# Drivetrain Power Loss

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#### TiPi

##### Well-Known Member
Log Member
OK, I'm trying again: take a motorbike with an engine that delivers 100kW at the flywheel. If your arguments about shaft drives being 80% efficient is correct, then there would be 20% turned into heat. Our bike would then generate 20kW of heat in the drive shaft, couplings and rear axle.
Now take that 20kW and look how you would remove that amount of heat:
20kW is roughly the heat that has to be removed from a 15-18kW engine. If you look at an air-cooled industrial engine of 15kW (20hp), you will see lots of cooling fins and a substantial fan to move air through those fins to keep the engine temperature below 200deg C (cylinder head). I have not seen any BMW, Moto Guzzi or Japanese bike that has such an extensive cooling system for the shaft drive, ever. They all have an alu rear axle housing and possibly an alu swing arm, with no fins or only some small ribs. So there is no extensive cooling happening. That simply means that the heat generated is small enough so that it can be dissipated to the surrounding air without cooling fins, baffling, air dams and fans. And that amount is around 1-2%, anything more would need dedicated cooling. The shaft drive is only slightly less efficient than a good chain, as many of us have been trying to explain.

#### DangerZone

##### Well-Known Member
HBA Supporter
OK, I'm trying again: take a motorbike with an engine that delivers 100kW at the flywheel. If your arguments about shaft drives being 80% efficient is correct, then there would be 20% turned into heat. Our bike would then generate 20kW of heat in the drive shaft, couplings and rear axle.
Now take that 20kW and look how you would remove that amount of heat:
20kW is roughly the heat that has to be removed from a 15-18kW engine. If you look at an air-cooled industrial engine of 15kW (20hp), you will see lots of cooling fins and a substantial fan to move air through those fins to keep the engine temperature below 200deg C (cylinder head). I have not seen any BMW, Moto Guzzi or Japanese bike that has such an extensive cooling system for the shaft drive, ever. They all have an alu rear axle housing and possibly an alu swing arm, with no fins or only some small ribs. So there is no extensive cooling happening. That simply means that the heat generated is small enough so that it can be dissipated to the surrounding air without cooling fins, baffling, air dams and fans. And that amount is around 1-2%, anything more would need dedicated cooling. The shaft drive is only slightly less efficient than a good chain, as many of us have been trying to explain.
It's unclear what you are trying to do with so many wrong asumptions. Some motorcycle drive shafts are more efficient than others, it does not always have to be a strict 20% efficiency loss. It also varies depending on speed and gear. Then, an engine temperature close to 200 degrees centigrade (cylinder head) is boiling hot and means your engine is pretty much gone. Normal temperatures are usually 80 - 90 - 100 degrees tops, anything above that means your engine has a design flaw.

How about you try to answer what you call a motorcycle shaft drive differential?

##### Well-Known Member
This is getting so very boring.
It's no use arguing with someone so deluded and resistant to facts.

#### Pilot-34

##### Well-Known Member
Danger Zone,
I doubt that it will help but did you see this?

you can call it a final drive, an angle drive or rear axle drive
It was directly followed by this;

But it doesn't do anything like a differential!

A differential allows a single input shaft to drive two output shafts with different speeds.
And between them explain most peoples take on differentials and final drives

#### DangerZone

##### Well-Known Member
HBA Supporter
Danger Zone,
I doubt that it will help but did you see this?

It was directly followed by this;

And between them explain most peoples take on differentials and final drives
Didi you see this?

https://img.memecdn.com/What-do-you-call-someone-with-no-body-and-a-nose_o_139852.webp

So, nobody knows what a motorcycle shaft drive differential is called here, but they are telling me I could call it four diferent names:
1. A final drive
2. Angle drive
3. Rear axle drive
4. A thing which doesn't do anything like a differential

So, why should I call it four different names if millions of people are calling it a motorcycle rear shaft drive differential? Any idea how wild this idea sounds?

Q: "How do you call a gyrocopter?" A: "No DZ, that is not a gyrocopter! That is a thing which is not an airplane, but you could call it an aircraft, a flying thing or a thing which is not a helicopter." Hilarious.

#### Pilot-34

##### Well-Known Member
Are you got any idea how moronic it sounds to call something a differential that does not differentiate?

#### Vigilant1

##### Well-Known Member
Well, we do call convective heat exchangers "radiators" for no good reason.

Just stirring the (putrid, foul) pot . . .

#### eether54

##### Member
Fwiw all the manufacturers I'm aware of call them final drives. That said, it wasn't cause for a seizure if a customer called it a differential..
Also, three of the motorcycles sitting in my garage have one 90 degree direction change one universal joint a piece.
Aside from ease of gearing, the reason most guys Ditch shaft drive is to get rid of a bunch of weight. The same reason guys lighten flywheels. It's going to get you to the end of the dragstrip faster but you are not magically going to gain 20-35% more efficiency. There is more to driveline efficiency than solely the ability to accelerate a dyno.
Oh, and while calculating, chain drive bikes of any hp also have a rubber cush system..

#### TiPi

##### Well-Known Member
Log Member
I’m off to do better things, DZ will never see the light.

#### Aesquire

##### Well-Known Member
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 )

#### Tiger Tim

##### Well-Known Member
There are two ways to be the smartest person in the room, the easier one being to make everyone else leave.

#### Protech Racing

##### Well-Known Member
I have read the to and fro comments and think the main difference that is not taken into account by dangerzone is tyre loss on a dyno.
Axle mounted dynos prove this.
I use the same dyno tires on all of the VW race cars . at the same 38psi.

#### Protech Racing

##### Well-Known Member
The race bikes are all chain drive with the drive never changing direction through 2 bevel drives that the drive shaft requires. I expect the straight cut gears driving the roller bearing chain delivers around 92%\$ of the power to the wheel .
The shaft drive bikes operate at a low duty cycle with lots of oil frothing around in there . But still after a long pull the shaft and final drive housing is hot . Angle drive gears make heat.
I would also look a gain at the cogged belt VS chain drive efficiency values.

#### Dan Thomas

##### Well-Known Member
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

(My bold)

Now, THIS is a differential:

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.

Some term gets misused a few times and then it's entrenched in the jargon. Model airplane guys keep referring to "tip stall" when their model drops a wing when they get too slow, as if the airplane will stay level and not drop a wing unless the wingtip stalls, which is a result of not understanding stall progression. If they were right, all we'd need is the tips, not the rest of the wing.

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#### Dan Thomas

##### Well-Known Member
When I did my flight instructor rating we studied the Seven Learning Factors:

1. READINESS - Ensure students are mentally, physically and emotionally ready to learn.
2. PRIMACY - Present new knowledge or skills correctly the first time. (Teach it right the first time.)
3. RELATIONSHIP - Present lessons in the logical sequence of known to unknown, simple to complex, easy to difficult.
4. EXERCISE - Ensure students are engaged in meaningful activity.
5. INTENSITY - Use dramatic, realistic or unexpected things, as they are long remembered.
6. EFFECT - Ensure students gain a feeling of satisfaction from having taken part in a lesson.
7. RECENCY - Summarize and practice the important points at the end of each lesson, as last things learned and practiced will be remembered longest.

Let's zero in on that Primacy factor:

1. When students are presented with new knowledge or skills, the first impression received is almost unshakeable. This means that what you teach must be correct the first time. Students may forget the details of lessons, but will retain an overall image of the skill or knowledge for a long time. Frequently you will be required to perform manoeuvres in the aircraft before a student has had the necessary background training. You must perform those manoeuvres correctly or the student may imitate any errors you make. For example, before the exercise on Confined Areas, you and your student may be required to land in a confined area. Any poor example shown at this time would have to be "unlearned" when the exercise came up in a subsequent lesson.
I've bolded the key point here. This Primacy thing shows up everywhere: in the misuse of terminology, the misunderstanding of various concepts, the endless myths (old wives' tales) we find in any technology or skill. We used to get students coming to us with their PPLs (obtained elsewhere) and sometimes we had to undo a lot of poor training. It was difficult for both the student and instructor, and the student would sometimes push back relentlessly until you sat him down, showed him the textbook references and the physics, and sometimes you had to demonstrate, in flight, how his particular bad habit could kill him. Ignorant instructors make ignorant pilots. A prime example is the idea that carb ice is a wintertime thing; this is serious error, considering that carb ice is the single biggest cause of power failure in carbed airplanes, and it's just because the student wasn't taught the correct stuff. Some have a lot of trouble landing because their approach speeds are way too high; that busts a lot of airplanes too. They don't understand (or weren't listening when it was taught and didn't get it at all) the relationship between airspeed and angle of attack, and what the result of high airspeed/low AoA does to the airplane when it tries to land in that attitude. This is basic stuff.

The idea that powertrains lose big percentages of the power is likely a result of some poor instruction, or some idea promulgated by some folks that don't know what they're talking about. SGOTI's. Just look at the endless Youtube videos of pilots "teaching" how to do some stupid stuff.

#### wsimpso1

##### Super Moderator
Staff member
Log Member
you can call it a final drive, an angle drive or rear axle drive
Ring and pinion too.

#### BBerson

##### Light Plane Philosopher
HBA Supporter
I always thought it was the rear end.

#### mcrae0104

##### Well-Known Member
HBA Supporter
Log Member
...how it is done in the metric world.
1) Metric vs. imperial has nothing to do with this (as our Aussie--and presumably metric-friendly--friend TiPi will attest). Watts vs. BTU/h, to-may-toe vs. to-mah-toe.

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#### Dan Thomas

##### Well-Known Member
I always thought it was the rear end.
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.

#### BBerson

##### Light Plane Philosopher
HBA Supporter
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.