How to get coupler out of nose cone (big FWFG cone).

Well, if it was me I would fail to get it out and give up. Then figure out a way to ensure that the best way to get it out isn't to fly it. Epoxy would probably be involved.

Bat-mite said:

This sounds really promising. But I have some questions.

I'm not following you about securing the ratchet straps to the coupler. I assume you mean the outside of the coupler? I can't imagine any kind of tape holding them on with the amount of force that will be required to separate the pieces. And I can't picture how you would do it with rope.

Also, the eyebolt. Wouldn't it have to be really long, like three feet? Do they even make a 1/4-20 eyebolt three feet long?

If you see my other thread, you'll note that there is a lot of epoxy gunking up the inside of the coupler, and I can't slide the bulk plate in very far.

Do you have a picture or can you provide more details? Thanks.

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As for securing the ratchet straps , lay the straps flat , and using two inch gorilla tape , go around the whole coupler as much as you can . This will distribute the load . The bulkhead could be a 3 Inch diameter or smaller . You only need something strong enough not to break under load , or destroy your cone .

I've done this a bunch of times trying to fit a coupler into a nosecone, and this is what works.
Install the nosecone with the stuck coupler into a section of matching fiberglass airframe tubing.
Place a sheet of plywood on the floor, and bounce the open end of the airframe on the plywood.
The inertia of the coupler will extract the coupler into the airframe.

John

Maybe the coupler is slightly cocked. Install your nose cone into a body tube and roll the assembly over a smooth surface. Carefully observe the tip. If it wobbles up and down, gently whack it to wiggle until it is straightened out. It should come off easier then. It may require multiple repetitions of straightening and pulling.

Reinhard

Just for fun, you could get stupidly midevil on it! Pin on a sacrificial bulkhead to the bottom of the coupler. Add lots of tape for extra security. Have a small ejection charge in there... Or an air compressor fitting, and wrap the whole thing in lots of heavy blankets, or perhaps put it nose down into the ground leaving the coupler exposed. Blast it out!

(Too soon for an April 1 post, but ...)

Gerald

Blow it out, or blow it up!

PS - You can use water instead of compressed air, and it would be safer. Messier, but not as spectacular!

Either air or water under a bit of pressure should be able to go between the coupler and nosecone, and help remove the fiberglass dust. It is usually the fiberglass dust which causes the sticking. If you have a compressor and a spray nozzle, take it outside and spray around the edge of the coupler at an angle to blow out all the dust you can, each end of the coupler. Then spray directly between the two and see if you can get some to blow out the other side of the coupler. If you can get some dust out, it whould be easier to remove. Not easy, but easier, potentially a lot easier.

Heck, I'd even consider pouring in hydrogen peroxide, and see what comes out of the joint. The idea is to get the crap out that might be interfering with the parts sliding. If the coupler was jammed in with fresh fiberglass dust while the epoxy was still slightly green (not 100% cured) then a slight bond will have been formed. It is a weak bond but there is lots of surface area. I've seen it before but always managed to get the stuff apart, one way or another.

Gerald

You should name the rocket Excalibur.

Only other option is spend the $150.00 to $200.00 or so for a replacement nosecone and coupler. Get your rocket done and if you ever get the coupler out at your leisure, you can do another rocket or sell it if you don't bugger it up or break it. If you break it, you'll need a new one anyways. If you destroy the coupler getting it out, it would likely be the cheapest part to replace as opposed to the nosecone shroud. I say go into hock and get a new part if you are under the gun time wise. Kurt

Get some reinforced box tape. Wrap around the nose cone a couple of times and leave enough of a tag end that you can grip and pull. Now wrap another piece around the coupler in the opposite direction. Pull the ends away from each other and see if you can get the coupler to turn. If it'll turn, you should be able to get it out.

ksaves2 said:

Only other option is spend the $150.00 to $200.00 or so for a replacement nosecone and coupler. Get your rocket done and if you ever get the coupler out at your leisure, you can do another rocket or sell it if you don't bugger it up or break it. If you break it, you'll need a new one anyways. If you destroy the coupler getting it out, it would likely be the cheapest part to replace as opposed to the nosecone shroud. I say go into hock and get a new part if you are under the gun time wise. Kurt

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Coupler itself is $150. NC would probably be another $300 if I could get one. No way I'd make it in time for LDRS.

Bat-mite said:

Coupler itself is $150. NC would probably be another $300 if I could get one. No way I'd make it in time for LDRS.

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Just for kicks, I checked. Madcow has the coupler and cone listed, and for less than $300 total, but they are out of stock on the NC. Also, it would be white instead of black.

Bat-mite said:

Just for kicks, I checked. Madcow has the coupler and cone listed, and for less than $300 total, but they are out of stock on the NC. Also, it would be white instead of black.

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John,

I have an 8" black 5:1 FW/FG nosecone with an aluminum tip. It is from my 8" Jumbo Darkstar which is a slow build for 2019ish. I am okay doing a deal where you simply replace it when you can. Getting it to you is another thing, but I am attending LDRS and can drop it off as well as pull off whatever dimensions you need to confirm compatibility.

mpitfield said:

John,

I have an 8" black 5:1 FW/FG nosecone with an aluminum tip. It is from my 8" Jumbo Darkstar which is a slow build for 2019ish. I am okay doing a deal where you simply replace it when you can. Getting it to you is another thing, but I am attending LDRS and can drop it off as well as pull off whatever dimensions you need to confirm compatibility.

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Wow, that is very kind! Fortunately, Nate Lowrie is also flying a Formula 200 at LDRS and offered to let me borrow his. Still, I need it ahead of time to ground test, which is the biggest problem. I'm using five #8-32 shear pins, and I doubt Nate is (it's probably overkill). So charge amounts need to be determined. But I am overwhelmed by so many people's offers of support!

I have someone who may be able to help me tomorrow, same guy who is making my motor. If we can't get the coupler out, then I'll just try to epoxy the bulkhead inside as far in as it will go. If I do, I'll hang it upside down by the harness from my roof, just to make sure it won't pull out.

Bat-mite said:

Wow, that is very kind! Fortunately, Nate Lowrie is also flying a Formula 200 at LDRS and offered to let me borrow his. Still, I need it ahead of time to ground test, which is the biggest problem. I'm using five #8-32 shear pins, and I doubt Nate is (it's probably overkill). So charge amounts need to be determined. But I am overwhelmed by so many people's offers of support!

I have someone who may be able to help me tomorrow, same guy who is making my motor. If we can't get the coupler out, then I'll just try to epoxy the bulkhead inside as far in as it will go. If I do, I'll hang it upside down by the harness from my roof, just to make sure it won't pull out.

Click to expand...

If you do this, PLEASE put a few 1/4" bolts through the cone into the shoulder. That way there's no "hoping" it stays together.

patelldp said:

If you do this, PLEASE put a few 1/4" bolts through the cone into the shoulder. That way there's no "hoping" it stays together.

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I'll still have the threaded rod from the tip to a nylon-insert nut outside the bulkhead. I am not concerned about the coupler coming out; I am concerned about the epoxy joint holding the bulkhead to the coupler breaking loose.

I bet it would come out with shop press , some careful work lining up for pushing

Five #8 shear pins??? That sounds like an awful lot of shear pin.

Nathan said:

Five #8 shear pins??? That sounds like an awful lot of shear pin.

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I know. When I did my original calculations assuming the largest motor I might ever put in there, I became concerned about NC separation at apogee. The math worked at the time, but I don't have a copy of my calculations any more.

I can tell you that the NC is exactly ten pounds as built. It's probably overkill.

6g will create 894 lbF. Double shear strength for #8 6/6 nylon is 164 lbF. Five of those = 820 lbF.

6g for the main and 4.7g for the drogue ought to work. I might use two e-matches in series to get maximum burn.

Bat-mite said:

Wow, that is very kind! Fortunately, Nate Lowrie is also flying a Formula 200 at LDRS and offered to let me borrow his. Still, I need it ahead of time to ground test, which is the biggest problem. I'm using five #8-32 shear pins, and I doubt Nate is (it's probably overkill). So charge amounts need to be determined. But I am overwhelmed by so many people's offers of support!

I have someone who may be able to help me tomorrow, same guy who is making my motor. If we can't get the coupler out, then I'll just try to epoxy the bulkhead inside as far in as it will go. If I do, I'll hang it upside down by the harness from my roof, just to make sure it won't pull out.

Click to expand...

I am using 3 #4 pins (it's deploying through here at apogee) but if you end up borrowing mine we'll put 5 holes in the coupler for your #8 screws and tap them accordingly.

NateLowrie said:

I am using 3 #4 pins (it's deploying through here at apogee) but if you end up borrowing mine we'll put 5 holes in the coupler for your #8 screws and tap them accordingly.

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How did you arrive at that number? I ran a sim and looked at the acceleration of the ejection event at apogee, and used F = MA. Wish I still had my numbers....

Bat-mite said:

6g will create 894 lbF. Double shear strength for #8 6/6 nylon is 164 lbF. Five of those = 820 lbF.

6g for the main and 4.7g for the drogue ought to work. I might use two e-matches in series to get maximum burn.

Click to expand...

6g will cut it close and if anyone of those elongates instead of doing a clean break your in trouble. I always aim at using enough of a charge to break 150% of shear pins which means I would size the charge to break 7 of those pins.

3.5g is what I calculated for breaking 150% of 3 #4 pins and where I'll be starting.

On another note, I have a spare 16' rocketman chute I am not using if you want to borrow it.

Bat-mite said:

How did you arrive at that number? I ran a sim and looked at the acceleration of the ejection event at apogee, and used F = MA. Wish I still had my numbers....

Click to expand...

https://www.rocketryforum.com/showt...-Significant-Gravitas-Shortfall-(Formula-200) See my documentation in the first post, page 13 of the PDF.

Note my use of shear pins is just to prevent premature pop off because I am deploying through the nosecone break at apogee. It was designed to resist 6 times as much force as the roughly 20lb pressure force from the pressure differential. I didn't do an acceleration load calc for the shock force on the pins for mine like you need to do for yours because they need to hold on through the apogee deployment.

NateLowrie said:

https://www.rocketryforum.com/showt...-Significant-Gravitas-Shortfall-(Formula-200) See my documentation in the first post, page 13 of the PDF.

Note my use of shear pins is just to prevent premature pop off because I am deploying through the nosecone break at apogee. It was designed to resist 6 times as much force as the roughly 20lb pressure force from the pressure differential. I didn't do an acceleration load calc for the shock force on the pins for mine like you need to do for yours because they need to hold on through the apogee deployment.

Click to expand...

Right. I forgot that your deployment set-up is very different from mine.

Johnly said:

I've done this a bunch of times trying to fit a coupler into a nosecone, and this is what works.
Install the nosecone with the stuck coupler into a section of matching fiberglass airframe tubing.
Place a sheet of plywood on the floor, and bounce the open end of the airframe on the plywood.
The inertia of the coupler will extract the coupler into the airframe.

John

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HURRAY! HURRAY! HURRAY! HURRAY! HURRAY! HURRAY! HURRAY! HURRAY! HURRAY! HURRAY! HURRAY! HURRAY! HURRAY! HURRAY! HURRAY! HURRAY! HURRAY! HURRAY! HURRAY! HURRAY! HURRAY! HURRAY!

This method worked! Scott and I got it out this way! WOO HOO!!!!

:w: :happydeer: :handshake: :marshmallow: :wave:

Bat-mite said:

HURRAY! HURRAY! HURRAY! HURRAY! HURRAY! HURRAY! HURRAY! HURRAY! HURRAY! HURRAY! HURRAY! HURRAY! HURRAY! HURRAY! HURRAY! HURRAY! HURRAY! HURRAY! HURRAY! HURRAY! HURRAY! HURRAY!

This method worked! Scott and I got it out this way! WOO HOO!!!!

:w: :happydeer: :handshake: :marshmallow: :wave:

Click to expand...

Nice!


Steve Shannon

Glad to hear!

Oh man am I glad to heat that...
Good for you John...
I bet you're breathin a lot easier right now,, lol..

Teddy

lol love the simplicity, great to hear you are back on track and can relax a bit.