The Start of The SAB KR84 Design and Build.

buzzbomb

I know nothing!
Question to the experts on bungee launching.
I want to also incorporate a mounting plate in the inner structure to mount a hook for bungee launching, where do you put that hook? On the cg, forward or back of it?
Just remembering toy gliders, the rubber band always hooked under the nose.
 

Wildthing

Legendary member
Starting in the center and going to work my way out . Most of the inner structure is done other then on a front section I still need to add a plate to where I can bolt on a bungee hook.
CF rods run through the sections. I initially was going to run one solid piece of cf rod and have the wing mount from the top but changed my mind just because it will be heavy and high wing load so lets mount the wing from the bottom.

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Piotrsko

Master member
The closer to the cg you go aft, the more efficient the process is to produce altitude. Downside: the closer to the cg the hook is, the easier to break wings by minor attitude changes like that extra click of up trim or finger twitch of up. Using a winch, when you see the wings assume that bowed diehederal look, you slow down the winch or even stop for a second or so, toss in some down elevator trim. A bungee is all or nothing, you cant slow it, the BEST you can hope for is a full down elevator release of the hook as the plane speeds up. Many times it would get tangled up and require the landing with it attached which is a huge pain somewhere unpleasant.

See the comments made by @Hai-Lee to mayan about bungee launching test flights. I personally prefer to start about 2" forward of the TESTED cg and move back in 1/4" steps to no closer than 1/2 inch

This is also why most people carrying gliders use a nose hook for aero tow, and a cg hook for winch.
 
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Wildthing

Legendary member
The closer to the cg you go aft, the more efficient the process is to produce altitude. Downside: the closer to the cg the hook is, the easier to break wings by minor attitude changes like that extra click of up trim or finger twitch of up. Using a winch, when you see the wings assume that bowed diehederal look, you slow down the winch or even stop for a second or so, toss in some down elevator trim. A bungee is all or nothing, you cant slow it, the BEST you can hope for is a full down elevator release of the hook as the plane speeds up. Many times it would get tangled up and require the landing with it attached which is a huge pain somewhere unpleasant.

See the comments made by @Hai-Lee to mayan about bungee launching test flights. I personally prefer to start about 2" forward of the TESTED cg and move back in 1/4" steps to no closer than 1/2 inch

This is also why most people carrying gliders use a nose hook for aero tow, and a cg hook for winch.

Thank You
 

Wildthing

Legendary member
1st little piece printed, motor mount. :) CF rod will extend through the back section a few mm to align and go into the mount to lock it in place, 2 recessed nuts will be in that back section and motor will bolt in from the back side. That's the plan anyways :D

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mrjdstewart

Legendary member
all my bungee launchers are forward of the CG. i usually try and set it about half way between CG and the nose of the aircraft. if your bungee launcher has enough incline launching should not be an issue. this sunday i took nothing but bungee launched planes to fly and had a blast. been a long time since i flew nothing but speed all day.

laters,

me :cool:
 

Wildthing

Legendary member
Section 4 finally done after one mishap, 40% through the first print when the extruder passed over it knocked the print over.
Bottom side (blurry picture ) that is where the bungee hook plate is going to be mounted.

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Wildthing

Legendary member
Well plans are ready to take down to Staples and have printed out.
Printed a nozzle and nose cone, now to finish the canopy so it can be printed.
Did up some little plans for location measurements for some of the formers

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