Estes #1969 Saturn V: A cautionary tale

[ebruce1361]

Keep It Simple, Stupid. That's what they tell me, but I take a certain pleasure in complicated challenges.

Back in April last year, I had the crazy idea to jump on the bandwagon and buy one of the Apollo 11 commemorative Saturn V kits and modify it fly on a cluster of five D12 motors. It took my family and I several months to assemble this behemoth, but we did it and almost had it ready in time for the 50th anniversary. Unfortunately, schedule changes happened over and over and we didn't get to fly it until December 21st.





Now, the way I designed the cluster arrangement was very specific. The center tube was to be loaded with a D12-5 as a backup ejection, then the two outboard tubes that ran all the way through to the parachute bay were to be loaded with D12-3s for the primary ejections, and then the two shorter tubes (which had been sealed off with JB Weld bulkheads) were to have D12-0s to only offer additional thrust.







I ran this thing through Openrocket at least fifty times with minor variations to the motor arrangement to get the ideal delay time, and I was satisfied with the results. I knew I wouldn't break any altitude records with it, (it weighed 998 grams loaded), but it was stable. I spent the second half of the summer just working on the paint and details. I know a lot of people use the ten-foot rule when it comes to rockets intended to fly, but I wanted to put in the work. I wanted this to look just as good from a foot away as it would atop a column of smoke from 30 feet away.

When we went to the club meet, we started out flying our smaller stuff because it was pretty gusty, and to use up some old motors. Well, we had a few far drifters making recovery take longer than expected, so I was startled when the LCO announced they were wanting to wrap up for the day and wanted the last couple of racks set up.

Here's where I messed up. Honestly I think my design was good, albeit complex, but a momentary lapse in attention to detail made for a critical error. I inserted the D12-5 where it belonged, but I transposed the D12-0s and D12-3s by mistake. I didn't notice the error until after recovery.

Ignition of all five motors and liftoff was PERFECT! It was so beautiful and offered a healthy roar for the first two seconds or so.





Then things went weird. The nose section separated much earlier than it should have with the rocket still traveling at nearly full speed.



This of course tangled up the parachutes, and instead of the booster coming down under three chutes and the nose under one, the booster came under only two while the nose came in ballistic and buried itself eight inches in the soil. (Luckily the ground was soft and the only damage is the nose was dirty and the escape tower broke off the command module)




{STORY CONTINUES IN COMMENTS IN ORDER TO LOAD ADDITIONAL PICTURES}

 

[PhlAsh]

Pressure separation. It happened to my Candle on this last launch

 

[ebruce1361]

{CONTINUATION}
When I discovered the motor mix-up, I understood that the top of the D12-0s burning through pressurized the parachute bay and blew the nose off before any delay, and the burning chunks of propellant were sufficiently hot to burn through my nomex blanket and melted four shroud lines on one parachute (thankfully, the two parachutes that did deploy weren't damaged).




When I finally got around to untangling the parachute mess and cleaning up the booster, I discovered the worst part of all this. I was hoping to refurbish the rocket and have it ready to fly again before spring, but I found the sealed motor tubes that had the misplaced D12-3s in them were blown out through the sides. The ejection charges went off and pressurized the body between the centering rings and weren't strong enough to blow the main body apart, but were enough to crush the three other motor tubes. The internal damage is extensive and the only way I can think to repair it is to drill out the centering rings and hope to sand the inside of the body perfectly enough to allow me to install new motor tubes and centering rings without damaging or weakening the main body.






So, I have decided to retire this particular Saturn V and hang it in a place of honor in our dining room and build a replacement. With the new one, I intend to make a few changes. First, I need to pay closer attention to some of the cosmetic details I messed up on. Next is rail buttons instead of the tube lugs because this thing was WAY TOO heavy for the 1/4 inch rod and I ended up having to use five-minute epoxy to affix bigger lugs generously donated to me by another flier with an Estes Saturn V. Also, I am going to go for the Boyce Aerospace fin can to make the fins stronger and prevent the vacuform fairings from melting.

But the biggest change is going to be my motor mount arrangement. I intend to add vent holes to the centering rings between the motor tubes so if an internal explosion happens again, the pressure can vent out the back and not destroy the motor tubes. Also, I am going to more disciplined and buy actual plugged D12P motors instead of trying to engineer a sealed tube that may or may not withstand the pressure of a D12-0 or a D12-3 in the wrong place.

So, the old K.I.S.S. idea definitely holds true here, but don't be afraid to try something overly complicated. The challenge is fun and rewarding. Even with a failed flight and mortally wounded rocket, it was awesome!

(Onboard camera video; please excuse the incorrect date and my lack of editing skills):

 

[kuririn]

I would call that a qualified success.
I also agree with your analysis and choice to rebuild.
The Boyce fin can is heavier, so more nose weight will be needed.
May I suggest that the correct motors be written on the aft centering ring and pointing to the proper motor tube.
Instead of buying plugged motors, how about plugging the motor tube and cutting a hole in the motor tube and aft centering ring and venting the blowby gasses out the back? Or plug the tube and loosely fit the motor in. Enough to keep it from sliding out on the pad, but easily ejected when the gasses blow. Assuming your launch site allows motor ejection, of course.
If not for the motor switcheroo I think it would have been a nice flight!
Laters.

 

[NOLA_BAR]

Looking at your original motor mount design you might want to consider just extending all 5 motor tubes equal length. That way you just use 5 motors with the same delay. I’ve found that even using the same ejection delay there is always a slight variation. Basically you have 5 chances to eject the parachutes. Also consider using a heavier wall tubing like the ST-9 tubing from erockets for the motor mounts. Still you did a cool thing with the Saturn V!

 

[ebruce1361]

May I suggest that the correct motors be written on the aft centering ring and pointing to the proper motor tube.
Instead of buying plugged motors, how about plugging the motor tube and cutting a hole in the motor tube and aft centering ring and venting the blowby gasses out the back?

@kuririn
The sad part is I DID write the motor designations on the aft ring. And then I painted the rocket and enough overspray got inside the space in the back to cover up the writing.

As for your idea about the vented motor tube, that's not half bad!

@NOLA_BAR
I had initially thought of five full length tubes with matching ejection, but I thought on the off chance that the ejections DID go off all at the same time, I didn't want to risk blowing the body apart before the nose had a chance to eject. Looking back, that might actually work better anyhow because I can still stagger the ejections and have a mix of 3, 5, and 7 second delays with full tubes. Not to mention, I can get away with shortening the motor tubes to allow more room for the parachutes because this first one was mighty cramped inside!

Also, I'll look into using those stronger tubes you suggested instead of the standard paper ones.

 

[SecondRow]

Also, I am going to more disciplined and buy actual plugged D12P motors instead of trying to engineer a sealed tube that may or may not withstand the pressure of a D12-0 or a D12-3 in the wrong place.

I don’t think Estes makes D12-p’s anymore.

That looked like a really nice boost.

 

[Daddyisabar]

Oopsie! Rocket science is cruel, especially when using poor boy dual deploy. Nothing like those Ruskie boys who put the navigation package in upside down. Plugged motors are a good way to go. Reinforce your thin walled tubes with thin Ca in the building process. Then you will have poor boy phenolic tuning. Poor boy D12 plugged motors are very naughty.

 

[ebruce1361]

I don’t think Estes makes D12-p’s anymore.

That looked like a really nice boost.

Maybe that's why I opted for the D12-0 design to begin with. I can't remember.

 

[kuririn]

Just FYI, I bought some D11-P engines a while ago from LP2K:
https://lp2k.com/d-11p-3-engines-flying-model-rocket-engines-estes-1669/

 

[samb]

IDK. Based on the pictures and description, this looks like textbook drag separation. The heavy back end started it's deceleration and return to earth the second the motors started burning their delay grains but the front end wanted to continue the coast phase and the convenient separation point allowed it to do so. Borrowing an HPR technique, a couple of nylon shear pins might have held her together for a better outcome. Anyway, that's my Monday morning quarterback analysis . Kudos on a great build and willingness to stretch the envelope.

 

[ebruce1361]

IDK. Based on the pictures and description, this looks like textbook drag separation. The heavy back end started it's deceleration and return to earth the second the motors started burning their delay grains but the front end wanted to continue the coast phase and the convenient separation point allowed it to do so. Borrowing an HPR technique, a couple of nylon shear pins might have held her together for a better outcome. Anyway, that's my Monday morning quarterback analysis . Kudos on a great build and willingness to stretch the envelope.

I added 75 grams of weight to the Command Module to keep it stable with all the added tail weight, and the nose was a pretty tight fit especially with the nose section parachute cable going through. Granted, the Saturn V has plenty of drag from the textured wraps and fairings, but I don't think drag separation is what happened especially since the back of the nose shows some evidence of burn marks from the D12-0s coming through. However, it is certainly a possibility. I regret not flying it with my JL Altimeter3 to give me some speed and g-force data.

On my next build, I might go for a test using an intentionally under-powered motor that won't actually fly the rocket (or maybe even tether it to the ground) and make sure I have enough ejection force to break some shear pins and then fly it for real.

 

[afadeev]

the biggest change is going to be my motor mount arrangement. I intend to add vent holes to the centering rings between the motor tubes so if an internal explosion happens again, the pressure can vent out the back and not destroy the motor tubes. Also, I am going to more disciplined and buy actual plugged D12P motors instead of trying to engineer a sealed tube that may or may not withstand the pressure of a D12-0 or a D12-3 in the wrong place.

How about extending all five (5) MMT tubes all the way to the FWD bulk-head, and flying D12-3's (or a mix of D12-5's and 3's) in all 5 tubes?

This would eliminate the opportunity for future on-site mix-ups, and simplify the motor inventory management!

The tricky part will be validating the volume of BP in a D12 motor, and how many are required to deliver successful ejection. Long MMT tube + (4" Sat-V airframe) * (6+" of parachute packing space) is a lot of volume to pressurize before the nose cone starts moving. One D12 motor's ejection charge may not be enough, depending on how tight you seated the nose cone.
Ground testing may be warranted.

IDK. Based on the pictures and description, this looks like textbook drag separation.

I added 75 grams of weight to the Command Module to keep it stable with all the added tail weight, and the nose was a pretty tight fit especially with the nose section parachute cable going through. Granted, the Saturn V has plenty of drag from the textured wraps and fairings, but I don't think drag separation is what happened especially since the back of the nose shows some evidence of burn marks from the D12-0s coming through. However, it is certainly a possibility.

The soot on the Nomex blanket and back of the nose cone only guarantees that D12-0 burnout gasses (or D12-3 ejection charge) had reached those objects, not that they caused separation. If you can grab the rocket by the nose cone, shake it, and get airframe to separate -> that's drag separation in action. Very common on heavier large diameter HP rockets.
On a Sat-V with 5 D12s hanging off the back end, it's increasingly likely.

The key is the timing of the events: at what time in flight did the nose cone start drifting off?
If you have a video of the flight, it might help with this forensic analysis.
Not that it matters to the outcome, since you are retiring the airframe either way.

a

 

[ebruce1361]

If you can grab the rocket by the nose cone, shake it, and get airframe to separate -> that's drag separation in action. Very common on heavier large diameter HP rockets.
On a Sat-V with 5 D12s hanging off the back end, it's increasingly likely.

The key is the timing of the events: at what time in flight did the nose cone start drifting off?
If you have a video of the flight, it might help with this forensic analysis.
Not that it matters to the outcome, since you are retiring the airframe either way.

a

I do have video from the ground, but I still have yet to pull it off my wife's camera. As for the separation, I actually have to put some muscle into pulling the nose off and even had to sand it a bit after the paint dried because I couldn't get the nose into the body. Even now after the flight, attaching and detaching the nose requires some twisting.

I still like the staggered ejection because since the nose was so tight on this one (granted, the next one might not be as tight) that I worried about a single ejection charge being sufficient to eject the nose. I had the longer motor tubes run sixteen inches, so the portion of the body that needed to pressurize with the parachutes in it was only eight or nine inches deep. So for a simplified motor arrangement like you said, I think the easiest thing would be to run all five the full length, and throw in some D12-7s. They would be a last-ditch-effort ejection, but would more likely just fire into an open and empty body tube that the D12-3s or D12-5s already pushed the chutes out of.

 

[K'Tesh]

One thing you might want to check into is making some "Starlite" to create a fireproof layer on the areas were the blast from the D12-0s will be concentrated.

 

[ebruce1361]

One thing you might want to check into is making some "Starlite" to create a fireproof layer on the areas were the blast from the D12-0s will be concentrated.

As a pointy-eared wise man once said, "Fascinating."

Tell me more about this "Starlight" material.

 

[K'Tesh]

As a pointy-eared wise man once said, "Fascinating."

Tell me more about this "Starlight" material.

https://www.rocketryforum.com/threa...ade-in-the-kitchen-a-form-of-starlite.151564/

 

[cerving]

The First Rule of Scale: The more time and work you put into a rocket, the more likely it is to fail. MY Saturn V got blown in half by an 29mm/2G F33 cato. Fortunately, the real one did much better...

 

[David Schwantz]

On mine I ran a full length internal launch lug, just made a small oval hole for it to come out in the transition area. Although I did put buttons on later. Used LOC 4" main body tube, lite ply CRs, single 29mmt and she flies on AT G74-6W. Weighs in at 22 oz.

 

[Blast it Tom!]

Who doesn't have a soft spot for the Apollo-Saturn V? I'd show you my 1/100 desktop version, but gotta figure out how to upload images that aren't on "teh interwebs". And the new guy (me) just learned about "drag separation" - whether it happened to you or not, it's one of those things I'll tuck in my head.

I'd sure love to fly something like that - congrats on a very good design and build process. It should only get better! I must admit getting 5 motors to ignite all at the same time is quite the accomplishment! I sure hope I can do something like this after I retire!

 

[Blast it Tom!]

Thanks for the "like" ebruce1361. I have to get on to stuff like that. Now on the cluster ignition thread, I just realized that my spiffy single neutral cluster setup is fine for 3 motors, but sure isn't possible here. Did you take any pictures of your ignition setup? After all, you lit all 5 and that really is saying something!

 

[ebruce1361]

(sorry it's taken me all weekend to reply, my computer decided to be dumb)

Unfortunately, I didn't take any pictures of my igniter whip setup, and it was damaged during the drive home and will need to be rebuilt, but here is a diagram of what I built:



What I wanted here was a way to isolate each igniter separately to verify continuity at the pad. With each switch going to one half of each igniter pair, I could switch off all but one, check for continuity, switch that one off and test the next one and so on. This setup would also allow for the use of two, three, or four motor clusters as well just by switching off the unused pairs. The only challenge then is trying to keep any of the igniters from touching each other. For future clusters, I am going to make my own igniters with long enough insulated leads to keep them from touching anything and shorting out.

 

[Blast it Tom!]

Ah, yes I see, and much as I expected. Now I'm planning on upgrading our launch system, which at this point is simply clip to the rocket, clip to the battery and hit the switch. And you made me remember the old continuity check light. And dumb me... I figure in order to run a light bulb you have to have current, and having current in a circuit with an igniter in it does not bode well for launch control-ability! Yest I know there is a way to do it. So I figure an LED ahead of the switches indicating man (12V car battery or similar) voltage. Then as you have, 5 continuity check lights (I think you're just checking via meter?). But for launch you need one common switch... Hmm. I'll be poking around, I know there is a way to do this, but circuit design is a long way from my forte! My big thing is, I'll need a place to launch at some point and if that turns out to be a sanctioned event, I don't want someone telling me I cannot use my system because its too primitive or even unsafe by NAR/Tripoli standards. Sorry if this sounds stupid, I'm just getting back into this.

 

[ebruce1361]

The only dumb question is the question not asked, I always say. As for sanctioned approval, I used this rig at the December launch for Tripoli Tampa, so I doubt it would be an issue anywhere else. It's just a five-way clip whip with switches.

The launch system for the club was built by someone else, so I can't say exactly how it works, but when continuity is present, an LED for that pad comes on in the box. If I were to build a similar setup, I'd just send one and a half volts through the line with an LED in series in continuity check mode, and then switch to the full 12 volts for ignition power. Anyway, I just flipped through each switch one by one and made sure I had my light each time, then I switched all five to "ARMED" and hoped for the best.

 

[Blast it Tom!]

Wow, that brings up a whole new deal, one that's been in the back of my head. I intend to be "self contained." We have a pad, a 12V car battery, and I'm in the process of designing a box for it with the requisite switches, safety interlocks, lights, etc. But I really don't know if I'll go to sanctioned events or just find a big empty place (with permissions, of course). So if I'm self-contained, but end up at a Tripoli or Pittsburgh Space Command (NAR) launch, would my system need inspected or would I have to use theirs?

"Big empty places" are tough to find around Pittsburgh; but the sanctioned launches by the two groups I mentioned are a solid hour away, not something where you'd say, "Hey, it's a nice, calm clear afternoon - lets go launch!" as was the style when I was very young.

Sorry, a little off-topic.

 

[ebruce1361]

I hear ya on the inconvenience of the club launches. Our club only meets once per month, and the location is 40 miles from where we live. I'd love to find a field nearby where we can fly the smaller stuff, but that's difficult here in the Tampa bay area.

As for your system, I say go ahead and build your own rig, but you almost certainly wouldn't be permitted to use it at an NAR or Tripoli club event. Those clubs have their own equipment anyway, so it isn't even necessary. I have a few pads and launch controllers from when I was a kid, and I even still have my home-brew launch controller that I made from a computer power supply case and an old guitar cord, but none of them have been used in years since all I need to bring are the rockets and motors. (Some clubs even have a motor vendor on site if you need some all of a sudden)

 

[Nytrunner]

but gotta figure out how to upload images that aren't on "teh interwebs".

From Explorer: Just drag the image file into the text box where you're typing your post

From other places: just right-click the image you want to upload, select copy, then paste into the text box while writing your post. (to paste either right-click-> paste, or hit cntrl-v)

 

[Blast it Tom!]

Thanks, both of ya! Howdaya like that, just about like native Microsoft Vinders 10 ops!

So, back to the subject, 5 D motors at the bottom of that beautiful Saturn is a big chunk of mass. And I see no transparent fin extensions, which is really nice. but did you have to add mass up top to get it stable?

 

[ebruce1361]

Boy, DID I!
The command Module has all four clay blocks from the kit stuffed in it plus a good scoop of lead airgun pellets. The CM plus escape tower weighed a hefty 85 grams not including the paint, decals, or the masking tape for the surface textures. The capsule was so tightly packed, that I couldn't even glue the plastic end cap to the bottom because it stuck out just a bit too far. So, I just let the clay stick to it to hold it on. Fully loaded, the whole rocket weighed 998 grams.

 

[Blast it Tom!]

My glory! 2.2 lbs of rocket! Ok, I have a weird sense of humor...

"I only need two more grams, ma!"
(mom's off in another corner of the house)
"Huh? You need your two grandmas?"
"No, I want to make a kilogram!"
"That's absolutely horrid, don't talk about killing your gram! Now go to your room!"

All that came to mind when I thought you were just two grams shy of a kg. So... is there any way to test that besides the good ol' string test? Seems a bit much to expect you to whirl that beauty around out in the yard...

Next I want to whip out some quick calcs and try to figure out how far and fast 100 N-m of impulse could take you...