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aeajr
349 Posts |
 Posted - 08/28/2006 : 6:57:30 PM
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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
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 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 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. 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.
Here we are talking about the ability to change:
* Channels
* Frequency band
* Signal shift
* PCM
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 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 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. If your radio allows you to change
frequency modules to the local band, then pickup a receiver on the local
frequency band and be all set to fly with the radio you know so well.
Signal shift, or shift select, is the ability to switch between positive and
negative shift. Shift simply describes how the 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.
If you fly Hitec or Futaba, for example, these are typically negative shift
radios in North America. If you were to buy an Airtronics receiver, or a
plane that has a JR receiver, these are typically positive shift. You could
not use them with your negative shift radio. However if your radio can
perform shift select, you can have the radio transmit in the shift that the
receiver understands. It won't make your plane fly any better but it may
give you flexibility in the equipment you buy.
PCM is a special signal process that many fliers feel give them superior
control and glitch resistance. I can't comment on the validity of this but
many serious contest pilots use PCM receivers. If your radio has a PCM
feature, then you can use FM/PPM or FM/PCM receivers, at your option.
Again, this is a matter of flexibility and choice. Even if you don't plan
to fly using PCM today, you might want it in the future.
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:
http://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 a "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 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 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.
What you need to know about receivers:
> http://forums.flyesl.com/topic.asp?TOPIC_ID=258
Hitec Optic 6 - Set-up for a full house TD glider
http://forums.flyesl.com/topic.asp?TOPIC_ID=233
What mixes do you use?
http://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.
http://www.gliders.dk/triming_and_setup_of_a_glider_wi_eng.htm
Best regards,
Ed Anderson
aeajr on the forums
Long Island Silent Flyers |
Best regards,
Ed Anderson
ESL President,
ESL Newsletter Editor |
Edited by - aeajr on 05/24/2010 4:44:12 PM |
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lincoln
40 Posts |
Posted - 07/31/2009 : 5:53:10 PM
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Wow! You must type a lot faster than I do, and I'm not terribly slow.
First off, although I didn't read all of it, it's hard to go wrong with Ed's advice. However, I think standard radios, and RES models, don't get enough respect. Of course they go together. If your spoilers aren't oversized, you don't even need elevator compensation for the spoiler, as this is reasonably easy to provide yourself by holding some up.
If you go with RES and a simple radio, both the glider and the radio will take much less effort to set up. They'll also cost you less. Many years ago I came in first for the year in Sportsman flying a 2 meter RES glider (Sagitta 600) with a simple 4 channel radio against a whole bunch of people flying stuff like the 134 inch, aileron and flap Windsong. Remember, no matter how high tech you go, you cannot do better than a max with 100 landing points.
Having said that, if you MUST go full house, I think a very useful mix gradually transitions to reverse aileron differential as you feed in CROW. This retains your ability to turn, at least somewhat. Otherwise you may find it's as if you don't have any ailerons during your approach. I don't know what radios can do this now, but the Vision did.
I don't think more than a little aileron to rudder mix is justified, since sometimes you're using rudder into the turn and aileron out. I use just a bit, but I'm generally ok with no mix.
Differential isn't always a good thing. It's only correct around one airspeed (or, rather, lift coefficient). If you're going faster, it will yaw you too far INTO the turn. As it kicks in, it will act like a bit of down elevator as well. So it's probably a good idea not to go overboard, although I admit I once had a glider with no separate rudder servo, just a mechanical coupling, and it flew reasonably well. |
Lincoln Ross |
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aeajr
349 Posts |
Posted - 02/24/2010 : 10:23:06 AM
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Special considerations for HLG/DLG
When I wrote the original article above I had not been flying hand launch or discus launched gliders, or at least not much. So I want to add a few quick thoughts on the topics specifically focused on hand launched and discus launched gliders.
1) Launch presets
Most pure gliders benefit from some kind of launch mode or launch presets. This means that certain surfaces are moved to a predetermined position. On my winched planes this might be flaps and ailerons down 15% on launch and may involve some elevator preset too. I set them to this position by flipping a switch. At the top of the launch, I flip the switch off and the surfaces go to neutral. Where the control is located is dictated by the radio's programming or may be assignable according to your preferences. However most of us can get used to whatever we have available on our radios.
For hand launched and discus launched gliders it is different. A common launch preset is to have some up elevator available on release. As you launch your DLG you don't want to throw it up, but out. This provides a more efficient use of the spin and it helps avoid tip strikes. However you want the plane to climb, so a momentary application of up elevator might be helpful.
Many pilots set the launch preset, a little up elevator, on a switch that is spring loaded. This is usually the spring loaded trainer switch, if you have one. If you throw your DLG with your right hand, then the preferred position for this switch would be on the top left rear of the radio where the left index finger can reach it easily. So you might want to look for a radio that has the trainer switch on the top left and insure you can assign a mix to that switch.
However, a spring loaded switch is not required. When I first started DLG, my radio had the spring loaded switch on the top right. As a result I put my launch preset on a standard 2 way switch on the top left. I would set it back, away from me, then start my turn, giving me a little up elevator. Just after release I would flip the switch toward me, turning off the preset. This has a similar effect to releasing a spring loaded switch.
I find either as acceptable, you may not. But whether the switch is spring-loaded or not, you will want a switch to which you can assign a launch preset. Naturally if you throw with your left hand then this switch is going to need to be on the top right.
2) Camber presets vs. variable camber
Some HL pilots, such as myself, prefer our camber settings on presets/offsets that are switch controlled. Others prefer to use the left stick or a side slider to get variable camber settings. Either works as long as your radio supports this.
The presets I have, other than launch are:
Reflex
Normal/float
Thermal.
Landing
How your surfaces are set for each condition will depend on your airfoil. My primary DLG is a Polecat Aero XP-5 with a Drela Airfoil. How I have these set is not important.
What is important is that I use presets for all of these. I don't use any variable camber settings or controls. My left stick is not used during my DLG flights other than to control the rudder. And that is one of the reasons I use presets. I don't want my rudder movements to have a chance to change my camber settings. I find this to be more of a concern on my DLGs than on my hi-start or winched planes because I rarely catch my big planes in competition. But I try to catch my DLG all the time, so that means I have one hand on the radio and may be working the rudder as I reach to catch the plane.
I have tried my side slider, for full variable camber, but felt I was spending more time hunting for the right setting then I should. So I went to presets. Each of these presets is on a switch. Normal/float, reflex and landing are on the same 3 way switch which is a default on my radio so it makes this easy as these three are mutually exclusive. I would never have two of them on at the same time. My thermal setting is on a switch by itself. I suppose if I had a 4 way switch I would have them all one switch but I don't have a 4 way switch. I have used my thermal setting for landings, at times, when I don't want the strong stopping power of my landing mix.
For all of these mixes I have the option of adding some elevator into the mix, according to my preferences. I find this valuable and would suggest that you look at the mixes on any radio you are considering and insure that you can add elevator to the mix either as a standard feature or by utilizing user programmable mixes.
More sophisticated pilots may have more settings, more conditions or more complex mixes, but this is all I use for my DLGs. The point is not whether these are the right mixes, but how one can use switches to accomplish these conditions, where they might be located and how this might influence your choice of radio.
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Best regards,
Ed Anderson
ESL President,
ESL Newsletter Editor |
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Choosing a Sailplane Radio - What to Consider