Re: [bolger] Re: box keel & CB
Aircraft designers consider that compressibility effects begin above 200
mph. Thicker skin is required. Below 200, air is just as incompressible as
water. Don't confuse compressibility with shock wave formation which begins
about 450 mph; e.g. P-51 losses due to control reversal.
All airfoils work by hurling the fluid away from them.
At higher speeds, symmetrical foils are generally used. There is so much
extra lift from the wings (which are sized for landing and take off) that
the small gain from asymmetry is unneeded. Modern fighters gain a great
deal of lift from strakes along the side of the fuselage, sort of a return
to the full keel vs. fin keel?
About 40 years ago I read a small book by an aeronautical engineer stationed
at Muroc. In the Spring the salt flats would flood to a depth of a few
inches and the other guys would amuse themselves building and racing
propeller driven model boats. He was a sailor and so he devised a hydrofoil
craft with rigid foils which were fixed so the boat was always on the
starboard tack. The "sail" was also a rigid foil. He devoted a great deal
of space to the calculations which allowed him to balance the opposing
thrust and lift. Not a light read.
Roger
derbyrm@...
http://derbyrm.mystarband.net/default.htm
mph. Thicker skin is required. Below 200, air is just as incompressible as
water. Don't confuse compressibility with shock wave formation which begins
about 450 mph; e.g. P-51 losses due to control reversal.
All airfoils work by hurling the fluid away from them.
At higher speeds, symmetrical foils are generally used. There is so much
extra lift from the wings (which are sized for landing and take off) that
the small gain from asymmetry is unneeded. Modern fighters gain a great
deal of lift from strakes along the side of the fuselage, sort of a return
to the full keel vs. fin keel?
About 40 years ago I read a small book by an aeronautical engineer stationed
at Muroc. In the Spring the salt flats would flood to a depth of a few
inches and the other guys would amuse themselves building and racing
propeller driven model boats. He was a sailor and so he devised a hydrofoil
craft with rigid foils which were fixed so the boat was always on the
starboard tack. The "sail" was also a rigid foil. He devoted a great deal
of space to the calculations which allowed him to balance the opposing
thrust and lift. Not a light read.
Roger
derbyrm@...
http://derbyrm.mystarband.net/default.htm
----- Original Message -----
From: "Howard Stephenson" <stephensonhw@...>
> While it's true that air can be compressed and water cannot (or very
> little), an aerofoil at supersonic speed does not create lift by
> compressing the air. This night be counter-intuitive, but it's
> generally accepted scientifically. Only when it is moving at or very
> near supersonic speed will a wing, and other parts of the aircraft,
> start to compress air. One result is the familiar sonic boom, caused
> by the air being forced to move so fast that it is compressed. There
> is no sonic boom at slower speeds. (By the way, the speed of sound in
> water is extremely high).
>
> More at:
>
>http://www.aeromuseum.org/Education/Lessons/HowPlaneFly/HowPlaneFly.ht
> ml
>
> Athttp://www.turnertoys.com/G1/aeroScience/default.htmyou will see
> a debate about what actually causes the lift -- but there is no
> suggestion it is cause by the air being compressed. They are just two
> ways of looking at the same phenomenon, either as an application of
> Newtonian physics or of Bernoulli's theorem.
>
> The forces generated when water flows over a fin or c/b or whatever
> are generated in the same way as the forces generated when air flows
> over a subsonic wing.
>
> Howard
>
> --- Inbolger@yahoogroups.com, "Nels" <arvent@h...> wrote:
>
> > The differences are first, that the speed of movement is no way
> near the same and secondly, air compresses but water doesn't.
>
>
>
>
>
> Bolger rules!!!
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While it's true that air can be compressed and water cannot (or very
little), an aerofoil at supersonic speed does not create lift by
compressing the air. This night be counter-intuitive, but it's
generally accepted scientifically. Only when it is moving at or very
near supersonic speed will a wing, and other parts of the aircraft,
start to compress air. One result is the familiar sonic boom, caused
by the air being forced to move so fast that it is compressed. There
is no sonic boom at slower speeds. (By the way, the speed of sound in
water is extremely high).
More at:
http://www.aeromuseum.org/Education/Lessons/HowPlaneFly/HowPlaneFly.ht
ml
Athttp://www.turnertoys.com/G1/aeroScience/default.htmyou will see
a debate about what actually causes the lift -- but there is no
suggestion it is cause by the air being compressed. They are just two
ways of looking at the same phenomenon, either as an application of
Newtonian physics or of Bernoulli's theorem.
The forces generated when water flows over a fin or c/b or whatever
are generated in the same way as the forces generated when air flows
over a subsonic wing.
Howard
little), an aerofoil at supersonic speed does not create lift by
compressing the air. This night be counter-intuitive, but it's
generally accepted scientifically. Only when it is moving at or very
near supersonic speed will a wing, and other parts of the aircraft,
start to compress air. One result is the familiar sonic boom, caused
by the air being forced to move so fast that it is compressed. There
is no sonic boom at slower speeds. (By the way, the speed of sound in
water is extremely high).
More at:
http://www.aeromuseum.org/Education/Lessons/HowPlaneFly/HowPlaneFly.ht
ml
Athttp://www.turnertoys.com/G1/aeroScience/default.htmyou will see
a debate about what actually causes the lift -- but there is no
suggestion it is cause by the air being compressed. They are just two
ways of looking at the same phenomenon, either as an application of
Newtonian physics or of Bernoulli's theorem.
The forces generated when water flows over a fin or c/b or whatever
are generated in the same way as the forces generated when air flows
over a subsonic wing.
Howard
--- Inbolger@yahoogroups.com, "Nels" <arvent@h...> wrote:
> The differences are first, that the speed of movement is no way
near the same and secondly, air compresses but water doesn't.
--- Inbolger@yahoogroups.com, Mark <marka@h...> wrote:
first, that the speed of movement is no way near the same and
secondly, air compresses but water doesn't.
Therefore the lift may be created by the fact the water flowing over
the top does not encounter as much resistance. With an airplane wing
there is a vacuum that forms over the top of the wing creating lift.
With a wing keel there is less resistance on the flat upper surface
creating lift.
Angle of attack can also create lift, but you need forward speed in
order to do that. If the angle gets to high the vacuum becomes too
disturbed and the wing stalls. In the water it also stalls as eddies
create too much drag. Therefore flaps and rudders must stay inside a
certain range of motion to be effective, especially at the low speeds
of a sailboat.
But I don't really know this from a scientific point of view - only
from observation.
Nels
> > The Bolger swing wing has a completely flat top and a curvedboat down into the water,
> > underside. This would create lift in my view, and therefore less
> > wetted surface on the hull as the boat accelerates.
>
> If that wing worked on aircraft principles wouldn't it pull the
> since an airplane wing is curved on top?That is why I don't think you can compare them. The differences are
> Mark
first, that the speed of movement is no way near the same and
secondly, air compresses but water doesn't.
Therefore the lift may be created by the fact the water flowing over
the top does not encounter as much resistance. With an airplane wing
there is a vacuum that forms over the top of the wing creating lift.
With a wing keel there is less resistance on the flat upper surface
creating lift.
Angle of attack can also create lift, but you need forward speed in
order to do that. If the angle gets to high the vacuum becomes too
disturbed and the wing stalls. In the water it also stalls as eddies
create too much drag. Therefore flaps and rudders must stay inside a
certain range of motion to be effective, especially at the low speeds
of a sailboat.
But I don't really know this from a scientific point of view - only
from observation.
Nels
> The Bolger swing wing has a completely flat top and a curvedIf that wing worked on aircraft principles wouldn't it pull the boat down into the water,
> underside. This would create lift in my view, and therefore less
> wetted surface on the hull as the boat accelerates.
since an airplane wing is curved on top?
Mark