aeajr

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LEARNING TO USE A HI-START
by Ed Anderson
aeajr on the forums

I think one of the reasons we don't see more people flying
unpowered sailplanes/gliders is that they don't understand
how the planes are launched. Once someone tells them about a
hi-start or a winch, they shy away, again, because they don't understand.

I LOVE hi-start launching my Spirit 2 meter and my Sagitta
600 2 meter and even my 3 meter Airtronics Legend. It is
such a thrill to see the plane climb up to the sky then just
silently float off the line like a sailboat. I find the hi-start easier
than the club winch and I get great launches. If I can do it, you can do
it.

These links may be helpful for background about hi-starts.

What is a Hi-Start
http://www.labyrinth.net.au/~learmont/HiStart.html

This product review of the AVA RES Sailplane has some good
photos of a hi-start launch and a video of an actual launch.
http://www.rcgroups.com/articles/lif...r/ava/Ava1.wmv

Videos of actual hi-start launches
http://portfox.rchomepage.com/galler...pp3-launch.wmv

By comparison, this is a strong winch launch
http://static.rcgroups.com/gallery/d...0/7716mono.mpg


HI-START LAUNCHING - Getting Ready

First, let's be clear, what I will be focused on is NOT competition
launches. I am talking about safe sport launches. I am
sure someone will comment about maximum altitude and such.
I just want to help you get in the air safely.

Second, if possible, get a coach/instructor if one is
available and ignore all of this. This is ONLY intended for someone
who is unable to get help and must learn on their own.

Third, your plane must already be well trimmed and flying
straight and even from a hand throw. If you have been having
problems with getting good hand launches, ask questions here. It isn't
hard but there is a definite techniques to it. Getting good at hand
launches is important to good hi-start launches. Fail to do this and
the hi-start will turn your plane to junk!

Fourth and very important, make sure your tow hook is in the
forward most hole that your plane has. If you only have one
tow hook
location check to see that it is a little in front of the CG
of your plane. about 1/4" to 1/2" is a
good starting point. This will give you a more controlled
launch than the
more rear, competition positions. You can move it back
later, once you become comfortable with the hi-start.

OK? We understand the goal here? Safe and gradual build
up. Our goal is control, not ultimate height! That will
come later.


STARTING SMALL

I don't know what hi-start you have or how big it is, but if
it is a "full size" hi-start it probably has 30 meters/100
feet of elastic, usually latex rubber tubing, and 100-125
meters/300-400 feet of line. There is no reason why you
can't start right in with this full size unit. However, if
you feel this is
an awful big thing to handle on initial launches without a coach
you can start smaller. You can either get an up-start which is a
smaller version of a hi-start, or take your big hi-start and
only use part of it for your initial launches.

SHORTENING YOUR HI-START

Remember, this shortening step is optional.

To take a large hi-start and only work with part of it, we
will reduce the
length of the line and elastic that will be involved in the
launch. You can
cut the line, or replace it with a smaller piece during the
training phase.
DON'T CUT THE TUBING! We want to preserve the tubing, or
other elastic, as
a single piece as it will work better when you are ready to
use all of it.
We
will just change how it is secured so we are only using part
of it.

First the line. You can either cut the line, or buy another
piece of line
that is shorter. Line is cheap and it can be useful to have
line of
different lengths, so I will suggest you pick up some masons
line, or any
braded nylon or Dacron line at any hardware store. You want
something
with a working strength of 50 pounds or more. Nylon mason's
line is
typically
around 100-150 pounds working strength. Bright colors will
make it easier
to find the line in the grass. Mine are hot pink and hot
orange.
You can also use 50 pound test monofilament fishing line for
your 2 meter
plane but it will be harder to find in the grass than
mason's line. I
suggest you make up a couple of 50 foot lengths. As we
progress you can
join them using a knot, or I like to use heavy duty fishing
snap swivels.

To shorten the elastic I simply loop the elastic over the
spike 2-3 times at
some reduced length. Works fine.

LAUNCH INTO THE WIND!

Always launch into the wind. Whether it is a sailplane on a
hi-start, a
parkflyer or a Boeing 747, we always launch into the wind.

For learning purposes I would say calm air to 5 mph would be
a good starting
range. Gusty or swirling wind that changes direction a lot
is going to
complicate learning. Once you are accomplished, these will
be much less of
an issue. I have spent whole days hi-start launching in 15
mph winds which
can
really help take the plane high. Launches will be higher
with a breeze
than dead calm air.

One of the advantages of a hi-start over a winch is that it
is easy to
adjust your launch related to the wind. When your plane is
in your hand,
check the wind direction and move left or right so your
launch will be as
directly into the wind as possible. You can move right or
left to adjust to
a changing wind direction.


SETTING UP THE HI-START

Now we want to get to deploying the hi-start in preparation
to launch your
sailplane. You are going to stake one end of the hi-start
into the ground
using a 10-16 inch spike, large tent peg, screw in dog chain
anchor or some
other method. Make sure the stake that you put into the
ground is secure
and has a large enough washer on it so that the ring on the
hi-start will
not
pull off the stake. As extra insurance, you can also loop
the elastic over
the
spike for extra security. I usually do this.

If you start small, say 15' of elastic and 50' of line it
might feel a lot
easier to control, and the launch will be lower and the
energy smaller.
Again, this is just an assisted hand throw. We will use
this length
combination for this discussion. Remember that I am
assuming your plane
is well balanced and trimmed and that you can reliably hand
throw it and
control that hand throw from your radio. (If you are not a
master of the
hand
throw, put this down and go work on that!)

If your plane is flying well from a hand launch and your tow
hook is a
little in front of the CG then I am going to suggest that
you launch with
all
controls at neutral trim, or wherever the plane flies best
from the hand
throw. Remember you don't use the elevator to take the
plane up, the lift
of the wings will do that. In fact, as we will discuss
later, if you have
problems with pop-offs, you can put in 3-4 clicks of down
elevator to slow
down the rotation of the plane on the initial launch. Just
don't forget to
take it out once you are off the hi-start.

If you get your wings out of level on the launch, the plane
will tend to go
right or left when you throw it, just like a bad hand throw.
Use the rudder
to get it back to center and work on getting a level throw.

It is easy to control the launch force of a hi-start by how
far back we pull
it, which will determine the stretch on the elastic and the
energy of the
pull Do exactly what you would do on a hand throw.
Basically flat firm
throw
with level wings. The hi-start will continue the pull to
accelerate the
plane
giving the equivalent of a strong hand throw. However as
the hi-start will
pull it faster than a hand throw, it will start to climb.
This is what we
want.


TIME TO LAUNCH

Be sure your receiver and radio are turned on. Complete
your range check
and make sure all surfaces are moving in the right
direction. Now you can
hook the line to your plane's tow hook and pull back a
distance equal to the
length of the elastic, 15 feet in our example. You should
feel a pull on
the line, but should have no trouble holding the plane in
one hand. I like
to
grip my plane under the wings and hold it with the wings
over my head.

Now, check to make sure all of your controls are working
again. If
necessary, use your mouth to move the sticks and see that
everything is
working. Check the trims on your radio to make sure you
have not bumped
them out of place. Do this on EVERY launch ... forever!

Stand firm, don't walk or run with it, and just give it a
straight. firm,
flat throw, controls at neutral just like a hand throw. Get
your hands to
the controls on the radio ready to guide the plane, but
don't over control
it.
The plane should go out just like a hand launch, only with
more speed.
It should naturally climb a little. It should just fly off
the end of the
line. Let it glide out and drift down naturally, just as you
would on a hand
throw, just further. Be sure you have enough space in front
of the
launch to allow it to do this. You don't want to have to
turn on you first
hi-start to avoid hitting things.

You just completed your first hi-start launch.

How did that go? If it went left or right, you tipped the
wings when you
threw it or your plane is not trimmed to fly straight. Work
on it at this
length until you go out level and true every time.

Build up the strength of the pull over several launches.
Pull back one
length of the elastic. Launch from this until you are
comfortable. Then
pull it back 1 1/2 lengths of the elastic. Then try it at
twice the length
of the
elastic. Make sure you are going out straight and level.
For a 15 foot
piece of elastic that would be a 30 foot pull.

Then slide another 15-20 feet of tubing into the working
area of the
hi-start and add another 50 feet of line. You are now in
up-start range
with 25-40 feet of tubing and 100 feet of line. The plane
will launch
higher with this arrangement. You change nothing, let the
hi-start do the
work. Just don't forget to get the plane a strong push/throw
as you release
it. Don't just let go.

Keep adding elastic in whatever increments you like till you
get to the full
length. Add 3-5 times as much line as elastic till you add
it all back.
Again a typical full size hi-start is 60 to 100 feet of
elastic 250-400 feet
of line.

How far back you want to pull depends on the make and
diameter of the tubing
on your hi-start. If this is a commercial hi-start, read
the makers
recommendations and follow them. In general, with 1/4 -5/16
OD latex
tubing, pulling back two to three times the length of the
tubing should be
plenty for your 2 meter plane and should not over stress the
tubing. If you
are
using bungee cord you will likely not be able to pull back
that far as the
cloth
covering constrains it and bungee is typically much stronger
than the latex
tubing.

If you are using heavier tubing such as 3/8", 7/16" or 1/2",
a pull of 1
1/2 times the tubing length may be all you would want to do
with a 2 meter
plane. My hi-start rubber is 3/8" and I only pull back about
1 to 1 1/2
times the length of the tubing to launch my 2 meter planes.
At that pull I
can barely
hold the plane. I measured it once at 14 pounds of pull
which is stronger
than needed for a Spirit, for example. If you feel like
measuring, a pull
of 3-5 times your model's weight is a good target, or 6-10
pounds for the
typical 2 meter starter plane. I have launched my Spirit at
up to 14 pounds
of pull, as measured with a fisherman's scale.

Pop-Offs:

A pop-off occurs when the plane rotates so much during the
launch that it
releases the line early and "pops off" the line. This can
happen anywhere
but I have usually seen it within the first 150 feet of the
launch. Pop
offs can be
tricky to control. The plane may fly up at an extreme angle
then stall and
want to dive for the ground. More often it will pop off and
go into a loop
to the rear, behind you. I have found that most of the
time, if this
happens, you are best served to just help the plane finish
the loop rather
than
trying to prevent it. Fighting the loop often takes so much
energy out of
the plane that it will stall and you are fighting to keep it
from crashing
to
the ground.


If the plane starts popping off too soon, try putting a
click or two of down elevator on the trim before you launch.
Also make sure
your tow hook is in FRONT of the CG. About 1/4-1/2 inch is
enough. The
likelihood of a pop off will increase with the power of the
launch due to
the rotation of the plane from level to climb, so let's get
it under control
early. That is why we build up slowly.

As the pull gets stronger, the plane will fly out faster and
the lift of the
wings will take it higher naturally. No need to throw it
up, it will go up
on its own. You can launch the plane at a more elevated
angle as you become more comfortable with the hi-start and
get to know how your
plane launches.
Up to a 45 degree angle works well. Just remember that the
steeper the
angel the more important the throw. Don't just let go, give
it a
good push.

I have over 500 launches with my Spirit, Sagitta and Legend.
I launch at 20
to 45 degree up angle with neutral controls and the forward
tow hook
position. My planes climb beautifully and I don't give up
much to the winch,
if anything.

Using my smaller launcher (25' tubing and 100' line) I get
100+ feet
launches depending on the wind, without a zoom at the end.
With the larger hi-start (100' 3.8" tubing and 400' line)
I estimate I go
up 350-500 foot launches, depending on the wind, and can
zoom off of the end to gain more height if I want.

I was afraid of the hi-start but now I really enjoy it. If
you have someone
to coach you through the first few launches you will be
fine. If you don't, try this method.


The angle method for placing the tow hook
http://www.rcgroups.com/forums/showp...8&postcount=15

Here is another informational post for those who like more
technical detail - The Physics of Hi-Starts
http://www.charlesriverrc.org/articl...artphysics.htm

Sailplanes are Wonderful!
http://www.*********.com/forums/showthread.php?t=5356

If you are new glider pilot, this is a great resource:
http://forums.flyesl.com/topic.asp?TOPIC_ID=224

Video of 4M glider launch - Throw is bad, but he
gets it into the air.
http://www.youtube.com/watch?v=T-sYXc9gbUE

Rocketman612

My Feedback: (85)

Ed,
Thanks for the good info. I'm getting into sailplanes this season and have been soaking up all the info I can.

Pete

aeajr

My Feedback: (2)

I'll bet the thermals are great where you live. Don't let it get away from you.

BMatthews

Always good info Ed. Look for this to be stickied soon. Might be nice so that it's a one stop shopping opportunity to fill in on winches as well and then we can alter the title to winch and high start launch technique or some such.

aeajr

My Feedback: (2)

Your wish is my command.

LEARNING TO USE A WINCH
by Ed Anderson
aeajr

The joy of the winch is that you can control it. The challenge of the winch is
that you MUST control it, so you have to think about flying the plane and how
much force to apply with the pedal.

Almost any 2M+ plane can be winch launched. The trick is in controlling the
force of the pull. On all winches I have ever used, this is done by pulsing the
pedal/button that operates the winch. Full on gives you maximum pull and
maximum speed but also puts maximum strain on the wing spars. Most light built
up wood wings, can not take the full force, so you tap the winch pedal to
moderate that force. The trick is to learn how to do this WHILE time the throw
AND while you fly the plane AND you watch the wings for signs of stress.

I had tremendous coordination problems. If the plane went off angle I would
freeze on the pulses, causing full pedal force, braking a wing. The next time I
might not have enough tension on the line and when I threw the plane the plane
would stall before the winch had enough pull to fly it. CRASH.

Now, for many people this coordination issue is not such a big deal. For me it
was.

If you have an experienced winch pilot around, get them to help you. Have them
launch the plane for you so you can see how it is done. Then have them launch
and pedal while you fly the plane up. Then switch places so you operate the
pedal and they fly it so they can coach you. Then you take the radio and the
pedal and have them throw the plane. This way you only add one operation at a
time. When those operations are comfortable then you can do it all.

I have found that faster shorter, evenly timed taps provide a more even, less
stressful load on the wings. Long pulses followed by gaps seems to put more
stress on the wings as you build force, then let it off. This seems to flex the
wings more than short fast taps. Those long on long off tend to flap the wings,
so to speak.

If you have a covered wing, you can look at the flex of the wing but another
indicator of stress is wrinkles in the covering. On my Spirit wing, when I
launch it off my very strong hi-start, at 14 pounds of pull I get some wrinkle
in the covering. At 10 pounds of pull, I don't see it. If you start to see
wrinkle on the covering back off a bit.

The other thing that is tricky is the throw/release. On a hi-start, there is
tension all the time so when you throw the plane it is under constant pull
immediately. With the winch you have to control how much tension, how much to
build up before you throw the plane and when to start tapping. If you don't
have enough tension, the plane will stall. Too much and .... CRACK...

Naturally you also have to keep the plane straight. With a hi-start it is
easier because the tension is there, you can take a comfortable stance, then
throw the plane with flat wings. With the winch you are pulsing, judging the
tension, preparing to throw AND making sure the wings are level. Easy.

I might be making this sound too complicated, but I will tell you that I had a
LOT of trouble learning to use the winch. Now it is my main launch method.

With my Spirit and similar light planes, I do not tension the line very much. I
feel pull on the line but I do not build it up enough to pull much of the line
off the ground. This way the curved line provides some cushion for the pulses.
For my Thermal Dancer and my Legend, I build up a lot of force before I throw
the plane. Much of the line is off the ground and I have a very very strong
force, but these planes can take a full pedal launch.

OLLIE's SUGGESTION

Here is a practice exercise in controlling the winch that does not endanger a
plane. This was suggested to me by Ollie, an extremely knowledgeable sailplane
pilot.

Hold the launching ring in your hand so that if it is pulled hard it can leave
your hand it without taking any flesh with it or jerk you off your feet. You
might consider using a glove. Don't put your finger through the ring. Don't
wrap the string around anything. When I do this, I usually hold the chute or
the ring between my thumb and index finger so if I over pulse, the line will
just be pulled out of my fingers.

At first, tap the pedal so lightly that the winch doesn't even turn. While
maintaining the rhythm of the tap, gradually increase the length/strength of the
on cycle until the briefest contact is made and the winch starts to pull. Keep
the taps as short and light as you can. Do this so you have no trouble holding
the line.

Vary the rhythm to control the pull on the line. You vary the pull by the
frequency of the pulses. Feel the cycles of pull and imagine this force on your
plane. If you use a hi-start, try to control the pull so that it is like the
pull on your hi-start. Long bursts with long gaps tend to jerk the plane but
they do prevent the pressure from building up too much. Feel what the plane
will feel. Short frequent pulses will give you a more steady pull. You vary
the force by how much on time you give it.

Practice until you can maintain a constant pull without having to release the
ring. Then practice some more until you can maintain the constant pull while
holding a
conversation with someone else. Then practice some more until you can do it
while working math problems in your head or any other mental exercise that
requires your full concentration

A discussion on learning to use a winch
http://www.rcgroups.com/forums/showt...4&goto=newpost

If you are new glider pilot, this is a great resource:
http://forums.flyesl.com/topic.asp?TOPIC_ID=224

Videos of a winch launch
http://www.youtube.com/watch?v=9kbpC...eature=related
http://static.rcgroups.com/gallery/d...0/7716mono.mpg
http://www.youtube.com/watch?v=kduHwG2FoHY

Winch throw
http://static.rcgroups.com/gallery/d.../7716throw.mpg

Winch launching
http://www.soaringissa.org/tech_tips..._launching.htm

Zoom off the end
http://home.comcast.net/~bsli40/3MGnome_Launch.MOV

http://www.rcgroups.com/forums/showt...=using+a+winch

Winch launch of a full scale glider
http://www.youtube.com/watch?v=lixRcsQN55Y&NR=1