ahaynes

I have an OMP YAK 54 47" ARF. I want to correctly locate the proper CG as best I can before I drill the holes to mount the engine. I am new to this sport and the instructions are not exactly clear to me. How far back should the center of gravity be measured at the leading edge of the wing? And should this be measured at the wing root next to the fuselage?

Thanks
Andy

Spacey

Hi Andy,

Yes you should measure right from the front most Leading edge of the wing at the root right next to the fuselage. Obviously this CG is just a recommended starting point and you should adjust it in flight to your liking. I can imagine the CG given in the manual is fairly conservative and I would recommend you leave some room to move the CG around and more probably back. So if you mount the motor try to rather have the reciever battery in the front part of the wing along with the electronics so you have some room to shift the CG back later without moving the motor.

ahaynes

Thanks for the info. What was concerning me was that the CG was running a little aft with the electronics forward in the wing and the motor as far forward as I felt comfortable. I believe this will be a good starting point.

Thanks again

Andy

Spacey

Hi Andy,

All of a sudden I'm worried again that I might be lying to you. What does the instructions say the position of the CG should be? If you want to you can give me the weekend (Sorry I don't have internet access at home) and I will check where the CG is on my trusty old Yak? I know I checked it at one point and gave the details to someone else here on the forums too. I'll do a search quickly, maybe I can find it again.

Edit: Sorry searched everywhere and can't find the info. I'll have to check mine over the weekend for you.

Cheers
Rudolf

profile540

Spacey i would be interested in that info. i have a kit that is just about finished........thanks

ahaynes

In the instructions it states that the CG should be 1.75-2.0 inches behind the wing spar. In this model that is the planking behind the leading edge. I hope to finish in the morning and if the weather permits make the first flight tomorrow.

Andy

Spacey

My sincere apologies folks. I knew as I was locking the door to the flat this morning that there was something I forgot in the back of my mind. This was evidently it. I've put a reminder on my cel to check it out tonight.

Andy: That 2" behind the spar sounds about right yes. You would measure that from the back of the two main wing spars ie the two 1/4" balsa stock sitting at the highest (More or less) peak of the wing's airfoil. It can be difficult to spot the spars under the wing centre section sheeting if the joints were filled up well but you can just use a ruler and run it along the back of the spar over the open structure of the wing to find where the spar is running right up against the fuselage.

ahaynes

Thanks Spacey. I flew the plane this weekend and was very pleased. I am breaking-in a new engine which kept dying inflight. I made I guess 8 dead stick landings. However the plane flew great. I am looking forward to trying a little 3D when the I get the motor figured out.

Thanks
Andy

Spacey

Congrats on the maiden Andy! I sure hope you get that motor figured out soon so you can let this bird show you a couple of new tricks.

I checked my CG last night and it is indeed 2" behind the main spar or 4,92" from the LE.

AFSalmon

My Feedback: (3)

Thanks Spacey and I apologize for not responding to this one. But sounds like we have it solved. Yes, the spec CG is measured from the wing main spars which can also be located from the rear edge of the leading edge sheeting.