Blade Sailing

[Brent Drake]

The reason is that rotorcraft blades are always "flapping", in the original sense of the word, and using the same word for two different (although related) things gets confusing.
In order to differentiate "normal" flapping from the problem being discussed in this thread, people have been using "sail" to describe the advancing blade flying upward when the retreating blade stalls. I imagine people use it because it's a lot shorter than saying "retreating-blade stall".

So it should be called retreating blade stall as it always has.
Let's keep it simple.

 

[AgentCheese]

The reason is that rotorcraft blades are always "flapping", in the original sense of the word, and using the same word for two different (although related) things gets confusing.
In order to differentiate "normal" flapping from the problem being discussed in this thread, people have been using "sail" to describe the advancing blade flying upward when the retreating blade stalls. I imagine people use it because it's a lot shorter than saying "retreating-blade stall".

Kind of agree with Brent. Blades teeter, not flap. Teetering good...Flapping bad.

 

[Abid]

Kind of agree with Brent. Blades teeter, not flap. Teetering good...Flapping bad.

Hate to get into semantics but teetering is flapping hinge. Just a specific kind

 

[WaspAir]

Kind of agree with Brent. Blades teeter, not flap. Teetering good...Flapping bad.

The blades on my A&S18A have flapping hinges and do not teeter (the same for any articulated system such as the J2 and all the old Pitcairn, Cierva, and Kellets). Teetering impossible...flapping essential.

Helicopter people (who vastly outnumber gyro people in the rotorcraft world) have a precise meaning for "flap" and it has nothing to do with blade sailing. They also use "retreating blade stall" in the context of extreme high speed forward flight at 100% rotor rpm. The problem confronting gyro pilots accelerating for takeoff is practically very different and is deserving of its own term for clarity. Blade sailing fits that bill for me.

 

[Brent Drake]

Teach how to get a hand-spun rotor up to speed?
Teach stick shake on takeoff?
The vital signs of rotor speed need to be taught by all instructors.
Exactly what to look for and to show what can happen and does happen because of lack of knowledge.
Most of the old days and rotor management are not taught these days.

 

[AgentCheese]

Hate to get into semantics but teetering is flapping hinge. Just a specific kind

Yes, but neither 'sail'!

 

[Vance]

For me sailing a blade is when the retreating blade stalls and the advancing blade continues to produce lift and sails because of too much indicated air speed for the rotor rpm and disk angle.

This appears to me to be unique to gyroplanes.

Most gyroplanes will not go fast enough to have retreating blade stall like a helicopter and the blade stalls from the inside out rather than the outside in as in a helicopter.

Some part of a gyroplane rotor is always stalled.

A gyroplane wont fly forward without some sort of flapping hinge because of disemetry of lift.

Some people when they refer to blade flap in a gyroplane are referring to the teeter limits being exceeded.

i don't think it matters what it is called; two much indicated airspeed for the rotor rpm and disk angle is a bad thing in a gyroplane.

 

[Aerofoam]

Been lurking on this thread...
This is all semantics, but important ones at that.
It seems flapping is a term that originated from the early hinge design as a generic term describing the up and down movement
through the flight path.
Not a great descriptor in my opinion, but maybe good for the hinge type...
Actual flapping should be described as bad, because it would be followed by loud banging noises that should be avoided...

In actuality, a gyro blade IS sailing.
This is one of the concepts that seems to have alluded some of the gyro-community.
I have even read authoritative definitions of gyro blade behavior that are not correct because of the lack of understanding
of "Apparent Wind" which is a term used in the racing sailing circles all the time.
You can easily look at the retreating blade of an auto gyro as an iceboat sail going down wind, but being tightly sheeted because the
apparent wind has rotated so far forward that it appears from the perspective of the sail/blade as if the craft is sailing upwind. (they can reach speeds over 120mph.)
They are generating forward speed based on the exact principle happening in an auto gyro blade.
Lift is a product of that forward driven speed.
The sailing theory "Bible" is "Marchaj, Sailing Theory and Practice" and clearly describes this.
I think the term "Blade Sailing" should apply to the normal proper flight path/rotation of the bladed in the airflow because that is what they are doing....
When the blade stops sailing, the real problems start....

 

[rcflier]

Teach how to get a hand-spun rotor up to speed?
Teach stick shake on takeoff?
The vital signs of rotor speed need to be taught by all instructors.
Exactly what to look for and to show what can happen and does happen because of lack of knowledge.
Most of the old days and rotor management are not taught these days.

Hand starting an eurotub can't be easy...
And I'm not experimenting with my expensive aircraft.
A few gyrogliders would go a long way.
But we are so few and far apart, that it's unrealistic -
unless it becomes a a requirement to borrow a gyroglider.
Maybe tethered (kiting) in strong wind at first.

Cheers
Erik

 

[Abid]

Honestly I could give two hoots about semantics. Simply put you have retreating blade stall during takeoff. Because it is in a certain circumstance, we will call it blade sailing because flapping of blades is happening at every moment in its flight regimen. If you don't like to call it blade sailing but insist on calling it flapping, fine. It is just more confusing a term because it does not separate it from normal flapping of blades due to teetering hinge which btw teetering is also flapping on a central hinge as opposed to an offset flapping hinge.

As Mike and I clearly discovered with live measurements, people are not having blade sailing accidents because they are at too low RPM with stick back and then simply accelerate so fast that they have a retreating blade stall. That is not what is happening. No matter what the pilot tells you I am quite convinced that is not the normal Blade Sailing accident. The accident is because the pilot went back to neutral stick takeoff of his Cessna airplane. Sped up with neutral stick and "Rotated" like in his Cessna. Meaning he/she pulled the stick back at 40 knots. That would only take a couple of seconds and less than a couple of inches of pull to cause a sudden and clear disaster. THAT is what has been happening.

So the main problem in all these accidents is not pulling the stick all the way back before ground roll. Period!!!
Basically going back to taking off your Cessna. Also, not having a clue once you remembered that the stick wasn't pulled back on what to do now. What they have been doing is pulling the stick back and that is completely OPPOSITE of what you should do. You have already screwed the pooch. Just eat crow, cut power, put stick forward and apply wheel brakes and bow your head in shame and taxi back all the way to re-start. And practice this abort during training or on flight review with your instructor with you. Because I think your instructor never before actually practiced aborting takeoff roll mid stream with you most likely

 

[Aerofoam]

Honestly I could give two hoots about semantics. Simply put you have retreating blade stall during takeoff. Because it is in a certain circumstance, we will call it blade sailing because flapping of blades is happening at every moment in its flight regimen. If you don't like to call it blade sailing but insist on calling it flapping, fine. It is just more confusing a term because it does not separate it from normal flapping of blades due to teetering hinge which btw teetering is also flapping on a central hinge as opposed to an offset flapping hinge.

As Mike and I clearly discovered with live measurements, people are not having blade sailing accidents because they are at too low RPM with stick back and then simply accelerate so fast that they have a retreating blade stall. That is not what is happening. No matter what the pilot tells you I am quite convinced that is not the normal Blade Sailing accident. The accident is because the pilot went back to neutral stick takeoff of his Cessna airplane. Sped up with neutral stick and "Rotated" like in his Cessna. Meaning he/she pulled the stick back at 40 knots. That would only take a couple of seconds and less than a couple of inches of pull to cause a sudden and clear disaster. THAT is what has been happening.

So the main problem in all these accidents is not pulling the stick all the way back before ground roll. Period!!!
Basically going back to taking off your Cessna. Also, not having a clue once you remembered that the stick wasn't pulled back on what to do now. What they have been doing is pulling the stick back and that is completely OPPOSITE of what you should do. You have already screwed the pooch. Just eat crow, cut power, put stick forward and apply wheel brakes and bow your head in shame and taxi back all the way to re-start. And practice this abort during training or on flight review with your instructor with you. Because I think your instructor never before actually practiced aborting takeoff roll mid stream with you most likely

OUCH!!!

 

[Abid]

OUCH!!!

Too blunt?

 

[Aerofoam]

Just a vivid mental picture, I didn't realize leveling the disk after initial roll out was "A Thing"
Frightening....
Has anyone ever put a sailplane like vario on the rotors, so you have an accelerating upward pitching audio tone indicating increasing RPM and a decelerating lowering tone indicating lowering RPM?
It seems like that would be a good indicator because you would not want to hear a lowering tone on take off...

 

[WaspAir]

Blade sounds already vary in pitch with rpm that way.

 

[Aerofoam]

Blade sounds already vary in pitch with rpm that way.

But you can't adjust the blaring volume!

 

[Abid]

Just a vivid mental picture, I didn't realize leveling the disk after initial roll out was "A Thing"
Frightening....
Has anyone ever put a sailplane like vario on the rotors, so you have an accelerating upward pitching audio tone indicating increasing RPM and a decelerating lowering tone indicating lowering RPM?
It seems like that would be a good indicator because you would not want to hear a lowering tone on take off...

Not only is it A Thing. It’s the Only Thing. Any other thing is likely to cause rotor blade sailing/flap if you have forgotten to have stick back and sped up to a good speed. Any attempt to pull stick back now is an invitation for the rotor blade sailing event. The faster and more you pull back the deeper the blade sailing event. You will be lifted up on one main wheel and most likely the front wheel will be up as well and you will flip over or if lucky you will smack back down 90 degrees off your intended heading with your tail chopped, mast bent and undercarriage and front wheel damaged and that’s if you are lucky and don’t flip over.

On you beeping sound. No but there is a rotor RPM gauge that I glance at on every takeoff run. Works very well

 

[Resasi]

Blade sail/flap/retreating blade stall, as the phenomenon is generally known, is an event that is being explored more throughly now by Mike G Abid Chris and others. It's causes...and results, are generally unfortunately known, but the finer points are now being more scientifically explored, and instruments being developed that can warn of the impending event.

Rotor aerodynamics are a little more complex than that fixed wing aircraft, and can be critical during the take off phase in gyros where it can cause very rapid loss of control when not fully understood and correct techniques not applied.

Avoiding a stall during take off on a fixed wing aircraft is a relatively simple exercise, avoiding blade sail/flap during a gyro take off not quite so straightforward, and getting it wrong a little easier if the causes not fully understood.

These recent advances a welcome step up in gyro flight safety.

 

[Brent Drake]

Hand starting an eurotub can't be easy...
And I'm not experimenting with my expensive aircraft.
A few gyrogliders would go a long way.
But we are so few and far apart, that it's unrealistic -
unless it becomes a a requirement to borrow a gyroglider.
Maybe tethered (kiting) in strong wind at first.

Cheers
Erik

You shouldn't have to experiment. Your instructor should have shown you how to accomplish this and stick shake when taking off.

 

[rtrhd]

Great discussion. Thank you Abid, Vance, and others for your efforts in educating the gyroplane pilot community. Part of the issue is the woefully and I do mean woefully inadequate study material available for gyroplane specific aerodynamics at the pilot level. The "FAA Gyroplane Flying Handbook" is 22 years old and although there is some good information to be had there it is, again, woefully inadequate to address some of the gyroplane hazards.

On the helicopter side we are constantly aware of the same phenomenon during start up and shutdown. The company I fly for has wind limits and gust limits for operation even though the Rotorcraft Flight Manual does not specifically limit. If a blade sails on a Bell 206 Long Ranger model during start-up or shut-down the winglets on the horizontal stabilator can be whacked off or damaged. When starting up and shutting down it is imperative to place the cyclic into the wind to lower the angle of attack on the advancing blade.

It's the same issue everybody has been discussing. Too little rotor rpm for, in this case, wind and/or gusts.

I have several hundred hours teaching the Auto Gyro models (MTOs, Cavalon 914/915, and Calidus). As a professional pilot for my vocation, I teach the POH and all available published sources from people alot smarter than I. The AutoGyro POHs have several WARNINGS, CAUTIONS, and NOTES that I would harp and preach on. There is no substitute for knowing your machine. It's your money and your life. I would tell my students that I fly several different aircraft and I only do this part time and I know the limits so you need to too as it is the only aircraft you are flying!

We need more gyroplane courses/seminars on FAA WINGS and we need a good updated publication specifically addressing these safety issues that are brought up here on the forum.

One of the things I really try to do is prior to takeoff silently go thru abort steps (Throttle IDLE Stick Forward). Especially if you fly other category and class aircraft as I do just doing a quick little silent rehearsal can do alot of good. Keeps the muscle memory sharp during times of startled or surprise.

Lastly, we wouldn't let students do touch and go's or stop and go's. Every landing was a full stop. Zero flapping accidents or incidents. Food for thought. It's a pain and you lose time but it does help to eliminate flapping accidents/incidents in my opinion.

 

[Abid]

Great discussion. Thank you Abid, Vance, and others for your efforts in educating the gyroplane pilot community. Part of the issue is the woefully and I do mean woefully inadequate study material available for gyroplane specific aerodynamics at the pilot level. The "FAA Gyroplane Flying Handbook" is 22 years old and although there is some good information to be had there it is, again, woefully inadequate to address some of the gyroplane hazards.

On the helicopter side we are constantly aware of the same phenomenon during start up and shutdown. The company I fly for has wind limits and gust limits for operation even though the Rotorcraft Flight Manual does not specifically limit. If a blade sails on a Bell 206 Long Ranger model during start-up or shut-down the winglets on the horizontal stabilator can be whacked off or damaged. When starting up and shutting down it is imperative to place the cyclic into the wind to lower the angle of attack on the advancing blade.

It's the same issue everybody has been discussing. Too little rotor rpm for, in this case, wind and/or gusts.

I have several hundred hours teaching the Auto Gyro models (MTOs, Cavalon 914/915, and Calidus). As a professional pilot for my vocation, I teach the POH and all available published sources from people alot smarter than I. The AutoGyro POHs have several WARNINGS, CAUTIONS, and NOTES that I would harp and preach on. There is no substitute for knowing your machine. It's your money and your life. I would tell my students that I fly several different aircraft and I only do this part time and I know the limits so you need to too as it is the only aircraft you are flying!

We need more gyroplane courses/seminars on FAA WINGS and we need a good updated publication specifically addressing these safety issues that are brought up here on the forum.

One of the things I really try to do is prior to takeoff silently go thru abort steps (Throttle IDLE Stick Forward). Especially if you fly other category and class aircraft as I do just doing a quick little silent rehearsal can do alot of good. Keeps the muscle memory sharp during times of startled or surprise.

Lastly, we wouldn't let students do touch and go's or stop and go's. Every landing was a full stop. Zero flapping accidents or incidents. Food for thought. It's a pain and you lose time but it does help to eliminate flapping accidents/incidents in my opinion.

Great points. Where in South Carolina are you at and if you don't mind me asking since you are a gyroplane CFI (I think) what's your real name. There are people calling me and asking me for references for CFIs in different states.

My rule of thumb for minimums is 120 takeoffs and landing including touch N Go's and stop and go's. 30 full initial takeoffs with pre-rotations. 8 abort takeoff procedures done correctly when instructor starts simulating a shaking stick on ground roll