sreyoB yrraL
(AVSIG Member)
09/20/15 12:29 PM
Helicopter with robotic legs

I know very little about helicopters but this looks pretty cool...

https://youtu.be/NnN9cxY9Y-o


Dave Siciliano (ADS)
(Top Gun)
09/20/15 12:36 PM
Re: Helicopter with robotic legs

Certainly would solve a problem if they could properly sense and keep the rotor fairly level. Still, one had four legs which would provide four separate landing points. Skids distributed weight over a larger area for landing on softer surfaces.

Ralph Jones
(Top Gun)
09/20/15 06:48 PM
Re: Helicopter with robotic legs

In theory, a helicopter would be more stable in hover if the rotor were on the bottom. If it had about eight of those legs, maybe they could dance around the blades <g>.

Dave Siciliano (ADS)
(Top Gun)
09/20/15 08:39 PM
Re: Helicopter with robotic legs

Quote:

In theory, a helicopter would be more stable in hover if the rotor were on the bottom. If it had about eight of those legs, maybe they could dance around the blades <g>.




Interesting. Might be difficult to load infantry guys on that when running :) Is that because of ground effect?


Ralph Jones
(Top Gun)
09/20/15 09:00 PM
Re: Helicopter with robotic legs

Quote:

Is that because of ground effect?



No, swashplate geometry. Moving the cyclic stick tilts the swashplate, and that varies blade pitch in the correct sequence to make the rotor disk parallel to the plate.

Say the fuselage makes an uncommanded pitch-down movement. The swashplate tilts along with it, tilting the rotor disk forward and producing a forward force component at the top of the mast -- which pitches the fuselage further forward.

Now put the rotor on the bottom. A pitch-down movement still rotates the swashplate forward, the rotor still tilts forward, and still produces a forward force component -- but it's acting below the CG and tends to pitch the fuselage up.

It would also demand a different control technique. With the rotor on top, to get into forward flight, you make a forward stick movement and then relax most of it; with the rotor on the bottom, you'd have to move the stick aft first, then move it slightly forward of center. Much like riding a unicycle.


Bill Bridges - 9S1
(Top Gun)
09/20/15 11:41 PM
Re: Helicopter with robotic legs

Quote:


No, swashplate geometry. Moving the cyclic stick tilts the swashplate, and that varies blade pitch in the correct sequence to make the rotor disk parallel to the plate.

Say the fuselage makes an uncommanded pitch-down movement. The swashplate tilts along with it, tilting the rotor disk forward and producing a forward force component at the top of the mast -- which pitches the fuselage further forward.






Ralph,

This may be semantics, but the swash plate doesn't move the rotor disk, it changes the pitch in the rotor blades based on input received through the intermixing bell crank from the cyclic/collective. This change in pitch tilts the rotor disk.

I don't see the point in the legs. They would just add weight. I've landed on slopes numerous times where the tips of the main rotor blades were no more than three feet off the ground. Landing on slopes and pinnacles are non-issues for military pilots, it's what we do. :-))

Ralph looking forward to continuing our conversation about the swash plate. :-))

I never thought much about the rotor disk being on the bottom other than when doing a split-S in a Cobra. Seemed like it worked just like it did when it was on top. :-)))

the other bill


Ralph Jones
(Top Gun)
09/21/15 08:37 AM
Re: Helicopter with robotic legs

Quote:

This may be semantics, but the swash plate doesn't move the rotor disk, it changes the pitch in the rotor blades based on input received through the intermixing bell crank from the cyclic/collective. This change in pitch tilts the rotor disk.



That's pretty much what I said. The cyclic and collective sticks tilt (and elevate) the lower swashplate and the upper swashplate translates that orientation into the rotating reference frame of the rotor. The actual variation of blade pitch is controlled by pushrods and bellcranks attached to the upper swashplate, and the rotor then tilts into the swashplate's orientation.

In other words, the swashplate doesn't move the rotor disk, but tells it where to move itself.



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