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Old 09-21-2019, 07:39 PM
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teflonrocketry1 teflonrocketry1 is offline
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Default Estes SA-2061 Sasha

Another spectacular kit by Estes! Attached are several screen shots and the RockSim simulation files I created for the Estes SA-2061 Sasha. Simulations for both the 2 stage and single stage configurations are attached. I avoided using pods so these simulations should be compatible with Open Rocket software; if someone has time this design looks great with the decals added.
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Name:  Estes Sasha Two Stage 3D.jpg
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Size:  199.4 KB  Click image for larger version

Name:  Estes Sasha Single Stage Sim.jpg
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Size:  207.2 KB  Click image for larger version

Name:  Estes Sasha Two Stage Sim.jpg
Views: 25
Size:  224.3 KB  
Attached Files
File Type: rkt Estes SA-2061 Sasha 72710 Two Stage ORK.rkt (100.0 KB, 25 views)
File Type: rkt Estes SA-2061 Sasha 72710 Single Stage ORK.rkt (58.0 KB, 9 views)
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Old 10-04-2019, 01:54 PM
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I noticed you have the Estes E12 motors as a selection. Where does one get the files needed to upgrade Rocksim with these motors? I've been using E9 motors, but would love to use the E12 for my simulations.




John Boren
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Old 10-04-2019, 03:08 PM
Scott_650 Scott_650 is offline
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Quote:
Originally Posted by JumpJet
I noticed you have the Estes E12 motors as a selection. Where does one get the files needed to upgrade Rocksim with these motors? I've been using E9 motors, but would love to use the E12 for my simulations.




John Boren


Thrustcurve.org has the RASP (.eng) files that should work in both RockSim and OpenRocket. Not sure how RockSim does it but in OR you can tell it where to look for the motor data files then the added motors show up in the pick list.
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Old 10-04-2019, 03:15 PM
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Thank You.



John Boren
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Old 10-05-2019, 10:15 AM
frognbuff frognbuff is offline
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I just started building the Sasha. I really like the old-school Soviet surface-to-air missile feel of it. I was wondering though - would there be any real impact to the model if the sustainer "wings" and "control fins" were aligned instead of being offset 45-degrees? I wouldn't think so, but you never know.

If they lined up, it would look even more like an SA-2!
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Old 10-05-2019, 11:17 AM
Scott_650 Scott_650 is offline
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Quote:
Originally Posted by frognbuff
I just started building the Sasha. I really like the old-school Soviet surface-to-air missile feel of it. I was wondering though - would there be any real impact to the model if the sustainer "wings" and "control fins" were aligned instead of being offset 45-degrees? I wouldn't think so, but you never know.

If they lined up, it would look even more like an SA-2!


Thatís an interesting question. The intuitive answer for me would aligning the fins would lower drag - but not necessarily since this would give you a bit of a split fin style design.
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Old 10-05-2019, 08:58 PM
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Aligning the control fins with the sustainer wings puts the control fins into the turbulent wake created by the forward wing fins. This makes the control fins less efficient, and in a worst case scenario, the steering force of the control fins could be completely negated, making for a much less stable configuration. Check out the article titled "Increasing Rocket Aerodynamic Performance" by Thomas Salverson on page 42 in the May/June 2019 edition of Sport Rocketry. Essentially (on the right side of page 48) the portion of the fin inside the turbulent wake of the airflow behind a reducing transition doesn't do anything for the rockets stability. It is suggested that while a transition section below a wider payload section decreases the aerodynamic drag on a rocket, it induces a wake that interferes with and decreases the effectiveness of the rockets fins, and these fins should extend out beyond the rockets body until they are in the laminar airflow region beyond the diameter of the transition. I suggest the same effect will occur when the wing and control fins on the Sasha model rocket are aligned, especially since they are more than one body tube diameter apart. You might want to also visit this thread about a "box kite" like fin configuration that doesn't fly stable; https://forums.rocketshoppe.com/showthread.php?t=17929
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Old 10-05-2019, 09:40 PM
Scott_650 Scott_650 is offline
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Fiddling around with the single stage version in Open Rocket shows mo substantive difference with the fins rotated or aligned. Estes C6 motor takes it to 390ish feet either way. It does change the look a bit but not enough for me to prefer one over the other - truth be told I like the ESAM better than the Sasha but both are nifty designs .
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Old 10-05-2019, 09:59 PM
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Neither Open Rocket or RockSim currently have the ability to correct for this known aerodynamic effect. For the worst case scenario with the fins aligned, I ran the simulations without the control fins in place and looked at the models stability. The stability margin on the Sasha with an E12-6 becomes 0.74 and 1.10 with a D12-5. The ESAM-58 gives a stability margin of 0.74 on a C6-5 and 0.96 with a B6-4. Both of these simulations assume that the control fin set is not in place and don't take into account the fins weight, so the stability margin should even be worse. Since I am an experimentalist I suggest you build the model(s) with the fins aligned and make a flight as above where I suggest the stability margin is much less than 1 (E12-6 in Sasha and C6-5 in ESAM-58) and let us know how it goes. There is nothing like a real world proof of concept.
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Old 10-05-2019, 10:19 PM
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If built per the kit and flown with two E12 motors the Shasha has a stability margin around 1.5 if memory serves me, so I'm not sure where you are getting your stability numbers from. The single stage model has a similar stability margin.


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