Level 2 questions

The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

mohmes

Well-Known Member
Joined
Mar 26, 2013
Messages
104
Reaction score
0
I am in the process of building a Madcow 4" Phoenix and plan to launch it on a CTI J330 for my L2 attempt.

The instructions state that I should drill a small 1/8" hole in the chute compartment to allow venting. I have also read/heard that I should use shear pins. I am assuming that I should do one or the other, but I am curious what the experienced guys think. Simulations show the launch reaching just over 4060 feet with a max speed of 565 mph.

The other question that I have is about who to certify with. I am both Tripoli and NAR and so is my club. Should I go for both or just one of them? Is there an advantage to certifying with one over the other?

Thanks for your help!
 
First off, good luck on your L2! The purpose of the vent hole is to allow the initial atmospheric pressure to normalize during the rockets ascent without overpressurizing the compartment causing premature separation. The higher and faster the flight the more critical the need for a vent becomes.
Shear pins seem to be more subjective. I use shear pins at all separation point then ground test to verify adequate separation force. I mostly build FG birds, but for any paper separation points I embed a brass shim to ensure repeatable shearing of the nylon screw and longevity of the hole. This is not absolutely necessary and the use of "shear tape" or friction fit works well on drogue sections for many fliers.
 
Do both I assume this is dd and you don't want the apogee charge to deploy the mains.
a good reference is "Modern High Powered Rocketry" by Mark C. a must have for all HP flyers...
 
The other question that I have is about who to certify with. I am both Tripoli and NAR and so is my club. Should I go for both or just one of them? Is there an advantage to certifying with one over the other?

Both, but indirectly -- pick one to do the cert under (take the test, do the flight, file the paperwork). Then, once your new card that shows your level, photocopy it and mail a copy to the other organization.

NAR and Tripoli recognize each other's certifications, and both will record you as Level 2.

-Kevin
 
Two major differences between NAR and Tripoli for L2: what's on the test (view the sample tests on each club's web site), and the requirements for a successful flight.

With NAR, the rocket must be recovered and able to be flown again without repair. For example, if you dent your nose cone or scuff your tubes, you could turn around and fly it again with no repair, even though you might want to improve it later.

With TRA, the flight must succeed "as intended." So, if you use dual deployment and get a main at apogee, or no main at all, you fail.

I certified with NAR. Due to my not having enough vent holes in my AV bay, my main never deployed. But the rocket was recovered, and although there was a dent in the nose cone, it could fly again. Had I been certifying TRA on the same launch, I would have failed, because my DD was not successful.

Neither club requires DD on a cert flight, and many people do not use it; however, if you wish to get to level 3, you must demonstrate the ability to do a successful DD flight with a level 2 motor.
 
Oh, and one other thing. TRA makes you mark your CP and CG on the airframe. NAR does not. Not a big deal, as you should always know them before launching anything. But if you don't like scribbling on your rocket....
 
With TRA, the flight must succeed "as intended." So, if you use dual deployment and get a main at apogee, or no main at all, you fail.

I'm not sure where you're getting that information - it doesn't match what's on the Tripoli website.

-Kevin
 
I'm referring to these two rules:

"The certifying member must witness the rocket ascend in a stable manner and descend in stabilized manner controlled by the recovery system."

"Any of the following will result in non-certification for a certification flight: No recovery system deployment or tangled recovery system deployment"

Robert DeHate certified me, and he told me, "If this was a Tripoli certification, I'd have to fail you," because my main didn't deploy.
 
snipped
With TRA, the flight must succeed "as intended." So, if you use dual deployment and get a main at apogee, or no main at all, you fail.

snipped again

Neither club requires DD on a cert flight, and many people do not use it; however, if you wish to get to level 3, you must demonstrate the ability to do a successful DD flight with a level 2 motor.

Main at apogee is OK, no main-no cert.

A flight with electronics is required before doing a L3 cert launch but not DD

I have never launched a DD rocket and am L3

Mark
 
I'm guessing that the two sets of rules were meant to be the same, but since they were written by different people the wording differs. They are often over-interpreted (like the shunt in the NAR rules) by fliers as well as by TAP/L3CC members.

That said, there is a lot of latitude for the TAP/L3CC mentor, which allows them to fail someone who doesn't appear willing or able to fly safely (as it should be).

Switching organizations because one thinks certification will be easier suggests to me someone who isn't ready yet.
 
Last edited:
Just to be clear, the Madcow 4" Phoenix is not a DD but I am wanting to fly with electronics - just makes it so much more fun with an Altus TeleMetrum!

As for which one to certify with, I was actually contemplating trying to do a cert with both since I am a member of both. The only thing that might deter me is that I really have no interest in experimental motors so I think that a NAR certification test might be a better fit for me. Mainly I just wanted to make sure that no one had a strong opinion of certifying with one over the other for some reason I had not heard about. I like to do things right - not easy.

The other question about using shear pins and the vent hole. I am assuming that the vent hole is small enough that the ejection charge will still be able to break the shear pins. This was my only concern trying to do both.
 
I'm referring to these two rules:

"The certifying member must witness the rocket ascend in a stable manner and descend in stabilized manner controlled by the recovery system."

"Any of the following will result in non-certification for a certification flight: No recovery system deployment or tangled recovery system deployment"

Robert DeHate certified me, and he told me, "If this was a Tripoli certification, I'd have to fail you," because my main didn't deploy.

Without knowing the size of your drogue, I can only make the assumption that it descended too fast to be considered safe. I wouldn't have signed it under either organization, for safety reasons.

-Kevin
 
Just to be clear, the Madcow 4" Phoenix is not a DD but I am wanting to fly with electronics - just makes it so much more fun with an Altus TeleMetrum!

As for which one to certify with, I was actually contemplating trying to do a cert with both since I am a member of both. The only thing that might deter me is that I really have no interest in experimental motors so I think that a NAR certification test might be a better fit for me. Mainly I just wanted to make sure that no one had a strong opinion of certifying with one over the other for some reason I had not heard about. I like to do things right - not easy.

The other question about using shear pins and the vent hole. I am assuming that the vent hole is small enough that the ejection charge will still be able to break the shear pins. This was my only concern trying to do both.

I guess nothing says you can't certify both at the same time. Take both tests and have you same/different cert. team(s) sign off both sets of papers. But not really a big difference if you do NAR, TRA, or both IMO.

As for your desire to not do Research, it doesn't really matter as far as TRA is concerned. You can't use Research to certify with anyway. And your not any less of a TRA guy if you stick with commercial your whole flying life.

As for pins and vent hole. Pins are really useful/needed on heavy nose cones where you add a lot of weight or where the NC is connected to a piece of tubing and separates at the bottom of the tubing, thus making for a heavier frontal section. This is because you have greater inertia with the heavier frontal sections and drag separation is more likely. Vent holes are NOT needed with most shear pins, and only increase likely hood that the NC won't separate. If you do vent holes, you place it just below the separation joint. As for size and quantity, check this out. As for which to go with, if it is not seriously heavy, I would stay away from pins. I had a flight that ground tested fine, but only 2/3 pins sheared, and my main did not deploy. Since I had an NC w/o weight, I regret the decision to use pins, and will friction fit in the future.

https://www.rocketryforum.com/showthread.php?52044-Static-port-calculator
 
Last edited:
From an oldtimer...Get your cert, THEN play with electronics. Why complicate a simple procedure. I agree electronics can be fun, but get the cert, then play. Trust me, you will NOT be sorry.
 
The nose is heavy in this rocket - have to add a lot of weight to keep it stable because of the long fins moving the CP forward. The rocket is short and only has a single deploy.

So just to make sure that I am following you correctly, the concern and reason for using the shear pins would be that the nosecone may have enough momentum to pull itself out of the rocket once the motor starts coasting? (Since there is no drogue section or dual deploy then there is nothing else to pull the nosecone out.) I had the feeling that doing both pins and a hole wasn't the best idea.
 
With TRA, the flight must succeed "as intended."

That sounds like the rule for an L3 cert, not L2.

My $.02 - certify with NAR since ANY NAR member can administer the test and witness the flight, whereas you need to fiddle-faddle around with Prefects/TAPs for a TRA cert. Keep it simple.
Likewise for deployment - I certainly suggest sticking with single deploy/motor eject for an L1 or L2 cert, then getting fancy with electronics later on. That's exactly how I did it.

Good luck with the cert!

From an oldtimer...Get your cert, THEN play with electronics. Why complicate a simple procedure. I agree electronics can be fun, but get the cert, then play. Trust me, you will NOT be sorry.
Exactly.
 
I've used the Altus TeleMetrum in my L1 rocket so this isn't new to me. I am more interested in the data it provides but having the more controlled ejection capability is nice too. However, the cert flight will most likely be just a motor ejection as I am starting to work on getting my FEL and don't know if I will have it in time.
 
I'm referring to these two rules:

"The certifying member must witness the rocket ascend in a stable manner and descend in stabilized manner controlled by the recovery system."

"Any of the following will result in non-certification for a certification flight: No recovery system deployment or tangled recovery system deployment"

Robert DeHate certified me, and he told me, "If this was a Tripoli certification, I'd have to fail you," because my main didn't deploy.

We had a TAP resign because he refused to follow new rules. In short, if a cert flight pops main at apogee, weather intended or not, the cert is successful. I personally agree with this. I would allow an L2 if main fails but rocket is recovered by drogue undamaged and flyable. I would also try to dissuade any L1 or L2 cert flights with electronics. I will only advise, what the flyer does is his business.
 
.....Neither club requires DD on a cert flight, and many people do not use it; however, if you wish to get to level 3, you must demonstrate the ability to do a successful DD flight with a level 2 motor.
Neither NAR or TRA require dual deployment at any certification level, however if you have flown any L motor or larger or any 75 mm casing or larger you had to use electronic deployment because these motors are not allowed to have motor ejection.

So while all Level 3 flights require electronic deployment, and both NAR and TRA L3 cert flights require redundant electronics, Tripoli also requires at least one previous L2 flight using electronic deployment. NAR does not, however if the rockets electronics have not been flown before, you must show by ground testing that they will work. I know several folks who flew their L3 cert rocket on a K or L motor prior to their L3 cert flight just to make sure everything was working as intended so they would pass their L# cert on the first attempt.......

Bob
 
Neither NAR or TRA require dual deployment at any certification level, however if you have flown any L motor or larger or any 75 mm casing or larger you had to use electronic deployment because these motors are not allowed to have motor ejection.

So while all Level 3 flights require electronic deployment, and both NAR and TRA L3 cert flights require redundant electronics, Tripoli also requires at least one previous L2 flight using electronic deployment. NAR does not, however if the rockets electronics have not been flown before, you must show by ground testing that they will work. I know several folks who flew their L3 cert rocket on a K or L motor prior to their L3 cert flight just to make sure everything was working as intended so they would pass their L# cert on the first attempt.......

Bob

Also, most longer 54mm motors (Aerotech 54/2560, CTI Pro54-6GXL, etc) are plugged as well.
I certainly support the L3 "checkride" flight option, too. While not required, I really liked being able to make sure sure everything in my rocket worked correctly, and making any small changes as needed. I flew my L3 rocket on an L850W before certing with the M1297W a month later.
 
The nose is heavy in this rocket - have to add a lot of weight to keep it stable because of the long fins moving the CP forward. The rocket is short and only has a single deploy.

So just to make sure that I am following you correctly, the concern and reason for using the shear pins would be that the nosecone may have enough momentum to pull itself out of the rocket once the motor starts coasting? (Since there is no drogue section or dual deploy then there is nothing else to pull the nosecone out.) I had the feeling that doing both pins and a hole wasn't the best idea.

You understand me correctly. Drag separation is an issue, especially if the booster section is draggy and the NC is heavy. Shear pins (2-56) require a significant force to break. WAY more than the differential pressure between the inside (higher pressure) and the outside at apogee (the lower pressure). So I suggest no vent hole if you use shear pins. And if you are using motor ejection, make sure you don't have a ginoumous volume to pressurize. If you can seal the nose cone up so the inside of it is a sealed volume, that helps reduce the total volume you have to pressurize to pop the NC
 
Back
Top