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Author Topic: Dawn Patrol: Majestyk, Square Eagle flying/warping/crashing fun  (Read 686 times)
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Victor
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« on: January 16, 2012, 01:07:01 PM »

I've been out flying my two P-30s, a Majestyk and a Square Eagle.  I was having problems with the Square Eagle, it stopped climbing, and even on the burst, would just do low circles, and fly into the ground with winds remaining.  Remembering reading something from the FFQ Coupe Survey, Andrew Longhurst talking about a "dreaded flat first circle", which he attributed to wash in on the left wing (when flying in right circles) I went home and checked, and sure enough, the left wing outer panel had definite raised leading edge, which got worse the longer I flew.  I blame myself for this problem, as I used the wrong sticks in the outer panels, and the wing is too bendy, plus it looks like the original bad warp, when I first built it, has come back, so I'll remake the wing.

I do all my flying lately at dawn, both in order to have the whole sportsplex field to myself (otherwise filled with soccer players) and to hopefully have still wind and no thermals, to avoid losing models in the relatively small field (about 800 x 800 feet, surrounded by tall trees).  I've fished the Majestyk out of trees twice.  Anyways, it is usually below freezing, like this morning, with frost, and the tissue always loosens up; then tightens up once back inside.  I'm wondering if that is causing problems, as each model sees this repeated every time I take them out to fly.

This morning, the Majestyk was acting squirrely, instead of so nicely like it originally was.  It was acting skittish, and even a tiny little breeze seemed to make it tippy, sometimes swooping in a long recovery from a stall, and not flying in the typical smooth, clock-like circles.  I noticed that the left outer wing panel was significantly warping the trailing edge up; the whole TE on the left panel was cupping, and the tip was especially cupped up, which would be severe wash out, right?  Anyways, on the third flight, it did something that it had never even seemed to have the tendency to do, it did a left wingover and went straight down vertical into the ground.  Surprisingly, it only broke two longerons and the fin popped off.    Some pics of the warps and damage.
 
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Dawn Patrol: Majestyk, Square Eagle flying/warping/crashing fun
Dawn Patrol: Majestyk, Square Eagle flying/warping/crashing fun
Dawn Patrol: Majestyk, Square Eagle flying/warping/crashing fun
Dawn Patrol: Majestyk, Square Eagle flying/warping/crashing fun
Dawn Patrol: Majestyk, Square Eagle flying/warping/crashing fun
Dawn Patrol: Majestyk, Square Eagle flying/warping/crashing fun
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Victor
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« Reply #1 on: January 16, 2012, 01:16:43 PM »

You can see the Majestyk had an earlier repair, where I broke one longeron while holding in the cold with numb fingers, and squeezed too hard.  So I had installed a couple lightweight 3/32 panels to stiffen it up, plus added a couple extra sticks, like Bargle suggested.  As delicate as the fuselage seems to be, from the aspect of crushing it while holding it, it proved to be surprisingly strong to survive the straight down dive into frozen ground with only a couple crunched longerons, and no damage to the wing or stab.  An easy repair.

In trying to understand the Majestyk's erratic flying, I did notice that the CG had moved slightly rearward, from my earlier repairs, so it wasn't at 65 percent as the plan suggested; probably around 70 percent chord.  So between the left wing panel TE warp, and the slightly more rearward CG, does either one, or both, explain the left wingover during a right circle (it appeared to happen when it circled into facing the wind; as it turned into the wind, it did the sharp left wingover, then dove straight down without any attempt to pull out of the dive).

Victor
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crashcaley
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« Reply #2 on: February 12, 2012, 06:13:07 PM »

Hi Victor,  Just found your new thread.  Neat that you can sneak in a few flights before the place is innundated with the kids.
  I'm not sure what you meant by cupping TE.  I think you mean that it had the center is bending down.  I'm not sure, but are you sanding the TE along the grain when you are shaping it?  If you are, that will cause the TE wood to curl.  You should sand across the grain.  What I do is find a wire that is the same height as the front of the TE, and find another wire that is the thickness that I want the rear of the TE to be.  I then just sand away across the grain until the sanding block scrapes the tops of the wires
  Another thing you might try is keeping a wing panel you just doped, pinned down for a day or so.  Even nitrate dope, if I am not mistaken, shrinks a little after things feel dry to the touch.
  I set up my warps with shims under the areas to lift up.  I use balsa that is wrapped in scotch tape, so things don't stick once the wing surface is doped.  Make sure you place a couple of other shims along the length of the wing TE to keep that propped up also.  I have quite a few thicknesses set up for that.  I found out once that the TE can bow if you only prop up the wingtip TE.  Bow down just as you described.
  Anyway, great to hear you having a lot of flying.  Hope you can keep the tree retrievals down, though I'd sweat those trees know when a model is near, and reach out and grab them.   Grin  Caley
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What's stall speed?  Undecided
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« Reply #3 on: February 20, 2012, 01:27:33 AM »

From what you have described Victor in terms of warps – it’s highly likely that they and the aft Cg caused your wing over.

I have only had a little experience with some over powered Squirrel’s and I can reproduce your problem readily by using too much washout in the left wing.

It’s the difference in the washout that can lead to problems. Excessive washout on the left wing would be dangerous as it would combine with the motor torque to roll the model to the left.  A very likely scenario with low pitch stability from a CG too far aft and dihedral a little on the low side, a wing over leading to a spiral dive would develop.

As this is a well proven design I’m sure you will regain the performance by returning the warps back to the original settings, following Caley’s good advice.

Perhaps on your next project it would be worth considering Mylar/tissue as this would give much better moisture protection,

John
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Victor
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« Reply #4 on: February 20, 2012, 10:10:17 PM »

Thanks Ozpaf, and Caley
Yes, it was behaving quite nicely when I first built it, but it looks like the cycling of dampness/dryness allowed some warps.  I definitely want to learn to do the tissue over mylar, at least for the wing and the stab.  I was planning on trying that for my next effort with a Square Eagle (I bought another kit after Christmas, I want to make one with some lightening holes in the fuse sides, and the tissue/mylar); I have another wing I want to experiment with, that I'll put on my current wingless Square Eagle.  I have an ON28 wing that I've stretched out to 30 inches, and I was planning on putting that one on the SE body.

Another thing, I'll start leaving the wings and stab held down for a few days after I dope them, instead of taking them in a few hours after they dry.  It sounds like the dope slowly shrinks a little bit more over the course of a few days.

Yes Caley, trees are sentient, at least when it comes to kites, model rockets, and model airplanes; it is quite uncanny.

Victor
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