Estes SA-2061 Sasha

[teflonrocketry1]

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.

[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

[Scott_650]

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.

[JumpJet]

Thank You.



John Boren

[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!

[Scott_650]

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!

That’s 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.

[teflonrocketry1]

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

[Scott_650]

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 .

[teflonrocketry1]

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.

[JumpJet]

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.


John Boren

[teflonrocketry1]

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.


John Boren

John,

You are correct! What is being discussed is the situation where the forward fin set is aligned (directly in line or on the same plane) with the aft fin set and not rotated 45 degrees with respect to each other as per the Estes instructions. There is new wind tunnel data to suggest that if the fins are aligned above one another the turbulence from the upper set of fins will negate some of the stability imparted by the lower set of fins. A kit built as per the instructions will not have the upper and lower fin sets aligned, they will be rotated along the airframe 45 degrees from each other.

[Scott_650]

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.


John Boren

I’m sending this from my tablet so I can’t access OR but I ran the sims just a little while ago watching the Buckeyes beat Sparty, if memory serves OR showed an even higher margin for the single stage configuration than that. Though I was running the simulation with an Estes 18mm C6 motor, not a 24mm motor.

[frognbuff]

Fantastic discussion! I went ahead and built to the kit plans. Man, there is like 12 acres of balsa on this thing! It feels like I've been sanding for days.

I definitely will NOT paint it like the hang tag. Way too cartoonish. I think I'll go for some "spray can camo" like the old Magnum SAM-3. Then use a couple of the red stars for color, plus the details that look like they belong on a missile. None of the "SA-2061" markings. To each his own, eh?

[ghrocketman]

Agree with finishing like the old Magnum SAM-3.
I'm going to have to order one... Like I need more on my build pile.
Kinda goes with the 1/11 scale R/C F-4 I'm finishing up.

[frognbuff]

Here she is: Estes SA-2061 Sasha ala Centuri Magnum SAM-3. I used Krylon ultra-flat paints. They cover well - thick and smooth - and they dry incredibly fast. Sadly, the wide, flat spray pattern was not ideal for doing the camo. Nevertheless, I like the result. I used only the "access panel" decals from the kit. The Russian star is from my stash - bigger than the kit stars, and with the proper red border. Can't wait to fly her!

[teflonrocketry1]

Nice job on the Sasha! You have inspired me to finish working on mine.