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n85ae
Joined: 14 Mar 2007
Posts: 403
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 Posted: Mon Jun 25, 2007 5:52 am Post subject: Broken battery Box |
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Bruce Line asked me to forward this to the list:
Hi Jeff, I am sending a few photos that you may be interested in and I suggest you check this out on your plane before you fly it again. It started when on my last preflight I noticed a small (maybe 1/4 " long tear in the fabric below the battery access panel. When I ran my finger over the tear , I felt something hard protruding through. This began to peak my interest, so I pulled the battery access panel off and was shocked to find that the hole in the fabric was from the aft aluminum angle that makes up the aft attach point on the battery box. Upon further investigation, I found that 5 out of the 6 battery box attach points had failed and the box was resting on the rudder cables. As you can well imagine this could have ruined my day as just a few flights before I was doing spins. The attach failures were varied. On the aft end of the box, the aluminum angle broke where it attaches to the eye bolts and the other failures where from broken adel clamps. There were rub marks worn into the bottom of the box from the rudder cables because the box had slid down and rested on the cables-not good. I will send several photos to document the mess. Would it be possible for you to forward this info to the list to get the information out to guys with aft mounted batteries . This is a very big deal and shows an area with a big design flaw. The reason for the failure is unclear. I did not have a hard landing (other than my usual technique) but I do operate from rough grass strips alot. The spins may also be a causal factor. All that weight (my battery is the 22 lb variety) gyrating around may have tore it free. I am reengineering the attach points to be much stronger and will probably switch to a lighter Odyssey battery to fix the problem. I will send several photos in sequence. Bruce
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Float Flyr
Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland
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| Posted: Mon Jun 25, 2007 7:47 am Post subject: Broken battery Box |
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Bruce:
I'm trying to figure out where the long "bolts" cracked off the battery box. Can you get a picture showing the orientation of the tabs that were cracked off?
The Adel cushion clamps will crack where they did if they are installed with the load above the mounting bolts.
[img]cid:420234615(at)25062007-2317[/img]
Noel Loveys, RPP, AME intern
Campbellton, Newfoundland,
Canada
Kitfox Mod III-A, 582, B box, Ivo IFA
Aerocet 1100s
noelloveys(at)yahoo.ca (noelloveys(at)yahoo.ca)
[quote] --
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Noel Loveys
Kitfox III-A
Aerocet 1100 Floats |
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n85ae
Joined: 14 Mar 2007
Posts: 403
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| Posted: Mon Jun 25, 2007 8:28 am Post subject: Re: Broken battery Box |
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Here's one more pic
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n85ae
Joined: 14 Mar 2007
Posts: 403
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| Posted: Mon Jun 25, 2007 8:30 am Post subject: Re: Broken battery Box |
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One more view
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smokey_bear_40220(at)yaho
Guest
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| Posted: Mon Jun 25, 2007 2:06 pm Post subject: Broken battery Box |
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--- n85ae <n85ae(at)yahoo.com> wrote:
| Quote: | Bruce Line asked me to forward this to the list:
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| Quote: | ...Upon further investigation, I found that 5 out of
the 6 battery box attach points had failed and the
box was resting on the rudder cables......
---------------------------------------------------
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Thanks for the warning. I believe we all need to
think "what if" when we build and not let a mode of
failure threaten us, if we can avoid it. No, "It
works or we die" items should go without a backup.
Since I have an NSI Soob, I also have an aft battery
of the same weight. I don't like dead weight to
balance the plane either, so I mounted the ELT in the
tail behind the battery instead of lead.
The ELT requires a 100 G mount, therefore I designed a
common mount for the battery and ELT to achieve that
for both. It is made of stainless steel and weighs
about 3 lbs, if I remember correctly, when you include
the heavy cargo strap that holds the battery in and
adds to its security.
I truely believe the tail and battery case will fail
long before my box. You could lift the plane by it.
It also has a bottom box beam that sits between the
rudder cables and prevents the battery from being able
to fall and bind the cables.
But I must admit my plane is not one of the lightest,
nor have I backed up the 6 primary wing bolts with a
BRS chute. The 39 lbs were just not justified by the
accident reports. But I still sweat that one.
Kurt Schrader
S-5/NSI turbo
CAP prop
Florida and Panama
Sick sense of humor? Visit Yahoo! TV's
Comedy with an Edge to see what's on, when.
http://tv.yahoo.com/collections/222
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Float Flyr
Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland
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| Posted: Mon Jun 25, 2007 3:04 pm Post subject: Broken battery Box |
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The part where the tabs broke off looks like it was a fabricated part that was bent in a brake to form the frame. The bend was made across the grain of the metal but the tabs were running with the grain of the metal and were prone to cracking under stress.
I would suggest that you make a plate with the grain of the aluminium running lengthwise and rivet it to the bottom of the battery box. If you really wanted to you could use a piece of extruded aluminium for the part. The grain on extruded aluminium angle is always along it's length.
On the other end where the Adel clamps broke install a couple of extension tabs down instead of up so the tension on the Adel clamps is reversed ( tension not compression). This will be opposite to the direction shown in AC43... Then again the load is different.
[img]cid:982433322(at)25062007-2341[/img]
[quote] -----Original Message-----
From: owner-kitfox-list-server(at)matronics.com
[mailto:owner-kitfox-list-server(at)matronics.com (owner-kitfox-list-server(at)matronics.com)] On Behalf Of n85ae
Sent: Monday, June 25, 2007 2:00 PM
To: kitfox-list(at)matronics.com
Subject: Re: Broken battery Box
--> Kitfox-List message posted by: "n85ae" <n85ae(at)yahoo.com>
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Noel Loveys
Kitfox III-A
Aerocet 1100 Floats |
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kitfox(at)ida.net
Guest
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| Posted: Mon Jun 25, 2007 7:31 pm Post subject: Broken battery Box |
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I am no engineer, but the damage looks like it was caused by flex. The same
for the clamps. The long bolts will let the weight move the box mounts. Ever
so slightly. Resulting in cracks and then failure. Brackets should be bolted
right to the tubes. Even if that means runing vertical angle to bolt the box
onto. Just my thoughts.
Albert Smith
MudLake, Idaho
5TD NSI turbo ,CAP
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Float Flyr
Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland
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| Posted: Tue Jun 26, 2007 3:58 am Post subject: Broken battery Box |
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Especially when the flex is with the grain of the metal!
[img]cid:409045511(at)26062007-1453[/img]
Noel Loveys, RPP, AME intern
Campbellton, Newfoundland,
Canada
Kitfox Mod III-A, 582, B box, Ivo IFA
Aerocet 1100s
noelloveys(at)yahoo.ca (noelloveys(at)yahoo.ca)
Do not archive
[quote] --
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Kitfox III-A
Aerocet 1100 Floats |
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