Wanted: FinSim Help

Are there any FinSim users here who could run a few simulations for me? The details are discussed in
this thread.

Never mind. Bruce Levison responded in the other thread. That guy is a simulation wizard!

Bob,

Thanks for the accolade!..

I thought you were the "Simulation Wizard", since you always beat me in the EMRR virtual rocketry contests.

Bruce S. Levison, NAR #69055

I design rockets that exploit the limitations of Virtual Rocket World, while your designs are much closer to reality. For example, virtual rockets can break Mach with balsa fins and paper tubing. Virtual rockets can be made from 25 feet of BT-5 tubing and still won't kink during flight. I wouldn't want to try that in the real world.

I liken it to Scrabble. Many of the top Scrabble players in the world know little or no English. To them, the words are just arbitrary symbols that have specific point values, with little appreciation for their real-world meaning.

This isn't related to Bob's earlier post, I just didn't want to create a new thread on the same topic. Can someone finsim Deuce fins (airfoiled)? I need to know if they can take about 450mph (the speed it would achieve on a pair of D13-7W motors). If it makes any difference (I assume it would, due to air density), I will be launching it from around 5000 feet ASL. Thanks in advance.


Chris.

Chris,

It took me a while to find my Deuces Wild simulation file. I changed the fin profile to airfoil but this didn't change any of the maximum speed numbers. FimSim version 2.3.0 isn't sophisticated enough for that kind of analysis yet.

Here are the results in critical not to exceed velocities:

Divergence 647 mph Flutter 560 mph

Stress analysis at 5000 ft ASL with butt joint fins using 1/16 inch fillets of Elmer's wood glue at 1 degress AOA: 456 mph, 459 mph with 1/8 wood glue fillets. This increases to 730 mph (the strees limit of the balsa) if you use 1//16 inch Epoxy fillets. Since you are close to the limit, wood glue might not be the best choice. A good Epoxy glue would be better to use!

Bruce S. Levison, NAR #69055

Thanks very much. I will reinforce them with epoxy, now that I know that it needs it. When I fly it, I will try to post pics (if I can catch it )

Speaking of fin sim, I looked at the web page info, but uncertain whether it would be of use in looking at mach 2, sandwich construction say of g10/balsa wrapped in CF. Also does it look at CD as you make the fins wedgier/
J

denverdoc,

You would have to enter the CF covered, G-10 Balsa sandwich as a user defined material into the FinSim program which means you will need to know its Modulus of Elasticity, density, Poisson's ratio and Yield stength. If you can't get these numbers its not worth the trouble of running the program, especially for Mach 2 flights. The FinSim program does not calculate the Cd of the fins and ignores their cross sectional shape.

Bruce S. Levison, NAR #69055

That was my fear, basically little material sci know-how, just look-ups for very common materials.
Does it at least readily export the fin dimensions to a drag/sim prog so you can work back and forth a bit?
J

Originally posted by denverdoc
That was my fear, basically little material sci know-how, just look-ups for very common materials.
Does it at least readily export the fin dimensions to a drag/sim prog so you can work back and forth a bit?
J

Click to expand...

You have to manually enter the fin dimensions, the latest version no longer has RockSim compatibility.

Bruce S. Levison, NAR #69055

Bruce,
Thanks but I was under the impression that finsim was part of a family of software that included some very sophisticated software at the top, and better than rock-sim when it comes to trans and hypersonic flights at the bottom. I like rocksim, but the results at mach are patently absurd in some cases. Does it interface with these progs?
Otherwise, any suggestions?
J

There is a family of software but is not fully integrated. For Cp determination of supersonic flight HyperCFD is the program to have to determine Center of Pressure and Coefficient of Drag to ultimately determine the stability of a design. Then you will need AreoFinSim to simulate the structural integrity of your model. Fianlly, you will need AeroDrag and Flight Simualtion to simulate the rockets ascending flight. Total cost for all three is $215.00.

Then you will also need a good parachute drift calculator to simulate the descending flight to the ground like:

https://www.rocketreviews.com/tool_drift_rate.shtml

Bruce S. Levison, NAR #69055

Thanks Bruce, I understand. Curious is you have any of these products besides FinSim and your impression. Thats a lotta scratch for a guy saving up for a GPS/telemetry system (arguably the software is a higher priority!)
J

I have a few AeroRocket products FinsSim of course, also AeroCFD, HyperCFD, AeroCp and Aero Drag. I use them to confirm and verify other rocketry software. The CFD programs are a little more involved and technically intense than your typical simulation softwares, they are useful to calculate the Cp and Cd of a rocket for both sonic and subsonic flights. I usually enhance my other flight simulation programs with the values obtained from the CFD results. The CFD programs have been verified against wind tunnel and actual flight data so I have more confidence in their accuracy. AeroCp is an easy to use Barrowman Cp calculator that has a limited fin and body tube stress analysis algorithm built in. AeroDrag allows you to simulate Cd versus velocity and to look at the contribution of each part to the total Cd. It is the only program I know of that allows for open or closed Ram jet type nose cones. It also has a a flight simulation program that directly uses the Cd data that you simulate. The flight simulation is kind of basic in that it only gives altitudes and not range data; so you know how high a flight might go but do not see the effects of wind and launch guide angle etc.

That's it in short. The CFD programs have a definite learning curve, you need to read and understand the manual or help files that come with the programs.

Bruce S. Levison, NAR #69055

Thanks again; Pm'ed you about a specific question,
J

Originally posted by denverdoc
Thanks again; Pm'ed you about a specific question,
J

Click to expand...

Did you get/see my reply?

Bruce S. Levison, NAR #69055