The Optimist

(Stock Electric Propeller Vehicle Showcase): Bringing power to the people!

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About the blade pitch, usually I set it to 30 degrees to the airflow. But I only use this on takeoff, for flying I usually set the authority limiter to -70  to reduce the blade angle. If the engine is powerful enough you can set the authority limiter up to -90 to get some extra speed. I try to optimize the engine so that it can reach the max speed with the authority limiter set to -70. That way I can use the higher blade angle for takeoff, and then just toggle the cruise mode via the hotkey. No need to fiddle with the authority limiter slider in flight.

Today I finally managed to build a working seaplane, it can carry 6 Kerbals at max speed about 150 m/s. It took me quite a few tries to find a hull configuration that can land on the water without doing a front flip or destroying the rotor blades.

Also I'm not sure if this is some sort of a bug or something else. After the first water landing the plane could takeoff with only about 50% trim on each engine. After the second water landing I had to give it full trim on the engines in order to takeoff and the plane couldn't reach its max speed. I'll have to do some more testing to find the cause to this.

MzU0kek.png

qABYmUp.png

https://kerbalx.com/Rade/Galeb

Edited by _Rade
Updated the model

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hmmm...

i made a new propeller that is more reliable, but longer, and i'm trying to get it to redock but i just cant figure out how :/

any suggestions?

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Problem with the docking ports is that they have to move away from each other a certain distance before they can redock. Unless you can do something like that you wont be able to redock two parts.

For the Dunasoar I've used the claw located inside the engine nacelle to grab the rotor when the plane is not in use. It works quite well, only downside is the engine have to be considerably bigger because you have to fit the claw inside the fairing.

KTMREaQ.png

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I came up with this idea today: since the reaction wheels give torque not force, it'll be better to have props closer to the axis if the hinge is reliable and has marginal friction. Does this hold in ksp, or is this just a thought?

EDIT: Just found that shorter wings greatly increases the performance, matching my hypothesis.

 Are there some props with TWR 4 on high speed? I found that mine gets TWR of 2.

Edited by Reusables
Got some observations.

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The amount of lift you get depends on how fast the propeller blades are moving, so it makes sense to move them further away from the rotor axis. That way, if you assume that in the both cases the propeller is spinning at the same speed, the engine with the prop blades further away from the rotor will have more thrust.

What might be happening is that engine that you're using doesn't have enough torque to spin the propeller at the full speed when the rotor blades are moved further away from the rotor axis. But when you move the blades closer the engine can spin them faster and they provide more thrust.

For example small engines that I'm using, they have 20 reaction wheels, when I put 3 propeller blades on them they work great at low altitude, but lose thrust at higher altitude. That is because the propeller can spin close to the 50 rad/s (which is the max rotation speed the game allows) at low altitude, but if you go higher the propeller is still spinning close to 50 rad/s but the propeller blades provide less thrust because the atmo is less dense.

However if I put 5 propeller blades on this engine, it will have lower speed at low altitude and higher speed at high altitude. Because now the engine can't spin the 5 bladed propeller at full speed at low altitude, but if you go higher the engine can spin the prop close to 50 rad/s and 5 bladed prop will give you more thrust than 3 bladed prop, simply because it have bigger surface area.

I hope this helps.

btw. how did you manage to measure the thrust on the propeller?

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1 hour ago, _Rade said:

The amount of lift you get depends on how fast the propeller blades are moving, so it makes sense to move them further away from the rotor axis. That way, if you assume that in the both cases the propeller is spinning at the same speed, the engine with the prop blades further away from the rotor will have more thrust.

What might be happening is that engine that you're using doesn't have enough torque to spin the propeller at the full speed when the rotor blades are moved further away from the rotor axis. But when you move the blades closer the engine can spin them faster and they provide more thrust.

For example small engines that I'm using, they have 20 reaction wheels, when I put 3 propeller blades on them they work great at low altitude, but lose thrust at higher altitude. That is because the propeller can spin close to the 50 rad/s (which is the max rotation speed the game allows) at low altitude, but if you go higher the propeller is still spinning close to 50 rad/s but the propeller blades provide less thrust because the atmo is less dense.

However if I put 5 propeller blades on this engine, it will have lower speed at low altitude and higher speed at high altitude. Because now the engine can't spin the 5 bladed propeller at full speed at low altitude, but if you go higher the engine can spin the prop close to 50 rad/s and 5 bladed prop will give you more thrust than 3 bladed prop, simply because it have bigger surface area.

I hope this helps.

btw. how did you manage to measure the thrust on the propeller?

I measured the thrust with weights and the acceleration it gets on vertical ascent.

And, isn't 50rad/s too fast? I got similar thrust with more wing surface minus the additional drag to the airstream on the loway atmosphere. I personally think that the full speed would get disadvantage from the friction, which gives less lift per the torque. (Due to the constant L/D and more friction torque compared to drag torque)

Also, front lift per drag torque is inversely proportional to the radius of the propeller fins in the theory.

Edited by Reusables
I was wrong about citing the wiki page

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In my experience faster the prop is moving the better thrust you get from the blades.

I did a quick little experiment to test the lift you get from the rotor blades. First engine uses 4 blades placed close to the rotor axis, it is powered by 20 reaction wheels. The second engine uses 2 blades which are slightly offset from the rotor axis, and it is powered by 26 reaction wheels. Second engine had to be slightly more powerful in order to be able to spin at same speed as the first engine.

Anyways, even tho both engines are spinning at the same speed, the blades on the second one are generating approximately double amount of lift compared to the blades on the first engine. And that's only because the difference in speed between the blades on two rotors.
 

Spoiler

 

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Also here is another example on how to determine engine thrust. The plane is flying at it's max speed, on the panel on the left total drag for the plane is ~17.2kN, so in order to keep flying at that speed the engines must be able to provide same amount of thrust. On the second picture one of the rotors is selected and the panel on the left is showing total drag for the rotor as negative ~8.6kN and total lift as ~1.9kN. I'm guessing the game is confused by the  rotors and that's why it the drag is negative. But if you multiply that drag by 2 you'll get almost exact match for the drag created by the plane.

There is also little bit of the drag caused by the propeller blades (6*0.22kN) and by the nosecones at the front of the rotor (2* ~0.35kN) which gives us the total drag for the plane at 19.22kN. In other words each engine produces about 9.6kN of thrust at the max speed for the plane. Not counting the fairing the TWR for just the engine is 0.48.
 

Spoiler

 

zqrlZ9J.png

51j6sMX.png

 

 

 

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2 hours ago, _Rade said:

In my experience faster the prop is moving the better thrust you get from the blades.

I did a quick little experiment to test the lift you get from the rotor blades. First engine uses 4 blades placed close to the rotor axis, it is powered by 20 reaction wheels. The second engine uses 2 blades which are slightly offset from the rotor axis, and it is powered by 26 reaction wheels. Second engine had to be slightly more powerful in order to be able to spin at same speed as the first engine.

Anyways, even tho both engines are spinning at the same speed, the blades on the second one are generating approximately double amount of lift compared to the blades on the first engine. And that's only because the difference in speed between the blades on two rotors.
 

 

Also here is another example on how to determine engine thrust. The plane is flying at it's max speed, on the panel on the left total drag for the plane is ~17.2kN, so in order to keep flying at that speed the engines must be able to provide same amount of thrust. On the second picture one of the rotors is selected and the panel on the left is showing total drag for the rotor as negative ~8.6kN and total lift as ~1.9kN. I'm guessing the game is confused by the  rotors and that's why it the drag is negative. But if you multiply that drag by 2 you'll get almost exact match for the drag created by the plane.

There is also little bit of the drag caused by the propeller blades (6*0.22kN) and by the nosecones at the front of the rotor (2* ~0.35kN) which gives us the total drag for the plane at 19.22kN. In other words each engine produces about 9.6kN of thrust at the max speed for the plane. Not counting the fairing the TWR for just the engine is 0.48.
 

 

 

That's not what I meant, what I said was about TWR.

To clarify, my point is that thrust per torque is smaller for bigger friction and inversely proportional to the radius of fins, and the thrust per torque is critical to the TWR.

Since the stable angular velocity is achieved when the wheel torque is equivalent with friction torque and lift&drag induced torque. Because L/D ratio is the same given the same AoA, Thrust by the lift per the lift&drag force is same for the same geometry. Since ift&drag torque is the force multiplied by the fin radius, Thrust per (wheel) torque is better for smaller prop. diameter and smaller friction torque per wheel torque. And it's obvious that friction torque per wheel torque is bigger for faster rotation speed.

In detail, Thrust is proportional to the square of the propeller fin radius while the torque does to cubic of it: http://en.wikipedia.org/wiki/Propeller, look at the theory section.

This is really critical with the TWR, since the most of the engine mass is from the reaction wheels and the generator if the prop wings are not too big. Configuration of 20 small reaction wheels powered by 6 radioactive generatoes weighs 1.48t, while Stayputnik bearing should be under 0.5t and 8 fourth elevons weigh 0.32t. In my case, it gets worse since I uses 20 mk1 sized reaction wheels for bigger thrust, while the bearing remained the same and prop fins weigh 0.92t. The wheels and generators weigh over 3.5t.

I think TWR is what only matters with the prop engines. Even with the bigger thrust the plane with the engine wouldn't fly well with less TWR since the engine mass gives certain lift requirements which causes increased drag.

About the measurement, I measured the thrust without the drag of props since it's the thrust which the plane gets. So the thrust will be bigger for faster speed if I added the drag.

Edited by Reusables
Added wiki link

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On 4-1-2017 at 6:34 AM, Jon144 said:

I did my own tests of this a while back and I believe Azimech did too. In my builds I have found that in the current aero model its best to have low angle of attacks in order to decrease the drag generated by the surfaces in order for them to spin faster and generate more lift. Drag and total power of the rotors does not scale evenly with angle of attack based on how the difference in the angle of attack changes drag and the speed that they can rotate. I'm not explaining this very well but you probably get the point. 

In short usually rotors with less drag will produce more power than slow rotors with high angles of attack. This is opposite from the old aero model we had. 

Yes. During the Errordynamics of 0.90 I noticed the same behaviour as with NeoAero when using modded propeller pitch, just at different angles. During 0.90 I could set my turboprop speed record with blades at 85 degrees. Terrible acceleration and climb. Using the opposite, 32 degrees, resulted in max static thrust but that made almost any airplane incapable of flight due to massive drag ... they suddenly turned into helicopters. And this was before I could build a stock prop pitch (that came with 1.1 and meant the final breakthrough for the turboprop).

Positive side effect of the lower blade angles for rotors: less dissymmetry of lift and less risk of getting retreating blade stall. My first helicopter had a max allowed speed of 25 m/s and I would fight it all the way. My newest flies 85 on stock autopilot with ease. Blade angle: 3.6 degrees. Rotor speed: 29 rad/s.

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Found out that high speed performance is more important than stationary TWR itself. So my analysis was wrong for planes :P

It needs higher rotor speed to perform well on high speed, which requires higher angular speed.

Since there is strict limit of 50rad/s in ksp physics engine, the performance is quite limited.

Also friction tends to be bigger with higher angular speed, especially when the angular speed approaches the physics limit of 50rad/s.

So.... decided to go wider. (bigger diameter)

 

Anyway, in process of trying to make an Eve SSTO, made propellers with TWR 1.88 for low speed(120m/s) on 3950m.

(Drag of the engine is excluded; It  TWR down to 1.5~1.6, propellers weigh 13t, 6.5t for each)

t9BMkNs.png

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I tried my hand at making a near replica of my favorite aircraft, the Consolidated B-24 Liberator!

nAoXzyM.jpg

She's slow and heavy, but still gets the job done of course!

KerbalX: https://kerbalx.com/Skyshrim/b-24-bro-loaded

Edited by Skyshrim
forgot the kerbalx link. oopsie!

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Just now, Skyshrim said:

She's slow and heavy, but still gets the job done of course!

Much like the real thing.

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I'm linking this here for the sake of chronicling the history of stock propellers. This person, Squiddy, claims to have exceeded 343 m/s in level flight. There seems to be no public craft file, though.

 

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Level flight? the 5 degree dive on the navball couldn't be clearer.  Nitpicking, but still impressive.  Hope to see more...

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5 hours ago, fourfa said:

Level flight? the 5 degree dive on the navball couldn't be clearer.  Nitpicking, but still impressive.  Hope to see more...

apparently they checked using the horizontal speed indicator on the f3 menu.  I think.

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On 5/16/2017 at 4:40 AM, Rath said:

apparently they checked using the horizontal speed indicator on the f3 menu.  I think.

No. It was in the IVA mode. Which also indicated a 5 degree dive.

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Last week David Nielsen held a contest for the fastest stock propeller powered plane, and he had a chance to test fly this plane. So I don't really have doubts it can get over Mach 1 barrier.

 

Yesterday another guy put  up video showing the plane that goes faster than 360m/s.

 

This is quite doable if you know how to abuse the KSP aerodynamics, so far I've managed to get to ~333m/s, and with the few tweaks this plane should be able to go over Mach 1.

khTZTw5.png

 

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Not to be a spoil sport, but with these supersonic electric jets, it kinda looks like its a planes with some random elevons going in a ring around it, barely related to the actual plane

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24 minutes ago, qzgy said:

Not to be a spoil sport, but with these supersonic electric jets, it kinda looks like its a planes with some random elevons going in a ring around it, barely related to the actual plane

Yes it does. This is a limitation in KSP sadly. Its a good thing they are trying to break speed records not 'looks like a real aircraft' records, huh? :D:wink:

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Teensy tiny electric helicopter!

2Lm7Kxx.jpg

0.792 tons sans Kerbal, although the Kerbal does tend to help with the helicopter pitching up. Tends to top out at about 30 m/sec in level(ish) flight.

Still has a few quirks (such as the wobbly bearing) I'm trying to fix and/or optimize, which is why I'm putting it here rather than its own Spacecraft Exchange page.

Kerbalx link

Enjoy, and feel free to pick it apart if you like the bearing, etc.

(My apologies for the thread bump)

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I'm sorry if you've seen this before! But this is for people who haven't. Sorry if this is spammy!

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Here's a prototype electric propeller plane that can fit in a Mk3 cargo bay so it can be taken to Duna.  The propeller is re-attatchable using junior docking ports, while it is spinning full speed the centripetal force keeps them far enough away that they don't magnetize.  It also has folding wings.  The funny looking landing gear, in theory, allows it to drive back into the cargo bay to be taken home or transported to other parts of Duna.

It does have some problems though, the wing often re-docks slightly off center and spinning up the propeller knocks the plane over without a launch clamp to hold it.

YBcO7yh.png

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