Friction and Gravity
Insert a dart into your blow gun then give it a blow: Normally we would
expect that the tip of the dart would slide on the bottom of blowpipe,
right in the middle of the "way". Unfortunately this is only the very seldom
the case!
Friction:
In reality there is friction between cone and wall of Blowpipe. The un-equal
distributed friction forces will cause that the tip of dart does move to
the right or left inside the blowpipe. Wort case it will even move straight
up.
Result is that at each shot the dart leaves the muzzle in a different
angle. It is obvious that this will cause a deviation of flight direction
of dart. The dart does not hit the center of target. If the dart would
leave the muzzle always in same angle it would be easier to hit the center
of the target.
Methods to make Friction as low as possible:
1) Use flexible film cones
2) Every 15 shot clean Blowpipe with Dish Water Soap.
Little soak a wadden with Dish Water
Soap and push or pull it through the blowpipe.
The Dish Water Soap has an additional
very positive effect:
It tends to disable moist condensation
and therefore if tends to disable the growing of water drips on the inner
walls
of blowpipe. Note: water drips
cause unwanted drag to the dart cone movement ( kind of friction)
Gravity:
Another extremely critical situation is if the blowpipe is bend, and the
bending direction is downwards (to ground)
Normally the gravity force would keep the tip of dart down at bottom
of blowpipe.
The dart is traveling very fast through the blowpipe. If the pipe is
bend downwards the tip can't fall that fast
downwards than the bottom seems to move down. ( more than one "G" acceleration
is not possible)
The dart tip looses bottom contact and will move randomly left or right
or up. Result is that at each shot the dart leaves the muzzle in a different
angle. It is obvious that this will cause a deviation of flight direction
of dart. The dart does not hit the center of target. If the dart would
leave the muzzle always in same angle it would be easier to hit the center
of the target.
Example: If you shoot your dart with 56m/s and your 2 meter Blowgun
is bend 2.5cm downwards then the dart tip starts to loose bottom contact.
Methods for prevention:
1) use a blowgun which is absolutely straight.
2) bend blowgun a little bit (2 mm per meter), while shooting always
hold the blow gun in a way that direction of bend is upwards.
Theory and table for comparison of Darts ( also available as excel
file )