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Radio
Control Model World - Jul '94
by
Stan Yeo
INTRODUCTION
An
analysis of 'arrivals at my local slope over the last few weeks
revealed that 90% of the crashes resulting in damage occurred after
the decision to land had been made. Occasionally there was a mishap
on launching but there were surprisingly few crashes as a result
of flying error during the 'lie back and enjoy it' section of the
flight. An analysis of the landing accidents suggested that they
were the direct result of basic flying skills falling apart under
pressure.
The
purpose of this article therefore is to help the not so confident
flyer develop the skills required to carry out a successful landing.
My definition of a successful landing is one where the model 'arrives'
in a comparatively elegant (controlled) manner, undamaged and within
a reasonable distance of the pilot (20 - 30 metres). These skills
will develop naturally over a period of time but progress will be
much quicker if the pilot understands what they are and adopts a
systematic approach to learning them.
The
skills required of the pilot are he/she must be able to:
1.
Fly the model in a straight line away from the slope in a controlled
shallow dive.
2.
Fly the model cross wind, parallel to the slope face, constantly
making adjustments for fluctuations in wind strength.
3.
Fly the model toward themselves, instinctively reversing the Rudder/Aileron
controls.
4.
Control the attitude of the model in a tight turn under pressure.
5.
Recognise the flying speed of a model irrespective
of ground speed.
Obtaining
these skills needs a conscious effort as the percentage of a normal
flight that contributes towards developing them is quite small.
So how do we develop them? Many years ago I once asked a top model
flyer how he became so good. The curt reply was "practice".
He then proceeded to tell me how he would pick one manoeuvre and
practice it continually until it was perfect. Whilst it is not necessary
to aim for the same level of perfection we should be aiming for
a high level of competence if, for no other reason than to stop
needlessly bending models.
PRACTISING
THE MANOEUVRES
The
most important thing to remember when practising manoeuvres is to
keep the model high and a reasonable distance from the slope. There
are two main reasons for doing this:
1.
It is easier to judge the attitude of the model with the horizon
as a reference.
2.
If the manoeuvre does go wrong there is less risk of damage because
there is more space in which to recover the model back to normal
flight.
Consequently
all manoeuvres recommended in this article should be carried out
at a reasonable height and distance from the slope. Obviously as
you become more competent then the closer the manoeuvres can be
carried out to the slope.
The
Dive
Being
able to fly the model in a controlled shallow dive is fundamental
to the landing approach. Not only is it is imperative, that whilst
landing, the nose of the model is not allowed to point upwards,
but it is often necessary to 'drive' the model forward on the final
approach in a shallow dive to penetrate into wind. To do this the
pilot must be able to hold in a small amount of down elevator, against
the control stick springs, and steer the model at the same time.
This is not easy particularly if the model is coming towards you.
The way to practice this manoeuvre is to position the model just
in front of the slope, at a height of approximately 50 ft, and dive
the model away from the hill at an angle no greater than 20 degrees
whilst at the same time keeping the wings level and the model flying
away from the hill. The dive angle will depend on the model, the
'draggier' the model the greater the angle. Initial attempts usually
result in the model diving off to one side with very little ground
being gained away from the slope.
After
successfully completing the dive the excess speed gained must be
dissipated without the model entering a 'zoom' climb and presenting
the underside of the aeroplane to the wind. If the model is allowed
to enter a nose up climb it will not only get blown back by the
wind but it could also enter a vicious stall. Having sacrificed
height for a more forward position the model will now be low in
the sky and an uncontrolled stall, close to the hill, could prove
embarrassing. The way to prevent this happening is to very gently
ease off on the down elevator until the excess speed has been 'bled'
away. If the model does start to 'zoom' re-apply the down elevator
and try again, more gently. If the model does stall it is unlikely
to do so without dropping a wing in which case use this to your
advantage and complete the 360 degree turn. Trying to recover the
model against the turn could take longer and prove more hazardous.
The 'zoom' climb is usually more of a problem with rudder elevator
trainers than three function intermediate models.
Flying
Crosswind
Being
able to fly crosswind is again very important to being able to land
a model successfully. Most landings techniques involve flying crosswind
at some point. In light wind conditions the best lift is found close
to the slope face and if the model is to be kept airborne the pilot
must be competent at crosswind flying.
There
are two fundamental skills to be mastered in crosswind flying. One
is flying the model on a predetermined track relative to the ground.
The other is flying the model towards yourself and instinctively
reversing the control inputs. Instinctively reversing the control
inputs is the more fundamental skill and probably the most difficult
to master.
Reversing
the Controls
One
way to approach this problem is, first work out a personal rule
which suits you that will automatically reverse the control inputs
when the model is flying towards you i.e. always move the control
stick towards the down-going wing or left = right, right = left.
Then keep repeating it to yourself when the model when the model
is in this position. One day, after the process has become instinctive,
you will suddenly realise that you are no longer using this 'prop'.
It may help to practice 'reversing' the control inputs with the
model on the carpet at home before trying it out on the slope. At
the very least I would certainly give it some thought, away from
the flying site, if only to implant your own personal solution into
your sub-conscious.
The
second step in developing this skill is to start doing large 360
degree turns and neutralising the rudder or levelling the wings
if an aileron model, when the model is coming towards you at 45
degrees. After one or two seconds re-apply the rudder/aileron control
and complete the turn. The most important thing to remember is the
original direction of the turn!! This is very important as flyers
often forget what manoeuvre they were doing prior to getting disorientated.
Novices, trying to land, frequently forget the model was turning
left or right when it is coming towards them nose on. Silly I know,
but these things happen under pressure.
From
this humble beginning, gradually extend the time the model is flying
towards you, reverse the direction of the turn and reduce the angle
the model makes to the slope until it is parallel. At the same time,
try putting in the opposite control for a short period before completing
the turn. The next step is to extend the length of the 'crosswind'
leg and fly the model closer to the hill. You will have by now noticed
that the model is being blown sideways towards the hill. To counteract
this the nose of the model must be turned into the wind slightly,
the amount depending on the strength of the wind. Due to the continuous
fluctuations in wind strength this angle will need continual adjustment
if the model is to be kept on track. As your crosswind flying skills
develop so will your ability to automatically reverse the control
inputs when the model is flying towards you.
Turning
Exercises
When
a model aeroplane is banked beyond 10 - 15 degrees, particularly
a rudder elevator model, there is a tendency for the nose drop and
the model to enter a spiral dive. If the spiral dive is not controlled
then the model will lose height and build up speed. When the wings
are levelled this excess speed will result in the 'zoom' climb mentioned
previously. Being able to control the angle of bank and the attitude
of the model in a turn is again fundamental to good flying. Sometimes
tight turns are necessary but the tighter the turn the more difficult
it is to carry out, hence the need for practice.
The
secret to good turns is to use the right amount of up elevator to
keep the nose up (without stalling the model) and at the same time
remove some, or all, of the banking control input (rudder/aileron)
as the turn becomes established. This is most important on rudder
elevator models, because an element of the applied rudder is also
down elevator. Practice doing turns and see how tight you can get
them without stalling the model or building up excessive speed.
Once you have mastered single 360 degree turns try multiple 360
degree turns and complete turns in one direction immediately followed
by one in the opposite direction (figure 8's).
Most
landing techniques require the pilot to fly downwind, turn crosswind
and then turn into wind for the approach and landing. Both the crosswind
turn and the turn into wind are hazardous but for different reasons.
The crosswind turn because there is a tendency to over-bank and
the in to wind turn because the model often enters a steep climb
on completion of the turn.
The
main reason for over-banking on the crosswind turn is the pilot
has overestimated the airspeed of the model because of the its high
ground speed. So when the decision to turn crosswind is made, usually
too late, the model is slow to respond. The pilot, on realising
the model has gone too far downwind, starts to panic and inputs
more control. The resulting turn is much too tight with insufficient
elevator to stop the nose 'digging in'. If the pilot is able to
prevent a crash at this point the model often ends up flying downwind
with a crash waiting to happen. The secret is to:
1.
Maintain the model's flying speed on the downwind leg.
2.
Initiate the crosswind turn in plenty of time remembering that the
model will continue to travel downwind until the crosswind track
is established.
The
turn into wind presents a different problem. Here the model has
a tendency for the nose to rise as it leaves the turn allowing the
wind to get underneath it and blow it backwards in a deeply stalled
condition. From this there is little hope of regaining control and
making a safe landing. The two main reasons for the nose of the
model rising as it leaves the turn are:
1.
The airspeed is too high for the attitude of the model.
2.
The up elevator applied in the turn is not removed quickly enough.
To
counteract this tendency the pilot must be ready to apply a small
amount of down elevator. It is at this point that all those hours
spent 'contour flying' the hill and practising flying towards yourself
pay dividends as this is a crunch situation that requires a cool
nerve and a steady hand. It is worth remembering that the wind is
at its strongest at the top of the slope due to the venturi effect
of the hill (see diagram).
SUMMARY
The
aim of this article is to help you develop the basic flying skills
needed to make safe landings the norm rather than the exception.
Having read the article I hope it has helped you to analyse the
skills required and given you a clearer picture as to how to develop
them.
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