Prawnik

How much surgical tubing do I need to build a homemade Upstart-type luanch system, designed for 2m and larger sailplanes?

I have the line and parachute and stake from an old upstart, just no surgical tubing.

kamakasi

My Feedback: (3)

Depends on how much room you have at your field + how high of a launch you want. figure 4x's the rubbers length+ stretching the rudder 4x's it's length will get you in the ball park for how much room you need. Example is 100' of rubber x 4 = 400 + 400 of line = 800'. I've set my hi-starts up with splices at the mid points in both the rubber and the line. This way if I want to practice landings or wind up with out much room I can shorten the hi-start.
Don't get cheap on the rubber. A high quality mandrel dipped latex will be much better in launching and longevity.
Also you need to size the rubber to weight of the plane. Depending on the plane the rubber should supply a pull of 3 to +5x's the plane weight. Floaters on the light end, glass slippers on the high side.
I've got a 32oz floater that launches just fine at 8 lb. of pull. (4x) I've also have a slipper that weights 28 oz. but likes 11 lb. of pull. (6.3x) no one hi-start will do everything ask me I own 4 all for different planes and wind conditions.
The hose monster 2m competition is a good middle ground.
Get your self a fish scale and use it to get a feel for what your planes can handle.
Remember if you have a head wing to back off on the tension or to apply some down trim other wise you run the risk of folding the wings. Unless of course the plane is made for a gonzo type winch launch.

kwmtrubrit

My up-start actually has 50ft of tubing. On the other hand, my hi-start has 100ft. You probably also had 50ft on yours.

aeajr

My Feedback: (2)

Here is a great link for understanding hi-starts. I use this when I am
explaining sailplanes to friends.
http://www.labyrinth.net.au/~learmont/HiStart.html

I have a Great Planes Spirit 2 meter and a Sagitta 600 2 meter. Similar in
size and weight to a Gentle Lady.
htttp://www.greatplanes.com/airplanes/gpma16.html

I have two hi-starts.

Practice hi-start/up-start

This one is a home made up-start with 25' of 7/16" latex tubing (1/16 wall)
that I bought on e-bay. It is really stronger than what I need for this plane.
5/16 OD tubing woudl be more appropriate.

My launch pull is around 13 pounds as measured with a fish scale. At that I
can just about hold onto the plane. I added 100 feet of pink mason's line
that I bought at home depot. Then a snap swival to attach the parachute. I
made the
parachute out of a pink golf hat. I use this one for practicing launches and
landings. Most days I add another 50 feet of line with snap swivals. It would
be better matched to the plane if the tubing was 5/16" with a 6-8 pound pull.
This rubber is strong enough to launch 3 meter full house sailplanes with no
problem.

Using this strong rubber, I can get about 150'+ launchs which is just right
for launch and land practice. If there is a strong breeze, say 7 MPH, I add
another 50 feet of line because I can get more of a kite effect and add 30-60
feet to my launch.

Big Hi-start

My main hi-start is from Northeast Sailplanes. I it is their "Pinnacle
X-Large " model.
http://www.nesail.com/pinnacle.html

This Hi-Start has 100' of 1/2" rubber with a 3/32 wall. Again, this is really
stronger than I need for a 2M Spirit. I bought it in anticipation of moving
into larger planes later. This one can launch 3+ meter sailplanes with ease.
I now have an 80 ounce Airtronics Legend and this hi-start can launch it with
ease.

It has 390 feet of hot pink line that is identical to the mason's line that I
got at home depot. I get 400-500 launches with this one. I often approach the
launches that others get off of the club winches. The more experienced pilots
can really zoom off the top of the launch with this hi-start.

Keep in mind that I have a huge field to work with. Here is a picture of the
field. http://www.lisf.org/Pictures/29070035.jpg

Our field is about 800' by 1600' so I can lay out a 500' hi-start, pull back
75-100 feet and have room to work. For the larger planes, they pull my
hi-start back 200+ feet and really send the plane up.

Hope this is useful info.

For anyone who might be reading this who is interested in gliders/sailplanes
but not flying them yet, you might find this thread of value:
http://lisf.proboards13.com/index.cg...num=1070740602