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07-04-2014 07:41 PM  6 years ago
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seahorse bob

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Arvada CO

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Pitcairn PA-33C
I've been flying autogyros for a few years and enjoyed them except for needing a pre-rotator for shorter takeoff and extremely small cross wind conditions for landing without tipping over and ruining hand made blades. The pre-rotator motor and gear and direct control head almost constitute the typical heli setup. With this in mind, I decided to combine a helicopter setup in an autogyro fuselage.
I've long admired Harold Pitcairn for developing virtually all the essentials that made the helicopter possible. Sikorsky paid royalties from the beginning for Pitcairn's patents on cyclic and collective controls and lead/lag hinges, etc. All the rest had to pay after extended court battles. Although Pitcairn was a champion of the autogyros simplicity, he realized the importance of the hovering capability. In 1939 he started developing his own helicopter by doing a design study taking his already flying PA-33 and converting it to a helicopter. The first effort was a gyrodyne type with a pylon on the side of the fuselage and a small anti-torque rotor facing forward for best efficient thrust. Control issues ended this effort and the XR-9 was developed instead. The XR-9 was very good but late in coming so we don't hear much about Pitcairn's helicopter these days.
I had started building a scale PA-33 in 1/5.5 scale but decided to make it a full helicopter instead of autogyro. My rationalization was that the Pitcairn design team could have extended the PA-33 to a tail rotor instead of the side rotor gyrodyne project. I used some small 3-views and photographs to make my plans.

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07-04-2014 07:56 PM  6 years ago
Mojave

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Palos Verdes, Ca. USA

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That is just too cool! You are a very talented builder! Happy 4th!!!
Barry
All helis and planes have an expiration date stamped on them...you only find it after you crash!!
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07-04-2014 08:56 PM  6 years ago
seahorse bob

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Arvada CO

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I should have explained that Pitcairn used PA-33B designation for their gyrodyne version so I use PA-33C for my imaginary version.
This model flies like most any model rc heli with only a substantial tendency to act like a weather vane making it different. Sometimes, the tail rotor authority is marginal when the wind velocity gets above 20 mph. I enjoy it most in calm conditions.
I've been building balsa models for 50 plus years so that determined my construction design and method. I first laid plans and put the heli mechanics over to determine fit, etc. I used Titan X50E fbl mechanicals because they were easily available and I'd used them before. Now, they are discontinued but I understand the replacement will be extremely close. I designed a truss framework of balsa sticks and then made bulkheads to give the nice round form of the fuselage. I found the well done radial cowl from Great Planes 1/5 scale WACO biplane was just right and utilized it. I used my favorite Solartex colored fabric and repainted the cowl using Krylon Fusion paint to match. It comes with a dummy engine. I was uncertain if I might need ballast in the nose so I installed a 450 sized main shaft and gear so I could spin up the front prop like an autogyro. It turned out not to need any ballast so the front prop just windmills. It turns the correct direction with a headwind but backwards in a tail wind!
It came out to less than 9 lbs. ready to fly. I use a Scorpion 4025 890kv motor at 6s turning the smallest 13 tooth pinion for a gear ratio of about 10.3. I easily get 8 min. flights.
It's been an interesting project and sure gets a lot of double takes when I fly it. Mostly I hear "what is it".
Here are some misc. photos showing the construction. Let me know if there are any questions and I'll be happy to answer them.

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07-04-2014 09:04 PM  6 years ago
seahorse bob

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Arvada CO

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I thought I'd show some more photos that were taken in bright sun light that might show more details.

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07-04-2014 09:05 PM  6 years ago
doorman

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Sherwood, Arkansas

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Something Different!!!
I agree... this is a very cool machine...
Thinking outside the "box" makes this a great hobby, and with your vision and talents make it happen...
Very nice...
Happy Fourth!!!

Stan
AMA 2918-Team Spin Blades,,Castle Creations, Unique Aircraft
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07-04-2014 09:11 PM  6 years ago
seahorse bob

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Arvada CO

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Here are some photos to show more details of the finished model.

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07-04-2014 09:19 PM  6 years ago
seahorse bob

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Arvada CO

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Hi you guys and thanks for the compliments and Happy Fourth of July.
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07-30-2014 08:44 PM  6 years ago
seahorse bob

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Arvada CO

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Here is some video of the Pitcairn flying:

Watch at YouTube

Thanks to Jeff for the video.
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07-30-2014 09:16 PM  6 years ago
seahorse bob

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Arvada CO

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And here's a little more video:

Watch at YouTube

Thanks again to Jeff
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