Topic Subscribe
WATCH  1 page1583 viewsPOST REPLY
JR AMERICAS . HeliDirect . Heli-Max
. .

Flybarless Rotor Head Systems

 >

Flybarless co-axial

Morris

Senior Heliman

Hong Kong

Anyone think of this? I am thinking of one that no mixer is needed even it is CCPM. Am I correct?

11-18-2007 Over year old.
Wheelhaus

Veteran

Denver

I don't quite understand what you're talking about.. a flybarless coax? why? It would be awfully expensive and heavy to put gyros on a heli that already can stabilize itself...

..........
Dave

12-03-2007 Over year old.
Morris

Senior Heliman

Hong Kong

Dave,

I did not state clearly. A flybar on conventional head system is actually a mechanical gyro, if I can put it this way. That is why we need two gyros for cyclic stablization. But if we have a co-axial flybarless head. Would the counter rotation balance itself so there is no need for gyros.

I agree the head would be heavier, but if we compare a conventional flybarless heli (with two cyclic gyros) with a co-axial flybarless (no need for gyros) the weight should be more or less the same.

Still we may minimise the drag for the flybar... May be not because we have two more blades ...

So this is what in my head

12-03-2007 Over year old.
copperclad

Elite Veteran

NY

hi Morris

yes, CPPM would be the way to go , with collective pitch and yaw would be effected by differential pitch between the two rotors , i have a small fixed pitch machine i built with shogun parts and a larger collective pitch machine i built with raptor 30 parts

i have been thinking about building a flybarless coaxial , they have three bladed designs , i have been thinking about a two bladed design , here is a cad drawing i have been working on although i have not built it yet

here is a photo of the 30 sized CP i built , 550mm mainblade , this is a few weeks before it was finished , it uses a stabilizer bar on the upper rotor and the landing gear is off a Raptor 90 and a second photo after it was finished and flown

12-03-2007 Over year old.
Wheelhaus

Veteran

Denver

Morris, I understand all the physics behind a standard flybar head, I only misunderstood your intentions. I thought you were referring to a MICRO coaxial like the Blade CX.

For the first picture posted by copperclad, I believe you would need gyros because its essentially just two rigid/semi-rigid scale heads. An individual rotor would produce a pitch-up effect (when heading into the wind) no matter which direction it rotates, so two counter-rotating heads would still produce a pitch-up effect. This "self pitching" is what the flybar is designed to counteract.

The second picture would not need a gyro because its only a scaled-up version of the Blade CX. Only the lower rotor has cyclic control, the upper rotor is self-correcting, constantly fighting any inputs from the wind/movement.

Copperclad, I assume the second picture is designed to use only a fixed pitch setup? It would be nearly impossible to control torque distribution if only the lower rotor had collective pitch and the uppe rotor stayed at the same pitch... It would yaw left anytime colelctive was increased.

..........
Dave

12-03-2007 Over year old.
copperclad

Elite Veteran

NY

hi Wheelhaus

yes , it is an overgrown CX on steroids , the bottom rotor is ECCMP , so collective pitch and cyclic , the upper rotor has collective pitch and cyclic is controlled by the stabilizer bar , the upper rotors collective is controlled by a control rod up through the center of the inner drive shaft , it controls the height of the stabilizers pivot point , which in turn controls the upper rotors pitch , dana

edit
the cad drawing would be collective and cyclic on both rotors with yaw being effected through differetial pitch , the height of the two rockers at the very top would be controlled through a control rod not pictured , this would allow you to change the pitch of just the upper rotor , where as the swashes would move both rotors together in collective and cyclic , it is very similar to a gyrodyne system i saw , i am not saying it would work , only that this is where my head is at on the design

12-03-2007 Over year old.
copperclad

Elite Veteran

NY

An individual rotor would produce a pitch-up effect
hi Wheelhaus
my understanding , and please correct me if i'm wrong , the rotor hit by wind produces more lift on one side than the other , because one side is advancing into the wind and the other side is retreating , so the advancing blades speed would be ( rotor RPM + wind speed ) and the retreating blades speed would be ( rotor RPM - wind speed ) and because of gyroscopic precession there is a 90 degree shift , so instead of roll , like you might expect , you get a pitching motion

i thought since the two rotors are turning in oposite directions they canceled each other out in this effect , it is one of the advantages a coaxial has over a conventional heli , dana

here's a link to what i am talking about , and a clip from the article
Helicopters powered by coaxial rotors are also generally capable of higher speeds or able to bear greater weight than single-rotor aircraft. This superior performance is due to the sheer physics of how rotors work. Every conventional helicopter has a maximum speed at which it can no longer produce sufficient laterally balanced lift and maintain controllability on the rotor due to retreating blade stall.

While these same phenomena affect the individual rotors of coaxial designs, the effects of one rotor are essentially canceled out by those of the other rotor, allowing for higher do-not-exceed speeds that are limited more by engine power and design structural limits than by control issues.
http://www.sharc.co.uk/html/case_sikor.htm

12-03-2007 Over year old.
Wheelhaus

Veteran

Denver

Ah, ok that's a very cool idea...

As for the article you quoted, it's only talking about lift differential and forward speed. A single rotor heli may be speed limited because this lift differential becomes too large. By balancing the lift differential the heli can utilize a faster forward speed...

Look at it this way...
A CW rotor will generate excess lift on the left side, 90 procession causes a pitch up effect as the blade rotates to the nose of the heli. This rotor disc will lift on the left side and drop on the right due to natural flapping.

A CCW rotor will generate excess lift on the right side, 90 procession causes a pitch up effect as the blade rotates to the nose of the heli. This rotor disc will lift on the right and drop on the left due to natural flapping.

Excessive forward speed could cause the rotor discs to get dangerously close on the left-hand side of the heli (assuming the bottom rotor is CW) if the dampers are not stiff enough to prevent excessive flapping.

So if I am correct, it will still pitch up in FFF unless there's other strange dynamics I'm unaware of... In a hover, I guess the stability depends largely on how sensetive the controls are. Since you have a LOT of disc area, you will have superior disc loading and big lift capabilities.

..........
Dave

12-03-2007 Over year old.
copperclad

Elite Veteran

NY

hi
my understanding ( and i'm the first to admit i could be confused ) was that although the lift is created on one side of the rotor ( by wind ie forward speed ), gyroscopic precession causes the rotor to pitch up ( not to the side ), my only knowledge on this is just what i have heard pilots talking of and articles i've read

i have a few small flybarless helis , i fly and although they are not as smooth as the same models with flybars , they are quite flyable , i also understand they are a handfull in the wind without something like the V-bar

with my building coaxials , it has just been a slow progression in design , i see there are a number of people who have built 3 blade per rotor coaxials both with and without flybars and stabilizers , and it got me thinking about a 2 blade per rotor flybarless design , so i have just been toying with the idea , i believe gyrodyne (sp?) built a small one around WWII ( unmanned ) for launching off ships , i would like to try it , but it is still only on the drawing board , so many projects , so little time , dana

12-03-2007 Over year old.
WATCH  1 page1583 viewsPOST REPLY
Scorpion Power System . Ron's RC Helicopters . Thunder Power RC
. .

Flybarless Rotor Head Systems

 >

Flybarless co-axial

 Print TOPIC Advertisers 

Topic Subscribe

Saturday, September 20 - 8:55 am - Copyright © 2000-2014 RunRyder   EMAILEnable Cookies