Advice for first flight...

[rsbhunter]

You all have helped me so much, now I need a couple engines/ reloads. I have the Aerotech 29/40-120 hardware, but I don't know what to start with. I'm looking for 600-800 ft apogee, and don't mind using one time use motors for the first time. I have a Madcow DX3 2.6" rocket. I did add an Aerotech retainer, but everything else is as it came. I've got to admit I'm alittle nervous...it's a step up in $$$ if I screw up! Suggestions for starting motors that will get to 6-8 hundred feet, as I'm going to go to a 30" chute for the hardback ground we have here....Thanks for any advice, and I would Sim it if I had Rocksim, but that has to wait til next month or 2...rsbhunter

 

[Art Upton]

You all have helped me so much, now I need a couple engines/ reloads. I have the Aerotech 29/40-120 hardware, but I don't know what to start with. I'm looking for 600-800 ft apogee, and don't mind using one time use motors for the first time. I have a Madcow DX3 2.6" rocket. I did add an Aerotech retainer, but everything else is as it came. I've got to admit I'm alittle nervous...it's a step up in $$$ if I screw up! Suggestions for starting motors that will get to 6-8 hundred feet, as I'm going to go to a 30" chute for the hardback ground we have here....Thanks for any advice, and I would Sim it if I had Rocksim, but that has to wait til next month or 2...rsbhunter

OpenRocket IS FREE and the SIM for your Rocket is is probably already available pre-done. It will read RockSim files as well.

https://openrocket.info/

 

[Art Upton]

I downloaded a RockSim file and then saved it out as a OpenRocket File in OpenRocket.

But you need to make your rocket weight to make the sim work OK.
What does your full rocket with NO motor weight and I will rerun them?

 

[Art Upton]

^ that build seems lite with 446g weight. So we need to know how much yours weights.

 

[tsmith1315]

OpenRocket IS FREE

And awesome.

And it has tons of features, but most simple rockets like the DX3 can be done bare bones simple if you want a quick verification of stability and estimated altitude.

And there is tons of support here on TRF by many of the folks who donated their valuable time to make it happen.

Look here for more info:
https://www.rocketryforum.com/threa...t-23-09-is-now-available-for-download.183186/

 

[rsbhunter]

I downloaded a RockSim file and then saved it out as a OpenRocket File in OpenRocket.

But you need to make your rocket weight to make the sim work OK.
What does your full rocket with NO motor weight and I will rerun them?

View attachment 639039

I still have to do paint work..I appreciate the offer...I did download open rocket on my windows laptop, but could not find out how to import rocksim file from madcow, or open in open rocket...Thank you very much...rsbhunter

 

[tsmith1315]

I did download open rocket on my windows laptop, but could not find out how to import rocksim file from madcow, or open in open rocket

The file downloads from Madcow in a zip file:





You need to extract it. Just click on it and you can see what's in the zip file. Extract the .rkt file:





Now you have a .rkt file. OpenRocket will open those, but it defaults to looking for .ork files only.

Just select 'All Rocket Designs" in the "Files of Type" drop down box, and navigate to where you saved the extracted file:



After you've opened it, save it and OpenRocket will save it as an .ork file by default.

I've done that and attached it here. This design is unmodified otherwise.

 

[Art Upton]

I still have to do paint work..I appreciate the offer...I did download open rocket on my windows laptop, but could not find out how to import rocksim file from madcow, or open in open rocket...Thank you very much...rsbhunter

You Save the FIle to your hard drive. Launch Open Rocket and use open, it defaults to only list ORK files just like notepad defaults to list only TXT file. Change the drop down listing list ORK files and change to it "all files", it will show the downloaded files and then click on it to open.

Here is the ORK file I saved from doing the above with the SIMs I selected on motors you wanted to see.

 

[rsbhunter]

Thanks to all!!!! Using the download box in your posts, in opened in open rocket!! But, i have no clue HOW you got the ork. file? i downloaded JAVA, I tried everything i could to get the zip file from madcow to either ork, or upen rocket. None of my screens looked like your screen shots (but i appreciate the time and effort of you doing that). I go into my files, and it shows dx3.zip? Anyway, I now have it on open rocket, will it stay there? what do i have to do to keep it in OR? Thanks to all, this stuff was so much easier in the younger days.....rsbhunter

 

[neil_w]

Thanks to all!!!! Using the download box in your posts, in opened in open rocket!! But, i have no clue HOW you got the ork. file? i downloaded JAVA, I tried everything i could to get the zip file from madcow to either ork, or upen rocket. None of my screens looked like your screen shots (but i appreciate the time and effort of you doing that). I go into my files, and it shows dx3.zip? Anyway, I now have it on open rocket, will it stay there? what do i have to do to keep it in OR? Thanks to all, this stuff was so much easier in the younger days.....rsbhunter

1) You don't need to install Java if you use one of the installers from openrocket.info.
2) If you save the file as an ORK file (default), then it will open in OpenRocket thereafter (double-click the file to open it, or go into OpenRocket and then File->Open).

 

[tsmith1315]

I go into my files, and it shows dx3.zip?

Yes, the file from Madcow is inside a .zip file. That's usually done when there are multiple files to send at once. They are put into a single folder and compressed. The .zip extension tells you that. Not all manufacturers zip them, but most are in the Rocksim file format.

You can't open the zip folder from within OpenRocket, so you should do that outside of OpenRocket. Just navigate to the file, click it and you should be able to see what's in there. Highlight the file you want to get out of the zip folder and extract it. Follow the prompts to save it where you want it.

At that point, you can open dx3.rkt directly with OpenRocket. When you are ready to finish, just save it as an OpenRocket design. like Neil shows above.

 

[rsbhunter]

Forgive my ignorance, I read you can change a .zip file to an .ork file. Do I just change the .zip?. I hate not understanding something, and I can't grasp the .zip vs .ork and changing to .ork. But, I did find out a f35 engine on the dx3 simulation gives me the altitude I'm aiming for(if rocket is in madcow's file specs) Again, I will keep messing with it....Thanks to everyone who waded through my confusion. I s rocksim easier?

 

[Art Upton]

Forgive my ignorance, I read you can change a .zip file to an .ork file. Do I just change the .zip?. I hate not understanding something, and I can't grasp the .zip vs .ork and changing to .ork. But, I did find out a f35 engine on the dx3 simulation gives me the altitude I'm aiming for(if rocket is in madcow's file specs) Again, I will keep messing with it....Thanks to everyone who waded through my confusion. I s rocksim easier?

No , A zip file is a container of many files generally.

Forget about ZIP files.

Normally you get a RKT file on the internet searching for it. Like I did and found it on Rocket Reviews for the Mad cow.

Here there is a thread that contains hundreds of ORK files for rockets.

For now, you can just download the ORK file I posted here until you figure out how ZIP files work on computers. They have nothing to do with rockets, they are used to compress lots of files together.

Here it is again.

\

 

[David_Stack]

But, I did find out a f35 engine on the dx3 simulation gives me the altitude I'm aiming for(if rocket is in madcow's file specs)

Remember to update your file so that the weight of the rocket in the simulation is the actual weight of your finished rocket, then run your flight simulations.

 

[rsbhunter]

ok, i understand the zip file purpose. is there a way to go from rkt to ork. ? but for now, you guys have done more than help me, you saved my sanity..... THANK ALL OF YOU...rsbhunter

 

[neil_w]

Load the RKT file into OpenRocket, then save it as ORK file, as I described above.

 

[bjphoenix]

ok, i understand the zip file purpose. is there a way to go from rkt to ork. ? but for now, you guys have done more than help me, you saved my sanity..... THANK ALL OF YOU...rsbhunter

You can force openrocket to open a .rkt file, then do a "save as" and tell it to save in open rocket format. I do that frequently for my own use.

 

[smstachwick]

Here’s the instruction book from Madcow, with some estimated altitudes on common motors.

https://www.madcowrocketry.com/content/pdf/dx3.pdf

Since this is a heavy-ish rocket you’ll need a certain amount of initial thrust to get it moving. Those higher-thrust options really start appearing in the F range, which will push it slightly higher than you’re looking for.

However, I’d still recommend you build it (which it appears you did, I need to look more carefully), record a final weight/CG, and sim it on a bunch of motors to figure out if you can get enough thrust to get it off the rod safely but still stay in the altitude range you’re looking for. I know the AeroTech E28 reload is a bit of an overachiever off the rod for its class, that might be worth looking into. Aim for at least 30mph and deployment as close to optimal delay as possible.

I also wouldn’t worry about overshooting your altitude target slightly, just don’t be reckless with it. You don’t need to be peeking through 1400ft on a G80.

Note: I looked and looked and looked but I didn’t find the F20J (the “J” indicating Blackjack propellant) that’s recommended in the instructions. I thought it might be an out-of-production type but instead that appears to be an error. AeroTech makes an F20W with White Lightning propellant to this day, that’s likely what’s intended.

 

[rsbhunter]

Thanks, I ordered th Jolly Logic chute release. Being able to set chute opening at less than apogee will be a big help. I do have a Aerotech 29/40-120 engine casing and hardware. Do the one time use motors correlate to a reload for the Aerotech ? I know ow there's more to it, but it "seems if I keep the weight reasonable, that max thrust of 50-60 puts me in the altitude range to start. I will be messing with open rocket alot so I can adjust the parameters to be accurate for this rocket....again, I know it can be a pain to answer questions from recycled newbies, but is honestly appreciated.rsbhunter

 

[neil_w]

There are generally no exact equivalents between reloads and single-use motors. Some are offered one way, some the other, for whatever reason.

seems if I keep the weight reasonable, that max thrust of 50-60 puts me in the altitude range to start.

Presumably you mean “total impulse”, not thrust. Thrust is not highly correlated to altitude.

 

[Scott_650]

Lots of good info here - OR is a great tool, fun to play around with in its own right and perfect for fine tuning, but for simple 3/4FNC rockets Thrustcurve.org is surprisingly accurate and typically close enough for picking motors and delays.

Don’t be put off by motors that are in the “slow off guide” category - that value can be changed by the user, the default setting is very conservative so any motor with a thrust to weight close to 10:1 and a launch velocity close to 15 m/s will work in reasonably calm conditions.

The DX3 is fairly beefy so it’s going to be a challenge getting a motor with enough initial thrust that also keeps you under your goal - staying under approximately 1K feet is probably closer to reality and still pretty low, especially if you have plenty of recovery room.

 

[rsbhunter]

There are generally no exact equivalents between reloads and single-use motors. Some are offered one way, some the other, for whatever reason.

Presumably you mean “total impulse”, not thrust. Thrust is not highly correlated to altitude.

Yes, alot of new terms and abbreviations!!!!

 

[4regt4]

You might look at the F67W single use motor. It's "punchy" off the rod, but has less Ns (total impulse) than most other 29mm F motors. It sort of fits between the 24mm and 29mm F motors. I use them a lot for 1st flights.

Hans.