Multiplex EasyGlider PRO, 21 4226 Building Instructions

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Bauanleitung 03 ... 10
Building instructions 11 ... 19
Notice de construction 20 ... 33
Istruzioni di montaggio 34 ... 41
Instrucciones de montaje 42 ... 49

© Copyright by MULTIPLEX 2008 Version 1.0

BK / KIT EasyGlider PRO # 21 4226

F

PRO

vorgesehen für die MULTIPLEX
Brushless-Antriebe # 33 2636 u. # 33 2642
oder als Segler

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EasyGlider PRO KIT # 21 4226

Examine your kit carefully!

MULTIPLEX model kits are subject to constant quality checks throughout the production process, and we sincerely hope that you
are completely satisfied with the contents of your kit. However, we would ask you to check all the parts (referring to the Parts List)
before you start construction, as we cannot exchange components which you have already worked on. If you find any part is
not acceptable for any reason, we will gladly correct the defect or replace the item in question once we have inspected it. Please
send the part to our Model Department, being sure to include the purchase receipt and a brief description of the fault.
We are constantly working on improving our models, and for this reason we must reserve the right to change the kit contents in
terms of shape or dimensions of parts, technology, materials and fittings, without prior notification. Please understand that we
cannot entertain claims against us if the kit contents do not agree in every respect with the instructions and the illustrations.

Caution!
Radio-controlled models, and especially model aircraft, are by no means playthings. Building and operating them safely
requires a certain level of technical competence and manual skill, together with discipline and a responsible attitude at the
flying field. Errors and carelessness in building and flying the model can result in serious personal injury and damage to
property. Since we, as manufacturers, have no control over the construction, maintenance and operation of our product s,
we are obliged to take this opportunity to point out these hazards and to emphasise your personal responsibility .

Additional items required for the EasyGlider PRO:

Adhesive and activator:

Use medium-viscosity cyano-acrylate glue (“cyano” -

not styrofoam cyano) for this model. Epoxy adhesives produce what initially
appears to be a sound joint, but the bond is only superficial, and the hard resin breaks away from the parts under load.
Hot-melt glue (from a glue gun) is a useful alternative adhesive.

MULTIPLEX radio control system component s for EasyGlider

PRO:

RX-7-SYNTH receiver 35 MHz e.g. A-band Order No. 5 5880
alternatively 40 MHz Order No. 5 5882
or
Micro IPD UNI receiver 35 MHz e.g. A-band Order No. 5 5971
alternatively 40 MHz Order No. 5 5972

Tiny-S UNI servo (2 x required) Elevator / rudder Order No. 6 5121
Nano-S UNI servo (2 x required) 2 x aileron Order No. 6 5120

Extension lead, 400 mm UNI Aileron servo, 2 x Order No. 8 5029
optional: separation filter lead, 200 mm UNI Aileron servo, 2 x Order No. 8 5035

Battery charger:
MULTIcharger LN-3008 EQU Order No. 9 2540

For LiPo, LiIo and LiFe batteries with 2S or 3S cells, and NiMH and NiCd batteries with 4 to 8 cells.
EasyGlider PRO power set Order No. 33 2636

Contents: Motor - Himax 2816 - 1220, speed controller- BL-27 II, 10” x 6” propeller, collet adaptor, propeller driver, spinner
EasyGlider PRO tuning power set Best.-Nr. 33 2642

Inhalt:
Motor - Himax 3516 - 1130, Regler - BL -37 II, Luftschraube 12x6, Spannzange, Mitnehmer, Spinner

Flight battery Li-BATT BX-2100 mAh 2/1 2100 Order No. 15 7130

Li-BATT BX-2500 mAh 2/1 2500 Order No. 15 7190
Li-BATT BX-3200 mAh 2/1 3200 Order No. 15 7135

Propeller driver and spinner for EasyGlider PRO Order No. 73 3500

Additional items required for the

glider variant only

NiMH receiver battery, 4 / 1800 mAh Order No. 15 6007
Mini switch harness with charge socket Order No. 8 5045
Aero-tow release Order No. 72 3470

Tools:

Scissors, balsa knife, side-cutters.

Note: remove the illustration pages from the centre of the building instructions.

Specification: Glider Electric glider

Wingspan 1800 mm 1800 mm
Overall length 1110 m m 1110 m m
All-up weight approx. 710 g with standard power system approx. 810 g
Wing area, FAI approx. 41.6 dm² FAI approx. 41.6 dm²
Wing loading approx. 17 g / dm² approx. 20 g / dm²
RC functions Elevator, rudder, aileron as glider, plus throttle

GB

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Important note
This model is not made of styrofoam™, and it is

not possible
to glue the material using white glue or epoxy . Please be
sure to use cyano-acrylate glue exclusively , preferably in
conjunction with cyano activator (”kicker”). We recommend
medium-viscosity (thick) cyano. This is the procedure with
Elapor®: spray cyano activator on one face of the joint; allow
it to air-dry for around two minutes until the surface
appears to be “dry”, then apply cyano adhesive to the other
face. Join the parts, and

immediately position them

accurately.

Please take care when handling cyano-acrylate adhesives.
These materials harden in seconds, so don’t get them on
your fingers or other parts of the body. We strongly
recommend the use of goggles to protect your eyes.

Keep the adhesive out of the reach of children!

1. Before starting construction

Please check the contents of your kit before you start
construction. You will find Figs. 1 + 2 and the Parts List helpful
here.

Completing the fuselage and tail panels

2. Preparing the “snakes”

Check the length of the elevator snake sleeves 43 and 45, and
shorten them if necessary.

43 3 / 2 Ø x 785 mm
45 2 / 1 Ø x 850 mm

Steel 41 0.8 Ø x 875 mm, insert!
Repeat the procedure with the rudder snake sleeves 44 and

46.

44 3 / 2 Ø x 785 mm
46 2 / 1 Ø x 850 mm

Steel 42 0.8 Ø x 875 mm, insert!
Aerial sleeve 47 3/2 Ø x 785 mm (shorten if
necessary)

3. Installing the snakes in the fuselage shells
Important: the fuselage tail boom is considerably

strengthened and stiffened by the addition of the snake outer
sleeves 43 and 44, which must be glued full-length to the
shells in order to obtain the full effect. The same applies to the
aerial sleeve 47.
Check that the snakes operate smoothly and freely, and take
care not to allow glue to run into the outer sleeves.

Left-hand fuselage shell:

Install the complete elevator snake (wire rod length = 875
mm) in the left-hand fuselage shell; the pre-formed end
should be at the front (servo end).

Fig. 3

Position the snake outer sleeve 43 flush at the front of the
fuselage shell, as shown in Fig. 4. Lay the shell down flat and
run cyano along the whole length of the outer sleeve 43 and
the channel in the fuselage to glue the parts together strongly.

Fig. 5

Right-hand fuselage shell:

Install the complete rudder snake (wire rod length = 875mm)
in the right-hand fuselage shell. The pre-formed end should
be at the front (servo end).

Fig. 6

Position the snake outer sleeve 44 flush at the front of the
fuselage shell, as shown in Fig. 7. Lay the shell down flat
(note the locating spigot; place the fuselage shell over the

corner of the table) and run cyano along the whole length of
the outer sleeve 44 and the channel in the fuselage to glue the
parts together strongly.

Fig. 8

4. Installing the aerial sleeve

Trial-fit the aerial sleeve 47, cut it to length and glue it in the
right-hand fuselage shell - taking care not to bend or distort
the moulding.

Fig. 9

5. Installing the tow-hook

Glider version: glue the towhook 32 in the moulded recess in
the fuselage shell 4.

Fig. 9

6. Installing the motor mount

Glue the motor mount 34 in the right-hand fuselage shell, and
wipe away any adhesive which is squeezed out. The exposed
face of the motor mount will later be glued when the shells are
joined; take care to keep adhesive off this area. Note that the
motor mount should also be installed in the glider version, as
it adds considerable strength.

Fig. 10

7. Installing the servos in the fuselage shells

Set the servos to “neutral” (centre) from the transmitter, and fit
them in the moulded recesses in the left and right fuselage
shells, as shown in Fig. 11. If you are using different servos,
you may have to trim the recesses slightly to obtain a close fit.
Lay the servo leads in the channel, running from bottom to top,
and tape them in place. Apply a drop of cyano to the servo lugs to
attach them to the foam material. Connect the pre-formed ends
of the wire pushrods to the servo output arms, and push the
arms onto the servos at an angle of 90° to the servo sides (don’t
forget to fit the servo output screws). Glue the plastic latch catches
22 in both fuselage sides as shown. Glue the extension leads in
the cable holders

36, positioning the ends flush as shown in the
detail drawing. Glue the cable holders 36 in the moulded
recesses in both fuselage sides, pushing them in as far as they
will go. Deploy the leads carefully and glue the fore-and-aft
formers 37 in place.

Fig. 11

8. Joining the fuselage shells

The most suitable adhesive for this stage is thick cyano-acrylate,
used in conjunction with activator.

Caution: for the tuning version the balance weights 2 x 33 should
first be glued in the recesses at the tail, as shown in Fig. 12.

The first step is to check “dry” (no glue) that the fuselage shells
3 + 4 fit together accurately; it may be necessary to carry out
minor trimming.

Spray cyano activator on the joint surfaces of the fuselage shell
4 and leave it to air-dry for about two minutes.
Apply cyano adhesive to the joint surfaces of the fuselage shell
3, then join the parts carefully , taking care to align them accurately
and immediately. Note that the fuselage joint line must be
perfectly straight - no bends allowed!

Fig. 12

9. Installing the rudder hinge

Glue the rudder hinge 31 in the tail end of the fuselage using a
small amount of cyano. Take great care that no glue gets onto
the hinge pivot axis.

Fig. 13

Use a sharp balsa knife to cut a central slot for the rudder hinge
31 in the leading edge of the rudder. Take care: injury hazard!

13

Extend the slot in the rudder 5 downward by about 3 to 4 mm, as
this makes it easier to install the rudder and tailplane at a later
stage.

Fig. 14

10. Attaching the horn to the rudder

Use a pair of side-cutters to cut down the projecting spigot of the
rudder horn 24 to a length of about 2 mm. Insert the swivel
pushrod connector 25 in the second hole from the inside of the
rudder horn 24, and secure it with the washer 26 and nut 27.
Caution: note the orientation of the swivel connector! Tighten the
nut very carefully so that the barrel swivels smoothly: it should
not wobble, but must not jam. Apply a tiny drop of cyano to the nut
(on the tip of a pin) when you are satisfied. Fit the grubscrew 28
in the threaded hole in the swivel pushrod connector 25 using
the allen key 29 provided. Apply cyano activator to the moulded
recess in the rudder, then glue the rudder horn 24 in the recess,
with the row of holes facing the hinge pivot axis.

Fig. 15

11. Freeing the elevator and rudder

Cut a 1 mm slot at each end of the elevator, which is attached to
the tailplane 12. Move the rudder and elevator to and fro repeatedly
in order to make the hinges free-moving - do not separate the
control surfaces!

Fig. 16

12. Attaching the horn to the elevator

Insert the swivel pushrod connector 25 in the outermost hole in
the elevator horn 24, and secure it with the washer 26 and the
nut 27. Caution: note the orientation of the swivel connector!
Tighten the nut very carefully so that the barrel swivels smoothly:
it should not wobble, but must not jam. Apply a tiny drop of cyano
to the nut (on the tip of a pin) when you are satisfied. Fit the
grubscrew 28 in the threaded hole in the swivel pushrod
connector 25 using the allen key 29 provided.
Apply cyano activator to the moulded recess in the elevator, then
glue the horn 24 in the recess, with the row of holes facing the
hinge pivot axis.

Fig. 17

13. Gluing the fin to the tailplane

Glue the fin 13 to the tailplane 12, setting it exactly at 90°.
Check this with a tool such as a setsquare.

Fig. 18

14. Gluing the tail assembly to the fuselage

Position the tail assembly on the fuselage “dry” (no glue), and
check that the parts fit correctly: first insert the hinge 31 in the
rudder 13, then slide the assembly forward onto the fuselage.
Check in particular that the tailplane 12 is a snug fit on the
fuselage, without any gaps, and lies parallel to the wing saddle
at the front of the fuselage. Y ou can check this by laying the GRP
wing joiner 40 on the wing saddle, fixing it in place exactly at
right-angles to the fuselage centreline using paper masking
tape. Now sight along the fuselage from the nose, and align the
tailplane with the wing joiner. When you are confident that the
parts can be positioned correctly, the tail assembly can be glued
to the fuselage permanently. Check once more for correct
alignment and a close fit before leaving the glue to harden. A little
extra care at this stage is well worthwhile, as it avoids long-term
disappointment in a model which refuses to fly straight.

15. Securing the rudder and elevator pushrods

Slip the wire pushrods 41 and 42 through the swivel pushrod
connectors 25, set the servos and control surfaces to neutral
(centre), and tighten the socket-head grubscrews 28 in the
connectors to secure the pushrods.

Figs. 19 + 20

Completing the wings

16. Freeing the ailerons

Cut a 1 mm slot at each end of the ailerons, which are attached
to the wing panels 8 and

9. Move the ailerons to and fro repeatedly
in order to make the hinges free-moving - do not separate the
control surfaces!

Fig. 21

17. Attaching the horns to the ailerons

Insert the swivel pushrod connectors 25 in the outermost holes
in the aileron horns 24, and secure them with the washers 26
and the nuts 27.
Caution: be sure to produce a handed pair (different left and
right)! Tighten the nuts very carefully so that the barrels swivel
smoothly: they should not wobble, but must not jam. Apply a tiny
drop of cyano to the nuts (on the tip of a pin) when you are
satisfied. Fit the grubscrews 28 in the threaded holes in the
swivel pushrod connectors 25 using the allen key 29 provided.
Apply cyano activator to the moulded recesses in the ailerons,
then glue the horns 24 in the recesses, with the row of holes
facing the hinge pivot axis.

Fig. 22

18. Installing the aileron servos

Set the servos to “neutral” (centre) from the transmitter, and fit
the output arms on the servos at 90° to the case sides - 1 x left
and 1 x right (mirror-image pair).
Trial-fit the servos in the moulded recesses in the wing panels 8
and 9: you may need to carry out minor adjustments to suit the
type of servo you are using. Apply a drop of hot-melt glue to each
slot in the wings for the servo mounting lugs, and immediately
press the servos into the recesses; apply an extra drop of glue if
necessary.

Fig. 23

19. Installing the aileron pushrods

Connect the pre-formed end of the steel pushrods 30 to the
outermost hole in the servo output arms, and slip the plain end
through the swivel pushrod connectors 25. Set the ailerons and
servos to neutral, and tighten the grubscrews 28 to secure the
pushrods.

Fig. 23

20. Deploying the aileron servo leads

Lay each servo lead in a curve running towards the wing joiner
channel, and extend it with a 400 mm extension lead: the leads
can either be soldered together or connected using the standard
plug and socket. You will find a notch in each of the spar covers
10 and 11 designed to accommodate the connectors. Now deploy
the extension leads in a straight line along the front face of the
spar channel, standing on edge.
The servo leads must project from the underside of the wing
roots by 60 mm on the left and 75 mm on the right, as this makes
it possible to connect them to the extension leads glued in the
cable holders 36. The remainder of the extension leads can be
stowed in the channel and secured.

Figs. 23 + 24

21. Installing the spar covers

Carefully trial-fit the spar covers 10 and 11 in the wing panels 8
and 9. When you are confident that the covers are a close fit, and
can be installed flush with the wing surface, they can be glued in
place permanently using cyano. Ensure in particular that no
adhesive gets onto those surfaces of the wings into which the
GRP wing joiner 40 will be inserted later. Please don’t fit the
wing joiner 40 in the wings until you are certain that there is no
active adhesive inside the channels. The best way to ensure
this is to spray activator inside and wait for about five minutes. If
you neglect this warning, you may find that you can

never sepa-

rate the wing panels again.

14

Deploy the servo leads in the channel in the spar covers, and
secure them with a little glue (hot-melt adhesive or contact
cement). Don’t use cyano for this, as it tends to make the cable
insulation brittle.

Fig. 23

22. Checking the wing joiner system

The model can now be assembled using the GRP wing joiner
40: slide the wing panels onto the joiner until they are 5 cm short
of the fuselage on each side, then connect the plugs on the
aileron extension leads to the sockets installed in the fuselage.
Slide the wings closer to the fuselage, and you will find that the
connected leads help to locate them properly. Finally push the
wings into the fuselage on both sides.
Check that the wing panels 8 and 9 are a snug fit (no gaps)
where they meet the fuselage. If they are excessively tight, carefully
compress the edges of the wing root where they enter the
fuselage recess. Note: the wing panels should not be glued to
the fuselage. This enables you to remove the wings to make the
model easier to transport.

Fig. 25

23. Installing the canopy latch lugs

First glue the canopy former 35 in the underside of the canopy 7,
then push the two latch tongues 23 through the former, and set
them flush. Apply thick cyano to the serrated edges - no activator
in this case! - then insert the latch tongues in the slots in the
canopy . Immediately fit the canopy on the fuselage and allow the
latch tongues to engage in the latch catches 22. Check the
position of the canopy on the fuselage without delay, then wait
about one minute before cautiously re-opening the canopy. S pray
activator on the glued joints between the latch tongues and the
canopy former 35.

Fig. 26

General note on the receiving system installation

The remaining airborne equipment can now be installed in the
cabin area. Before you fit the receiver battery permanently it is
important to check the model’s Centre of Gravity (CG); you can
often correct the balance point at this stage by shifting the
batteries.
Velcro t ape (hook tape 20 + loop tape 21) is supplied for securing
the receiving system components, but please note that the
adhesive layer on the tape is not sufficient for this application, so
apply cyano to reinforce the joints.
In both versions of the aeroplane the receiver should be installed
aft of the servos, again using Velcro tape. Thread the aerial wire
(attached to the receiver) into the plastic sleeve 47, which has
already been installed. The easy way to do this is to file a length
of steel rod to a point, then slip it through the sleeve 47 from the
tail end. Push the point into the end of the aerial insulation and
apply a drop of cyano to the joint. You can then pull the aerial
through the sleeve from the tail end.
The model is designed for the installation of an MPX aero-tow
release, # 72 3470; the mechanism is simply glued in the glider
nose 5. A short length of snake outer sleeve runs from the release
unit towards the tow release servo, passing through the centre
of the battery pack as shown. The linkage takes the form of a
length of 1.2 mm Ø steel rod.

Fig. 27

Motor + receiving system installation in the electric-powered
version

Our recommended components have been thoroughly tested,
and are well matched to each other.
If you wish to use different units, especially if they take the form of
a more powerful motor, then it is your responsibility to ensure
that the airframe is “up to the job”.

Install the motor and tighten all screws thoroughly. Deploy the
power cables in such a way that they cannot possibly foul any of
the motor’s moving parts. Tape the wires to the fuselage.

Fig. 28

The speed controller can be attached to the fuselage side
adjacent to the receiver, using Velcro tape.

The intended location of the flight battery is the space aft of the
receiver. The battery should be positioned in such a way that
little or no ballast is required to balance the completed model.
Secure the battery with Velcro tape in the usual way.
Now complete all the receiving system connections as described
in the instructions supplied with your radio control system. Check
that all the cables are secured well, but are not under strain or
tension.

Fit the propeller driver on the motor output shaft. Allow about 1
mm clearance between the rear face of the driver and the
fuselage.

Attach the propeller blades to the propeller driver , and tighten the
pivot screws fully, but not excessively. The blades must be able
to swing down under their own weight when you hold the model’s
nose up.

Switch the transmitter on, connect the flight battery to the speed
controller, and the controller to the receiver. The controller you
are using must feature a BEC (Battery Eliminator Circuit) system,
i.e. the receiver draws power from the flight battery.
Switch the motor on briefly, and check the direction of rotation of
the propeller. When test-running the power system remove all
light, loose objects behind the model, and hold it really firmly.

Caution: even small motors and propellers represent a serious
injury hazard!

Setting the control surface travels

The control surface travels must be correct, otherwise the model
will not respond harmoniously to the controls. All travels are
measured at the widest point of the control surface concerned.

Elevator
up - stick back (towards you) - approx. + 8-10mm
down - stick forward (away from you) - approx. - 8-10mm
Rudder left and right approx.15-20mm
each way

Ailerons
up approx. + 15 mm
down approx. - 6 mm
Spoilers - both ailerons up approx. + 20 mm
Spoiler mixer (elevator trim compensation)

approx. - 4 mm

Fig. 29

The “Spoiler” function is designed to shorten the landing
approach by deflecting both ailerons up simultaneously. At the
same time the appropriate down-elevator trim is mixed in, so
that the model maintains a stable attitude. This function can only
be implemented if your radio control system features suitable
mixer facilities.
Please refer to the instructions supplied with your RC system for
details of this.

Note: when you apply a right-aileron command, the right-hand
aileron - as seen from the tail, looking forward - must deflect up.

If you cannot set the stated control surface travels using your

15

radio control system’s adjustment facilities, you may need to re­install the swivel pushrod connector in a different hole in the
horn.

Gilding the lily - applying the decals

The kit is supplied with a multi-colour decal sheet, part 2. Cut out
the individual name placards and emblems and apply them to
the model in the positions shown in the kit box illustration, or in
another arrangement which you find pleasing.

Balancing the model

Like every other aircraft, your EasyGlider PRO must be balanced
at a particular point if it is to fly efficiently and stably. Assemble
the model completely, ready to fly. Corrections are possible by
altering the position of the receiver battery or the flight pack. If
this is still not sufficient, add nose ballast or tail ballast until the
model balances at the stated point.

The Centre of Gravity should be at a point 70 mm back from the
leading edge of the wing, measured where the wings meet the
fuselage. Mark this point on the underside of the wing roots with
a waterproof felt-tip pen. Support the model at the marked points
on two fingertips, and the aeroplane should balance level. Make
any adjustments required, and mark the location of the airborne
components once you have found the correct position in the
fuselage, so that you can be sure always to replace the battery in
the same position.

Fig. 30

Preparing for the first flight

For the first flight wait for a day with as little breeze as possible.
The early evening is often a good time.

If this is your first model aircraft, your next step is to ask an
experienced model pilot to help you, as things usually do not go
well if you try to manage on your own. Y our local model flying club
should be able to help you find someone, or - failing that - your
nearest model shop may be able to assist you. Our flight
simulator for the PC can also provide valuable experience prior
to your “first real steps” in model flying.
You can download the simulator at no charge from our website
www.multiplex-rc.de. You will also need the matching interface
cable for your MPX transmitter; this is available from model shops
under Order No. # 8 5153.Be sure to carry out a range check

before the first flight.

Just before the flight, charge up the transmitter battery and the
flight pack (or receiver battery) using the recommended
procedures. Ensure that “your” channel is not already in use
before you switch on the transmitter.

Ask your assistant to walk away from the model, holding the
transmitter. The aerial should be fitted but completely collapsed.
Your assistant should operate one of the functions constantly
while you watch the servos. The non-controlled servo should
stay motionless up to a range of about 60 m, and the controlled
one should follow the stick movements smoothly and without
any delay. Please note that this check can only give reliable result s
if the radio band is clear of interference, and if no other radio
control transmitters are in use -

even on different channels. If the
range check is successful, repeat it with the motor running
(EasyGlider Electric only). There should be no more than a very
slight reduction in effective radio range with the motor turning.
If you are not sure about anything, please don’t risk a flight. Send
the whole system (including battery, switch harness and servos)
to the Service Department of your RC system manufacturer and
ask them to check it.

The first flight ...

Glider:

A test-glide from shoulder level, directly into wind, will give you
an approximate idea of the model’s “trim”, i.e. whether it is set
up correctly, or whether the control surfaces or transmitter trims
need to be adjusted. If the model swings away to one side,
move the rudder trim slightly in the opposite direction. If the model
banks - one wing lower than the other - apply slight aileron trim
correction.

Hand-towing

This is the classic method of launching a glider to height. Attached
to a suitable length of towline, the model is pulled up by your
assistant running into wind; the glider will rise up the line in a
similar fashion to a kite. The towline first needs to be prepared
as follows: tie the towring and a pennant to the “model” end of
the line. The ring is engaged on the towhook 32, the towline
unwound and your assistant (launcher) takes the free end and
walks upwind until the line is taut. The model should be held
under gentle tension before it is released. The launcher watches
the model (over his shoulder), adjusting his pace to maintain a
steady rate of climb. T ake care not to overstress the model during
the launch; this is a particular danger in a fairly strong wind.

Bungee launching

This is the easiest method of launching a glider of this size, as
no assistant is needed, and launch heights of around 100 m are
easily achieved. From this altitude quite long flying times can be
achieved, and they will be even longer if you manage to contact
a thermal, although this does depend on the prevailing weather.

Thermal flying

Making the best use of flat field thermals is not particularly easy,
and calls for considerable skill and experience. Areas of rising
air are harder to detect and recognise at a flat field, because they
tend to occur at higher altitude than at the hillside, where it is
often possible to find lift while the model is cruising along the
edge of the slope and then circle away in it. A thermal at a flat field
which occurs directly overhead is very hard to recognise, and to
exploit it to the full requires a highly skilled pilot. For this reason
it is always best to go thermal seeking off to one side of where
you are standing.

Y ou will recognise thermal contact by the glider’s behaviour. Good
thermals are obvious because the model will climb strongly, but
weak thermals take a practised eye to detect, and you will need
a lot of skill to make use of them. With a little practice you will be
able to recognise likely trigger points for thermals in the local
landscape. The ground warms up in the sun’s heat, but heat
absorption varies according to the type of terrain and the angle
of the sun’s rays. The air over the warmer ground becomes
warmer in turn, and the mass of warm air flows along close to
the ground, driven by the breeze. Strong winds usually prevent
thermal build-up. Any obstruction - a shrub or tree, a fence, the
edge of a wood, a hill, a passing car, even your own model on
the landing approach - may cause this warm air to leave the
ground and rise. Imagine a drop of water on the ceiling,
wandering around aimlessly, and initially staying stuck to the
ceiling. If it strikes an obstruction it will fall on your head. A triggered
thermal can be thought of as the opposite of the drop of water.

The most obvious thermal triggers include sharply defined snow
fields on mountain slopes. The air above the snow field is cooled,
and flows downhill; at the edge of the snow field, part-way down
the valley, the cool air meets warm air flowing gently uphill, and
pushes it up and away as if cut off by a knife. The result is an
extremely powerful but bumpy thermal bubble. Your task is to
locate the rising warm air and centre your model in it. You will
need to control the glider constantly to keep it centred, as you