2157 Build Help

Hello! Brand new to the forum.
After a 20 year hiatus, I got back into rockets to share the experience I enjoyed in my youth with my kids. I Bought several kits for them for Christmas and then scratch built an 0652 Patriot which was one of my favorite kits long ago... My next build will be a 2157 Saturn V. Right away I knew I was going to mod it, as it had to fly with the F1 bells. I have been searching several different sites for hints and the configuration that was the closest to what I was had in mind was the one that rosko_racer did. It is a 1x24 + 4x18 cluster. Since this will be my first cluster build, I want to make sure I don't overlook any details. However there are a few questions I cannot find the answers to and I was hoping for some help.

1. rosko_racer - What lenght did you use for the 18mm engine tubes?

2. When doing the cluster I want to vent the 4 outboards to help eject the chutes. My theory is that it would aid the ejection from the 24mm motor and not stress the lower part of the Sat V. However in many of the builds I have seen the outboards are not used to help blow the chutes. Is there a reason for this?

3. Obviously I do not want to melt the bells. How close can I mount the tips of the 18mm Engine to the bells without melting them?

4. I want to brace the fins as this seems to be a weak point on the 2157. I have seen some buildups recommending .030 Styrene. I have never worked with this before and was wanting to know where is the best place to get it?

5. The engine bell fairings seem to be very thin as well. Does anyone have a recommendation as how to strengthen them? Or is it not necessary?

Thanks!

I'm only going to address #2--I always use a primary motor to blow the chute. Timing is a big deal, mixing motors and counting on them being dead on balls with timing is dicey at best. Plus you add weight with the extra venting/structure. Just not really needed.When it comes to recovery I use the KISS rule

#4. you can get styrene sheet in the .020 -.030 range at walmart and hardware stores.. look for the "for sale" signs,..usually around the same area where mail box's and house numbers are.

it's very inexpensive
the graphics easily sand off

Stymye - Thanks! That was just the sort of help I was looking for.

Hornet Driver - I agree, I want to keep it as simple as possible. The attached photo is from rosco_racers build and the concept I plan to use. As you can see the 18mm motor mounts are open to the top but the support for the 24 mm motor mount is completely sealed at the top. What I fear is that the ejection charge from the "C" engines will have no place to go and overpressure the lower rocket causing damage (or crack the paint/vacuum wraps at a minimum). What would you suggest in this case to vent the ejection charge?

To answer your questions:

1. The 18mm tubes are 6 inches long and the inside has a coat of epoxy passed the engine block to protect against the exhaust of the motors as I plan to put outboard C6-0s.

2. I guess it is kinda hard to find an 18mm and 24mm motors that have the same boost and delay... Can someone answer this better? You would have to use all 18mm or all 24mm to match the boost and delay.

3. I place the bells to match the end of the MM tube and the motors will be half an inch pass that... for extra measure. I gues you can get away with .3 or .25 inches.

4. Go with styrene fins. Not hard to make. Create a template of the fins and always use it while cutting the fins. They are strong and light. Do not have to worry about weight too much since you are clustering the Sat V. Epoxy works great at gluing these to the BT.

5. After gluing the fins and the fairings I used 30 minute epoxy to re-enforce the internal joints, much like the fillets on normal rocket fins. I later covered the bottom of the fairings with cardstock and coated it with CA. If I had to do this again, after the epoxy sets, I would go with another mix of epoxy and let it coat the interior of the fairings for added strength.

I hope this helps. Post questions or PM me if you have further questions or want more pictures as I still have not installed the MM assembly, but will do this weekend.

- RPR

Bushman said:

Stymye - Thanks! That was just the sort of help I was looking for.

Hornet Driver - I agree, I want to keep it as simple as possible. The attached photo is from rosco_racers build and the concept I plan to use. As you can see the 18mm motor mounts are open to the top but the support for the 24 mm motor mount is completely sealed at the top. What I fear is that the ejection charge from the "C" engines will have no place to go and overpressure the lower rocket causing damage (or crack the paint/vacuum wraps at a minimum). What would you suggest in this case to vent the ejection charge?

Click to expand...

OK, as I look at the pic your 18's are sealed and your single 24 is open. That really only leaves you a couple options. 1- use plugged 18's --no ejection charge-- as used on some boost gliders or 2- clip the end of the retainers and let the motors blow out --not really a good solution and frankly has some risks--like fires:y:. The plugged motors can be hard to locate at your local hobby shop. Go online and you'll have no problem. Nice build so far !!

rosko_racer - THANKS for the info!!
When I decided to cluster the Sat V one of the biggest questions I had was that of the timing between the 24mm and 18mm engines. After all the research I did, it is obvious that you cannot match them perfectly. However, according to the Estes Data, the D-12 has a burn of 1.65 seconds and the C6 has a burn time of 1.85 seconds, so they are .2 sec off. If you get delays of 3 seconds each, they are pretty close. My goal is to have the 24mm engine blow the top stage and actually vent the 18mm's through the top of the main body tube. Since there is a .2 sec delay the top stage should be off, but the chutes not open yet, but the timing is tricky. In that respect I am still trying to figure it out. But like Hornet driver pointed out, ejecting the engines is dangerous in too many respects, especially since I will have children in attendance. Shooting hot casings back to earth is certainly a hazard to the spectators as well as the rocket.

Oh - and definitely going with the styrene fins... The vacuum molded parts are just way to flimsy. I also go the build from your other post... What epoxy would you reccomend that doesn't eat the vacuum formed parts?

hornet driver said:

OK, as I look at the pic your 18's are sealed and your single 24 is open. That really only leaves you a couple options. 1- use plugged 18's --no ejection charge-- as used on some boost gliders or 2- clip the end of the retainers and let the motors blow out --not really a good solution and frankly has some risks--like fires:y:. The plugged motors can be hard to locate at your local hobby shop. Go online and you'll have no problem. Nice build so far !!

Click to expand...

The plan is to use C6-0s for the outboard motors and a D as a central motor. The outboard motors will remain on the rocket during flight and rcovery, no ejecting them. The epoxy layer inside the 18mm BTs should provide some protection against the fire and heat being shoot up as the propellant finishes burning and it should be released through the nozzle (in theory). I can also use a reload 24mm for the central motor and leave the others without an engine. Not many options but I do like the idea of a five-cluster Saturn V taking off!!! :wink:

I have not considered the differences in burn time... more research is needed.

Just plug the C6-0's with epoxy. I do it all the time when I cluster D's. and dont go quoting me anything about "modified motors" either. It has been a long time practice in the hobby, and even a part of some cluster rockets instructions. Just go have fun.

jimzcatz said:

Just plug the C6-0's with epoxy. I do it all the time when I cluster D's. and dont go quoting me anything about "modified motors" either. It has been a long time practice in the hobby, and even a part of some cluster rockets instructions. Just go have fun.

Click to expand...

+1

I have successfully plugged C6-0's with 5 min epoxy. Mix some up and drip it down the top of the motor. Just make sure to relabel your motor so you don't mistake it for a for real C6-0.

rosko_racer said:

To answer your questions:

1. The 18mm tubes are 6 inches long and the inside has a coat of epoxy passed the engine block to protect against the exhaust of the motors as I plan to put outboard C6-0s.

2. I guess it is kinda hard to find an 18mm and 24mm motors that have the same boost and delay... Can someone answer this better? You would have to use all 18mm or all 24mm to match the boost and delay.

3. I place the bells to match the end of the MM tube and the motors will be half an inch pass that... for extra measure. I gues you can get away with .3 or .25 inches.

4. Go with styrene fins. Not hard to make. Create a template of the fins and always use it while cutting the fins. They are strong and light. Do not have to worry about weight too much since you are clustering the Sat V. Epoxy works great at gluing these to the BT.

5. After gluing the fins and the fairings I used 30 minute epoxy to re-enforce the internal joints, much like the fillets on normal rocket fins. I later covered the bottom of the fairings with cardstock and coated it with CA. If I had to do this again, after the epoxy sets, I would go with another mix of epoxy and let it coat the interior of the fairings for added strength.

I hope this helps. Post questions or PM me if you have further questions or want more pictures as I still have not installed the MM assembly, but will do this weekend.

- RPR

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Click to expand...

I thought this post was an appropriate one to jump on the thread resurrection bandwagon. Haven't seen much from rosko lately but I sure would like to find out how those plugged 18mm motor tubes have held up. I mean the Saturn V had 5 motors in the 1st stage, right ? Just sayin...


photos courtesy of rosko_racer