National Tower Scores?

[Random Human]

Well, I can report a couple of scores from the teams I worked with- a bit down the order- 13th in B, and 14th in C.

Both met 29cm circle bonus- we decided to see what we could do with the (good) jigs we had, rather than take on new, non-circle bonus jig building. Preston MS weighed in at 7.4, carried right at full-2290, breaking right at the end. 5/32 legs, 1/32 x 1/16 Xs only, 10 X sets. Xs cut from 9gr 3 x 36” sheet. Top ladder from very low density 1/8, bottom ‘tension band’ 1/16 wide from 1/64th sheet. Legs running at a 9% safety factor on design BS (BS tested at 2cm longer than installed length). Some interesting bits of drama to get there-

On the way to testing, got run into on the stairs, and tower (weighing 6.7) was broken. However, last weekend, doing final test, the test tower held full. As soon as last sand went in, grabbed the bucket, took load off. Reminding them that stuff happens, suggested that they take it along as a backup (since building event devices were going via a van with a team parent driving). So, after the disaster on the stairs, a run back to get the backup….. But, there’s one more layer to the story of the little backup tower that could. Before its test last week, it was stored in a storage room at school, and someone went in and broke it- leg break about 3cm down from the top, and two of the top ladder pieces. Leg break splinted w/ two pieces of 1/64th sheet. So, one data point on the question of can a tower that’s seen full load do it again. It had seemed really solid at the end of the test- no sounds, no visible distortions. I think if the 6.7gr tower hadn’t gotten broken, it would have gone to/near full load, btw….

Fossil’s was very similar to Preston’s, but with 11 X sets, and a little lower SF (one leg at 5%). Both ran reinforcement strips at the center of the lower Xs that were longer than bottom Xs in a non-circle bonus configuration- bottom 3 X sets on B, bottom 4 X sets on C; 1/32 x 1/16, laminated on outside of one X, and inside of the other; 4, 3, 2, 1cm long on C, 3, 2, and 1cm long on B. Both ran straight legs (no slight outward bowing to try to get Xs working only in tension).

So, a little bit disappointing, but on the other hand, not bad. So proud of the builder's hard work, and great learning, absorbing the why and how of the engineering....

Wonder how the tower rules for next year are going to be modified..?

I think next year... theres a possibility of having that "2 part" configuartion like back in 2011, also bonus and height are gonna change.... Otherwise, not too intresting things.. in my opinion

[Dohnnovan]

Well, I can report a couple of scores from the teams I worked with- a bit down the order- 13th in B, and 14th in C.

Both met 29cm circle bonus- we decided to see what we could do with the (good) jigs we had, rather than take on new, non-circle bonus jig building. Preston MS weighed in at 7.4, carried right at full-2290, breaking right at the end. 5/32 legs, 1/32 x 1/16 Xs only, 10 X sets. Xs cut from 9gr 3 x 36” sheet. Top ladder from very low density 1/8, bottom ‘tension band’ 1/16 wide from 1/64th sheet. Legs running at a 9% safety factor on design BS (BS tested at 2cm longer than installed length). Some interesting bits of drama to get there-

On the way to testing, got run into on the stairs, and tower (weighing 6.7) was broken. However, last weekend, doing final test, the test tower held full. As soon as last sand went in, grabbed the bucket, took load off. Reminding them that stuff happens, suggested that they take it along as a backup (since building event devices were going via a van with a team parent driving). So, after the disaster on the stairs, a run back to get the backup….. But, there’s one more layer to the story of the little backup tower that could. Before its test last week, it was stored in a storage room at school, and someone went in and broke it- leg break about 3cm down from the top, and two of the top ladder pieces. Leg break splinted w/ two pieces of 1/64th sheet. So, one data point on the question of can a tower that’s seen full load do it again. It had seemed really solid at the end of the test- no sounds, no visible distortions. I think if the 6.7gr tower hadn’t gotten broken, it would have gone to/near full load, btw….

Fossil’s was very similar to Preston’s, but with 11 X sets, and a little lower SF (one leg at 5%). Both ran reinforcement strips at the center of the lower Xs that were longer than bottom Xs in a non-circle bonus configuration- bottom 3 X sets on B, bottom 4 X sets on C; 1/32 x 1/16, laminated on outside of one X, and inside of the other; 4, 3, 2, 1cm long on C, 3, 2, and 1cm long on B. Both ran straight legs (no slight outward bowing to try to get Xs working only in tension).

So, a little bit disappointing, but on the other hand, not bad. So proud of the builder's hard work, and great learning, absorbing the why and how of the engineering....

Wonder how the tower rules for next year are going to be modified..?

I think next year... theres a possibility of having that "2 part" configuartion like back in 2011, also bonus and height are gonna change.... Otherwise, not too intresting things.. in my opinion

The two part tower is what i meant by two directional tower(because you have the bottom part at one angle, and the top part is just going straight up)

[SomeKid]

Marie Murphy got 3340, which was third place.

[Crtomir]

However, last weekend, doing final test, the test tower held full. As soon as last sand went in, grabbed the bucket, took load off. Reminding them that stuff happens, suggested that they take it along as a backup (since building event devices were going via a van with a team parent driving). So, after the disaster on the stairs, a run back to get the backup….. But, there’s one more layer to the story of the little backup tower that could. Before its test last week, it was stored in a storage room at school, and someone went in and broke it- leg break about 3cm down from the top, and two of the top ladder pieces. Leg break splinted w/ two pieces of 1/64th sheet. So, one data point on the question of can a tower that’s seen full load do it again. It had seemed really solid at the end of the test- no sounds, no visible distortions. I think if the 6.7gr tower hadn’t gotten broken, it would have gone to/near full load, btw….

We re-tested a couple of our towers that held all the weight at a competition, and they held all the weight again in practice. These were towers, similar to the one you described, which were designed to get the bonus (wider at the base), and scored about 2200 and 2600. However, I think the really lightweight towers we build for State that didn't go for the bonus (narrower at the base) would not have re-tested to full capacity.

I'm still curious as to why none of the towers were able to get 3800 or better at Nationals? Were the teams just "playing it safe"? Did they not want to risk too much with the team score on the line? Or was there systematic testing errors? Was the humidity too high? Any opinions? I was hoping to see a team break 4000. Maybe all the teams used up their best wood during the season and at States. Some states are really competitive to get to Nationals.

[MattH2018]

I'm still curious as to why none of the towers were able to get 3800 or better at Nationals? Were the teams just "playing it safe"? Did they not want to risk too much with the team score on the line? Or was there systematic testing errors? Was the humidity too high? Any opinions? I was hoping to see a team break 4000. Maybe all the teams used up their best wood during the season and at States. Some states are really competitive to get to Nationals.

The top score in C division was 3280. I know we were by no means playing it safe but I can't speak for others. The humidity did affect it somewhat: we massed our tower before we left and when we were in the dorms the night before and it was 4.49 grams, however when they massed it when we checked in, it had gained weight and was up to 4.57. I don't know if it affected other towers this much though

[Balsa Man]

I'm still curious as to why none of the towers were able to get 3800 or better at Nationals? Were the teams just "playing it safe"? Did they not want to risk too much with the team score on the line? Or was there systematic testing errors? Was the humidity too high? Any opinions? I was hoping to see a team break 4000. Maybe all the teams used up their best wood during the season and at States. Some states are really competitive to get to Nationals.

The top score in C division was 3280. I know we were by no means playing it safe but I can't speak for others. The humidity did affect it somewhat: we massed our tower before we left and when we were in the dorms the night before and it was 4.49 grams, however when they massed it when we checked in, it had gained weight and was up to 4.57. I don't know if it affected other towers this much though

A lot of factors at play, so likely no single answer/factor. That weight increase from ambient humidity is 1.78%. That's not very much. I've not seen/found any real data on balsa, in terms of modulus of elasticity vs moisture content. Data from other wood at.....lumber dimensions does suggest that if....wet enough, there's some loss in stiffness/MOE. My guess is a 1-2% change isn't gonna be.....material- as in enough to make a measurable difference in outcome. You'd think the most likely 'systematic testing error' would be if test surfaces weren't perfectly level. Not being there to know, I'd bet a) they were very carefully leveled at the start, and b) there were periodic checks. With the test rigs on a hard surface, I wouldn't expect material variation. Having 'used up best wood', taken in conjunction with the interesting, and always in play, variation of properties between two pieces that as far as you can measure are 'the same', can and does have a material impact on outcome. And the closer to the limits you're playing, the more likely you are to run into an unsuspected/undetected variation the wrong way. And even with serious program/attempt to get to really special/high performance wood, there are limits- time sorting through, measuring, assessing, and the cost of a lot of good sticks to sort through to find the best. Bottom line? Over the years, I've seen both years like this, when expectations from prior results just..... aren't quite met, and years when expectations for Nationals are exceeded (and not coming from some neat, new/creative design/engineering approach). When you get into the upper end of competitive level, its very small differences, intentional and unintentional, that decide the outcome.

[a boy]

The humidity affected us too, increased mass from 6.17g to 6.24g

[dholdgreve]

This, being the first year for towers,I think maybe most took a "Play it Safe" approach, This, coupled with substantially higher humidity than found in many parts of the country, which raised the mass of the towers, thus lowering the scores even when carrying the same loads all contributed. I watched carefully from 9:00 AM until almost noon, and only saw one table adjustment during this time. The actual top was slid an inch or 2 toward the C testing by the E/C. I don't know the logic, and I doubt it had any affect on the later tests, but it was curious. As far as I could tell, the table top was not rechecked for level at that point or any other while I was there. I'm not positive, but I think the testing apparatus was sitting on a short level loop carpet. Again, not ideal, but probably not significant.

From what I could tell, all of the E/Cs and assistants did a truly remarkable job, taking the time to talk to the competitors... and not just small talk... after testing, they spent considerable time discussing potential design improvements with each team. While I certainly understand that allowing carrying cases near the testing opens up potential opportunities to weigh one tower and test another, I think this could be overcome with a box check when entering the immediate area, and allowing only 1 tower in 1 box. I can't imagine any other reason for not allowing boxes in the testing area. I know of at least 3 teams that were forced to test already broken towers. Did it happen because the towers were out of the box? I don't know... maybe they were broken in transit... I just think it wrong to make the kids take the towers out of the box, then walk down a flight of dimly lit stairs, through the crowd of other coaches and spectators as well as their competition without ant protection for their towers..

[Crtomir]

While I certainly understand that allowing carrying cases near the testing opens up potential opportunities to weigh one tower and test another, I think this could be overcome with a box check when entering the immediate area, and allowing only 1 tower in 1 box. I can't imagine any other reason for not allowing boxes in the testing area. I know of at least 3 teams that were forced to test already broken towers. Did it happen because the towers were out of the box? I don't know... maybe they were broken in transit... I just think it wrong to make the kids take the towers out of the box, then walk down a flight of dimly lit stairs, through the crowd of other coaches and spectators as well as their competition without ant protection for their towers..

I agree. They should have let the students keep their towers in boxes. Was the check-in/weighing done far away from the testing? It's usually best if they check-in and weigh the towers right next to the testing stations.

[dholdgreve]

It was a little strange... the venue was sloped seat lecture hall that probably could seat 100 to 150 people. It had 2 doors plainly marked (1 for C Div, 1 for B Div). It appeared that there was a check-in, check out table at the top of the stairs, just inside the door for each division. Kids would come in and check in at the top table, then sit down until called to the "stage" area. No boxes were allowed in the stage area,so the kids had to take the towers out of their protective boxes at their seats and carry them down to the stage area, where it was weighed, checked in, then tested. Of course there were parents and coaches standing on the steps, trying to take pics of the teams currently testing, because they cordoned off the bottom 4 or 5 rows of seating... They had the lights turned down pretty low, so the live video feeds of the towers being tested would be more visible...

like I said, the E/Cs did a great job! I totally understand why each of the issues were resolved in the manner that they were... nevertheless, I think the resolutions to one set of problems very well may have created a new set of issues that was not resolved.

One solution might be to use those first 4 or 5 rows as a staging area for the 2 or 3 teams in the process of checking in or testing. Someplace away from the general public, coaches, photographers, and all but a couple of other teams to place the boxes. Just a thought