LVL 1 cert build advice

[BlackAndChrome]

First of all I must say that the deciding factor in many if not all of my design/building/material decisions is price, unfortunately I don't have enough money to buy high end fiberglass components and/or kits, I'm barely scraping by for getting the money to afford the size of impulse motor I want. Please let that thought be a guiding factor in the greatly needed advice that may be needed in all aspects of my productions and plans. Now that I got that out of the way on to the rest of the topic...

Here in a couple months I would like to be getting my Jr. LVL 1 certification. I've been in the Process of building my rocket for some time now but a few large problems have been standing in my way.

First of all to start you off with an overview my rocket is being built entirely from scratch, although precisely created I must add. My tendencies for overbuilding and creating overstable rockets are immense. The main body tube is a 9.6cm wide with 4mm thick walls, it's a salvaged fragile object shipping tube that sustained no damage. The nose cone will be turn by me on a lathe out of pine, my prototype nose cone in the picture below was turned out of a 4"X4" but was slightly too small. The fins will be 3/16" or 1/4" ply recessed into the body and adhered to the motor tube as well as short strand glass for fillets and probably foamed internally. All attachment points for parachute lines are U-bolted into the home made (drill press hole cutter) centering rings that also retain the motor mount tube. The parachute is a 5 or 6 foot gym exercise chute (kids stand around it shaking to make balls fly upward like "popcorn") that I need to add lines to.

The motor is a Rouse-Tech 38/600. My reasoning for this was my want to use heavy walled body tubes as well as pine nose cones that I could make and heavy weight rockets in general. I wanted to not have to buy any other casing even for high end LVL1 flights. It's really unfortunate that somebody happened to knock the casing off my table and it hit concrete. So at this point I can get any other 38mm casing but I would like to stay up in the high end of LVL 1 impulses.

The main thing that concerns me is my ability to find someone willing to sign off on a scratch building minor's attempt at level 1 certification. Especially a builder that at first glance appears to want the largest engine without reason.Unfortunately I am related to no one that participates in HPR so things are kinda difficult. Therefore any advice on what I could do to ensure my ability to find a sponsor would be great.

A couple more general questions...

Would 3/16" ply be heavy enough for a 480 N/s motor?

What is a average fin height related to body diameter?

Is there a rule of thumb for parachute:weight ratio?

This is the damage that my casing took from a hard fall. People wonder why I don't have parties anymore...

My slotted fin/motor section as well as the remainder of the tube that the payload section will be cut out of and my practice run of a nose cone and parachute. I began to glass the nose con but stopped after I closer inspection of it's fit with the tube.

"business end" with a motor retention system consisting of recessed T-nuts and mirror hangers. Beautiful job with the epoxy I know, was really proud of that. I began this rocket almost a year ago, my neatness with epoxy has increased tenfold, but the I am sure of the strength of the bond. I'll probably go back and fill in the rest with casting epoxy just for a nice neat look.

U-bolt embedded in spacers on a short piece of 38mm motor mount to connect the parachute line to. The method will be cloned on the forward end or a long threaded I-bolt will be embedded in the nosecone depending on how I decide to extend the body tube to increase stability.

Thank You,
-Nick Meyer

 

[Handeman]

B&C, welcome to TRF. It looks like you have a pretty nice rocket in the works.
My first advice, don't scrap the nose cone yet. Add another layer of glass to the shoulder and see if you can improve the fit. Also, you don't need glass over a pine nose cone. Sand it smooth and paint it. Save any added weight for building up the shoulder.
The BT looks very similar to what I build my L1 with, 2" ID, 1/8" thick wall. I certed on a I110W and the next flight was an I1299N. It held up to both just fine. Don't worry about the BT.
As for the rest, don't worry about strength. With that tubing, 3/16 fins, TTW attachment, and good fillets, it will be plenty strong for the motors that fit the 38/600 casing.
Run plenty of sims on it. Make sure your selected ejection delay is right. High speed is the chute killer at ejection. Also, taking a printout of the simulation can do a lot for the sponsor and let him know that you know what you're doing.

 

[DAllen]

First of all I must say that the deciding factor in many if not all of my design/building/material decisions is price, unfortunately I don't have enough money to buy high end fiberglass components and/or kits, I'm barely scraping by for getting the money to afford the size of impulse motor I want. Please let that thought be a guiding factor in the greatly needed advice that may be needed in all aspects of my productions and plans. Now that I got that out of the way on to the rest of the topic...

Why bother with getting an L1 then? I mean seriously...Have fun with the hobby. Don't let it be some gigantic financial burden in your life. I donno...just a thought.

Here in a couple months I would like to be getting my Jr. LVL 1 certification. I've been in the Process of building my rocket for some time now but a few large problems have been standing in my way.

First of all to start you off with an overview my rocket is being built entirely from scratch, although precisely created I must add. My tendencies for overbuilding and creating overstable rockets are immense. The main body tube is a 9.6cm wide with 4mm thick walls, it's a salvaged fragile object shipping tube that sustained no damage. The nose cone will be turn by me on a lathe out of pine, my prototype nose cone in the picture below was turned out of a 4"X4" but was slightly too small. The fins will be 3/16" or 1/4" ply recessed into the body and adhered to the motor tube as well as short strand glass for fillets and probably foamed internally. All attachment points for parachute lines are U-bolted into the home made (drill press hole cutter) centering rings that also retain the motor mount tube. The parachute is a 5 or 6 foot gym exercise chute (kids stand around it shaking to make balls fly upward like "popcorn") that I need to add lines to.

The motor is a Rouse-Tech 38/600. My reasoning for this was my want to use heavy walled body tubes as well as pine nose cones that I could make and heavy weight rockets in general. I wanted to not have to buy any other casing even for high end LVL1 flights. It's really unfortunate that somebody happened to knock the casing off my table and it hit concrete. So at this point I can get any other 38mm casing but I would like to stay up in the high end of LVL 1 impulses.

The main thing that concerns me is my ability to find someone willing to sign off on a scratch building minor's attempt at level 1 certification. Especially a builder that at first glance appears to want the largest engine without reason.Unfortunately I am related to no one that participates in HPR so things are kinda difficult. Therefore any advice on what I could do to ensure my ability to find a sponsor would be great.

Well, there really isn't a good answer. You are going to have to start going to a local NAR club and ask around and get to know the people there. Continue documenting your build in detail and maybe someone would be willing to sign off on it.

A couple more general questions...

Would 3/16" ply be heavy enough for a 480 N/s motor?

I don't see a problem with that especially since you are using through-the-wall mounting techniques.

What is a average fin height related to body diameter?

Aesthetically, I have found that usually the fin span = the body diameter. You will also want to consider performance characteristics as well.

Is there a rule of thumb for parachute:weight ratio?

Parachute calcualtor can be found here:

https://www.rocketreviews.com/tools.shtml

Your 6' exercise chute is probably going to be plenty strong but waaaaay too big.

This is t
he damage that my casing took from a hard fall. People wonder why I don't have parties anymore...

That needs to be fixed prior to flying I would think. I have no idea how to fix something like that.

My slotted fin/motor section as well as the remainder of the tube that the payload section will be cut out of and my practice run of a nose cone and parachute. I began to glass the nose con but stopped after I closer inspection of it's fit with the tube.

"business end" with a motor retention system consisting of recessed T-nuts and mirror hangers. Beautiful job with the epoxy I know, was really proud of that. I began this rocket almost a year ago, my neatness with epoxy has increased tenfold, but the I am sure of the strength of the bond. I'll probably go back and fill in the rest with casting epoxy just for a nice neat look.

U-bolt embedded in spacers on a short piece of 38mm motor mount to connect the parachute line to. The method will be cloned on the forward end or a long threaded I-bolt will be embedded in the nosecone depending on how I decide to extend the body tube to increase stability.

Thank You,
-Nick Meyer

I like the idea of a "total" scratch build however, I have avoided using this kind of tubing because it is quite heavy compared to regular tubing and is a non-standard size. Also, it has a tendency to fray at the exposed ends so I would put a very light coating of either epoxy or CA glue to prevent the fraying from happening. A 480ns motor should have noooo problem lifting the heavier tubing though.

Hope that helps! Good luck.

-DAllen

 

[SpartaChris]

The main thing that concerns me is my ability to find someone willing to sign off on a scratch building minor's attempt at level 1 certification. Especially a builder that at first glance appears to want the largest engine without reason.Unfortunately I am related to no one that participates in HPR so things are kinda difficult. Therefore any advice on what I could do to ensure my ability to find a sponsor would be great.

Do you frequent high power launches in your area? The best thing you can do is get with someone who's able to do the certification and talk to them about your plans and feel them out a bit. If you don't have someone you can contact, then just be prepared to answer every question imaginable under the sun about your rocket. You might need to know things like where your center of pressure ad gravity are, what the expected altitude is, what the descent rate is, what the thrust to weight ratio is. You also might need to answer any questions about the construction process. Level 1 isn't a super involved certification, so it's not like you'll have to present pages and pages of schematics and formulas. Just be prepared to answer most basic questions.

A couple more general questions...

Would 3/16" ply be heavy enough for a 480 N/s motor?

Oh yeah, that certainly shouldn't be a problem. You shouldn't even need to glass them. Many people even go with 1/8" and are just fine, so 3/16" should easily get the job done.

The thing to remember with fins isn't just so much the material thickness, but the shape of the fin as well. Some fin shapes will have a lot more drag than others. One simple resource you can use is the fin flutter calculator on ROL: https://www.info-central.org/design_finflutter.shtml

What is a average fin height related to body diameter?

To be honest, I have no idea. I think the rule of thumb is 2X diameter of the body tube, but I think it's also going to be a matter of preference. As a rule, the bigger your fins are the more stable the rocket, so plan accordingly.

Is there a rule of thumb for parachute:weight ratio?

The chute should be big enough to give you anywhere from a 15-20 fps descent rate.

Hope that helps.

 

[AndyC]

Looks like a nice build so far. A friend at our local club built a rocket from 3" shrink wrap tubes for his level 2. The stuff is very thick like yours, and nearly indestructible. Heavy though. All he bought was a LOC nosecone, a chute and some little bits; the rest of the parts were scrounged. Very cheap way to go. Hardest part was getting the paint nice - those tubes suck up primer & paint like there is no tomorrow.

I was on this site today, and they fix motor tubes. Dunno if they can fix a dent - looks like they cut to a shorter length. They also specialize in EX cases, so may not do threading. Anyway, there may be other places as well - Rouse Tech? I think I remember seeing a thread on the old TRF discussing fixing cases - there was some concern over whether they could be used at launches that allow only certified motors (fixing them might count as modifying them). Someone here might know for sure, but its probably a good question to ask the repair place if you decide to get your tube repaired.

 

[BlackAndChrome]

My first advice, don't scrap the nose cone yet. Add another layer of glass to the shoulder and see if you can improve the fit. Also, you don't need glass over a pine nose cone. Sand it smooth and paint it. Save any added weight for building up the shoulder.

The reasons I decided to scrap the nose cone was mainly because when I cut it down I spent a lot of time just running a strip of emery cloth over it while it spun, this proceded to cut the soft wood much faster than the age rings leaving waves in the end. The only purpose of the glass was to increase diameter to fit the tube, I enjoy tunrning stuff on the lathe so a new cone out of an adequate sized piece of stock would be much easier than trying to glass it a couple more times.

I've entered the data into the trial version of Rocksim (really should look into just buying it) but I need to get everything massed so I can get accurate stability info.

Thanks for the advice

@DAllen

I can't deny part of me craves the roar of High power engines and the sight of a 6' tall rocket flying through the air

The chute has a 4" wide vent in the top of it. I'd assume I would be better off capping that and sizing it down to the necessery size? Or maybe just making/finding a different one?

I emailed the guy from Rouse-Tech, he says the motors trashed... smack in the face for a budget minded person.

I like the idea about sealing the ends, I was just thinking about that looking at the aft end photo.

@SpartaChris

I've been to a couple Kloudbuster events in Argonia KS (230 miles away). I live in Kansas but I really just need to find some place in southern Iowa or Nebraska because it's actually closer.

-Nick Meyer

 

[BlackAndChrome]

those tubes suck up primer & paint like there is no tomorrow.

I was on this site today, and they fix motor tubes. Dunno if they can fix a dent - looks like they cut to a shorter length. They also specialize in EX cases, so may not do threading.

Yeah, no joke about the paint on that tubing, I put 4 coats of Krylon on before I even had enough of a shell to cut the fuzzies off!

As for the motor I just got a message back from Tom Rouse (I actually asked about having it cut and rethreaded) confirming no hope for the casing. It's what I expected the moment I heard it hit the floor. Even if I did get the closures to thread I'm sure I'd get some odd looks from whoever had to watch me load it considering there would always be a lot of bind, and I'm already going against the grain enough as is.

On the bright side I guess it will probably make a good case for one hell of a Potassium Nitrate+sucrose engine.

 

[MarkM]

Looks like you've actually thought this design out quite a bit. With Jr Level 1 you need a mentor to purchase the motor (since you are not legally allowed to do so), build the motor and install it, and supervise the rest of the flightprep. I don't know many fliers who would do this for a minior who shows up to a launch and "out of the blue" wants to try a Jr Level 1. As others suggested, you should attend a few NAR launches and get to know your fellow fliers. Establish report with them, describe your rocket. They will probably give you a lot of advise and once they feel comfortable with your knowledge they will probably have no problem acting as your mentor.

Your chute is huge for this rocket. A rocket this size will probably be fine on about a 3' or 4' chute depending on final weight.

Good luck

 

[DAllen]

I've entered the data into the trial version of Rocksim (really should look into just buying it) but I need to get everything massed so I can get accurate stability info.

If you are going to make a habit of building rockets from scratch (which is a good thing ) I would highly recommend buying the full version of Rocksim even if the budget is a little tight. RS isn't always a good way to accurately determine altitude but it is a great way to calculate CP. The key to RS is to enter the data as accurately as possible (especially when using non-standard parts) which includes weight, CG and the paint finish for items in the airstream.

Determining stability is HUGE when scratch building and RS takes a lot of the hassle out of it. I swear by RS because I have yet to have a scratch built rocket go unstable on me. There are other programs out there and I know nothing about them and how they compare to RS.

-DAllen

 

[BlackAndChrome]

Yeah, I definitely need to see about going to a few local launches, like I said though I also need to find some place a lot closer than 200+ miles. I'd love to go to more launches but it's far enough were my parents don't want me driving that far too many times or putting that many miles on the car. It would probably be better a lot more efficient to find someone over the internet and communicate with lots of pictures than to drive a combined total of 1200+ miles before knowing someone well enough to get them to sign off.

Speaking of which anybody no of any launches closer to the Kansas City KS area than Argonia KS (kloudbusters)? Although it's nice to launch knowing that the only thing around for many miles is dirt...

Or at that... Anyone in the KS area want to sign off on a rocket?

Thanks,
-Nick Meyer

 

[DAllen]

Get in touch with these folks:

https://www.teeniemunde.org/

Looks like an active TRA club about 123 miles from Kansas City.

The Kloudbusters field is awesome but that is a looooong drive from KC to Argonia. I drove 15 hours from Michigan to Argonia this summer to go to LDRS and I thought that last 3 or 4 hours from KC was going to kill me.

-DAllen

 

[BlackAndChrome]

Considering that they are Tripoli based would that be a problem for getting sign-offs on a NAR jr cert?

-Nick Meyer

 

[DAllen]

Considering that they are Tripoli based would that be a problem for getting sign-offs on a NAR jr cert?

-Nick Meyer

Oh yeah...well... there is that. There are a lot of people who have dual membership in both the NAR and TRA. Maybe shoot them an email and see if there are any NAR members in that club. If there are and they are willing to sign off on your rocket you are all set for Jr. L1. Most rocket clubs I have found are quite easy to work.

-DAllen

 

[MarkM]

Oh yeah...well... there is that. There are a lot of people who have dual membership in both the NAR and TRA. Maybe shoot them an email and see if there are any NAR members in that club. If there are and they are willing to sign off on your rocket you are all set for Jr. L1. Most rocket clubs I have found are quite easy to work.

-DAllen

But isn't there still an issue with insurance for a NAR Jr L1 flying at a TRA-sanctioned launch, which does not recognize the NAR Jr L1? Or does NAR insurance follow the flier?

 

[DAllen]

I don't think so since when the Jr. L1 is obtained the senior L1/L2/L3 "officially" signs the flight card I think. I have to believe that if a senior L1 is taking responsibility for a Jr. L1 it really shouldn't matter to TRA insurance. Even after you get a Jr. L1 it is my understanding that a senior L1 still has to sign off on the card on all future H and I flights.

https://www.nar.org/hpcert/jrhppreq.html

I believe the key term in that document is "sponsor." I would read the whole thing but I have to go to bed.

-DAllen

 

[dave carver]

Ive used VCP and WRASP for years and have had no problems with rockets I've designed with them and you can't beat for free. The guy who programed VCP is a member of TRF, at least he was in the old incarnation.

Just google them up and get started. If the motor you want isn't in WRASP just ball park it, 240 neutons in 1.5 seconds is 240 neutons in 1.5 seconds, if you know what I mean. Exact numbers arn't exact in the first place with a possible swing of 20% on a delay in either direction from stated time.