Post by Ed Anderson on Mar 22, 2009 14:53:14 GMT -5
Choosing a Sailplane Radio - What to Consider
by Ed Anderson
aeajr on the forums
This is being written for the new or relatively new sailplane/glider pilots
who are interested in flying thermal duration sailplanes. I will make a few
comments on slope planes, but these are not the main focus of the article.
This discussion is going to be more about points of consideration rather
than which is the best radio. The "best" is always that one that is just a few $$ out of your price range or the one that is going to be released next year. Whatever you get, there will always be one that is better at a higher price or that will be released the month after you get yours. So let's throw away that "best" idea. Let's focus on what features and functions you might like to have and their relative importance. Others will have opinions that differ from mine as there is no one right answer. But at least this
can get you thinking.
If you want to ask questions about specific radios, or if you want to share your budget and your goals, I and others can make specific recommendations, but don't be surprised if we don't all recommend the same thing. We each have our opinions.
If you are the club champ or the radio wizard in your group, turn the page because this is not for you. However if you don't mind reading though, you may wish to add your comments. Others will benefit from you knowledge, insights and experience. I am not sensitive, so feel free to disagree, but please keep the comments polite. Flame wars benefit no one.
Ultimately, the recommendations I make are based on people's budget and goals. I try to understand how much they have to spend and where they want this radio to take them. Then I try to focus them on the key decision points I will outline below.
For new flyers, the goals may be more modest, so the introductory radios may be fine for you. However, if you are committed and plan to push ahead aggressively AND you have the budget, then you may want to step into one of the more advanced radios. In my opinion you can not buy too much radio,
but you can buy too little.
Standard vs. Computer Radios
I will not be considering any standard radios during this discussion. They may meet the lifetime needs of a glider pilot who is interested in casual weekend flying of simple rudder/elevator, or even rudder/elevator/spoiler gliders. A 2 or 3 channel standard radio will get you into the air. You can certainly fly full house sailplanes on a 4 channel standard radio and have a lifetime of soaring enjoyment. Never let anyone tell you that you
MUST have a hot shot computer radio to fly gliders/sailplanes because it just isn't true. I have several standard radios that I have used to fly gliders, both thermal and slope. However I have since moved them all over to computer radios for convenience and for enhanced control. The standard radios, like my old typewriter, pretty much gather dust and will likely be
given to friends to help them get started.
If you want more on this subject you may wish to read the content at this link:
Don't Buy a Standard Radio
www.wattflyer.com/forums/showthread.php?t=4454
What computer radios provide are options and opportunities for those who want them. They offer features that can make set-up faster and easier and can make it very convenient to move between several planes. From an actual flying point of view, they can help you get the most out of your plane as well as help reduce the workload of the pilot so s/he can focus on the plane
and the conditions rather than manipulation of the surfaces. Believe me, commercial airline pilots have plenty of computer power to help them fly. Since the price of a computer radio is so reasonable, why shouldn't you have the same advantage.
LET'S START WITH THE BASICS
Sailplanes and gliders, which I will use interchangeably, come in a variety of configurations. The simplest are the rudder/elevator planes that have dihedral or polyhedral in the wings. They have been the favorite trainers for years and some people spend a lifetime enjoying them.
To R/E we can add spoilers, which carries the RES designation. You can also find REF planes which add flaps to rudder/elevator controls. There are also aileron/elevator planes, A/E, which are more common on the slope than as thermal ships. When we have a combination of ailerons, elevator, rudder and flaps, A/E/R/F, we call this a full house sailplane. You can have a plane that has flaps and spoilers, or ailerons and spoilers without flaps, but
this is unusual.
Of course, you can have a motor, but I am focused on pure flight, so no motors on my sailplanes. If you have an electric motor, a simple on/off switch is all you need for motor control. We will likely be using that "throttle" stick for glide path control rather than the motor. Other than this, I won't be discussing motors.
How many Channels?
While there are some interesting four and five channel computer radios, I am going to recommend you get a computer radios with six or more channels. I don't see any real benefit for having less than six channels, as the cost difference is small and the benefits of 6 or more channels is high. Even if you are flying a rudder elevator sailplane today, next year you may be adding spoilers or flaps or going to a full house plane in the future, so get a radio that can handle that so you aren't going back to the radio market right away.
Here is a typical channel breakdown, how many and what they are used to control. These apply to electrics, glow, gas and gliders.
Rudder - 1
Elevator - 1 or 2
Ailerons - 1 or 2
Spoilers - 1 or 2
Flaps - 1 or 2
tow hook - 1
landing gear - 1
Motor - 1
That makes 4, 5, 6, up to 12 channels depending on what kind of plane you have and how you set it up. So how many do you need?
In my opinion, most sport flyers will be well served for a long time with a 6 channel entry to mid level sport computer radio. If you are a more serious sailplane pilot or contest flyer, you probably want a minimum of 7 channels and support for a 4 servo wing. ( more on 4 servo wings later)
Basic Features
Most currently available new computer radios offer the following features. Regardless of what you are flying, I highly recommend your radio have these features.
* Model Memories
* Low Battery Warning
* Digital Trims
* Timer ( one or more )
* End Point Adjustment/Adjustable Travel Volume
* Dual Rates on ailerons and elevator; rudder is optional.
* Elevon and V-tail mixes
Minimum Recommended Surface Mixes
After model memories, surface mixes are one of the great features that computer radios bring to the game. Input to one control can move 2 or more servos in a coordinated fashion to create the kind of surface control you are looking for. This can reduce the pilot's workload while providing very consistent behavior. In most cases, when it makes sense, these mixes can be overridden during the flight or can be turned on and off.
The following list is what I would consider the minimum set I would want in a radio that would be used for flying sailplanes, be it thermal or slope. Where two surfaces are listed, the first is the master and the second follows it. I will discuss these in more detail later, but wanted to get the list part stated up front as people are usually looking for these lists. Most are focused on planes with ailerons or full house planes, but I note where even simpler planes can benefit.
* Exponential on aileron and elevator. Rudder would be a plus.
( all planes)
* Flapperon/Spoileron - requires two aileron servos on separate channels
* Aileron differential - requires two aileron servos on separate channels
* Aileron-rudder mix ( coordinated turns )
* Flap or spoiler to elevator mixing for landing and glide path control.
Very useful on RES, REF or full house planes.
The goal of these mixes is to make the plane easier to fly more smoothly, more efficiently with less drag and more controllability. In addition we gain some level of glide path control to assist with landing accuracy or to help us get out of booming thermals. With these tools you can have a more enjoyable sport flying experience or be more competitive than would be easily achievable with a standard radio.
More Advanced Mixes
These would typically be activated by a switch, dial or other control when needed. You could go through the entire flight and not use these but they give you that extra measure of control or convenience that you may desire. Note, that many computer radios have "free" or user definable mixes so you may be able to create a mix that is not specifically listed, but don't assume
that is the case. Check to see if that free mix can do what you want.
* Flight modes such as launch, cruise, speed, landing, thermal, etc
* Camber Control -
moves the whole trailing edge at once to reshape the wing
* Crow/butterfly/airbrakes - helps with precision landing
These mixes are mostly focused on changing the shape of the wing during flight which changes the wings's lift/drag characteristics. Since we are flying without a motor, the ability to "retune" the wing to the needs of the moment can be very helpful in getting the most out of the current lift conditions or getting out of a bad situation. These would all likely be
able to be turned on and off during the flight so that we can use them according to the situation.
For example, if you have flaps and ailerons, a launch mix might drop the flaps 20 degrees and the ailerons 20 degrees giving your wing a more undercambered shape. This might also include some up or down elevator, depending on your plane. This generates tons of lift but also creates more drag. While this might be detrimental during normal fight, when you have the force of the hi-start or the winch pulling your plane up, you can afford
this extra drag to gain higher launches.
Having launch set up as a flight condition means that you flip a switch and the plane's surfaces move to a predetermined position for launch. Just before you finish the climb, you flip that switch off to go into normal flight/cruise mode. Quick, easy and convenient surface control activated by as switch. While you might be able to do some of this on a standard radio,
the work load would be high and getting consistent behavior would be much harder. Computer radios make it easy!
The Four Servo Wing
One of the features that I feel sets apart the "sport radios" from the "advanced " radios is the ability to directly address all four wing servos, each on its own channel. The sport radios can fly a plane with 4 servos in the wing, but they require that the flaps be on one channel through the use of a Y cable. This means that you have 4 servos but you are controlling them as if they were 3 servos. Where the 4 servo wing support comes in handy is in trimming and in aileron-flap mixing. There may be others, but these are where I have used this capability.
Typically you won't find this on a radio with less than seven channels, and most have eight or more channels. Read the manual or the specs and look for this feature. If you don't see it mentioned, look for how flaps are set-up. If both flap servos are assigned to the same channel, you don't have 4 wing servo control.
When you have both flaps on a Y cable you must trim them mechanically to get them synchronized. This can be done but it can be tricky and time consuming. It is very important that the flaps move together. If one flap moves further than the other anywhere through its throw it will tend to cause the plane to roll left or right making the plane more difficult to control. Flap trimming can be done using servo arm/control horn arm
placement, making sure the control rods are the same length and by adjusting the clevis screws to get them even. Then you can trim the flaps together using the radio to get that final zero point and the end point for down flaps.
However if you can address each flap individually from the radio you can do final trimming from the radio, which is a great convenience. You can also use an aileron/flap mix to have the flaps follow the ailerons for more, or smoother roll authority. I use this on my planes. This is not a necessary feature but if you are going to invest in a "serious" sailplane radio, you will want to be able to address the four wing servos individually.
Frequency Options and Opportunities 2.4 GHz and 72 MHz
In North America there are two primary radio systems for RC flying, 72 MHz and 2.4 GHz. There are others, but these are the most popular.
Spread Spectrum or 2.4 GHz are often used interchangeably. This is not technically correct but for practical purposes you can consider them the same thing.
The new 2.4 GHz radio systems have several advantages over the older 72 MHz systems.
Channel conflict his handled automatically. On 72 MHz you have to be careful not to fly on the same channel as another pilot. The 2.4 GHz radios handle this automatically. As such, they avoid "frequency conflict" at the field. This occurs when two 72 MHz pilots have planes on the same channel. One has to wait while the other one flies. On 2.4 this problem goes away.
One installation situation to note has to do with carbon fiber fuselages. Because 72 MHz antenna are over 39" long, they can be easily installed to avoid the signal blocking nature of carbon fiber. However 2.4 GHz receivers have very short antenna of just a few inches. It is much harder to get these outside the carbon fuselage, but it can be done. While advances are being made in this are, if you are planning to fly a plane with a carbon fuselage, you should be careful about how you install any radio system to be sure the signal is not blocked.
Note that many airplane makers are now modifying their designs to make them more 2.4GHz friendly. They are reducing the amount of carbon in the design by using other high strength materials. So this problem should be reduced over time.
There are other benefits with 2.4 GHz and new features are being added to the new radios all the time. But it is clear that 2.4 GHz is the wave of the future. Virtually all new radios are being released on 2.4. The 72 MHz market is falling off fast. This is leading to a very big used market for old 72 MHz stuff so there should be ample supply of receivers and such for many years to come.
If you are new to RC flying, or looking to upgrade your radio system, you should give 2.4 GHz very serious consideration.
If you do have, or are buying a 72 MHz radio, here are some things you will want to know.
More on Mixes
Let's walk through a flight and see where some of this mix stuff might be used.
We have our plane set up on a 6 channel computer radio. We have the following features and mixes enabled and active all the time.
* Exponential on aileron and elevator
If you want to better understand Expo, take a look at this article:
www.rcgroups.com/forums/showthread.php?t=331087
* Aileron differential -
Up aileron goes up more than the down goes down.
Less drag as well as other benefits
* Aileron-rudder mix
by automatically adding rudder to the ailerons we get a smoother,
more efficient turn reducing drag and enhancing control.
* Flap-elevator mix for landing.
Automatically helps keep the plane level when we apply the flaps
as we are landing.
Time to launch!
- We flip that switch for our launch setting. Flaps come down maybe 20 degrees and the ailerons come down 10 degrees. We launch the plane and send it up the launch line. At the top of the launch we will turn this off so that we are in normal cruise mode. We are now 400-600 feet up and looking for lift.
Let's go hunting!
We spot some lift and we start to circle. We might flip on Elevator-flap mix, so when we pull up elevator we get a tiny bit of flap to help us climb smoothly in a thermal. Or we might turn on "thermal" flight mode mix to slightly droop the flaps and ailerons to give the wing a bit more lift. We climb high and enjoy the ride.
We lose the lift so we turn off our thermaling mix and go hunting again. We hit some fast falling air; sink. We want to run through some sink, so we flip our camber/reflex preset and the flaps and ailerons move up a little to reflex position and the plane moves quickly through the sink. When we are in more buoyant air we flip this off.
We catch some lift and circle up again. We turn our thermaling mixes on.
We have been in this thermal for 20 minutes or so. We might be at 1000 feet and have ridden the thermal about 1/2 of a mile down wind. Time to head home and prepare to land.
During our return run we will fly in cruise or we might turn on that
reflex preset again to help us penetrate through the head wind.
Remember we have no motor so we are flying upwind in a glide.
As we approach the field we want to have more energy than we need to make it to the landing mark because a gust might hit us, or we might hit some sink and lose altitude fast, causing us to fall short. Best to come in with more energy than we need.
As we get close to the landing zone and are confident, we can start to use that flap-elevator landing mi , or, if we have spoilers we might use a spoiler-elevator mix. If we have a more advanced radio we might use the crow (butterfly) mix, to help us slow down and bleed off altitude without gaining too much speed. As we judge our speed we may we may use a partial landing mix or go to a full landing position to really put on the breaks.
We might control this landing mix from a switch, from a dial, or more commonly f rom the "throttle" stick. As we pull back, we deploy more and more of the surfaces to slow us down.
If we have judged the wind, the plane and the field correctly, and have used our radio with skill, we come to a nice soft landing right on the mark and score this as a successful flight.
Cool?
Summary
While you can fly most sailplanes on a simple three or four channel standard radio, the use of a computer radio can provide enhanced control. The incremental cost is small and the benefits are large.
This is all fun and exciting stuff, but consider your goals and ambition for your flying. Consider the types of planes you will be flying and which features your radio might need. Only then can you start to determine which radio is right for you at a price you can afford.
It takes time and work to learn how to use the advanced features of any radio and how they work with YOUR planes. However you can still use most of these advanced radios as simple 4 channel radios in the beginning. If you can afford the investment, having those advanced features my allow you to
move into the more advance flying more quickly.
If you are a sport pilot or a casual contest flyer out to have some
soaring fun, a 6 channel entry level or mid range sport computer
radio is probably all you need. If you want to get all you can out
of your planes, or if you are a serious contest flyer, then buy a
feature rich radio of 7 or more channels that has 4 wing servo
support and includes sailplane mixes. You will pay more up front but your radio will carry you further into the future.
Consider your needs, wants, desires and your budget. Buy all the
radio you can afford today, then learn to use it and go enjoy flying your sailplane.
Clear Skies and Safe Flying!
==========================
Here are some additional resources that you may also find helpful.
No need to buy a Used Radio
www.rctower.com/forum/viewtopic.php?p=1251#1251
What you need to know about receivers:
www.rchangout.com/forums/radio-electronics-motors-and-accessories/t-what-you-need-to-know-about-receivers-12151.html
Hitec Optic 6 - Set-up for a full house TD glider
forums.flyesl.com/topic.asp?TOPIC_ID=233
What mixes do you use?
www.rcgroups.com/forums/showthread.php?t=290071
This is more for competition pilots, but if you like to look
at some of the advanced stuff, this might be fun. It is a translation,
so take your time as you read it.
www.gliders.dk/triming_and_setup_of_a_glider_wi_eng.htm
by Ed Anderson
aeajr on the forums
This is being written for the new or relatively new sailplane/glider pilots
who are interested in flying thermal duration sailplanes. I will make a few
comments on slope planes, but these are not the main focus of the article.
This discussion is going to be more about points of consideration rather
than which is the best radio. The "best" is always that one that is just a few $$ out of your price range or the one that is going to be released next year. Whatever you get, there will always be one that is better at a higher price or that will be released the month after you get yours. So let's throw away that "best" idea. Let's focus on what features and functions you might like to have and their relative importance. Others will have opinions that differ from mine as there is no one right answer. But at least this
can get you thinking.
If you want to ask questions about specific radios, or if you want to share your budget and your goals, I and others can make specific recommendations, but don't be surprised if we don't all recommend the same thing. We each have our opinions.
If you are the club champ or the radio wizard in your group, turn the page because this is not for you. However if you don't mind reading though, you may wish to add your comments. Others will benefit from you knowledge, insights and experience. I am not sensitive, so feel free to disagree, but please keep the comments polite. Flame wars benefit no one.
Ultimately, the recommendations I make are based on people's budget and goals. I try to understand how much they have to spend and where they want this radio to take them. Then I try to focus them on the key decision points I will outline below.
For new flyers, the goals may be more modest, so the introductory radios may be fine for you. However, if you are committed and plan to push ahead aggressively AND you have the budget, then you may want to step into one of the more advanced radios. In my opinion you can not buy too much radio,
but you can buy too little.
Standard vs. Computer Radios
I will not be considering any standard radios during this discussion. They may meet the lifetime needs of a glider pilot who is interested in casual weekend flying of simple rudder/elevator, or even rudder/elevator/spoiler gliders. A 2 or 3 channel standard radio will get you into the air. You can certainly fly full house sailplanes on a 4 channel standard radio and have a lifetime of soaring enjoyment. Never let anyone tell you that you
MUST have a hot shot computer radio to fly gliders/sailplanes because it just isn't true. I have several standard radios that I have used to fly gliders, both thermal and slope. However I have since moved them all over to computer radios for convenience and for enhanced control. The standard radios, like my old typewriter, pretty much gather dust and will likely be
given to friends to help them get started.
If you want more on this subject you may wish to read the content at this link:
Don't Buy a Standard Radio
www.wattflyer.com/forums/showthread.php?t=4454
What computer radios provide are options and opportunities for those who want them. They offer features that can make set-up faster and easier and can make it very convenient to move between several planes. From an actual flying point of view, they can help you get the most out of your plane as well as help reduce the workload of the pilot so s/he can focus on the plane
and the conditions rather than manipulation of the surfaces. Believe me, commercial airline pilots have plenty of computer power to help them fly. Since the price of a computer radio is so reasonable, why shouldn't you have the same advantage.
LET'S START WITH THE BASICS
Sailplanes and gliders, which I will use interchangeably, come in a variety of configurations. The simplest are the rudder/elevator planes that have dihedral or polyhedral in the wings. They have been the favorite trainers for years and some people spend a lifetime enjoying them.
To R/E we can add spoilers, which carries the RES designation. You can also find REF planes which add flaps to rudder/elevator controls. There are also aileron/elevator planes, A/E, which are more common on the slope than as thermal ships. When we have a combination of ailerons, elevator, rudder and flaps, A/E/R/F, we call this a full house sailplane. You can have a plane that has flaps and spoilers, or ailerons and spoilers without flaps, but
this is unusual.
Of course, you can have a motor, but I am focused on pure flight, so no motors on my sailplanes. If you have an electric motor, a simple on/off switch is all you need for motor control. We will likely be using that "throttle" stick for glide path control rather than the motor. Other than this, I won't be discussing motors.
How many Channels?
While there are some interesting four and five channel computer radios, I am going to recommend you get a computer radios with six or more channels. I don't see any real benefit for having less than six channels, as the cost difference is small and the benefits of 6 or more channels is high. Even if you are flying a rudder elevator sailplane today, next year you may be adding spoilers or flaps or going to a full house plane in the future, so get a radio that can handle that so you aren't going back to the radio market right away.
Here is a typical channel breakdown, how many and what they are used to control. These apply to electrics, glow, gas and gliders.
Rudder - 1
Elevator - 1 or 2
Ailerons - 1 or 2
Spoilers - 1 or 2
Flaps - 1 or 2
tow hook - 1
landing gear - 1
Motor - 1
That makes 4, 5, 6, up to 12 channels depending on what kind of plane you have and how you set it up. So how many do you need?
In my opinion, most sport flyers will be well served for a long time with a 6 channel entry to mid level sport computer radio. If you are a more serious sailplane pilot or contest flyer, you probably want a minimum of 7 channels and support for a 4 servo wing. ( more on 4 servo wings later)
Basic Features
Most currently available new computer radios offer the following features. Regardless of what you are flying, I highly recommend your radio have these features.
* Model Memories
* Low Battery Warning
* Digital Trims
* Timer ( one or more )
* End Point Adjustment/Adjustable Travel Volume
* Dual Rates on ailerons and elevator; rudder is optional.
* Elevon and V-tail mixes
Minimum Recommended Surface Mixes
After model memories, surface mixes are one of the great features that computer radios bring to the game. Input to one control can move 2 or more servos in a coordinated fashion to create the kind of surface control you are looking for. This can reduce the pilot's workload while providing very consistent behavior. In most cases, when it makes sense, these mixes can be overridden during the flight or can be turned on and off.
The following list is what I would consider the minimum set I would want in a radio that would be used for flying sailplanes, be it thermal or slope. Where two surfaces are listed, the first is the master and the second follows it. I will discuss these in more detail later, but wanted to get the list part stated up front as people are usually looking for these lists. Most are focused on planes with ailerons or full house planes, but I note where even simpler planes can benefit.
* Exponential on aileron and elevator. Rudder would be a plus.
( all planes)
* Flapperon/Spoileron - requires two aileron servos on separate channels
* Aileron differential - requires two aileron servos on separate channels
* Aileron-rudder mix ( coordinated turns )
* Flap or spoiler to elevator mixing for landing and glide path control.
Very useful on RES, REF or full house planes.
The goal of these mixes is to make the plane easier to fly more smoothly, more efficiently with less drag and more controllability. In addition we gain some level of glide path control to assist with landing accuracy or to help us get out of booming thermals. With these tools you can have a more enjoyable sport flying experience or be more competitive than would be easily achievable with a standard radio.
More Advanced Mixes
These would typically be activated by a switch, dial or other control when needed. You could go through the entire flight and not use these but they give you that extra measure of control or convenience that you may desire. Note, that many computer radios have "free" or user definable mixes so you may be able to create a mix that is not specifically listed, but don't assume
that is the case. Check to see if that free mix can do what you want.
* Flight modes such as launch, cruise, speed, landing, thermal, etc
* Camber Control -
moves the whole trailing edge at once to reshape the wing
* Crow/butterfly/airbrakes - helps with precision landing
These mixes are mostly focused on changing the shape of the wing during flight which changes the wings's lift/drag characteristics. Since we are flying without a motor, the ability to "retune" the wing to the needs of the moment can be very helpful in getting the most out of the current lift conditions or getting out of a bad situation. These would all likely be
able to be turned on and off during the flight so that we can use them according to the situation.
For example, if you have flaps and ailerons, a launch mix might drop the flaps 20 degrees and the ailerons 20 degrees giving your wing a more undercambered shape. This might also include some up or down elevator, depending on your plane. This generates tons of lift but also creates more drag. While this might be detrimental during normal fight, when you have the force of the hi-start or the winch pulling your plane up, you can afford
this extra drag to gain higher launches.
Having launch set up as a flight condition means that you flip a switch and the plane's surfaces move to a predetermined position for launch. Just before you finish the climb, you flip that switch off to go into normal flight/cruise mode. Quick, easy and convenient surface control activated by as switch. While you might be able to do some of this on a standard radio,
the work load would be high and getting consistent behavior would be much harder. Computer radios make it easy!
The Four Servo Wing
One of the features that I feel sets apart the "sport radios" from the "advanced " radios is the ability to directly address all four wing servos, each on its own channel. The sport radios can fly a plane with 4 servos in the wing, but they require that the flaps be on one channel through the use of a Y cable. This means that you have 4 servos but you are controlling them as if they were 3 servos. Where the 4 servo wing support comes in handy is in trimming and in aileron-flap mixing. There may be others, but these are where I have used this capability.
Typically you won't find this on a radio with less than seven channels, and most have eight or more channels. Read the manual or the specs and look for this feature. If you don't see it mentioned, look for how flaps are set-up. If both flap servos are assigned to the same channel, you don't have 4 wing servo control.
When you have both flaps on a Y cable you must trim them mechanically to get them synchronized. This can be done but it can be tricky and time consuming. It is very important that the flaps move together. If one flap moves further than the other anywhere through its throw it will tend to cause the plane to roll left or right making the plane more difficult to control. Flap trimming can be done using servo arm/control horn arm
placement, making sure the control rods are the same length and by adjusting the clevis screws to get them even. Then you can trim the flaps together using the radio to get that final zero point and the end point for down flaps.
However if you can address each flap individually from the radio you can do final trimming from the radio, which is a great convenience. You can also use an aileron/flap mix to have the flaps follow the ailerons for more, or smoother roll authority. I use this on my planes. This is not a necessary feature but if you are going to invest in a "serious" sailplane radio, you will want to be able to address the four wing servos individually.
Frequency Options and Opportunities 2.4 GHz and 72 MHz
In North America there are two primary radio systems for RC flying, 72 MHz and 2.4 GHz. There are others, but these are the most popular.
Spread Spectrum or 2.4 GHz are often used interchangeably. This is not technically correct but for practical purposes you can consider them the same thing.
The new 2.4 GHz radio systems have several advantages over the older 72 MHz systems.
Channel conflict his handled automatically. On 72 MHz you have to be careful not to fly on the same channel as another pilot. The 2.4 GHz radios handle this automatically. As such, they avoid "frequency conflict" at the field. This occurs when two 72 MHz pilots have planes on the same channel. One has to wait while the other one flies. On 2.4 this problem goes away.
One installation situation to note has to do with carbon fiber fuselages. Because 72 MHz antenna are over 39" long, they can be easily installed to avoid the signal blocking nature of carbon fiber. However 2.4 GHz receivers have very short antenna of just a few inches. It is much harder to get these outside the carbon fuselage, but it can be done. While advances are being made in this are, if you are planning to fly a plane with a carbon fuselage, you should be careful about how you install any radio system to be sure the signal is not blocked.
Note that many airplane makers are now modifying their designs to make them more 2.4GHz friendly. They are reducing the amount of carbon in the design by using other high strength materials. So this problem should be reduced over time.
There are other benefits with 2.4 GHz and new features are being added to the new radios all the time. But it is clear that 2.4 GHz is the wave of the future. Virtually all new radios are being released on 2.4. The 72 MHz market is falling off fast. This is leading to a very big used market for old 72 MHz stuff so there should be ample supply of receivers and such for many years to come.
If you are new to RC flying, or looking to upgrade your radio system, you should give 2.4 GHz very serious consideration.
If you do have, or are buying a 72 MHz radio, here are some things you will want to know.
More on Mixes
Let's walk through a flight and see where some of this mix stuff might be used.
We have our plane set up on a 6 channel computer radio. We have the following features and mixes enabled and active all the time.
* Exponential on aileron and elevator
If you want to better understand Expo, take a look at this article:
www.rcgroups.com/forums/showthread.php?t=331087
* Aileron differential -
Up aileron goes up more than the down goes down.
Less drag as well as other benefits
* Aileron-rudder mix
by automatically adding rudder to the ailerons we get a smoother,
more efficient turn reducing drag and enhancing control.
* Flap-elevator mix for landing.
Automatically helps keep the plane level when we apply the flaps
as we are landing.
Time to launch!
- We flip that switch for our launch setting. Flaps come down maybe 20 degrees and the ailerons come down 10 degrees. We launch the plane and send it up the launch line. At the top of the launch we will turn this off so that we are in normal cruise mode. We are now 400-600 feet up and looking for lift.
Let's go hunting!
We spot some lift and we start to circle. We might flip on Elevator-flap mix, so when we pull up elevator we get a tiny bit of flap to help us climb smoothly in a thermal. Or we might turn on "thermal" flight mode mix to slightly droop the flaps and ailerons to give the wing a bit more lift. We climb high and enjoy the ride.
We lose the lift so we turn off our thermaling mix and go hunting again. We hit some fast falling air; sink. We want to run through some sink, so we flip our camber/reflex preset and the flaps and ailerons move up a little to reflex position and the plane moves quickly through the sink. When we are in more buoyant air we flip this off.
We catch some lift and circle up again. We turn our thermaling mixes on.
We have been in this thermal for 20 minutes or so. We might be at 1000 feet and have ridden the thermal about 1/2 of a mile down wind. Time to head home and prepare to land.
During our return run we will fly in cruise or we might turn on that
reflex preset again to help us penetrate through the head wind.
Remember we have no motor so we are flying upwind in a glide.
As we approach the field we want to have more energy than we need to make it to the landing mark because a gust might hit us, or we might hit some sink and lose altitude fast, causing us to fall short. Best to come in with more energy than we need.
As we get close to the landing zone and are confident, we can start to use that flap-elevator landing mi , or, if we have spoilers we might use a spoiler-elevator mix. If we have a more advanced radio we might use the crow (butterfly) mix, to help us slow down and bleed off altitude without gaining too much speed. As we judge our speed we may we may use a partial landing mix or go to a full landing position to really put on the breaks.
We might control this landing mix from a switch, from a dial, or more commonly f rom the "throttle" stick. As we pull back, we deploy more and more of the surfaces to slow us down.
If we have judged the wind, the plane and the field correctly, and have used our radio with skill, we come to a nice soft landing right on the mark and score this as a successful flight.
Cool?
Summary
While you can fly most sailplanes on a simple three or four channel standard radio, the use of a computer radio can provide enhanced control. The incremental cost is small and the benefits are large.
This is all fun and exciting stuff, but consider your goals and ambition for your flying. Consider the types of planes you will be flying and which features your radio might need. Only then can you start to determine which radio is right for you at a price you can afford.
It takes time and work to learn how to use the advanced features of any radio and how they work with YOUR planes. However you can still use most of these advanced radios as simple 4 channel radios in the beginning. If you can afford the investment, having those advanced features my allow you to
move into the more advance flying more quickly.
If you are a sport pilot or a casual contest flyer out to have some
soaring fun, a 6 channel entry level or mid range sport computer
radio is probably all you need. If you want to get all you can out
of your planes, or if you are a serious contest flyer, then buy a
feature rich radio of 7 or more channels that has 4 wing servo
support and includes sailplane mixes. You will pay more up front but your radio will carry you further into the future.
Consider your needs, wants, desires and your budget. Buy all the
radio you can afford today, then learn to use it and go enjoy flying your sailplane.
Clear Skies and Safe Flying!
==========================
Here are some additional resources that you may also find helpful.
No need to buy a Used Radio
www.rctower.com/forum/viewtopic.php?p=1251#1251
What you need to know about receivers:
www.rchangout.com/forums/radio-electronics-motors-and-accessories/t-what-you-need-to-know-about-receivers-12151.html
Hitec Optic 6 - Set-up for a full house TD glider
forums.flyesl.com/topic.asp?TOPIC_ID=233
What mixes do you use?
www.rcgroups.com/forums/showthread.php?t=290071
This is more for competition pilots, but if you like to look
at some of the advanced stuff, this might be fun. It is a translation,
so take your time as you read it.
www.gliders.dk/triming_and_setup_of_a_glider_wi_eng.htm
