Need help with stock propeller

[Azimech]

32 minutes ago, Geschosskopf said:

Stock props technically don't actually move entire planes with the thrust from their blades.  That moves only the shaft itself, and for this the EC required is as OK as for any other electrical thing in the game.

What moves the plane is a physics-less spatial adjustment to prevent the shaft from clipping into the part in front of it as the shaft moves forward.  Newton's 2nd and 3rd laws are ignored during this adjustment, but this movement still causes wings to make lift.  That's how the tiny amount of EC makes a big plane fly.

So, to fly higher and faster, you need to increase the forward velocity of the shaft, so this spatial adjustment happens more often and with greater magnitude.  However, the prop needs air for the shaft to move so ypu can only get so high, whereas a ladder drive works in space

Pardon me but you're saying that KSP does things differently with the thrust from propeller blades than real life? Interesting.

How is the technology behind a thrust bearing different from real life and how is it, in your words, "physics-less"?

Here's a stock propeller cargo plane for Eve I built over a year ago. It's old tech but should still work. There are better solutions for the bearings nowadays.

https://kerbalx.com/Azimech/77I-Azi17-Anista-v1

[Spricigo]

2 hours ago, AeroGav said:

It already goes to orbit (i have tested that several times with hyperedit )  provided you can somehow get it above 20km or so at flying speed (not stalled).    At this altitude the air is about the same thickness as it is on Kerbin at 7km.  Below that point the ISP and thrust fall away to practically nothing.

I can only imagine the amount of thought you put on this. So I know that my comment risks to sound naive,  but if there's a chance to be of some use that is what your endeavor bring to my mind:

What I'm wondering is if switching a couple of nevs for chemical rockets (lets suppose a pair of Darts) wouldn't allow you to start that phase a bit lower or cut some mass.

Even if that results in the same mass there's the fact that with chemical propulsion mass will decrease quicker. 

2 hours ago, AeroGav said:

I tested all the stock ones with hyperedit and the Dart (aerospike) has the best ISP at Eve sea level.

I'd like to point  that the massively more powerful Vector and Mammoth are not far behind in the Isp department.

 Also remember that many returns from Eve are planned to depart from some conveniently high mountain.

It may not address the concern of how much is left to crash. But the same happens with the traditional staged rocket. 

[Cpt Kerbalkrunch]

43 minutes ago, Spricigo said:

I can only imagine the amount of thought you put on this. So I know that my comment risks to sound naive,  but if there's a chance to be of some use that is what your endeavor bring to my mind:

What I'm wondering is if switching a couple of nevs for chemical rockets (lets suppose a pair of Darts) wouldn't allow you to start that phase a bit lower or cut some mass.

Even if that results in the same mass there's the fact that with chemical propulsion mass will decrease quicker. 

I'd like to point  that the massively more powerful Vector and Mammoth are not far behind in the Isp department.

 Also remember that many returns from Eve are planned to depart from some conveniently high mountain.

It may not address the concern of how much is left to crash. But the same happens with the traditional staged rocket. 

This is pretty much exactly what I was thinking when I talked about swapping the Nervs for Darts. I thought engines with more power, coupled with the propellers, would help get the ship high enough where a Nerv could be more useful. I'm a huge fan of the Vector as well. The only real problem with it is that it burns through fuel at an alarming rate. Might be worth pursuing to get the ship off the surface and as high as possible so the weaker engines can take over.

[AeroGav]

@Spricigo  and @Cpt Kerbalkrunch

You must not have seen my efforts with mk1 of this ship on 

 

I tried putting oxidizer tanks , droppable ones even.  Problem is,  8 tons of liquid fuel and oxidizer only get you about 1200m in height.     It's the same ratio of 8 tons of rocket needed to lift 1 ton of payload to get from sea level to 20km as you get with a rocket. 

 Using wings just means you can get away with a TWR 3 or 4 times less , which given Eve's gravity of 1.7x Kerbin's is 100% necessary if you are going to use nukes.   But it does not alter the amount of propellant needed to gain a given amount of height.   Climbing uses the same amount of energy in a rocket as it does in a plane,  wings just counteract the "gravity loss" required to stand still (not fall back down).         

Chemical rockets use a high TWR to minimise gravity loss instead. With chemical propulsion you generally add less dry mass by just cramming engines onto your craft to make up for gravity loss, than by using wings.  With nukes and jets, other way round.

On Eve sea level, the Dart gives an ISP of 230.   The next best engines are the Mammoth and Vector, at 193.      If we want a TWR of 0.63 on Eve for a rocket plane, we either need 5 Darts or 1 Vector.  I built a really simple test craft (one orange tank, plus a smaller white one, and a mk2 command pod) to see what's the best propulsion - 

Despite saving 1 ton with the higher TWR engine, our delta V is still less on the vector.   Since the Dart is better at altitude, this gap is only going to grow as we climb.

 

[Geschosskopf]

11 hours ago, Azimech said:

You'll find that designing a proper engine and propeller is quite a challenge. There's some real engineering here.

Yeah, they've been around for years in one form or another, although today they're much more refined.  No denying it, they're marvels of tinkering and have a huge gadget factor.  But they're still functionally the same as the ladder drive, just substituting the shaft for the Kerbal, and thereby exploiting a loophole in the game's physics.

 

11 hours ago, Azimech said:

Pardon me but you're saying that KSP does things differently with the thrust from propeller blades than real life? Interesting.

How is the technology behind a thrust bearing different from real life and how is it, in your words, "physics-less"?

Here's a stock propeller cargo plane for Eve I built over a year ago. It's old tech but should still work. There are better solutions for the bearings nowadays.

https://kerbalx.com/Azimech/77I-Azi17-Anista-v1

Yes, I'm saying that stock props produce zero thrust from shoving air backwards. They produce the appearance of thrust by pushing the fixed part at the front of the shaft forward via the collision system.  Of course, mod props don't shove air backwards, either, because there's no air to shove.  And for that matter, rockets don't throw reaction mass backwards, either.  Doing any of these things would require the game to model the movements of countless discrete particles of gas, and it already has enough trouble keeping up with a few hundred to a few thousand rocket parts .

So in KSP (and every other flight-related game I know of), there's no "physical" atmosphere in the same sense that the ground is "physical" (collidable).  Instead, "atmospheres" are defined by mathematical equations which determine the forces the atmosphere would produce on parts moving through them.  Motion in KSP is all about determining what forces are being applied to a collection of parts from thrust, gravity, and atmosphere, figuring the resultant net force and moment, then moving the parts in accordance, repeat.  Everything else, such as rocket exhaust plumes, is just eye candy.  Rocket fuel simply ceases to exist, it doesn't become exhaust, mod prop blades spin but don't move any air, etc.

So, with a stock prop, the SAS units in the shaft spin.  The wing parts (blades) attached to them thus also spin.  Because they're in an atmosphere, this motion causes aerodynamic forces to affect the movement of the blades, so they move forward besides spinning.  This motion is using the same physics system that applies to conventional motion in KSP so there are no exploits going on so far.  However, the shaft is attached to the plane by a stretchy docking port, so moves forward relative to the docking port.  This causes the front end of the shaft to clip into the part in front of it, which is displaced by the collision system to eliminate the clipping, without regard to inertia, F=ma, or equal and opposite reactions.  This pulls the rest of the plane forward.  When this happens, it's likely that the stretch in the docking port is reset as well, pulling the shaft back and the rest of the plane forward, again without paying attention to Mr. Newton.  And because the plane is being moved through the "atmosphere" by all this, its wings have atmospheric forces applied to them, and thus you get flight.  Because the source of the plane's motion is physics-less, this motion is greatly out of proportion to the energy you put in by spinning the shaft.

It's easier to understand this when considering the ladder drive.  Here, you have a ladder with some other part positioned at the end of it so that the Kerbal's head will hit this part while the Kerbal's arms and legs are still on the ladder.  The Kerbal is analogous to the shaft, the blocking part is analogous to the part at the front of the shaft.  As long as the Kerbal's arms and legs are still on the ladder, the Kerbal can move forward, so he clips into the blocking part.  In real life, Newton's 3rd law would prevent motion---the force of the Kerbal against the blocking part is countered by the equal and opposite reaction.  But in KSP, the blocking part is moved forward by the physics-less collision system, dragging the ladder with it, and the Kerbal is dragged along with the ladder  Thus, you get motion in the direction the Kerbal is climbing.  And acceleration, too, so that it's possible eventually to go to other planets this way.

[Helmetman]

@AeroGav Isn't it better fund wise to purely make a TSTO from Eve?
You said you were going to drop the props at altitude, so it basically is a TSTO, although I mean it a bit differently my way.

I think weight and fund wise you'd end up better by just decoupling the whole aircraft part and use a high TWR upper stage to achieve orbit and save the props. This can actually be more then one stage. (Three Stage To Orbit?)
Or is that called a 3STO lol... just MSTO then.

You could save the 1st winged stage with the max physics range mod or whatever it's called and achieve some way to re-dock the rocket upper stage to the top so you have some sort of reusable system. Unless it must be absolutely stock.

Purely speaking on the basis of concept though. I wouldn't know what is more efficient in the end and hope you can get it to work your way. 

Edited September 22, 2017 by Helmetman

[EpicSpaceTroll139]

I'd suggest first making a prop plane that can fly on Kerbin before trying to make one that works on Eve. You might think it would be easier to make something fly with Eve's thick atmosphere, but that thick atmosphere makes it a lot harder to get good rpm on the prop. 

Kerbin can give you practice, then double or maybe even quadruple the torque for Eve.

I haven't made anything other than a helicopter style thingy work on Eve (it crashed like 5 seconds after take off due to inadequate stability control), but that's mostly because I haven't invested a lot of effort. I'd suggest fewer and possibly slightly longer blades on those props too. It might seem like more blades = more thrust, but past a certain point the drag results in lower rpm and thus less lift --> thrust.

Edited September 26, 2017 by EpicSpaceTroll139
Lift might suit some people's views better

[leos101]

On 9/21/2017 at 3:46 AM, Geschosskopf said:

This is easy enough to answer. As I understand things from reading what more knowledgeable folks have written, 1 EC/sec = 1 kJ/sec = 1 kW =~ 1 hp.  The very top-end, high-octane, turbo-supercharged, late-WW2 frontline combat aircraft engines in service use, optimized for power-to-weight ratio, developed about 2500-3000 hp at war emergency power (for short duration, using water, methanol, and/or nitrous oxide injection from a low-capacity tank).  A single RTG produces 0.8 EC/sec =~ 0.8 hp.  Therefore, to get anything remotely approaching realistic power out of a "stock propeller", you need 2500 hp / 0.8 hp/RTG = 3125 RTGs  on EACH SHAFT..

Therefore, stock "propellers" are exploits/cheats same as the old infinigliders.  QED.

Hi! I think you made a mistake. Here is a perfectly good kw to hp calculator: 1 kW = 1.341 hp. As for the aircraft engine question, stock 'propellers' requiring thousands of RTGs per shaft seem unrealistic compared to historical engines optimized for power-to-weight ratio outputting around 2500-3000 hp at peak power. The kw to horsepower converter highlights the exploit nature of overpowered 'propellers'.