Mike Mas
Full Time Senior Member
Posts: 4127
Loc: Roanoke VA USA
Reg: 02-20-00
|
07-16-03 02:08 AM - Post#23048
RE-PRINTED FROM ROTORY MAY / JUNE 03
Using a little theory - let's first examine our machine while inverted in an effort to better understand its behavior. While I can't recall anyone mentioning it before, the first and most important thing that happens to a helicopter while inverted, is the helicopter changes from a clockwise rotor system, to one that is counter-clockwise in rotor direction . . . .
To start this segment off, let's look back for a moment in an attempt to capsulize the advancements of R/C helicopters. Advancements in our hobby are categorized in three groups: pilot, mechanical, and electronics.
Pilot - There is no doubt that the style of flying R/C helicopters has substantially changed. With the combination of simulator pre-training and the new technology of gyros, aerobatics have all but dominated recent helicopter flying.
Mechanical Aside from the re-introduction of CCPM mixing, with its share of growing pains, r/c helicopters as we know them, have remained pretty much unchanged. To prove a point, if you were to put together an 18 year old Schluter Champion, install a 70-90 engine, put on a good set of carbons, add a heading hold gyro, and some 30% fuel, the Champion could easily compete and accomplish most any maneuver executed by today's machines. While there has been a continuous introduction of new equipment, for the most part, they fall into what I call a Cookie Cutter
Electronics - The first thing that comes to mind is our radio control systems. However, other than minor cosmetic menu changes, the actual high-end radio systems remain the same. As I look back at the Futaba 1024 or JR PCM-10 of ten years ago, there are few significant improvements. Feature wise, radio systems from a decade ago still provide ample control of our models. On the flip side, with the advent of the heading hold gyro, twenty-five percent of the transmitter features such as, revo mixing, tail curves, idle up tail rotor tracking adjustments, and the needed program mixes to keep the tail behind the canopy, are now just useless baggage. Since it's highly unlikely that any serious competition pilot is going to fly with a standard gyro, the next wave of mid to high end radios need to be simplified by removing those menus.
In other areas of electronics, the two most significant changes have been in flight simulation and the stabilization of the tail rotor. Gyros, and their amazing ability to lock the tail, have become the key element in bringing new people to our sport. It is almost at the point where a new pilot only has to concentrate on three channels. Thanks to our new generation of heading hold gyros, anyone who wishes to fly R/C helicopters can now do so.
As we all know, flight simulators have opened a new era in model simulation. Now, regardless of how busy you are, it's possible to fly for 3 or 4 hours a week and never leave the house. After pre-flight training on a simulator, it's now possible to actually hover your helicopter for the first time, without breaking it. It's also not uncommon to be able to perform aerobatics on the simulator before you can even hover. Always seek qualified help from a fellow pilot on your first flight.
With the combination of the HH gyro and simulator, more and more guys are moving from sport and contest flying, to aerobatics (3D). At my local flying field, I jokingly refer to some of those maneuvers as, Flyin Flipovers, Piro Maniacs, Spinning Spasms, and Inverted Ignoramuses. Now that the tail stays behind the machine, the amount of new maneuvers possible is staggering. In some cases, the best maneuvers are discovered when someone loses control. Overall, this new style of flying is good for the sport of helicopters, since it keeps the interest level up.
I have a saying, For every bit of good on a helicopter, there's some bad elsewhere. This holds true for the new style of flying as well. While most pilots are concentrating 100% of their efforts upstairs, many are missing one of the key elements of becoming an accomplished flyer, and that is to master your Precision Ground Work, which I have now renamed, 3G - Three Dimensional Ground work.
While I partly feel responsible for starting this 3D thing back in the 70s, my intentions then were to expand the aerobatic capabilities of helicopters. Aerobatics were never intended to eliminate hovering (ground work) all together, or the way our models mimic full scale.
If this presently fits your style of flying, as much as I hate to say it, you're only getting half the picture when it comes to flying an R/C helicopter. Good ground work (3G) is equally as difficult as aerobatics or 3D. In fact, precision ground work can be more difficult than 3D. If you make a mistake performing a 3D maneuver, generally speaking, you're the only one that knows it (if you don�t crash). On the other hand, if you make a mistake doing some ground work, it�s easily recognized. This is the very reason that the ground work or hovering, are the most important maneuvers during FAI competition, since they are performed directly in front of the judges.
In this segment of the Mas Technique, and the few that follow, we'll work on making you a more rounded pilot; this will include understanding what is actually happening to the machine on the ground. Learning good ground work (3G) will also improve your flying �upstairs� as well. As part of this first article, I have included my Mas Tech Setup, along with my Phase II setup for new pilots.
In order to understand what's really happening with our models, let's first review a little heli theory. Once understood, I guarantee your ground work will dramatically improve on your next time out. An all too common phrase, which I hear frequently on our Internet Forums and Chats (www.rotory.com), is pilots attempt to get their cyclic and tail rotor control (right & left) exactly the same. You know, 6 degrees of swashplate tilt to the right, and 6 degrees to the left should result in identical roll rate, right Wrong! I don't want to disappoint anyone, but this line of equal control thinking is theoretically impossible with helicopters.
Depending on rotation, one roll is with torque, and the other is against the torque. A roll to the right is a totally different animal than a roll to the left. The same applies to the tail rotor. Performing a 360 to the left is very different than a 360 to the right. Keep in mind; the tail rotor blades must hold positive pitch to counteract the torque of the main rotor. As you add right tail rotor, the tail blades simply add more pitch. However, with a left input, they must first go to zero pitch, then increase pitch in the other direction. Helicopters are different inverted as well. A tumble, or roll from upright to inverted is different than a tumble or roll from inverted to upright. We'll get back to this. Let's continue on the ground and examine what�s happening.
We're in hover, and everything seems normal. We blip in a little cyclic every second or two to keep the machine where we want it. Essentially, this is normal activity assuming that there is little wind and all things are pretty much equal with regard to the rotor systems. While it seems as if the control system is acting in a linear fashion, on both cyclic and tailrotor, in reality nothing is really balanced in the control system at all. The most important factor that affects our model helicopters is, �Helicopter Lean. It's a topic that�s rarely mentioned and seldom, if at all, written about. This phenomenon can be easily witnessed by observing the helicopter in flight. A helicopter that has a clockwise rotor system, when viewed from the rear, will hover leaning to the right, just as a counter-clockwise rotor system will lean to the left. There are a number of forces acting on our model helicopter that cause it to lean in flight, the main factor is caused by a combination of torque from the main rotor and tail rotor. Remember, for each action, there must be an equal re-action. As you lift your machine off the ground (clockwise rotation) you will notice the left skid lifts off first, and then the right. As you lift up to a hover, look at the disk angle in relation to the ground (use eye protection), it's immediately apparent that the model leans to the right. This same lean also applies to full-scale helicopters.
Years ago, I performed an extensive amount of research and testing on helicopter lean. I carried out many tests, some which shifted the center of gravity to the opposite side of lean by adding weight. Afterwards, I then re-located the fuel tank. I concluded that, for the most part, there was minimal benefit from changing the machine, and lean was something that we had to live with.
While at first, lean might seem immaterial, in reality, the lean (torque) of a helicopter has everything to do with precision hovering. The next time you go out with your machine, I would like you to perform a simple test. As you lift the machine in hover, kick the tail so the machine is nose-in, in front of yourself. Next, I want you to perform a five-second, nose-in 360-degree circle around yourself, to the right. As you perform this maneuver, watch the rotor disk on the machine. You'll notice that when performing the maneuver to the right, the disk now becomes almost level. You'll also notice that the 360-degree nose-in maneuver, only took cyclic input to move it completely through the maneuver.
Next, let's do the same five-second 360-degree nose-in circle to the left. You�ll find that it's totally different. Unlike moving to your right, when you move the helicopter laterally to the left, it requires not only cyclic input but it also requires additional collective as well. In fact, it is actually the collective that moves the machine around the circle, rather than the cyclic. You�ll also notice the rotor disk is now leaning considerably more than it did in hover. Of course, lean happens regardless of whether the machine is nose-in or tail-in. The reason I asked you to perform the maneuver nose-in was because lean is more apparent to the pilot with the canopy facing you, rather than the tail. This simple maneuver shows that indeed our models do not move in a symmetrical manner.
For ground work (3G), with a clockwise machine, you'll always want to move the helicopter laterally, to the helicopter�s left side, or in the opposite direction of its natural lean. So when performing a 360 tail-in circle, you�ll want to move to the machine�s left. Performing a nose-in circle, you'll move it to your right, the machine�s left. As I mentioned, when the machine is moving laterally, to its right, it's the collective that actually makes it move to the right and not so much the cyclic input. If you apply only right cyclic, the helicopter will begin moving to the right, and momentarily it will begin to descend pretty much in-line with the lean of the rotor disk.
While all this might seem un-important, as you progress to ground maneuvers such as a fast, tail down at a 75-degree angle, 360 outside circle outside of yourself (see intro image), the correct direction will mean doing it or not doing it. This maneuver takes almost full collective to perform, if you're going in the wrong direction, you�ll quickly run out of both cyclic and collective control.
While it's not within the scope of this article to completely cover this topic, exercising the proper direction during maneuvers, either in 3D or 3G will make a considerable difference of your overall proficiency. With our models, whether on the ground or in the air, learning about helicopter lean (torque) and learning how to use it to your advantage can determine whether you become a successful pilot or not.
TAIL ROTOR
If you were to apply full tail rotor control to a helicopter in hover, with no wind and with the cyclic trimmed at true center, after a few times around you would notice the machine start to oscillate slightly about the base of the skids. This oscillation of the main rotor disk will worsen the longer you hold the tail rotor control in.
Those of you who have seen my competition machines, may have noticed that I tilt my tail rotor transmission approximately 4-5 degrees, so the centerline of the tail rotor shaft points to an imaginary point towards the centerline of the main rotor. While this is not done to eliminate the main rotor lean, it does improve the helicopter's hovering, lateral, and forward flight characteristics. Without getting too technical, as our helicopter is in hover, it essentially hangs from the centerline point of the main rotor. As the tail rotor compensates for the torque of the main rotor, due to the fact the tail rotor is located 3-5 inches below the centerline of the main rotor head, as you add an input, the force is actually applied 3-5 inches below the plane of the rotor. In effect, a sustained or quick tail rotor input causes the main rotor disk to move out of plane (see fig. 2).
The second reason I designed some tail rotor tilt or angle into my machines is, with the tail rotor tilted up, it also provides some lift to the aft section and that makes a considerable difference in forward flight. As we enter forward flight, and as the tail rotor gains transitional lift, it provides a bit of negative angle to the main rotor disk in flight. This level or slightly negative angle, helps prevent pitch-up in forward flight. Note: This tilt mod is not recommended for 3D flying, where the tail rotor speed and workload is increased dramatically in both directions. In addition, the direction of thrust of the tail rotor is equally important with this modification.
While I was flying Schluter Heli-Boys, I suggested to Dieter Schluter the need to raise the tail rotor up into the centerline of the main rotor to eliminate this problem. Some six months after, a Swept-Up Tail mod was released as an option. While the concept worked fine, the modification did not. The mod used a standard automotive speedometer cable that often failed. In addition, the weight of the cable made the machine tail heavy. On the plus side, I have noticed that the new generation of electrics is now offering a swept-up tail mod. I'm making a public appeal to manufacturers; we need swept-up tail rotor systems on our models. Now that heading hold gyros are moving the tail around the machine faster than ever, there is even more need to move the tail rotor back up, in-line with the main rotor plane.
INVERTED FLIGHT - Getting back to inverted flight, it's important to note, while a helicopter is inverted its behavior is different from its behavior upright. Let's examine our machine while inverted and use a little theory to help us understand its behavior. While I can't recall anyone mentioning it before, the first and most important thing that happens to a helicopter, while it's inverted, is the helicopter changes from a clockwise rotor system, to a counter-clockwise system. This in itself makes the machine feel and fly different. The advancing blade is now on the opposite side of the helicopter. So are the effects of a counter-clockwise helicopter such as, aileron effect and tail rotor over steer. On a clockwise machine the helicopter has a natural tendency to turn to the right as speed increases, now it will go to the left inverted.
Getting back to my G3 article (ground work), the direction we discussed for when moving the machine laterally is now in the opposite direction while inverted. Another important fact is our model has a quicker roll rate from inverted to upright. The reason is simple; while the machine is inverted, it has no pendulum stability, so inputs are much quicker since they need not lift the fuselage (mechanics). On the other hand, while the machine is upright, the weight of the fuselage tends to make the helicopter more stable, since there is a natural tendency for the machine to remain level. This is somewhat like a high-wing airplane. So as you can see, there is more than meets the eye on forward and aft tumbles and rolls.
Another fact is while our machine is inverted, the rotor system is not as efficient when it�s upright. While upright, the main rotor takes in clean undisturbed air through the entire disk area. However, while inverted, not only are the mechanics and canopy disturbing the inflow of air, the tail rotor blades are creating high and low pressure areas located in the 1/3 tip region of the main blades. This is the exact area where all the lift is generated. This disturbed air is being ingested into the rotor system thereby, reducing its efficiency. While the performance difference is minimal, it's still there.
Well I'm quickly running out of space, so I would like to leave you with a task to help make you a better pilot. It's simple; fly your helicopter just as much with the heading hold gyro off, as you do with it on. With the advent of heading hold gyros, you'll find that your throttle/rudder hand is almost idle at times. In order to master helicopters, you need to work your mind and continue to develop your reflexes. Part of mastering a model helicopter is taking the matter in to both hands. It's common knowledge, the right hand is controlled by the left side of the brain, and the left hand is controlled by the right side. In some respect, it's like two PCs, one for your right and another for your left. If you're like the rest of us mortals, you have a good and bad hand. If you don't believe it, try signing your name with your opposite hand. The point I'm trying to get at is if you deprive yourself of training, you'll continue to have just that, a good hand and a bad one.
Years ago, as part of my training for model helicopters, and to further develop my slow left hand, I would keep a rubber band around my index and middle fingers on my right hand as a reminder not to use them. I began opening doors and performing tasks with my left hand. It was tough; I had to actually force myself to use my bad hand. Nevertheless, it can and will make a difference. Other training exercises in my quest to master helicopters and help build reflexes were accomplished by flying with the cyclic and tail rotor trims off-center during practice. At one period, I even went as far as to remove the transmitter springs from the sticks.
I could go on and on, but it's not within the scope of this article to cover what I would like with regard to both ground work (3G) and aerobatics (3D). In an upcoming issue, I will continue the 3G maneuvers in an effort to help get guys back on the ground and enjoying the other half of flying model helicopters.
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galifrey
Senior Member
Posts: 227
Loc: UK
Reg: 12-28-02
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 07-19-03 12:53 PM - Post#23208
In response to Mike Mas
hmmm
a very thought provoking article Mike
I am off now to find some elastic bands for my right hand...
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Jim Mahoney
Senior Member
Posts: 2243
Loc: California
Reg: 06-17-03
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 07-19-03 04:12 PM - Post#23214
In response to Mike Mas
Hello Mike,
Rotory has always been a very good magazine but the last few issues have been outstanding! 3G and the Mas Technique all together, good stuff! Your taking the time to explane things like helicopter lean is what many modelers and myself enjoy. Modelers and heli types in particular love to understand and try to master complex ideas. Maybe any one part of our Helicopter systems are not complex it is the combination of all the subsystems and their interactions that make a complex machine.
I am sure that all the heli types are happy that you are willing to put a reprint on line for all to see and study!
That is very unselfish of you. Thanks!
I usually get my issue of Rotory from Helicopter world (Century) but now I am going to subscribe.
Mike we are waiting for all the information and ideas that you can bring to us, if only Rotory could keep its present quality and become a Weekly Magazine! Of course you would never have time to fly then, so the way it is, is OK.
Thanks and happy flying,
Cherokee Jim Mahoney 
Multiplex - ACT Radios, Youngblood Gyros & Governors, YS Engines, Blitz AVRO 90 - Phoenix Simulator - A123 Batteries - Mikado Helicopters - Hacker Motors & Controllers
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Mike Mas
Full Time Senior Member
Posts: 4127
Loc: Roanoke VA USA
Reg: 02-20-00
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07-20-03 12:31 AM - Post#23223
In response to Jim Mahoney
Hey guys thanks for the kind words - In the next issue (Sept) there is another 3G / 3D Mas Tech article along with reviews on the Picollo Pro - Century Hummingbird - Quickie 15 - Proper menthod of checking shaft runout - 3D profile on Henry Caldwell, plus more!
Mike Mas
"we know around here"
ROTORY ~ THE MOST TRUSTED NAME IN R/C HELICOPTERS
Get Your Free Issue of Rotory
http://www.rotory.com |
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Beej
Senior Member
Posts: 340
Loc: UT, USA
Reg: 06-24-03
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07-21-03 03:45 AM - Post#23295
In response to Mike Mas
Mike,
I read through a couple of your issues from the hobby store, and well...
I subscribed with no regrets.
| BJ
It's not a crash. It's a nicely executed pancake maneuver. |
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JoeK
Member
Posts: 55
Reg: 06-18-03
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07-21-03 06:54 PM - Post#23323
In response to Beej
Great article Mike, while I have not yet gotten to the point of nose in hover ( I will one day ) I understand a lot better now why the heli reacts so different when going in a right 360 vs a left 360 ( tail in for me ) .
Thanks again Mike.
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Mike Mas
Full Time Senior Member
Posts: 4127
Loc: Roanoke VA USA
Reg: 02-20-00
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07-22-03 04:27 AM - Post#23350
In response to JoeK
JoeK,
Hello - just keep at it - work the two points where the machine goes in and out of nose-in. In the next issue, I have some great maneuvers that will help you with nose-in and all other angles.
Mike Mas
"we know around here"
ROTORY ~ THE MOST TRUSTED NAME IN R/C HELICOPTERS
Get Your Free Issue of Rotory
http://www.rotory.com |
|
crash&burn
Professional User
Posts: 89
Reg: 08-05-06
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MAS TECH 3G ROTORY MAY 03
09-02-07 01:29 PM - Post#85308
In response to Mike Mas
Hi Mike...I cant express how gratefull I felt by your example of the Shluter Champion being a bird of competition to this day, with the right electronics in it. A champ was my first bird and it holds a special place im my heart...But here is my question...considering that the bird is hardware and electronics are software can the hardware progress to a level that is at least a factor of 10(maybe anti gravity) from what a bergen is???
| helicopters cant fly...they beat the air into submission |
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Jim Mahoney
Senior Member
Posts: 2243
Loc: California
Reg: 06-17-03
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Re: MAS TECH 3G ROTORY MAY 03
09-05-07 06:21 AM - Post#85361
In response to Mike Mas
Hello All,
Here is Mike's 3G Article in easy to read form:
RE-PRINTED FROM ROTORY MAY / JUNE 03
Using a little theory - let's first examine our machine while inverted in an effort to better understand its behavior. While I can't recall anyone mentioning it before, the first and most important thing that happens to a helicopter while inverted, is the helicopter changes from a clockwise rotor system, to one that is counter-clockwise in rotor direction . . . .
To start this segment off, let's look back for a moment in an attempt to capsulize the advancements of R/C helicopters. Advancements in our hobby are categorized in three groups: pilot, mechanical, and electronics.
Pilot - There is no doubt that the style of flying R/C helicopters has substantially changed. With the combination of simulator pre-training and the new technology of gyros, aerobatics have all but dominated recent helicopter flying.
Mechanical Aside from the re-introduction of CCPM mixing, with its share of growing pains, r/c helicopters as we know them, have remained pretty much unchanged. To prove a point, if you were to put together an 18 year old Schluter Champion, install a 70-90 engine, put on a good set of carbons, add a heading hold gyro, and some 30% fuel, the Champion could easily compete and accomplish most any maneuver executed by today's machines. While there has been a continuous introduction of new equipment, for the most part, they fall into what I call a Cookie Cutter.
Electronics - The first thing that comes to mind is our radio control systems. However, other than minor cosmetic menu changes, the actual high-end radio systems remain the same. As I look back at the Futaba 1024 or JR PCM-10 of ten years ago, there are few significant improvements. Feature wise, radio systems from a decade ago still provide ample control of our models. On the flip side, with the advent of the heading hold gyro, twenty-five percent of the transmitter features such as, revo mixing, tail curves, idle up tail rotor tracking adjustments, and the needed program mixes to keep the tail behind the canopy, are now just useless baggage. Since it's highly unlikely that any serious competition pilot is going to fly with a standard gyro, the next wave of mid to high end radios need to be simplified by removing those menus.
In other areas of electronics, the two most significant changes have been in flight simulation and the stabilization of the tail rotor. Gyros, and their amazing ability to lock the tail, have become the key element in bringing new people to our sport. It is almost at the point where a new pilot only has to concentrate on three channels. Thanks to our new generation of heading hold gyros, anyone who wishes to fly R/C helicopters can now do so.
As we all know, flight simulators have opened a new era in model simulation. Now, regardless of how busy you are, it's possible to fly for 3 or 4 hours a week and never leave the house. After pre-flight training on a simulator, it's now possible to actually hover your helicopter for the first time, without breaking it. It's also not uncommon to be able to perform aerobatics on the simulator before you can even hover. Always seek qualified help from a fellow pilot on your first flight.
With the combination of the HH gyro and simulator, more and more guys are moving from sport and contest flying, to aerobatics (3D). At my local flying field, I jokingly refer to some of those maneuvers as, Flyin Flipovers, Piro Maniacs, Spinning Spasms, and Inverted Ignoramuses. Now that the tail stays behind the machine, the amount of new maneuvers possible is staggering. In some cases, the best maneuvers are discovered when someone loses control. Overall, this new style of flying is good for the sport of helicopters, since it keeps the interest level up.
I have a saying, For every bit of good on a helicopter, there's some bad elsewhere. This holds true for the new style of flying as well. While most pilots are concentrating 100% of their efforts upstairs, many are missing one of the key elements of becoming an accomplished flyer, and that is to master your Precision Ground Work, which I have now renamed, 3G - Three Dimensional Ground work.
While I partly feel responsible for starting this 3D thing back in the 70s, my intentions then were to expand the aerobatic capabilities of helicopters. Aerobatics were never intended to eliminate hovering (ground work) all together, or the way our models mimic full scale.
If this presently fits your style of flying, as much as I hate to say it, you're only getting half the picture when it comes to flying an R/C helicopter. Good ground work (3G) is equally as difficult as aerobatics or 3D. In fact, precision ground work can be more difficult than 3D. If you make a mistake performing a 3D maneuver, generally speaking, you're the only one that knows it (if you don’t crash). On the other hand, if you make a mistake doing some ground work, it’s easily recognized. This is the very reason that the ground work or hovering, are the most important maneuvers during FAI Competition, since they are performed directly in front of the judges.
In this segment of the Mas Technique, and the few that follow, we'll work on making you a more rounded pilot; this will include understanding what is actually happening to the machine on the ground. Learning good ground work (3G) will also improve your flying “upstairs” as well. As part of this first article, I have included my Mas Tech Setup, along with my Phase II setup for new pilots.
In order to understand what's really happening with our models, let's first review a little heli theory. Once understood, I guarantee your ground work will dramatically improve on your next time out. An all too common phrase, which I hear frequently on our Internet Forums and Chats ( www.rotory.com ), is pilots attempt to get their cyclic and tail rotor control (right & left) exactly the same. You know, 6 degrees of swashplate tilt to the right, and 6 degrees to the left should result in identical roll rate, right Wrong! I don't want to disappoint anyone, but this line of equal control thinking is theoretically impossible with helicopters.
Depending on rotation, one roll is with torque, and the other is against the torque. A roll to the right is a totally different animal than a roll to the left. The same applies to the tail rotor. Performing a 360 to the left is very different than a 360 to the right. Keep in mind; the tail rotor blades must hold positive pitch to counteract the torque of the main rotor. As you add right tail rotor, the tail blades simply add more pitch. However, with a left input, they must first go to zero pitch, then increase pitch in the other direction. Helicopters are different inverted as well. A tumble, or roll from upright to inverted is different than a tumble or roll from inverted to upright. We'll get back to this. Let's continue on the ground and examine what’s happening.
We're in hover, and everything seems normal. We blip in a little cyclic every second or two to keep the machine where we want it. Essentially, this is normal activity assuming that there is little wind and all things are pretty much equal with regard to the rotor systems. While it seems as if the control system is acting in a linear fashion, on both cyclic and tailrotor, in reality nothing is really balanced in the control system at all. The most important factor that affects our model helicopters is, Helicopter Lean. It's a topic that’s rarely mentioned and seldom, if at all, written about. This phenomenon can be easily witnessed by observing the helicopter in flight. A helicopter that has a clockwise rotor system, when viewed from the rear, will hover leaning to the right, just as a counter-clockwise rotor system will lean to the left. There are a number of forces acting on our model helicopter that cause it to lean in flight, the main factor is caused by a combination of torque from the main rotor and tail rotor. Remember, for each action, there must be an equal re-action. As you lift your machine off the ground (clockwise rotation) you will notice the left skid lifts off first, and then the right. As you lift up to a hover, look at the disk angle in relation to the ground (use eye protection), it's immediately apparent that the model leans to the right. This same lean also applies to full-scale helicopters.
Years ago, I performed an extensive amount of research and testing on helicopter lean. I carried out many tests, some which shifted the center of gravity to the opposite side of lean by adding weight. Afterwards, I then re-located the fuel tank. I concluded that, for the most part, there was minimal benefit from changing the machine, and lean was something that we had to live with.
While at first, lean might seem immaterial, in reality, the lean (torque) of a helicopter has everything to do with precision hovering. The next time you go out with your machine, I would like you to perform a simple test. As you lift the machine in hover, kick the tail so the machine is nose-in, in front of yourself. Next, I want you to perform a five-second, nose-in 360-degree circle around yourself, to the right. As you perform this maneuver, watch the rotor disk on the machine. You'll notice that when performing the maneuver to the right, the disk now becomes almost level. You'll also notice that the 360-degree nose-in maneuver, only took cyclic input to move it completely through the maneuver.
Next, let's do the same five-second 360-degree nose-in circle to the left. You’ll find that it's totally different. Unlike moving to your right, when you move the helicopter laterally to the left, it requires not only cyclic input but it also requires additional collective as well. In fact, it is actually the collective that moves the machine around the circle, rather than the cyclic. You’ll also notice the rotor disk is now leaning considerably more than it did in hover. Of course, lean happens regardless of whether the machine is nose-in or tail-in. The reason I asked you to perform the maneuver nose-in was because lean is more apparent to the pilot with the canopy facing you, rather than the tail. This simple maneuver shows that indeed our models do not move in a symmetrical manner.
For ground work (3G), with a clockwise machine, you'll always want to move the helicopter laterally, to the helicopter’s left side, or in the opposite direction of its natural lean. So when performing a 360 tail-in circle, you’ll want to move to the machine’s left. Performing a nose-in circle, you'll move it to your right, the machine’s left. As I mentioned, when the machine is moving laterally, to its right, it's the collective that actually makes it move to the right and not so much the cyclic input. If you apply only right cyclic, the helicopter will begin moving to the right, and momentarily it will begin to descend pretty much in-line with the lean of the rotor disk.
While all this might seem un-important, as you progress to ground maneuvers such as a fast, tail down at a 75-degree angle, 360 outside circle outside of yourself (see intro image), the correct direction will mean doing it or not doing it. This maneuver takes almost full collective to perform, if you're going in the wrong direction, you’ll quickly run out of both cyclic and collective control.
While it's not within the scope of this article to completely cover this topic, exercising the proper direction during maneuvers, either in 3D or 3G will make a considerable difference of your overall proficiency. With our models, whether on the ground or in the air, learning about helicopter lean (torque) and learning how to use it to your advantage can determine whether you become a successful pilot or not.
TAIL ROTOR
If you were to apply full tail rotor control to a helicopter in hover, with no wind and with the cyclic trimmed at true center, after a few times around you would notice the machine start to oscillate slightly about the base of the skids. This oscillation of the main rotor disk will worsen the longer you hold the tail rotor control in.
Those of you who have seen my competition machines, may have noticed that I tilt my tail rotor transmission approximately 4-5 degrees, so the centerline of the tail rotor shaft points to an imaginary point towards the centerline of the main rotor. While this is not done to eliminate the main rotor lean, it does improve the helicopter's hovering, lateral, and forward flight characteristics. Without getting too technical, as our helicopter is in hover, it essentially hangs from the centerline point of the main rotor. As the tail rotor compensates for the torque of the main rotor, due to the fact the tail rotor is located 3-5 inches below the centerline of the main rotor head, as you add an input, the force is actually applied 3-5 inches below the plane of the rotor. In effect, a sustained or quick tail rotor input causes the main rotor disk to move out of plane (see fig. 2).
The second reason I designed some tail rotor tilt or angle into my machines is, with the tail rotor tilted up, it also provides some lift to the aft section and that makes a considerable difference in forward flight. As we enter forward flight, and as the tail rotor gains transitional lift, it provides a bit of negative angle to the main rotor disk in flight. This level or slightly negative angle, helps prevent pitch-up in forward flight. Note: This tilt mod is not recommended for 3D flying, where the tail rotor speed and workload is increased dramatically in both directions. In addition, the direction of thrust of the tail rotor is equally important with this modification.
While I was flying Schluter Heli-Boys, I suggested to Dieter Schluter the need to raise the tail rotor up into the centerline of the main rotor to eliminate this problem. Some six months after, a Swept-Up Tail mod was released as an option. While the concept worked fine, the modification did not. The mod used a standard automotive speedometer cable that often failed. In addition, the weight of the cable made the machine tail heavy. On the plus side, I have noticed that the new generation of electrics is now offering a swept-up tail mod. I'm making a public appeal to manufacturers; we need swept-up tail rotor systems on our models. Now that heading hold gyros are moving the tail around the machine faster than ever, there is even more need to move the tail rotor back up, in-line with the main rotor plane.
INVERTED FLIGHT - Getting back to inverted flight, it's important to note, while a helicopter is inverted its behavior is different from its behavior upright. Let's examine our machine while inverted and use a little theory to help us understand its behavior. While I can't recall anyone mentioning it before, the first and most important thing that happens to a helicopter, while it's inverted, is the helicopter changes from a clockwise rotor system, to a counter-clockwise system. This in itself makes the machine feel and fly different. The advancing blade is now on the opposite side of the helicopter. So are the effects of a counter-clockwise helicopter such as, aileron effect and tail rotor over steer. On a clockwise machine the helicopter has a natural tendency to turn to the right as speed increases, now it will go to the left inverted.
Getting back to my 3G article (ground work), the direction we discussed for when moving the machine laterally is now in the opposite direction while inverted. Another important fact is our model has a quicker roll rate from inverted to upright. The reason is simple; while the machine is inverted, it has no pendulum stability, so inputs are much quicker since they need not lift the fuselage (mechanics). On the other hand, while the machine is upright, the weight of the fuselage tends to make the helicopter more stable, since there is a natural tendency for the machine to remain level. This is somewhat like a high-wing airplane. So as you can see, there is more than meets the eye on forward and aft tumbles and rolls.
Another fact is while our machine is inverted, the rotor system is not as efficient when it’s upright. While upright, the main rotor takes in clean undisturbed air through the entire disk area. However, while inverted, not only are the mechanics and canopy disturbing the inflow of air, the tail rotor blades are creating high and low pressure areas located in the 1/3 tip region of the main blades. This is the exact area where all the lift is generated. This disturbed air is being ingested into the rotor system thereby, reducing its efficiency. While the performance difference is minimal, it's still there.
Well I'm quickly running out of space, so I would like to leave you with a task to help make you a better pilot. It's simple; fly your helicopter just as much with the heading hold gyro off, as you do with it on. With the advent of heading hold gyros, you'll find that your throttle/rudder hand is almost idle at times. In order to master helicopters, you need to work your mind and continue to develop your reflexes. Part of mastering a model helicopter is taking the matter in to both hands. It's common knowledge, the right hand is controlled by the left side of the brain, and the left hand is controlled by the right side. In some respect, it's like two PCs, one for your right and another for your left. If you're like the rest of us mortals, you have a good and bad hand. If you don't believe it, try signing your name with your opposite hand. The point I'm trying to get at is if you deprive yourself of training, you'll continue to have just that, a good hand and a bad one.
Years ago, as part of my training for model helicopters, and to further develop my slow left hand, I would keep a rubber band around my index and middle fingers on my right hand as a reminder not to use them. I began opening doors and performing tasks with my left hand. It was tough; I had to actually force myself to use my bad hand. Nevertheless, it can and will make a difference. Other training exercises in my quest to master helicopters and help build reflexes were accomplished by flying with the cyclic and tail rotor trims off-center during practice. At one period, I even went as far as to remove the transmitter springs from the sticks.
I could go on and on, but it's not within the scope of this article to cover what I would like with regard to both ground work (3G) and aerobatics (3D). In an upcoming issue, I will continue the 3G maneuvers in an effort to help get guys back on the ground and enjoying the other half of flying model helicopters.
Mike is there any way to change Fonts and Font size?
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Edited by Jim Mahoney on 09-05-07 06:06 PM. Reason for edit: No reason given.
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