Radio Control Giants-2011/08

Author: Sal Calvagna

Edition: Model Aviation - 2011/08
Page Numbers: 104,105,106

Radio Control Giants

Sal Calvagna [[email protected]]

Jack Clemens builds his final Macon

WELCOME BACK. We’re smack in the middle of summer. That means warm days, barbecues, ice cream, and lots of RC activity.

Plan to attend one of the Giant Scale events in your area. If gas prices are giving you second thoughts, grab a couple of friends and share the expense. Not all aircraft have wings or rotors. In this month’s column there are three fantastic models: one with three wings, one with two wings, and one with no wings at all.

GTM 1/4-scale Fokker Dr.I (Rudy Vinalet / flown by John “Chip” Koenig)

The first model is a Glenn Torrance Models (GTM) 1/4-scale Fokker Dr.I, built by Rudy Vinalet of Hialeah, Florida, and flown by owner John “Chip” Koenig of Boca Raton, Florida. The airplane received a respectable static score of 95.898 in its first Top Gun competition early this year.

The kit is scale in outline and appearance, as are all GTM models. The Dr.I is powered by an O.S. Gemini FT-160 twin-cylinder glow engine swinging an 18 x 6 Xoar World War I–style propeller. Rudy installed a Sonic-Tronics/McDaniel R/C onboard glow driver.

The model is covered with Solartex material and painted with WarbirdColors water-based urethane. The radio is a Futaba 2.4 GHz FAAST system utilizing digital servos. Please visit GTM’s website listed in “Sources.”

Royal Aircraft Factory S.E.5a (Heyward Macdonald)

Heyward Macdonald of Charlottesville, Virginia, scratch-built this nice-looking, self-designed Royal Aircraft Factory S.E.5a. It took him nine months to draw the plans and construct the model.

The S.E.5a spans 60 inches, weighs 8.8 pounds, and is powered by a 900-watt outrunner electric motor.

Heyward states that he could have reduced the weight further; however, he built the wings with the scale number of ribs—224 to be exact. Current wing loading is a mere 17 ounces per square foot. Finishing touches include homemade wheels and a sprung undercarriage. The rudder servo is connected through a gyro to improve ground handling and the model has an FMA Co-Pilot II installed in case Heyward gets into trouble in the air. (Author’s note: I’ve seen Heyward fly and I doubt that he’ll ever make use of the FMA Co-Pilot.) Nice work, Heyward!

Jack Clemens and the USS Macon (ZRS-5)

Jack Clemens of Brentwood, California, writes that in the 1940s he did a lot of modeling, but that family and work kept him away from any serious projects until his retirement in 2002. A photo from the 1930s shows that Hangar One at Moffett Field in Sunnyvale, California, housed one of the Navy’s giant flying aircraft carriers: the rigid dirigible USS Macon (ZRS-5). The hangar, off of Highway 101, is now nothing more than an oddity for the thousands of people who pass by on their daily commute. Jack believes that building a scale model of the Macon and one day flying it in the giant hangar would be a fitting tribute. Here’s what Jack has written:

“The history of the Macon is well-documented, but in summary it was a giant dirigible capable of carrying, launching, and retrieving scouting aircraft to serve as the preradar ‘eyes of the fleet.’

“Distinguished from blimps that were shaped like balloons that dangerously distorted when flown at high speeds, the Macon employed a rigid exterior airframe which held its aerodynamic shape at any operating speed. First flown in April 1932, the Macon operated out of Moffett Field in support of the Pacific Fleet until it was lost in a weather-related accident off the Monterey, California, coast in February 1935.

“The airship contained 12 gasbags for buoyancy, a hangar deck housing up to five Curtiss Sparrow Hawk airplanes, a trapeze device for launching and retrieving the aircraft, crew quarters for 50 men, eight directed-thrust motors, and an underslung command control cabin.

“The airframe was constructed from lightweight duralumin girders running the length of the cigar-shaped hull with 12 main frames forming the circular cross sections. The airship was immense at 785 feet in length and over 130 feet in diameter. Six million, five hundred thousand cubic feet of helium filled the 12 gasbags to provide lift.”

#### Construction

A request to the Smithsonian resulted in many archived photos and an overall drawing of the airship’s interior. Construction that matched the original seemed the best approach using balsa wood as the structural material for light weight. Very thin, 50 micro-inch metalized Mylar was selected as the lightest material available to contain the helium.

Computer modeling allowed some fairly decent estimates of weight and lift. In airships, the weight increases as the square of the dimensions whereas the lift increases as the cube of the dimensions, so bigger tends to be better.

My calculations showed a size of at least 20 feet in length would be necessary for the model to achieve buoyancy. A scale of 1 inch to 1 meter provided the required size, which would just fit diagonally in our two-car garage. Patterns for the gasbags just fit onto the available 4-foot-wide rolls of Mylar.

Construction of the main frames (rings) consisted of building 36 pyramids from 3/32 x 1/16-inch balsa for each of the 12 frames. The largest of the main frames measured just over 40 inches and weighed just over an ounce. Longerons of 1/16 x 3/16 balsa run the length of the hull and space the main and intermediate rings.

A cradle consisting of a long beam and 12 Y-shaped supports was constructed to support the hull during assembly. Each main frame was clipped to a foam spider support with a circular hole at the center. A piece of plastic irrigation pipe served as mandrel to align the rings during assembly. Two laser levels helped keep things aligned during the build. Silver Coverite MicroLite was used to cover the hull.

The fins were built on bench-top support fixtures and attached to the hull individually. Because of the concern over the weight of the large-area fins, they were covered with 5-micron Risteen MicroLite film. Window frames in the hull form the attachment point for each of the small “Firefly” electric motors. Where the prototype housed the motors in the hull and drove the propellers through shafts and bearings, the model houses the motors on outriggers and drives the propellers directly.

While scale in size and proportion, the model lacks some details of the original. The additional weight of the launching apparatus and aircraft were felt to be beyond the payload of the original design.

The control car houses the radio electronics. Three motors on each side provide primary propulsion while one independently throttled motor swivels from horizontal to vertical to provide downthrust to aid in maneuvering during landing. Rudder and elevator controls are actuated through a cable and pulley system.

Small hatches allow the deflated gasbags to be inserted into the hull. Each bag has a filler tube for filling with helium and a dump valve to empty spent gas. As each bag is filled, the ship becomes noticeably lighter. The ship becomes buoyant with each bag filled to 80–90% capacity. Weights are added to the nose or tail to bring the model into horizontal balance.

#### Flight

The original dream of flying in Hangar One will not be possible. Since the start of this project, the hangar at Moffett has been declared off-limits because of contamination from years of aircraft maintenance in the building and deterioration of the asbestos siding originally applied as a fire preventative. Personnel at the Moffett Museum are working with NASA on a plan to fly the model in one of the two smaller hangars at Moffett Field built to house anti-sub patrol blimps during WWII.

(Editor’s note: On April 21, 2011, workers began to dismantle and demolish the historic former home of the USS Macon. NASA has plans to restore the structure, but a request for approval has yet to make it through Congress. See the "Sources" listings for a link to a newspaper article about the demolition.)

“The current model is my third attempt to finish a flying model of the Macon. I began work on Macon I in 2003 and finished it in early 2006. I had made a lot of mistakes and it was on the heavy side.

“I had inflated the airship several times in my garage to test the buoyancy and balance and was waiting for a calm evening to test-fly it. My wife and I went out one night only to find the hull on the floor with a giant hole in it. Apparently, our cat decided to use the model as an intermediate platform when jumping down from a high shelf where he loved to sleep.

“While the entry hole appeared repairable, the exit hole had destroyed the majority of the hull. I had no idea how to jig and fixture the remnants for repair so I stuffed the remains of this 'Cat-a-clysmic' event into two shopping bags and started on an improved (and lighter) Macon II.

“Macon II was finished in October 2008. I flew a number of short test flights and found the eight motors to be more than adequate to move the ship at a brisk speed. A calm afternoon led to a longer flight which scared a couple of people sunbathing by the pool.

“Later that week, the local forecast called for calm early-morning winds. An early start was not adequate for the several hours it took to fill and balance the airship, so there was a slight wind by the time I got it launched. A gust carried the Macon over the house and by the time I could get around back, it had drifted quite a way off.

“My inexperience showed when I found I could not get the model to come back and I lost sight of it over a grove of trees. A couple of hours of searching orchards and fields turned up nothing. I pretty much gave it up for lost.

“The Macon had come to roost about 5 miles away in a prune orchard. A trip to the farm in a rental truck found only the collapsed rear two-thirds of the hull. Again the remains neatly fit in two grocery bags and I considered it the end of the story.

“Of all people, my wife encouraged me to give it one more shot and so, Macon III was born. More care and lightening culminated in the current model. I am extremely wind shy and am waiting for favorable weather before doing more tests on a tether. For sure, this is the last rigid airship in my garage.”

What a great story and fantastic model! You know what they say, Jack. The third time's a charm. The very best to you with your upcoming flights.

That's all for now. Remember, check those onboard battery systems. Cycle test and replace as necessary. If your battery packs are a few years old, just replace them; it's not worth the risk. MA