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Old Aug 26, 2012, 09:53 AM
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Using mega bungees for a small team Select

I am considering a specific spec of rubber for a team select and regular event in Canada. We have typically had challenges getting enough towers, consistent towing and finding enough gear etc. Our turnout is typically less than 8 pilots for a TS. Getting enough help can actually be a make or break it deal so we need a way to reduce the labor. We tried setting up a two day event to draw a bunch of pilots who might help for 7 rounds of a TS but no one was interested.

I am going to spec a pair of bungees capable of doing a 5 second tow if required or alternatively allowing the pilot to launch short for strategy so we can use a working time for the event. We can test the viability of the launch system by doing a ladder match and if the rubber passes then we can order 6 more and do a mass launch event in Mission at the sod farm we typically do our TS events at. This would also be an amazing venue for a WC or open contest.

The manpower requirements drop to just 8 throwers maybe less if you throw your own plane vs. 16+ towers but also the challenges for an official multiple launch solution also go up. The thrower would have to run and retrieve the bungee in an event of a pop off or relight. That's not the end of the world to me.

We considered the concept of matched winches as well but we don't have the matched gear and trying to maintain a fair launch system when pilots bring winches is too time consuming. I know it's been done but I also know the overall feedback has been that it's still not quite fair across the field. Also, asking pilots to bring a winch across Canada is an expense few of our pilots would accept.

We have great pilots east of BC and I would like to see them come out and fly at a TS

Let's hear your thoughts -
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Old Aug 26, 2012, 01:51 PM
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David

I think your onto something. Why wouldnt something like this work if everyone is getting the same launch. I personally like the idea. I think it would actually level the aying field for a team select process. But im a newbie when it comes to f3j.

Joe
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Old Aug 26, 2012, 02:04 PM
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Originally Posted by J. Wydronek View Post
David

I think your onto something. Why wouldnt something like this work if everyone is getting the same launch. I personally like the idea. I think it would actually level the aying field for a team select process. But im a newbie when it comes to f3j.

Joe
Everything is a compromise - notables bring up the point that lite planes with super low wing loads will have an advtange - but thats true on a J launch too...

However, if you bring a really heavy model and the buncgee is not strong enough...you will get crushed so the bungees have to be pretty robust in order to accomodate larger models. Maybe something that requires 60-70 pounds to retain it at the defined stretch point, can deliver that level of power over at least 4 seconds...
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Old Aug 26, 2012, 03:29 PM
launch low, fly high
New Zealand, Hawke's Bay, Havelock North
Joined Dec 2004
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This is an interesting concept. It would definitely be a fun event to fly.

The issues are:
1) Puts a high premium on the throwers ability to pull back the bungee.
2) In no wind or downwind/crosswind, the optimal launch is very different than launching with a powered system.
3) In moderate to strong winds, the energy stored in the bungee may be much more than the typical F3J towline.

This could be a fun event. There will be a bit of a learning curve for some due to the above differences.
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Old Aug 26, 2012, 04:06 PM
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Originally Posted by Joe W View Post
This is an interesting concept. It would definitely be a fun event to fly.

The issues are:
1) Puts a high premium on the throwers ability to pull back the bungee.
2) In no wind or downwind/crosswind, the optimal launch is very different than launching with a powered system.
3) In moderate to strong winds, the energy stored in the bungee may be much more than the typical F3J towline.

This could be a fun event. There will be a bit of a learning curve for some due to the above differences.
1) Agreed - the power of the bungee almost requires dedicated throwers comfortable with fairly high tension. Thats not too tough to find and most timers used to the J tasks would be acceptable.

2) Yea wind changes are a challenge. In the given area I am thinking in Mission BC we basically get a consistent wind change at 2 pm so the field could invariably be mapped out with two wind changes in mind.

3) Yes, you could kite to a considerable launch if you wanted to gamble with the conditions - A working time is of considerable importance here.

The challenges which have been raised are that the event itself strays from J too much but I think its an acceptable evil given the experiences with trying to match the F3J event to the T - when the best laid plans fall short on a 2 man tow concept you dont have the best outcomes either. We tend to get some good towers and also some great intensions and what results is one lane constantly out launching the rest. Rotations dont really resolve that issue if you are the last guy in line to get the "good team"...

anyways when I get back home ill be talking to Areofoam to see what we can rig -
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Old Aug 26, 2012, 04:23 PM
launch low, fly high
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Joined Dec 2004
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The issue with #3 is actually airframe related. When there is wind, the energy that gets stored in the stretched bungee during a launch will be far greater than what is stored in a handtow monofilament line. My little bungee with only 3.5m of rubber has shredded a couple of planes due to the energy returned in the zoom... In order to get a reasonable 5 second tow in light to zero wind, you will need maybe 10m of rubber if not more. I'd be very wary of launching from my bungee in any wind if it had 10m of rubber.

One other issue with bungees in a true F3J format is the potential for entertainment in untangling the lines for a relaunch situation. For a single launch format, "death-match zipstart" style, the bungee works very well.
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Old Aug 26, 2012, 05:39 PM
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Dave- My5/8" zip start launched my Supra to the moon, hard as hell to pull back and hold with one hard but maybe dedicated thrower could pull harder and farther. 1/2" are better for death matches but I'd guess the 5/8" would better represent f3j. What about using mono too?

Being zips are so cheap you could set up two right next to each other use one and the second could be pre stretched a little and hooked up to a stake ready for pop offs or relights.

I think your going the right direction to solve the issue. Bottom line is everyone is launching the same way.
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Old Aug 26, 2012, 07:53 PM
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Originally Posted by Joe W View Post
The issue with #3 is actually airframe related. When there is wind, the energy that gets stored in the stretched bungee during a launch will be far greater than what is stored in a handtow monofilament line. My little bungee with only 3.5m of rubber has shredded a couple of planes due to the energy returned in the zoom... In order to get a reasonable 5 second tow in light to zero wind, you will need maybe 10m of rubber if not more. I'd be very wary of launching from my bungee in any wind if it had 10m of rubber.

One other issue with bungees in a true F3J format is the potential for entertainment in untangling the lines for a relaunch situation. For a single launch format, "death-match zipstart" style, the bungee works very well.
Joe

What would be a set of hose and line length, and size, that would represent the best compromise between energy and general conditions, for an event.


robert
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Old Aug 29, 2012, 12:01 PM
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Quote:
Originally Posted by Joe W View Post
The issue with #3 is actually airframe related. When there is wind, the energy that gets stored in the stretched bungee during a launch will be far greater than what is stored in a handtow monofilament line. My little bungee with only 3.5m of rubber has shredded a couple of planes due to the energy returned in the zoom... In order to get a reasonable 5 second tow in light to zero wind, you will need maybe 10m of rubber if not more. I'd be very wary of launching from my bungee in any wind if it had 10m of rubber.

One other issue with bungees in a true F3J format is the potential for entertainment in untangling the lines for a relaunch situation. For a single launch format, "death-match zipstart" style, the bungee works very well.
Hey Joe, I think Keith has the same spec rubber you own from Aerofoam. IT was an excellent solution to practice short J like tows but I did not think it would offer the power distribution opotion of 4-6 seconds. It seemed that all the energy was out in under 2 which would be a difficult curve to master for some. I think a slightly smaller spec - 10 or more meters and some mono would give effective launches over 4-6 seconds but ill need to contact Marc at Aerofoam and start the experiement.

Im more prone to do this than not at this point - I would love to do a major contest up here but im not sure we would get enough people.
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Old Aug 29, 2012, 01:28 PM
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Just for the record, I love the idea. Go David!

Mike
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Old Aug 29, 2012, 03:26 PM
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thanks for the support.
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Old Aug 29, 2012, 06:31 PM
launch low, fly high
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Originally Posted by Robert Burson View Post
Joe

What would be a set of hose and line length, and size, that would represent the best compromise between energy and general conditions, for an event.


robert
Robert,

Not sure that I can provide a good answer on this one. So much of the answer is strongly dependent on the capability of the thrower. If the thrower can pull back to 90 lb reliably, the answer is a bit different than if the thrower can pull back to 60 lb reliably.

For most people, my bungee could be a potential disaster with a hair trigger at 90 lb of tension. There are so many ways that things can go wrong, and there is a LOT of energy stored in the bungee.


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Originally Posted by webbsolution View Post
Hey Joe, I think Keith has the same spec rubber you own from Aerofoam. IT was an excellent solution to practice short J like tows but I did not think it would offer the power distribution opotion of 4-6 seconds. It seemed that all the energy was out in under 2 which would be a difficult curve to master for some. I think a slightly smaller spec - 10 or more meters and some mono would give effective launches over 4-6 seconds but ill need to contact Marc at Aerofoam and start the experiement.

Im more prone to do this than not at this point - I would love to do a major contest up here but im not sure we would get enough people.
Interesting. I wonder what launch pre-tension you guys were using on Keiths bungee? For zero wind, the zoom needs to occur reasonably quickly for the best launch height. I have about 65 m of line on mine, and get about 130-140 m of height in zero wind when I pull back to about 90 lb of line tension prior to the throw. With a little bit of wind I get up to around 200 m of height. The launch height drops off quickly if one does not start with high tension.

It may be appropriate to use a smaller diameter bungee with more length to reduce the launcher requirement.


I do like the concept, and would enjoy flying with this format.
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Old Aug 29, 2012, 07:17 PM
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Originally Posted by Joe W View Post
Robert,

Not sure that I can provide a good answer on this one. So much of the answer is strongly dependent on the capability of the thrower. If the thrower can pull back to 90 lb reliably, the answer is a bit different than if the thrower can pull back to 60 lb reliably.

For most people, my bungee could be a potential disaster with a hair trigger at 90 lb of tension. There are so many ways that things can go wrong, and there is a LOT of energy stored in the bungee.




Interesting. I wonder what launch pre-tension you guys were using on Keiths bungee? For zero wind, the zoom needs to occur reasonably quickly for the best launch height. I have about 65 m of line on mine, and get about 130-140 m of height in zero wind when I pull back to about 90 lb of line tension prior to the throw. With a little bit of wind I get up to around 200 m of height. The launch height drops off quickly if one does not start with high tension.

It may be appropriate to use a smaller diameter bungee with more length to reduce the launcher requirement.


I do like the concept, and would enjoy flying with this format.
I seeriously doubt we are anywhere near 90 lbs. Likely closer to 70 max but I never really tried to pull seriously hard. I just wanted enough tension to get off the line quickly.

I totally agree, requiring a thrower to hold 90 is just asking for a problem but if the system was matched well and only 60 lbs required by a dedicated thrower with two hands - thats a lot easier.

I sent an email to Marc and Aerofoam - ill start some experiements and keep the reports up.
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Old Aug 29, 2012, 08:06 PM
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I think this is a great idea, David! Getting away from towers and/or winches greatly decreases the demands on manpower/field size/cost/etc. Shooting for a bungee launch system that's reasonable (60-70 lb pull) would provide a reasonable launch ... and as long as everyone is using equal spec bungees, you're golden.

It might be difficult to duplicate true F3J launches, but that shouldn't be the goal ... getting more people involved in F3J-type flying would be great ... man on man flying with a simple, inexpensive launch system would be priceless!
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Old Aug 30, 2012, 01:23 PM
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I think this is a great idea, David! Getting away from towers and/or winches greatly decreases the demands on manpower/field size/cost/etc. Shooting for a bungee launch system that's reasonable (60-70 lb pull) would provide a reasonable launch ... and as long as everyone is using equal spec bungees, you're golden.

It might be difficult to duplicate true F3J launches, but that shouldn't be the goal ... getting more people involved in F3J-type flying would be great ... man on man flying with a simple, inexpensive launch system would be priceless!
The attractive feature here is that we could very easily gain a 200 meter launch - thats not an issue. As Joe stated these bungees can store amazing power with even just a little wind. I used 100 feet (30 meters) of 4 meter rubber and 150 meters of mono from Marc Mech at Aerofoam composites. With a lite a head wind I got easily close to 400 meters one day...but that was over about 20 seconds...not suitable for a J style event.

We will not be able to do a 200 meter launch in 2 seconds but that does not really matter as long as the launch mechanism is the same across the field and effectively meets the needs of the advanced short tow pilots and the conservative 4-5 seconds of tow rquired for that angle of flying.


Having enough power to launch to full height or come off and go for the lift in 1-2 seconds preserves the strategic option of J that is so exciting.

Making it even across the field without a tow team means as a pilot you can practice the skills required and not worry that your tower might sprain an ankle or the more afluent teams with critical masses of support show up with linebackers and pro pitchers to out throw and launch you...

I want a system that allows for a MOM contest where differentiators between pilots are made at the sticks whenever feasible. I want less complexity and cost for regions that just simply cant absorb a matched winch approach and can't count on volunteers for towing.

I talked with Marc a few minutes ago and he is willing to let me experiement with some other spec rubber in an effort to gain an understanding of what I need. He lives within driving distance of me and given his product range is perfect for the intended purpose I expectto have a solution shortly.
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