Go Devil 38 on a Loki K627, or How I Leaned to Stop Worrying and Love 3D Printing

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Holee guacamole! Nice consolation for the V2. Impressive fincan. I just filleted mine on but am not doing anything larger than a 720 case. I'm surprised the short antenna EggFinder gave you information over the top. Did you see any
relevant GPS altitude readings during the flight? I find I don't get anything that comes close to reality (altitude reading, lat/long is fine) with the EggFinders but it's designed to find one's rocket. For that it's pretty darned good and economical. Can always download the
info afterwards from the altimeter. I have my setup with a Raven and a mag switch so someday it'll go. Kurt
 
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Just beautiful..... I'm excited to do my GD29 I just picked up. I will get the Go Devil 38 next. Any chance you want to sell some 3D printed stuff for it?

I wouldn't sell the sled. It is not a high quality print as it is very thin in order to get everything in. It needs the all thread to really become structurally sound. It also wobbles a bit on printing, even with a wide brim, so it ain;t as pretty as many other parts. The charge wells and drill guides maybe, but they aren't really finished products. I don't know how general they would be. I'd be happy to develop the charge wells to a broadly applicable design, but they aren't there yet.
 
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Great flight. Really no need to do tip 2 tip. I used to be a believe in that. Of coarse its great insurance but for most flights not necessary. I flew a 3 inch min diameter on a m 1850. exceeded mach 2. No tip 2 tip. I did use some expensive epoxy. Hysol (loctite) HP-120. From my experience that is all that is required. Now if I was doing a 98mm min diameter and pushing the envelope I would do tip 2 tip. But anyway nice rocket.

I want to do a 54mm min diameter with the loki M with head end deployment. I would probably build that without tip 2 tip but use the expensive epoxy.

The Go Devil comes with 1/16" fiberglass fins. They are very flexible. Tip to tip is highly recommended with fins this thin and flexible on flights over mach. Expensive epoxy or not fin flutter is a real thing.

Yeah, not all fins are created equal. The fins on the GoDevil can be easily flexed, even once attached and filleted. I agree that not everything needs t2t, but I really don't want to make rocket confetti and I had about 7 yards of cloth already. The t2t adds very little weight if you squeeze out the excess epoxy well.
 
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Holee guacamole! Nice consolation for the V2. Impressive fincan. I just filleted mine on but am not doing anything larger than a 720 case. I'm surprised the short antenna EggFinder gave you information over the top. Did you see any
relevant GPS altitude readings during the flight? I find I don't get anything that comes close to reality (altitude reading, lat/long is fine) with the EggFinders but it's designed to find one's rocket. For that it's pretty darned good and economical. Can always download the
info afterwards from the altimeter. I have my setup with a Raven and a mag switch so someday it'll go. Kurt

I think the highest I saw on the GPS was 17k and change agl, which is about right as the site is a little over 1000 agl. This one and the old school model I flew in my Mongoose had alts in the neighborhood of what the altimeters said.
 
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The Go Devil comes with 1/16" fiberglass fins. They are very flexible. Tip to tip is highly recommended with fins this thin and flexible on flights over mach. Expensive epoxy or not fin flutter is a real thing.


I am sure you can get it with 1/8 inch if you ask. If madcow wants to make a sale then they will do it.
 
I am sure you can get it with 1/8 inch if you ask. If madcow wants to make a sale then they will do it.

You can probably get carbon plate fins too, but that doesn't mean there is never a need for tip to tip reinforcement. Sorry that you missed my point.
 
You can probably get carbon plate fins too, but that doesn't mean there is never a need for tip to tip reinforcement. Sorry that you missed my point.


Of course there is. I have done a ton of tip 2 tip vacuum bagged and not vacuumed bagged. Fiber and carbon. I am saying for max altitude in some situations you dont need to do tip to tip. Yea if you just use regular epoxy for fillets and such you want to do tip 2 tip. Please PM me if you want to discuss more about tip 2 tip.

Go look at my 2 stage build thread. I flew the booster at airfest last week. 1/8 Carbon fiber fins and airframe. No tip 2 tip. I used hysol hp-120. Exceeded Mach 2. There is a time and place for both. Yes, when you do level 3 motors in min diameter you will understand.
 
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As I have neglected to say it thus far, thanks for all the kind words on the build and flight.

It was really a fun build, and let me try a few things that will probably be standard kit in my future builds.

This is a really nice kit for the money too. The range of motors you could fly is great. You could get it in the air fine with a punchy F, and obviously you can go to K, so 6 "letters" of motor options is sweet for a $70 kit.
 
As I have neglected to say it thus far, thanks for all the kind words on the build and flight.

It was really a fun build, and let me try a few things that will probably be standard kit in my future builds.

This is a really nice kit for the money too. The range of motors you could fly is great. You could get it in the air fine with a punchy F, and obviously you can go to K, so 6 "letters" of motor options is sweet for a $70 kit.


My buddy Bill K. flew his Go Devil 38 on a Loki J712 it was a great flight.
 
Good thread...

Like so many others, I too have a GD 38 and the Loki 38/1200 case. Haven't bought the K627 yet, but I have the other K (K1127?) in the bag, daring me to use it. After all, what's the point of a 38mm K if you're not going to put it in a MD bird?

Only thing I'm waiting for is to do T2T on the fins - something I've not attempted previously, so a bit anxious as I want to do it correctly. I don't want to just slap on epoxy-soaked FG and try to press out all the excess.

Can you please clarify how you did your fin beveling? I neglected to do this off the bat, and I think I'm paying for it in terms of altitude. My GD 38 constantly underperforms sims by about 30%. I suspect the fins, but it's possible there is a motor configuration issue (I've been using a 38mm tailcone Rousetech aft closure, which may put the nozzle too far up the tail). Of course, in review, it seems your GD underperformed by 15-20%... Did you tower-launch or use fly-away guides?

Again, thanks for an informative thread!
-e
 
Good thread...

Like so many others, I too have a GD 38 and the Loki 38/1200 case. Haven't bought the K627 yet, but I have the other K (K1127?) in the bag, daring me to use it. After all, what's the point of a 38mm K if you're not going to put it in a MD bird?

Only thing I'm waiting for is to do T2T on the fins - something I've not attempted previously, so a bit anxious as I want to do it correctly. I don't want to just slap on epoxy-soaked FG and try to press out all the excess.

Can you please clarify how you did your fin beveling? I neglected to do this off the bat, and I think I'm paying for it in terms of altitude. My GD 38 constantly underperforms sims by about 30%. I suspect the fins, but it's possible there is a motor configuration issue (I've been using a 38mm tailcone Rousetech aft closure, which may put the nozzle too far up the tail). Of course, in review, it seems your GD underperformed by 15-20%... Did you tower-launch or use fly-away guides?

Again, thanks for an informative thread!
-e

I did my beveling by hand. I taped a full sheet of 220 grit to the bench, and worked the fin back and forth across it. In your case with the fins on the bird already a sanding block or sanding bar is probably the way to go. T2T isn't that hard. Just leave some excess, and trim it with a box cutter when the piece is still leathery. Then just clean up the edges with a sanding block.

I launched my flight out of an 8 ft tower. I built an adjustable tower a few years ago. Great to launch from, but sucks to transport and carry
 
If you get a router table and fit your Dremel to it you can get good results with a fairly simple jig and some sanding bobbins:

JigAndFin.JPG

I use this for my fins now. Gives very consistent bevels and is easy to use. Worth spending the time to make the jig.

Got good performance out of a Tomach 54mm (Mach 1.8 and 21.5k' :)) with the beveled fins.
 
If you get a router table and fit your Dremel to it you can get good results with a fairly simple jig and some sanding bobbins:

View attachment 327819

I use this for my fins now. Gives very consistent bevels and is easy to use. Worth spending the time to make the jig.

Got good performance out of a Tomach 54mm (Mach 1.8 and 21.5k' :)) with the beveled fins.

Very cool, thanks for sharing! I now have an excuse to buy a router table!!
 
It was only a cheap one from Aldi, but good value for money.

OTT: Can you elaborate on the jig please? I'm and IT guy coming at rocketry in my my late 30s and all my "making stuff" experience comes from only done one term of basic high school wood/metal work...

It's the hardware / physical construction I'm learning most of all..

As soon as something needs a jig of some sort, I've typically shied away - I'm trying to fix that. ;-)
 
Hey, great work Chris! She sure was speedy; glad it all came back in great shape with some mach rash!

It's threads like these that transition me from "no interest in that kit" to "gotta have one of those"! Darn you!:wink: Well done!:cool:
 
Nice build Chris. Makes me want a 3D printer.


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Hey, great work Chris! She sure was speedy; glad it all came back in great shape with some mach rash!

It's threads like these that transition me from "no interest in that kit" to "gotta have one of those"! Darn you!:wink: Well done!:cool:

 
Got the mighty Loki K627 LR and #25 nozzle from Chris at Airfest. Built the motor in the hotel room, and had it ready to go on Sunday.

Pad weight 4.9 lbs.

If you were at Airfest on Sunday, this is the little rocket that came out of the tower on the 40s bank probably around or just before noon.

The flight was dead straight, and absolutely hauling ass. When the ignitor lit the motor smoked for a second or so, and then left that tower like a scalded cat.

The EFmini of course stopped sending data on boost, but picked back up just before apogee. Maintained data all the way to landing, and picked it back up when we got within 1/4 mile of it on ground. Walked right up to it about .8 miles from the pad. Rocket basically undamaged except the leading edge of each fin has pitting running it's length...not surprising given the speed. I'm actually glad I didn't see any delamination. The decals were melted/peeled almost completely off. I know they produce drag, but I wanted to rip them off in flight...kind of a Mach trophy.



The data (yes barometric, so not fully accurate, but certainly in the neighborhood).

Top speed: 2571 ft/s (Mach 2.28)
Broke Mach 1: ~600 ft based on hiccup in data
Alt: 16871

Lower than expected, but again baro only so good on high performance flights, and fun regardless. Also, I angled the tower away from the crowd probably 4-5 degrees. If something went wrong I didn't want it coming down anywhere near people.



So, that's it. This was my fastest build ever at about 2 weeks. I know there were ways to do things differently, but built "my way" would have been impossible in that time without the guides and parts I was able to print. No parts were damaged in flight, and once it is cleaned up, and the leading edges repaired it will be ready to fly again, but I don;t know what to put in it now. Maybe a higher acceleration Loki.

I have finally gotten around to repairing this rocket, and it turns out I didn't have any pitting on the leading edge of the fins. Instead, the clear coat "melted" and flowed on the entire rocket, and just flaked off on the leading edges of the fins. After a lot of acetone and quite a few shop clothes the rocket is naked, and ready for a new sacrificial clear coat. I'm thinking the Loki K1127 this year at Airfest.
 
I'm thinking you should get a second one, and build a 2 stager.. K1127 on the bottom, K627 on top :)

I like the way you think, but no. I have a 2 stage Darkstar Jr planned for that niche. Once I learn non-MD 2-stage, then the big fun begins.
 
I'm thinking you should get a second one, and build a 2 stager.. K1127 on the bottom, K627 on top :)

Coupling might be hard with MD on the bottom and the top. As far a fin pitting goes, you might consider slathering the leading edges of the fins something like Cotronics 4525IP as an ablative but the self life sucks and the cost is very high: https://www.cotronics.com/catalog/05 4525 4525IP.pdf After a flight, re-sand the leading edges and repeat the application.

Me? As I've said, I'm impressed with the laminated fincan. Laminating like Cl(VII) did for a K motor allows for very nice safety margins and I believe 1/8" fins aren't needed in that case. Mine? I just have the stock fins stuck on with Cotronics 4525IP but the biggest thing I can use is a J500 720N-s case so I think the lamination isn't needed in my situation. Kurt
 
I was in a serious rush by this point, so you are only getting a few pics, and some post flight.

A sled was made to carry the Magnetic Switch, RRC3 and LiPo to power it. Same battery as for EF-mini, I'm trying to standardize around it as I bought a bunch last time they were in stock. It was difficult to make these fit in the 38 mm bay, but it worked out. You can't really see it in the pic but me TRA and NAR numbers are printed into the sled for whatthat is worth...probably nothing.



To give the most room possible in the drogue section only 2" of coupler is aft of the vent band. The band epoxied on with Aeropoxy, and is the only other use of adhesive outside the fins. The body tube drill guide was used to space the 3 vent holes, and they were drilled to a diameter I don;t remember right now.

The bulkheads end up needing a lot of stuff. the drogue needs 2 charge wells, recovery attachment point, sled all thread cap nuts x2, and terminal blocks. Yes, I know there are ways to get around all of these like through the bulkhead ematches, and glove finger charges, but I like everything very securely attached, so no free floating charges. To make spacing easy a drill guide was prepared for the bulkhead that snapped onto the center hole, and outer edge. Shown is an earl version, but a second version included 4 holes for the terminal block connections too. The Charge wells were 3D printed too. A double well for the drogue compartment (Drogue and Aux on the RRC3), and a single well for the main. To hold these on the have the same three holes as the enter and sled all thread, and get sandwiched under all three. The guides were used to drill the holes, and the terminal blocks were solder to wires and potted in epoxy into the bulkhead.



The charge wells contained FFFFg. Drogue: 0.25 g, Aux: 0.5 g (NOT coming in ballistic, maybe in pieces, but not ballistic), Main: 0.7 g. The wells have held up after ground testing and flight with little damage...they look gnarly, but after you scrape off the crud they are fine. I would guess these would be good for about 10 flights, and are easy to replace as they are only mechanically attached.

Chris,

I’m in the midst of a similar build, and took inspiration from your printed bulkhead plus charge wells. (Early test version with more refinement needed)

IMG_0304.jpg

I’m wondering how you routed the e-matches. Are there holes for the leads that aren’t visible, or did you just run the e-match leads over the top of the container?

Thanks in advance for your advice.
Bill
 
Well on your way. A few details on the charge wells to help you along.

- The minimum wall thickness was 2 mm (you may get away with less, but I know that works for repeated use.
- I just snaked the wires over the top of the well in this case. Since it was a higher-ish alt flight I wanted to ignite the powder from the top instead of the bottom.
- Tape doesn't stick very well to PETG, so be careful when taping in your charges. A notable exception to the lack of stick is the aluminized tape for HVAC stuff.
 
Awesome work! 3D printing has transformed the hobby for me too. My latest build has a fully printed AV bay and NC tracker. Not to mention all the guides I have created along the way. I have the Go Devil 54 for my next build. your 3D printed MD retainer is a great idea!
 
Awesome work! 3D printing has transformed the hobby for me too. My latest build has a fully printed AV bay and NC tracker. Not to mention all the guides I have created along the way. I have the Go Devil 54 for my next build. your 3D printed MD retainer is a great idea!

Thanks, that particular do-dad is available through my website: Bare Minimum Diameter Retainer

I sell the same nosecone tracking bay shown in this thread there too.
 
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