Ultimate Perfomance Coaxial
09-08-2007, 08:54 AM
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Ultimate Perfomance Coaxial
Hi all,
I just responded to Chris1379 with some thoughts about the coaxial helis. As usual, the more I think the deeper I get into this stuff, so the reply perhaps overran its welcome.
But the reply did generate some thoughts and I'll throw it out as its own post.
Currently coaxial helis are pretty much at the bottom of the RC Helicopter food chain. They are an excellent place to start. I am still of the belief that these helis can be made to fly way outside of the design performance envelope. Many of us fly coaxial because we aren't ready for single rotor or we realize our limitations and we simply aren't going to fly a single rotor. But the mechanics / dynamics of a coaxial helicopter is most certainly not second rate. Look at the Sikorsky X2.
[link=http://Sikorsky Coaxial]http://aeronode.com/aero/18/sikorsky-twin-rotor-x2-ground-run-in-october[/link]
That's some cool stuff. I honestly believe that there will come a time when those of us who appreciate a coaxial will have a performance heli to play with. We are seeing the possibilities as we mod the humble little CX/2. We have a lot of work to do and that will require learning to fly better as we boost the performance envelope.
So let's look at what we know.
FLYBAR: The shorter lighter flybar works. We get hover and performance and the balance between the two is adjustable. For this talk, dial the flybar in for "Barely able to hover, but goes like crazy".
BATTERY:We know that there is performance to be had in battery tech so for this talk let's assume we have a higher density pack. I use a Common Sense RC lipo. It's larger than the stock but the V's and A's are the same. It's bigger so it has more power. With the mods to my heli, I'm still at the stock weight with the bigger lipo.
MOTOR: Ndoren uses ball bearing motors and his posts will tell what he uses. Nicer sounding and easier spinning, they do put out more power per amp.
WEIGHT: Less is more. Boom weighs less than body. No canopy saves a bit. Tail is just a counterbalance on a coaxial heli. It can be extremely light weight weight, if fragile. Move the battery for balance.
BLADES: I read a post talking about shortening blades. I haven't done it yet, but I'm certain that there is a length that will serve us better than stock. I'll cut an inch off a set of blades in the future and post the results. I'll bet the rotors spin faster due to less drag and a shorter arc at the tips. And the higher rpm will add stability and make up the lift loss from the short blades. Should work well with the ball bearing motors. The shorter blades will be stiffer and the shaft lengths can be shortened so the heli looks less 'coaxial'. And the closer the blades can be without clacking, the more they work together providing more lift.
The bugger in this is going to be getting the flybar to cooperate with the higher rpm and short rotor blades ( which won't clack, if you care). As I alluded to earlier, as I change things and get more performance I tend to call the results "Unstable". The truth may be that I'm getting closer to the flight characteristics of a single rotor heli and I have a devil of a time with those. Until we get the performance smooth and stable, the problem may well be in our ability.
I think that the ultimate in performance helis (not sure about 3D) with the ability to go fast, turn fast, hover stable and basically rip around the yard will have a coaxial drive head. With no need for a tail rotor look at the power saved for the main rotors. And the coaxial unit is more compact with shorter blades. Because of the aerodynamics of a coaxial rotor head, far more lift is provided per watt (this has been proven in the real world).
Thoughts?
I just responded to Chris1379 with some thoughts about the coaxial helis. As usual, the more I think the deeper I get into this stuff, so the reply perhaps overran its welcome.
But the reply did generate some thoughts and I'll throw it out as its own post.
Currently coaxial helis are pretty much at the bottom of the RC Helicopter food chain. They are an excellent place to start. I am still of the belief that these helis can be made to fly way outside of the design performance envelope. Many of us fly coaxial because we aren't ready for single rotor or we realize our limitations and we simply aren't going to fly a single rotor. But the mechanics / dynamics of a coaxial helicopter is most certainly not second rate. Look at the Sikorsky X2.
[link=http://Sikorsky Coaxial]http://aeronode.com/aero/18/sikorsky-twin-rotor-x2-ground-run-in-october[/link]
That's some cool stuff. I honestly believe that there will come a time when those of us who appreciate a coaxial will have a performance heli to play with. We are seeing the possibilities as we mod the humble little CX/2. We have a lot of work to do and that will require learning to fly better as we boost the performance envelope.
So let's look at what we know.
FLYBAR: The shorter lighter flybar works. We get hover and performance and the balance between the two is adjustable. For this talk, dial the flybar in for "Barely able to hover, but goes like crazy".
BATTERY:We know that there is performance to be had in battery tech so for this talk let's assume we have a higher density pack. I use a Common Sense RC lipo. It's larger than the stock but the V's and A's are the same. It's bigger so it has more power. With the mods to my heli, I'm still at the stock weight with the bigger lipo.
MOTOR: Ndoren uses ball bearing motors and his posts will tell what he uses. Nicer sounding and easier spinning, they do put out more power per amp.
WEIGHT: Less is more. Boom weighs less than body. No canopy saves a bit. Tail is just a counterbalance on a coaxial heli. It can be extremely light weight weight, if fragile. Move the battery for balance.
BLADES: I read a post talking about shortening blades. I haven't done it yet, but I'm certain that there is a length that will serve us better than stock. I'll cut an inch off a set of blades in the future and post the results. I'll bet the rotors spin faster due to less drag and a shorter arc at the tips. And the higher rpm will add stability and make up the lift loss from the short blades. Should work well with the ball bearing motors. The shorter blades will be stiffer and the shaft lengths can be shortened so the heli looks less 'coaxial'. And the closer the blades can be without clacking, the more they work together providing more lift.
The bugger in this is going to be getting the flybar to cooperate with the higher rpm and short rotor blades ( which won't clack, if you care). As I alluded to earlier, as I change things and get more performance I tend to call the results "Unstable". The truth may be that I'm getting closer to the flight characteristics of a single rotor heli and I have a devil of a time with those. Until we get the performance smooth and stable, the problem may well be in our ability.
I think that the ultimate in performance helis (not sure about 3D) with the ability to go fast, turn fast, hover stable and basically rip around the yard will have a coaxial drive head. With no need for a tail rotor look at the power saved for the main rotors. And the coaxial unit is more compact with shorter blades. Because of the aerodynamics of a coaxial rotor head, far more lift is provided per watt (this has been proven in the real world).
Thoughts?
09-08-2007, 12:15 PM
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RE: Ultimate Perfomance Coaxial
That Sikorsky guys are coming with coaxial heli's! It's not what they are know for! 
.
(We all know the S-61 (Sea King), the S-64 (Tarhe) (freight/firefighters), the S-70 (Blackhawk), etc)
If they have faith in coaxial, we should too! They (probably
) have a bit more knowledge about the coaxial workings.
Props for another soloboss' special.
Some things to add/question:
FLYBAR: Being the counter-force on the movement you put into the lowerrotors, you'll want to set this to your liking.
For example i've only just bought an adjustable flybar, but with my servolinkages in the second hole, i found that it's pretty easy to completely mess up the flight stability.
I'll try with the servolinks in normal/stock position somewhere this week. What setting are yours on Solo?
BATTERY: Too bad the CX2 can't fit a bit bigger batteries, like the Lama V4 can. Then it'll be possible to use an 1100mAh 25C! (Which gives the Lama around 25 min of flighttime on stock stuff). I'll try to squeeze one in probably around next weekend and see how it goes! I'm waiting on DN Power versions (1x 850mAh 15C and 1x 900mAh 10C) and post my results with stock and Xtreme engines.
MOTOR: Still running on stock, awaiting Xtremes to arrive. I've only heared good things about them, but i'll see for myself. Couldn't find Ndoren's experiences (not behind a PC).
WEIGHT: I'm afraid my CX2 is getting 'fat' because of all the alloy parts, but as my precision scale isn't there yet, i cant really tell the difference. Upgraded after only 3 days, so no real experience on this one. Would be nice to find out though.
BLADES: Some LHS' around here also say that they've found the flight to be a bit more 'aggresive' and less alt. drop in sharp turns (due to blade bending) on coaxials. I don't dare to try yet, because they don't sell CX2-type blades around here, only bladegrip versions. Is there someone to give/make a scientific statement on this one?
BODY: I'm getting really sick and tired of my stock 'rear-end', it's wobbly, very sensitive to any kind of airmovement other than the heli's (and in corners it is even thrown of by that!). I wonder what the effect of the 'wings' (both horizontal as vertical) is on the body, IMO it's just estatic/looks-wise, but maybe some kind of forward stability? Although it flies fine without the body at all...
I found that it's real easy too mess up the stability of the CX2. Just a battery hanging out a bit, bent flybar (reminder to self: i should get me one of those CF versions!), just a little bit of tension/drag or too much play, bladetracking, blade flex (it seems to me blades can get 'old' and flex way more?) and so on. But when we have all of this figured out and nicely balanced, it's a dream to fly!!!
I hope there'll be a manufacturer (like Align), who's willing to fabricate (not just for show!) a bigger, better version of a coaxial heli!
For example one on 3700KV motors, with carbon frame and blades, real CNC'd parts, a proper gyro and ESC, able to fit large LiPo's...
But again, i'll probably should keep on dreaming
.(We all know the S-61 (Sea King), the S-64 (Tarhe) (freight/firefighters), the S-70 (Blackhawk), etc)
If they have faith in coaxial, we should too! They (probably
) have a bit more knowledge about the coaxial workings. Props for another soloboss' special
.Some things to add/question:
FLYBAR: Being the counter-force on the movement you put into the lowerrotors, you'll want to set this to your liking.
For example i've only just bought an adjustable flybar, but with my servolinkages in the second hole, i found that it's pretty easy to completely mess up the flight stability.
I'll try with the servolinks in normal/stock position somewhere this week. What setting are yours on Solo?
BATTERY: Too bad the CX2 can't fit a bit bigger batteries, like the Lama V4 can. Then it'll be possible to use an 1100mAh 25C! (Which gives the Lama around 25 min of flighttime on stock stuff). I'll try to squeeze one in probably around next weekend and see how it goes! I'm waiting on DN Power versions (1x 850mAh 15C and 1x 900mAh 10C) and post my results with stock and Xtreme engines.
MOTOR: Still running on stock, awaiting Xtremes to arrive. I've only heared good things about them, but i'll see for myself
. Couldn't find Ndoren's experiences (not behind a PC).WEIGHT: I'm afraid my CX2 is getting 'fat' because of all the alloy parts, but as my precision scale isn't there yet, i cant really tell the difference. Upgraded after only 3 days, so no real experience on this one. Would be nice to find out though.
BLADES: Some LHS' around here also say that they've found the flight to be a bit more 'aggresive' and less alt. drop in sharp turns (due to blade bending) on coaxials. I don't dare to try yet, because they don't sell CX2-type blades around here, only bladegrip versions. Is there someone to give/make a scientific statement on this one?
BODY: I'm getting really sick and tired of my stock 'rear-end', it's wobbly, very sensitive to any kind of airmovement other than the heli's (and in corners it is even thrown of by that!). I wonder what the effect of the 'wings' (both horizontal as vertical) is on the body, IMO it's just estatic/looks-wise, but maybe some kind of forward stability? Although it flies fine without the body at all...
I found that it's real easy too mess up the stability of the CX2. Just a battery hanging out a bit, bent flybar (reminder to self: i should get me one of those CF versions!), just a little bit of tension/drag or too much play, bladetracking, blade flex (it seems to me blades can get 'old' and flex way more?) and so on. But when we have all of this figured out and nicely balanced, it's a dream to fly!!!
I hope there'll be a manufacturer (like Align), who's willing to fabricate (not just for show!) a bigger, better version of a coaxial heli!
For example one on 3700KV motors, with carbon frame and blades, real CNC'd parts, a proper gyro and ESC, able to fit large LiPo's...
But again, i'll probably should keep on dreaming
09-08-2007, 03:30 PM
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RE: Ultimate Perfomance Coaxial
ORIGINAL: shufflez
That Sikorsky guys are coming with coaxial heli's! It's not what they are know for!.
(We all know the S-61 (Sea King), the S-64 (Tarhe) (freight/firefighters), the S-70 (Blackhawk), etc)
If they have faith in coaxial, we should too! They (probably) have a bit more knowledge about the coaxial workings.
>>>AMEN! And I'm with them all the way. I'd love to be on the leading edge of the "coaxial revolution"!
Props for another soloboss' special.
Some things to add/question:
>>>Shoot - I'm a good listener.
FLYBAR: Being the counter-force on the movement you put into the lowerrotors, you'll want to set this to your liking.
For example i've only just bought an adjustable flybar, but with my servolinkages in the second hole, i found that it's pretty easy to completely mess up the flight stability.
I'll try with the servolinks in normal/stock position somewhere this week. What setting are yours on Solo?
>>>You are just now getting into adjustable flybars?? You are going to have some great fun with this new variable!! I've been all over the map with them - from ultra light (flybar rod with no weight at all) - to 3 weights on each end). For what it's worth, the extremes aren't worth bothering with - oops, there I go again. I may have run across the hot setup and I'm not good enough to fly it! I'm flying a CX, not a CX2. I am in the stock link locations and my performance boost is entirely the flybar.
BATTERY: Too bad the CX2 can't fit a bit bigger batteries, like the Lama V4 can. Then it'll be possible to use an 1100mAh 25C! (Which gives the Lama around 25 min of flighttime on stock stuff). I'll try to squeeze one in probably around next weekend and see how it goes! I'm waiting on DN Power versions (1x 850mAh 15C and 1x 900mAh 10C) and post my results with stock and Xtreme engines.
>>>I always want to be at or below stock weight. I'll trade pretties for weight anytime. If I can reconfigure the heli and jam a bigger battery in, that's what I'll do.
MOTOR: Still running on stock, awaiting Xtremes to arrive. I've only heared good things about them, but i'll see for myself. Couldn't find Ndoren's experiences (not behind a PC).
WEIGHT: I'm afraid my CX2 is getting 'fat' because of all the alloy parts, but as my precision scale isn't there yet, i cant really tell the difference. Upgraded after only 3 days, so no real experience on this one. Would be nice to find out though.
>>>Ndoren has had nothing but good things to say about them "the extreme 180 ball bearing motors with replaceable brushes and vented. These are a direct drop in replacement". Interesting that ndoren has every alloy replacement part available on his heli. He is not using grip type blades. His flight weight and mine are nearly identical. He is using boomtown boom and skids.
NEALL - will you jump in here and help me out?? I hate speaking for someone else! Anyhow, My flight weight is 224 grams. Stock is 227 gm. With the big battery I'm at 227- right at stock weight with about 20% more capacity.
BLADES: Some LHS' around here also say that they've found the flight to be a bit more 'aggresive' and less alt. drop in sharp turns (due to blade bending) on coaxials. I don't dare to try yet, because they don't sell CX2-type blades around here, only bladegrip versions. Is there someone to give/make a scientific statement on this one?
BODY: I'm getting really sick and tired of my stock 'rear-end', it's wobbly, very sensitive to any kind of airmovement other than the heli's (and in corners it is even thrown of by that!). I wonder what the effect of the 'wings' (both horizontal as vertical) is on the body, IMO it's just estatic/looks-wise, but maybe some kind of forward stability? Although it flies fine without the body at all...
>>>I pulled the little wings off of mine and saw improved forward flight. It's aerodynamic vertical pressure, not weight (obviously). Then on the advice of others I went to the stersman (boomtown) boom and skids. No more skid breaks and the tail doesn't 'drive' the heli any more. I can fly through doorways and around furniture and walls. The stock tail sucked into walls, furniture and doors like a magnet. My fast forward was better with the body, but the control is better with the boom.
I found that it's real easy too mess up the stability of the CX2. Just a battery hanging out a bit, bent flybar (reminder to self: i should get me one of those CF versions!), just a little bit of tension/drag or too much play, bladetracking, blade flex (it seems to me blades can get 'old' and flex way more?) and so on. But when we have all of this figured out and nicely balanced, it's a dream to fly!!!
>>>Yep. It's all in the setup. The devil is in the details. I really think that the guys who give up and call these junk will never find a heli they will like. They don't attend to the details. The guys who outgrow the coaxials and move up aren't in that group. They certainly do get it.
I hope there'll be a manufacturer (like Align), who's willing to fabricate (not just for show!) a bigger, better version of a coaxial heli!
For example one on 3700KV motors, with carbon frame and blades, real CNC'd parts, a proper gyro and ESC, able to fit large LiPo's...
But again, i'll probably should keep on dreaming
>>> Everything that we fly or read about started as an idea that became someone's dream.
Here's some more information since you seem to share my fascination with this;
Our fearless pioneers of aeronautical design have proven that a moving surface, such as a helicopter blade or other form of an impeller, creates a region of high energy air known as vortex behind itself as it struggles to produce lift. This vortex is made up of turbulent air particles, excited by the blade, under different pressures and temperatures from the cool and calm air that surrounds them. Unfortunately, in case of the blade, vortex does little to produce lift. It can be useful in keeping airflow close (laminar) to the rear top of airplane wing under high angles of attack, but in our case, it just robs the engine of its power. The most effective way to deal with this robbery is to put another blade, just behind the first one, and spin it in the opposite direction. This is called counterrotation and here's what happens - the second blade sneaks up on the turbulent wake left by the first blade and straightens it out by giving it an equal whack in the opposite direction, harnessing some of the energy (inertia). Counterrotating propellers and rotors will produce up to 30% more force or thrust than the regular ones, driven by the same engine.
There are other benefits when counterrotation is applied to a helicopter. During some abrupt maneuvers tail rotor takes away up to 30% of engine power from the rotor system. Coaxial helicopter does not need a tail rotor because rotors turning in the opposite direction cancel out each other's torque and use all of the engine power to produce lift. Precession, another unwanted gyroscopic phenomena, is also canceled along with the dissymmetry of lift.
I'm done. I have to go mow grass. It finally stopped raining.
Mark
That Sikorsky guys are coming with coaxial heli's! It's not what they are know for!
.(We all know the S-61 (Sea King), the S-64 (Tarhe) (freight/firefighters), the S-70 (Blackhawk), etc)
If they have faith in coaxial, we should too! They (probably
) have a bit more knowledge about the coaxial workings. >>>AMEN! And I'm with them all the way. I'd love to be on the leading edge of the "coaxial revolution"!
Props for another soloboss' special
.Some things to add/question:
>>>Shoot - I'm a good listener.
FLYBAR: Being the counter-force on the movement you put into the lowerrotors, you'll want to set this to your liking.
For example i've only just bought an adjustable flybar, but with my servolinkages in the second hole, i found that it's pretty easy to completely mess up the flight stability.
I'll try with the servolinks in normal/stock position somewhere this week. What setting are yours on Solo?
>>>You are just now getting into adjustable flybars?? You are going to have some great fun with this new variable!! I've been all over the map with them - from ultra light (flybar rod with no weight at all) - to 3 weights on each end). For what it's worth, the extremes aren't worth bothering with - oops, there I go again. I may have run across the hot setup and I'm not good enough to fly it! I'm flying a CX, not a CX2. I am in the stock link locations and my performance boost is entirely the flybar.
BATTERY: Too bad the CX2 can't fit a bit bigger batteries, like the Lama V4 can. Then it'll be possible to use an 1100mAh 25C! (Which gives the Lama around 25 min of flighttime on stock stuff). I'll try to squeeze one in probably around next weekend and see how it goes! I'm waiting on DN Power versions (1x 850mAh 15C and 1x 900mAh 10C) and post my results with stock and Xtreme engines.
>>>I always want to be at or below stock weight. I'll trade pretties for weight anytime. If I can reconfigure the heli and jam a bigger battery in, that's what I'll do.
MOTOR: Still running on stock, awaiting Xtremes to arrive. I've only heared good things about them, but i'll see for myself
. Couldn't find Ndoren's experiences (not behind a PC).WEIGHT: I'm afraid my CX2 is getting 'fat' because of all the alloy parts, but as my precision scale isn't there yet, i cant really tell the difference. Upgraded after only 3 days, so no real experience on this one. Would be nice to find out though.
>>>Ndoren has had nothing but good things to say about them "the extreme 180 ball bearing motors with replaceable brushes and vented. These are a direct drop in replacement". Interesting that ndoren has every alloy replacement part available on his heli. He is not using grip type blades. His flight weight and mine are nearly identical. He is using boomtown boom and skids.
NEALL - will you jump in here and help me out?? I hate speaking for someone else! Anyhow, My flight weight is 224 grams. Stock is 227 gm. With the big battery I'm at 227- right at stock weight with about 20% more capacity.
BLADES: Some LHS' around here also say that they've found the flight to be a bit more 'aggresive' and less alt. drop in sharp turns (due to blade bending) on coaxials. I don't dare to try yet, because they don't sell CX2-type blades around here, only bladegrip versions. Is there someone to give/make a scientific statement on this one?
BODY: I'm getting really sick and tired of my stock 'rear-end', it's wobbly, very sensitive to any kind of airmovement other than the heli's (and in corners it is even thrown of by that!). I wonder what the effect of the 'wings' (both horizontal as vertical) is on the body, IMO it's just estatic/looks-wise, but maybe some kind of forward stability? Although it flies fine without the body at all...
>>>I pulled the little wings off of mine and saw improved forward flight. It's aerodynamic vertical pressure, not weight (obviously). Then on the advice of others I went to the stersman (boomtown) boom and skids. No more skid breaks and the tail doesn't 'drive' the heli any more. I can fly through doorways and around furniture and walls. The stock tail sucked into walls, furniture and doors like a magnet. My fast forward was better with the body, but the control is better with the boom.
I found that it's real easy too mess up the stability of the CX2. Just a battery hanging out a bit, bent flybar (reminder to self: i should get me one of those CF versions!), just a little bit of tension/drag or too much play, bladetracking, blade flex (it seems to me blades can get 'old' and flex way more?) and so on. But when we have all of this figured out and nicely balanced, it's a dream to fly!!!
>>>Yep. It's all in the setup. The devil is in the details. I really think that the guys who give up and call these junk will never find a heli they will like. They don't attend to the details. The guys who outgrow the coaxials and move up aren't in that group. They certainly do get it.
I hope there'll be a manufacturer (like Align), who's willing to fabricate (not just for show!) a bigger, better version of a coaxial heli!
For example one on 3700KV motors, with carbon frame and blades, real CNC'd parts, a proper gyro and ESC, able to fit large LiPo's...
But again, i'll probably should keep on dreaming
>>> Everything that we fly or read about started as an idea that became someone's dream.
Here's some more information since you seem to share my fascination with this;
Our fearless pioneers of aeronautical design have proven that a moving surface, such as a helicopter blade or other form of an impeller, creates a region of high energy air known as vortex behind itself as it struggles to produce lift. This vortex is made up of turbulent air particles, excited by the blade, under different pressures and temperatures from the cool and calm air that surrounds them. Unfortunately, in case of the blade, vortex does little to produce lift. It can be useful in keeping airflow close (laminar) to the rear top of airplane wing under high angles of attack, but in our case, it just robs the engine of its power. The most effective way to deal with this robbery is to put another blade, just behind the first one, and spin it in the opposite direction. This is called counterrotation and here's what happens - the second blade sneaks up on the turbulent wake left by the first blade and straightens it out by giving it an equal whack in the opposite direction, harnessing some of the energy (inertia). Counterrotating propellers and rotors will produce up to 30% more force or thrust than the regular ones, driven by the same engine.
There are other benefits when counterrotation is applied to a helicopter. During some abrupt maneuvers tail rotor takes away up to 30% of engine power from the rotor system. Coaxial helicopter does not need a tail rotor because rotors turning in the opposite direction cancel out each other's torque and use all of the engine power to produce lift. Precession, another unwanted gyroscopic phenomena, is also canceled along with the dissymmetry of lift.
I'm done. I have to go mow grass. It finally stopped raining.
Mark
