# Vibration free powerplant.

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#### Cardmarc

##### Well-Known Member
If you want vibration free, try a Mazda rotary engine. There are vids of them running with a full wine glass set on top of the engine! No spillage! Why even use ‘pistons’?

PMD

#### wsimpso1

##### Super Moderator
Staff member
Counterrotating cancels torque reaction and make less prop noise.
A mean effective pressure of 4 to 5 bar will only need little turbo and cold inlet crankcase in series.
Exhaust piston can then be oil cooled if needed.
Achates can make more usefull engines using the twin AC generators method but it is a free country and not my money.

It seems to me that you are fixing crankshaft spacing upon need for prop separation, then taking the rpm and piston speed that gives... Usually that sort of "design coupling" produces unwanted side effects. With a gear train, you can drive the prop(s) from which ever shaft suits, or make the prop spacing independant of engine configuration, and run the crankshafts in the direction and rpm that makes sense. Gear sets are widely used in the world and way lighter than e-machines.

Understand that in addition to fighting drift between the two crankshaft speeds, you will also have 2500-3500 rad/s/s firing level pulses. The net torque from being out of synch will look like a sinusoid with the mismatch in acceleration being fought by the e-machines on each crank. That drives bigger e-machines than just to hold cranks together with steady state torque.

With the intake port on one end and exhaust on the other end, do we not expect asymmetry of crankshaft torque? That too will add load to the e-machines keeping the crankshafts roughly synched.

The longer I look at it, the more desirable a simple gear train becomes from directions of weight, cost, vibe, and effectiveness.

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#### WonderousMountain

##### Well-Known Member
Prof. Neils,

What techniques do you have available & intend to use prototyping this OP twin? A successful engine needs skillfull machinists and post production tests performed.

All the Best,
CK LouPai

#### Niels

##### Well-Known Member
Prof. Neils,

What techniques do you have available & intend to use prototyping this OP twin? A successful engine needs skillfull machinists and post production tests performed.

All the Best,
CK LouPai

None as I still like my inverted V2 better .
I am an old man and start loosing things out of hands .
I only use my lathe for things less than 2-3kg mass.
It has been fun thinking of the Junkers scheme and world do not really needs 30kW aeroengines.

#### Armilite

##### Well-Known Member
There was never an OPOC (opposed piston opposed cylinder) snowmobile engine of the type being discussed here. Neither were VW's, Corvairs, or BMWs.
=======================

The Thread is "Vibration free powerplant." not OPOC Engines and the Engine was referred to as just Opposed. Rotary Engine were also mentioned, not an OPOC either. So were talking about an Engine that doesn't really exist, just someone's pipe dream, that isn't really needed or they would have built it years ago. The Opposed Engines as I said weren't popular in Sleds, or Cars, Vans, Trucks or they would still be using them. As I also said most Opposed Aircraft Engines have been dropped Hp per Weight & Cost, also. Some Companies have literally spent Millions on R&D and Time trying to perfect these different Engines. The average guy doesn't have the \$ or the Time to do it right to make one Saleable and it's COST/WEIGHT would be to prohibitive for you use on a Home Built Aircraft. The JET Engine killed the Piston Engine 70+ Years ago.

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#### Armilite

##### Well-Known Member
You are confusing opposed cylinders with opposed PISTONS. OPOC engines have only one cylinder for each opposed pair of pistons with a crankshaft at each end. Being mostly 2 stroke cycle, there haven't been many around for emissions reasons for some time (the Commer TS3 being the last in a production road vehicle I can think of). While they have two crankshafts, they have no cylinder head nor valve gear and save a lot of weight, complexity, cost and efficiency by being such a simple design. They are also "uniflow" engines in that inlet is on one side and mass of combustion gasses keeps moving the same way to exhaust on the other side.

Here is a good video giving you a quick summary:
===============================

I can see now what you're talking about, but like you said, "Being mostly 2 stroke cycle, there haven't been many around for emissions reasons for some time" and " While they have two crankshafts, they have no cylinder head nor valve gear and save a lot of Weight, Complexity, Cost, and Efficiency by being such a simple design." Maybe to you, but to not 99% of the people on here. First, you have (2) Crankshafts so more Weight, has more complexity than a standard 2 Stroke. You didn't say how much hp, Cost, Weight? Most people on here hate 2 Strokes, can't even rebuild a Standard 2 Stroke let alone a Hybrid. Rotax's biggest 2 Stroke they offered was the 618UL. Simonini 802cc, Hirth was I think 625cc. Sleds go up to 1000cc. Sled & Jet Ski Racers go up to about 2000cc today. The Part 103 Ultralight World needs a Single that is less than 65lbs, that make ideally 30-40hp, the Small Kitplane World needs a 40-60hp or 60-80hp depending on MTOW. Large Kitplanes need 100+hp. No Certified Airplane will use a 2 Stroke Engine no matter how good an engine it is. If you use the simple 7cc to make 1hp rule with a Tuned Pipe at 6500rpm.

30hp x 7cc = 210cc

35hp x 7cc = 245cc
377UL 368.4cc/35hp= 10.525cc with a Muffler!

40hp x 7cc = 280cc
447UL 436.7cc/40hp= 10.917cc with a Muffler!

45hp x 7cc = 315cc

50hp x 7cc = 350cc
503UL 496.9cc/50hp= 9.938cc with a Muffler!

One of the best Engines the Simonini Victor 1 Super [email protected] 400cc/54= 7.407cc to make 1hp using 9.5cr! 400cc/7cc= 57.1hp if using 11.5cr.

#### PMD

##### Well-Known Member
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I can see now what you're talking about, but like you said, "Being mostly 2 stroke cycle, there haven't been many around for emissions reasons for some time" and " While they have two crankshafts, they have no cylinder head nor valve gear and save a lot of Weight, Complexity, Cost, and Efficiency by being such a simple design." Maybe to you, but to not 99% of the people on here. First, you have (2) Crankshafts so more Weight, has more complexity than a standard 2 Stroke. You didn't say how much hp, Cost, Weight? Most people on here hate 2 Strokes, can't even rebuild a Standard 2 Stroke let alone a Hybrid. Rotax's biggest 2 Stroke they offered was the 618UL. Simonini 802cc, Hirth was I think 625cc. Sleds go up to 1000cc. Sled & Jet Ski Racers go up to about 2000cc today. The Part 103 Ultralight World needs a Single that is less than 65lbs, that make ideally 30-40hp, the Small Kitplane World needs a 40-60hp or 60-80hp depending on MTOW. Large Kitplanes need 100+hp. No Certified Airplane will use a 2 Stroke Engine no matter how good an engine it is. If you use the simple 7cc to make 1hp rule with a Tuned Pipe at 6500rpm.
The OP opened this thread about a much larger engine with OPOC design. What he proposed would probably be far too heavy for aircraft use (with the M/G function and hardware). For aviation, they have a hundred+ year history of being relatively light, extremely efficient but due to 100-75 year old fuel injection tech, not very powerful. Also, they are ideally suited for 2 cycle uniflow construction using diesel and/or jet as fuel - so yet another big plus for aviation use. 2 cycle diesels are very different animals from 2 cycle SI counterflow or loop scavenged engines. As to cost and power: OPOC diesels have been built at very low HP (small outboard) but long ago but mostly have been fairly large engines. No reason (see Achates once again) they can't be made in 4-6 place genav sizes. There have also been some 80-100HP designs over last 30 years, but for any of these to really be affordable there needs to be some mass market application that turns out parts and/or whole engines that can be used or adapted for aviation. This is what is going on with most JetA engine designs - using automobile engines as source.

I don't think they can scale down into the 40kW range mostly due to the size of injection components needed for CI, but actually could be built easily as an SI engine in that range. BUT, of course, it still gets back down to no sense trying to develop a whole engine for such a tiny market - ends up being very expensive.

On the two stroke thing: I have built literally hundreds of two cycle powered commercial airboats, mostly Rotax powered (503 days) and while I am not exactly 2 stroke SI crazy, they did an excellent job for us and let's face it, there is a massive component of sport aviation that simply wouldn't exist without them. Hard to beat the power/weight numbers.

#### n3puppy

##### Well-Known Member
=======================

The Thread is "Vibration free powerplant." not OPOC Engines and the Engine was referred to as just Opposed. Rotary Engine were also mentioned, not an OPOC either.
The JET Engine killed the Piston Engine 70+ Years ago.
While the title doesn't say opposed - In Posts #11, #12 and #16 Niels explained the type of engine he was discussing and asking input on - OPOC. Not opposed engines as used in Snowmobiles, VW.s, Corvairs, BMWs

OPOC engines have been around since 1882

Per post #32 - Achates Power is actively working on a commercial OPOC design for modern applications.

As far as complexity -Two crankshafts are no more complicated/heavy than one parallel twin Rotax motor.
Rotax or OPOC 2 pistons, 2 rods, 4 crank webs, 4 bearings minimum.
Rotax 2 Heads OPOC - zero.

In post #12 the design goal of [email protected] ( [email protected] ) was given before M/G
Rotax 447 - [email protected]

Need is relative- Jet engines may not be the future powerplant of choice for Ultralight Craft

#### Armilite

##### Well-Known Member
While the title doesn't say opposed - In Posts #11, #12 and #16 Niels explained the type of engine he was discussing and asking input on - OPOC. Not opposed engines as used in Snowmobiles, VW.s, Corvairs, BMWs

OPOC engines have been around since 1882

Per post #32 - Achates Power is actively working on a commercial OPOC design for modern applications.

As far as complexity -Two crankshafts are no more complicated/heavy than one parallel twin Rotax motor.
Rotax or OPOC 2 pistons, 2 rods, 4 crank webs, 4 bearings minimum.
Rotax 2 Heads OPOC - zero.

In post #12 the design goal of [email protected] ( [email protected] ) was given before M/G
Rotax 447 - [email protected]

Need is relative- Jet engines may not be the future powerplant of choice for Ultralight Craft
================================

Dude, if the OPOC Engines haven't caught on in 139 Years, your wasting your Time & Money! Just as many Companies jumped on the Wankle Rotary Engine account it was New, none could make it last long till Mazda did. There has hardly been any New Designed Engines come out that made any difference. Today there are some Small Cheap Jet Engines, but their Gas Hogs, so on 5 Gallons they don't go very far. 2 Stroke, Piston Port, Reed Fed, and Rotary Valve, are still the best engines for Part 103 and Small Kitplanes. Some of the Honda/Clone Singles/V Twins do show some promise. People have been trying to use VW, 1/2 VW, Subaru, Mazda, Corvair, etc., Car Engines for 40+ Years on Airplanes, which most are too Heavy for Part 103 and I don't think there is (1) of the 750+ Airframe manufacturers ever adopted any of them Engines! Even these Newer Brand Name 2 Stroke manufactures, per Rotax they have a 300hr TBO, but there are 582UL's and 503UL's with 1300+ hours and still Flying, Polini 450hr TBO, Simonini 600hr TBO, Hirth 1000hr TBO @75% Power, I have never heard what Compact Radial has for a TBO. Show me a VW, 1/2 VW, Subaru, Mazda, Corvair, etc., making 400hrs, 500hrs, 600hrs?

I could see an Opposed Piston Diesel Engine with a Turbo for Cars & Trucks, maybe Large Kitplanes. Where in a Plane they could burn Jet Fuel. Talk to me in 10+ Years when they get the kinks worked out for just Car & Truck use. With Global Climate Change, I seriously doubt anyone will be ordering Diesel Cars & Trucks. CA is already calling for Electric Cars & Trucks & Semi's.

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#### n3puppy

##### Well-Known Member
================================
Dude, if the OPOC Engines haven't caught on in 139 Years, your wasting your Time & Money!
People have been trying to use VW, 1/2 VW, Subaru, Mazda, Corvair, etc., Car Engines for 40+ Years on Airplanes, which most are too Heavy for Part 103
Show me a VW, 1/2 VW, Subaru, Mazda, Corvair, etc., making 400hrs, 500hrs, 600hrs?
The OPOC engine has been around for 139 years and keeps reappearing.
Why? Because it offers a number of potential advantages if some of the mechanical limitations are solved. As technology improves it may make a Spark ignition, petrol fueled OPOC economically feasible.

Way back in the 70's Rotax played around with Direct fuel injection, and Fresh air to transfer port engines. Direct Injection is common now. Fresh air to transfers could also be employed to further reduce emissions.

Horse and buggies were replaced by cars because of visionaries who took chances to improve the status quo. Of course Henry Ford didn't have the benefit of internet folk telling him he was wasting his time and money.

BTW - my Part 103 Legal N3-Pup with Global 1/2 VW had about 400 hours on it when the new owner flew it home with good compression

#### Armilite

##### Well-Known Member
The OP opened this thread about a much larger engine with OPOC design. What he proposed would probably be far too heavy for aircraft use (with the M/G function and hardware). For aviation, they have a hundred+ year history of being relatively light, extremely efficient but due to 100-75 year old fuel injection tech, not very powerful. Also, they are ideally suited for 2 cycle uniflow construction using diesel and/or jet as fuel - so yet another big plus for aviation use. 2 cycle diesels are very different animals from 2 cycle SI counterflow or loop scavenged engines. As to cost and power: OPOC diesels have been built at very low HP (small outboard) but long ago but mostly have been fairly large engines. No reason (see Achates once again) they can't be made in 4-6 place genav sizes. There have also been some 80-100HP designs over last 30 years, but for any of these to really be affordable there needs to be some mass market application that turns out parts and/or whole engines that can be used or adapted for aviation. This is what is going on with most JetA engine designs - using automobile engines as source.

I don't think they can scale down into the 40kW range mostly due to the size of injection components needed for CI, but actually could be built easily as an SI engine in that range. BUT, of course, it still gets back down to no sense trying to develop a whole engine for such a tiny market - ends up being very expensive.

On the two stroke thing: I have built literally hundreds of two cycle powered commercial airboats, mostly Rotax powered (503 days) and while I am not exactly 2 stroke SI crazy, they did an excellent job for us and let's face it, there is a massive component of sport aviation that simply wouldn't exist without them. Hard to beat the power/weight numbers.
===================================>

I could see an Opposed Piston Diesel Engine with a Turbo for Cars & Trucks, maybe Large Kitplanes, but not for Part 103 or even Small kitplanes. With the Global Climate changes and Politicians pushing for Electric Cars, Trucks, Bikes, even Semi Trucks, and Commerical Planes, and Snowmobiles. I don't follow ATV and Jet Ski much, but I wouldn't doubt their headed that way also.

I seriously doubt anyone will be Buying any Diesels in the near future, no matter how good they are.

Myself, I believe in Simplicity like a Rotax 277UL, 377UL, 447UL, 503UL, etc. Most, Home Built Ultralights and Small Kitplanes only need 26hp to 100hp.

A properly built 185UL is 184.2cc/7cc= 26.3hp! Built 1945 - 2009!

A properly built 277UL is 268.8cc/7cc= 38.4hp! Only (2) Rotax Engines are probably viable for Part 103. Built 1978 - 2008!

A properly built 377UL is 368.4cc/7cc= 52.6hp!

A properly built 447UL is 436.7cc/7cc= 62.3hp!

A properly built 503UL is 496.9cc/7cc= 70.9hp!

A properly built 462UL is 463.0cc/7cc= 66.1hp!

A properly built 532UL is 521.3cc/7cc= 74.4hp!

A properly built 582UL is 580.9cc/7cc= 82.9hp!

A properly built 618UL is 617.2cc/7cc= 88.1hp!

A properly built Skidoo/Rotax 670 is 669.2cc/7cc= [email protected]! A 670 turned 6750rpm same as the 618UL it can make 103hp! A 670 can be Big Bored to (82.5mm x 70mm) 748.6cc!

All of these Rotax Engines above can be Big Bored for more CC = More HP! In reality, probably 36hp+ pushes most Part 103 past the 55-knot Full Power Speed. The 277UL & 503UL can go up to 82mm with a new Sleeve.

A Rotax 912 comes in 80/100hp!

O-200 comes in 100hp.

Lycoming O-235 comes in 100hp!

There are 32+ different 2 Stroke Engine manufacturers some making 15 different Single Engines from 100cc to 400cc just for Sleds.

Do we really need another Engine?

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#### PMD

##### Well-Known Member
I could see an Opposed Piston Diesel Engine with a Turbo for Cars & Trucks, maybe Large Kitplanes, but not for Part 103 or even Small kitplanes. With the Global Climate changes and Politicians pushing for Electric Cars, Trucks, Bikes, even Semi Trucks, and Commerical Planes, and Snowmobiles. I don't follow ATV and Jet Ski much, but I wouldn't doubt their headed that way also.

I seriously doubt anyone will be Buying any Diesels in the near future, no matter how good they are.

Do we really need another Engine?
None of the above will burn Jet A, diesel, bio-D, fryer grease, etc. CI engines are truly multi-fuel. The you list also all require separate re-drives. Finally: most of the engines you list would be considered extremely high polluters so probably have very short future.

As I said: there won't be any such engine unless someone builds one in volume for another purpose. You will note that most of the engines you list exist for a different reason. Also as several have mentioned: the thread wasn't about 103 and small engines, it was about an OPOC proposal. A 277 Blowtax won't haul 6 people no matter how good the tuned pipe is.

#### Niels

##### Well-Known Member
I have had the honour of talking with Eric Bratt that was driving force behind the F16XL like Saab Draken.
He had been pilot of the Swedish Stuka during war2.His oppinion on small aircraft was that there had been no advance in fourseater aluminium aircrafts since Messeschmidt 108 from thirties.The way forward was stronger material and ligther and stronger and more reliable engines.So according to him we need no further aeroplane design butter better engines

#### PMD

##### Well-Known Member
Clearly neither he nor you have been following development of the Otto Celera. Incorporates existing technology just more thoroughly interpreted and integrated. Already flying.

#### Niels

##### Well-Known Member
Clearly neither he nor you have been following development of the Otto Celera. Incorporates existing technology just more thoroughly interpreted and integrated. Already flying.
Just like Boing 737Max

#### PMD

##### Well-Known Member
Just like Boing 737Max
In fairness, the Boeing 737 up until the engine change that resulted in the "max" was a truly fantastic airplane. The issue was related to management trying to modify a design to allow use of same pilots without a new rating for a new design by calling it the old design. There have been few airplanes since the DC3 that were actually so very good at meeting their design and utility goals.

The Otto Celera is far, far beyond the incremental progress made by Boeing and Douglas in commercial aircraft - ever. It is far closer to the giant leap in applied technology that resulted in the Lockheed SR-71. Similarly, the RED V12 represents a lesser but still significant step forward in the 500+ HP propeller driven world.

#### Niels

##### Well-Known Member
That is what I was thinking - Propellor loads - but a little different view.

What happens in a climbing turn?
Load is different on inside and outside props due to arc of the turn.

Granted not as bad as widely spaced twin engines mounted on different wings. But still there.

The way to find out is maybe to make a quarter scale aerobatic model with two electric motors ,two props(Mirrored) and then regulate two independent power controlers to keep props in synch.By measuring the power consumed to each and sample data or relay them back to sender it will be possible to estime ratio of varying torque of electric gen/mots to mean torque during wild maneuewering.

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#### Niels

##### Well-Known Member
The kW/kg estimation of the wonder engine twin prop consist of two parts.
First is the CE part
second is the two electric machines.
The CE part is easy.
If McCullough could make engines that ran more than a million revs 1945 so can we with same mass/volume if we see same maximum pressure in cylinder.
Maximum pressure must somehow be related to Brake Mean Effective Pressure and Compression ratio.

#### Niels

##### Well-Known Member
Numbers McCulloch O-100-1:
Bmep 5.6 bar 21.3 kg/liter

Wonder engine needs 4.2 bar and 1.2 liter trying to make 30kW at same compression ratio.(8 to 1)
Mass of fly-ready engine minus electric synchro can be less than 19kg using 1955 technology.

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#### Niels

##### Well-Known Member
Estimating the nessesary mass and torque capacity of electric synchro depends on type of aeroplane.
If plane can roll one turn per five seconds(is that realistic?) and props are synchroed to 60 rps we need some power tranfer from one to the other as one will do 60.2 and the other59.8 rps relative to the incomming air.
Power to a prop is a cube function of rps.
Instead of each absorbing 15kW one will need 15.150 and the other14.850 or roughly 150W from one side to the other.
Friction difference is to be avoided like Covid if it leads to seizure .
One way can be to have a infrared camera in each crancase monitoring piston temperature.
Friction difference can be estimated by letting engine run full power and then cut fuel,ignition and synchro and then study run down .
If we dimension for say 3kW max difference we need two electric machines of 1.5kw at 60rps capacity.
Emrax numbers indicate less than 1 kg for each machine.Quite some of the metal in the Emrax configuration is already accounted for in the mass of the CE.
We are still in phantasyland ,but at a higher level ,and state that flyable enginemass can be ca 21kg for 30kW prop power.