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Old Nov 19, 2006, 02:55 PM
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turbonut's Avatar
upland CA
Joined Dec 2004
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cg testing witha chuck glider

Hi Guys, I needed to do some testing of the cg on a me163.I didnt want to do any more damage to my model testing.So I made a chuck glider and added quarters taped to the side as a ballast.then maked the side in 1/8th in. I started at the recommended 3.5 in mark and adjusted from there..my best glide came with the cg at 5/8in back..this coresponds with what my model was doing..My conclusion is that a more aft cg is needed also I was hand launching the plane which I feel was not enuff airspeed for the wing sufaces to be effective..Maybe a javilin toss would help..Any way my question at this point is will the cg need to be adjusted to a higher gross weight of the model vs the glider..I asume it should be the same I will just need more airspeed to carry the weight..I posted here in edf because most of the smart guys hang around here )
Scott
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Old Nov 19, 2006, 07:55 PM
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bmiller's Avatar
Newport Beach, CA
Joined May 2002
5,745 Posts
Scott I think you're right, the CG should react the same way on the model.
Some of the gurus can figure it out mathmatically if you post a pic of the bottom of the entire airframe.
Bruce
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Old Nov 19, 2006, 08:11 PM
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Kevin Cox's Avatar
St. Louis Intl, Missouri, United States
Joined Jan 1997
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What were the properties of your best glide? Same size helps but it is more important that the wing sweep (wing plan form) matches. Being off on the plan form yields a different CG position. Looks like your ok there.

For me,

1) Moderately fast, no pitch or arching flight path.

2) For deltas or wings it has to have some (little) reflex (up elevon) and still fly like #1
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Old Nov 19, 2006, 10:07 PM
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turbonut's Avatar
upland CA
Joined Dec 2004
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Hey Bruce, I hope to have some of the guys confirm my findings.
Kevin, the wing is same as the model..I ws pretty carfull to match it up. the best glides were fast toss then a stedy down hill glide.as the speed came up it tended to flatten out just a touch..which made for some pretty cool landings for a uncontroled glider..I did also add 1/8 reflex because that is what the model uses.The biggest problem I think I found is it needs lots of airspeed to flyoff well.
Scott
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Old Nov 19, 2006, 11:30 PM
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United States, TX, Fort Worth
Joined Jun 2000
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What is your wing loading?

I predict you need a really fast launch to get away with a flying wing model like this.


The CG does not really change due to weight changes.....it should fly fine at any weight...jsut faster.

You might need some considerable up trim for the launch and retrim in the air.
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Old Nov 20, 2006, 12:01 AM
DELTAS RULE
corsair nut's Avatar
tehachapi, CA
Joined Jan 2006
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well it did nose dive pretty dang hard that one time. it may help having it farther back good luck!
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Old Nov 20, 2006, 06:35 AM
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Larry Dudeck's Avatar
Williamsville, NY, USA
Joined Sep 2000
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I have built four (4) chuck gliders over the past six years. In each case, the glider was a quarter scale of the actual model. My gliders were made of card board with no air foil and I tried very hard to make the glider plan form symmetrical to the actual model. Typical wing spans were about 12" and they weighed less than 1 ounce.

All my "flying" was done indoors, usually in the living room. So the total glide distance might have been 12 to 15 feet. My aim was to achieve a flat glide path with a slight nose down attitude. I did this by adjusting the ballast, usually a paper clip.

I would "launch" the glider in an underhanded throw and pay attention to the attitude. Nose up, move the paper clip forward, etc., etc. Once the correct ballasting was determined, it was a simple matter to locate the balance point of the glider. Measuring from the tip of the nose to the balance point, I would multiply that distance by 4, apply this new distance to the full size model. Bingo, the balance point is defined.

A chuck glider can be looked at as a simple, low velocity wind tunnel and I have found this method to give excellent results in locating the balance point.
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Last edited by Larry Dudeck; Nov 20, 2006 at 06:43 AM.
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Old Nov 20, 2006, 06:46 AM
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Joined Apr 2002
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http://www.rcgroups.com/forums/showt...ght=x+4+bantam

See post 49

I had a very similar problem with CG postion! I am sure the CG position is correct but the Bantam which is very similar aerodynamically to a Me163 suffers from a roll/pitch couple that no-one can explain.

best regards

Robert
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