one engine hovercraft?
TMB
one engine for lift and thrust with some sort of a constant speed prop with
reverse thrust? has anyone heard of such a design preferably with the
capability to carry 6 people. Thanks
A.J.P.M. Koevoets
TMB wrote:
Its no problem building one with a single engin. More over its the best
possible sollution
for a Hovercraft. as the are simple to handle.(only one throtle). The
combination with a reverse thrust is however difficult to achieve. No real
effective systems besides a reversable pitch prop are available but a revers
pitch prop is very expensive. If you want to transport 6 persons your looking
at a design using a 110 hp diesel or a 140 hp petrol engine. I'm cuurently
working on a design in aluminium of a six-seater craft.
Yours sincerly
Joost Koevoets
Googolplex
: TMB wrote:
: > I have noticed that many hovercraft use two engines. Is it possible to use
: > one engine for lift and thrust with some sort of a constant speed prop with
: > reverse thrust? has anyone heard of such a design preferably with the
: > capability to carry 6 people. Thanks
: Its no problem building one with a single engin. More over its the best
: possible sollution
: for a Hovercraft. as the are simple to handle.(only one throtle). The
: combination with a reverse thrust is however difficult to achieve. No real
: effective systems besides a reversable pitch prop are available but a revers
: pitch prop is very expensive.
"Buckets" to send the air 180 degrees ARE effective...though their thrust is
only about 1/3 the unobstructed thrust. Once I'm "over the hump," I can
continue indefinitely running backward...using my buckets to blow air over my
shoulders.
Ken Roberts
> : possible sollution
> : for a Hovercraft. as the are simple to handle.(only one throtle). The
> : combination with a reverse thrust is however difficult to achieve. No real
> : effective systems besides a reversable pitch prop are available but a revers
> : pitch prop is very expensive.
i beg to differ with the 'best possible solution' issue.
for lake cruising and such i can agree, but for most of the applications where i use a hovercraft,
you frequently want high lift and low or no thrust. try maneuvering a narrow stream up rapids and
over rocks with a single engine craft. you'll tear it up, because you'll either not have enough
lift or have too much speed!
perhaps a very experienced operator could do this, but i won't be there for quite some time.
a solution that's more complicated for the operator isn't necessarily the worst solution. it just
requires more training and skill to operate.
Earl
: requires more training and skill to operate.
While that's true...there is at least one exception to your scenario; if your
hovercraft has an adjustable reversing system, the forward thrust can be
effectively a separate variable from the lift.
Thinking of both of your points, it seems to me that with a separate lift/thrust engine layout you
will have two controls and with a single engine/reverse bucket layout, you will have two controls. The
operation of both will require about the same coordination. Considering time, weight, materials cost,
and fabrication, the two systems may also be about equal. I have'nt done any research into the
comparative efficiencies of the two types of systems so that is a question mark. The only real gain I
see on the single engine/bucket system is that you have reverse capability. But then, there is nothing
that says you can't install reverse buckets on a twin engine system either.
A.J.P.M. Koevoets
Ken Roberts wrote:
> > : Its no problem building one with a single engin. More over its the best
> > : possible sollution
> > : for a Hovercraft. as the are simple to handle.(only one throtle). The
> > : combination with a reverse thrust is however difficult to achieve. No real
> > : effective systems besides a reversable pitch prop are available but a revers
> > : pitch prop is very expensive.
>
> i beg to differ with the 'best possible solution' issue.
>
> for lake cruising and such i can agree, but for most of the applications where i use a hovercraft,
> you frequently want high lift and low or no thrust. try maneuvering a narrow stream up rapids and
> over rocks with a single engine craft. you'll tear it up, because you'll either not have enough
> lift or have too much speed!
>
> perhaps a very experienced operator could do this, but i won't be there for quite some time.
>
> a solution that's more complicated for the operator isn't necessarily the worst solution. it just
> requires more training and skill to operate.
When I was working for Hovertrams i build them 10 petrol powered 5 seaters and a diesel powerd one.
They were equipped with the simple but inefficient combined lift and thrust system. and equiped with
a simple shuttre system in the back of a duct. Power was controlled using a twist - grip throt. on the
steering bar. We took them out for flood relief work and for a demonstartion at force 7 on the
Liverpool coast in the UK. They were easy to handle and with all the controls combined you could
concentrate on the obstacles and not on the different settings.
Basic traning took abouth 3 days. As I did most of the test flights with the prototypes. Having flown
craft up to 4000 lbs of payload I had to get used to the quick reactions of the smaller craft I
allways founs the speed wasn't importand as long as you got the job done.
.
Ken Roberts
> : requires more training and skill to operate.
>
> hovercraft has an adjustable reversing system, the forward thrust can be
> effectively a separate variable from the lift.
yes, but how to reliably and inexpensively make that work on my hovercraft? i've thought about it
for quite some time, and while i can think of ways to do it 'damn the cost' i can't think of a
simple way that's practical for the recreational user. i'm living comfortably, but still have a
hard time keeping my machine flying due to the repair and maintenance costs. some of this is
repurchasing from bad ideas i've tried, but it all adds up even if you just try to fix something
that's broke.
Ken Roberts
> Thinking of both of your points, it seems to me that with a separate lift/thrust engine layout you
> will have two controls and with a single engine/reverse bucket layout, you will have two controls. The
> operation of both will require about the same coordination. Considering time, weight, materials cost,
> and fabrication, the two systems may also be about equal. I have'nt done any research into the
> comparative efficiencies of the two types of systems so that is a question mark. The only real gain I
> see on the single engine/bucket system is that you have reverse capability. But then, there is nothing
> that says you can't install reverse buckets on a twin engine system either.
the reverse thing would be a very big boone, at least for an inexperienced driver like me.
one thing you missed though is that if one engine goes out the twin is better for getting to shore.
i've had each engine go out. if your thrust engine quits, you can lean the craft and move maybe
5mph on the air that escapes from the light side. if your lift engine quits the thrust engine makes
maybe 5mph before water gets scooped into the lift duct. either way beats paddling.
if you could come up with a reliable system of splitting thrust and lift, and also if you could have
a reversible design (either or both of these) it would vastly improve the craft as a whole. you
could use a larger engine, which seems to be more reliable. i think they also tend to have better
mufflers on them, and better vibration damping. having a reverse would be very good. there are
crafts out there that use both of these, i imagine. some of the crafts with features similar to
this cost a whole bunch of money, though.
while some of us are driving machines that were 'factory' made, others are driving homebuilts. mine
was a compromise: i have a homebuilt that someone else made. however, i wouldn't want something i
couldn't modify or tinker with. that's the whole point.
Ken Roberts
>
> For a medium sized hovercraft (4-8 people), I often wondered if a
> totally hydraulic system was the way to go. The main motor runs a
> variable displacement pump that matches demand, and the lift and thrust
> motors would be hydraulic. You would have independant control of lift
> and thrust.
>
> The thrust motor would be reversible with simple valving, twin thrust
> motors could be diffential so you could turn on the spot.
>
> In addition, you have a power source available for skirt lifters,
> pumps, whatever ... The main motor only runs at a the speed required
> to match the load.
>
> Not exactly in the sports league though.
ya, i'm not sure you could get it to fly. hydraulics are very heavy and also not very efficient
when used at high speeds. i think it may work if you have aircraft-quality pumps, but even there
they don't use them for a major component of total power. they operate flaps and landing gear and
stuff like that.
i'm sure that someplace they make hydraulics of lightweight materials, but the cost? even the heavy
stuff is pretty expensive when you're talking about hydraulic motors.
the next thing, when you start talking about the snappy response a hydraulic motor has when
reversing direction, you might suffer prop damage or something similar someplace else. not to
torque problems when you change the direction of a spinning prop like that.
i also thought electric might work, but again you get into some serious money.
you could do it fairly well with a proper transmission, or with a variable pitch prop at either lift
or thrust or both, but these things also cost if they're to be done right.
bob windt has experimented with homemade variable pitch props, but they didn't really look safe to
me. too much to go wrong if they're made of wood like that. i don't have the tools or skills to
make one from metal, and that would be expensive anyway. the webers make theirs of foam, and if you
master that i guess you could make one variable pitch. i haven't heard of anyone else whose made
props of foam. plastics i don't know anything about.
Ken Roberts
> ya, i'm not sure you could get it to fly. hydraulics are very heavy and also not very efficient
> when used at high speeds. i think it may work if you have aircraft-quality pumps, but even there
> they don't use them for a major component of total power. they operate flaps and landing gear and
> stuff like that.
hate to reply to my own post, but just to set the record straight i'd like to see a good method to
drive both props from one engine too. i'm just playing devil's advocate because i want a realistic
view, not a fairy-tale one. for some of the members of this list, hovercrafts are fairy tales. to
me, it's a hole in the water into which i throw money. i'd like these solutions, but i'd like them
to be affordable.
John Holden
C. Bailey
oil cooler, and or large reservoir. Efficiency has never been a trademark
of hydrostatic systems.
Chris
John Holden wrote in message <37549D...@psych.usyd.edu.au>...
PetteriU
ignoreth...@worldnet.att.net wrote:
> John Holden wrote:
> >
> > For a medium sized hovercraft (4-8 people), I often wondered if a
> > totally hydraulic system was the way to go. The main motor runs a
> > variable displacement pump that matches demand, and the lift and
thrust
> > motors would be hydraulic. You would have independant control of
lift
> > and thrust.
> >
> > The thrust motor would be reversible with simple valving, twin
thrust
> > motors could be diffential so you could turn on the spot.
> >
> > In addition, you have a power source available for skirt lifters,
> > pumps, whatever ... The main motor only runs at a the speed required
> > to match the load.
> >
> > Not exactly in the sports league though.
>
and also not very efficient
> when used at high speeds. i think it may work if you have
aircraft-quality pumps, but even there
> they don't use them for a major component of total power. they
operate flaps and landing gear and
> stuff like that.
>
but the cost? even the heavy
> stuff is pretty expensive when you're talking about hydraulic motors.
>
> the next thing, when you start talking about the snappy response a
hydraulic motor has when
> reversing direction, you might suffer prop damage or something similar
someplace else. not to
> torque problems when you change the direction of a spinning prop like
that.
My contribution to this subject:
http://www.uq.net.au/~zzihayne/
(at the end of the page)
Sure it is probably expensive, but also flexible. I think is would be
much more easier to fit couple of hydraulic hoses than long belt with
"#n" pcs of pulleys inside a hovercraft.
And the weight, yeah, it probably is not suitable for small crafts !
--
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Matt Armstrong
good answer to it, so here goes: Why can't the power steering pump
be used on larger craft? (automobile engine powered of course) I know
that these pumps generate pretty good flow and pressures, would it be
enough to drive a hydraulic motor of sufficient power to lift the
craft? Just a thought, since many of the auto-engines which are looked
at for craft already have a nice pump system built right in. I am sure
they would have to be modified to run with a slightly different fluid
or something, but otherwise, would it work?
-Matt
Nickjokay
>drive both props from one engine
Here's another two prop one engine set up. A couple years ago Universal was
fooling around with snowmobile variable clutches to independently regulate the
lift and thrust fans/props.
Nick
C. Bailey
hydstrostatic drive have been low RPM applications.
Typically speed control is accomplished by valves i.e. the pump operates at
full capacity at all times and, you simply bypass oil from the hydraulic
motor to the low pressure line. Or in other words, a flow splitter from
high pressure to low pressure line.
If you aren't concerned about weight, you could also use a shaft drive and
pillow blocks to transfer power from back of hovercraft to front ......
Chris
PetteriU wrote in message <7j5eve$ako$1...@nnrp1.deja.com>...
Ken Roberts
> hydstrostatic drive have been low RPM applications.
me, too! tell me, though: are those hydraulic lines oversized? what i'm getting at is, the way i
understand it, the biggest problem with hydraulics is the friction inside the hoses and stuff. if
they use oversized line, maybe they cut back on some of that.
another thing that may shed light: they're claiming 30 knots on a 19-20' craft with 150hp.
universal hovercraft's uh-19p is supposed to go 80-90mph on 120 total hp. granted, the uh craft is
probably lighter, since it's not enclosed and hasn't got the polish. but how much of that 150hp is
going to the hydrostatic drive's inefficiencies?
> Typically speed control is accomplished by valves i.e. the pump operates at
> full capacity at all times and, you simply bypass oil from the hydraulic
> motor to the low pressure line. Or in other words, a flow splitter from
> high pressure to low pressure line.
i looked into this once, for a different application. there are certain types of hydrostatic
pumps/motors that have an adjustable displacement. picture a cylinder head that looks like a
revolver's (pistol) bullet clip. the tie rods are fixed to a flywheel that rotates at the same
speed as the cylinders but is at an adjustable angle so that the pistons move a certain amount.
if the drive is functioning as a pump, then having the pistons not move during a rotation is zero
flow, and having them move a lot is max flow. if it's functioning as a motor, the opposite is
true: max movement is slowest rpms, and minimum movement approaches infinite rpms. there would be
a limit, of course.
you could use one of these things as the pump, and maybe a conventional hydrostatic motor as a
motor. they're expensive, but maybe not much worse than a 20hp lift engine?
anyone know?
> If you aren't concerned about weight, you could also use a shaft drive and
> pillow blocks to transfer power from back of hovercraft to front ......
i thought about that too. what about a car or truck's drive line? the big hollow tubes? of
course, maybe you could make one yourself for the lower horsepower. thinner walls on the tubing,
smaller diameter, whatever. next, how do you adjust your speed?
the best thing i can think of would be something that totally ignores engine rpm and maintains lift
at whatever you set it at. think of a snowmobile transmission in reverse. only thing, you'd need
to be able to set the constant rpm to be whatever you want.
Snowbound
I have the same photo(s) of the hydraulic lift fan you posted. The craft in
question was called a "Mustang" on the website I found it on and was for
sale or lease in Australia. The company Starspray PTY that was selling the
craft does not manufacture the craft but had used the craft in the filming
of the new FLIPPER television series a few years back and I saw it
regularily on tv. I don't have the URL for the website anymore but I do have
the contact numbers for the company that had the website.
The single photo of the hydrostatic drive lift fan that was posted was the
only photo (and info) on the subject on the website.
I do have some specs. on the craft though....
Length 19'6" (5.99 metres)
Width 8' (2.4 metres)
153 hp fuel injected engine driving 2 ducted props.
Craft has dynamic pitch and roll control (???)
7 person capacity (600kg)
Speed 30 knots (smooth water)
Cruise 12-13 knots
I have 8 more photos of this craft that go with the set of 2 already posted
if anybody is interested....
I am in no way affiliated with this craft I was just curious when I found
it.
I hope you find this info useful.
Lance.
bniz...@my-deja.com
http://www.uq.net.au/~zzihayne/
does anyone know how much they wanted for the craft
Regards
Brian
In article <7krat5$2g...@enews4.newsguy.com>,
Andy Finkel
I've found that installing a electrically controlled variable air splitter on
my Scat II helped quite a bit. (I got the variable splitter from GPL
Enterprises in Florida). Installation was fairly straightforward, with some
fiberglass cutting, riveting, etc. to look forward to, and tolerance for error
in the plans is reasonable.
It makes a big difference in how well the craft can be controlled. I can
direct almost all the air to lift, for instance, which means I can go as slow
as I like down rapids. I can also cut down on lift to go faster :-) Or add
most lift to not be as bothered by some of the larger boat wakes.
It also eliminated most problems getting over the hump on water, even carrying
two people. All I have to do is put it to full lift, fill the cushions, then
let some air go to thrust ... and I'm over the hump.
Now if I could just figure out some way to make the Scat quieter :-)
Andy Finkel
Microsoft is a "scrappy" company in exactly the same sense that Godzilla is a 'scrappy' monster.