Re: More Quotes
--- Inbolger@yahoogroups.com, "Howard Stephenson"
<stephensonhw@a...> wrote:
All of these are
a lot of lift....Whooooops!!!!!
All seriousness aside,I enjoy your informative posts Howard and look
forward to reading more,even it is not directly related to Bolger
boats(or maybe it is?)
Peter Lenihan
<stephensonhw@a...> wrote:
All of these are
> applications of the same principle that produces lift in fins,Reminds me of a girlfriend I once had who was always able to produce
> leeboards etc.
a lot of lift....Whooooops!!!!!
All seriousness aside,I enjoy your informative posts Howard and look
forward to reading more,even it is not directly related to Bolger
boats(or maybe it is?)
Peter Lenihan
see below where I argue with the great man again
go. You might use 1 or 2 hp to go 50mph! The boat he is talking about
has a full keel. Very low aspect ratio and probably not a good place for
a real foil. Planar lifting surfaces tend to have a lot in common if of
medium to high aspect ratio, but this one is very low, and for low
aspect ratio, things get weird. The above quote has always irked me a
bit, I must confess. But it looks to me like the boat is designed
reasonably for what it is.
thing. Airliners use their wings so much that they glide at something
like 15 or 18:1. Some years ago a 767 even made a dead stick landing!
Airplane designers go to a GREAT deal of trouble to REDUCE the power
required to go whatever speed it is they go. Except maybe for
ultralights, but that's another story.
glider pilot is probably to disconnect the ailerons (control surfaces on
wings). I've flown model gliders, and the ones most like real ones NEED
those ailerons. Lift in the way we mean it is a force perpendicular to
the flow. Don't get hung up on gravity. The air and the water are 100%
buoyed up, and don't know about gravity. But they do know to push on a
surface with a foil at an angle of attack moving through them. Sailplane
wings are to catch the air and slow the descent the way a trumpet is to
catch a rasberry. Don't get hung up on "partial vacuum". At our speeds,
air might as well be incompressible. If you integrate the pressures
around any object in the water, you will get the net force from the
water, except for a bit of viscous drag. (Note that I am not talking
about drag from separated flow and the like, which will be much more.)
The pressure will be a little lower on the side the object is being
pushed toward by the water. That's your "partial vacuum", and it's
pretty small.
don't want to adopt the usual definition, use another language. What you
are suggesting is basically a stalled surface and will create a lot more
drag if you have to move forward. I should probably give up soon, I suppose.
>Nels wrote:Sailplane power input is close to nil, too, considering how fast they
>
>"A sailboat keel is often thought of as analogous to an aircraft's
>wing, but there's a significant difference. All aircraft are powered
>(Gliders by gravity), whereas a sailboat has to operate efficientely
>with power input close to nil. It's possible that the flat keel
>forced on this design by the structural material (plywood) is not bad
>for her performance. BWAOM Page 140."
>
go. You might use 1 or 2 hp to go 50mph! The boat he is talking about
has a full keel. Very low aspect ratio and probably not a good place for
a real foil. Planar lifting surfaces tend to have a lot in common if of
medium to high aspect ratio, but this one is very low, and for low
aspect ratio, things get weird. The above quote has always irked me a
bit, I must confess. But it looks to me like the boat is designed
reasonably for what it is.
>snipYah, but we were talking about slow airplanes. And slow is a relative
>
>It seems that almost anything will "fly" if enough power is applied
>to propel it fast enough. At some point the foils main function is to
>control the linear movement. Fast airplanes become guided missiles at
>some point, as are fast powerboats and cars.
>
thing. Airliners use their wings so much that they glide at something
like 15 or 18:1. Some years ago a 767 even made a dead stick landing!
Airplane designers go to a GREAT deal of trouble to REDUCE the power
required to go whatever speed it is they go. Except maybe for
ultralights, but that's another story.
>Not sure why you care how it's controlled, but a good way to kill a
>A glider gets it's "lift" from rising air currents but is always
>falling earthward by the force of gravity which is converted to
>forward motion by tilting the nose down. It is controlled by the
>elevators and rudders, not the wings at all which are mostly surfaces
>to catch the air and slow the descent. Any wing lift is created by a
>partial vacuum above the wings surface, same as with a sail on a boat.
>
glider pilot is probably to disconnect the ailerons (control surfaces on
wings). I've flown model gliders, and the ones most like real ones NEED
those ailerons. Lift in the way we mean it is a force perpendicular to
the flow. Don't get hung up on gravity. The air and the water are 100%
buoyed up, and don't know about gravity. But they do know to push on a
surface with a foil at an angle of attack moving through them. Sailplane
wings are to catch the air and slow the descent the way a trumpet is to
catch a rasberry. Don't get hung up on "partial vacuum". At our speeds,
air might as well be incompressible. If you integrate the pressures
around any object in the water, you will get the net force from the
water, except for a bit of viscous drag. (Note that I am not talking
about drag from separated flow and the like, which will be much more.)
The pressure will be a little lower on the side the object is being
pushed toward by the water. That's your "partial vacuum", and it's
pretty small.
>False distinction. Lift is lift. Force perpendicular to the flow. If you
>Not sure how any of it applies directly to sailboat keels. A slab
>keel like MICRO prevents leeway mostly through resistance, which is
>considerable. Try holding a board perpendicular to a water flow. I
>just don't see where any so-called "lift" is involved, particularly
>at the slow speed of a MICRO.
>
don't want to adopt the usual definition, use another language. What you
are suggesting is basically a stalled surface and will create a lot more
drag if you have to move forward. I should probably give up soon, I suppose.
--- Inbolger@yahoogroups.com, "Howard Stephenson"
<stephensonhw@a...> wrote:
their lift by rotating aerofoils. Propellors for aircraft and boats
generate the thrust neede to move them forward by using engine power
to move carefully shaped foils through a fluid. All of these are
applications of the same principle that produces lift in fins,
leeboards etc.
Howard
<stephensonhw@a...> wrote:
>That's true enough, but only the most powerful military aircraftI forgot about helicopters and some vtol aircraft. Helicopters get
>have engines that can produce more thrust than the weight of the
>aircraft.
their lift by rotating aerofoils. Propellors for aircraft and boats
generate the thrust neede to move them forward by using engine power
to move carefully shaped foils through a fluid. All of these are
applications of the same principle that produces lift in fins,
leeboards etc.
Howard
--- Inbolger@yahoogroups.com, "Nels" <arvent@h...> wrote:
at some point, as are fast powerboats and cars.
That's true enough, but only the most powerful military aircraft have
engines that can produce more thrust than the weight of the aircraft.
These can fly vertically upwards at a constant speed, or even
accelerate. If you compare the total static engine thrust of any
commercial jetliner you will find it is a lot less than the total
weight of the aircraft. (You can find this info. very easily from
thousands of sources on the www). They are able to fly because their
wings provide lift.
manner. Sorry you can't be convinced, Nels.
Howard
> It seems that almost anything will "fly" if enough power is appliedto control the linear movement. Fast airplanes become guided missiles
> to propel it fast enough. At some point the foils main function is
at some point, as are fast powerboats and cars.
That's true enough, but only the most powerful military aircraft have
engines that can produce more thrust than the weight of the aircraft.
These can fly vertically upwards at a constant speed, or even
accelerate. If you compare the total static engine thrust of any
commercial jetliner you will find it is a lot less than the total
weight of the aircraft. (You can find this info. very easily from
thousands of sources on the www). They are able to fly because their
wings provide lift.
> However I realize that most sailors believe this to be the case... as do all those who have studied the subject in a scientific
> Cheers, Nels
manner. Sorry you can't be convinced, Nels.
Howard
"A sailboat keel is often thought of as analogous to an aircraft's
wing, but there's a significant difference. All aircraft are powered
(Gliders by gravity), whereas a sailboat has to operate efficientely
with power input close to nil. It's possible that the flat keel
forced on this design by the structural material (plywood) is not bad
for her performance. BWAOM Page 140."
"The bottom is dead flat over the keel, the most powerful shape to
carry sail on any given displacement. The shallower the body, the
less overall draft is needed to make the lateral plane available.
It's been established in recent years that sharp deadrise is not a
good idea if you don't need to stow inside ballest." BWAOM Page 147.
"It's my opinion that vertical sides make the fastest boat." Page 150
*****************************
I don't really follow how the model airplane and aerobatic airplane
performance relates to sailboats.
It seems that almost anything will "fly" if enough power is applied
to propel it fast enough. At some point the foils main function is to
control the linear movement. Fast airplanes become guided missiles at
some point, as are fast powerboats and cars.
A glider gets it's "lift" from rising air currents but is always
falling earthward by the force of gravity which is converted to
forward motion by tilting the nose down. It is controlled by the
elevators and rudders, not the wings at all which are mostly surfaces
to catch the air and slow the descent. Any wing lift is created by a
partial vacuum above the wings surface, same as with a sail on a boat.
Not sure how any of it applies directly to sailboat keels. A slab
keel like MICRO prevents leeway mostly through resistance, which is
considerable. Try holding a board perpendicular to a water flow. I
just don't see where any so-called "lift" is involved, particularly
at the slow speed of a MICRO.
However I realize that most sailers believe this to be the case and
it seems to work for them:-)
Cheers, Nels
wing, but there's a significant difference. All aircraft are powered
(Gliders by gravity), whereas a sailboat has to operate efficientely
with power input close to nil. It's possible that the flat keel
forced on this design by the structural material (plywood) is not bad
for her performance. BWAOM Page 140."
"The bottom is dead flat over the keel, the most powerful shape to
carry sail on any given displacement. The shallower the body, the
less overall draft is needed to make the lateral plane available.
It's been established in recent years that sharp deadrise is not a
good idea if you don't need to stow inside ballest." BWAOM Page 147.
"It's my opinion that vertical sides make the fastest boat." Page 150
*****************************
I don't really follow how the model airplane and aerobatic airplane
performance relates to sailboats.
It seems that almost anything will "fly" if enough power is applied
to propel it fast enough. At some point the foils main function is to
control the linear movement. Fast airplanes become guided missiles at
some point, as are fast powerboats and cars.
A glider gets it's "lift" from rising air currents but is always
falling earthward by the force of gravity which is converted to
forward motion by tilting the nose down. It is controlled by the
elevators and rudders, not the wings at all which are mostly surfaces
to catch the air and slow the descent. Any wing lift is created by a
partial vacuum above the wings surface, same as with a sail on a boat.
Not sure how any of it applies directly to sailboat keels. A slab
keel like MICRO prevents leeway mostly through resistance, which is
considerable. Try holding a board perpendicular to a water flow. I
just don't see where any so-called "lift" is involved, particularly
at the slow speed of a MICRO.
However I realize that most sailers believe this to be the case and
it seems to work for them:-)
Cheers, Nels