The catch 22 of autorotation on gyroplanes

Aviator168

Member
Joined
Feb 3, 2012
Messages
122
Location
New York
We all want a fast plane. But with autorotation, the faster we go, the larger the disk AoA. This is due to the faster the plane flies, the higher the speed difference between the advancing and retreating blades. The way to solve this is to increase rotor rpm and this is usually done with tilting the mask back which increases the AoA of the rotor disk, and that counters directly to the increase of traveling speed. So, at present, the top speed of an gyroplane is about 100mph give or take a few I am afraid.
 

WaspAir

Supreme Allied Gyro CFI
Joined
Oct 21, 2006
Messages
4,751
Location
Colorado front range
Aircraft
Bell 47G-3B-1 / A&S 18A / Phoebus C, etc.
Total Flight Time
stopped caring at 1000
We all want a fast plane. But with autorotation, the faster we go, the larger the disk AoA.
That's not how it works.
Higher speed is flown with a lower disc angle, not higher.
This is due to the faster the plane flies, the higher the speed difference between the advancing and retreating blades. The way to solve this is to increase rotor rpm and this is usually done with tilting the mask [sic: mast] back which increases the AoA of the rotor disk, and that counters directly to the increase of traveling speed. So, at present, the top speed of an gyroplane is about 100mph give or take a few I am afraid.
Rotor rpm will naturally increase somewhat with increased forward speed. Dissymmetry of lift increases with forward speed, which is compensated by flapping until you eventually get into retreating blade stall. If collective control is available, you can delay onset of retreating blade stall by reducing collective pitch allowing an increase in rotor rpm.
 
Last edited:

Jean Claude

Junior Member
Joined
Jan 2, 2009
Messages
2,104
Location
Centre FRANCE
Aircraft
I piloted gliders C800, Bijave, C 310, airplanes Piper J3 , PA 28, Jodel D117, DR 220, Cessna 150, C
Total Flight Time
About 500 h (FW + ultra light)
with autorotation, the faster we go, the larger the disk AoA.
Certainly no.
Here, the test in flight of Pitcairn PCA2 according Naca report 475.
Do not confuse flapping angle with attack angle.
Sans titre.png
 

Aviator168

Member
Joined
Feb 3, 2012
Messages
122
Location
New York
P.S.
In 2002, Ken Wallis (then about 86 years old) flew one of his designs at 129 mph.
I like to see the spec of that gyroplane.

Edit. After digging around a bit. I found this.

“I know it can do better,” he said. “129mph was done in adverse conditions with a lot of wind blowing. I know that if I started tomorrow I could make an aircraft that could go faster but at this age I have got to gather the enthusiasm to start again.”

I don't know if he meant head wind or tail wind.
BTW. That 129mph run of his, was over 1.9km. Not a sustained flight.
 
Last edited:

Vance

Gyroplane CFI
Joined
Oct 30, 2003
Messages
16,298
Location
Nipomo,California
Aircraft
Givens Predator
Total Flight Time
2400+ in rotorcraft
In my opinion the forward speed of most gyroplanes is limited by horsepower and stability, not dissymmetry of lift.

Most manufactures test their design and set the velocity never exceed (Vne) based on how the aircraft handles. They want an average pilot to be able to safely fly the aircraft up to Vne.

Most careful pilots do not exceed Vne.
 

Vance

Gyroplane CFI
Joined
Oct 30, 2003
Messages
16,298
Location
Nipomo,California
Aircraft
Givens Predator
Total Flight Time
2400+ in rotorcraft
Power aside. Isn't the faster it goes, the more stable? (not consider flutter)
No. Most gyroplanes have a happy speed and above or below that they are less happy (stable).

I have flown gyroplanes that become less stable as they approach Vne.
 

WaspAir

Supreme Allied Gyro CFI
Joined
Oct 21, 2006
Messages
4,751
Location
Colorado front range
Aircraft
Bell 47G-3B-1 / A&S 18A / Phoebus C, etc.
Total Flight Time
stopped caring at 1000
I don't know if he meant head wind or tail wind.
BTW. That 129mph run of his, was over 1.9km. Not a sustained flight.
Wallis held many officially sanctioned and recognized world records and knew what was required to get them awarded under the rules. Speed records are conventionally set over a measured and observed short course in level flight and not awarded for tailwind aided runs.

He's due some respect for a long history of accomplishments.
 
Last edited:

ventana7

Gold Member
Joined
Dec 17, 2003
Messages
1,491
Location
Salida, Colorado
Aircraft
Xenon Gyroplane, Cessna 182
Total Flight Time
960
No. Most gyroplanes have a happy speed and above or below that they are less happy (stable).

I have flown gyroplanes that become less stable as they approach Vne.
My experience in about 15,000 miles of XC trips trying to maximize speed matches Vance's comments. As you go faster and the disk gets flatter and flatter you reach a point where the stick is very twitchy- tiny movements have exaggerated diversions from straight and level. This makes flying more tiresome. So while you could find a max speed you could go on a short course speed run it is not something you would want to maintain in actual XC flying. My Xenon is very happy at about 85-90 mph. I often fly it at 100 mph. Above that the fun factor diminishes.

Rob
 

AirCommandPilot

Just a fledgeling
Joined
Feb 24, 2014
Messages
601
Location
Houston
Aircraft
Air Command Elite #003
Total Flight Time
88
P.S.
In 2002, Ken Wallis (then about 86 years old) flew one of his designs at 129 mph.
Somewhere I heard Sir Wallis used very short rotors maybe 16'? I can't seem to find where I read/heard it though so maybe it's not true.
 

Aviator168

Member
Joined
Feb 3, 2012
Messages
122
Location
New York
As you go faster and the disk gets flatter and flatter you reach a point where the stick is very twitchy- tiny movements have exaggerated diversions from straight and level. This makes flying more tiresome.

Rob
I can understand this. It is like a FW with anhedral low wings. But the solution to this is to add a pair of dihedral wings.

Somewhere I heard Sir Wallis used very short rotors maybe 16'? I can't seem to find where I read/heard it though so maybe it's not true.
Interesting. That also means the rotor had to spin much faster.
 
Last edited:

Tyger

Active Member
Joined
Nov 25, 2017
Messages
515
Location
Germantown, NY
Aircraft
Magni M16
Total Flight Time
330
Was Ken Wallis actually "Sir Kenneth"? I had not heard that before.
 

Greg Vos

Active Member
Joined
May 26, 2019
Messages
292
Location
Cape Town
Aircraft
R44/22 H269/300 MD 500 Magni (all); Xenon RST; DTA; ELA; MTO
Total Flight Time
2480 odd (1300 gyro hours & counting)
We all want a fast plane. But with autorotation, the faster we go, the larger the disk AoA. This is due to the faster the plane flies, the higher the speed difference between the advancing and retreating blades. The way to solve this is to increase rotor rpm and this is usually done with tilting the mask back which increases the AoA of the rotor disk, and that counters directly to the increase of traveling speed. So, at present, the top speed of an gyroplane is about 100mph give or take a few I am afraid.
Hi Aviator168 .... your comment the faster we go the larger the AoA? Who taught you this? ..... your description and understanding is a concern to me? It’s ok if your a new student and have not yet completed the course on gyro ...
, but if your Licensed and flying it could be you have little understanding of what’s going on with the rotor? Then the next question is how did you pass the Aircraft T&G section of the Pilot licence? and how did your instructor sit down and and explain in detail dissimitry of lift?

Wnen I read post like this the first thing that comes to my mind......it’s time for ground school🤔🤔
 

WaspAir

Supreme Allied Gyro CFI
Joined
Oct 21, 2006
Messages
4,751
Location
Colorado front range
Aircraft
Bell 47G-3B-1 / A&S 18A / Phoebus C, etc.
Total Flight Time
stopped caring at 1000
No. MBE + Military honours
The title I've most seen often used for him was "Wing Commander".

Lest we focus too much on him, the claimed performance for the Groen Hawk 4 was 130 mph cruise at 75% power with Vne of 150. The point of citing either was to indicate that there is no built-in practical aerodynamic gyroplane speed limit at 100.
 
Last edited:

ventana7

Gold Member
Joined
Dec 17, 2003
Messages
1,491
Location
Salida, Colorado
Aircraft
Xenon Gyroplane, Cessna 182
Total Flight Time
960
The title I've most seen often used for him was "Wing Commander".

Lest we focus too much on him, the claimed performance for the Groen Hawk 4 was 130 mph cruise at 75% power with Vne of 150.
I saw the Hawk 4 take off and fly many times. 150 mph may have been another one of David Groen’s unrealized dreams. David Groen’s main skill was not aircraft design, it was getting investors to part with large sums of money. And he was a master at that. (I was not one, as I had shares given to me).

Rob
 

C. Beaty

Gold Supporter
Joined
Apr 16, 2004
Messages
9,876
Location
Florida
An important operating parameter of a rotor is the ratio of rotorblade tip speed to translational speed, designated by the Greek letter μ (mu).

The most efficient speed, the best L/D ratio, occurs at a mu of 0.35; in other words when forward speed equals 35% of tip speed. For example, at a tip speed of 400 fps, most efficient forward speed is 140 fps or 95 mph.

Top speed, limited by retreating blade stall is typically reached at a mu of 0.5.
 
Top