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Teacher
Edition Contents
Skill,
Tools, & Craftsmanship
Cutting
& Drying Fish
Sharpening
Nails,
Pegs, & Lashings
Falling
Trees &
Small-Scale
Logging
Guns
Chainsaw
Clutch & Chain
Ice
Pick
Shelters
Wood
Stoves
Wall
Tents
Steambaths
Insulation
& Vapor Barriers
Gas
Lamps & Gas Stoves
Travel
Piloting
A Boat
Boat
Design
Magnetos
& Spark Plugs
Carburetors
Compression
Outboard
Motor Lower Unit
Outboard
Motor Cooling System
Dogsleds
Snowmachine
Tracks
Snowmachine
Clutch
Snowshoes
Winter
Trails
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Activities
- Put gasoline on a rubber band. What happens? Put a rubber band
outside in the cold. How flexible is it below zero? Why aren’t
tracks made of real rubber?
Gasoline will quickly dissolve the rubber in a rubber band.
- Look at the different snowmachine tracks in the village. How
do they compare in length and width? Do some have metal cleats?
Do any have racing stars? Of all the different kinds, which is
the most popular in your village?
- Measure the surface area of the tracks plus surface area of
the skis of different machines. Compare the surface area to the
weights given in the snowmachine specifications. How many pounds
per square inch does each one represent? Are there relationships
between the psi of trail machines contrasted with racing machines?
- Draw the patterns of the bottom of the tracks. Compare them.
Compare them with four-wheeler tire patterns. Are there any similarities?
- Find old tracks around the village. Compare their thickness.
Diagnose why each one broke (cracking, wear in certain places).
Try bending a piece of track that has been out in the cold. Try
bending the same piece of track once it has been inside for a
while. How much difference is there? Speculate how much more power
it takes to turn a cold track than a warm one.
- Carefully try to cut a piece of snowmachine track. Can you
appreciate the technology that made it this tough?
- Ask the people in the village what they do when a track breaks
far away from home.
- What uses have people found for discarded snowmachine tracks
in your village?
They make great walkways before the porch on a house. They
aren’t slippery, and people clean their feet on them.
- Compare the suspension systems of the machines in your village.
Do some still have bogie wheels? Talk to people that own the two
different kinds. What are the advantages of each? Find a discarded
slide rail. Does it look like it wore out because of snow or gravel?
Try to cut it with a knife. Is it hard? What uses have people
discovered for used slide rails? Inquire how much new slide rails
cost and how hard they are to install. Identify the part of the
track that slide rails run against. How is this different from
the rest of the track? Are the bearings on the bogie wheels sealed
bearings? What do you think happens when the seals go bad? What
can you learn about increasing the life of bearing seals?
Slide rail material is quite hard for a plastic. They are fairly
inexpensive and are easy to change once the track is removed.
Bearing seals? Stay out of water and dirt.
- Look at the skis on different machines in your village. Talk
with people who use the plastic skins that fit under the skis.
What do they say? What is the surface area of the average ski?
Compare skegs on the different skis.
- Measure the distance between the skis on different machines.
Is there a difference? If so, why do you think this is so? What
do snowmachine owners say about skis being close together or farther
apart? Is it important? If so, under what conditions?
Wider skis are more stable, especially at high speeds.
- Talk to several people who have installed the sheets of plastic
under the belly of the snowmachine. Do they notice a significant
difference? Why did they install the plastic in the first place?
- When did snowmachines first come to your village? Ask the older
people how they have changed over the years. What about them has
improved? What about them has not improved? Why do they think
machines are better than dogs?
Student Response
- Why wouldn’t a track made out of natural rubber last on
a snowmachine in Alaska?
It would stretch too much and be dissolved by gasoline and
oil.
- Why are there nylon cords in the track as well as Kevlar?
To keep the Kevlar from tearing
- What is the problem with a very large track?
It takes a lot of energy just to turn it.
- What is the problem with a small track?
It sinks deeply into the snow.
- What is the problem with a track that is too smooth? Too rough?
Too smooth doesn’t have enough friction to pull a load
or climb a hill. Too rough will dig in when traveling on powder
snow.
- What kind of track would you want to operate in deep powder
snow?
High surface area
- What kind of track would you want for racing? For pulling big
loads on hard trails?
Racing: smaller track with cleats and stars.
Big loads on hard trails: wider track with cleats.
- Skis are designed to have very little friction in a direction,
and considerable friction in a direction.
Forward, sideways
- What is the purpose of skis besides steering?
Provide surface area to keep the machine on top of the snow
as much as possible.
- Why do some people put plastic skins on skis?
They greatly reduce friction and increase flotation.
- Why do some people have belly plastic installed?
Reduce friction in deep powder and protect the belly.
Math
- A machine weighs 375 lbs. The track is 15” x 47” in
contact with the trail. The skis are 5” x 30” each with
plastic shoes. What is the average psi of this machine on the
surface of the snow?
.373 psi
- A racing machine weighs 489 lbs. The track is 15” x 40”
in contact with the snow. The skis are 5” x 24” each.
What is the average psi on the surface of the snow?
.582 psi
- A long track uses 25% more energy to turn than a short one.
Turning a short track represents 9% of a machine’s effort.
If Pete usually spends $350 a year on gasoline approximately how
much is he paying for the convenience of having a long track?
$7.87 not expensive at all.
- Having plastic ski skins and plastic on the belly of a machine
saved 12% of a machine’s effort. They cost $75 to purchase.
If Moxie usually spends $425 for gas on his trapline, will the
plastic on the skis and belly pay for themselves in the first
year?
No. $51 is less than the original $75. But they will pay for
themselves the next year. However the difference is in performance
and handling, not just in gas savings.
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