L2 Rocket Design Questions

[user 30299]

Yup, have been looking at some forged eyebolts on McMaster Carr.

How did you make sure that centering ring was completely level before epoxying it? Also, because I will have 3 centering rings, I won't have access to one side for internal fillets. What's your process for this?

Thinking through your build sequence and looking at your OR file :

What are you using for a motor retainer?

Do you have any lengths of 3" body tube or 75mm motor tube sitting around? Maybe 10" or more in length?

 

[haon151]

Thinking through your build sequence and looking at your OR file :

What are you using for a motor retainer?

Do you have any lengths of 3" body tube or 75mm motor tube sitting around? Maybe 10" or more in length?

Have a more updated OpenRocket file attached here. Motor tube from PML

 

[user 30299]

What are you using for a motor retainer- to hold the motor in the motor tube?

Z-clips? Aero Pack? , etc.

 

[haon151]

Centering rings from LOC

What are you using for a motor retainer- to hold the motor in the motor tube?

Z-clips? Aero Pack? , etc.

Centering rings from LOC have clips

 

[user 30299]

Centering rings from LOC

Centering rings from LOC have clips

Ok, so you're using a z-clip.

 

[haon151]

Ok, so you're using a z-clip.


View attachment 574465

Yep

 

[user 30299]

Yep

I asked about scrap lengths of 3" body tube and 75mm motor tube. Use one of these to push the middle centering
ring into its final location in the body tube. This will give you a straight and steady push to the location since the ring
will want to drag a bit on the rocket's motor & body tubes.

You'll be pushing the middle centering ring into the body tube from the Fin end.

This of course is after you epoxy the motor tube & top centering ring assembly in the body tube.

The 3" or 75mm tubes fit over your 54mm motor tube, but don't come in contact with the rocket's body tube.

 

[haon151]

I asked about scrap lengths of 3" body tube and 75mm motor tube. Use one of these to push the middle centering
ring into its final location in the body tube. This will give you a straight and steady push to the location since the ring
will want to drag a bit on the rocket's motor & body tubes.

You'll be pushing the middle centering ring into the body tube from the Fin end.

This of course is after you epoxy the motor tube & top centering ring assembly in the body tube.

The 3" or 75mm tubes fit over your 54mm motor tube, but don't come in contact with the rocket's body tube.

I see what you're getting at now. Unfortunately, I don't have extra. I was thinking through it and maybe it's best to start with the middle ring. I can put the fins in their through slots and make sure it's flush that way while I epoxy the top side of the middle ring. Remove the fins and epoxy the second side. The last two centering rings are only 1/2 inch from either end so they will be easier to access.

 

[thzero]

I see what you're getting at now. Unfortunately, I don't have extra. I was thinking through it and maybe it's best to start with the middle ring. I can put the fins in their through slots and make sure it's flush that way while I epoxy the top side of the middle ring. Remove the fins and epoxy the second side. The last two centering rings are only 1/2 inch from either end so they will be easier to access.

It's painful yeah.

When using 3 rings (one at top of the motor tube, one at top of the fin, and one at the bottom of the fin) if not building the fins outside of the can, I usually do
a) attach the top and middle fins to the motor tube
b) ring of glue slightly above where the upper ring will go, and then insert the tube by pulling the motor down into position and using a fin in the slot to make sure that its flush
c) mount the fins and do the internal filets, as doing so also get a filet between the ring and body tube's joint. yes, the middle ring doesn't have a filet on top of it.
d) once fins are mounted and all, then ring of epoxy below where the bottom ring is, then slide the ring up into place and flush against the fins, then filet the joint between ring and body tube.

 

[user 30299]

I see what you're getting at now. Unfortunately, I don't have extra. I was thinking through it and maybe it's best to start with the middle ring. I can put the fins in their through slots and make sure it's flush that way while I epoxy the top side of the middle ring. Remove the fins and epoxy the second side. The last two centering rings are only 1/2 inch from either end so they will be easier to access.

If you start looking around the house, the apartment, work or school - you will find a mailing tube, or some kind of
cardboard tube that will work perfect. You can even go to the Dollar Store and buy a tube for a couple of bucks.

Cardboard tubes and a good selection of wood dowels are your best friends when building rockets.

Once you have all your parts sitting on the bench (kitchen or coffee table), be sure to walk yourself through a
full dry run on your assembly process - a couple of times. You may want to include a "make-believe" for applying
the epoxy - such as reaching down into the body tube. Then decide if this gets you an acceptable assembly.

Think it through, then walk it through. A dry run helps fill the holes in our thought process.

 

[haon151]

It's painful yeah.

When using 3 rings (one at top of the motor tube, one at top of the fin, and one at the bottom of the fin) if not building the fins outside of the can, I usually do
a) attach the top and middle fins to the motor tube
b) ring of glue slightly above where the upper ring will go, and then insert the tube by pulling the motor down into position and using a fin in the slot to make sure that its flush
c) mount the fins and do the internal filets, as doing so also get a filet between the ring and body tube's joint. yes, the middle ring doesn't have a filet on top of it.
d) once fins are mounted and all, then ring of epoxy below where the bottom ring is, then slide the ring up into place and flush against the fins, then filet the joint between ring and body tube.

Thanks for the visual, I appreciate it.

 

[haon151]

If you start looking around the house, the apartment, work or school - you will find a mailing tube, or some kind of
cardboard tube that will work perfect. You can even go to the Dollar Store and buy a tube for a couple of bucks.

Cardboard tubes and a good selection of wood dowels are your best friends when building rockets.

Once you have all your parts sitting on the bench (kitchen or coffee table), be sure to walk yourself through a
full dry run on your assembly process - a couple of times. You may want to include a "make-believe" for applying
the epoxy - such as reaching down into the body tube. Then decide if this gets you an acceptable assembly.

Think it through, then walk it through. A dry run helps fill the holes in our thought process.

Yeah definitely will do plenty of dry runs to make sure I get it right. I think I'm going to try and do this.
Last question, would you do more than 18ft of cord in each tube? I've heard 3-5x the length of the rocket. Does this mean total or in each section of dual deploy? 18ft is below 3x.

 

[user 30299]

Yeah definitely will do plenty of dry runs to make sure I get it right. I think I'm going to try and do this.
Last question, would you do more than 18ft of cord in each tube? I've heard 3-5x the length of the rocket. Does this mean total or in each section of dual deploy? 18ft is below 3x.

I personally start with 4x the total length of the rocket. That usually gets you a reasonable and acceptable starter length.

Longer is always better.

The rocket's weight is a factor too.

You can fine tune the length once you have a better handle on the rocket's final weight and recovery setup.

My EZI has 25 ft. harnesses. Never had an issue with the length. The 7/16" size could have easily been 3/8"
and still perform fine.


There are quite a few rules of thumb for the harness length, and that can change if you're using nylon vs. kevlar.

If you do a search on Harness Length in this Forum you will find plenty to read, drown from, and feel a whole lot smarter.

 

[b.wieting]

I can't disagree with this.
I'm probably not the right person to respond, since I did my L1 cert with DD because I wanted to do that. For my L2, DD was a given since I used a K motor and wouldn't fly that high at my field without DD. I don't think "complicated" or "single point failure" is really the issue. I think it has a lot more to do with what rocket you built, how high it will go on your cert flight, and most importantly, how high it will go on the motors you want to fly it on after your cert, and what altitudes your home field can handle.

In my opinion, that is something you should learn while flying L1 before going for L2. In my case, 3,000 ft., depending on the day, was a good max altitude for apogee deploy. Most days, 6,000 to 8,000 was a good max for DD. Either way, you need to learn to fly the field and learn how high you can safely fly under various weather conditions.

I think if you want to fly K and baby L motors on 54mm then you should fly a cert rocket that can handle those motors. Even on a baby J, you need to prove, not just for the cert, but to yourself, that your rocket will be able to recovery correctly on your field. If you want to fly large J, K and L motors, I don't see any reason you shouldn't fly a cert flight that shows you can do that.

I endorse your views. I rebuilt my L1 for dual deploy, had fun, and learned a lot before deciding to try L2. Then, the L2 was motor eject, a "low and slow" 7.5" rocket, oversized chute. Simple.

Since then I modified and flew the 7.5" a few times dual deploy, just last weekend to 6500' AGL on a L1390G. Fun!!

PS electronics bay layout is sure easier with large diameter.

 

[haon151]

I personally start with 4x the total length of the rocket. That usually gets you a reasonable and acceptable starter length.

Longer is always better.

The rocket's weight is a factor too.

You can fine tune the length once you have a better handle on the rocket's final weight and recovery setup.

My EZI has 25 ft. harnesses. Never had an issue with the length. The 7/16" size could have easily been 3/8"
and still perform fine.


There are quite a few rules of thumb for the harness length, and that can change if you're using nylon vs. kevlar.

If you do a search on Harness Length in this Forum you will find plenty to read, drown from, and feel a whole lot smarter.

Alright sounds good. I'll probably order that last once I can get accurate weights on everything else

 

[Glasspack]

Having learned just about every discipline for L2 at my overly long L1 (and MPR) stage, and having gotten off my butt for my L2 two years ago, I'm going to go ahead and say that I agree with Handeman on his recommendations. I was comfortable with DD, having had over a hundred DD launches, and plenty of L1 launches on full size L1 motors in 4" birds.......so my L2 project was just another build, and my L2 launch was just another 'new rocket' launch.

Another reason for building a fully L2 capable bird is that my L1 was a beefed up MP rocket, and hardly suitable for flying any other L1 motors. I had to build another rocket to do that. I chose to build my L2 bird as a 'fully capable' instead of a one-off.

I did my L2 as a scratch built, 4" 54mm motor mount, full dual redundant DD with GPS in the nose. It's a rocket that I can fly from 1500ft to 8000ft comfortably to 'fly the field' and it will eat anything L2 in 38 or 54 that's installed in it. It's large enough to work on easily, large enough to see comfortably all the way up to 8K, and flexible enough to fly mid and large fields that are suited to L2 motors.

As to your question of needing GPS, that's a personal decision. Most of us can see a 4" rocket up to 6-8K, depends on paint and sky conditions. I think that 'altitude' is really only 50% the determining factor. Field conditions (trees/hills/scrub/line-of-sight to terrain) is at least 50% of it, too.
Bayboro (5 square miles of zero trees and soft plow or low crops) I don't see it as necessary up to about 10K, MDRA Higgs, with all it's trees and ditches and limited sight lines I use it 100% for anything going over 2K.
Similarly, soft plow or sod farm, usually not necessary, but let the beans or corn get over knee high and I use GPS nearly 100%. If you haven't experienced knee high crops eating even the largest of rockets yet, you're in for a real treat the first time you experience it!
Not mandatory, but saves a lot of angst when you can walk right up to it.

Bonzai,


Is that LVL2 model you speak of a cardboard or fiberglass model. ?

I was so set on doing dual deploy with my LVL2 cert, but there is soooo much more wisdom in this forum than me alone. I know better.

I am almost to the testing stages of my LVL2 bird. It too is a scratch built 4" model W/54mm motor, made from kit pieces. All Paper tubes and plywood bulkheads. The fins are canvas phenolic....
Designed to be fully DD capable.
But......I want to Certify using motor eject with a JLCR.

My only fear so far is the length of it.
(Just about 8 ft tall) and getting it fast enough off the rail to be safe,
but low enough in altitude to be successfully recovered with a JLCR.

 

[Banzai88]

Bonzai,


Is that LVL2 model you speak of a cardboard or fiberglass model. ?

I was so set on doing dual deploy with my LVL2 cert, but there is soooo much more wisdom in this forum than me alone. I know better.

I am almost to the testing stages of my LVL2 bird. It too is a scratch built 4" model W/54mm motor, made from kit pieces. All Paper tubes and plywood bulkheads. The fins are canvas phenolic....
Designed to be fully DD capable.
But......I want to Certify using motor eject with a JLCR.

My only fear so far is the length of it.
(Just about 8 ft tall) and getting it fast enough off the rail to be safe,
but low enough in altitude to be successfully recovered with a JLCR.

I built my own design with LOC tubes, hand cut 1/4" plywood fins, and fiberglass overwrap using Soller Composites woven sock.

Your best bet in answering some of your questions is a quick trip through Open Rocket coupled with an evaluation of your prospective launch field.

 

[thzero]

My only fear so far is the length of it.
(Just about 8 ft tall) and getting it fast enough off the rail to be safe,
but low enough in altitude to be successfully recovered with a JLCR.

OpenRocket and sim it. That'll give you a decent handle on it. With CG, CP and weight you could use the ThrustCurve simulator too to get a rough idea.

I suspect with a cardboard built, and any non long burn J you'll see good results off a 72" rail.

 

[thzero]

I built my own design with LOC tubes, hand cut 1/4" plywood fins, and fiberglass overwrap using Soller Composites woven sock.

That was mine but in 3" instead of 4".

 

[Glasspack]

I built my own design with LOC tubes, hand cut 1/4" plywood fins, and fiberglass overwrap using Soller Composites woven sock.

Your best bet in answering some of your questions is a quick trip through Open Rocket coupled with an evaluation of your prospective launch field.

Thank You Bonzai

I have my model in Rocksim and OR.
I have been and will continue to run simulations to help me with motor selection....want to fly it at LDRS 41

 

[Glasspack]

OpenRocket and sim it. That'll give you a decent handle on it. With CG, CP and weight you could use the ThrustCurve simulator too to get a rough idea.

I suspect with a cardboard built, and any non long burn J you'll see good results off a 72" rail.

Thank You
I do use rocksim and Open Rocket alot