[NSRCA-discussion] Part 2-Its a miracle!!!

[John Pavlick]

Gray,
 That's good news. At least the plane will live to fly again AND maybe a lesson was learned here somewhere. Like I said, I'm not using NiMH airborne packs anymore. I haven't had any major catastrophes but I've had a couple of close calls. The latest was with a good quality 4-cell pack. I had one season on it. It sat idle for a while then i decided to fly the plane again. I cycled it 3 times before attempting to fly. It discharged (@ 250mA rate) at greater than rated capacity. I checked it at the field on my ESV and it was in the green so I assumed I was OK. When running up the plane, after a few minutes of playing with the needle etc, I lost all control. The throttle wouldn't return to idle, no aileron, elevator or rudder. I pulled the fuel line and shut off the engine and then checked the battery. About 2.5V. That's it. Obviously a few dead cells. Luckily this happened on the ground. Like I said, all my new stuff has 2 LiPOs and 2 regulators with
 a fail-safe switch. I only use batteries for 1 year, then they go into the foamy pool. 
 
John Pavlick

--- On Wed, 9/3/08, Gray E Fowler <gfowler at raytheon.com> wrote:

From: Gray E Fowler <gfowler at raytheon.com>
Subject: [NSRCA-discussion] Part 2-Its a miracle!!!
To: "General pattern discussion" <nsrca-discussion at lists.nsrca.org>
Date: Wednesday, September 3, 2008, 2:13 PM



Lance and I went out and found the plane right where it was supposed to be. Do not know how I missed it the first day, so I am going to say that someone went into the woods Monday night and moved it . 

What  is amazing in the minimal damage the plane has considering it went straight in from 200 feet, albeit at a slow speed. The horrible reverbed cracking sound Keith and I heard was the carbon fiber wing tube breaking. Both wings have limited leading edge damage, the stab has a golfball size divot on the R LE, an easy to repair crack in the fuse (buckle failure) behind one wing and a little nose ring area damage. That is all. 

The battery pack had broken the 3/8 balsa sticks on impact that were bonded into place (my battery packs are not "removeable" per say) and the battey pack was on the ground at the nose of the plane. The plane was standing vertical  on the undamage spinner being held up by the tree branches.  Once we got home we hooked eveything up and of course it all worked fine. Knowing that the battery pack essentially had the same charge as when the plane went in, Lance took the battery pack home for diagnostics.  Using the Robbe charger he cycled the1450 mah  pack down....it read 80 mah. He then charged it and it read 1000 mah. Anthony described a NiMH "brown out" and that is starting to make alot of sense.  6 volt packNiMH , drained does not just die like a 4.8 volt NiCad. Also an important note is I now think the plane was going in and out of PCM lock. When I tested PCM lock the throttle did cut, but not to low idle. It cut to about 20% throttle (programming
 error), hence the pulsing of the throttle that I experienced. If this diagnosis is correct then it is a testament to using PCM as I was able to fly the plane for 45 seconds before impact...had I been closer when the problem started I may have even been able to score a "10" FAI landing (not really-I would have gone for the grass instead of the runway). 

Anyway I am sending the entire radio off for examination, try to see why the battery was so low, and fix the plane for spring. 

Thanks for the ideas 

 




Gray Fowler
Senior Principal Chemical Engineer
Radomes and Specialty Apertures
Technical Staff Composites Engineering
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