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Let's settle this? RockSim vs OpenRocket vs RASAero

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sundevilEP

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Hello all,

Would love a down and dirty clarification on when (and why) to use certain softwares for different designs. In attempting to design a rather unorthodox 54mm MD for an altitude competition we have run into numerous different opinions on the "best" simulation software for various situations. So, I will ask the community:

What's the best software for Mach+ designs? Why? Subsonic?
What software is more reliable for stability calculations? Why?

I've skimmed the forums but haven't found a collective thread on what to use, when, and why.

Appreciate any help!

Evan
 

mkadams001

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Any and all sim softwares are welcome... I haven't heard or used most of them, but whatever works! Any experience with MindSim?
Yes, I use MindSim every day. It's good for more than just rockets too.
 

rstaff3

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I just MindSimmed the discussion that may arise after the general populace chimes in on the originally listed programs. LOL

I am a RockSim user. It was far superior to OpenRocket in all ways when first introduced, as OR didn't exist. For a long time it was superior in every way but price. Now, I have to defer to those who actually use OpenRocket. I am still a diehard RockSim guy up until the next release and the attendant cost, at which time I may switch too.
 

AlphaHybrids

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I use OpenRocket to start, then switch to RASAero. I'm within 2% on RASAero when I nail down my inputs. These are minimum diameter flights over 25k.

Edward
 

Pat_B

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I've never used OR, but saw a post somewhere where someone was talking about it not having the feature to enter a custom drag coefficient. If that's true, then it makes it much more difficult to fine tune the software to the actual flight results.
 

samb

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Help! Where is MindSim?
Mindsim is the software that most people run on the hardware between the ears. :)


The real Jedi Masters just look at a drawing or pickup a model and go: "Yep, that's about right" or "Needs a couple ounces in the nose".
 
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Chuck Rogers

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From the RASAero web site, here are some comparisons with altitude data:

http://www.rasaero.com/comparisons-alt.htm

Average error 3.38%. These comparisons include some very high altitude, high Mach rockets. (40K to 120K ft, up to and over Mach 3.)


Comparisons with in-flight measured drag coefficient (CD) data (see the two Violent Agreement flights):

http://www.rasaero.com/comparisons-flight.htm


All of the above comparisons were run with RASAero Version 1.0.2.0. They are being re-run with the new RASAero II (available as a free download) for future updates to the web site.


Chuck Rogers
Rogers Aeroscience
 

rstaff3

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Just a random question. I know the baro sensors can be very accurate, but how accurate/variable is the pressure model of the atmosphere?
 

Chuck Rogers

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Just a random question. I know the baro sensors can be very accurate, but how accurate/variable is the pressure model of the atmosphere?

Interestingly, some of the rockets in the altitude prediction comparison table on the RASAero web site carried multiple altimeter types. The notes at the bottom of the table detail some of those, but one interesting example is:


Ray Kinsel A-601 Flight with a P4935 Motor:

Note 5: Altitude based on GPS data. Rocket also carried two barometric altimeters and an accelerometer. Altitudes from the different onboard instrumentation were the following:

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.


So this flight had GPS, two different barometric altimeters, and an integrated accelerometer. You can see the different altitudes (all very close) above.


Chuck Rogers
Rogers Aeroscience
 

Buckeye

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Hello all,

Would love a down and dirty clarification on when (and why) to use certain softwares for different designs. In attempting to design a rather unorthodox 54mm MD for an altitude competition we have run into numerous different opinions on the "best" simulation software for various situations. So, I will ask the community:

What's the best software for Mach+ designs? Why? Subsonic?
What software is more reliable for stability calculations? Why?

I've skimmed the forums but haven't found a collective thread on what to use, when, and why.

Appreciate any help!

Evan
The key to your question is the word "unorthodox." Please explain.
 

Pat_B

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Just remember that some of the sim programs are mostly used for stability purposes. They get you closer to altitude once you've done some flights and backed in the cd.

On the other hand, when you are doing initial design work for performance and want to look at minimizing drag based upon your design changes, you'll need more of a CFD type program.
 

mpitfield

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The right answer is all of the above.
+1. I run all three. I own RS and use OR and RASAero as well.

RS is great for below Mach flights and fairly accurate, however the faster you go the more it seems to be off. There are several threads on the forum as to why, which of course I cannot find or remember well enough to regurgitate. RS is also not free so if you want to use if beyond the trail period then you need to purchase it from Apogee.

OR is much more accurate on flights over Mach, qualify that I have only been to Mach 1.89, so I cannot comment on anything over M2. OR is open source and free and the guys who develop it are very accessible. I have spoken to them on several occasions and they are genuinely concerned with how the program works. There are also a bunch of users on the forum who can do some neat things in OR, I believe K'Tesh is one of them and he has published how to threads. At least I think it was him so forgive me if it is not.

RASAero is a very no frills basic simulator but it is accurate and I use it to validate OR results. Not to say that is what it is limited to but that is how I currently use it with my limited knowledge. I have also read, but cannot say otherwise, that it is a reliable tool for high velocity launches M3 and above. However unlike RS which will run on both Windows and Mac, as well as OR, whihc is Java based so again Windows and Mac, RASAero only runs on Windows.
 

rstaff3

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Interestingly, some of the rockets in the altitude prediction comparison table on the RASAero web site carried multiple altimeter types. The notes at the bottom of the table detail some of those, but one interesting example is:


Ray Kinsel A-601 Flight with a P4935 Motor:

Note 5: Altitude based on GPS data. Rocket also carried two barometric altimeters and an accelerometer. Altitudes from the different onboard instrumentation were the following:

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.


So this flight had GPS, two different barometric altimeters, and an integrated accelerometer. You can see the different altitudes (all very close) above.


Chuck Rogers
Rogers Aeroscience
Thanks. GPS gives a good data point to compare to.
 

sundevilEP

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The key to your question is the word "unorthodox." Please explain.
A 54mm with transitions pieces down to 29mm. RockSim stability and attitude simulations are encouraging. OpenRocket hates it and RASAero seems to land between the two. Max speed is Mach 1.7 with a K300.

That being said, we are leaning towards a more conventional design that eliminates potential stability and construction issues.
 

scsager

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I was not impressed with the copy protection junk that was left on my computer by a "trial" installation of Rocsim a few years back.

I have OpenRocket installed on my desktop machine, and the laptop I bring to the launch site.

I also have the Android version on my tablet, and my phone.

There is no android or iPhone version of Rocksim.

Cost is the single biggest difference between Rocksim and OpenRocket. You can design all kinds of cool rockets with Rocksim. OpenRocket will do the same... plus you will have enough money left over to actually buy the parts and build them.

I saved myself about $250 by using OpenRocket. I'm completely satisfied with it.
 

Zebedee

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I use OR - it seems to be pretty accurate as long as I am realistic with what I set my component finish to (hint it's usually not polished).
 

Buckeye

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A 54mm with transitions pieces down to 29mm. RockSim stability and attitude simulations are encouraging. OpenRocket hates it and RASAero seems to land between the two. Max speed is Mach 1.7 with a K300.

That being said, we are leaning towards a more conventional design that eliminates potential stability and construction issues.
OK then. My opinion:

Drag:

1. RA (Best for supersonic, but flight sims are a pain because you need to manually add motor mass and CG)
2. OR
3. RS (poor transonic and supersonic)

Cp:

1. RS (Barrowman and Rocksim methods available. Allows for more complicated geometry.)
2. OR (More conservative with wind in the simulation)
3. RA (Heard complaints about stability. Fixes implemented in RA II, but may be too soon to tell.)

So, overall, I find myself using OR most of the time as a happy medium.

Also, you forgot Thrustcurve to batch simulate many motors for quick filtering. Then fine tune in one of the above software.
 

Buckeye

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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)

Chuck Rogers
Rogers Aeroscience
Excellent data comparison. Well, they are not that close, really. There is a 12% discrepancy in the measurements. Other than motor thrust files and firings which can vary wildly, 12% is greater than the usual variation that people screw up in their simulation inputs, like mass, Cd, and weather. See also Peak of Flight articles issues #240, #242, #257 which explain how altimeters work and their 10% calibration errors. So, many times simulations are more consistent and "better" than the test data.
 

les

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There is a 12% discrepancy in the measurements. Other than motor thrust files and firings which can vary wildly, 12% is greater than the usual variation that people screw up in their simulation inputs, like mass, Cd, and weather.
Depends on how you look at it. Taking the average of the 4 measurements, the differences are +/- 5.7%.
 

BayouRat

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I use RockSim the most. For the flight envelope we fly in it seems to give me the most accurate flight simulations. I used it for all the Tiki Bar Rocket simulations. For such an odd rocket it was surprisingly accurate. The fact that I've been using it for 15 years is a plus. I know how to dial in my designs to get the most accuracy from the simulation.

I've used RAS Aero as a secondary sim. for high speed, high altitude rockets. It's a bit more complicated to get right. It's much harder to enter any complex designs. But great at aerodynamic drag coefficients in the supersonic realm.

I don't use Open Rocket. I do like the drawings and the final rocket painted pictures. So I like the graphics. I tried to use it but always fall back to RockSim because I have it tweaked and I know how do waht I want to do.

So I would rank them

1st Place RockSim
2nd Place RAS Aero
3rd Place Open Rocket
 

wighty44

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Just wondering how "easy" it is to import a RockSim RKT file into Open Rocket?
 

Samuron

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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.

Just wondering how "easy" it is to import a RockSim RKT file into Open Rocket?
Really easy, for conventional configurations, but if you have pods like on a Trident or Vega, it doesn't accept them.
 
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mlrtime99

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Slightly on topic - I'm hoping to buy a 4" 5:1 VK nosecone this weekend but was surprised when OpenRocket said this would reduce my altitude ~7000ft compared to the current 4" 5:1 Ogive. As I understood it, the Ogive is a very good all-rounder but the VK nosecone should be much more efficient above mach (where this rocket spends 75% of its time).

Is the ogive really the ideal shape or is this one of those cases where I should pay attention to the "simulation may be inaccurate above supersonic speeds".
 

markkoelsch

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Slightly on topic - I'm hoping to buy a 4" 5:1 VK nosecone this weekend but was surprised when OpenRocket said this would reduce my altitude ~7000ft compared to the current 4" 5:1 Ogive. As I understood it, the Ogive is a very good all-rounder but the VK nosecone should be much more efficient above mach (where this rocket spends 75% of its time).

Is the ogive really the ideal shape or is this one of those cases where I should pay attention to the "simulation may be inaccurate above supersonic speeds".
In Rocksim, the performance of a nosecone is based on the area. I did some testing of real world versus sim. To cut to the chase, when Simming the VK nosecone in Rocksim use a conical nosecone of the same length and weight- this will get you close.
 

mlrtime99

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OpenRocket definitely understands VK nosecones

nose.png

I'm just surprised that a 4:1 Ogive nets so much more maximum altitude than this 5:1 VK
 

Chuck Rogers

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Cp:

3. RA (Heard complaints about stability. Fixes implemented in RA II, but may be too soon to tell.)
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
 
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