Critique?

[YodaMcFly]

So, as a learning experiment, I created an OpenRocket file for a 29mm-powered, sport scale Hawk Motor test vehicle (proof of concept for the Orion sounding rocket), based on Peter Alway's drawings (either from the Kitbash booklet, or one of the RotW supplements, I don't remember which).

So, what I'm hoping for is that one or more of you gurus could tell me what I did wrong, what (if anything) I did right, etc ... This is basically my first "serious" project in OR.

Thanks
Adrien

View attachment Hawk_Test_29.ork

 

[K'Tesh]

I'll download it when I can (I've got a couple of classes in a few minutes), and for some reason, I can't seem to download anything at this moment. I'm hoping a reboot will solve that problem.

 

[K'Tesh]

Ok... rebooted, and downloaded a copy of it. Those fins seem really thick for a rocket this small. As to the rest, I'm not familiar enough with the design to be able say.

 

[YodaMcFly]

Sorry, I guess I wasn't entirely clear on what I'm looking for... I'm fairly confident in the dimensions, except for those fins; I have no clue what happened there, they were supposed to be 3/16" ...

It's all complicated by the fact that I originally did this before I sold my house (so, back in February) ...

At any rate, my bigger concerns were "did I do something wrong with OpenRocket?" Did I forget something? Things like that ...

Thanks for the feedback.

 

[Rex R]

well lets see...d/l the file and loads it up, right, shroud line length should be equal to chute diameter, the CRs look a bit thick (1/8" would work), the fins threw for a bit till I switched to the finished view...nope I don't see any real design issues. I do have a suggestion though, put in a chute shelf(CR) 8" or 9" down the tube else your wadding etc. will end up atop the motor tube (and shift your cg aft).
Rex

 

[K'Tesh]

FWIW, fins like those (trapezoids) are a lot easier to do with freeform. The only shape of fins I wouldn't use freeform fins for are elliptical or tube fins

 

[YodaMcFly]

Thanks for the feedback.

 

[neil_w]

FWIW, fins like those (trapezoids) are a lot easier to do with freeform. The only shape of fins I wouldn't use freeform fins for are elliptical or tube fins

I take a slightly different view... if I'm sure my fins are going to *stay* trapezoids, I'll use the trapezoid fins rather than the freeform. I find them quite easy. If I think there's a chance they might evolve into something different (this would be during design phase of course) then I'd just go straight to freeform, so I don't need to delete and re-enter them later.

Either one works; use whichever you're more comfortable with.

 

[YodaMcFly]

In this case, the fins are pretty much fixed; they were cut-down Nike fins. As I understand it, this specific configuration made exactly one flight.

And, freeform fins in OR scare the crap out of me. :wink:

 

[YodaMcFly]

Hmm ... You learn something new every day. And, in retrospect, this lesson makes sense.

I figured out how the CRs and fins got so thick, and with such bizarre numbers: I originally "drew" this in OR as a 24mm motor in a BT-55. Somewhere along the lines, I decided I wanted to play with it as a 29mm, so rather than risk screwing up the math, I used OR's "scale" feature. Not realizing that *everything* got scaled ...

Again, thanks to all for the hints ... Now that I'm almost settled in Virginia, maybe I can start doing model-stuff again...

 

[K'Tesh]

Freeform fins are easy!

You can take an image of the fin drawn in as a bmp, gif, jpeg, jpg, png, or wbmp, and import it in. The root edge of the fin must be touching the bottom edge of the image, and the fin will be solid black, with the rest of the image filled in with solid white. For boat tails, the fin can have just a single point touching the bottom edge.

Once the fin is displaying on the rocket, you'll likely need to scale it. So, lets say that your fin with a root edge of 7" has somehow become one with a 24" root edge... You just click the "Scale Fin" button, make sure that the scale from has the 24", and the to has 7", and allow the computer to do the work for you. As you know, you'll need to restore the thickness of the fin (from the general tab) to make sure that it isn't .005" thick now (when it was supposed to be .125" or whatever).

Any oddities can be deleted by holding the "control key" and then clicking on it.

Or

You can just create a rough appearance of the fin, then highlight the point in the matrix, and enter in the actual X,Y values of each point. Unfortunately, at this time, there is no way to do -Y values, so Phantom Body Tubes (PBTs) are needed for fins that extend below the body tube (not fin tabs, but things like the V2's fins, or fins on boat tails/transitions).

It's really easy, you don't have to know any of the angles, or what the sweep length is.