CG on delta wings

[LevelUphill]

Hi All

I`m busy building a foam delta wing jet. Where would the center of gravity be ? In the middle of the wing or do we go for 30% from the front of the leading edge of the wing ?
For some reason i think the CG must be right in the middle of the wing.

Help much appreciated

Thanx:(

[TMorita]

The CG should go near the rotor shaft, of course!! :)

Toshi

[LevelUphill]

OK i understand what you say about the rotor shaft. I think i did not give anough info on my plane. The plane is a pusher prop much like the pico jet from ripmax. No DF.

Thanx:)

[LevelUphill]

OK i understand what you say about the rotor shaft. I think i did not give anough info on my plane. The plane is a pusher prop much like the pico jet from ripmax. No DF. It uses a normal speed 400 motor with an pusher gunther prop at the rear between the Elevons

Thanx:)

[Sture Smidt]

Post or send me a sketch of your planform. Include all relevant dimensions. Then I will calculate the NP and suggest a CG.

SS

[Martyn McKinney]

The rule for finding CG is that it is approximately 25% of the mean aerodynamic chord.

To find the mean chord, divide one side of the wing into 2 sections of equal area.

The chord at this point is the mean chord.

The CG should be at 25 to 30% from the leading edge at this point.

[Fred Bronk]

Hmm, should I move this or not? CG in a foamy wing,,,,,,,,

Moving to modeling science as there a formula for CG in flying wing.

FB

[Gastronom]

Hey guys, could you help me locate the center of gravity for my plane? I worked on it all weekendand have it almost ready to fly, ust gotta set the CoG. Here is a sketch, not very good one I might add but it does have dimensions. Please help ASAP..

Thanx,
Donald

[Lancair]

Sorry cant really decipher your drawing.

Have a look here (http://ourworld.compuserve.com/homepages/slope_scale/page17.html).

Should get you in the ballpark.

Lancair

[Gastronom]

What couldn't be deciphered?? I tried that web site this morning but I lack the umm skillz to come up with the CoG for this plane.

Anyone else have any ideas??

[Ollie]

See:
http://www.rcgroups.com/forums/showthread.php?s=&threadid=161059
If the pizza or other cardboard available isn't big enough just accurately scale down the planform until it fits the cardboard available. For best CG accuracy the outline and other drawn lines must be as accurate as possible and the size as large as possible.

[Gastronom]

Thank both of you for trying to assist me with this. I feel as though it may never get done :-( I'll try and get a picture tonight of the airplane then maybe you'll know what I'm tallking about..

[Gastronom]

OK, could osmeone use the dimensions above and this picture to tell me what the COG should be? I really want to fly this but won't risk it until after the COG is set. Thanx for youy assistance with this matter.

Donald

[Gastronom]

maybe a bottom view is easier to see, here is a pic..

[Sparky Paul]

Presuming a 15% c.g., it works out this way..
give or take..

[Gastronom]

Very Kewl Man!!!
So let me make sure of what I am supposed to do.
The balance point @ root chord 14.45 , is that the distance from the tip that I should measure back from the front to reach CoG?

[Sparky Paul]

Originally posted by Gastronom
Very Kewl Man!!!
So let me make sure of what I am supposed to do.
The balance point @ root chord 14.45 , is that the distance from the tip that I should measure back from the front to reach CoG?
.
That's the distance along the center chord you measure back, from the motor mount.

[Gastronom]

Kewl Man, Yer a life saver, rather an airplane saver!!! I'm gonna give tha ta shot, maybe be able to fly tomorrow at lunch. I'll keep ya informed on the characteristics.
MAN, thanx again!!!

[Gastronom]

Sparky, Thank you so much for the assist so far, but I am still having problem with this thing, can't seem to figure it out.. :mad:

I've been going over the numbers that you input in the formula, first I don't have a clue as to why whaich number went where, second I have questions about the numbers that you used for me.
The distance from the nose to the rear of the control surfaces in the center of the plane is 28.5 and the control surfaces are about 6" - so should that # in the calculation you did for me be 22.5? If so would that change the CoG or not??

Oh yeah the shoe is a size 11.5 . Funny, took me a couple dayz to figure out what the 9 was coming from. hehehe

Again, Thank you for your assistance. Dunno, maybe I'm just being nervous about the whole thing. Heck in my younger dayz I'd have just thrown it and seen how it flew then worried about CoG.:D

I've searched everywhere to locate that cog program that you posted a picture of, but can't locate it. Would you do me a favor and give me the link?

[Sparky Paul]

Your original sketch shows 28-1/2" for both the leading edge length along the leading edge, and the same dimension in the center.
The center is NOT the root chord, if it stops at the rear of the wing, without including the control surface. Adding this makes the root chord 34-1/2". If the 28-1/2" is the total length of the root including the surface chord, then the c.g. position moves forward.
Strictly speaking, the leading edge for the computation should be located at the center of the extension of the leading edges... some distance ahead of the firewall, but for this situation that's not critical.
The c.g. calculator I use is at:
http://www.palosrc.com/instructors/cg.htm
Note you have to presume a c.g. position..
for a delta, 15% is realistic. It can go aft..
This is the change for the 28-1/2" root chord..

[Gastronom]

Oh Man! Your great, Wish you were closer so I could take ya to dinner. I'm gonna fly that bugger this weekend for sure, might be the last 70 degree weather for the rest of the year..
Man thanx again..