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Author Topic: Airfoiled Stabes, good idea or no?  (Read 654 times)
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50+AirYears
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« on: July 06, 2010, 01:33:57 AM »

I also asked this on the catapault launch forum, but thought I'd also ask this in the HLG forum, just to make sure I get the max exposure.

When I started building gliders back in grade school, I got the idea it'd be good to sand an airfoil into the stab. I've been doing this since the late 50s. I've also normally had a problem with the glider going over into a dive after reaching the top of the climb, and often taking most or even all of the altitude from the launch. At 66 years, I can't really afford to lose this altitude. Could the lifting airfoil be trying to push the nose down, until enough speed bleeds off, and the glider enters normal flight? Should I stop sanding an airfoil, and just round the stab edges, even in the 1/32" balsa I often use?
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« Reply #1 on: July 06, 2010, 06:03:05 AM »

At launch speed, the stab may be "lifting". As the speed bleeds off in the glide the model may settle in.
IMHO, I would stop the airfoiling and go with rounded edges.

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Tmat
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« Reply #2 on: July 06, 2010, 08:20:11 AM »

Basically, I agree with Duco. But it depends on the thickness of the stab. With small gliders using 1/32" tail surfaces rounded leading edges should be sufficient. With larger gliders using 1/16" balsa I sand a tapered wedge-like airfoil (see the catapult glider response) with rounded leading edges.

Both hand launch gliders and catapult gliders tend to suffer from the behavior that you describe. It is part of the nature of having fixed surface models that have to very different flight regime speeds. Thus in order to control the climb, the glider has very little decalage and will have a very small Static Stability Margin. Some other solutions are to increase the stab area a bit, or increase the tail moment arm or add a small amount of decalage (with a CG shift forward) and trim for a bit more of a spiral climb.

Or switch to tip launch gliders where you can use much more decalage and thus enjoy greater glide stability.


Tony
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« Reply #3 on: July 06, 2010, 03:50:28 PM »

Thanks for the suggestions. I'm currently rebuilding a Graupner Mini with a Spruce/CF Tube fuse instead of all wood. (the original spruce fuse started rebreaking old breaks!) I think I'll replace the stab which I'd previously airfoiled with a 1/32" with rounded edges. Maybe save some need for nose weight. The stab from the Graupner kit reminds me of old Sterling kits. It's balsa, but almost hard enough to use for a firewall for an .010. For that matter, I've used softer sheet wings on 1/2A CL planes.

I've got a Blue Ridge Super Chuck in the Queue. I think for that one, I'll try the wedge airfoil.  Seems to me that would also give me some decalage to help with the pull out. About the only time I've ever used decalage in a small glider was either with a Phillip's entry on the wings, or once on an old nostalgia that had almost 2 degrees built in. That one looped like my old Walker 74 gliders.

I've also been trying the tip launch with my Graupner slipper. Don't know if it's my age, or the Slipper's 22" wing is too small, but I've so far only managed one decent launch, and 4 repair sessions. At least I got to see a few clips on You-Tube showing several different techniques. I might look into building the Sweepette 3D from FM for a larger tip launch glider. Don't want to give up gliders until my shoulder disintegrates from abuse, and I want to delay that as long as possible.
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« Reply #4 on: July 06, 2010, 05:09:04 PM »

Is your Slipper the DL version? Graupner has the standard Slipper and the Slipper DL with the + tail (their version/interpretation of discus launch) which I've been meaning to obtain out of plain curiosity - they're WAY too heavy in stock form, as you found out.
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« Reply #5 on: July 06, 2010, 05:11:19 PM »

I'd say that a proper tip launch glider (Lee's Sweepette 28 or 36D, TimB "turn-up" and any of Stan B's designs) will extend the life of your shoulder and allow you to throw pain free for years to come. The slipper is not a proper glider. It's a toy imo. I'd really recommend one of Stan B's Dynomite kits as a can't miss TLG that will work for you.

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« Reply #6 on: July 06, 2010, 05:35:43 PM »

It's the Slipper HLG. Sometimes does a nice axial roll right after a tip release.  Haven't had an H-L catalogue for a couple years, since before the DLG was available. Definitely heavy. Heavier than the Flashes I used to make, probably the best design I ever built. Great flyers during early trim flights, lost quite a few of them to thermals, except during contests. The good ones fly away, the not-so-good stay with you. The Graupner gliders would make good templates for future construction using contest balsa. Good thing before I was laid off, I made lots of use of the workout room my employer had. One of the torture devices adapted quite well for my throwing motion. Also, I learned 20 years ago that a certain amount of stretching was needed before chucking them. That's now about 10 minutes before the first throw, and a minute or two after each. Also do some shoulder stretches just before each toss.

Boy, seems I'm adding planes to my to-do list faster than I can build them off it. If I keep trying to build at this rate, I won't have any time to fly- - or store the new planes.
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« Reply #7 on: July 06, 2010, 09:39:24 PM »

>SNIP<

Boy, seems I'm adding planes to my to-do list faster than I can build them off it. If I keep trying to build at this rate, I won't have any time to fly- - or store the new planes.

I'm already PAST that point! Grin Cheesy
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« Reply #8 on: July 07, 2010, 01:55:02 AM »

Actually, I did have a good flying day at my club field Sunday. 2 RC flights, 16 HLG and CLG flights, one rubber power. It was so hot,peaking at 95 degrees, 12 mph winds, nobody else out there put up more than one flight. That's how I happen to have a Graupner Mini wing needing a new fuse. My scale says the old kit stab weighed 3.2 grams, the new one from contest balsa is just barely 1. I think the finished Mini was about 1.6 ounces.

So far this year, I've logged (I do keep a log) at least 92 flights, mostly glider, but also rubber, cl, and rc,

I'm in to my 20th year of All Weather flying. And that ain't easy on the Sunny Southern Shore of Lake Erie.
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« Reply #9 on: July 07, 2010, 09:56:42 PM »

Finished the recycled Mini. Here's a picture. Gotten to the point on trim flights where the park across the street is too small. Going to have to take it out to the college or RC field for final trim. Ended up 1 3/8 ounces (38 gm). I think the original mini was closer to 1 5/8 ounce. While I was weighing it, I figured I'd weigh my other gliders as well. Some sound unbelievably light, and I wonder how I've been able to throw the Slipper without hurting myself.

Slipper (kit), 2 1/8 ounce, 60 gm. Thermic 18, scratch, 3/8 ounce, 12 gm. Thermic 18, Scratch, 1/2 ounce, 14 gm. Straight up, kit cat, campbell, 3/4 ounce, 20 gm. Cat A Piglet, Campbell Kit, 3/4 ounce, 20 gm.
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