Is it a clone? No, a scratch? No...

[astronboy]

Is it a clone? No, a scratch? No... It is what the original kit should have been, IMHO.

Based on a thread on Yahoo's Old Rockets, I have redesigned the ESTES Nike X into a 18mm 2 stage rocket.

To obtain stable flight on the sustainer, I had to ever so slightly enlarge the middle set of fins. You will not even notice!

I started to build this baby tonight. I have gathered all of the parts, and cut the tubes and fins. Assembly starts tomorrow!!

 

[astronboy]

For those without Rocsim, here is a 2D pic:

 

[teflonrocketry1]

I took a look at your RockSim file; it looks great! I suggest using a shorter delay in the sustainer such as C6-5, C6-0 combination instead of a C6-7, C6-0. See the attached RockSim Version 7 file. I also moved the launch lugs off the fin line by using a radial offset of 12 degrees for them.

Do you intend to use 1/8 inch thick balsa for both the sustainer and booster fin sets? I like to use stronger materials in the booster fins since they tend to be larger and have to survive tumble recovery.

I also put the parachute and shock cord further down into the body tube, this is where they will end up due to the forces at lift-off. The design still maintains about one caliber of stability with the RockSim equations, this should be more than adequate especially if you intend to fly the model as a two stage only. If not you could add some nose-weight to bring the CG forward.

Bruce S. Levison, NAR #69055

 

[astronboy]

Thanks Bruce.

Those little details are just what I was looking for in advice. As for the 1/8" Balsa. Yes, I plan on using it for both stages. I have some carefully squared away 1/8" Grade C - 'fisheye grain'- rock-hard balsa that I have been saving for the proper model. I figured that as the booster will need to sustain a rather tough landing, I should use the grade C for this design. I scour the Balsa at every hobby shop I run across looking for grade C, and have a small carefully hoarded collection of it. I included it on the sustainer mostly for looks: to match the booster.

I would also ask for suggestions on the booster section: I had originally thought of tucking a booster streamer or two into the bottom of the upper stage. Any thoughts? I ran the booster through a simulation by itself, and Rocsim shows the CG only 1" ahead of the CP after burnout. I am thinking that this, combined with the open front end would cause the booster to tumble. Will it do so in your experience, or should I add the streamers ?


I should be posting some pics of the booster a bit later tonight after the last fin has set.

 

[astronboy]

Actually, I just reviewed the data, and it appears that CG is only 1/2" ahead of CP after burnout. So much the better!!

 

[teflonrocketry1]

The booster should tumble; I get a static margin of around 0.27 (3/8") for the booster with the spent motor in it. If you already built the booster, do a drop test onto a soft surface from 8 feet up or so and see if it indeed does tumble. I do not suggest putting the streamer up in the end of the sustainer you are inviting trouble if the streamer gets stuck when it melts or singes from the hot gases escaping during staging.

Bruce S. Levison, NAR #69055

 

[astronboy]

Thanks. I was hoping it would tumble... Anyway, I have all of the fins attached. They of course need double fillets, and I will soak the insides of the stuffer tube with CA, but the booster is assembled. I used a leather hole punch to make three 3/16" vents in the BT-20, and 4 in the outer BT-55.

 

[powderburner]

I have to vote with teflonrock on this one, leave the streamer off the booster unless you absolutely MUST use a deployable recovery system.

Booster tumble recovery works just fine. It is simple, cheap, light, reliable, etc etc. About the only time it goes wrong is when you launch from a paved surface like a parking lot (DUH!) and the booster gets dinged when it lands, but you will get the same damage if it lands there under a streamer or parachute.

Anyway, there is almost always a way to make a booster tumble, but if the balance won't work out you could make it break apart. When I was a kid, I saw a rocket with a break-up booster that worked really cool. The booster stage had left and right halves, with the BT split down the middle (I think each half had two fins attached). The motor tube was attached to one side only. The two halves were held together with some kind of ring at the very bottom (the ring was part of one of the halves) and the upper stage slipped over the front and held it together. When the thing staged, the two halves split apart and tumbled down (I think they were tethered together).

And to stop the wadding/recovery from sliding aft inside of long BTs, I remember a reader suggestion from one of the old rocketry magazines (Estes newsletter?). Using a short length (1/4 inch or so) of splice or joint material, glue some balsa or spruce strips inside the tube in a 'criss-cross' pattern, leaving most of the tube open. Add fillets, and coat the exposed wood with epoxy. Slide this assembly inside the front of your BT, down to where you want the bottom of your wadding/recovery materials to stay, and glue it into place. This will hold everything in a forward position while under launch acceleration, and still let the ejection gasses through to finish the flight.

 

[astronboy]

Thanks guys.

I will forget the streamer. I was mostly hoping that it would prevent this booster from streamlining in, but as it will tumble, that is fine with me.

I like the idea of a 'break apart' booster. I will keep that in mind for a future project... maybe the two halves could be held together with elastic thread that is burned through by the ignition of the upper stage (like a BG with a moving wing)

I am thinking out loud here, and would appreciate any comments:

I have also been dabbling with the idea of a baffle... using it to not only protect the recovery system, but also as a bulkhead to keep the laundry up in the tube where I want it. It would have the added advantage of adding weight ahead of the CG for some added stability.

Would there be a problem with having a baffle so far up the tube, say 4" from the front end? Something like the baffle in the attached rocsim file:

 

[astronboy]

Here is a screen print. The baffle is in red:

 

[powderburner]

Myself, I might leave a bit more than 4 inches in the nose, but then again, your plan is probably just fine as is. While the pieces are still accessible during assembly, you may want to coat the inside of the mid and aft BT to help stand up to the hot ejection gases.

 

[astronboy]

I sure will. The inside of the front end of the booster will be soaked with CA, both in the BT-20 and BT-55.

 

[teflonrocketry1]

The design looks a lot better with the ejection baffle in place. The sustainers static margin as per the RockSim equations increases to 1.65!

Four inches down from the top of the body tube; doesn't seem like there will be enough room for a parachute, remember that the nose cone's shoulder takes up a half inch of that space. I suggest doing a test fit with the parachute and streamer on some spare body tubing to see how deep you actually need to place the baffle inside the body tube.

Bruce S. Levison, NAR #69055

 

[astronboy]

I was thinking about the nose cone shoulder myself as well. Due to space limitations, I will cut off the 'cone' of the pnc shoulder, and insert a balsa bulkhead into the remaining portion. This shoud gain me another 3/4." The remaining shoulder is 1/2" long. I always hate to add nose weight, as this just increases the chance of 'ESTES dent upon ejection, but I will add a little if I must. I will do a test fit of the laundry, and move the baffle back if necessary. However, as I am only using a 12" chute, I do not see much of a space issue.

The sustainer is going together tonight, despiet the -5 temp. I should have some pics tomorrow.

I would like to thank everyone who has assisted me on this thread. I am learning a lot!

 

[powderburner]

teflon,
You were probably thinking the same thing I was: not enough room for wadding and parachute in that 4 inch space. But astronboy will not need to use ejection wadding if he has a good baffle design. The folded 'chute should fit OK within 2 or 3 inches.

astronboy,
You may have some reason for wanting to mod the NC (cut off base, add balsa plug) but remember the famous old rocketry slogan: KISS. Keep It Simple, Stupid. I think there is something to be said for leaving the plastic NC as is and simply locating the baffle another inch deeper. But this is YOUR design, so I'll be quiet now.

 

[astronboy]

Thanks for the advice powderburner. I agree with the KISS concept, but I have made this mod several times in the past, so I am not too worried about it. Yes, a triple plate baffle should protect the laundry, and the 1.3" L baffle is a lot shorter than the 3" or so of wadding that I would normally use. I am still open to any ideas and mods as none of the recovery system has been installed yet.

 

[astronboy]

OK the sustainer is assembled. I am in the process of building the baffle, which will be coated inside and out with CA. Interestingly enough, even without the parachute, or the baffle, the CG is forward of the Rocsim. Here are a few pics of the assembled booster and sustainer:

 

[astronboy]

And here they are, but pulled apart.