Ahh.  That's better.

I lost my old bender.  Dangit.  So I made a new one.  This one is better because I made the other one without the flat, and it'd rotate around in the vice.  A really cool one would be hexagonal -- but I don't have any hexagonal stock in my stash, and I ain't gonna make any!

like Steve aid - you need to add a bit of structure to take the landing load.  Ply 1/2 ribs on each end of the gear block, and some 1/16th vertical grain shear webs front and back to box the area directly below the gear legs will give it much more resistance to bending / rotational loading when you come in a bit hot and the grass is dragging hard on the wheels / gear.

Just a box made of sheet balsa that tie the gear blocks to both upper and lower spars, and ply 1/2 ribs to strengthen the ribs where the blocks are anchored.

Tim...You're putting in more than two of those half-ribs, right? Two per side is marginal, three per side is a good thing for a rough field, esp. with mole holes.  Steve

and fuse mounted gear is even better yet,, the twister wing is a marvel of resilience,, it can take a lot of abuse and be easily repaired,, but poking gear legs through the center section sheeting is one of those fatal things for the wing,, IMHO,,

I've been seduced by the notion of trike gear, and by the fact that I've only suffered from one pilot-induced crash this entire year, and only four overall (all, by the way, over the asphalt at Delta Park -- that place is cursed).

If the wing does sustain damage from the gear, it's most likely going to be the wheels poking through the covering and perhaps breaking the lower spars in a pancake landing.  I'm pretty sure that the center section/gear assembly is now stout enough that anything that takes it out would have taken out most of the plane anyway.

I could do fuselage-mounted trike gear, but it'd have to reach way back from the front of the wing to the correct wheel location.

Simple cure for gear puncturing the wing, is to leave it off.      Besides look how more ground clearance you have then. 

Wing tips help.

I'm not sure if you're pulling my leg or not -- the Twister calls out 1/8" lite-ply plates, so in using 3/16" balsa I'm doing both a weight and aesthetic upgrade.

 I used 1" tips on both of mine, made covering easier yet.

 Walter

IIRC, the original Fancherized Twister utilized much thicker wingtips...maybe 1/2"--but were still flat with rounded corners "consistent with" the original.  I believe there was a picture in the Model Aviation Columns of the wingtip undergoing covering with monokote.  The edges of the wingtip block had been modestly rounded--maybe a 1/16" or so radius all the way round.  Then the flat "tip" was covered with one small piece of monokote ironed "around" the corners and then trimmed with a razor blade with just 1/8" or so on the flat "airfoil" edge.  This allowed the main covering to be applied to the "airfoil" edge of the tip with just a tiny overlap with the previously applied "tip" covering.   The main surface covering was then trimmed neatly "even with" the very end of the wing.  That left maybe 1/8" or so of overlap with that tip radiused piece. A hot iron gradually moved around the radiused tip left a nearly undetectable joint between the two but was permanently adhered.

This was a much easier and more elegant solution to attempting to cover the end of the tips with the same piece used for the top or bottom of the panel.  I can't even imagine trying to do it that way!

Ted

p.s.  I just verified that there are pictures of the process in the second of the three columns dedicated to the "FT".  It was in the August, September and October 1987 ('87!!!!) issues of Model Aviation and should be viewable on the AMA website.

Tim,

Twister is looking good, I'll be starting on mine next month, looks like fun, I'm about 2/3rds of the way through my Voodoo build, I'm having a riot with this build, just building it for fun, not worrying about being to fancy, just a decent fun flyer. Can't wait to start on my Fanched Twister.


Jim Hayes
AMA 988835

I love watching a plane get over engineered.

Stab.  Yes, I should just whack it out of 3/16".  No, I ain't gonna.  This is probably going to weigh about the same, but it should be loads more rigid in torsion.

    Unless you cover it with plywood, I don't think so. The diagonal "ribs" only help in the fore/aft direction, not up/down or torsion.

I mostly agree with you on the ribs not helping in the up/down direction -- that strength depends mostly on the spars.  If the ribs were chordwise they wouldn't contribute at all -- but if you bow the stab downward at the tip, all the fibers in the tops of the ribs will be in tension, and all the fibers in the bottoms of the ribs will be in compression.  I don't think they contribute to any significant degree, however.  But, ignoring the ribs, the stiffness (not breaking strength) of a beam goes as thickness cubed, and the surface is twice as thick (3/8 vs. 3/16).  So if you ignore the leading edge, the trailing edge alone is eight times as stiff per unit of chordwise depth, which means that they're as stiff up and down as a slab of 3/16" material with a 3" chord. 

Ignoring the material that's going to get beveled off for hinging.  And unless I flubbed my math.

As far as the ribs helping in torsion -- they do.  Honest.  After trying to think my way through your comment without writing anything down I'm a lot less sure just how much they participate, or if my "more stiffer" comment holds, but if you fix the center of the stab and twist a tip, the fibers in the tops and bottoms of the ribs will be put in tension or compression; this will resist torsion on the stabilizer.  My gut feel is that it'll contribute at least as much torsional stiffness as the spar(s), but I couldn't prove that without doing a bunch of math, and if you took into account the fact that wood is an anisotropic material that's stiffer along the grain than it is across it, the ribs are going to look a lot better if you take that anisotropy into account than if you don't -- and I'm not that much of a structures guy.

Tim, how thick is the stabalizer of the "KISS!"? I know the ribs are diagonal, and since the covering has been baggy and loose for a few years now, you should be able to get a read on the torsional stiffness of it and use that as a reference.  Steve

It's about 1/4" thick, and checking is a good idea.

You are going to video this machines first flight, aren't you?

Make the nose an inch longer than the Blue Meanie!  Steve

Tim, I'm not sure if the aft end is hollow or not, and also not sure if it's 1/64" or 1/32" plywood. Ask Mike! When you build the 'hollow' fuselage, do NOT use any sort of white glue or other water based glue, 'cause it'll warp. CA or epoxy is good. FWIW, I built a CG Buster for NW Sport Race with 1/64" ply on the sides of the kit 1/2" balsa...like an oak plank in stiffness. Maybe overkill for a stunt model? The tail surfaces didn't vibrate at all, even with the Fox .35 wound up tight on a 9-6.  Steve 

Tail feathers put aside, even if I don't have them hinged yet.

Steve, when you recommend not using water based glue on a hollow fuselage, I assume that was from grim experience.  How did you clamp the fuse up?  On a board with plenty of weights, "in the air" or what?  My two experiences with this have been positive -- but then, I do this by gluing it all up, then stacking every available heavy thing I have on top and leaving it alone for a day or two.

Fuselage sorta-started.  At least the plans are slapped down.  Aesthetic changes have been made in honor of Bob Hunt's 1976 Nationals win (and it makes the build easier, too).  I'll be using a 1/2" framework with 3/32" sides -- that pencils out to being just as stiff as a solid 1/2" fuselage, although more susceptible to breakage.

Yes, I'm going to make Salem.

I'm not sure if it's clear from the foreshortened and sideways plan, but the last three or four inches of the fuselage -- following the plan of the Genesis -- are behind the elevator hinge line.  So I was kind of thinking of them as "fin", and scheming on ways of taking structure out, perhaps by shortening the actual fuselage laminate and replacing the back end with sheet.

Lots of structure around the stab mount has to be a good idea, though.

Remember, Tim, that fuselage design will really emphasize square maneuvers.  The hard straight lines really show "flat" areas of the pattern.  The rounds may not present as well as another shape, but the experts can overcome it.  Just make sure you work on those squares!

BIG Bear
RNMM/AMM

Richard:

I don't have a Ford Adjuster -- my hammers top out at two or three pounds.  But then, three out of four of the derelict vehicles on my property are GM, while only one out of three of the working ones are GM.

Bill:

I know -- Dick Mathis discusses fuselage shape and it's effect on judges perceptions in his book "How to Fly U-Control".  He sings the praises of a soft, swoopy fuselage shape to make mistakes on the straight lines less obtrusive.  To further his point, he has a very Mathis-ish drawing of a Chizzler on the same page.

So I built exactly the wrong thing for my skill level.  But that shape's been riding me for the last 25 years (since the August 1977 Flying Models, as a matter of fact), and I'm going to get it out of my system!

If I really wanted a fuselage shape to cover all of the flying sins at my skill level, it would have to look like this, but I ain't gonna build it:

I'm out of harf-inch balsa!  Egad!

I'm laminating the left side nose cheek (ply & two sheets of 1/4") separately.  Then tomorrow when it's all set up I'll carve & sand it to a nice looong taper so it meets the fuselage smoothly, as Mike Haverly taught me (by the simple expedient of building the Kiss some time ago).

I like house jacks.  Not only can you jack up houses with them, but they make half of a nice clamp (with the Earth being the other half).

Yup.  I was wishing for some cast-iron "bricks".  Maybe I should make some cement weights with handles for this kinda stuff.

In order: Some spacers to go through all the layers on non-maple between the motor and the mount, the nose mocked up ready for gluing and, the airplane mocked up for the Very First Time.

If this flies like utter crap I'm really not going to be happy with myself.