Way back in 1975, my friend, Jerry Flynn, and I (Kirt
Blattenberger) assisted Dick Weber in his successful flight
on June 14, 1975, that set a new FAI Closed Course Record of 225
miles in 5 hours and 38 minutes. We were both flaggers to signal
when the Tortoise has passed the distance markers. See the credits
on page 37 in the actual magazine. The Tortoise got its name by
virtue of the craft having landed near a turtle on the runway. It
was a long day, with everyone being sunburned by the end of it.
We were all members of the Prince Georges Radio Control Club (PGRC).
Note: This article on the
was previously posted with the magazine pages in image format. Now,
this version has been OCR'ed (optical character recognition) so
that all of the text is searchable.
652 Miles Per Gallon!
Richard R. Weber
Setting a new FAI Closed Course Record of 225 miles in
5 hours and 38 minutes, the Tortoise landed with 55% of its fuel
still in the tanks.
In the autumn of 1973 I decided to go after FAI distance and
duration records. I had completed a satisfying summer of pylon racing,
but there were not enough Quarter Midget races in my area. World
records offered a new challenge.
After setting the record, the designer displays
the airplane and complete support system. Size of the ship is only
slightly larger than pattern jobs. Covering is transparent Super
MonoKote. Wing is half blue and half yellow, colors which show up
best against any sky background.
The first order of business was to find an engine that would
run economically, so engine tests were initiated. From the outset
I intended to use a diesel engine because it runs longer than glow,
without the complication and interference of ignition. However,
most of the engines tested were glow, since they were available.
An engine that runs economically on glow fuel should be even better
as a diesel. Articles were found on records set by Bertrand, Giertz,
Hill, Hirota, Kaiser, Reed and later Giertz. The engines they used
ranged from .15 to .49 cu. in. displacement. After many hours of
running about 20 different engines, I chose a Supertigre 29 RV.
One of the reasons for this choice was that since the same basic
crankcase is used up to a .46, it seemed that it should be strong
enough to convert to a diesel.
Next it was time to bone up on aerodynamics. I gathered many
books and articles on the subject. Perhaps the most useful book
found was Man Powered Flight by Keith Sherwin. The problems it considers
are quite similar to those encountered in distance or duration models,
viz., designing to fly with minimum power. Another valuable book
for the dedicated modeler is Fluid-Dynamic Drag by S. F. Hoerner,
which contains the results of a great many airplane drag experiments
relevant to model design. A third source of information deserving
more attention than we give it is the collection of NACA annual
reports from the 1920's and 1930's.
There are three record categories stressing fuel economy: Duration,
Closed Course Distance, and Straight Line Distance. Closed course
distance was chosen first because it requires a smaller plane than
Duration and is a much easier undertaking than driving several hundred
miles (and back) for Straight Line Distance. The Straight Line Distance
record also requires more reliability, because the landing point
must be specified within 500 meters before take-off.
Preparing for the flight the author is engrossed
with the plumbing. Tanks. two 48-oz. plastic detergent bottles extend
3 in. in front of wing to 5 in. behind. Radio is midway between
the wing and stab with hatch on top of fuse.
The airplane went through numerous design stages, keeping in mind
the FAI limitations. These include a maximum weight of 11.02 pounds,
maximum flying surface loading (wing and horizontal tail) of 24.57
ounces per square foot, and maximum engine displacement of .61 in3.
Early sketches were beautifully streamlined, but by the time construction
began the design had become rather simple, not unlike its record-setting
predecessors. Its chief features are the tapered wing with a genuine
Clark Y airfoil, and a built-up fuselage with no formers or cross
A hefty shove is an important take-off assist.
On record flight the run was about 600 feet. Plane weighs 5 1/2
lbs. without fuel, 10 1/2 loaded.
The fuselage is filled from firewall to tail with fuel and radio
components. There are two fuel tanks, made from 48 oz. plastic detergent
bottles, extending from 3" in front of the wing to 5" behind. A
hatch between the wing and stabilizer provides access to the radio.
The model is covered with transparent Super MonoKote. To assist
visibility under various sky conditions one wing panel is dark blue
and the other is yellow. Experience has shown that one color or
the other is easily seen against any sky background. The complete
airplane weighs 5 1/2 pounds without fuel and nearly 10½ pounds
Radio was Kraft 6-channel with two-third brick
in airplane. Engine was Super Tigre R/C .15 Diesel conversion. Glow
case proved inadequate for sustained Diesel running.
The radio control system had to be reliable, compact, and easy
on the battery. A check of the current drain of several systems
indicated that the Kraft 3-channel brick would be ideal. I obtained
a brick which was then converted to my transmitter frequency of
53.2 MHz. Some additional work by Doug Spreng of Kraft Systems reduced
the servo current drain further. I planned to use rudder and elevator
controls, but the third channel would be available for engine control
Close up of the special field box containing
the interlace equipment described in article. A compact arrangement.
The batteries for the airborne radio system were four C cell
NiCads, rated at 1.5 AH and found to exceed 2 AH. The NiCad transmitter
battery pack is good for only four or five hours, so I made an interface
box to charge the transmitter batteries and power the transmitter
simultaneously. It contains meters to monitor the current and voltage
supplied to the transmitter. It also has a potentiometer to vary
the current. This interface box connects the transmitter to the
battery in my field box or to a car battery. It was used about half
the time during the record flight.
During the summer of 1974 I flew RC planes with diesel engines
in order to become familiar with their characteristics. I would
like to encourage much wider use of diesels. Contrary to popular
belief, diesels start easily and they can be throttled down like
the best glow engines. Perhaps my most notable flight of 1974 was
on September 2 with a heavy Box Fly Jr. powered by a Supertigre
15 R/C diesel. It took off the ground and flew with the engine running
for 1 hour and 45 minutes on four ounces of fuel.
Result of ground loop ending in grass was snapped
fuselage. Repairs took only a half hour. Controls were elevator.
rudder and needle valve: Pressure fuel system was used with homemade
regulator between tanks and needle valve. Four C cell NiCads supplied
airborne radio. Transmitter pack good for only four or five hours.
Interface box permitted simultaneous charging of batteries, power
Initial flight tests on the new record model began on December
23, 1974. A fuel cutoff was connected to the third servo for ending
test hops. I tried a variety of likely propellers with the plane
carrying two pounds of water and 11 ounces of fuel. Surprisingly
little difference in air speed was found between the different test
props. The final choice was a Power Prop 11-7½, just like on your
big pattern ship. Later flights gradually increased the fuel load,
to ascertain whether the shifting CG and increased weight would
present any problems; generally they did not.
The fuel system consisted of two pressurized plastic tanks connected
in series, followed by a fuel pressure regulator. Tests were all
satisfactory, although a problem developed later.
On May 10, 1975, we gathered for an official attempt on the FAI
Closed Course Distance record, sponsored by the Prince Georges RC
Club and the Goddard MAC.
Present were John Sites, CD, Luther Jackson, Eric Baugher, Ken Greenhouse,
Ron Moltz and Chet Opal. I estimated the chance of success at 50-50,
since we knew of no problems but the plane had never been flown
longer than 75 minutes. It was not a propitious day. At take-off
the 10- plus-pound airplane ground looped and went into the grass
beside the runway. The fuselage broke in half behind the wing. A
brief discussion ensued and Ron Moltz was off to his home for some
Hot Stuff and sticky MonoKote. To my amazement the plane was repaired
and flying half an hour after he returned. The official flight was
only fifteen minutes old when the engine went lean and slowed down.
Then it repeatedly improved and went lean in random fashion. We
worried about it when it was very lean, but it kept on running.
Lap times, which had been running 52-54 seconds in the beginning,
soared to over 70 seconds, but still it ran. After an hour of this
I had just decided to stop worrying, convinced that it would continue
to torment us all day long, when the engine stopped suddenly after
Tortoise airframe details.
When the plane landed we found that the rear engine bearing had
pushed out the bottom of the crankcase. We theorized about several
possible causes of the problem: faulty regulator, lean needle-valve
setting causing overheating and deposits on the piston crown, which
raised the compression too high, or fatigue from detonation during
earlier bench testing of the engine. The possible problems were
all rectified. The regulator was reworked, the needle valve was
hooked up to servo control and a brand new crankcase was found.
The second attempt on the record was on June 14, 1975. The officials
were Luther Jackson, CD, Dean Smith, Chet Opal, Eric Baugher, John
Tallman, Jerry Flynn, and
Kirt Blattenberger. After one of the test flights to adjust
the engine, the plane landed near a tortoise walking on the runway.
We immediately concluded that this was a good omen. Since the plane
was nameless, it was dubbed the Tortoise, for its slow but steady
When the tanks were filled the ground looping of May reappeared,
but the plane took off on the fourth attempt, after a ground run
of about 600 feet. The old record was 338 laps (kilometers) around
the course defined by two pylons 500 meters apart. Since FAI records
must be broken by 2%, our magic number was 345 laps. The flight
went without major problems. Occasionally the motor would go lean,
but the new mixture control took care of this. Sometimes when the
motor sounded fine, I would set it leaner to see if it would sag;
usually it did and was immediately set richer again. As we were
nearing the record, at about lap 341, the engine went quite lean,
but the needle valve was quickly opened and each of us held his
breath. When lap 345 was completed, there was a round of cheers,
for the record was ours!
The engine then seemed happier, probably because we were not
so concerned. Talk of 400 and 500 laps began to sound reasonable,
but it ended abruptly at the end of lap 363, when the engine stopped
without warning. The plane glided in to a smooth landing at the
center of the course. It had flown 363 kilometers (225 miles) in
5 hours and 38 minutes, averaging 40 mph.
Upon removing the wing we were overjoyed to see what looked like
75% of the fuel remaining! There would be another day and a longer
record for the Tortoise! Then we noticed that a check valve in the
pressure system had failed to allow air into the tanks to replace
the fuel removed, and the tanks were partially collapsed from engine
suction. A subsequent measurement showed that 55% of the fuel actually
remained. This works out to about 650 miles per gallon.
The problem which stopped the plane was found to be the same
one we had in May: the bottom of the crankcase broke under the main
bearing. The reason for the problem is now clear. The high-compression
loads of diesel operation exceed those which the crankcase can tolerate
for extended periods of operation. If a stronger engine can be found,
and I believe it can, the plane should be capable of 500 miles on
a closed course and more on a straight line course. With a larger
wing and lower rpms, maybe it can exceed the present duration record
of 14 1/2 hours set last year by Lars Giertz of Houston.
An assault on world records cannot be made without the help of
many people. My greatest help came from Dean Smith, whose engineering
expertise and machining abilities were indispensible. Dean and I
kicked around many ideas and went down our share of dead ends before
finding the right combination. Dean made the pressure regulator,
the parts for the diesel conversions, and many other parts used
in the assorted experiments we tried. I also benefitted from discussions
with Don Jehlik and Cliff Telford, both world champions and gentlemen.
Editor's Note: A straight-line distance RC performance record
of approximately 266 miles was established by the author on August
16. The record is in the process of being homologated by FAI. Take-off
was at 9:31 a.m. from Newton, Kan. and the landing took place at
4:49 p.m., at Enole, Nebr.
Posted March 23, 2012