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Old Feb 28, 2008, 01:54 PM
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Simple tip from the 2 ch pilots

Quote:
Originally Posted by rdeis
Hmm.. Actually yes, I think. The longer tail moment arm does make the airplane less sensitive to CG.

I still think, though, that the most desirable handling qualities for very light air are quite different than the ones you want in heavy air. CG's just one of the tools that you'd use to reconfigure. Ballast is another.
Ballast is prime! Mass increases airspeed, airspeed damps CG deltas. Maintaining CG location, and increasing mass just regulates the model's handling characteristics.
Every time you shift CG, you end up flying a new machine.
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Old Feb 28, 2008, 02:30 PM
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Ah! Now we're on the same page! Just different strokes, as you said.

I'll move CG just a little to get off the hairy edge of stability, then ballast if it's still difficult to handle. Depends on how strong and variable the winds are. I'll try ballast only next time I have the opportunity to experiment.
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Old Mar 01, 2008, 11:21 PM
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Just wanted you guys to know..... I got back into gliders about a month ago after being out of it for ten years. I wasn't worried about the highstart at all since I used to do it it all the time. But I read this thread a few days ago just killing time. I wasn't nervous until I felt the tension on the line. The only thought that kept going through my head was, "Well, I built this one and I can build another." I gave it a gentle throw and it went arrow-straight right up to the top of the line and then came loose beautifully! Sadly, there was no lift this afternoon by the time I got to fly and I came down like a space shuttle! But thanks for the tips on getting up there! They helped knock some of the rust off.

John Haas
(Hossfly72)
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Old Mar 01, 2008, 11:38 PM
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Welcome back to silent flight. May the lift be with you.
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Old Mar 02, 2008, 02:21 AM
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Suggestion:
Unless your glider is very light or you have a rotator cuff problem, throw hard. And straight forward. Otherwise, little gust hits, one tip stalls more than the other, and you're rolling and yawing like mad, close to the ground. If you throw hard you have airspeed right away, and therefore you have more control and a stall is less likely. If you've got a really good arm you can probably get away with throwing with the nose up some, but wait until you are back into it.

However, with a fairly small RES glider, the disaster scenario above may not occur for quite some time. Didn't with me.

Enjoy.
Quote:
Originally Posted by Hossfly72
Just wanted you guys to know..... I got back into gliders about a month ago after being out of it for ten years. I wasn't worried about the highstart at all since I used to do it it all the time. But I read this thread a few days ago just killing time. I wasn't nervous until I felt the tension on the line. The only thought that kept going through my head was, "Well, I built this one and I can build another." I gave it a gentle throw and it went arrow-straight right up to the top of the line and then came loose beautifully! Sadly, there was no lift this afternoon by the time I got to fly and I came down like a space shuttle! But thanks for the tips on getting up there! They helped knock some of the rust off.

John Haas
(Hossfly72)
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Old May 28, 2008, 05:45 PM
launch height can't fix stupid
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Anyone ever have the ring on the parachute spread over the tow hook, clamping it to the sailplane? Happened to me recently. Pulled the high start to where the sailplane was sitting, had a lot of tension on the line when I hooked up. Noticed I had a problem when I went to zoom and it didn't come off. Once on the ground it was obvious what the problem was. Scary way to try and fly a $1k airplane.
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Old May 28, 2008, 05:53 PM
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How many lbs of pull did it take to spread the ring?
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Old May 28, 2008, 10:37 PM
launch height can't fix stupid
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Had it near what I could pull back comfortably on a 1/2" tube. It was the cheaper split ring on the chute. Will be replacing with the heaviest duty one I can find and making sure that it hasn't split over the hook before letting go.
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Old May 28, 2008, 11:26 PM
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The other thing that can happen with a glider with a skinny nose is that the line can get over the nose. If you don't notice this before you launch, it probably won't come off until you land. So just fly in circles around the stake. Had this happen recently with the Ava. A bit scary, but I'd been there before so I knew what to do, though I did try to shake the high start off first.
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Old May 29, 2008, 01:17 AM
Guz
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Quote:
Originally Posted by corsha99
Anyone ever have the ring on the parachute spread over the tow hook, clamping it to the sailplane? Happened to me recently. Pulled the high start to where the sailplane was sitting, had a lot of tension on the line when I hooked up. Noticed I had a problem when I went to zoom and it didn't come off. Once on the ground it was obvious what the problem was. Scary way to try and fly a $1k airplane.
Been there, done that. It wasn't a $1K craft, but a stick build (my first), basically priceless to me.

Afterwards I've always soldered the split rings together. Used a propane torch and plumbers solder and flux. Put in a vise when soldering
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Old May 29, 2008, 07:09 AM
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I use solid, welded rings most of the time. I too have 1/2" tubing that can generate as much as 30 pounds of pull. That is too much to use with a split ring.
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Old May 29, 2008, 07:14 AM
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Just a tip on hi-start launching, make sure you have done a test glide first. Before any ship hits the hi-start of the winch, I make several hand glides to confirm balance and trim.

Not only will this give you more confidence for that first launch but it will catch things like a reversed rudder, wrong plane profile or that balance weight you forgot to put back after you "fixed" something.

If you have tall grass available, that is always the best place to do hand throws of a model you have never flown before.

I find this very helpful in confirming the elevator trim. If there is too much up, then it is going to want to pop-off on the hi-start launch. And if there is too much down it will either launch flat or try to dive. Neither is good.

So, before you winch it or hi-start it, hand trow it.
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Old May 29, 2008, 10:56 AM
launch height can't fix stupid
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I was trying to fly around in circles but the line got hung up on something, spun the sailplane around and I ended up "landing" upside down. To everyones surprise the only damage was a chunk out of the leading edge and a crease way out at the tip. Put some tape on it, a little CA on a few spots, and flew it again. This time made sure that the ring was on correctly.

Will solder up the rings and see how that works out. Thanks for the advice.
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Old Dec 14, 2008, 02:38 PM
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Going back to post #58...Knots weaken the tubing into which they are tied. A great deal is written about which knots weaken the most. Any angle, kink, or knot, stresses the tubing unevenly so the knot becomes a weak link in the hi-start. Although some knots are claimed to only weaken to about 80% of rated strength, other knots weaken to about 50%. And, as the tubing grows older, gets worn, or is damaged by sunlight or chemicals - expect considerably less strength. Yes, a knot may work as some have indicated, but a tubing repair that does not call for a knot, is well worth considering.
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Old Nov 02, 2009, 06:44 AM
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THE EFFECT OF CG ON HIGH-START LAUNCHING

Let me share an experinece I had yesterday to illustrate a point. And I am going to take you through my thought processes as I discovered and corrected the problem.

My main planes are a Supra and an AVA. I use these for contest flying in the Eastern Soaring League where I launch off winches. My Thermal Dancer has been relegated to a back-up plane position. I had not flown it in months, but I had it out yesterday. What I relate here was experienced on a winch, but it applies to HS launching as well. What we are giont to discuss is the impact of moving the CG.

Before I launched the plane, I did a hand throw. Seemed it needed a couple clicks of up to give me the glide I wanted. Having done that and completing a good range check, it was time to launch. Well I popped off 3 times in a row. Once I did get the plane in the air, it was flying very poorly. A dive test indicated the plane was nose heavy.

I have done several repairs to the nose and fuselage area of the Thermal Dancer over the time I have owned it. This has resulted in the plane becoming somewhat nose heavy. Since I have no removeable weight in the nose, I added 1/4 oz of lead to the tail over a year ago.

After some trial and error, I realized the tail weight was missing and added it back. I added 7 grams, about 1/4 oz, right in front of the verticle fin. This would be like taking about 3/4 to 1 oz of weight out of the nose. This sifted the CG back, giving my plane a much better balance. Several hand throws confirmed this and allowed me to adjust the elevator trim, removing several clicks of up trim. Now I was getting a nice smooth glide.

Now I was getting great launches and the plane was flying much better. WHY????

Because the plane was nose heavy, this CG was shifted forward, as compred to my normal CG. This effectively moves the hook position rearward in relation to the CG. I may have actually had the hook behind the CG. The further back the hook, relative to the CG, the more unstable the plane becomes on launch. Most people have the hook 3/8 to 1/8 inch in front of the CG. On my competition planes I have it right on the CG. But having it behind the CG makes for extremely difficult to control launches and a great tendency to pop-off.

By putting that weight on the tail, I effectively shifted the CG rearward. Now the hook was back in its proper position relative to the CG and the launches were as I expected them to be, straight, steep and high.

The second issue that comes up is that a nose heavy plane requires a lot of up elevator trim. That up trim on the elevator can become very effective at the speeds that a hi-start produces during the launch. This can lead to pop-offs. By shifting the CG back, I was able to remove some of that up trim, thus removing my tendancy to over rotate and pop-off.

I share these experiences because they apply equally to the hi-start and to the winch. The position of the hook, relative to the CG is critical to a smooth, high launch. If you change the CG of your plane, be aware of how this will change the relative position of the hook.

If you have a high tendency to pop-off on launch, consider that your plane might be nose heavy. Or, if you like the balance of your plane, consider setting up a launch mix that adds a few clicks of down elevator during the launch. This will prevent that over rotation during the critical first 50 feet of the launch. You can flip that mix off somewhere along the arch of the launch.
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