L1 Cert Zephyr Build. Need some help...

[burritoman1]

I've been stuck on my Zephyr build for about a year now, due to an issue I've ran in to. As you can see in image 1, the rail that runs along the length of the motor tube and aligns the centering rings, is ever so slightly tilted. Unfortunately by the time I noticed this, it was already JB welded to the tube.







As a result, when inserted to the body tube, the lower centering ring is rotated relative to the upper one. The fin slot is no longer aligned with slot in the body tube, making it impossible to insert



My (admittedly poor) solution was to sand the slots for the rail of the lower centering ring until there was enough play to rotate it back into the alignment. However, after half an hour of sanding I was only able to get a few degrees of wiggle room.


A solution I am considering is just 3d printing (or laser cutting out of balsa if necessary) the lower centering ring, with the slot for the rail rotated about 5mm or so. I don’t have the dimensions for the ring, I could estimate with a caliper although I’d be very thankful if someone could provide them.

Alternatively, I could use a Dremel to carve out a larger chunk of the centering ring, although that solution doesn’t seem very reliable to me.

If anybody has any thoughts or ideas I’d be very grateful for them.

Thanks

 

[burritoman1]

While I'm at it, might as well ask another question about my L1. I understand that I need a high power motor for my L1 cert, but I need to possess a L1 cert to buy the motor. Seems like a bit of a catch-22...

My guess is that I'm supposed to contact the vendor who will be attending the launch and tell them I'm going for my cert, but I'd just like to confirm.

 

[smstachwick]

While I'm at it, might as well ask another question about my L1. I understand that I need a high power motor for my L1 cert, but I need to possess a L1 cert to buy the motor. Seems like a bit of a catch-22...

My guess is that I'm supposed to contact the vendor who will be attending the launch and tell them I'm going for my cert, but I'd just like to confirm.

Get your paperwork in order and arrange for a certification witness. Give the vendor an email or phone call to let them know you’re going for a certification attempt and they should clear you. They’ll probably require your ID and proof of NAR/Tripoli membership.

You can also just borrow or buy a motor from a certified flier, or supply the funds and have them conduct the transaction on your behalf.

Regarding your centering ring, I think your best bet is to have it laser-cut out of birch ply or similar. Balsa is probably a too soft and weak for a centering ring in a rocket of this size.

Maybe somebody else who has the kit can get you the CR and slot dimensions. Sorry I can’t be of help with that

 

[David Schwantz]

For future, if you used epoxy to glue the tube, heat will soften it and you can scrape it off and start all over again.

 

[Rob Campbell]

I recommend opening the fin slots in the centering rings so you can get the fins aligned. Shim the slots with balsa for a snug fit and be generous with your epoxy fillets.

 

[bobbyg23]

I've been stuck on my Zephyr build for about a year now, due to an issue I've ran in to. As you can see in image 1, the rail that runs along the length of the motor tube and aligns the centering rings, is ever so slightly tilted. Unfortunately by the time I noticed this, it was already JB welded to the tube.



View attachment 572276



As a result, when inserted to the body tube, the lower centering ring is rotated relative to the upper one. The fin slot is no longer aligned with slot in the body tube, making it impossible to insert

View attachment 572277

My (admittedly poor) solution was to sand the slots for the rail of the lower centering ring until there was enough play to rotate it back into the alignment. However, after half an hour of sanding I was only able to get a few degrees of wiggle room.
View attachment 572278

A solution I am considering is just 3d printing (or laser cutting out of balsa if necessary) the lower centering ring, with the slot for the rail rotated about 5mm or so. I don’t have the dimensions for the ring, I could estimate with a caliper although I’d be very thankful if someone could provide them.

Alternatively, I could use a Dremel to carve out a larger chunk of the centering ring, although that solution doesn’t seem very reliable to me.

If anybody has any thoughts or ideas I’d be very grateful for them.

Thanks

Cut the end of the alignment rail so you can rotate the centering ring into the correct position. It's only purpose is alignment so it won't hurt anything.

 

[tsmith1315]

My (admittedly poor) solution was to sand the slots for the rail of the lower centering ring until there was enough play to rotate it back into the alignment.

That's a perfectly fine solution. Use a wood file to enlarge the slot, it shouldn't take 5 minutes.

Or do this:

I recommend opening the fin slots in the centering rings so you can get the fins aligned. Shim the slots with balsa for a snug fit and be generous with your epoxy fillets.

Or this:

Cut the end of the alignment rail so you can rotate the centering ring into the correct position. It's only purpose is alignment so it won't hurt anything.

 

[bjphoenix]

While I'm at it, might as well ask another question about my L1. I understand that I need a high power motor for my L1 cert, but I need to possess a L1 cert to buy the motor. Seems like a bit of a catch-22...

It would seem like a Catch-22 but you are allowed to buy an L1 motor for your cert attempt. Anybody who sells motors will know this and will have dealt with it many times in the past.

 

[MikeT]

While I'm at it, might as well ask another question about my L1. I understand that I need a high power motor for my L1 cert, but I need to possess a L1 cert to buy the motor. Seems like a bit of a catch-22...

My guess is that I'm supposed to contact the vendor who will be attending the launch and tell them I'm going for my cert, but I'd just like to confirm.

Just tell the vendor it's for a certification attempt. Theymay want you ID and NAR or Tripoli card emailed. I had no problem buying my L1 and L2 motors. that way.

 

[Rob Campbell]

It would seem like a Catch-22 but you are allowed to buy an L1 motor for your cert attempt. Anybody who sells motors will know this and will have dealt with it many times in the past.

There may be a vendor on site to buy from. I bought my L1 cert motor from Chris Short at the 2021 GTITS launch. I just told him it was for a cert flight.

 

[techrat]

As others have suggested, you can widen the slots for the alignment bars in the CR, or, just cut the tabs off the motor mount so you can swivel the rear centering ring as much as you like. I'm also building a Zephyr, and didn't run into the issue you had, but I did a lot of test-fitting and lining things up before appying any glue. JB-weld seems a little overkill for a cardboard and wood rocket, but, everyone has their own tastes.

I've been using the 30-minute Bob Smith epoxy, but also used wood glue in some places, like the upper centering ring, since I couldn't get epoxy in there, so I just "flowed" wood glue around the circumfrence, and called it a day on that. I figure the external and internal fillets would keep the rest of it strong enough.

I also don't like attaching the shock cord to the motor mount, so I instead built a half-baffle (basically a centering ring with large holes cut in it), and centrally mounted the eye-bolt into that and that gets glued into the 4" coupler that joins the two body tube halves. This half-baffle also prevents the parachute from being forced downward into the motor mount during the high-G loads during launch. From the tests I have done with mid-power rockets, this solution seems to work well.

 

[Dave S.]

I ran into some very similar issues on a rocket with a design a lot like yours with "keys' to line things up.

I opened up the slots in the aft ring with a dremel to make sure I would be able to spin it whichever way it needed to go to get it to line up properly and not block the slots.





I did a lot of dry fitting before using any epoxy anywhere.

I think I first epoxied the "keys" to the MMT, then the forward ring. I test fit it into the body tube and since the slots were so wide, I spun the aft ring a bit to make sure it would not block the slots for the fins. I also dry fit the fins at the same time to make sure they would go in place. When I was sure the aft ring was positioned correctly and all the fins would go in place, then I attached the aft ring to the MMT, then the MMT/rings assembly into the body tube, then the fins.

I'm no expert, but I have learned to dry fit everything 5 times before using any adhesives.

Sometime before gluing the rings/MMT into the body tube I made the attachment for the shock cord.

Here are some more pictures I took during this:

 

[burritoman1]

I ran into some very similar issues on a rocket with a design a lot like yours with "keys' to line things up.

I opened up the slots in the aft ring with a dremel to make sure I would be able to spin it whichever way it needed to go to get it to line up properly and not block the slots.

View attachment 572534
View attachment 572535


I did a lot of dry fitting before using any epoxy anywhere.

I think I first epoxied the "keys" to the MMT, then the forward ring. I test fit it into the body tube and since the slots were so wide, I spun the aft ring a bit to make sure it would not block the slots for the fins. I also dry fit the fins at the same time to make sure they would go in place. When I was sure the aft ring was positioned correctly and all the fins would go in place, then I attached the aft ring to the MMT, then the MMT/rings assembly into the body tube, then the fins.

I'm no expert, but I have learned to dry fit everything 5 times before using any adhesives.

Sometime before gluing the rings/MMT into the body tube I made the attachment for the shock cord.

Here are some more pictures I took during this:




View attachment 572542
View attachment 572543


View attachment 572551


View attachment 572553

View attachment 572554

I finally found my dremel so I think this is what I'll end up doing. You're right about the dry fitting, I think I'll probably 3D print some kind of rig to make sure everything lines up. And thank you for the generous amount of images, I was having trouble figuring out how large of a notch i should cut into the aft centering ring.

 

[Black Bart]

I L-1 with a Zephyr. The build went well. If you have fitment problems, Apogee will send you new parts. They make many of this kit. If the tolerance is slipping they want to know.

 

[Lotronex]

If you have access to a laser cutter, I would just cut the parts out yourself. Otherwise, Apogee sells all the parts individually, you can get an entire new engine mount for about $25, less if you can salvage any of the parts.