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Angle of prop shaft - theoretical question.
We have an inboard and, of course, the prop shaft exits the hull at an angle. I just drove by a similar (but different brand) of boat and it appears it's prop shaft comes out at less of an angle. My first though it that a angle that gives a more push forward and less push "up" would be more efficient. Is that about right?? |
Angle of prop shaft - theoretical question.
"Gary Warner" wrote in message ... We have an inboard and, of course, the prop shaft exits the hull at an angle. I just drove by a similar (but different brand) of boat and it appears it's prop shaft comes out at less of an angle. My first though it that a angle that gives a more push forward and less push "up" would be more efficient. Is that about right?? Yes but the real gain in effiency comes from the fact that the pitch on the blade on one side now more closely equals the pitch on the opposite side. This also means it takes less rudder to maintain a straight line and therefore less drag. Gordon |
Angle of prop shaft - theoretical question.
On Thu, 3 Jun 2004 12:06:33 -0700, "Gordon" wrote:
"Gary Warner" wrote in message ... We have an inboard and, of course, the prop shaft exits the hull at an angle. I just drove by a similar (but different brand) of boat and it appears it's prop shaft comes out at less of an angle. My first though it that a angle that gives a more push forward and less push "up" would be more efficient. Is that about right?? Yes but the real gain in effiency comes from the fact that the pitch on the blade on one side now more closely equals the pitch on the opposite side. This also means it takes less rudder to maintain a straight line and therefore less drag. You'll also get less propwalk when reversing the boat with the lesser shaft angle from horizontal. Steve |
Angle of prop shaft - theoretical question.
On Thu, 3 Jun 2004 12:06:33 -0700, "Gordon"
wrote: Yes but the real gain in effiency comes from the fact that the pitch on the blade on one side now more closely equals the pitch on the opposite side. This also means it takes less rudder to maintain a straight line and therefore less drag. ========================================== This sounds like it ends up closing the loop on the "prop walk" discussion and starting around the mullberry bush again. We pretty well established that boats with horizontal shafts had just as much prop walk as those with angled shafts. My guess is that it all comes down to a resolution of force vectors in the vertical and horizontal plane, using shaft angle with the bottom of the boat as the vector direction. |
Angle of prop shaft - theoretical question.
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Angle of prop shaft - theoretical question.
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Angle of prop shaft - theoretical question.
You'll also get less propwalk when reversing the boat with the lesser
shaft angle from horizontal. Steve Why? Because while the propeller shaft is not parallel to the surface, the flow of water past the propeller is. The physics of this relationship make one side of the prop more effective in reverse than the other, depending upon which way the prop is rotating. |
Angle of prop shaft - theoretical question.
Prop walk is the "sum" of a number of factors - prop rotation (left or
right), prop pitch, shaft angle, vessel trim, wind, current, hull form. A right hand prop, SHOULD, back to port .... a left hand prop (G fixed pitch), SHOULD, back to stbd ..... BUT, results will vary for any and/or all of the reasons above, and in addition, whether you are all ready turning and/or have headway or sternway. When you start out on a boat, figure the "SHOULD" first, then standby to learn the "oops" and vagaries, that WILL apply due to any of the factors, listed above. Try not to think of it as your enemy and learn to use it. otn |
Angle of prop shaft - theoretical question.
On 4 Jun 2004 11:32:26 -0700, (basskisser) wrote:
(Steven Shelikoff) wrote in message ... On 4 Jun 2004 04:17:35 -0700, (basskisser) wrote: (Steven Shelikoff) wrote in message ... On Thu, 3 Jun 2004 12:06:33 -0700, "Gordon" wrote: "Gary Warner" wrote in message ... We have an inboard and, of course, the prop shaft exits the hull at an angle. I just drove by a similar (but different brand) of boat and it appears it's prop shaft comes out at less of an angle. My first though it that a angle that gives a more push forward and less push "up" would be more efficient. Is that about right?? Yes but the real gain in effiency comes from the fact that the pitch on the blade on one side now more closely equals the pitch on the opposite side. This also means it takes less rudder to maintain a straight line and therefore less drag. You'll also get less propwalk when reversing the boat with the lesser shaft angle from horizontal. Why? My theory is that , all else being equal, a boat with a greater shaft angle will have less thrust in the horizontal direction to counteract the sideways force from the prop paddle-wheeling and at the same time will increase the sideways "spinning" component of the rotational force from the prop. Think of it this way: If you have the shaft completely vertical and spin the prop, the main motive force will be straight up and not push the boat anywhere. You've minimized the "paddle-wheel" sideways effect but that total force is very small. However, you've also maximized the torque rotational force that will try and spin the boat in the same way as putting a single mixer blade in a bowl of batter will try and spin the bowl and that force is huge compared to the paddle-wheel force. As you lessen the angle of the shaft, you start to increase the sideways paddle-wheel force but again, that's a very small force. The direction of the "mixing bowl" rotational force changes from trying to spin the boat to trying to list the boat. Also, you get more motive force in the proper direction to allow you to counteract both the "paddle-wheel" force and the "mixing bowl" force. When the shaft is completely horizontal, the rotational force is all in the direction that creates list as you apply power and none is trying to rotate the boat. I believe this has the greatest effect on reducing prop walk since the rotational force can be very large. While a small change in shaft angle has a small effect on the ratio of the vector components of that force, the total force is so great that a small change in the ratio of the vectors can have a large effect on the handling of the boat. Also, you have the maximum amount of thrust in the proper direction to help handle the remaining sideways paddle-wheel force, which is the least of all of them. That's my theory and I'm sticking with it. lol Steve I don't agree. If the direction of the prop and shaft, relative to the centerline of the boat never changes, and the cause of the "prop walk" But it is changing. That's the variable we're changing, the angle of the shaft. I.e., as the shaft angle gets closer and closer to coming straight out of the boat with no downward angle, the prop walk gets less and less. Or stated another way, the greater the angle of the shaft the greater the prop walk. And that's due to the torque of the shaft, which is applied more and more as a force to rotate the boat as the downward angle of the shaft is increased. When the shaft is straight back with no downward angle, the torque force from the shaft causes the boat to list but doesn't rotate it in the water. is from the rotational force, it would make no difference what the angle of the prop is relative to the horizon. It could be anywhere from horizontal, through 90 degrees to horizontal, and the rotational force would remain the same. The rotational force from the prop remains the same. But what it does to the boat depends on the angle of the shaft relative to the boat. If the shaft is vertical, it will try and rotate the boat in the horizontal plane, i.e., prop walk. If the shaft is horizontal, it will try and rotate the boat in the vertical plane, i.e., list. Anywhere in between vertical and horizontal and some of the force will try and rotate the boat while some will cause list with the list increasing and the prop walk decreasing the closer to horizontal you get. Steve |
Angle of prop shaft - theoretical question.
Steven Shelikoff wrote:
But it is changing. That's the variable we're changing, the angle of the shaft. I.e., as the shaft angle gets closer and closer to coming straight out of the boat with no downward angle, the prop walk gets less and less. Or stated another way, the greater the angle of the shaft the greater the prop walk. And that's due to the torque of the shaft, which is applied more and more as a force to rotate the boat as the downward angle of the shaft is increased. When the shaft is straight back with no downward angle, the torque force from the shaft causes the boat to list but doesn't rotate it in the water. The rotational force from the prop remains the same. But what it does to the boat depends on the angle of the shaft relative to the boat. If the shaft is vertical, it will try and rotate the boat in the horizontal plane, i.e., prop walk. If the shaft is horizontal, it will try and rotate the boat in the vertical plane, i.e., list. Anywhere in between vertical and horizontal and some of the force will try and rotate the boat while some will cause list with the list increasing and the prop walk decreasing the closer to horizontal you get. Steve Using your theory, Steve, the stern would walk the same way whether the prop was a left hand or right hand wheel... and this is not the case. I have always been under the impression, on straight inboards, that the lower half of the propellor, the arc furthest from the boat/hull surface, is the one that does the most work/thrust (eg. surface piercing drives, etc.). The prop has better "bite" in the less turbulent water away from the hull. This has been my experience too... Correct Craft & Century inboards: RH prop, walks to port in reverse, favors left turns in forward... (the opposite of your explanation if taken to the extreme of a 90 degree propshaft angle). Mastercraft inboard: LH prop, walks to starboard in reverse, favors right turns in forward. (again, the opposite of your explanation if taken to the extreme of a 90 degree propshaft angle). The rotational force of the shaft/prop is transferred primarily to the attitude of the boat on a single screw craft. Rob |
Angle of prop shaft - theoretical question.
On Sat, 05 Jun 2004 11:06:08 -0400, trainfan1
wrote: Steven Shelikoff wrote: But it is changing. That's the variable we're changing, the angle of the shaft. I.e., as the shaft angle gets closer and closer to coming straight out of the boat with no downward angle, the prop walk gets less and less. Or stated another way, the greater the angle of the shaft the greater the prop walk. And that's due to the torque of the shaft, which is applied more and more as a force to rotate the boat as the downward angle of the shaft is increased. When the shaft is straight back with no downward angle, the torque force from the shaft causes the boat to list but doesn't rotate it in the water. The rotational force from the prop remains the same. But what it does to the boat depends on the angle of the shaft relative to the boat. If the shaft is vertical, it will try and rotate the boat in the horizontal plane, i.e., prop walk. If the shaft is horizontal, it will try and rotate the boat in the vertical plane, i.e., list. Anywhere in between vertical and horizontal and some of the force will try and rotate the boat while some will cause list with the list increasing and the prop walk decreasing the closer to horizontal you get. Steve Using your theory, Steve, the stern would walk the same way whether the prop was a left hand or right hand wheel... and this is not the case. Actually, no it wouldn't. The torque is in a different direction depending on whether the prop is right or left handed so the boat would turn in a different direction. I have always been under the impression, on straight inboards, that the lower half of the propellor, the arc furthest from the boat/hull surface, is the one that does the most work/thrust (eg. surface piercing drives, etc.). The prop has better "bite" in the less turbulent water away from the hull. This has been my experience too... This is true. That's one of the causes of prop walk, not the only one though. That's why a boat with the prop further from the hull will have less prop walk. But that's not what the question was. The question is why a small change in the shaft angle (say only 10 or 20 degrees) will have a dramatic effect on the amount of prop walk. To have that large an effect with such a small change you have to have a large total force and the one you mentioned above creates a very small force. But when the shaft is completely horizontal, it's the main propellor related force causing prop walk. Tilt the shaft down a little and it becomes overwhelmed by the torque force. Correct Craft & Century inboards: RH prop, walks to port in reverse, favors left turns in forward... (the opposite of your explanation if taken to the extreme of a 90 degree propshaft angle). But the prop shaft is not 90 degrees. If it were, the boat would turn opposite the direction of the prop since it's the only prop related force being applied. Also, not all boats with a RH prop will walk the same way. It depends on the specific configuration of the boat including shaft angle, type of prop, how far the prop is from the hull, etc. My boat is a single screw inboard with a right hand prop and it backs to starboard with a pretty severe case of prop walk. Mastercraft inboard: LH prop, walks to starboard in reverse, favors right turns in forward. (again, the opposite of your explanation if taken to the extreme of a 90 degree propshaft angle). Same comments as above. The rotational force of the shaft/prop is transferred primarily to the attitude of the boat on a single screw craft. Exactly what I said. i.e., the torque from the prop will primarily cause the boat to list when the shaft is at or near horizontal. As you increase the downward angle (or upward angle for that matter although I don't know of many boats with an upward pointing shaft) the rotation force from the shaft/prop will more and more cause the boat to rotate and less and less cause the attitude (list) to change. You can realize just how much rotational force from the shaft/prop there is since it's big enough to cause a noticable list. Apply the same size force from the paddle wheel affect in the direction to cause list and you probably won't notice a thing. I'll agree that on most boats, the rotational force from the torque of the prop/shaft is not the main contributor to prop walk and is a much greater contributor to list. But what we're talking about here is what forces that contribute to prop walk change as the shaft angle changes. And the torque effect certainly does. Steve |
Angle of prop shaft - theoretical question.
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Angle of prop shaft - theoretical question.
Another P.S. The change in direction of applied force from the torque of the prop/shaft is only one part of the theory. The rest is the change in the amout of paddle wheel effect as the angle changes as well as a change in the amout of available thrust in the proper direction to counteract the prop walk as the shaft angle changes. I'm always willing to adjust the theory.:) Steve |
Angle of prop shaft - theoretical question.
steve, bone up on "P-torque" or "P-thrust" or more accurately "asymetrical
thrust". It is a common problem for aircraft with "conventional" landing gear (meaning two wheels up front and one on the tail), and has been fully understood since the early days of WWII. Another P.S. The change in direction of applied force from the torque of the prop/shaft is only one part of the theory. The rest is the change in the amout of paddle wheel effect as the angle changes as well as a change in the amout of available thrust in the proper direction to counteract the prop walk as the shaft angle changes. I'm always willing to adjust the theory.:) Steve |
Angle of prop shaft - theoretical question.
gene, you are one horse**** pilot, if you are any pilot at all, for not being
able to tell the difference between conventional gear and trikes. Let me inform you a tad. when the aircraft is rolling with the tail down, the angle of attack one side of the prop circle is greater than on the other side, because of the forward movement of the craft. The side of the prop with great a of a developes more thrust and pulls the aircraft forward faster than the other side of the prop. than means the aircraft pulls to one side. This is often (erroneously) referred to a P-Torque, because it feels like the engine is torqueing the aircraft to the side. In fact, it is P-Thrust, or asymetrical thrust that is causing the aircraft to veer. be carefull, gene. Remember what the FAA taught you, "Safety is no accident". You need to do some boning up on your pilot skills, gene, or maybe hang up your googles. (JAXAshby) wrote: steve, bone up on "P-torque" or "P-thrust" or more accurately "asymetrical thrust". It is a common problem for aircraft with "conventional" landing gear (meaning two wheels up front and one on the tail), and has been fully understood since the early days of WWII. So..... what conundrum of JaxWorld prevents this from affecting tricycle gear aircraft, as well?? (Sure takes a lot of right rudder to keep every aircraft, conventional or tricycle, I have flown on the center line.) You *do* realize, of course, that most of the forces felt in this regard are from propeller swirl impinging upon the vertical stabilizer? And, that said, given the arm of a 16" boat screw vs a 8 foot or better aircraft propeller, it makes the effect of P-factor minimal, at best, in a nautical scenario (unless, of course, you would like to include things like WWII battleship propellers, just to prove the laboratory experience in deference to real life). -- 23' Grady White, out of Southport, NC. http://myworkshop.idleplay.net/cavern/ Homepage http://www.southharbourvillageinn.com/directions.asp Where Southport,NC is located. http://southharbourvillageinn.linksysnet.com Real Time Pictures at My Marina http://www.thebayguide.com/rec.boats Rec.boats at Lee Yeaton's Bayguide |
Angle of prop shaft - theoretical question.
"JAXAshby" wrote in message ... Snip personal attack Let me inform you a tad. when the aircraft is rolling with the tail down, the angle of attack one side of the prop circle is greater than on the other side, because of the forward movement of the craft. The side of the prop with great a of a developes more thrust and pulls the aircraft forward faster than the other side of the prop. than means the aircraft pulls to one side. This is often (erroneously) referred to a P-Torque, because it feels like the engine is torqueing the aircraft to the side. In fact, it is P-Thrust, or asymetrical thrust that is causing the aircraft to veer. be carefull, gene. Remember what the FAA taught you, "Safety is no accident". Snip more personal attack (JAXAshby) wrote: Lordy, a lucid and correct answer from Jax. Who would have thunk it! Mark Browne |
Angle of prop shaft - theoretical question.
Used to be on a ship that would trim by the head ( 3' +) when fully loaded.
Put the engine half astern - back like a sumbitch to port (fixed pitch RH). Even keel - half astern - back like a sumbitch to port. Trimmed by the stern - half astern - back like a sumbitch to port. Power used, is another one of those factors (otn missed that one) which will increase propwalk. It's not always easy to tell which factor may or may not be increasing or decreasing or even IF there is any difference because of it. For my money, the basic issue (propwalk) is caused by prop rotation and all other factors may assist or decrease it, but the basic "phenom" occurs when you rotate the prop. Shen |
Angle of prop shaft - theoretical question.
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Angle of prop shaft - theoretical question.
I'm sorry I missed the original post. I'm responding to the thread, not this
post in particular. The "p-factor," of the upcoming and downgoing propeller blades having different angles of attack, is the least signifcant reason for asymmetric propeller thrust, although the most often touted. I came across a little article in Flying years ago which did the math, and the effect is very small. There are something like five reasons that a tail-dragger will yaw one way, the p-factor being only one. In my previous boat, Stella B, (www.ctlow.ca/StellaB/StellaB.html), I had about the same asymmetric thrust whether the outdrive was trimmed in or out. So much for prop angle. The main effect is from the spiral prop wash. In reverse, where asymmetric thrust is virtually always more pronounced, the top half of the prop wash vortex strikes the hull, and pushes it sideways. The effect will vary depending on the underwater hull shape, the angle of the prop shaft, design of prop ... So, a right hand propeller in reverse turns counter-clockwise. The top half of the spiralling prop wash is moving to port, and pushes on the hull, yawing the stern to port. The bottom half othe spiral is mostly in clear water, pushing on nothing. I hate to say "end of discussion," because that sounds arrogant, and I still have things to learn, but I am very sure that for most practical purposes, that is it. Charles ==== Charles T. Low - remove "UN" www.boatdocking.com/BDPhoto.html - Photo Contest www.boatdocking.com www.ctlow.ca/Trojan26 - my boat ==== "trainfan1" wrote in message ... Using your theory, Steve, the stern would walk the same way whether the prop was a left hand or right hand wheel... and this is not the case. I have always been under the impression, on straight inboards, that the lower half of the propellor, the arc furthest from the boat/hull surface, is the one that does the most work/thrust (eg. surface piercing drives, etc.). The prop has better "bite" in the less turbulent water away from the hull. This has been my experience too... Correct Craft & Century inboards: RH prop, walks to port in reverse, favors left turns in forward... (the opposite of your explanation if taken to the extreme of a 90 degree propshaft angle). Mastercraft inboard: LH prop, walks to starboard in reverse, favors right turns in forward. (again, the opposite of your explanation if taken to the extreme of a 90 degree propshaft angle). The rotational force of the shaft/prop is transferred primarily to the attitude of the boat on a single screw craft. Rob |
Angle of prop shaft - theoretical question.
charlie, if spiral prop wash is the reason for p-thrust ever wonder why a tail
dragger with the tail down experiences so much more sidesways turning than the same aircraft at the same speed with the tail horizontal? The "p-factor," of the upcoming and downgoing propeller blades having different angles of attack, is the least signifcant reason for asymmetric propeller thrust, although the most often touted. I came across a little article in Flying years ago which did the math, and the effect is very small. There are something like five reasons that a tail-dragger will yaw one way, the p-factor being only one. In my previous boat, Stella B, (www.ctlow.ca/StellaB/StellaB.html), I had about the same asymmetric thrust whether the outdrive was trimmed in or out. So much for prop angle. The main effect is from the spiral prop wash. In reverse, where asymmetric thrust is virtually always more pronounced, the top half of the prop wash vortex strikes the hull, and pushes it sideways. The effect will vary depending on the underwater hull shape, the angle of the prop shaft, design of prop ... So, a right hand propeller in reverse turns counter-clockwise. The top half of the spiralling prop wash is moving to port, and pushes on the hull, yawing the stern to port. The bottom half othe spiral is mostly in clear water, pushing on nothing. I hate to say "end of discussion," because that sounds arrogant, and I still have things to learn, but I am very sure that for most practical purposes, that is it. Charles ==== Charles T. Low - remove "UN" www.boatdocking.com/BDPhoto.html - Photo Contest www.boatdocking.com www.ctlow.ca/Trojan26 - my boat ==== "trainfan1" wrote in message ... Using your theory, Steve, the stern would walk the same way whether the prop was a left hand or right hand wheel... and this is not the case. I have always been under the impression, on straight inboards, that the lower half of the propellor, the arc furthest from the boat/hull surface, is the one that does the most work/thrust (eg. surface piercing drives, etc.). The prop has better "bite" in the less turbulent water away from the hull. This has been my experience too... Correct Craft & Century inboards: RH prop, walks to port in reverse, favors left turns in forward... (the opposite of your explanation if taken to the extreme of a 90 degree propshaft angle). Mastercraft inboard: LH prop, walks to starboard in reverse, favors right turns in forward. (again, the opposite of your explanation if taken to the extreme of a 90 degree propshaft angle). The rotational force of the shaft/prop is transferred primarily to the attitude of the boat on a single screw craft. Rob |
Angle of prop shaft - theoretical question.
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Angle of prop shaft - theoretical question.
charlie, you don't understand what "action/reaction" means. the prop wash has
not have to "push" on anything but the prop, just like a rocket ship in space. The top half of the spiralling prop wash is moving to port, and pushes on the hull, yawing the stern to port. The bottom half othe spiral is mostly in clear water, pushing on nothing. |
Angle of prop shaft - theoretical question.
gene, it is nice to see that you came to your weak senses and agree with me and
the rest of the world. gene, you are one horse**** pilot, if you are any pilot at all, for not being able to tell the difference between conventional gear and trikes. Oh, I can tell the difference.... and the similarities. Let me inform you a tad. when the aircraft is rolling with the tail down, the angle of attack one side of the prop circle is greater than on the other side, because of the forward movement of the craft. The side of the prop with great a of a developes more thrust and pulls the aircraft forward faster than the other side of the prop. than means the aircraft pulls to one side. This is often (erroneously) referred to a P-Torque, because it feels like the engine is torqueing the aircraft to the side. In fact, it is P-Thrust, or asymetrical thrust that is causing the aircraft to veer. You are amazingly close to correct. However, perhaps you should consider that the angle of attack changes with respect to relative wind.... and that changes when the taildragger (and the tricycle gear to a lesser extent) transitions to flight attitude. You knew that, right? Or did you think that they just popped up into the air? be carefull, gene. Remember what the FAA taught you, "Safety is no accident". So... this is evidence that you are an authority on the FAA, too! How many FAA certifications or designations do you hold? You need to do some boning up on your pilot skills, gene, or maybe hang up your googles. You can see all of this in your monitor? Having visions?...... are you wearing those too-tight speedos again? -- 23' Grady White, out of Southport, NC. http://myworkshop.idleplay.net/cavern/ Homepage http://www.southharbourvillageinn.com/directions.asp Where Southport,NC is located. http://southharbourvillageinn.linksysnet.com Real Time Pictures at My Marina http://www.thebayguide.com/rec.boats Rec.boats at Lee Yeaton's Bayguide |
Angle of prop shaft - theoretical question.
On Sun, 06 Jun 2004 00:28:20 -0400, Wayne.B
wrote: On 05 Jun 2004 22:44:53 GMT, (Shen44) wrote: the basic issue (propwalk) is caused by prop rotation and all other factors may assist or decrease it, but the basic "phenom" occurs when you rotate the prop. ============================================ Of course, but what is the cause of the asymetric thrust? THAT is the question. Everyone agrees that a prop with a horizontal shaft still exhibits prop walk, implying that the bottom the prop is more efficient at providing thrust than the top. Lots of theories have been provided but none that seem totally convincing since prop walk still exists to one degree or another on deep props, that have plenty of hull clearance. That's probably because it's a combination of several effects that all contribute. Anyone who throws any theory out there that contains as part of it's explanation some way that the thrust on one part of the prop is different than on another part of the prop is probably correct. Also, any explanation that contains part of it's explanation some way tha the thrust from the prop gets translated into a rotational force on the boat is probably correct. For instance, no matter how deep the prop, the water on the lower side is still going to be under ambient higher pressure than the water on the top. So by moving the prop far away from the hull you may have minimized the effect of hull turbulence on the top part of the prop. But you haven't done anything about the pressure difference. Steve |
Angle of prop shaft - theoretical question.
including P-51's?
charlie, if spiral prop wash is the reason for p-thrust ever wonder why a tail dragger with the tail down experiences so much more sidesways turning than the same aircraft at the same speed with the tail horizontal? Uh..... duh..... .......could it be because tail draggers have larger vertical surface areas on the empennage to maintain directional control at slow ground and air speeds? -- 23' Grady White, out of Southport, NC. http://myworkshop.idleplay.net/cavern/ Homepage http://www.southharbourvillageinn.com/directions.asp Where Southport,NC is located. http://southharbourvillageinn.linksysnet.com Real Time Pictures at My Marina http://www.thebayguide.com/rec.boats Rec.boats at Lee Yeaton's Bayguide |
Angle of prop shaft - theoretical question.
gene, you dum-dum. exactly as I said, you do not understand "action/reaction".
go call some junior high school science teacher and ask him/her to explain it to you, then come back here. you won't have need for further discussion once you understand just what "action/reaction" means. charlie, you don't understand what "action/reaction" means. the prop wash has not have to "push" on anything but the prop, just like a rocket ship in space. The top half of the spiralling prop wash is moving to port, and pushes on the hull, yawing the stern to port. The bottom half othe spiral is mostly in clear water, pushing on nothing. ROFLMAO...... prop powered rocket ship in space! I wonder what is pushing on *that* prop.......??? Scotty........ please beam Jax up..... has di-lithium crystals have apparently cracked up. -- 23' Grady White, out of Southport, NC. http://myworkshop.idleplay.net/cavern/ Homepage http://www.southharbourvillageinn.com/directions.asp Where Southport,NC is located. http://southharbourvillageinn.linksysnet.com Real Time Pictures at My Marina http://www.thebayguide.com/rec.boats Rec.boats at Lee Yeaton's Bayguide |
Angle of prop shaft - theoretical question.
oh, damn. here we had hope for you.
gene, it is nice to see that you came to your weak senses and agree with me and the rest of the world. Yet another ill founded and incorrect conclusion. Whatever you aren't, you *are* consistent. -- 23' Grady White, out of Southport, NC. http://myworkshop.idleplay.net/cavern/ Homepage http://www.southharbourvillageinn.com/directions.asp Where Southport,NC is located. http://southharbourvillageinn.linksysnet.com Real Time Pictures at My Marina http://www.thebayguide.com/rec.boats Rec.boats at Lee Yeaton's Bayguide |
Angle of prop shaft - theoretical question.
no matter how deep the prop, the water on the lower side
is still going to be under ambient higher pressure than the water on the top. the pressure difference due to water depth is inconsequential. The pressure change is less than 0.5 pound per foot of depth. the compressibility of water is near zero. even on a 15" prop, the center of effort difference between top and bottom blades is less than about a foot. These ar truly miniscule forces as compared to the force needed to move a multi-thousand pound boat in a noticeable fashion. |
Angle of prop shaft - theoretical question.
wait a minute. wasn't it you that claimed the alleged p-thrust was actually
spiral prop wash on the rudder? Yup, that was you. So how come you are now telling us that making the rudder *bigger* would stop this alleged p-thrust? dumb. including P-51's? Especially the P-51....... .....it is a lesson in what happens with a design employing too small control surface(s) for slow speeds. The P-51 was a purpose built aircraft made to fly high and fast.... ground handling and slow speed flight was sacrificed to this end. It was impossible to manually hold this aircraft on the runway if you forgot to trim the rudder. Ground handling, take-off, and landing in this aircraft was so poor that some British divisions suffered losses of as much as 60% just trying to learn how to fly the thing. Uh..... ever flown one? Wanna go there? -- 23' Grady White, out of Southport, NC. http://myworkshop.idleplay.net/cavern/ Homepage http://www.southharbourvillageinn.com/directions.asp Where Southport,NC is located. http://southharbourvillageinn.linksysnet.com Real Time Pictures at My Marina http://www.thebayguide.com/rec.boats Rec.boats at Lee Yeaton's Bayguide |
Angle of prop shaft - theoretical question.
Ok, teach...... tell me about how a prop-powered space ship
works..... I said nothing whatsoever about a prop-powered space ship. you did. I did say that "action/reaction" -- as in either a rocket ship OR of a boat prop -- means that neither "pushes" against anything at all. Than means that thrust comes from the action/reaction of the prop and water NOT action of the prop and reaction of the hull. dumb, you are. |
Angle of prop shaft - theoretical question.
gene, I am sure you don't realize it, but your post below states you believe
aircraft spiral left as they fly. way to go, gene. wait a minute. wasn't it you that claimed the alleged p-thrust was actually spiral prop wash on the rudder? Yup, that was you. So how come you are now telling us that making the rudder *bigger* would stop this alleged p-thrust? dumb. Jax your post is idiotic. (2) The rudder is the only tool available to *counteract* the left turning tendency (including "p-thrust") of the aircraft. The bigger the rudder the more command available at slow speeds. Unless, of course, JaxWorld pilots take off dragging the right brake....what do they do when the main gear comes off the ground? -- 23' Grady White, out of Southport, NC. http://myworkshop.idleplay.net/cavern/ Homepage http://www.southharbourvillageinn.com/directions.asp Where Southport,NC is located. http://southharbourvillageinn.linksysnet.com Real Time Pictures at My Marina http://www.thebayguide.com/rec.boats Rec.boats at Lee Yeaton's Bayguide |
Angle of prop shaft - theoretical question.
gene, your comprehension of English is sadly lacking. you agreed with this
statement AND disagreed. You agreed by stating the spiral prop wash caused the aircraft to turn (thus smaller rudder is better) and disagreed by stating that a larger rudder will stop the spiral prop wash. English does confuse you, doesn't it gene. (1) Please cite the post where I said that a smaller rudder would stop "p-thrust." |
Angle of prop shaft - theoretical question.
gene? what word didn't you understand? prop wash, as rocket exhaust, does not
have to push against anything. Ok, teach...... tell me about how a prop-powered space ship works..... I said nothing whatsoever about a prop-powered space ship. you did. I did say that "action/reaction" -- as in either a rocket ship OR of a boat prop -- means that neither "pushes" against anything at all. Than means that thrust comes from the action/reaction of the prop and water NOT action of the prop and reaction of the hull. dumb, you are. You said, and I quote, ".....the prop wash has not(sic) have to "push" on anything but the prop, just like a rocket ship in space." Here's your sign. -- 23' Grady White, out of Southport, NC. http://myworkshop.idleplay.net/cavern/ Homepage http://www.southharbourvillageinn.com/directions.asp Where Southport,NC is located. http://southharbourvillageinn.linksysnet.com Real Time Pictures at My Marina http://www.thebayguide.com/rec.boats Rec.boats at Lee Yeaton's Bayguide |
Angle of prop shaft - theoretical question.
JAXAshby wrote:
steve, bone up on "P-torque" or "P-thrust" or more accurately "asymetrical thrust". It is a common problem for aircraft with "conventional" landing gear (meaning two wheels up front and one on the tail), and has been fully understood since the early days of WWII. For christsakes, Jax, at least get the term correct, it's P-factor you cretin. Just for grins how about telling us all about your taildragger flying experience. For a know-nothing wannabe you sure pump out a lot of bull**** about stuff you obviously have no personal experience with. Rick |
Angle of prop shaft - theoretical question.
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Angle of prop shaft - theoretical question.
Another wrong assumption, Jax.....
it was not an assumption, gene. it was a statement of fact. |
Angle of prop shaft - theoretical question.
gene, learn English and then continue to post here.
From: "Gene Kearns" Date: 6/6/2004 5:12 PM Eastern Standard Time Message-id: On 06 Jun 2004 20:54:30 GMT, (JAXAshby) wrote: gene, your comprehension of English is sadly lacking. you agreed with this statement AND disagreed. You agreed by stating the spiral prop wash caused the aircraft to turn (thus smaller rudder is better) I never said rudder. I said, "....larger vertical surface areas on the empennage...." The rudder is a mixed blessing, but is the only control surface capable of offsetting the left turning tendency..... sorry you are confused. and disagreed by stating that a larger rudder will stop the spiral prop wash. English does confuse you, doesn't it gene. (1) Please cite the post where I said that a smaller rudder would stop "p-thrust." Apparently, your confusion arises from the fact that you don't understand the subtle differences between the terms "stop" and "counteract." Here's a hint..... you aren't going to "stop" it as long as you use one propeller per shaft. -- 23' Grady White, out of Southport, NC. http://myworkshop.idleplay.net/cavern/ Homepage http://www.southharbourvillageinn.com/directions.asp Where Southport,NC is located. http://southharbourvillageinn.linksysnet.com Real Time Pictures at My Marina http://www.thebayguide.com/rec.boats Rec.boats at Lee Yeaton's Bayguide |
Angle of prop shaft - theoretical question.
the original (and incorrect) term was "P-Torque". that was replaced (to some
extent) by the term "P-Thrust" as in asymetrical thrust due to the angling of the disc of the prop relative to forward motion. "P-Factor" is now used by idiots and for idiot who don't have a clew what is going on. btw ricky, you must the only person on the planet who claims to have an Airline Transport rating who doesn't know the difference between slots and slats. steve, bone up on "P-torque" or "P-thrust" or more accurately "asymetrical thrust". It is a common problem for aircraft with "conventional" landing gear (meaning two wheels up front and one on the tail), and has been fully understood since the early days of WWII. For christsakes, Jax, at least get the term correct, it's P-factor you cretin. Just for grins how about telling us all about your taildragger flying experience. For a know-nothing wannabe you sure pump out a lot of bull**** about stuff you obviously have no personal experience with. Rick |
Angle of prop shaft - theoretical question.
no, gene. the prop pushes against the water, NOT the prop wash. and yes you
did state that prop walk is due to the prop wash spiralling, and thus pushing against god knows what. dumb, gene, as in stupid on your part. gene? what word didn't you understand? prop wash, as rocket exhaust, does not have to push against anything. I saw no mention of..... rocket ... did you say that prop wash does not have to push against anything? I thought it pushed against the propeller...... oh.... are you confused, again? -- 23' Grady White, out of Southport, NC. http://myworkshop.idleplay.net/cavern/ Homepage http://www.southharbourvillageinn.com/directions.asp Where Southport,NC is located. http://southharbourvillageinn.linksysnet.com Real Time Pictures at My Marina http://www.thebayguide.com/rec.boats Rec.boats at Lee Yeaton's Bayguide |
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