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General control line discussion => Open Forum => Topic started by: Tim Wescott on January 30, 2011, 05:33:52 PM
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I'm putting the finishing touches on my Buckized Skyray, trying to figure out how long to make the tailwheel strut, and whether I need to make it adjustable.
I suspect I'm going to want to experiment with the stance no matter what, so I think I'll just plan on adjustments (probably with pliers -- this _is_ a Skyray, and one that I can't claim BOM credit for). So what's the tallest I'll ever want the tail?
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I wouldnt want to have it longer than when the model is sitting on the ground with the main wheels in standard position the bottom of the fuse is level ( Horizontal ) to the ground. Even that is VERY high.
I like to have it on a slight angle upward but not a 45 o Slant. Just experiment with chockin the rear up until it " sits " and looks right.
Not a big fan of little stubby tailwheels..
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Tim...Make the TW strut of a useful sized wire. Too flexible, the launcher person can't feel whether or not he/she's pushing down on the tail strut or not. If the launcher is pushing down, the model will have a good chance of nosing over when released. That's not good.
If you're flying off a stooge, flex won't matter, but don't rely on the TW strut to anchor the plane. Dan used to run a hunk of leadout cable for redundancy, but I'm not sure he still does this. If you make it of 2mm+ wire, and the mounting is very stout, you probably don't need to. However, the actual axle should not be on the main wire, but bound and soldered to the main wire. Not everybody can pull off that sort of solder joint, but if the tailwheel goes wonky, it's not a huge deal. Sta-Brite low temp silver solder is a good bet, if you use their flux and a torch. Having the stooge wire come loose can be dangerous, as you might expect, and the K&S music wire in the LHS is pretty much junk. I've read that the reason is that it's not drawn through the die a second time, so indicated by the dull finish, but I don't know if that's fact or fiction. D>K Steve
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Set'er up 'bout like so, giv'er take just a smidge...
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Tim,
You probably get sick of listening to me talk about the Center of Gravity but, nonetheless........
Much more important than the length of the tailwheel wire is where the main gear wheels touch the ground with respect to the CG. This is yet another reason for having a really close idea where the optimum CG will be when you're laying out the model.
If you work hard to make sure the wheels touch the ground (not the axle, the actual point of contact of the wheels to the hard surface) is located 15 degrees forward of the CG you can make the tail wheel any height you want because you'll be able to touchdown on the main gear and pretty much be able to expect the airplane to scoot right along the ground in a perfect wheel landing. This is how those big semi-scale ships which sit very nose high on all three gear are still able to make 40 point takeoffs and landings. This "secret" was graciously provided by Wild Bill Netzeband shortly after he taught the Wright Brothers how to fly in circles.
The number 15 is pretty much magic for any halfway decent surface, concrete or closely mown grass. If you routinely fly off of long or "grabby" grass you might want to fudge forward just a few degrees to account for the grass grabbing the wheels. The best protection against that problem I learned from Bob Baron at the 1982 WCs in Sweden where our practice field was genetically similar to a hay field. Bob replaced his ~two inch wheels with a pair of three inch Williams Bros "skinny" wheels which did a fine job of cutting through the hay without altering the landing gear itself. After seeing his success with them I've never used any wheel remotely "chubby" on my main gear and almost never have a real problem flying off even shoddy surfaces
Once you've located the main gear wheels appropriately you can adjust the tail wheel height to suit your fancy (or to provide prop clearance for takeoffs).
Ted Fancher
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Agreed, good points and great info Ted. Just depends how picky one wants to get.
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Thanks Ted. That makes a lot of sense.
Actually the grass at the field I fly is in good shape -- it's the ground that resembles a wartime airfield after a bombing raid. We're working on that...
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Mine is wire with a loop on the end for a stooge.
Works great.
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Mine is wire with a loop on the end for a stooge.
Works great.
OK, Brother, where's that snazzy NAVY paint scheme??????
;D
Big Bear
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Tim....if you come to Tulip Flying Field....you'll want a short stubby tailwheel! LL~ When taking off from the "Tulip Tundra", you'll appreciate a steep angle of attack, short take-offs and keeping your prop outta the grass will be pretty much the order of the day. If you have a shiney marble floor to take off from, then hey....taxi that pretty plane for all you're worth! ;D
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If you work hard to make sure the wheels touch the ground (not the axle, the actual point of contact of the wheels to the hard surface) is located 15 degrees forward of the CG you can make the tail wheel any height you want because you'll be able to touchdown on the main gear and pretty much be able to expect the airplane to scoot right along the ground in a perfect wheel landing.
Is there some serious drawback in having the wheels further forward? I can see having the wheels too far back is not good.
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OK, Brother, where's that snazzy NAVY paint scheme??????
;D
Big Bear
Well Big Bear I found out what it was going to cost and went the cheap route. I just put some checker board trim on the tail and wing tips. Did not want to dump a bunch of $$$ into it
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Is there some serious drawback in having the wheels further forward? I can see having the wheels too far back is not good.
The farther forward the wheels are the more likely it is for the plane to bounce and to ground loop. With wheels right at the CG the start of every landing would be perfect -- only later, when the plane nosed over and scraped its spinner on the pavement, would every landing be embarrassing.
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Is there some serious drawback in having the wheels further forward? I can see having the wheels too far back is not good.
Bouncing on landing - hit the ground, it noses the airplane up, and it takes off again.
Brett
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Bouncing on landing - hit the ground, it noses the airplane up, and it takes off again.
If you've ever flown one of those old-timer freeflight cabin models converted to RC you'll know this in spades. Those things put the wheels right under the prop to give the plane the best chance at an uncontrolled landing, and it is exceedingly difficult to come to a smooth landing with one of them -- particularly since, as soon as the thing is no longer flying, it'll ground loop!