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  #41  
Old 02-19-2009, 12:55 PM
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CPMcGraw CPMcGraw is offline
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John,

I just worked up your tube fin design on RockSim 9, to see if there were any issues that V5 might have missed. Hope you don't mind the changes made. The tube fins are not performing as well as the simulated balsa fins would make you believe. This may come as a surprise, but they're too long.

What I did was start trimming the length of the tube fins until they were half the original length - 1.5" instead of 3" - and this brought the A10-3T loaded model to a flyable margin of 1.08. I don't understand the way RockSim calculates the stability margin yet, so I can't give you an explanation why.

With a 1.5" tube fin set, the loaded margin was 1.08, requiring 3/8th oz of ballast. The nose cone was changed to a balsa version (in keeping with the SEMROC components requirement). My simulation gets 308' altitude, with a Dv of 7.73 FPS, with all three motors burning. The 1/2A3-2T gets a respectable 142', with a Dv of 20 FPS. Not bad...

Have a look at the attached screenshots. I'm attaching the V9 RKT file, but you won't be able to open it up and view it with V5. What you might want to do, though, is download the V9 demo, so you can see the new file. It's still free, you just won't be able to save anything.
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Name:  XFNC Challenge TF 3D.jpg
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Name:  XFNC Challenge TF Sim Runs.jpg
Views: 93
Size:  219.4 KB  
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File Type: rkt XFNC Challenge TF.rkt (59.4 KB, 92 views)
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  #42  
Old 02-19-2009, 03:39 PM
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Quote:
Originally Posted by CPMcGraw
John,

I just worked up your tube fin design on RockSim 9, to see if there were any issues that V5 might have missed. Hope you don't mind the changes made.

Craig,

I don't mind at all! In fact, I was hoping you would take a look at it and make any changes that were needed, so thanks for doing that.

Quote:
The tube fins are not performing as well as the simulated balsa fins would make you believe. This may come as a surprise, but they're too long.

What I did was start trimming the length of the tube fins until they were half the original length - 1.5" instead of 3" - and this brought the A10-3T loaded model to a flyable margin of 1.08. I don't understand the way RockSim calculates the stability margin yet, so I can't give you an explanation why.

How did the original design perform in RS 9? I picked 3" tube fins so you could just use 2 BT-60's for the body tube and fins. Also, that relative length is similar to, say, the Quest Totally Tubular and other tube fin kits I've seen. With your changes, you can use 3 BT-60's to make 2 body tubes and 2 sets of fins, which works nicely, too.

Quote:
Have a look at the attached screenshots. I'm attaching the V9 RKT file, but you won't be able to open it up and view it with V5. What you might want to do, though, is download the V9 demo, so you can see the new file. It's still free, you just won't be able to save anything.

I can save it, change the file extension to .txt, and view it with Windows Notepad. I've done that several times for other rockets when I've wanted to see a parts list or performance information.

How does your revised design perform if one of the A10-3T's doesn't light? That's a reasonable scenario, and even more so for relatively inexperienced flyers.
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  #43  
Old 02-19-2009, 03:47 PM
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Is there a V9 demo yet? Last time I looked (2 days ago) there wasn't.
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  #44  
Old 02-19-2009, 06:52 PM
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Quote:
Originally Posted by Solomoriah
Is there a V9 demo yet? Last time I looked (2 days ago) there wasn't.


I guess the V9 demo is lagging a bit. I know they're working out a few kinks in the release version that we've spotted here...

You might be able to see the RKT file with the V8 demo, since I didn't use any PODS in the revision. Try downloading that to use as a viewer. Hopefully they'll have a full V9 demo soon. The website still says "January 2009", so I'm sure that was the original intent. Version 9 was a major re-write.
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  #45  
Old 02-19-2009, 07:21 PM
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Quote:
Originally Posted by JRThro
How did the original design perform in RS 9?


I had to go back and work up a Mk I version. Deleting the balsa fins and working with just the 3" tube fins, you have to add 3/4 oz of ballast to the shoulder of the NC to get a margin of 1.15, loaded with 3 A10s. Performance on this version gets about 265' altitude, with a really good Dv of only 3.22 FPS. This surprises me, with all that ballast added. Even the 1/2A3-2T did OK, with an altitude of 104' and a Dv of only 8.07 FPS.

Quote:
How does your revised design perform if one of the A10-3T's doesn't light? That's a reasonable scenario, and even more so for relatively inexperienced flyers.


Using your original version, a one-engine-out launch still gets 147' with a Dv of 22 FPS, so it's still a relatively safe bird. A two-engine-out situation won't even get off the pad. My revised version should be similar.
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Name:  XFNC Challenge TF Sim Runs Mk I.jpg
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  #46  
Old 02-20-2009, 08:57 AM
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Looks nice!

Seeing those numbers, I'm not sure now why you shortened the tube fins to 1.5" in your revision. Can you explain that? I find the relatively longer tube fins more esthetically pleasing, personally.
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  #47  
Old 02-20-2009, 11:48 AM
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Quote:
Originally Posted by JRThro
Looks nice!

Seeing those numbers, I'm not sure now why you shortened the tube fins to 1.5" in your revision. Can you explain that? I find the relatively longer tube fins more esthetically pleasing, personally.


I think it was the initial stability margin after removing those simulated fins. It was only about 0.5 (minimum required margin is anything over 1.0), and I was looking for a way to increase the margin without adding ballast. Ballast is adding mass, and I was trying to keep from doing that. It still took some...

But your version came out better than mine, even with the additional mass added. And you're right, the longer tubes do look more appropriate, more proportional. I just have this "thing" against adding dead weight to a model if I can avoid it...
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  #48  
Old 02-21-2009, 11:19 PM
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Quote:
Originally Posted by CPMcGraw
I just have this "thing" against adding dead weight to a model if I can avoid it...

Sure, I can understand that, and I don't like doing it myself!
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  #49  
Old 03-06-2009, 03:46 PM
Jeff Walther Jeff Walther is offline
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Quote:
Originally Posted by Doug Sams
BTW, FWIW, I was given a challenge a few years ago to use the A10-3T in an upper stage, without zippering or shredding. Here's what I came up with. It uses BT-55 and it works pretty good
.


I am continually entertained by your devotion to the Midget. I just finished painting my Midget clone. The Midget is a fine looking rocket. A little of my blue ran under the tape onto the white. Sigh.
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  #50  
Old 03-06-2009, 04:09 PM
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Quote:
Originally Posted by Jeff Walther
I am continually entertained by your devotion to the Midget. I just finished painting my Midget clone. The Midget is a fine looking rocket. A little of my blue ran under the tape onto the white. Sigh.

Thanks

When I get wickers, I usually just wipe them off with a Q-tip wetted with alcohol. My experience has been that oil-based enamels, when wet, can be wiped up easily this way without marring the finish of the underlying, dry coat. That is to say, alcohol wipes wet RustOleum off dry RustOleum without marring. But it tends to dull the finish on Krylon (old) and Testors. FWIW. YMMV.

Another solvent to try would be mineral spirits / turpentine. And I know for sure NOT to use lacquer thinner

But the key is that some of the wickers can be erased this way, as long as you get them while they're wet.

Doug

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