Optimizing power from rotors

[KerikBalm]

I was just wondering if anyone had insights on how to optimize the lifting power of rotors/maximum speed.

Does torque decrease as rotors get closer to their maximum RPM?

To optimize lifting power (for a given radius of the blade disc), do we want high RPM, or low RPM and lots of wing area?

I was also wondering how lifting power is relative to G and air pressure. On Eve, the atmosphere is much thicker, so its like operating a rotor with 5x the surface area on Kerbin. The gravity is 1.7x higher, so lifting 10 tons on eve is like lifting 17 tons on kerbin.

Does the thicker air make it easier to lift payloads on eve despite the higher gravity?

 

As far as optimizing for speed, I'm guessing that a larger rotor diameter helps, so that for a given RPM (again, does lower RPM result in higher torque, if torque drops off as it approaches maximum RPM?), the blade angle can be shallower? I saw @Brikoleur made a contra rotating helicopter reach over 100 m/s, with the rotor closer to parallel to the direction of motion than perpendicular to it.

So far my tilt rotors are maxing out at between 93-94 m/s, so I'm wondering if for some reason in KSP, a helo can get faster than a tilt rotor? How does one optimize for forward speed with these new rotors?

[Guest]

I think the reason the experimental helo went so fast was basically brute strength, it's a small helo driven by a very powerful motor and a rather a big rotor. I'm fairly confident a tilt rotor with a similar spec would go even faster. I will probably try to make a really fast tilt rotor one of these days to see. 

FWIW I haven't cracked 100 m/s on Kerbin with a tilt-rotor either, but then I haven't tried.

Edit: I made a quick try. I slapped four heavy rotors on the Ikarus-D. It went up to 122 m/s with six-blade rotors made with FAT control surfaces. I didn't attempt further optimisations to see if I could get it to go past that, other than trying with 4-bladers (slower, weaker) and larger diameter rotors (no difference to top speed, but so much lifting power it almost tore itself apart when I increased pitch.)

As to Eve, from my first attempts it appears that rotors are more effective on Eve because of the thicker atmosphere so they certainly won't limit your lifting power. Engine power however does. You might want a gizmoed double motor there where a freewheel + single rotor is ample on Kerbin for that reason. Duna is the opposite, the limiting factor is the rotor's ability to produce lift so you'll want more blades and a bigger disk; however you won't need as much motor because of the lower gravity and the fact that you will be rotor-limited more than power-limited.

Edited June 20, 2019 by Guest

[KerikBalm]

Got just over 160 m/s today with a tilt rotor, pics tomorrow morning.

I then switched to a quad rotor design for better handling in hovers, and less strain on the servos (less likely that the nacelles get ripped off), and could move around a jumbo 64 tank at over 100 m/s

Tested the design on Eve, it had a habit of ripping the nacelles off in the thick atmosphere, so I have to be careful about the range of AoA, and transitioning, but I was able to get a jumbo 64 tank payload moving at 72m/s in a slight climb on Eve.

Unloaded, it was doing over 90 m/s

Edited June 21, 2019 by KerikBalm

[Guest]

I forget where I saw it but someone made a post about torque stacking. It had pics and stuff and looked pretty instructional  

(also a tad condescending with some of the wording but hey, I couldn’t have thought his method up so I guess he earned it.)

((maybe a search for “order of intelligence” would locate it but I’m too lazy. Sorry T_T)

Edited June 21, 2019 by Guest

[Guest]

@KerikBalm do you find those wing connectors work better than e.g. Big S elevons?

[KerikBalm]

I didn't try big s elevons (the sts style ones) I just picked them bc they have a better lift:mass ratio. Iirc they also have a higher lift rating (more lift per part = less parts).

I think, based on looking at the files long ago (but after 1.0), that wing segments have better L/D than control surfaces.

The next step is to try it with my sub, which is a bit heavier... I may want to try to get my sub size down a little more

[Geschosskopf]

On 6/20/2019 at 4:10 AM, KerikBalm said:

I was just wondering if anyone had insights on how to optimize the lifting power of rotors/maximum speed.

Does torque decrease as rotors get closer to their maximum RPM?

To optimize lifting power (for a given radius of the blade disc), do we want high RPM, or low RPM and lots of wing area?

In my tinkering, I think torque affects the acceleration of the blades.  That is, the higher the torque, the faster the rotor reaches whatever RPM you have it set for, provided you can keep the fuselage from spinning the other way instead.  Also, I think higher torque enables the rotor maintain higher RPM against the ever-increasing drag.  Torque also seems to help get and keep big, heavy rotors spinning even at lower speeds.

I have an aesthetic distaste for rotors spinning so fast their joints stretch and you've got blade pieces magically hanging more than their own length away from the part they're attached to.  So I prefer to keep the RPM down where that doesn't happen.  To get the necessary "thrust", this might mean I need more blades, which also helps keep the RPM down.

It seems to me that rotor-based props don't actually make "thrust" by shoving a fluid atmosphere backwards like real props do.  Instead, because they're made of wing panels or control surfaces, they function the same way wings normally do in KSP.  That is, if they move forward through the atmosphere with a positive AoA, a lift force magically appears on their upper surface and pulls them in that direction.  Thus, the blades pull the rest of the plane along.

The bottom line, therefore, is that to increase "thrust" (actually "pull"), you want to maximize the lift the blades create.  This argues both for higher RPM and larger blade area, although these things compete with each other.  However, the blades are almost perpendicular to the direction the plane as a whole is moving.  Thus, the blades act like deployed airbrakes---the faster the plane as a whole moves forward, the greater the drag from the blades impose on forward motion.  And the bigger the blade area, the greater the "airbrake" effect of the prop.  This is probably why there's such a seemingly low speed limit for rotor-based props.

It might be, therefore, that variable pitch props might give higher speed.  They'd work exactly backwards from real life, using fine (flat) pitch for takeoff to maximize "pull" at low speeds, then use course (steep) pitch for cruise to reduce the frontal area drag.  However, increasing blade pitch has to be mindful of exceeding the blades' critical AoA in the direction they're spinning, to avoid stalling the blades.  So pitch changes should probably be pretty small and might not have enough effect to bother with.

[KerikBalm]

4 minutes ago, Geschosskopf said:

It seems to me that rotor-based props don't actually make "thrust" by shoving a fluid atmosphere backwards like real props do.  Instead, because they're made of wing panels or control surfaces, they function the same way wings normally do in KSP. 

IRL, props do function like wings. And wings do push air down as they go by, so this isn't saying all that much

Quote

The bottom line, therefore, is that to increase "thrust" (actually "pull"), you want to maximize the lift the blades create. 

Yes, but you also have to keep in mind that the lift vector is always normal to the plane of the wing. Therefore when you get to high AoA, its pulling more "sideways" than forward. The slower the wing section moves, the more its pitch must be to still make lift as the craft moves forward. For a given RPM, a greater rotor diameter results in higher velocity of the wing/control segments, and thus more efficient low pitch blades.

I sense that torque drops off as RPM approaches max RPM, so I think the key is rotor diameter

[Geschosskopf]

6 hours ago, KerikBalm said:

IRL, props do function like wings. And wings do push air down as they go by, so this isn't saying all that much

Somewhat, but it's not their main thing.  Props (and jets and rockets) function in real life by shoving fluids to the rear so Newton's 3rd Law moves the vehicle forward.  Were this not the case, there'd be no propwash.  Thus, all these types of engines create actual thrust and work via Newton's 3rd Law.  Planes are not pulled forward by the lift of the prop blades (or the compressor blades of a turbofan), but are pushed forward by the reaction of shoving fluid backwards.

But in KSP, the atmosphere is not a fluid.  No part of it moves in relation to the rest of it, so props do not shove air backwards--there is zero propwash.  The atmosphere is just a volume of space within which the mere motion of parts, no matter how that's caused, magically creates lift and drag forces on those parts that don't exist in vacuum.  Thus, rotor-based prop planes move forward solely due to the lift forces acting on their blades.    This is a HUGE difference from real life.  It's also very different from the mod prop engines, which under the hood are just rockets with different animations.

 

6 hours ago, KerikBalm said:

Yes, but you also have to keep in mind that the lift vector is always normal to the plane of the wing. Therefore when you get to high AoA, its pulling more "sideways" than forward. The slower the wing section moves, the more its pitch must be to still make lift as the craft moves forward. For a given RPM, a greater rotor diameter results in higher velocity of the wing/control segments, and thus more efficient low pitch blades.

I sense that torque drops off as RPM approaches max RPM, so I think the key is rotor diameter

Yup, as you increase blade pitch, the lift vectors have more cosine loss towards forward motion but at the same time they also get longer, so the loss is less than the cosine of a constant force, although there are diminishing returns here.  But at the same time, the blades offer less frontal area drag to the motion of the plane.  At some point, these curves cross, which is the max possible speed of a rotor-based prop.  Or maybe increasing blade pitch increases rotational drag first.  Either way, you hit a limit.

As to torque, to me it's a measure of the maximum power output of the rotor.  You don't necessarily use it all.  The more you use, the more EC/sec the rotor consumes, just like how rover wheels don't always consume their full listed EC/sec once you're up to speed.  But, the capability is always there.  Thus, the amount of torque actually USED, and thus the power consumed, might decrease once the rotor is at its max RPM, same as with rover wheels, but should you increase the load on the rotor, the torque you still have available will be there to maintain the highest RPM possible.  Either this is the max RPM you've set for the rotor or whatever lower value the torque can manage against the load.

The wider you make the rotor diameter, the more leverage its drag has so the more torque is required to maintain any given RPM,, regardless of blade pitch.  So again, you hit a limit.  Rotors only have so much torque and all their max RPMs are less than infinity.  And eventually you'll find an amount of rotational drag that the rotor's max torque can't overcome.

Thus, there are practical limits to all aspects of rotor-based prop design:  max rotor torque, max rotor RPM, and both the frontal and rotational drag forces on the blades, which increase whether you increase RPM or prop diameter.  There's seemingly no getting around this.

[KerikBalm]

3 hours ago, Geschosskopf said:

Planes are not pulled forward by the lift of the prop blades (or the compressor blades of a turbofan), but are pushed forward by the reaction of shoving fluid backwards.

The two are one and the same.

Wings produce lift by Newton's 3rd law as well. The primary difference between the concepts you seem to have, is that one moves a large masd of air at low velocity (thus low total KE), and one moves a smaller mass of air at higher velocity.

The aerodynamic principles are exactly the same.

[Geschosskopf]

8 hours ago, KerikBalm said:

The two are one and the same.

Wings produce lift by Newton's 3rd law as well. The primary difference between the concepts you seem to have, is that one moves a large masd of air at low velocity (thus low total KE), and one moves a smaller mass of air at higher velocity.

The aerodynamic principles are exactly the same.

Um, no, that's incorrect.  There are 2 totally separate things going on with REAL props.  Yes, there's a little bit of lift, but the main thing is "paddling".

Lift intentionally has very little to do with the 3rd Law because it does not rely on reaction mass.  That is, wings do not shove air down to react the plane up.  If that was how lift worked, you'd be flattened by the weight of a plane passing low overhead.  Instead, the object of wing design is to move as little air as possible because imparting movement to the air sucks energy away from moving the plane (aka drag).  As a wing moves forward, its shape and angle of attack creates a pressure differential in the surrounding fluid, higher on the bottom and lower at the top.  Thus, the partial vacuum on the top sucks the wing upwards (or, the higher pressure on the bottom tries to expand into the partial vacuum, pushing the wing ahead of it).  That is lift.

Props (and turbofan blades), however, create propulsive force by using reaction mass, so are all about the 3rd Law.  The blade physically shoves a wad of air backwards and the 3rd Law pushes the plane forward.  It's exactly the same thing as rowing a boat or how a paddlewheel ship works.  The oars/paddles shove water backwards and the reaction force moves the boat forward.  Thus, REAL props have more in common with rocket engines than wings.  It's just that prop planes don't have to carry their reaction mass around with them.  This is "paddling" and is the main thing happening with real props.

HOWEVER, in KSP (and most video games not going all-out on flight simulation), the atmosphere is not really a fluid--it really doesn't have any substance at all.  It's just a mathematically defined volume of space where extra calculations happen that don't happen in vacuum, these calculations being designed to fake the aerodynamic forces in a "close enough" manner.  Thus, there's no way to shove a wad of "air" backwards to get the 3rd Law "paddling" reaction of real props, because there's no air to shove.  This robs KSP rotor-based props of the primary propulsive method of real props, leaving them to rely entirely on the fake lift generated by the KSP aerodynamics system. 

This is why KSP rotor-based props perform so poorly compared to real examples.  It's why rotor-based paddlewheel boats in KSP work even worse.  With props, you basically have a wing that's creating most of its lift parallel with the desired direction of travel, which means that the wing's surface area is pretty much perpendicular to the desired direction of travel.  Lift is a relatively weak force, barely enough to balance the weight of a plane in level flight.  Thus, there's a low limit on the amount of propulsive force you can get from a rotor-based prop.  And the faster the plane moves forward, the greater the drag becomes from the blades acting like airbrakes in the air ahead of the plane.  When this drag equals the forward component of the blade lift, the plane can't go any faster.

Edited June 22, 2019 by Geschosskopf

[KerikBalm]

http://www.aeroman.org/html/newton_s_laws_and_lift_rev.html

 

 

Edited June 22, 2019 by KerikBalm

[KerikBalm]

1 hour ago, Geschosskopf said:

Um, no, that's incorrect.  There are 2 totally separate things going on with REAL props. 

...

Lift intentionally has very little to do with the 3rd Law because it does not rely on reaction mass.  That is, wings do not shove air down to react the plane up.  If that was how lift worked, you'd be flattened by the weight of a plane passing low overhead.  Instead, the object of wing design is to move as little air as possible because imparting movement to the air sucks energy away from moving the plane (aka drag).  As a wing moves forward, its shape and angle of attack creates a pressure differential in the surrounding fluid, higher on the bottom and lower at the top.  Thus, the partial vacuum on the top sucks the wing upwards (or, the higher pressure on the bottom tries to expand into the partial vacuum, pushing the wing ahead of it).  That is lift.

Again...1 and the same, not 2 separate things.

That pressure differential causes air to move down. Lift can be entirely explained by action and reaction. There would be a serious problem if it couldn't.

You don't get flattened when a plane flies over you because the force is very widely distributed.

And yes, it takes energy. Contrary to what you say, its designed to move as much air as possible, as slowly as possible.

The energy lost is 1/2mv^2, while the force made is proportional to mv.

Thus you minimize energy losses by moving more air, but slower

[Geschosskopf]

10 hours ago, KerikBalm said:

Again...1 and the same, not 2 separate things.

That pressure differential causes air to move down. Lift can be entirely explained by action and reaction. There would be a serious problem if it couldn't.

You don't get flattened when a plane flies over you because the force is very widely distributed.

And yes, it takes energy. Contrary to what you say, its designed to move as much air as possible, as slowly as possible.

The energy lost is 1/2mv^2, while the force made is proportional to mv.

Thus you minimize energy losses by moving more air, but slower

Nope, nope, nope, nope, nope.  You are completely wrong here, I'm afraid.  If you can't see that, then you should go do some more research

Yes, a plane moving through the air necessarily causes the air to move somewhat.  The plane and the air can't occupy the same space so the plane pushes the fluid air out of the way.  But only to the least extent possible, because moving the air wastes energy,  This is why streamlining is a thing.

HOWEVER, this minimal movement of the air can be put to use to create lift.  Lift comes from fluid dynamics, specifically Bernoulli's Principle, which can be derived from Newton's SECOND Law, not the 3rd.  It's a conservation of energy thing.  The air atop the wing moves a bit faster than that below, causing it to have lower pressure and creating a partial vacuum.  The higher pressure below attempts to re-establish equilibrium and carries the wing with it.  That is how aerodynamic lift is made.

If lift worked via Newton's 3rd Law as you mistakenly believe, then there'd be no difference between airplanes and helicopters.  But they're demonstrably different, as I shall now demonstrate....

I believe we can agree that helicopters are all about the 3rd Law, "paddling" to use air as reaction mass, right?   Helicopters hover and maintain altitude by countering gravity head-on with the 3rd Law reaction force, same as a jet or rocket VTOL.  And I'm sure you're familiar with the strong, often dangerous winds under a low-flying helicopter.  That wind is the reaction mass, accelerated by the rotor, and the volume of air and the speed it's moving are all necessary to counter the gravitational pull on the mass of the helicopter as a whole.  It's exactly like being in the exhaust stream of a rocket or jet with the diameter of the helicopter's rotor disk.  Agreed?

OK, then if wings worked the same way as helicopter rotors (using the 3rd Law), then to lift a plane of the same mass as the helicopter, the wings would have to shove down just as much air just as fast.  But an airplane's wing area is only a small fraction of the rotor disk area of a helicopter of the same mass (rather than a larger area as you posited above).  Therefore, to generate the same gravity-countering reaction force from a much smaller area, the airplane's wing would have to accelerate the air to a much higher downwards velocity than the helicopter's rotor to get the same mass-flow rate as the helicopter.  Therefore, the wind felt under a low-flying plane would be even more intense than that under a helicopter of the same mass.

But this is not the case.  In fact, there is no perceptible downdraft under a low-flying plane, because wings DO NOT use the 3rd law to generate lift.  They use fluid dynamics.  Totally different animal.

Edited June 23, 2019 by Geschosskopf

[SRB]

On 6/20/2019 at 5:10 AM, KerikBalm said:

I was just wondering if anyone had insights on how to optimize the lifting power of rotors/maximum speed.

Does torque decrease as rotors get closer to their maximum RPM?

To optimize lifting power (for a given radius of the blade disc), do we want high RPM, or low RPM and lots of wing area?

I was also wondering how lifting power is relative to G and air pressure. On Eve, the atmosphere is much thicker, so its like operating a rotor with 5x the surface area on Kerbin. The gravity is 1.7x higher, so lifting 10 tons on eve is like lifting 17 tons on kerbin.

Does the thicker air make it easier to lift payloads on eve despite the higher gravity?

 

As far as optimizing for speed, I'm guessing that a larger rotor diameter helps, so that for a given RPM (again, does lower RPM result in higher torque, if torque drops off as it approaches maximum RPM?), the blade angle can be shallower? I saw @Brikoleur made a contra rotating helicopter reach over 100 m/s, with the rotor closer to parallel to the direction of motion than perpendicular to it.

So far my tilt rotors are maxing out at between 93-94 m/s, so I'm wondering if for some reason in KSP, a helo can get faster than a tilt rotor? How does one optimize for forward speed with these new rotors?

Can you make hinges to make a fully articulated/semirigid rotor?  KSP simulates https://en.wikipedia.org/wiki/Retreating_blade_stall, which limits forward speed for a single-rotor helicopter because eventually the roll force will be so powerful that even maximum cyclic won’t be enough and you will lose roll control of your helicopter, and doesn’t t have the bendable materials needed to make the blades for a rigid/hingeless rotor.

IDK about max speed for a twin-rotor helicopter or for a prop plane/tilt rotor.

https://en.wikipedia.org/wiki/Helicopter_rotor

https://en.wikipedia.org/wiki/Helicopter_flight_controls

Edited June 23, 2019 by SRB
Typo

[Hotel26]

13 hours ago, KerikBalm said:

Again...1 and the same, not 2 separate things.

An airfoil generates lift via Bernoulli's effect, creating a pressure differential between the upper and lower surfaces of the airfoil.  An efficient wing deflects the airflow as little as possible to avoid drag, especially induced by turbulence.

Propellers usually operate as airfoils, but aim to deflect the airflow (using Bernoulli's effect).  The result is a vortex followed by eddying (turbulence).  (Some of the same with wings, from the wingtips.)

A car and a truck are the same, both using an internal combustion engine, but quite different in purpose.  Similarly, wings and propellers are both airfoils but one used to produce 'lift' and the other to produce 'thrust'.

 

Edited June 23, 2019 by Hotel26

[AngrybobH]

2 hours ago, SRB said:

Can you make hinges to make a fully articulated/semirigid rotor?

Yes. I have built a fully articulated(without cyclic because we don't have anything to simulate that) rotor with stock hinges. I dumped the lead/lag portion because of kraken attacks and the added weight is bad for rotor speed. Flapping hinges work mostly as you'd expect. Sometimes, though, they can overcompensate and reverse the roll and I am unsure as to why. You still end up with a maximum speed, based on min/max value of the hinge, before forward flight causes asymmetric lift to be too unwieldy for your craft. But, the max power of the rotor is usually hit first, at least with the things I have built.

2 hours ago, Hotel26 said:

Similarly, wings and propellers are both airfoils but one used to produce 'lift' and the other to produce 'thrust'

And to add to this, you can have props that produce thrust without having wing shaped blades(see ceiling fans). At my shop I have a fan with basically sheet metal blades that produces a 30MPH wind. It is on wheels and must be chocked or it will drive around the shop. As I understand it you cannot get decent subsonic flight without a typical wing shape. In KSP you get no lift from angling a structural panel into the 'wind' because it has no magical lift value and KSP does not model the thrust that would be produced. In KSP a fan would not cool you on a hot day.

[KerikBalm]

5 hours ago, Geschosskopf said:

If lift worked via Newton's 3rd Law as you mistakenly believe, then there'd be no difference between airplanes and helicopters.  .

Aside from one rotating, there isn't. That's why thy are called rotary wings

 

1 hour ago, AngrybobH said:

As I understand it you cannot get decent subsonic flight without a typical wing shape.

You would be wrong, as a typical flat wing paper airplane, or a rubber band powered balsa plane with a wing consisting of a flat sheet of balsa (with a rectangle cross section) will demonstrate

3 hours ago, Hotel26 said:

Propellers usually operate as airfoils, but aim to deflect the airflow (using Bernoulli's effect).  The result is a vortex followed by eddying (turbulence).  (Some of the same with wings, from the wingtips.)

A car and a truck are the same, both using an internal combustion engine, but quite different in purpose.  Similarly, wings and propellers are both airfoils but one used to produce 'lift' and the other to produce 'thrust'.

Yes, they have different purposes, but the aerodynamic principles, as you seem to acknowledge, are the same, which is my point.

[Hotel26]

16 minutes ago, KerikBalm said:

but the aerodynamic principles, as you seem to acknowledge, are the same, which is my point.

I actually agree, in general terms, with both of you (i.e. and Geschosskopf), because I think you both have some reason and because the disagreement, if any, is only due to the subtlety of the aerodynamics.  So you could say my intent is only to facilitate the communication and avoid simplistic renditions.

"It's better to seek understanding than correctness"

Edited June 23, 2019 by Hotel26

[KerikBalm]

I suggest that we take the discussion of wings vs propellers to the science and spaceflight forum, and return to the topic of how to get the most out of the rotors for flight in KSP's aerodynamic model.

[Guest]

I found the thing I was thinking of!

mebe this will help

[SRB]

6 hours ago, AngrybobH said:

Yes. I have built a fully articulated(without cyclic because we don't have anything to simulate that) rotor with stock hinges. I dumped the lead/lag portion because of kraken attacks and the added weight is bad for rotor speed. Flapping hinges work mostly as you'd expect. Sometimes, though, they can overcompensate and reverse the roll and I am unsure as to why. You still end up with a maximum speed, based on min/max value of the hinge, before forward flight causes asymmetric lift to be too unwieldy for your craft. But, the max power of the rotor is usually hit first, at least with the things I have built.

I’m not sure how this was made, but it looks interesting: 

 

[Guest]

Okay, I'm weighing in. I've been working on a very particular optimisation problem. I want to make a 100% recoverable (in theory anyway) Eve launch system, capable of delivering one (1) kerbal from the surface of Eve to orbit, and repeating this mission after refueling and reloading. Again, in theory anyway.

To do this, I'm building a helicopter that will fly as high into Eve's atmosphere as it can, then light up its rocket to get into as close to a suborbital trajectory as it can. Then I release the orbiter which goes to orbit. This in turn means I need rotors that (1) maximise lifting capability per gram of dry mass and (2) are robust enough to stand the stresses of the Evian atmosphere.

What I've discovered so far:

(1) As far as I can tell, Big S Elevon 2s make the best rotor lifting surfaces. I've tried wing connectors and other elevons, and these just lift best.

(2) I get most lifting power per gram with the following power solution: 

- 1 heavy rotor
- 1 flat servo
- 4 small servos for collective control
- 4 Big S Elevon 2s for rotor blades

The lifting unit is a classic contra-rotator, with the heavy rotor sitting on the flat servo, and the blades (2 in each direction) sitting on the small servos clipped to the top and bottom half of the heavy rotor. 

(3) Well known fact, but still: rotors scale with size, up to a point where there are diminishing returns. Mine are about as wide as the VAB.

I've tried a variety of other solutions for this but this is the best I get. My craft weighs in at just under 50 tons, and it's powered by three of the above lifting units. It's currently at about 24 km altitude, climbing at about 7.5 m/s. Peak climb was 14.9 m/s between 13 and 15 km. The optimal collective setting appears to be 7 degrees, up until about 23 km when it starts slowly falling.

Edited June 23, 2019 by Guest

[AngrybobH]

3 hours ago, Brikoleur said:

What I've discovered so far

My discoveries are in agreement with yours. The 7 degree pitch seems to be nearly the same on all my designs. A couple of powerful (modded) rotor designs liked 8 degrees. Modding the g-11 rotor does not produce expected results, doubling the power does give double the rotation speed, quadrupling also does not give double the rotation speed. 

 

6 hours ago, Dale Christopher said:

mebe this will help

This is cool and opens another avenue to try for MOAR power. If 7-8 degrees of pitch is all the blades like, more/longer blades are required but then more power is need for it to perform reliably.

6 hours ago, SRB said:

I’m not sure how this was made, but it looks interesting:

Thanks for posting that. I'm probably going to lose hours upon hours mixing that design with mine.

[Geschosskopf]

18 hours ago, KerikBalm said:

Aside from one rotating, there isn't. That's why thy are called rotary wings

(heavy sigh).  You've been building rockets too long, my friend.  You can't see the differences between being in vacuum and being immersed in a fluid medium,.  There are more ways to generate useful forces than simply hurling reaction mass astern.  I'm sure you've heard of electromagnetism?  OK, if you believe in that, then you should be open to the possibility that maybe, just maybe, creating a pressure differential in a fluid can also create a force without reaction mass.  You know, kinda how suction cups work?  Lift and suction cups both rely on normal atmospheric pressure trying to restore equilibrium, all without reaction mass.  Open your mind

Quote

You would be wrong, as a typical flat wing paper airplane, or a rubber band powered balsa plane with a wing consisting of a flat sheet of balsa (with a rectangle cross section) will demonstrate

Um, no.  Angle of attack, same as with the symmetrical KSP wing sections.  Sure, some air is deflected downwards by the inclined surface but this surface is not moving relative to the air ANYWHERE near as fast as a helicopter blade.  What happens is, the angle of attack creates a lower pressure on top as a small amount of air suddenly has to fill a void that wasn't there before, and the small amount of air deflected downwards creates a higher pressure below because air is compressible.  So, pressure differential and lift.  NOT reaction mass.  At all.

Again, if it was all about the 3rd Law and thus reaction mass, you'd have AT LEAST the same downdraft underneath a wing as you do under a hovering helicopter.  More even.  If you're throwing air down to counter gravity, and air only weighs so much per unit volume, you have to either move the same amount at the same speed or less at a higher speed.  There's no getting around that of if you're relying on the 3rd Law.  As airplanes demonstrably do not blast away the air under them, they obviously do not rely on the 3rd Law for lift.  Simple as that.

17 hours ago, KerikBalm said:

I suggest that we take the discussion of wings vs propellers to the science and spaceflight forum, and return to the topic of how to get the most out of the rotors for flight in KSP's aerodynamic model.

I see no point in that.  You can't think in any terms but the 3rd Law, even when shown that's not even what's happening here.  And all I've been trying to do is answer your OP question.

But I'll try 1 more time.  Real props and helicopter rotors derive most of their propulsive and/or lifting thrust from your favorite thing, Newton's 3rd Law.  But, because the KSP atmosphere is NOT a fluid, nor even a substance, the 3rd Law does NOT apply even to rotor-based KSP helicopters.  Such craft are NOT swimming in reaction mass as they are in real life, so cannot hurl anything astern no matter how vigorously they spin their props or rotors.  Thus, the ONLY thing that moves rotor-driven craft in KSP is the aerodynamic lift generated by the rather wonky aero calculations.  These calculations were designed SOLELY to APPROXIMATE the behavior of fixed wings without having to deal with all the intricacies of actual fluid dynamics, but broad strokes are good enough to fake it.  So you know what that means?  KSP aerodynamic lift therefore doesn't rely on the 3rd Law, either, due to the lack of reaction mass, same as real lift   

When we as players make home-made props without benefit of Module_Engine, we are taking KSP's aero system to a place it was never designed to go.  So disappointment is assured.  That is the answer to your question, in general terms.  Now, we can tinker and rig up things to exploit holes in the KSP aero system, but there are harsh limits to what is possible here.  Get used to it.

Edited June 24, 2019 by Geschosskopf