Blade Sailing

[ferranrosello]

Additionally, this is the situation in the 90º azimuth. At lower and higher azimuth all AOAS are smaller.

 

[Jean Claude]

...you have calculated the AOA od an airfoil in the 75% of the blade. All blade elements between 75% and 100% are working at lower AOA’s.

Of course! And also, all blade elements between 0 and 75% are working at higher A.o.A's
As I said, it just for an easily understand of phenomena that the blade is reduced to an element taked at 75%R

How do you know that an AOA of 12.8º in a blade element is stalled? It depends on the airfoil and

Observe the curves of the usual NACA 0012. The stall of 8H12 is even earlier

in a rotating blade the blade elements are able to fly at much bigger AOA’s than a fixed wing with no stall.

You probably confuse the A.o.A with the pitch setting.

 

[ferranrosello]

No. It is not a confusion. I have read this about retreating blade stall in helicopters. The full stall state doesn’t happen when the 90º azimuth position is fully stalled. It happens when de stall spreads about 30 to 40º of azimuth.

 

[ferranrosello]

Thank you for the information you have posted.

 

[Jean Claude]

Depending on whether it is a helicopter or gyrocopter rotor, the area where the stall occurs in forward flight is very different:

 

[Tyger]

It seems possible to me, but not destructive, that it is the too fast maneuvering of the control stick that pushed the stops to meet the blades, faster than the roll or pitch rate of the rotor moves it away from them.

Now that I can definitely visualize...

 

[Doug Riley]

Yes, that really happens in gyro flight. It's especially common with heavy blades such as McCutchen Skywheels and (I imagine) one-piece extruded blades.

Example: in executing hard, rapid S-turns, the pilot will sometimes feel a "slapback" in the stick as the rotor hits the teeter stops during the reversals. This indicates that the rotor hasn't had time to precess (tilt) to the commanded orientation.

This phenomenon probably helps to prevent the pilot from stalling a blade with an overly-aggressive control input.

OTOH, it probably DOESN'T prevent stalling a blade in a violent PPO. The force applied to the spindle by the pitching airframe is so great that the spindle bolt may bend and/or the teeter stops may distort, allowing the retreating blade to stall and strike the tail or prop.

I'm indebted to Chuck Beaty and Greg Gremminger for much of this analysis.

 

[Abid]

I don't know if in a bad flapping take off condition the retreating blade is stalled or not. What I know is that the entire required flapping movement cannot be achieved, and consequently the dissymmetry of lift is not cancelled.

Define "bad flapping takeoff condition"
If you are saying this is where retreating blade cuts the tail or prop blade or flips over in all new production designs then its not just hitting the stops, its retreating blade stall that has happened

 

[Abid]

"Big pressure" is a rather imprecise term...
Can you (or anyone reading this) explain why a hard left bank might cause that?
Would it be less likely in a hard right bank?

The blades are being loaded so they may go out of track and stick may shake more but beyond that I do not understand what he is describing.
Jean Claude may opine better.
Perhaps the guy was not a smooth pilot and ham fisted like many GA airplane pilots are coming into gyroplanes and he moved the stick so fast that the rotor loosely bound to airframe lagged behind. That may create this temporarily but I would take that dude for some lessons in finesse because he/she lacks it.

 

[Jean Claude]

When a rotor undergo a continuous rate of roll, it is because the blades produces the necessary cyclic forces, i.e that the control plane precededs the tip path plane with an angle proportional to the rate (fig 1).

When the pilot wants to obtain a continuous roll rate of the aircraft, he tilts the control plane. The roll rate is then constant when the tip plane is symmetrical (fig2)

If the flapping stops have a smaller margin than the control plane stops (*), then they can hit it, but this is safe because here it is only the hand force that pushes the flapping stops against the blades.

(*) The margins of the flapping stops are different between the right and left sides due to the transverse flapping angle b1

 

[Tyger]

I think it hilarious that Jean Claude, with over thirteen years on the forum and 2,359 always incisive postings, is still given the soubriquet "Junior Member". I am not sure why I am a "Super Member", but some admin person certainly ought to award that to him.

 

[Resasi]

Have been following this discussion with great interest. Some great information.

Wryly amused at the earlier description of the so-called 'simple' aerodynamics of gyro rotors.

Yes, we should all know the main causes of blade flap/sailing.

Yes, we should know the indications of blade sail/flap.

Yes, we all should know how to avoid, and corrective actions if encountered.

But I still feel personally that gyro aerodynamics is not simple, and always fully understood by many gyro pilots

 

[Abid]

Have been following this discussion with great interest. Some great information.

Wryly amused at the earlier description of the so-called 'simple' aerodynamics of gyro rotors.

Yes, we should all know the main causes of blade flap/sailing.

Yes, we should know the indications of blade sail/flap.

Yes, we all should know how to avoid, and corrective actions if encountered.

But I still feel personally that gyro aerodynamics is not simple, and always fully understood by many gyro pilots

I still have not seen anything that shows me they are extremely complex in their effect. Blade sailing is always due to retreating blade stall. You cannot go hitting your tail and chop your prop without stalling the retreating blade after first 75 to 100 rotor RPM. Simple.

 

[Abid]

When a rotor undergo a continuous rate of roll, it is because the blades produces the necessary cyclic forces, i.e that the control plane precededs the tip path plane with an angle proportional to the rate (fig 1).

When the pilot wants to obtain a continuous roll rate of the aircraft, he tilts the control plane. The roll rate is then constant when the tip plane is symmetrical (fig2)

If the flapping stops have a smaller margin than the control plane stops (*), then they can hit it, but this is safe because here it is only the hand force that pushes the flapping stops against the blades.

(*) The margins of the flapping stops are different between the right and left sides due to the transverse flap angle b1


View attachment 1155117

Yup sloppy technique but nothing bad will happen. Just shows your piloting technique is not smooth

 

[Resasi]

I still have not seen anything that shows me they are extremely complex in their effect.

You're "...in their effect." Rather alters what I have said.

 

[Kevin_Richey]

I think it hilarious that Jean Claude, with over thirteen years on the forum and 2,359 always incisive postings, is still given the soubriquet "Junior Member". I am not sure why I am a "Super Member", but some admin person certainly ought to award that to him.

A prior-iteration rotary wing forum software initially labeled all new members as JM. Then, after reaching various numbers of postings made by that forum member, the forum "upgraded" their forum subtitle labels. That feature disappeared a long time ago, but the ability to change it to what we wish it to read was also left in the dust.

The same situation was w/ anyone who donated $ to the operating costs, such as "Gold Supporter".

 

[Aerofoam]

I'm on another forum that uses the same software, but has some differences, the label can be changed to anything by the member once they are no longer a newbie. It also doesn't automatically set "Watch" to any thing you reply to.
But it's basically the same, I suppose those features are chosen by the admins.

 

[Abid]

Here is caught on video how people do the blade sailing/flapping accidents today
Look at his rotor disc angle as he moves forward. The stick is definitely not all the way back. His pre-rotation is probably 180 to 200 RRPM but then he does not pull the stick back.
Now the rotor RPM does not increase and starts to decrease and then he suddenly pulls the stick back and its game over.
Unless you are doing pre-rotation to 300 RRPM in an AG model with rotorhead 3, you have to pull the stick back before moving forward so fast and if you realize you have not pulled the stick back but kept it centered somewhere, then don't pull it back. Its over. Abort by cutting power to idle and braking and smoothly putting stick forward and start all over again.
It is better than breaking your nose wheel, flipping over and skidding down the runway. In AR-1 not one has flipped over because of landing gear stance and give but the nose wheel gets a load of side load and can break off

 

[Greg Vos]

Here is caught on video how people do the blade sailing/flapping accidents today
Look at his rotor disc angle as he moves forward. The stick is definitely not all the way back. His pre-rotation is probably 180 to 200 RRPM but then he does not pull the stick back.
Now the rotor RPM does not increase and starts to decrease and then he suddenly pulls the stick back and its game over.
Unless you are doing pre-rotation to 300 RRPM in an AG model with rotorhead 3, you have to pull the stick back before moving forward so fast and if you realize you have not pulled the stick back but kept it centered somewhere, then don't pull it back. Its over. Abort by cutting power to idle and braking and smoothly putting stick forward and start all over again.
It is better than breaking your nose wheel, flipping over and skidding down the runway. In AR-1 not one has flipped over because of landing gear stance and give but the nose wheel gets a load of side load and can break off

This guy has less than 100 hours in a gyro…he does have apparently over 11000 ( eleven thousand hours in FW) this tells me he must be a professional pilot . ..?

 

[Abid]

This guy has less than 100 hours in a gyro…he does have apparently over 11000 ( eleven thousand hours in FW) this tells me he must be a professional pilot . ..?

Where did you see those time figures. Yes, he likely could be a professional pilot but means little in a gyroplane. It probably hurts him. Not help in this instance.