RunRyder - Shifting CG as control method instead of cyclic pitch?

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CAD - Engineering - Technical > Shifting CG as control method instead of cyclic pitch?

soupisgoodfood
Senior Heliman
Location: New Zealand

Hi. I'm interested in converting static plastic heli models to RC versions, there seems to quite a few people out there doing this.

I've been trying to think of a way to reduce the complexity of getting all the mechanics inside such a small space, and keeping the scale realism by not having giant fly-bars etc.

One of the main problems I've been looking at is keeping the CG correct without having to place big items where they can been seen.

Then I thought, why not use CG as a method of control, and be rid of all the small complex mechanics?

Here is the basic idea: The main rotor is fixed pitch, completely. The ESC controls the "collective", "cyclic" control is achieved by shifting the CG of the heli -- this could just be as simple as putting weights on 2 servos.

What do you guys think? Obviously, it would not fly like a normal RC heli, but as long as it can be flown in a scale-like fashion, that's all I care about.

12-13-2006 Over year old.

HOMEPAGE

Havoc
Key Veteran
Location: Ky.

They have made RC autogyros that have worked in a similar way. So it's been done for banking side to side.

12-13-2006 Over year old.

rroback
Key Veteran
Location: Irvine (UCI), Ca

flying by shifting c.g. isn't as easy, or obvious as it sounds. I'm helping a friend, who is working on a serious research project at our school (UCI) working on airplane flight soly with cf shifting. It works for planks, but the system must be smooth, and it takes a lot of fine tuning. for heli's, especially of anything size, it's impossible.

Rhett... I can't fly, luckily the HC Profi Can!

12-22-2006 Over year old.

Havoc
Key Veteran
Location: Ky.

Quote
for heli's, especially of anything size, it's impossible.

Unless the CG you are shifting is the entire mechanics of the "heli" via tilting the rotor disk. But I don't think its the way to go either.

12-23-2006 Over year old.

Portblock
Veteran
Location: Van Nuys, CA

if its realy small, and simple toy, just use one servo, for foward/reaward shift in weight, and use the tail to turn.

I assume it will not be full blow forward flight, but drift foward or drift rearward.

.....

12-24-2006 Over year old.

HOMEPAGE

SSN Pru
Elite Veteran
Location: Massachusetts

Quote
I'm interested in converting static plastic heli models to RC versions, there seems to quite a few people out there doing this

they are not converting the plastic models to RC. they are merely using the fuselage of the static model as a scale fuselage and they are using a REAL full collective/cyclic model for the mechanics.

pru

If you avoid failure, you also avoid success.

12-31-2006 Over year old.

jkempxx
Senior Heliman
Location: Tullahoma TN

Shifting the cg enough to provide adequate control response would probably require moving relative large weights at a fast rate and most likely require very powerful and fast servos with resulting heavy batteries. Often the cg can be moved a fair amount without a noticeable effect on control.

01-01-2007 Over year old.

rcbirdpilot
Heliman
Location: Scottsdale Arizona

I have plans for an ultralight personal helicopter that relies on leaning one way or the other to fly in different direction. I have also read somewhere that the hughes 500 is so stable that a pilot could move the heli by leaning in a direction hands off the cyclic and move the heli place to place

01-12-2007 Over year old.

stickyfox
Key Veteran
Location: Troy, NY, US

How about pumping fluid? Something heavy like glycerin or glycol, or sulfuric acid? Mercury maybe?

Or fuel perhaps... A friend of mine did a masters thesis involving something similar for platform leveling, and it's also been used as a damping system for skyscrapers.

-fox

02-18-2007 Over year old.

HOMEPAGE

soupisgoodfood
Senior Heliman
Location: New Zealand

Quote
they are not converting the plastic models to RC. they are merely using the fuselage of the static model as a scale fuselage and they are using a REAL full collective/cyclic model for the mechanics.

Really? I thought all those little plastic rotor components and fake plastic engines would work fine

Talking about getting picky over semantics...

The helis didn't fly before, and they do now, that's a conversion.

Quote
Shifting the cg enough to provide adequate control response would probably require moving relative large weights at a fast rate and most likely require very powerful and fast servos with resulting heavy batteries. Often the cg can be moved a fair amount without a noticeable effect on control.

This is what I'm worried about. Of course, heavy batteries make good weights. I'm guessing it would be enough for smooth movements, but the problem comes for making fast corrective movements.

I've left this idea, now. I've decided the best option is to make it easy to remove the working head so that the original plastic head can be installed for when it's on display. I should also be able to save myself some very expensive CNC parts this way, since the realism isn't so important.

02-21-2007 Over year old.

HOMEPAGE

rcbirdpilot
Heliman
Location: Scottsdale Arizona

The plans that I have talk about the heli being fixed pitch. There is no swash and the rotor does not tilt, it is fixed. It is said to hang the heli by the top of the main shaft without the rotor head installed and adjust the center of gravity including the weight of the pilot so the helicopter is balanced perfectly. To climb increase the throttle, to move in either direction lean slightly in that direction, it has a variable pitch tail rotor operated by pedals for yaw. As for your tail it could be a fixed pitch tail and adjust the tail rotor speed to yaw

02-24-2007 Over year old.

Portblock
Veteran
Location: Van Nuys, CA

Just an FYI, lookup Gyroscopic Precession.

I was experimenting with a prop attached directly to a brushless, aimed upward like a helo, and when the CG shifted forward, the mock heli tilted to the right. (CW blade rotation) There is a 90 degree shift on inputs. I completly forgot all about this. I was going to try to hook up a CCPM baseplate to the bottom of the motor.

well, I will experiment more later.

.....

03-19-2007 Over year old.

HOMEPAGE

MaceT
Heliman
Location: Fort Worth, Texas

What about tilting the main shaft itself.
has there aver been a design that tilted the mast to acheive directional change. seems ike it would be a simpler design than a swashplate.

03-20-2007 Over year old.

SSN Pru
Elite Veteran
Location: Massachusetts

try spinning a bicycle tire while holding its axle. tilting a large spinning object with a lot of rotational inertia would generate more problems and complexity than using a swashplate.

pru

03-20-2007 Over year old.

Portblock
Veteran
Location: Van Nuys, CA

Tilting a shaft has 2 items of concern off the top of my head:

1: tilt angle not enough for flaring or hard banking. (maybe not enough for serious forward flight)

2: when tilted forward (CW rotor) the heli would imediatly bank to the right (90 CW force)

but then again its fun to experiment with it.

.....

03-20-2007 Over year old.

HOMEPAGE

kangarooster
Senior Heliman
Location: Orlando Fl-USA

I was only able to make it work with a coaxial rotor head.
I see no reason for further R&D.

04-02-2007 Over year old.

Portblock
Veteran
Location: Van Nuys, CA

With counter rotating blades you have two directions for preccession, thus canceling each other out. I didnt even think of doing it that way, I was using the 90 degree precession to tilt, followed by 90 offset in tilt for forward flight. However, I agree with you, for me, no further experimenting for now.

.....

04-03-2007 Over year old.

HOMEPAGE

kangarooster
Senior Heliman
Location: Orlando Fl-USA

It was an interesting project. Nice to think outside of the box once in a while.

04-03-2007 Over year old.

human213
Senior Heliman
Location: malibu

Sikorskie did it first...

...and then developed a proper cyclic mechanism...

michael

06-12-2007 Over year old.

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