[Vwdiesel] something worth trading the A4 in for

[Kurt Nolte]

Val Christian wrote:
>> Oh, and your engine would need to be able to produce 100% of the hp 
>> necessary to begin accelerating the vehicle's mass at low RPM points, as 
>>     
>
> 	Not hp, rather torque.  A gas turbine is an example of 
> 	an engine which has high torque at low output shart RPMs.
> 	Diesels are not as good, but they do have more torque at 
> 	lower RPMs, favorably impacting drivability.
>   

As you yourself will later say, you use hp to accelerate. Torque pulls, 
horsepower accelerates. So yes, you would need something that would 
produce the -horsepower- necessary to -accelerate- the car at 
near-wheel-speed RPM... unless you want to utilize a device that 
modifies the speed the wheels see, that is, a transmission...

The gear reduction on the output shaft of a gas turbine is a 
"transmission" too. Fixed speed for the most part, but it's a 
transmission nonetheless. It involves the use of gears of varying sizes 
to accomplish the purpose of modifying a prime mover's input 
characteristics to better accomplish a desired output characteristic 
set. In this case, the high-RPM, (relatively) low torque output of the 
gas turbines themselves into the lower RPM, much higher torque output 
shaft characteristics.

> 	However gas turbines near output shaft stall, are not 
> 	as efficient as diesel engines.  
>
>   
>> opposed to being able to wind it out to its peak HP point to do your 
>> standing acceleration.
>>
>> In other words, you'd need a V8 to move a Rabbit around.
>>
>>     
>
> 	No, you simply need a configuration where suitable torque is
> 	available at low wheel RPMs.
>   

And thus, a transmission. Or an engine that produces all your hp needs 
(torque @ RPM) down at the bottom end, while still having breathing room 
left up top for cruising. Bigger engines produce more low-end torque 
(and thus hp) as a byproduct of their larger displacements and/or longer 
strokes.

Without a transmission, your wheel RPM = engine RPM, remember.
> 	HP is needed for acceleration, but it's also needed for 
> 	max cruise (drag) and hill climb (lift).  
>   

Here, by the way, is the aforementioned instance of HP being necessary 
to accelerate.
> 	A 48 hp Rabbit, heading into a 50 knot wind, is speed limited
> 	due to increased aerodynamic drag on the Rabbit.  With a 
> 	50 knot headwind, don't expect a road speed much over 60 mph.
>   

Your landspeed would only be 60mph, but your effective windspeed most 
certainly isn't 60mph at that point. The commentary about 23hp being 
sufficient is assuming no headwind, but simply what is necessary to move 
a vehicle through calm air at a given speed on flat ground. Lots of 
similar assumptions are made by these hawkers, why can't I make a 
(common) assumption of my own?

The claim is that electric cars don't "need" a transmission. Why would 
they, peak torque output at 0RPM, you've got lots of power down low!

And sure, you can brute force muscle your way into motion like that, 
using an oversized, higher torque motor than you need, but it would be 
-like powering a Rabbit with a V8, just to avoid using a transmission.- 
Going to a bigger, torquier mover just so you don't have to involve 
gears between the mover and the wheels.

-Kurt