Way back in 1975, my friend,
Jerry Flynn, and I 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 article titled, "652 Miles
Per Gallon," in the November 1975 issue of Model Aviation magazine.
We were not at all involved in all the painstaking effort that Dick had put into
preparing his model for the record flight. This account of William Bertrand's trials
and tribulations in finally setting a new radio control world endurance record is
valuable insight into what it can take to achieve such a goal. test after test on
engines, fuel, airframe, radio system, fuel tanks, fuel feed systems, and other
minute details would likely frustrate most people to the point of abandoning the
effort, but it is persistence and good nature that keeps people like William and
Dick going.
Eleven Hours of Luck - Record Breaking Mystic

A proud man with the smile of success. Note reflectors located
for extra visibility.
William F. Bertrand
The endurance mission presents the greatest design problems by far.
How the world's RC record was broken holds interest for all of us.
At one time or another, I think we all read about somebody setting a record and
say to ourselves, "I think I'll take a crack at the record!" This happened to me
several times before I ever got beyond the stage of talking it over with friends.
When Bob Dunham broke the speed record, I started sketching designs. The final urge
came in the spring of 1966 when Red Gunning, who had been working on the endurance
record for some time, asked Bill Laubengayer and me to act as timers. He had to
land after six hours with radio trouble, but when I watched Red, I thought this
shouldn't be too hard.
I should try instead of just thinking and talking about it. Then Red threw in
the final challenge, "Why don't you try it?" I couldn't resist any more; I would
start my ship when I got back from the Nationals. I looked at Red's design, got
all the info I could from him, and started to give the design of my ship some serious
thought. I finally got started in Sept., 1966.

Near the end of the flight, the Mystic makes a low pass. Many
Indian City RC members helped with attempt.
I needed a ship that would carry a maximum payload with a minimum of power. Since
the radio was a constant weight regardless of ship size, I decided the bigger the
ship, the less percentage of load the radio would be. The FAI rules allow 2325 sq.
in.; I decided to go with 2300 sq. in. to stay within the safe limit. The next problem
was power. How small an engine could I fly with this monster? I thought maybe a
.19, but probably a .25 or .29, depending on how light I could build the ship. I
started the design using every trick I knew to keep it light and came up with a
couple of new ones along the way.
The fuselage was built with a triangular section behind the wing, because it
saved the weight of one piece of quarter square 36" long. The fuselage cross section
was kept to a minimum because this meant less wood, silk and dope. All wood was
selected with light weight being the prime concern. At this point, the fuselage
was constructed and turned out very well at 4 1/2 ounces without covering.
The wing was next. A thick Clark Y-section was chosen for its high lift and tolerance
to changes in the center of gravity which might be encountered with fuel sloshing
in the tanks. After much thought, it was decided to use geodetic construction. By
this method, a wing could be built much stronger than any conventional wing. The
wing looked very difficult to build, but once started, I was amazed at how simple
a project it was.
There are three spars in the wing: On the inboard sections they are made up of
two 1/4" squares with 1/4 x 1/8" cross-members. On the outboard sections, the spars
are made of two pieces of 3/16" sq. with 3/16 x 3/32" cross-members. The leading
edge is made of 1/16" sheet rolled into a 1 1/4" tube with 1/4" thick styrofoam
plugs every 3" for compression strength. The trailing edge is conventional 1/16"
sheet, top and bottom. The geodetic structure is made of 3/16 x 1/16" on the center
sections and 1/8 x 1/16" on the outer sections. With these methods, the wing weighed
only 22 ozs. uncovered and would take three G's on an 11-lb. airplane before it
was even covered. This would likely double with covering, but I didn't have the
guts to try it after it was covered. This point was pretty well proven later, when
on a landing, the plane flipped over with a full load of fuel and remained undamaged.

Skin and bones in flight. Bill removed all the color and adhesive
from the MonoKote where it does not touch the frame. Less weight. Structure stained
by RIT dye aided visibility.

Weight and wing and tail area are limited by FAI rules to 11
lbs. and 2,325 sq. in. Note how the tank fairs into the fuselage shape. Proper tank
design and fuel delivery system all-important.
The stab uses a symmetrical section and was made with a single spar built up
of two pieces of 1/4 x 1/8" with 1/4 x 1/8" cross-members. The leading and trailing
edge are 1/4" sq., with the geodetic structure being 1/8 x1/16". The completed stab
weighed only 3 ozs. without covering.
The entire model was covered with yellow MonoKote, because it has a good durable
finish without more weight than lightly doped silk. This weight was then drastically
reduced by removing the color from the MonoKote everywhere except around the edges
of each panel. It was necessary to leave this, as the color is also the glue that
holds the MonoKote. I also felt that I needed some color to make the ship easier
to see at high altitudes. Visibility was further improved by spraying the entire
structure with red dye dissolved into thinner. The dye was Rit clothes dye (I used
one package dissolved into a pint of thinner). The package of dye weighs about 1/2
oz. and thinner completely evaporates. If it all went on the plane, I would add
only 1/2 oz. About 95% of the spray went on my basement floor. Reweighing after
a couple days, I could not detect any increase in weight over the undyed structure.
I now had a ship complete, less radio, servos, engine and tank, that weighed
only 1 lb. 13 1/2 oz.; it looked like I could make the minimum weight. Decided to
use a Min-X reed-type radio, as it has several advantages for this kind of flying.
One of these was its superior interference immunity, due to the sharp selectivity
of the reeds themselves. Another is the low battery drain on the receiver and servos
when no command is called for. To help keep the battery drain as low as possible,
I used very wide neutrals on the elevator and rudder. This was done by applying
small strips of MonoKote to the ends of the printed-circuit return switches of the
Controlaire servos. I used half the rudder travel as trim, and the elevator was
trim from half way up to full down. This system allowed the whole flight to be made
with only an occasional short beep on the transmitter; the servo motor having to
move only a couple of revolutions.
I followed Red's lead on the batteries and used Burgess Alkaline type energizer
cells. In addition to this, I sat in the basement watching TV for many an hour running
tests just to assure myself the batteries were adequate.
The engine was the real problem now. I started running tests on everything I
had and found nothing significant until I came to an old Enya diesel. This engine
would swing a 14-6 prop 3,750 rpm on only 4 ozs. of fuel per hour on the ground.
Later, this jumped to about 5 1/2 ozs. in the air. The engine worked well, but refused
to throttle almost entirely. I decided to go with the Enya, and let it run full
bore.
An important element in the success of the attempt was the reliable Super Tigre
.15 RC diesel, which turned the 12-6 prop powerfully and had a steady slow idle.

The fuel system between he main tank and the engine has a header
tank with cork float and valve. It's simple and effective.

Fueling the Mystic with three quarts of diesel fuel - 20% Ucon
oil, 40% ether, and 40% kerosene.
The next problem was a float chamber. I tried several different designs without
making one work to my satisfaction unless it was too large or too heavy. The final
design turned out to be simple and light. It was made from a cut-down 6 oz. plastic
bottle for the reservoir with a metal lid that would just fit the inside diameter
of the bottle. The lid was held in by three screws around the outside edge. Through
the center of the lid, was soldered a piece of 1/8" brass tubing extending :1/2"
inside and 1" outside. This tube had 3/4" piece of neoprene tubing attached on the
inside. The float was a cork with a piece of .032 music wire stuck in the top. This
rode inside the brass tubing and a blob of solder on the wire would close off the
neoprene tubing when the float reached the proper level.
The first test flight was made on Oct. 16, 1966, with just an 8-oz. clunk tank
stuck in between the rubber bands on top of the wing. The ship handled like a dream,
but didn't prove anything, as it weighed only 4 lbs. 2 oz. at this point. The Enya
with a 14-6 would take the ship up to about 4000' in less than a half hour.
The following Wednesday, Red called me and said he and Gordon Pearson were going
to make an attempt on the next Saturday; could I make it? I told him I would try.
I still didn't have a tank and didn't have time to experiment with a plastic for
vacuum forming that would hold up in the fuel or even find out if I could get off
with a full load of fuel. I switched to a K&B .45, as I knew this would have
the power to get the ship up there. For a tank, I would use a plastic gallon fuel
jug strapped on top of the wing. I had to have some new fuel, and I knew nothing
about fuels. I went back and reread Maynard Hill's article; decided to try his mixture.
It worked so well, I was amazed. I ran tests in my garage (to keep the noise down)
on the engine Wednesday and Thursday nights. Friday night, I flew two hours with
the K&B .45 and gas mix; it worked. I called Red that night and we agreed to
try for a 6 a.m. takeoff.
Saturday, Oct. 22, I was up at 4 a.m. calling my crew: Paul Secan, Bill Laubengayer
and Al Olada. By 5:30 we were at the field. Red was delayed until 7:00. We couldn't
do anything until he got there, as he had the scales to weigh in with.
Red and Gordon were in the air in short order. They had followed my lead and
installed diesels in their ships while I had gone backward, and was using glow.
After weighing, fueling, and reweighing, I tried to start the K&B only to find
my starting battery dead. We tapped one cell on the car battery and got started.
Everything seemed all right and the .45 pulled the ship with a full gallon of fuel
like a skyrocket. I let it climb to about 1,000' and throttle back - then the trouble
started. The engine started to get rich and the ship started down; high throttled
again, and it didn't help. The wind was now gusting about 15 mph and on landing,
the wind caught the Mystic and turned it upside down. We all thought that the wing
had had it. The geodetic construction paid off, as she just bounced on the wing
like a rubber ball. Upon inspection, we found only a couple of spar cross-members
knocked loose.
Why had the engine suddenly gone so rich? A hurried job on a fuel filter had
been done the night before. This had been sealed with Selastic rubber, which didn't
have sufficient time to cure. A strip of this rubber had gone down into the float
chamber and caused it to stick, flooding the engine.

Min-X reed system with very wide neutral Controlaire servos for
minimum battery drain and maximum interference resistance.

The tank is the bulky thing below the wing. It is made up of
balsa and brass. All fueled up, the plane weighed 11 pounds at takeoff.
The float chamber was cleaned, filter removed, ship refueled and reweighed for
another attempt. Now the engine would not keep running. I added propylene oxide
to the fuel to help the ignition. This worked, only now the K&B was running
too hot from lack of oil. One thing led to another and pretty soon it was too late
to make an attempt; it would be dark before the record could be broken.
Both Red and Gordon were having trouble with their engines and had to come down
after an hour or two on several different attempts.
During the winter, I built a tank of balsa that would attach to the wing. It
looked like a cabin sitting between the wing and fuselage. The tank was lined with
drafting vellum and coated with epoxy. This tank would hold a gallon of fuel and
added only 3 oz. to the weight. About this time, I was able to obtain a Super Tigre
.15 RC diesel and tests showed it would turn 4,000 rpm on the 14-6 at almost the
same fuel consumption as the Enya. This extra rpm would help on the takeoff and
the Tigre throttled down to about 1,000 rpm without ever missing a beat. I couldn't
have asked for more.
I started to experiment with diesel fuel and tried many different combinations
before coming up with the final mix. This fuel was 20% Ucon oil, 40% ether and 40%
kerosene. I used the Ucon oil instead of castor oil because it does burn; this,
in a small way, contributes to the power and makes for a cleaner ship. I think a
good, clean, all-around diesel fuel would be 25% Ucon 37-1/2% ether, 37-1/2% kerosene.
Now everything was ready. All we had to do was wait for spring and good weather.
In April, I made a test flight and everything went fine. On the test flight, I used
an 8-oz. plastic tank tied on top of the wing, in order to keep the main tank clean.
We had set April 22nd as our first attempt, but had to cancel as the wind was up
to about 25 mph; much too high for a ship of this type.
The next attempt was set for May 6. On the Wednesday before, I decided to try
the ship with a full load. I still flew using the 8-oz. tank above the wing, but
filled the main tank with water. This was intended to keep the tank clean and would
weigh about a pound more than the fuel. The water kept the tank clean, along with
the radio and servos. After an hour flight, I brought the Mystic down and found
the tank had leaked. There was a half inch of water in the fuselage and the receiver
was half covered. I still find it hard to believe that the receiver was still working;
maybe I should try a submarine.
I was convinced the extra few ounces for a brass tank were well worth the safety
of not having a repeat of that flood. A brass liner was made and installed inside
the wooden structure at a cost of 4 ozs.
On Saturday, May 6, we were all at the field at 6 a.m. The plane was weighed,
fueled, reweighed and in the air at about 7:30. The flight ended after seven hrs.
59 mins. I had spiraled down from about 4,000', and the engine quit about ten minutes
later. It was assumed that the fuel feedline had lost its prime, as fuel went to
the front during the spiral, and the fuel line to the float chamber was high in
the front of the fuselage. A new feedline was made so that I was sure flow was downhill
all the way.
On Saturday, May 13, 1967, I was up again at 4:30 a.m. calling the crew. We were
at the field at 5:45 weighing in; the empty weight was 5 lbs. even. I decided to
carry the same fuel as the week before (3 quarts), because I had had a quart left
in the tank after eight hrs. The fuel consumption goes down as the ship gets lighter,
requiring less power.

An important element in the success of the attempt was the reliable
Super Tigre .15 RC diesel, which turned the 12-6 prop powerfully and had a steady
slow idle.
I hand launched the Mystic at 6:21 a.m. The Super Tigre was turning a 12-6 at
6,000 rpm and she climbed out beautifully at 10 lbs. 2 oz. The sun was shining,
and the sky was full of small clouds at about 10,000'. This meant a lot of thermal
activity when it got a little warmer. After about five minutes, I had to throttle
back as the ship was already getting too high. About 9 a.m., the sky started to
clear; by 10, there wasn't a cloud in the sky. I couldn't have had a better day,
as this meant I wouldn't have to fight the up and down drafts. I could relax on
the chaise lounge and occasionally make a correction. About 11 o'clock I wanted
more down trim and found I was already in full down. At this point, I assumed the
elevator had slipped out of the saddle; but after the flight was over, we found
I just didn't have enough down elevator. This problem never amounted to anything,
as the wind never got up to more than about 10 to 12 mph; but it could have been
a real problem.
I can't say that anything else unusual happened on the whole flight. She just
flew and flew until at about 5:34 p.m., the Super Tigre ran out of fuel. The airplane
was about 200' in the air. I made one pass down the field; turned around and landed.
The touchdown was at 5:38 (only 16' from the point of the takeoff) 11 hrs. 17 min.
and 47 seconds later. (I'll bet I get more flying time in one day then a lot of
you fellows do in a month.) Upon examining the ship, a pint of fuel still remained:
enough for at least another couple of hours. The fuel filter was plugged, causing
the engine to quit.
All the equipment used was strictly stock. The only changes being that of adding
MonoKote to the servos to make them have broad neutrals. The Min-X was a set that
had been used for several years, prior to being installed in my ship.
I wish to take this opportunity to thank my wife (Shirley), Red Gunning, Paul
Secan, Bill Laubengayer, Clyde Atkinson, Jack Steele, Don Gaskell, Tom Bell, Tom
Byrnes, Maynard Hill, The Indian City Radio Control Club, Min-X, Super Tigre, Controlaire,
Top Flite, Sig and many others who in some way contributed to my being able to set
this record.

Mystic Radio Control Model Airplane Plans
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