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Need Help in the CG of my super-sport Electric 48"

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Need Help in the CG of my super-sport Electric 48"

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Old 09-14-2018, 09:36 PM
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suzonka
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Default Need Help in the CG of my super-sport Electric 48"

my super-sport fly's well only with a lot of nose weight and the recommended 30% mark from the leading edge of the main wing which is rectangular 48" X 9"
so what I have done to-modify the wing is clip it so now its a 42 "clipped wing . and it fly's much better to suit me its faster and more fun. Any way back to the extra weight I had in the nose , can I take some of the 4 oz lead out of the nose now that I made the wing shorter ,its still a rectangular shaped wing so how does this work when you have the same width wing yet longer verses shorted in length yet same wing design ?


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Last edited by suzonka; 09-14-2018 at 09:40 PM. Reason: spell check
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Old 09-15-2018, 05:49 AM
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The wing span has nothing to do with the CG. You can however do a couple simple flight tests to see if the CG that you are currently flying with is ideal or not. First though you need to measure the airplane to see where your engine thrust line, wing incidence and stab incidence are. Then take note on where your elevator trim is. With an engine thrust at zero up or down, a wing incidence at .5 degrees positive and a stab incidence of zero, you should require no elevator trim. If you have up elevator trim with everything else as described then the odds are that you can remove some of that weight. Another test I like to do in an inverted 45 degree climb. Once established take note what the airplane does hands off. A proper CG will be a subtle arc towards the canopy to level inverted fligh that should take about 5 seconds. A slightly aft CG will have the airplane hold the 45 degree downline or even steepen the climb. However the first step to getting any airplane correctly flight trimmed is knowing what you are starting with.
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Old 09-15-2018, 11:18 AM
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The shorter wing makes the plane slightly statically lighter aft the CG, perhaps too little to notice.
The wing has less lift capability now, which has to be compensated with faster flight.
Total lift produced by the wing at level flight is the same, as the weight of the plane is.
The tail surface is bigger respect to the wing area now, reason for which its negative lift is bigger at required bigger flight speeds.
Any deviation in relative incidence to the wing is now magnified due to reduced wing area/tail area ratio and increased level speed.
As stated in previous post, you will need to carefully experiment with incidence, tail trim and nose weight, in order to find the minimum safe nose weight, keeping the CG location about the same at the beginning of the process.
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Old 09-15-2018, 11:08 PM
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Default cg and nose weight

Originally Posted by speedracerntrixie View Post
The wing span has nothing to do with the CG. You can however do a couple simple flight tests to see if the CG that you are currently flying with is ideal or not. First though you need to measure the airplane to see where your engine thrust line, wing incidence and stab incidence are. Then take note on where your elevator trim is. With an engine thrust at zero up or down, a wing incidence at .5 degrees positive and a stab incidence of zero, you should require no elevator trim. If you have up elevator trim with everything else as described then the odds are that you can remove some of that weight. Another test I like to do in an inverted 45 degree climb. Once established take note what the airplane does hands off. A proper CG will be a subtle arc towards the canopy to level inverted fligh that should take about 5 seconds. A slightly aft CG will have the airplane hold the 45 degree downline or even steepen the climb. However the first step to getting any airplane correctly flight trimmed is knowing what you are starting with.
inverted thank you
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Old 09-16-2018, 05:33 AM
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My test for CG on any sport type plane and even a factor on a pattern plane is watching how the plane behaves when landing. After all, CG, like all flight trimming, is really about getting the fight characteristics you want. The tests are just a tool.
I go to idle on approach with the nose level. If the nose drops significantly on its own and I have to add throttle to raise it, the plane is too nose heavy. If the nose holds its position until a sudden stall happens, the CG is neutral. If the nose rises on its own, it's too tail heavy.
Optimum CG is a matter of opinion within an acceptable range. I don't like my planes set up neutral because the Texas wind will toss them around too much. So the behavior I look for in landing is the nose dropping just a little on its own as the plane slows but not so much that I can't flare without adding throttle. For a pattern plane, I'll also check knife edge performance and spin entries and exits as part of the process too.
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Old 09-16-2018, 04:14 PM
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Default ​​​​​​​cg after clipped wing

Originally Posted by jester_s1 View Post
My test for CG on any sport type plane and even a factor on a pattern plane is watching how the plane behaves when landing. After all, CG, like all flight trimming, is really about getting the fight characteristics you want. The tests are just a tool.
I go to idle on approach with the nose level. If the nose drops significantly on its own and I have to add throttle to raise it, the plane is too nose heavy. If the nose holds its position until a sudden stall happens, the CG is neutral. If the nose rises on its own, it's too tail heavy.
Optimum CG is a matter of opinion within an acceptable range. I don't like my planes set up neutral because the Texas wind will toss them around too much. So the behavior I look for in landing is the nose dropping just a little on its own as the plane slows but not so much that I can't flare without adding throttle. For a pattern plane, I'll also check knife edge performance and spin entries and exits as part of the process too.
Your answer is what Im looking for because landing is the most important part of bringing the plane in smoothly and especially not having a nose over on some of the war birds. today was a good day and a perfect set up in the CG on this one plane I have tail dragger type. so after a smooth landing I throttled up a little to bring the plane back to me on the grass runway . well the plane lifted off the ground about 3 feet then I lowered the throttle and flared the elevator and it landed perfect lightly and smooth so the guys in the club thought I was doing some kind of magic tricks but I wasnt, ,just dumb luck.

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Old 09-17-2018, 03:32 AM
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Nosing over is more about the landing gear layout than the CG. CG is all about flying characteristics, while the landing gear is all about ground handling. That said, a shift in the CG can improve or hurt the landing gear layout because its placement on the plane relative to the CG has a lot to do with how well the plane ground handles. Some warbirds are notoriously difficult on the ground because the original designers chose a less than optimal layout in order to boost flight performance or save weight.
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Old 09-17-2018, 12:40 PM
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Default ​​​​​​​landing gear to cg

Originally Posted by jester_s1 View Post
nosing over is more about the landing gear layout than the cg. Cg is all about flying characteristics, while the landing gear is all about ground handling. That said, a shift in the cg can improve or hurt the landing gear layout because its placement on the plane relative to the cg has a lot to do with how well the plane ground handles. Some warbirds are notoriously difficult on the ground because the original designers chose a less than optimal layout in order to boost flight performance or save weight.
thank you yo have explained this very well.
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Old 09-20-2018, 05:35 AM
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I agree that flight testing is the way to decide, but I do a different test. I trim to fly level, any speed, but I use a moderate cruise, at a good altitude. Note that how you trim for level flight will depend on where the CG is, but you will do it by observing the plane. Then put the plane in a dive and release the controls. If it is nose heavy it will pull out abruptly (because you would have needed a lot of up trim to fly it level). If it is close to neutral, it will just keep going down until you pull out. Theoretically it could tuck under, indicating that it is tail heavy, but you'd have problems long before you got to the test.

Most people like a little stability, meaning a tendency to pull out of the dive. Some planes I fly quite neutral, i.e., it goes where you point it, with respect to pitch.

There is a formula for estimating CG before you start. The factors are wing area, stab area, tail arm and wing chord. So actually, if you reduce the wing span the CG could go back a bit. It's probably too small an effect to be noticeable. And anyway, the purpose of the formula is only to get you in the ball park before you do the flight test.

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Old 09-20-2018, 07:21 PM
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I've been a part of a lot of CG threads over the years. It's right up there with engine tuning as topic that people get way too stressed out about and new people tend to overthink and ridiculously bad advice gets tossed around about. The designer knows what the CG should be, and any of the online calculators that take the tail specs into account will give you a good starting place if you don't have the manual. After that it's all about feel, how the plane behaves in the air. Within a range, CG is a matter of personal preference. Go fly the plane and see what you think. We can't tell you what feels right to you.
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