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cbonnerup

More Senior Every Day
Joined
Aug 27, 2010
Messages
508
Location
Greenville, NC / USA
Aircraft
Building a Gyro, modified J4B2
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Well, I'll make one.
Does anyone have a drawing/sketch of the A&S18A rotor-head? Alternatively, any links/info re: fixed pitch-change mechanisms (discrete change) for JTO autogyro's would be appreciated.

Have not sent PM to Waspair as of yet.

Thanks ladies and gentlemen,
Chris
 

WaspAir

Supreme Allied Gyro CFI
Joined
Oct 21, 2006
Messages
4,757
Location
Colorado front range
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Bell 47G-3B-1 / A&S 18A / Phoebus C, etc.
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stopped caring at 1000
Here's how it works.

The 18A has a fully articulated, swash plate controlled, three-blade rotor system. It also has a manual hydraulic pump, operated by a handle next to the pilot's seat that looks like a collective control (it isn't a true collective, but it is used to change pitch). The hydraulic pressure can be re-directed by use of buttons (electrical switches) that act through solenoids.

To prepare for spin-up, a button is pushed on the panel, (labelled "DE-PITCH") to direct the hydraulic pressure to move the swash plate. When the pump handle is then stroked up and down a few times, the hydraulics will move the swash plate to pull all three blades into flat collective pitch, working against springs that urge them toward a positive pitch angle. When you reach max pressure for the pump (there's a gauge on the panel so you can tell) the blades will have zero collective pitch and the springs will have maximum displacement. The blades have a symmetrical airfoil, so flat pitch means no lift and minimum drag for the rotor during spin up. You are now sitting still on the runway, with the blades flat, brakes held, and the engine at low rpm (900 - 1100 on a Lycoming O-360 that goes to 2700), constant speed prop set for climb, and low prop thrust. Hydraulic pressure is maintained and opposes the springs and keeps the blades flat for the next step.

The pilot next selects the "CLUTCH" button. Further pumping of the handle will slowly engage a multi-plate clutch so that the engine drives the rotor blades and accelerates them. After the clutch is fully engaged, the throttle is advanced until the rotor reaches approximately 370 rpm in flat pitch. Most of the engine power is going into the rotor system rather than the prop at this point. Anti-torque during this spin up comes from the tires while you sit on the ground, with the pilot holding the brakes. This spin up is far in excess of the normal flight rpm of around 240, and that stores lots of excess energy in the heavy blades (50+ pounds each for three blades, diameter 35 feet).

When the blades are fully spun up, if the pilot wishes to do a jump takeoff, he pushes a small button on the top of the throttle. This disengages the clutch, puts in a one second delay, and releases the hydraulic pressure that was holding flat pitch. All engine power is now going to the prop. The rotor blades, responding to spring force on the swash plate, all pop up to about 8 degrees of pitch, while still spinning at about 370 rpm. In response, the aircraft will jump up (and slightly forward, the forward motion coming from the prop thrust), climbing helicopter-like while extracting the extra stored energy. No anti-torque is needed because the engine is de-clutched before you ever break ground.

As the aircraft climbs up in the jump, the rotor now carries the weight of the aircraft, some rpm is lost, and the blades start to cone upward. A delta-3 angle in the hinges provides pitch/cone coupling, so that the increased coning leads to a reduction in collective pitch. By the time the rotor has decayed down to normal flight rpm, the collective pitch is down several degrees from the initial 8, at a good autorotative pitch setting. The aircraft has also accelerated to adequate flight speed (thanks to the prop thrust) to permit climb out from there. You are now in flight as a gyroplane.

The pitch/cone coupling means that the pilot doesn't have to do any collective adjustment to go from the high pitch used for the helicopter-mode jump to the lower pitch autorotation-mode forward flight; it all happens automatically. All he needs to do is push the button and steer the aircraft.
 

WaspAir

Supreme Allied Gyro CFI
Joined
Oct 21, 2006
Messages
4,757
Location
Colorado front range
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Bell 47G-3B-1 / A&S 18A / Phoebus C, etc.
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stopped caring at 1000
in flight adjustment

in flight adjustment

Farrington developed an STC that allowed for pilot trimming of the collective pitch. A mini-toggle switch on top of the stick actuates a motor (a Piper flap motor, I think) that will move the swash plate to change pitch / rpm, continuously within a range. A pair of lights (green and amber) illuminate to show the extremes of travel. Of the two 18As in my hangar, one has this mod and the other doesn't.

As a light pilot (who sees low typical rotor rpm when solo), I find that I can approach the edge of retreating blade stall at high forward speed, so that my limiting speed is determined by vibration / comfort rather than engine power. Bumping the rpm up a little with the collective pitch trim delays the onset of those issues and lets me fly at higher airspeed.
 

cbonnerup

More Senior Every Day
Joined
Aug 27, 2010
Messages
508
Location
Greenville, NC / USA
Aircraft
Building a Gyro, modified J4B2
Total Flight Time
12 hrs PP; others as available
Thank you very much WaspAir,
Excellent and lucid description - I had assumed some positive pitch failure mode using springs.

Perhaps one day I may be able to see it up close and personal. Must be very well engineered to get Certification.

Kind Regards,
Chris
 

hjajr

Newbie
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Mar 31, 2008
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Talihina,Oklahoma
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gyro,helicopter,fixed wing
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Reason asking is that it would be good to get another hour in a 18A as a refresher. Not tat I could ever afford to buy one again but it is possible if I ever get this land sold and one might come up for sell.
I am over in Sacramanto right now at a friends. Im waiting to find a load to get me back towards Oklahoma. I do a little Hot Shotting with my F-350 and 31' trailer. I picked up a older Air Command from Kevin in Portland that I have with me. Will be trying to find a particle load to put on the trailer to get me home.
I may be better going your way to get one and may to be able to afford a hour if you ave the time. It really depends on me finding a load also.
 

WHY

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miami,oklahoma
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Hi Harry

Good to know about your "Hot Shot" freight work,, I think there could be some real use of it at times here in the gyro world, keep us reminded from time to time.

Tony
 

hjajr

Newbie
Joined
Mar 31, 2008
Messages
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Location
Talihina,Oklahoma
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gyro,helicopter,fixed wing
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Be good to help when I can. Its so hard to line up loads from a place to a place with only 31' of space. Iv had to do over 3000 miles to make picking this gyro work out.
 

WaspAir

Supreme Allied Gyro CFI
Joined
Oct 21, 2006
Messages
4,757
Location
Colorado front range
Aircraft
Bell 47G-3B-1 / A&S 18A / Phoebus C, etc.
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stopped caring at 1000
Mr. Stark do you give dual in your 18A?
Reason asking is that it would be good to get another hour in a 18A as a refresher. Not tat I could ever afford to buy one again but it is possible if I ever get this land sold and one might come up for sell.
I am over in Sacramanto right now at a friends. Im waiting to find a load to get me back towards Oklahoma. I do a little Hot Shotting with my F-350 and 31' trailer. I picked up a older Air Command from Kevin in Portland that I have with me. Will be trying to find a particle load to put on the trailer to get me home.
I may be better going your way to get one and may to be able to afford a hour if you ave the time. It really depends on me finding a load also.
It's not insured for dual instruction at the moment (there's not a big demand, because most folks want to fly in Sport Pilot eligible gyros these days, and the 18A requires at least a Private rating).

We do have one for sale -- 50 hours since ground-up rebuild, $150K.
And I'm happy to take anybody on the forum for a friendly ride for nothing.

This is it:

WOH 2010 - COOL GYRO LANDING .wmv - YouTube
 

RotoPlane

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Jan 4, 2008
Messages
3,203
Location
Gilboa, Ohio USA
The original 18A (can't remember the company now) was covered by Flying or perhaps Plane & Pilot, but the article didn't delve very far into how the rotor worked, at least not as well as post 2 & 3....thanks J.R.

I had high hopes for the Heliplane and even more for the Avian....
 

hjajr

Newbie
Joined
Mar 31, 2008
Messages
769
Location
Talihina,Oklahoma
Aircraft
gyro,helicopter,fixed wing
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3100
Mr. Stark! The red one is the one for sell? Does it have the Rotor trim switch for flatning out the pitch for a faster speed? What would be maximum cruise with it and without it? I assume the one you are keeping is the one in your Aviator picture?
 
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