Control Model World - Nov '95
by Stan Yeo
During the non-flying
periods of my trips to the slopes I regularly lapse into my 'Desmond Morris' mode (you
know, him of the Naked Ape and Human Zoo fame) and observe the way people fly their
models. This is quite enlightening as it is often possible to highlight areas of weakness
in a modeller's flying skill and predict the type of accident that will befall them (watch
out Stans about!). This is not always the case as some models demand so little of the
pilot, except on landing, that it is difficult to form an opinion. As a result of these
observations I have come to the conclusion that most modellers fly very conservatively, or
at least the ones I meet. Very few flyers 'throw' their models around as if there were no
tomorrow. Most are content with stooging around and doing the occasional loop and the odd
roll. This is in no way meant as a criticism of this style of flying, each to his own. The
object of the exercise is to enjoy ones-self and I have spent many a happy hour cruising
up and down a slope in light lift on a balmy summer's evening. But when the lift is good I
often ask myself why is it that modellers are not a little more adventurous in their
flying. Is it because they have no interest in aerobatics or is it, as I suspect, a lack
of confidence to have a go, after all nobody likes to take their model home in bits.
Whenever I bend a model two thoughts race through my mind. One, how am I going to repair
the model so that it is still presentable, and two, how am I going to find the time to
carry out the repair?
'conservative' flying does little to improve overall flying skill or increase confidence
in your flying ability. This was brought home to me a few years ago when I took up full
size gliding again after a lapse of almost 30 years (I learnt to fly in the ATC on T31s
and Sedburghs). I was never a confident flyer and in fact I gave it up originally because
someone scared the living daylights out of me on a check flight, consequently the things
that frightened me then came back to haunt me again. Spins in the 1960s were not a
compulsory part of the ab initio training but they are now so the closer I got to
re-soloing the more apprehensive I became until one day when I could put it off no longer
I bit the bullet so to speak. After doing a couple I was left wondering what was all the
fuss about. Now at the end of a good soaring flight, if I have height to burn off, I will
do a few spins, not only does it keep me in current practice but it gets the blood
circulating before I attempt a landing! The same applies to performing aerobatics with a
model, it develops flying skill and builds confidence. It could be the difference between
staying up in marginal conditions to ending up with a pile of bits or not flying at all.
WHERE TO START
The first point to
consider before attempting to fly aerobatics is the safety aspects of models, people and
property. If the sky is crowded or there are a lot of people wandering around or the
conditions are marginal it would be prudent to postpone the 'adventure' until conditions
are more favourable. After all you do not want to 'bend' your model let alone hit someone
with all the consequences that may bring.
Points to remember to
remember before carrying out aerobatics are:
1. Have you got
2. Is the model
structurally sound and capable of carrying out the manoeuvre?
3. Where are the other
4. Have you made
sufficient allowance for the model being blown back on the wind? i.e. is the model far
5. Have you learnt the
sequence of control movements required to carry out the manoeuvre? Practice them at home
with a friend holding the model and simulating the manoeuvre in response to your control
6. Plan the manoeuvre so
that the model exits the manoeuvre pointing into wind. If the model does not exit the
manoeuvre into wind it is likely there will be a panic control input to turn it into wind
away from the slope.
7. Where possible have
an experienced aerobatic flyer on hand to talk you through the manoeuvre and highlight
areas of weakness.
8. Always remember what
manoeuvre you are performing and the stage the model has reached. This may sound a bit
fundamental but you would be surprised how many flyers forget when things start to go
wrong and let 'instinct' take-over with often disastrous results.
CARRYING OUT THE
there are four distinct
stages to performing an aerobatic manoeuvre:
1. The preparation.
2. The dive.
3. The manoeuvre.
4. The recovery.
This consists of
carrying out all the necessary safety checks, some of which are mentioned above and
positioning the model in the right place in the sky to carry out the manoeuvre.
Positioning is the most important part of any aerobatic manoeuvre. If it is
not right at the start of a manoeuvre then it will get progressively worse during the
manoeuvre. Most aerobatic competitions, even at club level require that the manoeuvres are
carried out crosswind i.e. along the face of the slope. Into wind loops do not score
points! Initially flyers will find this difficult so until you are confident in performing
a manoeuvre into wind do not attempt it crosswind. Some may disagree with this advice but
the object of the exercise is to practice the manoeuvre and keep the model
in one piece. Into wind manoeuvres do not look as pretty as those carried out crosswind
but they do reduce the risk of a serious accident.
The ideal position to
start most manoeuvres is with the model straight in front of you, at an angle of
approximately 60 degrees to the horizon and at a height 150 - 200 feet (50 - 65 metres).
This is of course a subjective measurement as it is very difficult to judge a models
height without some form of external reference. The 60 degree angle to the horizon is the
critical yardstick as it helps to ensure the model is a sufficient distance away from the
slope to carry out the manoeuvre.
Once the model is in the
correct position it can be dived to build up speed to carry out the manoeuvre. Diving was
discussed at some length in an earlier article ( July '94 RCMW) but essentially the most
efficient way to build up speed with the minimum height loss is to dive at an angle of 15
- 30 degrees. The more efficient the model the shallower the dive angle. Diving at an
angle greater than 45 degrees is definitely not a good way to build up speed as so much
energy is lost during the recovery that often there is insufficient left to carry out the
manoeuvre properly. Most models need to be dived for at least 4 seconds before they have
built up sufficient speed to carry out the manoeuvre. The dive angle and dive time is very
much dependant on the type of model and the prevailing conditions and can only be
determined by experience.
Some manoeuvres such as
the roll require that the model be returned to level flight before the manoeuvre is
carried out. On some models returning the elevator to neutral is sufficient whilst on
others a small amount of up elevator may be required. Again experience will dictate the
amount of control required.
At the start of an
aerobatic manoeuvre the model has a certain amount of energy in excess of that which it
has in normal flight. It is this excess energy that is used to carry out the manoeuvre. If
too much energy is used at the beginning of the manoeuvre by erratic or excessive control
movements then it is likely that the model will fail to complete the manoeuvre
successfully. It will either 'flick' roll out of it in the beginning or fall out of it at
the end through lack of speed. A successful aerobatic manoeuvre is one that is performed
smoothly with energy used at a uniform rate throughout. Being able to fly smoothly is a
pre-requisite of a good aerobatic flyer. It also pays dividends in marginal lift
conditions when the slightest hint of over-control would mean a premature arrival.
On completion of the
manoeuvre the model must be returned to normal level flight either flying in the same
direction or in the opposite direction as in the case of a stall turn. Ideally, for novice
aerobatic pilots, the model should finish up pointing into wind, hopefully above slope
height! This means that before carrying out the manoeuvre the exit from it should be
planned in advance i.e. the model should be correctly positioned at the start of the
The basic aerobatic
manoeuvres most pilots would like to master are the Loop, Roll, Outside Loop (bunt),
Inverted Flying, Stall Turn, Cuban Eight and the Spin. There are others of course but they
are not within the scope of this article (it is long enough already!) As mentioned before
my approach to performing some of the manoeuvres may offend some dedicated aerobatic
flyers but please remember the purpose of this article is to encourage the inexperienced
flyers to have a go at slope aerobatics by minimising the risks.
This is the most basic
of aerobatic manoeuvres and one that I recommend is initially practised into wind.
Position the model as previously described i.e. straight in front, at an angle of 60
degrees and approximately 150 to 200 feet high. Dive the model, straight, wings level, to
build up speed, again as previously outlined and then slowly apply approximately 25 to 30%
of the available up elevator to smoothly enter the loop. If the model has insufficient
speed or not enough up elevator has been applied the model will stall. Recover and try
again, this time either building up more speed or using more elevator control as the
situation dictates. This time, assuming the model has sufficient speed and you have
applied the right amount of up elevator continue with the loop until the model is upside
down. When the model is upside down and has just started the recovery dive slowly release
some of the applied up elevator. This will help to prevent an inverted stall and to allow
the model to build up speed for the recovery to level flight. For the recovery slowly
re-apply the up elevator until the model is again in level flight. To prevent the model
zooming up into a stall it may be necessary to apply a small amount of down elevator until
the excess speed has been 'burnt off'.
Common faults when
performing a loop are:
1. Incorrect initial
positioning i.e. model off to one side, too low or too close to the hill.
2. The dive is either
too steep or not held on long enough to build up sufficient speed.
3. The loop is not
entered with the wings level and the model corkscrews off to one side during the loop.
4. Too much up elevator
at the start of the loop resulting in either a very tight loop that could overstress the
model, a flick roll, or the speed being 'scrubbed' off leaving the model with insufficient
speed to complete the manoeuvre.
5. Too much up elevator
at the top of the loop resulting in an inverted stall or poor recovery.
6. Too much elevator
during the recovery resulting in a zoom climb and stall.
introduction of rudder or aileron control when applying up elevator resulting in the model
'screwing out' of the loop.
Once you have
successfully looped the model a few times try a loop with a little more speed and less
elevator. This will open the loop out and should the model start to screw off to one side
there will be more time to apply control correction, that is once you have worked out
which way to apply it! Experiment with the manoeuvre until you have got the feel as to how
much speed and elevator is required. This will take a few sessions and when you are
confident that you have mastered into wind loops try crosswind loops. These are often
easier because you can see what the model is doing and there is less wind variation during
the manoeuvre. Take care though that you leave enough space between the hill and the model
because all the time the model is performing the manoeuvre it is drifting back towards the
hill. Remember also, which direction you need to turn to get back into wind after you have
completed the manoeuvre.
The roll is another
manoeuvre, the rudiments of which are best learnt flying into wind. the secret to
performing a good roll is to:
1. Have sufficient
2. Recover the model to
a level attitude before commencing the manoeuvre.
3. Good co-ordination
between the aileron and elevator controls.
To perform a roll first
position the model as for a loop but a little lower. A roll does not require quite as much
speed as a loop consequently the dive is shorter and can be started closer in. Dive as
before to build up speed, recover to a level attitude and apply full aileron. As
the model starts to roll inverted progressively apply a small amount of down
elevator to keep the nose up during the inverted phase of the manoeuvre. The amount of
down elevator required will vary widely from model to model; the less symmetrical the
section the more down elevator. Once the model is fully inverted and starts to recover to
the upright position so the elevator is returned to the neutral position. Sometimes it may
be necessary to apply a small amount of up elevator to stop the nose dropping at the end
of the roll but be careful as too much up applied at this point will cause the tail to
'wag'. For initial attempts it is often easier if you start the manoeuvre with a slightly
nose-up attitude this way there is often no need to apply down elevator correction.
As you have probably
realised the most difficult part in performing this manoeuvre is the synchronisation of
the elevator control input with the lateral rotation of the model and this is one reason
full aileron control is used during early attempts at rolling. Another reason is a large
proportion of models do actually require full aileron to successfully complete a roll.
Minor control input
errors will manifest themselves as rear end waggling. More severe errors will
result in loss of control. If this happens let the controls go and after a suitable pause
recover the model from the ensuing dive. Novice pilots will find it virtually impossible
to fly their way out of these situations. It does require a certain amount of
height and it may sound a bit drastic but, a common failing among tyro pilots is not to
admit defeat in these circumstances and try to fly their way out of trouble, often with
disastrous results. Most models when out of control will, if left to their own devices,
end up in a dive, recovery from which is usually straightforward. Try it. Position the
model at a safe altitude and briskly apply full control on all control surfaces. Hold for
a second or so and then let the sticks go. The model may flick roll and start to
spin but when the controls are neutralised a dive will result, honest!!
Very few slope flyers
that I meet fly inverted for any length of time, possibly because very few have aeroplanes
the symmetrical sections. It is possible to fly inverted with non symmetrical sections but
it requires much better lift conditions. Once again initial attempts at inverted flying
are best practised into wind. To enter the inverted position build up a small amount of
speed and perform a half roll. As with the roll, slowly apply down elevator to prevent the
nose dropping when the model is upside down. The amount of down elevator required will be
slightly more than that for a complete roll. Once inverted keep the wings and nose level.
This will require a steady hand and the suppression of your natural instincts! Developing
the ability to suppress these natural instincts i.e. not to over control is invaluable in
tight situations and could mean the difference between an undamaged model and a bag of
bits. Incidentally whilst the Rudder and Elevator controls are reversed upside down the
Ailerons are not (fortunately).
Should the nose of the
model start to 'nod' or should the model sink rapidly release some of the 'down' (up
actually!) elevator and allow the speed to increase slightly. The model is at the point of
stalling and in a high drag situation. The most common fault when flying inverted is over
control, particularly the elevator. To overcome this try flying with reduced control
throws i.e. use rates. Recover from the inverted position by completing the other half of
the roll, not forgetting to use up elevator on the recovery.
As your confidence
increases practice gentle 45 degree. turns left and right, always recovering into wind.
During these turns increase the 'down' elevator to prevent the nose dropping i.e. just as
you would apply up elevator in a turn with the model the right way up. It is my experience
though that slightly more 'up' elevator is required when inverted. Once you have mastered
these turns try a complete 360.
If you find the model
close to the slope, inverted and sinking rapidly DO NOT PANIC. Gently turn the model into
wind and inch it forward away from the hill, avoiding any sudden control movements. DO NOT
attempt a panic recovery, it is a recipe for disaster. If you keep your nerve the worst
that will happen is the model will land inverted. So what, the forward speed will be low
because the model is flying into wind, sink will also be low because the model is still in
lift albeit insufficient to keep it airborne. I have been in this predicament a number of
times and the most damage the model has sustained is a broken fin. The alternative, a
panic recovery attempt, invariably results in a much more severely damaged model.
The Stall Turn
The stall turn is a
simple manoeuvre that is sometimes difficult to get right because timing, speed and
positioning are all important. A stall turn looks similar to a skate board zooming up a
ramp, performing a 180 degree turn at the top before zooming back down again. The
manoeuvre must be performed crosswind with the 180 degree turn INTO wind i.e. a stall turn
performed from left to right would require LEFT rudder.
Start the manoeuvre a
little way out from the slope, off to one side at a height of 50 to 100 feet (15 - 30
metres). Enter a shallow dive to build up a little speed. Pull up into a wings level
almost vertical climb, and as the speed drops off apply FULL rudder. The model should,
with the aid of the wind (hence the into wind turn) perform a 180 degree rudder turn!! The
difficulty in performing this manoeuvre is judging:
1. The speed on entry
(not too fast or too slow).
2. The angle of climb
(approximately 80 degrees).
3 When to apply full
It is possible to cheat
a little if the manoeuvre is not working out as desired by applying a small amount of
aileron at the start of the turn and a 'dab' of down on the exit. The stall turn is a very
pretty manoeuvre when performed properly but it does require good judgement and a model
with an effective rudder.
The Cuban Eight
We are now getting into
the more advanced aerobatics by combining two or more manoeuvres into one. If viewed from
the side a Cuban Eight looks like a figure eight laid on its side with a twist in the
middle. Hence the eight in the name, I do not know where the Cuban came from
perhaps someone could enlighten me. It consist of two loops sharing the same entry and
exit that are joined together at the crossover by two half rolls.
Sounds complicated, so
how do you do it? Firstly, perfect your cross-wind looping technique because this
manoeuvre must be performed cross-wind. Next position the model off to one side, a good
distance out from the slope (the model will get blown back during the manoeuvre) at a
reasonable height. Dive to build up speed and start the first loop. When the model is
coming down vertically during the second half of the loop, perform a half roll away from
the slope and start the second loop. Again, when the model is coming down vertically,
carry out another half roll into wind and recover, hopefully in the same position as when
you started the manoeuvre.
When performing a Cuban
Eight there are three main problem areas:
1. The model was
incorrectly positioned and or aligned at the start of the manoeuvre resulting in the model
getting too close to the ridge.
2. Incorrect speed on
entry (normally too slow)
3. Insufficient speed
for the second loop because of a poor first loop.
Alignment is probably
more of a problem than positioning. The model should enter the manoeuvre wings level and
flying parallel to the slope. The speed on entry into the first loop should be a shade
faster than that for a normal loop. After completing the first half roll do not 'snatch'
at the up elevator on the start of the second loop as this will 'kill' the speed making it
virtually impossible to complete it satisfactorily. Likewise the up elevator applied
during the recovery should be gradual to allow the model to regain normal flying speed on
exit. It is possible to cheat a little by stretching the manoeuvre at the
crossover. This will allow the model to regain the speed lost during the first loop making
the second loop easier to perform.
The Outside Loop or
The outside loop or bunt
is similar to the conventional loop except of course it is performed below the entry
flight line as opposed to above it. The other main differences are the type of model that
will perform a bunt and the speed on entry to the manoeuvre. To perform an outside loop
satisfactorily a model with a fully symmetrical section is required. Semi-symmetrical or
asymmetrical sectioned models will perform outside loops but with varying degrees of
difficulty depending on how 'clean' and efficient they are. With flat bottomed sectioned
models it is almost impossible. Another factor which affects the quality of manoeuvres is
the drag / volume to weight ratio of the model. With a light model it is often
difficult to build up enough speed / energy to complete the manoeuvre satisfactorily.
Start the bunt as per
initial attempts at looping i.e. high and into wind but a little further out. The main
reason for carrying out the first attempts into wind is that the wind will assist the
model during the recovery phase. Start the manoeuvre with a dive to build up speed and
then level out. Gradually re-apply down elevator to enter the manoeuvre taking care to
keep the wings level. As the manoeuvre progresses continue to gradually increase the down
elevator until the model is again in level flight where upon the elevator control is
returned to neutral. Too much down elevator at the bottom of the bunt could result in the
model rolling out of the manoeuvre. Most embarrassing if the advice high and wide has not
been followed. Fully symmetrically sectioned models will require less down elevator than
less symmetrically sectioned models. The main problems encountered when performing a bunt
are similar to those for a loop i.e. not entering the manoeuvre wings level and as a
consequence screwing out.
The spin is best
described as a stalled spiral dive. It requires plenty of height and for the model to be a
good distance out from the slope. A lot of height is lost in a spin and the model gets
blown back towards the slope during it. For a model to spin satisfactorily it must have a
minimum of rudder elevator control. Aileron elevator controlled models generally do not
spin very well as it is difficult to establish the required spin speed necessary to keep
the model in the fully stalled condition. Spins with aileron elevator controlled models
generally end up with the model in a spiral dive and an even greater loss of height.
To enter the spin point
the model into wind and slowly ease the elevator back to gently enter a
stall. At the point of the stall apply FULL up elevator, FULL left or right aileron and
FULL rudder in the same direction as the aileron. To exit the spin return the controls to
neutral and recover from the ensuing dive. Most models will come out of a spin without
needing to use anti-spin rudder or aileron. If however nothing is happening after half
turn of returning the controls to neutral apply opposite rudder until the spin stops and
then use up elevator to recover from the resulting dive. The secret to a good recovery is
knowing how many turns or fractions of a turn the model takes to stop spinning so that the
model can be recovered into wind. This angular movement is then used to determine when the
controls are neutralised i.e. if a model takes half a turn to recover then the controls
are neutralised when you can see the top of the model. This is very important as a
downwind recovery will often require a panic turn into wind to avoid colliding with the
Inverted spins are
similar to upright spins except that the rudder and aileron controls are crossed
i.e. applied in opposite directions as the rudder control is reversed when upside down.
Recovering inverted is quite difficult and will require considerable practice as the
normal control neutrals cannot be used as a reference points.
The essence of good
aerobatic flying is planning, positioning and empathy with the model. Smooth control
movements and efficient use of the available energy are also fundamental ingredients. I am
not a competition aerobatic pilot so my methods may differ from those of the experts.
Aerobatics are an important part of flying, they build confidence and increase flying
skill. The purpose of this article is to remove some of the mystique of aerobatic flying
and encourage you, the average modeller, to broaden your aerobatic horizons and have a go.
The manoeuvres described hear are not the only ones there are many more. Try inventing
some of your own and stringing them together to form a montage. It goes without
saying however that when performing aerobatics safety must be uppermost in your mind
particularly if there are other flyers and spectators about.
One final point.
Aerobatic flying will show up any inaccuracies in a model's state of trim such as warps of
the flying surfaces, asymmetric control response and out of balance wings etc. so it is
worth spending a little time checking for these problems and sorting them out if you want
the model is to perform at its best.