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Old Feb 03, 2008, 03:47 AM
dare to thermal
Mannheim, Germany
Joined May 2004
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Randy,

if you are reducing the decalage of the wing, you have to go back with the CG (remove some nose lead), and normally you have to reduce the elevator throws a bit too.
Do you know the "dive-test"? IMOfor good thermal senitivity the plane should be close to neutral stability. -> http://www.rcgroups.com/forums/showt...st#post7099460

Have fun!
Bernd
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Old Feb 03, 2008, 11:38 AM
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Eastern North Carolina
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Bernd,

I have not adjusted the wing decalage. I have not tried the dive test yet. Maybe today. I read your link. I did notice that the plane nosed up hard upon entering the one thermal I found. According to you link, that suggest a neutral CG. I'll keep playing.

Randy
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Old Feb 14, 2008, 11:13 PM
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Anthing to report?
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Old Feb 24, 2008, 01:49 PM
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I'm still waiting for the alignment of the weather, weekend, and time to occur again. I did add about a quarter's worth of weight to the tail area the last time out. The air was completely dead. This weight seemed to help. I did get a 12 min flight. I have not removed the proportional amount of weight from the front. Would this setup be different if conditions are windy?

Would a "ballast tube" be useful, how, and how do I build one.

I may get out today. It looks promising.

Randy
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Old Feb 24, 2008, 02:12 PM
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Quote:
Originally Posted by PLRDad
I'm still waiting for the alignment of the weather, weekend, and time to occur again. I did add about a quarter's worth of weight to the tail area the last time out. The air was completely dead. This weight seemed to help. I did get a 12 min flight. I have not removed the proportional amount of weight from the front. Would this setup be different if conditions are windy?

Would a "ballast tube" be useful, how, and how do I build one.

I may get out today. It looks promising.

Randy
On my Thermal Dancer, when the air is dead calm, I add a quarter to the tail to make the nose lighter and more responsive, but I find I can't manage it when there is more than about a 3 or 4 mph wind, so I take the quarter off. It is only .2 oz, so it is not worth the hassel to dig out weight from the nose for those few times I like it this way.

On a Spirit, you can just create a ballast box under the wing area. Put it dead on the CG. Then, when it gets windy you can add ballast.

An alternative is to glue in velcro strips that you can use to secure ballast. I sometimes use batteries as ballast. But i only add Ballast when the wind gets over about 8 or 10 mph.
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Old Feb 24, 2008, 06:36 PM
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Finland
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573 Posts
aeajr: thanks for this thread. I studied before maidening my new sailplane today. Although I didn't follow all the 'rules' I had good use of the knowledge shared.
Thanks again aeajr and the rest of RCgroups.

http://www.rcgroups.com/forums/showthread.php?t=823630
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Old Feb 27, 2008, 03:42 PM
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Selective Hearing

Quote:
Originally Posted by aeajr
On my Thermal Dancer, when the air is dead calm, I add a quarter to the tail to make the nose lighter and more responsive, but I find I can't manage it when there is more than about a 3 or 4 mph wind, so I take the quarter off. It is only .2 oz, so it is not worth the hassel to dig out weight from the nose for those few times I like it this way.
Dr Drela came to my conclusion when discussing CG location. CG should be adjusted for handling without regard to favoring one airspeed. The induced error for aerodynamic correction for slow flight is as insignificant as Walt Disney’s Dumbo feather.
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Old Feb 27, 2008, 04:51 PM
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I'm not sure I understand, histarter- are you arguing that his quarter is a bad thing, or are you agreeing with him?

I've had similar results on my Ascent, on calm days it flies better and signals lift better with a little weight added to the tail, but on turbulent days it's very difficult to handle with the CG that far aft so I take the extra weight off the tail.
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Old Feb 27, 2008, 04:57 PM
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Quote:
Originally Posted by PLRDad
I did notice that the plane nosed up hard upon entering the one thermal I found.
That's not unusual, depending on the strength of the thermal. The more neutral the CG, the more pronounced the airplane's reaction to thermal entry will be. That's why moving the CG back makes it signal lift better.

That's also why moving it forward tames the behavior in bumpy/windy conditions.

Ballast is useful for increasing the airspeed and inertia to help you handle rough weather better. (Not reccomended for the beginning pilot that ought not to be in up rough weather )

I actually just finished repairs on a Spirit that's been neglected and broken in my garage for a very, very long time. Looking forward to my first hi-start launch in years! Wahoo!
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Old Feb 27, 2008, 05:40 PM
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Quote:
Originally Posted by rdeis
I'm not sure I understand, histarter- are you arguing that his quarter is a bad thing, or are you agreeing with him?

I've had similar results on my Ascent, on calm days it flies better and signals lift better with a little weight added to the tail, but on turbulent days it's very difficult to handle with the CG that far aft so I take the extra weight off the tail.
Not a bad thing, just critical tunning for profile that has a minimal shift in CP as alpha increases. Meaning the crutch may become negitive with altitude gained, or is truly the correct CG location and something else may be the problem creating an original noseheavy condition.
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Old Feb 27, 2008, 06:24 PM
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Ok, I think I understand you. Not certain yet.

With my Ascent I find the quarter to make it lighter in the nose, and more sensitive to inputs of all sorts. Handles like a race car-- turns because you *think* it hard!

The problem is that in heavy air "signals the lightest lift" turns in to "easily upended" so I remove the quarter to shift the CG forward and get more stable handling qualities.
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Old Feb 27, 2008, 07:09 PM
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The Ascent is a very light electric plane in the 54 inch wing span, 20 ounce range, if I know what plane you are talking about. A quarter on the tail of that plane is HUGE. I would consider a dime a lot on that plane.

The quarter concept was talking about 2M/78" planes that typically weight 30-40 ounces all the way up to 3.5M planes that could weight 65-90 ounces. Here a quarter is a small to moderate adjustment.
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Old Feb 27, 2008, 09:08 PM
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Originally Posted by aeajr
The Ascent is a very light electric plane in the 54 inch wing span, 20 ounce range, if I know what plane you are talking about. A quarter on the tail of that plane is HUGE.
True. I was speaking figuratively to keep the terms we're using consistent-- I actually use a small amount of clay.
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Old Feb 27, 2008, 10:51 PM
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different strokes

Quote:
Originally Posted by rdeis
Ok, I think I understand you. Not certain yet.

With my Ascent I find the quarter to make it lighter in the nose, and more sensitive to inputs of all sorts. Handles like a race car-- turns because you *think* it hard!

The problem is that in heavy air "signals the lightest lift" turns in to "easily upended" so I remove the quarter to shift the CG forward and get more stable handling qualities.
Interesting thought, tunable inertia...hmm?
This is an effect I attempted to minimize with a short moment arm.
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Old Feb 28, 2008, 11:07 AM
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Originally Posted by histarter
Intersting thought, tunable inertia...hmm?
This is an effect I attempted to minimize with a short moment arm.
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.
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