LMH 120A Corona (2001)


In 2001 Light Machines brought out a revised model, the Corona 120A, being a 110 fundamentally redesigned for electric power.  The basic layout remained along with the main drive train however, the main frame was redesigned to remove the fuel tank, replace the engine with the electric motor and provide securing for a flight battery.  Whilst electric models were gaining in popularity, they all had the same problem of low relative power to the same weight glow engine and also heavy battery weight for a reasonable flight endurance.  To help counter these deficits the Arlton Gyro was removed as low weight piezo gyro's of a reasonable price were available and bigger main blades were fitted to give more lift and reduce the rotor disc loading; a longer tail boom was then required to give clearance for the tail rotor.

'Standard' tail layout   Corona blade comparison.

Revised Corona specifications

Main rotor diameter:

30in (762 mm)

motor type:

Electro-Fusion 7

Speed Controller (ESC) Electro-Fusion 35

Fuselage length:

29.4 in (671 mm)

Battery pack required

6-8 Cell

Weight (dependant on battery size)

44 oz (1300 grams) approx

Disc Loading 0.062 oz/Sq in (0.291 gram/Sq cm)

As can be seen from the specifications, the weight had increased dramatically by 60% from the 110 models however, with the longer blades the disc area had also increased by 55% and thus the overall disc loading remained near enough the same.  The result being that rotor characteristics remained very similar to its predecessor and so did flying characteristics with the overall weight  increase making the model more stable and better able to cope with turbulence.

The model was marketed with two options;

1) Basic Combo Kit - 120 Helicopter, Electro-Fusion 7 motor and Electro-Fusion accessories pack.

2) Standard Combo Kit - As the basic kit plus Electro-Fusion 35 Speed Controller and standard accessory pack.

Most bought the Standard kit as it included the matched ESC for the motor and both kits additionally required full radio plus gyro and battery pack of choice; the Basic Combo was bought if the intention was to fit a brushless motor from the start.

The motor provided was not considered the best available and reports of 'dying' after only 5-10 flights were common.  One reason for this lack of longevity was that brushed motors required careful 'running in' which was not always appreciated.  Without this care the motor /commutator contact was damaged causing lots of 'sparking' and high resistance so the motor efficiency drastically reduced and power dropped sharply.  Higher quality motors such as the Kyosho Atomic Force were recommended as these motors generally did not require the same level of running in and also provided more power.  The speed controller provided with the kit was a relabelled Castle Creations Pegasus 35 (Set-up manual here) which had a reputation for poor 'arming' however, this was due to the arming set point being very close to a transmitter zero stick position and so the cure was to either extend the throw slightly for minimum stick or move the trim point down; problem solved...!!!

Another problem arose concerning the increased incidences of tail boom strikes; because the blades were flexible and now much longer if touch down occurred with some back stick held on; the boom could be caught.  Obviously the trick is not to do that but it could be prevented by fitting a 'rotor deflector'; this was a flat piece of wood or aluminium about 50mm long secured to the tail boom in the area where the tip would strike and angled down by 10mm towards the direction the rotor would strike.  If the blade then tried to go below the edge of the boom this 'ramp' deflected the blade upwards thereby preventing a strike and generally not causing any damage.

The tail gearbox was also not as strong as the previous model 110 and tail blade strikes could damage teeth.  Unfortunately the flexibility of the legs which were designed to absorb 'heavy' landings without damage tended to cause the blades to touch down so fitting a more substantial tail support helped prevent contact under these circumstances.

It was also found that it was better to use two of the four dot blade grips which reduced the blade incidence from that recommended in the manual as this requiring higher revs for the same lift thus giving quicker head response.  This was especially so when higher performance motors were used as the lower head speed of the standard setting did not allow them to perform efficiently.

LMH-120A Construction manual  -  2001 Corona version

LMH Operators guide  -  2001 version and supplements the build manual.

Technical Bulletin 10 - Dec 2001 - Additional info for Fusion 35 speed control and mounting of motor.

http://www.rcgroups.com/forums/showthread.php?t=185388  -  Excellent 'Forum' build article with lots of photo's plus detailed Corona build

As technology improved the standard brushed motors were replaced with brushless types of lower weight and significantly more power thus enabling better performance and the introduction of Li-Po type batteries allowed for either decreased flying weight of more often than not for the same weight an much extended duration.

Later built machines with brushless motors.