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aeajr
477 Posts |
 Posted - 07/19/2006 : 09:19:40 AM
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LEARNING TO USE A HI-START
by Ed Anderson
aeajr on the forums
Updated 12/17/2014
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. It is such a thrill to see the plane climb up to the sky then just silently float off the line like a sailboat on the sea. I find
the hi-start easier than the club winch and I get great launches. If I can do it, you can do it.
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
http://www.workflow.as/jogrini/video/bungee.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 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/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 monofilament fishing line 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 so I can add and remove easily.
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 12-16 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.
Here is a video that shows the set-up of a hi-start and launching a sailplane. It is pretty good and will help to make the rest of this clearer. https://www.youtube.com/watch?v=ru0tyLi6L74#t=43 |
Best regards,
Ed Anderson
Long Island Silent Flyers
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Edited by - aeajr on 11/02/2009 06:38:44 AM |
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aeajr
477 Posts |
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aeajr
477 Posts |
Posted - 08/31/2006 : 08:22:52 AM
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Height - The idea that you need a winch to get a high launch is a mistake.
Most people just need a stronger hi-start than what they are using. A soft
hi-start will give a plane a gentle launch and get good height. But if you
put some more powerful rubber on you can get stronger and higher launches
AND you can add more line giving you even higher launches.
I have 3 hi-starts. Each is a different length and a different strength and
I use them for different purposes.
Short - Upstart -
This is a homemade unit. It has 25' of 7/16 rubber with 1/16 wall. I bought
the rubber on e-bay. I added 100-150 feet of line. I use it to launch a 2M
and 3M planes. The parachute is made from a golf that I cut up and sewed a
line into so I could mount the rings.
For lighter planes I use 150 feet of line and launch at 10 pounds pull with
from a 60 foot stretch. Spirits, Gentle Ladies, Easy Gliders do well with
this.
At 75 foot stretch I get about 15 pounds pull. I have launched 3M 75 ounce
planes with it using 100 feet of line.
At 50 foot pull I launch my Zagi slope plane at the thermal field for fun or
to work on the trim.
This is a great practice launcher for low flights to launch and lands, and
the like. I have also used it to get planes up an over trees to get them out
to slope lift. I keep it on a plastic reel that is sold for outdoor
extension cords.
Medium - Home Made
Here I use 50 feet of 3/8 rubber with 1/8 wall that I purchased off e-bay
for $15. This is a red rubber that is used for exercise machines.
I added 225-275 feet of line. This one lives at my Dad's house with a Spirit
2M. Again stronger than I need for the Spirit but the Spirit goes up great
at 12-14 pounds at about 100 feet pull with the 275' of line. Again I keep
it on a plastic reel made for electric extension cords. I think that I
would get about 20 pounds of pull if I pulled it back to 150 feet. That
again should be able to launch a 4-5 pound 3M plane on 200 feet of line.
Large - Northeast Sailplanes Pinnacle L- Rated for 3+M planes. This was my
first hi-start. I bought it used on e-bay before I knew what I was doing.
It has 100' of 3/8 rubber with 3/32 wall + 400-500 feet of line. At 150 feet
pull I am
again at 12 pounds of pull for Spirits, GLs, or even some 3M planes, like
the Bird of Time. At 300' pull I get about 24 pounds of pull. I have
launched 80 ounce 2.9 M Legend and a variety of 3M + planes. I use 500 feet
of line for the smaller planes and 400 feet of line for the larger planes.
I would not hesitate to put up a 4M 6 pound plane on this one but I will
admit that at full pull, this is a beast to hold. Best done with two people.
What is best for you?
At our glider club, the NESail Large is the standard choice for most people
for 2.5-3.5M planes. For 1.5-2.5 M planes, and even light 3M planes, like
the Bird of Time, the NE Sailplanes Pinnacle Standard hi-start might be a
better choice. These are just general guidelines, not rigid rules. As you
can see, they overlap. If you have a larger hi-start and a lighter plane,
just don't pull it back as far but if you are going to be in that
smaller/lighter space for a long time, you are better off with the Standard
vs. the Large. You will get better, less stressful launches.
With a 5 mph breeze I can put any of my planes at almost full length on any
of these hi-starts. On the medium and large I even take a zoom off the end.
Not as powerful a zoom as I can do on the winch, but most woodies can't take
that strong of a zoom anyway. I really give up nothing to the winch on the
medium and large hi-start unless I am comparing to a competition sailplane
that can take a full pedal launch and full power zoom.
The NESailplanes Pinnacle has been the standard brand at our glider club.
(edit: as of 7/11 this is no longer avail - NE Sail appears to be out of business)
http://www.nesail.com/categories.ph...8b917bea25f51ae
WE now have several 3M Aerofoam Hosemonsters and they are excellent provinding about 19 pounds of pull at a 3X stretch. They have an excellent reputation.
Aerofoam. http://www.aerofoam.com/hosemonster.html
They cost more but he is using a very high quality rubber that will stretch
out beyond 3X pull. I am told it gives a very uniform release of energy.
Many say it is worth the price.
Best regards,
Ed Anderson
aeajr on the forums
Long Island Silent Flyers
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Edited by - aeajr on 07/21/2011 04:06:12 AM |
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aeajr
477 Posts |
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aeajr
477 Posts |
Posted - 11/02/2009 : 06:36:40 AM
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THE EFFECT OF CG ON HIGH-START LAUNCHING
Let me share an experinece I had yesterday to illustrate a point. And I am going to take you through my thought processes as I discovered and corrected the problem.
My main planes are a Supra and an AVA. I use these for contest flying in the Eastern Soaring League where I launch off winches. My Thermal Dancer has been relegated to a back-up plane position. I had not flown it in months, but I had it out yesterday. What I relate here was experienced on a winch, but it applies to HS launching as well. What we are giont to discuss is the impact of moving the CG.
Before I launched the plane, I did a hand throw. Seemed it needed a couple clicks of up to give me the glide I wanted. Having done that and completing a good range check, it was time to launch. Well I popped off 3 times in a row. Once I did get the plane in the air, it was flying very poorly. A dive test indicated the plane was nose heavy.
I have done several repairs to the nose and fuselage area of the Thermal Dancer over the time I have owned it. This has resulted in the plane becoming somewhat nose heavy. Since I have no removeable weight in the nose, I added 1/4 oz of lead to the tail over a year ago.
After some trial and error, I realized the tail weight was missing and added it back. I added 7 grams, about 1/4 oz, right in front of the verticle fin. This would be like taking about 3/4 to 1 oz of weight out of the nose. This sifted the CG back, giving my plane a much better balance. Several hand throws confirmed this and allowed me to adjust the elevator trim, removing several clicks of up trim. Now I was getting a nice smooth glide.
Now I was getting great launches and the plane was flying much better. WHY????
Because the plane was nose heavy, this CG was shifted forward, as compred to my normal CG. This effectively moves the hook position rearward in relation to the CG. I may have actually had the hook behind the CG. The further back the hook, relative to the CG, the more unstable the plane becomes on launch. Most people have the hook 3/8 to 1/8 inch in front of the CG. On my competition planes I have it right on the CG. But having it behind the CG makes for extremely difficult to control launches and a great tendency to pop-off.
By putting that weight on the tail, I effectively shifted the CG rearward. Now the hook was back in its proper position relative to the CG and the launches were as I expected them to be, straight, steep and high.
The second issue that comes up is that a nose heavy plane requires a lot of up elevator trim. That up trim on the elevator can become very effective at the speeds that a hi-start produces during the launch. This can lead to pop-offs. By shifting the CG back, I was able to remove some of that up trim, thus removing my tendancy to over rotate and pop-off.
I share these experiences because they apply equally to the hi-start and to the winch. The position of the hook, relative to the CG is critical to a smooth, high launch. If you change the CG of your plane, be aware of how this will change the relative position of the hook.
If you have a high tendency to pop-off on launch, consider that your plane might be nose heavy. Or, if you like the balance of your plane, consider setting up a launch mix that adds a few clicks of down elevator during the launch. This will prevent that over rotation during the critical first 50 feet of the launch. You can flip that mix off somewhere along the arch of the launch.
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Best regards,
Ed Anderson
Long Island Silent Flyers
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aeajr
477 Posts |
Posted - 06/29/2011 : 09:10:17 AM
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SOURCES FOR RUBBER AND HI-START PACKAGESThis needs to be updated from time to time.
My favorite, NESailplanes seems to be in trouble. No one seems to be able to get in touch with them, so forget the Pinnacle hi-starts.
OTHER SOURCES
Hobby-Lobby - hi-start rubber or full hi-start packages - well known for quality products
http://search2.hobby-lobby.com/psearch/svc/search.php
Aerofoam - Hosemonster - rubber alone or full packages
reputed to be the best
http://www.aerofoam.com/complete_highstarts.htm
HobbyKing - rubber only. I don't know much about these. 30 foot pieces only so you would have to join them for a larger HS.
http://www.hobbyking.com/hobbyking/store/uh_power_Search.asp
You can find e-bay listing for theraband rubber
A guestimate would be that red would be good for 2M, Green for typical 3M, Black for extra strong or larger than 3M. Anyone have actual pull measurements for this stuff?
Tower Hobbies - Low cost - they work but I only recommend these for people on a very very tight budget. Use the HD for 2M or above. Probably Ok to 100" wing span. Standard is for under 2M gliders.
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXYXK5&P=7
You can buy latex rubber tubing on e-bay, just make sure that whatever length they offer is one piece. You can see offers for 100 feet but it comes as a bunch of 5' sections which would be common use for this stuff.
Assuming you find 30, 50 or 100 foot pieces here are the size breakdowns as I have seen them used. others may provide different advice. I tend to like my HS a little stronger. You can always pull a little less but if you need more pull and you don't have it you are stuck.
5/16" OD - Good standard HS good for 1.7M up to about 3M or about 64 ounces, (4 pounds)
3/8" OD - Good HS for 2M up to about 3.5M or about 88 ounces. (5.5 pounds)
1/2" OD - Good for 3M up to about 5M or about 10 pounds |
Best regards,
Ed Anderson
Long Island Silent Flyers
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Edited by - aeajr on 08/01/2011 5:13:01 PM |
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aeajr
477 Posts |
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Learning to use a Hi-Start
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