.
Was on the web and found this

http://www.flycorvair.com/thrust.html.

80 horsepower at 2750 rpm on a 72 inch prop is 265 meter per second tip speed and You are not allowed to fly in many parts of Europe and a lot of other crowded places.
American small arms and noise tolerance is not easy to export.
The O 200/Cub combination is not the future and I have reconsidered the functional model I want to builld based on some moped conrod parts I have.
60 mm stroke times two and bore 40 mm ie of the shelf chromed piston rings.
Some pictures.
If some one north of the Alps are tempted to join the moneyless fun and share the Glory (In heaven I asume) let me know.


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## makoman1860 (Jun 17, 2014)

So what you are telling me in short, is that you are trying to find an engineering solution to a social problem? 
 The way things look, Europe might just restrict themselves out of ever needing a new aviation engine. I am glad I live in a place where people still run outside to catch a glimpse of that airplane that just buzzed their house instead of phoning in a noise complaint.


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## mu38&Bg# (Jun 17, 2014)

Your comment about Hirth, is that with the Orbital system? 160g/kWh in 300cc two stroke? The best I read about Hirth/Orbital is 330g/kWh. I think you have to be realistic with BSFC.

This adaptation of an auto diesel looks intriguing. http://flyeco.net/smart_diesel.html


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## Niels Abildgaard (Jun 17, 2014)

dieselpilot said:


> Your comment about Hirth, is that with the Orbital system? 160g/kWh in 300cc two stroke? The best I read about Hirth/Orbital is 330g/kWh. I think you have to be realistic with BSFC.
> 
> This adaptation of an auto diesel looks intriguing. http://flyeco.net/smart_diesel.html



Hello Greg

It was 160 gram/bhph.
Hirth did not tell me what system.
Maybe a full mechanical high pressure like gutbrod 1952
NSU Lux 200ccm motorbike returned 200 gram /bhph in the early fifties.
Fuel octane and compression ratioes are higher today so below 200 are realistic.
Austrian engine developers AVL claimed 245 gram/kWh on a 100 ccm two stroke semidirect injection.
Orbital must have done better than 330 gram/kWh.

Combination of the three cylinder fourstroke diesel- toothed belt reduction(?)- and high inertia propeller is not flying me over hostile terrain.


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## Niels Abildgaard (Jul 4, 2014)

The endless journey ( I had the vision 1988) takes a new turn.
In DDR a lot of motors was made and unused spares are cheap and awailable

http://www.crazybikes.net/el308_1.html

so here comes next scheme for trying.
Stroke 68.5 mm bore aprox 48 mm and based on crankcase and cranks as found in Germany

Angle Grinders are cruel.


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## Tin Falcon (Jul 4, 2014)

The other day a friend e-mailed me about the Boeing Phantom Eye project . 

The interesting thing here is the power plants are ford engines. Similar to used in the ford ranger and or fusion. 
the main tweak is tuning them to run on Hydrogen. Stored in liquid form. the original reports mention turbo chargers but with a 65K foot  flight level I think they are carrying Liquid O2 as well. 

I expect All the nuts and bolts are safety wired as well. 

My son had a ford ranger that had dual spark plugs IIRC this is something typical in AC engines. 

Interesting though in the day of high speed turbo/jet engines  that Boeing  powers there latest UAV  with something akin to what is found in the family car or truck.

Good to see ford building aircraft engines again. 
Tin


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## Niels Abildgaard (Jul 4, 2014)

Hello Tin Falcon

The Pietenpol Aircamber was one of the first homebuilts that multiplied.
Engine was a Ford A direct drive.
Can we get some information on this high altitude thing?
If it is a fourcylinder geared one,what kind of coupling gearing?
In the mean time the horrible angle grinder criminal has struck again.


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## Tin Falcon (Jul 4, 2014)

> Can we get some information on this high altitude thing?


Just Google Boeing Phantom eye.  there are various videos  out there. This project has been in development for a couple years. They are now field testing the prototype. 
Tin


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## Niels Abildgaard (Oct 7, 2014)

Somehow it feels wrong to use discarded engines for proving my wild ideas.
It cannot be said that I have not tried to make suitable crankshafts but up til now in wain.They either wobled or looked wrong.
My getting wiser engine shall (for the time being) look something like second picture and third picture shows the critical connection of hardened conpin to crankdisc.
The conpin is casehardened ,that means the outher mm is very hard and core not so but tough.
It is easy to turn end to shape shown using a homegrown tangental carbide tool.
It is then put on disc and pulled tigth by the M8 12.9 Unbrako screw using 25 Nm torgue giving ca 2 tons force.Screw can stand 2.5 tons ultimately.
I then removed the screw and pressed further with 8 tons.
The V shape valley in disc is now about .8 mm wide and pin is unchanged.
Very cheap fast and easy.
It migth even work.


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## roleic (Oct 29, 2017)

Dear Neals,
I hope you are well. Thanks for your many posts on 2-stroke diesel aircraft engines. I agree that they are underrated and deserve a closer look. However the double piston version with 2 crank shafts seems very heavy (and costly) especially for aircraft engines. The Jumo 205 from the 1930ies came from the airship era and was not suitable for high performance aircraft. But the concept of a light, 2-stroke, Schnuerle ported,  single crankshaft, exhaust turbo-charged, inter-cooled, diesel engine with a modern, highest pressure injection system (common rail, piezo valve control) would make very much sense especially in a V or radial layout. The big advantage with that concept is that you don't need to feed the air intake through the crank case as in traditional 2-stroke engines but in separate lines allowing for a normal oil lubrication of the crankcase creating oil free exhaust gases like in 4-stroke engines. If the engine is started with compressed air out of a light kevlar composite tank, spinning up the engine AND the turbo charger, and not with an electric starter as in cars, which does not spin up the turbo, you could reduce the mechanical compression ratio to take more advantage of the turbo charger at all altitudes. It could leave all other piston engines behind in terms of power per weight ratio (second only to gas turbines), fuel efficiency (second to none), low noise without reduction gear due to high torque at low engine revs. Such an engine could be so superior that it could become an interrupter for traditional aircraft engines which are mainly built by corporations being a part of the US military industrial complex with close ties to the US government (including FAA making certification extra difficult) and clandestine services (scaring foreign authorities from certifying and investors from investing). That leaves only the small experimental, home- and kit-built market. That is where Rotax started AFAIK... The main technical challenge is the injection system. The other main challenge is to gain enough money in the kit-built market to afford to jump over all hurdles the authorities put in your way to certification for the bigger general aviation market.


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## Niels Abildgaard (Oct 29, 2017)

Hello Rolleic

Glad You have read it.
My aircraft engine thinking is Otto (spark ignition) engines only.
Diesels are useable for ships and locomotives  maybe , but not for flying.

Some examples here

http://archive.is/G9Hpk

Young people in Copenhagen claimed 210 gram petrol for one kWh and a very good WV diesel is 195 that is 15 gram difference for say 60 kW makes 900 gram per hour in favour of a diesel  engine that is probably 6-8 kg more heavy.
No deal.


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## Mechanicboy (Oct 29, 2017)

Niels Abildgaard said:


> Diesels are useable for ships and locomotives  maybe , but not for flying.
> .



Reading this further..

https://en.m.wikipedia.org/wiki/Aircraft_diesel_engine


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## WOB (Nov 16, 2017)

Niels Abildgaard said:


> 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.



I didn't see this question asked, so pardon me if it has.  Why a V configuration?  It shakes.  A 180 degree flat twin does not shake.  See http://sense.net//~blaine/twin/twin.html

WOB


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## Rheanr4 (Nov 16, 2017)

An interesting thread.  Especially for me.  I have been flying behind a Continental O-200 for the past 10 years here in the USA.  I see no reason that I won't be flying behind that engine in the next 10 years. 

Reg


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## Niels Abildgaard (Nov 16, 2017)

WOB said:


> I didn't see this question asked, so pardon me if it has.  Why a V configuration?  It shakes.  A 180 degree flat twin does not shake.  See http://sense.net//~blaine/twin/twin.html
> 
> WOB



Rigth, but a flat two or four   torques.
The difference you feel sitting in a C 172 with either a 6 or 4 cylinder engine is due to different reaction torque variations.
A 90 degree V2 two stroke will be closer to a 6 cylinder than a 4 cylinder four-stroke torquewise.
A  fourstroke flat 4 does not shake but a 4  inline does two times per rev.
A 90 degree V2 twostroke will shake two times per rev one fourth of what the corresponding inline 4 fourstroke would have done.


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## Niels Abildgaard (Nov 16, 2017)

Rheanr4 said:


> An interesting thread.  Especially for me.  I have been flying behind a Continental O-200 for the past 10 years here in the USA.  I see no reason that I won't be flying behind that engine in the next 10 years.
> 
> Reg



People from  lower and envious classes will considder leaded fuel criminal.
Future aircrafts designers will be led astray by lower engine and fuel mass.


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## 99Norton (Nov 18, 2017)

Hello,
        I've just been reading this thread and noticed there was no mention of the Rootes TS3 which is a great design which with modern materials could be made even lighter.

http://www.oldengine.org/members/diesel/rootes-listerts3/ts3.htm


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## Niels Abildgaard (Nov 19, 2017)

99Norton said:


> Hello,
> I've just been reading this thread and noticed there was no mention of the Rootes TS3 which is a great design which with modern materials could be made even lighter.
> 
> http://www.oldengine.org/members/diesel/rootes-listerts3/ts3.htm



There is an awfull lot of highly loaded bearings that do not rotate but oscillates.
Two strokes with reasonable piston speeds gives push all time and no pull where an oscilating bearing can be lubricated.That is why small petrol two strokes have needle bearings in piston.


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