Not too long ago I heard about someone who crashed their plane during the landing sequence. Everything was going just fine when suddenly the plane lost power/control and torque-rolled in on the base leg right before turning to final for what should have been an uneventful landing.
The pilot surmised it was the receiver. Instead, a closer examination ultimately discovered the true source of the problem: The UBEC overamped causing a brown-out condition where all controls were momentarily lost. This is never a good situation to be in but when turning onto the base leg to set up for final approach, especially so. Your speed is slower, altitude lower and usually a lot is going on with your model (flaps and retracts extended all while working all of the control surfaces in unison).
In this particular case the UBEC which was rated for 5 amps spiked above that due to the sudden simultaneous load that was placed on the electrical device. What specifically caused the lethal spike in amperage? It turns out the the pilot dropped his flaps (that were on a slow-timed sequence) and his retracts at the same time all while simultaneously controlling the servos for the ailerons, elevator and rudder. It was a perfect storm which overloaded the unit creating a brown-out ultimately causing a brief loss of aircraft control.
On the base leg, a brief brown-out could be all it takes to create a crash since altitude is at a premium. While no guarantee, a higher altitude could have perhaps saved the plane in this instance.
Lessons To Be Learned...
This unfortunate story serves as an excellent example on good landing technique. One thing that immediately sticks out to me is when the pilot chose to flip his gear and flap switch at the same time. With the flaps (and I assume gear) on a slow-timed sequence this places a lot of stress on the components all while simultaneously working each control servo.
A safer way to perform the landing setup and sequence would be to flip the gear switch first (sometimes I will fly a complete pattern with gear down before landing) no later than the beginning of your downwind leg, then once the gear is completely down and locked then flip your first notch of flaps. Once fully established on the base leg (or final approach) flip your final notch for landing flaps. Performing these sequences at different points of your landing setup is irrelevant. The important thing to remember is not to perform these tasks at the same time as it places too much strain on your electrical components.
What's The Difference Between A BEC and UBEC?
That's a mighty fine question, and frankly I am not the best authority on that topic so I will leave that to Pilot Scott from FliteTest.com who does a fine job explaining the difference. Another question you might have is "What if the pilot had a 10 amp-rated UBEC instead of a 5 amp-rated UBEC? Would that have saved a brown-out situation?" While I cannot say with 100% certainty since I do not know what exact model, components or power system he had at the time of the crash I feel fairly confident that yes, 10 amps would have been sufficient enough to handle the amp spike in that simultaneous event.
A UBEC is essential insurance to to keep your controls working under a LVC (Low Voltage Cutoff) situation, but it's moot if you strain the UBEC beyond it's amperage capabilities. If you are not sure and want to protect your model, it pays to invest in a UBEC that has a higher rated amp capability just for the peace of mind alone.
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