E-Sky Lama model helicopters

The E-Sky Lama family of model helicopters comprises small, 4-channel, remote controlled electric coaxial helicopters produced by E-Sky. These include the original Lama, the Lama V2, Lama V3 and Lama V4, a series of coaxial remote control helicopter aimed specifically at beginners in the world of r/c helicopters.

Like other similar co-axial models, the Lama V3, V4 and Co-commanche are mass manufactured in China and are sold ready-to-fly (RTF) out of the box, requiring the pilot to only charge and install the standard 7.4 V 850 mAh 2-cell Li-poly battery.

Model revisions

The various models in the series share the same mechanical (motors and running gear setup) by and large, differing mainly in their central electronic control unit (combining the functions of receiver, mixer, Electronic Speed Control and Gyro, also known as the "4-in-1" unit), and in their external appearance and construction (canopy and tail design, but also body/main frame), as well as their servo linkage arms. The Esky Co-commanche, sometimes advertised as the Esky Lama V5, is effectively a Lama V4 with a later canopy design. The tail rotor on some of the Lama models is for aesthetics only and serves no function during flight.

The design

Like other coaxial remote control helicopters, the aircraft's power is generated from a dual DC motor system driving co-axial, counter-rotating blades. The "4 in 1" unit is a dedicated electronic control unit combining the functions of a receiver, mixer, gyroscope and electronic speed control. This control unit regulates both motors' speed to provide altitude control (climbing and descending), as well as the relative individual motor speed to provide automatic heading hold and yaw control. The transmitter and receiver modules use FM modulation for the radio signal carrier and Pulse-position modulation (PPM) for the control signal.

The helicopters use a simplified coaxial rotor system, with two pairs of rigid fixed-pitch coaxial counter-rotating rotors, of which only the lower one is fully controllable by a swashplate, while the upper one is only stabilized by an inertial fly bar. The swashplate movements are controlled by a pair of micro servos. These servos combined with the throttle and mixer controls of the "4 in 1" unit enable the pilot to control all 3 axes of movement as well as altitude for the helicopter.

This particular simplified coaxial rotor arrangement is shared by many beginner and entry-level electric helicopters. The design has the advantage of being mechanically simpler compared to the collective pitch coaxial arrangement with two swashplates, usually found in real coaxial helicopters.

This design however poses some limitations on the aerobatic ability of any helicopter using it, in particular regarding its maximum speed and its ability to negotiate wind and to perform rapid air maneuvers without becoming critically unstable.

pecifications

* Main rotor diameter: 340 mm
* Body weight: 230 g
* Length: 360 mm, width: 85 mm, height: 175 mm;
* Power system: 2 x 180-series motor
* Transmitter: 4 channel FM PPM
* Mix controller: 4-in-1 controller (contains receiver, gyro, mixer, and speed control)
* Servo: 8 g, 1.3 kg·cm, 0.12 sec/60°
* Battery: 7.4 V 850 mA·h Li-polymer battery

General points of discussion

Considerations on the coaxial rotor system used

Due to the complexity of the typical coaxial rotor systems, there are relatively few commercial hobby-grade model helicopters using a complete collective pitch coaxial rotor system, most of them being DIY projects or limited production editions [http://www.rcgroups.com/forums/showthread.php?t=748235] [http://www.cad-modelltechnik-jung.de/projekte/kamov_modell_trainer.htm] . Nevertheless, there are some simplified coaxial designs which eliminate certain mechanical parts, resulting in commercially viable and mass-producible designs, such as the Esky Lama series.

Differential rotor speed control with fixed pitch blades

In recent years, many radio-controlled helicopter manufacturers started adopting a simplified coaxial design for their beginner models, which results in relatively easy to fly and stable design compared to a traditional single rotor design with a tail rotor. This simplified design typically consists of a coaxial rigid rotor system with fixed-pitch blades and a single swashplate controlling the cyclic pitch of the lower rotor's blade, while the upper rotor is not controllable but only inertially stabilized by a set of counterweights called a "flybar". Due to the lack of a collective pitch mechanism on either rotor, two separate motors are used (one for each rotor) and yaw control is achieved by differential speed changes between the motors. This design eliminates much of the complexity due the use of a single swashplate and no collective pitch mechanism, resulting in easily mass-producible and relatively easy to control helicopters. However, while mechanically simpler, this design has some limitations like limited maneuverability and aerobatic ability. In particular, there is an increased risk of blade clashes during maneuvers (the upper rotor colliding with the lower rotor due to inertia). This is caused by the upper blades not being directly controlled, causing their plane of rotation to remain stationary and resist any induced changes during maneuvers, while the plane of the lower blades can be controlled directly. Also, exceeding a certain pitch or roll angle results in the upper, heavily stabilized set of blades rendering the helicopter unstable and unresponsive, usually resulting in an uncontrolled speedup and crash in the direction of the roll as the top blades "drag" the rest of the helicopter, a condition commonly referred to as "death roll". The differential rotor speed control design also has the drawback of not scaling well to larger and more powerful helicopters, due to the increased weight of more powerful motors with separate running gears and its reliance on precise differential motor speed control, something more difficult to achieve at higher powers and with internal combustion motors.

Fixed pitch coaxial rotors with tail rotor

A different simplified fixed-pitch coaxial rotor variant using a single gas motor has been proposed [http://www.rcgroups.com/forums/showthread.php?t=749654] , which achieves yaw control with a traditional tail rotor, while the majority of the torque is being canceled by the counter-rotating rotors themselves, which can now share the same running gear (mechanically interconnected) and necessitate no differential speed control.

Flight characteristics and performance

The general experience has been that the E-Sky Lama helicopters are only capable of flying indoors or outdoors on a completely calm day with no, or very little, cross wind. Modifications (see below) can be made to the Lama series and other similar helicopters to assist the r/c pilot flying outdoors with limited effect, in particular installing longer shafts that increase inter-rotor distance, harder blades and more powerful motors, as well as weight-reducing modes. As stock, like other dual rotor co-axial model aircraft, the E-Sky Lama pilots are advised not to fly in such conditions as cross winds.

The upper set of rotor blades (A) are stabilized by a weighted fly bar which counters tilting movements. The lower set of rotor blades (B) are designed to steer the helicopter by tilting a "swashplate" which in turn tilts the entire rotor by changing the pitch in a complicated process called "cyclic".

If the helicopter's tilts excessively (roll or pitch angles become excessive), this can lead into the upper, inertially stabilized upper rotor to strike the lower one, in particular during abrupt maneuvers. This is colloquially known as a "blade strike" or "blade clash", causing the aircraft to instantly descend out of the air and possibly damaging the blades themselves. This hazardous flight condition can be induced either by pilot input (aggressive controlling) or by weather conditions (strong crosswinds).

Also, exceeding a certain angle of roll or pitch even without a blade strike may cause the helicopter to go out of control and crash, as the top stabilized blades' weight and angular momentum will tend to render the helicopter unstable and insensitive to corrective control input. This can be caused by too aggressive maneuvering or just a sudden gust of wind, either resulting in an excessive roll or pitch angle. This flight condition is usually referred to as "death roll" by enthusiasts, and it may or may not be occur concurrently with a blade clash.

Modifications and design upgrades

Replacements for standard plastic parts

There are many modification available for all Lama helicopters, which replace certain plastic mechanical parts such blade grips, the swash plate, servo linkages and rotor heads with aluminum parts, allegedly offering increased durability and mechanical strength, although not necessarily improved flight characteristics. Other parts that can be replaced include the landing skids and battery holder assembly as well as the motors, which can be replaced with more powerful motors of the same form factor. Balance and weight are key to successful flight and the helicopter may need to be adjusted after the new parts are added; some reports claim degraded performance from metal replacement parts.

One particular modification provides an extended (longer) upper rotor head, which increases the distance between the upper and lower rotors and allows for faster turns and roll/pitch changes without causing a blade strike.

Upgrades for the standard rotor blades

Owners may upgrade the standard blade rotors (made of flexible black plastic) with more durable blades usually referred to as "Xtreme blades", made from thicker white PP. These blades are thicker than the standard ones, stronger, and can withstand more severe strikes and collisions than the standard ones, without developing cracks or breaking. Their airfoil shape is also claimedfact|date=December 2007 to generate more lift than the standard ones, however they also have an increased weight and angular momentum, which reduces agility and control response somewhat.

Other upgrades

Lithium Polymer (Lipo or Li-po) batteries have advanced significantly in recent years, allowing small high output versions to be produced at low cost. All of the stock E-Sky helicopters are supplied with a 7.4v 850 mAh battery. It's possible to use higher capacity batteries ranging from 900 to 1600 mAh or beyond, as long as they are 7.4v, the helicopter can handle the extra weight, and they fit in the frame.

ee also

*E-flite Blade CX

External links

* [http://www.helihobby.com/download_files/Lama_v4.pdf E-Sky Lama V4 instruction manual]
* [http://www.twf-sz.com/ Official homepage of E-Sky]