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Old Aug 27, 2006, 12:06 AM
From Earth to the Moon!
albireo's Avatar
Sacramento, Ca.
Joined Jul 2003
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Can't I buy a catapult/launcher???

After destroying my pusher jet with hand launches I thought I'd just buy a catapult or bungee launcher. I've searched all over the R/C Groups here and don't see even one to buy... All I see are ones you build. I'd so rather buy one and put it together...
Is there anything out there I can just buy??

Thanks!
Joe
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Old Aug 27, 2006, 01:23 AM
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thomanie's Avatar
Trondheim, Norway
Joined Jun 2003
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Markos at Warbirds-rc.com sells a bungee "system" (cord + pedal). Around $100 total.

Terry at TDM Models has what seesm to be some nice catapult plans - no kit available though...

Sadly enough, I guess the reason why there ain't many selling catapult launchers (almost) ready to go are legal issues with things that can hurl other things through the air at high speed...

Thomas
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Old Aug 27, 2006, 01:49 AM
From Earth to the Moon!
albireo's Avatar
Sacramento, Ca.
Joined Jul 2003
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How about the "Vasa Launch Rails " from Hobby Lobby??
http://www.hobby-lobby.com/launcher.htm

Would this be a good choice?
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Old Aug 27, 2006, 02:03 AM
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Trondheim, Norway
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You still need the bungee cord with the VASA setup - but yes it will definately work as well. It looks a little flimsy in the pics, but I haven't seen it first hand so I may be very wrong.

The ramps only mission is to launch the plane at an angle, so it doesn't need a lot of beefiness really.

Thomas
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Old Aug 27, 2006, 02:11 AM
From Earth to the Moon!
albireo's Avatar
Sacramento, Ca.
Joined Jul 2003
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The problem is that I can't just look at something to make it. I'm a knucklehead that needs STEP BY STEP directions... I could build something I had those, as long as I could get the parts at my local Lowes. I'm horrible at making things out of wood...

Thanks for replying!
Joe
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Old Aug 27, 2006, 06:05 AM
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Darling Downs Qld Australia
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Make it out of PVC, very easy, just need hacksaw and joiners. And it just all pushes together and can just pull it apart to fit in the car



Nic
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Old Aug 27, 2006, 06:05 AM
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keven64's Avatar
United Kingdom, England, Burnley
Joined Apr 2001
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old ideas

Joe,

My local model shop sells rubber for rubber powered models - like in the good ol' days...

Years ago, I got a box containing a LONG length of '1/4" flat'; folded it into two, tied a knot at each end, and tied string around the rubber on each side of each knot... this was the kind of string sold at the post office for wrapping parcels in brown paper.

I then tied one end of the rubber to the blunt end of a stick ( a sharpened 3/8" birch dowel ), and tied the other end to a short length of string with a wire ring on other end of that...

It takes far longer to type than to do it...!

The same shop sells plastic tow hooks - which are fixed to your model with a small woodscrew at each corner... and so require no major surgery - provided your model has enough material in the right place.
My models are all own-designs and mainly balsa-built, so they invariably have...

At the field, the stick was pushed into the ground, and the wire ring was hooked around the plastic hook.
I had only to walk backwards a little way whilst holding the model TIGHTLY over the fuselage at the wing position ( slightly behind the CofG ), and let go...

This 'system' was used for around 4 years - and 'catapulted' many different models - including one with an OS.10 engine, and small gliders weighing around 2lbs.

As my back problems now preclude the handlaunching of model planes, I think I shall make myself another catapult.
( I wonder if my back is up to putting enough strain on the rubber for a successful launch ? )

Keven.
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Old Aug 27, 2006, 08:18 AM
Now in TN!
J Morgan's Avatar
Chapel Hill, TN USA
Joined Apr 2001
24,080 Posts
Try this one. I built one of these, easy and local parts other than the bungee. Have used it for a couple of years and it works great.

http://www.rcgroups.com/forums/showt...Pedal+Launcher

Bungee from www.aerofoam.com

J
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Old Aug 27, 2006, 02:42 PM
From Earth to the Moon!
albireo's Avatar
Sacramento, Ca.
Joined Jul 2003
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Ok guys, I'm off to build a launcher!
My F-86 dream lives! After I destroyed my pusher yesterday and lost all my confidence (after hundreds of perfect hand launches), my F-86 was not going up!
Joe
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Old Aug 28, 2006, 12:40 AM
From Earth to the Moon!
albireo's Avatar
Sacramento, Ca.
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Ok, now it's built!
I just need tips on using it.
Do I launch and then start the motor after it's airborne? If I can start further up the ramp and/or not start the motor I don't have to worry about prop damage... Do I really need all 4 feet of my rails to get it up? I'm trying a 25oz F-15 pusher for my first tries...
Tips appreciated!!!
Joe
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Old Aug 28, 2006, 02:19 AM
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Trondheim, Norway
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If you're bungee'ing a prop model you MUST wait with the throttle until you see that the cord is WELL clear of the model!

I can tell you from first hand experience that the prop will catch the cord and wind it thoroughly around the propshaft if you hit it too early. This makes a nice "arrestor hook" - about 10 ft in the air... I guess you can see what happens next *ouch*

I use about 5 times the model weight for bungee pull, and use a fish scale to get the pull right. That should get you in the right ball park.

You must use so much rail so that the airplane has speed enough to fly when it leaves the ramp. This would be dependant on model aerodynamics, weight and bungee pull (experience helps determine). My 25 oz EDF Hawk starts about 1/2 up my 2ft ramp and gets going nicely at 5x pull.

Also note that bungee hook position on the model plays a key part in how the model leaves the ramp. Forward hook position will give more speed and less altitide, rearward hook position will give less speed but more height. Gliders normally have the hook close to the CG to get as much height as possible with enough speed to fly. We want less height (10 ft will be perfect) with a lot more speed, so we move the hook somewhat forward. Trial and error will tell you the best position for the hook - or have a look at where others placed theirs on a similar model.

Thomas
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Old Aug 28, 2006, 02:56 AM
From Earth to the Moon!
albireo's Avatar
Sacramento, Ca.
Joined Jul 2003
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Great help Thomas. I was going to spend the morning tomorrow making my launcher HIGHER to leave room for the prop to clear. I was wondering why all the launchers I saw were so low in the rear... I thought maybe only the EDF guys used them this way!
I guess I'll leave it as is and give it a hurl! Maybe I should pick something up at my LHS to throw for my first try? Perhaps a cheap glider or something...
Any thoughts on my F-15? The wings and elevators aren't the same level. The elevators are lower than the wings by at least an inch. Should I make the rails wide so it sits on the wings (they sit on the rails 2/3 of the way to the tip this way) so the elevators sit inside the rails or set the rails skinny so the jet rides on the elevators for launch (in this mode the nose is lower since the wings are higher, making for an initial nose lower than level launch).
Joe
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Old Aug 28, 2006, 04:47 AM
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A larger foam chuckie glider can be nice to gain some experience with if you feel you want to.

With the F-15, I'd space the rails so that only the wings rests on them. Add enough space between the rails so the elevators don't catch the front rail supports as it exits the ramp - makes for a short but spectacular flight...

I'd try not to let the model rest on the elevators, as they are normally more fragile than the wing. If you have a full flying stab your servo(s) will take a beating as well this way. The nose down attitude you describe is not good for launching.

You could also rest the model on a U shaped foam block on top of closer positioned rails to get the angle right and make the elevators clear the ramp. Launch the foamblock with the model and it will drop away from the model as it exits the ramp.

PS: Take great care when working with a bungee launcher - make sure it is properly secured and aimed correctly.

Thomas
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Old Aug 28, 2006, 05:09 AM
From Earth to the Moon!
albireo's Avatar
Sacramento, Ca.
Joined Jul 2003
1,518 Posts
More great advice, I appreciate it so very much!
It is being secured by some steel spikes in three places, so that should do it. I will have an assiatant for my first few launches.
Since I'm not starting the motor until I'm well clear of the launcher and cord I can start my jet at the very back and get all the 4 feet to launch with... I like the block idea, I hadn't thought of that.
Great stuff, thanks.
Joe
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Old Aug 28, 2006, 06:24 AM
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PM sent in re to one I can sell you that is almost identical to J Morgans in Post #8 above.
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