Vibration free powerplant.

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Niels

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It becomes tempting to try and build a reduced scale model as cheap as possible.
Is there somewhere one can buy two or three bladed ,mirrored but else identical model props say 300 to 400 mm diameter?
Synchronisation of shafts can be done with a crossed chain(Wrigth Brothers 1903) or a timing belt twisted 180 degree.
 
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wsimpso1

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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.
One million revs at 60 per second is 4.63 hours. Not much of a durabity target for anything except a one use airplane.
 

wsimpso1

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If plane can roll one turn per five seconds(is that realistic?)
No, it is not. Common max roll rates of non aerobatic small airplanes exceed 120 degrees per second with many exceeding 180 degrees per second. This alone requires an order of magnitude larger synch torques. Spin entry and spins will have yaw rates around the 1 turn per second range, with hugely different airflows to props separated by a couple feet - spin yaw center of rotation is typically near airplane centerline, with the two props traveling in different helix angles. Spin entry and spins are part of standard category certification, so this is not even a possibility for a "no aerobatics" placard. There are also snap rolls out there on the order of 360 degrees per second in yaw and very briefly applied yaw rates above 30 degrees/second are common. Both will put in substantial asymmetry in prop torques.

None of this is including the effect of any asymmetry of accels due to port and piston mass asymmetry, nor the inherent effect of any out of synch of the two cranks to drive the cranks further out of synch.

I suspect that the current estimation of prop synchronization torques and energy are being greatly underestimated. While a "no aerobatics" placard may seem an option, spin entries and quick roll and yaw corrections are expected - having the engine immediately stop makes the resulting recovery from these expected unusual attitudes much more challenging, and I suspect is an unacceptable failure mode. Please get serious about the amount of asymmetry in prop torque available and the amount of synch torque and energy needed.

Billski
 
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Niels

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Thank You for comments.
Numbers and calculations will be even more usefull .
I plan on supplying the infinite 30 kW market for aeroplanes that cannot be rolled faster than once per two seconds.
If cranks get out of sync ,fuel and /or ignition will be cut and props can windmill until situation changes.
It will shake like an old single cylinder motorbike but stay together for some minutes
 

wsimpso1

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Thank You for comments.
Numbers and calculations will be even more usefull .
I plan on supplying the infinite 30 kW market for aeroplanes that cannot be rolled faster than once per two seconds.
If cranks get out of sync ,fuel and /or ignition will be cut and props can windmill until situation changes.
It will shake like an old single cylinder motorbike but stay together for some minutes
Imagine this - you are flying over a spot on the ground, looking at something. You add some back pressure perhaps a bit of rudder keep it in sight and the airplane commences a spin entry with a rapid yaw and roll to one side. Recovery is executed by full rudder against the yaw rotation and the stick comes forward aggressively. The rotation stops and you are now in a banked dive, which is recovered from by coordinated rudder and aileron toward wings level and then elevator to level flight. That is standard spin recovery. But the props have wound down and stopped because the cranks went out of synch during the spin entry. You now have a forced landing right now because the engine cut out.

Is that the performance you want? I don't even care about it shaking, I care about a pilot first doing a spin recovery immediately followed by doing a forced landing because the engine stops. Can you reasonably expect a pilot to execute both of these cleanly and safely, right after one another? In the US, this makes for lawsuits, while aviation authorities in many countries will likely figure out you have this nasty failure mode and ground airplanes with this engine.

While cutting fuel and spark makes sense when the cranks go out of synch, I suspect that this mode should require an immediate and automated synch and re-start.

All of this brings us to another question - while alternators on the cranks may be able to maintain crank synch while running, how do you expect to synch cranks for engine start? Seems like the e-machines on the cranks would have to be be pretty powerful rotary actuators as they must synch the cranks while cranking the engine for start as well as automatically maintain crank synch while running.

E-machine coupling of the cranks that allows us to do everything we might do with an airplane begins to look pretty heavy and complicated compared to a nice simple gear train...

Billski
 
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Niels

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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.


Newer technology
Lycoming io390
BMEP 11bar / 22kg/l
Wonder engine same compression ratio 9:1
Needed BMEP 4.2 at 1.2 liter gives 30kW for a fly ready mass of ca10kg.
Wonder engine has better stroke bore ratio,
no camshaft and no cylinder heads so estimate is conservative.

I am working on the way to describe Synchro torque needed if Cranks and generators are out of phase.Patience please
 
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Niels

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Asume that Lycoming cylinder pressure is 42 bar around 30 degree after top dead center.
Wonder engine has one crank at 31 degree and one on 29 degree and due to lower needed BMEP we asume a pressure of 16 bar.
Crank arms are 60mm and connecting rods 170mm and piston top areas 0.05 sq m.
The 31 degree will give166Nm and the 29 degree 155Nm
Difference 11Nm.
From the Emrax link (My Bible) we can se that the type 188 (mass 7 kg) can handle 55Nm
I cannot know how many pole pairs are involved but let me asume 12 pairs in each machine.
 
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TopherJA

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Could you fold this engine in half and make it into a vtwin with a single crankshaft and a head that connects the two cylinders forming the shared combustion area. Porting and single flow remain the same. The v angle provides the offset angle between intake cylinder and exhaust cylinder. Be a much simpler mechanical solution.
 

Niels

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Could you fold this engine in half and make it into a vtwin with a single crankshaft and a head that connects the two cylinders forming the shared combustion area. Porting and single flow remain the same. The v angle provides the offset angle between intake cylinder and exhaust cylinder. Be a much simpler mechanical solution.
Puch of Austria made that many years ago and it was a very good motorbike.


but it was certainely not vibration free and that is what I have a go at.
I am thinking rather hard how to model mathematically how my arrangement will react to being in an inverted flat spin.
 

PMD

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Could you fold this engine in half and make it into a vtwin with a single crankshaft and a head that connects the two cylinders forming the shared combustion area. Porting and single flow remain the same. The v angle provides the offset angle between intake cylinder and exhaust cylinder. Be a much simpler mechanical solution.
This has been done in the past - actually called a "Folded" opposed piston layouut. Problem with that is you need massive counterweighting in the crank since both pistons ascend and descend together - like a big single. Hardly an appropriate design for a vibration free airplane engine
 

Niels

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My son and a friend in a VL-3 aeroplane visited me some years ago.
Friend was part owner and it was nice to try piloting again.
A week later it spun in and two other part- owners died.
One of them had sailplane aerobatic rating and they had asked for permission to do some airwork.
I do not think power level had any influence.
Radar showed a very fast end.
Sons friend is now part owner of a polish built Vans two seater and find it almost as nice as the VL-3 but more expensive to opperate.
A low mass/cost 60kW powerplant has surely some use in future.
A single 1.70m prop doing 40rps are allowed noisewise on some small airports.
Two props 1.3m dia 0.85m apart will sweep same area and thus have same efficiency (more or less).
Wonder engine geometry with 0.85m shaft separation allows two piston strokes of ca 140mm and if we think 12.5 mps acceptable as piston speed, they shall do 45 rps.
For connecting rod clearance we need ca 100mm bore.
Swept volume will thus be close to 2.2 litre.
We need a bmep of 6 bar to make 60kW
A compression ratio of 8 is maybe possible without leaded fuel.
Lycoming IO390 materials,heat treatment etc needs 22kg per litre for a BMEP of 11bar and have same compression ratio.
Wonder 60kW engine can be 24kg for engine parts.
The combustion engine parts will try to diverge.
The leading crank will enjoy more expansion and do less compression.
It has been calculated for the 30kW engine above to vary between zero to 11Nm during one revolution for two degree divergence. For the present 60kW version it can be asumed to be ca 6Nm per degree as mean value.Mean is more important than peak as there is a lot of rotary energy in rotating parts.
It will beneficial to all man kind if someone here can exctract the corresponding stabilizing mean torques from two Emrax machines in paralel.If we asume that two 188 machines will do, we can have a vibration free/ very low noise 60kw aeroengine with a mass of 24 plus two times 7 equals 38 kg.
This will be passive stability like decent airplanes but if we regulate actively like F16 it will be much less.
 
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wsimpso1

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I am thinking rather hard how to model mathematically how my arrangement will react to being in an inverted flat spin.
The limiting case would be axis of yaw rotation in line with one prop, net zero torque on that prop, other prop at max torque and having P factor torque oscillations. The average torque mismatch will be the torque of one crankshaft. The oscillatory mismatch will be from P-factor inputs at blade passing frequency. You would have to then integrate the accel curve on the loaded prop twice to get rotation error that you have to null out. Since blade passing will likely be at least 2 per rev and is drawn at 3 per rev, the vibratory angle error might be small enough to keep in bounds…

Synch torques are probably like brace forces to prevent column buckling - really small around zero deflection, but get big in a hurry as deflection increases.

I suspect the other big issue is syncing the two cranks for starting.

Billski
 

WonderousMountain

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This proposed prop-power was on my mind bugging me and dawning it is the wrong, or abnormal use case, here is the perfect opportunity to make a twin that has four props. Maybe for eccentricity, or as a tech test bed, but as a twin in four prop configuration, the merits can be carefully assessed.
download.jpeg
 

WonderousMountain

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Never got around to joining this site,
but I read the comments whenever a
search results in a relevant thread. It
will answer your AeroModelling query.
 

Niels

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It will answer your AeroModelling query.
Thank You for link. Very,very interesting that one can buy so much for so little.
Spin testing my wonder engine will be less dramatic in model size and just as relevant.
First step in PARE Spin recovery is to reduce power.
The first to realise that we are spinnig is the power controller between props.
If it has a feeling that power exchange is getting asymmetric it shall reduce throttle to idle
For keeping the two idling props in a spin synchronized their synchro engines must have a certain size.
We therefore need to know how much velocity and difference in air velocity the two propellers see during a spin.
Any voluntaries?
 

wsimpso1

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First step in PARE Spin recovery is to reduce power.
If synch is inadequate, the engine will have already lost synch before you or the controller can reduce throttle. Then there is the issue that builder-pilot community is unlikely to buy any engine with automated power reductions built in. Too many ways for it to put the pilot in a forced landing….

We therefore need to know how much velocity and difference in air velocity the two propellers see during a spin.
Any voluntaries?
I already provided the limiting case. Full power on the one with a radius from the rotation radius and a decent helix angle, zero power on the one at the rotation axis, going straight down, and big P-factor on each prop blade as they go around. This may overstate actual worst case, but given the range of airplane responses possible, it is probably not a huge over-estimate.

The investigator has to do the math.

Billski
 

Armilite

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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.
==========================

A Mazda Rotary can be converted to burn Jet A and are extremely Smooth running, but they're Heavy even with the Aluminium Housings and put out a lot of Heat. Also been Turboed. Finding a Good Reduction Drive is the biggest problem.
 

PMD

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

A Mazda Rotary can be converted to burn Jet A and are extremely Smooth running, but they're Heavy even with the Aluminium Housings and put out a lot of Heat. Also been Turboed. Finding a Good Reduction Drive is the biggest problem.
As I understand it, there are a few very well proven re-drives for the Mazda rotaries up to some pretty decent power levels. The thermal efficiency is limited by the huge surface area that the moving combustion chamber needs due to the very design and geometry of the engine. There are far better ways to burn Jet fuel in an airplane (and I really do NOT mean in a turbine). The rotaries are incredibly smoothe but if going to compression ignition the heat rejection would make them hard to keep running on something like a long power off descent. Of course, spark ignition (which is how I think rotaries running on jet or diesel have already been run) or spark assisted CI would solve that issue. They really are not that heavy, especially with aluminum side plates and peripheral porting (ideal for constant speed such as aircraft use).
 
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