General Discussion

[iYOA]

it doesnt necessarily have to hold 15kg in order to have the best ratio since they arnt putting a greater emphasis on weight held this year.
in fact, the winning tower at nats a few years ago was 4.1g and held 13.something kg. I think we will probably see a lower ratio this year because of the greater importance of being 70cm

[jma]

Thank you Mr. Joeris for your post. The information you gave is very helpful to us and all other kids as new builders. Best wishes to your team this year.

[Balsa Man]

Thank you Mr. Joeris for your post. The information you gave is very helpful to us and all other kids as new builders. Best wishes to your team this year.

Thanks, jma. Glad it was helpful. Your comments about this all being new (and mystifying) got me thinking about all the "so how does this all work?" questions I had when my older son came home one day 10+ years ago and told me he was on the bridge building event for Science-O. This board has been an important part of my learning over the years. So, I figured it was worth the time to lay out some of the important basics.
Look forward to hearing of your progress as the season goes on.

[Balsa Man]

What is considered a good score this year? This would probably just be an opinion

Well technically you want the lightest tower that holds 15 kg and is 70 cm tall.

it doesnt necessarily have to hold 15kg in order to have the best ratio since they arnt putting a greater emphasis on weight held this year.
in fact, the winning tower at nats a few years ago was 4.1g and held 13.something kg. I think we will probably see a lower ratio this year because of the greater importance of being 70cm

iOYA is absolutely right. Scoring this year is back to an absolute efficiency basis [weight carried divided by weight of structure (multiplied times a height factor)]. If you have a tower that carries full load, and another that weighs half as much, and carries just a bit over ½ load, the light one wins. Definitely something to think about, and maybe play with. That said, I have to say, particularly for a C-Div tower, the chimney for a 70cm tower – at 55 cm long - is mighty long and skinny. I didn’t fully appreciate just how long and skinny till we got our jig pieces cut out. Overall structural rigidity – stiffness – that it doesn’t twist or bend, is going to be really critical. Just a little bit of distortion in each braced section, added up over 55cm, will very quickly get to be enough to take the tower out. To go “really light” you’re looking at either really low density leg wood, or really small cross-section (like 1/16th square). Maintaining sufficient structural stiffness with either without loosing efficiency because of a lot more bracing will be a serious challenge. I look forward to seeing if anyone can pull it off.

As to scores this year, and I’d hardly call it an opinion- more an educated guess, preliminary calculations suggest that getting under 11 grams for a 70cm C-tower holding full load will be “good” (a winner in many if not most Regionals, medaling in many if not most State meets). 10 grams will be really good. With the dimensions in the rules this year, you can extrapolate from last year; base section dimensions are the same- just a significantly longer chimney. If you know what your base section and top section weighed last year, add weight of base plus 55/35 times what your top section weighed to get a 70cm weight estimate. For example, a 50cm tower from last year that weighed 8.4 grams with the additional 20cm of top section will come out around 11.2 grams at 70cm….. Such a tower, carrying 15kg, would score 87.05 at Regionals and 73.66 at State. We’ll see as folk get into actual building and testing.

[deezee]

What is considered a good score this year? This would probably just be an opinion

Well technically you want the lightest tower that holds 15 kg and is 70 cm tall.

it doesnt necessarily have to hold 15kg in order to have the best ratio since they arnt putting a greater emphasis on weight held this year.
in fact, the winning tower at nats a few years ago was 4.1g and held 13.something kg. I think we will probably see a lower ratio this year because of the greater importance of being 70cm

iOYA is absolutely right. Scoring this year is back to an absolute efficiency basis [weight carried divided by weight of structure (multiplied times a height factor)]. If you have a tower that carries full load, and another that weighs half as much, and carries just a bit over ½ load, the light one wins. Definitely something to think about, and maybe play with. That said, I have to say, particularly for a C-Div tower, the chimney for a 70cm tower – at 55 cm long - is mighty long and skinny. I didn’t fully appreciate just how long and skinny till we got our jig pieces cut out. Overall structural rigidity – stiffness – that it doesn’t twist or bend, is going to be really critical. Just a little bit of distortion in each braced section, added up over 55cm, will very quickly get to be enough to take the tower out. To go “really light” you’re looking at either really low density leg wood, or really small cross-section (like 1/16th square). Maintaining sufficient structural stiffness with either without loosing efficiency because of a lot more bracing will be a serious challenge. I look forward to seeing if anyone can pull it off.

As to scores this year, and I’d hardly call it an opinion- more an educated guess, preliminary calculations suggest that getting under 11 grams for a 70cm C-tower holding full load will be “good” (a winner in many if not most Regionals, medaling in many if not most State meets). 10 grams will be really good. With the dimensions in the rules this year, you can extrapolate from last year; base section dimensions are the same- just a significantly longer chimney. If you know what your base section and top section weighed last year, add weight of base plus 55/35 times what your top section weighed to get a 70cm weight estimate. For example, a 50cm tower from last year that weighed 8.4 grams with the additional 20cm of top section will come out around 11.2 grams at 70cm….. Such a tower, carrying 15kg, would score 87.05 at Regionals and 73.66 at State. We’ll see as folk get into actual building and testing.

Good point... holding the maximum load is not as important, but this year the higher it is the higher the score multiplier, right?

[Balsa Man]

Good point... holding the maximum load is not as important, but this year the higher it is the higher the score multiplier, right?

Yup. Pure efficiency times a multiplier, and that multiplier goes up as you move from Regionals, to State, to Nationals. The scoring value/advantage from height becomes more important as you advance. And, interestingly, it looks like, even for a regional tower (where the height bonus is the least), how do I say this....the rate at which the height bonus goes up is greater than the rate at which efficiency goes down as you add extra height and the weight that goes with that height (based on some weight per unit length of last year's chimney section)....

[lllazar]

A question regarding glues for balsa wood - for scioly events i've always stuck with thin CA (and ambroid cement for helis) but i'm currently building a bridge for recreation that I think will need really strong joints in specific locations. What would you guys say is the strongest glue for balsa wood, neglecting all other factors such as drying time and weight?

I'm thinking along the lines of epoxy, but not quite sure. Help?

[CopperPenny]

Are we allowed to post links to sites outside of Scioly?

If so, I found one listing several glues and their properties when used with balsa wood.

[lllazar]

Yes, I would think you'd be able to do that.

[CopperPenny]

http://www.specializedbalsa.com/glue.php

That site had the some glues and descriptions. Hope it helps!