Help My son has comitted me to building 2 rockest with mis alligned fins for Science

I have been building rockets since 1985, but never really thought of testing the effects of fin straightness on rocket flight. I feared it would only cause an unstable flight. Now due to a mock up science fair my Sons school is conducting, he decided to find out What IF. We have built 3 Sizzler models (boy are they smaller than they used to be!) and we placed the fins straight 90 degrees on one, at a slight angle 110 degrees on another and a large angle 140 degrees on the third. I live in a an area where the weather over the last few weeks has not been suitable for launches, but his data is due Friday. We attempted a launch today, but the wind picked up to around

10 MPH and the rocket was not recovered. I expect we will have to fake the data, but I'm not sure what exactly will happen. Will the rocket fly, but have altitude decreased by the spin, is it more likely it will fly out of control, or will I see little difference? Please respond, I can't find any simulators that permit me to angle the fin to the body and produce results. All the usual programs assume I am smart enough never to improperly install fins on the tube without really saying why.


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No need to fake the data. Download the test version of Rocksim and build the rockets in the sim program. Program in your launch data and fly them in simulation.

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has the program.

Reply to
Reece Talley

I don't believe Rocksim offers the option of canting the fins (or if it does, I'd like to find it!)

The theoretical rate of rotation at given velocity can be calculated by

Nx=Vrocket/[2*pi*Rfin*Tan(pitch angle)]

where Nx= rotational velocity in revs/sec Vrocket is the velocity of the rocket in ft/sec RFin is the radius of the fins from centerline of rocket to tip of fin Pitch angle = 90- fin inclination angle

I went through trying to get FinSim's SpinSim to work with RockSim 8, with no luck. Finally I just plugged the above info into a spreadsheet populated with CSV info from RockSim. The formulae I used are taken from the SpinSim documentation by John Cipolla.

Kevin OClassen

Reply to
Kevin OClassen

rocksim 7 & 8 can 1 through 8 fins, any shape, at any rotation, so you can make it do anything radial. offset is more difficult but can be done. sort of.

Reply to
Cliff Sojourner

Faking the data is a pretty sorry example to set for your son. Do you think he's a Korean stem cell researcher or something like that?

Either report the missing rockets (which ought to be a legitimate outcome) or build new rockets. But don't fake data.

There's a word for that sort of behavior: FRAUD.

Bill Sullivan

Reply to
The Rocket Scientist

Rule #1: Don't fake any data.

Part of conducting an experiment is to try to explain the reason for an outcome whether you predicted it or not. Why did you lose the rocket? was it because of the flight characteristics from the combination of the wind and the fin angle? Did the rocket wind c*ck like it should have if you set the launch angle as close to zero as possible, or did it fly higher and more straight because of the spin from the fin cantor? From what is he basing his initial theory of the behavior of the rocket? Stines book? Those are the things that you need to explain. It's still a valid experiment. Didn't you observe the take off or video tape it? How did you measure the altitude? Did you use the Estes altitude tool?

Gates son did an experiment very similar to this that won him the California State Science Fair. His experment was the effect of spin on altitude if I remember correctly. HIs didn't go as expected either and he lost one of his or it core sampled or something if I remember, but that was all put in his results too. He had a link to his paper a long time ago and it was very impressive. Maybe Erik can upload it again for everyone to see.

I'm still trying to teach my son the proper way to write a lab report. Showing him my college lab books only gets him so far. I see the most difficult part for kids is they don't know how to describe results effectively or completely.

Good luck


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