First Design After Coming Back to Rocketry

Hello,

I recently joined the forums after getting my itch back for Rocketry after a hiatus. I only at the time fly Low Power stuff (C Engines) and enjoy scratch builds. I downloaded Open Rocket and am wondering am I missing anything while designing my rockets? This is the first one I designed in it and not just putting parts together at a table. I know I'm missing my motor hook as I have no clue how to add it.

Any help or suggestions would be sweet!

Thanks.



View attachment First OR Design.ork

Some parts are not available currently, best you can do is add a mass object in the proper location to get the si correct. The are ways to add one visually but K'tesh has a whole thread on visual tricks with OR, like using phantom tubes, etc. However the visuals are not necessarily good for the sim, just the aesthetics.

For the motor hook, I add a mass object with a 2.75" length, 0.024" width, and a mass of 1.12g, with a radial distance slightly over half the tube O.D.

Just one of many ways

[EDIT] Oh, and make sure to take advantage of the parts database whenever possible. I didn't know about that for a long time. Makes designing so much easier and more practical

Yea I was happy to find the parts database. It does get a little confusing when trying to build bigger rockets as parts don't always work together even from the same manufacturer. displays the warning: Discontinuity in rocket body diameter.

I will be ordering the parts to build this one up hopefully within the week. Still not sure if I'm missing anything in the rockets design. my parachute might be a little big may drop it down to a 10" or 12"

Welcome back to the hobby!

That "Discontinuity in rocket body diameter warning seems to appear in many of my builds as well. I didn't get it when I opened your file, however.

Switching to a 12" plastic brings the decent rate to 15fps, which seems fine.

I saw you were running simulations with the Aerotech single use 18mm D motors. Those are fun! If you have never used them, be aware that the ignitors take more voltage/amperage to get them to light. A regular Estes controller won't do the job. I hook my system up to my car battery. Oh, and don't fly a light rocket with a D on a windy day. Ask me how I know

A discontinuity warning can be caused by any part whos diameter is slightly off from the one next to it. First place to check is Nose Cone O.D. to airframe . The NC might be 1.6" and the airframe 1.63" this can cause a discontinuity error, its usually somethinh small like that. I can also be a part thats internal like a parachute that if you set the packed diameter to large it protrudes through the airframe wall.

Sometimes checking off automatic wherever possible fixes the discontinuity message.

It happens often that for example, a nose cone OD set at 4.16 with body tube OD set at 4.16 will get the discontinuity warning, but checking Automatic for the diameter on the nose cone, nothing changes, but will no longer get the message. I don't know whats going on there, but it works.

It seems OR is finicky with things, I usually have to adjust/tweak a bit when converting from a Rocksim file just to not get the warning

Looks nice! I never worry about details like motor hooks other little particulars when simulating. It is an inexact science to begin with. Well, technically it is exact, but with far too many real life factors to know exact results.

So I plug in the real CG and weight, check for stability margins with my basic shapes, and look for rough values on apogee and ideal delay. Sometimes I will go back and readjust, but mostly I make a mental note of "this rocket slightly overperforms sims" or "that rocket flys a good bit lower than the computer says" instead.

Now you should build it!