Quantcast

Go Devil 38 L2 Cert Build

The Rocketry Forum

Help Support The Rocketry Forum:

dford

Tada
Joined
Apr 23, 2016
Messages
330
Reaction score
1
Plan is to do a first time MD for a level two certification flight. I'm hoping the mighty fine people on TRF Can give me a hand with that. I want to launch it off in the J500s, white lightning or fast jack. They send it to around mach 1.5-1.8 or so at 10k+ I figured if i'm going to go for it i might as well go for it.
I'm using a "stock" .ork file and after weighing and measuring all parts out of the box this is what it looks like. Minus the switchband I bonded on and weighed as well.
View attachment MyGD38.ork

The fin alignment jigs were off
20160915_102408.jpg
so I made new ones off www.payloadbay.com, glued them onto cardboard and trimmed them out. I didn't like how they sat so I searched around some more, and found this thread.

I had some material laying around to make it. And it worked.
20160922_142652.jpg20160922_142632.jpg
I figured I was safe to get moving on shaping the fins. I went with a 2-1 bevel on the leading and tip, round them from top gradually into a 3-1 bevel on the trailing edge with more of a knife edge. At least that is what i tried to do. I also left a bit more meat on top and bottom where the fin would be bonded to the airframe to get as much contact as I could. I used micrometers to measure out the 2-1 and 3-1 on a popsicle stick to maintain consistency. It is a lot easier to mark multiple places this way I think.
20160915_120617.jpg
I'm going to do 1/4" fillets so I sanded less around the quarter inch contact areas. I wanted as much meat to bond as possible.
I used a palm sander for the fins with 60 grit to get it close. I then wet sand 220-1500 grit to make them nice.
I have two fins bonded on and the third will be tonight. I'll let them cure fully fully until tomorrow night.
20160922_143303.jpg
Once the kiddos go to sleep I plan on doing about a 3/4" corner tape on the fins/airframe to get about half an inch onto the fins/airframe...i'm going to use pro set 125/229 and eglass, single ply. After i bonded one fin and felt how stout they were I figured one ply would be enough. Unless you guys think otherwise? I haven't flown this fast before so it really is unknown territory for me...

I have a nose tracking sled on order for an eggfinder. Banzai tipped me on a thread with a link to www.shapeways.com. So I ordered the red 3d printed sled. Figured it'd make my life easier. It should be here tomorrow as well.

I think i should be able to begin working on the tracking build without actual tracking electronics and just the sled?

The plan is to kind of order a section at a time, build a section at a time.

I do have about an 18" chute i made id like to use as a drogue and a 30" chute for the main.
I'm going with a SLCF for deployment along with my A3. Why not right? It'll be interesting to compare data between the two and OR.

I haven't done tracking nor DD or MD.:surprised: I'll have a lot of questions i'm sure. I hope for some guidance along the way.

Additional Edit: I placed the fins just a hair over one caliber from the tail end at 1.5"
 
Last edited:

ksaves2

Lifetime Supporter
TRF Lifetime Supporter
Joined
Nov 25, 2009
Messages
5,981
Reaction score
294
What are you going to use for motor retention? What are you using for a switch? Going to use a Mayhem Rocketry Rail Guide? That upper bay is pretty darned tight for a 30" parachute. If I had mine to do again, I'd do two allthreads in the ebay and use an EggTimer Quantum so I could activate wirelessly.

Another concern I have is the black profusion nosecones. I've had a flight where the reception was spotty in a well designed nosecone bay. Hoist the nosecone tracker up in the air on a tree branch overhang and do a range check before flying.
Might I suggest you do something like a lower power J motor for a certification flight attempt as opposed to trying to punch the rocket up high if you are not test flying with a lower impulse first. If your EggFinder malfunctions for any reason,
you likely will never see the rocket again unless you're lucky it comes down right next to you. I believe carbon base lampblack is used to color the tubes black. It may attenuate the Rf from the 900Mhz tracker. I'm in the same boat as you and
haven't flown mine yet but I'm going to do another range test again before I make the flight with a J500. Rf attenuation can be frequency and is power dependent so another tracker might not be affected.

Ok, the other thing is the stock tube is too short for a large impulse J like a J1000 or a Loki 38mm K so forget those unless you buy longer tube(s). If you're going to buy longer tubes, might as well get a 3" longer upper bay tube as
you will likely be able to cram that 30" chute in there more easily. In that tight space, if you get burn holes in the larger chute should still come down soft enough for a successful certification.

If just sticking with a J500 or lower, you can get by fine with scuffing the tube and using a good epoxy like Pro 4500 with a healthy fillet. Lamination is not necessary unless you want to do it to acquire experience. You planned description above sounds pretty darned good if that's what you want to do. J1000's and K's a guy laminated his fincan with carbon fiber and got Mach 2.5 out it successfully.

There's a couple of threads on the GoDevil here. The one with mine shows how not to do the ebay. Mine works but was done to prove I could use out of production hardware. My nosecone tracker bay is for a Tele-GPS and an "on the roof test" showed decent range but I'm going to repeat it as I'm getting paranoid with age. Tracker is on the 70cm Ham band. Best of luck with your build and you don't have to "really" punch it on the certification flight. Get certified, re-prep and then punch it the second flight of the day. Kurt Savegnago
 

dford

Tada
Joined
Apr 23, 2016
Messages
330
Reaction score
1
What are you going to use for motor retention?
I'm leaning towards a simple flat washer sized to the inner diameter as close as I can and 1/4" plywood. I had talked to a buddy about machining alluminum alloy with holes in the side for screws, through the airframe. But he was saying he couldn't use machine shop time for personal business and I didn't really want to have more holes and screws in the airframe anyways.
What are you using for a switch?
I honestly am thinking about taping the wires for power. I have read quite a few failures due to switch failure. IF i change my ways i'll be using a featherweight magnetic switch. Unless suggested something else that makes sense.
Going to use a Mayhem Rocketry Rail Guide?
That is my intention. Keeping the spirit in minimum diameter as much as possible.
That upper bay is pretty darned tight for a 30" parachute.
I have a 30" chute already and the drogue here. After seeing the price of quality new chutes I wanted to check what I had before jumping into new purchases. Even if I do need to buy a new chute, i'm really not stressing it. I just wanted to check what I am working with first. Of course, getting a larger chute to work would help upon landing. I may even pick up a new drogue/main simply because it is a good excuse to buy a new chute ;)

If I had mine to do again, I'd do two allthreads in the ebay and use an EggTimer Quantum so I could activate wirelessly.
Thanks for the tip on the E Quantum. I haven't looked into it much and to be honest, i'm probably swayed by the SLCF due to advertising and reading a lot of people use them in their rockets.
Hmm. Now that I have looked into the quantum my only concern would be the "machlock" feature. This is where I have ZERO experience.

What is the machlock feature for the SLCF? Why would I need it per se? Do I really need it?

I like the wi-fi aspect of the eggtimer for sure. I already have an A3 i have to remember to "record" pre flight and the quantum would only add to the checklist on my phone at the rail.
If I remember right, 2x3/16" all threads right? The dimensions of the eggtimer would require half inch+thickness of sled. I think with all those dimensions it should work? The Ebay is probably the least I have put a lot of thought into out of the entire build thus far...I figured it to be pretty straight forward versus tracking in the nose cone.

Ok, the other thing is the stock tube is too short for a large impulse J like a J1000 or a Loki 38mm K so forget those unless you buy longer tube(s). If you're going to buy longer tubes, might as well get a 3" longer upper bay tube as
you will likely be able to cram that 30" chute in there more easily. In that tight space, if you get burn holes in the larger chute should still come down soft enough for a successful certification.

If just sticking with a J500 or lower, you can get by fine with scuffing the tube and using a good epoxy like Pro 4500 with a healthy fillet. Lamination is not necessary unless you want to do it to acquire experience. You planned description above sounds pretty darned good if that's what you want to do. J1000's and K's a guy laminated his fincan with carbon fiber and got Mach 2.5 out it successfully.

There's a couple of threads on the GoDevil here. The one with mine shows how not to do the ebay. Mine works but was done to prove I could use out of production hardware. My nosecone tracker bay is for a Tele-GPS and an "on the roof test" showed decent range but I'm going to repeat it as I'm getting paranoid with age. Tracker is on the 70cm Ham band. Best of luck with your build and you don't have to "really" punch it on the certification flight. Get certified, re-prep and then punch it the second flight of the day. Kurt Savegnago
I really have no intention on putting anything bigger than the J500 range in this rocket. Part of me is saying to go smaller and a part of me is saying why? Another reason to go with this case and motor size is since it is the largest i'm putting in it, i'd be able to epoxy the retaining bulkhead in and not have to worry about wanting to stuff a larger case in. I intend on using a simple eye bolt to secure the case in the rocket through a threaded forward closure.

I also wanted to mention reguarding the additional ply I'm adding, I don't feel like I need practice per se. I've done hundreds of layups before on million dollar parts. I'm more worried about the fin flutter when I bust mach with it...
The velocity of this thing is what trips me out and makes it super exciting to build with care and precision :D
 
Last edited:

dford

Tada
Joined
Apr 23, 2016
Messages
330
Reaction score
1
20160923_085229.jpg
This is basically how the fins came out on both sides. I couldn't get to the squeeze out on the inside of the jig without making a bigger mess. I didn't want to tape off for the intial bond because I didn't want to get tape stuck underneath anywhere. I have some really nice fine tip grinding tools for my dremel I'll use to clean up any excess before I lay fillets.

20160923_090548.jpg
These are some of the different titanium grinding tips I like to use. Very helpful for precision.

20160923_085302.jpg
Tracking sled arrived.
20160923_085317.jpg
Top and bottom photos
20160923_085441.jpg
It fits snug into the nose coupler.

I'll get on the corner tapes a little later today.

Debating on taping off the entire fin can to resin wipe the entire thing for aesthetics. We will see.


:marshmallow:EDIT: :madnote:
Changed my mind. The area between the fins is small enough it wouldn't make sense to run corner tapes. So why not run a ply 1/2" beyond the fillet from fin to fin? Then I get to thinking, I may as well run a full ply across from fin tip to fin tip. Maybe I am overthinking it but I think having six small tapes would be less aero efficient than having three "short" plys. Even more efficient having 3 full ply.

I think i'm going to add a few drop of dye from the Rockepoxy into the Pro Set and make the entire fin can black. Sort of like a black strip.

I also think I am going to go against my normal train of thought which would be to lay a 45 ply and instead lay a 90. There isn't much play in the fin vertically which the 45 would be more useful to correct. Rather, the fin will most likely flutter laterally in which the 90 would provide a lot more stiffness to.
If anyone is unsure what the heck i'm talking about i'll do my best to show photos while I am doing the lay up later.
 
Last edited:

Banzai88

Lvl 1,Wallet....Destroyed
TRF Supporter
Joined
Jul 15, 2015
Messages
2,362
Reaction score
546
I used 4-40 set screws through the sides of the nose cone coupler to hold the sled/base plate in, with the coupler epoxied in to the nose cone. I've flown it that way several times in a different rocket (Formula 38), and it works just fine.

To get it out, I run the set screws in until they clear the inner diameter of the coupler. They remain in the material of the sled, and don't 'disappear' anywhere in the field!

Right now I'm not using the magnetic switch feature of the sled, as my TX simply comes on when I plug it in, but I'm debating on putting in a screw switch on the bottom of the legs like on the APE nose bays.
 
Last edited:

markkoelsch

Well-Known Member
Joined
Mar 18, 2009
Messages
4,364
Reaction score
148
Just friction fit the motor, and then use aluminum tape over the motor end and body tube. It works.
 

dford

Tada
Joined
Apr 23, 2016
Messages
330
Reaction score
1
Just friction fit the motor, and then use aluminum tape over the motor end and body tube. It works.
If I went with your idea, will you commit to replacing the motor case and possibly the rocket if the ejection charge blows its guts out of the rockets behind?
 

dford

Tada
Joined
Apr 23, 2016
Messages
330
Reaction score
1
I used 4-40 set screws through the sides of the nose cone coupler to hold the sled/base plate in, with the coupler epoxied in to the nose cone. I've flown it that way several times in a different rocket (Formula 38), and it works just fine.

To get it out, I run the set screws in until they clear the inner diameter of the coupler. They remain in the material of the sled, and don't 'disappear' anywhere in the field!
I'm sort of confused putting your description together. The set screws hold it past the diameter of the coupler? The coupler is epoxied to the nose cone? Do you have a nut epoxied in the sled to run the bulk head down against the coupler?
Sorry for being slow....
 

Banzai88

Lvl 1,Wallet....Destroyed
TRF Supporter
Joined
Jul 15, 2015
Messages
2,362
Reaction score
546
Epoxy coupler into nose cone, allow to cure. Drill two holes 180 degrees opposed in the coupler at the correct height for the holes in the risers of the sled, and open up the holes in the sled (They're about .405 inch up from the bottom surface). Tap holes to 4-40. Bolt eye bolt and nose cone bulkhead to the bottom of the nose cone sled. Insert sled assembly into the coupler/nose cone. Run 4-40 x 1/4 set screw into the holes, flush with the surface of the coupler, partly into the risers, partly into the fiberglass of the coupler. To remove the sled so you don't lose the set screws, screw them IN so that they remain captive in the sled risers, remove.

Designer of the sled intended it to use #6 set screws. I found that #4s work just fine.

See pictures on this thread here: http://www.rocketryforum.com/showth...y-own-Go-Devil-38-build&p=1585358#post1585358

Some folks, alternately, would set the coupler up as a cup, and bolt the coupler into the nose cone.
 
Last edited:

dford

Tada
Joined
Apr 23, 2016
Messages
330
Reaction score
1
Epoxy coupler into nose cone, allow to cure. Drill two holes 180 degrees opposed in the coupler at the correct height for the holes in the risers of the sled, and open up the holes in the sled (They're about .405 inch up from the bottom surface). Tap holes to 4-40. Bolt eye bolt and nose cone bulkhead to the bottom of the nose cone sled. Insert sled assembly into the coupler/nose cone. Run 4-40 x 1/4 set screw into the holes, flush with the surface of the coupler, partly into the risers, partly into the fiberglass of the coupler. To remove the sled so you don't lose the set screws, screw them IN so that they remain captive in the sled risers, remove.

Designer of the sled intended it to use #6 set screws. I found that #4s work just fine.

See pictures on this thread here: http://www.rocketryforum.com/showth...y-own-Go-Devil-38-build&p=1585358#post1585358

Some folks, alternately, would set the coupler up as a cup, and bolt the coupler into the nose cone.
...oh... duh ... :facepalm:

Okay. I gotcha now. I like this way far more than putting holes in the outer airframe of the nose cone

Reguarding the 56 shear pins (screws) wouldn't it work to set the pin, then slide a utility knife over the airframe surface, cutting the head off to make it flush? The pin would still shear as planned I'd think with less air flow disturbance...
 
Last edited:

ksaves2

Lifetime Supporter
TRF Lifetime Supporter
Joined
Nov 25, 2009
Messages
5,981
Reaction score
294
Me? I went ahead and drilled three holes in my coupler and used 2-56 buttonheads to hold the nosecone shroud to the coupler with the aft coupler bulkhead epoxied in place. Yeah I have to deal with the Frankenstein look and the potential drag increase but a few hundred feet loss doesn't bother me for the ease of sliding the press-fit tracker sled in and out. The nosecone shroud is too thin for flathead screws so I didn't bother. I have a 15k waiver at the home field I want to stay under anyways. Kurt
 

dford

Tada
Joined
Apr 23, 2016
Messages
330
Reaction score
1
Me? I went ahead and drilled three holes in my coupler and used 2-56 buttonheads to hold the nosecone shroud to the coupler with the aft coupler bulkhead epoxied in place. Yeah I have to deal with the Frankenstein look and the potential drag increase but a few hundred feet loss doesn't bother me for the ease of sliding the press-fit tracker sled in and out. The nosecone shroud is too thin for flathead screws so I didn't bother. I have a 15k waiver at the home field I want to stay under anyways. Kurt
Shear pins to hold the nose\coupler\ebay to airframe until deployment...

I'm with the idea that leaving it without runs the risk of drag separation while slowing to apogee
 
Last edited:

dford

Tada
Joined
Apr 23, 2016
Messages
330
Reaction score
1
Well apparently Pro Set doesn't really like to be mixed with the dye that comes with Rockepoxy.
:facepalm: it basically turned the ProSet to WAY more of a flow :facepalm:
So basically when I went to apply it my glass kept peeling away creating voids everywhere. I was getting pretty razzled I tell you what. So I went outside and finished the lay up in the sun to encourage it a little to set faster and fix the void issue.
:y:My revchem cup exo'd uber fast once I had gone outside:y:
Luckily I had "enough" applied before that happened. The black dye didn't even work very well and left me with a real crummy watery black look.
Unfortunately I didn't get pictures during that step of the mayhem but here is what I did get.


20160924_160229.jpg
Here I want to show I was using the material at a "90" The weave is running perpendicular <-^ each other rather X at a "45"
I did that mostly to stabilize fin flutter in case I ran into that issue later on.

20160924_163158.jpg
Just taping off. Nothing fancy


20160924_165149.jpg
Rockepoxy fillets
20160924_165115.jpg
And another picture of the same


This is where I did the lay up and took ZERO pictures of the actual layup. I am sorry for missing it but like I said, it was pretty friggin frustrating! :mad:


20160925_211246.jpg
This is post cure. I didn't use peel ply. My intention was for the resin to work the way I had planned and give a nice deep black and not to be like a running faucet all over the place...boy was I wrong. SO this is a LITTLE sanding to kick the blush off.

20160925_211301.jpg
At this point I decided the black didn't stick in the Pro Set because it didn't have any filler to stick to like the Rockepoxy does. So to remedy two issues I was facing I opted to "resin" wipe it with Rockepoxy. I mixed a little at a time and it went a long way considering I was only going for a thin layer to:
A) Dye the entire fin can black like I had intended in the first place
B) Fill any of the bumpy bumpy spots created from the glass.
Which is unavoidable unless your layup is on flat steel that has been DA'd for composite work and vacuum bagged. Even then we only get a truly flat surface tool side if done right.


20160925_222701.jpg
So this is it right after I wiped it.
20160925_222814.jpg
Wasn't sure how the photos would come out
20160925_222749.jpg
So I took three for reference.

I used a lot of popsicle sticks to smooth it onto the surface. While it was going through the first "phase" of hardening I kept wiping it with my finger to smooth it out as much as I could.

I am certainly debating on wet sanding it completely smooth but I am worried it will knock off the nice shine that comes with Rockepoxy.

Has anyone tried to wet sand rockepoxy and been able to get a nice shine still??? :confused2:To be honest i'm pretty surprised at how much it weighed after all the added material. Which wasn't much

I think i'll let the fin can be for a bit unless I do decide to wet sand. That will be a day to day process i'm sure getting it to polish again. That is unless someone has input not to.
For now i'm going to turn my attention towards the nose cone area. More so getting the sled installed so when the eggfinder gets here I just throw it in and test away with Kurts advice.

I'm still looking for black powder. I have a lot of friends that own a lot of guns but they don't own black powder. They own some other stuff (i'm not a gun guy) to reload there shells.

Edit: Fin weight before 1FG ply, fillets and resin wipe: 53g
Weight after: 94g
 
Last edited:

OverTheTop

Well-Known Member
TRF Supporter
Joined
Jul 10, 2007
Messages
4,337
Reaction score
1,570
Location
Melbourne Australia

markkoelsch

Well-Known Member
Joined
Mar 18, 2009
Messages
4,364
Reaction score
148
If I went with your idea, will you commit to replacing the motor case and possibly the rocket if the ejection charge blows its guts out of the rockets behind?
Absolutely not. Then again, this is how most flights were done before Aeropacks. Heck, I helped a guy do his L1 in Saturday. He messed up his retainer position such that the only way he could do his L1 cert was to friction fit. It took five minutes tops. Friction fit the motor with masking tape, and a layer of aluminum tape over the end of the motor and boat tail. Single deploy and that motor did not budge- had to use a pair of pliers to remove it.

It works when done correctly.
 

markkoelsch

Well-Known Member
Joined
Mar 18, 2009
Messages
4,364
Reaction score
148
What epoxy did you use for your tip to tip fin layup? I see it was Pro Set, but which specific product.
 

dford

Tada
Joined
Apr 23, 2016
Messages
330
Reaction score
1
What epoxy did you use for your tip to tip fin layup? I see it was Pro Set, but which specific product.
125/ 229. Pro Set slow. At first I thought the ratio was off but it came out of a calibrated dispenser.

The company I used to work is literally like two blocks from me. Which makes it nice because I have quite a few friends still working there.
 
Last edited:

markkoelsch

Well-Known Member
Joined
Mar 18, 2009
Messages
4,364
Reaction score
148
Fair enough. I have see a couple people have issue with laminations, only to find out that they were not using a laminating system. Just wanted to rule that out.
 

dford

Tada
Joined
Apr 23, 2016
Messages
330
Reaction score
1
Absolutely not. Then again, this is how most flights were done before Aeropacks. Heck, I helped a guy do his L1 in Saturday. He messed up his retainer position such that the only way he could do his L1 cert was to friction fit. It took five minutes tops. Friction fit the motor with masking tape, and a layer of aluminum tape over the end of the motor and boat tail. Single deploy and that motor did not budge- had to use a pair of pliers to remove it.

It works when done correctly.
What was he trying to use for motor retention? I don't doubt friction fitting not working when done properly. That doesn't mean I am guaranteed it will work every time I launch my rocket though. It only takes once in my opinion
I could lose a very expensive motor case or epoxy in a bulked with eye bolt and be reassured. No to mention the eyebolt sErving two purposes.
A) motor retention
B) shock cord mount without having to epoxy in a permanent shock cord.

I'm new to dual deploy also. I don't know how having my own charge blasting at the motor would work. I appreciate the tip but to be honest I'm simply not that confident in friction fitting. I already am throwing in a lot of unknown variables.
 
Last edited:

ksaves2

Lifetime Supporter
TRF Lifetime Supporter
Joined
Nov 25, 2009
Messages
5,981
Reaction score
294
Shear pins to hold the nose\coupler\ebay to airframe until deployment...

I'm with the idea that leaving it without runs the risk of drag separation while slowing to apogee
I use 3, 2-56 buttonhead screws to hold the nosecone shroud to the coupler and two 2-56 nylon screws for shearpins
to hold the coupler to the airframe.

IMG_20150520_220557.jpgIMG_20150520_220319.jpg

Kurt
 

ksaves2

Lifetime Supporter
TRF Lifetime Supporter
Joined
Nov 25, 2009
Messages
5,981
Reaction score
294
What was he trying to use for motor retention? I don't doubt friction fitting not working when done properly. That doesn't mean I am guaranteed it will work every time I launch my rocket though. It only takes once in my opinion
I could lose a very expensive motor case or epoxy in a bulked with eye bolt and be reassured. No to mention the eyebolt sErving two purposes.
A) motor retention
B) shock cord mount without having to epoxy in a permanent shock cord.

I'm new to dual deploy also. I don't know how having my own charge blasting at the motor would work. I appreciate the tip but to be honest I'm simply not that confident in friction fitting. I already am throwing in a lot of unknown variables.
A tight parachute pack might make it easier to blow out the motor case but it's less likely since it's a small chute
if any at apogee. If secured with the recovery harness at the forward closure rocket may tumble down for a nominal
albeit unusual main chute deployment so all won't be lost...... Except if the certifier says that's not supposed to
happen and considers it a DNF since it's expected that the motor should be retained in the rocket.

BTW your fincan looks plenty strong. You should have no fear there. Many get by with thick fillets with no problem.

Kurt
 

blackjack2564

Crazy Jim's Gone Banana's
TRF Supporter
Joined
Jan 18, 2009
Messages
9,057
Reaction score
1,158
Location
Savannah Ga
What is your "ready to fly" weight...at this point?
Just pile all everything going into airframe on scale.

Proper glue chosen will hold fins on with no T-T on project this small.

PS... I WOULD guarantee return of motor case IN the airframe...if you friction fitted exactly as I would.
Rear 1/4 spiral wrapped tape on motor....aluminum tape over motor onto airframe joint.. it works/has worked for decades.
I just friction fitted a M in my minimum diameter flown at Airfest.
 

dford

Tada
Joined
Apr 23, 2016
Messages
330
Reaction score
1
What is your "ready to fly" weight...at this point?
Just pile all everything going into airframe on scale.

Proper glue chosen will hold fins on with no T-T on project this small.

PS... I WOULD guarantee return of motor case IN the airframe...if you friction fitted exactly as I would.
Rear 1/4 spiral wrapped tape on motor....aluminum tape over motor onto airframe joint.. it works/has worked for decades.
I just friction fitted a M in my minimum diameter flown at Airfest.
Total weight = 539g, 1.11 lbs. Below is my current .ork file. The only thing off is the "eggfinder coupler" in the file. Not sure what happened there. I don't actually have the harnesses or chutes. These weights came with the "stock" .ork file. I also don't know the exact weight of the lower motor bulkhead.
The 539g comes from the manufacturer parts, plus the 3D tracking sled from shapeways and what I did to the fins...

Okay. SO much advice to ride friction fit. Would I have to epoxy a harness in?
If not then I assume I would have to use a threaded forward closure with an eyebolt?
If I don't place a bulkhead above the motor how do I ground test?
Should I just duct tape the end closed tight?:lol:
Honest question I really don't know.

Unfortunately I live in California and can't fly Loki. I'm not aware of any 38mm K motors I could use. If I didn't place a bulkhead I could potentially add a coupler and fly Loki out of state later...:confused: and the fins would for sure be beefy enough...
To be completely honest in a way I wish I didn't add a ply. But I'm living with it.

View attachment 1MyGD38.ork
 
Last edited:

markkoelsch

Well-Known Member
Joined
Mar 18, 2009
Messages
4,364
Reaction score
148
What was he trying to use for motor retention? I don't doubt friction fitting not working when done properly. That doesn't mean I am guaranteed it will work every time I launch my rocket though. It only takes once in my opinion
I could lose a very expensive motor case or epoxy in a bulked with eye bolt and be reassured. No to mention the eyebolt sErving two purposes.
A) motor retention
B) shock cord mount without having to epoxy in a permanent shock cord.

I'm new to dual deploy also. I don't know how having my own charge blasting at the motor would work. I appreciate the tip but to be honest I'm simply not that confident in friction fitting. I already am throwing in a lot of unknown variables.
If you have room for an Aeropack or similar go for it. That said, I have seen one of the epoxied on ones come off in flight- once.

As to the friction fit- where are the other guys who have done a lot of this. Paging Crazy Jim, Tim Lehr, and many others.
 

blackjack2564

Crazy Jim's Gone Banana's
TRF Supporter
Joined
Jan 18, 2009
Messages
9,057
Reaction score
1,158
Location
Savannah Ga
Total weight = 539g, 1.11 lbs.

Okay. SO much advice to ride friction fit. Would I have to epoxy a harness in?
If not then I assume I would have to use a threaded forward closure with an eyebolt?
If I don't place a bulkhead above the motor how do I ground test?
Should I just duct tape the end closed tight?:lol:
Honest question I really don't know.

.
I applaud you for this ambitious attempt.

You have a very good weight so far, considering everything you are attempting to cram in your project.
No need to epoxy anything in.

Here are some simple solutions to consider for FF [friction fit]:
First the forward closure can be easily modified as seen in pics. Machine screw through sides to hold shock cord. There is blue tape wrapped around threads to keep cord from fraying on sharp edges of threads. I assumed AT hardware since you mentioned J-500, I have other methods for CTI hardware also.

Or you can get a threaded closure for E-bolt. You can also wrap/tie cord around the flat area of closure between the knurled knob and flat area.

DSCN3818.jpg DSCN3823.jpg

DSCN3822.jpg

1/8 inch. kevlar 750 lb would suffice for your recovery needs. Teddy at One Badhawk has it very reasonably priced. 50ft for 12.00? I think.

FF : The tape is spiral wrapped, overlapping the previous edge so it won't "curl" back when forced into airframe. I fit mine so it "screws'' into airframe with a final bump on the ground to push it in. After flying you may/maynot need to push motor out by inserting a dowel/pvc pipe etc. into airframe, and pushing/banging motor out. Best done as soon as possible after flight.
Many times if still warm, I can unscrew motor.

First you fish the shock cord through the airframe.
Then attach to forward closure.
Finally insert into airframe and tape over exterior. [This is one of my 54mm projects]

DSCN5595.jpg DSCN5592.jpg


DSCN5590.jpg DSCN5589.jpg

For graphite nozzles [snap ring hardware] one would wrap the tape on motor above the nozzle, so heat sink doesn't turn the tape to goo.

Just FF the motor for ground testing. Simple. Hope this helps you visualize FF method.

Edit: please note...using Aluminum metal duct tape, not your everyday grey duct tape !
This stuff really works well.
 
Last edited:

BDB

Absent Minded Professor
Joined
Aug 22, 2015
Messages
2,135
Reaction score
389
Jim, would you mind sharing your solution for CTI cases too? I know that CTI makes a forward closure that is compatible with Aeropack MD retainers, but they claim it shouldn't be used as a shock cord attachment point.

Also, would it make an difference if the Al tape was used with a tapered rear closure? I don't think so, but I thought I should check since thats what I'm hoping to do in the near future.
 

Tonimus

Well-Known Member
Joined
Jul 9, 2014
Messages
1,511
Reaction score
3
Jim, would you mind sharing your solution for CTI cases too? I know that CTI makes a forward closure that is compatible with Aeropack MD retainers, but they claim it shouldn't be used as a shock cord attachment point.

Also, would it make an difference if the Al tape was used with a tapered rear closure? I don't think so, but I thought I should check since thats what I'm hoping to do in the near future.
I can't speak for the shock cord anchor, but as long as your nozzle is flush (or almost) with the end of the tapered rear closure, you're fine. In fact, it should work better because the smooth surface would have better tape adhesion.
 

blackjack2564

Crazy Jim's Gone Banana's
TRF Supporter
Joined
Jan 18, 2009
Messages
9,057
Reaction score
1,158
Location
Savannah Ga
Jim, would you mind sharing your solution for CTI cases too? I know that CTI makes a forward closure that is compatible with Aeropack MD retainers, but they claim it shouldn't be used as a shock cord attachment point.

Also, would it make an difference if the Al tape was used with a tapered rear closure? I don't think so, but I thought I should check since thats what I'm hoping to do in the near future.
Aero-pac works entirely different. I just modifying to put an E-bolt in,for recovery attachment, then friction fit.


Tapered closure.... no difference. Tape works fine on all.

CTI closures...38 & 54's, this was discussed with Dr J, before I used them.

3/16th's [#10] eyebolt for 38
1/4 in for 54's;
If there is a threaded insert....use it.

For both:

If no insert, you must first straighten out the taper in the 54mm BP touch hole, Hand twisting a 3/16's bit will do it.
Rough up inside walls of bp well [after removing bp] with heavy sandpaper or gouge with screwdriver, etc.

Add a nut to threads on E-bolt. Twist into touch hole, will require downward force so threads will self tap.
Only thread in until you hit delay grain.
you want the nut "floating" a bit above bottom of well so when you pour epoxy into the well it flows around the nut, grabbing it.
Any 5-10-20 minute will do or have ready when gluing a kit together and use excess from any other pour.

I'm cheap so after flying...I whack closure with hammer on side, remove & re-use the E-bolt.


DSCN3806.jpg DSCN3440.jpg
 
Top