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Original Year
 1993
# of pieces
 191
Categories
 Other:  Watercraft
Dimensions
 26(L)x14(W)x10(H)
Features
 Rotating propeller
thrust vectoring
Other Views

8824 Hovercraft
iso revolve
Click the image to download the LDraw file of this model.
Model by Benjamin Wendl
I love things that are different and this boat, released in 1993, certainly fits that criteria.  It is the only Technic hovercraft (save 8246 which hardly counts).  I'm not sure why it was not repeated as this is a very good rendition of a small hovercraft.  The hidden wheels control "steering" while the rear pusher propeller follows along.  The propeller also rotates as the wheels are turned when the model moves.

This model includes the first use of the 16 tooth clutch (idler) gear, the first use of the rubber bumpers, and the first and only use of the angled rubber bumpers.

Features
Directional Control
There are 4 wheels hidden under the skirt which control drive and direction of the craft.  The pair of wheels in the rear control the steering which makes the tail swing out white turning like a real hovercraft.

The steering is controlled by an overhead "hand of god" control.  The wheel turns a pair of axles through a set of 8 and 24 tooth spur gears.  The second axle houses the wheels.  A toothed connector is locked to the same axle.  Another vertical axle at the end of this connector becomes the main bearing for the drive propeller.  This causes the propeller to turn along with the wheels when steering.




 steering1     steering
Click for an animation of the steering in motion.
Propellers
The front wheels drive the 4 blade propeller.  Connected to the wheel axle is a set of 14 tooth bevel gears.  Next, a 24 tooth crown mates with an 8 tooth pinion.  As you can see in the computer image, the next two stages involve 16 tooth spur gears.  The two dark gray gears are idler gears in that they have a round bore and are not connected to the axles which guide them.  The axles merely serve as centering bearings.  The rear-most of these idler gears is concentric with the vertical steering axle.  This allows the 24 tooth crown gear attached to the prop to pivot around this axis when turning side to side.  At the same time, the propeller can be spinning to provide thrust.
 props     props
Click for an animation of the prop in motion.
Skirt/Wheels
This model features a series of rubber skirts which only appeared in 1993.  These skirts attach to 1x4 Technic beams with flanges on one side.  The skirt with a 45 degree angle only appeared in this one set.

Although the skirt pieces have no functional value, I was always surprised that they were never reused.  Still, they must not be very popular builders because they are not very expensive despite their rarity.
 skirt
 

Other Views
Side View
side view
Top View
top view
Front View
front view
Back View
back view
Computer Render
Render

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