Absolutely, J! I remember an IBM 360 that took up a house, and you had to punch the program on cards! But that was then... 🙂 I worked out Barrowman's CP calc in Excel. Doesn't agree with modern CP calculators as I thought it would, but certain assumptions were in the orignal equations. I always split the difference. 🙂 I'm still setting the MAWD at 2 sec. mach delay. Not gonna happen, but, hey, I'm forever hopeful. 🙂

Chris, the trade-off in using the nose weight to move the CG is fine, but remember, your rocket will become "overstable" if you do it that way as you add weight to the nose... so wind is your worst enemy. It's actually everyone's worst enemy--well, that and a lot of things you can't control. At least, the "overstable" assumption is my gut guess... I had a really rough day, so my mind is kinda off tonight. Check it with your sim.

Actually I just did. It currently is hovering around 1.2 calibers (with noseweight), and the CG is pretty much central (the noseweight balances out the motor weight). As for mach - I break it, but not by much, 818mph is my latest sim. I think it should be pretty good, but we'll see once I finish the actual rocket and plug in measured values. I'm hoping to have a fairly light structure though (as if you couldn't have guessed that already with my carbon tube 😉 )

1.2 is great, Chris. You're on your way. However, with all this talk, I picked my rocket up to take a look at it... and noticed I'd set it next to something that ate into the paint. This really isn't gonna be my year. 🙄 😀

Yeah - I've had that feeling before 🙄

As for mine - it looks great on the sims - way above what I ever expected for the contest - but we'll have to see how close it actually comes to the simmed results.

To clarify -- I think Rocksim is dead on (in genera)l. That said, I think the G80 file, at least the OLD G80, is way, way, way, way off. The new one seems to be potentially even worse, and in some cases it actually projects HIGHER altitudes than the old load.... never mind the fact that the new G80 is 100NS vs. the old one being 120NS. I also used the new G80 motor and sim file in a Team America Egg Loft contest and was *not* impressed with the sims. Some were off by as much as 30%. Projections in every case were higher than actual performance.

Overall, I think Rocksim in deadly accurate. It has some flaws regarding Blackjack motors.... But for optimal mass? Very good. For White Lightning, most Blue Thunder, and Cesaroni motors? it is astoundingly accurate. I'll bet we can find 40 circumstances within the club of Rocksim being within 1% of a projected flight.

Many of the Icarus flights were incredibly close to the target altitude over the years. Many years, if you didn't come w/in 1% on Icarus, you got 3rd or 4th place -- and there may have only been five flights. AMAZING.

JW

Yes - I've been amazed by rocksim before. My Black Brant at mile high mayhem was my closest to simmed yet - it got 5120' out of a projected 5137. I can only hope it's as accurate on my SSS rocket.

SpaceCAD comes within two hundred feet for a 4k flight, which is 5%. You know, guys, I think the extra $50 bucks, compared to SpaceCAD's $49+, for RockSIM is worth it. I'm sold. Both use the same eng.dat files, I think. I have the same results with the new load going higher. It's just not right. So I'm experiencing the same problems. I'm going with what I have SSS-wise, but after my L3, I'm getting RockSIM. I'm trying to remember when I got my first copy. Late 80's, definitely early 90's. Don't know who sold it back then, Apogee? I'm sold now though.

Pretty sure Apogee has been doing it all along. I can't say anything about older versions, or reminisce about the good old days with building size computers less capable than my calculator ( 😉 ), but I love V8 (actually version 8.0.1f16) - well worth the money. Does just about anything you want, though still no strap on boosters.

I'm one of 40 circumstances. Two flights at Hartsel BB were dead on with RockSim. The first was projected to 1800', actual was 1776. The second was 3000', actual was 2980.

Both flights were the first using an RRC2.

kp

I actually use Rocksim V4.0, which is ancient. "Dance with who brung 'ya", as the old adage goes. V4.0 is the first/last version I've ever used....

I paid for 7 and the upgrade to 8. I use 7 for most of my stuff because 8 seems to be over optimistic all around on sims. 7 seems to be right on vis a vis optimal weight simulation, 8 - because of the overoptimistic sims, I haven't messed with so much, though I do like some of the features better.

With all the sim programs, the biggest problem I've run into is the quality of the motor files. While many motors seem dialed right in, quite a few are not. There are glaring errors even in manufacturer's .eng files on stupid stuff like casing length and even diameter. In cases like the G80 or the J350 where there have been more than one version, there is little to differentiate the versions.

In the club launch logs for this site, our motor database is even more fouled up than the Rocksim files. I've heard the same complaints from SpaceCad users too. I've been working to correct this, (and also create a clean set of .eng files for Rocksim) but with 500+ motors, this is a huge clerical effort and quite frankly I'm more interested in vacation right now. I'll probably get to it this coming fall/winter.

Warren,
When you get those files cleaned up, post them. We'd all be very grateful. That is one hell of a daunting task. Most would probably pay you for them. Sell them on the Internet. SpaceCAD uses the same .eng files that RockSim does.

Yea, I think with the sub-mach stuff and good motor data, Rocksim does fine. Its Mach plus where it breaks down, largely due to the Datcom methodology imo. I noticed no diff in sims between v7 and v8 and even queried Apogee founder on this during the annual mtg. He was unaware of any changes in the basic computational engine. But his partner does the physics poriton so possible some changes were made Tim was unawares. What I want it still won't do--which is accurate drag calcs at greater than Mach 1.5, strap ons, BG stability, unusual staging, etc. That said at 100 bucks still a marvelous product.

But in where it counts for me--high performance rocket sims--see v8 as a huge disappointment with more video game features added and no beef. I think the aero stuff is more accurate at transonic flights but is unfortunately ergonomic wasteland.
JS