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Old 02-24-2016, 07:06 AM
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JollyPopper
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Default weight distribution

What percentage of tptal weight should be on the tail wheel of a tail dragger?
Old 02-24-2016, 07:51 AM
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Lone Star Charles
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I don't know that I have ever heard this expressed as a percentage. I believe that the less weight on the tailwheel, the better the high-speed handling. I am usually satisfied if the aircraft, if not moving, will settle on its tail if released from an attitude that is slightly forward of level. Pretty unscientific, but that's my story.
Old 02-24-2016, 08:21 AM
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JollyPopper
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I don't know if anyone has done this but it seems that there should be an optimum percentage of weight on the tail wheel. For instance, 40% on each main and 20% on the tail wheel or 45% on each main and 10% on the tail wheel or maybe something else, but there should be some ball park guide line for weight distribution. Maybe????????
Old 02-24-2016, 08:25 AM
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HighPlains
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The placement of the main gear and the CG of the model is what is usually considered. Also the surface that you are flying from. Grass needs a more forward placement of the wheels than pavement.
Old 02-24-2016, 04:58 PM
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All Day Dan
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HighPlains has it right. You're concerned about the wrong thing. Dan.
Old 02-24-2016, 08:07 PM
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radfordc
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Roughly 20% based on the models I've checked.
Old 02-25-2016, 06:18 AM
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JohnBuckner
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HighPlains is absolutely correct and stating as a formula to use for gear placement in a percentage is just about impossible. Or about like suggesting there is only one size prop for any given engine with no consideration given to type airframe, pilot skills and types of performance being attempted. Most important of all and the best indicator is the distance forward or to the rear of the actual flight CG.

Here is just one of the compromise in play here: Main gear relationship with CG. The very easiest location for the main gear (in the case of a taildragger) in terms of bounce free and simple landings is directly at the actual CG. As were almost all earlier full scale post war gliders/sailplanes but there is a problem when we hang an engine on. Now when we slow down and perhaps are lazy of poorly trained with elevator skills guess what the nose is going to drop and we destroy the propellors.

The obvious solution is to move the mains back a short distane from the CG and put the third wheel under the nose. Remember though we are talking about a taildragger in this example --so-- the solution is instead to move main gears footprint forward of the CG quite a bit. Lets go back now to that perfect main gear footprint/CG relationship which is directly at the flight CG but now we know we must move the main gears footprint forward to protect that pesky propeller.

Moving that main gear footprint forward introduces another problem though that is when simply stated is: The further forwar this footprint is from the CG the greater will the tendency for this gear arraignment to bounce and cause the airplane to bounce excessively and be what I term as a: Boinger on landing. There have been a number of otherwise good airplanes but ones that were very difficult land well because the mains were just to far forward.

Building/designing airplanes, full scale or models to rigid formulas just does not allways work well.

John
Old 02-25-2016, 06:27 AM
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Set the CG per the plans. Don't worry about percentage of weight is on each wheel.
The CG as called for in the plans is just a starting point anyway. Go fly and set CG to your preference.
remember that a tail heavy airplane will be sensitive in pitch if flyable at all. A nose heavy airplane won't want to slow down on approach nor will it flair.
you want the airplane to set level or slightly nose down when balanced on the CG. With an empty full tank
Old 02-25-2016, 01:44 PM
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radfordc
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As a rule of thumb you should see about 15-20% of the weight on the tailwheel. If you find it varies much from that you may have a CG problem or have the main gear out of optimum position. Here is an example: my FMS P-51 with 3300 battery weighs 2605 grams and has 458 grams on the tailwheel. This is 17.5%. If I put in a much larger battery the CG would go forward and the weight on the tail would be less. Vice versa for a much smaller battery...the CG would be aft and the weight on the tail would increase.
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Old 02-26-2016, 11:42 AM
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Lone Star Charles
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Originally Posted by radfordc View Post
As a rule of thumb you should see about 15-20% of the weight on the tailwheel.
Is that with the airplane level, or is it with the tailwheel on the ground? Where did you find the rule you cited?

Thanks
Charles
Old 02-26-2016, 01:12 PM
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JollyPopper
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OK, guys, let me clarify this thread a bit. I am not attempting to set up an airplane. We have another member running a thread concurrently to this one in which he is attempting to determine what size engine to run on an airplane. He has an old Stick that weighs over eight pounds and he has to put 12 ounces of weight in the nose to get the CG in the correct place. Well, eight pounds seems way too heavy for a .40 size Stick with a 58 inch wingspan. With his having to add 3/4 lb. of weight to the nose, I was assuming it was tail heavy so I was attempting to find out just how much weight was actually on the tail wheel. I'm GUESSING that it should not be over 20% of the total weight of the plane which in this case would be about 1.6 lbs IF 20% is a valid number. Then I find out it is a tricycle gear. Blew my thought process all to hell. It still seems to me that there should be a range of total weight that should be on a tail wheel.
Old 02-26-2016, 02:27 PM
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radfordc
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Originally Posted by Lone Star Charles View Post
Is that with the airplane level, or is it with the tailwheel on the ground? Where did you find the rule you cited?

Thanks
Charles
It's with the tailwheel on the ground just as shown in the pic of the FMS P-51. I doubt it's "cited" anywhere since it's not really a factor that you should need to worry about. It's just my observation.
Old 02-26-2016, 08:20 PM
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jester_s1
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It doesn't really matter how much weight is on the tailwheel as long as there is some. The CG is set by measuring the wing's mean aerodynamic chord and locating it in the right place there as verified by flight testing. Then the main gear position is set based on the ground handling characteristics.
Old 02-27-2016, 06:25 AM
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He probably has bigger worries than how much weight is on the tail wheel. Based on the numbers you provide, and an assumption of a 12" wing chord, the wing loading is 26 oz/sq.ft. That is one heavy stick! With that high wing loading it is going to fly like rock.

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