[NSRCA-discussion] Lost Abbra

Mon Aug 7 07:09:01 AKDT 2006

I've been reading this thread and I serously doubt the NiMH batteries had anything to do with the crash. NiMH batteries aren't new on the market for goodness sakes and they've been working very very well on probably billions of flights. Sure we have digital servos, but in truth our loads aren't really very high and certinally not for and extended draw.  

I would think if low voltage had caused the loss of control then once the snap stopped, even though you had little time before hitting the ground, you still would have had enough time for the RX to come back to life. Remember, the battery did discharge 1540 mah on the ground.

As to the servo that was locked at full throw, if this had occurred in the air the plane would have been spiraling on it's way down and your other surfaces would have still worked. Therefore, you can rule out the jammed servo, that most certinally happened upon impact.

As to the IMAC guys having low impedance problems I can buy this, but keep in mind these guys have two to three servos on each surface, their planes weigh 40 lbs, and they slam the controls like crazy doing blenders and such. The usage by pattern planes isn't even in the same galaxy. 

Most likely this was a simple case of lock-out due to reception. There could be some other factor, but I would hate to see anyone go back to NiCADs due to this incident.

Keith Black  
  ----- Original Message ----- 
  From: vicenterc at comcast.net 
  To: NSRCA Mailing List ; NSRCA Mailing List 
  Sent: Monday, August 07, 2006 7:44 AM
  Subject: Re: [NSRCA-discussion] Lost Abbra

  Thanks Chris,

  You are right.  The event was so fast.  Going down hill at 45 degrees didn't give me too much time.  

  I went to NiMh two years ago. Looks like I am going to go back to NiCads.  Several fellow pilots are telling me about the voltage drop problem of the NiMh.  Probably, the battery was not the cause of the crash but I think I am going to feel more confident going back to NiCads.  I went to NiMh because they are lighter for a given capacity.  I agree that there has been a lot of comments in regard the low impedance.  However, I really don't want to use NiMh after having this problem. 

  I am planing to send the radio to JR for a complete check out.

  Vicente "Vince" Bortone
    -------------- Original message -------------- 
    From: "White, Chris" <chris at ssd.fsi.com> 

    Hi Vince, very sorry to hear about your Abbra loss...not much time to recover or evaluate the problem considering where it happened.  For what its worth, I've heard of airplane losses due to over-demand voltage during snaps .  I also hear many of the giant scale guys are using "low impedance" nimh batteries when using nimh because of servo over-demand during certain maneuvers such as snaps.    After hearing the low-impedance story I went to Hangtime Hobbies and am now flying their KAM 1800 6v low impedance packs.  Their site is worth a visit just for the read. 

    www.hangtimes.com/nobsbatteries.html

    I hope you find closure on the cause.  

    Chris White

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    From: nsrca-discussion-bounces at lists.nsrca.org [mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of vicenterc at comcast.net
    Sent: Monday, August 07, 2006 5:49 AM
    To: NSRCA Mailing List; NSRCA Mailing List
    Subject: Re: [NSRCA-discussion] Lost Abbra

    Ron,

    I checked all servos but throttle and one aileron servo.  All are working on the bench fine.  One of the aileron servos gears is locked in maximum travel position and I am assuming that was caused in the crash.  However, I could be wrong.

    Thanks,

    Vicente "Vince" Bortone

      -------------- Original message -------------- 
      From: Ron Van Putte <vanputte at cox.net> 

      On Aug 6, 2006, at 9:50 PM, vicenterc at comcast.net wrote:

      The battery was a little over a year old. I cycled the battery after the crash and got around 1540 mah. It was freshly charged and I was in the second fly. I use around 200 mah per fly so the battery was close to 2000 mah. I always charge at C/10 and never fast charged. 

      I am discharging the battery now at 500 mah. I discharged the first time at 250 mah. I will keep increasing the discharge rate to check if I find something wrong. 

      I am willing to bet that you will find a bad servo. Maybe Jim Oddino or one of the other radio wizards can explain, but a single servo can cause the whole system to crash.

      Ron

        -------------- Original message -------------- 
        From: "Scott Anderson" <scott at rcfoamy.com> 

        How old are the NiMh batteries... People have found the have a steep drop off when going bad..

        scott

          ----- Original Message ----- 

          From: vicenterc at comcast.net 

          To: NSRCA Mailing List ; nsrca-discussion at lists.nsrca.org 

          Cc: Fred Huber 

          Sent: Sunday, August 06, 2006 10:19 PM

          Subject: Re: [NSRCA-discussion] Lost Abbra

          Fred,

          Usually I called pilot (and/or mechanic) error until I find the cause of the crash. I haven't been in this position in a very long time. I tend to agree with you since it was clear that I didn't have control. However, the radio is working even after such a crash. There was a comment at the field that NiMh batteries can cause this problem. I will check the battery as much as possible (cycle increasing the current draws) but not sure if the test will be valid.

          Thanks,

          Vicente "Vince" Bortone 

            -------------- Original message -------------- 
            From: "Fred Huber" <fhhuber at clearwire.com> 

            In that case... it may have gone to lock out just as it was finishing the snap... rather than your control input to get out of the rotation, the surfaces go to neutral, it over-rotates and then plays lawn dart.

            No response at all its very easy to thing failsafe lockout. Since the engine was already at the failsafe setting, you don't have that indicator to confirm (or refute) the lockout.

            I wouldn't call it pilot error when the control input attempts you made simply had no effect...

              ----- Original Message ----- 

              From: vicenterc at comcast.net 

              To: nsrca-discussion at lists.nsrca.org 

              Sent: Sunday, August 06, 2006 7:15 PM

              Subject: Re: [NSRCA-discussion] Lost Abbra

              I am wrong below in regard the fail safe in regard the fail safe. The fail safe is programmed to cut the engine and set the control surfaces at neutral. 

              Vicente "Vince" Bortone

                -------------- Original message -------------- 
                From: vicenterc at comcast.net 

                Yes, yesterday afternoon I lost my Abbra. I was doing the 45 degree down with snap. After the snap, I could not control the plane. This is my recollection of events:

                1. I over rotated the snap for a kittle more than 90 degrees. It was clear to me at that early stage that something was going wrong. I snapped to the right. 

                2. My friend Charlie was calling for me. He also noticed and said something to put it back in position. I told him that the plane was not responding. 

                3. First reaction was to give full left to get it back upright. The ailerons did not respond. When I realized that, I tried to take it out of the dive by given down elevator since was pracically in inverted position. It did not respond. It that aptitude everything goes very fast. Finally, I tried to give up elevator but was already too late. I am aware that I applied these control input. It was clear to me that there was no reaction. I was able to realize that I didn't have control and I could not avoid the crash. 

                4. I did not have time to do anything with rudder and throttle. Throttle was at idle. 

                5. When we checked the crash site. One aileron servo was buzzing hard. I disconnected the servo. Therefore, my first impression that the battery flew off and it got disconnected with the force of the snap was not valid.

                6. I took the plane home as it came from the crash. I disconnected only the ailerons servos. I checked the radio and everything is working fine. Only two servos are not working. The throttle servo that was practically destroyed in the crash and one aileron servo that the gears were stripped. I believe that this was caused by the force of the impact. There was not evidence of flutter in the ailerons before the crash or structural damage after coming out of the snap.

                7. I believe that the plane was well over stall speed after the snap. Therefore, the plane was not in stalled condition. However, I could be wrong.

                7. I use JR all around with digital servos. PCM receiver with fail safe programmed to cut engine and leave the servos in the last commanded position. 

                8. I use 2300 mah NiMh battery (4 cells AA Sanyo). I checked the battery voltage and was at 5.15 volts after the crash. Discharged the battery and gave 1540 mah using 250mah rate. I am planning to cycle the battery with higher loads. 

                9. It was very hot day. The plane was sitting in the sun and it was second fly of the day around 2:00 PM. Easily was close to 100 oF. 

                At this point, I have to admit that has to be pilot error since I have not been able to find a definitive cause of the crash. It is clear that the snap initiated some kind of failure. Other pilots think that the NiMh battery gave up at high currents during the snap and caused the crash. I have been flying this type of battery for two years now with no problems. 

                I am informing this to the group since I would like to have your feedback. If someone had a similar problem and found the cause of the crash, please let me know. I am going back to my backup plane (the old hydeout). I have a brand new Abbra so need to put it together. 

                Thanks and have a nice day,

                Vicente Bortone

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