Hey Rocketry Forum! Looking for some advice

[Joesephus]

Hey everyone! I am brand new to rocketry, never flown a rocket in my life, and I am trying to build a 30-foot tall rocket that will fly at Mach 1.7 to an altitude of 30,000 feet powered by my custom built N-motor that I am also trying to make........

Just kidding

A bit more seriously though, I am relatively new to the sport and want to go for my L1 soon (will likely do one or two MPRs first). Below is the design that I think I'm ready to settle on:



Designed in OpenRocket, 3" diam main tube, and the shown wider 4" nose cone section. The wider section at the front serves the purpose of reducing the rocket's apogee, but the main reason why I included it is of course because it looks awesome. To allow for the rail buttons to reach the launch rail, I plan on putting half-inch 3D-printed blocks that would sit on the body tube. The rail buttons would be bolted directly onto the blocks. My main question is really simply if this is a good idea and if there are any ways this could go super wrong. My initial thoughts were that there may potentially be large bending moments over the body tube due to having high drag in both the front and the rear of the rocket, but this should only really be an issue if the rocket is flying sideways, in which case I would likely have larger issues on my hands. I also want to know if it would be better to lean towards a larger stability value due to the wider section. What are your thoughts?

While I am here, I may as well also ask about my "chute block." It's just a ring of plywood to stop the parachute from stuffing all the way down the body tube towards the motor during launch. This seems to me like a good idea but I have never seen anyone else do it. Is it just not necessary?

Last question is regarding the fins. I have been told both to use 1/8 in plywood and that 1/8 in plywood would totally not work and that I must go with at least 1/4 in. Is 1/8 in plywood strong enough for a build like this?

Thanks for all the help!

 

[dhbarr]

Just be aware that what you've designed is too heavy to fly without a waiver, so no practice flights on your own.

Have you made your own transitions before? I wouldn't worry much about off the shelf components, but you're putting a lot of faith in whatever's holding the nose into the wind.

Good luck, nothing immediately unreasonable assuming you have the 3d printing experience to make those standoffs pretty robust.

 

[cls]

the shelf for the parachute is a good idea, not really needed for this design, it's not super long

rail button offsets work fine. look at Nike Smoke and Honest John designs to see a variety of ways to do it. 3D printed isn't necessary, I use small wood blocks. never seen issues with offset drag or causing pitch or roll, no worries there.

1/8" plywood is ok for the fins, a little light so more appropriate for a super light low drag rocket, which is not what you are building here.

3/16" is ore appropriate. 1/4" is overkill.

you will discover the fundamental truth about rocketry here. if you ask 2 rocketeers how to do something, you'll get 3 answers!

 

[Hobie1dog]

to the forum.

 

[teepot]

I put 1/4" ply fins on 90% of my rockets. It stays flatter that thinner ply. Less warp. It also depends on what type of surface the rocket is landing on. Nice soft grass or a hard as rock dry lake. I fly off a dry lake. It's hard on rockets. I have seen failed certs because of broken fins. I would suggest you hedge your bet and go with stronger fins. And use a chute size bigger than you need. Build it like a tank. If you want to try the design out before the cert build a down scale. And welcome to the Forum.

 

[cwbullet]

Welcome to the forum.

I would strongly recommend you start smaller and concept the bird first. Find a local club and mentor to ensure you built and fly this safely.

 

[tsmith1315]

Is 1/8 in plywood strong enough for a build like this?

LOC uses 1/8" plywood in their kits up to 4" or so, L1 & modest L2 flights.

 

[neil_w]

Have you made your own transitions before? I wouldn't worry much about off the shelf components, but you're putting a lot of faith in whatever's holding the nose into the wind.

Yeah, that short front BT section + transition is a non-trivial piece of work. Maybe 3D print those two parts as a single piece. And plan to separate the rocket below the transition.

 

[Voyhager3]

I'd go with the 1/4" fins just to be safe, and do fin tabs, you might have to widen the slot on the BT since most are slotted to 1/8". And your rail button idea will probably work, but I'd recommend just using a 3 piece rail button (standard style). And the big thing is to re-weigh your parts before you fly to update the sims, as the CG might switch up on you.

I do like that design though!

 

[lakeroadster]

Hey everyone! I am brand new to rocketry, never flown a rocket in my life, and I am trying to build a 30-foot tall rocket that will fly at Mach 1.7 to an altitude of 30,000 feet powered by my custom built N-motor that I am also trying to make........

Just kidding

A bit more seriously though, I am relatively new to the sport and want to go for my L1 soon (will likely do one or two MPRs first). Below is the design that I think I'm ready to settle on:

View attachment 565193

Designed in OpenRocket, 3" diam main tube, and the shown wider 4" nose cone section. The wider section at the front serves the purpose of reducing the rocket's apogee, but the main reason why I included it is of course because it looks awesome. To allow for the rail buttons to reach the launch rail, I plan on putting half-inch 3D-printed blocks that would sit on the body tube. The rail buttons would be bolted directly onto the blocks. My main question is really simply if this is a good idea and if there are any ways this could go super wrong. My initial thoughts were that there may potentially be large bending moments over the body tube due to having high drag in both the front and the rear of the rocket, but this should only really be an issue if the rocket is flying sideways, in which case I would likely have larger issues on my hands. I also want to know if it would be better to lean towards a larger stability value due to the wider section. What are your thoughts?

While I am here, I may as well also ask about my "chute block." It's just a ring of plywood to stop the parachute from stuffing all the way down the body tube towards the motor during launch. This seems to me like a good idea but I have never seen anyone else do it. Is it just not necessary?

Last question is regarding the fins. I have been told both to use 1/8 in plywood and that 1/8 in plywood would totally not work and that I must go with at least 1/4 in. Is 1/8 in plywood strong enough for a build like this?

Thanks for all the help!

When in doubt... build hell-for-stout!

I'd go 1/4" for the fins, and I'd turn the entire conical nose - nose tube -nose rear transition as a one piece part made from pine on a wood lathe. If needed, it could be counter bored to reduce weight.

Or, revert to witchcraft, and have it 3d printed.

But (I like big buts) since you mentioned building a couple mid-powered rockets first... I'd down size this design to fly on a G74-4, but build it durable enough to fly on a HP motor, like a H128-6, that is just a bit more powerful than the G74.

This allows you to fly it a couple times on the G74, and put it through it's paces, before using the HP motor for the L1 attempt.

 

[Ez2cDave]

Just be aware that what you've designed is too heavy to fly without a waiver, so no practice flights on your own.

Not necessarily . . . You can apply for a waiver, as an individual.

Dave F.

 

[dhbarr]

Not necessarily . . . You can apply for a waiver, as an individual.

Fair enough. I usually assume people getting started would rather drive a couple hours and make new friends than deal with bureaucracy, but maybe this person likes paperwork.

 

[Ez2cDave]

Fair enough. I usually assume people getting started would rather drive a couple hours and make new friends than deal with bureaucracy, but maybe this person likes paperwork.

Some people might prefer to test in private, for whatever reason.

Dave F.

 

[John SChultz]

My $0.02 is to re measure your cg with different size motor mass. Your reverse trap' fins move cp forward, I recommend more stability for first flights. Also if you later go with a bigger motor the stability might be too tight. Very exciting.
Don't use a circular ring as a shelf. Either use a bulk plate with 3 or 4 big holes or cut out flats from either side so you get a span across the diameter with plenty of blow by for ejection. Mount your shock cord eye bolt in the center of the span with a fender washer on motor side.
You should plan for shock cord on both sides of the 'chute and some sort of gas protection.
1/8" is too thin and bendy unless laminated with satin glass. Try to engineer a way to pass thru body tube and attach to motor tube. Reverse fins tend to flutter compared to long swept leading edges so fast motors will make interesting flights unless they're goodly rigid

 

[Titan II]

I usually assume people getting started would rather drive a couple hours and make new friends than deal with bureaucracy...

Not if they are smart.

 

[dpower]

Agree that it's so close to the 1500g limit, I'd try to lighten it a bit so you can fly w/o waiver, on G motors. 3D standoffs will work fine, just give them a solid attachment to the BT. With wood standoffs, wood glue makes an excellent bond. With plastic standoffs, I'd want to put the bolts through the airframe to some blind nuts, or wood screws into a CR or small wood block. I've flown my L1 rocket a number of times, and it flies just fine on 1/8" fins with a wider span than your design, so I'm in the 1/8" camp. As long as they're not crazy large, they will be plenty strong, assuming good plywood, I used 6-ply. The CR to hold the parachute up high is not an uncommon design to keep the CG sufficiently forward - it'll be fine if the center hole is reasonably large.

 

[dr wogz]

Salut! Bienvenue!!

I'm in Montreal as well. hit me up for any & all advice you need!

 

[Joesephus]

Awesome! Thanks for all the help! I've settled on using 1/4 in plywood just because I already bought some and it will significantly reduce the rocket's apogee. I also changed the design a bit so that instead of having a shelf for the chute, the motor tube is now a full 18 in long with a third centering ring at the top.

Hopefully, I'll be posting some updates on the flight sooner rather than later

Salut! Bienvenue!!

I'm in Montreal as well. hit me up for any & all advice you need!

Salut!!

That's awesome! Hope to meet you at some point! I've got a lot of questions

 

[dr wogz]

Salut!!

That's awesome! Hope to meet you at some point! I've got a lot of questions

reach out any time!

(I'm on the west island, and deal with a few local university teams)

 

[Joesephus]

reach out any time!

(I'm on the west island, and deal with a few local university teams)

Oh no way! I'm on Space Concordia's rocketry team. I'm in Cote des Neiges area but I hang out a bunch downtown near campus of course.

I'll pm you

 

[charrington]

I never used a shelf for the recovery. I would always just take a bunch of dog barf (cellulose insulation) and stack it up until the parachute would lay in a good place. Getting a plywood ring in their straight seems like a hassle to me. Dog barf is cheap and also acts as protection from the hot gases produced by the ejection charge. If you add a few inches of it then there's not even a need for nomex.