AEAJR

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/liftzonemag/2004/mar/ava/Ava1.wmv

Videos of actual hi-start launches
http://portfox.rchomepage.com/gallery/movies/Stepp3-launch.wmv

By comparison, this is a strong winch launch
http://static.rcgroups.com/gallery/data/500/7716mono.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 someo ne 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 inital 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 whereever 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 450 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.

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

That plane was made to fly. Fly it!

rwmson

Excellent article Ed - nicely done!

Sky Sharkster

Thanks, Ed, great article!
Ron

TLyttle

Yup, all info is correct.

Once you have your model trimmed for histart launch, ya get kinda arrogant about it (or at least I did).... I seldom pull back any more than 20 paces if there is ANY wind, set the trims and just let go. I have done this with the TX sitting on the ground, no input required until the model floats off the line. If I want to get into light lift, I trim in a bit of up, until the model is at the end of the line indicating a thermal, then zoom off the line.

In light winds, I annoy the experts by zigzagging up the line, gaining height with every sweep. Try this with a model you are familiar with, it really is fun!

AEAJR

[quote=TLyttle;92931]
Once you have your model trimmed for histart launch, ya get kinda arrogant about it (or at least I did).... I seldom pull back any more than 20 paces if there is ANY wind, set the trims and just let go. I have done this with the TX sitting on the ground, no input required until the model floats off the line. If I want to get into light lift, I trim in a bit of up, until the model is at the end of the line indicating a thermal, then zoom off the line.
quote]

This may be a cute stunt but I would not endorse doing this at any time with any model.

TLyttle

Yeah, I guess it was a stunt, but the point to the beginners was that launching off a histart is NOT all that complicated. The lesson was not wasted, and it made the beginners more relaxed about the process.

Quite often, I would use the same "stunt" with their own models once they were trimmed. That is my point: proper TRIMMING allows you to use a histart without fear or stress, either to the model or the modeller, and allows a lot of latitude in a launch.

AEAJR

Do you avoid contests because they are flown off winches and you practice on a hi-start? Let me give you a different prospective. If you don't fly contests you are missing out on a lot of fun.


Our club contests and our Eastern Soaring League contests are all done off
winches. However anyone can have their plane launched for them off the
winch if they are not talented on a winch. I did this for several Novice
class flyers at a recent ESL event. In my first ESL contest others launched the plane for me.

Are you at a competitive disadvantage if you don't have a winch to practice on? Sure, but compete anyway!

There is no question that a super strong ship can achieve greater height off
a winch than a hi-start. And there is no question that a typical sport
class plane can not take the stress of the extreme zooms that the super
competition class planes can handle.

Having said that, I say, who cares? I compete in club and Eastern Soaring
League contests. I may never win either but I have so much fun at the
competitions it really doesn't matter if I win. And I get so much support
and good coaching from the advanced pilots that I would have to be a fool
not to compete. These are flying lessons from the best!

I share what I learn with those who want it. They can use it in whatever
way they wish. But the idea that you can't compete because you don't have a
super ship just does not cut it with me.

I was at my first Eastern Soaring League with a Sagitta 600 2M RES glider.
The only 2 meter in the contest. I finished dead last, but I finished.
Some others did not finish. I had a grand time and I was a better flyer for
it.

I did most of my practice flying off a Hi-start! At the contest other flyers launched my plane off the winch for me. Worked out fine and they were happy to do it.

I then got a 15 year old Airtronics Legend that flies like a tank. 4
contests on that one. It is now my back-up plane. I have managed to move up to NEXT to last. Having a frickin ball!

On the Legend, I practiced on the winch and on the hi-start.

Now I have a PoleCat Thermal Dancer. Still not an Icon or a Supra or a
Sharon. Maybe I can achieve mid pack. That would be nice, but frankly I am always flying for my personal best. Perhaps someday that will get me a prize. But when I make a personal best, it always makes me smile. Hitting the center of the landing circle is such a high!

I encourage you and other flyers to enter contests for the fun, for the
friendship and for the learning. And, if you are an active contest pilot, I
encourage you to take that hand of a reluctant flyer and bring them into the
contest fold. Believe me they will thank you.

Clear Skies and Safe Flying!

AEAJR

Maximizing Launch Height Using a Hi-Start
by Ed Anderson
aeajr on the forums

While the winch is the preferred method to get the most height on a launch,
you can get awesome launches off a hi-start if you know what to do. The
advantage the winch has is that you can control the pull throughout the
launch. With a hi-start, the pull is maximum on initial release then
decreases throughout the launch. But that does not mean that you can not use the same techniques the winch launchers use to gain extra height.


ELEVATOR AND CG

The further back the CG, the easier it is for nose to come up during the
launch. If your plane tends to launch fairly flat and you find you need up
elevator to get it to rotate, try moving the CG back slightly. Then fly the
plane. It will be more responsive and will read lift better. You may find
that you have to add some down trim after moving the CG back. This is
because you have been using up trim to hold up that heavy nose. This
process will reduce drag and make for a better flying plane.

I usually start my gliders at the most forward CG recommended by the MFG,
then over a series of flights, I move it back till it gets too twitchy to
handle, then I move it forward a little till it gets stable enough for me to
fly it. Many competition pilots have the CG so far back that I can not
handle their planes.

If you have a computer radio, try adding some expo. This will soften the
response around the center of the controls making it easier for you to
manage smooth flight with a plane that has a more rearward CG.

You should not have to apply any elevator during the launch. If you are,
then you are introducing drag which reduces speed and does not increase
lift. Try working your CG back and see how it flies. It will launch better
when the CG is further back and you will need little or now elevator to get
the nose up. The placement of the tow hook will likewise impact the need
for elevator on launch. I cover that next.


HOOK AND THROW

Hook placement will make a big difference in your launch height. The closer
the hook is to the CG, the steeper the rotation of the plane during launch.

The optimum situation is that your plane climbs at about a 70-80 degree
angle presenting the most resistance to the contraction of the rubber. This
takes the plane through the largest arch and produces the longest time of
launch, extracting more energy from the pull and translating it to height.
If there is a breeze and your launch angle is steep enough, the rubber may
never fully contract during the launch giving you the greatest height
possible. You will use that remaining tension in the line when I cover the
zoom, later in the discussion.

When you launch initially, if you have enough pull on the line, throw the
plane up at about a 30 to 45 degree angle rather than out flat. This gets
the plane through the rotation faster getting it into this max lift position
sooner. The throw really makes a difference. It gets you up to flying
speed faster which is important the closer you have the hook to the CG.
Typical hook position is about 1/4" in front of the CG, but having it closer
will usually give you higher launches.

Note that , as you move the CG back, as advised above, you are moving
further and further away from the hook, so you may need to adjust hook
position just to maintain your current hook/CG position. Also note that the
further back the hook placement, the closer to the CG, the harder the plane
is to control on launch. It will stall easier on initial release, so it is
vitally important to give it a good throw and not just let go.

When moving your hook back, you may wish to have someone help you during this adjustment phase by either throwing the plane for you, or working the radio. This way the hands are on the sticks at all times. If the throw goes bad or if you have moved it back too far, you will be better able to respond. If the plane stalls on the launch, a little down elevator for a moment will help it gain speed and you may be able to save the launch. Once you have it where you like, you should be able to launch it by yourself.


ZOOM

It is possible to "zoom" off a hi-start, in a similar fashion to what is
done with a winch. The bounce is not as dramatic, but still, you can gain
additional height if you get the timing right.

When the model is about 80% through its arc, and while there is still
tension on the line, rather than just flying off the line, you nose down for
less then a second, then pull up hard. The weight of the hi-start, and any
remaining tension, will help to accelerate the model to a higher speed. The
down/up pull then translates this speed into altitude. I do this with all
my planes. The Spirit, the most fragile of my gliders, picks up at least 50
feet this way. With a moderate breeze and a fast plane, you can do even
better. If you have an aileron plane or aileron/flaps, and a computer radio
that will allow you to reflex the wing, this can help you gain even more
height.


CHANGING THE WING

If you have flaps, deploy them on launch. If you have ailerons and a
computer radio, then drooping the ailerons also will add even more lift upon launch.

By creating more under camber, more bottom curve, you create an airfoil that
produces more lift. It also produces more drag, but during the launch, when
you have the pull of the hi-start, you can afford this drag to gain the
lift. This will create a longer arc and a higher launch.

Launch - Flaps or flapperons down for initial launch: Usually 10-20 degrees
is enough, but every plane is different, you have to experiment. I have seen
launch positions as high at 45 degrees on the flaps. If you have the
ability, droop the ailerons too.

Throw the plane hard with the nose up at around 45 degrees or higher.

Mid arc - If you have a computer radio and can set a reflex position, about
70% up the line you switch to reflex. This is where the ailerons/flaps are
actually moved up slightly from their normal position. On most airfoils,
the RG15 foil being a know exception, this creates a high speed/low
drag/lower lift setting that is great for gaining speed. Now you want to
accelerate the glider to gain speed.

Zoom - Around 80% though the arc you do the down/up while at maximum speed,
still in reflex. The down lasts less than a second and the up is strong.
Go for a climb angle of 60-90 degrees, depending on the plane and the pilot.
You have to experiment to see what works best for you.

Level - As it climbs it will lose speed. Before the plane loses all its
speed, you level the plane, go to normal wing position and start your hunt.
If you are stalling at the top of the launch, resulting in a drop in the
nose and loss of height, then you are waiting too long to level the plane.
It should look like the plane just leveled onto a table with no drop of the
nose. This is your best launch height.

You can still zoom with a simple 2 channel plane, but if you can change the
airfoil during the launch, you can gain even more height. If you have
flaps but no computer radio, you can still go though this sequence using the
flaps. Where I call for reflex, just move the flaps to normal flying
position. Ahhhh, the joy of computer radios.

Using a winch, this sequence can gain 150-300+ feet, if you have a strong
plane. It can be quite dramatic.

Using a full size hi-start with enough pull, you can do about 25-50% of
that. The limiting factor is that you can't increase the power at the end
of the launch like you can on a winch. However you are also unlikely to
overstress the wings off a hi-start. I have seen planes fail on zoom, using
a winch, when the pilot was too aggressive on the zoom. I have never seen a
plane fail when zooming off a hi-start, but I am sure it can be done.


GIVE IT A TRY!

If you go through all the steps above, you may find that you are getting
higher launches without the zoom. This is great!

Then you can try adding the zoom, but tune the CG and hook positions first
as these are more important. But you can try a zoom on any plane, the
benefits will just not be as great as when the plane is tuned properly.

If your plane drops at 100 feet per minute during its glide, and you can
gain 50 feet on the launch, you just gained 30 seconds of flight time. And
thermals tend to be larger in radius the higher you go, so you have a larger
target. If you can gain 100 feet, the flying experience can be quite
different.

The more sophisticated the plane and the more flexible the radio, the more
you can tweak the launch. The longer and stronger the hi-start, within
reason, the higher your launches.

Even with a simple R/E plane, you can improve your launch height by going
through these steps. You will get higher launches, longer glides and likely
find more thermals than you did before.

Other resources can be found in the handbook. I hope this has been
helpful.

The New Glider Pilot's Handbook
http://forums.flyesl.com/topic.asp?TOPIC_ID=251

AEAJR

We are thinking of trying a new approach for our hi-start. This involves using a pully at the other end of the field, like the one used on a winch.

You spike the hi-start near your end of the field, run the string through the pully then back toward the launch point. Hook it to the plane, then walk back.

This stretches the rubber toward the pully. Now, when you launch, the rubber stays on the ground and the plane does not have to carry the weight of the rubber into the sky.

Let you know how well it works.

jooNorway

Very interesting AEAJR!

One of my (many) attempts to "make" more sailplane-pilots in my club began one-and-a-half year ago, using my "fullsize" rubber hi-start (30 meter rubber, 120 meter line) and I asked everyone to try my new EasyGlider for a flight. A short instruction and away they flew. I did throw the plane, but didn`t touch the radio.
Soon i discovered that the EasyGlider were to slow and lightweight for the big hi-start, and tried to make a mini-version for the next day. 10 meter rubber, 60 meter line and then it worked much better. The lightweight planes like EasyGlider didn`t like the heavy weight of so much rubber, and lost height because the newbies didn`t have the skill to pull hard enough, and of course not to zoom.
The "small" bungee is often used, and there are half a dozen EasyGlider pilots in my club today who are not afraid of launching their gliders

Your idea sounds great, reducing the weight in the "airborne" line/rubber sounds like success in my ears!

AEAJR

We launch Easy Gliders off full size hi-starts all the time, but they are 2M hi-starts. The plane is so light that it will get ahead of a heavier hi-start and just fly off hte line.

Also, the stock hook position is not optimized for a hi-start, it is optimized for a tow launch using a string and a runner. Move the hook back and you will get better, higher launches with it.

We also launch the EG off the winch with good success.

WillKrash

Ed...get a chance to try the hi-start with the turnaround pully? Results?

Mike

AEAJR

No I haven't. It is pretty cool weather around here and I normally don't like to put out the hi-start under 50 degrees. Add that to the fact that I have a winch and there is no reason to risk damage to the rubber. It will probably wait till spring.

Up&Away

However, if your ailerons are only at the tip of the wing (like my Filip600Sport) the lowered ailerons can also induce tipstal.

flyranger

Ed, I am slowly moving into "pure" gliders from electric motor gliders. I am a scratch builder, preferring balsa over foam and other exotic materials. What I need, if you or some of the other readers have it, is a pic of the actual "hook" installation in a 2m glider? How much internal bracing is needed? How big is the hook? Thanks in advance.

AEAJR

Tow Hooks
http://www.hobby-lobby.com/towing.htm

http://www.hilaunch.com/

Tow hook
http://www2.towerhobbies.com/cgi-bin...?&I=LXKAM9&P=7

Spirit Manual
http://www.greatplanes.com/parts/index.html


The photos below show the interior of my Spirit. Ignore the battery. That was an experiment I did with adding a power pod to the plane. It worked but I prefer it as a pure glider.

There is a piece of 1/8 ply that has 3 blind nuts embedded in it. They are about 1/2" in front of the CG, about 1/4" in front of the CG and one on the CG, or something like that. That is one approch. You can use one of the hook kits above, or just buy a blind nut, and thread a 6 or 8 penny finishing nail to fit it.

The ply can be a bit larger if you are not sensitive to weight. It is just there to spread the load so your hook mount does not pull through the balsa.


Sometimes they cut a slot in the bottom of the fuselage, about an inch long, back it with a piece of ply, then embed the blind nut in a piece of 1/4" ply or basswood that you can slide back and forth along the slot to adjust your hook position.


If you are new to hi-start launching, put the hook about 1/2 inch in front of CG. That won't give you the highest launches, but the launches will be more stable. Then move it back as you get better. The further back you get it, the steeper the angle of climb, but the harder it is to control and more prone to stalling, so the throw becomes enven more important.


Hope that is what you needed.

Lip84

subscribe!

You guys are a freaking GOLD MINE of information. Its like reading a 2000 year old manual for life or something...

Great stuff!

TLyttle

Add all the experience of these guys together, and it IS 2,000 years!

I find that those T-nuts don't add significant weight; put in a row of them if you like, just like AEAJR said, from the c/g to well near the l.e. and pick the one you like. Back when I had hair, we used to have adjustable towhooks that allowed up to an inch or more adjustment (EK? seems that is what I used), now you have to innovate unless you can find a good supplier. There ain't a lot of mystery to this, just some common sense and a bit of experience.

AEAJR

IF you take one of those T-nuts/blind nuts and mount it in a piece of 1/4" plywood, you can cut a 1" slot in the bottom of the plane starting 1/4" behind the CG going forward. Now you can slide the hook back and forth to adjust the CG. Start with it all the way forward. Get comfortable and work it back over time and watch the height of your launches increase, jsut by moving the tow hook.

nicklanigan

Hi there.

Am brand new to flying gliders, but have had a very successful first day out today! (ie, nothing broken). Followed the guidance in this forum re hi-start.

Only problem I had was some difficulties with the hi-start.

Managed to get the glider up in the air everytime, but the hi-start seemed to struggle a bit.

I was using it in long grass (I have a farm). The nylon part seemed to easily snag in the long grass, causing the lift to end abruptly.

The stake in the ground holding the hi-start was also about 1-2m (3-6 foot) above the launch spot, making the snagging worse. Field has long very gentle slope in it.

I don't think I ever had the tubing off the ground, so the launches were pretty low in altitude. Because I was learning I didn't want too much pressure on the line, and it didn't matter that much.

Is this a normal problem? I do have the option of mounting the hi-start anchor to the top of a fence post, which would probably allow me to get the whole hi-start off the ground when I'm ready to launch.

Look forward to your advice,

Thanks,

Nick. (New Zealand).

Sky Sharkster

Hello Nick, Welcome to Wattflyer!
Good to hear you're having sucess with your glider, once you catch a thermal it's really addicting!
Having the line snag is a fact of life with hi-starts, most glider sites have the grass cut short for this very reason. If this is not possible, sometimes "whipping" the line side-to-side just before the launch will clear it. I've never tried raising the stake end, that might work also, but the rubber end is so heavy it will drag the line down (near the stake) before launch.
As far as actually lifting the tubing off the ground, this usually only occurs in very windy conditions. The tubing wieghs more than the glider, so the lift from the acceleration (wing lift) can only do so much. Also, the time when you need to lift the tubing (at the top of the arc) is also the slowest part of the climb.
How long is the line part of your hi-start? For 2 meter gliders I use 400' of line and the tubing is (I believe) 75'. The 400 foot altitude, even without a "zoom" launch, is high enough for a few circuits of the field.. If there's lift around, you should have several minutes to find it.
So, you might lengthen the line portion of the high-start, perhaps move the towhook back a small amount and accelerate at the end of the launch to zoom off. Each of these, done carefully, should help maximize the altitude. A little more "stretch" of the line before launch can help also, but this eventually becomes a "wing stress test" and you only get one chance to be wrong!
Good Luck!
Ron

AEAJR

Nick,

I was very pleased to read your post. Welcome to silent flight. You are going to love this.

I belive I can help you on all points as I have similar problems with grass. our field is not cut often and at times i have launched with the grass 3 feet high.

You need to lay the grass down if you can. This can be accomplished in several ways.

First, try to pick a spike point that will give you the clearest path to the launch spot. Avoid bushes, sticks, tufts of grass and the like.

If you walk to the spike point several times, retracing your path carefully, that will typicaly lay the grass down. Or if you can run your car up and down to the spike, that is even better. Use the weight of the car to lay the grass down. The path doesn't have to be wide but the wider the better.

When you walk out to get the chute, again, walk that line to the spike, then turn 90 degrees to go to the chute. Then walk back to that line and walk that path over and over. This will get the grass out of your way.

Another approach would be to use a weed wacker to cut a path in the grass that will fee up the line. Again, you don't need a lot, but the more the better.

As for height and picking up the rubber, there are many factors that impact how the line rises. Most of the energy for the launch comes from the rubber. The rest comes from your throw and from the wind.

If you don't pull very far you won't get a lot of energy. So you may not have had enough pull in order to lift the rubber. Or your rubber may not be strong enough.

On hi-start launches I lift most of the rubber off the ground every time. If there is a bit of a head wind and the plane is well matched to the rubber, you can lift it all and get REALLY high launches.

Your hi-start rubber and hook position will dramatically impact how high you launch and how much of the rubber you can lift. Also your CG setting will impact the launch. If the plane is nose heavy you will get a fairly flat launch. You will find with thermal duration gliders that, over time, you want to try and move the CG back which allows the nose to rise more easily on launch and makes the plane more responsive in the air. But for your early flights, set it according to the plans/instructions.

I don't think having the spike higher than the launch point will matter, except that it will help keep the line and rubber out of the grass to some degree. Try it on top of a fence post. When you tension the line, it sould raise most of the line out of the grass and that should help.

The following info would help:

What plane are you using, including wing span?

If this is a ready made hi-start, please provide a link to info. If you made it yourself, we need the following info:

What are the lengths of the hi-start rubber and string.
How thick is the rubber? Is it hollow? Give OD and ID of the tube.
Is it fabric covered bungee? That makes a HUGE difference.
What kind of line are you using?


Where is your tow hook placed relative to the CG?

If you can get a scale, like a fish scale, measure the pull you are placing on the rubber. You need at least 3X the weight of the plane to get a good launch and 4X or 5X are typically better except for VERY light planes.

For example, a GP Spirit is about 2.5 pounds so I need about 7.5 pounds of pull for a good launch. If I have 10 pounds of pull I will get a higher launch.

Without this info, we really know nothing about your launches or how to improve them.

TeslaWinger

I didn't see mentioned that to be CAREFUL when you are walking it back and your hand is sweaty. Keep your face out of the path between the plane and that force. It'll rip yer face off if your hand slips!

The most frustrating part of a Hi Start is that when thermals come cycling thru they change the wind direction and you find the line to be now 45 degrees or more off the wind direction!

Making a steep turn on launch to get into line with the wind before the dash to the top is a trip! Its like flying a 2 line stunt kite! Once you experience a good high launch (wind helps a lot!) you will be hooked! After my first 30 minute soaring flight from such a launch I am now a believer.

AEAJR

If you have the room, the best thing to do in this circumstance is to just change your launch point so that you are facing into the wind. This is one of the advantages of the hi-start over a winch. It is easy to move with a hi-start. Of course if your field is narrow or something is in the way, this doesn't work too well. However my field is large and I can just walk sideways to align with the wind.

You are right about holding the hi-start. When I hi-start my larger planes, where the pull will be over 25 pounds, I hook the plane, then tuck the nose under my arm and walk back facing away from the peg with the plane facing toward the peg. one wing is across my body. Pretty hard for it to get away, but turning round can be tricky. Good ot have your radio on a neck strap so both hands are free.

nicklanigan

Thanks for the advice - I was kind of hoping you weren't going to say the grass needed to be flattened - it's a long way!

To answer your queries -

It's a Tower Hobbies Vista - 2m wingspan - an ARF. I have actually built and flown a glider before - about 15 years ago! Was a kit glider, with a motor system. Unfortunately lasted about 10 seconds. Took 15 years to recover from it! I remain convinced to this day that the problem was the motor system - too much to worry about on a first flight. I feel I've proven this by having no major problems with this new glider! (and I'm not trying to start a debate about motor systems!).

I figured this time I'd get an ARF that is mighty cheap as I'd have little "invested" in it should the worst happen again. You can imagine my relief at it all going well.

Tow hook location is the most forward hole, well in front of the CG.

Hi-start is a dynaflite heavy duty model. http://www.dynaflite.com/accys/dyfp8301.html

I know I didn't need this model hi-start for this glider, but it only cost $5 more than the standard one, and will presumably be fine once I graduate to something bigger.

The glider seemed to do all the right things - went up in the air in a hurry, and went pretty much straight up without needing much in the way of rudder control. I did notice that it didn't really drop the line properly - this may have been because of the nylon snagging? Tended to have to waggle the elevator up and down a bit to drop the line off. I'm guessing that this may have been me trying to get the plane off too early? The nose seemed to be still pointing upwards at this point - in hindsight I think I probably felt that it was stalling and I needed to get it off the line?

I don't know how much tension I was launching with, but it was getting a fair pull on it. It wasn't particularly easy to hold it while my 2 year counted down from 10 to a launch. I'm not sure if this tension went right to the anchor though - given the snags only part of the line may have been under tension. Hope this makes sense. Will get a fishermans scale to measure next time.

While I'm writing, I'd appreciate advice on what would be a good 2nd plane.

Reason I'm writing this now is I appreciate it takes a fair while to build a kit, and am thinking about starting soon - we're heading towards winter in the southern hemisphere. I'm keen to get a reasonably priced kit, and it's easiest if someone major stocks it - like Tower Hobbies. Shipping can be a problem from smaller places to NZ.