Rocketry Warehouse Mongoose 54 build thread by CW

Guys,

I am going to do a build thread for the forum. I am going to do it by committee. I will ask questions as I go and you can provide input on the steps.

What form of retention should I use?

TAPE? Slimline? Aeropack MD?

cwbullet said:

What form of retention should I use?

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Tape or AeroPack. Nothing external.

If you will be using a case with I bolt for recovery I would use tape.

patelldp said:

Tape or AeroPack. Nothing external.

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Agreed

I might build 2 and use one with a slimline to compare flights.

I would go with the Aeropack internal for minimum diameter. I am doing a Mariah 38 build right now using this method. Haven't yet decided though how I am going to secure the internal retainer just yet though. I am throwing around the idea of tapping it and then using screws to hold it. I am however concerned that there will not be enough threads to hold onto in the tap as the metal is very thin. Another idea I have been contemplating is drilling it and then using PEM nuts on the retainer in a very similar fashion to drilling and tapping, but giving more threads to hold onto. I don't want to permanently mount the retainer because there will be times I want to use AT motors and other times I will use Loki motors and the position will need to be changed. I do have the extension rods, however I will fly this on my home field with G loads and on an away field with J's, so there will be a huge difference in case lengths.

I would say tape and then if you are using Loki, Aerotech or a 54mm CTi motor with a plugged and tapped forward closure, I would screw an eyebolt into the front closure and attach the shock cord to that. I'm not sure how much retention it would offer but at least if the case falls out (doubt it will) it'll be attached to something.

What set up options do you see to have the flexibility to fly both 54mm and 38mm motors?

Crash-n-Burn said:

What set up options do you see to have the flexibility to fly both 54mm and 38mm motors?

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This always strikes me as odd. Why build a 54mm carbon fiber rocket unless it's purpose-built for 54mm motors?

CW, I built a MD 38mm scratch rocket and used a Slimline. I also used Aeropoxy lightweight filler to make an aerodynamic, smooth transition to the Slimline. In terms of max altitude, it consistently fails to achieve the same or similar heights as a Blackhawk 38 without an external retainer, sometimes by quite a bit. And, the fins are airfoiled, it has a VK nosecone and airframe smoothed out really well.

I built my Madcow Tomach with the Aeropack MD motor retainer. It works well, but getting everything to unscrew right is a trick, and a little temp thread locker in strategic points helps a lot in getting the assembly out. Performance is awesome--got 14.4k on a K805G first flight (also used AT tailcone aft closure).

I'd recommend the Aeropack MD motor retainer, but shove that puppy as high up as the longest motor will require.

As for the 38mm option on a 54mm rocket, why? 54mm motors already range from the 54/426 I to a 54/2800 L. What would a 38mm motor add that you cannot already do with a 54mm version?

patelldp said:

This always strikes me as odd. Why build a 54mm carbon fiber rocket unless it's purpose-built for 54mm motors?

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It is a lightweight kit that can easily fly on 38mm motors (or even 29mm)
My access to fields that support 54mm motors is limited; I have better access to fields that support 38mm motors.
I may only have 1-2 opportunities a year to fly 54mm motors but have monthly opportunities to fly 38mm motors.
I would like to maintain the option for those rare 54mm motor opportunities - so would prefer not to install a 38mm MMT if possible.
CTI 38mm 3 grain I's are $10-15 cheaper than 1 grain 54mm I's.

Crash-n-Burn said:

It is a lightweight kit that can easily fly on 38mm motors (or even 29mm)
My access to fields that support 54mm motors is limited; I have better access to fields that support 38mm motors.
I may only have 1-2 opportunities a year to fly 54mm motors but have monthly opportunities to fly 38mm motors.
I would like to maintain the option for those rare 54mm motor opportunities - so would prefer not to install a 38mm MMT if possible.
CTI 38mm 3 grain I's are $10-15 cheaper than 1 grain 54mm I's.

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That is dead on. Often, I fly on a small field. Flying on a 38 mm motor might keep it on the field.

I have been testing the rocksim on H, I, J motors and have found that it fly high on an I. An I motor will take it to 4000-5000 feet.

I will use an Aeropack MD

cwbullet said:

That is dead on. Often, I fly on a small field. Flying on a 38 mm motor might keep it on the field.

I have been testing the rocksim on H, I, J motors and have found that it fly high on an I. An I motor will take it to 4000-5000 feet.

I will use an Aeropack MD

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Hi Chuck,

Subscribed.

Although I never did a build thread, or any build thread for that matter, for my carbon fiber 54mm Tomach, I still jumped through the same hoops you are now. I ended up using an Aeropack MD retainer but it's not without it's challenges. By far the easiest and least expensive route to go is tape but I seem to have a mental block on that one so I have never pursued it past a LPR D motor, again my mental block before you friction fit guys get yer nicker in a knot :wink:

The challenges, which you may have already thought of is where and how to mount the Aeropack. I opted to drill 3 holes @ 120 degrees, about mid way through the Aeropack body. I then used my dremel to really scuff up the backside of the retainer and epoxied some self clinching nuts, which is what I had in stock. This allows me to remove the Aeropack so I can service it, and I have had to replace the eye-bolt which got bent after one flight, as well as swap out the recovery harness, more importantly I now have the option of moving it up or in my case down for smaller motors, which of course means drilling more holes.

So far I have flown it from a CTI 1 Grain I445 Vmax to the biggest hardware, the Loki 54/2800. and I simply used a threaded rod extension instead of drilling additional holes. Considering I designed the rocket around the Loki hardware this helps me to add a bit of weight to off-set any difference in hardware, not quite, but it does put a little bit where it needs to be.

cwbullet said:

... I will use an Aeropack MD

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Cool, I like it. I'm thinking about doing the same but I'm not entirely familiar with all the hardware. I'm also primarily flying CTI. If you'll allow me the liberty of a question...

Do we need:
Aeropack 54mm MD Retainer
CTI Pro38 and Pro54 Delay/Eject Closure Adaptors
5/16-18 Extensions for M38 and M54
Aeropack 54/38 motor adaptor

...and will this set of hardware give the flexibility to fly CTI 3-6 grain 38s and 3-6 grain 54s?

Alright, forget the last post. I did the math. This is all based on positioning the Aeropack at the ideal minimum height for a 54mm 6G CTI case.

Case length diff. - 54mm 6G to 54mm 3G = 9.93"
Case length diff. - 54mm 6G to 38mm 6G = 6.04"

The longest 5/16 Extension is 6.6". So based on that alone, you can configure the rocket to fly a 54mm 6G or a 38mm 6G but you could not fly a 54mm 3G since the extension will not span the difference in the 3G to 6G case length.

Therefore, with spacers in the CTI case, you can fly 38mm 4, 5, and 6G motors and 54mm 4, 5, and 6G motors. You will also be able to fly 1, 2, and 3G 54mm cases in a friction fit configuration. There is no option (aside from customized work or a different motor retention option) to fly a 38mm 1, 2, or 3G case.

I would appreciate if someone can validate these findings. I did this off of data from the Apogee website.

Crash-n-Burn said:

Alright, forget the last post. I did the math. This is all based on positioning the Aeropack at the ideal minimum height for a 54mm 6G CTI case.

Case length diff. - 54mm 6G to 54mm 3G = 9.93"
Case length diff. - 54mm 6G to 38mm 6G = 6.04"

The longest 5/16 Extension is 6.6". So based on that alone, you can configure the rocket to fly a 54mm 6G or a 38mm 6G but you could not fly a 54mm 3G since the extension will not span the difference in the 3G to 6G case length.

Therefore, with spacers in the CTI case, you can fly 38mm 4, 5, and 6G motors and 54mm 4, 5, and 6G motors. You will also be able to fly 1, 2, and 3G 54mm cases in a friction fit configuration. There is no option (aside from customized work or a different motor retention option) to fly a 38mm 1, 2, or 3G case.

I would appreciate if someone can validate these findings. I did this off of data from the Apogee website.

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You don't need to use their extension rods you can make your own from threaded rod, so yes you can fly any combination of case and manufacturers in the case of differing thread sizes.

Here is a link to my post on the CTI thread for anyone who has questions on using the MD retainer with CTI https://www.rocketryforum.com/showthread.php?35532-CTI-Cesaroni-Technology&p=1508174#post1508174

mpitfield said:

You don't need to use their extension rods you can make your own from threaded rod, so yes you can fly any combination of case and manufacturers in the case of differing thread sizes.

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I made my own from all thread and all thread couplers. I bought a 10ft length of all thread, so I have enough to make a custom extension for any motor I want. I also went the route of using screws to hold the MD retainer in, and the ability to remove it has come in useful.

Chuck,

A couple of thoughts. If you place a bulkhead fwd of the motor, there will be no ejection charge force on the motor (assuming electronics deploy), thus tape should do it. If you go with tape (with or without bulkhead), you can "calibrate" your friction fit. First, take a fish scale (mass measurement device for weighing fish, not the anatomical part on a fish) and attach a clamp to it. Then test the force required to separate the joint above the motor. When you load the motor and tape it, check that it doesn't release with 2x or even 3x the force required to separate the joint. You will then have quantifiable assurance for you and the RSO that the motor will not come out.

All good thoughts. I will use aluminum all thread to make my own extensions and either aeropack MD or a custom bulkhead.

cwbullet said:

All good thoughts. I will use aluminum all thread to make my own extensions and either aeropack MD or a custom bulkhead.

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Agreed, good intel on creating custom extensions.

I will start Saturday. I had a little computer issue that I had to fix.

I have all the parts to start.

cwbullet said:

Guys,

I am going to do a build thread for the forum. I am going to do it by committee. I will ask questions as I go and you can provide input on the steps.

What form of retention should I use? TAPE? Slimline? Aeropack MD?

Click to expand...

Use the method Wayne mentioned in this thread: https://www.rocketryforum.com/showt...-Happy-Hour-Mongoose-54&p=1512477#post1512477

Bulkhead plate and coupler is provided. One would need PEM nuts (easily had from ebay) and the U bolt along with the screws to affix the retainer in the airframe. Doing it "Wayne's Way" one can
remove the assembly and replace the shockcord. I bought an Aeropack and it's a loose fit. Yeah, one can drill and tap it but I've always thought the eyebolt was a wimpy affair. Also only fits AT motors without having to make an adapter for others like Loki.

One would have to just mount it up as high in the airframe they care to secure it and make threaded rod adapters for each length motor they desire to use. It's the way I'm going to do mine.

I've done two MD 38mm rockets with epoxied AT MD adapters and am being as fastidious as all get out to avoid shockcord wear. Once they sustain significant heat wear, the rockets will need to be retired if they don't crash first. Wayne posted his pictures and I hit myself in the head. Glad I hadn't started building yet. His I think is the best if you expect to use your rocket more than a couple of times. Kurt Savegnago

Thanks. CF bulkhead and couplers would be lighter,

I wonder if you could machine down some delrin and use that as well.

mpitfield said:

I wonder if you could machine down some delrin and use that as well.

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Ahhhhh,

Cheaper to use what's provided with the "collection of parts":wink: Another thing, on the two 38mm rockets I mentioned above, I implanted shockcord protectors on both, but the first ground test on my LOC tubed project I cooked the shockcord protector
pretty good and had to replace it. I went ahead and made a boric acid/borax fire proofing solution and soaked sheets of cardboard in it. I let them dry and cut strips that I can put between the lower end of the shockcord/protector and the charge cup to protect the lower end of the shockcord closest to the charge against the immediate hot flash. Works pretty good in protecting the "shockcord protector" from the worst of the flash. Some of the partitions stay with the rocket, sometimes they get blown out but on the ones I recover, it is readily seen that they take the brunt of the burn well and save on the protector and the shockcord. Something to keep in mind if you have to permanently implant a shockcord anchor and want to protect it as much as possible. Cook the daylights out of a shockcord protector and you'll find you have to replace it quickly. This disposable fire resistant cardboard is easily replaceable and can "protect the protector" for maximum life and use.

Crash-n-Burn said:

The longest 5/16 Extension is 6.6". So based on that alone, you can configure the rocket to fly a 54mm 6G or a 38mm 6G but you could not fly a 54mm 3G since the extension will not span the difference in the 3G to 6G case length.

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You can also Daisy chain the extensions together, I actually flew a couple weekends ago using 4. My rocket is designed to fit a pro98 6gxl and I flew it with a pro54 4g. I had to make a special centering ring for the extensions so that i could actually screw everything together. Also, if you do this you MUST make sure there is a thrust plate at the base to transfer the motor thrust into the airframe, otherwise the rods can buckle when they are that long, and bad things will happen.

Something nobody told me and I didn't realize until I'd bought the whole set was that the aeropac extensions can basically be replaced by 5/16 alllthread as long as you have a coupling nut, so essentially you can make your own as long as you want pretty cheaply.

Very true as long as the motor as a 5/16 thread. I chose aluminum to save weight.

I would use aluminum tape. Really strong, low drag, low weight.