A10-3T xFNC "Challenge"
 

Not much of a challenge, actually. I've mentioned before that I am a 4-H project leader, and also that my budget doesn't allow for RockSim. Now, I'm happy enough on my own designing and testing rockets the "old fashioned" way; but for the kids, I like tested if not proven designs.

So here's the deal. I have a mess of A10-3T engines, courtesy of Wal-Mart. I'd like an optimal (3,4)FNC rocket design, using only parts available from Semroc. By "optimal" I mean (a) stable and (b) around 10 FPS at deployment (or less if possible). Altitude is not important; small field fliers are fine. Designs able to use Semroc laser cut fins would be a big plus, since these rockets will be built by kids (and hopefully, being posted here, not just by my students).

If I had RockSim, I'd crank it out and be done. But I don't. Anyone want to take it on?


Extra Credit: 2x and 3x cluster rockets designed for A10-3T engines, same criteria as above. Would be good for the more "advanced" students (2nd year and above). Of course, the centering rings would have to be handmade, but I did say "advanced" didn't I?

Take a look at freeware like wRASP. I've been living off the Palm version for several years now.

But for some crazy reason, I'd say that an A10-3 in an adapter would be perfect in a Baby Bertha.



Well, if you want LOTS of extra credit, one of our section members built a rocket called the D80, a cluster of EIGHT A10-3T in a BT-70 body tube with the old balsa BNC70 nose cone. It's a pretty cool flier, and I keep thinking about building one myself.

A First Answer to the Challenge
 

Solo,

Here are three very basic, easily-buildable single-engine designs that meet your criteria. They are all ST-10 size models, which means they should have a nice "feel" in their hands. Not too small, like a BT-20 or ST-7 design, and not too large, like a BT-55 or ST-13 design. All of these use a standard 36" x 1/8" rod for launch.

The fin pattern is slightly modified from what RockSim offered. They are larger, and they are 1/8" thick balsa. That should also be a plus for small fingers, in that it has a bit more ruggedness when being handled.


XFNC Challenge #1:

Length: 21.10"
Diameter: 1.04" (ST-10)
Fin Span: 6.04"
Weight: 1.04 oz

A10-3T.....292'......Dv 8 FPS......Deploys on the way UP



XFNC Challenge #2:

Length: 31.10"
Weight: 1.42 oz

A10-3T......205'......Dv 8 FPS......Deploys on the way DOWN



XFNC Challenge #3:

Length: 29.10"
Weight: 1.36 oz

A10-3T......217'......Dv 5 FPS......Deploys AT APOGEE

A Second Answer to the Challenge
 

Solo, here's a two-engine cluster for your "advanced" group. I increased the diameter to ST-13, and used four fins of 1/8" balsa instead of three. The model takes a 16" parachute to recover at about 12 FPS on landing.

Length: 40.40"
Diameter: 1.34" (ST-13)
Fin Span: 6.84"
Weight: 2.50 oz

Launch rod: 36" x 1/8"

(2) A10-3T......256'......Dv 5 FPS

Hope these designs fit your needs!

Excellent, Craig, thanks! Can I ask a favor? A parts list would be nice. I can probably guess my way through it, but it would be much quicker with a list.

Mini Hydra?

What a cool idea! Do you think the 3 sec delay would be long enough for a 7 engine cluster launch?

I suspect the 3 second delay will severely limit clustering the A10-3T. It's a hard-kicking engine with almost no follow-through; a heavy enough rocket to hold it down to a low DV might be too heavy for the low tail of the thrust curve.

Just musing, no simulations or data to back it up.

Our club members D80 actually works pretty well on a cluster of 8 A10-3Ts.

Take another look at the NAR certification sheet for the A10. If you average the WHOLE burn time, it's an A2, not an A10. It's got a .6 second very low thrust tail in addition to the delay.

And I might as well take this opportunity to point out that motors rarely have the delay they are labeled with. In the case of the A10-3T the delay is 2.35 seconds, not 3. Virtually all of the Estes motors have significantly shorter than advertised delays. If you are worried about ejection velocity, check the data sheet rather than use the number the motor is marked with.

I understand that... I'm hardly a newbie here. But it doesn't change my thesis... I'm interested in rockets that will work with A10-3T engines. RockSim, as I understand it, uses the thrust curve data as well as the certified delay value... it doesn't take the designation at face value.

I don't deny its usefulness, but I can't justify $100.00+ for software. Perhaps if I was the sort to spend $$$$ on high power rockets... but for me, it's not worth it. I can build a LOT of rockets for the price of RockSim.