Increasing Fuse length and Cof G
03-25-2016, 11:43 PM
#29
Oh BMatthews, what have I done to deserve this. All I wanted was support your point of pretty rearward balance, and I just thought I take it to both extremes - no tail (and sweep) at all and really big undercambered tail.
I'm the last one suggesting the "lifting stabilizer", on the contrary. You really don't seem to remember our discussions five years ago (e.g. my earlier post in the same thread). All I was saying is that the undercambered airfoils of freeflight wings have a strong down-pitching moment and that way contribute to the rear balance. Yes, they do, just try a moment plan or use a NP calculator which takes moment into account. Of course NP doesn't shift, but balance does if you change airfoil moment, or incidences/decalage change noticeably. And a big stab, say 33% of wing area, with cambered airfoil contributes noticeably to the overall down-pitching moment and the rear balance position. Thats all.
And the flying plank is an academic example, meaning that even a configuration without any stabilizing measures can be stable. The interesting point is that the balance has to be behind 25%, not ahead. The diagram shows that a balance at 28% makes for about 7 or 8 degrees AoA. (Not 6 degrees, that's only where the moment starts to become noticeable.) That's pretty much but not quite stalled, and it's an academic example. It works for thicker airfoils as well because they as well have a moment at higher AoAs. They tried it in the 1930s as a small test glider in a hall, it has whiskers, I don't have to do it again.
As a funny aside, I even tried such balsa chuckies following a book about the basics of model flying. Not only conventional tail, but also swept flying wing, flying disk, and flying plank. And indeed all except the plank had some form of decalage or reflex, the plank going to show the extreme case. Alas, that was only 50 years ago. :-)
I'm the last one suggesting the "lifting stabilizer", on the contrary. You really don't seem to remember our discussions five years ago (e.g. my earlier post in the same thread). All I was saying is that the undercambered airfoils of freeflight wings have a strong down-pitching moment and that way contribute to the rear balance. Yes, they do, just try a moment plan or use a NP calculator which takes moment into account. Of course NP doesn't shift, but balance does if you change airfoil moment, or incidences/decalage change noticeably. And a big stab, say 33% of wing area, with cambered airfoil contributes noticeably to the overall down-pitching moment and the rear balance position. Thats all.
And the flying plank is an academic example, meaning that even a configuration without any stabilizing measures can be stable. The interesting point is that the balance has to be behind 25%, not ahead. The diagram shows that a balance at 28% makes for about 7 or 8 degrees AoA. (Not 6 degrees, that's only where the moment starts to become noticeable.) That's pretty much but not quite stalled, and it's an academic example. It works for thicker airfoils as well because they as well have a moment at higher AoAs. They tried it in the 1930s as a small test glider in a hall, it has whiskers, I don't have to do it again.
As a funny aside, I even tried such balsa chuckies following a book about the basics of model flying. Not only conventional tail, but also swept flying wing, flying disk, and flying plank. And indeed all except the plank had some form of decalage or reflex, the plank going to show the extreme case. Alas, that was only 50 years ago. :-)
Last edited by UStik; 03-26-2016 at 04:29 AM. Reason: typos, wording
03-26-2016, 08:42 AM
#31
My Feedback: (41)
03-26-2016, 11:09 AM
#32
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UStik, I owe you an apology. I read more into your post than was there while I was in a bit of a mood and itching for a debate.
Rapptor, to be fair to your case I do agree that for most cases just switching things around and keeping the same CG is OK. And let's face it. Most general sport models within a close range of span where the wings will fit easily from one to the other are all roughly the same wing to tail area ratio and generally don't have radically different length fuselages. So if it looks more or less right then it'll fly fine.
But consider what is going to happen if you start swapping parts between radically different shapes. Such as put a 2 meter glider wing onto a Jr Falcon fuselage and tail. Or on more performance level models such as higher end sailplanes. If you do that and then want to trim the CG for best performance then all this stuff really does matter. But for general sport flying? Not so much and "close enough" is "good enough".
Rapptor, to be fair to your case I do agree that for most cases just switching things around and keeping the same CG is OK. And let's face it. Most general sport models within a close range of span where the wings will fit easily from one to the other are all roughly the same wing to tail area ratio and generally don't have radically different length fuselages. So if it looks more or less right then it'll fly fine.
But consider what is going to happen if you start swapping parts between radically different shapes. Such as put a 2 meter glider wing onto a Jr Falcon fuselage and tail. Or on more performance level models such as higher end sailplanes. If you do that and then want to trim the CG for best performance then all this stuff really does matter. But for general sport flying? Not so much and "close enough" is "good enough".
03-27-2016, 03:14 AM
#34
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Hi Rapptor,
I just had had a look around that Westwing reference of yours including most of the rest of the site.
You might want to look for some better reference material.
That is by far and away the most incorrect material I have ever read I'm afraid. It's just plain wrong in nearly everything it says, even the odd correct thing is only sort of right, but then completely misapplied.
I'm sorry, I don't mean to come across as being nasty about it, I'm not, I think the author has some idea it's just that he gets it the wrong way around nearly every time. eg 'the canard cannot stall before the main wing' actually it has to, otherwise the aircraft will be unable to recover.
Dave H
I just had had a look around that Westwing reference of yours including most of the rest of the site.
You might want to look for some better reference material.
That is by far and away the most incorrect material I have ever read I'm afraid. It's just plain wrong in nearly everything it says, even the odd correct thing is only sort of right, but then completely misapplied.
I'm sorry, I don't mean to come across as being nasty about it, I'm not, I think the author has some idea it's just that he gets it the wrong way around nearly every time. eg 'the canard cannot stall before the main wing' actually it has to, otherwise the aircraft will be unable to recover.
Dave H
03-30-2016, 10:33 PM
#37
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It seems like CATA has long gone, and the correct answer has been given, but to reiterate.
If the tail volume (area X length) is increased then the neutral point moves aft. Therefore the balance point can be moved aft, and to keep the model flying similar to the way it did, should be moved aft.
Dave H
If the tail volume (area X length) is increased then the neutral point moves aft. Therefore the balance point can be moved aft, and to keep the model flying similar to the way it did, should be moved aft.
Dave H
Last edited by gerryndennis; 03-30-2016 at 10:40 PM.
04-21-2016, 10:15 AM
#39
My Feedback: (41)
hi rapptor,
i just had had a look around that westwing reference of yours including most of the rest of the site.
You might want to look for some better reference material.
That is by far and away the most incorrect material i have ever read i'm afraid. It's just plain wrong in nearly everything it says, even the odd correct thing is only sort of right, but then completely misapplied.
I'm sorry, i don't mean to come across as being nasty about it, i'm not, i think the author has some idea it's just that he gets it the wrong way around nearly every time. Eg 'the canard cannot stall before the main wing' actually it has to, otherwise the aircraft will be unable to recover.
Dave h
i just had had a look around that westwing reference of yours including most of the rest of the site.
You might want to look for some better reference material.
That is by far and away the most incorrect material i have ever read i'm afraid. It's just plain wrong in nearly everything it says, even the odd correct thing is only sort of right, but then completely misapplied.
I'm sorry, i don't mean to come across as being nasty about it, i'm not, i think the author has some idea it's just that he gets it the wrong way around nearly every time. Eg 'the canard cannot stall before the main wing' actually it has to, otherwise the aircraft will be unable to recover.
Dave h
c/g goes with the wing for r/c . Full scale does have some "wiggle room .
Put any wing, on any fuse ,, same wing c/g
04-21-2016, 01:00 PM
#40
Senior Member
And your point is?
Take any wing and put it on another fuselage just anywhere and you'll most probably have a disaster. Put it on the new fuselage so the CG will wind up in the same place on the wing it was when the wing was on the first fuselage, and it may fly ok.
If you believe that RC aircraft differ from full scale, in that full scale has a CG range but RC don't, where did you come up with that?
Take any wing and put it on another fuselage just anywhere and you'll most probably have a disaster. Put it on the new fuselage so the CG will wind up in the same place on the wing it was when the wing was on the first fuselage, and it may fly ok.
c/g goes with the wing for r/c . Full scale does have some "wiggle room .
04-21-2016, 03:49 PM
#42
My Feedback: (41)
and your point is?
Take any wing and put it on another fuselage just anywhere and you'll most probably have a disaster. Put it on the new fuselage so the cg will wind up in the same place on the wing it was when the wing was on the first fuselage, and it may fly ok.
If you believe that rc aircraft differ from full scale, in that full scale has a cg range but rc don't, where did you come up with that?
Take any wing and put it on another fuselage just anywhere and you'll most probably have a disaster. Put it on the new fuselage so the cg will wind up in the same place on the wing it was when the wing was on the first fuselage, and it may fly ok.
If you believe that rc aircraft differ from full scale, in that full scale has a cg range but rc don't, where did you come up with that?
if you balance a plane ,and lets say it needed 5 oz lead in nose !!! If you were to ,, move the wing ,,back..
Maybe 1 or 2 inches ,, no ballast would be needed !!!!
Same wing c/g point!!! Lololhahaha
04-21-2016, 05:28 PM
#43
Senior Member
nope
The CG that was wrong to begin with let's say was an inch too far aft. Let's say it was 6" from the prop nut, ok? I believe everyone would agree, there is only one CG and it's in the wrong place and that place is 6" back. So, tell us all how you're going to move a heavy component like the wing and not change the location of that bad CG. OK?
As for "same wing c/g point".................. There wasn't a correct one to begin with. There was a place the mfg suggested it should be. But the c/g that existed when you saw it would take 5 ounces to move the CG to where it belonged, moved forward didn't it. From one place to another. Two different places. And notice no mention is made of where it was on the wing.
You're playing with semantics, and not getting that right either.
But let's forget semantics.
The CG location helps determine pitch stability and the sensitivity of the pitch control. The real purpose of it's location is to insure the pilot can control the pitch and the plane is adequately stable so that same pilot's workload is reasonable. Pitch stability and controllability are a function of the horizontal tail for the most part. That's why the formulas include them.
If you look at the descriptions in the formulas online, you'll see static margins explained. Pay attention to them and what they mean, and you'll discover they help you set elevator throws based on your choice of margin.
So where did you come up with the idea that RC planes don't have a CG range? They usually don't have wings that can be adjusted forward and aft.
04-21-2016, 05:39 PM
#44
Senior Member
Pitch stability/controllability isn't just a function of the Static Margin (CG location). The controllability is also a function of the elevator throw.
That'd be a big DUH a few years back. Unfortunately, a lot of modelers learned "all there is to know" without any mention that "elevator throw affects pitch response".
That'd be a big DUH a few years back. Unfortunately, a lot of modelers learned "all there is to know" without any mention that "elevator throw affects pitch response".
04-22-2016, 11:32 AM
#45
I find it amusing how a stupid question can generate so much response and the OP has never responded. It's almost like he just wanted to start and issue and see what happens.
04-22-2016, 12:43 PM
#46
My Feedback: (41)
same?
Nope
the cg that was wrong to begin with let's say was an inch too far aft. Let's say it was 6" from the prop nut, ok? I believe everyone would agree, there is only one cg and it's in the wrong place and that place is 6" back. So, tell us all how you're going to move a heavy component like the wing and not change the location of that bad cg. Ok?
As for "same wing c/g point".................. There wasn't a correct one to begin with. There was a place the mfg suggested it should be. But the c/g that existed when you saw it would take 5 ounces to move the cg to where it belonged, moved forward didn't it. From one place to another. Two different places. And notice no mention is made of where it was on the wing.
You're playing with semantics, and not getting that right either.
But let's forget semantics.
The cg location helps determine pitch stability and the sensitivity of the pitch control. The real purpose of it's location is to insure the pilot can control the pitch and the plane is adequately stable so that same pilot's workload is reasonable. Pitch stability and controllability are a function of the horizontal tail for the most part. That's why the formulas include them.
If you look at the descriptions in the formulas online, you'll see static margins explained. Pay attention to them and what they mean, and you'll discover they help you set elevator throws based on your choice of margin.
So where did you come up with the idea that rc planes don't have a cg range? They usually don't have wings that can be adjusted forward and aft.
Nope
the cg that was wrong to begin with let's say was an inch too far aft. Let's say it was 6" from the prop nut, ok? I believe everyone would agree, there is only one cg and it's in the wrong place and that place is 6" back. So, tell us all how you're going to move a heavy component like the wing and not change the location of that bad cg. Ok?
As for "same wing c/g point".................. There wasn't a correct one to begin with. There was a place the mfg suggested it should be. But the c/g that existed when you saw it would take 5 ounces to move the cg to where it belonged, moved forward didn't it. From one place to another. Two different places. And notice no mention is made of where it was on the wing.
You're playing with semantics, and not getting that right either.
But let's forget semantics.
The cg location helps determine pitch stability and the sensitivity of the pitch control. The real purpose of it's location is to insure the pilot can control the pitch and the plane is adequately stable so that same pilot's workload is reasonable. Pitch stability and controllability are a function of the horizontal tail for the most part. That's why the formulas include them.
If you look at the descriptions in the formulas online, you'll see static margins explained. Pay attention to them and what they mean, and you'll discover they help you set elevator throws based on your choice of margin.
So where did you come up with the idea that rc planes don't have a cg range? They usually don't have wings that can be adjusted forward and aft.
04-22-2016, 12:49 PM
#47
My Feedback: (41)
"gullows" made balsa ,throw gliders..
Main wing had a "slot"
you could ..slide wing forward "loops ..slide it back"" level flight . Nose weight was ;always; the same, place and, amount .
Moving the wing change balance !! Last lesson for today.
Ague with someone, your teaching them>. {face red} ??
04-23-2016, 02:51 AM
#48
Senior Member
being that you fired first shot.. Ill dumb it down for you..
"gullows" made balsa ,throw gliders..
Main wing had a "slot"
you could ..slide wing forward "loops ..slide it back"" level flight . Nose weight was ;always; the same, place and, amount .
Moving the wing change balance !! Last lesson for today.
Ague with someone, your teaching them>. {face red} ??
"gullows" made balsa ,throw gliders..
Main wing had a "slot"
you could ..slide wing forward "loops ..slide it back"" level flight . Nose weight was ;always; the same, place and, amount .
Moving the wing change balance !! Last lesson for today.
Ague with someone, your teaching them>. {face red} ??
By changing the location of the wing relative to the tail, the tail gains more effect or loses effect. It's primary function is pitch stability and it's ability to do that changes when it's leverage decreases. It's size doesn't change but it's leverage does. When it's got enough leverage it will hold the gliders pitch steady. The glider will fly level. It also happens that it balances the lift from the tail with the pitching moment generated by the wing, but that's another lesson. There happens to be a number of aerodynamic things going on that are significant to the pitch of models other than balance. All of them will be working at the same time. Weight distribution is one, but not all. And it's not the most important either. In fact, they're all important.
Humans seem compelled to think lots of complex things are far simpler than they are. Balancing an airplane, especially a model airplane, is one of those. A simple glider is a good example of how just one way to balance it really isn't doing just one thing. It's also a good example of why very, very few of our present model airplanes have wings that can be adjusted fore and aft. Those hand gliders that do often change their aero and weight balance when thrown and those friction held wings shift under load.
This model stuff really isn't sound bite simple.
Last edited by da Rock; 04-23-2016 at 06:57 AM.
04-23-2016, 03:05 AM
#49
Senior Member
BTW, the glider's tail not only is gaining or losing effect when it's moved forward/aft, it's also gaining or losing amount and direction of lift. Horizontal tails work in "downwash" (and sometimes it can be "upwash", however the "up" and "down" can just be thought of + or - ) which can be more important than balance. anyway......
Moving the tail relative to the downwash generator obviously would change the effect of that wash. Full scale aircraft often have the benefit of stabilizer trim to deal with some of that mess. And it's not that simple, because the forces also change with different speeds, something that also happens with the balance of airplanes. Nothing is sound bite simple is it...
Keep in mind that the weights of (and in) our models don't change very much, while it's speed often has quite a bit of range. At slow speed the things on our models that keep it stable often don't work with very much power. That's one reason it's good to have the balance sorted out to be within the CG range for a model before it's maiden flight.
Moving the tail relative to the downwash generator obviously would change the effect of that wash. Full scale aircraft often have the benefit of stabilizer trim to deal with some of that mess. And it's not that simple, because the forces also change with different speeds, something that also happens with the balance of airplanes. Nothing is sound bite simple is it...
Keep in mind that the weights of (and in) our models don't change very much, while it's speed often has quite a bit of range. At slow speed the things on our models that keep it stable often don't work with very much power. That's one reason it's good to have the balance sorted out to be within the CG range for a model before it's maiden flight.
Last edited by da Rock; 04-23-2016 at 03:09 AM.
04-23-2016, 06:42 AM
#50
My Feedback: (41)
btw, the glider's tail not only is gaining or losing effect when it's moved forward/aft, it's also gaining or losing amount and direction of lift. Horizontal tails work in "downwash" (and sometimes it can be "upwash", however the "up" and "down" can just be thought of + or - ) which can be more important than balance. Anyway......
Moving the tail relative to the downwash generator obviously would change the effect of that wash. Full scale aircraft often have the benefit of stabilizer trim to deal with some of that mess. And it's not that simple, because the forces also change with different speeds, something that also happens with the balance of airplanes. Nothing is sound bite simple is it...
Keep in mind that the weights of (and in) our models don't change very much, while it's speed often has quite a bit of range. At slow speed the things on our models that keep it stable often don't work with very much power. That's one reason it's good to have the balance sorted out to be within the cg range for a model before it's maiden flight.
Moving the tail relative to the downwash generator obviously would change the effect of that wash. Full scale aircraft often have the benefit of stabilizer trim to deal with some of that mess. And it's not that simple, because the forces also change with different speeds, something that also happens with the balance of airplanes. Nothing is sound bite simple is it...
Keep in mind that the weights of (and in) our models don't change very much, while it's speed often has quite a bit of range. At slow speed the things on our models that keep it stable often don't work with very much power. That's one reason it's good to have the balance sorted out to be within the cg range for a model before it's maiden flight.