need delta cg
 

I built a delta wing speed 400 and it measures 30 wide x 20 nose to tail, whats the cg for this model

RE: need delta cg
 

Same as for any other. Draw a line from the tip leading edge to the root trailing edge. Draw another line from the root leading edge to the tip trailing edge, making an "X". At the point the lines cross, measure 25% - 33% of the total chord back from the leading edge. This will be the proper CG.

Every plane needs a CG, or "Carl Goldberg" to fly. This point is named after the venerable designer of RC planes, Carl himself. Most kits include a "Carl" with the instructions or even printed right on the plans. If your plane doesn't have one, I have a few left over from abandoned kits. I'll be glad to sell you one. Just drop me $10 + $20 shipping and I'll send one right out. :D

Dr.1

RE: need delta cg
 

Hi Thanks but I need to know where is the root leading and root trailing edge

RE: need delta cg
 

Hi Thanks but I need to know where is the root leading and root trailing edge

??? How about the rear and front edge of the wing, respectively?

Dr.1

RE: need delta cg
 

[X(]NOPE.. CANT USE 25% TO 30% ON DELTA..15% WORKS SUPER..VIGGIN IS A GOOD EXAMPLE RD

RE: need delta cg
 

See at the pic. how to set CG at delta wing.. Better between 10 and 15% instead 25% :D

Jens Eirik

RE: need delta cg
 

:DA BIGGGGGG YEP,TO THAT.. NICE PIC.. I CANT LOAD PICS.. RD

RE: need delta cg
 

Of course you can. I flew my [link=http://members.cox.net/~marsavage/Dart/index.shtml]F-106 EDF[/link] with the CG set at 25% MAC and it flew great. If anything, it probably needed to be moved back a little.

Here's where it was balanced:

http://members.cox.net/~marsavage/Dart/f-106plan.gif

And, here it is in the air at the 2002 Mid-Winter Electric meet in San Diego where it won 1st Place, Unlimited Scale:


http://members.cox.net/~marsavage/Dart/f-106flyby.jpg

RE: need delta cg
 

;)FROM PICS IT LOOKS TO BE ABOUT 15%,, ??? MAYBE WE MEASURE DIFFERNTLY

RE: need delta cg
 

If you were to measure the total length of the MAC, then measure the distance of the CG on the MAC, you'd find that the CG is at 25% of the MAC. (Acutally, I think it's 23%, but what's 2% among friends, right?)

I always take my wing planforms to the centerline of the aircraft, which isn't shown on the drawing posted above. The MAC location is shown on the starboard wing.

Take a piece of paper and hold the edge up to the MAC. Mark the paper with the MAC, then fold the page so that the MAC is divided in quarters, then compare the folds with the location of the CG and you'll find that the first fold (25%) is just behind the CG shown on the drawing.

When calculating CG, most people make the mistake of only measuring the exposed wing, which is why they might think the CG is at 15% of the MAC, but unless you include the portion of the wing hidden inside the fuselage, you'll get a false perception of where the MAC is located and where the CG is located on the MAC.

Here's another example of a CG calculation that I did for a MiG-29. I flew my MiG-29 model at the location shown on the drawing below and it flew perfectly.

Notice that the wing planform not only carried to the centerline, but also includes the blended forebody. Failure to do both would almost certainly guarantee that the model will be extremely tail-heavy.

Dan