Right On Target
 

I was hoping to get her up to 1500 with D power, but had no Idea about an E. These seem a likely possibility. Thanks

Craig

Thanks for posting the Orion RockSim file!

.

New Plan -- Rhemus
 

This is a simple design with great performance, low Dv numbers, and good looks as a sport modroc. It has over 1000' capability on a C6-5.

Length: 16.92"
Diameter: 1.04" (ST-10)
Fin Span: 5.04"
Weight: 1.262 oz

A8-3.......217'......Dv 2 FPS
B4-4.......498'......Dv 10 FPS
C6-5......1039'......Dv 11 FPS

Enjoy!

New Design: Interstellar Traveler
 

Great job with all the new designs Craig. Looks like my build pile just got a little bigger :rolleyes: .

Here is a design I call the Interstellar Traveler. I was going for a vintage look again, so I hope you all like it. Lately I seem to be in a design rut or you might call it a design block or information overload. All three of my personalities can't figure out which :D .

Here are the flight specs:

Interstellar Traveler
Launch guide length: 36.0000 In

MOTOR----MAX. ALTITUDE----DEP. VELOCITY
B4-4 --------272.04549 Ft-------20.4662 ft/s
B6-4 --------281.21422 Ft-------15.8254 ft/s
C6-5 --------729.72207 Ft-------0.5625 ft/s


Enjoy and Thanks Again, JP

James Pierson
NAR# 77907

Andromeda Update for 1-14-2007
 

Here's an updated set of fin patterns, including the slots for the shrouds and two centering rings. The rings close off the passage of air through the shrouds, effectively turning them back into simple tubes, and not allow them to act as ringfins.

Hey Craig - it's looking good. I'm looking forward to building this one.

I'm hoping the second prototype comes out lighter than the first one. Somehow the weight built up in the construction, and killed any chance it had of flying correctly. It took a full quarter ounce of lead to bring the CG/CP margin into the safe zone, on top of that.

If the second prototype balances where RockSim says it should (and I have my doubts even now), the flight performance should be quite good on a "B". I think RockSim is calculating the weight of the nose cone heavier than Carl's BC-760 actually is, and it's throwing the margin out of whack. I need a digital scale that can resolve finer points than a typical postal scale.

ADDENDUM: THAT'S ONE PROBLEM! RockSim is recording the weight of the nose cone as being 0.2258 oz, while the SEMROC website is saying the nose cone only weighs 0.09 oz. That's roughly 2.5X what it should weigh. What this means is, RockSim is over-estimating the typical weight of bulk balsa. I will go into the file and re-compute the design based on the website weight, and report on the results shortly.

Andromeda Update for 1-14-2007, Part II
 

I was right in thinking the CG would be adversely affected by the change in weight. Look at these numbers:

OLD:

Weight: 1.9115 oz
CG: 14.845" from tip of nose cone
CP: 18.5037" from tip of nose cone
Margin: 3.52


NEW:

Weight: 1.7757 oz
CG: 15.6683" from tip of nose cone
CP: 18.5037" from tip of nose cone
Margin: 2.73

Just in this change in the weight of the nose cone, the CG was pushed backwards nearly 7/8".

Now, interestingly enough, it suggests that I might still be able to launch Prototype #1 and achieve something near the original projected altitude. I just need to compensate with some ballast, and plug those shrouds. The school where I fly will be out tomorrow for MLK day, but we're expecting rain and colder temps by evening. It may be a crap shoot, but I'm going to try and get in a couple of flights with it if possible.

Revised Plan -- Andromeda
 

Here is the Andromeda Mk. V, with some corrections. The model has been lengthened with the addition of a 4" piece of ST-7. This shifts the CG far enough forward that it has the correct margin for a C6-5 motor. The final weight is still below the original weight computed by RockSim.

Length: 27.95"
Diameter: 1.64" (ST-16 shrouds)
Fin Span: 5.799"
Weight: 1.8053 oz
CG: 18.6329"
CP: 22.4176"

A8-3......147'......Dv 15 FPS......34"
B4-4......388'......Dv 3 FPS.......27"
B6-4......398'......Dv 5 FPS.......30"
C6-5......910'......Dv 14 FPS......28"

All motors reach flight velocity on a standard launch rod.

Enjoy!

Revised Plan -- Andromeda Mk VI
 

The Andromeda has been a work-in-progress for some time, now, and I hope you don't mind the constant revisions. Discovering the issue with the ring fins and simple inside tubes didn't help, but at least I have a better understanding of what to expect in future designs with this detail. Now, as I look more at the last-posted version (Mk V.2) I see the need to "dress it up" just a bit. So with that, I give this additional caveat: These details add visually to the design, but they also kill about 150' off the top altitude with the C6. I don't think it's the weight as much as it is the negative stability this detail works against the static margin when applied to the forward shroud, and what I had to do on the rear shroud to compensate. Visually, these details make sense...

Length: 27.95"
Diameter: 1.64" (ST-16 shrouds)
Fin Span: 5.799"
Weight: 2.022 oz

CG: 19.5362" [empty location]
CP: 22.8574"

B4-4......316'......Dv 16 FPS
B6-4......324'......Dv 12 FPS
C6-5......756'......Dv 7 FPS

All motors in this list reach flight velocity on a standard launch rod. The A8-3 had poor overall performance and required a longer rod, so it was dropped.

Enjoy!

Addendum: As with all the other issues in RockSim, I think this detail issue is over-calculated by the program. These shroud details should never have caused as much instability as shown. The problem is these items had to be created as FINS, and not as raised surface items, which probably would not affect the flow of air to the same degree. I am sure, with more research into the program, I can compensate for the extreme effects. I really need to pull out those older "Peak Of Flight" newsletters and rummage through them for anything on fins...