CMP Yak 50 CG problem
06-27-2007, 03:56 PM
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CMP Yak 50 CG problem
Hello:
I recently bought the CMP yak 50. Today I went to cg it -- it is balancing at over 6" back. It appears the company says to have it at 4.7". It will take ~5 oz. in the nose to balance. I have a .40 two stroke in it, but it weighs almost 6 lbs. Just wondering why mine came out so tail-heavy. Has anyone else had this problem??
P.S. I have the battery as far forward as it can go.
Garret
I recently bought the CMP yak 50. Today I went to cg it -- it is balancing at over 6" back. It appears the company says to have it at 4.7". It will take ~5 oz. in the nose to balance. I have a .40 two stroke in it, but it weighs almost 6 lbs. Just wondering why mine came out so tail-heavy. Has anyone else had this problem??
P.S. I have the battery as far forward as it can go.
Garret
06-27-2007, 05:40 PM
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RE: CMP Yak 50 CG problem
Garrett - I have had no experience with the 50 size CMP Yak, but expect to maiden their 140 size in the next few days. Both of these planes have a tendency to be tail-heavy (based upon experiences of other owners and their forums). Let me suggest that you consider what I have done so that you either do not have to add weight, or it is a small amount that must be added.
If you look at a full-scale Yak 55, you will notice that the spinner is some distance from the cowl. I understand this allows the prop to operated more efficiently on the full-scale (see photo).
Bear in mind, I all ready had my OS 160 mounted, but removed it from the mount, plugged the mounting holes with a hardwood dowl, CA'd them into place, sanded smooth and painted it with permanent Marks-a-lot, and re-drilled the mounting holes with the engine mounting lugs flush with the front of the motor mount. This placed the backplate of my spinner some 1-1/8 of an inch forward of the cowl and allowed me to use my engine weight to compensate for this problem. I also placed my battery forward of the firewall on the opposite side of the engine cylinder to counter-balance that big hunk of metal by expoxing a lite-ply mount to the side of the firewall with the battery running long-ways from the firewall forward. If this isn't enough to achieve the balance you desire, check out a spinner weight at your LHS. They come in one ounce and two ounce sizes (and yes, even using these ideas, I still had to use a two ounce spinner weight and 3/8 of an ounce to the motor mount, and 3/8 of an ounce to the left wing) but I was able to achieve lateral balance as well as nose to tail CG that was recommended.
I'm sure there are other good ideas out there and that someone will post to your forum, but these worked quiet well for me and are often overlooked. My plane came out weighting 13 pounds (heavy I know, but it is a heavy plane) but some are adding 10 to 12 ounces to the nose to achieve the proper and reccomended CG, where-as I only added a total of 2-3/4 ounces (more than I wanted, but happy that I didn't have to add 10 to 12 ounces).
Hope this helps, and if the photo of the full-scale Yak doesn't work, send me an e-mail at [email protected] and I'll return you an e-mail with the photo attached.
If nothing else, remember that "Experience is a hard teacher. She always gives the test first, and the lesson some time later!"
Phillip
If you look at a full-scale Yak 55, you will notice that the spinner is some distance from the cowl. I understand this allows the prop to operated more efficiently on the full-scale (see photo).
Bear in mind, I all ready had my OS 160 mounted, but removed it from the mount, plugged the mounting holes with a hardwood dowl, CA'd them into place, sanded smooth and painted it with permanent Marks-a-lot, and re-drilled the mounting holes with the engine mounting lugs flush with the front of the motor mount. This placed the backplate of my spinner some 1-1/8 of an inch forward of the cowl and allowed me to use my engine weight to compensate for this problem. I also placed my battery forward of the firewall on the opposite side of the engine cylinder to counter-balance that big hunk of metal by expoxing a lite-ply mount to the side of the firewall with the battery running long-ways from the firewall forward. If this isn't enough to achieve the balance you desire, check out a spinner weight at your LHS. They come in one ounce and two ounce sizes (and yes, even using these ideas, I still had to use a two ounce spinner weight and 3/8 of an ounce to the motor mount, and 3/8 of an ounce to the left wing) but I was able to achieve lateral balance as well as nose to tail CG that was recommended.
I'm sure there are other good ideas out there and that someone will post to your forum, but these worked quiet well for me and are often overlooked. My plane came out weighting 13 pounds (heavy I know, but it is a heavy plane) but some are adding 10 to 12 ounces to the nose to achieve the proper and reccomended CG, where-as I only added a total of 2-3/4 ounces (more than I wanted, but happy that I didn't have to add 10 to 12 ounces).
Hope this helps, and if the photo of the full-scale Yak doesn't work, send me an e-mail at [email protected] and I'll return you an e-mail with the photo attached.
If nothing else, remember that "Experience is a hard teacher. She always gives the test first, and the lesson some time later!"
Phillip
06-28-2007, 10:25 AM
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RE: CMP Yak 50 CG problem
Thank you for the response. I believe I have fixed the problem. Adding a 2 oz. spinner weight far our on the nose and a little in the cowl seemed to balance it out pretty well.
