Fred's NARTREK Gold Journey

[Fred Garvin]

I've completed NARTREK Bronze:
60 Second Flight, Parachute Recovery, B motor max.
60 Second Flight, Streamer Recovery, B motor max.
2 Stage Flight
D motor or larger flight

I've completed NARTREK Silver:
Payload Flight
3 Motor Cluster Flight
30 Second Glide Recovery Flight, B motor max but try to do it on an A.
Scale Model Flight and Evaluation

Now I'm working on the final level: NARTREK Gold. Since I haven't seen any build threads on this, and search turns up only stuff from 2004 and 2006, I thought I'd do a Build Thread to document the journey and also maybe get some tips and help along the way. I have Rocksim and the following to use as reference:
Handbook of Model Rocketry, G Harry Stine
Model Rocket Design and Construction, Tim Van Milligan
Centuri TIR-33 Calculating Center of Pressure (supplied with NARTREK Gold packet)
Centuri TIR-30 Rocket Stability in Flight (referenced in NARTREK Gold packet)
Centuri TIR-100 Altitude Performance

The requirements for NARTREK Gold are to design, build, fly and mathematically predict performance and determine drag coefficient of a scratch built rocket.

1. Design your own model rocket. It may be a sport, contest or payload model. Compute the Center of Pressure (CP) using the Barrowman Method or calculate the CP using one of the available computer programs. Estimate the Center of Gravity of your model with the largest expected rocket motor installed. Evaluate the static stability of your model. Compute the predicted altitude of your design, assuming various drag coefficients (CD). You may do this using the Centuri Report TIR-100 or Estes TR-10 and TR-11, or you may use one of the commercially available or freeware programs available on the Internet.
2. Build and fly your rocket design. Determine the altitude to which it flies by using standard tracking system methods or by use of an on-board altimeter. You may also use a stop-watch and the drop-streamer method described in Handbook of Model Rocketry, Chapter 17, by G.Harry Stine. Make at least three (3) flights with each of at least two (2) types of motors and compute the average altitude achieved for each motor type. This is a minimum of at least six(6) flights. Using this data and your previous flight performance calculations, estimate the actual drag coefficient of your model. Record the flight information and the results of your calculations on the Flight summary Sheet that came with your Gold packet. Be sure to complete the comparison of predicted to actual performance.

I've got a design in mind and I've been working on draft sketches of it. My objective is to build a rocket that is very simple to model, reliably predictable, and uses best practice methods and "Rules of Thumb" for aerodynamic stability. I want to avoid anything crazy or clever in design. Just keep it simple, traditional and build a really great flier. After quite a bit of sketching, changing, and thinking, I've come up with a good design that is essentially an Astron Sprint with Nike Smoke Fins.

Once I finish a decent quality design drawing (not a freehand sketch), I'll post it in this thread along with my logic for each design element. I've got parts on order from FlisKits and RocketChutes, and I'll do a Rocksim on it to do all the stability and performance modeling. It's been 30+ years since I've had to do any advanced math, so attempting the calculations by hand is going to be hard for me....unless anyone is interested enough in this to maybe help out. After all, it doesn't say anywhere in the packet that you can't ask for help....quite the opposite really; they encourage it! I'll try to get my design drawing done, scanned and posted soon. Sunday is going to be a good day to stay inside....we're going from a high around 76 on Saturday, to 21 by Sunday morning! An Arctic front with a 50+ degree temperature drop in 12 hours. December in Texas. Shorts and tshirts one day, snowmobile suits the next.

 

[Forever_Metal]

op:op:op:op:op:op:op:

Oh yeah, this is gonna be great!

fm

 

[Nytrunner]

This is cool! I've read about it but haven't talked to someone thats pursued it seriously.

I've been debating whether I want to do Nartrek levels as I progress in HPR. Got behind already since I'm L1 now.

If you want to reduce reliance on Rocksim/OpenRocket, you could try using the Lever Law to calculate a) the shift in CG when adding an engine to the empty model, and b) how much weight to add at the nose to shift the CG into a stable position. I caught myself one day thinking "crap, I want to figure out what an H will do to my Leviathan refit's CG, but I don't have my laptop so I'm stuck........Wait a sec, I have an engineering degree...."

 

[Fred Garvin]

My reliance on Rocksim is directly proportional to my lack of mathematical ability.....

 

[NAR29996]

I got stuck on my Gold level when the kids were born. I'm not sure where the last 36 years have gone...

 

[Nytrunner]

Lever law is super simple. I'll pm you an example sometime soon.

 

[Micromeister]

I did my NARTREK Gold Level 24years ago. Shorty before Roc-sim and other consumer computer design/sim programs were on the market. That said: Doing the Cp -Cg calculations in lone hand wasn't that diffcult with Centuri or Estes Techincal reports TIR-30- Stability of Model Rockets (Centuri 1970's), TIR-33- Calculating Center of Pressure (Centuri-Jim Barrowman-1970's). and TIR-100- Altitude Prediction - Charts (Centuri-1970's). I have to say I truely treasure these pamphlets as pure Model Rocketry GOLD. If you can find copies of these booklets they are well worth whatever priece they demand.

My NARTREK Gold model is Model # 127 Goldie DX which is still in my flying fleet originally completed & flown on 08-13-1992. It is an awsume little flying machine. The Rocket is a BT-55 tapered Boattail to BT-50 model 17.375" long, recovery on 2" x 120" Orange crepepaper streamer. I don't have the hand drawings of this model scanned but still have them deep in my files. All the hand drawn calcualations were added to the drawings a copy of which was sent with photos of the model to NARTREK HQ at the time. Flying on D12-5 or D12-7 and C6-3 with adaptor it is just a joy to fly and recovery by streamer.

The gold level is a very worthwhile endeavor that ever Mod-Rocker should have a chance to attempt. For what it's worth; I believe doing the CP-CG and predicted altitude calculations by hand are also something everyone should do at least once or twice as it gives a much greater insight into what is actually taking place on the various parts of our models than the much quicker use of computer programs. I 'm No math wiz, but to this day I often forgo use of Roc-Sim and OR to do my CP-CG & predicted altitude calculations long hand as a brain exercise just for the fun. You'll be amazed at the difference in answers seen compared to either programs predicted altitudes which are almost always 8-10% or more to high.

For some reason I can't seem to upload photos to the forum currently. I'll try again later after contacting the mods.

 

[NAR29996]

I found 2 of the 3 on line. Not sure why they all aren't on the Estes Educator site.

https://www2.estesrockets.com/pdf/TIR-33_Center_of_Pressure.pdf
https://www.yumpu.com/en/document/view/47782668/tir-100-model-rocket-altitude-performance

 

[Fred Garvin]

Thanks for those links....I do have quite a few of them already:
Centuri TIR-24, 30, 33, 52, 100, 123
Estes Classic Collection (TR-1, 2, 3, 4, 5, 6, 7; TN-1, 3, 4, 6)
Estes TR-8, 10, 11
Tracked down all the PDF's online....studying Tim's book, Model Rocket Design and Construction. Tim's book is fantastic. If you don't have it, get it. Worth every penny!

 

[Fred Garvin]

You know, I have to be honest.....I've built so many kits, as most of us have, and could really just fab up a rocket from scratch and it'd fly fine. We all could. I kinda thought, going into this, that was pretty much what it would be.

But no! It's not....I could do it that way, sure....but once I started really working designs in Rocksim, and studying the chapters in the Handbook, static and dynamic stability in Tim's book....plus the TIR's....I'm looking at things I'd never known before....I've got 4 different sims now I'm playing with, all the same except the fins...and that's where it's at. My design uses a 5:1 Ogive that purposely trips the boundary layer at the shoulder to even out the laminar flow down the 18" BT-55 body. I've got a design with large trapezoidal fins, small trapezoidal, elliptical, and clipped deltas. 3 fins....4 fins....change sizes and positions.....what a difference the fins make! I change a little thing...the size say, and the CP moves and the flight sims change. Some changes make it worse, some better. Some look great but don't fly so well. They all fly fine of course, it's the little tweaking that makes one design fly 50' higher than another, makes one leave the rod at 31 mph, another at 37......one has a 2.9 caliber, another has 1.2.....and it's all in the fins and where they are.

I've honestly never considered such things....but now I look at all the kits in my fleet with a new eye....and an appreciation for wild designs like the Black Star Voyager. Anywhoo....I'll settle on something soon and post up my final design here, before I start building.

 

[Nytrunner]

Rocksim has boundary layer data? Dang, if only they'd fix the Mach+ simulations.......

You're absolutely right, you could totally build a rocket that flies fine just by eye. But when you want to optimize and push for performance, thats where you have to break out the numbers.

Looking forward to pictures!