weight VS stability
08-10-2009 | 07:01 PM
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From: Vaughan,
ON, CANADA
weight VS stability
I have a 4 channel foamie that ive been flying for 3 months now, but i dont think im enjoying it as much as could be. Flying it is not hard but landing is a nightmare. I can never bleed off enough speed, the plane always comes in too fast. Every time i try to slow down the plane becomes very unstable and hard to control (especially the roll) and i know im not stalling it because I can fly it even slower at altitude. Every time i try to put it down at its comfortable speed it does not want to land, it just keeps on floating until im forced to either plow it into the ground or go around and try again. The plane came with a metal weight that was to be used for balancing but when i check my plane without the weight it is balanced just fine, so i left it out thinking a lighter plane would be more nimble. So my question is:
If i was to add weight to the aircraft, will it improve or disprove the stability of the aircraft on approach and during level flight; will the plane slow down faster when the throttle is reduced, and will it stop floating when the throttle is cut low to the ground?
Thanks in advance for all your help
If i was to add weight to the aircraft, will it improve or disprove the stability of the aircraft on approach and during level flight; will the plane slow down faster when the throttle is reduced, and will it stop floating when the throttle is cut low to the ground?
Thanks in advance for all your help
08-10-2009 | 07:16 PM
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From: Homestead,
FL
RE: weight VS stability
Hard to say not knowing the airplane! Add the weight and fly the airplane to see how it reacts you can always remove it if you don't like the results.
08-10-2009 | 07:45 PM
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From: Vaughan,
ON, CANADA
RE: weight VS stability
i am in the process of weighing it down right now, im just afraid if it worsens the stability il be coming home with foam chunks rather than a plane
08-10-2009 | 08:38 PM
#4
RE: weight VS stability
You're asking different things. Stability is not necessarily directly proportional to wing loading. If you have the center-of-gravity where it is stated on the plans or instructions then it should be stable enough to glide in without power. Unless it is a highly aerobatic model and they have the COG in a neutral spot - and then it may be a handful at low speed.
You could be trying to land too slow. Some designs will tip stall at low speed - just like real aircraft. If this has tapered wings (a warbird, say) you might just have to keep up some steam.
Flying "on the prop" does allow you to move slowly through the air, but that is not flying. That is making the engine carry stalled wings through the air. If you are flying level "at altitude" then the aircraft will do the same regardless of height above the ground. Wings don't know how far up they are (and don't care). A foamie may have some ground effect, but it wouldn't be much and I doubt it would be more than a few inches of "cushion". I think it may be the illusion that aircraft look like they are moving faster the closer they get to the ground because you have more and closer visual references.
Adding weight to the model will increase wing loading and make it fly faster (and require a higher approach speed).
A solution wold be to mix the ailerons so that they both raise slightly - killing some of the wing's lift (spoilers - the opposite of flaps).
Or just land faster. ;-)
You could be trying to land too slow. Some designs will tip stall at low speed - just like real aircraft. If this has tapered wings (a warbird, say) you might just have to keep up some steam.
. . . i know im not stalling it because I can fly it even slower at altitude.
Adding weight to the model will increase wing loading and make it fly faster (and require a higher approach speed).
A solution wold be to mix the ailerons so that they both raise slightly - killing some of the wing's lift (spoilers - the opposite of flaps).
Or just land faster. ;-)
08-10-2009 | 09:27 PM
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RE: weight VS stability
Oh Boy.......
adding weight is never the best option to improve performance.
Adding weight to a plane that already lands too fast is like adding fuel to a fire.
Try making the plane lighter by substituting lighter onboard equipment and also work on moving the CG back in increments until you can flare the model on a deadstick final.
adding weight is never the best option to improve performance.
Adding weight to a plane that already lands too fast is like adding fuel to a fire.
Try making the plane lighter by substituting lighter onboard equipment and also work on moving the CG back in increments until you can flare the model on a deadstick final.
08-11-2009 | 04:01 AM
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From: Wellington, SOUTH AFRICA
RE: weight VS stability
I have found that a CG which is aft - tends to make the plane floaty and it just wants to fly on a landing.
A plane which is more nose heavy will tend, apart from making it land faster, but will make it easier to get the plane down won't it? Where as a tail heavy plane floats and floats if you don't control your landing - then it stalls and falls. My edge has that tendency. You bring it in and if you are not concentrating on what you are doing - it will just float by on very low speed and sometimes stall (then you have to work quick and precise with your fingers) and then with almost no airspeed the plane will "drop" to the ground.
A plane which is more nose heavy will tend, apart from making it land faster, but will make it easier to get the plane down won't it? Where as a tail heavy plane floats and floats if you don't control your landing - then it stalls and falls. My edge has that tendency. You bring it in and if you are not concentrating on what you are doing - it will just float by on very low speed and sometimes stall (then you have to work quick and precise with your fingers) and then with almost no airspeed the plane will "drop" to the ground.
08-11-2009 | 05:35 AM
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From: FrederickMD
RE: weight VS stability
ORIGINAL: Korps
I have found that a CG which is aft - tends to make the plane floaty and it just wants to fly on a landing.
A plane which is more nose heavy will tend, apart from making it land faster, but will make it easier to get the plane down won't it?
I have found that a CG which is aft - tends to make the plane floaty and it just wants to fly on a landing.
A plane which is more nose heavy will tend, apart from making it land faster, but will make it easier to get the plane down won't it?
A plane that is truly neutrally balanced (not a CG that is aft) will not normally drop the nose when it stalls. Depending on the lateral balance, the similarity of the wings on both sides, and the torque from the motor, when the wing stalls, the plane will tend to drop a wing and enter a spin. This is the "floaty" behavior described above. The stall is quick to occur, and why many people have difficulty learning to land an aerobatic plane.
A nose heavy plane WILL drop the nose. This behavior requires using the elevator to compensate. As the plane slows down, the elevator becomes less effective, requiring more up elevator to keep the plane level. It is possible that the plane will not have enough airspeed to keep the nose level, which causes the nose to drop, and then air speed increases until the plane reaches an equilibrium, or hits the ground. This is why nose heavy planes must land faster. It is not easier to get them on the ground.
If any plane won't descend with the engine at idle, wings level and nose level, then the idle speed is way too high. This can be addressed by lowing the engine idle, or trying a lower pitched prop. To land the plane, the lift produced by the wings must be less than the weight of the plane. Once the engine idle is low enough, its simply a matter of using the elevator to reduce the airspeed (up elevator will slow the plane down) and allow the plane to sink onto the runway. Some people do this just before touchdown (the flair) and others set the plane in that attitude during the approach. Personnally, I think the flare is more difficult. I teach my students the mantra "Wings level, Nose Up" on approach.
Brad
08-11-2009 | 06:01 AM
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From: Wellington, SOUTH AFRICA
RE: weight VS stability
ORIGINAL: bkdavy
Sorry, but this is probably the worst description and reflects a misunderstanding of the relationship between CG and the handling characteristics.
A plane that is truly neutrally balanced (not a CG that is aft) will not normally drop the nose when it stalls. Depending on the lateral balance, the similarity of the wings on both sides, and the torque from the motor, when the wing stalls, the plane will tend to drop a wing and enter a spin. This is the ''floaty'' behavior described above. The stall is quick to occur, and why many people have difficulty learning to land an aerobatic plane.
A nose heavy plane WILL drop the nose. This behavior requires using the elevator to compensate. As the plane slows down, the elevator becomes less effective, requiring more up elevator to keep the plane level. It is possible that the plane will not have enough airspeed to keep the nose level, which causes the nose to drop, and then air speed increases until the plane reaches an equilibrium, or hits the ground. This is why nose heavy planes must land faster. It is not easier to get them on the ground.
If any plane won't descend with the engine at idle, wings level and nose level, then the idle speed is way too high. This can be addressed by lowing the engine idle, or trying a lower pitched prop. To land the plane, the lift produced by the wings must be less than the weight of the plane. Once the engine idle is low enough, its simply a matter of using the elevator to reduce the airspeed (up elevator will slow the plane down) and allow the plane to sink onto the runway. Some people do this just before touchdown (the flair) and others set the plane in that attitude during the approach. Personnally, I think the flare is more difficult. I teach my students the mantra ''Wings level, Nose Up'' on approach.
Brad
ORIGINAL: Korps
I have found that a CG which is aft - tends to make the plane floaty and it just wants to fly on a landing.
A plane which is more nose heavy will tend, apart from making it land faster, but will make it easier to get the plane down won't it?
I have found that a CG which is aft - tends to make the plane floaty and it just wants to fly on a landing.
A plane which is more nose heavy will tend, apart from making it land faster, but will make it easier to get the plane down won't it?
A plane that is truly neutrally balanced (not a CG that is aft) will not normally drop the nose when it stalls. Depending on the lateral balance, the similarity of the wings on both sides, and the torque from the motor, when the wing stalls, the plane will tend to drop a wing and enter a spin. This is the ''floaty'' behavior described above. The stall is quick to occur, and why many people have difficulty learning to land an aerobatic plane.
A nose heavy plane WILL drop the nose. This behavior requires using the elevator to compensate. As the plane slows down, the elevator becomes less effective, requiring more up elevator to keep the plane level. It is possible that the plane will not have enough airspeed to keep the nose level, which causes the nose to drop, and then air speed increases until the plane reaches an equilibrium, or hits the ground. This is why nose heavy planes must land faster. It is not easier to get them on the ground.
If any plane won't descend with the engine at idle, wings level and nose level, then the idle speed is way too high. This can be addressed by lowing the engine idle, or trying a lower pitched prop. To land the plane, the lift produced by the wings must be less than the weight of the plane. Once the engine idle is low enough, its simply a matter of using the elevator to reduce the airspeed (up elevator will slow the plane down) and allow the plane to sink onto the runway. Some people do this just before touchdown (the flair) and others set the plane in that attitude during the approach. Personnally, I think the flare is more difficult. I teach my students the mantra ''Wings level, Nose Up'' on approach.
Brad
08-11-2009 | 07:35 AM
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From: Greenville, SC
RE: weight VS stability
ORIGINAL: gaRCfield
I have found that planes slow down better for landing with a more aft CG.
I have found that planes slow down better for landing with a more aft CG.
To answer your question, though....lighter planes are more stable (except in heavy winds, but that's not a can of worms I'd advise opening up).
08-11-2009 | 08:08 AM
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RE: weight VS stability
ORIGINAL: combatpigg
Oh Boy.......
adding weight is never the best option to improve performance.
Adding weight to a plane that already lands too fast is like adding fuel to a fire.
Try making the plane lighter by substituting lighter onboard equipment and also work on moving the CG back in increments until you can flare the model on a deadstick final.
Oh Boy.......
adding weight is never the best option to improve performance.
Adding weight to a plane that already lands too fast is like adding fuel to a fire.
Try making the plane lighter by substituting lighter onboard equipment and also work on moving the CG back in increments until you can flare the model on a deadstick final.
I have been a long-time proponent of adding weight to planes. A plane has to be light to fly, but "light" is a subjective term. How light is light?
Well... It has to be lighter than a battleship for sure, but like everything else in the world, people take things to extremes. A thick shake should be thicker than milk, so some people come to the false conclusion that "Thicker is better". So now, some fast-food restaurants make shakes that are so thick you can't suck them through a straw! That is not better!
Every airplane has an optimum weight - and even that will vary from one pilot to the next. Just because mine is lighter than yours doesn't mean it's going to fly better. I have built 5 versions of a particular airplane (The Great Planes Ultra Sport). On onee of them, I went through a lot of trouble to make it really light. It still flew well, but not nearly as well as the other four.
So, by all means, add the weight - they put it there for a reason. And, as it's been said, a nose-heavy plane will have a hard time slowing down, so when you add the weight, re-check the CG.
08-11-2009 | 08:09 AM
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From: FrederickMD
RE: weight VS stability
My apologies if my comment seemed harsh, but being the beginners forum, it is important that incorrect information be identified. Many people, particularly beginners, misunderstand that the CG ranges provided by the manufacturers are not between tail-heavy and nose heavy. Most manufacturers recommendations tend to have the aftermost CG recommendation very close to neutral. A tail heavy plane will be aerodynamically unstable. A neutrally balanced plane will be sensitive, but for the most part stable. As the CG moves forward, stability increases, but elevator sensitivity is reduced.
Now you will hear that 3D flyers like their planes to be slightly tail heavy. This is somewhat true, but one has to recognize the true relationship between the aerodynamic center of lift and the angle of incidence. the AC will, in fact, move backward on the wing as the angle of attack increases, causing the plane to enter a more stable aerodynamic condition as the AOA increases, which is why a certain degree of "tail heavy" can be tolerated for high alpha flight. A "tail heavy" plane will be easier to hover, but its going to take a greater degree of skill than most beginners to get it in the air and trimmed out. If the AC does not move far enough for the plane to enter the stable condition before transitioning into the hovering condition, it will try to flip around backward into the wind. A plane so balanced will be extremely sensitive, if not unstable, at higher speeds.
Brad
Now you will hear that 3D flyers like their planes to be slightly tail heavy. This is somewhat true, but one has to recognize the true relationship between the aerodynamic center of lift and the angle of incidence. the AC will, in fact, move backward on the wing as the angle of attack increases, causing the plane to enter a more stable aerodynamic condition as the AOA increases, which is why a certain degree of "tail heavy" can be tolerated for high alpha flight. A "tail heavy" plane will be easier to hover, but its going to take a greater degree of skill than most beginners to get it in the air and trimmed out. If the AC does not move far enough for the plane to enter the stable condition before transitioning into the hovering condition, it will try to flip around backward into the wind. A plane so balanced will be extremely sensitive, if not unstable, at higher speeds.
Brad
08-11-2009 | 08:20 AM
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From: Wellington, SOUTH AFRICA
RE: weight VS stability
I agree with your above post bkdavy, and no apologies are necessary - I was wrong and you corrected me - that's the way you learn.
It's just out of my own experience which I commented on in regard to - I seem to be able to put a plane, which is more "nose heavy", down easier and faster (not refering to speed but to time and precision) than a plane, which is more "tail heavy". This could perhaps just be because of the way I make my approach and the way I fly - and having nothing to do with the CG (which I might have misunderstood it for).
I thank you for correcting me and identifying information which I have miss interpreted.
It's just out of my own experience which I commented on in regard to - I seem to be able to put a plane, which is more "nose heavy", down easier and faster (not refering to speed but to time and precision) than a plane, which is more "tail heavy". This could perhaps just be because of the way I make my approach and the way I fly - and having nothing to do with the CG (which I might have misunderstood it for).
I thank you for correcting me and identifying information which I have miss interpreted.
08-11-2009 | 08:25 AM
#15
My Feedback: (8)
RE: weight VS stability
ORIGINAL: victorzamora
I couldn't agree more! Nose heavy planes have a hard time of bleeding off the speed that a more neutral plane has no problem burning. A plane with a neutral CG will be able to pick the nose up and come in in a VERY slight harrier. Full-scale planes do this. Your descent is NOT controlled by your elevator...it's controlled by your throttle.
ORIGINAL: gaRCfield
I have found that planes slow down better for landing with a more aft CG.
I have found that planes slow down better for landing with a more aft CG.
I found that when I started flying planes last year, all my planes had a forward CG. I kept that going into my more aerobatic/sporty planes as it is what I was used to. The first time I flew a plane with a neutral CG, I remember using elevator on approach and the plane dropped it's tail and came in nose up and bled off all kinds of speed. It was then that I learned that throttle controls the descent and elevator controls the speed.
08-11-2009 | 10:27 AM
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From: littleton,
CO
RE: weight VS stability
Also if you can fly it slower at altitude you can fly it on to the runway. like a slow touch and go and cut your throttle at touch. I got this from the hz super cub I cant land it without power
ORIGINAL: combatpigg
Oh Boy.......
adding weight is never the best option to improve performance.
Adding weight to a plane that already lands too fast is like adding fuel to a fire.
Try making the plane lighter by substituting lighter onboard equipment and also work on moving the CG back in increments until you can flare the model on a deadstick final.
Oh Boy.......
adding weight is never the best option to improve performance.
Adding weight to a plane that already lands too fast is like adding fuel to a fire.
Try making the plane lighter by substituting lighter onboard equipment and also work on moving the CG back in increments until you can flare the model on a deadstick final.
08-11-2009 | 10:56 AM
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From: Vaughan,
ON, CANADA
RE: weight VS stability
OK i think i will add a little bit of weight and balance the plane better and see how it will fly and land. Most importantly, i will return the ailerons to the stock setting. When the plane arrived the ailerons were both pitched up like spoilers... naturally i did not think that leveling them out would make a huge difference (its my first 4 channel plane and it is a war bird corsair with the double dihedral) I think me removing the spoilers was the initial cause of this problem (Thanks to Charlie P. for pointing it out to me).
Thanks for all of the input, the information presented is very valuable to me.
I will come back here in a couple of hours and tell you if the spoilers fixed the problem.
Thanks for all of the input, the information presented is very valuable to me.
I will come back here in a couple of hours and tell you if the spoilers fixed the problem.
08-11-2009 | 11:08 AM
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From: Vaughan,
ON, CANADA
RE: weight VS stability
the way the plane lands would have to disagree, i only landed it good once, it was my very first flight out of the box with the spoilers.
08-11-2009 | 11:16 AM
#20
RE: weight VS stability
if the airlerons were pitched up at the neatral point they were killing alot of lift but also helping to prevent tip stall. remove the spoiler effect a little at a time
08-11-2009 | 01:06 PM
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From: Vaughan,
ON, CANADA
RE: weight VS stability
well i just came back from the test flight. The plane flew better and on approach was a lot more stable. I did a wide approach, came in shallow and faster than usual, throughout the descend the plane was rock solid, with a uniform descent rate, looked like it was going to be a picture perfect landing. The moment the gear touched the ground the plane took a front flip and broke the motor off the motor mount.
I will try to reduce the spoilers little by little after repairs as aerowoof suggests.
I am starting to believe that the terrain i land on is the biggest problem and not the plane. My usual landing spot is a grass field (its a bit patchy and tall) and every time i "land" on it something breaks. there is a small dirt field beside it that is a lot better for landing, but there is no room to fly there.
I will try to reduce the spoilers little by little after repairs as aerowoof suggests.
I am starting to believe that the terrain i land on is the biggest problem and not the plane. My usual landing spot is a grass field (its a bit patchy and tall) and every time i "land" on it something breaks. there is a small dirt field beside it that is a lot better for landing, but there is no room to fly there.
08-11-2009 | 03:09 PM
#23
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RE: weight VS stability
The road from the flying field back to the hobby store is paved with lead.
Build a plane with the lightest materials and most intricate and powerful components money can buy, then tape a bunch of lead chunks to it to make it fly better.
Telling a guy to add weight to a Corsair that is already coming in too hot, then having him actually go out and pile it up is a shame.
Build a plane with the lightest materials and most intricate and powerful components money can buy, then tape a bunch of lead chunks to it to make it fly better.
Telling a guy to add weight to a Corsair that is already coming in too hot, then having him actually go out and pile it up is a shame.
08-11-2009 | 04:33 PM
#25
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RE: weight VS stability
Chances are good that a scale or semi-scale Corsair is already pushing the limits weight-wise for what a lot of flyers would call a good flying model. All flights must end with a landing eventually and having a model that is too heavy to land slow and predictably enough to avoid damage is not my idea of what you want.
Shifting weight around inside the model is usually where you begin. The worst I've ever seen is when the hobbyist has lead glued both inside the cowl and at the tail
.
I would switch to a lower pitched prop and try to get the battery as far aft as possible.
The ailerons should be even with the bottom of the wing for flying but you can experiment with flaperons coupled to the elevator to improve slow speed flight. Start out with very little flap and see if you can tell the difference at a safe height.
Shifting weight around inside the model is usually where you begin. The worst I've ever seen is when the hobbyist has lead glued both inside the cowl and at the tail
.I would switch to a lower pitched prop and try to get the battery as far aft as possible.
The ailerons should be even with the bottom of the wing for flying but you can experiment with flaperons coupled to the elevator to improve slow speed flight. Start out with very little flap and see if you can tell the difference at a safe height.
