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The rule book calls for a loop of 1/4″ rubber…..
Could I use a loop of 1/8″ instead if I wanted to?
It doesn’t say, “up to 1/4″ rubber”, or “1/4″ max”.I take it to mean 1/4″ only. Does it?
4.1. A hand-held catapult is composed of a
dowel not exceeding six (6) inches in length and a
two-strand loop of 1/4 inch flat model airplane
rubber (FAI, Pirelli, etc.) made from a piece that is
18 inches long to form a loop about nine (9) inches
long. One end of the rubber loop shall be
attached to one end of the dowel.
4.2. The hand-held catapult is to be provided….The 6″ dowel, 1/4″ rubber, 18″ long, and 9″ loops are the do not exceed dimensions. And of course the lengths of all items are the “unstretched lengths”.
Smaller gliders need lighter catapult launchers. I frequently find that a shorter loop works better with 1/4″ rubber.
We had the same problem in the UK with a restriction on loop width and length when the class was first started. Luckly the problem was spotted early and we now have a maximum rubber weight of 2grms; no other rubber restrictions. This enables a lot of flexibility which means you can match the rubber to the model better and is easy to process. It has made the class popular as a result. I’d lobby your national body for a change (noting that you can still use the current rubber dimensions if you wish) using the UK as an example.
Clearly, the AMA rule indicates a maximum length of the stick but really offers no variation in either the length or width of the rubber.
I can see where some variation is allowed in the loop length[“about nine(9) inches”] but it has to be made from 18″ of 1/4″ rubber.
It’s the 1/4″ that I find limiting. Not only does it prevent someone from using a single stand of 1/8″ but they can’t use two strands of 1/8″ either!In another area of the rule, I find it intriguing that only “flat model airplane rubber” can be used. What happens if I have used a different source of rubber in a Dawn, P-30 or other rubber event. Is it now “model airplane rubber” even though no one else may be using it? Say a bungee cord guts has properties that I want to explore, it can’t be rip it apart and used[just for instance].
Dennis
The rubber is 1/4″ flat rubber, typically .042 thick. But you can use anything less in width than that like 3/16, 1/8, 3/32 or whatever you like.
The rule is not to be followed because it is not written correctly. Ask Lee Hines and Stan Buddenbohm about their interpretation. But if you went to 3/8″ rubber, you would be clearly in violation, or a 18.5″ total length, or a 9 1/4″ loop. Or if you find heavy rubber bands with .05 or thicker, that would be a violation….. why? It is assumed that everyone will use normal rubber motor material with standard thickness (.038 to .042″)
The rule is also not clear about the type of rubber, thickness, weight, etc, and nobody even checks the rubber unless someone challenges you on it.
The rule was written to disallow 2 poles with 10 feet of rubber stretched between, and being able to bungee launch large models. Compared to that, it is more specific, but still not clear.
What kind of rubber is Tim Batiuk using? I am using 1/4″ FAI super sport of a current vintage. But for smaller gliders, like 12″, I go down to 1/8″.
If I’m not happy with the wording then I should get a rules proposal off in the next few days!
Dave, there are some CD’s[and pilots] that don’t agree with your interpretation. It is poorly worded. I wonder if my wording will come out any better! LOL!
Dennis
The rule says 1/4″ by 18″ of model plane rubber, tied into a loop and affixed to a 6″ stick.
This cleary disallows 1/8″ or any other width rubber.
The 6″ stick prevents someone from using a 24″ stick and thus stretching that bit of rubber even farther.
I found some 1/4″ rubber bands at th Office store that are twice as thick as Tan SS. They outweigh TanSS by twice or more. I am certain that they would be awesome as a catapult. I have been told that it is not legal, as the rule clearly states ‘Model Plane Rubber’.
You are allowed to wind the loop onto the stick so as to get a taut pull for the launch.I see no ambiguity in the rule as written.
I have spoken about the rule with one of the guys who started the movement/event. This catapult has the effect of limiting the size of the planes that can be flown and not by accident. I was in favor of allowing 2 loops 1/8″ equal to the 1/4″ . My reasoning that more guys have 1/8″ rubber than 1/4″. Now I am not in favor of changing anything. I splurged and purchased a 1/4lb box of 1/4″ TanSS. Now I have several years worth of catapults. Be still my heart.Fellow forum readers,
Dave Edmonson asked me to respond with my take on the CLG launcher rules interpretation.
In response to having CD inspection, yes, it is done. At the Nats and randomly at other comps.The hand held item called a “dowel’ clearly states it is not to exceed 6 inches.
Dowel may imply ‘wood’, but it does not say, nor does anyone I know care, what the material is.
Some CLG fliers have nice metal handles with screwtops which contain clay, tools and spare launcher rubber.As for the ‘1/4inch flat model airplane rubber[FAI, Pirelli, etc]…18in long…’that is pretty clear what is intended.
That said, I would welcome and support a rules change to allow some
more readily available sizes, which EQUAL the same cross sectional area as 1/4.
I even think a weight rule change to 3 grams of rubber MAXIMUM is quite reasonable.
I have weighed my 18 inch loops of 1/4 FAI and get between 2.8 & 3.2 grams with lube.So Dennis, or anyone of you out there, start a rules proposal along those lines & I will support it.
I hope this helps and gives perspective.
Ciao,
Lee
I have to agree that the way the rules are written, it does seem to say a 1/4″ wide strip of rubber no longer than 18″. Is a 16″ loop OK”? What is the tolerance on the strip length of rubber? Is it allowed to stretch as it is used? Is 18 1/2″ about 18″?
However, I can’t believe that a smaller size would be excluded. For example the juniors in the 8-12 age category are more comfortable with a smaller glider, and pulling some lighter rubber.
The other problem is there is no definition of 1/4″ rubber. Is .280″ Ok? Is .252 OK, or is .251 OK? What is the tolerance of this 1/4″ rubber? Or if it is truly supposed to be .250, can it go as low as .180?
Weight would equal things out with a maximum weight. Or perhaps the contest director cuts 20 strips of rubber 18″ long, and you must use that for the contest? This surely would cure the search for magic rubber for catapult launchers.
Anyhow I think the rule is unclear, and should be clarified to eliminate confusion. Normally maximums are called out, and you just need to be under the maximum for things that become better with increases, and minimums for things that become better with decreasing values.
Guys,
To help you draft a new rule, here is the current BMFA rule for the UK :-
“The glider must be launched by a catapult, powered only by rubber.
The maximum weight of the rubber allowed is 2grms and can be made up into any number of strands of any length.
The rubber may be attached to a handle. The maximum handle length shall be 6″.”
This was done by Phil Ball as he realised that his arm length gave him a considerable advantage in stretching a single loop of rubber as the rule was originally written (it was very similar to the US rule at that time). This revised rules will give you the flexibility you require. For example I’ve used 6 strands of 1/8″ rubber me but Phil still beats me of course.
After extensive testing I’ve now found that carefully stripping rubber from a ’65 Chevy tyre gives me the best material for catapult models ………..
Thanks ALL for listening as well as voicing thoughts!
I’m off for a day of flying in the record highs expected today.
Tonight I’ll post what I think is a simple clarification to the rule.
And remember, if there’s any part of the rule you feel strongly about, that has affected fliers, please propose your own version!I don’t think anyone wants to change the intent of the rules. I would not want to see multiple loops allowed.
The maximum length of stick: Less than 6″.
The maximum dimension of rubber: .255 width x .045 thick x 18.0 long laying flat.
Must consist of one loop attached to the stick.
According to Tim Batiuk:
“The rule is vague but common sense dictates that using less power in the
launching device is not an advantage, so who cares…”
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