# Thread: True or False Helicopters in Forward flight

1. ## True or False Helicopters in Forward flight

Hello,
As I understand some about physics and aerodynamics, an instructor whom has experiance maintaining helicopters told me something that seems to conterdict my understandings.
Anyone who has flown a single rotor helicopter should know this to be either true or false...
So here it is....

True or False?
When flying faster and faster in forward flight of a single rotor helicopter, the cyclic needs to be moved to the right (or to the left for forigen helos with an oppsite rotating main rotor)

Thanks,
-Jonathan

2. Member
Join Date
Jul 2009
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735
How does the airspeed relative to the blade change when the helicopter's airspeed speed changes?
Will the blade going forward have the same airspeed as the blade going back?
What do you need to change to keep a blade's lift the same when airspeed changes?
How do you do this?

3. Originally Posted by jeroen79
How does the airspeed relative to the blade change when the helicopter's airspeed speed changes?
Will the blade going forward have the same airspeed as the blade going back?
What do you need to change to keep a blade's lift the same when airspeed changes?
How do you do this?
There's a name for this, something like retreating blade stall, or similar?

4. Member
Join Date
Jul 2009
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735
Dissymmetry of lift, to be precise.
However, retreating blade stall has the same causes but starts at higher speeds.

5. Member
Join Date
Mar 2009
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396
In laymen terms, the blade on one side is moving forward, the blade on the other side is moving backward as they rotate around the hub.

At hover, both sides are moving the same "speed" and generate the same lift.

As the chopper moves forward, the forward moving blade is (in effect) moving faster and the backward moving blade is moving slower relative to the surrounding environment.

Theoretically, if you could accelerate to a high enough speed, eventually the "backward" moving blade would be stationary and the forward moving blade would be moving at double normal speed. Think of a car tire rolling down the road. The "top" of the tire is moving double the speed of the car while the "bottom" is stationary relative to the ground. Turn that on it's side and you have the example I just described above.

The blade moving slower creates less lift so moving the cyclic to one side sets a different angle of attack for the blade on the slow side than the angle of attack on the fast side to help even out the amount of lift from each side.

Does that explanation help?

-dc4bs
Last edited by dc4bs; 07-02-2009 at 05:21 PM.

6. My points exactly... Dissymetry of lift....

For the helo to fly it needs uniform lift arround the rotor...
so to compensate so that both sides have the same lift
and give the Retreating blade MORE AOA.

Because the rotor acts like a gyro the swash plate
has a 90 degree advance built into the flight controls.

So moving the cyclic forward will give the advancing blade less AOA
and the retreating blade MORE AOA.

However my question was Is there any SIDE movment nesscary?
An old helo mechanc and A&P instructor of mine said that
side movment is nesscary to compensate for dys symetry of lift.
However what I just explaned from my own understanding of
the physics involved conterdict that.
A side movment of the Cyclic, to the right will cause the rotor blades
over the nose and tail to change AOA.

So the question: To Anyone who has flown a single rotor helicopter, is
there a sideways cyclelic movment required in forward? If so woudlnt it
limit turning ability?

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