aeajr
Posts: 5612
Joined: 1/14/2003
From: Long Island,
NY, USA
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Which radio for scale gliders? Others will tell you what to buy. I am
going to try and explore some key features and channel uses to help you
understand what to look for and why. I will mention some radios at the end.
This is not a simple topic, so grab a cup, this will take a little while.
During this discussion I am going to use Hitec/Futaba channel assignments as
the examples. Since I have a Hitec Prism 7X and a Futaba 9C, I know these
layouts best. I will also assume you know something about computer radios and
the use of surface mixes, so I am not going to explain every mix I might want
to use on a full house or scale sailplane.
If you are not familiar with computer radios, this article might be helpful.
Radio Systems Part 2 - Computer Radios -
http://www.rcezine.com/cms/article.php?cat=&id=65
I am going to focus on how many channels you will need and some very valuable
features to look for in a radio.
Most scale gliders will have ailerons, rudder and elevator. Most have a tow
line release for aerotowing. Most will also have either spoilers or flaps,
and some have both. Some also have landing gear. So what you need depends on
what plane you are flying.
At a minimum, scale planes would need at least 5 channels to account for the
tow hook.
Surface/ channel # (futaba/hitec typical layout)
A = 1
E = 2
F/S = 3
R = 4
TR = 5
That means a Hitec Laser 6 standard radio could fly this plane but would not
offer us any channel mixing. I don't recommend standard radios for full house
or scale sailplanes.
In practice, we typically use two channels for ailerons and flaps so we have
one servo/channel per surface. To do this we are going to need a computer
radio to mix the split channels together, to have the servos work together.
When deployed this way, this is commonly refered to as the 4 servo wing. The
ability to control 4 servos independantly is a significant breakpoint in the
computer radio market. There are those that can do it and those that can't.
While we could use either, if we are going to bring the plane to its full
potential, we will want a computer radio that can manage a 4 servo wing, each
on its own channel.
First, this makes it easy to trim the surfaces from the radio. It also allows
us to change how a surface is used during the flight.
For example, if both flaps are on one channel via a Y cable, then we can move
them up and down together. However if they are on two channels, we can flip a
switch and have them follow the ailerons to improve roll response. This
video illustrates this arrangement as quad ailerons:
http://airfieldmodels.com/video/quad_ailerons.wmv
Here the flaps follow but at about 50% of the ailerons:
http://airfieldmodels.com/video/flaps.wmv
If we have ailerons on separate channels, we can have the up aileron go up
more than the down aileron. This is called differential ailerons and helps
reduce drag.
The 4 servo wing allows us to do camber control. This will allow us to
change the shape of the wing by moving the whole trailing edge as a unit. It
changes the flight characteristics of the wing so we can tune it to different
situaitons during the flight. If the ailerons are on one channel, we can't do
that.
This video shows a variety of movements, two of which illustrate a small
movement up and down together to change the entire trailing edge:
http://airfieldmodels.com/video/quad_flaps.wmv
Crow and Butterfly, are also in common use. In this mix, flaps go down and
the ailerons come up to really slow the plane quickly. Normally the elevator
is mixed in to help keep the plane level. This video illustrates crow.
http://airfieldmodels.com/video/butterfly.wmv
Likewise when winch launching your sailplane you will probably want a launch
set-up. This typically involves dopping the flaps about 30 degrees and the
ailerons about 15 degrees. This helps maximize lift during the launch. If both
ailerons are on one channel, you can't drop them together. Best to have them
on two channels.
So the message is that there is big value in having a 4 channel/4 servo wing.
Here is a sample layout using the Futaba 9C recommended channel assignments.
Surface / Channel
R Aileron 1
Elevator 2
throttle stick 3 ( used to contol other functions or a launch motor)
Rudder 4
R Flap 5
L Flap 6
L Aileron 7
Tow rel. 8
That would be 7 channels. However, many radios tie channel 3 to the throttle
stick. It is common to use the throttle stick to control the landing mixes I
illustrated above, so we may lose the use of channel 3. If that is the case,
we will need 8 channels.
If your radio will allow you to move channel 3 control to a switch to work the
tow release, or perhaps a motor, then we can get away with 7 channels. If you are looking at a 7
channel radio, look for the
ability to assign this channel to a switch AND support for the 4 servo wing.
However I am going to play it safe and assume we need 8 for the rest of the
illustration.
Would we ever have use for more than 8 channels? Of course! There is always
more stuff we can put on a plane.
We will use my Ventus 2C as an example. I have the plane laid out as shown
above on 8 channels However my wings also have spoilers, though I don't have
them set-up right now. While I could put each spoiler on a separate channel
and create a 6 servo wing there is no real need for this and my radio doesn't
support it. I would put both spoilers on one channel. That takes me to 9
channels.
I could also add landing gear and use the 9th channel for that. If I wanted
the spoilers AND landing gear, I would need 10 channels in my current set-up.
If I didn't have 10 channels, I could put the flaps on one channel to free up
a channel to accomodate both the spoilers and landing gear. That would work,
but I would lose flexability on how I trim and control the plane, as described
above.
So, you can "make things work" depending on the features of the radio and your
willingness to give up some flexability.
I have a Futaba 9C which will give me what I need to manage the Ventus 2C. It
has a maximum of 9 channels so I would have to work within that constraint. I
am not sure if I can move channel 3 to a swich. I never looked because I have
enough channels for my current set-up without this feature.
Can I fly it with a less flexible radio? Sure!
A Futaba 7C, could fly my Ventus but it does not support 4 servo wings, so I
would give up some flexibilty.
A Futaba 6EXA or a Hitec Flash 5SX could fly it if I put the flaps together on
one channel and the ailerons together on one channel.
Standard radios, like the Hitec Laser 6, could fly it, however don't buy a
standard radio to fly full house or scale sailplanes. If you have one and
have to make do, that's fine but it would be a mistake to buy one for this
kind of plane.
We can look at the Futaba 9C Super, which appears to have replaced the 9C at
$290, as an entry level radio for this environment.
http://www.servocity.com/html/9ca_super_systems.html
http://www.futaba-rc.com/radios/futk75.html
The super can do more than the original 9C, so it may be all you will ever need.
However there are many radios that could handle theese requiremts. Perhaps
there are some at lower cost, but I am not aware of them.
Some examples of more expensive radios to look at would be the Airtronics
Stylus, Multiplex Royal Evo 9, the JR 9303 and and a bunch of others. These
all run in excess of $400 and some a lot more. And these are no where near
the top on the price chart. There are radios that run over $2000 with 14
channels. If you got the $$, enjoy!
So, many radios can fly a full house sailplane and many can fly a full house
scale sailplane, but if you want to really bring the plane to its full
potential, you are going to need a computer radio that, at a minimum, has full
support for a four servo wing and probably has at least 8 channels.
PS: Read this only if you like to dabble in deeper technical stuff. This
article is on advanced set-up of a full house sailplane. Definately not
something a beginner, or even a many experienced ailplane pilots need to do.
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
< Message edited by aeajr -- 3/20/2005 10:19:36 AM >
_____________________________
Clear Skies and Safe Flying!
Ed Anderson
Moderator
Park Pilot Program Partner
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All Forums >> RC Airplanes >> RC Gliders, Sailplanes and Slope Soaring >> Good Glider Transmitters 
Good Glider Transmitters - 
There is a Tx only for sale now for $175 - that's a bit high I tink, but shows you can get full house for under $250. 
