CG Question
01-04-2010 | 01:40 PM
#1
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From: Racine,
OH
CG Question
I have the GP Sukhoi SU-31 and I put a RCGF 50 CC engine in it. Perfect fit. However, they are calling for the CG to be 5-11/16" from the leading edge and I am nose heavy. That measurement is about 2 inches from the back of the spar. If I get on the edge of the spar, it balances. It says that you can move the CG up 3/4" after the maiden flight if necessary, but it still won't balance even with weight added. I have everything moved back as far as I can in the fuse and have added several ounces with no balance. How critical is it. Will it work if you just get it close? Any suggestions?
01-04-2010 | 03:50 PM
#2
RE: CG Question
If you balance on the spar, you will be 1-1/4” off the forward limit; hence, the model will be way nose heavy and it will not fly well, making flaring and take-off’s difficult or impossible.
Just add weight as far back as possible and rebalance to 5-11/16” behind the LE at the fuse.
An overpowered model is seldom light.
A heavy model will always fly better than an improperly balanced one.
Your model should not be too nose heavy as to locate the balance point forward than 4-15/16” behind the LE at the fuse.
Your model should not be too tail heavy as to locate the balance point aft than 6-7/16” behind the LE at the fuse.
Good luck!
Just add weight as far back as possible and rebalance to 5-11/16” behind the LE at the fuse.
An overpowered model is seldom light.
A heavy model will always fly better than an improperly balanced one.
Your model should not be too nose heavy as to locate the balance point forward than 4-15/16” behind the LE at the fuse.
Your model should not be too tail heavy as to locate the balance point aft than 6-7/16” behind the LE at the fuse.
Good luck!
01-04-2010 | 05:36 PM
#3
My Feedback: (221)
RE: CG Question
25 to 30% back from the leading edge at the fuselage is safe for most any airplane. Take that percentage times your cord at that location and see where you are. Nose heavy is way safer than tail heavy. Your optimal balance can be ascertained in the air with a simple flight testing procedure, but for now, I would use the 25-30%. Nose heavy, you will need a little more speed on final, a slightly steeper final approach, and a more deliberate flair, but you will be perfectly fine. Fortunately, the Sukuoi isn't snap-happy and sensitive to elevator like the Cap is. See how it flies and adjust the CG AFT, 1/4" at a time, till she has a very slow relatively level sink rate, wings level, in a glide, and both right side up and inverted. When this is accomplished, you will be able to slow down and glide in to landing.
01-04-2010 | 08:33 PM
#4
RE: CG Question
Hello Guitarman.
I've been flying planes similar to yours with similar power plants - several of the 27% GP Extra 330S ARF and I also have the Edge 540 ARF in the same series. Both are powered by DL50s and both required tail weight - around 2-1/2 oz. in the Extra if my memory serves me correct. These planes weren't designed for 50cc engines, thus the nose-heavy situation. Rest assured both of mine fly delightfully balanced as recommended with the tail weight. On my most recent Extra I even mounted the battery near the horizontal stab and it STILL required some tail weight (although I used the pull/pull rudder servo setup instead of the tail-mounted servo which probably would have negated the additional ballast).
Here are some pics of the lead in the tail of one of my Extras.
Hope this helps.
Tim
I've been flying planes similar to yours with similar power plants - several of the 27% GP Extra 330S ARF and I also have the Edge 540 ARF in the same series. Both are powered by DL50s and both required tail weight - around 2-1/2 oz. in the Extra if my memory serves me correct. These planes weren't designed for 50cc engines, thus the nose-heavy situation. Rest assured both of mine fly delightfully balanced as recommended with the tail weight. On my most recent Extra I even mounted the battery near the horizontal stab and it STILL required some tail weight (although I used the pull/pull rudder servo setup instead of the tail-mounted servo which probably would have negated the additional ballast).
Here are some pics of the lead in the tail of one of my Extras.
Hope this helps.
Tim
01-05-2010 | 07:54 AM
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From: Racine,
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RE: CG Question
ORIGINAL: krproton
Hello Guitarman.
I've been flying planes similar to yours with similar power plants - several of the 27% GP Extra 330S ARF and I also have the Edge 540 ARF in the same series. Both are powered by DL50s and both required tail weight - around 2-1/2 oz. in the Extra if my memory serves me correct. These planes weren't designed for 50cc engines, thus the nose-heavy situation. Rest assured both of mine fly delightfully balanced as recommended with the tail weight. On my most recent Extra I even mounted the battery near the horizontal stab and it STILL required some tail weight (although I used the pull/pull rudder servo setup instead of the tail-mounted servo which probably would have negated the additional ballast).
Here are some pics of the lead in the tail of one of my Extras.
Hope this helps.
Tim
Hello Guitarman.
I've been flying planes similar to yours with similar power plants - several of the 27% GP Extra 330S ARF and I also have the Edge 540 ARF in the same series. Both are powered by DL50s and both required tail weight - around 2-1/2 oz. in the Extra if my memory serves me correct. These planes weren't designed for 50cc engines, thus the nose-heavy situation. Rest assured both of mine fly delightfully balanced as recommended with the tail weight. On my most recent Extra I even mounted the battery near the horizontal stab and it STILL required some tail weight (although I used the pull/pull rudder servo setup instead of the tail-mounted servo which probably would have negated the additional ballast).
Here are some pics of the lead in the tail of one of my Extras.
Hope this helps.
Tim
01-05-2010 | 07:55 PM
#6
RE: CG Question
On the Extra there's no balsa back there (on the bottom of the fuselage). I just cut the MonoKote. But if you examine the photos closely you can detect a balsa stick across the front of the opening between the stringers under the covering. I slipped that in and glued it into position after I cut the hole, then ironed the MonoKote down to it. That way, the covering is supported and you can simply iron a patch into place. If you ever need to adjust the amount of weight you can remove the patch, then replace.
