New Build. Have Questions.

[Valkyrie]

It's been quite a while since I've done anything with rockets. I built a 3" LOC Iris with the plan of getting an L1 cert but I never was able to find the time. I was deployed and life just got in the way. The rocket sits unflown but I'm planning on flying it with a 29mm G motor and an adapter later this year to shake things out. I bought a JLCR and am gonna see how that works out. Hopefully I get back on track.

Anyway. The new build. I cato'd a Ventris last fall. Not sure what happened but using an aerotech 29/40-120 case and an E16-7 it made it 10' off the rod and blew apart violently. The forward closure blew out and into the dog barf and the entire fin can and motor section was shredded. The delay grain and ejection charge remained intact. The case and aft closure are fine, the threads on the forward closure are stripped off though. I ordered a new one.

So I wanted to build another rocket to replace the destroyed one and Was shopping around just went and ordered a Madcow TWFG 2.6" 38mm DX3. And it came today. Maybe I'll get the L1 done this fall and get to fly it also. It's packaged for it to be configured as a DD but I'm thinking SD with the chute release and utilizing the AV bay for an altimeter.

Before I get too too deep into it, I am considering using plastic rivets to keep the DD configuration optional. Or should I just fix the nose assembly and go SD with the chute release and just access the AV bay from the aft end of the nose assembly? I'll start the motor mount tomorrow just the centering rings. I'll try to put up pictures.

Last question. This is a stout build. Would I be able to fly this on any larger G motors in a 29mm adapter and the 29/40-120 case to shake things out first?

I am thinking a metallic red paint paint scheme with gold accents, kinda Ironman looking.

 

[OverTheTop]

Before I get too too deep into it, I am considering using plastic rivets to keep the DD configuration optional. Or should I just fix the nose assembly and go SD with the chute release and just access the AV bay from the aft end of the nose assembly? I'll start the motor mount tomorrow just the centering rings. I'll try to put up pictures.

How about putting M3 threaded inserts in the NC and that way you can screw the NC onto the airframe, or use M3 nylon screws as shear pins if needed. If you don't like metric you could consider 2-56 or 4-40 (or something else) similarly. The nylon remaining after shearing removes quite easily from the threaded inserts with a small drill usually.

 

[K'Tesh]

I suggest that you Sim the rocket with values obtained from your build to determine if the rocket is too heavy for your intended motor.

 

[dhbarr]

g76g would be your best bet once you arrive at a reasonable weight estimate. By far the highest peak thrust in that casing.

 

[rharshberger]

g76g would be your best bet once you arrive at a reasonable weight estimate. By far the highest peak thrust in that casing.

G138T for highest peak thrust in the 29/40-120, but its a HPR cert required motor (if in USA).

 

[DavidMcCann]

I have a couple of the 2.6" screeches. Basically the same rocket, different fins.

Build photos- https://www.flickr.com/photos/[email protected]/albums/72157647408994783
some flights- https://www.flickr.com/photos/[email protected]/albums/72157652603347240

weeeeee--

If it balances stable, you may be able to fly just the booster and the nose cone on a G. Built and with the full payload section and chute, mine weighs 5.5 pounds. A G76 would be 2.9:1 thrust to weight. A Loki G80 would be 3:1. I'll go pretty low, but I just wouldn't do that in this rocket.

I'd built it with plastic rivets for the av bay, and drill 2-56 holes for the nosecone. When flying SD, put SS screws in the nose. when DD, nylon screws as shear pins.

I use 1.6 gram charges on this rocket.

 

[Valkyrie]

Great info gents. I have some ideas now. Regarding threaded inserts. I know what they are but can't seem to find anything that might work in the way I am imagining them. I was thinking of epoxying nuts on the inside of the tube as an anchor for the screws that will hold the nose cone and use round head SS machine screws for the job. Or is there model specific anchors out there?

I'm gonna work on getting the motor mount assembly going today. Just the forward centering ring and the shock cord eye bolt installation. I'll leave the aft ring off to fillet the fin roots to the motor tube later on.

A paint question. I'm going with a metal flake red paint. I plan on using red oxide rustoleum primer. I figure the dark primer will be easier to cover with a similar colored top coat rather than the gray rustoleum primer. Am I thinking right?

 

[Nathan]

For red paint I normally use light gray or white primer. Otherwise it may end up a lot darker red than you expect. Depends on how translucent the red is. Metalflake paint, which has bigger flakes than normal metallic paint, usually totally hides the primer so it may not make any difference.

 

[DavidMcCann]

I've been doing all my harnesses like this- It's not like you're going to get an arm down to the eyebolt to ever replace it.

 

[dhbarr]

G138T for highest peak thrust in the 29/40-120, but its a HPR cert required motor (if in USA).

I always forget about that one, thanks for the good reminder.

 

[DavidMcCann]

I always forget about that one, thanks for the good reminder.

noce motor, I've flown a few. But it's a case killer so I've decided to pretend it doesn't exist.

 

[Valkyrie]

I've been doing all my harnesses like this- It's not like you're going to get an arm down to the eyebolt to ever replace it.

I plan on the same or very similar. I have 3/16" kevlar braid and plan on a loop epoxied to the motor tube with JB weld. How long to extend the loop? To the top of the booster section?

 

[Valkyrie]

I got the motor tube and forward CR assembled. I used a length of 3/16" kevlar epoxied along the tube as the recovery retention and ended it about an inch short of the top of the booster section. Close enough I can grab it and change out the shock cord easily. I used JB weld for this. The CR is epoxied in place with Devcon 2 part 5 minute epoxy and Ill add a fillet around the circumference of the top of the forward CR tomorrow when the JB weld cures. I cannot seem to upload the pictures though.

I am going to epoxy the nose cone to the coupler this evening. and then start thinky on the AV bay asembly.

 

[DavidMcCann]

Before you install fins, slide the av bay in the rear of the booster. Use the slots to mark the coupler. Make the lines run the length of the av bay. Then transfer the lines up ontotbthe payload. Bam. Spots for rivets marked

 

[Valkyrie]

Before you install fins, slide the av bay in the rear of the booster. Use the slots to mark the coupler. Make the lines run the length of the av bay. Then transfer the lines up ontotbthe payload. Bam. Spots for rivets marked

Now that's thinking. Thanks!

It won't be until later in the week for the fins I think.

 

[Nytrunner]

On a rocket this small, why complicate things with threaded inserts? Rivet all the things!

That's just me though, I love rivets. ;D

 

[Valkyrie]

I'm still thinking SD with the chute release and just forget the rivets and stuff altogether.

Regarding the AV bay. I obviously need some sort of static ports for the altimeter? Where to locate them and how large?

 

[Nytrunner]

I'm still thinking SD with the chute release and just forget the rivets and stuff altogether.

Regarding the AV bay. I obviously need some sort of static ports for the altimeter? Where to locate them and how large?

If you forget the rivets, they will never forgive you.....

For altimeter ports, Perfectflite's stratologger manual (downloadable) has a good "hole diameter as a function of bay volume" guide.

I think Madcow just told me to drill four 1/8" holes in my Patriot's payload section (4"diam * ~16"long)

 

[Valkyrie]

If you forget the rivets, they will never forgive you.....

For altimeter ports, Perfectflite's stratologger manual (downloadable) has a good "hole diameter as a function of bay volume" guide.

I think Madcow just told me to drill four 1/8" holes in my Patriot's payload section (4"diam * ~16"long)

where did you locate the holes? Through the centering band?

 

[Nytrunner]

where did you locate the holes? Through the centering band?

If you use a switchband, that's probably a really good place. It keeps both tubes fixed and the holes are always lined up.

If you build without a switch band, then you'll want to drill them on the side that's fixed in a tube (by gluing, rivets, or bolts) for the same reason: alignment.

I like the thread title. Like: Have Gun, Will Travel. (or Have Rocket, Will Launch)

 

[Valkyrie]

If you use a switchband, that's probably a really good place. It keeps both tubes fixed and the holes are always lined up.

If you build without a switch band, then you'll want to drill them on the side that's fixed in a tube (by gluing, rivets, or bolts) for the same reason: alignment.

I like the thread title. Like: Have Gun, Will Travel. (or Have Rocket, Will Launch)

Thanks a lot. I'm gonna drill them through the switch band.

 

[Valkyrie]

I know I am getting ahead f things but I assume that friction fitting the booster and the rest of the rocket is probably not a good idea? Just dry the he fit is loose but not sloppy. I am still on the fence with the DD. If I am using the chute release then I really don't need the DD set up and I really don't plan on DD anyway, was just thinking I might want to in the future. So I may just use machine screws or nylon rivets and then shear pin the booster side. Any thoughts?

 

[OverTheTop]

So I may just use machine screws or nylon rivets and then shear pin the booster side. Any thoughts?

If you use nylon screws or rivets treat them as if they could shear. Make sure there is a harness between the two part in case they unexpectedly break :wink:

I normally use stainless steel countersunk screws myself for the fixed mating.

If you use countersunk screws it will probably mean you won't be able to use shear pins in the same locations in the future. The countersinking makes for a knife-edge that could easily cut the shear pins. If you are not going for performance a few pan head screws would not detract from aesthetics or performance significantly.

 

[Nytrunner]

I know I am getting ahead f things but I assume that friction fitting the booster and the rest of the rocket is probably not a good idea? Just dry the he fit is loose but not sloppy. I am still on the fence with the DD. If I am using the chute release then I really don't need the DD set up and I really don't plan on DD anyway, was just thinking I might want to in the future. So I may just use machine screws or nylon rivets and then shear pin the booster side. Any thoughts?

If you hold the front half of the rocket and pick the whole thing up vertically, the motor section should stay on. But if you start shaking the assembly with your one hand, then the booster should start working it's way off.

I've heard that's a good way to judge booster/payload fit.

 

[CzTeacherMan]

1) yes, use plastic rivets... Don't lock yourself into SD just because. Might as well leave it flexible. I fly DD rockets SD every now and then, especially since the Advent of the JLCR
2) yes, some high they're G motors should be fine, depending on how you build

 

[Valkyrie]

Sounds good.

So far I have been able to get the AV bay complete. I plan on an Altimeter Three. I drilled three 1/16" static ports in the transition band at 120 degree intervals. Looking at some calculators I found online, that should be plenty.

I just finished up the initial install of the motor tube. Of course there's a lot to do with fin mounting and filleting the fin roots but it's going faster than I expected.

I should have the basic airframe complete by the end of the week. After that I'll be out of town for a couple weeks so paint will have to wait. Going with the plastic rivets for the nose section to keep my options open and I'll use shear pins for the booster section. Do I use three or four shear pins and what size?

 

[Nytrunner]

Unless the booster section is REally loose, I think you'd be safe without shear pins on it.

Are you worried about drag separation pulling the rocket apart after burnout? For a 3" rocket flying 29mm motors, that shouldn't happen unless you put a crazy I in there.

 

[DavidMcCann]

Unless the booster section is REally loose, I think you'd be safe without shear pins on it.

Are you worried about drag separation pulling the rocket apart after burnout? For a 3" rocket flying 29mm motors, that shouldn't happen unless you put a crazy I in there.

My screech did mach 1.2 a few times, had one 50G flight, and I had a camera mounted to the booster, and it still didn't drag separate.... Like Nytrunner says, it's gotta be super loose to worry about it, and even then I'd probably use tape on the coupler before shear pinning it.

 

[Valkyrie]

My screech did mach 1.2 a few times, had one 50G flight, and I had a camera mounted to the booster, and it still didn't drag separate.... Like Nytrunner says, it's gotta be super loose to worry about it, and even then I'd probably use tape on the coupler before shear pinning it.

Interesting. It's pretty loose. If I ever get tge time to actually certify I'd like to put big motors in it. I'll monkey with tape and see how it goes. A lot of work to be done yet. Waiting for the motor tube to cure in place before I install the fins. I need a jig to keep them square. Trying to conjur up something in the garage.

 

[DavidMcCann]

with the fins being 1/16, I found my estes jig worked perfectly, lol

it flies straighter than anything else I have, almost silly-
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