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Centre of Gravity

#1
Hi guys,

This subject is one I have not made peace with as I am still in the beginning phases of building my own planes / scratch builds. I usually get all my plans from http://www.parkjets.com/ which I must say is a great resource of free plans, BUT 90% of the plans don't have an indication of where the CG of the planes are, which is a bit of a challange when going out for your maiden flight.

Advise I have been give so far is as follows :

1. CG should be about a third of the plane's lenght from the front of the plane, but I found that this is not always 100% true.
2. A nose heavy plane is better than tail heavy plane, so it's best to start balancing your plane with you battery / weights from the nose...

Is there anyone that might have some other advise for me as I am about to maiden this baby of mine today some time

http://www.parkjets.com/tomhe-f-18/
Thanks flitetest for this forum
 

lobstermash

Propaganda machine
Mentor
#2
Ah, jets, easy to build, hard to balance... My first guess at the CG of a new plane is generally by feel (with a bias toward the nose of course), then correct from there. From looking at the plan, my guess at the balance point would be about the point of where the wing becomes parallel to the fuse (as in, where the angle stops). Or just back from there (0.5-1cm or so).
 

Bongose

Junior Member
#3
If you place the CG at 25% of the mean aerodinamic chord then you are almost every time on the safe side with straight wings and wings with minor to medium sweep back. Large wing sweep angles likes the CG more foreward.

regards
Jan
 
#7
Good news, the "rather nose heavy than tail heavy" worked wonders. I had the battery about 3 inches from the tip of the nose, and it took off without going out of control. Usually my new projects crashes into the ground before the plane even completes it's first maiden. I had to move the battery back some more, about 12 inches, and now it really flies much better.

I had to also in the end add so ailerons because aileron movement only on the tail did not give me enough drag thus the banking and yanking was a very slow process. I added some ailerons on the main wings to see if it will improve steeing performnce.

Here's a seak peek at my progress so far

 
#10
that amount of throw is really great, the response on rolls is very fast, and I must say I never had so much fun with a plane like this.

the 2200KV Turnigy Brushless motor with HobbyKing 40A ESC reallly makes that plane fly very fast!