Merlin flight duration - D. Ross article

[billg]

I just read Don Ross' June 01 article on the Megatech Merlin. I have been flying a Merlin for the last month and I like it very much. But, I'd sure like to know how Don got 7 minutes full power/15 minutes cruise duration. I get 4-5 minutes at best. My only difference is that I'm using their newer 7 cell NiMh battery. Could that extra cell weight cut the duration so drastically???

[josef]

The standard propeller is the main problem. Read on...

With the out-of-balance 12" prop that comes with the Merlin, it draws 8 amps of current at full throttle according to my own measurement. Way too much. After running it at full throttle for a few minutes, the motor is too hot to touch and hold. At half throttle it wobbled so much that the motor shook itself loose and it seperated from the aircraft in flight. I resorted to tying the engine to the wing mounting with a piece of string to prevent that from happening again.

You can try this: I re-propped mine with a GWS EP-9070 and it now draws 6 amps at full bore and 3.8 amps at half throttle. I guess that when the prop unloads in flight, the current drawn at half throttle will be even lower.

With the original prop I also battled to make 5 minutes, even while using low throttle settings. With the smaller propeller I make 8 - 9 minute flights all the time and the motor runs cooler.

Some more advantages with the smaller prop are: no vibration at half throttle, It cruises and even gains altitude at just less than half throttle, less torque effect resulting in smaller rudder trim changes at different power settings, less drag in the glide mode.

O-yes, talking of drag, getting rid of that stupid plastic seat will also improve duration, because the decreased drag will allow you to fly straight and level at even lower power settings and that translates into longer flights.

My record with the standard battery is 12 minutes, 15 seconds after sunset in light rain after hand-launching it and flying it to about 100 feet of altitude at half throttle and then throttling back even more to just maintain altitude.

I have al LOT of fun with it. It is my first electric. I have flown I.C. engine planes and gliders on and off for 15 years now.

Good luck.