Airfoils for Gyroplane rotor blades

All these shots are at San Carlos. The blue one, if you look closely, is named "Drag Queen", because it's really good at making drag. The red one I called The Red Menace (you have to be old to understand that reference). The last shot has my Bell in the foreground and the blue 18A in the middle.
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And a constant speed prop too. The Lycoming has no attach points to mount such a transfer mechanism and the dyna-focal mount is exclusive also to the rear of the engine, I expect there was a bit of head scratching to engineer the mount for the belts. Also as the
propeller flange is extended because of the pulley adapter, extra stresses are imparted to the crank, did Lycomimg beef up the bushings to accommodate? I like the 4130 welded tubing fuselage. The designer has to have his plans drawn correctly and the builder as accurate as the designer. Regretfully this requirement of craftsmanship is seen as a hindrance to the garage home workshop builder. I expect this is why Ron Herons’ beautiful creation, Little Wing was not as popular as it should have been.

Thenak you for the image. It was a treat to see them.
 
These things were factory built, per a Standard Airworthiness production certificate, so the design and build were always professional (Fairchild, of A-10 Warthog fame, built the prototypes). Lots of hydraulics. The spin up shaft was only loaded up when the clutch was engaged on the ground for about a minute per flight, so engine mods weren't deemed necessary. The drive section you see in the photos was tube frame, but the rest of the ship is monocoque.
 
Did the designer create his own rotor head or is it an adaptation? How does the swash plate follow the movements do the lead lag hinge? Does the swash plate cyclic arrangement negate the need for a flapping hinge on each blade? So I’m guessing there is a collective of some fashion and the cyclic functions much as one would expect in a light helicopter. I have very little time in a Hughes 300.

Back to the engine mount, is the engine more or less caged and tubing extends from the engine mount proper aft, to support the belt and pulley arrangement? I see the trim is hydraulically controlled too. I expect linear actuation was in short supply back in the day. Having the clutch and its weight under the rotor head and CG is smart also.

have you ever lost power while transitioning from a jump takeoff? A 37’ rotor spun up 50%??? over the cruise RRPM will have a lot of inertia. You can’t go flat on the collective, no choice but to lower the nose and ride it in. I expect the first jump was a bit of a sensory overload. Cat shot gyro style.

As you might have guessed, I’ve been quite intrigued by the 18A for sometime now. I got a sign off in a Lycomimg Parsons, not “Black” in 92. I had a Cessna and PPL SEL INST by then and it was just easier to fly what I had. Then in early 2004, I went to sea for 15 years and that squished any flying of any sorts pretty much. I retired a few years back and working to get back in the air.
 
It's fully articulated and there's a flapping hinge on each blade, but the order of the hinges may seem slightly unconventional (moving outward from the mast, flapping, lead lag, feathering). Look closely at the second photo and you can see the of the end of the flapping axis as a black disc. This head is unique to this aircraft although inspired by an obscure helicopter design.

From the pilot's stand point, the collective is essentially two position : hydraulic pump it all the way down to flat pitch for spin up, and pop it up abruptly to launch pitch (about 8 degrees) to take off. Delta 3 couples pitch and coning, so it drops to more like 4 degrees for flight (all without pilot intervention as coning increases and rrpm falls).

Normal spin up was to 370 rpm while flight with typical load was 240. Three blades weigh well over 50 pounds each, so there's plenty of inertia. When you punch the takeoff button it disengages the clutch and waits 1 second for the prop to spool up before adding rotor pitch, so as you jump you have full thust and you gain airspeed as you rise. The jump is up and forward. Never lost power except for practice (bless you, Lycoming), but you don't pitch down, you ride it forward and settle on those long grasshopper oleo gear legs.

Collective is changed in flight only slightly as a trim. A squat switch on the gear prevents engaging the clutch or pumping down the collective in flight.
 
Sorry guys, I arrived late to the party. Referencing back to posts 1, 6, & 7, I fly with the aforementioned set of “red blades” except mine are white and 29 ft. diameter. Having experienced this uncommanded pitch up as described I am interested in better understanding of the phenomenon and future avoidance. My understanding thus far is that this is not caused by retreating blade stall and instead the lack of torsional rigidty allowing the advancing blade to twist to a greater AOA when speed increases. The rotor rpm is kinda low (290-310) and I theorize that maybe more revs might make things more stable. I also have a set of 28’s that have not yet flown so will be trying those this Spring. Being on an open frame gyro it gets uncomfortable over about 65 knots anyway so Having divergence at 75 is not too bad, Mostly I guess it would be nice to have a bit more stable ride when experiencing convection. Mike mentioned that Chuck had suggested a possible fix. Do you recall what that was and would it be retrofittable.
 
Sorry guys, I arrived late to the party. Referencing back to posts 1, 6, & 7, I fly with the aforementioned set of “red blades” except mine are white and 29 ft. diameter. Having experienced this uncommanded pitch up as described I am interested in better understanding of the phenomenon and future avoidance. My understanding thus far is that this is not caused by retreating blade stall and instead the lack of torsional rigidty allowing the advancing blade to twist to a greater AOA when speed increases. The rotor rpm is kinda low (290-310) and I theorize that maybe more revs might make things more stable. I also have a set of 28’s that have not yet flown so will be trying those this Spring. Being on an open frame gyro it gets uncomfortable over about 65 knots anyway so Having divergence at 75 is not too bad, Mostly I guess it would be nice to have a bit more stable ride when experiencing convection. Mike mentioned that Chuck had suggested a possible fix. Do you recall what that was and would it be retrofittable.
The only fix I could see that could be done to existing blades would be possibly a trim tab. The fix that Chuck suggested would be a complete change in construction to achieve quarter cord balance.
 
Happened to Glen Kerr, of Utah, @ one of the ROTR events. He was flying his Butterfly (single seat) gyro w/ 25' McCutchen Skywheels & related he was going 80+ mph when it occurred.

I haven't heard of the sudden un-commanded pitch up in a single seat gyro b/4 his experience. Thought it was only heavy 2 place machines, @ high A/S, say 70+.
 
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The only fix I could see that could be done to existing blades would be possibly a trim tab. The fix that Chuck suggested would be a complete change in construction to achieve quarter cord balance.
Is it quarter cord balance or torsional (lack of ) stiffness? How would a trim tab therefor affect stiffness? If the blades are seeing, guessing,300 mph at the tips, how can an increase of 10 mph created such an issue? I can, however see an angle of attack being exceeded and a sudden stall occur. We all agree that input affects are not felt until 90° of rotation. How then is the force being applied to pitch up? Is this sudden lift occurring at 90° of the advancing blade suddenly causing an extreme amount of lift at this point? To have more lift at that point then it is inferred an increase in angle of attack caused the sudden lift. Would it not be logical that an increase of AOA at this speed felt by the rotor at this point being the driven section, that an accelerated stall would occur? If the blade then failed by twisting downward, then loss of lift would occur.
The solution of a trim tab would in theory keep the AOA constant. But, it seems this is also ties to lower RRPM. Why would this pitch up not manifest itself on departure if the machine is lightly loaded? The faster the RRPM the greater airspeed retreating blade stall occurs. For me the issue of why is far from settled.
 
It may help to view the blade as a flying wing (Stuck in a tight flat turn!).
If a flying wing has a cg aft. of it's center of lift, any pitch diversion will continue unless it is countered by a control input.
If the lift force is forward of the cg, the wing will want to pull up all the time. (The rotor blade is held in check by the grip)
I am guessing that it takes a certain amount of RRPM and loading to overcome the torsional rigidity of the this blade, but when it does start to diverge, it is self amplifying until it loses energy from the sudden climb out.
I would say anyone who experienced this event is lucky to be able to talk about it.....
 
Is it quarter cord balance or torsional (lack of ) stiffness? How would a trim tab therefor affect stiffness? If the blades are seeing, guessing,300 mph at the tips, how can an increase of 10 mph created such an issue? I can, however see an angle of attack being exceeded and a sudden stall occur. We all agree that input affects are not felt until 90° of rotation. How then is the force being applied to pitch up? Is this sudden lift occurring at 90° of the advancing blade suddenly causing an extreme amount of lift at this point? To have more lift at that point then it is inferred an increase in angle of attack caused the sudden lift. Would it not be logical that an increase of AOA at this speed felt by the rotor at this point being the driven section, that an accelerated stall would occur? If the blade then failed by twisting downward, then loss of lift would occur.
The solution of a trim tab would in theory keep the AOA constant. But, it seems this is also ties to lower RRPM. Why would this pitch up not manifest itself on departure if the machine is lightly loaded? The faster the RRPM the greater airspeed retreating blade stall occurs. For me the issue of why is far from settled.
From my understanding it is both. The blade is not quarter cord balanced. In smaller disk sizes it doesn’t seem to be a factor due to the stiffness of the blade in torsion. Up to 27’ foot blades it was not an issue it was the disk sizes above that where the problem manifests itself. I am no expert and am going by the limited knowledge imparted on me by Chuck Beaty and My Father.

Chuck once said that putting a trim tab on them would possibly counteract the tail heaviness of the blades and possibly keep them from twisting uncommanded to positive pitch. He also said that this is the reason Bensen had a small trim tab on the outer tip of his metal blades. He was afraid of the same thing happening. From my understanding although having been almost universally adopted as the perfect airfoil for gyroplane use the 8H12 is actually not very good and only chosen by Dr Bensen because of its ease in hand starting. This copy cat gyro industry just keeps using it with very little knowledge, if any about airfoil behavior or design.

The airfoil used on Dragon Wings rotors is a much more efficient one. The difference in drag is very noticeable. So much so that one of our friends accused the blades of having “too much lift”. His VW powered Bensen was flying around at around 3/4 throttle as opposed to full throttle he was used to. He kept over shooting his landings as well due to the reduced drag the glide ratio was quite a bit higher.

The only disadvantage the airfoil used on Dad’s Dragon Wings was the higher stall speed along with the abruptness of the stall. This made hand starting them more difficult for the average person. It could be done with a finesse technique as opposed to the typical brute force that other blades of the 8H12 accepted. Once someone was shown the proper way to do it and they were patient it was not a problem. The problem with most of us humans is we lack patience in anything and place the blame for that other than where it belongs with the person.

We used to laugh at the marketing of said Red blades using a 70’s model Corvette Stingray driving up on them as ramps. This was to demonstrate the strength of the design. Unfortunately because of a lack of understanding of aerodynamics that strength was the not the important one. The important one of torsional rigidity was ignored.

I’m very surprised that some hothead that had his Gyro do that uncommanded pitch up never arranged to have a little conversation behind the woodshed with the designer. This especially after it happened over and over in front of many fly-ins. He was made aware of the problem and basically said there was nothing wrong with them.
 
In my opinion, the low drag of the DW rotors comes mainly from the work of its blade sections at higher CL. In other words, the aerodynamic pitch setting is larger. This decreases the Rrpm at equal load.
Thus, the profile power reduced and improves the L/D ratio of the rotor but makes it more difficult to launch by hand.
And also, due to the low Rrpm the divergence of the longitudinal flapping angle will occur at a slower forward speed
 
And also, due to the low Rrpm the divergence of the longitudinal flapping angle will occur at a slower forward speed
Jean Claude would you elaborate on that statement, please?
Maybe I'm thinking about it wrong, but it would seem that the lower RRPM would allow a HIGHER forward speed before divergence.
 
The divergence of the longitudinal flapping angle occurs because the A.o.A of the retreating blade reaches stall angle.

It therefore appears at advancing factor Mu lower when the angle setting is larger.

If you added at this a Rrpm lower, due to the high CL, then the forward speed which divergence appears much decrease with the higher pitch
 
To clarify just a bit: Bensen blades were not true 8H12 (McCutchens are more accurate). The '12 has a convex bottom surface, while Bensen blades, both woodies and metal, had dead-flat bottoms. Made them easier to build, and the flat bottom was an easy reference point for measuring pitch.

Reflex adds trim drag to a blade (much as a down-loaded H-stab adds trim drag to a FW plane). Therefore, any designer who is chasing efficiency would like to minimize trim drag by using less reflex than needed to produce a zero pitching moment.

Some gyro blade designs have employed virtually ZERO reflex. No doubt the designer hoped that the torsional stiffness of the blade would prevent the twisting of the blade at higher blade airspeeds. And sometimes that worked, and other times it did not.

Anecdote: My best gyro-flyin' buddy died many years ago in the crash of a Cloud Dancer motorglider. The plane went straight in after a typical departure stall-wing drop.

It turned out that the plane was designed without download on the H-stab. Instead, the wing's pitching moment was offset (at one airspeed only!) by aft CG. The normal CG was at 40% or more of wing chord. To make the pitching moment worse, the wing had a drooped trailing edge (the opposite of reflex). These design tactics are used in some sailplanes for the sake of drag reduction. The consequence in this case, though, was that the plane was statically divergent with respect to airspeed. Once it slowed up, it tended, on its own, to slow up even more. This was not entirely clear in the flight manual; it probably should have been written in bold capitals. Moreover, the real stall speed, per another friend with many hours in this model, was considerably higher than disclosed in the manual.

For me, this crash was a bitter lesson in pitching moment and CG location. I still miss my man Bill.
 
To clarify just a bit: Bensen blades were not true 8H12 (McCutchens are more accurate). The '12 has a convex bottom surface, while Bensen blades, both woodies and metal, had dead-flat bottoms. Made them easier to build, and the flat bottom was an easy reference point for measuring pitch.

Reflex adds trim drag to a blade (much as a down-loaded H-stab adds trim drag to a FW plane). Therefore, any designer who is chasing efficiency would like to minimize trim drag by using less reflex than needed to produce a zero pitching moment.

Some gyro blade designs have employed virtually ZERO reflex. No doubt the designer hoped that the torsional stiffness of the blade would prevent the twisting of the blade at higher blade airspeeds. And sometimes that worked, and other times it did not.

Anecdote: My best gyro-flyin' buddy died many years ago in the crash of a Cloud Dancer motorglider. The plane went straight in after a typical departure stall-wing drop.

It turned out that the plane was designed without download on the H-stab. Instead, the wing's pitching moment was offset (at one airspeed only!) by aft CG. The normal CG was at 40% or more of wing chord. To make the pitching moment worse, the wing had a drooped trailing edge (the opposite of reflex). These design tactics are used in some sailplanes for the sake of drag reduction. The consequence in this case, though, was that the plane was statically divergent with respect to airspeed. Once it slowed up, it tended, on its own, to slow up even more. This was not entirely clear in the flight manual; it probably should have been written in bold capitals. Moreover, the real stall speed, per another friend with many hours in this model, was considerably higher than disclosed in the manual.

For me, this crash was a bitter lesson in pitching moment and CG location. I still miss my man Bill.
If you remember Doug the first several years dad produced blades they have very little reflex. Once he figured out how to change his oven and tooling to put more in he did. This enabled him to eliminate the trailing edge rivets. It made the blades a little less efficient but a much more docile flying set of blades. I flew one set of non reflexed blades. I didn’t like them at all told Dad I wouldn’t fly them again and he should sell them.
 
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A small collection of reports for all those interested in autogyro blade profiles is available here:
https://magentacloud.de/s/pZRTxbt9mE89wGK

The password is naca8h12 (all lower case). The stanislawski report is a more recent one which gives values for variations on the 9H12M profile and proposes a variable plan form. Another interesting one might be the PractialIssues....., which gives a few values of several profiles with and without trim tabs.

Have fun and may there always be an inch of clearance between your aircraft and the nearest obstacle...;-)

Cheers,

Jürgen
 
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A short extract from Naca 7905 recalled by Juergen:
"During the 1950Bs, laminar airfoils were extended to helicopters with the introduction of the series 6: (NACA 63A012-63A015) and of the laminar series with a low %, especially designed for helicopters (9H12).
However, the performances obtained were inferior to predictions and in the sixties one witnessed a return to the conventional NACA airfoils and their derivatives"
I wonder how they can expect better performance at the present time if they rely on datas that still neglects key points, including the cyclic bias attack.
 
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A small collection of reports for all those interested in autogyro blade profiles is available here:
https://magentacloud.de/s/pZRTxbt9mE89wGK

The password is naca8h12 (all lower case). The stanislawski report is a more recent one which gives values for variations on the 9H12M profile and proposes a variable plan form. Another interesting one might be the PractialIssues....., which gives a few values of several profiles with and without trim tabs.

Have fun and may there always be an inch of clearance between your aircraft and the nearest obstacle...;-)

Cheers,

Jürgen
Thank you for the treasure of information found in the website your provided. The paper presented by WIeńczySłaW StaleWSkI
Institute of aviation, al. krakowska 110/114, 02-256 Warsaw, Poland, [email protected] in particular is a most interesting read. I was struck by the beauty of the rotor plan form presented on page 91. Some objects seem to be destined to fly just by their shape. The old adage referring to a car, “ It looks fast standing still,” an be applied to that plan form and is a refreshing departure from the long square-ish rotors of today. Just like the superior wing of the Submarine Spitfire where no two ribs were the same, it was a manufacturing nightmare to produce them regardless of the increased performance.
 
I have already given my opinion on the low reliability of these predictions based on 2D analysis of blade profiles when it works with oblique attack

Added to that, according to my spreadsheet, such a 10 m rotor with 5 degree pitch setting would have only 295 rpm at 600 kg. This means that a blade should weigh about 30 kg for a usual coning of 2.75 degrees.
So, how could the little root of this 120 mm chord and 13 mm thick blade support this bending at rest?
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