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#1
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Drum dia and torque
Reducing the drum size has more effect on torque than I realized. My
spreadsheet shows 953 lb-ft for 48", 242 lb-ft for 36" and only 85 lb-ft for 24". What do you think? Bob -- ---------------------------------------------------- This mailbox protected from junk email by MailFrontier Desktop from MailFrontier, Inc. http://info.mailfrontier.com |
#2
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Bob Johnson wrote:
Reducing the drum size has more effect on torque than I realized. My spreadsheet shows 953 lb-ft for 48", 242 lb-ft for 36" and only 85 lb-ft for 24". What do you think? Maybe this was a private email that escaped onto the newsgroup, but I suggest the torgue should be proportional to diamenter; i.e., the 24" drum torque should be 475 lb-ft. -- Change "netto" to "net" to email me directly Eric Greenwell Washington State USA |
#3
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On Wed, 17 Nov 2004 11:13:26 -0600, "Bob Johnson"
wrote: Reducing the drum size has more effect on torque than I realized. My spreadsheet shows 953 lb-ft for 48", 242 lb-ft for 36" and only 85 lb-ft for 24". What do you think? I think that there is someting confusing here ... the torque will not vary with the drum size if it is shaft driven ... the line tension will vary inversly with diameter ... tension x diameter = constant (torque) Give us more to go on. George |
#4
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"Bob Johnson" wrote in message news:_DLmd.1161$3I.654@okepread01... Reducing the drum size has more effect on torque than I realized. My spreadsheet shows 953 lb-ft for 48", 242 lb-ft for 36" and only 85 lb-ft for 24". What do you think? Bob I think Bob's working on something like this. http://www.lippmann.de/germany/produkte/hoistline.html The Lippmann folks manufacture Dyneema "plastic" winch cable. They are claiming a 950 meter (~3100' AGL) winch launch on a 2000 meter (~6500') runway. They also note 3000 launches at one club without a break. This puts the total per launch cost (fuel, maint. cable replacement etc...) at about 1.5 Euro. Now that's cheap flying. Bill Daniels |
#5
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"Bob Johnson" wrote in message news:_DLmd.1161$3I.654@okepread01...
Reducing the drum size has more effect on torque than I realized. My spreadsheet shows 953 lb-ft for 48", 242 lb-ft for 36" and only 85 lb-ft for 24". What do you think? Bob Something is wrong here.....you need to read your info or your spreadsheet doesn't make any sense....!!!??? Torque measured where? The drum diameter has nothing to do with the torque!!! Is this for which drum application? Need more and correct info in order to give you some numbers. |
#6
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The drum diameter has nothing to do with the torque!!!
Sure it does. The rope has a certain amount of tension on it, usually measured in lbs. The rope is pulled off the drum at a certain distance from the center or rotation. That distance is the moment arm. The torque is the tension X moment arm, hence inch lbs or ft lbs. Jim Vincent N483SZ illspam |
#7
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"Jim Vincent" wrote in message ... The drum diameter has nothing to do with the torque!!! Sure it does. The rope has a certain amount of tension on it, usually measured in lbs. The rope is pulled off the drum at a certain distance from the center or rotation. That distance is the moment arm. The torque is the tension X moment arm, hence inch lbs or ft lbs. Jim Vincent N483SZ illspam And, in practice, constantly changing, generally increasing, depending on design and layup. Frank Whiteley |
#8
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"F.L. Whiteley" wrote in message ... "Jim Vincent" wrote in message ... The drum diameter has nothing to do with the torque!!! Sure it does. The rope has a certain amount of tension on it, usually measured in lbs. The rope is pulled off the drum at a certain distance from the center or rotation. That distance is the moment arm. The torque is the tension X moment arm, hence inch lbs or ft lbs. Jim Vincent N483SZ illspam And, in practice, constantly changing, generally increasing, depending on design and layup. Frank Whiteley The following is the summation of a couple of decades of thinking about winch launch. Winch drum torque is a complicated subject. It involves glider behavior, engine torque and power curves and the winding characteristics of the winch drum. Drum torque cannot be described without understanding all the other variables. The glider acts to demand both cable tension and cable speed. (Cable Speed x Tension = Power) The winch engine, controlled by the winch driver, tries to meet that demand while holding the glider airspeed at a value requested by the pilot. Note: The winch driver can control either glider airspeed or cable tension but not both. The torque on the drum shaft varies with demand and is limited by the engines Wide Open Throttle (WOT) torque curve. (And, of course, the breaking strength of the weak link.) If the winch is unable to meet cable tension demand, the glider airspeed will decay with increasing pitch attitude. If the winch meets or exceeds the demand, the glider airspeed will increase when the nose is raised. If the gliders airspeed decays with increasing pitch angle, then the glider is rapidly approaching the stall AOA since the wing loading is also increasing with pitch attitude. If the airspeed increases with increasing pitch, then the AOA will remain more nearly constant. The later is a safer condition. The actual radius of the drum depends on the quantity of cable wound onto the drum at any moment. If the instantaneous radius is one foot then the torque in foot/pounds equals cable tension in pounds. This is a typical mid-launch condition. If the cable tension is to remain equal to the gliders gross weight throughout the launch, which is desirable, then the torque at the drum shaft must increase with the increasing drum radius even as the drum RPM is reduced, to maintain a constant glider airspeed. This places heavy demands on the winch engine. Engines capable of very high torque at low RPM are desirable. Diesel engines typically have their torque peak just above idle. If the highest engine RPM is 2100 RPM then the engine torque capacity will increase even as the drum RPM decreases. In other words, diesel WOT torque curves tend to match the demand of winch launch. This explains why diesels are popular winch engines. Spark ignition engines tend to have torque peaks closer to the max RPM utilized by the winch. As the launch progresses, the torque capacity declines rapidly with RPM even as the demand increases. Sorry for the lecture and apologies to our metric friends. Now, lets build some winches. Bill Daniels |
#9
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"F.L. Whiteley" wrote in message ...
"Jim Vincent" wrote in message ... The drum diameter has nothing to do with the torque!!! Sure it does. The rope has a certain amount of tension on it, usually measured in lbs. The rope is pulled off the drum at a certain distance from the center or rotation. That distance is the moment arm. The torque is the tension X moment arm, hence inch lbs or ft lbs. Jim Vincent N483SZ illspam And, in practice, constantly changing, generally increasing, depending on design and layup. Frank Whiteley Definition of Torque: The Torque on an object about some pivot point is due to the action of a force on the object. (So, if this is drum of a winch on a shaft I am assuming) Magnitude of the Torque: t = "Force" times the "Lever Arm" = (Component of the Force perpendicular to Lever Arm) x (Lever Arm - the distance between the pivotal axis and the point where the force is applied) = Fp l = (Force) x (Perpendicular line of action lever arm - the shortest distance between the pivot point and the line of action of the force through the body) = F lp = (Force) x (Lever Arm) x sin(angle between the two) = F l sin(q) Direction of Torque: · The more exact definition is that the torque is that the torque is the cross product of the lever arm with applied force. · The torque's direction is perpendular to both the direction of the lever arm and the direction of the force. The direction can be found using the right hand rule. I Units: N m * These are the same units as a Joule, but nobody uses Joules. There must be some deep connection which nobody has yet discovered. Any ideas ? Torque on a Body A force is applied to an irregular shaped body on a frictionless, horizontal surface. The location the point of application of the force can be altered by dragging the application-point. The magnitude and direction of the applied force can be altered by dragging its tail. Displayed are the torque, the magnitude and direction of the force, the lever arm, and the angle between the force and the lever arm. Also displayed are the perpendicular values of the applied force and the lever arm. Just my few thoughts....jk |
#10
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Hi Bill --
Today we towed in light wind and so turned 2300 engine RPM in the climb. The 454 c.i. torque/hp curves show the engine was generating about 430 lb-ft torque and 200 hp at these revs. Now here is where I tend to go off the rails. Just 75 hp is required to lift a 1100 lb sailplane 1700 ft in 45 sec. I know there are some aerodynamic and mechanical losses but it's hard to believe they amount to some 125 hp. Bob -- ---------------------------------------------------- This mailbox protected from junk email by MailFrontier Desktop from MailFrontier, Inc. http://info.mailfrontier.com "Bill Daniels" wrote in message newsxAnd.71122$5K2.10295@attbi_s03... "F.L. Whiteley" wrote in message ... "Jim Vincent" wrote in message ... The drum diameter has nothing to do with the torque!!! Sure it does. The rope has a certain amount of tension on it, usually measured in lbs. The rope is pulled off the drum at a certain distance from the center or rotation. That distance is the moment arm. The torque is the tension X moment arm, hence inch lbs or ft lbs. Jim Vincent N483SZ illspam And, in practice, constantly changing, generally increasing, depending on design and layup. Frank Whiteley The following is the summation of a couple of decades of thinking about winch launch. Winch drum torque is a complicated subject. It involves glider behavior, engine torque and power curves and the winding characteristics of the winch drum. Drum torque cannot be described without understanding all the other variables. The glider acts to demand both cable tension and cable speed. (Cable Speed x Tension = Power) The winch engine, controlled by the winch driver, tries to meet that demand while holding the glider airspeed at a value requested by the pilot. Note: The winch driver can control either glider airspeed or cable tension but not both. The torque on the drum shaft varies with demand and is limited by the engines Wide Open Throttle (WOT) torque curve. (And, of course, the breaking strength of the weak link.) If the winch is unable to meet cable tension demand, the glider airspeed will decay with increasing pitch attitude. If the winch meets or exceeds the demand, the glider airspeed will increase when the nose is raised. If the gliders airspeed decays with increasing pitch angle, then the glider is rapidly approaching the stall AOA since the wing loading is also increasing with pitch attitude. If the airspeed increases with increasing pitch, then the AOA will remain more nearly constant. The later is a safer condition. The actual radius of the drum depends on the quantity of cable wound onto the drum at any moment. If the instantaneous radius is one foot then the torque in foot/pounds equals cable tension in pounds. This is a typical mid-launch condition. If the cable tension is to remain equal to the gliders gross weight throughout the launch, which is desirable, then the torque at the drum shaft must increase with the increasing drum radius even as the drum RPM is reduced, to maintain a constant glider airspeed. This places heavy demands on the winch engine. Engines capable of very high torque at low RPM are desirable. Diesel engines typically have their torque peak just above idle. If the highest engine RPM is 2100 RPM then the engine torque capacity will increase even as the drum RPM decreases. In other words, diesel WOT torque curves tend to match the demand of winch launch. This explains why diesels are popular winch engines. Spark ignition engines tend to have torque peaks closer to the max RPM utilized by the winch. As the launch progresses, the torque capacity declines rapidly with RPM even as the demand increases. Sorry for the lecture and apologies to our metric friends. Now, lets build some winches. Bill Daniels |
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