Drivetrain Power Loss

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DangerZone

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Motorcycle shaft drives don't need to differentiate rotational speed between 2 wheels, since there's only one drive wheel. ( ignoring fringe off road 2X2 bikes that don't use shaft drives. )

There are various ways to dampen or redirect the torque trying to raise & lower the rear wheel on the swing arm. None matter to us here. They don't apply to airplanes and aren't differentials.
You are absolutely right about what you wrote. However, you are completely disregarding that the shaft driven motorcycles need to differentiate torque applied to two axles: one on the wheel and the other on the swingarm. Also, toque and power are the good sides of the deal, but torsional vibrations, inertial vibrations, driveline virbations and velocity fluctuations are the bad sides of the deal concerning motorcycle drive shafts. It seems many here have some odd idea these will not affect efficiency. I like your optimism, but reality does not work that way.

Finally, who cares if you can't find a name for "the thing which is not a differential, but many call it a differential"? I'll just keep on calling it a differential beacuse millions of people call it that name, unless you have another better standard or official name for the freaking thing. If you got nothing, I can't call it nothing. Now, does this "thing which is not a differential" lose efficiency big time? Yet, it does. Much more than straight bevel gears, which are noisier and less strong, but apparently do not lose so much efficiency.
 

BJC

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Finally, who cares if you can't find a name for "the thing which is not a differential, but many call it a differential"? I'll just keep on calling it a differential beacuse millions of people call it that name, unless you have another better standard or official name for the freaking thing.
One necessity for the study of any science is consistent, proper use of names, definitions and units.

The so-called “renewable energy” crowd has, for decades, lost credibility because they interchange “power” and “energy” when making claims, then complain that people who correct them are trying to obfuscate the issues.

Stress, strain, work, energy, mass, force, momentum, fuel, oxidizer, et al, are specific things. Reasonable discussions without proper definitions are impossible.


BJC
 

Sockmonkey

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The so-called “renewable energy” crowd has, for decades, lost credibility because they interchange “power” and “energy” when making claims, then complain that people who correct them are trying to obfuscate the issues.
Ooo, I hate when they do that. This is why I avoid science articles unless I have someone in that field to ask about the subject because the people who write them usually misunderstand the results or terms used.
 

mcrae0104

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You are absolutely right about what you wrote. However, you are completely disregarding that the shaft driven motorcycles need to differentiate torque applied to two axles: one on the wheel and the other on the swingarm.
The final drive gear on a motorcyle transmits torque to the axle and does not "differentiate" anything.

Wikipedia:
1618789967537.png

Merriam-Webster:
1618790011034.png
 

rv7charlie

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The so-called “renewable energy” crowd has, for decades, lost credibility because they interchange “power” and “energy” when making claims, then complain that people who correct them are trying to obfuscate the issues.
About 85% of the so-called 'aviation' crowd makes the same mistake. Like every time someone thinks that a 1.5 lb lithium battery can replace their 15 lb SLA without any limitations.
 

Dan Thomas

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The hypoid gears are usually stronger and quiter, but at the cost of losing more efficiency than sprial or other gears. If I am not mistaken, many modern cars and trucks ditch the hypoid and spiral gears to increase efficiency.
Front wheel drives don't use hypoids. They don't need to; there's no need to change the direction of rotation 90°. They just use helical gears like everywhere else.

Hypoids use a high-pressure gear lube that reduces the friction to nearly nothing. I don't remember ever seeing scorched paint on a differential case, as would be common if they lost a lot of power through friction, meaning heat. Not even on heavy trucks doing tremendous pulling, like the logging trucks in the northwest mountains.
 

poormansairforce

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Stupid me...... here I thought I had joined Home Built Airplanes and apparently found a rogue forum about motorcycles, u-joints, differentials, and auto suspension design none of which apply to airplanes. I guess if I ever happen to build an airplane with those parts I'll come here......🙃

This whole thing started with a claim of significant losses using shafts. Most PSRUs have 2 shafts linked by a belt, gears, or chain. Please explain these large losses from this viewpoint! We are not dealing with motorcycle parts and pieces nor long, complicated paths to transmit torque. Just 2 shafts linked with one of the above along with the same bearings and possibly some seals.
 
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DangerZone

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One necessity for the study of any science is consistent, proper use of names, definitions and units.

BJC
You are absolutely right, and I am still waiting for you and everyone else here to provide a proper name for "the thing which is not a differential".

The final drive gear on a motorcyle transmits torque to the axle and does not "differentiate" anything.
Ok, sorry for the grammar. Did you understand the problem of the axle torque and wish to provide an engineering solution for swingarm deflection when power is applied, or you thought that correcting my words would make the shaft effect go away and disappear?

Front wheel drives don't use hypoids. They don't need to; there's no need to change the direction of rotation 90°. They just use helical gears like everywhere else.

Hypoids use a high-pressure gear lube that reduces the friction to nearly nothing. I don't remember ever seeing scorched paint on a differential case, as would be common if they lost a lot of power through friction, meaning heat. Not even on heavy trucks doing tremendous pulling, like the logging trucks in the northwest mountains.
We were talking about motorcycle shaft drives which often use hypoids for the 90° direction of rotation.

Please understand that everything you typed here is correct. I asked what you called a motorcycle differential, and you answered what is a differential. There is no doubt that what you wrote is true and we agree on what a differential is, but it does not answer the question what you call this thing. We talked about motorcycle shaft drive "90° direction of rotation mechanisms in shaft drive motorcycles" (there, I skipped the word "differential"), and you wrote that front wheel drives don't use hypoids, which is also correct. But it does not answer the efficiency loss in hypoids used in motorcycle shaft drives, friction is not the only loss.

The same goes for the start of this thread. I point out that efficiency losses in a motorcycle shaft drive are much higher than 1%, and many here asume that all losses must turn to heat. When I explicitly write that not all losses are heat, and post a video which shows the effects of torisonal vibrations, inertial vibrations, driveline vibrations and velocity fluctuations - nobody comments. Neglecting all these effects could lead to a lot of problems if someone on HBA tried to do a shaft drive prop, and the BD-5 is a great example when people neglect these effects in an aircraft solution. They don't go away. if you don't write about them.

Those who understand these effects could have much less efficiency losses if they decide to design or build a PSRU and/or a shaft driven propeller in a homebuit aircraft.
 

AdrianS

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People have stopped replying because you are wrong, and you won't admit that you don't understand basic physics.

For the last time (from me), engine power 'lost' is not destroyed. It is converted to another form, eg. heat, noise, etc. If you're not capable of understanding this, we'll never get anywhere.
 

ghostrider

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I´ll have a go at it.

Just read through the thread and it ought to be abundantly clear to any observer that there are experts here with many years of experience in fields that are relevant to the topic. The topic being drive train losses. Great. What are they? Power applied to a drive train that does not contribute to the end goal of the appliance, loosely defined. What is their nature? Generally friction, but other examples have been listed in the thread. Relative to friction how large are these other types of losses (sound, vibration asf.)? Vanishinly small if the system is well designed which we will assume. These vanishingly small other losses, what do they end up as when they have dissipated? Heat. How does friction show up? As heat. All losses will end up as heat (vibration included, but the designer should aim to minimise them as they could lead to premature failure, which is generally the overriding consideration). They may express themselves as something else for a while but the end result is heat. It is like a train line, it has a few stops along the way and a final destination. The train may stop at one or two of the stops but the final destination is the same. So, this heat needs to be dissipated. Heat dissipation at the rate that would be necessary for the power levels suggested would either require a design effort in the form of a heat exchanger or result in a very large delta in temperature. Either would increase the rate of heat exchange. Drive shafts and final drives do not generally sport large heat exchangers and they can safely be touched with bare hands even after long periods of operation. This leaves only one variable in the equation. The amount of energy dissipated. It can´t be very large or one of the two outcomes described above would manifest. Hence their level of efficiency is high. Maybe not quite as high as a (well adjusted, lubricated and clean) chain. But they do not dissipate 5-15 kW of power or any where near that. They would become searingly hot. It is just that simple. If the power was disspated as vibration the bike would be sitting in your garage after a ride shaking itself to bits. That generally does not happen. But the exhaust keeps ticking away for a while after shut down. That indicates a high delta T situation in the process of dissipating. All of this has been expressed before in the thread by several others. Experts in drive trains and transmissions. I think they might know a thing or two about power transmission and losses.
 

Pilot-34

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Off topic: I appreciate good engineering, and I'm sure it would be great to ride a really well tuned motorcycle (and be skilled enough to wring it out).
OTOH, I feel lucky to enjoy many cheap, common thrills. Tearing around the track in a little 5hp rental go-cart is fun (crummy suspension and all). I'd enjoy a thoroughbred dirt bike, but an old Honda MiniTrail can still bring me a lot of smiles. I enjoy a nice steak, but a good pizza is never a disappointment.
Sometimes I wonder if I flew a Pitts a few times if I'd then find less responsive planes to be a disappointment, or less fun. After all, I was fine with dial-up internet until I got broadband. But, I think I'd still enjoy flying other aircraft and wouldn't get spoiled. They are all different and I can learn something from every one of them, and I can have fun flying them.
The key to enjoying flying in any airplane is to fly it for what it’s for.
A c-150 is great when you wanna excuse to get in the air and peek at your neighbors pond and work on pinpoint grass landings .
A c-207 will make you grin when you are hauling 2 friends and 3 moose home in one trip.
And you might be happier with a citation if you commute daily from Chicago to Phoenix
 

mcrae0104

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... I am still waiting for you and everyone else here to provide a proper name for "the thing which is not a differential".
It’s called a final drive.

Did you understand the problem of the axle torque...
Yes, I do understand shaft effect. My first bike was a shaft-driven ‘82 XJ650, which gave me a practical education on it.

...and wish to provide an engineering solution for swingarm deflection when power is applied, or you thought that correcting my words would make the shaft effect go away and disappear?
I don’t wish to, because shaft effect is generally unrelated to aircraft design applications, which do not have a swingarm, nor a 90-deg final drive, nor do they experience the relatively rapid changes in power output that drives shaft effect. In particular, shaft effect is unrelated to drivetrain power losses.
 

DangerZone

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People have stopped replying because you are wrong, and you won't admit that you don't understand basic physics.
I am wrong and I do not understand basic laws of physics because I do not believe that drivetrain losses from crankshaft to rear wheel could be less than 1%? That's a good one. Hilarious.

For the last time (from me), engine power 'lost' is not destroyed. It is converted to another form, eg. heat, noise, etc. If you're not capable of understanding this, we'll never get anywhere.
So finally, you admit my claim that not all losses are heat. That's progress. Now see all the links I posted on this thread and then we can discuss specifics.

I´ll have a go at it.

Just read through the thread and it ought to be abundantly clear to any observer that there are experts here with many years of experience in fields that are relevant to the topic. The topic being drive train losses. Great. What are they? Power applied to a drive train that does not contribute to the end goal of the appliance, loosely defined. What is their nature? Generally friction, but other examples have been listed in the thread. Relative to friction how large are these other types of losses (sound, vibration asf.)? Vanishinly small if the system is well designed which we will assume. These vanishingly small other losses, what do they end up as when they have dissipated? Heat.
Thank you for your try. Are you aware that all losses are not heat and that some drivetrain systems, just like engines, can be more or less efficient by design? You have shown the perspective based on an assumption that engines and drivetrains are perfectly designed, not well designed. In a perfect world, or in Space, this could be so. In the real world, an engine or a drivetrain design is a compromise. It is as good as it gets. Not perfect. It has losses, and not all losses turn to heat. Billski's claim of less than 1% losses in a motorcycle drivetrain are close to what is called an Ideal machine - Wikipedia.

Did you try to verify your assumption and ask yourself: if all losses turn to heat, why don't all Harley Davidson motorcycles constantly overheat? They have the lowest efficiency in the world, less than 19% efficiency. They don't even have water cooling, only air cooling. Then ask yourself, how efficient are the most efficient internal combustion engines in the world? A very efficient Mercedes Benz diesel could be slightly less than 50% efficient, and still overheat less than a typical HD motorcycle. Just like engines, drivetrains can be more or less efficient, hence the motorcycle chain and shaft analogy.

The topic of this thread is about losses concerning Mechanical efficiency - Wikipedia and Work (physics) - Wikipedia, which is slightly different than engine efficiency and Energy conversion efficiency - Wikipedia. True, heat dissipates like I already wrote. Well designed systems have an efficient cooling system and engineering solutions to reduce efficiency losses. A typical example would be ditching the hypoid gears and using regulars ones for more efficiency, at the expense of more noise and less strength.

All losses will end up as heat (vibration included, but the designer should aim to minimise them as they could lead to premature failure, which is generally the overriding consideration). They may express themselves as something else for a while but the end result is heat. It is like a train line, it has a few stops along the way and a final destination. The train may stop at one or two of the stops but the final destination is the same. So, this heat needs to be dissipated. Heat dissipation at the rate that would be necessary for the power levels suggested would either require a design effort in the form of a heat exchanger or result in a very large delta in temperature. Either would increase the rate of heat exchange. Drive shafts and final drives do not generally sport large heat exchangers and they can safely be touched with bare hands even after long periods of operation. This leaves only one variable in the equation. The amount of energy dissipated. It can´t be very large or one of the two outcomes described above would manifest. Hence their level of efficiency is high. Maybe not quite as high as a (well adjusted, lubricated and clean) chain. But they do not dissipate 5-15 kW of power or any where near that. They would become searingly hot. It is just that simple. If the power was disspated as vibration the bike would be sitting in your garage after a ride shaking itself to bits. That generally does not happen. But the exhaust keeps ticking away for a while after shut down. That indicates a high delta T situation in the process of dissipating. All of this has been expressed before in the thread by several others. Experts in drive trains and transmissions. I think they might know a thing or two about power transmission and losses.
Again, this is your assumption. In theory, yes. A substantial amount will turn to heat, like I already wrote before. But that is not all. In reality, it is much more complicated. For example, the inertial losses do not have to turn to heat, but often lead to inertial vibrations. Velocity fluctuations? Driveline losses and slips? Torsional vibrations? You think they all must turn to heat? People who neglected all losses in the past have had exactly the same idea and ended up with broken engine mounts or other stuff and an engine which was NOT overheated. You are doing the same thing here and neglecting reality by saying a designer should design the engine ideally. No matter what reality sets as limitations. Believe it or not, most designers usually are not aware of some torisonal vibrations or inertial losses, or some other losses, simply because they do not calculate them and think they are not there. Or they think these losses are irrelevant.

I believe this is your problem, many here think inside a box. I showed everyone the method I use (again, it is not mine, many engineers do it the same way Drivetrain losses (efficiency) – x-engineer.org ) and this method accounts for all driveline losses from crankshaft to rear wheel. The same could be done for a system from crankshaft to propeller. This is easily verifed by measuring the power (and torque) at the crankshaft, and then at the rear wheel. Most of you claim this is wrong, that I am wrong. Why? Probably because most have not tried that before. So, am I really wrong because I measure stuff and calculate? Doubt it. Why don't you do it and see your results? Most people will probably never do that because there would be a huge difference between the calculated and real results. And 1% losses in a motorcycle shaft drivetrain are way beyond reality, somehwere in Neverland.

It is just that simple.
You know what? You are right. It is simple, there are more interesting threads than this one. :)
 

TFF

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Being a little hard on terminology when everyone here knows what he is saying. It’s about loss of energy and there is a disagreement on how much. It’s been a long time since I had a bike. My 73 Yamaha 750 3 cylinder probably waisted a lot of hp in the final drive, where my 92 Honda CBR600F2 was at the height of the horsepower racing wars. Every trick counted. I believe the SCCA stopped people from using motor oil for wheel bearings in the Spec Racer class, because it was an advantage. Gear oil, as necessary as it is , is a power loss. Weight of components are a loss in power, configuration is a loss in power. It all adds up. Quality of manufacturing adds up. Person designing adds up. The math might be right, but the quality is usually not there. Surprisingly, not to someone really building it. There is always a tool, shape, coating that is just not obtainable at whatever price level you are at. Something at a volume of 10-20 a year and has to support a shop is going to trade high tech for it works. Consumer really doesn’t know in general.
 

ghostrider

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I am wrong and I do not understand basic laws of physics because I do not believe that drivetrain losses from crankshaft to rear wheel could be less than 1%? That's a good one. Hilarious.



So finally, you admit my claim that not all losses are heat. That's progress. Now see all the links I posted on this thread and then we can discuss specifics.



Thank you for your try. Are you aware that all losses are not heat and that some drivetrain systems, just like engines, can be more or less efficient by design? You have shown the perspective based on an assumption that engines and drivetrains are perfectly designed, not well designed. In a perfect world, or in Space, this could be so. In the real world, an engine or a drivetrain design is a compromise. It is as good as it gets. Not perfect. It has losses, and not all losses turn to heat. Billski's claim of less than 1% losses in a motorcycle drivetrain are close to what is called an Ideal machine - Wikipedia.

Did you try to verify your assumption and ask yourself: if all losses turn to heat, why don't all Harley Davidson motorcycles constantly overheat? They have the lowest efficiency in the world, less than 19% efficiency. They don't even have water cooling, only air cooling. Then ask yourself, how efficient are the most efficient internal combustion engines in the world? A very efficient Mercedes Benz diesel could be slightly less than 50% efficient, and still overheat less than a typical HD motorcycle. Just like engines, drivetrains can be more or less efficient, hence the motorcycle chain and shaft analogy.

The topic of this thread is about losses concerning Mechanical efficiency - Wikipedia and Work (physics) - Wikipedia, which is slightly different than engine efficiency and Energy conversion efficiency - Wikipedia. True, heat dissipates like I already wrote. Well designed systems have an efficient cooling system and engineering solutions to reduce efficiency losses. A typical example would be ditching the hypoid gears and using regulars ones for more efficiency, at the expense of more noise and less strength.



Again, this is your assumption. In theory, yes. A substantial amount will turn to heat, like I already wrote before. But that is not all. In reality, it is much more complicated. For example, the inertial losses do not have to turn to heat, but often lead to inertial vibrations. Velocity fluctuations? Driveline losses and slips? Torsional vibrations? You think they all must turn to heat? People who neglected all losses in the past have had exactly the same idea and ended up with broken engine mounts or other stuff and an engine which was NOT overheated. You are doing the same thing here and neglecting reality by saying a designer should design the engine ideally. No matter what reality sets as limitations. Believe it or not, most designers usually are not aware of some torisonal vibrations or inertial losses, or some other losses, simply because they do not calculate them and think they are not there. Or they think these losses are irrelevant.

I believe this is your problem, many here think inside a box. I showed everyone the method I use (again, it is not mine, many engineers do it the same way Drivetrain losses (efficiency) – x-engineer.org ) and this method accounts for all driveline losses from crankshaft to rear wheel. The same could be done for a system from crankshaft to propeller. This is easily verifed by measuring the power (and torque) at the crankshaft, and then at the rear wheel. Most of you claim this is wrong, that I am wrong. Why? Probably because most have not tried that before. So, am I really wrong because I measure stuff and calculate? Doubt it. Why don't you do it and see your results? Most people will probably never do that because there would be a huge difference between the calculated and real results. And 1% losses in a motorcycle shaft drivetrain are way beyond reality, somehwere in Neverland.



You know what? You are right. It is simple, there are more interesting threads than this one. :)

Ok, grand. How do the losses that are not heat dissipate?

Why dont harleys overheat? Really? Is this a serious question? They don´t produce much power so even though the losses are a substantial fraction of the energy in the fuel the engine reaches equilibrium with the environment. The fact that you bring up the example and comparison between the HD and the MB and suggest that their overheating should be related to their efficiency is nonsense. They are systems that are designed to work. Why would a system that is designed a certain way overheat? Thats like saying a long bridge would fail because you heard that a shorter one did once. How long is a piece of string?

Yes you calculate, but you use incorrect and sometimes quite absurd assumptions and bad data so your results are likely unreliable.

If the drive train absorbs all this power where does it go?

Torsional vibrations? Really? What does that generate? Oh, that would be heat. But parts can fail before they overheat, especially if they resonate.

I could not possibly have assumed anything about engines because I did not mention an engine in my original post. And having a discussion about a poorly designed system makes no sense, so yes I assume that quite a bit of work went in to mitigating negative properties of the system.

I think you are confusing what people say when they mention numbers. A ball bearing is about 99% efficient according to your source. A mesh gear 98-99%. Several of those in a series will lead to an over all efficiency of the drivetrain in the case of the motorcycle of around 90%. A chain drive bike might be 91% overall and a shaft might be 89%. So the shaft drive comes with a small penalty over the chain but that doesn´t mean that all of a sudden the whole drivetrain loss happens in the final drive.
 

Dan Thomas

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You are absolutely right, and I am still waiting for you and everyone else here to provide a proper name for "the thing which is not a differential".
That's not our problem. That's yours, along with the other bike people. YOU come up with an accurate name for it. "Differential" is completely wrong. "Final drive" makes more sense and is used in many other similar applications.
 

Aesquire

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and I am still waiting for you and everyone else here to provide a proper name for "the thing which is not a differential".
Final Drive Unit.
Because it's the last link from engine to output/wheel/propeller.

Or 90 degree gear case.

Both are correct, descriptive, and in common use by the manufacturers.

Differential is a different critter.

I can't apologize for guys on E-bay who use the wrong words. They are in error.
 

Aesquire

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Re: all inefficiency becomes heat.

technically true, but difficult to measure sometimes. The noise of a gear train isn't heat, at your ear, but eventually dissipates as heat in the larger environment. So there's a efficiency percentage lost that isn't measurable by putting a thermometer on the noisy gear case.

I freely admit I don't know the correct number, percentage of loss here! I can only point out false assumptions.

Not every energy loss is easily measured as heating the gizmo. In the real world, these things exist, work, and don't vaporize when in use. So X kilowatts of lost power isn't all in one place.
 

Aesquire

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But, I think I'd still enjoy flying other aircraft and wouldn't get spoiled. They are all different and I can learn something from every one of them, and I can have fun flying them.
Sure!
I enjoy a minibike or a race machine.... Depending on the shape my spine has to take. ;)
After 40+ years of motorcycle riding, I decided top speed, towing a trailer, or 1/4 mile times were not priorities. I did like banking and cranking, acceleration G loads, ( cheap thrills ) and great brakes. ( to save me from my own misjudgment ). Thus my choices may not please others.

Ditto in aviation. I don't have the budget or need for going to Vegas in a day, so I don't care much about high speed commuter craft. I do admit to a bit of envy & lust for the Rocket "hop up" craft evolved from the Vans awesome line. :)

Drive train design discussion is very relevant to the folk looking at ( just for example ) low Aspect Ratio planes with engines and props arranged differently than a Cub or a Comanche. Looking at existing road vehicle equipment and asking if it will work for your application is logical.
 
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