Bungee starts with Sailplanes

[wish]

Hi,

I'm not sure if it's the right place, because it's not a F3x thing... but have you guys ever meassured bungee launches? We are trying to figure out how high we can get... ;)
The bungee height is determined by flying as high as possible and then fall down a bit to make sure no thermal effects where in the start phase... like in the following diagram.

http://www.rcgroups.com/forums/showatt.php?attachmentid=1447914&stc=1

Recorded height was 510.5ft in this case, but I've already gone over 540ft.

I'm flying an unballasted Opus-V @ 1.6kg (=56.4oz).

Nowadays height dataloggers are small and not very expensive anymore, so here in Germany we are making a small competition out of it.
I would like to know if you have some values in the US to compare...

Regards,

Bob

[guillaume83]

Hi Bob,

your numbers are very impressive !!

I use 14.7m of "Bungee" Mega Rubber from EMC Vega (the 12.8mm one given for up to 5Kg gliders) with about 15m of straight line to launch my F3B models and the height achieved is nothing like yours !! Maybe 70m or so....I have a Zlog altimeter which I haven't tried out but I will to get accurate values.

I have been wondering if I shouldn't cut the 14.7m of bungee in half to double the strength with a bit more line (30m?) in order to get higher.

Guillaume

[SaltyOne]

Bungee launches used to be legal for F3b. I'm not sure if they are still legal? I watched the US team selection trials in the 1970's in upstate NY (won by Dwight Holly) and competitors were getting launches over 350 meters with bungees. This was measured with surveying equipment. Small electronic altimeters weren't available in those days. The key was a servo activated releasable tow hook. The competitors would fly up wind and then turn around and fly down wind. Repeating the pattern until the bungee was stretched to its limit. It was quite impressive. The planes were literally a speck in the sky before they released from the bungee.

George

[wish]

Hi,

@Guillaume; on http://irq.dyndns.org/flitschenwettbewerb/ you can see our new contest list for different configurations in rubber (i.e. 1S1P or 1S2P or etc etc) also solo or with help of a starter what kind of plane... and many other information so we can compare simular starts with the bungee. Tomorrow will be a good day (1st weekend after starting the list with good weather as well in Germany) where many of the guys who have been informed about the competition will submit there data.
Please feel free to ad your starts with information (14,7m will be 2S1P for example) to the list as well... maybe for the time being with country initials behind your name) if you can undestand the German language. If not please ask me... I'll translate it.
@george; this start you mention is not the bungee start I mean, at least I think. I think you are talking about highstarts with rubber. But that's al lot longer rubber with a even longer line. We don't use the normal high start hook, but build in another hook just in front of the nose of the plane. This way you shoot the plane in horizontal first (with speeds meassured by radar over 250km/h) an pull pretty hard after it flies over the point where the rubber is back to it's normal length. Now the plane flies at high speed up into the sky. If you need more info please let me know...

I think this weekend we will probably see some movie material and heights over 200m (656ft)... because there are some crazy ones among them ;)

The competition is at the moment pretty easy going, you can do it alone, don't even need evidence or a person with you as witness. That will come though, just a matter of time I think.

Regards,

Bob

[SaltyOne]

Bob,

I guess we are talking about different methodologies. The bungees at the F3b trials were very small in diameter (maybe 50 mm or less ?). They were the minimum diameter required to lift the sailplane. That is why they stretched so much. What you're talking about sounds very interesting. Things must happen in a hurry with your method and would require a very strong sailplane, and a very strong pilot.

George

[Bernd Brunner]

George,

bungee-launching described by Bob means horizontal accelleration to more than 100mph in 1sec, release and then the vertical climb to more than 300ft. It´s a incredible fast launch...

Bernd

[Wing-span]

Sounds like we need a video clip to demonstrate ;)

[Florrain]

Here are 3 small clips demonstrating bungee launches with one single 7m strand of the same EMC-Vega rubber:

clip1 (http://www.youtube.com/watch?v=f8CoI9IW1ds)
clip2 (http://www.youtube.com/watch?v=D7lMTsbXNr8)
clip3 (http://www.youtube.com/watch?v=d20ZWGF6_K0)

2 strands of that same rubber like Bob uses with his Opus must give very impressive acceleration indeed :eek:

[Biest]

Hallo Together,

last Weekend new Rekords where made ;)

http://irq.dyndns.org/flitschenwettbewerb/

A Video ist available on Youtube : http://www.youtube.com/watch?v=uNZ5KuRzLAk

Next Week we try to beat the 200m :D

Tobias Reik

[Wing-span]

This is a also a method used to launch from the top of a slope when the wind is low. But not necessarily so powerfully.

[Biest]

Show is going on.

yesterday we bet the 300m Mark :D

http://www.rc-network.de/forum/showthread.php?p=973112#post973112
Video of the Day´s Work: http://media.rc-network.de/showphoto.php/photo/3090

Komplete Resultlist at http://irq.dyndns.org/flitschenwettbewerb/

Regards,
Tobias