Thursday, June 5, 2014

Still Learning With 2.4 MHZ RC

After replacing the nickel metal hydride battery in my Shadow 2-meter glider I thought my troubles were over with battery issues in that airplane. I found out I had more to learn when it comes to 2.4 radio systems. I flew the glider with the new battery for some test flights and then flew it again without a full charge. The expanded scale voltmeter showed the battery was still well into the green but after a couple of short flights my glider went into a spiral dive crashing into the ground just next to a street.  I was really amazed there was not more damage, only an area around the wing hold down area of the fuselage was broken.

Shadow 2-meter Sailplane

After the crash I thought the receiver was flashing which I learned afterwards indicates an error condition in the receiver. I tested the voltage again with the expanded scale voltmeter and it was still in the green.  From questions I asked on the RC Soaring and Sailplane Society forum on Facebook, I learned that in flight battery voltage can easily drop if there is a large load causing receivers to fail.  Expanded scale voltmeters are not that accurate for testing either, the battery needs to be tested under load. This glider has 6 servos and two of the servos are rather old, this can be a large load. Many people are using another cell or some type of lithium battery with a regulator to keep the voltage from being too high for the receiver. 

After the Crash

I epoxied the broken piece back and tried to fly the glider again. Someone with a mild electric winch took the plane up. We noticed the canopy fall off on launch which has never happened before, this should have been a clue that something was wrong. I flew around fine but on landing I noticed the wing was not straight, sure enough my repair had failed.  Someone with the same type of glider gave me good advice how to do a proper repair covering a large area of the fuselage with fiberglass cloth and using a slower drying epoxy.

Area With White Patches was Repaired With Fiberglass

Canopy Held on With Wire at Both Ends

Last evening I flew the Shadow again with a full charge and with the two flap servos unplugged; now there were only four servos draining the battery. The glider flew perfect, after a couple of gentle launches I pulled back harder on the hi-start and got better altitude. Soon the glider was in lift; and going up. It was after 5:00 p.m. so I was rather amazed to find lift so good but there had been big puffy cumulus clouds all day.  This was really fun, the glider flew rather fast but it was going up.  I tried the thermal mode preset I had set on the ailerons and it did slow the glider down.  Normally I am flying this glider when there is more wind and it is 
hard to see the speed difference. Landing was rather fast without flaps but that is fine.

Data Logger Worked on Receiver in my Radian

Voltage was still well into the green after flying for a total of 25 minutes, I called that enough. I have not been able to get the flaps to change with the ailerons in different flight modes on my new Spektrum DX9 transmitter yet. The manual leaves much to be desired, it does not go into enough detail about how all the many functions operate.  I purchased the Spektrum data logger but I found out the particular receiver model I have is not listed as one to work the data logger. 

This might sound very frustrating but I am really having fun with this glider. It flies so smooth and handles the wind so much better than my trainer gliders. When I obtain another glider of this type, I will look into a different battery system and a receiver supported by the data logger. 

Bill Kuhl

Nickel Metal Hydride Battery Story

Comparing Two 2-meter Gliders

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