Horror Story

This happened a couple of weeks ago, I watched the video, should have a copy in a few days. A well respected local builder and pilot, been in the hobby a LONG time
buys a 104" P-38. Installs two G-26's, JR 10X, PCM, flys the plane for a year without incident. This year he decides to replace the battery pack with a new unit to insure he has no problems. He buys a new pack, charges it for fifteen hours and installs it. At a giant scale meet, he is now flying the plane for the first time with the new pack. During the take off roll, he feels that something is rotten in Denmark so he attempts to abort the take off. When he throttles back, the plane instead takes off on its own. Banks OVER the spectator area and proceeds to fly around for eight minutes, doing various loops and circles, totally ignoring any input from the transmitter. Plane finally drifts out about a half mile from the field, goes into a death spiral and hits a concrete pad, destroying pretty much everything. The one thing that did survive was the new battery pack. Complete with shorted cell. (6 Volt, around 2000MAH). My perception of mistakes made: 1) He installed the pack without cycling it a couple of times. 2) He didn't check it with some sort of loaded ESV before the first flight 3) He used a single pack and switch assembly on a $2500.00 plane when he should have been using some sort of battery redundancy. The only good thing to come out of this, besides the fact that no one was hurt, is that now he, and all of his friends will be paying much closer attention to their battery packs from now on. The only question I have is if he had two packs and switches, would a dead shorted cell have dragged down the second pack and insuring the same outcome?
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A shorted cell on a 6 volt pack would have left him with what 90% of the rest of the modelers fly on. 4.8 volts. It was not the shorted cell that caused the crash.
No battery ESV check before first flight? Inexcusable! -- Red S. Red's R/C Battery Clinic http://www.rcbatteryclinic.com Check us out for "revolting" information.

copy
giant
pack.
he
ignoring
destroying
battery
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The battery pack had about 3.8 volts in it when tested after it was removed from the what was left of the plane. They charged it on a known good charger and voltage once again dropped below 4 volts. I guess we all assumed that there was a short. ???

insure
so
instead
mile
flight
was
dead
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More like 2 cells. Was this a name brand pack?
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Even still, no one can say for certain that the battery was definately bad during the flight. The crash may have damaged the cells.
--
Paul McIntosh
Desert Sky Model Aviation
  Click to see the full signature.
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Paul The plane flew fine for over a year, the only thing changed was the battery pack. He flew another plane without incident with the same transmitter (JR 10X) The battery pack was intact, still in its undamaged padding. The only other thing would have been the receiver. I didn't ask him about that. Someone told me that he had fail safe set up for control hold. The guys who were there at the time said it appeared the plane went into and out of fail safe at least once before it was destroyed. ??? Bill
says...

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If it went in and out of failsafe, it had sufficient power to do so. In most PCM systems, if you lose power the servos all stay in the last position coded. They wouldn't be wandering around.
--
Paul McIntosh
Desert Sky Model Aviation
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Hard to say what was really happening. Speculation was that the battery pack was supplying voltage at varying levels before it finally gave up the ghost.
says...

was
good
assumed
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'scuse me? Every-repeat every- large plane, from 1/4 scale Extra's up, that i have see droop the surfaces when power goes off. that means that whatever aerodynamic forces are acting on the surfaces will move them at will...there is no way a servo stays locked in position with no power to it...unless you buy some sort of special, custom servo...
Roger
Paul McIntosh wrote:

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Don't know about the brand of pack. The owner of the plane is not known for cutting corners. Knowing the guy, I would guess that it was a name brand pack.
says...

removed
charger
that
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for
How about the corner that says "thou shalt give your pack an ESV check before its first flight"?.
-- Red S. Red's R/C Battery Clinic http://www.rcbatteryclinic.com Check us out for "revolting" information.
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Seems to me that that is on the order of "Breath in, breath out!" ;>)

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And every other flight therafter!!!! I check my batteries every 2-3 flights. I put to much into my planes to let a low battery ruin my day. My planes don't like dirt naps. Eddie Fulmer AMA 63713
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Why not check them before every flight? That makes sense to me. You're taking a chance doing it every other flight. Joe L.

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taking a

If you cycle you batteries a couple times a season, and chart them, the chances are low of having a problem. As long as you know where you are on the discharge cycle, there is a good safety margin. -- Jim in NC
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I had a similar type of incident recently and got similar results with my ESV. Localized it to the battery pack and called it a day. I was lucky in that the failure occured just after engine start but before plane was released. Chilling thoughts!

a
time
a
fly
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closer
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Since I am new to the hobby and unfamiliar with some of the terms would someone define ESV please.
Thanks
Ray
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Expanded Scale Voltmeter. I think what these guys are alluding to is a tester that applies some load to the pack, rather than just measuring the unloaded voltage.
MrBonk www.mrbonk.com

someone
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And the expanded means you can read finer than tenths of a volt.
What are commercial ESV loads? I use a home-brew digital with a 350ma resistor in line. -- Jim in NC
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What is the color code on a 350ma resistor Jim? ;>)

the
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