Big thanks to
www.FrSky-RC.com for providing the Receiver unit for this project :)
Last year when I converted my first RedWing to RC I had seen on Youtube a man bungee launching a Multiplex Fox conversation. I was interested by the idea you could bungee launch something this size in EPO not wood and not have it rip to pieces, yet it worked and he flew a good 5+ minutes.
Since that time I've been keeping an eye on HobbyKing for 6MM bungee line (10 meters) to come back in stock. Now it is I already ordered 2 lengths. Now the RedWing needs a bungee hook, but how to make it so it doesn't rip the nose of the model? Well there is no guides, there is no real guides for making regular hooks either, just diagrams of the hook itself or people adding it on to models already pre-designed to fit a hook.
So I was working on past gliding experience and figured for EPO the best way is to spread the pulling force of the bungee line across the entire fuselage for maximum strength.
The hook itself can be various sizes and materials but I favour 2MM steel rod because its so strong. You can see I bent a 3CM hook where the line will go, followed by a 5CM straight and finally a 1CM 90 degree bend from the hook on the side. This will stop twisting and allow for a better fixture.
Best of all the whole steel hook is only 3 grams which is excellent. Notice the bend is smooth and not pointed, if the bend comes to a "wedge" point it could trap the bungee ring after tension of launching and result in it NOT releasing your plane!
To spread the stress load I'm using 4MM carbon fibre rod down the entire bottom of the fuselage. It will serve as a mounting point for the hook but also re-enforce the fuselage itself further besides the whole bungee reasoning.
I used carbon fibre "tow" and wrapped it around the hook to the carbon fibre rod, then used CA glue to fix it all in place. The bond is very very strong and can be trimmed down with a pair of scissors afterwards.
The "hook" point that is used should be IN FRONT of your COG (center of gravity) usually 2.5CM/1" is good enough, any further forward and when your plane gets height it will slip off early. Put it behind COG and when you launch it the model will instantly pitch up into a stall, releasing the model which is bad and even more so if it's still really low!
The side arm of the metal hook would just rip through EPO foam, so I'm adding a 2MM plastic board using UHU glue to take the direct pressure and spread it out over a larger surface area. Note the front of the hook has been slotted in at the top to stop it being able to move left right.
From the bottom side that'll actually be visible on the model all you see is the hook itself. Again pay attention there is no "snag" points for the bungee ring to get wedged in.
If your going to re-enforce your model no matter if it is for this or wing enforcements etc always properly create a gully exact size for your piece to fit snug. So you can see here I've cut out all the foam about 1MM smaller than required.
UHU por was used again applying to both surfaces, waiting 10 minutes then fixing in place, when you push the rod into place excess UHU may come out, just wipe it with your finger up and down the CF rod until smooth, don't waste it :)
The last stage is insulating the rod and plate. I fly over grass, mud and sand so I don't want lots of garbage getting in there. I use glass fibre tape over the entire span of the rod. This is also good to stop wear damage on landings in the future.
The whole modification took about 40 minutes to do including UHU por drying time. The result however is a VERY strong hook, I've seen hooks on 3 meter gliders not as strong as this lol.
The best bit is now the entire model weight including battery (AUW) is just 155 grams!
Part 2: Nincoair Redwing conversation - adding a bungee hook to fuselage
