Blade Flapping....

[Super-Hornet]

In this post, there are 2 topic inside.
1. What is blade flapping? (Thread starter)
2. What is blade fluttering? How to fix it?


SH

[Murdanny]

In this post, there are 2 topic inside.
1. What is blade flapping? (Thread starter)
2. What is blade fluttering? How to fix it?


SH

Thanks Super-Hornet! i read bout blade flapping but i just wanted to know how is it practical our RC helis...

[Murdanny]

Yeah , its very very weird. Like when i hover tail in , on the right side of the heli , the blades will track , but on the left , they dont.

check ur damper? lol !

[Super-Hornet]

As I said in my last few post.

Without blade flapping (or teetering) in or R/C heli, the rotor disc cannot tilt. Rotor disc cannot tilt, it causes symptom or behavior of:
1. Vibration just before heli starts to tilt.
2. Stress to main shaft and hub.
2a. If it is flybarless or multibladed, it is stress to the cyclic servos also.
3. Damping vibration.
4. Reduced pitch up in forward flight.

EDIT: Both R/C heli and real, full size heli actually has a lot in common. Actually the rules and design in full size heli also applies to the R/C heli as well. After all, both are helicopter.

SH

[Murdanny]

yo, none of the above. all checked. but the heli was decommissioned since. the fluttering goes: madly out of track suddenly, rpm drop rapidly till u can see the blades, heli vibrates like a vibrator. i was running on flybar.

the blades needs a new heli la...

[Murdanny]

For Teetering design, the rotor head is teeter at the rotor shaft. The purpose of the O Ring damper is... well, dampen the movement. For the normal "Virtual Teeter axis" type of design, without the O-Ring to hold the spindle shaft in place, it cannot teeter very well. For that kind of design, the O-Ring act as a:
1. To hold the spindle shaft in place.
2. Dampen the teetering movement.
3. Dampen the spindle shaft from moving forward and backward.

For the "Virtual Teeter axis" design, the weak point of this design is that, if the O-Ring damper is too soft, it causes the unwanted blades lead or lag on both blades (Remember it is tie together by a spindle shaft). Those lead/lag on both blades will cause the whole heli to "out of phasing". Too hard damper, and u end up like no teeter at all.

For multibladed head design, there are normally 3 types of design:
Fully articulated rotors.
Semi-rigid rotor.
Rigid on the hub.

For Fully-Articulated rotor design, each blades can individually "Flap" and "Lead/Lag". (For teeter, one blade flap up, the other is force to flap down and vise verses)

For Semi-rigid rotor design, each blades can independently only flap up or down. No lead/lag hinges.

For Rigid on the hub, there is no flapping or lead/lag hinges on the rotor hub...Instead, the blades is design to flap up/down directly on the blades itself.

In our R/C heli, u might say that the blades can lead/lag with the screw that hold the blade to the blade grip. This is not really a lead/lag movement because the blades do not have something to "dampen" or to restrict the blades from going lead/lag and then tries to push/pull it back to the neutral position again.

One of the important reason for the blades to be able to flap is to able to tilt the rotor disc. This is very important because:
1. If rotor disc cannot tilt, all the stress is goes directly to the hub or the main shaft itself. Have u ever seen a main shaft bend due to too much 3D maneuver in mid air? Some of us saw it in Bishan before.
2. When u apply cyclic to either forward/backward or left/right, the rotor disc tries to tilt be due to rigidity in the rotor and couple with the air resistance when the rotor disc is turning, the servo cannot push the swash plate to tilt. This causes the cyclic servos to overload and u see the heli actually vibrate before the whole heli start to move to the direction u apply the cyclic.
3. On the ground, on a heli with wheels undercarriage, when u apply forward cyclic, the rotor disc cannot tilt. When rotor disc cannot tilt, the heli cannot move (taxiing) forward on the runaway.

SH

This is great!

[edmond22]

As I said in my last few post.

Without blade flapping (or teetering) in or R/C heli, the rotor disc cannot tilt. Rotor disc cannot tilt, it causes symptom or behavior of:
1. Vibration just before heli starts to tilt.
2. Stress to main shaft and hub.
2a. If it is flybarless or multibladed, it is stress to the cyclic servos also.
3. Damping vibration.
4. Reduced pitch up in forward flight.

EDIT: Both R/C heli and real, full size heli actually has a lot in common. Actually the rules and design in full size heli also applies to the R/C heli as well. After all, both are helicopter.

SH

Great info SH,

Just a question, in regards to pt 1. If supposed I applied heavy cyclic to the heli and the heli sorts of shudders before each collective/ cyclic application, is this also a sign of hard damping? I get this sometimes if I get to sloppy with my collective and cyclic management.

Yeah , its very very weird. Like when i hover tail in , on the right side of the heli , the blades will track , but on the left , they dont.

Hey Heli Fanatic, I experienced this once and it was due to my bent flybar that is almost not noticeable. The blade will track one side only.

[Super-Hornet]

.. If supposed I applied heavy cyclic to the heli and the heli sorts of shudders before each collective/ cyclic application, is this also a sign of hard damping? I get this sometimes if I get to sloppy with my collective and cyclic management... .

It should be. U can try using slightly weaker damper and see how.

BTW, I have some typo in the previous post. It should be
WITHOUT teeter/flapping hinges in R/C:
1. Vibration just before heli starts to tilt.
2. Stress to main shaft and hub.
2a. If it is flybarless or multibladed, it is stress to the cyclic servos also.
3. Vibration in the rotor is translated to the heli (no damping)
4. Pitch up in forward flight.


SH

[Murdanny]

Okay..i have a question about lead lag hinges.

I understand that lead lag hinges is to help the rotor blades from spinning to fast from blade flappng due to coriolis effect.

but how? from what i read, it captures/absorbes the moment of the blade spinning fast. is it true?

[tucfaz]

Did you check if your optician have not switch your lenses??

Happen to me once before.. Wrong washer (collar) use in the blade grip.. squeezing the damper.. But mine is both side wrong.. Hoover no problem, but slight cyclic input, one side of the blade goes out of track..

Sorry for the joke..

Yeah , its very very weird. Like when i hover tail in , on the right side of the heli , the blades will track , but on the left , they dont.

[Super-Hornet]

Okay..i have a question about lead lag hinges.

I understand that lead lag hinges is to help the rotor blades from spinning to fast from blade flappng due to coriolis effect.

but how? from what i read, it captures/absorbes the moment of the blade spinning fast. is it true?

When blade retreat, it causes to spin faster. Just like those ice-staking doing spinning...when they retreat their hands closer to body, they spin faster. Hands fully out, it slow down. U can try that by spin yourself around the computer/office chair. U collapse your hand closer to body, u spin faster.

SH

[Murdanny]

When blade retreat, it causes to spin faster. Just like those ice-staking doing spinning...when they retreat their hands closer to body, they spin faster. Hands fully out, it slow down. U can try that by spin yourself around the computer/office chair. U collapse your hand closer to body, u spin faster.

SH

understood. but how can lead lag compensate the blades from spining faster?

[Super-Hornet]

EDIT:
Here from Wikipedia and in some websites as well. I think this should explain better on the lead/lag hinges:

http://en.wikipedia.org/wiki/Helicopter

"The vertical hinge, called the lead-lag or drag hinge, allows the blade to move back and forth. This movement is called lead-lag, dragging, or hunting. Dampers are usually used to prevent excess back and forth movement around the drag hinge. The purpose of the drag hinge and dampers is to compensate for the acceleration and deceleration caused by Coriolis Effect"

[Super-Hornet]

If u interested, u can read a document called:
"Introduction to Helicopter Aerodynamics Workbook" from Naval Air Training Command, Texas.

URL:

http://www.ultraligero.net/Cursos/helicoptero/Introduccion_a_la_aerodinamica_del%20_helicoptero.pdf

[Murdanny]

If u interested, u can read a document called:
"Introduction to Helicopter Aerodynamics Workbook" from Naval Air Training Command, Texas.

URL:
http://www.ultraligero.net/Cursos/he...elicoptero.pdf

thanks! i think most of us take for granted all these few things that makes helicopters fly. =)

thank you!