Madcow Mongoose 38mm Carbon Fiber Minimum Diameter Build Planning

[kevinkal]

I picked up a 1.6" Carbon Fiber Mongoose Minimum Diameter kit at last Friday's Door Buster sale. Since then, I've been reviewing various related Minimum Diameter threads for both the Mongoose 38 and similar Blackhawk 38. I started this thread to open discussions and share ideas and methods for building this kit. I am new to minimum diameter kits, and look forward to learning more about how things are done and why.

I've been working on an Open Rocket Model, and have basically modeled the kit components per the description on the Madcow site for the Mongoose 38. I don't expect to receive the kit until next week... possibly later given the sales volume that Madcow is undoubtedly handling. I'm planning to go standard Dual Deploy using a StragoLoggerCF and a small 2S 180mAh LiPo. I'm also planning to integrate an EggFinder Mini GPS Tracker in the fiberglass nosecone along with a small 2S 300mAh LiPo. I included an Aeropack minimum diameter motor retainer as well. The weight is shaping up to be something over 27 ounces without a motor. Stability numbers seem to be working out well for all motors I've simulated thus far. I'll update the model when I get my hands on the actual parts, but I believe the model is going to be close to reality. For anyone interested, I've uploaded the OpenRocket model, and also exported and uploaded a RockSim version as well.

Open Rocket Mongoose 38 model:
View attachment Mongoose38_KK.ork

RockSim Mongoose 38 model:
View attachment Mongoose38_KK_rocksim.rkt

Some images of the model:
No Motor:


With an AeroTech RMS 38/1080 J570W


Simulation Results for various AeroTech RMS motors:


I currently have 3 AeroTech 38mm RMS cases, the 360, 720 and 1080. I don't plan on purchasing any other case hardware, but will likely pick up the 38mm Reload Adaptor System, along with a threaded forward closure for use with the RAS.

 

[mpitfield]

So far I like your choices. You might want to consider, if not already, making the AeroPack removable, instead of gluing it in. It adds a minor bit of complexity to the build but the ease of maintenance is worth it. If you do move forward with the AeroPack MD retainer you might want to send an email to Teddy at One Bad and inquire on having Teddy make you a recovery harness with an integrated eyehook to swap with the existing one that comes with the retainer. That is unless your harness can slip through the eye hook as it is. Logistically you may want to add a switch to the tracker in the nosecone so you can turn it on while on the pad, vs. at your prep table. I like the magnetic switches for this. Fin attachment will be something for you to consider as well. I have two 38 mm MD rockets and in both cases I did a T2T, single layer 3K 2x2 twill layup. I am under no illusion that this was required for a 38 mm MD build. However I did it for the experience for when it will be required, and my plans include some pretty serious builds going forward. To my way of thinking there is much to be learned when it comes to composite layups and it does not make any sense that when I do need it, it is my first time doing it. Bottom line think about your long term goals and use this build as a stepping stone towards them, that is if you have given that any thought.

Sent from my ONEPLUS A3000 using Rocketry Forum mobile app

 

[manixFan]

I also picked up one of these kits and have already received it. I was thinking it was the same thin tubing used in the 54mm CF Mongoose I had but it's much heavier. I plan on flying it on the CTI 6XL and the Loki 38mm 1200 (K627). I'll use the same Pro Line epoxy for the fins I used on the 54mm version which survived Mach 2.3 or so with no extra fiberglass, just decent fillets. Motor retention will be friction fit.

I hope to have Adrian's new tracker (Featherweight) and will use a Raven for the altimeter. I like having accelerometer data for high performance rockets. This will be a BALLS rocket - a bookend to the 98mm CF Mongoose I plan to fly next year.

In spite of not being thin will tubing it's a great value at the Black Friday price.


Tony

 

[kevinkal]

I've been eyeballing the Raven3 myself. It's nice. I'm with you.. it's nice to have acceleration data. Is his new tracker available yet? I've been having good results with my eggfinder stuff.. so I'm definitely going to pick up an EF Mini.
While it's not the thinnest CF tubing, I think it's just slightly heavier than thin wall FG. It should be much stiffer/stronger too. I'm not sure what that buys... it should add a bit stiffness to the fin can area. I expect that the 3/32 thick fins are a bit overkill... perhaps we'll need to take a look at them in Aero Fin Sim.
Was there any Proline 4500 in the kit? If not, I'll be needing to pick some up. I have plenty of RocketPoxy, but I believe Proline 4500 has better heat resistance.

 

[kevinkal]

That's pretty good that you received your kit already. My order status says:
This order is marked as
"Awaiting Fulfillment

Your Order Contains:

• 2 x Chute Blast Protector 06"x06"
• 1 x 1.6" Carbon Fiber Mongoose (Minimum Diameter)
• 1 x Aero Pack 38mm Minimum Diameter Retainer, with Bypass Holes (M38BE) "

 

[kevinkal]

So far I like your choices. You might want to consider, if not already, making the AeroPack removable, instead of gluing it in. It adds a minor bit of complexity to the build but the ease of maintenance is worth it. If you do move forward with the AeroPack MD retainer you might want to send an email to Teddy at One Bad and inquire on having Teddy make you a recovery harness with an integrated eyehook to swap with the existing one that comes with the retainer. That is unless your harness can slip through the eye hook as it is. Logistically you may want to add a switch to the tracker in the nosecone so you can turn it on while on the pad, vs. at your prep table. I like the magnetic switches for this. Fin attachment will be something for you to consider as well. I have two 38 mm MD rockets and in both cases I did a T2T, single layer 3K 2x2 twill layup. I am under no illusion that this was required for a 38 mm MD build. However I did it for the experience for when it will be required, and my plans include some pretty serious builds going forward. To my way of thinking there is much to be learned when it comes to composite layups and it does not make any sense that when I do need it, it is my first time doing it. Bottom line think about your long term goals and use this build as a stepping stone towards them, that is if you have given that any thought.

Sent from my ONEPLUS A3000 using Rocketry Forum mobile app

I'm not sure what I'm going to do with motor retention. It seems that most if not all locations are out of stock on the Reload Adaptor Systems, and the threaded plugged forward closures are pretty expensive. Perhaps I'll go with tape for retention, and the AeroPack Retainer just for a Kevlar anchor point for now.

I was looking at Ted's new 3/16" tubular Kevlar. He sells it with 2 and 3 loops, but in 25' lengths. I'm not sure that we need or want 25' times 2 of shock cord in these.

 

[OverTheTop]

I'm not sure what I'm going to do with motor retention.

Just go with the Aeropack MD, and locate it to take the longest motor you think you might fly. You can use spacers for holding shorter motors. That's how most of my HPR stuff is rigged.

I personally would not use tape. It doesn't inspire confidence for me, and probably shows motor retention was treated as an afterthought. YMMV.

I have quite a few Ravens. Good gear.

 

[mpitfield]

I'm not sure what I'm going to do with motor retention. It seems that most if not all locations are out of stock on the Reload Adaptor Systems, and the threaded plugged forward closures are pretty expensive. Perhaps I'll go with tape for retention, and the AeroPack Retainer just for a Kevlar anchor point for now.

I was looking at Ted's new 3/16" tubular Kevlar. He sells it with 2 and 3 loops, but in 25' lengths. I'm not sure that we need or want 25' times 2 of shock cord in these.

A 25' harness may seem excessive, but it is not for this rocket. If it fits then I would go with it, if not then look to shorten it. As far as friction fit retention, as OverTheTop said "I personally would not use tape. It doesn't inspire confidence for me". Having said that, there are a lot of very experienced and respected flyers who have used it successfully, and continue to do so. So even though it is not something I and others are a fan of, it would be ignorant to deny their results. So do what works for you.

 

[mrwalsh85]

Logistically you may want to add a switch to the tracker in the nosecone so you can turn it on while on the pad, vs. at your prep table.

This. I used the Mini with the small battery that everyone recommends at Airfest. I can't help but wonder if my battery died during the long wait on the pads, because I lost signal during descent (around 5000 feet) and could not find it again. Tracker didn't work upon retrieval so it's safe to assume it was pretty dead. Also, the battery wouldn't charge up so I bet it's shot now. Still learning about LiPo's.

 

[Buckeye]

I'm not sure what I'm going to do with motor retention.

Read Crazy Jim's Blackhawk38 build thread. Is it the bible for 38mm MD techniques. Here is a super easy anchor point:

https://www.rocketryforum.com/showt...wk-prototype-first-look-!&p=490000#post490000

I use this and a couple other tricks that Jim mentions. If using CTI, dump out the black powder and epoxy an eyebolt in the plastic forward closure touch hole to use as another anchor point/retention. I was also leery of friction fit, but it just works. The wrap of aluminum tape around the motor rear closure and airframe is most important.

 

[manixFan]

Just go with the Aeropack MD, and locate it to take the longest motor you think you might fly. You can use spacers for holding shorter motors. That's how most of my HPR stuff is rigged.

I personally would not use tape. It doesn't inspire confidence for me, and probably shows motor retention was treated as an afterthought. YMMV.

I have quite a few Ravens. Good gear.

Folks go back and forth with friction fit. I have flown my 54mm CF Mongoose with the CTI 6XL motor with only friction fit. It was not an afterthought – it was designed that way. I've used friction fit since I started flying (now over 15 years) and have never lost a motor.

However I've witnessed multiple failures of folks who used eyebolts (screwed into the forward closure) to retain their motor and had them unscrew during descent under chute. I helped recover a rocket at Airfest this year where that exact failure occurred. So using a threaded bolt or rod to retain a motor is certainly no more foolproof than friction fit.

What works for me may not work for you. But please don't treat it like it's somehow inferior to other forms of retention.


Tony

 

[kevinkal]

This. I used the Mini with the small battery that everyone recommends at Airfest. I can't help but wonder if my battery died during the long wait on the pads, because I lost signal during descent (around 5000 feet) and could not find it again. Tracker didn't work upon retrieval so it's safe to assume it was pretty dead. Also, the battery wouldn't charge up so I bet it's shot now. Still learning about LiPo's.

I'm glad you found your rocket after loosing the tracker signal.

How many mAh was the battery you were using, and how many cells did it have?

Many smaller low C ratted LiPos will have an integrated protection circuit in them that will "shut off" if the voltage goes to 3.0 volts per cell. I forget exactly how, but if your LiPo has a protection circuit, it may be possible to apply a certain voltage across the LiPo to re-enable it... then charge it fully. There's lots of good (and bad) information on the web.

LiPo chargers are typically configured to perform a voltage check before they start charging. If a LiPo without a protection circuit was drained below 3.0 volts per cell, then the charger will not charge it and report a problem with the battery. If you know that the LiPo was drained at a slow rate to below 3.0 volts per cell, it is possible that the battery wasn't damage too bad and it may be possible to gently "force" charge them gently to just above 3.0 volts per cell, then put them on a LiPo charger to fully charge them. Did I mention Gently? There is a risk that this will cause the LiPo to burst into flames.. but using gentle charge currents, I haven't seen that happen.

I'm feeling pretty good about using a 300mAh 2S (7.4V) LiPo for the Mini. (When fully charged they are 8.4V.)
They are what Cris recommends with the EF Mini tracker. Here's what he says in the Mini Assy Manual:
"Powering your Eggfinder Mini
The Eggfinder Mini requires 4.5V-9V, with a nominal working current of about 70 mA. However, when first powering up it may have peaks of up to 200 mA as the GPS module acquires satellites. For this reason, we recommend that you use a 7.4V 2S LiPo battery pack; just about any one you buy will have enough capacity for run your Eggfinder Mini board for at least two hours. A 300 mAH 7.4V 2S LiPo is ideal, it’s a little smaller and lighter than a 9V battery and will easily power your Eggfinder Mini for over 4 hours.
...
If you have a 38mm minimumdiameter rocket, a 200 mAH 2S LiPo works fine, and it’s quite small. We’ve also seen some 300 mAH batteries that are relatively square, and actually fit in an 18mm tube."

I haven't determined how I'm going to mount the EF Mini and battery in the nosecone yet.. nor how I'll secure the nosecone bulk plate. With larger rockets, I've epoxied a modified centering ring into the base of the nosecone coupler. The centering ring will have a number of holes with PEM nuts around it. A smaller diameter bulk plate is bolted to the face of the centering ring and serves as both the shock cord mount and the tracker mounting base. I'm imagining a simplified and scaled down version of this:

 

[kevinkal]

Read Crazy Jim's Blackhawk38 build thread. Is it the bible for 38mm MD techniques. Here is a super easy anchor point:

https://www.rocketryforum.com/showt...wk-prototype-first-look-!&p=490000#post490000

I use this and a couple other tricks that Jim mentions. If using CTI, dump out the black powder and epoxy an eyebolt in the plastic forward closure touch hole to use as another anchor point/retention. I was also leery of friction fit, but it just works. The wrap of aluminum tape around the motor rear closure and airframe is most important.

Thanks for that link. I have read this and a few other min diam threads. It is an excellent read. I also found some Blackhawk assembly instructions at Wildman and, if I'm not mistaken, the instructions are a compilation from that thread. The PDF file is too large for me to upload here.

 

[TBob]

I haven't determined how I'm going to mount the EF Mini and battery in the nosecone yet.. nor how I'll secure the nosecone bulk plate. With larger rockets, I've epoxied a modified centering ring into the base of the nosecone coupler. The centering ring will have a number of holes with PEM nuts around it. A smaller diameter bulk plate is bolted to the face of the centering ring and serves as both the shock cord mount and the tracker mounting base. I'm imagining a simplified and scaled down version of this:
View attachment 331883 View attachment 331884

I picked one of these for my EF mini: https://www.rocketryforum.com/showt...gFinder-Mini-Sleds-and-All-Thread-Free-Mounts

It's a great design, very well made and a perfect fit in a Madcow 38mm cone.

 

[Cl(VII)]

I picked one of these for my EF mini: https://www.rocketryforum.com/showt...gFinder-Mini-Sleds-and-All-Thread-Free-Mounts

It's a great design, very well made and a perfect fit in a Madcow 38mm cone.

Thanks for the good words. Glad you like it.

 

[kevinkal]

I picked one of these for my EF mini: https://www.rocketryforum.com/showt...gFinder-Mini-Sleds-and-All-Thread-Free-Mounts

It's a great design, very well made and a perfect fit in a Madcow 38mm cone.

Thanks for that. I'll be weighing options for a while.. hmm.

Aside, what kind a critter is that in your avatar that's about to try out your Amber Ale?

 

[TBob]

Thanks for that. I'll be weighing options for a while.. hmm.

Aside, what kind a critter is that in your avatar that's about to try out your Amber Ale?

It's a baby pig of some variety. Full disclosure...it's not my pig and not my beer. I don't condone serving beer to pigs. It's a waste of beer and probably not good for the pigs. It does make a cute photo though.

 

[kevinkal]

I'm taking a close look at going with Adrian's Featherweight Raven 3 Altimeter and 38mm Av-Bay. However, I find myself with some concerns...


Featherweight's 38mm Av Bay kit shown without a coupler. The kit is meant for 2.0" couplers.

Coupler Length...
I would like to use a section of the Carbon Fiber coupler that comes with the Mongoose kit. I'm thinking that I'd bond 1/2" of the coupler into the payload tube, and then have perhaps 2 or 3 inches into the booster. I will not need a switch band. If the coupler is a nice snug fit, I would go with a 2.5" coupler, but if it's a sloppy fit, I'd make the coupler 3.5" long to get a little more rigidity at the Avionics Bay-2-Booster joint. As the 38mm Av-Bay kit is meant for just 2.0" couplers, I would have to fabricate longer 4-40 threaded rods and some sort of stop to secure the Raven and Battery etc. A longer coupler would likely result in a more violent drogue ejection, as the "barrel" would be 2x longer allowing more time to accelerate the rocket sections away from each other when the charge pressurizes the booster. Something to think about.

Shock Cord Attachment...
I'm a bit leery of using just a single 4-40 threaded rod as the attachment point for the shock cords. I'm finding myself thinking about how to use 2 or more of the threaded rods in parallel to distribute the load and ease my concern.
I just ran some numbers.. if the 4-40 threaded rod has a stress area of 0.006 sqin, has an ultimate tensile strength of just 55 ksi, and ignoring stress concentrations, a single threaded rod would not fail until 330 lbs. If higher strength threaded rod could be found, that number would go up proportionally. Ok, perhaps that threaded rod would work out fine for this purpose.

Using the magnetic switch in a Carbon Fiber Rocket...
Does using a Carbon Fiber coupler and airframe present any problems when using the Featherweight Magnetic Switch that is integrated into their 38mm Active Bulkhead?

 

[manixFan]

<snipped for brevity>...Using the magnetic switch in a Carbon Fiber Rocket...
Does using a Carbon Fiber coupler and airframe present any problems when using the Featherweight Magnetic Switch that is integrated into their 38mm Active Bulkhead?

I've used the switches in a couple of CF rockets with no issue. I also used the Raven and the 38mm bay in a MD diameter. I did this by butting the bay up against a glued in coupler and then holding it in place with 'stopper' held in place with a couple of plastic rivets. It was a pain to run the charges for the drogue but it worked very well. If I do the same with the Mongoose I'll cut the coupler shorter and use set screws so they are flush. It's much lighter than using the supplied A/V bay and aluminum caps. I don't attach any recovery to the A/V bay, it's attached to the stopper that holds A/V bay in place.

Lots of ways to make it work, part of challenge of a 38mm MD rocket. I especially like the magnetic switches in MD rockets because of course they don't require holes in the airframe.

I also use aluminum all-thread, nuts, and washers in my MD rockets when possible as it is still plenty strong enough but quite a bit lighter. That's also one of the main reasons I use friction fit - hard to get much lighter.

Haven't decided what chute I will use but am leaning towards a 30" Iris Fruity Chute.


Tony

 

[Cl(VII)]

CF blocks RF, but won't pose a problem with a magnetic field.

 

[markkoelsch]

I'm not sure what I'm going to do with motor retention. It seems that most if not all locations are out of stock on the Reload Adaptor Systems, and the threaded plugged forward closures are pretty expensive. Perhaps I'll go with tape for retention, and the AeroPack Retainer just for a Kevlar anchor point for now.

I was looking at Ted's new 3/16" tubular Kevlar. He sells it with 2 and 3 loops, but in 25' lengths. I'm not sure that we need or want 25' times 2 of shock cord in these.

Motor retention is easy. Go old school. Friction fit with masking tape. Once snug, put a wrap of aluminum tape over rear of rocket and motor then wrap around nozzle end of motor. If done correctly it is not leaving the rocket.


Sent from my iPhone using Rocketry Forum

 

[Buckeye]

I'm taking a close look at going with Adrian's Featherweight Raven 3 Altimeter and 38mm Av-Bay. However, I find myself with some concerns...

I like the Raven, but I never understood this av-bay design. The wiring is tricky for the uninitiated. It looks good for extreme performance on super-lightweight rockets, but I don't trust it for sport flying heavy FG/CF where most guys over-build. The instructions suggest anchoring the recovery system with a couple strands of kevlar around a #4-40 nut. No way!

A 'conventional' av-bay will work just fine with the small batteries and altimeters available. Heck, CJ crammed a 10-year-old altimeter and a 9V alkaline into his BH38 build!

 

[terryg]

How are you folks planning on finishing this kit? The filament wound carbon fiber has a different appearance then the carbon fiber fabric based rockets that I am used to seeing. I ordered the eggfinder mounting kit from Chris Bender and I think I am going to go with the 38 mm anchor point from giant leap. For motor retention, I am deciding between friction fit and a slimline retainer (which would more easily allow the use of 29 and 24 mm motors). I have never lost a friction fit motor. Usually, it is just the opposite, as it can sometimes be hard to get them loose. This might be an excuse to get the Loki 120 case and fly the smaller hazmat free reloads (love the Loki Cocktail).

The 38 mm sleds from additive aerospace are also tempting:

https://www.additiveaerospace.com/collections/altimeter-sleds

 

[ksaves2]

This. I used the Mini with the small battery that everyone recommends at Airfest. I can't help but wonder if my battery died during the long wait on the pads, because I lost signal during descent (around 5000 feet) and could not find it again. Tracker didn't work upon retrieval so it's safe to assume it was pretty dead. Also, the battery wouldn't charge up so I bet it's shot now. Still learning about LiPo's.

If you lose a rocket with a lithium battery for a length of time, the lipo batteries will be trashed. If your electronics do an auto-cutoff before the voltage
gets too low like the 70cm Beeline GPS's you might be able to salvage the 1S battery after a week or so but most of the rest of the trackers out there will
trash the batteries if left on past the acceptable cut-off voltage.

Don't bother to try to do anything to "save" a trashed lipo. Just send it to the recyclers and get a new one. Kurt

 

[ksaves2]

Motor retention is easy. Go old school. Friction fit with masking tape. Once snug, put a wrap of aluminum tape over rear of rocket and motor then wrap around nozzle end of motor. If done correctly it is not leaving the rocket.


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Er.......ummmmmm......well, Just make sure you don't use shearpins on the sustainer then! Kurt:bangpan:oint::lol::surprised:

 

[crossfire]

I have never had friction fit fail me. Masking tape thrust ring and friction fit for the motor is how it was done for many years. Things have changed for the better but it still has its place in rocketry.

 

[thequick]

Does wiFi work with CF tubing? Thinking eggtimer Quantum.

 

[ksaves2]

Does wiFi work with CF tubing? Thinking eggtimer Quantum.

Stick the Quantum inside the tubes and find out. I suspect it might have decreased range. You might have to have your device right next to the ebay to get it to work. Perhaps someone who's flown a Quantum in CF can reply?

Cripes, I had an Rf switch that had very decreased range when inside of red dyed glass tubes. I had to pull the antenna wire out of the static port to get any range when I was doing a deployment ground test. I didn't want to be
standing right next to the rocket for the test. Kurt

 

[OverTheTop]

If you are looking for strong and light metal rods you can get custom spokes made up at your local bike shop. The more serious shops have the machine for rolling the threads. If you go titanium instead of stainless steel they are rated to about 280kg each. You need to specify the length and the thread is a fixed distance along each end.

Thread for these is 2-56.

Also, rolling the threads work-hardens them, rather than cutting threads with a die which causes stress raisers at the thread roots.

 

[markkoelsch]

Er.......ummmmmm......well, Just make sure you don't use shearpins on the sustainer then! Kurt:bangpan:oint::lol::surprised:

Wrong Kurt. If you have a problem you are not doing it right. Done it many times with shear pins and have not lost a motor.


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