Espritmodel.com Telemetry Radio

The Global Vx400

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.

Splash


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.

Discussion

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Old Jul 12, 2006, 11:59 PM
Rem The Wasp CV-7 9/15/42
SammyB's Avatar
Santa Clarita,CA
Joined Apr 2004
1,685 Posts
Will be testing tomorrow...the exact mag plane. Thanks Brett!
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