Saturn V with clear fins

[tbzep]

Has anyone run the CP on the Saturn V with and without clear slip-on fins that were supplied with the old Centuri (or early Estes) kit? I'd like to know how much difference there is.

[teflonrocketry1]

I have attached the RockSim files I created for both of these scenarios with the Estes K-39 Semi-Scale Saturn V. The CP is better with the plastic fins, 13.89" and the stability is 0.60 on a C6-5 motor, the more scale like fins give a CP of 13.26" and 0.43 caliber of stability. I simulated the 4 engine shrouds as a single transition. The more scale like fins (paper) are slightly distorted by RockSim, they are slightly larger in size, so the actual CP would be less and stability margin would be worse. I don't know of any other old Centuri/Estes Saturn V kits that have clear plastic fins and the ones in this kit don't "slip on".

[mwtoelle]

The K-36 Saturn V had clear plastic slip on fins that fit over the scale balsa fins. The clear fins were necessary because the back of the motor mount was at the bottom of the BT-101, rather than nearly 4" from the bottom like the Centuri KS-12, Estes 2001, and Estes 2157. I haven't seen the new Estes 1969 version yet, so I can't comment on it at this time.

[tbzep]

Both the Estes K-36 and the Centuri Saturn V had clear add-on fins. The Estes kit used a sandwich of two pieces that the modeler glued together on three of the edges. The Centuri kit used a single sheet with a pair of slots that you bowed out to slip over. This made the fin have a slightly cambered shape and gave the Saturn a nice slow rotation. IIRC, on a single D12, by the time it ejected it had rolled somewhere between 1/2 and one full rotation. Since the real Saturn had a roll program, it should give it mission points!

[BARGeezer]

Both the Estes K-36 and the Centuri Saturn V had clear add-on fins. The Estes kit used a sandwich of two pieces that the modeler glued together on three of the edges. The Centuri kit used a single sheet with a pair of slots that you bowed out to slip over. This made the fin have a slightly cambered shape and gave the Saturn a nice slow rotation. IIRC, on a single D12, by the time it ejected it had rolled somewhere between 1/2 and one full rotation. Since the real Saturn had a roll program, it should give it mission points!
Correct me if I'm wrong, since I'm still a relative sim newbie, but if the outer design remained the same, wouldn't the CP of the older kit (without the clear fins) be the same as this one?
https://www.rocketreviews.com/unknown-estes-saturn-v-1100-scale.html
I'm assuming the balsa fins of the older kit were the same size as the styrene fins of the newer ones. And moving the motor mount up 4 inches would only affect the CG, not CP right?

Finding the CP with the clear fins on can be done by adding them onto the components of the Rocksim file. The template is on the shroud templates page here:
http://www.spacemodeling.org/jimz/k-36.htm

As far as kits with clear fins, I know of 3 by Estes: Thor Agena B (K-28), Gemini Titan (K-21) and the aforementioned Semi-scale Saturn V (K-39).

BTW the smaller Saturn had permanent TTW clear fins with the scale fins emulated by a glue on paper silhouette. So I did a small mod on my clone by gluing a strip of tubing just above the fairings to act as a rear flange, and slipping the clear fins down from the top. Replaced the paper silhouette fins with fiberboard scale fins. This way I could remove the clear fins for display. And if I had to do it over I would replace the printed paper wrap ons and instead print the pattern onto decal paper. Woulda, coulda, shoulda. Cheers.

[tbzep]

Correct me if I'm wrong, since I'm still a relative sim newbie, but if the outer design remained the same, wouldn't the CP of the older kit (without the clear fins) be the same as this one?
The K-36 had smaller fins than more modern releases. I don't know if the 2001 (balsa) 2157 and 1969 all have the same size fins. I only have a 2001 and a Centuri kit built so I can't compare the 2157 and 1969 versions.

[BARGeezer]

The K-36 had smaller fins than more modern releases. I don't know if the 2001 (balsa) 2157 and 1969 all have the same size fins. I only have a 2001 and a Centuri kit built so I can't compare the 2157 and 1969 versions.
Then how about this: take the balsa fin template from the K-36 plans and sub it in for the styrene fins in the components section of the linked Rocksim file. Do the same with the clear plastic fin template. Should give you the two different CPs.

[tbzep]

Weeeell, that's why I posted it. I don't have Rocksim. ;)

[teflonrocketry1]

I made a better simulation for the K-39 kit with the paper fins (no distortion), I also attached the simulation file that includes both fin sets (paper and plastic).

I am working on the Estes Saturn V K-36 simulation, I hope to include as much detail as possible, the Saturn V .rkt file at rocketreviews.com is very basic, it does not even take into account the fin fairings and escape tower.

[teflonrocketry1]

Attached are my preliminary simulations for the Estes Saturn V, K-36, 1/100th scale with and without the plastic fins. I still need to size and place the body wraps better and include the electrical, pressurization and systems tunnels as well as all the other surface details.

CP with plastic fins is 32.903", stability margin with 3 x C6-3 motors 1.06, altitude 183' AGL. CP with just the balsa fins is 29.770", stability margin with 3 x C6-3 motors 0.52, altitude 208' AGL. Although this suggests that the clear plastic fins might be needed for flight stability RockSim gives a stable flight in 7mph winds with just the balsa fins.

Again I simulated the engine shrouds as one transition section of the same length and overall base diameter. You should be able to open and use these files with Open Rocket freeware http://openrocket.info/.

[teflonrocketry1]

Attached is my completed simulation of the Estes K-36 Saturn V kit. For an accurate simulation you will need to remove either the plastic fin set or the balsa fin set depending on which configuration you are using. The engine shrouds are simulated as one conical transition with its diameter set to that of the maximum radial distance from the center at the end of the engine shrouds.

[ghrocketman]

Clear plastic fins on anything just plain SUCK.
Use enough nose weight to fly with SCALE fins.

[teflonrocketry1]

Instead of added nose weight you could possibly use induction stabilization: https://www.apogeerockets.com/education/downloads/Newsletter379.pdf
Blackshire informed me about this possibility and I am planning on building one of these finless missiles http://usnavymuseum.org/photos/SLBMs.asp to test out this concept.

[tbzep]

Thanks.

Unfortunately OpenRocket can't attach the free form fin set to the transition so the fins aren't included.

[teflonrocketry1]

Thanks.

Unfortunately OpenRocket can't attach the free form fin set to the transition so the fins aren't included.

I created the attached OpenRocket file for the out of production Estes Saturn V K36 with both the plastic and balsawood fin sets. Remove one or the other fin set as desired.

Can someone with more OpenRocket experience especially with clustering motors please check this simulation?

Thanks,

[tbzep]

I created the attached OpenRocket file for the out of production Estes Saturn V K36 with both the plastic and balsawood fin sets. Remove one or the other fin set as desired.

Can someone with more OpenRocket experience especially with clustering motors please check this simulation?

Thanks,
The .ork file worked. It looks like I could do a lot of different things with the K36 if I use the clear fins. It really kicks the CP on back there.

[dwmzmm]

Little over 10 years ago I flew my vintage Centuri Saturn - V without the clear slip on fins; added some Play Doh in the nose area (Service Module bodytube) to bring the CG forward more. Flown down at Needville, TX using three C6-3's, the boost was a bit squirrely, but as can be seen in this video, straightened up after burnout and flew just fine.

https://youtu.be/0uTm-rbvQJk

[ghrocketman]

Maybe 3 D21-4s would work better.

[luke strawwalker]

Maybe 3 D21-4s would work better.

Which equals more tail weight and thus requires more nose weight to correct the CG/CP relationship... more nose weight means slower acceleration and more impulse required to achieve a given level of performance (speed/altitude). Thus it can become a "vicious circle"... (similar to the Ares V debacle).

Sometimes it's best to just make the fins a little bigger... :)

Later! OL J R :)

[teflonrocketry1]

I made a better RockSim file with separate engine fairings and both the plastic and balsa fins. Be sure to only include whichever set you are flying with. This simulation contains pods so it won't work in OpenRocket.

[teflonrocketry1]

I also updated the Semi-Scale Saturn V Estes K-39 with separate engine fairings and both the plastic and balsa fins. Be sure to only include whichever set you are flying with. This simulation contains pods so it won't work in OpenRocket.

[PaulK]

I also updated the Semi-Scale Saturn V Estes K-39 with separate engine fairings and both the plastic and balsa fins. Be sure to only include whichever set you are flying with. This simulation contains pods so it won't work in OpenRocket.Thanks, this will come in handy when I build mine!

[mojo1986]

If the clear fins are left off and you just go with the small scale fins, any idea where the centre of pressure would be?

I have a K-39 that I built with 5 BT-5 engine tubes. If I knew the centre of pressure I could install 5 mini A engines and then add sufficient nose weight to bring the CG ahead of the CP.

[luke strawwalker]

If the clear fins are left off and you just go with the small scale fins, any idea where the centre of pressure would be?

I have a K-39 that I built with 5 BT-5 engine tubes. If I knew the centre of pressure I could install 5 mini A engines and then add sufficient nose weight to bring the CG ahead of the CP.

I remember reading somewhere sometime someone said with "stock" scale fins, if you balance it at the front of the second stage, it'll be stable. I can't recall exactly where or when I read it nor by whom...

Later! OL J R :)

[teflonrocketry1]

If the clear fins are left off and you just go with the small scale fins, any idea where the centre of pressure would be?

I have a K-39 that I built with 5 BT-5 engine tubes. If I knew the centre of pressure I could install 5 mini A engines and then add sufficient nose weight to bring the CG ahead of the CP.

For the Estes Semi Scale Saturn V K-39 kit RockSim calculates a CP of 11.7602 inches from the tip of the nosecone on the escape tower with just the scale fins in place, an unstable situation by -0.50 calibers with a C6-5 motor installed. I had to put 1.5 ounces of weight into the BT-52 section to get a margin of 1.13, see attached RockSim file. I tried to create a simulation with the 5 x BT-5 motor tubes installed and using 2 centering rings; RockSim calculates a margin of stability of 1.11 calibers with 5 x A10-3T motors installed and 1.75 ounces of weight installed at the top of the BT-52 tube at the bottom of the balsa section. Since there is some uncertainty in this simulation, I urge you to use caution when making this flight for the first time, 1.75 ounces still might not be enough added nose weight for a stable flight especially on a windy day.

[mojo1986]

Bruce, that's just super! Thank you!


Joe