Vibration free powerplant.

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Niels

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A Hummel size plane will perfprm well with a 1360mm prop driven by 30kW.
It will perform just as well with two 1012mm props placed 700 mm apart ,counterrotating and each absorbing 15 kW.
Swept areas are the same and that is somehow important

combipropi.jpg
 

Tiger Tim

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A Hummel size plane will perfprm well with a 1360mm prop driven by 30kW.
It will perform just as well with two 1012mm props placed 700 mm apart ,counterrotating and each absorbing 15 kW.
Swept areas are the same and that is somehow important
Looks good on the surface but beware, there are aerodynamic losses at wing tips and propeller tips. Each of your props could certainly “absorb 15kW” as you put it, but much more will be lost to tip drag since your system has six tips to the traditional propeller’s two.
 

don january

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Vibration,fuel consumption,weight,and prop type is an area I'm looking at on my Taylor-monoplane. Other areas of concern is radiator location and Instrumentation. I have firm belief in the Rotary engine for a craft. Sure would fit the cowling nice.👍
 

don january

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A Taylor Monoplane with a rotary would be a real performer.


BJC
Yes I can see a few going around the pylons hoping for a payday. If a belly fuel tank is added then that may be a good area for the radiators on each side much like a P-51 belly scoop and low vibration on firewall from the Rotary.
 
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Armilite

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A Hummel size plane will perfprm well with a 1360mm prop driven by 30kW.
It will perform just as well with two 1012mm props placed 700 mm apart ,counterrotating and each absorbing 15 kW.
Swept areas are the same and that is somehow important

View attachment 116736
=============================

A Hummel Type Aircraft, Gross Weight: 850 lbs = 385.5535 kg / 10 kg = 38.55535 kw needed = 51.70358 hp needed. 51.7hp at 75% Power = 38.7hp.

Used for Powerplant: 1 × Volkswagen air-cooled engine four cylinder, air-cooled, four stroke automotive conversion, 85 hp (63 kW). 85hp at 75% Power = 63.75hp!

Stall Speed: 46 mph! How much hp needed to stay above that Stall Speed?

A 1/2 VW weighs like 95 lbs, so what does a Four Cylinder VW Weigh? You still need to stay in that 4 Cylinder Weight Envelope.

A Twin Engine setup also still needs to be able to Fly if (1) Engine Fails, so probably minimum 38hp Engines.

  • Gross weight: 850 lbs (386 kg)
  • Empty weight: 457 lbs (207 kg)
  • Useful Load: 393 lbs.
  • Fuel capacity: 20 U.S. gallons x 6 lbs = 120 lbs. 393 - 120 = 273 lbs.
 

Niels

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It is a Junkers spark ignited with a 80mm bore and strokes of 120mm.
Cranks are 700mm apart.Volume is 1.2 liter.
60rps of 1012mm props give tip speed of 190m/sec and mean piston speed of 14.4m/sec
A BMEP of 4.2bar will give the wanted 30kW,15 on each shaft.
WW2 drone engines was 22kg per litre and contained the maximum pressure from running with a BMEP of 4.9bar and 1to 8 compression ratio..My proposal has 4.2BMEP,no cylinder heads and 2:3 bore stroke ratio so it is not unreasonable to estimate mass without the two permanent magnet rotors to be ca 22 kg.
 
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wsimpso1

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The picture might mean something to someone who already knows this concept, but to this engineer, nope, it is unclear. The illustration in post 11 has what appear to be exhaust ports and injector holes that are off center, asymmetrically arrange intake ports, and only shows one piston while clearly there are two crankshafts.

Design Review:
  • Outwardly, it does appear to be a lightweight Junkers opposed piston two-stroke engine;
  • Single row large circumference ball bearing supporting each crankshaft will have difficulty staying put under the bending moments from compression and firing, and will not support the shaft against moments input to the prop flange from P-factor and gyroscopics;
  • The tiny clearances around the crank-rod system will result in large windage losses and will have difficulty draining oil exhausted from the bearings back to a sump for cooling and recirculation;
  • No provisions are shown for pressure lube of the crank and rod bearings, nor for cooling/lube of the pistons;
  • No provision is shown or explained for keeping the two crankshafts in synch. Compression ignition on opposed piston engines will only work if both pistons approach TDC simultaneously or at least close to simultaneously, so synching the crankshafts is needed;
  • No provisions are shown nor explained for induction air. These types of engines generally require a minimum of a blower for induction air to start and run. Best efficiency and power output is achieved with forced induction by a turbocharger.
The traditional Junkers opposed piston diesel engine is mirror imaged across the center of the combustion chamber, with the cranks turning the same direction (both clockwise or both counterclockwise) to counter second order vibrations of crank-rod schemes. They very definitely have firing order torsional vibration of the crankshaft. While translational firing reactions into the airframe can be avoided with such an arrangement, rotational reaction parallel to the crank axis at firing order will come in through the mounts. Rotational reactions in other axes can be nulled out very nicely with these types of engines, particularly when six cylinders (and twelve pistons) are used, as in the big Jumo engines of the 1930's/40's.

Once you have gearing between the crankshafts to keep them synched, you can choose to drive one or more propellors from anywhere in the gear train.

All of the symmetry of the Jumo's appears to be missing from the design illustrated in post 11. This design may be further along than the illustration shows. I await the rest of the details.

Billski
 

challenger_II

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Fisher County, Tx. USA
My 1835 VW, as mounted in the Longster, weighs 137#.


=============================

A Hummel Type Aircraft, Gross Weight: 850 lbs = 385.5535 kg / 10 kg = 38.55535 kw needed = 51.70358 hp needed. 51.7hp at 75% Power = 38.7hp.

Used for Powerplant: 1 × Volkswagen air-cooled engine four cylinder, air-cooled, four stroke automotive conversion, 85 hp (63 kW). 85hp at 75% Power = 63.75hp!

Stall Speed: 46 mph! How much hp needed to stay above that Stall Speed?

A 1/2 VW weighs like 95 lbs, so what does a Four Cylinder VW Weigh? You still need to stay in that 4 Cylinder Weight Envelope.

A Twin Engine setup also still needs to be able to Fly if (1) Engine Fails, so probably minimum 38hp Engines.

  • Gross weight: 850 lbs (386 kg)
  • Empty weight: 457 lbs (207 kg)
  • Useful Load: 393 lbs.
  • Fuel capacity: 20 U.S. gallons x 6 lbs = 120 lbs. 393 - 120 = 273 lbs.
 

Niels

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Aug 15, 2019
Messages
144
I am working of an up to date version but for interested there are some twenty years old pages here
Junker1
and another version
Junkers 2
Junkers3

The comments guide me to where more explanation is needed so let them flow.
 

n3puppy

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Jun 25, 2019
Messages
270
The comments guide me to where more explanation is needed so let them flow.
Ok my question.
The Junkers 3 post talks about not needing gears to keep pistons in sync.
Use permanent magnet generators to do that.

I can see how at cranking speeds to start, it could work.
But at full power - If the magnets are strong enough overcome combustion forces and keep pistons in sync - how does the engine generate enough excess torque to turn the props?
 

PMD

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Martensville SK
Where to begin. As Billski already pointed out, single cylinder opposed piston engine would have HUGE crankcase airflow issues, thus why they need to be in at least two cylinder layout. Then, to even think of 4 cycle is preposterous - and something given up on 100 years ago. The whole point of such an engine is to NOT have cylinder heads, valves and all of the unnecessary junk associated with wasting half of the engine's time, effort, space and weight with double excess of powerless strokes. The real magic is in exploiting not only 2 cycle tech, but realizing this is a UNIFLOW engine that doesn't pee away a bunch of energy turning the cylinder airflow around to puke it out the same way it came in. Now, in the weigh thing: the gensets simply add massive amounts of weight that don't make any sense. The crank synchronizing gear train is much lighter, simpler and more reliable that another ton of electrical garbage. Also: the synchronization of the cranks is extremely critical - the "exhaust" piston leading the "intake" side by about 14 degrees (and CRITICAL to be very accurately maintained). Finally: spark ignition? Why in the name of anything logical would one put such a silly fuel into an engine that is ideal for heavier distillates and compression ignition (EXACTLY as Prof Junkers figured out once again 100 years ago (he had flyable engines at end of WW1).

Oh...forgot: the angular velocity/momentum variations from a big single OP engine would result in HUGE issues for prop drive(s). It is difficult enough with 2 cylinders thus why the sweet spot for such engines is 3. Also: when you talk about 120mm strokes, the engine becomes extremely wide (when horizontal) - good for your dual prop concept, but IMHO you are going down a road of incredible wasted weight and complexity to do something that has long ago been established as the simple, workable and highly proven way to go about it. Also: very large OP engines really need to be mounted on a vertical cylinder axis (once again, as per the Junkers 205 example).

If you really want to exploit the unique properties of OP engines, take a look at the Napier Deltic, Junkers 223 and much later "barrel" layout engines (the latter really interesting for aviation layouts).

Oh: on the "vibrationless" count? Having one massive piston on one side and a tiny one of the other will make for an extremely vibrating prime mover.
 
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Niels

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Aug 15, 2019
Messages
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Ok my question.
The Junkers 3 post talks about not needing gears to keep pistons in sync.
Use permanent magnet generators to do that.

I can see how at cranking speeds to start, it could work.
But at full power - If the magnets are strong enough overcome combustion forces and keep pistons in sync - how does the engine generate enough excess torque to turn the props?

My generators work like two big power stations supplying a common grid.If one starts to get in front of the other it will deliver more power that sligthly unload to the sister and help her catch up.
They are AC generators and if they are connected in antiphase nasty things happen.
The two pistons have same bore and stroke and seeing same pressure ingniting or not they will convert same power.
Difference can be friction and underside piston pumping,but they are hopefully not near the max power capacity of generators.The real job of keeping pistons in bounds are done the normal way by cranks.When everything is nice and even the generators will generate no power.
 

Niels

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Aug 15, 2019
Messages
144
Where to begin. As Billski already pointed out, single cylinder opposed piston engine would have HUGE crankcase airflow issues, thus why they need to be in at least two cylinder layout. Then, to even think of 4 cycle is preposterous - and something given up on 100 years ago. The whole point of such an engine is to NOT have cylinder heads, valves and all of the unnecessary junk associated with wasting half of the engine's time, effort, space and weight with double excess of powerless strokes. The real magic is in exploiting not only 2 cycle tech, but realizing this is a UNIFLOW engine that doesn't pee away a bunch of energy turning the cylinder airflow around to puke it out the same way it came in. Now, in the weigh thing: the gensets simply add massive amounts of weight that don't make any sense. The crank synchronizing gear train is much lighter, simpler and more reliable that another ton of electrical garbage. Also: the synchronization of the cranks is extremely critical - the "exhaust" piston leading the "intake" side by about 14 degrees (and CRITICAL to be very accurately maintained). Finally: spark ignition? Why in the name of anything logical would one put such a silly fuel into an engine that is ideal for heavier distillates and compression ignition (EXACTLY as Prof Junkers figured out once again 100 years ago (he had flyable engines at end of WW1).

Oh...forgot: the angular velocity/momentum variations from a big single OP engine would result in HUGE issues for prop drive(s). It is difficult enough with 2 cylinders thus why the sweet spot for such engines is 3. Also: when you talk about 120mm strokes, the engine becomes extremely wide (when horizontal) - good for your dual prop concept, but IMHO you are going down a road of incredible wasted weight and complexity to do something that has long ago been established as the simple, workable and highly proven way to go about it. Also: very large OP engines really need to be mounted on a vertical cylinder axis (once again, as per the Junkers 205 example).

If you really want to exploit the unique properties of OP engines, take a look at the Napier Deltic, Junkers 223 and much later "barrel" layout engines (the latter really interesting for aviation layouts).

Oh: on the "vibrationless" count? Having one massive piston on one side and a tiny one of the other will make for an extremely vibrating prime mover.
Another wise guy.Thank You
 
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