Kit Review: FVK Bravo - FVK Modell

AUTUMN 2007
THE BEACON
PAGE 10
Kit Review: FVK Bravo
by John Dickison
Why Bravo?
After wondering what
model to move on to after
my power trainer and an
old Middle Phase, I decided
to go for an electric
glider; something that I
could fly at my local field
in the evenings, and at the
slopes at Ivinghoe (with
the motor disabled of
course).
I eventually settled on the
FVK Bravo, mainly because
it was about the size
I wanted (2m span) and
the fuselage was big
enough to take an outrunner
motor rather than the more expensive inrunner
/ gearbox combination.
My only concern was that the wing had aileronsonly,
but I decided to opt for this rather than its big
brother, the Signal (2.4m), which also has flaps. The
Bravo is sold as a hotliner but, for my purposes, it
would be an efficient glider with the emphasis more
on attitude than altitude.
After checking out the model at http://www.fvk.de/
Englisch/ and Brian Anderson’s build photos at
rcgroups.com, I sent him a cheque. Three working
days after he received it a very substantial cardboard
box arrived at my door. The model was well
packed with bubble wrap, and all the remaining
space filled with scrunched-up newspaper – so no
chance of any damage.
First Impressions: The Wings
The wing structure is foam / veneer. It is said to
have “glass cloth strengthening”; whether this is
over the whole wing surface, I don’t know.
The wings are very precisely made, with an absolutely
perfect middle joint comprising a 10mm diameter
x 200mm solid GRP rod, and a steel pin further
back. The GRP rod fits into the wings tube like
a piston, squeezing the air as it goes. The two wing
halves join with an amazingly precise fit. The wing
tips are particularly beautiful, curving up smoothly
to a point. Aerodynamically, I guess it must be
fairly efficient, with a triple taper plan shape and
MH32 aerofoil.
Two circular recesses are neatly pre-cut for the aileron
servos. The ailerons themselves are hinged
along the top edge with a vee cut underneath. I’m
not sure how the hinge is made but it feels fairly
substantial - not just a film covering.
The covering is Profilm, white on top and orangeyred
underneath. It’s absolutely crease free and perfectly
cut (how do they get such straight edges?).
There is the odd spec of dust under the covering,
but you have to look closely to see it.
Tee-tail and Fuselage
By contrast, the tee tail is a very simple affair, basically
6mm sheet with a rounded LE and tapered
elevator section, attached with what looks like diamond
tape with vee groove underneath. The whole
unit is attached to the seat at the top of the fin with
two nylon bolts.
The fuselage is a strong elegant white epoxy GRP
moulding with a clearly visible, but smooth, join
along the centre line. Carbon reinforcement is used
around the cockpit and wing apertures. Forward of
the fin the fuselage is generously proportioned—not
a bad thing for the odd less than perfect landing.
The fin section is quite thick so that it can accommodate
both rudder and elevator servos. I assume
that this also helps provide a stiff platform for the
tailplane.
The motor bulkhead is 3mm ply, pre-glued into the
fuselage, with a centre hole ready cut. The cockpit
is pre-cut from immaculate shiny black GRP, approximately
0.6mm thick.
Joining system
The wing attaches to the fuselage via two steel LE
pins and two nylon bolts at the rear. Curiously, no
load spreader plate is supplied for the wing bolts,
and after seeing the wing surface around the screws
bow very slightly, I decided to make a plate from

AUTUMN 2007
THE BEACON
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some glass PCB. In the fuselage the wing bolts tap
in to what looks like 3mm ply under the GRP.
Again, I played safe and glued some metal nuts to
the ply.
A bag of bits included: nylon bolts, control rods,
plastic clevises, control horns, and wire for that
clever way of holding the canopy on.
Instructions are packed into two sides of A4 with
diagrams and text for: build, setup, and power system.
They also cover the non-electric version of this
model. Being new to this game, I had to email
Brian a “few” times with questions, and he was
most helpful.
Power System
I opted for the only out-runner recommended, the
AXI 2826/10. The instructions show that with a
14x9.5 prop and 3S2P LiPo this draws 46A. I actually
used a 3700 mAh 3S1P LiPo and a 14x9 prop
(because that was in stock). The AXI website shows
this arrangement to be about 72% efficient, which I
guess is the price for not using an in-runner with
gearbox. I used a Jeti 40 controller as recommended
on the AXI site.
I struggled a bit with spinners and all the gubbins
for the folding prop blades, but eventually settled on
an open nose spinner for good cooling (hopefully).
The one I chose is an all-in-one item and, unlike
others I tried, it didn’t require a large hole in the
ply bulkhead. The instructions say to use a 41mm
spinner, but I could only find 42mm and 40mm and
I plumped for the latter.
Prop and spinner assembly
Getting down to assembly
I think I probably hold the unofficial world duration
record for a Bravo assembly but, in my defence, this
business of gluing servos in is all a bit scary to the
uninitiated!
I started at the back, hinging the rudder with the
pinned tab hinges supplied. The wood at the back of
the fin was surprisingly hard. Then followed multiple
test installations of a pair of HS81 MG servos.
This was fairly awkward because they had to keep
going in and out through the hole in the side of the
fin.
I packed the lower/rudder servo with balsa, so that
the servo arm poked out as far as possible. The elevator
servo was packed the other way to allow its
arm to sit within the fin, just clearing the inside of
the skin. The arm was cut down from a huge one I
had that normally takes a brass clamp ring. Anyway
it did the job, although I had to relieve the
metal clevis slightly.
Hitec HS 81 MG’s are a tight fit
The elevator pushrod is a simple threaded steel rod
and requires an exit hole at the top of the fin. Similarly,
I had to enlarge the rudder horn slot. I went
to the trouble of making the more robust elevator
horn shown in the instructions - it wraps round the
TE to the top surface. I took the precaution of using
soft locking compound on all threads before gluing
the servos in place. This was bit of a puzzle, the procedure
being: both servos in
through the hole, screw in the
elevator pushrod, glue and
pack the rudder servo, slide
the elevator servo out of the
way, apply the glue for it, slide
it back and pack with balsa –
or something like that. Fortunately,
it all went well and, after
the epoxy had gone beyond
the point of no return, both servos
operated correctly.
Elevator linkage
Motor Installation
The AXI motor is a fairly easy fit in the nose, but
the leads exit the motor at 90 deg and were hard up
against the side of the fuselage. I seriously considered
cutting the fuselage to allow the leads to poke
out but in the end, I just about found enough space
for them, by doubling the thickness of the ply bulkhead
and recessing part of the new wood next to the
leads. Also, to allow slightly sharper bend radius, I
ever so carefully cut back some of the stiff plastic
around the leads where they exit the motor - all a
Modified bulkhead

AUTUMN 2007
THE BEACON
PAGE 12
Bravo (cont)
After a chat with Mike Shellim on the benefits of
the Multiplex Cockpit SX, I changed from my Futaba
EX6 to the SX. The SX was a revelation in so
many ways, but the main benefits in this case were
reduction of aileron differential with aileron-spoiler
and proper servo travel limits. I set the control surface
travels to the “aerobatic” settings given in the
instructions, rather than “thermal”.
Motor fitted to bulkhead
bit near the limit but I got away with it.
I cut cooling holes in the bulkhead to match up with
the motor openings and, after giving the ply a coat
of sanding sealer, the motor was mounted using the
standard four screws with locking compound. The
motor leads were taped to the fuselage wall to stop
them touching the moving part of the motor body.
Radio Installation
I used HS 125 MG servos for the ailerons. These got
the full treatment; mounts cut off, roughed up with
silicon carbide paper, degreased, and then glued in
with 5 minute epoxy. I found that the circular cutouts
in the wing needed enlarging. After doing the
rather fiddly ply lining, the servos were blocked in
and glued.
Hitec HS125 MG servos glued in place. Looks neat!
I glued the supplied aileron horns onto the surfaces,
after cutting away the film, rather than using the
optional height adjustable ones mentioned in the
instructions.
For the Rx battery I used an 800mAh Sanyo AAA
NiMH pack. The Rx battery was mounted close to
the CG, with a Futaba R147F receiver just behind
it. The Flight Power 3700 25C LiPo was probably
not the best shape for this model, but I managed to
adjust its position to get the CG about right. It was
secured using foam and Velcro. I added a couple of
tubes to help get the cooling air past the receiver
and battery foam – well that’s the theory.
The aerial went out through a hole I made in the
top of the fuselage and then up to the top of the fin
in the standard draggy power model fashion. All
connectors were standard Futaba type.
Various components ready for final assembly
Woo hoo—first flight!
After a motor test run and with the CG set at the
most forward recommended point (70mm from the
LE), I headed for my local field. It was a beautiful
sunny morning, with a light breeze along the length
of the field. I was pretty nervous about throwing my
precious glider into the air; at 1.6 kg it was no
feather weight and would require a hefty launch.
Also, I made a last minute change from mode 6 to
mode 2, i.e. swapping throttle/spoilers, so that the
slightly tricky right-hand slider was confined to
spoilers.
The moment of truth arrived, I set the motor to
about half throttle and ran forward and hurled the
Bravo into the unknown. To my relief, it flew perfectly
straight in a shallow climb and, after what
seemed like an age of being unable to take my eye
off the model, I found the right hand stick and took
control.
Favourable Impressions? You Bet!
My first impression was that of precise, stable handling.
The glide performance was so good that I could
glide in on a test approach at about 30ft from the
far end of the field and still be at a good height by
the time it passed me. Overhead passes on low
power revealed the slightly eerie presence of this
model, with its large bird-like wings rock steady
and the motor humming menacingly.
Gliding down it became apparent that this model
could exhibit Klingon style cloaking, and for a few
terrifying seconds I found myself staring at what
appeared to be empty sky!
A few slow circuits showed that the skinny MH32
aerofoil would take considerable abuse in tight low

AUTUMN 2007
THE BEACON
PAGE 13
speed turns without a hint of tip stall. Being relatively
new to almost zero dihedral, I sensed that
lack of concentration would be punished severely
with this model.
Landing
Finally it came to the first landing; over the fence at
the far end of the field, aileron spoilers full up about
100ft away at about 20ft high, and it came in without
any fuss whatsoever. All my concerns about
landing without crow braking were gone.
Further launches followed. Getting more adventurous
in the climb, I used full throttle and was
amazed. This model can scream up vertically faster
than anything I have ever seen. It’s as if someone
had switched the sign on gravity! Once or twice it
did a little jump in these manic climbs – possibly
ESC noise?
Loops were fast and smooth but, given my limited
piloting skills, I didn’t go any further than that.
Landings can be flared if required, giving rise to a
gentle but curious nose up attitude in ground effect.
After 20 minutes on each battery I found that they
only needed a half charge. On this basis, 30 minute
flights without thermals should easily be possible.
Cooling did not appear to be a problem, but I think I
will have to keep an eye on it when I start using
high power for longer.
In Summary
The Bravo is exactly what I expected and more. It’s
a high quality, well designed and versatile electric
glider that is well supported by the UK distributor.
Launching and landing cause no real drama. You
can thermal it, or glide in at low level swooping
around with the occasional squirt of amps, but push
the throttle forward and it all gets seriously fast,
the main limitation being pilot ability to keep up
with it. I see no reason why a less powerful motor
would not suffice for “normal” flying.
I’ve yet to explore aerobatics properly, and I guess
the aerofoil would not be great in prolonged inverted
flight, but that’s not really what this model
is all about. I’m certainly looking forward to the
next flying session.
John Dickison
Kit Specification
Span
Length
Weight:
Wing Profile
Controls
2 m
1.09 m
0.85 kg
MH32
Cost £163
Manufacturer
UK Distributor
Rudder, Elevator, Ailerons (2 servos),
Motor Speed
FVK
Brian Anderson