Need some help with my Zephyr

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Bruce Hoffman

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I’m about 75% down building my Apogee Zephyr that I plan on doing my L1 cert with using a H100W motor. I checked the CP and CG today was all the stuff the packed in the nose and they are almost identical. I know I need at least 1.0 body width in front of the CP. where did I go wrong? Too much epoxy? Is adding a ton of weight to the NC going to mess anything up. Thanks in advance.
 

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K'Tesh

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I see this is your first post, and you're already going for L1... COOL!!! Welcome!

As long as your motor is powerful enough to get the rocket off the rail at a safe speed, and without so much mass as to drag your CG back to below the CP you should be good. You'll need to pay careful attention to your delay if you're going with motor ejection. If you go with an electronic deployment at apogee then you'll be OK (presuming that the hardware works properly).

Redundancy is your friend.
 

Bruce Hoffman

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Going with a motor ejection. Apogee had it listed about 9 ounces lighter then I am as well. No way I used 9 extra ounces and it’s not even painted yet.
 

thzero

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Kinda odd that with stuff in the nose that your CG is equal to the CP. Put your rocket in OpenRocket and see once you've added the weight of your rocket, etc.
 

Bruce Hoffman

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That’s what I thought to. The only thing I’ve added was a metal aerotech 38mm retainer. The motor is 9.4 oz alone but still.
 

mbeels

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Just curious, where did you get the CP position from? A Rocksim or Openrocket sim, or something else? That doesn't seem like an excess amount of epoxy....

And welcome to the forum!
 

mtnmanak

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I have built a number of Zephyrs, so have a bit of experience here.

I wouldn't be too concerned about the overall weight being high, I find that when I am done with a Zephyr it is about 10-12 ounces heavier than the listed weight on Apogee's site.

The CG being the same as the CP, though, is kind of shocking. I have built Zephyrs very heavy with a lot of epoxy and never had the CG less than 2 calibers in front of the CP. Even with a heavy motor, the CG stays more than 1 caliber away.

Unless you changed something from the parts provided in the kit, the CP should be 44.89" from the tip of the nosecone. Are you saying the CG is also around 44.5" with the H100 loaded?
 

mtnmanak

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And, to be clear, you should not fly the rocket with the CG and CP at the same location. That is known as "neutral stability" and, as Harry Stine notes, this means "there are no stabilizing and restoring forces present in the model during flight. It is free to wander anywhere in the sky, and some of its wanderings may be wild and unpredictable."

If there is even a slight breeze, a neutrally stable rocket will go all over the place. No RSO would/should let you put a rocket on the pad like that.

Hopefully this is a dumb question, but you did attach the two body tubes together for a total booster length of 36", correct?

If you do need to add nosecone weight, consider modifying your nosecone with a bulkhead and eye-bolt as John Coker shows here:


That gives you more flexibility over the nose weight and gives you nosecone a better anchor point that the little plastic arm.
 

Adam3836

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Definitely want to figure out the cp cg discrepancy to have a stable flight but also I put some thought into making sure to have a good amount of thrust off the pad I have flown CTI H133 many times on the zephyr and it jumped quick off the pad
Obviously everyones builds could be slightly different with how heavy or not you lay the epoxy
Good luck sir
 

Bruce Hoffman

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And, to be clear, you should not fly the rocket with the CG and CP at the same location. That is known as "neutral stability" and, as Harry Stine notes, this means "there are no stabilizing and restoring forces present in the model during flight. It is free to wander anywhere in the sky, and some of its wanderings may be wild and unpredictable."

If there is even a slight breeze, a neutrally stable rocket will go all over the place. No RSO would/should let you put a rocket on the pad like that.

Hopefully this is a dumb question, but you did attach the two body tubes together for a total booster length of 36", correct?

If you do need to add nosecone weight, consider modifying your nosecone with a bulkhead and eye-bolt as John Coker shows here:


That gives you more flexibility over the nose weight and gives you nosecone a better anchor point that the little plastic arm.
belay my last. I’m a idiot. I used my metric tape measure that I use to set up suspension. I marked the CP at 1014.2 instead of 1140.2 so I was 126mm off. So now that I measured the CP correctly I have about 4 7/8” between the CP and CG in the right direction. And I wasn’t going to fly it until I had at least 1.0 difference. I’ve done a ton of reading and nothing good comes out of that lol. Thanks for the help it’s truly appreciated. I’m still about 10 ounces heavy but I’m trying to stay low and slow for the L1 anyway lol.
 

mtnmanak

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belay my last. I’m a idiot. I used my metric tape measure that I use to set up suspension. I marked the CP at 1014.2 instead of 1140.2 so I was 126mm off. So now that I measured the CP correctly I have about 4 7/8” between the CP and CG in the right direction. And I wasn’t going to fly it until I had at least 1.0 difference. I’ve done a ton of reading and nothing good comes out of that lol. Thanks for the help it’s truly appreciated. I’m still about 10 ounces heavy but I’m trying to stay low and slow for the L1 anyway lol.
Sounds good!

The Zephyr is a really safe rocket for Level 1 flights. It flies well and can take a beating. Once you get your Level 1, add a coupler and another section of body tube for a "payload bay" and you have yourself a nice tidy dual deploy Level 2 bird. Good luck!
 

Bruce Hoffman

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Sounds good!

The Zephyr is a really safe rocket for Level 1 flights. It flies well and can take a beating. Once you get your Level 1, add a coupler and another section of body tube for a "payload bay" and you have yourself a nice tidy dual deploy Level 2 bird. Good luck!
after watching the last video I want to add a eBay to the nose like he did. Cutting those perfect circles in plywood might be tough though lol.
 

mtnmanak

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after watching the last video I want to add a eBay to the nose like he did. Cutting those perfect circles in plywood might be tough though lol.
A hole saw works. It can be difficult finding the exact right size of hole saw you need. A while back, I got one of these to cut bulkheads, centering rings, etc:


Eventually, as I continued on my high power journey, I decided to go past that and got a full CNC machine. I use a Shapeoko 3, but that model has now been upgraded to the Shapeoko 4 and Shapeoko Pro:


I am not sure how I lived without a CNC for so many years! I use it for many more things than rockets, but I also can't think of a rocket I have built in the past year that I didn't CNC something, and that includes LPR and MPR. For my Level 3 project, I CNCed 56 parts for that rocket:

 

SkywackerJim

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after watching the last video I want to add a eBay to the nose like he did. Cutting those perfect circles in plywood might be tough though lol.
You can buy the bulkhead plates too. Order them with the extra tube and coupler. Get one that fits inside the coupler and one that fits the tube. Get two of each for both ends of the coupler tube.
 

ThirstyBarbarian

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That’s going to be a fun rocket for you. I’ve seen several cert flights on Zephyrs, and they were perfect. In my opinion, it’s in the right diameter and weight range for a nice, easy L1 cert flight. Good luck, and have fun!
 

Bruce Hoffman

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A hole saw works. It can be difficult finding the exact right size of hole saw you need. A while back, I got one of these to cut bulkheads, centering rings, etc:


Eventually, as I continued on my high power journey, I decided to go past that and got a full CNC machine. I use a Shapeoko 3, but that model has now been upgraded to the Shapeoko 4 and Shapeoko Pro:


I am not sure how I lived without a CNC for so many years! I use it for many more things than rockets, but I also can't think of a rocket I have built in the past year that I didn't CNC something, and that includes LPR and MPR. For my Level 3 project, I CNCed 56 parts for that rocket:

I’ve actually been looking into a laser cutter that will cut 4mm plywood. What’s your opinion on those?
 

mtnmanak

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I’ve actually been looking into a laser cutter that will cut 4mm plywood. What’s your opinion on those?
They sound awesome - who doesn't love lasers?!

Can't really opine on them, though, I have no experience with them. I have seen others on TRF who use them, so posting a question about it may get some good feedback. That CNC machine depleted my "machine budget" for the past year in terms of both money and space in my "shop" (aka, my garage), so I would love a laser cutter, but that is going to have to wait. I probably will add a 3D printer at some point first, though.

One thing I love about having a CNC is that I can cut through a lot of materials besides plywood - aluminum, fiberglass, acrylic, etc - at thicknesses up to maybe 2 inches, which is mostly dependent on how long of a cutter I am using. However, for thinner and lighter material (thin ply, cardboard, chipboard, paper, etc), it sure sounds like a laser cutter would be great to have.
 

thzero

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Were the spirals that bad? For LOC tubes thus far (54mm, 2.63" and 3") I've never bothered to fill them as they are so light and you can't see them from more than a foot or three away.
 

Bruce Hoffman

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Were the spirals that bad? For LOC tubes thus far (54mm, 2.63" and 3") I've never bothered to fill them as they are so light and you can't see them from more than a foot or three away.
One slot wasnt bad at all the other is pretty deep. I already had sanded so much at this point i just filled them lol.
 

Bruce Hoffman

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Monkeys.
We need trained monkeys!

What are the slots in the fins for?
it’s a apogee zephyr and they came like that. I almost filled them because going for my L1 and I don’t want them to break off but I think they are rugged enough. We shall see.
 

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