For perhaps most people engaged in
model airplane flying today, it is hard to imagine a time when having even a single channel
of remote control was considered a giant leap in capability. Commercially available rudder-only
(RO) systems came on the scene back in 1950s or so, and were common up through the 1970s.
The earliest systems used tube amplifiers and lead acid batteries, but by the time they
disappeared from the pages of modeling magazines transistors and nickel cadmium (NiCad)
batteries were the norm.
At first, simply successfully taking off, flying around a bit, and landing successfully
was considered quite feat. As time went on and pilots became more adept and equipment
became more reliable, that was no longer good enough. There is something about a model
airplane that begs for aerobatics, and those aero pioneers were not about to let only
a single control- rudder - stop them from performing loops, rolls, inverted flight, and
even Immelmann turns. This story from the July 1957 issue of American Modeler
is a tutorial on how to become a rudder-only aerobatic pilot.
You Can STUNT Your Rudder Plane
Most R/C plane kits include written instructions for building the plane and some go
quite thoroughly into preliminary balance. But they leave you right there with nary a
word on aerobatics. In one way this is understandable, for many builders have no particular
interest in stunting-at least in the beginning. Just as well, too, for it is smart to
learn how to control your new R/C model in gentle turns. Better to get thoroughly familiar
with its action in general before you start to get violent.
Incidentally, it is always good practice to go through the AMA R/C Pattern Event maneuvers
rather than just making aimless turns in the air; you'll find it sharpens your control
quite a bit to have some definite goal to attain, like producing several perfect pattern
sequences in a row.
But now let's say
that you have learned to control your plane pretty well, and are starting to "throw it
around" a bit. You'll be surprised at what you can do in this line with just a rudder
control plane. Beginning R/Cers can learn to do very acceptable loops, rolls, Immelman
turns, etc. we tell you how in just a moment.
First, a quick review of trim requirements. Every design has its own angular setup
of wing and stab, proper location for CG, motor offset and down thrust.
every plane is different; even planes made from the same plans may require different
Hidden warps, unnoticed fin offsets, even lopsided fuselages play their dastardly
part here. Rudder planes normally are adjusted to fly under full power in a moderate
and steady climb, with no "scallop" or swooping action. See Dwg. A.
Your trim should be such that when the engine cuts, the plane goes into a smooth glide,
likewise devoid of swoops. If it glides nicely, but climbs tab steeply, it is probable
that you need more down thrust; add this a little at a time.
If the model glides
straight, but tends to turn under power unless you keep giving, opposite rudder, you
should look to your engine offset-which means that you point the engine to one side or
the other, away from a straight ahead line. Dwg. B illustrates both down thrust and offset.
The latter usually is needed to the right, since torque reaction to the direction of
prop rotation tends to roll the model to the left under power; by pointing the prop slightly
to the right. you can compensate.
Models seldom need up thrust, or left offset. But we have flown one requiring the
latter, so you can't make hard and fast rules here. One other point: if you change the
size or pitch of the prop, you will usually find a different offset (and sometimes down
thrust as well) is required. This is entirely normal. In any case, before you go in for
stunting, try and get the plane to climb evenly and travel in a straight line.
While a model will fly nicely, and climb at a reasonable rate, with a given size of
engine, it is often necessary to increase the power, to get real stunt ability. Yet -
sad to say - some models won't stunt well. even if way over-powered; they just weren't
designed for it.
For best stunting,
of course, a light weight model is the thing: keeping the wing loading down is the surest
way to success. If you have a heavy model and just can't get it to loop, it may be necessary
to substitute next larger size engine. Before you do, though, try the easier tricks,
such as different sizes of props, hotter fuels, anything that will enable your engine
to put out more power.
R/Cers generally use larger props on their engines than will allow the latter to develop
maximum power. So try the next smaller prop diameter, or put on a narrow-blade prop if
you have been using wider-bladed ones. Heavy planes usually fly faster; if you have made
changes to your plane that give a weight increase, you might find it necessary to use
a higher-pitched prop to retain a good climb. If so, it would probably be smart to use
the next smaller diameter, to allow the engine to turn up at an efficient speed.
For flight in windy
weather, some modelers keep a special shim to slip under the trailing edge of the wing,
or to give a bit more positive angle to the stab. This makes the model fly flat and fast
and "bore" into the wind without excessive climb. But don't forget to remove the shim
if there is no wind next time you fly, or the model may make a long and shallow power
flight right into the ground!
One other necessity for good stunting is a fuel tank and feed system that will allow
top engine power in any position. Pressure tanks or those that have a swivel on the outlet
tube have been found satisfactory.
Now to the stunts themselves. A plane that is adjusted normally will drop its nose
when held in a sharp turn. If you hold the rudder full on for any length of time, a spiral
dive will develop. Try holding the rudder hard to one side (after you climb the plane
to a safe altitude) and note the reaction. If the ,nose drops rather sharply, speed builds
up and the plane spirals down at an alarming rate, you are ready for some stunting. (See
Dwg. C) If not, you probably don't have enough rudder action.
To stunt, you must have a means of gaining excess speed, and in a rudder-only plane
the only way this can be done is via the spiral dive (note that this is not a spin; we've
never seen a rudder-only plane spin-in fact many planes with elevator control can't be
made to do a true spin).
Probably the simplest
stunt is the Wingover, which can normally be accomplished by allowing the plane to gain
speed in a 180 degree turn, after which it will be headed down at a moderate angle. It
is then straightened out, whereupon it will start to climb due to the excess speed. Just
as it gets near stalling speed, With the nose pointed upward at a fairly steep angle,
you hit full rudder. This should bring it around 180 degrees again, and back down the
original path, as in Dwg. D.
Normally, the prettiest and cleanest maneuvers are made with an absolutely straight
and level recovery after you have finished the stunt; in a rudder plane, this is impossible,
but you can kill the excess speed by holding just enough rudder to let the plane turn
without losing altitude (that is, not enough so that it will drop into a spiral). Actually,
since practically all stunts produce a loss of altitude, it is smart to use up your excess
speed in a climbing turn, to get back the height you have just lost.
let's try a Roll. Here again, lots of speed is required; normally hot planes can gain
sufficient speed for this in a half turn of spiral. So do your half turn, give opposite
rudder to straighten out and start a climb, then hit hard rudder again, just as the nose
starts to rise. Dwg. E. Your plane should do what is generally called in R/C circles
a "rudder roll." Actually, this is a sort of horizontal spiral; just the same, it's very
spectacular! For this maneuver, you need lots of rudder action and a plane that really
travels. Plenty of power is also a necessity. A hot ship can do roll after roll, without
losing altitude, though you can lose height, if you wish; the roll is a fine way to bore
upwind in windy weather, since the plane can be held level, or can be brought lower,
while still heading directly into the wind at fairly high speed.
It might be thought 'that a model would roll best by taking advantage of prop torque--that
is, roll the opposite way from which the prop turns. This might be helpful in some case,
but it seems more important to roll in the direction that the plane turns the more sharply-which
isn't always with torque. Some planes will roll (and spiral dive, for that matter) only.
in one direction.
How about a Loop? Really very simple. You will probably need to hold the speed-gaining
spiral dive for at . least a full turn, and maybe two or three, for you'll need lots
of zip to go up over the top. As you pull out of the spiral with opposite rudder to straighten
out the plane and start it climbing, you might need to apply slight rudder either side
to keep it arcing up in a straight 'path; applying slight rudder is all you can do, besides
just waiting to see if she has enough speed to get up over the top without stalling.
Once over, you still keep neutral rudder (or give slight corrective blips) till the plane
has come back down to level again; it will be going at high speed here and you may be
able to do one or more additional loops without stopping! Dwg. F. Coming out of the last
one, put 'er into that climbing turn to get back all the altitude you've lost.
If you can do a decent loop and roll, you can combine parts of each to do two more
maneuvers-the Immelmanurn and the Split-S; actually these are exact opposites of each
other. For theturn and the Split-S; actually these are exact opposites of each other.
For the Immelmann, do a good half-loop, then right at the top, hit hard rudder (, do
a good half-loop, then right at the top, hit hard rudder (Dwg. G). Plane should roll
out without too much loss of altitude and be flying level in the opposite direction from
which it started the half-loop. Some craft have trouble completing a loop because they
don't have enough power (or are too heavy) to get up over the top, yet still retain flying
speed; such jobs often do nice Immelmann, though, tending to roll level as they lose
flying speed near the top of the loop.
A Split-S is just the reverse (Dwg. H); you do a half-roll, then just as the plane
is upside-down, hit a blip of opposite rudder to bring it into straight ahead flight.
It can go only one way - down - and will do the last half of a loop. Some planes lose
a surprising amount of altitude' in this maneuver, so do the first few high!
A good pilot with a hot and maneuverable plane can do a very reasonable Cuban-Eight,
but it takes split-second timing. Check Dwg. I first. You go into it from the usual spiral
dive, and work the controls as though you were doing an Immelmann; however, let the nose
of the' plane fall quite a bit after you get over the top of the half-loop, before you
roll out. The plane will then be headed downward when you simply repeat the Immelmann
with a delayed half roll, to complete the Eight.
Once you have mastered these
stunts, there's nothing much more we can tell you. Maybe you will find a way to do outside
loops with your Rudder-Only plane; if so, you tell us 1 .
As new techniques and ideas come along they'll be covered in "AM's" Radio Control
news'n'views column each month. Keep an eye on that department and advise us if you develop
any new maneuvers. Think of having one named after yourself!
September 14, 2015