Scale power?

[BrianG]

Just idle curiosity, but people talk mostly about scale speed. We know that it is not simply a matter of model scale X model speed, but the square root of the scale X model speed.

So, it stands to reason that scale power (HP and torque) doesn't follow the same rule. I figure since both horsepower and torque are functions of weight, you'd find the ratio of the real weight to scale weight. Then, apply that ratio to your model's HP and torque figures.

For instance, my Ultra GTP weighs about 9lbs fully loaded. The "real world" car would probably weigh about 4500lbs. That's a ratio of 500:1. Plugging in a current value of 75A @ 18.5v in my setup gives me 1.8HP and 2.58ft-lbs of torque. Multiply those by the ratio of 500 gives me scaled up values of 929HP and 1290ft-lbs of torque. Judging by the way these models perform, those figures seem about right.

Any thoughts? Again, this is just speculation...

Thats interesting stuff.I'm curious to know if you adjusted your hp to weight ratio to be the same as the real thing,if the scale speeds would be similar.

[BrianG]

Hmm. Not sure if that would be a valid comparison for most setups. Most of the time, the top speed is limited by the battery voltage and motor kv. It simply winds out. If used with a multi-gear tranny to take advantage of the power better, they could probably get pretty darn close.

For instance, with that same ultra GTP car, the calculated top speed is approx 48mph. Scaled up, that's 135mph. Again, that's a single speed, and not for lack of power.

I figure it's safe to say the GTP could go, say, 90mph with a muti-speed tranny on my setup. Scaled up, that's 254mph. You think a 929HP car with almost 1300ft-lbs of torque could do ~254mph? I think so, if done right. After all, that's about the same speed and power as a Bugatti Veyron...

You think a 929HP car with almost 1300ft-lbs of torque could do ~254mph?

Yeah I don't think a car dedicated to racing would have any problem with that.Now if they'd only make 1 brushless with lipos then a fair comparison could be done.

[redshift]

I had a similar thread a while back.... http://www.rc-monster.com/forum/show...e+perspectives

Someone will get the formula right one of these days, will it be BrianG? :)

[BrianG]

Yeah, there have been a few threads about scale this or that, but nothing really definite. I did find how to scale speed properly, but haven't really looked hard about scaling power. Kinda useless really, but still neat to tell people my little "toy" has almost 1,000 scale HP.

Where do you get that it would way 4500 pounds?

I googled the weights of GT1 class cars and came up with 2000-2500lbs. that might effect your claculations some.

Also scale speed will never be accurate because of wind drag. You cant scale up the wind drag when your running your rc. . .

[BrianG]

It was just an estimate based on my little Mazda3 hatchback (3k lbs). I looked a little more and saw that some of the higher-end vehicles don't weigh that much, but some, like the Veryon, weigh close to 4k lbs.

Of course it wasn't meant to be totally accurate, just interesting to say that I have ~900 scaled HP.

And anyway, like I said, it was idle thought.