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Meadowlark , a US indoor 20" span sport laser cut rubber model

Indoor rubber duration such as the Hanger Rat, Butterfly, Gymminie Cricket are a touch 'samey'. The Meadowlark from www.lasercutplanes.com is a welcome change and has the appearance of a 1980's F3B RC glider. I could not resist the challenge of a different, elegant design and ordered a kit from the US suppliers. This duly arrived within 7 days and in 60m the very well cut wood was assembled with the help of medium CA. Covering took a bit longer as my experience with HDPE (High Density Polyetheylene) covering was non existent. Photo mount spray adhesive (3M 77) was the way forward and the excellent instructions supplied with the kit were a great help.

The model was maidened at Impington on the 11th March 2012 and with a touch of nose weight, a smidgen of left RU and a soupcon of up EL, the Meadowlark flew exceptionally well in a very stable condition. The flying speed is commendably low and adds to the elegant 'sit' of the 5gm model in the air. The following graphic shows the author vainly trying to find the rear hook and cursing his failing eyesight. Note the very yellow Meadowlark model box on the right. This effectively protects ones loved ones from the arrival of the occasional Szklaruk bomber.

All good things come to an end and rubber is not my favourite power source. Accordingly, the possibility of electric power systems, as always, came to mind.

Raiding the micro brushed motor box gave me a Silverlit 4 mm x 12mm geared motor weighing a scant 1.3gm. I set this up with a Bob Blackburn Infra Red programmable controller and a 30mah 1s LiPo. This draws 185 ma at full load but the Meadowlark will fly on much less than this, I hope.

How elegant is this ?
 

Electronic graphic showing Bob Blackburn controller, 30mah LiPo and SIL connectors. You will recall that the Blackburn controller helped Bernie Nichols Caudron to first place in the UK FF Nats 2010.

The Meadowlark_E was trialed at Whittlesey on 23rd March. You may recall that the Blackburn controller divides the power output of the motor into 8 bands of approximately 12.5% increments. I have to admit that I had the thrust line of the motor incorrect and the model would not climb on an 8 setting (100%). Luckily I hit the wall , knocked the motor off and I CA'd it back on with a degree or two of upthrust. Meadowlark was transformed. It now climbed on a 6 (75%) and made a slow descent on a 5 (62.5%).

The conclusions thus far are……………..

The Silverlit geared motor is an ideal match for a Meadowlark_E conversion.
Give the motor a touch of upthrust to get the thrust line near to the CG.
The current draw on a power setting of 6 is estimated at 140-150ma, so a 30mah battery would run for 12.4 mins. Hence OK for a 10 min Indoor Electric record attempt at Nottingham in May.

Next steps……

For Indoor sport flying the Blackburn controller would be replaced with a Peterborough FET timer. This is not load controllable and would run at 100%. Climb rate could be attenuated by thrust line modification if the motor was attached by a 12BA pinch bolt. An alternative would be an Atomic Workshop Zombie……OK to 2 amps and load controllable.

An increase in span to 24" is on the cards as the electric conversion speeds the model up. I expect the Silverlit motor to handle this at 100% power and I need to cadge some 4 lb wood from the F1D fliers.

Ian Middlemiss March 2012