|
|
Wingspan:
|
60.75"
|
|
Wing area:
|
425 sq. in.
|
|
Weight:
|
26.5 oz.
|
|
Wing Loading:
|
8.95 oz./sq. foot
|
|
Airfoil:
|
Semi-symmetrical
|
|
Functions:
|
Aileron/rudder/elevator/throttle
|
|
Motor:
|
Watt-Age Super Cobolt 400, direct drive
|
|
ESC:
|
Watt-Age IC-30A
|
|
Battery:
|
8 cell 800mAh
|
|
Receiver:
|
Hitec 555
|
|
Servos:
|
ailerons: Hitec HS-55, v-tail: Cirrus CS-20
|
|
Transmitter:
|
Futaba 8UAFS
|
|
Construction:
|
Fiberglass fuselage, built-up balsa wings and
tail
|
|
Available From:
|
Hobby People
|
|
Introduction
This is my first electric sailplane. I have quite a few high
performance slope planes and several glow-powered planes, but
only two electrics so far: a Zagi 400X and a Mini Max park
flier. So, when offered the chance to review an electric
glider, I jumped at the chance.
The Vx-400 appears to be aimed at the low-intermediate level
pilot, who perhaps already has a rudder-elevator controlled
electric sailplane. It features a mix of what I would
consider “beginner” and
“intermediate” design elements, in that it has as
a simple, straight, built-up wing, combined with a sleek
fiberglass fuselage.
Kit Contents
On opening the box, you’ll find about six major
components, plus assorted hardware.
|
|
The main components.
|
The pre-painted fiberglass fuselage is nicely molded, and
seems fairly light. The firewall is molded into the nose and
the wing mounts are installed and pre-drilled. Something I
found a bit unusual is that the fuselage seems to have been
spray-painted rather then having a gel coated paint job. The
finish isn’t bad, but it’s not perfect either,
and in some spots the paint seems to have been applied quite
heavily. There’s also quite a bit of over-spray on the
inside of the fuselage.
The pre-painted fuselage.
|
Lots of room.
|
A tinted plastic canopy is included. It comes already trimmed
to fit, though I must say it doesn’t fit quite
perfectly to the molded in recess for it in the fuselage.
|
|
Pre trimmed tinted canopy.
|
The wing comes in three pre-covered parts: a flat center
section and two tip panels. The wings are of typical balsa
construction, with a fully sheeted d-box leading edge, and
open bays behind that. The ailerons on the outer panels are
pre-hinged, and there are servo bay ready to accept the
aileron servos.
|
|
The bottom of the left wing tip panel.
|
The specifications give no hint as to what airfoil is used,
but it does at least look like a modern sailplane section, in
that it is fairly thin and has a bit of camber. The wing planform is extremely
simple: it’s almost completely straight, with only a
hint of taper at the tips of the trailing edges. The center section is flat,
while the tip panels get attached at bit of an angle to give
some tip dihedral.
|
|
A look at the airfoil used on the wing.
|
The wings come pre-covered with a transparent red plastic
covering. he covering job is extremely good, with no wrinkles
and virtually invisible seams. Inside each wing panel is a
piece of string that’s to be used to pull the servo
leads through once the whole thing is assembled.
|
|
The wing center section. The servo lead strings are
visible through the covering.
|
The left and right v-tail pieces come pre covered as well.
They are also made from built up balsa, and come with
pre-hinged ruddervators.
|
|
One of the v-tail halves.
|
In addition to the major components, the plane comes with ply
servo and battery trays, ply wing joiner blades, a few other
pre-covered wood parts, push rods, control horns and other
assorted hardware needed to complete it.
Assembly
The Vx-400 is an ARF, though there are still a few major (but
not difficult) construction tasks. Never the less, there
aren’t too many steps needed to complete the model, and
it shouldn’t take very long for most people to finish.
The first step is to install the aileron horns. The horns
included with the model are nicer, and quite a bit different
then those shown in the instructions (though this would be an
issue later on).
With the horns installed, the next, and largest constructions
step, is to put the wing panels together.The tip panels are
held to the center section using a short plywood joiner
blade, which fits into a slot in the respective parts. I
trial fit the parts and found everything was aligned
correctly and ready to join. Before the panels are joined,
though, the servo lead strings in each panel must be tied
together so that the leads can be pulled through the
assembled wings later on.
|
|
One of the tips, almost ready to be joined with the
center section. Small paper tube keeps glue off of the
servo lead string.
|
With the first panel ready to be joined, I placed the center
section flat on the bench, and the outer panel blocked up to
provide the proper tip dihedral. I found that the ends of the
panels were not entirely flat, and did not quite meet
perfectly, causing a bit of a gap at the mating surface. On a
kit, I would have pulled out the sanding block at this
point to try to get everything perfectly flat. As this was an
ARF, and already covered, I was somewhat reluctant to do
this. I decided to go ahead and glue the parts together and
live with the small gap (and a bit of extra weight owing to
the extra epoxy needed to fill it).
Once the first panel was joined and the glue dry, I moved on
to the other panel. My experience with this one was the same
as the first, as I ended up with a small gap where the wing
parts joined here as well.
The rear wing mount bolt-hole is already drilled in the wing,
but you must remove some covering and glue in a small ply
reinforcement plate. The hole for the leading edge wing dowel
is also already drilled, but I found that it was a too small
for the included dowel, and had to be drilled out a bit.
|
|
Rear wing mount reinforcement.
|
The next step is to install the aileron servos. I soldered
extension leads to my servos, and then used the strings in
each wing to feed the leads through, from the servo bays to
the wing root. Once I had reattached the connectors to the
ends of my servo leads, I secured the servos in their
bays using a dab of epoxy to glue them in place, having
wrapped them in masking tape beforehand.
The aileron pushrods are hooked up once the servos are
secured. into the first little complication here. The kit
comes with precut aileron pushrod wires with z-bends on one
end. The z-bend end is supposed to hook up to the servo arm,
while the aileron horn end is secured with an
“EZ” type connector, that is held in place with a
tiny “e” clip.
The problem was, the supplied servo horns were so thick that
the e-clips could not be installed to hold the connectors on.
In the end, I went with a more conventional route: I soldered
a threaded joiner to the end of the pushrod, and used a
clevis to connect it to the aileron horn.
With the servos connected, I confirmed that I had the desired
amount of servo movement. The supplied servo horns are quite
large, so once I was satisfied with the range of motion I was
seeing, I cut down the horns to a more reasonable size and
rounded them off.
|
|
|
Aileron servo installed and connected.
|
I cut down the rather large aileron horn.
|
With everything installed, I found that the wing was somewhat
out of balance. The left wing needed a bit of weight, so I
drilled a hole in the wing tip and inserted a small nail to
get it balanced.
The final step in wing construction is mounting it to the
fuselage. All that’s needed to be done is to install a
blind-nut under the rear wing mount in the fuselage and to
glue a dowel into the leading edge of the wing. I did find
that the hole in fuselage's forward wing mount was a bit too
small for the dowel, though. I used an appropriately sized
drill bit, turned by hand, to widen out this hole so the
dowel would fit.
With the wing now test-mounted, I measured from each wing tip
to the tail to confirm the alignment. As it happens, there
was about a 1/8” difference between the two sides. To
fix this, I used a drill and file to move the leading edge
dowel mounting point a bit to the side, so that the dowel
could be placed in a position that would get the wing lined
up properly. Once satisfied, I glued the dowel in place and
confirmed that the wing mounted properly. With that, wing
construction was done.
Fuselage:
The first step is to cut some cooling slots in the forward
fuselage. Here the instructions are less then clear. Although
the text specifies where the slots are to be cut, the
illustration clearly shows the slots much further forward
then this. I decided to split the difference and cut the
slots between the text description distance and the distance
where the slots appeared to be in the in the illustration. It
should be noted that the hole at the end of the tail boom
provides the only air exit, but I didn't find over heating to
be an issue while I was testing the plane, so that seems
okay.
|
|
Cooling slots.
|
Now it was time to install the motor and speed control. I was
using the recommended Watt-Age Super Cobalt Speed 400 motor
along with the Watt-Age IC-30A speed controller. Once I had
done the recommended motor break in procedure, I followed the
instruction’s suggestion and soldered the speed control
wires directly to the motor poles, rather then using
connectors. I then drilled the mounting holes in the firewall
and mounted the motor. I finished it off by installing the
recommended prop, a Graupner 6x3 CAM folding propeller.
It was now time to install the ply servo and battery trays.
The cut outs in the servo tray needed to be lengthened just a
bit to accept the Cirrus CS-20’s I would be using for
the v-tail. The instructions mention that the inside of the
fuselage needs to be roughened up before the trays are glued
in place, but I’d argue that more then this is needed.
As mentioned earlier, there is quite a lot of paint
over-sprayed into the inside of the fuselage, so I tried very
hard to remove all the paint before gluing the tray in place.
After trial fitting the part and marking its position, I
epoxied it in place. I decided to hold off on gluing in the
battery tray, though. I wanted to verify that it would be in
the proper position to balance the plane once everything else
was installed.
|
|
The servo tray installed.
|
Installing the v-tail push rods is next. The push rods neet
to exit the fuselage just below the v-tail saddle, and slots
must be cut in the fuselage to accommodate this. The plastic
pushrods guides are then glued in at this spot, and once
again on a small block at the rear of the servo tray. I was a
bit concerned about the tubes not being supported anywhere in
the middle, though. I ran a few drops of CA down the outside
of each tube to secure them where they came into contact with
the fuselage.
|
|
A look at the push rod guides exiting the fuselage
below the v-tail saddle.
|
V-tail:
The v-tail must be assembled out of three parts: the two
v-tail halves and a central wedge shaped fairing that joins
them. The fairing is first glued to one of the halves. Next,
with the tips of both halves blocked up to achieve the
required angle, the other v-tail half is glued into place.
Once it was assembled, I test fit the tail to the fuselage
and found that the central fairing piece sat quite high above
the v-tail saddle. I ended up sanding down the bottom of the
v-tail assembly quite a bit to get it to fit flush.
|
|
The v-tail halves and their center joiner fairing.
|
Now came the last major assembly step: attaching the
v-tail. The
instructions mention that the tail saddle on the fuselage
should be roughed up before gluing the tail. In my opinion, it needs quite a
bit more then just roughing up, unless you want to have a
major aerodynamic piece of your airplane glued only to
paint! It took a bit
of elbow grease to remove all the paint from the tail saddle
area so I had a good surface to glue to.
With the fuselage prepped, I was ready to attach the
tail. Before gluing,
I taped a straight stick from one tip of the v-tail to the
other. I used this as
a sight to ensure that the v-tail was sitting level with the
trailing edge of the wing. The instructions mention nothing
about checking the v-tail incidence, but I went ahead and did
this by taping a stick to one the v-tail surfaces, parallel
to the root. I then attached a small level to the stick, and
put my incidence gauge on the wing. With the tail blocked up level,
the gauge indicated 1 degree of positive incidence. I was happy with this, so
I mixed up some 30-minute epoxy, and set the v-tail in place,
holding it with a small rubber clamp and checking the
alignment until everything was set up.
With the v-tail attached, the ruddervator horns can be
installed and connected to the pushrods. Because the pushrods exit the
fuselage at an angle, the horns must also be attached at an
angle. I must say that this is my least favorite parts of the
plane’s design.
I would much rather see a more typical v-tail sailplane
setup, with the pushrods exiting the opening at the rear of
the tail boom, as I find that type of setup both mechanically
and aerodynamically much cleaner. As with the ailerons, I opted
for a conventional linkage, using a clevis screwed on to a
coupler to attach the pushrod to the horn, rather then
using the supplied connectors.
|
|
The v-tail linkage.
|
Final assembly and setup:
With everything installed but the battery tray, I set about
determining the plane’s balance. It turned out it was a
bit tail heavy with the battery installed in the position
shown in the instructions. I ended up installing the tray
about one inch forward to get the plane to balance on the
spar, which is the recommended CG location (again making sure
to remove all the paint from the inside of the fuselage
before gluing the tray in place). This still left plenty of
room for the speed controller and receiver (the recommended
hitec 555). The final step was to mount the arming switch and
set up all the control surface throws.
Servo and battery tray installation.
|
The forward fuselage, showing the motor, ESC, and
battery tray. The receiver is hidden underneath the
angled battery tray. |
Final flying weight with a 500mAh battery was 26.5 ounces,
which is at the lower end of the manufacturers specified
weight of 26-28 ounces.
The instructions recommend the use of some sort of v-tail
mixing. You’ll either have to use a computer radio, or
use an onboard mixer for this, as this plane does need to
have rudder function. They also mention that using
aileron-rudder mixing is a good idea, but do not give a
suggested amount to mix.
For the ailerons, the instructions recommend using what I
consider to be a fairly large amount of differential for a
60” span plane…about 2.7:1 of aileron up to
aileron down. Strangely, if you don’t have a computer
radio to do this, the instructions recommend no differential
at all (one could easily set up differential mechanically in
this case).
|
|
|
A look at the tip dihedral and straight wing.
|
Propeller installation.
|
Additional control functions are also mentioned for the
ailerons, such as reflex, camber, and the use of spoilerons
(raising both ailerons) for braking. I went ahead and
programmed these functions on my transmitter (a Futaba
8UAFS). The spoileron setup was a bit unusual for me, in that
I usually put this control on the throttle stick. I was
unable to figure out how to disable the motor throttle
function on my radio, so I ended up putting spoilerons on
the snap roll switch. The down side of this is that
spoilerons became non-proportional…either full on or
full off. It turned out that they worked rather well though
(more on that in a bit).
Flying
The first flight took place on a rather blustery day in
conditions that weren’t exactly ideal for a thermal
plane. After verifying the balance and controls, my friend
gave the Vx-400 a toss, and off it went. Climb out was a bit
sluggish, but this proved to be the fault of an older battery
I was using, which had come out of my Zagi 400.
|
|
Climbing out on one of the first flights.
|
The plane required some left aileron trim, but otherwise
everything seemed well under control, and there were no trim
changes needed for power-on versus power-off flying.As noted,
though, conditions were very bumpy, and sink was in
abundance, making for some challenging flying. The plane
often seemed really sluggish on the ailerons, but in such bad
conditions, I couldn’t really draw any conclusions
about how good it flew.
Since my flight time was short owing to the old battery I was
using, I decided to try something different for the next
flights. I decided to try it out on one of the local slope.
Of course, this plane really isn’t intended as a sloper
flier, but I figured that flying in slope lift would give me
a better look at what handling issues there were, if any.
|
|
Launching into light slope lift.
|
The wind at the slope was light and smooth…perfect for
my purposes. I launched the Vx-400, and quickly discovered
that the suggested aileron control throws were entirely
inadequate. The airplane was still very sluggish in aileron
response. I landed, and changed the aileron differential to
around 1.5:1 by increasing the down aileron throw, then
re-launched…what a difference! Aileron response was
much improved, and I quickly had the Vx-400 cruising back and
forth across the slope in the light lift, occasionally using
a burst of power to climb higher. In fact, I got lots of
comments from onlookers as to how good it was flying. I tried
a few aerobatics as well. Rolls were a bit slow unless the
plane was moving under power, but it did loop nicely.
|
|
Fly-by under power.
|
When I was ready to land, I gave my all-or-nothing spoilerons
a test. Turns out that slamming on the brakes caused neither
pitch up nor pitch down. The plane just gradually slowed down
and lost altitude, so I'm pretty happy with the configuration
as-is. I was easily able to increase the amount of braking my
adding a bit of up elevator to hold the nose up.
|
|
Working the light lift.
|
With the most serious issues of aileron control behind me, I
began to test the plane out in flat field/thermal conditions
again. First, though, I got a new 8-cell 500mAh battery from
Hobby People, so I could get a fair assessment of the
power-on performance. The new battery drastically improved
the climb out performance, and duration. I’m not sure
I’d call the climb out “rocket-like,” as it
is described in the instructions (when using the suggested
power system configuration), but it was fairly brisk, and I
was certainly satisfied with it. I can get four to five good
climbs on a single charge.
The air conditions were much better on these subsequent
flights, and I continued to fine tune the setup. The Vx-400
seemed fairly efficient, and was able to range around pretty
quickly. I did some stall tests, and found that it has a
fairly mild stall, falling off gently to one wing or the
other. The plane is not exactly what I’d call a
floater, though, and you do have to keep the speed up.
It’s not going to hang around the sky like a Gentle
Lady.
|
|
Zipping by.
|
I was still having some issues with getting the plane to
quickly initiate a turn when flying at lower speeds, which
made getting into thermals somewhat difficult. I decided to
increase the differential a bit, back to about 2:1, and I
also eventually added nearly 100% aileron to rudder mixing.
I’m not a huge fan of flying with aileron-rudder mixing
all the time, but in this case, where so much was needed, it
seemed appropriate. It definitely helped out a lot, but I
still wasn’t entirely satisfied with the control
response I was getting.
As a final step, I decided to go ahead and start moving the
CG back to see if that would make a difference. The
instructions show the CG range at 2-¼” to
2-5/8” from the leading edge…or approximately
32-36% of the chord. I had already been flying the plane near
the aft limit, but I moved it back further by pushing the
battery as far aft as it would go. I test flew it this way,
and found a slight improvement.
To make a long story short, I continued moving the center of
gravity back by adding weight to the tail, until I
finally had the CG back to 3” behind the leading edge,
or about 43% of the chord. The result was a much better
flying airplane. It became much easier to throw the plane
into thermal turns, easier to hold turns, and the plane
indicated lift better. espite the aft CG, the plane did not
become overly pitch sensitive, nor did it seem to exhibit any
bad habits. About the only drawback is that it tends to want
to climb a bit too steeply when running under full power.
That’s easily remedied by holding a bit of down
elevator on climb out, though.
Once the settings were all sorted out, I really started to
have fun with this plane.When conditions have been right at
my local field, I’ve been able to get some long
flights, sometimes catching thermals just strong enough to
maintain altitude, and other times catching big boomers that
had the Vx-400 nearly specked out.
Conclusion
The Vx-400 offers easy construction, good performance, and no
real bad habits. It would probably make a good first aileron
plane for someone transitioning from a rudder/elevator
electric powered glider.
Jul 13, 2006, 12:59 AM
