Radio Control Jet International 2021-02-03

Magnificent CONCORDE

Concorde part 6

jet in the world!

similar to that of components used in full- Photo 6
size aircraft construction. (Photo 5)

Wings and Turbine nacelles

A great deal of work took place to turn the
CAD drawings into completed moulds for
the Concorde (Photo 6-7). When the
wing skins were laid up (Photo 8), the
glass/carbonfibre reinforcement strips
were added at the same time, the compu-
ter being used so that a check could be

Photo 7

Photo 8

made of every gram of glue and material used. The outer sec- Photo 9
tions of the wing are made of glassfibre as can be seen, with the
aerials being positioned in these areas (Photo 9). My favourite
photo is this one of the wing ribs, showing in detail just how thin
the scale wing section really is. (Photo 10-11-12) shows the
underside of the wing with the ribs and also the reinforcing
strips, all part of the “double T” construction. At times I wonde-
red if it might be easier to build a real aircraft than the Concorde
model, given its complication! (Photo 13). Getting close to the
end, the upper wing skin is glued into place, with the wing secu-
red in a massive support structure, ensuring accuracy, this also
being designed on the computer and cut out on a CNC milling
machine. As the pictures shows, although some of the

Photo 10 Photo 11

51

AUTHOR & PHOTOGRAPHER: OTTO WILDROITHER

Concorde build can appear as though it is being done by a pro- Photo 12
fessional, I actually only have a small workshop, where some
improvisation can be required. (Photo 14) Under a maintenan-
ce hatch lies the JetCat turbine interface, fuel tubing and fittings.
(Photo 15) The turbine nacelles are made up from flat sheets,
so nothing special (Photo 16), however getting the geometry of
the intake right was quite a challenge, and I tried to make this as
accurate as possible. (Photo 17). Because of the amount of
work required, I decided to build the final fully scale exhaust
outlets with thrust reversers at a later stage.

Tank system

Tanks in model jets tend to be of two main types: the most popu- Photo 14
lar are moulded fiberglass or Kevlar tanks together with a
secondary hopper tank, the alternative being the use of a single
bag tank.
There are two critical criteria when selecting a tank system: fir-

Photo 13
Photo 15

stly, the total weight of the system, and secondly, the location of Photo 16
the tank/s in the aircraft. In the case of a typical fibreglass tank,
the overall system weight of the tank system comprises the tank Photo 17
itself, plus the hopper tank and the fuel within the hopper tank, weight of the tanks bringing the overall total of approximately
which of course should never be exhausted. A single 6 litre tank 23Kg. When this is multiplied by the G factor (x8) it results in a
system can thus end up weighing as much as 1Kg! In compari- load of almost 200Kg during static testing, purely for the tanks
son, the weight of a bag tank with a capacity of 6 litres is less and fuel! This is a huge technical challenge that could easily
than 200 grams, and almost every drop of fuel in a bag tank can cause complete failure of the project.
safely be used. The use of four bag tanks, giving a total capaci- As well as this, I wanted to emulate as closely as possible the
ty of around 24 litres, results in a weight saving of around 3Kg overall layout of the Concorde, so I had decided to install the
when compared to a fibreglass tank system. tanks in the wing as per the original. With this in mind, the con-
Another important point that may not be obvious at first, is that clusion was to install the tanks in the wing, however this led me
the correct positioning of tank/s inside the airframe is extremely
important. When a large model goes through the approval pro-
cess, a distinction is made between the weight of the fuselage
and that of the wing. In contrast to traditional airliner models,
typically statically load tested to 4G, I really wanted to achieve
aerobatic approval for the Concorde, requiring test loading to
plus 8G and minus 4G, meaning that during the static test, eight
times the weight of the fuselage is loaded onto the wings.
Due to this it is easy to see why the fuselage and everything
inside it must be designed to be as light as possible. Twenty four
litres of Kerosene in the fuselage weighs around 22Kg, with the

52

Magnificent CONCORDE

Photo 19

Photo 18
Photo 21

Photo 20 such as during a landing approach, the remaining fuel could not
be picked up and supplied to the turbine, as it was collected in
on to the next challenge, how should the bag tanks be desi- the corner of the bag, due to the suction seal being in the mid-
gned? In Germany there are two manufacturers: Markus Richter dle of the bag. I also wanted to do away with the traditional felt
with his company https://richter-tankverschluss.de and Jens clunk, since generally turbine powered models shouldn't be
Pole’s company https://www.fuelbag.de. I got in touch with both using a felt clunk. I thus decided to fit a “Y” shaped tube pickup
companies and they each came up with a solution, both having in the tank, allowing fuel to be collected effectively from the cor-
a continuous tab on the left and right sides of the tank, these ners of the bag. Photo 19.
then being hung on carbonfibre rods inside the fuselage. Using CAD I designed several fuel caps and finally decided on
Unfortunately neither company was able to come up with an the system shown in photo Photo 20. With the “Y” pickup tube
ideal mounting system to secure a bag tank within the wing. Of in the tank and the vent holes in the cap itself, it was now pos-
course the space within the wing between a pair of ribs and the sible to fill the tank completely and with no bubbles present,
top and bottom skins actually forms a box, so the concept of a whilst then being able to empty the tank down to the very last
bag-in-box was born, rather like wine bags or the juice bags in drop. The whole system is of minimal weight, eliminates the
cardboard boxes that can be bought in supermarkets. need for a hopper tank and mounts neatly in the wing Photo 21,
To get some idea of how such a bag-in-box behaved in an air- in fact the perfect solution for the Concorde. The bag tanks were
craft, I built a box identical to that in the wing, produced from pre-assembled by me, Photo 22, although I had to send the
wood, with a glass lid Photo 18, allowing me to move this box tanks away to have the seams professionally welded
around to simulate aerobatics whilst watching how the bag tank (To be continued)
behaved through the glass lid.
Testing the tank like this showed that when the fuel level fell to Otto Wildroither
leave around 1 litre of fuel, and the tank was in the orientation it
would have when the model was in a gentle nose down attitude,

Photo 22

53





AUTHOR: DAVID GLADWIN

TECHNICALLY SPEAKING

POWERBOX IGYRO SAT degrees of bank. The model completed the turn to the start
point with EXACTLY the same bank angle as at the start,
Three issues ago, I described the basic workings of the again without any roll input at all. Any movement of the aile-
Powerbox iGyro SAT, a standalone gyro system which is cou- ron stick disconnects the AA function and the gyro reverts to
pled to PowerBox Core radios. At that time it was possible normal, damping, mode.
only to describe the basic workings of the system without a Loops were tried, and again, the model completed the loop
flight test. The device was hugely impressive but since that with the wings exactly level, as they had been at the start,
time it has been possible to evaluate the system where it without any aileron corrections whatsoever - extraordinary
counts, in the air, in this case in my long suffering PST accuracy. Inverted flight, again the exact bank angle or wings
Reaction jet, in which I have evaluated so many radios and level was held, and in 4 point rolls all the points were rock
associated electronic devices. steady.
For many years I have used gyro systems, both of the spin- Due CV restrictions on our flying I have not yet tried AA on
ning wheel type and latterly electronic, in a series of models. pitch but I have no doubt it will work on this function just as
These gyros have been coupled in the main to the rudder and well as on ailerons, and make rolls even more accurate, as
nosewheel steering functions, although more recently to the the gyro will keep the model pointing in a constant direction.
ailerons. In all cases the functionality of the gyros has been of An additional advantage is that in a crosswind take off or lan-
the pure damping mode, this giving excellent results, making ding when rudder is used to remove the drift, the gyro will hold
models much more “solid”; even the little Savex L-39 which wings level without any aileron input.
was extremely “skittish” due to its light weight and large fin, Of course, the gyro also has the facility to fine tune each out-
became much more stable, solid, and realistic. put as well as adjusting for airspeed with a GPS input. The
Although gyros such as the Weatronic system enable the use iGyro SAT is purely a sensor, the software is in the device to
of “hold” functions, it was the arrival of the iGyro SAT with its which it is connected. It is at the moment, however, only usea-
easily selectable damping/normal or “hold” functions; in flight ble on Powerbox receivers and the PowerBox Pioneer. Users
by a rotary dial, that meant it was realistically possible to try of other radios with need to use the larger PowerBox iGyro 3
the function on ailerons. PowerBox rightly describes the “hold” to achieve these results. However, I am so impressed with this
function as “Attitude Assist” rather than heading hold, but first Attitude Assist that ALL of my jets will use this feature in futu-
a few words about this function. re, certainly on ailerons, it is truly amazing. So, give it a try,
Before the arrival of the airliners with Flight Management once tried I am convinced you will be hooked!
Systems, (with highly capable digital autopilots) Boeing auto-
pilots had a function known as CWS, control wheel steering, STROBES
a form of superstabilisation.
With CWS engaged it was possible to set a pitch or roll attitu- The PowerBox Core is able to handle a large number of sen-
de with the normal yoke, but when input was released the sors, up to 250, and with the Vario sensor the values can be
autopilot maintained that exact attitude. This is exactly how seen on the screen, or alarms set to trigger announcements or
the PowerBox Attitude Assist works. When AA is selected, the warnings.
pitch or roll attitude at stick release is maintained with incredi- During recent evaluation flights of the Vario using my Hotliner
ble accuracy, the gyro reverting to normal mode if any further
control input is made, until THAT input is again released, after The tiny Powerbox iGyro SAT enables quite extraor-
which AA re-engages. The result is normal handling “feel” and dinary accuracy in both normal and Attitude Assist
response. mode. This unit is, however, just the sensing unit, the
AA can be engaged on roll, pitch or yaw axes but its use on software is in the receiver (from v1.65 onwards) or
the yaw function is discouraged for normal flying on fixed wing other Powerbox unit such as the Pioneer.
aircraft, as the AA response can cause resistance to turning,
so in this case only normal mode should be used.
For flight test AA was selected to be the default value of aile-
rons only. (It can also be assigned to pitch and yaw) The gain
control for the gyro can be assigned to a rotary control allo-
wing normal damping to be selected when the rotary control
is rotated one way, and attitude assist when rotated the other.
The centre position switches all gyro functions “OFF”. On the
first flight damping mode was used and the gain control adju-
sted to just below the point where oscillation started to occur.
It is very difficult to describe the feel of the damping mode, but
the aircraft felt noticeably more pleasant and stable, whilst still
being as responsive as normal. So far, so very good.
On the next flight AA was selected to see how well it held an
angle of bank, the result was quite extraordinary. Selecting
wings level, the gyro held wings exactly level for the length of
the field, without any roll control input whatsoever being requi-
red. Next, 360 degree turns were tried with both 30 and 60

56

TECHNICALLY SPEAKING

glider (a Simprop Lift Off), after looking down at the screen to Tiny strobes from Flying Tech are incredibly bright, weigh
observe values, it took a few seconds to reestablish visual con- just a few grams and simply require receiver voltage, no
tact with the glider. The thought occurred that strobe lights might controller needed. Cheap, too, at just over £5.00 each. Five
well hasten resumption of visual contact. modes (single, double or triple flash plus constant are possi-
Eventually I located very high power strobes from a drone com- ble, selected by simply shorting the two contacts seen at the
pany (Flying Tech) and these are now installed in the LiftOff, one top of the unit. Current drain is negligible.
on each side of the fin. The results have been highly impressi-
ve. These tiny strobes have amazing visibility, the strongest
flash I have seen on a model, even on a sunny Autumn afterno-
on, whilst on overcast days, they can’t be missed.
Each device weighs just a few grams and does not require any
form of controller, they are simply given receiver voltage via a
“Y” lead in a servo cable (without signal lead); 5 flashing
sequences are possible and are selected by simply shorting out
two contacts on the PC board upon which the strobes are moun-
ted. I use the triple flash, highly realistic, which as well as vastly
improving visibility, has a safety function, too. With the strobe
flashing it is an indication that the model is powered up or has
the engine running, invaluable in jet pits. It is an indication as
well, to the owner that his radio is switched on, no more forget-
ting to switch off and flattening batteries, Been there, done that!
Excellent value at just over £5.00 each, my sport jets are having
these strobes installed, as will my sailplanes, now I will know
which glider in the gaggle is mine!

V -SPEAK VARIOMETER and
AIRSPEED INDICATOR (ASI)

The PST Reaction is an excellent trainer jet with a large thick Two strobes fitted to a Lift Off glider, (my stick time here on
wing giving a low wing loading, allowing flight at very low spe- the farm during the Covid pandemic) one each side of the
eds, and is completely vice free. My Reaction has been used to fin, vastly improved visibility, even on Autumn days.
evaluate several radio systems, JR, Weatronic, Spektrum and
PowerBox Core, as well as other electronic devices. It has So, just what airspeed was being reached by the Reaction with
excellent aerobatic qualities too, and the big wing allows it fly its PST 1300 engine.
square loops with ease. After a recent flying session which inclu- The Reaction feeds its iGyro SAT with GPS speeds to adjust
ded tight radius square loops, I found the aluminium wing joiner sensitivity, but, of course, this is ground speed, airspeed chan-
to be to be bent, so just how much “G” was being pulled? The ged by wind effect. To obtain exact values an IAS sensor was
V-Speak Vario is an excellent device, incorporating an accelero- obtained, a device made by CB Elektronics in Germany.
meter function as well as a variometer and one has now been This is a plug and play device for the Core radio. When instal-
fitted to the Reaction. led in the Reaction in the workshop, zero was indicated and the
Flying normal diameter loops the “G” was recorded at plus 4 effect of a hair drier on the simple pitot tube gave a sensible rea-
(very similar to a loop in a jet trainer such as the Jet Provost) ding, but taking the model into the sunshine gave a reading,
with minus 3 during a Derry turn. On another flight with square when static, of 40 mph ! It appeared that the supplied clear sili-
loops, the “G” was 6 positive. Interesting numbers, and with the cone tubing connecting the pitot to the device allowed light to
Core it is possible to set a warning when the maximum G you
have selected is reached, whilst a double
press on the G value on the Core screen
gives the maximum and minimum values
obtained. The Reaction now has a car-
bonfibre wing joiner !

The V Speak Vario is both a variometer

with altimeter and an accelerometer. Tiny The long suffering PST Reaction has been the test bed for numerous electronic devices. It

both in physical dimensions and weight, but is the perfect jet trainer, highly aerobatic, capable of both high, 169 mph, and low speeds,

exhibiting extreme accuracy. the machine is totally vice free, including its reluctance to spin, however provoked!

57

AUTHOR: DAVID GLADWIN

As well as the vario function, height and On the Core the vario function The alarm values on the V Speak Vario can
rate of climb/ descent, this device can can be fine tuned to give the be set as required. Fullsize jets start to buffet
measure acceleration in all three axes. required tone at various climb when reaching max G, so this can be emula-
Z, the vertical, is perhaps the most and descent rates. ted with the V Speak by triggering vibration
important, X and Y are lateral and lon- when a high value of “G “ is reached.
gitudinal values. It is essential to mount
the device accurately to give true values. The CB Elektronics ASI device appears C/G’s, such as wooden trestles, hanging
to be very accurate when compared with frames or other devices, none of which
reach the sensing transistor. Replacing GPS groundspeed corrected for wind. are used to measure and calculate the
this tube with black Festo tubing blocked Small and light, it’s a “plug and play” C/G’s of full size aircraft, whilst the proce-
all light and restored proper function. device for PowerBox Core radios. The dure used in aviation can be directly rela-
This airspeed indicator is factory calibra- clear silicone tubing supplied with the ted to models and is really quite simple; I
ted against a Winter ASI (Winter make ful- unit MUST be replaced by a solid colou- have used it on many models over the
lsize instruments, mainly for sailplanes) red tube, e.g. Festo, to avoid spurious years. It would be quite difficult to place
and appears to be very accurate. readings due to light affecting the sensor. an A380 on a wooden trestle, so we can
Installation requires only a pitot tube, use, basically, the same procedures, par-
mine was produced from 1/8th inch dia- speed on approach. ticularly as we have no ordnance, pas-
meter brass tubing and spaced just over A very nice little unit which adds to the fun sengers or freight to worry about.
half an inch from the fuselage surface to of flying a jet model! To obtain an accurate C/G of the model
keep it clear of the boundary layer. requires only a set of bathroom scales or
On the Core the single cable plugs into similar, capable of measuring half of the
the P2 bus input of the receiver and aircraft’s total weight, obviously the more
detection is automatic. accurate the better, a tape measure or
On the morning of the test there was rule, paper and pencil and a basic calcu-
about a 10 mph breeze blowing. Passes lator, requiring just some very simple
into wind gave an IAS of 169 mph with a mathematics.
ground speed of 158 mph, whilst dow-
nwind passes showed 168 mph, with a The procedure is as
GPS groundspeed of 180 mph. follows:
In the afternoon the weather front had
moved on and the wind had dropped to BALANCING OF LARGE Firstly we need to establish a datum from
about to about 5 mph, this being reflected MODELS which the C/G is measured, and I use the
in the differences between IAS and GPS nose of the aircraft, which is just pushed
ground speeds, so the device appears to Jet models seem to be getting larger and up, square, against a wall from which we
be very accurate. Although the test was heavier and, as ever, correct balancing is take the measurements.
done using MPH, the device can be set to vitally important. The old method of The distance from each wheel axle, the
measure KPH or knots. When using the balancing a jet on one’s fingers has long two mains and one nose, from the datum,
Core it will be possible to set warnings at gone and would be particularly difficult on the nose against the wall, is then measu-
various speeds, useful to keep under the straight wing models. I see a variety of red. If the gear has trailing link or is at a
200 mph limit and to maintain minimum ways being used to obtaining correct considerable angle, then we measure

The simple pressure head is kept at least half Things in the Reaction are getting a bit crowded, but this IS a test and eva-
an inch, (1.2cm) from the skin to minimize luation model! Visible are two receivers, a Gyro, pressure sensor, battery and
position error due to the boundary layer. V Speak vario as well as a Sensor switch and BVM fill valves and gauges!

58

Large models can present a problem with TECHNICALLY SPEAKING
establishing the correct C/G. The procedu-
re described makes life simple. This is the
superb SkyGate Hawk of Jean Pierre
Zardini landing at the 2015 World Masters
at Leutkirch. The full size Hawk was pain-
ted in the colours of the first RAF Spitfire
when delivered to 19 Sqn at Duxford in
August 1938. My own Skygate Hawk was
balanced using this procedure and, unu-
sually, needed ballast in the tail.

Certain full size aircraft need ballast too, to correct C /G. Concorde had an aft C/G shift of 2 feet when it went super-
The Vampire T11 on which the writer trained in 1963/4 had sonic. To compensate, 7 tons of fuel were moved into the rear
200 pounds of lead discs in the nose to bring the C/G into the trim tank. This avoided the application of “Up” Elevon with
correct band after removal of the guns. This T11, with gran- associated trim drag, reducing drag and fuel consumption.
dson James, was one of the fleet flown by the writer, at 8 FTS
at RAF Swinderby, just a few miles from the museum, in TO ILLUSTRATE THE PROCEDURE LET’S
which it is preserved at Newark, Nottingham UK. RUN A SIMPLE EXAMPLE

from the point at which the leg is attached to the airframe. A model has a mass on each wheel of 8Kg and the wheels are
The weight or mass, on each wheel is then measured, it is 100cm from the datum, the nose. The moment on each wheel is
important to keep the model level, so books similar in thickness therefore 800Kg/cm from the datum so the total moments of
to the scales can be used to pack up the other two wheels whilst both mainwheels is 1600Kg/cm.
one is being weighed. The nosewheel is 50cm from the datum and has 1Kg of weight.
We now multiply the weight on each of the three wheels by its The moment is therefore 50kg/cm.
distance from the datum to produce three moments, and all The total moments are therefore 1650 Kg/cm, which when divi-
three values are added. That value will be in, say, Kilogram/cen- ded by the total weight, 17Kg, gives a figure of 97cm, which is
timetres. Of course, the units, pound /inches etc, don’t matter as the position of the C/G behind the datum; mark it with a cross
long as they are constant. !That is the actual, measured, C/G of the model now.
The three moment values are added together, and we now divi- If the actual, measured, C/G is BEHIND the required C/G, (tail
de that sum by the total mass, with the resultant figure being the heavy) let’s say by 5cm, then we need to create a moment
ACTUAL position of the aircraft C/G aft of the datum, the nose. which is enough to counter the out of balance amount.
On a piece of masking tape etc, mark that position on the air- So the total mass is 17Kg and the actual C/G is 5 cm behind the
craft, job done! required C/G, the moment is therefore 85Kg/cm, and we need
We now mark the position of the REQUIRED C/G on the tape to create a new moment from the required C/G which will be
and measure the difference in cm from the actual, measured equal and opposite to that 85Kg/cm.
C/G, and multiply that distance by the total weight. This creates If we could add mass/weight at say 40cm ahead of the required
a moment value from the required C/G position which needs to C/G, then the moment of 85 divided by 40 gives an answer of
be countered by an equal and opposite moment. 2.12Kg and that mass needs to be added at that 40cm point to
obtain correct balance.
If ballast was added at, say, 75cm forward from the required C/G
the required moment would remain the same, but the mass
would, of course, be less so the moment of 85 divided by 75
would require just 1.13Kg ballast.
In all three cases a moment of 85Kg/cm has been created and
the model is now balanced at the required C/G!
If the actual C/G is ahead of that required, then we simply rever-
se the corrective process to create the required moment.
Balance weight would be added behind the required C/G.
For a confidence check we can now repeat the exercise by remea-
suring the weights on the wheels and running the maths again. I
am confident you will find the new C/G is at the required C/G.
This can be accomplished in less time than it takes to read this
article, no trestles, suspension harness or other apparatus
required, and requires only one person for the operation!

David Gladwin

59

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AUTHOR: COLIN STRAUS - PHOTOGRAPHERS: COLIN STRAUS AND BOB PeTRIe

FlyFly

VIPERJET

I had never owned or flown a Viperjet, so Pilot with completed Viperjet, ready for first test flights.
when the opportunity arose to review the 2.2
metre wingspan example of this airframe pro- servos was quite straightforward, these hav- into the wing panels I found that due to the
duced by FlyFly I was delighted to accept. ing the supplied "L" brackets attached and size and design of the retracts they would not
Shipped direct from the factory in China, the then these in turn being secured to the sit down onto the retract mounts, in fact they
model arrived safely in two boxes, the inter- mounts in the wing. The twin horns were then sat more than 6mm above the above the
nal parts being well protected for their long glued into place into the control surfaces, mounts, this being due to the sideframes hit-
journey. Supplied with the model was a along with their cover plates, the covering film ting the small sections of wing rib remaining
matching set of JP electric retracts, oleos, under these having been carefully cut away at the base of the cutouts, thus it was not
wheels and brakes, 2 fuel tanks and twin wall first. All the control surfaces had been possible to cut any of this away to allow the
tailpipe with intake cone. The wing joiner was installed at the factory, but I found that some retracts to sit any lower. In the end I cut some
a good quality carbonfibre tube, whilst a pack of the pin hinges were insecure, so I used a 1/4" ply spacers and epoxied these to the
of small parts was included containing some small syringe to squirt a mixture of 20 minute mounts to raise the retracts just enough to
nice twin horns with small cover plates, as epoxy and milled fibre into the sockets of allow them to fit, although this did bring them
well as various bolts, screws, washers etc. these hinges, having warmed the mix in very close to the underside of the prefitted
One disappointment was the lack of any advance so that it would run easily into the outer gear doors, which in fact had to have
cockpit interior at all, not even a cockpit sockets - this proved to work well and solved small amounts of the inside surface ground
coaming/dashboard being provided, which is the problem. away for clearance. No linkage parts were
very noticeable through the large canopy. When I came to install the electric retracts supplied for the gear doors, but luckily I had
Although FlyFly cannot supply a cockpit inte-
rior, they do advise that cockpits from other
2.2 metre Viperjets can be used.
Construction of the model comprises a com-
posite fuselage with built-up and sheeted fly-
ing surfaces, these being covered in film.
Assembly commenced with the flying sur-
faces; the quality of the flying surfaces being
quite good, these being very conventional in
both design and construction - the film cover-
ing was neatly carried out, but a few bubbles
had developed during the models' travels,
these were easily removed with a heat iron.
Work commenced on the wings with the
aileron and flap servos and extension leads
being the first items to be installed. Fitting the

62

FLYFLY VIPeRJeT

How low can you go? Well later on the Viperjet
was less than 10cm above the runway at times.

Just above the "S" in "BOSS" an Another section of silver retracts and brakes. The set I had brought
area of the fuselage had been sanded paint that had been sanded back from JetPower was the kit set with 6 pri-
at the factory and then not repainted. down without refinishing. mary connections and 10 secondary - to clar-
ify, the primary connections (for flying control
An example of the very poorly pro- Inserting a drill bit the same diameter as the servos) are doubled, with contacts on both
duced holes in the wing roots of the anti-rotation pegs into the matching hole in sides of the connecting blade/socket, where-
fuselage for the wing anti-rotation pegs. the wing root shows just how poor the fit is. as the secondary (retracts/brakes/lights etc)
some small balljoints, horns and threaded rod ing edge of the wingtips did not match that of connections are single, as these are not quite
sections, so was able to make up what was the wing panels, and the chords also did not as critical. It was relatively straightforward to
required. match, with that of the wingtip being longer assemble the kit of parts (the UniConnect
Whilst fitting the moulded wingtip mouldings to than that of the wing panels. I had to carefully units are also available fully assembled, with
the wing panels I came across a couple of sand down the trailing edge of the wingtips to extension leads pre-fitted), although some
problems; firstly the holes for the carbonfibre correct this, luckily I had some matching paint thought had to be given to the sequence of
dowels used to attach the wingtips to the wing to make this good. soldering and assembly, to allow leads to be
panels did not line-up accurately, making it I had seen the very neat new UniCONNECT fitted on the inside faces of the blades. Once
impossible to fit the wingtips. I had to open up wing to fuselage connectors from uniLIGHT all assembled the units were then installed in
the holes in the outer ribs of both wing panels at JetPower last year, so I decided to use the the wing roots and the fuselage, so that as
until the wingtips would fit, at which point the set I had bought in the ViperJet, as this model the wings are slid into place the connectors
second problem arose - the angle of the trail- has two wing servos as well as electric automatically plug together. It should be
noted that the design of these connectors
means that they have a limited amount of
free movement, this allowing for any move-
ment of the wings under flying or take-
off/landing loads. Moving on to the fuselage,
which is in two sections, the mouldings
looked to be of reasonable quality, with ply
formers bonded into place, the break point of
the fuselage being just behind the air intakes.
The paint finish was rather poor, with a num-
ber of areas where the paint had cracked,
perhaps as it had been applied heavily and
without the fuselage having been sanded or
scuffed prior to painting, although these
cracks were unsightly rather than being struc-
tural, no evidence of the cracks being found

63

AUTHOR: COLIN STRAUS - PHOTOGRAPHERS: COLIN STRAUS AND BOB PeTRIe

With the main retract in place in 1/4" Ply packing sections were The trailing edge of the moulded
the wing the mounting lugs sit some cut out and epoxied into place to wingtips does not match the wing trail-
6mm above the retract mounts. support the main retract units. ing edge and had to be modified to fit.

Masking tape was applied to the cockpit area of the fuselage to mark out Air intake masked off to allow the
straight lines - Permagrit tools were then used to remove excess material. internal ducting to be painted.

Underside of the rear fuselage showing how the Additional ply sections were added to the rear cone
ventral fins cut across the pre-applied Shell decal. former to support the (smaller diameter) tailpipe.

in the fuselage mouldings themselves. I also down on the model when it is on the ground. middle of the decals.
found a number of areas where it appears Quite a few decals had been applied to the The ventral fins themselves have threaded
that painting flaws had been sanded back fuselage, but some of these had already rods bonded into them, these fitting into
with fine sandpaper, but no refinishing had started to flake off, as it seems that no protec- predrilled holes in the fuselage - here again
been carried out. The areas of the fuselage tive clear coat had been applied over the there was an issue, with the rear of one of the
hidden behind the air intakes had not been decals. I also found that the Shell decals on fins stopping short of the rear tailcone, whilst
painted, and although these cannot be seen the lower sections of the rear fuselage had the other was positioned further back, and
when looking from the side of the model, been fitted where the large ventral fins are overlapped onto the tailcone. The appear-
these areas are very visible when looking installed, so that these fins cut across the ance of the inside of the air intakes was very

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FLYFLY VIPeRJeT

The supplied nosewheel steering Short arm eventually used - note Fitting the tailplane halves to the fuselage
arm on the left side of the photo the micro servo that had to be showed that the hole in the alloy mounting
was far too long to be used, hitting used due to the size of the servo tab for the securing screw did not match the
the inside of the fuselage. mount fitted to the nose retract. position or size of the hole in the fuselage.

poor, both due to the external paint fading out The edges of the canopy frame were very poorly finished and took a lot of work to correct.
as it continued into the air intakes, and
because of the very poorly applied (and
never faired in) filler that had been added at
the factory. I did paint the inside of the air
intakes, but drew the line at sanding the
excess filler down, as this would have affect-
ed the external paintwork that wrapped
around the front of the intakes.
It proved impossible to slide the carbonfibre
wing joiner tube into the fuselage, as there
was a large build up of paint inside both ends
of the outer section of tube bonded into the
fuselage. I had to wrap some sandpaper
around a suitable slightly smaller diameter
tube and use this to gently remove the paint
from the inner surfaces until the wing joiner
would slide smoothly into place.

TMsehcaeutercrianianglostphyRe /cwCaansoMpgoylduieenldlpelrianscteoGwlpuhleail,csetwthwiteihtghlmuDeaedglnruiexetess. Note the different angles of the pins at Looking from above illustrates that
the front of the canopy frame, making the pins are anything but parallel,
it impossible to fit to the fuselage. which of course they should be.

Nice double horns with mounting plates are supplied in View of the turbine and the forward mounting of
the kit, along with good quality linkages and balljoints. tailpipe through the underside hatch in the fuselage.

65

AUTHOR: COLIN STRAUS - PHOTOGRAPHERS: COLIN STRAUS AND BOB PeTRIe

Unilight's UniCONNECT floating wing connector is The assembled UniCONNECT wing and fuselage connectors
available as a kit, seen here, or fully assembled with leads. complete with extension leads, note that the upper set of contacts
(for servos) is repeated under the tab, for maximum reliability.

UniCONNECT connector socket mounted in the wing root of the Viperjet. Wing connector in situ.

I was very disappointed to find that the two holes in each of the wing After suffering minor damage to the main undercarriage mounts at the end
roots of the fuselage were both much larger than the matching carbon of the first flying session I found that the oleo legs had seized solid, the rea-
anti-rotation pegs in the roots of the wing panels, and were anything son for this being evident in the galling of the leg components..
but round, see the photo for an example of this. Because of this, both
wing panels could rotate around the main wing tube, with the leading
edges able to move by at least 4mm vertically, something that would
have had a very negative affect on the flying performance and con-
trollability of the model, to say the least!
To correct this problem I found some brass tubing that was a tight fit
on the wing pegs, with short lengths of this tube being glued into the
oversized holes in the fuselage wing roots. Small amounts of filler
were then applied to fill any small gaps, with this then being rubbed
down, and finally the wing root section was given a coat of silver paint,
which matched the fuselage colour pretty well. I did also find that the
holes in the wing roots for the wing retaining bolts did not line up with
the prefitted spike nuts in the roots of the wing panels, but in this case
I was able to open up the holes in the fuselage to match those in the
wing roots, with a large washer bridging the enlarged hole and
spreading the load.
Turbine installation is through the underside hatch in the fuselage,
and this was quite straightforward, however test fitting the tailpipe

Main on-board equipment layout, including the PowerBox Source, Futaba R7014SB A poor photo, but it does show the ECU
receiver, JP retract controller and KingTech turbine fuel pump and ECU. battery and two radio batteries installed in
the nose, on a plate over the nose retract.
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FLYFLY VIPeRJeT

showed up another problem, in that the rear ous mounts and glue these to the appropriate canopy area of the fuselage, to get it looking
former in the fuselage had an internal diame- formers, the plates (the front plate had to be presentable. A more serious problem was
ter of 87mm, whilst the outer diameter of the shortened to fit where shown) then being with the locating pins at the forward end of
tailpipe at this point was only 79mm, requiring secured to these using small self tapping the removable canopy, these were far too
spacers to be made up and glued to the for- screws. long, had been covered in paint, and instead
mer to support the pipe. The clear canopy was supplied as separate of being parallel with each other (required if
When I commenced fitting all the on-board front and rear sections, these having to be the canopy frame was ever going to be pos-
equipment I was surprised to find that glued into the canopy frames by the builder. sible to fit) were at completely different
although ply hardware mounting plates had Before I could do this though I had to spend angles to each other, both horizontally and
been supplied there were no mounts for quite some time trimming and sanding the vertically. Clearly this canopy frame had
these, apart from the forward of the three edges of the frame, as the edges of the frame never been fitted to this or any other fuselage
plates, which had a pair of tongues that fitted were extremely uneven, and appeared to once the locating pins had been installed! As
into slots in the former to secure at least the have only roughly been cut out at the factory. they were securely glued into place, I used a
front end. Due to this I had to make up vari- I also had to do this to the inner edges of the powerful soldering iron to heat the pins until
the glue softened, at which point it was quite
Straight and level, the Viperjet proved particularly stable in flight. straightforward to twist them free. Once they
had cooled, I cleaned off all of the paint, cut
On approach with flaps extended and gear down. the pins down in length and carefully glued
them back into position, ensuring that this
time they were parallel and matched the
holes in the fuselage.
Two rather heavy but strong moulded plastic
fuel tanks were supplied in the kit, but no
mounts for these were provided. One tank, of
2400cc capacity, sits between the air intake
ducts, but on top of a former, so balsa blocks
were cut to shape to bridge the gap between
the fuselage base and the underside of the
tank, these being glued to the fuselage, with
the tank then being siliconed in place. The
upper tank, which contains 1000cc, was also
secured in place with silicon, in this case
being glued to the curved upper fuselage and
to the top of the air ducts. A filtered heavy
duty clunk was fitted in the main tank, with no
header tank being used.
When I came to fit the tailplane halves to the
fuselage I ran into another problem - the
tailplane halves are held in place with M4
screws into alloy sections bonded into the
tailplane structures. The centres of the M4
tapped holes are some 7mm from the root of
the tailplane, but the holes in the underside
on the fuselage for these had their centres
only around 4mm from the edge, whilst also
being only around some 2.5mm in diameter. I
had to carefully measure and mark out the
correct position for the screw holes in the

In the air at Baldock and curving round the camera with flaps down.

67

AUTHOR: COLIN STRAUS - PHOTOGRAPHERS: COLIN STRAUS AND BOB PeTRIe

fuselage, and then drill these without the drill The second flying session saw landings improve further, being even slower and smoother.
drifting into the existing holes. Once this had
been carried out it was possible to fit the without any noseweight being required. drop was the final outcome, giving confidence
tailplane halves, but I found that one tailplane First flights were made at the grass flying as it was fast approaching the time to land.
half did not match the fuselage correctly, with field of the North London Model Flying club, When the timer announced the fun was over,
the leading edge touching the fuselage, but which unusually for this excellent site was the Viperjet was turned into the landing circuit
the trailing edge being some 3mm out, there rather bumpy when flying took place, with the and the undercarriage lowered, half flap
being no way of correcting this short of build- grass also being somewhat longer than being set on the downwind leg, with full flap
ing a new tailplane half - in the end I found usual, possibly due to the restrictions brought being selected as the model rolled out onto
that there was enough flex to allow the about by the Covid-19 pandemic. its final approach, which proved to be nice
tailplane to be pulled into alignment, some Once the Viperjet was assembled and and steady. The touchdown was very
heavy duty clear tape then being used to checked over, a full range check was carried smooth, although a little fast, and the brakes
secure it in place. out and failsafe operation checked. Both soon brought the model to a halt, before it
Equipment used in the Viperjet included the tanks were filled and the KingTech K-120 fired was taxied back along the runway.
KingTech K-120G2 turbine, Futaba R7014SB up, which it did without fuss, as usual, after Further flights just reinforced the impression of
receiver and Futaba servos all round on the which the model was taxied out onto the run- a very smooth aircraft, that presents well in the
flying controls, PowerBox Source twin battery way. Once lined up, the throttle was opened air, and capable of easily carrying out all the
system with display and switch etc, and a and the model accelerated away well - it aerobatic manoeuvres I attempted. These also
total of 4 battery packs, two 2 cell 2200mAh quickly reached flying speed, and a solid pull confirmed that the calculated balance point
Li-Po's for the radio system, one 2 cell back on the elevator stick saw the model lift was just about perfect, the model being very
2200mAh Li-Po for the electric retracts and smoothly off the ground, with the landing gear stable with good stall characteristics, whilst
brakes and a 3 cell 3450mAh Li-Fe for the then being retracted as the model was just a small amount of forward pressure was
turbine. climbed to a safe altitude. It was clear that required to hold level inverted flight.
I did find another issue, this time with the some trimming was required, but nothing too Unfortunately, flying for the day was cut short
nose retract, with the steering arm and link- extreme, just a few clicks of aileron and eleva- following the fourth flight, when a strengthen-
age supplied being unable be used as the tor trim saw the model flying straight and level ing and gusty crosswind lead to a slightly fast
steering arm was far too long, and would hands-off. I was immediately impressed with and bumpy landing, although nothing
have protruded through the fuselage side. I how smooth the model was in the air, it felt extreme. When I checked the model over, I
used a shorter balljoint arm I had in stock to like I was flying a much larger model, or one found that there had been some slight dam-
overcome the problem. I was also surprised that had been fitted with a gyro, which of age to both of the main undercarriage mount-
to find that the steering servo mount on the course had not been installed in this model. ings, although this was only really visible on
retract unit was for much smaller than stan- Feeling very comfortable with how the model the underside of the wings. We were all sur-
dard servos, and in fact following a search was flying, I bought the Viperjet down for my prised at this as the landing had not been
the only servo I had that would fit was a expert photographer, Bob Petrie, to wield his particularly poor, and the undercarriage
Quartz micro servo, which although metal camera, although the poor light and dark sky mounting structure in the wings looked to be
geared did look rather undersize for the job - made this quite a challenge! Following a num- quite substantial, even including carbonfibre
time and flight testing would be required to ber of low curved passes I took the model up reinforcement.
prove whether it was up to the job or not. for a few basic aerobatics, with loops, rolls When I got back to the workshop I started to
Gear doors for the fuselage had been supplied and some inverted flight being completed, investigate the problem, with suspicion
loose with the kit, but no hinges, operating again the smoothness of the model impress- immediately falling on the oleo legs, as one
rams or actuators were included, so as the ing. With time passing, I took the Viperjet up leg appeared completely seized, the second
Viperjet was to be flown as a sport scale model to a safe height to test its slow flight abilities, also being exceptionally difficult to compress.
I decided not to fit these, at least at first. trying this without flaps and with the gear When I tried to dismantle the legs it took a
When I came to check the balance point of retracted at first. Reducing the power and great deal of effort to separate one of the
the completed Viperjet I was surprised to find raising the nose saw the speed gradually scissor arms from the main leg, and in fact it
that the instructions, which otherwise were bleed off, until the model was flying remark- took the use of a block of wood and a ham-
not too bad, recommended a position some ably slowly, however the stall, when it mer to gentle tap the offending arm, until it
75mm forward of the wing tube, this being occurred, was quite sharp, the right wing was possible to remove it. Looking at the
confirmed by the instructions showing the dropping almost 90 degrees and the model mating surfaces showed that they had severe
balance point in line with a pair of simulated proceeding to dive until airspeed was galling, and had effectively locked together,
fuel filler caps in the wing root sections of the regained. I lowered the flaps to the landing jamming the leg, and thus transmitting any
fuselage. This seemed excessively far for- position, retrimmed (just a little down elevator and all landing loads to the wing structure.
ward for a model such as this, and would trim being needed) and again slowed the When I checked the other oleo leg I found
have required a huge amount of noseweight. model down - this time the stall was at an that it had suffered the same problem, and
I very much doubt that the model would have even lower speed, and a more gentle nose was almost as bad as the first. This explained
flown had it been possible to load enough
weight into the nose to obtain the recom-
mended balance point, and after a rough cal-
culation it was decided to use the wing joiner
position as the balance point, as this position
made sense both for percentage chord and in
relation to the main gear position. With three
of the four battery packs installed on a small
tray above the nose retract mounting rails
and the last at the rear of the main tray, the
model balanced at this calculated position

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FLYFLY VIPeRJeT

the damage caused by what was not a particularly bad landing - need- the main tank is still well over half full, so even longer flights would
less to say, I cleaned up the mating surfaces of anti-rotation arms and easily be possible. My concern over the size of the nosewheel steer-
oleos, getting them as smooth as possible, and then lubricated them ing servos appears misplaced, with no problems at all so far, even
with grease when reassembling. In the future I will keep a close check during the first four flights off a rather rough grass runway.
on the oleos, in case the issue reappears. After around a dozen flights had been completed a further flying ses-
Carrying out repairs provide fairly simple, just cutting away some of sion saw the Viperjet being flown in a gusty crosswind. Although a few
the underside sheeting to the rear of the retract units, and then push- more flights were successfully carried out, eventually I was caught out
ing back into place the wing ribs that had been displaced, before by a particularly strong gust, and the model suffered a rather bouncy
regluing these and adding some triangular reinforcements, as well as landing, although again nothing too extreme, so I was very surprised
some fillets from a mix of epoxy and milled fibreglass. With this com- to find that the right wing panel had suffered quite a bit of damage,
plete I was able to replace the underside sheeting and recover the with the retract mounts having broken away, in turn breaking the
affected area, so that it was almost impossible to detect that any work upper wing skin away from the wing root rib, and splitting the trailing
had been done. edge spar. The landing really was not too bad, and all those watching
A second flying session off the long runway at Woodbridge saw a fur- were very surprised that any damage at all had occurred, let alone the
ther three flights being logged, this time the model was pushed hard, extent of the damage. A larger expanse of the bottom wing skin was
with every manoeuvre I was able to perform being attempted, these cut away this time, and once the wing structure was exposed it was
including both upright and inverted spins, low inverted passes, contin- easy to see that the ribs supporting the retract mounts were totally
uous, slow, four and eight point rolls, loops both inside and out, and insufficient for the job they are expected to fulfil, being so thin
loops with snaps at the top. I also enjoyed ultra low passes with full between the retract mounts as to offer no strengthening at all. A small
flap, and some very slow flypasts, before opening the throttle and piece of carbon fibre cloth bonded to the upper wing skin did little to
knife edging from horizon to horizon. There were no more landing improve the situation.
problems, in fact the model touched down beautifully on all three When repairing the damage I was able to carefully slot the various
flights. My timer is set to 7 1/2 minutes at present, and after landing wood sections back together, using a variety of adhesives, including
20 minute epoxy, aliphatic resin and both thin and medium cyano. To
Esensjsoioynin,gancdlepararbtlwueayskthiersouagththaerosellc.ond flying add the required strength to ensure similar damage would not happen
again I added 1/8" and 1/4" birch ply braces between the retract
mounts and along the outboard wing rib at the end of the mounts, as
well as triangular reinforcements at all areas of stress. Completing the
repair saw new underside sheeting fitted and the area recovered, the
outcome being a much stronger retract mount/wing root area. The sec-
ond wing panel, which had not suffered damage in the rough landing,
had all the reinforcements possible added, where access allowed.
Overall, the FlyFly Viperjet really is a bit of a conundrum - I was quite
disappointed with the quality of the model in a number of areas, the
paint finish of the fuselage was poor, and the instructions had a num-
ber of mistakes, in particular a balance point that was all of 75mm too
far forward! Against this the Viperjet is relatively inexpensive, and
really does fly very well indeed. Having now corrected the seized
oleos and reinforced the main retract mounts I look forward to many
more flights with the Viperjet, helping me forget all of the issues that
had to be overcome to get the model finished to a decent standard.
Of course I have reported all my findings to the factory, who have
responded that they will make sure that everything I raised will be cor-
rected with future production Viperjets - I hope that this is the case,
and if any readers do decide to buy and build a FlyFly Viperjet in the
future it would be good to hear if the improvements needed have in
fact been made, ideally please let me know by e-mail to
[email protected].

Colin Straus

www.flyflyhobby.com

The Viperjet is equally stable inverted. ScanFltighhetQvRidCeoo!de!

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