Gyropedia

[mceagle]

Is ”Gyropedia.com” a recognised reputable site?
i couldn’t find any information about its heritage or who was responsible for all the information supplied. I ask because I have an issue with a couple of questions presented and unless I am mistaken the answers are not technically correct.

 

[Vance]

Good morning Tim,

Phil Harwood is one of the main driving forces behind Gyropedia.

It is based on the input from a lot of instructors that belong to the International Association of Professional Gyroplane Training (IAPGT).

Because of the rapid growth in gyroplanes and so many unnecessary mishaps Phil feels a consistent standard for gyroplane training would have value.

Because it is supposed to be for all sorts of gyroplanes if there is a conflict the default is supposed to be the one least likely to cause a problem.

It continues to change and Phil welcomes input.

I am trying it out with one of my primary students.

Bob at Autogyro USA uses it for all of his clients and Britta is working into it.

I recently sent Phil 17 suggestions and he responded to each of them.
I have challenges with some of the weather, terrain and navigation because in England the weather and circumstances are often very different than they are in California.

Phil points out that a gyroplane doesn’t know what country it is flying over.

If you have some specific suggestions it would be helpful to everyone involved if you would share them with Phil.

I too would be interested in the experience you bring to the table as I feel there is value in it.

It is not intended to replace the flight instructor, only to give him tools and minimum standards.

 

[Greg Vos]

Having seen the program grow from the initial stages it seems to have come a long way, recently I was in discussions with a client who do military type training in the Middle East, the instructor of the school is certainly a big supporter of the gyropedia.

Having gone there for an interview and actually being offered a job one of the criteria is that all have to be gyropedia fluent, currently I am not a subscriber, I only get the emails and have limited access to its tutorial videos.

In our country it’s a very expensive program in Rand terms, and I’m still unsure if gyro instruction is supposed to be easy? the big selling point to us instructors is it makes our job easy? It also standardizes the program affording any instructor to pic up with a student at any stage provided said instructor is part of the program, in simple terms it’s uniformed system. ( so does the existing file system used where student and instructor indorse the progress - just saying )

My difficulty is that no person can learn a skill from you tube, I accept you tube does have value in transferring knowledge, in the interview with the gyropedia instructor I was told how easy it makes our job, and that all the prep work is done for us.

This is great however I still find value in preparing as an instructor for every lesson or lecture and I note that every student has a different learning curve myself not really concerned if I have to put in effort to get my lesson across. I believe it keeps me as instructor on top of my game.

I have been using Phil’s books for years as a reference but have also spent many hours on a white board explaining things and then doing actual demonstration to the student, in the lesson debrief I get a good feel of what the student has understood, and then give him homework for the next lesson.
i don’t think flight instruction should be a box ticking exercise ? I’m not knocking the program and hope it will be adopted and if it’s good I’m sure all commercial ppl/ cpl schools could adopt a similar world wide program.

In conclusion I was in a flight test with my helicopter instructor recently he is also a attack helicopter test pilot and a gyro CFI himself a training captain previously with Emirates in short we can say he knows a bit about flight and flight training.
His comment to me on gyropedia was exactly that ..... instruction is not to be easy on the instruction work load and flight instruction is not a box ticking game.

not being negative just posting my thoughts and comments as a gyro CFI

 

[Brian Jackson]

I recently subscribed as a soon-to-be student. Very impressive what I have seen thus far. I like the idea of an accepted standard. With everyone contributing such a wealth of input, you get an effect called "the wisdom of crowds" that tends to be more correct than any one individual. And ultimately the goal is safety for all.

 

[mceagle]

One of the questions I have an issue with is :-
“In a Gyroplane with a teetering rotor system in level flight at normal cruise speed, the lift of the advancing blade and the retreating rotor blades is equalised by the process of?”
The correct answer of the multiple choice is given as :-
“C...the advancing blade teeters up, reducing its angle of attack. The retreating blade teeters down, increasing its angle of attack.”

Is this is a deliberate over simplication for us “simpletons” or is it completely correct and I don’t understand the question correctly.
If the advancing blade saw increased airspeed then the increased air pressure would create an upward force on the blade and the reaction due to precessive forces would cause the blade to rise at the front of the gyroplane, not at the RHS, causing a tendency for the Gyroplane to climb which is compensated for the pilot with forward cyclic. It is quite evident when flying that the faster you go the more forward stick you need, such that if your aircraft is fast enough, you can run out of forward stick.
The lift of the advancing and retreating blades is equalised by the pilot using the “cyclic” stick to decrease the pitch on the advancing blade and increase it on the retreating blade, allowing the rotor disc to fly nearly level. This is normally only a few degrees “right” stick, depending on the forward speed, or in most cases the manufacturer would normally adjust the push rods to tilt the head slightly to the right when the stick is centred, to allow the cyclic pitch to change, compensating for the discrepancy in blade airspeed and consequently keeping the angle of the rotor disc nearly level (with a slight tilt left or right to compensate for the torque of the engine, but that is another issue).
In any case, the disc lift vector is perpendicular to the tip plane path of the rotors, meaning that if the advancing blade teetered up and the retreating blade teetered down, the disc would be a tilted to the left, meaning the disc lift vector to be inclined to the left, causing the gyroplane to turn left, and this is not the case in straight and level flight.
in short, the lift of the advancing and retreating blades is equalised by cyclic pitch variation, input by the pilot.

i couldn’t find a contact for Phil from that site so if I have a valid point, could someone pass it on for me please.

 

[Vance]

i couldn’t find a contact for Phil from that site so if I have a valid point, could someone pass it on for me please.

Phil Harwood <[email protected]> ([email protected])

 

[Vance]

One of the questions I have an issue with is :-
“In a Gyroplane with a teetering rotor system in level flight at normal cruise speed, the lift of the advancing blade and the retreating rotor blades is equalised by the process of?”
The correct answer of the multiple choice is given as :-
“C...the advancing blade teeters up, reducing its angle of attack. The retreating blade teeters down, increasing its angle of attack.”

Is this is a deliberate over simplication for us “simpletons” or is it completely correct and I don’t understand the question correctly.
If the advancing blade saw increased airspeed then the increased air pressure would create an upward force on the blade and the reaction due to precessive forces would cause the blade to rise at the front of the gyroplane, not at the RHS, causing a tendency for the Gyroplane to climb which is compensated for the pilot with forward cyclic. It is quite evident when flying that the faster you go the more forward stick you need, such that if your aircraft is fast enough, you can run out of forward stick.
The lift of the advancing and retreating blades is equalised by the pilot using the “cyclic” stick to decrease the pitch on the advancing blade and increase it on the retreating blade, allowing the rotor disc to fly nearly level. This is normally only a few degrees “right” stick, depending on the forward speed, or in most cases the manufacturer would normally adjust the push rods to tilt the head slightly to the right when the stick is centred, to allow the cyclic pitch to change, compensating for the discrepancy in blade airspeed and consequently keeping the angle of the rotor disc nearly level (with a slight tilt left or right to compensate for the torque of the engine, but that is another issue).
In any case, the disc lift vector is perpendicular to the tip plane path of the rotors, meaning that if the advancing blade teetered up and the retreating blade teetered down, the disc would be a tilted to the left, meaning the disc lift vector to be inclined to the left, causing the gyroplane to turn left, and this is not the case in straight and level flight.
in short, the lift of the advancing and retreating blades is equalised by cyclic pitch variation, input by the pilot.

As a gyroplane flight instructor in the USA I teach from the Rotorcraft Flying Handbook.

https://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/media/faa-h-8083-21.pdf complete with illustrations.

From the Rotorcraft Flying handbook with slight revisions for no drawings 3-6.

DISSYMMETRY OF LIFT

"When the helicopter moves through the air, the relative airflow through the main rotor disc is different on the advancing side than on the retreating side. The relative wind encountered by the advancing blade is increased by the forward speed of the helicopter, while the relative wind speed acting on the retreating blade is reduced by the helicopter’s forward airspeed. Therefore, as a result of the relative wind speed, the advancing blade side of the rotor disc produces more lift than the retreating blade side. This situation is defined as dissymmetry of lift. If this condition was allowed to exist, a helicopter with a counterclockwise main rotor blade rotation would roll to the left because of the difference in lift. In reality, the main rotor blades flap and feather automatically to equalize lift across the rotor disc. Articulated rotor systems, usually with three or more blades, incorporate a horizontal hinge (flapping hinge) to allow the individual rotor blades to move, or flap up and down as they rotate. A semirigid rotor system (two blades) utilizes a teetering hinge, which allows the blades to flap as a unit. When one blade flaps up, the other flaps down.

As the rotor blade reaches the advancing side of the rotor disc, it reaches its maximum upflap velocity. When the blade flaps upward, the angle between the chord line and the resultant relative wind decreases. This decreases the angle of attack, which reduces the amount of lift produced by the blade. As the rotor blade reaches the retreating side it flaps down. Due to downflapping, the angle between the chord line and the resultant relative wind increases. This increases the angle of attack and thus the amount of lift produced by the blade."

It appears to me that is what the answer says in Gyropedia.

I feel flapping is a poorly chosen word as it suggests something different that a tilted rotor disk which in my opinion is what results in forward flight in a gyroplane with a two blade semi rigid rotor.

At one hundred knots of indicated air speed my advancing blade at ninety degrees is seeing two hundred knots of airspeed and my retreating blade at two hundred seventy degrees is seeing fifty knots of airspeed. I feel this produces a significant difference in lift that needs to be addressed somehow.

In my opinion the teeter hinge manages this without significant pilot input and the angle of attack of the rotor blade is changed as described.

If I am moving the cyclic left as the speed increases it is nothing I am aware of.

 

[mceagle]

G’day Vance, how ya doing.
IMHO as a retired manufacturer, rotorheads we’re always slightly offset to the right, changing the pitch at the 12 o’clock and 6 o’clock positions, the reaction following 90° later, increasing the lift on the retreating blade and consequently decreasing it on the advancing blade - .
As forward speed increases you move the cyclic forward, not left. With the vast difference between rotor tip speed and gyro forward speed, in most cases this forward movement is barely noticeable by the pilot who does it instinctively. However it is quite noticeable if you accelerate from 30kts to 100kts.

 

[mceagle]

From the Rotorcraft Flying Handbook quoted above :- “As the rotor blade reaches the advancing side of the rotor disc, it reaches its maximum upflap velocity.”

To me this would appear to go against the laws of Gyroscopic Pression. The resultant “upflap” should be 90° later, or at the front of the Gyroplane.

 

[XXavier]

From the Rotorcraft Flying Handbook quoted above :- “As the rotor blade reaches the advancing side of the rotor disc, it reaches its maximum upflap velocity.”

To me this would appear to go against the laws of Gyroscopic Pression. The resultant “upflap” should be 90° later, or at the front of the Gyroplane.

Upflap velocity, not amplitude...

 

[WaspAir]

I have always preferred to think of it as a simple phase shift in periodic motion (as shown in these graphs) without unnecessarily importing more obtuse notions of gyroscopic precession. It only makes sense that you would reach your maximum height when you run out of upward velocity (otherwise, if you had any upward velocity left, you would still be moving upwards), and that puts the high point at the 12:00 position with simultaneous max height and zero up-speed. When you're at max up velocity at 3:00, you're still going up quickly, so you can't yet have reached the peak height. The blade descends all along the retreating side until the downward velocity reaches zero at the 6:00 position for the same reason (simultaneous min height with zero down-speed).

[For the calculus minded, for a sinusoidal position track, the first derivative (velocity) is the cosine, and the second derivative (acceleration) is the negative of the sine, which is just what these graphs show. A cosine is just a 1/4 period shift of a sine curve, providing the 90 degrees of apparent response that everybody talks about. It happens for a bouncing spring just as for a spinning object, and no resort to torques or precession is required to explain it.]

Vance, I think you would be less bothered by the "flapping" term if you spent more time around articulated rotors, where the action happens at the flapping hinge. It seems very natural usage for the A&S 18A and for most helicopters, if not for your Predator.

 

[Greg Vos]

Is this a tech discussion? Or a discussion around the merits of gyropedia and it’s implementation and advantages.

im not sure

 

[mceagle]

I ask as a technical question :- “the lift of the advancing blade and the retreating rotor blades is equalised by the process of?” - “the advancing blade teeters up, reducing its angle of attack. The retreating blade teeters down, increasing its angle of attack.”

Is this technically correct?

I believe that whether it’s difficult to explain or not, precession plays a paramount part in rotor disc behaviour.

From the little I have scanned of Gyropedia.com it appears to be a good and very relevant site with a lot of good information.

 

[Vance]

I ask as a technical question :- “the lift of the advancing blade and the retreating rotor blades is equalised by the process of?” - “the advancing blade teeters up, reducing its angle of attack. The retreating blade teeters down, increasing its angle of attack.”

Is this technically correct?

I believe that whether it’s difficult to explain or not, precession plays a paramount part in rotor disc behaviour.

From the little I have scanned of Gyropedia.com it appears to be a good and very relevant site with a lot of good information.

The explanation does not seem in conflict with gyroscopic precession to me Tim.

With an anticlockwise turning rotor as viewed from above the advancing blade starts rising at six o’clock and reaches maximum height at three o’clock ninety degrees later were it begins to sink and reaches equilibrium at twelve o’clock ninety degrees later where it begins its journey down as the retreating blade and reaches minimum height at nine o’clock ninety degrees later where it starts back up reaching equilibrium at six o’clock ninety degrees later.

What am I missing?

 

[WaspAir]

I believe that whether it’s difficult to explain or not, precession plays a paramount part in rotor disc behaviour.

The rotor disc is a conceptual construct, not a real object. Its outer boundary is a locus of points traced out by the blade tips. If one were to look at the three blades spinning around on an A&S18A, each coned upwards with load, each leading and lagging, each flapping up and down independently, one would see that it is not a solid object, but that the tip paths form the edge of an easily visualized virtual disc. You can talk about vector cross-products, torque, and precession of that conceptual disc if you wish, but it seems unnecessarily complicated to me, when the phase lag in the graphs above says everything that needs to be said. Nobody ever describes a bouncing spring with terms like precession, but it behaves the same way. I favor the simplest explanation. You start climbing at the low point; you reach max upward speed halfway between the low point and the high point; you stop climbing at the same moment you reach max height. On the retreating side, you reverse it to go back down. It's really that simple, and you don't need to imagine gyroscopes to understand it.

 

[WaspAir]

The explanation does not seem in conflict with gyroscopic precession to me Tim.

With an anticlockwise turning rotor as viewed from above the advancing blade starts rising at six o’clock and reaches maximum height at three o’clock ninety degrees later were it begins to sink and reaches equilibrium at twelve o’clock ninety degrees later where it begins its journey down as the retreating blade and reaches minimum height at nine o’clock ninety degrees later where it starts back up reaching equilibrium at six o’clock ninety degrees later.

What am I missing?

Vance, just to be clear, I am not suggesting anything inconsistent with precession, merely that precession is unnecessary to explain it (and makes it messier).

For your description above, it sounds to me that you are describing a disc tilted to the left (highest at 3, lowest at 9) but I am not at all sure that is what you meant.

 

[XXavier]

The explanation does not seem in conflict with gyroscopic precession to me Tim.

With an anticlockwise turning rotor as viewed from above the advancing blade starts rising at six o’clock and reaches maximum height at three o’clock ninety degrees later were it begins to sink and reaches equilibrium at twelve o’clock ninety degrees later where it begins its journey down as the retreating blade and reaches minimum height at nine o’clock ninety degrees later where it starts back up reaching equilibrium at six o’clock ninety degrees later.

What am I missing?

May I suggest a few corrections...? They follow:

With an anticlockwise turning rotor as viewed from above, the advancing blade starts rising at six o’clock, reaching a maximum climbing velocity at three o’clock. At that point, it starts to slow down its climb, but keeps moving upwards until, at 12 o'clock, the blade reaches a maximum height, its climbing velocity coming down to zero. Then, reversing its motion, it starts to sink, reaching maximum sinking velocity ninety degrees later, at nine o’clock. And a further ninety degrees later, at six o'clock, the blade reaches the lowest point of its orbit...

 

[Tyger]

The explanation does not seem in conflict with gyroscopic precession to me Tim.

With an anticlockwise turning rotor as viewed from above the advancing blade starts rising at six o’clock and reaches maximum height at three o’clock ninety degrees later were it begins to sink and reaches equilibrium at twelve o’clock ninety degrees later where it begins its journey down as the retreating blade and reaches minimum height at nine o’clock ninety degrees later where it starts back up reaching equilibrium at six o’clock ninety degrees later.

What am I missing?

I think he (and WaspAir) are saying that max height is at 12 o'clock (zero upward velocity), while max upward velocity (NOTmax height, as you just wrote) is what's at 3 o'clock.

 

[mceagle]

Now I’m getting confused. If you moved the cyclic forward such that the rotor head tilted 1° forward, that would decrease the pitch on the advancing blade (Eg from nominal 2° back to 1°) and conversely increase the pitch on the retreating blade (Eg from the nominal 2° up to 3°). Now you have 1° pitch on the advancing blade and 3° on the retreating blade. Would this not correct for the “dissymmetry” of lift?

I’ve got a feeling that we’re overlapping two different rotor behavioural characteristics here.

 

[XXavier]

Now I’m getting confused. If you moved the cyclic forward such that the rotor head tilted 1° forward, that would decrease the pitch on the advancing blade (Eg from nominal 2° back to 1°) and conversely increase the pitch on the retreating blade (Eg from the nominal 2° up to 3°). Now you have 1° pitch on the advancing blade and 3° on the retreating blade. Would this not correct for the “dissymmetry” of lift?

I’ve got a feeling that we’re overlapping two different rotor behavioural characteristics here.

In s/l flight, and for a given airspeed of the gyro, you need a rotor lift equal to the gyro's weight. For example, when the airspeed is low, you have to compensate by holding the stick back, so that you increase the AoA of the disk. When the gyro's airspeed is higher, the stick is held at a more forward position, because lift from the blades is higher due to the higher airspeed, and you don't need too much AoA of the disk.
But, for any airspeed of the gyro, and due to the difference in airspeed as seen by the blades, your rotor needs to compensate for the lateral lift difference by reducing the AoA of the advancing blade and increasing the AoA of the retreating blade. That compensation is done automatically by the freely teetering hub bar, the amplitude of that teeter being proportional to the difference of the airspeed seen by the blades.