Choosing a Sailplane Radio - What to Consider
by Ed Anderson
aeajr on the forums
Updated July 2011
This is being written for the new or relatively new sailplane/glider pilots who are interested in flying thermal duration sailplanes and need some advice about radios. 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 cannot 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. Standard radios don’t have model memories and have little if any surface mixing. Some include V tail and Delta wing but that is about it. But a 3 channel standard radio will certainly get you into the air. 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. I flew my first sailplane, a Spirit RES glider, with a standard 3 channel radio. It came as part of an RTF package, I did not buy that 3 channel radio by itself. I don’t use it anymore.
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 http://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 glider as well as help reduce the workload of the pilot so s/he can focus on the glider 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 model that have dihedral or polyhedral in the wings. They have been the favorite trainers for years but don't write them off as being just for beginners. Many people find a lifetime of enjoyment flying R/E gliders.
To R/E we can add spoilers. These carry the RES designation. You can also find REF planes which add flaps to rudder/elevator controls. And there are 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. It is these full house sailplanes that create the desire to have special sailplane/glider programming in your radio. We will discuss later how that programming may be used.
You can have a glider that has flaps and spoilers, or ailerons and spoilers without flaps, but this is unusual. Some of the scale gliders have these configurations.
Of course, you can have a motor. If you have a motor I will assume that it is used as an alternative to a winch or hi-start and that you will only be using to get to altitude. Therefore it could be controlled by an on/off switch rather than the left control stick. We will likely be using that "throttle" stick for glide path control on RES, REF and full house gliders rather than the motor.
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 to 2
Elevator - 1 or 2
Ailerons - 1 to 4
Spoilers - 1 or 2
Flaps - 1 to 4
Tow hook - 1
Landing gear - 1
Motor - 1
Other - 1
That makes 4, 5, 6, up to 18 channels depending on what kind of sailplane 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. Most e-glider pilots will want a minimum of 7 channels. If you are a more serious sailplane pilot or contest flyer you will see that most of the advanced sailplane/glider radios have 8 or more channels, sailplane/glider programming and support for at least four servo wing. We will discuss four servo wings later as I am talking about how the radio addresses those servos, not how many you have.
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
* Trims on the channels controlled by the stick(s).
* Timer (one or more)
* End Point Adjustment/Adjustable Travel Volume
* Dual Rates on ailerons and elevator; rudder is optional.
* Elevon/delta wing 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.
Where two surfaces are listed, the first is the master and the second follows, sometimes called the slave channel. 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.
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. These minimum mixes may be available under the “airplane” menu and may not be called out specifically for sailplanes. Even entry level computer radios are likely to have these.
* Exponential on aileron and elevator. Rudder would be a plus. (all gliders)
* 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. This can be very useful on RES, REF or full house planes and aileron only planes that are set-up for “flapperons”.
The goal of these mixes is to make the glider easier to fly more smoothly or 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. The landing mixes can also be helpful to slope pilots to land their glides in tight slope sites. 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.
Now we are getting to mixes that would normally be implemented with specific glider/sailplane programming. These are usually used on gliders that have ailerons or ailerons and flaps (full house) rather than R/E or RES gliders. Some of these may be able to be implemented by using your “user” mixes on a radio that does not have glider programming, but it can get complicated. I don’t consider those glider/sailplane radios, but you can make them work to some degree.
Flight modes can be thought of as changing your radio set-up to meet the needs of a specific situation. They often involve a change to the shape of the wing to better meet a special situation. You can think of your normal flying set-up as your “cruise” mode. All of your settings are based on your basic flying needs while you cruise around the sky looking for lift.
Flight modes might include launch, thermal, reflex, landing and perhaps others. As you can see by the names, these are modes of flying that occur under special situations other than when you are cruising. These modes would typically be controlled by a switch which may move surfaces to presets, change expo or surface rates and might even modify other settings from your normal “cruise” mode.
An example of a launch mode mix might drop the flaps 20 degrees and the ailerons 20 degrees giving your wing a more under cambered shape. This might also include some up or down elevator, depending on your glider. 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. Once you are off the line you turn off launch mode which puts you back in cruise mode.
Flight modes could change how you use one of your control sticks. For example you might have your left stick controlling the throttle of an e-glider during your “launch mode” then flip a switch to cruise and the throttle would no longer respond to the left stick. That left stick might now be responsible for your landing mix. The motor would no longer respond to the left stick.
You could go through the entire flight and not use all of these “modes” but they give you that extra measure of control or convenience when you want it.
How sophisticated and complex these modes will be depends on the software in your radio. The degree of control you have could be thought of as the difference between a basic sailplane radio and an advanced sailplane radio.
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 or more 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 on three channels. You don’t have individual control of each flap servo.
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 don'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 is not hard but it is time consuming. It is very important that the flaps move together. Flap trimming can be done using servo arm/control horn arm placement. 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 full house gliders when I am flying in windy or gusty conditions. This would be useful on the slope for aerobatics. 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.
Let's Take a Flight
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 channel computer radio. We have the following features and mixes enabled and active all the time.
* Aileron differential - Up aileron goes up more than the down goes down. Less drag as well as other benefits
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 our thermal camber mix to droop the trailing edge. Or perhaps an Elevator-flap mix, so when we pull up elevator we get a tiny bit of flap to help us climb smoothly in a thermal. We climb high and enjoy the ride.
We lose the lift so we turn off our thermal 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 mixe(s) on.
We have been in this thermal for 20 minutes or so. We might be at 2000 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. So it is 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 mix, 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 vary our landing mix. If it is on a variable control, such as the left stick, we can make small adjustments. If it is on a switch we may have off, 50% and 100% landing mix settings. We adjust according to what our radio allows us to do.
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.
Frequency Options and Opportunities 2.4 GHz and 72 MHz
This section is primarily for people who may be buying used equipment or who may be traveling outside of North America. If you are not one of these you can skip straight to the summary.
In North America there are two primary radio bands for RC flying, 72 MHz and 2.4 GHz. There are others, but these are the most popular. The terms spread spectrum and 2.4 GHz are sometimes 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 is 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. 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 a 72 MHz antenna is over 39" long, it 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 area, 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. If you are new to RC flying, or looking to upgrade your radio system, you should give 2.4 GHz very serious consideration.
72 MHz Radio Systems are primarily for people buying used equipment. Note that many 72 MHz radios can be upgraded to 2.4 GHz via an add in module.
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 used 72 MHz receivers and such for many years to come. If you do have, or are buying a 72 MHz radio, here are some things you will want to know.
* Frequency band
* Signal shift
Channel changing comes in handy if you are flying at a busy field and frequently run into conflicts that would keep you on the ground. If you can change the channel of your 72 MHz radio and receiver, you can switch to an unused channel and continue to fly. This is typically accomplished either by changing a channel module on the radio or by the use of a frequency synthesizer. Either way, the change takes a few seconds. Put a matching crystal in your receiver and you are good to go!
This can be extremely valuable if you do any serious contest flying as participation at some contests mandate no more than one flyer per 72 MHz channel. If someone else registers on your channel first, you may be locked out. If you can change channels, you simply switch to an open channel.
If you tend to travel to other countries to compete, your home frequency, such as 72 MHz in North America, may not be permissible in that country. In the UK, for example, they fly in 35 MHz. In France and Japan they have rules about 2.4 GHz radios that some US based 2.4 systems may not meet. Basically check before you go to be sure you can use your radio.
On 72 MHz, signal shift or shift select, is the ability to switch between positive and negative shift. Shift simply describes how the 72 MHz signal is encoded. I am not going to go any deeper into than that. Shift select becomes valuable primarily in the purchase of used equipment. Traditionally Hitec and Futaba are on negative shift. JR and Airtronics are positive shift.
PCM on 72 MHz is a special signal process that many fliers feel give them superior control and glitch resistance. PCM is specific to a radio brand, so you can’t use a Hitec PCM receiver with a Futaba PCM radio. Nuff said about that.
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. When looking for a radio to fly your airplane or glider consider your goals and ambitions 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 aircraft. 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 are flying full house gliders and you want to get all you can out of them for sport or contest flying, then buy a feature rich sailplane 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.
Hope this is helpful.
Clear Skies and Safe Flying!
Here are some additional resources that you may also find helpful.
I would say that if you are going to up grade to a new radio, it is important to look at the computer section of that radio above all else. Take for example the difference between the JR 8103 and the 9303 transmitters. Yes I know they are the older 72 radios, but this is a very good example of what I am talking about. The difference is only 1 channel and you would think that the radios would be pretty close, but look at the computer and you will see a world of difference. There were a lot of things that they just didn't think of when they built the 8 channel that when the 9 channel came out, everyone jumped on that one. You can find out what each radio will do simply by reading the manual and just about all of them are on the internet to download whenever you want to read it. Look at what it will do and how easy it is to do it.
The new 2.4 radios are pretty much the same thing. Read the manual and see just what it will do. The DX-7 is by no means a bad radio, but if you are looking for one that will handle full house sailplanes, then you can pretty much forget that one. The DX-6i is a very popular radio and I also see a bunch of people jumping on it simply because someone that doesn't know any better tells them to buy one.
You are never going to fly gliders, so why do you need all that fancy computer power in that transmitter? Let me give you an example. I have a Ultra Stick with flaps. I have several flight modes programed into that plane. One for take off with 25 degs of flaps with elevator mixed in to keep the nose down like it normally is during take off. Flaps mixed with ailerons so the ailerons are more effective. Flaps mixed with elevator so that work backwards from each other. Elevator goes up, flaps go down and elevator goes down and flaps go up. Makes for a better cornering plane like the old C/L pattern planes used. I also have crow mixed in for landing so I can come down fast without gaining a lot of airspeed. Why do I need all this programing on a simple plane like the Stick?? Because it is fun and I can do it, that's why. It is just fun to play with something like this and I have a ball every time I fly it. Do I have to have it, No, but that is half the fun of flying this plane. Can you fly this plane with a 6 or 7 channel radio? Sure you can, but you can't get all the mixes I have and that is half the fun.
One thing about the new 2.4 radios that everyone seems to forget to tell new people. Don't EVER fly behind something, like a tree. The receiver is blanked out and is not getting the transmitter signal while behind that tree and it is possible to crash that nice new plane before it comes out the other side. We have had two plane crashes at our field caused by this. 72MHz will go right through that tree, but 2.4 will not. Just remember that 2.4 is line of sight. That means if you can see it you have control, but if you can't see it, you don't. I still fly 72MHz and that is simply because around here, I am the only one flying on it. Everyone else just had to have the latest and greatest, which is the 2.4 radios. Yes I have a 2.4 also, but I will keep my 72 and love every minuet of it. There is nothing wrong with that radio and until they drop it from the FCC list, I will fly it.
What would I recommend for a new radio? I'll tell you, but you probably won't like it. Save up your money and by the best radio you can possibly afford. Don't just go out and buy a DX-6i now because that's all you can afford. Save up some money and get one that you know for sure you will be happy with for a long time. If that is the DX-7, then fine, but make sure it is the radio that will make you happy for a long time, unless you want to go out and buy another radio again just as soon as you find out that new 6i you bought is not able to do what you want. When I bought my 9303, it was just before the 2.4 craze hit. After they came out, I started looking at the radios and couldn't find what I was after, so I waited. I finally bought the Airtronics SD-10G as that was the radio that had everything I was looking for in a radio. Does that mean it is the radio for you?? Maybe not, it just depends on what you are looking for. I think it is the best radio on the market, but then I also bought one, so naturally I think that way. You may decide that the DX-7 is best for you. What ever you decide on, make sure it is THE radio that you want and not just something that you could afford right now.