SSSS / SSS

[Chris LaPanse]

I bet you could probably do it somehow, but it would be hard. My airframe at .01″ thick is more than strong enough, but I have tried 1 layer layups too, and they have essentially no strength from my limited experience. What you would need would be a tightly woven but thin fabric – like 3 wraps of 1oz if you could find it. Carbon nanotubes have the possibility to be MUCH stronger, but I doubt hobbyists will see them for quite some time 😆

[Warren B. MusselmanModerator]

Chris, I’ve wrapped tubes from 3 wraps of .75 oz glass… worked just fine for F motors and I probably could have gotten away with 2 wraps.

Warren

[Chris LaPanse]

Yeah – I’m sure that would work. I’ve done one that was just rolled paper with 3 layers of 1/2oz glass – worked fine, but it only had a C motor. Wasn’t sure what the limit would be for the G80, so I played it (relatively) safe with 2 wraps of 2oz carbon

[Anonymous]

Cross section, i.e. diameter is very important — smaller is better (duh). That said, optimal mass is extremely important as well. I’ve been profoundly amazed at Rocksim and it’s ability to predict optimal mass — at least with White Lightning, Blue Thunder, and essentially all Cesaroni loads. (Blackjack is another matter)

FWIW, I had to add ~3.15 oz. of lead to my recent G55 shot down in Hartsel. Optimal mass for that particular rocket was almost 7 oz. I came in very much under optimal mass, and had to make up the diff w/ the lead. Thankfully, lead shot doesn’t take much room. I also added a considerable amount of lead to my F rocket. My point is that it is very possible to build a rocket that does not have enough mass. Both my F and my G rockets had 2 wraps of 2 oz. glass over Apogee tubing.

I’ve added as much as 3,000′ of altitude to J rockets by adding lead. I’ve also added lead to keep the gees down, when the OM curve is very flat. I’d rather fly slower w/ fewer gees if it doesn’t cost me a lot of altitude. I’ve added as much as 60 oz. of mass to K rockets. Lighter is not always better…

[Conway StevensParticipant]

Ahh yes I have said and belive this my very self in several places and times. It comes down to trying to throw a feather or throw a rock for distance in essance. People forget alot abot the coast time that a rocket goes through and that with out enough mass or no mass it will lose that very important coast time. This is a good reason as to why I build the way I like to using fiberglass and CF and even kevlar laminates. Where it need be for strength but paying heed to the weight balance. Ive seen in many forums where people say dont glass dont this dont that. Because all you do is add un-needed and un-nessacary weight.and its overkill. If the job is done correctly it will help it reach that optimal point and create a stronger bird that will last longer. Or atleast what i have come to learn and belive.Hmm Thanks for those teachings JW..

[Bruce R. Schaefer]

Now, John, if Chris wants to fly lighter than he should, he has every right to… 😉 You said something earlier about sims having undependable, not right, screwy, etc. engine data for the G80T. Even though I use something other than RockSim–had one of the first versions, may still have it on a 5 1/4 floppy, it, too, gives results that just don’t seem right. In regard to weight, I’m just not getting good, sound results with SpaceCAD. I needed to add 2 oz. at one point, and that’s fine, but it has two G80’s: one a G80, with ~117 Ns, which indicates it’s the older version, and the G80T, with ~99 Ns, and that’s the one for the contest. Using either motor, I found the optimal weight, but I’m not sure which one is right. I’m getting a different weight for each motor, a substantial difference in weight. I’m just gonna split the difference and hope for the best. You just gotta get the mass that fits the motor moving as fast as it can and as far as it can go through the coast phase. I used to do this, back in the 60’s, WITHOUT software. You just took a guess, wrote it down, flew and had a friend measure the altitude until you got the optimum weight down.

[denverdoc]

chris can certainly speak for himself as he’s a rocksim maven and knows where to find the optimal mass button.

personally i like to distribute the weight as small fins and heavy nose may be statically stable but dynamically underdamped so it fishes too much for the zero point. once in a while you get a perfect undisturbed flight, but more often than not too much wiggle-waggle.
J

[Chris LaPanse]

Mine is intentionally coming in as light as possible, and I will add weight with lead shot as needed. My thought is that I can always make it heavier if need be, but not lighter, so I will bump it up to optimal mass with lead shot in the nose. This also allows me to keep the center of gravity at the center of the rocket, rather than towards the back, and keep the fins a bit smaller. Trust me – mine will be at optimum mass when I fly 🙂

[Bruce R. Schaefer]

Chris, I’d really like to see you win this. I’ve already blown, most likely, with two bad judgements that I can’t undo without starting over–and that’s not gonna happen, this year. I haven’t worked on altitude optimization since 1969, and this year’s SSS is just to get up to speed. But there’s always luck and next year, right?

[denverdoc]

Now, John, if Chris wants to fly lighter than he seem right. ….In regard to weight, I’m just not getting good, sound results with SpaceCAD. I needed to add 2 oz. at one point, and that’s fine, but it has two G80’s: one a G80, with ~117 Ns, which indicates it’s the older version, and the G80T, with ~99 Ns, and that’s the one for the contest. Using either motor, I found the optimal weight, but I’m not sure which one is right. I’m getting a different weight for each motor, a substantial difference in weight. I’m just gonna split the difference and hope for the best. You just gotta get the mass that fits the motor moving as fast as it can and as far as it can go through the coast phase. I used to do this, back in the 60’s, WITHOUT software. You just took a guess, wrote it down, flew and had a friend measure the altitude until you got the optimum weight down.

Bruce,

Those were the days–I still remember using a tty machine that was wired to the universitys mainframe computer that took up two story air conditioned bldg to write a barrowman program(sixties)

in the mid eighties after my first rebirth, had access to DOS based mini’s which could run sims pretty fast in well writen C with delta t’s of a mSec, and later obviously to 8086 based PC’s.

I was blown away to discover RSim after my second rebirth. While I have known issues with DATCOM methodology, what a marvelous tool we have at our disposal.

As to optimal mass, RS does this under ideal conditions. It may or may not be correct under real conditions, don’t know much about Space CAD, but assume it uses a similar algorithm. Really its not surprising that the two G80’s call for diff masses–the bigger the motor, the higher the optimal mass at least until mach 1. Then it may be better to fly lighter and pierce the soup to get on the other side where Cd starts to fall, or build heavier and avoid it altogether. THe G80 falls a little short of being in this category as mach is barely reached if at all. Certainly never get to the other side.
J

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