I am building a plane for aerial photography. I don't want to add the weight of landing gear, but I think it will be too big and awkword to try and hand launch. I think a bungee launch would work well, but I have never ever seen it done before so I have a few questions.

What kind of bungees do I need?
How do I attach the bungee to the plane?
How do I attach the bungee to the ground?
Do I need to do anything special when drawing back or launching?
Any other tips you can think of?

Ummmm. Is this to be a glider?

The model needs a stout hook (well anchored) just ahead of the center-of-gravity. No idea how to figure it for a deltas, but I used to use a bent bolt in a section of aluminum "C" rail that can be locked in position once the "sweet spot" is located. Too far forward and it doesn't climb as high, too far back and it stalls and the bungee pulls out (before it drags the model for a cartwheeling worm burner, you hope). The hook should be slighty "open" so the bungee ring will easily slide out at apogee.

The bungee itself is a minimum of 100 ft of surgical tubing and one or two hundred feet of nylon "cod line". A large spike at the tubing end and a stout parachute with a ring sewn to the center on the other. We used to double spike the ground end because the thought of that spike coming back in your teeth is a bit concerning. Stretch it back to double the length of the bungee and use a long screwdriver or another spike to hold the tension. Then, when you're ready, hook the ring to the model and ler her rip. First flights should be at only a 30 or 40% stretch on the tubing. Some gliders like a tad of up elevator, some do best with a tad of down. Depends where the hook is positioned.

I REALLY recommend a dummy camera mock-up in the nose of the same weight for the initial test launches. And always hand launch to trim a glider before using a quick-up.

This will be electric powered, I just need a way to get it in the air. The camera you see in the pics is a cheap $20, 35mm camera. It is pretty much the same size and weight as the digital camera I will eventually use.

I used the pig-tail type of dog stake that screwed into the ground. It also came with an attached swivel.
BUT, I'd be very very skeeerd of launching a delta wing that way. They don't have the lateral stability of a large span glider.

Well I don't need it to go balistic like a normal glider. I just need it to get 5-6 feet in the air at around 10-15 mph then I'll start up the electric motor and take it from there.

What's the point of the parachute?

That's only for the cord that goes a couple hundred feet up and the chute helps stretch the high start back toward you instead of ending in a pile close to the stake. We weren't aware you only wanted just a slight boost.

Why don't you simply add a belly skid rib to allow a grip for launching ? A couple of my planes had two finger holes in the underside.

So I don't need a few hundred feet of surgical tubing and 100-200 of nylong cord with a paracute on it? Cuase that does sound quite ecessive for this application. Also I'm thinking that having the hook on the plane being more forward of the cg than a normal glider would be beneficial for my needs.

You may want to look in the ducted fan forums. The kind of launch system that has been described in this thread is for gliders and you need the ducted fan style catapult so you don't loose lateral stability. Watch a glider on a hi-start or winch launch and you'll be surprised how much rudder they may require initially just after release. Watch an electric ducted fan being catapulted and there are no lateral stability issues.

Hogflyer

This is why I don't think it's practical unless you have a decent headwind. On a calm day, gliders launched at 45 deg's will still level out a bit till the wings take lift. I would think you'd still need to be back at least 50 feet so the shorter length would not pull the plane toward the stake.
I started flying RC with high start gliders about 1970. We flew on the front lawn of JoCo. Comm.College at the corner of 95th and Quivira until they expanded parking lots with those tall light poles. A couple of times, I got a spinning worm burner launch that shredded parts along the grass.

You can make a completely adequate bungee for your needs quite easily.

You need to get the airplane up to speed. No problem. You don't need a lot of altitude. No problem and that dovetails with not wanting a great long bungee. It's simple.

The glider bungees are the design you'll copy. Just use 1/4 each length. You'll need a hook as described above on the airplane.

The list of parts in the order they're assembled/used.
-A BIG NAIL. They're sold in Lowes Home Improvement or Home Depot. They're a couple of dollars. Get one of the bigger ones. This will be stuck into the ground deeply enough to safely anchor the contraption.
-A keyring. It'll just fit over the sharp end of the nail but won't pass over the head. One end of the rubber is tied to this.
-The length of rubber
-A length of cord it tied to the end of the rubber
-Another keyring. This one can be smaller. The loose end of the cord is tied to this. This slips over the towhook in the airplane.
-A length of ribbon tied to the keyring. This helps you find the end of the cord after your airplane flies off the towline and the line falls to the ground.

You'll use this just like glider guys use their bungees. A couple of points. It's going to be only as long as you feel is adequate to get your airplane up to flying speed. It'll actually need to be a bit longer than the shortest length that'd work simply because really short bungees are somewhat difficult to use. The length of the rubber determines how suddenly the energy is used up. You'll need a bit of time to get the airplane sorted on the launch and too short a rubber won't give that to you.

Your airplane will handle just like gliders do on a bungee. That is, if you place the towhook the same way gliders have theirs. When the bungee is pulled back with adequate force, the glider almost instantly assumes a safe climb angle as soon as you release it. The same should happen with your airplane.

Do not attempt to launch with your engine running. Matter of fact, be very careful to work out a safe way to insure it not turning on at any time until the airplane is heading up and very far from the launcher. This situation is the one that makes the entire plan a bit questionable.

Launching off a bungee takes some degree of strength and coordination. Throw a powerful electric motor/prop into this and you see the problem. I hope you see the problem. If you don't see a problem, forget about the bungee. If you do, work out a safe plan.

Is there anything that can be substituted for the surgical cord? It seems a little expensive and I would rather buy locally rather than ordering (I'm impatient)

What about the parachute?

Glider guys like to use a winch or bungee launcher rapid fire. Even when they're not queing up to launch and when they're launching at a leisurely pace, they still like to be able to easily find where the cord came down.

They setup the launching to work with the generally prevailing wind. Whatever the wind is doing when they setup is what guides them as to where to drive the anchor. The anchor will be as far upwind as needed. When they hookup the glider to the towring, they then walk directly downwind. Exactly downwind. Perfectly downwind. And they PULL that sucker to build good energy in the rubber. They then face exactly upwind and hold the glider high and pointed somewhat pointed up. They then shove a bit upward to make sure the tail doesn't hit them in the back of the head. (it doesn't often happen but....) If the towhook is placed right, the glider almost instantly points "almost straight up" and heads for the clouds like a rocket..... if the rubber was pulled tightly enough etc etc

The glider arcs up and forward and when nearly over the pin, the pilot dips the plane and the towhook slips the towring.......... AND NOW THE PARACHUTE DOES IT'S THING.

If you don't have a parachute in the system, the length of ribbon does something. Precious little, but something. If you watch it, it'll show you where to go get the working end of the bungee for the next launch. If you don't, it'll be out there somewhere. And will be easier to find than that towring.

But what about the parachute?????????

It will be tied into the system between the end of the cord and the towring. Matter of fact, chutes usually have a towring sewn into their very top. The end of the cord is tied to the "bottom" of the chute, to the end of all the shroud lines. The lines come together at the bottom and usually are tied to a very small ring. The towline ties to that.

When the glider's towhook is hooked into the ring in the top of the chute and you start walking to stretch the bungee, the tension on the line pulls the chute closed. As long as there is tension on the towline, the chute will stay closed. During the launch, there is TENSION. As soon as the airplane pops, the tension is gone. And the chute is probably still moving with some speed. It'll POP open.

The wind will then carry the chute straight downwind. It'll usually pull the cord out and keep it straight and with some length. It'll wind up indicating to the next glider flyer EXACTLY where he should line up his launch since he'll want to launch directly into the wind. When he picks up the chute, he can look back at the pin and know that he's looking straight upwind.

It's magic.

The starter motor out of a '75Ford with a BIG 12V battery.

Actually, I don't know of anything other than surgical tubing that works at all as a similar replacement. Other than a winch.

Not a good idea.

What happens with a glider or any airplane that is going to be launched this way is going to be the same for every one of the airplanes. The airplane/glider simply "feels like gravity just got stronger and is coming from wherever the pin is stuck into the ground".

The pull of the bungee is nothing more to the airplane than MORE gravity. And where do we want every one of our airplanes to deal with gravity? From the Center of Gravity of the airplane. The CG we so carefully adjust so the airplane flies decently is where we want the bungee to pull. Otherwise the airplane don't fly so good. Matter of fact, it might not fly at all. If the tow is from a point too far forward, the airplane winds up not having the power to steer itself.

Check out this thread on a bungee launcher for an electric DF.

http://www.rcuniverse.com/forum/m_4896404/tm.htm

Hogflyer