Submarine question
Joseph M. Dusio
I have a question regarding the physics of submarine propulsion.
Simply stated: Why don't they spin?
I think that this question only applies to single prop subs.
If you consider the purpose of the tail rotor on a helicopter is to
counteract the main blade's reaction on the body of the aircraft,
why then don't submarines spin along their long axis in the
reverse direction that their screw turns?
This question is not intended to spark a one-upmanship contest
or to test anyone's knowledge, I don't know and am just curious.
I'm guessing that it has something to do with
1) Weight at the bottom of the subs, and air in the top.
2) If the screw is turning slowly enough, its effect may be
negligible in comparison to the heft of the hull.
3) The fairwater, planes and the occasional ring around the screw
provide resistance.
Thanks in advance
Joe Dusio
Jack Holt
Number 2 is the primary answer. The screw simply doesn't have the
torque needed to spin the sub. The other factor is the bulk of the sub
itself. The water will not put up enough resistance to allow the screw
to rotate the sub.
Jack
Scott D. Orr
wrote:
>Gentlemen,
>
>I have a question regarding the physics of submarine propulsion.
>
>Simply stated: Why don't they spin?
>
As Jack Holt noted, the size of the propellor is so small compared to
the size of the sub that there's just not much torque involved
relative to the size of the sub.
Think about it: the rotor on a helicopter is huge (compared to the
helicopter), and it's prvoding enough upward thrust to overcome the
force of gravity--what a sub propellor is providing isn't anywhere
near 1G.
It's interesting to note though that a few propellor-driven planes had
torque problems. For example, one the fighters from WWI (the Sopwith
Camel I think?) had a nasty tendency to pull to the left--though this
was actually useful in combat, since it made the plane more
maneuverable (though only in one direction :).
Subs can have stability problems, though--for example, I'm told that
the USN tried making one without a sail, since the sail wasn't really
used for all that much. The result was that the boat rocked badly
from side to side, subject to whatever rogue currents happened along.
Scott Orr
Pappy Owen
wrote:
>On Mon, 24 May 1999 11:22:20 -0500, "Joseph M. Dusio" <du...@inav.net>
>wrote:
>
Quick sea story: We were testing main steam valves on one of the
640-class boomers while it was tied up beside the pier. Some
dickweed, however, tweaked the preliminary calibration without logging
it or telling anybody. As a result when we cracked open the throttles
for the first time, the valves slammed wide slam open! Reactor power
skyrocketed until the automatics caught it. There was a lot of
excitement, however, because the torque from the screw and reduction
gear tried to roll the boat away from the pier. A couple of lines
actually parted! A fun time was had by all, especially the nub who
was standing topside watch at the time!
Bottom line, you can develop screw torque but it's highly unusual. It
ranks up there with putting on reverse knots during a submerged
crashback. Not a good way to extend your career.
Greg Locock
>
> On Mon, 24 May 1999 11:22:20 -0500, "Joseph M. Dusio" <du...@inav.net>
> wrote:
>
> >
> >I have a question regarding the physics of submarine propulsion.
> >
> >Simply stated: Why don't they spin?
> >
> the size of the sub that there's just not much torque involved
> relative to the size of the sub.
OK
>
> Think about it: the rotor on a helicopter is huge (compared to the
> helicopter), and it's prvoding enough upward thrust to overcome the
> force of gravity--what a sub propellor is providing isn't anywhere
> near 1G.
And what do you think the tail rotor on a heli is for? Ventilation?
Cheers
Greg Locock
Scott D. Orr
Okay, you lost me. I think you misread what I wrote above, which was
contrasting a sub (which doesn't need a second rotor) with a
helicopter (which does).
Scott Orr
Kasey Chang
Guys, guys, the problem here is one of MOMENTUM.
While a chopper blade is thin, it spins a high RPMs. Net momentum is
significant enough to spin the chopper, which being an air vhicle must
be "relatively" light.
Subs, on the other hand are meansured in tons, the screw is MUCH smaller
and spins MUCH MORE slowly.
--
Kuo-Sheng "Kasey" Chang / spam-hater / Paradox guru / X-Com Guru
Sci-Fi Fan / Treknologist / Military buff / a guy (yes, male!)
--== Sent via Deja.com http://www.deja.com/ ==--
---Share what you know. Learn what you don't.---
Greg Locock
>
>
> Okay, you lost me. I think you misread what I wrote above, which was
> contrasting a sub (which doesn't need a second rotor) with a
> helicopter (which does).
>
Yes, I misread what you wrote. Sorry about that.
Cheers
Greg Locock
basilisk
Flank, Cavitate, will heel over a good 15 degrees from the torque, but
will settle out again. 1,888,000 ft/lbs can move a lot of weight. My
first boat, a 637 class, couldn't do that, but had the disconcerting
tendency for the stern to shake and make small circles in the water when
answering a flank bell.
Pappy Owen wrote:
>
> On Tue, 25 May 1999 00:53:33 GMT, sd...@ix.netcom.com (Scott D. Orr)
> wrote:
>
> >On Mon, 24 May 1999 11:22:20 -0500, "Joseph M. Dusio" <du...@inav.net>
> >wrote:
> >
>
> Quick sea story: We were testing main steam valves on one of the
> 640-class boomers while it was tied up beside the pier. Some
> dickweed, however, tweaked the preliminary calibration without logging
> it or telling anybody. As a result when we cracked open the throttles
> for the first time, the valves slammed wide slam open! Reactor power
> skyrocketed until the automatics caught it. There was a lot of
> excitement, however, because the torque from the screw and reduction
> gear tried to roll the boat away from the pier. A couple of lines
> actually parted! A fun time was had by all, especially the nub who
> was standing topside watch at the time!
>
> Bottom line, you can develop screw torque but it's highly unusual. It
> ranks up there with putting on reverse knots during a submerged
> crashback. Not a good way to extend your career.
>
> >As Jack Holt noted, the size of the propellor is so small compared to
> >the size of the sub that there's just not much torque involved
> >relative to the size of the sub.
> >
> >Think about it: the rotor on a helicopter is huge (compared to the
> >helicopter), and it's prvoding enough upward thrust to overcome the
> >force of gravity--what a sub propellor is providing isn't anywhere
> >near 1G.
> >
Scott D. Orr
wrote:
>Guys, guys, the problem here is one of MOMENTUM.
>
Actually, it has little to do with momentum--it's a matter of torque
(which produces thrust, and thrust produces momentum).
>While a chopper blade is thin, it spins a high RPMs. Net momentum is
>significant enough to spin the chopper, which being an air vhicle must
>be "relatively" light.
>
>Subs, on the other hand are meansured in tons, the screw is MUCH smaller
>and spins MUCH MORE slowly.
>
The key difference is that the torque on a helicopter, relative to its
mass, is much higher than the torque on a submarine--it has to be,
because the helicopter needs a LOT more acceleration just to stay
airborne.
The higher rotational speed is a byproduct of this, but you could get
the same torque, in theory,either by having a large rotor or by
running it at high speed.
Scott Orr
Graeme McTait
here - so forgive me If i've got the wrong end of the stick.
Don;t forget that the rotor blades of a chopper rotate through air ( a very
low viscosity fluid) and the sub's blades move through water ( very
viscous). If the subs screw was rotated in the air instead of water the
torque required to turn it at the same speed would be much LESS than when it
is imersed in the water.
But the two are different. The helo rotor is very light ( carbon fibre. thin
blades and all that) so is does not require much torque to turn it. A subs
screw is actually quite LARGE. And made of bronze alloy and weighs a hell of
lot more than a helo blades. So it is going to take more effort to turn it.
I haven't got enough info to calculate them, but I would imagine that there
is much MORE torque needed toturn a sub screw than a helo blade. Other wise
why have a huge nuclear reactor on a sub if the small engine on helo
generates more torque!!!!
The down force generated by the helo has only got to at least balance the
weight of the helo to stay aloft. ( maybe 10 tons). The screw on the sub has
to push several thousand tons of submarine through thick gloopy water and
quite a few knots).
The helo screw has to turn fast as it operates differently to that of the
sub screw. The sub pushes water behind it, whereas the helo is a rotating
wing, that generates lift due to the air flow over the aerofoil shaped
blades ( and so has to rotate fast to generate lift.
Also the subs screw is not meant to turn too fast - that produces cavitation
and makes the sub VERY noisy.
So the problem here is that the two vehicles travel in different
environmonts with very different fluid mechanicla properties. One vehicle is
very light, the other very heavy. One uses a propeller, one uses a rotating
wing.
Also a note on torque.
Torque is force x distance from pivot
you use more torque undoing a rusty nut from a bolt. To make life easier for
yourself you use a long handle spanner to apply less force but with a longer
distance - so the same torque as a lot of force applied with a short
handles spanner.
Torque relates to how difficult it is to turn something ( rusty nut needs
more torque than a well oiled one).
But I agree more rotational speed to the propeller/screw = more thrust
And that ends todays essay.
Scott D. Orr wrote in message <37589771...@enews.newsguy.com>...
Scott D. Orr
wrote:
>This thread was missing a lot of stuff, so I'm jumping into mid conversation
>here - so forgive me If i've got the wrong end of the stick.
>
>Don;t forget that the rotor blades of a chopper rotate through air ( a very
>low viscosity fluid) and the sub's blades move through water ( very
>viscous). If the subs screw was rotated in the air instead of water the
>torque required to turn it at the same speed would be much LESS than when it
>is imersed in the water.
The speed the rotor is turning out isn't _directly_ relevant to the
question--it's the torque, which is directly proportional to the
thrust or lift you get from the propellor (you just get more of it at
a given speed from water that you do from air, and you get more drag
as well, which is the equivalent of "friction" from the water).
>But the two are different. The helo rotor is very light ( carbon fibre. thin
>blades and all that) so is does not require much torque to turn it. A subs
>screw is actually quite LARGE. And made of bronze alloy and weighs a hell of
>lot more than a helo blades. So it is going to take more effort to turn it.
>I haven't got enough info to calculate them, but I would imagine that there
>is much MORE torque needed toturn a sub screw than a helo blade. Other wise
>why have a huge nuclear reactor on a sub if the small engine on helo
>generates more torque!!!!
>
The specific materials each is made of really aren't relevant for what
we're talking about: no matter what either is made of, the torque is
going to be directly proportional to the thrust provided. Period.
It may well be the case that the screw of a submarine produces more
torque than the main rotor of a helicopter--however, the submarine is
also much bigger than the helicopter. The important thing is that the
ratio of torque to the mass of the vehicle is going to be much, _much_
higher for the helicopter--because a helicopter needs more thrust
(just to keep itself airborne) than a sub does. The reason we're
concerned about a ratio, not the absolute amount of torque, is that a
given amount of torque will have a much greater impact when applied to
spinning a tiny helicopter around than when applied to spnning a huge
sub around.
>The down force generated by the helo has only got to at least balance the
>weight of the helo to stay aloft. ( maybe 10 tons). The screw on the sub has
>to push several thousand tons of submarine through thick gloopy water and
>quite a few knots).
>
The thrust needed to keep a helicopter up is equal to the thrust
needed to accelerate an object the mass of the helicopter by _1g_.
That is a LOT of acceleration, much, MUCH more than a sub is capable
of. We can conclude, therefore, that the helicopter rotor has a
greater ratio of torque to vehicle mass.
[Snip.]
Scott Orr
Graeme McTait
Would make a good exam question me thinks
adios
Grae
>[Snip.]
>
>Scott Orr
Pappy Owen
<basi...@magiccarpet.com> wrote:
That sounds about right. I never worked the last 688 flights, but my
initial quals were on the early S6G boats. That MS valve incident on
the MARSHALL, though, will last me for a lifetime.....
One of the Arthurs
correcting...
"Scott D. Orr" wrote:
>
[snip]
>
> The speed the rotor is turning out isn't _directly_ relevant to the
> question--it's the torque, which is directly proportional to the
> thrust or lift you get from the propellor (you just get more of it at
> a given speed from water that you do from air, and you get more drag
> as well, which is the equivalent of "friction" from the water).
Not exactly true. The amount of torque required is directly
proportional to the drag of the propellor, not the thrust/lift. A
more efficient propellor (higher lift-to-drag ratio) requires less
torque to produce the same thrust at a given speed.
[snip]
> It may well be the case that the screw of a submarine produces more
> torque than the main rotor of a helicopter--however, the submarine is
> also much bigger than the helicopter. The important thing is that the
> ratio of torque to the mass of the vehicle is going to be much, _much_
> higher for the helicopter--because a helicopter needs more thrust
> (just to keep itself airborne) than a sub does.
That is not obvious at all. A helicoptor only needs a few thousand
pounds of thrust to hover [the weight of the copter]. I suspect a sub
needs far more than that to push through the water at up to 50 knots.
No question that the thrust-to-mass ratio of a helicopter would be
much higher, however. That still does not necessarily imply the
torque to mass ratio is as high.
> The reason we're
> concerned about a ratio, not the absolute amount of torque, is that a
> given amount of torque will have a much greater impact when applied to
> spinning a tiny helicopter around than when applied to spnning a huge
> sub around.
It will have a much faster impact on a helicopter, but in both cases
the result would be the same... If the torque is not counteracted the
vehicle body will spin in the opposite direction to the propeller.
The copter has a small counter-torque prop on the tail. The sub has
fins, a sail, and a tail to accomplish the same purpose.
[snip]
> The thrust needed to keep a helicopter up is equal to the thrust
> needed to accelerate an object the mass of the helicopter by _1g_.
> That is a LOT of acceleration, much, MUCH more than a sub is capable
> of. We can conclude, therefore, that the helicopter rotor has a
> greater ratio of torque to vehicle mass.
It is a matter of force, not acceleration. F=m*a
The force from the prop keeps the copter in equilibrium. When the
copter is sitting on the ground, the same reaction force supplied by
the feet on the ground keeps the copter in equilibrium. I am sure
that a modern sub power plant puts out far more thrust force than the
average helicopter would need. Your final sentence is true, but it
doesn't follow logically (We can conclude, therefore...) from your
previous statements.
Frank
JD
<mar...@iu.net> held forth on "Re: Submarine question"
>Not exactly true. The amount of torque required is directly
>proportional to the drag of the propellor, not the thrust/lift. A
>more efficient propellor (higher lift-to-drag ratio) requires less
>torque to produce the same thrust at a given speed.
And what would we make of the fact that induced drag is
proportional to the square of lift?
There's just no way to escape drag once you start creating
lift/thrust. The best you can hope for with efficient foil designs
is to reduce parasitic drag and/or optimize for a particular
condition.
>That is not obvious at all. A helicoptor only needs a few thousand
>pounds of thrust to hover [the weight of the copter]. I suspect a sub
>needs far more than that to push through the water at up to 50 knots.
He's talking about a thrust to weight ratio.
>No question that the thrust-to-mass ratio of a helicopter would be
>much higher, however. That still does not necessarily imply the
>torque to mass ratio is as high.
Sure it does. <g>
Regards, JD
jdk...@earthlink.net
sa...@raycer.com
The reason for a sub not spin in the opposite direction of the
propellers is the same one for it not capsizing ie. it centre of mass
is lower than its 'hydrodynamic centre' (terminiology). The torque
generated by the propellers is not sufficient to overcome the
restoring force inherent in submarines designed with sufficient
stability. I think the fins and sails also help.
Sam
In article <375AB961...@iu.net>,
mar...@iu.net wrote:
> Sorry to jump in at this late date, but a few things still need
> correcting...
>
> "Scott D. Orr" wrote:
> >
> [snip]
> >
> > The speed the rotor is turning out isn't _directly_ relevant to the
> > question--it's the torque, which is directly proportional to the
> > thrust or lift you get from the propellor (you just get more of it
at
> > a given speed from water that you do from air, and you get more drag
> > as well, which is the equivalent of "friction" from the water).
>
> Not exactly true. The amount of torque required is directly
> proportional to the drag of the propellor, not the thrust/lift. A
> more efficient propellor (higher lift-to-drag ratio) requires less
> torque to produce the same thrust at a given speed.
>
> [snip]
>
> > It may well be the case that the screw of a submarine produces more
> > torque than the main rotor of a helicopter--however, the submarine
is
> > also much bigger than the helicopter. The important thing is that
the
> > ratio of torque to the mass of the vehicle is going to be much,
_much_
> > higher for the helicopter--because a helicopter needs more thrust
> > (just to keep itself airborne) than a sub does.
>
> That is not obvious at all. A helicoptor only needs a few thousand
> pounds of thrust to hover [the weight of the copter]. I suspect a sub
> needs far more than that to push through the water at up to 50 knots.
> No question that the thrust-to-mass ratio of a helicopter would be
> much higher, however. That still does not necessarily imply the
> torque to mass ratio is as high.
>
Sent via Deja.com http://www.deja.com/
Scott D. Orr
>
>Sorry to jump in at this late date, but a few things still need
>correcting...
Well no, you expanded on a couple of points, but you didn't correct
any actual errors on my part. I certainly don't mind the additional
comments, but it does irk me that you present yourself as "correcting"
me when what you say is in perfect agreement with very things I was
saying.
>"Scott D. Orr" wrote:
>>
>[snip]
>>
>> The speed the rotor is turning out isn't _directly_ relevant to the
>> question--it's the torque, which is directly proportional to the
>> thrust or lift you get from the propellor (you just get more of it at
>> a given speed from water that you do from air, and you get more drag
>> as well, which is the equivalent of "friction" from the water).
>
>Not exactly true. The amount of torque required is directly
>proportional to the drag of the propellor, not the thrust/lift. A
>more efficient propellor (higher lift-to-drag ratio) requires less
>torque to produce the same thrust at a given speed.
>
Yes, this is true, but since drag is directly proportional to
lift/thrust, it is--exactly--true that the torque is directly
proportional to lift/thrust. But you're right that different
propellors will have different ratios. I just didn't really feel the
need to get that deeply into things....
>> It may well be the case that the screw of a submarine produces more
>> torque than the main rotor of a helicopter--however, the submarine is
>> also much bigger than the helicopter. The important thing is that the
>> ratio of torque to the mass of the vehicle is going to be much, _much_
^^^^
>> higher for the helicopter--because a helicopter needs more thrust
>> (just to keep itself airborne) than a sub does.
>
>That is not obvious at all
Yes, it's quite obvious--if nothing else, the fact that the helicopter
requires a tail-rotor confirms this hunch.
>A helicoptor only needs a few thousand
>pounds of thrust to hover [the weight of the copter]. I suspect a sub
>needs far more than that to push through the water at up to 50 knots.
>No question that the thrust-to-mass ratio of a helicopter would be
>much higher, however. That still does not necessarily imply the
>torque to mass ratio is as high.
I was talking about the ratios, not the absolute numbers, as I said
quite clearly in the text you quoted above and in the text you quoted
below. And yes, I think it does imply that the torque to mass ratio
for the helicopter is much, much higher--there just can't be THAT much
difference in the efficiencies of the propellors.
>> The reason we're
>> concerned about a ratio, not the absolute amount of torque, is that a
>> given amount of torque will have a much greater impact when applied to
>> spinning a tiny helicopter around than when applied to spnning a huge
>> sub around.
>
>It will have a much faster impact on a helicopter, but in both cases
>the result would be the same... If the torque is not counteracted the
>vehicle body will spin in the opposite direction to the propeller.
>The copter has a small counter-torque prop on the tail. The sub has
>fins, a sail, and a tail to accomplish the same purpose.
The force required to counteract the torque is much less in the case
of the sub (which is, in fact, what I was saying). In fact, I'm not
sure that the sub's planes are even required for this (and you need
the planes for other things, anyway): as with a surface ship, the
shape of the boat by itself probably provides enough resistance to
overcome the torque.
As I mentioned much earlier in the thread, I'm given to understand
that the USN tested a sub without a sail once (but with planes, of
course)--the big problem, as I understand it, was not the the torque
from the propellor that caused a problem with stability, but rather
forces in the water itself (waves and such).
In any case, the reason a sub doesn't require a counter-rotor is
because the torque involved is so much less--the sub is more analogous
to a prop-driven airplane, which also doesn't require a counter-rotor
to remain stable.
>> The thrust needed to keep a helicopter up is equal to the thrust
>> needed to accelerate an object the mass of the helicopter by _1g_.
>> That is a LOT of acceleration, much, MUCH more than a sub is capable
>> of. We can conclude, therefore, that the helicopter rotor has a
>> greater ratio of torque to vehicle mass.
>
>It is a matter of force, not acceleration.
Which is precisely what I said. You know, before you "correct"
someone you might take the time to read what he says carefully.
[Snip.]
Scott Orr
One of the Arthurs
>
> On Sun, 06 Jun 1999 14:09:37 -0400, One of the Arthurs
> <mar...@iu.net> wrote:
> >> It may well be the case that the screw of a submarine produces more
> >> torque than the main rotor of a helicopter--however, the submarine is
> >> also much bigger than the helicopter. The important thing is that the
> >> ratio of torque to the mass of the vehicle is going to be much, _much_
> ^^^^
> >> higher for the helicopter--because a helicopter needs more thrust
> >> (just to keep itself airborne) than a sub does.
> >
> >That is not obvious at all
>
> Yes, it's quite obvious--if nothing else, the fact that the helicopter
> requires a tail-rotor confirms this hunch.
You missed the point. I know you are talking about the _ratio_.
It is the "much, _much_" that is not obvious. A helicopter needs a
tail rotor because in hover that is the only means it has of
counteracting torque.
Ships and subs have the mass of the ship times the offset of the
center of gravity from the center of bouyancy as the ship starts to
heel over. That restoring torque is "much, _much_" greater than the
restoring torque provided by a helicopter's tail rotor.
> >[snip] And yes, I think it does imply that the torque to mass ratio
> for the helicopter is much, much higher--there just can't be THAT much
> difference in the efficiencies of the propellors.
The difference is in the medium and its viscosity.
[snip]
> >> The thrust needed to keep a helicopter up is equal to the thrust
> >> needed to accelerate an object the mass of the helicopter by _1g_.
> >> That is a LOT of acceleration, much, MUCH more than a sub is capable
> >> of. We can conclude, therefore, that the helicopter rotor has a
> >> greater ratio of torque to vehicle mass.
> >
> >It is a matter of force, not acceleration. The force from the prop
> > keeps the copter in equilibrium. When the copter is sitting on the
> > ground, the same reaction force supplied by the feet on the ground
> > keeps the copter in equilibrium. [snip]
>
> Which is precisely what I said. You know, before you "correct"
> someone you might take the time to read what he says carefully.
It seemed you were implying that the answer was obvious based on the
fact that a helicopter is capable of much greater acceleration than
the sub is. That is true, but not relevant. The force required to
keep it in equilibrium is the same whether it is being supplied by the
rotor or by the ground.
Look, I am sorry I offended you, I certainly wasn't trying to start an
argument. You do seem to be overly sensitive to comments, however.
It is just a discussion group, after all.
Sincerely,
Frank
Scott D. Orr
<mar...@iu.net> wrote:
>"Scott D. Orr" wrote:
>>
>> On Sun, 06 Jun 1999 14:09:37 -0400, One of the Arthurs
>> <mar...@iu.net> wrote:
>[snip]
>
>> >> It may well be the case that the screw of a submarine produces more
>> >> torque than the main rotor of a helicopter--however, the submarine is
>> >> also much bigger than the helicopter. The important thing is that the
>> >> ratio of torque to the mass of the vehicle is going to be much, _much_
>> ^^^^
>> >> higher for the helicopter--because a helicopter needs more thrust
>> >> (just to keep itself airborne) than a sub does.
>> >
>> >That is not obvious at all
>>
>> Yes, it's quite obvious--if nothing else, the fact that the helicopter
>> requires a tail-rotor confirms this hunch.
>
>You missed the point. I know you are talking about the _ratio_.
>It is the "much, _much_" that is not obvious. A helicopter needs a
>tail rotor because in hover that is the only means it has of
>counteracting torque.
>Ships and subs have the mass of the ship times the offset of the
>center of gravity from the center of bouyancy as the ship starts to
>heel over. That restoring torque is "much, _much_" greater than the
>restoring torque provided by a helicopter's tail rotor.
Okay, that's true. I'll give you that this is the main reason a
helicopter needs a tail rotor--to elaborate, the difference here is
that the torque from the helicopter's rotor is in the horizontal
plane, while that the propellor from a prop-driven aircraft or a
submarine is in a vertical plane, and hence can be counteracted by
gravity.
However, it's nonetheless true that the helicopter's going to have a
much higher ratio of torque to mass.
>
>> >[snip] And yes, I think it does imply that the torque to mass ratio
>> for the helicopter is much, much higher--there just can't be THAT much
>> difference in the efficiencies of the propellors.
>
>The difference is in the medium and its viscosity.
>
But the lift is going to be increased by viscosity just as drag will
be. (Yes, there's a difference, but the lift/drag ratios would, I
think, be at least on the same order of magnitude--though I don't
really don't really know hydrodynamics.)
>> >> The thrust needed to keep a helicopter up is equal to the thrust
>> >> needed to accelerate an object the mass of the helicopter by _1g_.
>> >> That is a LOT of acceleration, much, MUCH more than a sub is capable
>> >> of. We can conclude, therefore, that the helicopter rotor has a
>> >> greater ratio of torque to vehicle mass.
>> >
>> >It is a matter of force, not acceleration. The force from the prop
>> > keeps the copter in equilibrium. When the copter is sitting on the
>> > ground, the same reaction force supplied by the feet on the ground
>> > keeps the copter in equilibrium. [snip]
>>
>> Which is precisely what I said. You know, before you "correct"
>> someone you might take the time to read what he says carefully.
>
>It seemed you were implying that the answer was obvious based on the
>fact that a helicopter is capable of much greater acceleration than
>the sub is. That is true, but not relevant. The force required to
>keep it in equilibrium is the same whether it is being supplied by the
>rotor or by the ground.
No, I was talking about force, but I used "thrust needed to
accelerate" because that's an easier concept for most people to deal
with.
>
>Look, I am sorry I offended you, I certainly wasn't trying to start an
>argument. You do seem to be overly sensitive to comments, however.
>It is just a discussion group, after all.
>
I know--but there are people who are so eager to show off their
knowledge that they don't bother to figure out whethere they agree or
disagree with the person they're replying to. I'm sorry if I
misjudged you.
Scott Orr
Mike O'Connell
I don't think torque/mass is relevent in the case of the helicopter.
The helicopter could weigh as much as the sub and it would still spin,
although much more slowly.
Mass of the sub is irrelevant too. The smallest torque would spin the
sub eventually no matter how massive it was.
Fins, sails and such dont do much for the sub either, except slow the
rotation due to increased drag about the sub's axis. The vanes could
counter the rotation if they were moveable AND the sub was travelling
at high enough speed so the vanes produced a high enough counter-torque.
This is similar to the helicopter tailrotor losing effectiveness to
steer at high airspeed.
The real answer is that the center of gravity exerts a torque about the
center of buoyancy when displaced from the vertical.
Mike O'Connell
In article <375e119c...@enews.newsguy.com>,
sd...@ix.netcom.com (Scott D. Orr) wrote:
> On Tue, 08 Jun 1999 18:47:01 -0400, One of the Arthurs
> <mar...@iu.net> wrote:
>
> >"Scott D. Orr" wrote:
> >>
> >> On Sun, 06 Jun 1999 14:09:37 -0400, One of the Arthurs
> >> <mar...@iu.net> wrote:
> >[snip]