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aviateer
Joined: 08 Aug 2008
Posts: 23
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 Posted: Mon Jan 26, 2009 7:21 am Post subject: Ski Tuck |
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Regarding the posting on the ski tuck, the problem may be with the rubber in the bungee. I had some problems with my landing gear bungee cord with below zero temperatures in that the gear would not come back up. So I had a "bow legged" Kitfox until it warmed up. I noticed that the rubber in the bungee was sort of gray. Where the bungee cords with the white rubber seem to snap back no matter how cold it is. I now only use bungee cords with white rubber. Some supply houses will check before they cut the bungee to your specified length.
Maybe the bungee was a little weak and did not hold the ski up all the way, allowing the slipstream at cruise speeds to grab the ski and pull it down.
Just a thought.
Kirk Martenson
Classic IV (Speedster?) with a sick 912UL
[quote][b]
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Lynn Matteson
Joined: 10 Jan 2006
Posts: 2778
Location: Grass Lake, Michigan
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| Posted: Mon Jan 26, 2009 12:40 pm Post subject: Ski Tuck |
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It was new rubber about 2 weeks ago, fresh from Aircraft Spruce, and
it is white rubber. I think I just didn't put enough tension on them
when I cut them to length. I'm going to shorten them by about an inch
or maybe 1-1/2". And of course with building skis, you just order 16
feet of the stuff, and hope for the best and freshest batch. One of
my Tony Bingelis books shows a chart of the thread colors used in the
covering of the shock cords, which would allow you to check the
manufacturing date of the cords, but none of the cords that I've
ordered over the years from Spruce has matched the chart...ever.
Lynn Matteson
Kitfox IV Speedster, taildragger
Jabiru 2200, #2062, 600.2 hrs
Sensenich 62x46
Electroair direct-fire ignition system
New skis done and flying
do not archive
On Jan 26, 2009, at 10:20 AM, Kitfoxkirk wrote:
| Quote: | Regarding the posting on the ski tuck, the problem may be with the
rubber in the bungee. I had some problems with my landing gear
bungee cord with below zero temperatures in that the gear would not
come back up. So I had a "bow legged" Kitfox until it warmed up. I
noticed that the rubber in the bungee was sort of gray. Where the
bungee cords with the white rubber seem to snap back no matter how
cold it is. I now only use bungee cords with white rubber. Some
supply houses will check before they cut the bungee to your
specified length.
Maybe the bungee was a little weak and did not hold the ski up all
the way, allowing the slipstream at cruise speeds to grab the ski
and pull it down.
Just a thought.
Kirk Martenson
Classic IV (Speedster?) with a sick 912UL
www.matronics.com/contribution _-
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Lynn
Kitfox IV-Jabiru 2200
N369LM |
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Float Flyr
Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland
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| Posted: Mon Jan 26, 2009 3:51 pm Post subject: Ski Tuck |
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Lynn:
That's because it isn't certified shock cord. If you get your cord from
Aviall expect to pay a lot more for it but it will come with a tag used to
certify the plane. Are the cords from Aviall any better? No, but the tag
is worth its weight in gold. A rule of thumb is to replace all chords every
five years. On our small planes we may get twice that life out of them.
Like everything else check them over in the fall when you install your skis.
Most chord will extend .61 % (from 1 ft. to 1.61 ft) so for the skis I
would have the stretched length around 1.5 times the length at rest. That
will give close to maximum lift on the chord without pulling it too much.
Noel
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Noel Loveys
Kitfox III-A
Aerocet 1100 Floats |
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Lynn Matteson
Joined: 10 Jan 2006
Posts: 2778
Location: Grass Lake, Michigan
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| Posted: Mon Jan 26, 2009 5:40 pm Post subject: Ski Tuck |
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Both Spruce and Wicks Aircraft Supply cite Mil-Spec numbers for their
shock cord...Spruce says theirs is pre-stretched "for an ultimate
elongation of 120-140%"
How is the tag worth it's weight in gold.....on an experimental pair
of skis on an experimental airplane?
I have even begun to follow FAA's suggestion to relax the cords when
parked overnight or longer....which is most of the time. I would
surmise that if it is common practice to change landing gear bungees
every two years, we may well get 5 years out of ski shock cords,
especially if relaxed as suggested....and kept out of sunlight for
most of their life.
Lynn Matteson
Kitfox IV Speedster, taildragger
Jabiru 2200, #2062, 600.2 hrs
Sensenich 62x46
Electroair direct-fire ignition system
New skis done and flying
On Jan 26, 2009, at 6:50 PM, Noel Loveys wrote:
[quote]
Lynn:
That's because it isn't certified shock cord. If you get your cord
from
Aviall expect to pay a lot more for it but it will come with a tag
used to
certify the plane. Are the cords from Aviall any better? No, but
the tag
is worth its weight in gold. A rule of thumb is to replace all
chords every
five years. On our small planes we may get twice that life out of
them.
Like everything else check them over in the fall when you install
your skis.
Most chord will extend .61 % (from 1 ft. to 1.61 ft) so for the
skis I
would have the stretched length around 1.5 times the length at
rest. That
will give close to maximum lift on the chord without pulling it too
much.
Noel
--
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Lynn
Kitfox IV-Jabiru 2200
N369LM |
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Float Flyr
Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland
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| Posted: Tue Jan 27, 2009 7:08 am Post subject: Ski Tuck |
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The tag isn't worth its weight in gold on any amateur built but you put
local hardware store stuff on a Super Cub and you may find out how valuable
a little yellow tag can be. In the meantime it's that little tag that
allows any aircraft supplier to charge more for it. So in a way it still
worth gold ... just not yours or mine.
Relaxing the tension on the chords will certainly help keep their tension
especially in cold weather. As for getting five years. It's more than
possible if they are taken care of as you mentioned, dark cool storage
space. I had my boat moored in my boathouse with bungee cord. It keeps the
boat centred in the house with the tides going up and down. After a couple
of years they need to be replaced at the first sign of wear! It is amazing
how fast they will disintegrate once wear starts to show.
Noel
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Noel Loveys
Kitfox III-A
Aerocet 1100 Floats |
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Lynn Matteson
Joined: 10 Jan 2006
Posts: 2778
Location: Grass Lake, Michigan
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| Posted: Tue Jan 27, 2009 11:44 am Post subject: Ski Tuck |
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I would never THINK of putting "local hardware stuff" on my plane in
that application, and in fact, I'd probably change the shock cords
every two years, or at least take a tension check every season, and
keep a log. The most expensive stuff is cheap enough for the less-
than 16 feet I use on my skis.
Lynn Matteson
Kitfox IV Speedster, taildragger
Jabiru 2200, #2062, 600.2 hrs
Sensenich 62x46
Electroair direct-fire ignition system
New skis done and flying
do not archive
On Jan 27, 2009, at 10:05 AM, Noel Loveys wrote:
[quote]
The tag isn't worth its weight in gold on any amateur built but you
put
local hardware store stuff on a Super Cub and you may find out how
valuable
a little yellow tag can be. In the meantime it's that little tag that
allows any aircraft supplier to charge more for it. So in a way it
still
worth gold ... just not yours or mine.
Relaxing the tension on the chords will certainly help keep their
tension
especially in cold weather. As for getting five years. It's more
than
possible if they are taken care of as you mentioned, dark cool storage
space. I had my boat moored in my boathouse with bungee cord. It
keeps the
boat centred in the house with the tides going up and down. After
a couple
of years they need to be replaced at the first sign of wear! It is
amazing
how fast they will disintegrate once wear starts to show.
Noel
--
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_________________
Lynn
Kitfox IV-Jabiru 2200
N369LM |
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Float Flyr
Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland
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| Posted: Tue Jan 27, 2009 4:24 pm Post subject: Ski Tuck |
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Lynn:
That's the way to keep your plane safe for years to come.
Noel
--
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_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats |
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