Question about skirt desighn
Darryl Meyers
Am just doing the research on the subject and all you guys have been a big
help, but I have come accross a subject as to which there seems to be very
little technical STUFF. Skirts, can anyone help me to understand them. How
are they constructed, how do they attach to the craft, are they full of air,
how does it get there?
If anyone can help or knows of a good web sight with info could you please
pass it along.
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Darryl Meyers
Ken Roberts
hovercraft. the skirt increases the effective hover height and decreases the
power required to get the craft to hover. obsolete machines such as the air
curtain machine used a huge amount of power just to stay hovering. a modern
recreational hovercraft that seats 4 people frequently will have only 10 hp
dedicated to lift.
all the skirts i'll describe have several things in common. the descriptions
i'll give are based on common recreational hovercrafts unless otherwise noted:
-they're made of some sort of fabric with a flexible rubber/plastic-like
coating.
-they occupy the outer edge of the bottom of the hovercraft--NOT the center.
-they are filled with air.
-they have a way to let air, water, sticks, and whatever else out.
-they must be continually replenished with a high volume of air.
-the air used to maintain the skirt, if any additional is required, is not a
large contributor to the lift force on the craft. the air in the space
enclosed by the skirt provides lift.
skirts are currently made in three basic types that i know of:
-bag
-finger
-combination of both.
bag skirts:
these are the simplest to make and are frequently used on homebuilt hovercrafts
as well as some commercial models. they take less material because there are
no folds. the air is fed in at one point, and the bag air flows all the way
around until it reaches a drain hole, usually at the opposite end of the craft.
bag skirts are fed one of three ways that i know of:
-serially: all the lift air goes into the bag. the holes in the bag point
into the central area under the hull which is enclosed by the skirt. this
is, to my knowledge, only used on large commercial crafts. i personally
can't imagine it to be nearly as effective as either of the other two
methods described here.
-in parallel with the lift air: the lift air is divided immediately downstream
of the lift fan, part goes into the bag, part goes into the central area.
this comprises most of the twin-engine and twin-fan crafts i've seen. it's
also frequently used in single-engine, single-fan crafts.
-reverse serially: the air is pumped into the central area enclosed by the
skirt. the skirt has openings on the inside to allow air into the skirt.
the air flows from the central area to the skirt, causing it to fill.
sevtec is the only brand i know of to use this design, though i see nothing
wrong with it for most applications.
finger skirts:
these skirts have a 'pleated' look. there are lots of skirts, each one
comprising a finger, mounted separately all the way around the edge of the
craft. there is a central attach point (an inner ring of points) and an ouer
ring, the outer ring is sometimes on the side of the craft near the bottom.
the basic design implies a sort of sling of skirt material, with an open space
pointed towards the inside area enclosed by the skirt. there are modifications
to this design. most finger skirt crafts i know of have modified segments in
back, so that water doesn't scoop up into the segment and slow you down.
finger skirts are fed two ways i know of:
-reverse serially: i'm calling it that only because of the similarity to the
reverse serial feed method of the bag skirt. air is pumped into the central
area enclosed by the skirt, under the craft. the air flows into the
individual segments, and the natural action of air flow pushes the segments
against each other to form a seal.
-through a plenum chamber: the air is pumped into a specially designed
distribution path all the way around the craft. there is a hole in the outer
hull above each finger. air flows from the plenum chamber into the finger,
causing it to inflate. air escapes from the finger to the area enclosed by
the skirt, causing the craft to lift.
combination skirts:
crafts using this method have a bag skirt on top and fingers underneath. the
way i understand it, there can be two methods to feed the fingers: they are
identical to the normal finger skirt feed methods, except that the plenum
chamber is replaced by the bag skirt. this is speculation on my part because
i've never seen one of these crafts personally, let alone been able to look
under it. to my knowledge, there are no recreational crafts which use this
method.
common recreational crafts use either finger skirts or bag skirts, or even
sometimes have a bag in one portion of the perimeter and fingers elsewhere.
bag skirts are cheaper and easier to make, but susceptible to damage which must
be either repaired or the entire skirt replaced. finger skirts have larger
initial investment, but damaged skirts can be replaced in moments, usually in
the field. i'm not sure if there are any other significant differences, since
i've never had a craft with finger skirts nor have i been around someone who
does.
Tony Westwood
Tony Westwood
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> you may find this site helpful
> http://thcc.freewebsites.com/Index/index.html
Goto technical and then skirt dessign it also has a weath of other useful
info