May 26th, 2009 captain
Being a biplane, the Megatch Avion competes with the Silverlit Palm-Z in the indoor flight arena. Arriving on the scene much later, it’s a much more refined design, being better than the Palm-Z in almost every respect.
Configuration
The arrangement of the Avion is similar to the Palm-Z, although much more stylish. A compact biplane with the pusher propeller mounted behind the top wing and driven through a single stage gearing. The lower wing is mounted at waist level which affords it extra protection at the expense of more aerodynamic interference with the top wing.
The large tail group is mounted on a single boom running from the base of the fuselage. The wires for the rudder actuator run up the inside of the boom. The horizontal tail surfaces have about 40% more area than the Palm-Z, while the vertical surfaces have more than double. The rudder on the Avion has almost four times more area than the Palm-Z.
The fuselage nose has a recess containing the on/off/charge switch, the charging socket and the infra-red receiver. A circular insert of softer foam is in the nose to reduce damage (to plane or person) in the event of a collision.
Controller
The controller is larger than Palm-Z, but has sticks rather than sliders and a proper trim wheel. It doesn’t win any points for style though.
Power comes from four AA batteries mounted in the back. For once you don’t need a screwdriver to fit them. The charging cable is hidden behind a door on the left of the fascia. To charge plug it into the Avion and push the switches on the controller and the Avion to the charge position. The left LED on the controller will glow red while charging and then change to green when complete.
Airspace
The full colour manual doesn’t quote minimum flying space dimensions. The Avion turns better than the Palm-Z, but flies faster so a similar minimum space of 6m x 7m x 3m seems reasonable. Stood in one place, the controllers maximum range limits you to a circle with a radius of about 7 metres. If you can move about then the room’s the limit. By walking up and down the central corridor, I can fly complete circuits around our open plan office.
The normal caveats concerning bright lights, direct sunlight and drafts apply.
Flying
After flying the Palm-Z, the first impression of the Avion is the increased speed with none of the bobbing motion. The second is more authoritative steering. With the Avion you actually feel as if you are doing the flying, rather than just nudging it around. With more control comes fewer crashes and it is easily possible to stay airborne for a complete charge. In my last test this was 10 minutes 10 seconds.
Unlike the Palm-Z the rudder works when gliding. This allows for nicely controlled landings, which is a big benefit in a room full of furniture.
The manual rudder trim wheel is also a big plus as it remembers the trim setting between flights. On the Palm-Z you have to re-trim every time the controller is turned on.
The Megatech brochure offers a wheeled undercarriage for the Avion. I’d like to try it out, but it’s only available in the USA. It would be interesting to try rise-off-ground launches and the extra weight would necessitate a higher flying speed and therefore even more rudder authority.
Conclusion
The Megatech Avion is the best indoor fixed wind aircraft I have flown and probably the best one on the market. It is so much better that I wouldn’t accept a Palm-Z if they were giving them away free.
It is still very light and can be damaged by hard impacts, so I wouldn’t recommend it for young children. The box says 12 to adult, but I would be confident giving it to a 10 year old.
Facts and Figures
Whats in the box
- Avion Biplane
- Combined infra-red transmitter and charging unit
- Full colour multi-language manual
You have to supply
Dimensions
- Length: 230 mm
- Width: 200 mm
- Height: 60 mm
- Weight: 8.4 grammes
Manufacturers Website
Available in the UK From
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March 19th, 2008 captain
The Palm-Z is a tiny single engine biplane designed for indoor flying. Everything you need to get flying is included in the box with the exception of four AA batteries. The multilingual manual features the unfortunately now common poor English, but with the pictures everything is clear enough. As will become clear latter, it is also worth investing in a roll of “Magic tape”.
With a 210 mm wingspan and 6 gramme all-up weight, the airframe feels fragile in the hand, but being it’s so light, will tend to bounce rather than crunch as long as it’s not diving under full power at the time. Any small cracks that do appear in the EPP wings can be repaired using the included self adhesive strips.
Aircraft Configuration
The Palm-Z has a stubby fuselage the houses the battery, receiver, motor and propeller. This also includes the power switch and charging point. The wings are attached top and bottom and then further braced by the twin booms running back to the tailplane. A pair of thin wires are routed along one boom to control the single central rudder. The rudder has a small magnet mounted forward of its hinge, sitting inside a copper coil. Varying the current in the coil changes its magnetic field and so pushes the rudder left or right. The fin is angled on the tailplane to prevent a turning force due to the spiral airflow in the prop-wash.
The motor drives the rear facing propeller through a large gear wheel. This increases propulsion efficiency as, for the same motor, a larger slow turning propeller produces more thrust than a faster small one. The downside is that gearing produces more noise. In the event of a crash, damage to, or from, the propeller is minimised, being enclosed by the wings, tail booms and tail surfaces.
Controller
The infra-red controller has a cradle where the palm-Z sits for charging. Once placed, move the power switch to the charge position and when the green LED goes out you are ready to fly.
The flying controls consist of throttle and rudder; both are spring loaded. The throttle is used to control climb or descent, the rudder direction. There are also a pair of trim buttons for the rudder. These allow you to get the aircraft flying straight with the Rudder set at neutral.
Before flying it is worth checking that the channel selector on the controller matches that printed on the underside of the lower wing. In the example below – Channel B.
Airspace
The manufacturers website quotes a minimum room size of 2.8m square although this would restrict you to flying in small circles. The manual recommends a room 6m x 7m x 3m which is more realistic. The transmitter has a quoted range of 5m so a 10m square room represents the upper limit. Any bigger and you are likely to lose control if the plane goes out of range. As the control system uses Infra-red to transmit signals to the aeroplane try to avoid rooms with strong lights or large areas of sun facing glass on clear sky days.
Flying Time
With the power on, a red light started flashing on the Palm-Z and pushing the throttle forward got the propeller spinning. The motor speed is stepped rather than fully proportional and oddly the rudder control does not start to work until the throttle is at step 2. This makes a controlled landing almost impossible.
With three quarters throttle set and a gentle (level) throw the Palm-Z was away. Initial flight consisted of a bobbing (climb/stall) motion suggesting that more nose-weight was needed. However, smooth flight was obtained by following the manual and reducing the throttle a little. Once the flight had settled down, increasing the throttle had the Palm-Z climbing to an unobstructed altitude. It flies at a gentle speed suited to the enclosed environment although with a pronounced node up attitude. As I had a large enough room the Palm-Z kept flying in large circles with just some throttle adjustments to keep it in the unobstructed vertical space.
Repeatedly pressing the left-trim button got the palm-Z flying straight and heading towards a wall. So, time to attempt a left turn. The slow flying speed had me expecting a leisurely turn. Instead, it banked over sharply, dropped the nose and turned quickly enough that it was past 180 degrees before I could straighten it up. The turn radius was under a metre.
Rudder operation is a case of all or nothing. The manual recommends you “strike but not hold” the rudder control during the turn. It is also suggests adding a little throttle to increase the rudder authority. The extra throttle will also help maintain height lost from the dropped nose.
So the first left turn was scary, but we were still flying. After a couple more left turns my confidence was improving, so I thought I would try a figure eight. The left turn went ok so I pushed the rudder control over to the right. The Palm-Z banked, dived, turned even sharper than when going left and before I could recover, was locked into a spiral dive that only stopped on hitting the ground. No damage was visible, although the rudder had over-ridden and stuck on the tailplane. I assumed that this had occurred during the crash.
Further flights followed in a similar pattern. A period of controlled flight that would suddenly end in a right spiral dive I could not recover from, even with full opposite rudder. Cutting the power at least led to a softer landing. Invariably, post crash inspection would reveal the rudder stuck on the tailplane and once that the tailplane has cracked next to the fin. This was repaired using the supplied self-adhesive strips.
A quick search of the Internet showed that I was not the only one suffering the right hand spiral dive problem.
To prevent the rudder over-riding the tailplane I extended it down using “Magic Tape” as shown in the photos. On further flights, the Palm-Z would still get locked into a right turn, but now it would maintain height instead of entering a spiral dive. Holding full opposite rudder would eventually break it out of the turn, heading in some random direction. A better solution, that allowed some control over heading, was to cut the throttle; wait for the Palm-Z to return to straight and level; then throttle up and continue flying.
Because the Palm-Z was turning so tightly when stuck in a right turn, I had the thought that perhaps the rudder was too powerful. The tailplane is cut to limit rudder travel but, with the tail fin skewed to reduce the prop-wash effects, the effective right turn travel is greater than the left.
To test the theory I added some layers of Magic tape to the tailplane to restrict the right rudder deflection. I used enough tape to reduce the right travel to almost zero. As expected when flown the Palm-Z could no longer turn right. Using scissors, a small slice of tape was removed. When flown this produced a large slow turn with immediate return to straight and level on releasing the rudder control. The trim/fly sequence was repeated until, with the right turn radius only slightly bigger than the left, recovery from the turn had developed a slight delay.
I was now possible to fly smooth figure 8′s back to back with the rudder control held over throughout the turn. Stress free flying at last.
Transmitter Hack
Whilst searching the web, I found a good video on YouTube that shows how to remove the spring from the throttle control. This makes for much smoother flights and stops your thumb being imprinted with the pattern from the throttle slider. There are a number of other mods that I will explore in a future post.
Conclusion
Although small and cheap, the Palm-Z cannot really be considered a toy. Even when modified to prevent a spiral dive, it is too fragile and requires a degree of concentration to keep it flying within all but the largest of rooms, that puts it beyond the wit of most children. The box suggests an age range of 8+ which seems about right.
With it’s biggest flying challenge being a smooth figure eight, it’s long term appeal is ultimately limited. There are two possible exceptions:
- It is possible to fly three Palm-Zs at once, so with to a large enough space there is scope for some friendly competition, including trying to knock your opponent out of the air.
- Being so in-expensive, there is little to be lost from modifying the basic airframe or even transferring the electronics to a new airframe. A search of the Internet shows a number of mods including adding wheels for rise-of-ground take-offs and creating a profile scale model of Polikarpov monoplane. (http://www.rcgroups.com/forums/showthread.php?t=727630)
Would I recommend the Palm-Z. Definitely! Even in the short term, you would be hard pressed to find this amount of fun for less than the £15 (including p&p) sale price. If you have always wanted to fly a remote controlled aeroplane here is the perfect entry point.
Postscript
Since this review was written I have completed the Hat-Cam that has allowed me to get some video of the Palm-Z in flight.
Just for fun – here is a collection of some of my not-so-successful moments, which at least demonstrate the palm-Z’s resilience and it’s need for a larger flying space.
Facts and Figures
Whats in the box
- Palm-Z aeroplane
- Combined infra-red transmitter and charging station
- Multi-language manual
- Wall hanging bracket
- Spare rudder
- Self adhesive repair strips.
You have to supply
- 4 x AA batteries
- Cross-head screwdriver in order to fit them.
Dimensions
- Span: 210 mm
- Length: 185 mm
- Height: 65 mm
- Weight: 6 grammes
Manufacturers Website
Available in the UK From
Posted in 2 ch, Aeroplane, Indoor, Modding, Review | No Comments »
