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Old 12-21-2009, 12:52 PM   #15
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The trailer settles because the axle loading is being increased as I described above, but any torque or moment developed still affects the pin weight.

To illustrate, would you agree that you can stack bricks in the rear of a utility trailer until the tongue jack comes off the ground? Most of us have been there and done that, or something like it. When this happens, the tongue weight is less than zero! The trailer pivots on the axle when the rear hits the ground and the tongue points toward the sky, right?

Rusty
Right, but think about an airliner taking off. Yes, it rotates off the main landing gear, but that's not the center of gravity (usually). When you add weight to the airliner your fulcrum is the center of gravity, and you're more concerned about the arm to center of gravity than the arm of the weight you've added to the landing gear (usually). So no matter where you put the weight, the airliner will still rotate off the main landing gear (one assumes). When Bryan mentions he gets a 3 to 1 ratio, I keep wondering if that's due to the placement of the axles (most likely) or is it a little more complicated with the floorplan and where the appliances are located? I think this needs more discussion at a rally with beer. David
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Old 12-21-2009, 12:54 PM   #16
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The airliner example is substantially more complex than a mere weight and lever arm situation such as we have with the overhung and pin weights being discussed. At takeoff, the airliner is in a transient (non-steady-state) condition where the weight is being transferred from the landing gear to the aerodynamic lifting surfaces (the wings and horizontal tail surfaces). In the case of the 5th wheel, the weight always rests on the axles and the pin - there's no where else for it to go.

For a 300 lb change in W2 to result in only a 100 lb change in W1, all else being equal, D1 must be 3 times D2. As you say, this could be accomplished by moving the axles rearward. Of course, this would result in a LOT of pin weight when the bike wasn't on the carrier to counterbalance it.

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Old 12-21-2009, 01:24 PM   #17
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Right, but think about an airliner taking off. Yes, it rotates off the main landing gear, but that's not the center of gravity (usually). When you add weight to the airliner your fulcrum is the center of gravity, and you're more concerned about the arm to center of gravity than the arm of the weight you've added to the landing gear (usually). So no matter where you put the weight, the airliner will still rotate off the main landing gear (one assumes). When Bryan mentions he gets a 3 to 1 ratio, I keep wondering if that's due to the placement of the axles (most likely) or is it a little more complicated with the floorplan and where the appliances are located? I think this needs more discussion at a rally with beer. David
David,
Brings back memories of yesteryear, computing weight/balance with the old 'slip-sticks' before everything became computerized! Compute that % of MAC (Mean Aerodynamic Chord) for the take-off and landing, since the overall weight/balance will change due to fuel burn-off and distance. My younger days in the back end of C-130s.
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Old 12-21-2009, 07:15 PM   #18
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OK - time to get this back on topic. dTardis - one ton sounds fine. Ask PI about the lift. If the lift creates a problem, don't let some engineer tell you he can solve the handling problems with software! Davydee
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Old 12-21-2009, 10:48 PM   #19
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Thanks for all the input. I will have to look further into the lift. I had planned on calling them to find out things like...
Do the re-enforce the frame?
Does it reduce the cargo weight cap?
By how much?
What is the max the motorcycle can weigh?

We have really just starting looking and have a million questions.
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Old 12-23-2009, 09:53 AM   #20
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We have really just starting looking and have a million questions.
To me, that's the fun part!!! Enjoy the hunt and don't settle for less than you want if at all possible! David
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Old 01-11-2010, 08:44 PM   #21
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To me, that's the fun part!!! Enjoy the hunt and don't settle for less than you want if at all possible! David
Thats what we are trying to do. We had a less than positive meeting with a dealer, but I feel better after trolling the board for while.
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