J350W- weight

Hey again,
I have a question that some of you more experienced rocketeers, especially if your level 2 certified, might be able to answer. I am currently contemplating a level two certification design for my dad. I plan to put it up on a J350W because it is much cheaper than using a 54mm J415 or J275W. Anyway the rocket's current design sets it at 8" in diameter and 10-12 feet tall. I think it'll probably end up being a 1/2 scale patriot with 1/4 or 3/8 inch birch ply for the fins and 3/8 birch ply for the CR's. The nosecone will be scratch made from styrofoam and fiberglass, a technique I know from another NEPRA member. Basically I am thinking that if I build it light it just might be light enough to get up and go on a J350W. The tubing is hardware store type Sonotube by the way, so it is very light and pretty strong(no need to fiberglass it). I would like to know what you think the maximum weight for a rocket to be that will go up safely on a J350W? I would hope it would reach at least 800 to 1200 feet. Rocksim says somewhere between 10-13 pounds but I would like some personal experience to back that up. Anybody know?

Dave

Maverick,

Here is the method used by most rocketeers; first, figure out the thrust, in pounds, of your motor:

EXAPMLE:

A G64W is a White Lightning load with 64ns of average thrust

So, use the following formula to find pounds of thrust:

NS thrust / 4.45 = Pounds of Thrust

64 / 4.45 = 14.38 lbs of thrust


Now, you want AT LEAST a 5 to 1 thrust ratio, especially on a newer model, so do the following:

14.38 lbs / 5 = 2.88 lbs

2.8 lbs is the HEAVIEST rocket you want to launch on a G64W

The weight (2.8 lbs) INCLUDES the weight of the Rocket WITH Motor

use this method for accurately calculating whether or not a motor is enough for any weight of rocket. Also follow these guidelines:

The calculations work well on a White Lightning Motor

For a Blue Thunder Motor, Less thrust could work, possibly 55-60ns, since the motor has much more thrust at ignition, then tapers off quickly

For a Black Jack Motor, use a motor that is AT LEAST 1 1/2 times the thrust of a White Lightning to be safe. For example, if you use a G64W, you would want AT LEAST a G96J for a Black Jack. This motor has a SLOW, gradually building thrust curve and, in order to get safe velocity off the pad, you need to increase the NS of the motor.

*****


If you want a ballpark figure whether a motor qualifies, Use the quick Field Method I use on the fly. Take your motor's Average Thrust and DIVIDE by 25!! It's a little rougher than the accurate formula listed above, but you can do it quickly in your head without a caculator and it provides a safe margin.

EG: G64W........64 / 25 = 2.56.........Your safe rocket weight with motor should not exceed 2.56 pounds; a ballpark compared to the accurate 2.88 with some extra fudge in there for safety!

Cya,

Carl Tulanko
TRA 08664 L2
NAR 79454 L2
Soon to be L3, I hope!

If it is a AT motor, they have the maximum lift off weight and thrust curves and everything else you would want to know on there web site.

Thanks guys,
That formula is pretty cool. Unfortunately I know that I could actually put a G64 in a 3.5 pound rocket (AT G-Force). So I am just looking for someone who has put a J350W in a big/ heavy rocket and findout the results. I know that it will lift an 11 pounder without trouble but I don't know if maybe I could go as high as 15lbs. The formula works for this at 15lbs but I would like to hear some confirmation of this.
Dave

My L2 rocket was made out of 8" quicktube, weighed ~15lbs, and flew great on a J350. Only the top foot of the tube is glassed. You can see it here:

https://www.rocketreviews.com/reviews/scratch/great_googly_moogly.html

Yes, With out a dought a J350 would lift this bird, but it will defently be low and slow. Personally I would think about going with the J420R or the J570w, to pick up the off the pad speed and get a little better altitude.

BTW, Welcome to the forum.

Tim

[email protected]

The flight was 'slow and low' compared to others, but that ain't necessarily bad. I got plenty of kudos as the whole flight was easily visible.

The J420R may give a bit more oomph off the line but the overall performance will not be better as it has less total impulse. At the time it wasn't available anyway. However, I do have one stashed for the spring

I picked the J350 over the J570 mainly because I was new to HPR when I built the rocket and bought the casing. In fact, I had not even flown my L1 flight when I began building my L2 rocket. Thus I was concerned over my building techniques and didn't want the higher impulse. In addition, my original estimates of the rocket's weight were WAY off...I didn't account properly for the epoxy, fiberglass, chute, etc. When i started, I even had delusions about flying it on 3 G-80's. Sill me.

The rocket has a 3" main tube to allow some options, so I am trying to decide whether to try it on a full J or a small K. Without added strengthening of the fins, I don't think I'd want to try it on anything bigger, even though the motor tube will allow it.

Alright, thanks guys. At least now I have enough confirmation of the design to go ahead with the "blue prints." Not to mention I now have an equation that I can use to estimate max liftoff weight, thanks. Since I am going ahead with the design, does anyone know where I can have custom CR's made to fit custom diameter tubes? I know PML cuts CR'S but I'm not sure if they do any nonstandard diameters. Also, anyone know where I can get a 38/720 Dr. casing cheap and a J350W reload?

Dave

Non-Standard tubes, eh!

It might be a good idea to look for someone who works with wood as a hobby and approach them with possibilty of making the components you'll need.

Then there's machine shops . . . But don't expect that they'll do it on the cheap.

I'd offer my services: but I'd need the tubes in my possession, as well as detailed drawings of the items you want produced. And aside from that, the geographical distance between us makes such a proposal impractical.

Good luck with your project.

Ardvark Rockets LLC made me a pair.....www.ardvarkrockets.com

That's great news.
Please let us know how construction progresses.

I have seen a J350 lift a 23lb rocket to about 650ft.
Lots-o-power there!

Very slow, Very low, but I never felt un-safe.

Good luck on your L2.

Todd

Thanks a lot guys. Looks like construction will begin as soon as christmas vacation. Finished "blueprints" and the design looks good; just have to run it through rocksim once more. The design is a stretched Army Patriot. Its about 20" longer than it should be. I am also considering upscaling the fins by 20% to increase stability and make it look a little more properly proportioned. I am confident that a J350W will lift this bird to a "safe" altitude. I will send in any photos or videos of construction and/or flights.
Thanks

Dave