The Silverlit Palm-Z
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
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