Bogus sim files posted online - why?

[SolarYellow]

I finally started paying attention to Quest and AeroTech kits. I went to RocketReviews and downloaded the .ork files there for the Novia and Icarus. Both of them have such obvious errors that I have to assume the files overall are complete garbage. For the name of the rocket inside the file I have "HOT MESS - DO NOT USE THIS FILE."

Novia:

• The .ork file lacks the steel motor retaining clip.
• Body tube ID/OD don't match Quest specs.
• It shows a 300mm ripstop nylon parachute instead of a 1- or 1-1/4-inch wide streamer.
• The fins are sorta shaped like the kit, but it appears it may be a "looks like the picture" situation compared to the photo of the fin sheet in Hobbylinc's reviews.

Icarus:

• Quest catalog recommends 24mm motors. This file has an 18mm motor mount.
• Quest catalog indicates dual 14-in chutes. This file has dual 12-in chutes. Note organization; one assigned to each tube while they are represented as both being in the lower tube below the coupler & bulkhead.

ETA: It turns out Quest has apparently change specs along the way. K'Tesh also simmed the Icarus https://www.rocketryforum.com/threads/kteshs-openrocket-files.123564/page-15#post-1817690 based on an older kit and it also has the 18mm mount and 12-in chutes. The weights are significantly different, and of course K'Tesh has a lot more attention to detail. Mostly, the rant can be about the Novia file, I guess.

I've heard about .ork and .rkt files having errors, but this is silly. It's like the Chinese 3D models of stuff that get posted online that are wildly inaccurate, made by just looking at a bunch of photos of the real thing downloaded from online. But for that, they creators can make money, so I get it. Nobody makes any money by posting stuff on RocketReviews.com. Why would someone even bother to put together completely bogus files and load them on the site?

The very first OR file I made, I made by opening the Hi-Flier bag and sitting at my desk with a Mitutoyo caliper and electronic gram scale as I measured each part. @K'Tesh has a wonderful OCD with his practices that we all benefit from. Making a file that isn't accurate is such a waste of time, for both the person who does it and the person who happens to download it.

 

[Tractionengines]

My files are always " adjusted" to match "my" build. If I post them they are a "jumping off point" for someone else...
If a file comes from "the" manufacturer, then it should be correct. But even they often have issues, because of model or material changes that occur over time, and the files don't get updated.

 

[Starfire73]

I think poor quality is probably a more accurate description than "bogus."

Could be any number of reasons:

• Nobody is vetting the files, they are available on the various sites as-is.
• Age of the contributor (could be a 12 year old, who knows?).
• Knowledge and experience of the contributor.
• The contributor's natural attention to detail.
• Did the contributor make mods? If so, did they indicate that they did?
• In minor cases - simple human error.

I do feel your pain though, that's why if it's a file I've created, reversed engineered, or at least thoroughly inspected for accuracy; I clearly note that for my own benefit in the file name or comments. I want to know if I've created the file, or at least if it has passed my inspection.

 

[Tractionengines]

From your examples. (Not manufacturer supplied)

Having a rocket that completely separates in the middle, with each part recovering under its own parachute; would have 2 chutes in the same compartment, but referenced to each section.

Changing chute by a size or two, or from small chute to streamer or vice-versa; is just matching it to your flying site. Removing a motor hook may be for friction fit, or adding a retainer (hopefully adding a mass object for retainer.)

Please use any Open Rocket or Rocksim file as a starting point. Only used as gospel AFTER you have personally verified everything.

 

[Tractionengines]

If you want super accurate sim files (still verify, weights, etc) see @K'Tesh files here. K'Tesh takes "great pains" to make them as absolutely correct as possible.

Thread 'K'Tesh's OpenRocket Files Index' https://www.rocketryforum.com/threads/kteshs-openrocket-files-index.148212/

 

[SolarYellow]

Cool, he does have an Icarus! I haven't seen many Quest sims from Jim, so it wasn't the first place I looked. Will play around with that. Already, I see there are a few similarities to the one I found on RocketReviews that don't match current specs, so I'll go back and soften my criticism of Mr. Schultz.

I figured it's implied by my first post, but of course, I don't expect a sim to be right until it actually matches the rocket. I usually have a "generic/standard" version of the file and one with "as-built" appended to the end that includes the paint and glue weights, etc. I build (and paint) with calipers and gram and milligram scales to track where the weight goes. My as-built sims done part-by-part generally match the finished rocket within a fraction of a gram and c.g. within a couple mm.

In the case of the Icarus, my plans include a different fin can and a 29mm motor mount for G64 (maybe G80) awesomeness, so I definitely won't be using Jim's file without checking everything.

 

[ThirstyBarbarian]

RocketReviews is just rocketeers uploading reviews, sims, and other info. It’s not quality checked by anyone.

Also, sim files are used by different people in different ways for different purposes. Some people want to know what the rocket will look like, some want to know the exact size and mass of every component, and some want to do flight simulations.

I’m in the last group, so all I really care about is that the outside profile of the rocket is accurate so that the CP and drag will be accurate, and the final mass and CG overrides for the rocket as a whole match my measurements of my own rocket as built. So for me, I don’t care about the masses of components or even if all the internal components are even included in the file. If the kit has an internal coupler joining two tubes to make a long tube, I don’t care if that’s in the file as long as the overall length of the long tube is accurate. I don‘t care if the centering rings’ weights are accurate or even if centering rings are left out of the file — I’m going to do a mass override for the completed rocket anyway. Retainers don’t affect flight, so I don’t care if they are included in the file. I don’t care if the nosecone shoulder is the right length as long as the outer profile of the cone is correct.

I’ve downloaded from RocketReviews before, and if all I want it for is flight sims, my process is to check the lengths and diameters of external body tubes and motor tubes, check the nosecone and fins for accurate shape, size, and placement (ignoring shoulders and fin tabs). Then I weigh and balance my own completed rocket and enter the mass and CG of my rocket into the file’s overrides. That’s all I need.

Of course some people use the files as an aid to actually building the rocket or for making clones, upscales, and modifications. Then you want a file with accurate components. That’s a different use case.

And then some people like using sim files to make accurate renders of the look of their rockets. I would say K’Tesh likes to do that. He’s making an art form. So sometimes he uses hacks and workarounds with non-functional components, or zero-mass phantom fins, or whatever the case may be to try to simulate the look of a motor hook or the painted livery on a fin or other aspect of the look of a rocket that isn’t fully supported by OpenRocket. That’s fine for that purpose, but I find those kinds of files to be a problem for flight sims, so I can’t use them for my purpose.

Anyway, those are some of the reasons the files you download for free from da interwebz might not suit your needs.

Probably the best thing for you to do is the either start with a downloaded file or start one from scratch, modify or make it as useful as possible for your purposes, then upload it to RocketReviews yourself with a review and commentary on your sim file philosophy and methodology.

 

[K'Tesh]

The very first OR file I made, I made by opening the Hi-Flier bag and sitting at my desk with a Mitutoyo caliper and electronic gram scale as I measured each part. @K'Tesh has a wonderful OCD with his practices that we all benefit from. Making a file that isn't accurate is such a waste of time, for both the person who does it and the person who happens to download it.

If you want super accurate sim files (still verify, weights, etc) see @K'Tesh files here. K'Tesh takes "great pains" to make them as absolutely correct as possible.

Thread 'K'Tesh's OpenRocket Files Index' https://www.rocketryforum.com/threads/kteshs-openrocket-files-index.148212/

Thanks for the kind words!

And then some people like using sim files to make accurate renders of the look of their rockets. I would say K’Tesh likes to do that. He’s making an art form. So sometimes he uses hacks and workarounds with non-functional components, or zero-mass phantom fins, or whatever the case may be to try to simulate the look of a motor hook or the painted livery on a fin or other aspect of the look of a rocket that isn’t fully supported by OpenRocket. That’s fine for that purpose, but I find those kinds of files to be a problem for flight sims, so I can’t use them for my purpose.

That said, OR is increasingly becoming capable of handling my hacks, and I'm working on folding in the fixes to make the sims more useful for flight data. I also try to be up front about what is and isn't capable of giving flight info, and made the "air fins" easy to find and delete.

 

[ThirstyBarbarian]

That said, OR is increasingly becoming capable of handling my hacks, and I'm working on folding in the fixes to make the sims more useful for flight data. I also try to be up front about what is and isn't capable of giving flight info, and made the "air fins" easy to find and delete.

Agreed. OR as getting better at that, and I know you are going back to some previous versions of your files and modifying them to take advantage of newer versions of OR. And you’ve always been upfront about the purpose of your files.

My main point is that people use OR for many different purposes, and one person’s use case might require a file that is not as useful for another person‘s.

 

[Scott_650]

RocketReviews is just rocketeers uploading reviews, sims, and other info. It’s not quality checked by anyone.

Also, sim files are used by different people in different ways for different purposes. Some people want to know what the rocket will look like, some want to know the exact size and mass of every component, and some want to do flight simulations.

I’m in the last group, so all I really care about is that the outside profile of the rocket is accurate so that the CP and drag will be accurate, and the final mass and CG overrides for the rocket as a whole match my measurements of my own rocket as built. So for me, I don’t care about the masses of components or even if all the internal components are even included in the file. If the kit has an internal coupler joining two tubes to make a long tube, I don’t care if that’s in the file as long as the overall length of the long tube is accurate. I don‘t care if the centering rings’ weights are accurate or even if centering rings are left out of the file — I’m going to do a mass override for the completed rocket anyway. Retainers don’t affect flight, so I don’t care if they are included in the file. I don’t care if the nosecone shoulder is the right length as long as the outer profile of the cone is correct.

One thing I keep meaning to explore but haven’t yet is to compare flight sims from OR to the results from Thrustcurve and check them against my own altimeter readings for straightforward 3/4FNC rockets - anyone else taken a leap down that rabbit hole?

 

[ThirstyBarbarian]

One thing I keep meaning to explore but haven’t yet is to compare flight sims from OR to the results from Thrustcurve and check them against my own altimeter readings for straightforward 3/4FNC rockets - anyone else taken a leap down that rabbit hole?

A long time ago I used an Altimeter 2 to check my OR sims. You can compare the altitudes and things like velocity. I could determine how close the delays were to apogee, too. It was kind of interesting, but I didn’t do much more with that.

I know someone who has used Rocksim, which I’ve never used, and apparently it has settings for surface roughness or drag of some kind that can be used to refine your flight sims. If you have an accurate sim file in terms of dimensions, mass, and Cg, you can record a flight on your altimeter, compare it to projected altitude in your sim, and then adjust the drag. If the rocket doesn’t achieve the projected altitude, add more drag to the sim and try again. He said you can really dial in your sims that way if you do it several times. You can also compare descent velocities and refine your chute Cg.

 

[Tractionengines]

Just as an FYI...In the new version of open rocket you can override CD as well.

 

[caveduck]

I've reviewed a number of the OR sim files found online. Most of the ones from certain manufacturers are terrible, often having a global mass and CG override applied at the end, which prevents you from easily modifying any of the components to see how it affects things. Some even had noticeable dimensional errors that affect the stability margin. To make them useful, you have to remove the overrides and make all the component masses correct.

K'tesh makes great ones but you must remember they are optimized for cosmetic fidelity rather than aerodynamic simulation accuracy. They are a fantastic starting point because the dimensions are going to be spot on.

Some very good sim files can be found linked in the old L3 documentation thread, which sadly has gone fairly inactive. But of course they are all for a certain general class of vehicle.

It is possible to get really good predictions. For my L3 (a Madcow Tembo 5.5), I had the liftoff mass within +/- 10 grams out of 15kg, and the predictions came out within 100ft of the eventual 8450' altitude.

Some things you should take note of if you're pursuing accuracy:

* For larger rockets, you'll need a glue allowance mass object to account for the 20-100gm of epoxy that holds the fin can together.
* Don't forget the motor retainer cap and rail guides
* If you use a tailcone retainer, you *must* enter it as a transition. The reduced base drag causes substantially higher altitude and also *reduces* stability margin.
* Be sure to model the parachute and shock lines in HPR rockets in the aft-most possible position in the tubes. That's where they're going to be after experiencing 10+ g's of acceleration to the rear.
* As you build, weigh and measure all the parts. Balsa and fiberglass can have significant weight variance from the "standard" database values. Same for TARC foam egg protectors.
* OpenRocket by default gives you 2 mph winds at liftoff, with vertical launch. That always results in a prediction a bit less than the maximum, and also makes the apogee a function of the launch guidance length and stability margin, since higher exit velocity and lower stability margin result in less weathercocking.

 

[cls]

Honestly, I've found it's faster for me to start from scratch than debug somebody's wrong sim. Nearly all of them on RR have something wrong, tubes, nose, length, fins, tabs...

 

[Dane Ronnow]

Honestly, I've found it's faster for me to start from scratch than debug somebody's wrong sim.

Same here. Clean slate, everything's yours. No surprises.

 

[JoePfeiffer]

One note on .ork files missing motor hooks (as mentioned at the beginning of the thread) -- some things really are too small to care about, and motor hooks are a good example. They make no difference aerodynamically, and miniscule weight. K'Tesh's brilliant hack abusing a fin to look like a motor hook makes appearance more realistic, but that's it.

 

[bad_idea]

Honestly, I've found it's faster for me to start from scratch than debug somebody's wrong sim. Nearly all of them on RR have something wrong, tubes, nose, length, fins, tabs...

Agreed. The one thing I've valued most from anyone else's sims is @K'Tesh 's DBRM nosecone hack, using the hemispherical tip as the cone, then building an ogive transition behind it. I wouldn't have gone to that trouble, but I suspect that OpenRocket appreciates the authenticity of his solution.

 

[K'Tesh]

One note on .ork files missing motor hooks (as mentioned at the beginning of the thread) -- some things really are too small to care about, and motor hooks are a good example. They make no difference aerodynamically, and miniscule weight. K'Tesh's brilliant hack abusing a fin to look like a motor hook makes appearance more realistic, but that's it.

Dude... I'm blushing...

It's my understanding that freeform Mass Objects will be included in a future release of OR. That will allow the engine hook to be removed from the aerodynamic calculation, as well as allowing OR to model things like AV Bay sleds.

Agreed. The one thing I've valued most from anyone else's sims is @K'Tesh 's DBRM nosecone hack, using the hemispherical tip as the cone, then building an ogive transition behind it. I wouldn't have gone to that trouble, but I suspect that OpenRocket appreciates the authenticity of his solution.

While I appreciate the shoutout, I can't take credit for that hack... Credit for that goes to Carl McLawthorn's sim of the Semroc Omega KV-64.

 

[neil_w]

Interesting thread.

Please use any Open Rocket or Rocksim file as a starting point. Only used as gospel AFTER you have personally verified everything.

Yes yes, a thousand times yes.

I do feel your pain though, that's why if it's a file I've created, reversed engineered, or at least thoroughly inspected for accuracy; I clearly note that for my own benefit in the file name or comments. I want to know if I've created the file, or at least if it has passed my inspection.

There are many, many places to embed useful information in an OR model. Component names, Rocket notes, comments on components… very useful for future reference, sadly underused in my experience.

I know someone who has used Rocksim, which I’ve never used, and apparently it has settings for surface roughness or drag of some kind that can be used to refine your flight sims.

Same thing in OR, although I think it’s easier now to just tweak the Cd override of the whole rocket.

I've reviewed a number of the OR sim files found online. Most of the ones from certain manufacturers are terrible, often having a global mass and CG override applied at the end, which prevents you from easily modifying any of the components to see how it affects things.

I don’t think this is a fair criticism of the manufacturer files. Accounting for adhesive and finishing weight is a bit off a black art, and it is standard practice to correct for that by overriding the completed rocket.

Rather, I think the criticism is more accurately directed at the application, which simply doesn’t provide any good facilities for dealing with this situation. I’m hoping we can come up with a decent solution in OR one of these days.

 

[JoePfeiffer]

It's my understanding that freeform Mass Objects will be included in a future release of OR. That will allow the engine hook to be removed from the aerodynamic calculation, as well as allowing OR to model things like AV Bay sleds.T

That's sort of aspirational. We'd like to, but we really don't know how to go about it and there are other things of higher priority.

 

[SolarYellow]

I don’t think this is a fair criticism of the manufacturer files. Accounting for adhesive and finishing weight is a bit off a black art, and it is standard practice to correct for that by overriding the completed rocket.

I'm kind of OCD, and as I mentioned earlier, I build with a gram (or milligram) scale. My last build, I weighed components and assemblies before and after gluing, so I could assign a mass object to each glue element and locate it appropriately in the rocket. I do the same with paint and with model airplane iron-on covering.

I do wish OR would accept another significant figure in the mass of components in grams. Don't need milligrams, but hundredths would be nice when getting detailed about things like shock cords, etc.

I know most people don't have better than 0.1 gram resolution on a digital scale, if that, but some of us do.

 

[Back_at_it]

Most SIM files out there need some type of tweaking. The files I have found even on some manufactures sites aren't very accurate. I'm not concerned with things like missing motor clips, streamers vs parachutes etc. I'm more concerned when I see something that is obviously wrong.

I've downloaded files where you can look at the rocket and know there is something wrong. For instance, I'm seeing a lot of files for the Blue Sapphire floating around that are just plan wrong. Someone posted one that showed the weight was over 5oz and the CP and CG were only an an half inch apart. Their file had the fins made of 3/16" plywood with plywood rings. The fin shape wasn't even close and the tube as too short. This was someone that claimed to have the rocket in their hands when they made the file.

If I'd take a few minutes and learn how to upload fines from a PDF my life would be easier but until then, I normally find something online then tweak everything to fit my build. I almost never build anything stock.

 

[K'Tesh]

Most SIM files out there need some type of tweaking. The files I have found even on some manufactures sites aren't very accurate. I'm not concerned with things like missing motor clips, streamers vs parachutes etc. I'm more concerned when I see something that is obviously wrong.

I've downloaded files where you can look at the rocket and know there is something wrong. For instance, I'm seeing a lot of files for the Blue Sapphire floating around that are just plan wrong. Someone posted one that showed the weight was over 5oz and the CP and CG were only an an half inch apart. Their file had the fins made of 3/16" plywood with plywood rings. The fin shape wasn't even close and the tube as too short. This was someone that claimed to have the rocket in their hands when they made the file.

If I'd take a few minutes and learn how to upload fines from a PDF my life would be easier but until then, I normally find something online then tweak everything to fit my build. I almost never build anything stock.

I'm polishing the Blue Sapphire file right now...

 

[Back_at_it]

I'm polishing the Blue Sapphire file right now...

Awesome. The ones that are posted here on this fourm are pretty accurate but go to Facebook and the quality is all over the place.

 

[K'Tesh]

It's posted now...

 

[ThirstyBarbarian]

It definitely seems like manufacturers could do a better job of accurately measuring and weighing their components, making sim files for their rockets that match the builds accurately, and weighing and balancing finished rockets so they can add a mass object for glue and position it the bring the Cg in line with the measured Cg.

I feel like some manufacturers that I really like don’t even bother to build and weigh their rockets, let alone make a good sim file. Weights shown on the packaging and marketing materials don’t even match the weight of the raw parts in the bag sometimes. LOC is an example. I like their kits but they don’t know how much their rockets weigh. The weight on a Mini Mag bag is something like a pound less than the parts in the bag. They don’t get lighter as you build them.

 

[jqavins]

From your examples. (Not manufacturer supplied)

Having a rocket that completely separates in the middle, with each part recovering under its own parachute; would have 2 chutes in the same compartment, but referenced to each section.

Changing chute by a size or two, or from small chute to streamer or vice-versa; is just matching it to your flying site. Removing a motor hook may be for friction fit, or adding a retainer (hopefully adding a mass object for retainer.)

Please use any Open Rocket or Rocksim file as a starting point. Only used as gospel AFTER you have personally verified everything.

I disagree. Files uploaded as ORK or RS files for this or that model should be exactly stock as near as reasonably possible, unless explicitly noted otherwise. The modifications you've noted are perfectly reasonable modifications, but please don't post them as (in this case) Novia.ork. Post them as Novia_modified.ork or some such.

I had a similar experience, looking for an RS file for the Quest Terrier-Orion, and I found one on Rocket Reviews. It was posted on a page all about the model - build experience, flying experience, dimensions, etc. - but the RS file had the Terrier MMT increased in size from 18 to 24 mm, and had a 24 mm motor in the Orion section where the model as made by Quest is single stage. It purported to be a file for the Quest kit, and that was basically a lie. I thought I was downloading a Quest Terrier-Orion, and what I got was useless to me.

I rarely use Rocket Reviews, and this is a large part of why.

 

[jqavins]

They don’t get lighter as you build them.

Well, if you sand them a lot...

That's one of the good things about Apogee: you can really expect the RS files for their kits to be spot on, within reasonable tolerance (since there's no accounting for glue and paint mass, the builder's finishing skill and motivation, etc.).

 

[SolarYellow]

It would be a neat gesture for Apogee to include mass elements for glue and paint with "typical" values based on their own builds as a reminder to users of the files that those are things and need to be accounted for.

 

[Ez2cDave]

Honestly, I've found it's faster for me to start from scratch than debug somebody's wrong sim. Nearly all of them on RR have something wrong, tubes, nose, length, fins, tabs...

Same here. Clean slate, everything's yours. No surprises.

Ditch the sims, altogether, and go "old school" . . . Do your own math / calculations and verify stability.

Frankly, I see so much reliance on "sims", nowadays, that a rocket, built from "sim files", amounts to little more than an "electronic kit" ( I hate kits ) . . .

Use your brain and don't "rely on the tech" !

Dave F.