Too light for L1 cert?

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Kelly

Usually remembers to get the pointy end up
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I'm designing a rocket for L1 cert, and I wanted to go scratch-built using materials I have on hand.

I have some 2" mailing tubes with a wall thickness of about 1/16". I designed a rocket in OpenRocket with a length of about 36" and using a 29mm motor. Trouble is, it only weighs a little over a pound (including the motor weight, and some NC ballast) and so it sims at close to Mach 0.7, 25g, and an altitude of over 3000ft with a minimal H motor. These seem like a bit more than I want to deal with for a cert flight. (Is it more than this tube, and 1/8" plywood fins, can take?)

Should I consider adding more weight, or making it draggier, to get a lower performance rocket?
Or, ditch the 2" tube and go to (say) 3" tube, which would naturally be heavier/draggier?
 
You could also cover it in 'fun fur' to make it as draggy as possible. Or 70's era shag carpet! :D

The motor will push. And that push will equal an altitude. If it's too high an altitude, adding weight or drag will reduce it. it's up to you what & how you want to add it..

Many 'L1' rockets seem to be in the 3" - 4" range, and usually a few pounds or so..

Start experimenting with tube dia., length, and the size & number of fins.. See what changes affect the end results..

In your OR design, have you weighed the components so they are real world weights? (You can give the components a weight override from their 'default' settings)
 
My co worker did his L1 on a stock Estes Partizon that was 2.6" and weighed in at 17 Oz w/o motor. Was 2600', but still within the edge of sight and recovered successfully on an H128W. If you've got the field and some binocs/spotters, then it may work. 0.7 Mach though... whew. Pick something low impulse... H115DM.
 
I'm designing a rocket for L1 cert, and I wanted to go scratch-built using materials I have on hand.

I have some 2" mailing tubes with a wall thickness of about 1/16". I designed a rocket in OpenRocket with a length of about 36" and using a 29mm motor. Trouble is, it only weighs a little over a pound (including the motor weight, and some NC ballast) and so it sims at close to Mach 0.7, 25g, and an altitude of over 3000ft with a minimal H motor. These seem like a bit more than I want to deal with for a cert flight. (Is it more than this tube, and 1/8" plywood fins, can take?)

3K feet for L1 cert is well within what would be expected. And nothing to worry about, assuming that keeps you well under the FAA waiver limit.
In reality, your rocket will not go that high as you will never streamline and refine it to what OR assumes as "polished" surface state. Expect 10-25% lower altitude when you actually fly.

The potential concern I would raise is the integrity of said mailing tube when subjected to 25G. I don't know how well that tube was constructed, or if it's held in place by anything other than dried spit and a layer of paper veneer.

It will probably hold anyway, but I would feel better flying on a 2+" tube sourced from a rocket specialty shop.


Should I consider adding more weight, or making it draggier, to get a lower performance rocket?
Or, ditch the 2" tube and go to (say) 3" tube, which would naturally be heavier/draggier?

If you want to go lower, pick a larger diameter tube (and a nose cone to go with that).
Larger diameter tubes will add a lot of drag. So will thicker fins.
So will throwing a 3"->2" centering ring sitting on top of your fins (acting as an air brake ;-).

As <Bat-mite> suggested, do consider JL CR to solve all your recovery/drift challenges for this, as well as other rockets.

a
 
I'll have plenty of altitude waiver, and recovery space. I just don't want (1) the rocket to shred on launch or (2) have to worry about losing it on a cert flight, or making it more complicated with DD, tracking, etc.
 
Light doesn't coast well so final altitude is limited. Think of throwing a golf ball verses a ping pong ball.


Sent from my iPad using Rocketry Forum
 
the only requirement is a launch and recovery, most rockets that Ive seen be "allowed" to launch after inspection don't shred, May I recommend an H-410 for your mailing tube? Your rocket should stay relativity low considering the type of mailing tube construction.

:)

Tom
 
I'll have plenty of altitude waiver, and recovery space. I just don't want (1) the rocket to shred on launch or (2) have to worry about losing it on a cert flight, or making it more complicated with DD, tracking, etc.

There is nothing complicated about tracking. Turn it on, stick the transmitter in, turn on the receiver. Use your phone to walk to the rocket. And JLCR is as simple as simple can be.

may i ask: what's motivating you to get your L1?
 
I don't think you'll have any shred issues. Your weak point is going to be your fin mounting- are they thru-the-wall and not unreasonably huge? If so, you're fine.

My L1 was a 38mm, 1lb 3oz or so paper/ply rocket on a CTI H90- my altimeter battery died, but sim says 4000' and mach 0.7. I had a tracker on board but it was a clear enough day that I didn't end up needing it. The JLCR definitely helped, though.

I would recommend just about any small H *other* than the H410. But that's just me. I had a 3-grain case already so I went with the H90, but a 4-grain skidmark or the aforementioned H115 Dark Matter single-use motor would be pretty cool too. It's all up to what you like... I personally like slow burns and/or sparkies but that's just me.
 
Fins are definitely TTW; bulkheads/centering rings plywood. Fins are trapezoidal and reasonably sized. Thanks for the feedback!
 
I personally like to keep them lower for easy recovery, and you do have to recover the rocket to complete the cert. On the other hand, there&#8217;s no penalty for failing the cert &#8212; you just try again later. And if you want to go scratch-built with mailing tubes, then you haven&#8217;t invested much, except time, especially if you use a single-use motor.

If you you decide you want to keep it lower, then more drag is a better solution than more weight. A 4&#8221; rocket is a good L1 cert size. Maybe you can find a 3&#8221; - 4&#8221; mailing tube?
 
My L1 cert was on a 54mm rocket that went to around 2000-2500 feet. It was on the edge of visible during the whole flight, but a red-orange chute at the top helped a lot. 1/16" wall isn't that much thinner than the LOC HPR tubing, so I'd just go for it. You could do a quick structural test by figuring the weight of the nose cone, multiplying by 25G and pushing that hard on the end of the rocket. If it all feels OK, then it should be fine in flight. If you're worried about seeing it, a reflective mylar streamer makes it easier to see.

A slower burning motor would be good for this, like an H54 if you fly CTI although slow burns tend to mean higher apogees. An H410 would not be the best choice. :)
 
I find it perplexing that posters rarely suggest tube fin rockets for L1 attempts. I did my L1 on an ASP That Tube Fin 29mm last year. The design uses standard BT-70 tubing. All I did was beef up the shock cord. With JLCR and a H115DM it reached only 1800 feet and was clearly visible the entire flight. Tube fins rock! My next HPR will be the LOC Cyclotron. I can't wait to send that up on a bigger H or I motor.

Tom
 
I find it perplexing that posters rarely suggest tube fin rockets for L1 attempts.
Tom

I don't like the appearance of tube fins, but I understand that's a personal choice. It had crossed my mind as a possibility when I suggested making it 'draggier', it's still an option I guess.
 
You could go with 1/4" plywood fins without rounded trailing edges. You might be surprised at how much lower that will make the sim. But if you add heavier fins, you might need more nose weight.
 
Fins are definitely TTW; bulkheads/centering rings plywood. Fins are trapezoidal and reasonably sized. Thanks for the feedback!

Sounds like a high performer, but one that can handle a small H. I say go for it.
 
Madcow or Wildman usually stock fiberglass metric rocket motor casing spec'd rocketry airframe tubes. These were somewhat pricier due to the odd ball sizes. Quite a few people have successfully L-1 certified on converted Estes kits. Larger diameter is more drag force to keep the rocket lower. If you go with tube fins where you just cut a tube to length then radial attach it will stay even lower and slower. The point of being low is to avoid GPS tracker costs, JLCR costs, and altimeter or timer complexity with deploy charges after you run out of motor delay timing. You could scratch a min diameter but it would go a mile or more up and lose sight with greater risk of not recovery if no tracker or lost tracker signal. Lighter rockets have less expensive recovery hardware. PML can CNC cut fins for you for a few bucks if you want it more professional looking. If you start with a 38mm motor mount and build it long and strong enough you can even use L-2 motors after L-1.
 
You can add more fins to increase drag, or design fins that look backwards, like the Quest Mean Green. Of course that changes your rocket design. If you have a bigger OD mailing tube, that would be a good route take.
 
Madcow or Wildman usually stock fiberglass metric rocket motor casing spec'd rocketry airframe tubes. These were somewhat pricier due to the odd ball sizes. Quite a few people have successfully L-1 certified on converted Estes kits. Larger diameter is more drag force to keep the rocket lower. If you go with tube fins where you just cut a tube to length then radial attach it will stay even lower and slower. The point of being low is to avoid GPS tracker costs, JLCR costs, and altimeter or timer complexity with deploy charges after you run out of motor delay timing. You could scratch a min diameter but it would go a mile or more up and lose sight with greater risk of not recovery if no tracker or lost tracker signal. Lighter rockets have less expensive recovery hardware. PML can CNC cut fins for you for a few bucks if you want it more professional looking. If you start with a 38mm motor mount and build it long and strong enough you can even use L-2 motors after L-1.
Can't believe I'm going to put this out there, but I agree with Andrew.

Going low and slow, avoid unnecessary costs (for now; JLCR, trackers), and 38 mm for future bigger flights.

I know ya really want to go scratch built but I'd go with a nice kit for level one. These kits are designed well and have been tested as reliable with more than just sims.

Or screw it, balls to the wall....you can always re-cert later... just don't kill anyone please.

Nate

Sent from my SM-G965U using Rocketry Forum mobile app
 
My question is, why are you designing a rocket that goes that high on a small H? What are you going to do when you get the L1 and want to fly full H and I motors? Are you building this rocket for just the one cert flight? To me, that seems a waste.

My suggestion is build something with a 38mm MMT that can fly on H and I motors and then cert low and slow on the baby H. When you're done you will have a rocket you can fly all L1 motors in. Then again I used 2" mailing tubes for my L1 cert rocket, but they were heavy duty tubes with 1/8" walls and I build it with DD. It flew to 4200 ft on and I motor on the cert flight and I had about 6 flights in it on I motors before I put an H in it. The point is that I had fun with the whole range of L1 motors in that one rocket, I didn't have to build another rocket after my cert to fly I motors.

Just my suggestion...
 
Points taken. I've started on a 3" version which sims much more tamely with an 'H' motor. The 2" version will be fun on smaller motors, or after cert with DD or a tracker.

Thanks all!
 
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