The Conservation of Energy... Is Broken. Breaking Ground Is A Perfectly Balanced DLC With No Exploits.

[Pds314]

TL;DR: prop blades are free energy devices.

This craft masses exactly 291437 kg.


It has two of the smallest electric rotor, each set to 1% motor size and torque. Each motor says it has 200 Newton*meters of torque, and has 8 of the smallest prop blade attached to each. The props are not deflected when undeployed, but are deployed by 19 control authority units out of 150.
After a long and slow acceleration up to 12 meters per second, this is the craft's status:


Note that we can know EXACTLY how much mechanical power the rotors should be generating. There are two of them, each applying 200 Nm of torque, currently spinning at 254.1 RPM. According to my calculations and several online calculators, that's 5321.5 Watts each of mechanical power.

Great, so we know we are getting 10643 Watts of mechanical power at the shaft. I mean, 15 HP in a 300 tonne craft is not great by any normal metric, but it's great that we know how much we have.

So logically then, the absolute best we should be able to do is increase our kinetic energy by 10643 Joules per second. In reality it should be substantially less due to inefficiency of the prop and any drag forces.

So how much kinetic energy do we have? Well our craft mass hasn't changed. So ke=0.5*m*v^2 is 0.5*291437 kg * (12 m/s)^2 = 20983464 J. So we started with 21 MegaJoules.

Cool. So let's watch as it accelerates.



Alright. 29 seconds have passed and it's at 13.0 m/s. It has also gotten a little less powerful but we don't need to worry about that.

How much energy did it gain? Well it now has 24626426.5 J of kinetic energy instead of 20983464 J. So it gained 3642962.5 of Kinetic energy in 29 seconds.

WAIT WHAT???!!!

So somehow, we just put 309 kJ of mechanical energy through a propeller, and got 3643 kJ of kinetic energy out of the thing. Perpetual motion is real!

Checkmate physicists!

Edited July 16, 2019 by Pds314

[Pds314]

Comparison with using basic fins as prop blades at much higher RPM and therefore power, instead of the DLC prop blades.

It took 1.5 minutes to accelerate 0.4 m/s on ~17 kW.

The KE change is 256464.56 J. That's what it makes in 15 seconds. So it's only about 15% efficent. Although that will likely improve somewhat as the speed increases. But even so, not to 1200%.





EDIT: I gave it over 10 more minutes to accelerate. It really can't get past 2.9 m/s.

Edited July 16, 2019 by Pds314

[KerikBalm]

Ok, so that torque exerts a force of 200 newtons at 1 meter. Work is force * distance. 254 rpm is 4.23 rotations per second each rotation, so the distance traveled per second at a 1 meter radius is 26.6 meters.

200*26.6 *2 (bc we have 2 motors)= 10.6 kW.. over 29 seconds is 308.5 kJ. Math checks out.

If it accelerated from 0 to 1 m/s in the same time:

ke=0.5*m*v^2 is 0.5*291437 kg * (1 m/s)^2 = 145.7 KJ which would be a very reasonable result, of about 50% efficiency... So either thrust needs to go way down as it accelerates, or energy consumption goes way up.

This part always made me have to go "huh", and double check things, and it seems related to oberth. A dV change of 1 m/s does not add the same amount of KE, yet with no preferred reference frame, how can we say we went from 1200 to 1201 m/ and not from 0 to 1 m/s. 

Basically, what we have here, is that the force and energy consumption are too similar at 1 m/s and at 12 m/s

 

[Kerbart]

1 minute ago, KerikBalm said:

Ok, so that torque exerts a force of 200 newtons at 1 meter. Work is force * distance. 254 rpm is 4.23 rotations per second each rotation, so the distance traveled per second at a 1 meter radius is 26.6 meters.

200*26.6 *2 (bc we have 2 motors)= 10.6 kW.. over 29 seconds is 308.5 kJ. Math checks out.

You could have saved yourself a good chunk of work (no pun intended) if you realize that work = torque * angular velocity. 200*4.23*6.28=5.3kW per engine.

[Pds314]

9 minutes ago, KerikBalm said:

Ok, so that torque exerts a force of 200 newtons at 1 meter. Work is force * distance. 254 rpm is 4.23 rotations per second each rotation, so the distance traveled per second at a 1 meter radius is 26.6 meters.

200*26.6 *2 (bc we have 2 motors)= 10.6 kW.. over 29 seconds is 308.5 kJ. Math checks out.

If it accelerated from 0 to 1 m/s in the same time:

ke=0.5*m*v^2 is 0.5*291437 kg * (1 m/s)^2 = 145.7 KJ which would be a very reasonable result, of about 50% efficiency... So either thrust needs to go way down as it accelerates, or energy consumption goes way up.

This part always made me have to go "huh", and double check things, and it seems related to oberth. A dV change of 1 m/s does not add the same amount of KE, yet with no preferred reference frame, how can we say we went from 1200 to 1201 m/ and not from 0 to 1 m/s. 

Basically, what we have here, is that the force and energy consumption are too similar at 1 m/s and at 12 m/s

 

Well there shouldn't be an Oberth effect for a prop beyond 100% efficiency lol. Yes, the energy from a given thrust should increase, but the thrust should not be static. Props DO have a preferred reference frame. And that is that of the air through which they are accelerating. Just like wheels or any other engine that needs to accelerate its environmental propellant from low speed to high.

You can see the stock wings do this fine as prop blades under any variety of situations. They aren't always super efficient without a lot of careful tuning but they are never overunity devices that I am aware of.

Edited July 16, 2019 by Pds314

[KerikBalm]

Well, on a related note, while it initially seemed that some of these rotors had really high EC or LF consumption, I've now learned what makes them tick, and can make very low power consumption designs... it seems like its related to this topic:

Carrying a 40 ton payload around kerbin at 170 m/s for 10 EC/sec from 4 standard rotors?

Lulz

[cantab]

It's already known that the propeller and rotor blades use some kind of "fudge factor" to increase their thrust/lift. It's intended to compensate for the game engine's RPM limit - the propeller *should* be spinning much faster but it can't. Your result therefore is unsurprising.

[Pds314]

42 minutes ago, cantab said:

It's already known that the propeller and rotor blades use some kind of "fudge factor" to increase their thrust/lift. It's intended to compensate for the game engine's RPM limit - the propeller *should* be spinning much faster but it can't. Your result therefore is unsurprising.

Would it be surprising if I could use it to make a plane that flies without an energy source? A self-powering turbine?

Edited July 16, 2019 by Pds314

[KerikBalm]

1 hour ago, Kerbart said:

You could have saved yourself a good chunk of work (no pun intended) if you realize that work = torque * angular velocity. 200*4.23*6.28=5.3kW per engine.

This again? Yes, in many cases, its easier, since we can ignore radius in that case, but here using a radius of 1, its:

Your equation: 200*(254/60)*2pi

My equation: 200*(254/60)*2pi

Now I added more explanatory text, but the actual mathematical operations are the same.

11 minutes ago, Pds314 said:

Would it be surprising if I could use it to make a plane that flies without an energy source? A self-powering turbine?

These were known before Breaking ground rotors. Its an exploit for sure, but IIRC they tended to start a positive feedback loop where RPM increased, parts moved ever more outward and forces got stronger and stronger until it tore itself apart, and it was difficult to adequately control, because putting the breaks on positive feedback loop a little too late means that the feedback overcomes the breaks, and all is lost

[Pds314]

5 minutes ago, KerikBalm said:

This again? Yes, in many cases, its easier, since we can ignore radius in that case, but here using a radius of 1, its:

Your equation: 200*(254/60)*2pi

My equation: 200*(254/60)*2pi

Now I added more explanatory text, but the actual mathematical operations are the same.

These were known before Breaking ground rotors. Its an exploit for sure, but IIRC they tended to start a positive feedback loop where RPM increased, parts moved ever more outward and forces got stronger and stronger until it tore itself apart, and it was difficult to adequately control, because putting the breaks on positive feedback loop a little too late means that the feedback overcomes the breaks, and all is lost

It operates fine at or above RPM limit. Jiggling is very much not damaging.

Edited July 16, 2019 by Pds314

[Jimmidii]

This reminds me of the Dwarven Water Reactor design in Dwarf Fortress.

[Superfluous J]

Every time YouTube suggests one of those "____ is perfectly balanced" videos I wish for a regular-expression blacklist feature.

It's a game. Enjoy your free power. I'll enjoy making planes that work due to these same effects. If they broke my plane to fix your exploit we'd both be sad.

[Kerbart]

5 hours ago, Pds314 said:

Well there shouldn't be an Oberth effect for a prop beyond 100% efficiency lol. Yes, the energy from a given thrust should increase, but the thrust should not be static. Props DO have a preferred reference frame. And that is that of the air through which they are accelerating. Just like wheels or any other engine that needs to accelerate its environmental propellant from low speed to high.

This is why jet turbine output is expressed as thrust, and why prop planes in general have power ratings.

Jet thrust remains fairly constant and doesn’t has an “oberth effect” on its power rating — the same engine generates a lot more power at 300 kmh than it does at 100 kmh because of fairly constant thrust at varying velocities,

With prop planes it’s exactly the reverse. KSP obviously has a fairly simplistic model for atmospheric flight. I’m not sure we want that fixed, because it will likely be at the expense of frame rates.

For the occasional “KSP spin off” game discussions, a high quality atmospheric flight simulator might be a great suggestion. For the game itself—we can now recover crew and craft using helicopters, and use drone-style probes on other planetary bodies that have an atmosphere and that’s more than we dreamt off three months ago.

[Snark]

Moving to Breaking Ground Discussion.

[IkranMakto]

It's a topic about new blades, but what about overpowered engines? R-7000 produces over 20000 hp on 400 rpm for example. That's 40% more than NK-12 produces - the most powerful turboprop in the world

[Bartybum]

I wonder if having tweakable prop discs as a single part would’ve been a better idea. That way you could use smaller fudge factors.

Edited July 18, 2019 by Bartybum