Could anybody help me sim this thing? Estes Cosmic Explorer

I'm attempting my first kit bash - a pretty simple one. I'm building an Estes Cosmic Explorer to accept an E BP motor. I love my standard-built one - it flies so straight and barely rolls at all! I'd like to see what it can do on an E.

My original Cosmic Explorer:



The launch video (Estes C6-5):

[video=youtube_share;Ys8giDCMDfk]https://youtu.be/Ys8giDCMDfk[/video]

I'm trying to create a sim of the rocket so I can check for stability with the added motor weight, and so that I can run flight simulations on it. But I'm having a hard time getting the thing to look right in OpenRocket. I was unable to find it on the RocketReviews.com Estes Rocksim library.

Specifically, I'm having problems with the fins. I've taken what I think are really careful measurements, using a digital caliper (though I'm not used to using one of those) and a protractor to get the angle of the fins, but when I input the data into OR, something doesn't look right about the rocket.

In fact, when I click 100% on the view drop box, and hold the fin up to the screen, it's not even the same size - the fin on the screen is a little shorter, spanwise, than the actual fin.

Making it even more difficult is that the fins have curved corners, and a little curve where the root meets the airframe. I don't know how to make curved shapes in the freeform fin shape function, so I've had to fudge that a little bit.

I was wondering if anybody could help me with this.

Here's a picture of what the rocket is supposed to look like:



Here's my attempt at simming the rocket:



I scanned the fin so you can see what it looks like. I've tried cropping this down to just the exposed part of the fin and uploading it into OR, but the program can't seem to determine the fin shape.

I've included a ruler for scaling:



Additional information, according to my best measurements:

Fin height: 2.222 inches
Root cord: 3.385 inches
Tip cord (guesstimate, because of the curved corners): 1.86 inch
Angle of the leading edge (from the root edge): About 42 degrees.
Angle of trailing edge: About 63 degrees.

Some of you guys seem really good at OR - would any of you be willing to take a crack at this?

Thanks!

You are probably well into "good enough" for what you are trying to do. Very minor geometry changes to the fins will not have an impact on the OR simulation.

This is very close to scale.
View attachment Cosmic Explorer Fin.ork

And here is a file that used your scan to import the fin shape with tabs added.

kj

View attachment cosmic explorer imported fins.ork

kjohnson said:

And here is a file that used your scan to import the fin shape with tabs added.

kj

Click to expand...

Thank you! That looks much closer. I don't know why I couldn't import the image - I cropped out everything but the fin itself, and still OR wouldn't recognize it.

Now one thing that I noticed that "doesn't quite look right" is the nosecone. Estes' nosecones tend to have a blunted point, whereas your sim has a sharp point. I suspect that you didn't get the balsa version with your kit, and if I'm not wrong it was sent with the PNC-55AO nosecone. You can download my sim of it here.



BTW, I like the lines of the Cosmic Explorer, it reminds me of the Centuri/Semroc Centurion (Read: I think an upscale is called for).

Ok... I'm interested... Here's what I came up with based on the fin templates from slickwilly. Mind you, as I started on mine, I was basing it off of the incorrect plans that were included with my Cosmic Explorer. Once I found the problem, I corrected the images and the .ork file that I created for it. I now have to build a new motor mount for mine.





Mind you... I've changed the launch lug to one for a 3/16" launch rod, the recovery to a streamer, and the motor mount to be capable of handling an E motor.

BTW, I observed that it would be possible to clone this without the coupler (the body tube's length is 18") (you'd only have to mask for the black/white joint).

View attachment Estes Cosmic Explorer (2421) (E Powered Mod).ork

K'Tesh said:

Ok... I'm interested... Here's what I came up with based on the fin templates from slickwilly. Mind you, as I started on mine, I was basing it off of the incorrect plans that were included with my Cosmic Explorer. Once I found the problem, I corrected the images and the .ork file that I created for it. I now have to build a new motor mount for mine.





Mind you... I've changed the launch lug to one for a 3/16" launch rod, the recovery to a streamer, and the motor mount to be capable of handling an E motor.

BTW, I observed that it would be possible to clone this without the coupler (the body tube's length is 18") (you'd only have to mask for the black/white joint).

Click to expand...

Woah, that is a sweet-looking sim! I meant to message you to see if you'd take a look at this thread - after subscribing to your nosecone thread, I figured you'd be interested!

Edit: Oh, yeah, I thought that about the coupler. Last time I built this, my coupler seized up when I went to put the tubes together, and I had a gap I had to fill with CWF. It's what's got me procrastinating on that step right now...

Slickwilly said:

This is very close to scale.
View attachment 251679

Click to expand...

That is awesome. Every time I try to sim something, even when I get the measurements right and there are no curved parts, it always looks a little off to me.

lcorinth said:

Edit: Oh, yeah, I thought that about the coupler. Last time I built this, my coupler seized up when I went to put the tubes together, and I had a gap I had to fill with CWF. It's what's got me procrastinating on that step right now...

Click to expand...

Four words: Bob Smith Industries' Epoxy

Or

One word: Zipperless

K'Tesh said:

Four words: Bob Smith Industries' Epoxy

Or

One word: Zipperless

Click to expand...

Those are those little bottles you find in hobby shops, right? I was thinking about getting those, for my Estes Leviathan build. That big coupler makes me nervous - too much risk of it seizing up with wood glue! And I'd like to try using epoxy for fillets.

In any case, I did use wood glue on the coupler for this rocket. It did start to seize up when I put the first half in - and it went in crooked. But I slid the other tube on it, and managed to temporarily break the bond by using the unglued tube as leverage. Once I'd got it straightened out, I applied a generous amount of glue into the other tube, and a little further in so the coupler would be most of the way in before it encountered any glue. With one quick motion, I got everything together, nice and straight.

Devcon works nicely, another 'problem' with white/wood glue is that it shrinks as it dries...so one can generally see where various parts have been glued into the airframe.
Rex