My very own Go Devil 38 build

I thought I would start my own build topic as I think I am getting lost in the Community Go Devil build. I ordered a Go Devil after seeing the build thread. A new minimum diameter at the 38mm size? Count me in! This is actually a bit risky for me. I had two level one flights on single deployment rockets and I had one flight on. Mariah 54 with an I motor (I forget the size). That flight the shock cord split at the lip of the sustainer tube. All three pounds hit the ground at terminal velocity two feet from a Cub Scout washing his hands after using the ports-potty. It buried itself 20 inches in the hard packed desert floor. The only damage was scrapes in the paint from the shovel I dug it out with. Haven't flown it a second time. Heebie jeebies up the wazoo.
Now that I got that off my chest on to my new Cub Scout killer.

the kit came sans fin guides. Unfortunate. Mac Performance came through for me though. Their fin guides are great. You can see them later in the thread when I show my vacuum bag rig.

Fins tacked on with JB Weld. Here it is dry fit on my stand. Note to self; dry fit parts slide apart. I dinged the tip of my pretty nosecone wen it fell off.

Aero Poxy for the fillets.

Still see some shiny low spots after sanding.
Note to self: the fins and body tube sand just as easily as the fillet. Don't sand gullies in them next time.

More narrative. I bought this in February and I want to fly it at LDRS. I Have had delays and interruptions with more on the way. Scoutmasters must attend Eagle Projects so there goes two of my remaining weekends. That however is a good problem to have.
I want to lake my Level 2 at LDRS. Bay Area Hobbies has a 38mm 6XL waiting for me. I will use a J530 as my largest motor. I will use a 3 grain I motor for my first flight as a shakedown flight.
My sim shows Mach 1.75 and 9300 feet.

I bought a 38mm sled for my RRC3 from Additive Aerospace. I used the rotary switch. Limbered up my soldering skills and got my RRC3 to beep satisfyingly. I don't have a picture and I'll add it later. I just ordered an Eggfinder Starter kit and I am having Connor McGrath solder it for me. That will save me time an likely save me $90 if I were to bungle the job.

I loaded up on Aero Pack retainers. I am going with Belt and suspenders. I have the slimline and the internal. I am using the slimline to retain the motor and the MD mount as a shock cord mount. I am paranoid about shock cords so I figure losing 0.2 Mach is cheap insurance on that Cub Scouts life.

Here is my CAD model showing the tip to tip plies and the slimline.
I think I can get away with the below attachment method for my sustainer shock chord. It will be buried 9 inches into the body and I won't be able to get it back out anyway.
Does anyone think that's a bad idea?

I modeled my plies and created a flat pattern in CAD.

I bought a Zeny vacuum pump from Amazon, $55 delivered. I cut up my plies.
That's the vacuum system.
I read Jarvis again. Note the 0.25 inch of tape on the edges to keep them from fraying.

Here I have put it all together without epoxy. I used blue tape to hold the plies on. My finishing resin has a 50 minute working time. I figure I should rehearse and get the application of the bagging system down to 25 minutes. Here is my first attempt.
Note the level of vacuum the Zeny supplies.
Also note how I used the Mac Performance fin guides to suspend my bag. I used the yellow sealing putty/tape to seal off the fin slots and to have something for my bag to attach to. I glued a mast onto one guide to hold my vacuum fitting.
I was pleased at how easy it was to do. I didn't timely first attempt as I was developing as I went I also learned some things. The bag folded crisply at the leading edge but left quite a fillet at the trailing edge. That is because I like to leave a base on my fillets. Personal taste. I know the tail of the tip to tip ply that hangs aft won't be pressed down onto the body. Solution? Cut the tail off. I need to create tapered fairing for the slimline anyway so that part of the body will be covered on a secondary operation. I will do the fairing after I do the tip to tip.

Trigger finger. Here is the vacuum gage

Look at the picture of the whole bagging system. Note the visible edge of the plies. It matches up with the CAD model. I was really stoked when I got all that together. This Saturday I am going to epoxy the plies for real.

I have one that I have yet to fly also. Im hoping we get good flying weather next month. I'll be watching.

With the internal retention I would ditch the external retainer.

Rather than looping a permanent install to the screw eye,simply loop down through it and back up again. At the top of the junction of the body tube, tie a loop in both ends. Tie your main shock cord through the two top loops of the body tube cord.

That way, if the body tube cord ever goes bad, you simply tape or tie something to it, and just pull a new one through to replace it.

Banzai88,
I think what you are describing is something I was thinking about. I have some 3/8 inch or thereabouts Kevlar tube. I was thinking of making a loop just big enough to go though the eye and stick both ends out past the body tube. I would tie or sew the ends together and maybe use some shrink tubing on the joint. I could then tie my main shock cord to that and always get at the knot. I could also replace the thick tube by inserting a thin line through the eye with some long forceps and pulling the thin line through. I would tie my thicker line to the thin line and then pull it through.
The thick line would alleviate my paranoia about shock cords parting.

What do you think of that?

TomSmith58 said:

I bought a 38mm sled for my RRC3 from Additive Aerospace. I used the rotary switch. Limbered up my soldering skills and got my RRC3 to beep satisfyingly. I don't have a picture and I'll add it later. I just ordered an Eggfinder Starter kit and I am having Connor McGrath solder it for me. That will save me time an likely save me $90 if I were to bungle the job.

Click to expand...

What are you going to use for a motor ultimately? If I were you and new with GPS tracking, I'd recommend you do some flights with lower power to start to make sure your setup works. I wouldn't be punching it to 9300' without a shakedown to a
lower ceiling to where you would stand a chance at recovery if something goes wrong.

I've already had that happen to me and the two positions that came across allowed me to find the rocket, dig it out and it'll be good to go with a new nosecone. https://www.rocketryforum.com/showt...-Mapping-Program-Update&p=1573624#post1573624

Oh, looking at your build I bet you could stick a J-1000 in there.

Kurt

TomSmith58 said:

Banzai88,
I think what you are describing is something I was thinking about. I have some 3/8 inch or thereabouts Kevlar tube. I was thinking of making a loop just big enough to go though the eye and stick both ends out past the body tube. I would tie or sew the ends together and maybe use some shrink tubing on the joint. I could then tie my main shock cord to that and always get at the knot. I could also replace the thick tube by inserting a thin line through the eye with some long forceps and pulling the thin line through. I would tie my thicker line to the thin line and then pull it through.
The thick line would alleviate my paranoia about shock cords parting.

What do you think of that?

Click to expand...

That works. When I do things like this, I use a sacrificial line that I run out the motor mount tube to get it all straight, but with something like this, anything would work.

You can use a double loop (down and back) and tie into the top (making for two pieces of line), or tie an alpine butterfly loop in your main cord 2x the length of your tube to your eye bolt, and loop the tag end through the eye, and then tie off into the alpine loop (making for one piece of line). Either way it uses about the same amount of material. Since your shock cord is strong enough, good knots can work in your favor to remove bulk, complication, and weight while providing a solution to a removable, inspectable, serviceable, replaceable cord.

Kevlar that's exposed to ejection charge I always remove after a day of flying and wash it. Maybe it's not necessary (most would say it's not), but it also serves as a preventative measure inspection point for wear. YMMV, do what makes you happy. I just like washing the rotten egg smell out of everything and not having to live in a skunk cave, and not getting all that junk on my hands at the field is a bonus.

Me, I always use a piece of shrink tube to cover the knot and the tag ends. Just makes for a neater presentation. Likely no one will ever see it, but it's like painting the pedals on a model car interior....I'll know they're there!

Kurt
My first flight is with a 3grain I180 motor in the Level one territory. I will go for Level 2 with a J381. Then I will punch it with a 6XL J580.

ksaves2 said:

What are you going to use for a motor ultimately? If I were you and new with GPS tracking, I'd recommend you do some flights with lower power to start to make sure your setup works. I wouldn't be punching it to 9300' without a shakedown to a
lower ceiling to where you would stand a chance at recovery if something goes wrong.

Click to expand...

In my personal opinion- I disagree with this in it's entirety. Here's why: If you bang in from 3300' you're screwed. If you bang in from 9700' - Just as screwed. Go for the gold. The big flight is what you want, so go for it. You're not going to learn anything on a lower flight that's going to save you on the bigger flight. All you do is add the risk that all flights carry with the lower flight, that might get in the way of the second.


To the OP- I'd skip the slimline, but thats just me. If you use the aeropack internally, there will be no pressure from ejection on the motor, so holding it in place with tape will be easy-peasy.

With the aeropack.... I'd drill and tap it, countersink it, and use 3 #4 screws to hold it in place.


I've got mine sitting in a box...and thats mostly my plan for it... (I'm actually just going to tape it in place with no retainers...and no T2T. First flight will be a Loki K1127)
I'm excited to get mine up..... I like your style of build thread, thanks for sharing.

DizWolf said:

To the OP- I'd skip the slimline, but thats just me. If you use the aeropack internally, there will be no pressure from ejection on the motor, so holding it in place with tape will be easy-peasy.

Click to expand...

+1. If you attach the motor to internal retainer properly then no way you need the Slimline--no tape even needed.

DizWolf said:

In my personal opinion- I disagree with this in it's entirety. Here's why: If you bang in from 3300' you're screwed. If you bang in from 9700' - Just as screwed. Go for the gold. The big flight is what you want, so go for it. You're not going to learn anything on a lower flight that's going to save you on the bigger flight. All you do is add the risk that all flights carry with the lower flight, that might get in the way of the second.


To the OP- I'd skip the slimline, but thats just me. If you use the aeropack internally, there will be no pressure from ejection on the motor, so holding it in place with tape will be easy-peasy.

With the aeropack.... I'd drill and tap it, countersink it, and use 3 #4 screws to hold it in place.

I've got mine sitting in a box...and thats mostly my plan for it... (I'm actually just going to tape it in place with no retainers...and no T2T. First flight will be a Loki K1127)
I'm excited to get mine up..... I like your style of build thread, thanks for sharing.

Click to expand...

Nope,

Respectfully, you're wrong David. Tom said he made two prior L1 flights and is going to go for L2. Doesn't look like he's done any tracking before. I think he's smart doing the I180 for the shakedown, J381 for the L2 to get it done and then
go blast it later. Didn't you have RW send you a longer sustainer tube to support the K motor? To fly like that, I believe you're all correct in your fincan treatments. I have the shorter sustainer and I believe the can will hold up with the
surface mount fins with Proline 4500 epoxy fillets with anything less than J500's. Kurt

P.S. I agree about the retainer if going with internal fixation. Nix any external retainer as it'll only create drag and perhaps knock off a few hundred feet.

ksaves2 said:

Respectfully, you're wrong David. Tom said he made two prior L1 flights and is going to go for L2. Doesn't look like he's done any tracking before. I think he's smart doing the I180 for the shakedown, J381 for the L2 to get it done and then go blast it later. Didn't you have RW send you a longer sustainer tube to support the K motor? To fly like that, I believe you're all correct in your fincan treatments. I have the shorter sustainer and I believe the can will hold up with the surface mount fins with Proline 4500 epoxy fillets with anything less than J500's.

Click to expand...

No disrespect taken. However, the idea of shakedown flight hasn't been proven to be a good idea. It won't do anything to make the big flight any less risky.

My sustainer on the go devil is stock, aside from being orange. The only thing I've ordered a longer tube for was my Villain. My plan is also just 4500 on the fins. It's held past M2, and even a K1127 should only take it to just under 2.

I'm not a fan of shake down flights either. With my luck the shake down motor would cato and take out the whole thing. If there is an issue of experience or knowledge, then gain that on a different rocket. If you're building a rocket to go big, then go big.

Nice build by the way. I'm in the process of building my go devil right now. I went with rocketpoxy fillets, no tip to tip.

So if I go with the internal motor retainer then what dimension do I use from the base of the sustainer to the base of the retainer? My 6XL is in transit to LDRS. I suppose I could wait till I get to LDRS and use my 6XL as a tool to properly locate the Aero Pack internal retainer. However I would like to get it done beforehand and done with authority. Does anyone know the proper dimension? Aero Pack hasn't answered my first email and is slow on the second.
Tom

I here you guys on the idea of going big. We talk like that at Boeing about real rockets too. I have three motors ordered from Bay Area Rocketry. I suppose I could fly them in reverse order!
As Donald Sutherland said in Backdraft, "Burn 'em! Burn 'em all!" With his best crazed look on his face. He's good that way.

TomSmith58 said:

So if I go with the internal motor retainer then what dimension do I use from the base of the sustainer to the base of the retainer? My 6XL is in transit to LDRS. I suppose I could wait till I get to LDRS and use my 6XL as a tool to properly locate the Aero Pack internal retainer. However I would like to get it done beforehand and done with authority. Does anyone know the proper dimension? Aero Pack hasn't answered my first email and is slow on the second.
Tom

Click to expand...

Here are the Pro38 specs: https://www.pro38.com/pdfs/Pro38_dimensions.pdf.

DizWolf said:

In my personal opinion- I disagree with this in it's entirety. Here's why: If you bang in from 3300' you're screwed. If you bang in from 9700' - Just as screwed. Go for the gold. The big flight is what you want, so go for it. You're not going to learn anything on a lower flight that's going to save you on the bigger flight. All you do is add the risk that all flights carry with the lower flight, that might get in the way of the second.


To the OP- I'd skip the slimline, but thats just me. If you use the aeropack internally, there will be no pressure from ejection on the motor, so holding it in place with tape will be easy-peasy.

With the aeropack.... I'd drill and tap it, countersink it, and use 3 #4 screws to hold it in place.


I've got mine sitting in a box...and thats mostly my plan for it... (I'm actually just going to tape it in place with no retainers...and no T2T. First flight will be a Loki K1127)
I'm excited to get mine up..... I like your style of build thread, thanks for sharing.

Click to expand...

Unfortunately for me the Grand Republic of California hasn't accepted Loki's qualification tests. I guess our extra requirements are too expensive. I would love to fly the K1127.

That is sad. I've got an AT 38/1320 I could be talked out of . j510w is another asskicker.

So Bob at Aero Pack was unable to help me with the proper dimension for the M38e from the end of the body tube. I think I am going to wait to glue it in till I get to LDRS and pick up my 6GXL case and motor from Bay Area Rocketry. Then I can glue it in place and be positive of the proper location. 5-minute epoxy doesn't take that long to cure. LDRS is a long event. I should be OK.

I just ordered the remaining hardware for internal retention of Cesaroni motors. I got the adapter from Aero Pack. Bob was. Out of extensions for the short motors so I ordered them from Apogee.