Where?I've read that all Estes rockets are designed for a minimum of 1.5 calibers. Obviously, longer rockets get more. If that's true, you'd have to really be out of whack in your build to have a problem, assuming you build to the instructions.
Where?I've read that all Estes rockets are designed for a minimum of 1.5 calibers. Obviously, longer rockets get more. If that's true, you'd have to really be out of whack in your build to have a problem, assuming you build to the instructions.
John Boren said something to that effect back when he was active on the forums.Where?
A sim *is* good enough when the design is within the capabilities of the software, regardless of weight.
There are plenty of scratch builds turning up these days. 3/4fnc where the builder has not done a sim and there's no-one with a laptop at the launch. A SUCCESFUL swing test gets it past the RSO and allows them to launch. So it's more useful than for just oddrocs.Shoot, I just make sure the CG is right with the loaded rocket and will be fine. If I gotta add nose weight, no big deal. Just add a bigger motor if one wants to fly higher. Swing testing is for modrocs. Certainly can't be done with larger projects easily at all! Invest in a good sim program and/or follow the manufacturers recommendations that come with a kit rocket. Kurt
Ah, the rope test. I've seen a college athlete wind up the heavy hammer.So what is the weight limit of a rocket to perform a swing test? If a sim is good enough for over the limit it's good enough for ones under the limit.
None to be had at any of the Hobby Lobbys around here... they discontinued carrying it. I've looked at 5+ in the area, since we're using them as the bases of a "kit bash" competition at our clubs 25th anniversary.I'm tempted to go buy more Baby Berthas at Hobby Lobby to build sorta-clones of BB, BBB, and Ranger. They are sooo cheap right now.
I'm not seeing how a swing test is seriously flawed. If it passes the swing test, it's going to be stable if the motor thrust to weight is sufficient to get it off the rod at an appropriate flying speed. Pretty simple really.i'd say put down your strings and get with the 2000's.....
seriously, swing tests are notoriously flawed. All those variables, some of which are completely out of control.
We can control string length
we can, in an extremely rough way, control speed
we can't control any cross winds because you can't control mother nature
We can't control our perception of what's happening while we worry about not smashing the rocket (no human can do two things well simultaneously)
we're not certain what other variables are present, and what their effect size is.
Yes, sims aren't perfect, but they give you a starting place.
there is some limitations. Know them and understand them.
I use Rocsim for most rockets
For high performance rockets, RS Aero II because it's just more accurate at speeds well above mach 1.
Odd Rocs will always create a challenge. the best solution is to get them far enough away that they can't come back to the flight line. Anyone who went to URRF in 2022 will tell you I flew my J powered 3 inch diameter superrocc (27.75 feet long) from the away cell..... it was never gonna get anyone from there!
This is why the swing test is not a good test for long rockets.
This is why the swing test is not a good test for long rockets.
Well, when I wrote the text you quoted, OzHybrid had not yet posted in this thread. So it's kinda silly for you to suggest that I should have read something that hadn't been written yet.
However, to the point, I've read the whole thread up until now and I don't think OzHybrid and I have any significant disagreement. My post was an explanation of some of the whys behind the whats that OH has expressed.
It's real world, but it's not a real flight, and the differences (which others have cited) are much more significant the differences between reality and a simulation.A simulation is a poor substitute for a swing test:
The simulation assumes all data is input correctly.The swing test is real world.
It's real world, but it's not a real flight, and the differences (which others have cited) are much more significant the differences between reality and a simulation.
The best thing that be said about the swing test is it isn't as hopelessly awful as the "cardboard cutout" method.
Absolutely. But that doesn't mean it's the best solution -today- for most rocket designs. The swing test certainly has its place for edge cases.Folks have been using Vern Estes' swing test for decades, successfully.
....The swing test certainly has its place for edge cases.
The best thing about the swing test is that if the RSO refuses to let to let you fly over stability concerns, you can demonstrate the swing test and if you pass he will let you fly.It's real world, but it's not a real flight, and the differences (which others have cited) are much more significant the differences between reality and a simulation.
The best thing that be said about the swing test is it isn't as hopelessly awful as the "cardboard cutout" method.
Sorry - you're making the assertion that 'any rocket less than 4 ft in length that are LP or MP' don't mesh well with simulation?If you define "edge cases" as any rocket less than 4 ft in length that are LP or MP... I totally agree.
Sure, but that's operator error in both the assembly and simulation.I'm sorry, but I need to chime in here. A simulation on a computer that has nothing to do with the actual rocket in question is a poor way to test anything IMHO. It doesn't take into account how you built that rocket. I can start with a fine kit that has tested stable before it was manufactured. But if I slather 32 ounces of Epoxy into the fin-can because I don't know what I am doing, I am going to throw off the CG by a considerable amount, no matter what the "Sim" says.
And I say this as someone with a great amount of experience at screwing things up.
Garbage in, garbage out. Mass and CG of the fully assembled rocket should *always* be measured and overridden in the sim before final analysis is done. Always.I'm sorry, but I need to chime in here. A simulation on a computer that has nothing to do with the actual rocket in question is a poor way to test anything IMHO. It doesn't take into account how you built that rocket. I can start with a fine kit that has tested stable before it was manufactured. But if I slather 32 ounces of Epoxy into the fin-can because I don't know what I am doing, I am going to throw off the CG by a considerable amount, no matter what the "Sim" says.
And I say this as someone with a great amount of experience at screwing things up.
Sorry - you're making the assertion that 'any rocket less than 4 ft in length that are LP or MP' don't mesh well with simulation?
- How long was the string?
- How fast did you spin the rocket?
- Did the rockets nose hang slightly below level?
Bingo!! Kit or scratch built, mass and CG should always be determined after the build and then entered into the sim. I've never weighed separate components on a scratch built rocket and entered it into the sim. I let the sim determine the mass according to the material used in that component. After built, weigh and determine CG. Adjust CG if needed.Garbage in, garbage out. Mass and CG of the fully assembled rocket should *always* be measured and overridden in the sim before final analysis is done. Always.
Both... do both. Run the sim and do the swing test. On LP or MP rockets, less than 4 ft in length.
Enter your email address to join: