Perhaps it is fitting that a man named "Wright" should have been
so successful in setting model airplane endurance records. Being
from New Zealand dismisses any possibility of a direct relationship
to Wilbur and Orville, though. Les Wright attributes a large part
of his success to having personally designed, built, and operated
a reliable radio control system for both his powered and non-powered
series of 'Mark' aircraft. His models were essentially very large
free-flight designs with radio control to keep them within eyesight.
There are multiple mentions of a 'relay-tor' device for control
surface movement. A Google search of the term turned up nothing,
but I assume from its description in the article that it is a combination
of a relay and actuator (hence the '-tor' part).
The Long Project
In Two Parts Part One
by Frank Bethwaite
The man who has accomplished more endurance flights than anyone
else in the world tells a fascinating story of experiments and developments,
good and bad, taking place over a period of many years. These are
the results in designs, glider and power, and in the radio.
The engine-on-strut designs were proved in
New Zealand. Author and power model, Mark 2.
Radio gear used on the record flight, relays
eliminated. Model capability over 40 hours.
My long-time friend Les Wright first flew a model under radio
control of sorts in 1935. By 1951 he had developed a reliable non-critical
system which was immediately adopted and used with every success
by the group which had gathered around him. Radio gear that worked
every time focused attention on the model, which until then had
been only a test vehicle. With radio problems no longer dominant,
the strictly radio members of the group dropped out, and diehard
free-flighters, their imaginations stirred by the design challenge
and ultimate possibilities of radio control, moved in one by one.
I was one of these late-comers. Les gave me a radio set, and
I had perforce to think of something to do with it. The absolute
world duration record had always challenged me. Design of the model
was not too much of a problem, but it had been idle to dream of
keeping a free-flight model in sight, hour after hour in New Zealand's
windy climate, unless the timekeeper was carried by aircraft. Cost
of a series of attempts would be prohibitive - I never fooled myself
by thinking that the first attempt would be successful. Overnight,
as it were, radio control offered me a cheap and practical method
of keeping the model in sight of the time-keeper, as opposed to
keeping the time-keeper in sight of the model. The project was born.
Les and I teamed up, he to supply the radios, and I to handle the
airframes, with a new and startling purpose behind radio control.
Our plan hinged upon the climate around Auckland. Prevailing
wind is Westerly and squally, but in summer steady North-easters
often blow. At any season there are a few random near-calm days.
Discussion with forecasters and study of meteorological records
convinced me that it would often be practical to slope-soar a glider
over suitable terrain, and that this technique offered real possibility
of long durations. For the rare calm days a power model would obviously
be required. Two models were envisaged from the outset; a glider
for slope-winds and a flying fuel tank for quieter days.
Les Wright's radio gear is a super-regenerative receiver wired
directly to an escapement which we call a relay-tor. No sensitive
relay is used. A hard valve detector (1R5 is transformer coupled
to a hard valve output (3S4). The transformer attenuates all frequencies
except the characteristic hiss of the idling super-regenerative
receiver. This hiss, rectified, is used to back off the output valve.
Hiss disappears on receipt of signal; the output valve then conducts.
Filaments use 1.5 volts at 150 ma. Plates use 45 volts: approximately
1 ma runs the detector and another 1/2 ma "leaks" through the output
stage to the relay-tor with idling rising to about 9ma on receipt
of signal. This current change from 1/2 to 9 ma at 45 volts has
proved enough to operate a well-made escapement direct; several
models have thus been flown. But the standard relay-tor is an escapement
mechanism fitted with a trigger arm so that friction loads on the
armature are reduced to one-fifth of the direct load. Operation
is left-center-right-center with turn held as long as the key is
The transmitter radiates on 35.7 mcs. Power, at 0.8 watt, appears
trivial compared with contemporary overseas practice, but control
is certain up to extreme visual range at least.
Fig. 1 - Sailplane Mark 1
Fig. 2 - Power Model Mark 2
Fig. 4 - Sailplane Mark 2 and Mark 4
Fig. 7 - Sailplane Mark 5
The two-control system developed for use in later models employs
a rudder, relay-tor modified so that it will perform its normal
function and, in addition, will operate a second relay-tor when
desired. The principle is to arrange two series contacts such that
they will both be closed only if a very short pulse is transmitted;
at all other times one or the other is open. In practice, all normal
control of the model is deliberate; the key is held depressed for
a minimum of about one-quarter second even when throwing away an
unwanted turn, and a definite snap action is necessary to select
the second control. The method is to slow down the rudder relay-tor
drive-shaft with a Bonner-type rattler, and to fit the two series
contacts, one as the "up "stop of the armature, and the other a
wiping contact set to make and break slightly before the "turn"
position of the drive-shaft is reached. During all normal deliberate
operation, the armature is always down and the first contact open
as the drive-shaft moves 90 degrees from neutral to turn, thus the
wiping contact does not complete any circuit. But, if at any time
a pulse is transmitted short enough to pull the armature down and
let it up again before the drive-shaft has rotated past the wiping
contact, then the two series contacts are both closed momentarily
and current flows briefly to operate the second relay-tor. No extra
batteries are needed and no modification to the transmitter is required.
We call this system "quick-snap"; it has proved absolutely practical
and reliable. Perhaps its greatest virtue is that its nature of
operation is such that confusion in the mind of the operator does
The practical virtue of this gear is its mechanical simplicity
and ruggedness, its freedom from requiring critical electrical adjustments,
and its tolerance to voltage variation. Installed in the model and
tuned, it will operate over a filament voltage range from 1.6 to
1.1 volts, and an HT range from 45 to 32 volts. Although lightweight
batteries are used in small models, it is customary for large models
to carry HT batteries of 8 ozs. weight which generally last six
months or more. Filament supply is usually one 3 oz. cell. Receiver
and case weigh 3 ozs., the relay-tor 2 1/2 ozs.; total installed
weight is normally 16 ozs.; plus another relay-tor for two controls.
The first glider (Mark 1) was designed to carry 16 ozs. of gear,
to fly at 30 feet per second or more, to be big enough to be seen
at range, and to be really tough. Following closely the proportions
of a highly developed A2 glider, it came out at 80" span, 60" long,
625 sq. ins. area with a 13% thick flat-bottom section, 80" of 1/4
x 1/24 rubber, which I wound 30 turns per inch (50% breaking) to
2,400 max. A 3 oz. Venner 5-amp/hr. accumulator stored a potential
20 hour's filament supply.
It still amazes me to recall its first flight. One warm day in
Sept. '52 we took the model to an inland valley up one side of which
a gusty wind was blowing. Once trimmed, it soared up and away from
a hand launch, flying easily and cleanly at several hundred feet,
and control proved so docile that I let a bystander fly it for several
minutes. After nearly half an hour the model was deliberately flown
into the downdraught over the windward side of the valley, and I
went home thinking how easy was this technique.
It was several months before I made the next successful flight,
and about two years before I found out why that first flight had
That glider was taken out, in the weeks that followed, on every
possible occasion, first to this slope and then to that. Gradually
I learned that a slope is not enough - a very abrupt rise is required.
I saw that unless the model is launched and can be held above the
level of the crest it will probably never rise at all. (This makes
hand launching critical at all times.) I found that the area of
lift near the crest of a slope is very small indeed, and is so close
alongside the crest that the slightest control error is disastrous.
I learned that lift could be expected from a warm wind, and that
little lift could be expected from even a strong cold wind. I discovered
the fearful turbulence that exists near the ground behind the crest,
and even in front of it unless the wind comes clean to the slope
- for this reason I now reject all slopes other than those facing
the open sea. The model meantime took a fearful beating, because
by the very nature of slope soaring a model hits steep country hard.
I watched seagulls as I had never watched them before, and observed
that at times they soared low along the exact line of the crest
with every bird following exactly the same flight path, yet a few
minutes later these same birds would be soaring hundreds of feet
up with strong lift evident over the whole area. I saw gulls below
crest level flapping along at the same time as those above crest
level were gaining height soaring. I worked out the technique of
hand launching as hard as I could throw, straight into wind off
the crest, with turn on such that the model would turn out of the
stall and hold the vital 20 or 30 feet gained. Slope soaring proved
bitterly cold. I wrapped up in an old duffle coat even in summer.
It was a great shock to my free-flight soul to go about eyeing the
country for the steepest and most exposed and windiest ridge for
a place to fly. Through all this time of disappointment and failure
there were many occasions when I would have given up if it had not
been for the memory of that first flight - which had soared away
so well, I now realize, solely because the valley had been emptying
itself of a big thermal bubble and this had been the key to the
first 100 feet of altitude.
Experience accumulated until I was able to pick those conditions
under which a clean launch and sustained flight could be expected.
On Jan. 7th, '53 a group of friends gathered and we flew the glider
for 1 hr. 9 mins. and landed it deliberately. The current FAI R/C
power record was then 40 mins., and no glider record had been established.
The object of that flight was to prove the paper channel between
New Zealand and FAI. A record claim was put in.
The N.Z. Model Aeronautical Assn. is affiliated to the Royal
N.Z. Aero Club, which is affiliated to FAI. The flight was accepted
as an NZ record, and forwarded to FAI on my behalf. In no time at
all FAI approval came back, followed in due course by the formal
"Diplome de Record." It was as simple as that.
Any project which, from the outset, envisaged durations of 8
hours or more was clearly going to run into trouble over the matter
of officials. The NZMAA is an old established body (early 1920's)
and their rules are as strict as any in the world. It is required
that two senior affiliated members be present throughout any record
flight, one to time and the other as witness. My work as a trans-ocean
airline captain knows no weekends, and the probability of my being
free on any day when the weather would be suitable for an attempt,
and at that time being able to talk two friends into devoting virtually
their entire day towards helping me on what would be on most occasions
yet another unsuccessful endeavor, looked remote. I perused the
FAI code sportif, .and asked the Council of the NZMAA to consider
the problem and advise me if any alleviation were possible. They
were most cooperative. A strict reading of the code sportif indicates
that an endurance record must hang on the testimony of one timekeeper
- "an official appointed by the National Aero Club" - and that the
various other officials need not be present throughout the entire
flight. (Consider, for example, the case of a model being followed
by a timekeeper in a light aircraft.) The NZMAA ruled that in the
case of a notified project which was continually under observation
by their officials, the testimony of one senior affiliated timekeeper
would be held to comply with FAI, provided that the launch was witnessed
and the flight in all other respects complied with the stricter
NZ rules. They also ruled that small movements of the transmitter,
essential to the operation of the flight, were considered permissible
within rule; "The transmitter shall not be moved during flight."
This was in response to two specific problems. I have often used
the runway of an airfield for take-off in an attempt with the power
model. Once airborne, it is mandatory that I quit that runway! And
cliff soaring has hazards enough without trying to land the model
right on the brink. If a model has been held under control for several
hours, it is clear that a small movement to some nearby vantage
point, for the purpose of a better and more feasible approach, should
not be held to invalidate the concept of control.
The glider was by now thoroughly "shocked." It was stripped and
re-glued, and fitted with a tow-hook. It surprised us. Delightful
to tow in a breeze, it carried 700 feet of 14 lb. nylon right overhead.
As we learned to handle it better in the pleasant flying over a
smooth airfield, we realized that to tow-launch the start of a slope-soaring
flight would be practical and would eliminate entirely the critical
hand-launch. So it has proved except for occasional trouble with
severe turbulence behind the crest. In the next few months we tried
twice to exceed the hour, but the model blew away backwards once
at 51 mins., and again at 63 mins. There was no room inside that
model to fit a second control for elevator, so, as the power model
was by then causing enough trouble, the glider was relegated to
The radio had never missed a beat. And there we can leave the
glider project meantime.
In designing the power model, I envisaged use of 2-control radio
gear such that the model could be both turned and controlled in
altitude. By FAI definition a model must weigh no more than 5 kilograms,
or 11 1/4 lbs. Radio gear would weigh 1 1/4 lbs. which left 10 lbs.
to be split between airframe and fuel. Throttle, to permit controlled
descent under power, was desired, and with these thoughts in mind
many likely motors were tested. The ideal motor would be reliable,
have a low specific fuel consumption, and be easily throttled.
Spark ignition burned little fuel and throttled well, but I could
find no way to prevent plug fouling during prolonged idling. Exit
spark. Glow motors were reliable, and throttled beautifully, but
they burned so much fuel as to compromise the whole idea of long
duration. Exit glow. Diesels seemed reliable and burned little fuel.
Tests began to concentrate on the Mills 1.3 cc. It would run indefinitely
using about 3.3 ozs./hrs., but, set like that, it would not idle.
With compression backed off and mixture enriched it would run just
as well, and idle well too, but at a consumption of 6 to 7 ozs./hr.
Exit idling. The concept changed to a model running at constant
power using elevator trim control to shallow dive to reduce altitude.
Sailplane, Mark 5, used to set International
records. On tow-launched flights, ship went overhead on 700
feet of line. Much was learned from a study of sea gulls in
flight, cloud formations.
Two tin cans soldered end to end made up
a pressurized tank for Mills. Span nearly 10 ft.
Power available would be about .075 hp., and thrust at a flying
speed of 25 ft. per sec. would be 10 to 12 ozs. assuming a prop
efficiency of 40%. As this design, too, would follow the proportions
of my well investigated A2, I was able to be reasonably certain
of what could be done with 10 ozs. of thrust. The A2 developed a
Lift/Drag ratio of 12.5/1. I believed that, by keeping the power
model as clean as possible, in particular tolerating no undercarriage
drag, it could be designed to develop at least 10/1 L/D. Thus with
10 ozs. thrust it should fly at 100 ozs. or better. I aimed for
a 30 oz. frame, 20 ozs. of radio, and 50 ozs. of fuel, and built
power model Mark 1. Span was 116", chord 12.5", area 1400 sq. ins.
Fuel was stored in a long plastic bag running span-wise between
the front and rear wing spars, and fed by gravity to a float chamber
near the motor. This model was built to its design weight, and flight
characteristics were most promising so far as ultimate performance
was concerned; but excessive flexure of the tail booms under elevator
download was at first frightening and shortly thereafter disastrous.
(Editor - This model had a built-up pod-type fuselage terminating
behind the trailing edge, and two long, slim booms extending from
under the wing, on either side, back to the tail, the stabilizer
being set atop the two vertical fins.) The faster the model flew,
the further back the center of pressure moved, and the greater became
the download required from the elevator. This download bent the
booms further down and made the elevator more positive, thus merely
aggravated the dive. It was realized at the same time that the method
of fuel storage was unsound as it would split the wing wide open
whenever the model took a bump on the wing tip. The concept was
revised to a conventional layout, housing the fuel within the fuselage
under the wing. The motor remained a pusher, partly to avoid slipstream
drag, but mainly to avoid the drag of a long undercarriage. Main
problem now was fuel storage and feed to the header tank.
Experiments with glorified Jim Walker tanks of plastic or rubber
which held 50 ozs. always eventually leaked or burst. Finally, I
decided that can manufacturers knew most answers about storing liquids,
and I soldered two 4" tin cans end to end. This tank, 4" dia. and
9" long, weighs nearly 8 ozs. but it has never leaked nor burst.
Fuel feed is by pressure. A stud drilled with an 80 gauge hole tapped
into the Mills crankcase delivers pressure enough to force fuel
up 16", and does not affect running.
The engine has its contra-piston tightened by punching while
in position. It is mounted on a rigid dural and balsa spar which
is itself spring-mounted to the fuselage. The whole assembly balances
almost at the crankshaft. The motor runs sweetly and smoothly with
negligible vibration passing through the springs to the fuselage.
The header tank is very lightly spring-mounted to the motor, such
that fuel lies quiescent while the motor is running. The float is
a piece of 1/4" balsa dipped several times in auto lacquer. The
float valve is a pin-head. Filters are tiny discs of filter gauze
thrust into fuel tubing with a matchstick. The whole system is simple
and visible, and it works.
Various fail-safe devices were considered, and an Aneroid capsule
was adapted to cut off fuel above 1000 feet, but it proved impractical.
None have been used.
Radio gear was initially a standard receiver operating a Bonner-type
escapement direct; the third position, when held, made a series
contact which reversed the elevator relay-tor setting. While this
control operated satisfactorily enough, I found it clumsy and unhandy
to use when in any trouble, and later changed it to "quick-snap."
Relay-tor power was a 10-foot length of 1/4 by 1/24th rubber which
I wound with 4,000 turns maximum.
Weight had by now risen to 77 ozs. without fuel. Flight and ROG
at this weight were encouraging. Fuel was added 10 ozs. at a time,
and the prop was cropped and tailored as seemed best as the load
increased. A perfectly balanced 9" by 4", of reasonable blade area
at the tips, thinned paper thin at the tips and highly polished,
proved best. At 110 ozs. the wheels flattened sideways under the
load and had to be replaced with stronger ones, after which the
model proved capable of consistent take-off and climb with the tank
full at an all-up weight of 125 ozs. It would without doubt ROG
at greater weight, but it is my practice to trim to use the excess
power to give more speed, for the model flies woefully slow.
Polite skepticism has been inferred in some overseas magazines
at the report of ROG's at this weight with only a .08 cu. in. diesel
for power. Given a free-rolling undercarriage directly under the
C.G., and unlimited hard, smooth runway to accelerate over, take-off
is not a problem. In theory at least a wing close to the ground
is more efficient than one in free flight, and thus it should be
possible to ROG at a weight at which the model would be unable to
climb away. In practice this model accelerates very slowly, waddling
for the first ten seconds, and a still air take-off uses up to 200
yards of runway and flat airfield in plenty thereafter, for the
angle of climb is almost zero.
So much for the model. In order to fly it seriously a day has
to be picked in advance during which the wind is unlikely to exceed
ten mph, and the necessary officials must be persuaded to come to
time and witness the take-off, which is best made about dawn to
take advantage of the morning calm.
At this point I must introduce Don Wilson, a quiet and talented
civil engineer. Top line with Wakefields, and a brilliant performer
with a hot stunt ship at the end of the lines (something I could
never master), Don now builds flawless and imaginative radio models
and flies them hard and well. From this point on, this story tells
how Don and I, as a team, have worked to turn theoretical possibility
into witnessed durations.
(To be Continued)
February 6, 2016