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So, I spent the afternoon building this:

sV6djIt.png

It's using two of the largest rotors in a contra-rotating arrangement, with four fuel cells as power.

My problem is, it stubbornly refuses to leave the ground, at least without tipping over and ripping the rotor blades off. I suspect this is something to do with the contra-rotating rotors cancelling each others' motion out, but I'm not sure. Since I've seen a lot of successful helicopters being build since BG released, I'm asking the experts how to get my chopper into the air safely.

Edited by RealKerbal3x
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1 minute ago, HebaruSan said:

Are the blades tilted at all? They look horizontal to me in that screenshot. They need to be rotated to generate lift:

  /
 /    ----> direction of motion
/

I believe they are slightly tilted, but I guess I should angle them more.

I won’t be able to play KSP again until tomorrow, but I’ll give your tip a go then :)

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35 minutes ago, RealKerbal3x said:

I believe they are slightly tilted, but I guess I should angle them more.

Anything between 3 and 25 degrees should generate some decent lift. 15 deg is a pretty decent safe zone.

Set your bottom rotor to Disengaged. It will counter the torque of the upper rotor. Right now it's unbalanced. (I can tell it's on because the blades are getting flung farther out.)

With the parts you've got, you could probably lift 30-40 tons, so it's not a power issue.

I suggest tearing apart @Brikoleur's similar craft: https://kerbalx.com/Brikoleur/BAK-52NS

I haven't flown any of his stuff, but I have no doubt it's high-quality.

Edited by FleshJeb
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(1) For a rotor of that size you need much more pitch. However I would recommend making a larger-diameter one.

(2) I highly, highly, highly recommend putting in collective -- just stick the rotor blades on the small servos and use one of the axes (I use up/down) to control the pitch.

(Also, your motors are way too powerful for a craft of that size. A single big motor like that can lift up to 70 tons with a nice big rotor.)

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2 minutes ago, Brikoleur said:

I highly, highly, highly recommend putting in collective -- just stick the rotor blades on the small servos and use one of the axes (I use up/down) to control the pitch.

I experimented a lot with fixed and control deployment-based rotors before I felt solid enough to move on to collectives. It's a great starting point for learning.

Quote

A single big motor like that can lift up to 70 tons with a nice big rotor

That's amazing. I would have thought that you'd run into diminishing returns with drag well before then. Have you tested with a smaller physics timestep to see if you can get more out of it?

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Just now, Brikoleur said:

(1) For a rotor of that size you need much more pitch. However I would recommend making a larger-diameter one.

OK, I guess I can stick another FAT-455 control surface on the rotor tips.

2 minutes ago, Brikoleur said:

(2) I highly, highly, highly recommend putting in collective -- just stick the rotor blades on the small servos and use one of the axes (I use up/down) to control the pitch.

Probably a good idea...I found that reaction wheels tend to be rather inadequate by themselves for controlling attitude, and it’s probably pretty tricky to keep a handle on the altitude with the torque controls alone.

7 minutes ago, Brikoleur said:

(Also, your motors are way too powerful for a craft of that size. A single big motor like that can lift up to 70 tons with a nice big rotor.)

Yeah, I figured. I originally built the helicopter with the smaller motors, but due to my other mistakes it wouldn’t lift off the ground and my first thought to remedy that was ‘moar powah’.

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  • 6 months later...

I have a question that i would really like an answer to.   I made a helo. And it get up and flys but as soon as it tilts to the side.  I cant get it to roll the other way without changing the pich of it.  How does one fix?

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Well, you'd need a cyclic for that... its generally too complex to bother with. Also there are issues with asymmetric lift once you leave a hover, unless you've got contra rotating rotors.

What I'm doing now is using 4 rotors, and Kal controllers, to control pitch, roll, and yaw by varying rotor speed as in a quad copter drone.

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