Swing Tests......do You???

[billeblurzz]

I kinda like to do swing tests! Sometimes when I can't exactly go out to LAUNCH rockets, I take some that I haven't firmed up yet and go out in the yard and experiment with nose weights! Does anyone else do this???....maybe you do but are not bored enough to PHOTOGRAPH it??? I guess it does look funny for a 50 year old guy out in the yard playing with "rockets on a string"!

 

[phaar]

I occasionally did this a while ago, but got too lazy to do it with some rockets I, for the most part, new were alright. I think it is pretty good idea to do it on the questionables.

 

[billeblurzz]

Since "I'm doing a SCIENTIFIC EXPERIMENT", my kids seem to put up with it and not worry about what the NEIGHBORS think!....but today my daughter came out and made me STOP!!! She did not think it was in the name of SCIENCE anymore!!!

 

[billeblurzz]

WHAT could have caused her to come out like a woman POSSESSED??? ...maybe it was the newly added ROCKET-THRUST SOUNDS emanating from my LIPS???

 

[flying_silverad]

last swing test i did was with my cat...head was forward and the tail was aft, just where it belonged.





Kidding.

really though, I do them once in a great while.

 

[jflis]

"Whosh!" man, I can see it now! LOL

Reminds me of when my son turned 3 and I decided that was old enough to park him in the middle of the yard while I played with my new paper airplane designs.... that way I had *him* as an excuse and I could fly someplace other than the basement... LOL

...of course, I made more of a "jet" sound...

 

[Ozymandias]

I haven't done an actual swing test in ages. I do all that stuff on the computer now. Welcome to the 21st century.

 

[JStarStar]

What's a komputer??

LMAO.... when I first 'retired' from rocketry in the early 70s, hand-held calculators had just been invented (and were super expensive - $200 or so, which would easily be comparable to over $1000 today).

When you did stability calculations then, you had to do all the math with pad and pencil. (Or use a slide rule, as I did learn for about one year and have since completely forgotten how to do.)

That's when the cardboard-cutout method was pretty much the way to go. IF you looked OK by the CC method, take it out and swing test... then, if it doesn't start flying tail-forward, all systems are go....

You young whipper-snappers with your consarned PC programs and 3D printouts and dynamic CP calculations and Cd simulations....


Just make sure when you do your swing tests, that you don't do it next to a tree or a brick wall.

 

[DynaSoar]

Originally posted by billEblurzz
I kinda like to do swing tests! Sometimes when I can't exactly go out to LAUNCH rockets, I take some that I haven't firmed up yet and go out in the yard and experiment with nose weights! Does anyone else do this???....maybe you do but are not bored enough to PHOTOGRAPH it??? I guess it does look funny for a 50 year old guy out in the yard playing with "rockets on a string"!

I do quite often. I use a chain of rubber bands. That way when I slow it down they shrink up, and it doesn't flop into the grass 15 feet away. I can usually get it to almost stop before it touches ground.

My scratch built "Skunk" is 12" longer in the body due to swing testing. Not for stability, but because one rubber band broke and it went straight into the wall of the house. I cut off the crumpled 6", and added a whole 18" body tube just because I could. Now, with the payload section, it's over 7 feet long. Now I carefully select my rubber bands.

 

[hokkyokusei]

Originally posted by billEblurzz
I kinda like to do swing tests! Sometimes when I can't exactly go out to LAUNCH rockets, I take some that I haven't firmed up yet and go out in the yard and experiment with nose weights! Does anyone else do this???....maybe you do but are not bored enough to PHOTOGRAPH it??? I guess it does look funny for a 50 year old guy out in the yard playing with "rockets on a string"!

Still photos? I have video of myself swing testing a ropcket!

 

[rstaff3]

Cool pics and amusing story And yes, I'll resort to a swing test when a design can't be modeled properly in Rsim. I ususally try to fudge them in Rsim and then confirm with a swing.

 

[jflis]

Tried swing testing the Richter Recker in the living room once...

...it wasn't a good thing...

(could you just *imagine*!??!)

 

[rstaff3]

Not too good an idea, eh? I've never tried swinging anything inside, other than the basement. Nothing much to damage.

 

[cls]

last swing test i did was with my cat

it's easier to swing test cats in the dryer.





just kidding!!!

 

[rstaff3]

The swinging part is easier, but getting them is a bitch!

 

[Fore Check]

I usually swing test anything I build from scratch, including upscales. I've found on several designs that even though I had the balance point where RockSim said it needed to be for a minimum of 1.0 stability caliber, it swung tail first. So, nose weight was added until that was corrected.

Hmmmm......

 

[DynaSoar]

Originally posted by Ozymandias
I haven't done an actual swing test in ages. I do all that stuff on the computer now. Welcome to the 21st century.

Check out my Descon entry "Sandman". There's nothing available to us common folks that can accurately model the sort of complex curved surface as the nose cone or 3-to-1 tube transitions. If I'm wrong, I'd appreciate a pointer. I'm sure I could find some Matlab stuff to display it, but calculating drag hypo and hyper Mach is a different animal.

If you've got something there at ERAU that can do so, I'd dearly love to collaborate. I want to know how big this can be scaled up effectively.

So far, all I have is swing testing, and that'll probably end with the 29mm version.

 

[flying_silverad]

Originally posted by Fore Check
I usually swing test anything I build from scratch, including upscales. I've found on several designs that even though I had the balance point where RockSim said it needed to be for a minimum of 1.0 stability caliber, it swung tail first. So, nose weight was added until that was corrected.

Hmmmm......

That's so true. And, conversely, I have had rockets that swing tail first, that fly fine when you get them to the launch pad.

 

[Micromeister]

Yep! I swing test stuff all the time...makes me dizzy...its' a blast

Yes I swing test just about ever PMC, Scale and Micro-Maxx model I create. I do not trust computer programs. No not one.

 

[Fore Check]

Originally posted by flying_silverad
That's so true. And, conversely, I have had rockets that swing tail first, that fly fine when you get them to the launch pad.

After swinging tail-first, what told you that it was ok to go ahead and fly the rocket?

 

[GL-P]

That's so true. And, conversely, I have had rockets that swing tail first, that fly fine when you get them to the launch pad.

I think it depends on how fast the air is moving over the wings. The faster a rocket goes, the more stable it tends to be. If I was bored I might calculate how fast a rocket was going on a swing test compared to how fast it would be going during launch. On the big powerful stuff I bet it there would be quite a difference.

 

[GL-P]

Just imagine what would happen if you let it go!!!

You should try Olympic class hammer throwing!!!

 

[cls]

If I was bored I might calculate how fast a rocket was going on a swing test

ok, I'm bored. lessee, a 5' string makes a 10' circle, or about 31.4' circumference. if you swing your rocket around in less than a second it will be "flying" through about 30 feet per second, or about 21 MPH.

hmm, maybe not fast enough: usually assume about 45 feet per second needed to make typical rockets start flying. so either swing a 5' string nearly twice a second, or swing an 8' string once a second...

 

[Micromeister]

Originally posted by cls
ok, I'm bored. lessee, a 5' string makes a 10' circle, or about 31.4' circumference. if you swing your rocket around in less than a second it will be "flying" through about 30 feet per second, or about 21 MPH.

hmm, maybe not fast enough: usually assume about 45 feet per second needed to make typical rockets start flying. so either swing a 5' string nearly twice a second, or swing an 8' string once a second...

The 8 feet string is getting better.... even my micro's use an 8foot string, standards LPRs 10 to 15feet.

It is true some models will not swing test, Very long models and marginally stable models, usually will not test well. This should be a RED FLAG... if your going to fly it anyway...make sure your alone and FAR away from others. If its going to fly at a club launch for the first time... call for a heads up! that's why we test stuff alway err on the side of SAFETY First. It never hurts to call for a heads up flight... but not calling for one very well could.

 

[slim_t]

The first time I did a swing test was on my first scratch rocket. It was a long skinny rocket with decent size fins. I thought for sure it was stable, but when I did the swing test it just wouldn't fly right. So I added nose weight until I got it right, but just knew it shouldn't need that much weight. I flew it and it flew perfect. But I just couldn't let it go. I started taking out nose weight a little at a time and flying it after each time. I ended up with 0 nose weight right back where I started and it still flew perfectly straight, and alot higher of course. I never did another swing test on any rocket after that.

Of course that was some time ago, and now I know I probably just needed a longer string and more speed. The rocket was just too long to get it swinging on a long string.

Now that I've seen these pics, I might have to do more swing testing. That Red Max in hyperspeed looks pretty cool.

Tim

 

[Stymye]

thats due to the high angle of attack of the rocket , The high angle of attack kills the fin lift and so the CP moves forward.

If the rocket points in random directions as you spin it, than it's neutraly stable(cp/cg around the same point) if it flys backwards it is negativly stable.

so.... longer rocket = even higher angle of attack
also too slow spin rate as was mentioned can give you a poor indication of stability as well.

 

[andysrockets]

Last swing test I did was an Estes Yankee about 10 years ago. Only way to get it to pass was to jam the biggest M8 bolt into the nosecone, as witnessed by an Aerospace engineer (it was his bolt BTW). The rocket flies perfectly OK built stock.

Swingtest is demonstrating stability with huge angle of attack. If your launch rod is long enough, then in flight angle of attack will be apporaching 0deg unless you're launching in a hurricane. Obviously near apogee, AoA will increase if your launching in a breeze.
I don't intend swingtesting another rocket... ever.

 

[WiK]

Hmmm

Maybe they should have swing tested that flying picnic table?


Phil

 

[andysrockets]

Originally posted by WiK
Hmmm

Maybe they should have swing tested that flying picnic table?

No need... mupp calculated everything on paper, and 'simmed' it too.