Museum Scale H-34

May 01, 2013 4 Comments by

Darrell Sprayberry of Dalton, GA has earned a reputation as one of the finest scale helicopter modelers in the world, and at this year’s Toledo Weak Signals Expo he placed first in the Helicopter class with his fantastic scratch-built H-34 Choctaw.

Also known as the Sikorsky S-58, the H-34 is an iconic design–perhaps the best piston-engine utility helicopter in the world before the arrival of turbine helis like the UH-1 Huey. Sadly, models of this outstanding helicopter are very rare, largely owing to the near impossibility of getting it to balance with nitro or gasoline power. Fortunately, this is no problem with electric power, where the battery pack can be placed well forward.

Darrell’s -34 is a masterpiece, with outstanding design engineering capped off by awesome scale details. He started the build in 2011, and the huge fuselage plug attracted lots of attention at that year’s IRCHA Jamboree. Since retiring last year, he has focused more heavily on the project, and the result is really something to see. I spent some time talking about this entirely original design with Darrell, and our wide-ranging discussion provided an interesting glimpse into the active mind of a world-class modeler.

Asked what scale the -34 was built to, Darrell laughed and said, “Seven feet long.”  He went on to explain, “What I found with these big helis is that seven feet is the magic number.  Any bigger than that, and they get really hard to transport. For me the main requirement is that it has to fit in the back of my Jeep.”

Expanding on this common sense approach to determining size and layout, Darrell remarked, “I’m not big on modeling with a computer.  I have a 4×8 white bench, and I’ll lay the hardware out to get an idea of how things will fit together. It really helps to see things actual size.”

The epoxy fiberglass fuselage was laid up in custom molds pulled off Darrell’s hand-carved plug. The body includes functional details like sliding doors and windows, and clamshell doors in the nose provide access to the battery packs.

The mechanics are also scratch-built and designed to fit inside the “doghouse” on top of the fuselage so that the scale cabin is completely open. The four-blade head has 880mm blades, for a total rotor span of 2.25 meters (89 feet). Hitec HS-7940TH high-voltage servos and a JR 11X radio provide the flight control.

Darrell flies electric helis exclusively, and he’s a big believer in the outstanding KDE motors, so he chose a 700XF-495 for power. The controller is a Castle Creations Ice-120HV, and the 12S battery pack is made up of two 8000-6S packs inside the magnetic clamshell doors in the nose. Even with the 8000-12S battery, the big machine still requires four pounds of lead to balance, and all-up weight is “in the high 30s.”

Head speed will be in the 1,000rpm range, but Darrell noted, “I always let the helicopter choose the exact head speed. Any given heli has a particular speed where it’s happiest.”  Like many full-scale helicopters, the H-34 has a proportionally smaller tail rotor diameter than is the norm for model helis. Because of this and because he likes to run realistically low head speeds, Darrell uses a higher tail ratio than is typical for pod and boom helis.  The H-34’s torque tube-driven tail hash a gear ratio of 6:1, so even at a low 1,000rpm head speed, the 4-blade tail rotor is still turning 6,000rpm, providing plenty of holding power.

At press time Darrell is working out final details preparatory to the maiden flight. I for one can’t wait to see the H-34 flying at IRCHA this summer.

What’s next?  Darrell has acquired the molds and tooling for IndyRC’s outstanding 1/7-scale AH-64 Apache and his company, Unique Aircraft (UniqueAircraft.com), will offer the Apache, Choctaw and other high-quality products to scale heli enthusiasts.  Given Darrell’s fertile mind, you can count on some amazing things to come.

 

 

 

HT15 Photo 5a

HT15 Photo 5b

HT15 Photo 5c
This is a model where the longer you look, the more things you see. From the scale rotor head to the detailed cockpit to the scale cabin with sliding door, the attention to detail is absolute.

HT15 Photo 6a

HT15 Photo 6b

With a long tail and snub nose, the H-34 makes a challenging subject for nitro or gasoline power. For his electric design, Darrell included clamshell doors with magnetic latches so that the 8000-12S battery could be positioned as far forward as possible. All-up weight is “in the high 30s.”

 

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About the author

A longtime contributor and the current "Heli Talk" columnist for Electric Flight, Jim has been heavily into aeromodeling for nearly 25 years. Electric warbirds are his main love, although in recent years helicopters have taken much of his attention. He is focused on scale helis and his favorite part of the hobby remains designing and scratch building.

4 Responses to “Museum Scale H-34”

  1. Jim Spice says:

    Atta boy Darrell, You’ve done it again!!!

  2. Steve Rogers says:

    Wow, when I saw the picture of this in the June 2013 issue of Model Aviation it took my breath away. I was a mechanic on these back in the early 1960′s when I was in the Marines. Got to fly a lot as a non-crew member(aka door gunner). Our squadron had a red turtle deck instead of yellow. Other than that, it could be me in the door with the machine gun and cargo strap. That was in the days before the “gunships.” We drew a lot of fire from the Laos side of the river. Took over 150 small arms hits on one four hour mission. That chopper could take a beating and keep flying. Some of our choppers had a little red kangaroo painted in the white portion of the star, but very few people ever got to see that or know what it meant.

  3. Robert Friday says:

    A nice model. I was a Crew Chief on one back in 1956 in the 11th Trans. CO
    located in Stuttgart, Germany. I looked all over for a model but never found one until now. Great job.

    Bob Friday

  4. Chris Keeping says:

    Absolutely superb it is so nice to see a Company producing a classic oldie. Any chance of a Wessex? When can a mortal like me be able to purchase one?

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