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Old Jul 03, 2008, 11:02 PM
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erich's Avatar
Holden , Massachusettes
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Ritz

After letting the rudder/stab joint cure for a day or so, took a good look at it. Had my doubts about gluing 2 fairly big pieces of wood, with such small contact area. The joint seems pretty solid however, even tried to pull it apart a little, but it held fast. So am using a similar method to add the 2nd rudder. After some doubts on how to do this, came up with a fairly simple solution. Before gluing, measured tip to tip from each rudder (top and bottom) to make sure they were perfectly parallel.

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Old Jul 04, 2008, 11:20 AM
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Holden , Massachusettes
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The kit came with 1/32" mw to be used for the wing mounts. Decided to try a wooden version, which I have seen at some indoor flyins. Made a U-channel with 1/8" balsa and mounted wing posts for LE and TE onto top of the channel. Streamlined the 3/16" sq. balsa, wing posts a little. Left about 1/4" of space in front and to the rear of the posts, so small rubber bands could be used to hold channel in place. Not sure if I saved any weight by not using the wire wing posts, but to me, it'll look better.

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Old Jul 04, 2008, 12:09 PM
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carbondale il
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Hi erich,
That's pretty much what I did for the SO. That way the CG can be found without having to add weight to the nose or tail just by sliding the wing post forward or backward. I use two small rubber bands. And the wing and post assembly can be removed easyly. Make sure you get the rubber bands on the motor stick before you add the prop and stab if these are permanently attached to the motor stick and tail boom. Maybe later I'll make a plane based on this SO design and because I'll know where to balance I can make the wing posts without using the rubber bands and extra weight. BTW, it was B Matthews who turned me on to this technique.
Kevin
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Old Jul 04, 2008, 09:57 PM
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The prop is a screw in type. But will probably still keep the rubber bands on the fuselage. Good tip. Yea, I've gotten a few good tips from BMatt....too. The man seems to know what he's doing...at least I hope he does!

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Old Jul 04, 2008, 10:06 PM
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Holden , Massachusettes
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Ritz

Ok...so this is my idea of how to attach the wing to wing posts. Didn't want to just rely on a butt joint where post meets wing so made these little tear-shaped cuffs to reinforce the posts. The 4 little square cleats are where diagonal braces from the posts to wing will be anchored. Added all these pieces before I started covering wing, that's why no tissue in photo of center section.

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Old Jul 05, 2008, 11:42 AM
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Holden , Massachusettes
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Tail section of this plane is finished. The thing came out heavier then I wanted, so did quite a bit of planing and sanding on the tail boom, which, was, by far the heaviest piece of wood in the tail group. Should have sanded the rudders a lot thinner, before gluing them on. To late now. All in all it looks pretty good. Now if I can just finish this.....@#$%^&* ....doping on of the tissue, I'd have a plane, that I could at least, try to fly.

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Old Jul 05, 2008, 03:01 PM
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carbondale il
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Hi erich,
There was no wind so I took the SO plane out to fly. With one loop of 1/8" it wouldn't do much. I tried two loops and moved the wing forward to the maximum position. It flew for only ten seconds. The 9 1/2" Ikara wide blade just didn't turn fast enough. I'm going to try the recommended 9 1/2" plastic Peck cut to 20cm and shaved. It looks like I'm going to have to add weight to the tail to balance. Anyway, I'm going to have to redo the thrust bearing assembly. I made the motor stick a little long in anticipation of this. Well, when there's "no wind" there is still a little bit flying in such a large field I have access to, at least the plane didn't get blown apart this time.
Kevin
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Old Jul 05, 2008, 05:59 PM
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Holden , Massachusettes
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You got lucky, again. Instead of adding weight to tail, can't you just move wing back a little? Pretty rare to get a totally windless day. Need a weather inversion to get a real no winder. Round here we've been getting thunderstorms almost daily. Good for the crops, not so good for aviation...

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Old Jul 05, 2008, 08:33 PM
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Holden , Massachusettes
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Took the slightly less then fatal, plunge, and started covering the rest of the wing. Don't know whether it's sanity or insanity, that's prevailed, BUT have started to cover 2nd wing tip using ...ye olde dope' ...method. Decided to forgo the glue stick. Applied 2 coats of the straight Sig nitrate to bottom of wing. Then added tissue using the 50/50 mix. Still took a lot of massaging to get tissue to stick. But finally got the bottom covered. This time trimmed it flush with edge of LE and TE. No overlap onto top of wing. Will give this a chance to cure some, before doing the top.

Ok have waited a day. The top went on a little faster. Either I'm (already) getting a little better at this, or the tops are easier then the bottoms. Anyway the right wing tip is now covered. Hallelujah!

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Old Jul 05, 2008, 09:18 PM
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erich, Moving the wing back does just the opposite, doesn't it? If the CG is at a given point?
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Old Jul 05, 2008, 11:38 PM
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I don't think so. The cg is actually more related to the wing then to a point on the fuselage. So moving the wing back WILL be like adding weight to the tail. In making indoor models the method of marking the balance point on the fuselage and then mounting the wing in relation to that point is just a method of balancing the plane without the use of weights. The actual CG is as I say related to the wing as in 50% of chord or so. A good way to check that the CG is right for a particular plane is to just do some practice glides. When the plane flies ahead without stalling or diving tendencies, the CG is about right. In other words just move the wing back and forth till you get the glide you want. This has to be done with the planes full flying weight.

Pretty sure I'm right about this. If someone knows this to be false please chime in and correct me.

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Old Jul 06, 2008, 10:03 AM
is it flying time?
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Wyandotte Oklahoma
Joined Oct 2004
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Erich,

Sorry, Kevin has it correct. The CG is based off of the overall airframe and the wing needs to be moved forward to move the CG towards the tail.

Jerry
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Old Jul 06, 2008, 10:46 AM
Manassas, VA
Joined Dec 2005
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I think of it this way. The ideal cg for any a/c and incidence configuration is a point located on the wing. So moving the wing back actually increases the moment of the nose so shifts the cg forward on the wing. Moving the wing forward shifts the moment of the tail and the cg moves back. Just think of it in the extreme positions of the wing. Make sense or am I all wet?
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Old Jul 06, 2008, 10:53 AM
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Holden , Massachusettes
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Will have to give it a try...... but thinking it over, I believe you and Kevin may be right.
If so I stand corrected. Thanks Jerry.

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Old Jul 06, 2008, 11:50 AM
slow but inefficient
Ron Williams's Avatar
Riverhead NY USA
Joined Dec 2000
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Actually, when you move the wing you're moving the center of pressure relative to the C.G. The center of pressure is where all the forces provided by the flying surfaces (wing and horizontal tail) are in balance. Wing goes back, C.G. goes forward and vice versa but what's important is to have the C.P. in the right position relative to the C.G.

The difference between the two is the Critical (or Constant) Margin of Stability (CMOS). C.G. too far behind the C.P. and you have tail heavy and erratic flight, instability that can be quickly over come but difficult to keep up with. C.G. too far ahead of the C.P. and you have a tendency to dive that must be overcome by manipulating the flying surfaces - more instability which takes longer to overcome. When the C.G. and the C.P. are in the same place the plane is said to be neutrally stable but practically, it can be a handful. For most freeflight planes, the best situation is to have the C.G. slightly behind the C.P. (hmmm, is that right?).
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