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Home✈️Aircraft🚁HelicopterHelicopter Main Discussion › Ever Notice How Pitch Controls Change On Spool Down?
12-24-2014 03:42 AM  5 years ago
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icanfly

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ontario

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Ever Notice How Pitch Controls Change On Spool Down?
What I'm saying is that I never liked spool down much because the right stick inputs caused the heli to do things it wasn't supposed to like tip over, because I fiddled with the stick after the heli was set down. Either that or I saw it tipping and tried to give it some correction only to worsen it. WHY?

You've heard of gyroscopic precession, your links at 90 deg to the blades, phase lag, and all that matters under power. If you spool down as I have discovered the right stick controls aren't the way they should be.

So I'm finished tossing in a newly fabbed upgrade tail shaft for my small 300zyx heli (man) this evening and upon spooling up on the basement floor in the house to test how the shaft is, no wobbly mess, I flick th and see the rotor go out of sync with the stick. This time I try it a second third and fourth time to observe the rotor input moving, about 45 degrees later. This is much like the swash actions on a fixed pitch heli, not 90 but 45 degrees.

It'll be a new orientation to learn that upon spool down the heli swash inputs may have to shift 45 degrees later, interesting.

Does this happen on ALL helis btw? and what is it about lack of power that fits into the equation? or is it just an effect of very low rpm?
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12-24-2014 04:14 AM  5 years ago
wc_wickedclown (RIP)

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long beach calif

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a friend of mines had a zyx on heli using phasing didnt fly so well
the zyx does not allow for electronic phasing
If you spool down as I have discovered the right stick controls aren't the way they should be.
thanks for the tip
Insha Allah made in america
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12-24-2014 01:22 PM  5 years ago
icanfly

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ontario

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zyx schmed y x, I plan to Skookum 720 a 700 one day, and I can toss the inexpensive gyro completely, someone has flown a 300 with only a tail gyro successfully, I sense some prejudice toward a person for the gear they own here.

"MAN", you'd think such a small bird would not click well with the nitro 600/700 crowd, yea, when my wee scale design is upscaled to that size I expect to push it over 200mph, bitches and friends. My 300 can be made to go over a hundred mph and I've probably had it up to that speed a few times. My ultimate plan is to push a heli supersonic. You say can't be done, I say you ain't seen nothin yet.

This all really focuses on landing on uneven ground and correcting while the heli is still spooled but not under power.

It's just a mysterious phenomenon the phasing shifts exactly 45 degrees while spooled down. Does this suggest the phasing will differ at very low head speed, and what makes power applied change the nature of phase lag?

You know, there's a ton of info out there on aerodynamics, but gyroscopic effects on a heli are mechanical.

anyway, there are no happy accidents on a comp program, are there?

The 45 degree offsetting has something to do with Delta3, if you know what that is.

I reason since the first 45 degrees of a rotor event, swash tilting under power, is of the blade ramping up to pitch and the last 45 degrees is the opposite, ramp down it might be noteworthy that the blade still have aero effect while turning at any rpm and at lower rpm is either immediate or delayed, the blades are experiencing flapping and delta3 hinging effects. This would be the cause of blades not held tightly at the tips by centrifugal force of rpm. Also, when your blades are under power they lag as power is turning the grips ahead of the grip axis, drag is forcing the blades backward slightly.

Ohh btw, last week a military paint Chinook passed overhead 1000ft directly overhead due south, whoooeeee, extremely rare sight to see.

sure is ironic a teenie weenie rc copter has helped me unlock the mysteries of the universe, EHH, lol.
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12-24-2014 04:28 PM  5 years ago
ssmith512

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Indianapolis, IN USA

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Angular momentum?Steve
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12-24-2014 06:49 PM  5 years ago
wc_wickedclown (RIP)

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long beach calif

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i wonder would using throttle hold when your skids hit the ground and keeping the thr a hair below mid stick would help would power down faster ?Insha Allah made in america
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12-24-2014 09:29 PM  5 years ago
icanfly

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ontario

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personally mine is shut down in st1 hitting th and full negative to slow it down bringing it mid stick near the end to hand stop it, ahh, I sometimes come in fast and hot too, battery alarm beeping like crazy. If I see the heli tipping its second nature to try correcting it. Often pulling the fingers off the sticks is the best plan of action.
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12-24-2014 09:51 PM  5 years ago
altima1779

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Toledo, oh u.s

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I am not an expert but I think this is more of a flybarless thing.

By removing the flybar you are taking the mechanical gyroscope/dampening system out of play.

Look for and read up on the NoBar threads, one of the biggest challenges the guys going flybarless without a gyro system is the heli becomes very sensitive to cyclic input, again this is because you no longer have a flybar to dampen inputs.

When your head speed is low and you give a cyclic input it is increased due to no flybar but your head speed is too low to allow the heli to physically correct to counter the initial stick movement.
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12-25-2014 02:58 AM  5 years ago
dkshema

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Cedar Rapids, IA

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I suspect the root cause of the apparent change in control phasing is due to the fact that the helicopter, aerodynamics, and control behavior changes due to the fact that the helicopter is now firmly fixed to an immovable object (earth).

From a very old copy of Model Aviation -- October 1990, accompanying a picture of Mike Mas doing his inverted landing, there is some interesting text associated with the pic. First, Mike inserted a two-inch long rod into his main rotor head, and would land, inverted, on about a 6-inch square block of plywood mounted on a waist-high support.

In the article (written by Larry Jolly), the following text appears:
The complexity of the maneuver stems from the fact that during touchdown the main rotor becomes a fixed, stationary point and hovering is accomplished by steering the fuselage which is the exact opposite of conventional steering, where the fuselage is the fixed point and the rotor moves during a control input. To complicate matters even more, during touchdown the control system becomes approximately 45 degrees out of phase while inverted, making control extremely difficult. A variation of this phenomenon can be felt when a helicopter is sitting on its skids and cyclic control is introduced during runup. As you push the stick forward, the result is forward and right.
The dynamics of the heli change when it no longer is free to move in any direction. Restrict its movement, you get unusual control results.

I also suspect being in ground effect has a large influence here, too.

Flybar, or Flybarless, it makes no difference.
-----
Dave

* Making the World Better -- One Helicopter at a time! *

Team Heliproz
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12-25-2014 06:30 AM  5 years ago
icanfly

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ontario

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yea thanks, that was a good reply there dkshema.

What the effect stems from is quite possibly the heli chassis actually becoming pushed down in the same but opposite amount directional pitch becomes while airborne yet is 100% on the ground since pitch has no damper to a fixed chassis. This would be one source of all cp rotor craft vibe, the higher the rpm and increased blade count the less of this phenomena should occur. For every action there is a reaction.

Have in all your life seen anyone ground control a wheeled rc heli?

and you might have thought this was leading nowhere.
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12-25-2014 10:27 PM  5 years ago
icanfly

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ontario

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after a few landings only minutes ago while testing out my small heli and landing on uneven ground as always it's comforting to know the heli is now controllable on the ground. I made a conscious effort to steer forward, left, right, and back and everything was 45 degree late on the tx gimbal translating to a phase shift of only half of the airborne 90deg phase lag on the heli.

cool science.
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