my macon model - RCCR Radio Control Club of Rochester

MY MACON MODEL
By Jack Clemens
How else can you build a model at 1/40 scale and still qualify as an RC Giant?
MOTIVATION:
I had done a lot of modeling in my youth in the 1940’s. Family and job kept me away from any serious projects
during my adult life and so my pent up urges had to wait until I retired in2002.
A poignant 1932 photo of the lighted and empty Hangar One at Moffett Field in Sunnyvale California awaiting
the Navy’s giant flying aircraft carrier which was never to return started the process. The giant hangar just off
Highway 101 is nothing more than an oddity to most of the thousands of motorists that pass by every day. It
struck me that it would be a fitting tribute to aeronautical history to return the Macon to its hangar in the form
of a model. So began the effort to model a replica of the earliest hi-tech project on the San Francisco
peninsula and fly the Macon one time in its cavernous Hangar One.
HISTORY:
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 pre-radar “eyes of the fleet.” Distinguished from
blimps that were shaped 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.
Some research turned up technical data on the Macon. The airship had a rigid exterior airframe which
contained 12 gasbags for buoyancy, a hangar deck housing up to 5 Curtiss ”Sparrow Hawk” airplanes, a
trapeze device for launching and retrieving the aircraft, crew quarters for 50 men, eight directed thrust motors,
and an under slung 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. 6,500,000 cubic feet of helium filled the
interior and provided the lift necessary for flight.
CONSTRUCTION:
A request to the Smithsonian resulted in many archived photos and an overall drawing of the airship interior.
Construction that matched the original seemed the best approach using balsa wood as the structural material
for light weight. Very thin, 50 microinch 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 gas bags just fit onto the available 4 foot wide rolls of mylar.
Construction of the main frames (rings) consisted of building 36 pyramids from 3/32x1/16 inch balsa for each of
the 12 frames. As in the prototype, the pyramids were joined with the bases facing outward and the apexes
pointing inward. Since dimensions of balsa parts could not be controlled as accurately as desired, an assembly
wheel with 36 radial spokes and pyramid holders that were adjusted radially to conform to the dimensions of
each ring to shape of the hull. The largest of the main frames measured just over 40 inches and weighed just
over an ounce. Longerons of 1/16x3/16 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 assembly. 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. No provision for
carrying an aircraft was modeled, although the very light weight of current micro-models now make this a
tempting possibility Likewise, interior cabin details added nothing to the flight characteristics and were ignored.
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 down thrust to aid in maneuvering
during landing. Rudder and elevator controls are actuated through a cable and pulley system.
Small hatches allow the deflated gas bags to be inserted into the hull. Each bag has a filler tube for filling with
helium and a dump vale to speed emptying spent gas. As each bag is filled the airship 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:
Airships can tolerate only light winds. This makes flying a very opportunistic event. The current Macon is a
successor to a nearly identical model that was lost to unexpected winds that came up suddenly. Since
transportation is a problem, so flights begin on the street in front of our home. Stormy spring weather has
prevented much flying , but as of this writing, the weather is improving.
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.
DIRTY LAUNDRY:
The current model is the third attempt to finish a flying model of the Macon.
I began work on Macon I in 2003 and finished it in early 2006. It had a lot of mistakes and 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 to a Mardi Gras party and when we returned, we found the
hull on the floor with a giant hole in it. Apparently, Roscoe, 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 8 motors to be more
than adequate to move the ship at a brisk speed – probably 20-25 mph. A calm afternoon lead to a longer
flight which scared a couple of people sunbathing by the pool. It was also spotted by the daughter of a
neighboring farmer (no, not that farmer’s daughter). 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 ways 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. Two days later, the farmer’s daughter found me. The
Macon had come to roost about 5 miles away in a prune orchard owned by her father-in-law. 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 extremely favorable
weather before doing more tests on a tether.
For sure, this is the last rigid airship in my garage.
Jack Clemen's flying scale model of the USS Macon. It's a RIGID airship, 20 feet long, and 40" in diameter.
Powered by eight electric motors.