Swedish yoke

[wolfy]

Thanks Chuck I had never seen that two blade machine.

wolfy

 

[Jazzenjohn]

Do you have an drawing of the 2 blade jump head Chuck?

 

[XXavier]

CB has probably more information on the subject, but this picture may be of interest:



It appeared in this recent paper:

 

[C. Beaty]

JJ, the book, Cierva Autogiros, contains several pages of Cierva’s patents for pitch-drag coupling but all are basically variations of the drawing above posted by XX.

None of Cierva’s jumpers was truly successful because skewed drag hinges don’t permit the increase of collective pitch to be greater than normal autorotative cruise pitch.

The first successful jumper was by Raoul Haffner, an Austrian living in Britain who developed a gyro with standard cyclic and collective pitch.

Haffner was interned as an enemy alien at the outbreak of WWII but took out British citizenship and became the developer of the Rotachute, the autogyro kite that inspired Bensen to develop the Gyrocopter.

 

[wolfy]

Chuck re hashing the round mast idea, reading another thread where you were saying aluminium tube could be bolted onto a square keel cheek plates by using gang nuts and two or three bolts per side so no crush tubes are required. Seems a simple way of incorporating a round mast, maybe not as good as 4130 but still better than 2x 2.5. Now to mounting 4130 x.065 (which seems very thin walled), naturally crush tubes would need to be welded in and increasing the width. Short of using a thick cheek plate and rebating to suit the crush tubes, can you suggest a simple way of mounting? And two or three bolts per end?

Cheers wolfy

 

[C. Beaty]

Wolfy, assuming your cheek plates are designed for 2” wide square/rectangular tube, then gang nutplates in round steel tube should be sufficient. ¼” nutplates are available with spacings from ½” on up. 7 bolts on each side with ½” spacing on 4” long cheek plates should hold just about anything.

Perhaps you should try the next larger wall thickness beyond 0.065”.

 

[wolfy]

Thanks for your help Chuck, doing it with gang nuts make's the conversion easy. I was originally nervous about having multiple bolts all in line but it is not timber it has no grain.

It looks like 2" is available in 0.083" hopefully that will remain nice and limber. I had no trouble with 0.065" besides bolting through it without weld in cross tubes. I am only a red neck engineer so tend to over build.

wolfy

 

[giro5]

available in 0.083 - I did not see this in the above chart from aircraft spruce. Next size up from .o65 is .095 which is probably what I would use if using 2 inch 4130 tubing. This wall thickness is about half way between 1/16 and 1/8 wall or about 3/32. With either .065 or .095 wall I would use cross tubes welded in. But like wolfy I am no engineer. On another web site I did see .083 wall tubing.

 

[giro5]

After reviewing the engine mounts I made from the KB2 plans I am about convinced that .065 wall with cross tubes for bolting on the cheek plates would be sufficient. If I could figure out where to look I would look at the strengths of 2 inch .065 wall 4130 vs 2 inch square 6061 aluminum tube.

 

[kolibri282]

The question can not be answered without the wall thickness for the 6061 and AFAIK we also need to know the state the 6061 is tempered to. Basically we need the yield strength of the two materials. Even then the question is difficult to answer because the limiting factor might not be yield- but fatigue strength, so we need to have those parameters for the the two materials as well.

 

[giro5]

It is hard for me to find a comparison between 2 inch rectangular 6061-T6 1/8 wall to 4130 round 2 inch tube .065 wall. One chart I did see listing 2 inch round tube for both metals with equal thickness showed the yield strength of the aluminum to be 21K lbs and the 4130 to be 92K lbs. breaking strengths was 27K and 105K. I think this is only useful to get a rough idea of the relative strengths.
As a shade tree home builder and certainly not of the caliber of some other members on this forum I am aware that welding in the cross tubes for the attaching bolts would have a weaking effect on the 4130 with out re heat treating the area but I would not have a clue on how to do this and would not if I built a 4130 mast. And not having a TIG welder which is recommended these days for 4130, I would use an OXY/Acetylene gas torch for the welding which I do have and just let the welds cool down in ambient air.

 

[giro5]

2 inch square tube 1/8 wall 6061-T6 aluminum is what I used for my mast on my plans built kb2. I could not find a comparison for the sq tube aluminum but on one web site comparing 2 in round tube of equal wall thickness I got the following numbers. Yield strength for the aluminum was 21K lbs, for the 4130 it was 92K. https://www.roguefab.com/tube-calculator/ is the web site I was looking at and I would only use these numbers to get a rough idea of the relative strengths of the tubes. And I may be interpreting the data incorrectly. Right now my kb2 has 27 ft rotorhawk extruded blades and they are very smooth with the aluminum sq tube. I got curious about rotor rpm and and installed a rotor tach but haven't flown it since. From other posts here my rotor rpm is probably quite low but my takeoff elevation is right at 5000 msl. If I ever build another gyro I am going to consider the 4130 2 in round tube for a mast and shorter rotor blades. I have some original Bensen 10 ft blades with a 2 ft Bensen hub bar but I have never bolted the blades on the bar to measure the actual total length. I am curious about the rotor rpm change if I ever install these blades.

 

[okikuma]

Hi Chuck,

That pretty much explains why Ken Wallis' gyroplanes had very little if any stick shake. A circular tube mast and essentially no extended hub bar with his rotor system. His wood rotor blades attached directly to the teeter block.

Wayne

 

[C. Beaty]

There’s more to this mast business than I fully understand, Wayne.
I chose 2.5” dia x 0.120 wall 2024 round tube because I had it on hand and it matched the stiffness of Bensen’s 2x2 6061 mast across the flats.
That was during the 1970s and I knew nothing about how Arthur Young’s rotor worked.
My first gyro was a stock Bensen that came about as a result of an employee, Bob Carbonell asking if he and his Cuban buddies, Ray More’ and Andy Garcia could use the company’s machine shop to build a Bensen during off hours. I said sure, I’ll even give you a hand but there’s no way in the world that I’d fly in such a contraption.
As things often happen, I did fly in that contraption and Bob’s buddies quit during the towline phase.
Eventually, Bob and I learned to fly with Bensen training manual in hand.
After a year or so, Bob decided to give up flying and go to law school. I gave him my half of the Bensen (our total investment at that point was $400, including the clay pigeon engine, a 72 Mac) so he could raise some money.
I built my round tube Bensen during that time or shortly thereafter and one of the first rotors I used was a set of Hughes 269 helicopter blades where the previous owner had sawn a taper in the root ends to mimic Bensen blades. Not believing there was sufficient inplane strength as a result of the taper, I built a hub with drag hinges and a door hinge arrangement at the hub center for coning. Smooth as glass and I had no idea the round mast had anything to do with it.
Bob, after graduating from law school and becoming established as a junior partner at a law firm, decided to build another Bensen. By that time, Bensen had come out with his twin 1x2 tube “redundant mast. I had structural bonding facilities and bonded Bob’s “redundant” 1x2 tubes together.
Try as we might, we could never get rid of 2/rev vibration in Bob’s new gyro. We even installed my rotor head on Bob’s new machine to no avail; not realizing mast stiffness was the culprit.
It was not until I had built a gyro with tail boom attached to the top of the mast and a very rigid pylon with violent, dangerous 2/rev vibration that I began to realize that mast stiffness played a key roll. Also, at about that time, “Birth of the Bell Helicopter” was shown on the Discovery channel and the lights came on. That resulted in the “slider” mechanism.
The best solution is a flexible, round tube mast.

 

[okikuma]

I agree with you Chuck, and I can see that other designers have also learned this lesson as you have.

The specially built aerial geophysics survey tractor gyroplane, Wagtail Kriek MkII, has a rotor mast is tubular, and is allowed to "float" between it's mounts to absorb the 2/rev vibration. The gyroplane as a 36' diameter rotor with rotor blade cord of 250 mm (9.843") in width. I noticed the rotor mast ability to "float" while I was watching the Wagtail Kriek MkII promotional video on YouTube. At about the 26 second mark, one can view the rotor mast "move about" inside the cockpit while the gyroplane is taxing over rough terrain. I just wonder how much that rotor mast moves during flight. There are several more camera shots from within the cockpit during flight, however there's a slight bit of vibration with the camera, so it is hard to view just how much the mast moves.

Wayne

 

[okikuma]

Perhaps Girabet uses a round tube design for ease in manufacturing. I'm not familiar enough with this model of gyroplane to know if the 2/rev stick shake is present or has been eliminated.

Wayne

 

[Kevin_Richey]

Perhaps Girabet uses a round tube design for ease in manufacturing. I'm not familiar enough with this model of gyroplane to know if the 2/rev stick shake is present or has been eliminated.

Wayne

Based on what Chuck B. has told us many times over the years re: round, limber gyroplane masts, & that Girabet appears to leave their mast free of triangulation & attachments other than that light bracket we see up high on it, their rotorblades must be very smooth in flight.

I noticed their engine support tubing has only little attachment brackets that appear to be welded onto the lower mast section.

 

[okikuma]

Hi Kevin,

I agree with the physics that Chuck has taught us.

To my eye and brain, the design and construction method for the Girabet is first for economic reasons. A simple, cut, bend, and weld, tubular airframe is much less labor intensive as compared to the Bensen style of square tube, flat plate, and right angle stock cut, debur, drill, debur, then assemble airframe. The use of round tubing is the only choice of material for the simpler method of construction. The cancelling effect of the 2/rev shake is just a second, added and positive benefit in this example.

BTW, I think the construction method for the Girabet is ingenious.

I mentioned previously about Ken Wallis' design and construction with a tubular mast and the absence of a hub bar where the rotor blades attach. I found a copy of the video Gyroplane Refrain, narrated by Roland Smith. In this one particular clip, Roland is flying with Ken Wallis on his WA-122 Rolls Royce/Continental O-240 powered gyroplane. During the flight, there is a good camera shot of how smooth/lack of vibration the cyclic is experiencing. I seriously think the combination of the tubular mast, and the lack of an extended rotor blade bar, along with finely balanced rotor blades is the secret to control the development of the 2/rev vibration.

Wayne

Wayne

 

[wolfy]

Interesting to note, while Ken's machine's use a round mast they are all also triangulated.
Show's his rotors are very stiff in plane to have a nice smooth machine.

wolfy

 

[wolfy]

Chuck if your still reading, after looking at a mates machine (a heavy single) with .083" 4130 mast I am now convinced .065" will be more than enough for my medium weight single.
He had some .065" tube also to have a look at, sometimes just a physical look is what's needed.
So what do you think about a solid nylon insert and 6 1/4" bolts going right through, spaced an inch apart? Gang nut's will be hard to get here.

Thanks wolfy