Magnum II

I am just starting to get back into rocketry, and I am feeling like a kid again. I am hoping to build a few MPR kits and to enjoy working my way up to HPR. Last month I launched with a great group of guys here in Rhode Island (www.rimra.org). I had my kids build some Estes E2X kits, and I dug a few of my old rockets out of the attic. All of them flew great, with one painful exception. One of my favorite rockets 25+ years ago was my Estes Magnum. It's a 2-stage with a clear payload bay that runs on a D12-0 booster and B or C engines for the upper stage. Here is a picture of me loading it onto the launch rod, my oldest daughter holding all that was left after the second stage spectacularly burned in mid-air, and the payload that was lost (courtesy of my youngest daughter).



I figure that I still have the nosecone, payload bay, coupler and some fins to use as templates, so why not completely rebuild it? But this time around, I want to build it so it will run on Estes E16 (29 mm) motors, since they weren't available when I was a kid. Presumably, I could also run 24 mm D, E, and F engines with an adaptor. I downloaded the plans for the original Magnum and then designed the mod in OpenRocket, but the simulation was giving me some weird data. I just downloaded the free trial of RockSim, but I'm wrestling with loading the E16 engines into the database, so I thought I'd open source my plans to you guys. Can I get your opinions on this?


View attachment Magnum II.rkt

Great pictures. The 29 mm motors are a bit heavyer so keep an eye on the Center of Gravity.
Mr. Bob
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Welcome to the forum!

The Magnum was instantly one of my favorites ever since I first laid eyes on it. I've built several (and blew up one). The latest is a D booster, E upper stage version that hasn't been finished yet.

You can check out my stock model of the Estes Magnum .ork file over here: https://www.rocketryforum.com/showthread.php?123564-K-Tesh-s-Open-Rocket-files&p=1432036#post1432036. Mind you, there's a snafu with the fins that I haven't resolved [EDIT] Now fixed[/EDIT]. I'll see if I can work on it again tonight, and get the definitive version uploaded.



I'm not at all familiar with RocSim. However, I've been known to play a little with Open Rocket, and it allows you to save in either format (.rkt/.ork).


For a 29mm powered version, I'd go and upscale it, but that would involve having an electronics package for the staging event.


Here's a couple of threads you might be able to use to help you with the payload section if you want to clone a couple of them:

https://www.rocketryforum.com/showthread.php?64571-Cutting-Clear-Tubing

https://www.rocketryforum.com/showt...s-when-you-use-the-wrong-brand-of-Clear-Paint

BTW, I found that Testors Gloss Bright Blue (1210) was the match for the decals if anybody still has an unbuilt/unfinished Magnum hiding in their stash.

Thanks, guys.

K'Tesh, "I've been known to play a little with Open Rocket" - understatement of the day! Have you ever looked at the Estes Hercules? I has the same continuous fin design in a two stage that you built into your version of Magnum. Hercules and Commanche 3 were some of my other favorites back in the day. (I was really into multistage), but both of them went to the great rocketland in the sky on their first launches. If all goes well with this Magnum II rebuild/mod, they may be next in line for resurrection. But I may need to invest in a GPS tracker/altimeter. (I'm open to suggestions.)

As for the screwy Open Rocket simulation data, I may be figuring it out now. ~2500 ft and 0.5 Mach sounds pretty awesome to me! Here is the simulation data using an E16-0 booster and an E16-8 second stage. Does this make sense to you guys?

Bob, Open Rocket says that the design is 2.4 caliber. So you are right; the weight of the engines has significantly moved the CG, but I think this is still within tolerances. Am I right about that?

Thanks for the insight,

Brenton

I just calculated the rate of descent for the tumbling booster stage at 18.5 ft/s. That sounds pretty fast to me. (Though the second stage is descending at an average rate of 13.8 ft/sec with a parachute.) Does anyone know if that is acceptable?

Sorry to bombard you guys with questions. I appreciate any input you can provide.

Brenton

BDB, I'm a bit of a newbie and not familiar with a lot of the stuff described above... however, I have recently built and flown a Loadstar II and think that it looks an awful lot like this Magnum that you are describing.... 2 stage, clear payload, Estes kit... I'm wondering if they just renamed it, or if I've missed something here.

Also, I have just assembled a Goblin by SEMROC, and noticed in the instructions, a reference to a "Magnum" instead of a "Goblin". It didn't make any difference in my assembly, but it caught my attention. Now I'm a bit puzzled by the reference.

Kirk G said:

BDB, I'm a bit of a newbie and not familiar with a lot of the stuff described above... however, I have recently built and flown a Loadstar II and think that it looks an awful lot like this Magnum that you are describing.... 2 stage, clear payload, Estes kit... I'm wondering if they just renamed it, or if I've missed something here.

Click to expand...

Kirk, you've missed this one... The name "Magnum" was used for a 2 stage BT-60 based rocket (24mm booster to 18mm sustainter powered)(and Magnum has appeared as part of the names of some of the early D powered rockets (Centuri Magnum Hornet, Magnum Jayhawk, Magnum SAM-3, etc). The Loadstar II/Warp II is a BT-60 payload section attached (via a transition) to a BT-55 based two staged rocket (18mm booster to 18mm sustainter power)

Estes Magnum:



vs

The Estes Loadstar II (aka Warp II):




OK, update on SNAFU: One of the variants of the Magnum that I did has an error with the fins, I don't know if it's my variant, or if it's the "stock" variant. All I know is that the boosters are not interchangeable and they were meant to be. I haven't had a chance to fix it, as I just bought a new computer and I wasn't able to get OR up and going on it (Windows 8.1). I've spent the day updating it and upgrading to Windows 10. Now I'm pooped and I just don't have the energy to tackle this at this time.

The Estes Magnum rocket kit was first reased as part of a starter set in 1988.
This was in response to the Enertek company and it's line of composite E/F/G powered rockets.
Estes wanted a 'bigger/adult' starter set to interest that part of the market.

Years later the Magnum rocket was sold by itself.

Initiator001 said:

The Estes Magnum rocket kit was first reased as part of a starter set in 1988.
This was in response to the Enertek company and it's line of composite E/F/G powered rockets.
Estes wanted a 'bigger/adult' starter set to interest that part of the market.

Years later the Magnum rocket was sold by itself.

Click to expand...

It worked with me... It's one SEXY rocket! :wink:

I completely agree....the Magnum is super-sexy.

Kirk, because I have a soft spot for multistage + payload bay, the Loadstar II is definitely on my list of kits that I'm interested in buying.

I've been doing some research online, and it looks like the booster's predicted tumbling decent rate of 18.5 ft/s is within tolerances according to Tim Van Milligan, but barely (13 to 19 ft/s, see p. 6). So I'm considering rigging a streamer to slow the decent and to make it more visible. That will take a little bit of engineering to fit a streamer between the stages and a little bit of luck to get it to unfurl properly. But I like the challenge.

Thanks for all of the input. I just ordered the parts for this project last night, and I'll start building as soon as they arrive. I'll keep you posted.

I've started working on the Magnum rebuild. It's not really an upscale; I'm building the same size of rocket, just enlarging the motor mount diameter to accommodate 29 mm black powder E16 and F15 engines. (Don't worry; Open Rocket shows that it is still stable with the extra engine weight.) I already cut and beveled the fins, and I'm pretty happy with how they turned out, but I just realized that I forgot to consider the direction of the grain. I'm simultaneously building an Estes Ventris, and I have to admit, it's through-the-tube plywood fins look way more study than mine.

Can I strengthen these fins by papering them, or are they doomed to break like this? Also, should I have designed through-the-tube fins?

BDB said:

I've started working on the Magnum rebuild. It's not really an upscale; I'm building the same size of rocket, just enlarging the motor mount diameter to accommodate 29 mm black powder E16 and F15 engines. (Don't worry; Open Rocket shows that it is still stable with the extra engine weight.) I already cut and beveled the fins, and I'm pretty happy with how they turned out, but I just realized that I forgot to consider the direction of the grain. I'm simultaneously building an Estes Ventris, and I have to admit, it's through-the-tube plywood fins look way more study than mine.

Can I strengthen these fins by papering them, or are they doomed to break like this? Also, should I have designed through-the-tube fins?

View attachment 271115

Click to expand...

If it were me, I'd seriously consider cutting new fins. Even with paper, those look too easy to pop off, and you'd be forever fixing it.

TTW is a good option, and should help (as long as it's well done) in keeping the fins on straight. My modern builds feature TTW.

I am making progress on the rebuild of my Magnum, so I thought I should share a little bit about how it is going. I modified my design a little by adding tapered portions to the training edges of the fins on the booster. I did this because I had to lengthen the booster to accept a 29 mm black powder E or F engine, so I took a little liberty with the booster fin design. I attached the new rocksim file (below), if anyone is interested. I also decided to use a 24 mm engine mount in the sustainer, as inspired by the original Magnum, which had two different diameters of engines in the two stages. For what it's worth, I think I'll call this rocket Magnum+, as it is not upscaled, but just a souped-up version with larger engine mounts.

View attachment Magnum+.rkt

Inspired by this tutorial, I decided to make my own balsa plywood fins to add some extra strength, so I glued two pieces of 1/16" balsa together and pressed them overnight. I'm not super-happy with how they turned out, but they are light and probably a little stronger than a single sheet of 1/8" balsa. I also papered the fins for added strength. This was my first time papering fins, and it was also frustrating, but it turned out ok....until I applied thin CA to the edges to seal them. It sealed great, but it ran everywhere (K'Tesh, I should have followed your method!). I ended up coating the fins with sanding sealer (I really like that stuff!) and sanding them until they were smooth(ish). We'll have to see how they look when painted.

But that wasn't the biggest issue. I used the automatic function in OpenRocket to generate the fin tabs, but it made both of the tabs the same length. This is a problem because the two stages have two different motor mounts. The tabs fit great for the booster with the 29 mm motor mount (middle picture), but they are not long enough for the sustainer's 24 mm motor mount (right picture). I probably should have recut them, but I opted to shave ~1/8" off of the lower edges of the sustainer's fins (not the tabs).



Despite all of these issues, I dry-fitted (is that a word?) the whole thing last night, and it looked great. Unfortunately I didn't take a picture, and now I'm traveling for work, so you will have to use your imaginations until I get back.

methinks that a portion of your difficulties with the fin tab 'length/height' stem from an incorrect dimension of the sustainer motor tube(in the design file), standard Estes bt50 outside diameter is 0.976" (heavy wall is 0.995"). not sure why you simulated a 'switch band' with a transition when a tube coupler with a piece of body tube in the middle would have worked (w/o the 'discontinuity')...however I'm sure you had your reasons . note; if you want a review of a design file, it generally works best to post it before you start building.
Rex

Thanks Rex!

I originally downloaded the rocksim file from rocket reviews, and then I just modified the engine mounts, the booster length and fins. The "discontinuity" issue was always there. While trying to fix it, I must have screwed with some of the body tube dimensions and then forgot to change them back. That surely led to the incorrect fin tab lengths. Thanks for catching the real discontinuity issue in the "transition" to the clear payload bay. For what it's worth, here is the corrected file.


View attachment Magnum+.rkt

I find that some folks (me included) tend to overthink things and go for the complicated solutions...I have developed the habit of asking myself just how I plan to build things, that generally is enough to remind me that simple is better . no doubt you will get to know the various tube diameters as you get more practice designing/build more rockets.
Rex

One thing I wish I could find is a balsa coupler that is a tad longer than the SOP version. Long enough to put in a ring of body tube needed to simulate the plastic coupler on the aft end of the payload.

I recently learned that you can order a long section of coupler diameter tube from BMS, but it wouldn't have the end caps for the payload section.

1/16" ply bulkheads are fairly easy to make.
Rex

K'Tesh said:

One thing I wish I could find is a balsa coupler that is a tad longer than the SOP version. Long enough to put in a ring of body tube needed to simulate the plastic coupler on the aft end of the payload.

I recently learned that you can order a long section of coupler diameter tube from BMS, but it wouldn't have the end caps for the payload section.

Click to expand...

BMS sells a 4" long NB-60.

I've been gluing on the fins over the past few days. Despite the issues that I have had with them, I'm pretty happy with the result. It just needs a little more work on the fillets, and then the finish. I really like the look of the tabs on the aft ends of the booster fins and I love the idea of the 29 mm engine mount in the BT-60 booster.

Looking good. It's really going to be up there when it stages.

Just thought I'd show the finished product.



I flew the upper stage only today on a D12-5. That was all I had time for, plus I was a little nervous about losing it in the wind. The flight was great but it spun like crazy the whole way up. I suspected that would happen because my poor-man plywood fins were a little warped. But either way, that was the first stage of success. And if anyone who didn't read this asks, I'll say I designed it that way for extra stability. :wink:

If I can get away from work, I'll try to fly both stages at the CMASS launch next week. I'll probably make an 24/29 mm adapter for the booster and fly it with some combination of C11/D12 engines. I think I'll wait until the Jolly Logic Chute Release comes out to load the sustainer with an E9 and the booster with a E12 or F15 (sims to ~3000 ft). This project seems like the perfect candidate for that system.

BDB said:

Just thought I'd show the finished product.

View attachment 273822

I flew the upper stage only today on a D12-5. That was all I had time for, plus I was a little nervous about losing it in the wind. The flight was great but it spun like crazy the whole way up. I suspected that would happen because my poor-man plywood fins were a little warped. But either way, that was the first stage of success. And if anyone who didn't read this asks, I'll say I designed it that way for extra stability. :wink:

If I can get away from work, I'll try to fly both stages at the CMASS launch next week. I'll probably make an 24/29 mm adapter for the booster and fly it with some combination of C11/D12 engines. I think I'll wait until the Jolly Logic Chute Release comes out to load the sustainer with an E9 and the booster with a E12 or F15 (sims to ~3000 ft). This project seems like the perfect candidate for that system.

Click to expand...

That is something I'd like to see.

Nice Job!

So I got greedy this weekend. I had flown the Magnum+ both as a singe stage and in a two-stage configuration with a C11-0 in the original booster several times. It was a beautiful day, the last launch of the year...time to load up the new mod booster with an E16-0!

It ended badly....


The booster flew spectacularly and it appeared to stage, but the C11-7 in the sustainer didn't ignite. This actually happened twice. The first time, the sustainer came down awkwardly, but was intact....so (foolishly) I tried again. Same result. Staging, but the sustainer failed to ignite. This time it came in ballistic--whistling the whole way down.

One fin broke from the BT (but it is repairable) the top of the sustainer BT was smashed (but repairable) and the clear payload bay was completely destroyed. The nose cone was lodged about 3" into the ground.

My hypothesis is that the booster separated due to pressure build up. The black powder propellant in an E16-0 engine only fills about half of the tube, so this may be more analogous to "gap staging." I suspect that I need to drill vent holes. But in this case, I think I would have to drill holes in the booster and through the cardboard casing of the engine itself. Has anyone else experience anything like this?

Sorry to hear about the damage to your rocket.

Interesting theory... Gap staging.

I had a Magnum fail to ignite the upper stage once. The booster separated, but the sustainer came in ballistic (total loss). However, this was with a D12-0 and a C6-7. I later used the C6-7 successfully as a single stage. This was long before I knew anything about drag separation or gap staging. I still don't know why the sustainer failed to ignite.

Two ideas you might try.

1. Use tape to make a more firm connection between stages (try to hold them together longer)
2. Vent between stages (try to keep the ejection charge from ejecting before the upper ignites)

In both cases a lit upper stage motor will separate them.

Just suggestions...

Ouch!

Hard to see a Magnum bite the dust...

I looked at an E16 while I was at Hobby Lobby this morning, A lot of air in there. Looks less than half full. I can definitely see there being enough air to separate a bit too early.

John Beans said:

Two ideas you might try.

1. Use tape to make a more firm connection between stages (try to hold them together longer)
2. Vent between stages (try to keep the ejection charge from ejecting before the upper ignites)

In both cases a lit upper stage motor will separate them.

Just suggestions...

Click to expand...

I agree with John tape the motors together if possible with a single wrap cellophane tape (scotch type /christmas wrapping tape) that way the ignition of the upper motor burns the tape through or at least keeps the motors together a bit longer.

Thanks for the input. The engines were taped together, but it is a bit difficult to do because they are two different sizes. The original Magnum worked great because the 18 mm sustainer engine fit perfectly inside the 29 mm booster engine, so you could overlap the two motors by ~1/16". But that isn't the case with the 24/29 mm combination. However, I should mention that I used masking tape instead of cellophane. I forgot that cellophane is recommended for staging. (It's only been 25 years since I last did this.) Do you guys know why we friction fit with masking tape but join stages with cellophane?

I started repairing the sustainer yesterday. It is actually a very quick fix. I'm just waiting on a BT60 payload bay from Estes, and I'll be ready to repaint.

For the booster, I'm going to try all of the above. I think I will sand the crud out of the aft end of the 24 mm sustainer engine casing next time, so it nests into the booster engine a little better, tape well and combine all of that with 3 x 1/8" vent holes in the centering rings and at the top of the booster engine casing.