Blade Sailing

It has been mentioned that a longer rotor allows a slightly higher speed before blade sailing. At the same time, it takes more energy to get the longer rotor up to that speed. Given the same amount of energy, the longer rotor won't get to the same RRPM as the shorter rotor. This doesn't seem to be an issue, however, as the engines being used seem more than powerful enough to reach an appropriate RRPM.

What is generally the limiting factor for reaching a higher RRPM when prerotating? I've heard some mention that the thrust overpowers the brakes. Couldn't this be fixed by changing the gear ratio of the prerotor? I'm mostly curious, as I've seen some say they can get to 300 RRPM while others are pushing pretty hard if they get to 150.
 
In step 3 it does say “At 130 r.p.m. ROTOR” which could cause confusion.
It should not cause confusion if you read what you are actually supposed to do at 130 (on my gyro it's more like 100) which is only to bring the stick to the rear, and fully engage the prerotator.
The idea is to keep the stick forward till the centrifugal "force" is sufficient to ensure the blades are not able to flex appreciably.
You want to have the stick to the rear to catch any ambient wind, and before you begin the takeoff roll, but until you get over 100 or so the blades are still a bit floppy, so bringing the stick all the way back before then can be risky.
Once the prerotator is fully engaged (i.e. the belts are not slipping at all) you can then increase throttle to get more rotor rpm.

At 130 r.p.m. ROTOR,
Place the control stick in takeoff position (rear limit stop).
Gently reach the limit stop (of the prerotation lever) while keeping a constant engine speed.
 
It has been mentioned that a longer rotor allows a slightly higher speed before blade sailing. At the same time, it takes more energy to get the longer rotor up to that speed. Given the same amount of energy, the longer rotor won't get to the same RRPM as the shorter rotor. This doesn't seem to be an issue, however, as the engines being used seem more than powerful enough to reach an appropriate RRPM.

What is generally the limiting factor for reaching a higher RRPM when prerotating? I've heard some mention that the thrust overpowers the brakes. Couldn't this be fixed by changing the gear ratio of the prerotor? I'm mostly curious, as I've seen some say they can get to 300 RRPM while others are pushing pretty hard if they get to 150.

Its just the complexity of pre-rotator system and ratios of gears etc. being used. AutoGyro gets to 300 rotor RPM but at around 5400 RPM full power on a MTO Sport 2017 and it didn't much to clear 50 foot that I saw at 240 RRPM with 2 people on tarmac. And at 5400 engine RPM that was a lot of stuff to put up with on brakes and so on.
 
Hi all,

My first post, I am a 7 hour student pilot. Reading this forum over the last year has helped me understand many gyro concepts much better.

If I were to ever buy a gyro, @Abid, your contributions as a manufacturer would encourage me to purchase an AR-1 over a Magni.

I know its an oversimplification, but could blade sailing be compared to balancing a spinning plate on the tip of a stick? Once the plate RPM drops instability increases dramatically.
 
Hi all,

My first post, I am a 7 hour student pilot. Reading this forum over the last year has helped me understand many gyro concepts much better.

If I were to ever buy a gyro, @Abid, your contributions as a manufacturer would encourage me to purchase an AR-1 over a Magni.

I know its an oversimplification, but could blade sailing be compared to balancing a spinning plate on the tip of a stick? Once the plate RPM drops instability increases dramatically.
Welcome to the forum.
What sort of aircraft is your seven hours in?

Blade sailing is only indirectly related to the spinning, it's a function of the retreating blade stalling (or at least creating too little lift) because it is moving backward relative to the direction of aircraft motion.

I suggest you try, or at least see, a few different gyroplanes before you actually think of which one to buy. 😊
 
Hi all,

My first post, I am a 7 hour student pilot. Reading this forum over the last year has helped me understand many gyro concepts much better.

If I were to ever buy a gyro, @Abid, your contributions as a manufacturer would encourage me to purchase an AR-1 over a Magni.

I know its an oversimplification, but could blade sailing be compared to balancing a spinning plate on the tip of a stick? Once the plate RPM drops instability increases dramatically.
Welcome to the Rotary Wing Forum ex_karo!

In my opinion a spinning plate works like a gyroscope and becomes less stable as it slows down.

A Rotor is an aerodynamic device and if we ask the airfoil (rotor blade) to produce lift at too high an angle of attack it stalls.

A typical airfoil will stall around 13 degrees to the relative wind.

A typical gyroplane rotor is tilted 17 to 20 degrees in the full back position.

The spinning is what changes the relative wind and allows the rotor blade to avoid a stall.

The retreating blade has the higher angle of attack because of the teeter so it is the first to stall.

Because the advancing blade has a lower angle of attack it continues to produce lift and runs the stalled blade into something.

If you don’t tilt the rotor back far enough it won’t accelerate as fast and allows the gyroplane to accelerate faster.

In my opinion too much airspeed (wind or forward motion) without enough rotor rpm is the fundamental cause of blade sailing.

If you rotor is not turning fast enough you don’t have aerodynamic control of the blades.
 
Welcome to the forum.
What sort of aircraft is your seven hours in?

Blade sailing is only indirectly related to the spinning, it's a function of the retreating blade stalling (or at least creating too little lift) because it is moving backward relative to the direction of aircraft motion.

I suggest you try, or at least see, a few different gyroplanes before you actually think of which one to buy. 😊
An M-16. We dont have a big gyro community, mostly Magni's. I guess as a student you look at the aircraft being used by your instructor an assume they fly the best 😄 but in my limited experience the M16 seemed great!

If I use the example of the zooming pilot accident that caused Abid to create this thread, my simple understanding would be that he pitched the nose up attempting what I would say is a maneuver for experienced pilots, this caused airspeed to decrease (I would imagine quickly). The pilot did not recognise that this maneuver would rapidly decrease RRPM due to lack of air passing through/over the rotor leading to loss of lift.

Im hoping my ability to understand and articulate these concepts improves over time!
 
Welcome to the Rotary Wing Forum ex_karo!

In my opinion a spinning plate works like a gyroscope and becomes less stable as it slows down.

A Rotor is an aerodynamic device and if we ask the airfoil (rotor blade) to produce lift at too high an angle of attack it stalls.

A typical airfoil will stall around 13 degrees to the relative wind.

A typical gyroplane rotor is tilted 17 to 20 degrees in the full back position.

The spinning is what changes the relative wind and allows the rotor blade to avoid a stall.

The retreating blade has the higher angle of attack because of the teeter so it is the first to stall.

Because the advancing blade has a lower angle of attack it continues to produce lift and runs the stalled blade into something.

If you don’t tilt the rotor back far enough it won’t accelerate as fast and allows the gyroplane to accelerate faster.

In my opinion too much airspeed (wind or forward motion) without enough rotor rpm is the fundamental cause of blade sailing.

If you rotor is not turning fast enough you don’t have aerodynamic control of the blades.
Thanks Vance, I think my response to Tyger was a poor attempt at explaining my understanding and maybe I am confusing theoretical concepts.

At the very least I guess the lesson is that without adequate RRPM you have very little to work with.
 
Hi Phil
I must be missing something in translation. Do you mean people talk about rotor management before but it just becomes an argument?
Or do you mean something else?
The fact that a big part of insurance increase in the US for gyroplanes is a result of insurance underwriters giving money out for Cavalon flip overs (mainly) that were avoidable right from takeoff or landing, its important to know what causes that.


To me its obvious that both Magni M24 as well as Cavalon are very short coupled and yes that is part of the issue but that does not seem to happen with such frequency in other countries so I have say its that US instructors do not train their students correctly or long enough or both. There really isn't another option in my view. One thing different might be that the US customer is probably older and probably has airplane experience prior than customers from other countries. I have nothing solid to support that though. Its just an educated hunch.
Hey Abid - no something else. I broadly agree with your initial post and I think the discussion of the same is fundamental to the future of gyroplane training. I hear the views expressed about POH and rotor management but in the past when the views expressed in post 1 have been aired the term rotor management and POH have been the counter claim. You'll get the POH used as a broad brush to explain that nothing else can exist and you'll get the term rotor management extend to wheel balancing and feel and that nothing else can exist.

This is a problem. It is a problem because it is my opinion that there is no accident report that has any accident pilot reporting his RRPM prior to the blade sail. i.e. The accident pilot says he pre-rotated to X and began his take off roll. Typically he his next recollection is about throttle inputs and then he remembers landing on his head. He may afterwards upon reflection think about what may have happened but what I have never read is the accident pilot giving you a clear view that he was monitoring his RRPM during the take off roll.

What that means is that you could claim that every single accident during this phase of the "flight" comes on the back of following the POH and rotor management such as it is.

My own view is that actually during the take off roll the pilot isn't actually practicing rotor management, he is practicing taking off. As far as rotor management is concerned during take off [of course comments relate to modern 2 seater] he is just pre-rotating and once he releases the brakes his broad assumption is that the ground roll will accelerate the rotor, and as much as others may protest that the accident reports I'm reflecting upon suggest I am correct.

Of course you are correct that there is a mathematical reason all of this happens - as you say it isn't magic - therefore you don't even need to know the absolute threshold, just give enough margin that is realistic to maintain and this problem disappears. I've talked about this a lot over several years and been pooh poohed to the point in the UK its viewed as dangerous thinking!

To your point on US Cavalon accidents - again talked about this for years, the accidents still happen... I agree with your view and I'd further say that the Cavalon design has many elements that add to the issue. The cranked keel, mechanics of the stick and the ergonomics mean the over pitching that often results in trying to obtain a wheel balance is uncomfortable. That leads to this nodding that is typical and directional instability. On the basis these accidents keep happening and the number of YouTube films you can find with all of these thing evident then no doubt the pilots need some help.

In the US you are not helped because you have no regulatory need to keep the training going and Cavalon is relatively new - look at Chris Lord, he was a representative of the importer and had single digit time on the aircraft. Of course that situation is going to be improving but its from a low base and you don't know what you don't know.
 
I think this thread arose from a discussion between Abid and myself. As some of you may remember Abid is in the process of installing the first pre-production GWS in an AR1, hopefully for Bensen Days. He obviously wanted to understand more about how the GWS predicted flapping/sailing and I referred him to the post that he quoted because I felt that the graphs answered his question.

I was a bit surprised that my original post received virtually no interest because I thought the graphs gave a simple picture of the phenomenon. Discussing it with Jean Claude we came to the conclusion that probably no one understood what they were seeing and that I had fallen into the trap of thinking that if I understood it everyone would. Either that or everyone understood and there was no need for a comment.

If you do want to learn more about these graphs and how the GWS works I shall be giving a talk/discussion at Bensen Days and hopefully Abid will be able to give those interested a demo in his AR1.
Mike G
 
Welcome to the Rotary Wing Forum ex_karo!

In my opinion a spinning plate works like a gyroscope and becomes less stable as it slows down.

A Rotor is an aerodynamic device and if we ask the airfoil (rotor blade) to produce lift at too high an angle of attack it stalls.

A typical airfoil will stall around 13 degrees to the relative wind.

A typical gyroplane rotor is tilted 17 to 20 degrees in the full back position.

The spinning is what changes the relative wind and allows the rotor blade to avoid a stall.

The retreating blade has the higher angle of attack because of the teeter so it is the first to stall.

Because the advancing blade has a lower angle of attack it continues to produce lift and runs the stalled blade into something.

If you don’t tilt the rotor back far enough it won’t accelerate as fast and allows the gyroplane to accelerate faster.

In my opinion too much airspeed (wind or forward motion) without enough rotor rpm is the fundamental cause of blade sailing.

If you rotor is not turning fast enough you don’t have aerodynamic control of the blades.
Best explanation I've ever read!
 
Hi all,

My first post, I am a 7 hour student pilot. Reading this forum over the last year has helped me understand many gyro concepts much better.

If I were to ever buy a gyro, @Abid, your contributions as a manufacturer would encourage me to purchase an AR-1 over a Magni.

I know its an oversimplification, but could blade sailing be compared to balancing a spinning plate on the tip of a stick? Once the plate RPM drops instability increases dramatically.

Hi
Welcome to Gyroplanes. And thanks for the kind words.
Yes you are essentially correct but perhaps for many reasons you may not think of. There is a great paper on slowed rotor autorotating that I read recently that goes in depth on the subject.

Basically we use the word Blade Flap or even Blade Sailing but actually what you have is aerodynamic stall of the retreating blade. This happens because of difference in lift in forward going blade versus retreating blade. Nature in its attempt to produce equality between the two and given the freedom of a flapping hinge increases the angle of attack of the retreating blade by flapping it down and decreases the angle of attack of the forward going blade by flapping it up.
Now obviously when an airfoil reaches its critical angle of attack it will stall and that is what happens to Blade Sail on retreating blade.
Since this is due to an attempt to equalize lift, it follows that it would not happen if difference in lift did not exist. That means there was no relative wind the turning rotors saw. That is why coming to a stop would help. So it’s not an opinion but a fact that slow rotor RPM and too fast a forward speed is what causes Blade Sailing or flap. We sometimes call this outrunning your rotors. In gusty enough conditions at low rotor RPM you can do this in theory even standing still. You have to simply imagine what airspeed your rotors are seeing.

In terms of centrifugal force. Well if you are past 50 rotor RPM according to Mike and Jean Claude you are usually already there and the rest of the RPM isn’t doing too much more. I haven’t done that calculation personally but I think they are likely correct. The rest is aerodynamic.
 
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To your point on US Cavalon accidents - again talked about this for years, the accidents still happen... I agree with your view and I'd further say that the Cavalon design has many elements that add to the issue. The cranked keel, mechanics of the stick and the ergonomics mean the over pitching that often results in trying to obtain a wheel balance is uncomfortable. That leads to this nodding that is typical and directional instability. On the basis these accidents keep happening and the number of YouTube films you can find with all of these thing evident then no doubt the pilots need some help.

In the US you are not helped because you have no regulatory need to keep the training going and Cavalon is relatively new - look at Chris Lord, he was a representative of the importer and had single digit time on the aircraft. Of course that situation is going to be improving but its from a low base and you don't know what you don't know.
Out of eleven Cavalon accidents investigated by the NTSB since the beginning of 2017 only two of them involved blade flap.

Most were low time pilot tricks.

Non appear to involve the Cavalon nod.

It appears to me that some people’s fantasies about Cavalon accidents and faults are not supported by the available data.

I feel as flight instructors in order to improve the accident rate we must first understand the accidents before we can make meaningful changes.


DATEN NUMBERFATAL?LOCATIONPHASEFLAP?
10/18/2021​
419LBYOKTAKE OFFNO
8/4/2020​
635BCNCASL FLIGHTNO
5/28/2020​
477AGYORIN FLIGHTNO
8/14/2019​
477AGNWATAKE OFFYES
6/18/2019​
882MNUTTAKE OFFYES
10/30/2018​
198LTYFLIN FLIGHTNO
3/26/2018​
442AGNNHTAKE OFFNO
11/18/2017​
953LSNAZLANDINGNO
11/17/2017​
470CHNNCMANUVERINGNO
5/27/2017​
721ENTXMANUVERINGNO
3/10/2017​
425AGNCALANDINGNO
 
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Out of eleven Cavalon accidents investigated by the NTSB since the beginning of 2017 only two of them involved blade flap.

Most were low time pilot tricks.

It appears to me that some people’s fantasies about Cavalon accidents and faults are not supported by the available data.

DATEN NUMBERFATAL?LOCATIONPHASEFLAP?
10/18/2021​
419LBYOKTAKE OFFNO
8/4/2020​
635BCNCASL FLIGHTNO
5/28/2020​
477AGYORIN FLIGHTNO
8/14/2019​
477AGNWATAKE OFFYES
6/18/2019​
882MNUTTAKE OFFYES
10/30/2018​
198LTYFLIN FLIGHTNO
3/26/2018​
442AGNNHTAKE OFFNO
11/18/2017​
953LSNAZLANDINGNO
11/17/2017​
470CHNNCMANUVERINGNO
5/27/2017​
721ENTXMANUVERINGNO
3/10/2017​
425AGNCALANDINGNO

Vance
Many accidents made claims with insurance but were never reported. There is an insurance underwriter sitting right in Tampa Bay in Bradenton, FL who pulled back from Gyroplanes after one year of paying 3 Cavalons at 150k+ with a very small pool of gyroplanes in their portfolio though I think a couple of them were flipovers right after landing or something like that. Its been since 2018/19. But this isn't second hand info. This is right from the guys mouth in our hanger. I have seen 2 Cavalons just here in Florida with damage from blade flap accidents. One of them tried to tell me it was trailer damage when trailer was pulled into the hanger. Right. It was a blade flap accident. And of course its all low time gyroplane pilots. That is completely true.
 
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Isn't one pilot responsible for three of those eleven accidents in Cavalons (one time each in TX, WA & the final, fatal one, in OR)?
 
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Vance i didnt introduce anything about Cavalon. I made no claim that any one issue was at the root. I just gave a generic response to Abid which just happened to be in this thread.

Vance: Out of eleven Cavalon accidents investigated by the NTSB since the beginning of 2017 only two of them involved blade flap.
Although even using numbers you accept that is over 18%. There is a question mark about take off stability in 419LB which is related to the same point, that makes it 3 & over 27% and the 2018 442AG accident is another stability issue which is entirely related to elements of what I said. So thats 4 & 36%.
 
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Whats changed. It's always been called blade flapping. Who decided to change it to blade sailing. That kinda sounds fun to blade sail. LOL
 
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".
 
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