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Old Nov 12, 2012, 01:29 AM
LSF - IV
Hostage-46's Avatar
United States, TX, Highland Village
Joined Jan 2003
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"...But isn't everyone looking for the best and most predictable performance with no tendency to stall, loop or whatever when you're not giving any stick inputs?... "

An "unstable" sailplane is more nimble and indicates lift better.

There are many long and well written threads on CG. Probably the biggest impact item on sailplane setup is CG.

Most of my flying buddies measure down to the the millimeter. I'll fly my ships, wings and conventional sailplanes at what most power guys would find unstable.

Anyway.... spars are in, covering next weekend

Dan in Dallas
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Old Nov 12, 2012, 05:44 AM
Never trust laughing dolphins
Joined Feb 2011
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Quote:
Originally Posted by Hostage-46 View Post
"...But isn't everyone looking for the best and most predictable performance with no tendency to stall, loop or whatever when you're not giving any stick inputs?... "

An "unstable" sailplane is more nimble and indicates lift better.

There are many long and well written threads on CG. Probably the biggest impact item on sailplane setup is CG.

Most of my flying buddies measure down to the the millimeter. I'll fly my ships, wings and conventional sailplanes at what most power guys would find unstable.

Anyway.... spars are in, covering next weekend

Dan in Dallas
Perhaps this is true once you are familiar with the instability, but why complicate things by making it less predictable?
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Old Nov 12, 2012, 10:42 AM
LSF - IV
Hostage-46's Avatar
United States, TX, Highland Village
Joined Jan 2003
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Quote:
Originally Posted by PHMX View Post
Perhaps this is true once you are familiar with the instability, but why complicate things by making it less predictable?
Start with the recommended CG, fly and move if needed based on preference. Moving the CG fore or aft a few mm at a time is hardly introducing an unpredictable scenario.
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Old Nov 12, 2012, 11:13 AM
Never trust laughing dolphins
Joined Feb 2011
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Quote:
Originally Posted by Hostage-46 View Post
Start with the recommended CG, fly and move if needed based on preference. Moving the CG fore or aft a few mm at a time is hardly introducing an unpredictable scenario.
I think even the slighest non-neglegible deviation from where CG should be will be very noticable though. Having flown countless of planes, helicopters and what not, a bad CG always resulted in unwanted drift or control issues.
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Old Nov 12, 2012, 12:53 PM
Some call me the other guy!
DoctorAudio's Avatar
Milwaukie , Oregon
Joined Feb 2003
4,367 Posts
A nose heavy plane flies poorly!
I tail heavy plane flies poorly once!
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Old Nov 12, 2012, 06:48 PM
Molon Labe
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United States, CA, San Luis Obispo
Joined Feb 2008
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Quote:
Originally Posted by doctoraudio View Post
a nose heavy plane flies poorly!
I tail heavy plane flies poorly once!
^like^
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Old Nov 12, 2012, 08:49 PM
LSF - IV
Hostage-46's Avatar
United States, TX, Highland Village
Joined Jan 2003
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Man I didn't mean to start a rant on CG....

Quote:
Originally Posted by PHMX View Post
I think even the slighest non-neglegible deviation from where CG should be will be very noticable though. Having flown countless of planes, helicopters and what not, a bad CG always resulted in unwanted drift or control issues.

Every airplane, model or full scale, has a RANGE of an acceptable CG. I'm not suggesting you fly beyond that range. On my Supra for instance, the recommended CG is 4". Turns out I like that an fly it regardless of conditions. Others will alter the CG, again by a very small amount 1/16 to 1/8 of an inch. Go forward and the ship is slightly more stable, suitable for gusty conditions. Move it aft as far and the airplane becomes very responsive to lift, such that the pilot can spot and maintain lift better at that CG compared to a more forward CG. Granted it is a higher workload on the pilot, however there is a benefit.
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Old Nov 12, 2012, 11:04 PM
Victim of C.D.O.
murdnunoc's Avatar
United States, TX, Lubbock
Joined Oct 2007
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Hostage, you didn't start anything.
You're right that there is a range, not just one specific location for CG.
The "BEST" location will, like all design features that affect performance of the plane, be the one that best meets the plane's intended flight characteristics.

A CG that is toward the rear of the controllable range will bring a plane that's more responsive. A must have for aerobatic planes. They need to be able to stall violently.
Aft CG also gives more efficient flight. More lift for less induced drag.
A pilot that's experienced can take advantage of the aft CG.
So your gliders do better with it at the aft end of the CG range.

Forward CG gives more stability at the expense of maneuverability. Too far forward means too stable. Read, can't move the nose...

I think you know all this. Good for a refresher for some, though.

PHMX,
Not sure how you figure a change in CG will make the plane constantly climb or dive. It can be trimmed for straight and level hands off with even a very forward or aft CG.
CG location determines how the plane departs or returns to stable flight when control input is given.
Does your radio have trims?
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Old Nov 13, 2012, 12:25 AM
Never trust laughing dolphins
Joined Feb 2011
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Quote:
PHMX,
Not sure how you figure a change in CG will make the plane constantly climb or dive. It can be trimmed for straight and level hands off with even a very forward or aft CG.
CG location determines how the plane departs or returns to stable flight when control input is given.
Does your radio have trims?
Using trims to compensate a bad CG is pure madness. If the CG is correct you do not need trims. Sure one could trim in wind, but that always backfires if you're flying circuits. The only reason one would prefer a slightly nose heavy plane is when the design allows for that, possibly making it more capable dealing with wind. And yes a bad cg totally influences flight behavior. It makes for an inefficient plane, regardless of full scale or RC.
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Old Nov 13, 2012, 05:44 AM
never mind the boll⁣⁣⁣ocks
brosius85's Avatar
Australia, NSW
Joined Dec 2010
1,256 Posts
mate do you even fly wings at all???

read murd's post again please...
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Old Nov 13, 2012, 07:34 AM
Victim of C.D.O.
murdnunoc's Avatar
United States, TX, Lubbock
Joined Oct 2007
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Or fly anything at all?
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Old Nov 13, 2012, 06:19 PM
LSF - IV
Hostage-46's Avatar
United States, TX, Highland Village
Joined Jan 2003
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Thank you gents.
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Old Nov 13, 2012, 06:52 PM
Flagstaff, AZ
dawsonh's Avatar
USA, AZ, Flagstaff
Joined Mar 2003
3,807 Posts
Hostage-46:

I have flow a bunch of CK's wings... all on the slope. My current TL50 is flying with at CG at 8 3/8" back from the nose. Very stable and just very slightly nose heavy. These are wonderful slope wings. I like them for their aerobatic abilities. They fly as well inverted as upright. I fly them at 19 ounces to 27+ ounces.

My RiteWing slope videos are here: http://vimeo.com/album/1176623

Have fun!

Dawson
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Old Nov 13, 2012, 07:15 PM
LSF - IV
Hostage-46's Avatar
United States, TX, Highland Village
Joined Jan 2003
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Excellent ! Just what I needed
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Old Nov 13, 2012, 08:14 PM
Expo is built into my thumbs
Hance's Avatar
USA, ID, Niter
Joined Jul 2008
4,474 Posts
I just finished up the glass this morning on a TL50 that CK cut me last spring. Mine was getting pretty beat up after it went in knife edge, full throttle because of a lockout. Me doing 2.5 rolls and yanking full elevator ten feet off the deck at full speed didn't help matters.

The TL50 is my all time favorite ritewing.
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