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Let's settle this? RockSim vs OpenRocket vs RASAero

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rharshberger

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I use RockSim the most; while I like the look of OpenRocket, may main use for a sim is upscaling, and the lack of pods limits it's usefulness.

I just downloaded RASAeroII, but I'm still learning it. I haven't gotten an imported .rkt to fly yet.


Really easy, for conventional configurations, but if you have pods like on a Trident or Vega, it doesn't accept them.
Or fins on a transition like the V2.
 

Chuck Rogers

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Depends on how you look at it. Taking the average of the 4 measurements, the differences are +/- 5.7%.
That was kind of my point. You have 4 altitude measurements, what's the actual altitude? Take the average, look at the variation from the average. Or throw out the integrated accelerometer data (although it's good to know how close it was, if on other flights that's the only data you have). The data's all there, and I note in the altitude comparison table which altitude I used as "the altitude" (the GPS altitude).

I think flights like this are great. 4 altitude measurements, 3 different types of altitude measurements, different brands of altimeters. The direct approach. Just fly them all on the same rocket on the same flight.


Chuck Rogers
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Buckeye

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Fixed in RASAero II. In fact, in my opinion RASAero II now has the best supersonic CP prediction.

One technique is to make a plot of CP, divided by the Barrowman subsonic CP, versus Mach number. A straight line of 1.0 until Mach 0.90, then the CP moves aft, and then the CP moves forward and at some point crosses back over the Barrowman subsonic CP position. The Mach number where this occurs is a key point.

For Open Rocket the CP pretty much immediately moves forward at supersonic Mach numbers. Conservative, but probably not realistic.

When you make this plot using RASAero II, I think it pretty much nails this cross-over point where the supersonic CP moves forward of the Barrowman subsonic CP value.

So I'd propose that RASAero II now has the best supersonic CP prediction. But it was just released, people will need to gain more experience with it. And more data will follow in the future.


Chuck Rogers
Rogers Aeroscience
Very cool. Thanks.
 

Buckeye

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That was kind of my point. You have 4 altitude measurements, what's the actual altitude? Take the average, look at the variation from the average. Or throw out the integrated accelerometer data (although it's good to know how close it was, if on other flights that's the only data you have). The data's all there, and I note in the altitude comparison table which altitude I used as "the altitude" (the GPS altitude).

I think flights like this are great. 4 altitude measurements, 3 different types of altitude measurements, different brands of altimeters. The direct approach. Just fly them all on the same rocket on the same flight.


Chuck Rogers
Rogers Aeroscience
OK, you guys were looking at standard deviation. I was thinking more about range. My point was that the range of measurements is on par with the range of simulation mistakes.
 

markkoelsch

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I would throw out the accelerometer. It is not measuring altitude so much as distance traveled in route to apogee great for telling you acceleration and velocity though.
 

Chuck Rogers

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I would throw out the accelerometer. It is not measuring altitude so much as distance traveled in route to apogee great for telling you acceleration and velocity though.
I agree great for measuring acceleration and velocity. Generally I really prefer integrated accelerometer data for velocity and Mach number. Early in the flight, until some short to moderate time after burnout, this data is quite accurate. For altitude (apogee altitude), I prefer barometric altimeter data, and when available GPS data.

But I've done data reduction for a few very high altitude flights where GPS failed to get a lock and get apogee altitude data, and barometric altimeter data was unreliable (apogee was over 100K ft). All we were left with was integrated accelerometer data.

From the Ray Kinsel A-601 flight data it was reassuring to see that for a very straight-up flight the integrated accelerometer apogee altitude was only 5% off from the GPS apogee altitude. And just like as Mark noted, it was 5% higher (the distance the rocket traveled was 5% higher than the vertical distance from the ground).


Ray Kinsel A-601 Flight with a P4935 Motor:

GPS 42,771 ft
Adept 42,231 ft (barometric altitude)
ARTS II 40,113 ft (barometric altitude)
ARTS II 44,924 ft (integrated accelerometer altitude)

The rocket had a very vertical flight, and landed only 2 miles from the launch site.


Chuck Rogers
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alexzogh

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+1 for openrocket & RASAero II.

While I purchased rocksim many moons ago, the software itself has been stagnant. It's been seven years since they've had a major point release (2008!), and the minor point releases have been primarily around fixing bugs in the anti-piracy libraries it uses, or keeping compatibility with major operating system upgrades. This is a lifetime in the software world, especially the simulation software world. I can't even compare the version of solidworks I had in 2008 vs the version I use now.

The current graphics card I'm using is over %1000 times faster then the one I used in 2008. (http://gpu.userbenchmark.com/Compare/Nvidia-GeForce-GTX-280-vs-AMD-R9-Fury-X/m8413vs3498).

While openrocket isn't perfect, it's still alive, and continues to grow as a product. The fact that it's open source is a bonus - I don't have to wait if I want something to work differently (did a major change two years ago to get oddrocs to sim better)
 

Pat_B

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I agree with you on the RS upgrades. It is indeed a stagnant program, and many of the bugs have been around for many years. I don't get the impression that there's someone who actively does bug fixes. It seems like every few years they might sit down to correct some issues, but there doesn't seem to be ongoing support.

I've also noticed that some rocket designs and simulations get corrupted the longer they're around. Our kids use RS and have to rebuild some of their designs occasionally because bugs get introduced.

That being said, it is overall a decent program. I've never concerned myself too much with the cost of RS simply because the cost/year is very inexpensive.
 

markkoelsch

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I agree with you on the RS upgrades. It is indeed a stagnant program, and many of the bugs have been around for many years. I don't get the impression that there's someone who actively does bug fixes. It seems like every few years they might sit down to correct some issues, but there doesn't seem to be ongoing support.

I've also noticed that some rocket designs and simulations get corrupted the longer they're around. Our kids use RS and have to rebuild some of their designs occasionally because bugs get introduced.

That being said, it is overall a decent program. I've never concerned myself too much with the cost of RS simply because the cost/year is very inexpensive.
I would think of the files are being altered/damaged you should check your hard drive for errors.

I do like Rocksim, but agree that it is stagnant.
 

Buckeye

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+1 for openrocket & RASAero II.

While I purchased rocksim many moons ago, the software itself has been stagnant. It's been seven years since they've had a major point release (2008!), and the minor point releases have been primarily around fixing bugs in the anti-piracy libraries it uses, or keeping compatibility with major operating system upgrades. This is a lifetime in the software world, especially the simulation software world. I can't even compare the version of solidworks I had in 2008 vs the version I use now.

The current graphics card I'm using is over %1000 times faster then the one I used in 2008. (http://gpu.userbenchmark.com/Compare/Nvidia-GeForce-GTX-280-vs-AMD-R9-Fury-X/m8413vs3498).

While openrocket isn't perfect, it's still alive, and continues to grow as a product. The fact that it's open source is a bonus - I don't have to wait if I want something to work differently (did a major change two years ago to get oddrocs to sim better)
Wow. Good points. Kudos to you for making changes to suit your needs.

I used to be very skeptical/critical of Open Source, but it is now certainly showing its strengths. In my work, Open Source software is disrupting the business, but generally for the better.

In this case, the major hinderance to RS is probably the fact that the one and only developer has a day job, and thus RS hasn't moved the needle in several years. OR, on the other hand, is spread amongst many and continues to grow. Where one developer steps out, another can step in. The odds of OR completely falling by the wayside are much smaller.

Nothing is stopping OR guys from profiting from their hard work and commercializing the product while still adhering to the GNU GPL. I would be perfectly OK with that.
 

John Beans

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I agree great for measuring acceleration and velocity. Generally I really prefer integrated accelerometer data for velocity and Mach number. Early in the flight, until some short to moderate time after burnout, this data is quite accurate. For altitude (apogee altitude), I prefer barometric altimeter data, and when available GPS data.

But I've done data reduction for a few very high altitude flights where GPS failed to get a lock and get apogee altitude data, and barometric altimeter data was unreliable (apogee was over 100K ft). All we were left with was integrated accelerometer data.
Ditto Chuck's points. Before I could chime in he said everything I would have.
 

rharshberger

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I am so looking forward to the next version of OR, and I have been trying to get better at inputting and interpreting data from RASAEROII. Since these will be my two main sim programs for my L3 project, along with FinSim.
 

ksaves2

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Hmmmmmm, I put a latest version of WINE in Ubuntu and got the netframeworks loaded. Seems RAS Aero is firing up and I see it can read Rocksim files now? I'll have to work with thit. I had a block with the travails of having to draw everything into
RAS Aero in the past. Guess one doesn't have to to that anymore. This looks cool. Kurt Savegnago
 

ksaves2

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Well,

Played with RAS Aero last nite cold without reading the instructions. Got a sim to work. Downloaded the instructions today and look forward to reading them. I like I can input old rocksim files and get a blast out of watching the CP move
forward with increasing Mach with the slider at the bottom. Cripes, no wonder we get away with it. Had to really get moving out before the CP moved appreciably. Kurt Savegnago
 

rharshberger

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Now that I have RasAero II somewhat figured out its much easier to use than it originally appeared. It would be nice if the motor nozzle diameter was easy to locate.
 

ksaves2

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Now that I have RasAero II somewhat figured out its much easier to use than it originally appeared. It would be nice if the motor nozzle diameter was easy to locate.
Yeah, for the AT stuff you can get the info off of their website. For other stuff you're sorta stuck measuring it yourself. I believe the info needed is the exit diameter. Kurt
 

rharshberger

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Yeah, for the AT stuff you can get the info off of their website. For other stuff you're sorta stuck measuring it yourself. I believe the info needed is the exit diameter. Kurt
It is the exit diameter, the easiest way I have found to find the AT ones is the RCS website lists the single use nozzles which are the same as the ones in the reloads, just have to make sure in a couple of cases to chose the right nozzle.
 

Chuck Rogers

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So I'd propose that RASAero II now has the best supersonic CP prediction. But it was just released, people will need to gain more experience with it. And more data will follow in the future.
Updating this old thread with "and more data will follow in the future."

I believe that since 2015 RASAero II has had the most accurate Supersonic CP predictions of any of the high power rocketry software packages.

See the RASAero II CP prediction comparisons with Supersonic CP wind tunnel data for the ARCAS sounding rocket in the following Rocketry Forum thread. In particular note the accuracy of the RASAero II Supersonic CP predictions at Mach 3 and Mach 4.
http://www.rocketryforum.com/showthread.php?130843-RASAero-II-Comparisons-with-Supersonic-CP-and-CD-ARCAS-Wind-Tunnel-Data

and the CP shift with Mach number, including my recommendation for using 2.0 calibers stability margin for all Supersonic Mach numbers, in the following Rocketry Forum thread:
http://www.rocketryforum.com/showthread.php?130690-Affect-of-mach-on-CP

Running the RASAero II software versions since 2015, and using a minimum Supersonic stability margin of at least 2.0 calibers, many rocketeers have had no stability issues with their Mach 3, and over Mach 3 flights using RASAero II.

There was one flight that had high altitude coning above 100K ft, a Jim Jarvis flight, shown below, and even on that flight from on-board flight data RASAero II was very accurately predicting velocity and altitude until the coning started.


Charles E. (Chuck) Rogers
Rogers Aeroscience


The match between the simulation and the flight data for that flight was really good. All I did to fit the data was to adjust to the actual flight timing. On high altitude flights, a good simulation is essentially, and there's no question where I go to get that.

JimView attachment 429695
 

Buckeye

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I enjoyed re-reading this thread. Haha, my tune has changed over the past 5 years!

OR is now the stagnant software and it is my least used tool. The CP prediction is too conservative and atmosphere/elevation models are wonky.

I like RS for design and most models, switching to RAII for transonic and supersonic projects. High accuracy at M=4 is cool and all, but how many hobbyists are in that realm?

Thrustcurve is my most used tool, by far. I just need to pick a good motor, run a quick ballpark sim, fly the damn thing, and be happy. I rarely do detailed simulation anymore.
 

Chuck Rogers

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High accuracy at M=4 is cool and all, but how many hobbyists are in that realm?
Mach 4 to Mach 5 high power/amateur rockets are rare, but they have been flown.

The RRS 50 Statute Mile Boosted Dart Project reached Mach 4.2 in 1996. A High Power Rocketry Magazine tech article on the flight is on the RASAero web site ( www.rasaero.com ) on the

< High Power, TRA Research, Amateur, High Altitude Rocket Flights Technical Report Downloads > page.


The 2004 CSXT GoFast rocket reached an apogee altitude of 380,000 ft above sea level and a maximum Mach number of Mach 5.18, with a burnout Mach number of Mach 4.99. This was the first amateur rocket to reach space by exceeding the altitude of the Karman line (100 km, 328,000 ft), and was the first hypersonic (greater than Mach 5) high power/amateur rocket.


The 2004 CSXT GoFast rocket flight data was published here on The Rocketry Forum:

https://www.rocketryforum.com/threads/2004-csxt-gofast-flight-data.125609/


The 2014 GoFast II rocket reached 385K ft above sea level and Mach 5.4. If you’d like to see what it looks like being onboard a Mach 5 spinning sounding rocket, with a yo-yo de-spin system, reaching space, here’s the video.



Actually Mach 3 high power rockets, and high power rockets reaching just above Mach 3, are becoming more and more common.


A note on the ARCAS wind tunnel data is that the supersonic aero data was for Mach 1.5 to Mach 4.5, putting Mach 3 (the region currently of interest for high performance high power rockets) in the middle of the wind tunnel data Mach number range.


Charles E. (Chuck) Rogers
Rogers Aeroscience
 
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