Drivetrain Power Loss

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Pilot-34

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Actually I’d say that a lot of the discussion of motorcycle reference could be relevant to buried engine twin propeller drive which is something that apparently several of us with an interest in sea planes have considered
 

Aesquire

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We're not the only ones arguing about this.



 

Aesquire

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Aircraft drive shaft systems are notorious for vibration issues because of our desire for light weight and propellers aren't Wheels!

that said, you do want to know how much cooling & associated drag you need with different drive technologies.

Take a hypothetical replica Vought V-173 Flying Flapjack. A central engine behind the pilot with driveshafts to the (2) 90 degree Final Drive units & shafts to the (2) propeller hubs. We'll assume a budget build using COTS components, so, for example, the (2 driveshaft) 90 degree central unit could be a cut down off road "rear end" aftermarket unit for a small mini truck or "4 wheeler". With a spool installed in the "rear end" so locked ( no differential ) with no clutch or other power wasting stuff & power to both props equally. And (2) 90 degree motorcycle Final Drive units.

Not the lightest possible, and a vibration calculation challenge, but rule of thumb ( "hey! Where's my Thumb?" ) engineering says if the parts are good for thousands of miles with over 100 hp. they might make it off the ground.
 

thjakits

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In this scenario - a "wheel on the ground"-dyno is a bit of a gamble on getting actual numbers.
As mentioned above - it is a decent tuning tool, where you compare "before/after/between" - but the actual absolute power numbers are to vague - too many variables from the rim to the roller...
A better way would be a hub-dyno - the generator/motor can be precisely calibrated - so whatever it reads has only drive-train losses to deal with - you could even have an adapter made and bolt it to the gearbox instead of the chain sprocket and this way take out any chain and hub losses...

Now , make no mistake - things are getting HOT on/in the bike, but the % losses mentioned above would be "powerplant level" - you should be able to run your house on 10kw output!!

thjakits
 

Sockmonkey

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I owned a car that had the rear disk brakes mounted on the inner end of the half-shafts, right beside the differential. This did a good job of reducing unsprung inertia, but made brake maintenance a real chore.
Seems like the kind of thing you'd only want on offroad vehicles where quick suspension response is more critical.

I remember reading about how the initial aircraft flight tests of the Fairchild Caminez engine caused horrible vibration, which seemed weird to me because the engine itself is perfectly balanced. From what I've learned on here, it must have been torsional vibration that did it in.
 

Dan Thomas

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Seems like the kind of thing you'd only want on offroad vehicles where quick suspension response is more critical.
It gives a smoother ride in cars. That mass, when encountering a bump, is reluctant to move quickly so it decelerates the car a bit. So the ride gets bumped vertically and horizontally.
 

galapoola

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Well, we do call convective heat exchangers "radiators" for no good reason.

Just stirring the (putrid, foul) pot . . .
Reminds me of that George Carlin joke, why call it a hot water heater, who needs to heat hot water?
 

galapoola

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Also, about the energy/heat phenomeno, I worked in a motion film laboratory and the processors would heat up all the liquid baths once the film was running. I always thought it was a chemical reaction but turns out it was friction. We’d have to use chillers somtimes to keep the temperture sensitive baths from over heating.
 

mcrae0104

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Not only is the ride smoother with less unsprung mass, the driver can maintain more precise control. Any time the wheels are relatively more or less loaded, more or less frictional force is available for acceleration, braking, or turning. The goal is to have the wheel in contact with the road without the lag of a massive swingarm/wheel/brake assembly throwing the system off with lag. Surely you've run through a dip or over a bump in a sweeper and felt the car yaw momentarily as a result, no? If not, maybe you need to drive faster. ;) It's not a matter of on-road vs. off-road; it's a matter of traction available vs. speed.

Wait, were we talking about airplanes not too long ago?
 

DangerZone

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Just because a guy parting out a bike he can't fix on E-bay calls it a differential doesn't mean it is one or performs that function. It's not, and it doesn't.

I call it a final drive unit, or rear wheel gearbox, or that stupid ribbed for her pleasure round thing in back if the salesman is an idiot. There have been shaft drive bikes with 2 U-joints ( CV joints ... Which are different, but the parts guy just looks up the car and ignores the wrong terminology, since... Customers.... ) but most just have one at the swingarm pivot.

I really don't have a lot to say about power loss in a drive train. But while playing with an IR camera on a bike at night, I could see rapidly cooling tire tracks from my buddy's XS1100 on the road behind him for several yards at 70 mph, and his shaft and final drive were warm, but far cooler than the engine, and similar to his tires. ( which were not uniformly warm )
A longitudinal engine crankshaft will have one U-joint, a transverse engine crankshaft bike will have two U joints. The drivetrain systems with a single U joint fail much more often due to neglected torsional, inertial and driveline vibrations. Most well designed bike shaft drive systems usually have two U-joints and a parallelogram. There are more reasons why they have two U-joints, why these joints have to be in phase, it is much more complex than some of you see it on the outside. Watch the following video if you want to understand the complexity of a motorcycle shaft drive (or any shaft drive), without going deeper into the difference of joints or velocity fluctuations.


What some of you here seem to have neglected are called torsional vibrations, inertial vibrations, driveline vibrations and velocity fluctuations, which happen in a shaft driven motorcycle. Do these affect efficiency? Yes, they do. But let's skip that for a sec and see if it is all the same in a chain driven bike. The chain driven bike has only the driveline vibrations, it is not (or is very much less) affected by torsional and inertial vibrations, and it skips the velocity fluctuations entirely since it does not have a drive shaft which repeatedly accelerates and decelerates every single turn. Does this shaft acceleration and deceleration on every signle turn lose efficiency? Yes, it does, quite a bit.

Some selections of entries in the definition of the term "differential:"

Definition of differential
(Entry 1 of 2)
1a: of, relating to, or constituting a difference

d: functioning or proceeding differently or at a different rate

entry 2 sense 1) or differentiation
3physics
a: relating to quantitative differences (as of motion or pressure)
b: producing effects by reason of quantitative differences


The motorbike guys are using the term incorrectly. This is common enough. They just don't know what a differential is or what it does.
It is possible the motorcycle guys are using the term incorrectly. However, the motorcycle drive shaft system has to differentiate the rotation of the wheel and the rotation of the swingarm axle. Without that, early motorcycles with a shaft drive had a problem of the swingarm diving upon acceleration instead of simply accelerating forward like motorcycles do. This effect is called the Shaft effect - Wikipedia and newer shaft driven motorcycles differentiate the power to the wheel from affecting the swingarm axle. It could be a language thing, some people call the shaft drive elongation joint a dog clutch while others call it a slip joint, or something else, depending on the design.

Not many rear ends around anymore unless it's in trucks or 4WD. The front wheel drive vehicles also have differentials but they'll look a bit different.

View attachment 109536
I have often heard people call this a homokinetic joint or plunging ball joint on the front wheel drive, with a difference between the outer (wheel side) and inner (differential side) homokinetic joint.

Front wheel drive is called transaxle. Not much here has anything to do aviation. But I did learn that shaft driven motorcycles have two 90° bevel gear sets. I looked at Machinery Handbook but it doesn't have efficiency for bevel or hypoid gears. It does say rear axels can get hot.
Interesting. Which Machinery Handbook are you using? It would be interesting to compare with other machinery handbooks, just to see the numbers...

BMWs, Hondas (like the Goldwing) have one bevel gear set because the crankshaft is longitudinal, the XS1100 and GSXG1100 have two because their crankshaft is transversal.
 

DangerZone

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We're not the only ones arguing about this.
Arguing? I thought we were discussing. :D

If some people would stop to think about this actually, everybody could be learning from each other. And flying on homebuilt shaft and chain driven planes in the future. :pilot:
 

TiPi

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I have often heard people call this a homokinetic joint or plunging ball joint on the front wheel drive, with a difference between the outer (wheel side) and inner (differential side) homokinetic joint.
The most common name for these joints is CV-joint (Constant Velocity joint). They are designed to overcome the rotational speed variations of the universal joint. Many cars are now using them in the front, rear or both axles. oOn some cars they also appear in the main drive shaft (as only one joint is needed to have a smooth torque transmission).
 

BBerson

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Interesting. Which Machinery Handbook are you using? It would be interesting to compare with other machinery handbooks, just to see the numbers...
It's Machinery's Handbook twentieth edition. It shows that worm gear can have poor efficiency. I was thinking hypoid might be similar with more sliding friction than simple spur gears.
 

Pilot-34

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A longitudinal engine crankshaft will have one U-joint, a transverse engine crankshaft bike will have two U joints. The drivetrain systems with a single U joint fail much more often due to neglected torsional, inertial and driveline vibrations. Most well designed bike shaft drive systems usually have two U-joints and a parallelogram. There are more reasons why they have two U-joints, why these joints have to be in phase, it is much more complex than some of you see it on the outside. Watch the following video if you want to understand the complexity of a motorcycle shaft drive (or any shaft drive), without going deeper into the difference of joints or velocity fluctuations.


What some of you here seem to have neglected are called torsional vibrations, inertial vibrations, driveline vibrations and velocity fluctuations, which happen in a shaft driven motorcycle. Do these affect efficiency? Yes, they do. But let's skip that for a sec and see if it is all the same in a chain driven bike. The chain driven bike has only the driveline vibrations, it is not (or is very much less) affected by torsional and inertial vibrations, and it skips the velocity fluctuations entirely since it does not have a drive shaft which repeatedly accelerates and decelerates every single turn. Does this shaft acceleration and deceleration on every signle turn lose efficiency? Yes, it does, quite a bit.



It is possible the motorcycle guys are using the term incorrectly. However, the motorcycle drive shaft system has to differentiate the rotation of the wheel and the rotation of the swingarm axle. Without that, early motorcycles with a shaft drive had a problem of the swingarm diving upon acceleration instead of simply accelerating forward like motorcycles do. This effect is called the Shaft effect - Wikipedia and newer shaft driven motorcycles differentiate the power to the wheel from affecting the swingarm axle. It could be a language thing, some people call the shaft drive elongation joint a dog clutch while others call it a slip joint, or something else, depending on the design.



I have often heard people call this a homokinetic joint or plunging ball joint on the front wheel drive, with a difference between the outer (wheel side) and inner (differential side) homokinetic joint.



Interesting. Which Machinery Handbook are you using? It would be interesting to compare with other machinery handbooks, just to see the numbers...

BMWs, Hondas (like the Goldwing) have one bevel gear set because the crankshaft is longitudinal, the XS1100 and GSXG1100 have two because their crankshaft is transversal.
Lol repeatedly using the word differentiate incorrectly does not change the meaning.
Great Swing but still a miss!
 

Aesquire

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A differential in a car or truck in the front or rear ( in a front wheel drive car the differential is inside the transmission ) allows/controls the speed difference between left & right wheels, when not going in a straight line. Otherwise there is skidding of the tires and big loads twisting axles.

If you look under a Jeep ( the classic WW2 looking ones are easier to see this on ) you see a short drive shaft with 2 U joints from transmission to transfer case, ( more or less under the front seats ) and 2 shafts going forward and back to the 2 rounded differential gear cases with axle housings out to the wheels. 6 U joints total.

If you look under a 2 wheel drive pickup truck there's just the one shaft with Universal joints from transmission to the rear differential and axle housing.

If you look under a modern front wheel drive car you will see a confusing mass of hoses, weird shapes, and oily dirt. There's a lot in there but I'd have to point so don't bother. :)

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.
 

Aesquire

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In drag racing, the differential in a rear wheel drive car is often locked, either by a mechanism ( various types ) or a "spool" or even welded to prevent differential wheel speeds to maximize and make even the forward motion desired.

That causes noise and tire wear. Bad handling! As in the car wants to push in a straight line when you corner. That's a racing compromise. Road racers & street cars have a far more complex differential to smooth cornering.

There's one type called a Detroit Locker, ( and other brand names) that has pawls that lock the rear wheels together under drive load, but permit the outside wheel to turn faster in curves. Often with a loud clicking sound. Same principle as an overrunning clutch used in Rotax 912 series engines and other aviation applications.
 

Aesquire

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Re: inboard brakes & unsprung weight

Formula One cars have brakes inboard from the wheels too. Both to hide the brakes from aerodynamic drag & reduce unsprung weight.

Unsprung weight is the enemy of good handling partly because the shock absorbers have to damp the inertia of the moving parts on the other side of the spring. ( from the bulk of the machine & you ) The springs support the weight of the vehicle. The parts unsupported are those attached to the wheels, drive shafts, rear ends, CV joints, etc ( unsprung weight) those moving parts all have inertia that has to be overcome to follow the ripples in the road or dirt.

So less unsprung mass total and by percentage is better.

My motorcycle, a Buell, was designed by a suspension expert & racer. A LOT of work went into 3 things in it's chassis design. ( branding term "trilogy of tech" )
1. A stiff frame so all loads are directly controlled, minimum bending and winding up & releasing. ( the famed killer Kawasaki H2 2 stroke would twist under hard acceleration and kick back, combined with a steep narrow power band that would suddenly load the tires and too flexible chassis... right off the road sometimes)

2. Centralized mass to reduce polar moment and ease direction change in yaw & roll.

3. Lowest practical unsprung weight.

So instead of 2 front brakes, 1 really powerful brake with 6 pistons and large diameter rotor. Light wheels. And moving everything possible from the unsprung to the spring supported side of the suspension system.

Much as wing mounted fuel tanks vs. fuselage tanks reduce the wing bending forces.

Pretty much all the design choices on a Buell are handling oriented. To the level of fuel tank center of gravity positioning and putting the heavy muffler under the bike, instead of hanging off the back, to ease yaw motion. Grand Prix race geometry.

It's all compromises. It's a lousy truck. It has a short wheelbase, extremely powerful front brake, and loads of torque, so an unwary rider can easily lift the front wheel under power ( lousy drag racing bike) or the rear wheel under braking. ( lousy idiot bike )

But if smooth cornering at speeds 95% of other road vehicles would launch themselves to oblivion at, are your desire? Out-fracking-standing.

The closest car analogy is a Shelby Cobra. In planes? Yak-55.
 

Vigilant1

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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.
 

DangerZone

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It's Machinery's Handbook twentieth edition. It shows that worm gear can have poor efficiency. I was thinking hypoid might be similar with more sliding friction than simple spur gears.
Thanks, just checked it out. It's interesting, it just says for the hypoid gears that the teeth are 1.5 to 2 times stronger (page 2192, 30th edition) without the approxiamte efficiency loss.

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.
 
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