RustyTumbles

HI all,

I wish to purchase a 3m high performance sailplane. However I don't own a winch of any kind!! I already have a bungee for my 2m sailplanes but I don't think it will launch a 3m bird!! So I was wondering if it is possible to use 2x100ft lengths of surgical rubber running parallel to each other? Then I only need to buy another 100ft of rubber rather than an entire winch setup, and just add the extra rubber when I want to fly the big bird. Will this system work?

kamakasi

My Feedback: (3)

You may over power the plane by using 2-100' lengths of rubber. All depends on the rubber size. I launch my 48 oz. 3 meter plane with a dynaflite heavy duty hi-start.If it were me I'd opt for spending the few extra bucks and getting the complete hi-start in the correct power range. Another thing to remember is that the line on that 2m hi-start might not be strong enough for a larger heavier ship. Check out Areofoam they have from what I've heard and an soon to experience some of the best h-starts going. If anything give them a call they are most helpful.

aeajr

My Feedback: (2)

Kamanski brings up good points.

How much will the new bird weigh all up flying weight?

What are the specs on your current hi-start, or is it acutally a bungee?

The HD hi-start Kamanski is using is 5/16 surgical tubing and 350 feet of line. It is rated for planes up to 120 inches.

You certainly don't need a winch to launch a 3 M plane unless you want one. There are plenty of hi-starts under $100 that will launch 3M and bigger.

If you rubber is less than 5/16 surgical, you could just pick up some stronger rubber, say 3/8 and switch the line, or use Mason's line which is what I use on my hi-starts.

I have two hi-starts. They have launched 2 M and 3 M planes.

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 a 2 meter plane but it gives plenty of pull in dead calm.

I added 100 feet of pink mason's line that I bought at home depot. I made the
parachute out of a pink golf hat. I use this one for practicing launches and
landings. It would be better matched to the plane if the tubing was 1/4" or 5/16". I
get a good but a little too powerful launch. This rubber is so strong that it
has been used to launch 3 meter full house sailplanes with no problem.

I can get about 100-120' launch with this set-up. If there is a strong breeze,
say 7 MPH, I add another 50-100 feet of line because I can get more of a kite
effect and add 30-70 feet to my launch.

Big Hi-start

My main hi-start is from Northeast Sailplanes. I think it is their "Pinnacle
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 2 M planes. I bought it in anticipation of moving
into larger planes later. This one can launch 3+ meter sailplanes 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. They call it the little bear. In fact some of the 2 meter guys won't use it because it is so strong.

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
100-200 feet and have room to work. For the larger planes, they pull my
hi-start back close to 300 feet and really send the plane up.

Hope this is useful info.

Sailplanes are Wonderful:
http://www.rcezine.com/cms/article.php?id=18

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

BMatthews

Good options all. One idea though. I like the concept of just adding a second rubber length but nothing says it has to be the same size as the original Kamakasi suggested that option but didn't follow through. If your present rubber is 5/16 or 3/8 you could just add a length of 1/4 or 3/16 for the amount of extra power you need.

One thing, with a 3 meter bird the wings are normally well overbuilt to survive pedal heavy winch launches. So if you decide to add a second rubber to the existing one (and assuming as suggested that the line, hardware and chute will handle the extra pull) I would tend to err on the side of going for too much power rather than too little. The model will handle it fine. It's going to be a heck'uva pull on your arm though so really concentrate on your launch throw to ensure you get a good throw and follow through. All that pull combined with a heavier model means that a launch loading induced stall becomes much more possible if you're in the habit of sort of just releasing the model with a casual push forward and up.

aeajr

My Feedback: (2)

3/8 rubber by itself is definately strong enough to launch almost any 2 M plane.

As for overbuilt wings, I don't know the bird you are planning to fly, but not all 3 M planes are designed for strong winch launches. I give you the ARF Bird of time that has had a rash of wing breaks reported off of winches. The mfg has revised their recommendations to Hi-start only.

5/16 will launch most 3M planes, though it might not be strong enough to get the highest launches. 6/16, or 3/8 is a significant step up. The half inch rubber I have will launch the average car, but still not a strong as a full pedal winch.

I measured the tension I put on my Spirit at launch using a fish scale and my 7/16 up-start. It was about 10 pounds, or 3-4 times the plane's weight. The limit is the abilty of the plane to take my squeeze to hold on to it. She goes up like a rocket.

With heavier plane and a stronger pull you could probably get it up to 15 pounds. That is still three times the weight of my 85 ounce 3 M Legend which is a very heavy plane. Plenty of pull.

BMatthews

Oh sure, you had to go and dredge up THAT one... OK, OK, so MOST 3 meter birds are built for strong duty.....

You a lawyer by any chance?

aeajr

My Feedback: (2)

Nope, just a guy who has seen wings break on winches.

I have never seen any plane of any strength or style break a wing on a hi-start, even mine, the one the club calls the "little bear".

kamakasi

My Feedback: (3)

For my larger ships I've just received my rubber from Aerofoam. I'm using their unlimited, 1/8" i.d. with 5/32" walls. I have yet to use it the weather has been against me. But hope to give it a try tonight on the Sailaires maiden voyage.
As for using 2 lengths of rubber my main concern is running out of pull early in the launch. You may have adequate tension at launch only to find out that the rubber has not been stretched to a sufficient length to maintain an decent amount on pull.
I do agree with BMatthews that is is better to error on the side of more power, just not to much. Maybe one step up say a 2m plane on an standard class hi-start on a 100" plane on a 3m hi-start. I would never launch my Spirit on my mega launcher. It would either pop off or just plane run out of gas or if I was feeling really mean fold the wings.