Turbulence in the rocket world...

This month has seen a few significant rocket-related disturbances in the Force:

Dr. Zooch rockets is going out of business - Dr. Zooch has for many years produced a line of ant-scale kits of various historical rockets (and a few of his own designs). They are what we call "builder's kits" - no laser cut fins, no plastic parts. You are given the raw materials and a set of instructions - which are very sarcastic and funny, btw - which you must use to turn out a fairly nice flying replica of the original. I have built 2 of his kits, and have several in my kit stash awaiting my attention.  Dr. Zooch had been making a little money off his kits, but Wes Oleszewski has recently suffered from some health issues and decided to close up shop. A shame - I really liked his kits (and his books - he is also a pretty good author).

Good thing I grabbed one of the last ant-scale Falcon Heavies...

My Dr. Zooch Thor starts another flight (Click to enlarge).

The other big news concerns Estes. As you may have heard, the big E's parent company Hobbico had gone into bankruptcy and was placed on the auction block. Despite some reassurances from John Boren (the Estes chief designer) that Estes was a profitable part of Hobbico (other divisions were posting the big losses) and it would be sold intact, many rocketeers were worried about the fate of model rocketry should Estes be broken up or fall into the "wrong hands." The rumor mill is now alive with the news that the company has been bought - intact - by Estes Industries, LLC, owned by the Langford family. This is great news, as the Langfords are long-time rocketeers and staunch supporters of the hobby. Back in high school, I met John Langford at a summer science program, and was amazed by his rocketry knowledge and talents (He was working on a scale Athena model for the Internats). Later, I started a career with NASA, while he went on to found and head a very successful aerospace company (Aurora Flight Sciences), which was just sold to Boeing. The Langfords are good at business and very, very smart, so I expect great things to happen with Estes under their watch.

But they will take charge too late to save the E9 and C11 motors, unfortunately. I'm going to miss them, as the C11 was the only viable booster below D impulse for 3 stagers like the Comanche-3, and the E9 was noted for its unpredictability - you never knew whether the rocket was going to have a flawless flight or disappear in a fiery cato, with pieces flying everywhere. Those of you who have flown E9's know what I mean - that twist of the gut that happens as you start the countdown from 5. It will soon be a thing of the past, at least for BP motors.

Finally, 2018 marks the 60th anniversary of Estes; they have come up with a very nice logo to mark the occasion:

I think i'm going to have to put this on a Scout, an Alpha, or a Bertha - trying to decide which. I'm also wondering what will be a good 60th anniversary paint scheme.

Same thing, every year...

I thoroughly enjoy being a TARC mentor; working with the teams is great, and I am thrilled to be part of the whole experience that is Team America Rocketry Challenge. However, mixed in with the enormous amount of good, there is always a little bad - small annoying things that crop up every year, things you try to eradicate through workshops, coaching, and cajoling. But no matter how hard you try, they appear year after year, like great cosmological constants of the universe. Last minute qualification attempts are one of these, but the one I want to focus on in this post is especially vexing to me - the tendency of most TARC teams (and mentors) to not understand the limitations of the Open Rocket or Rocksim simulations.

Every year, I join the teams at Pegasus during their practices, and every year someone always complains that their rocket is not reaching the altitude predicted by the simulations, falling short by as much as a couple hundred feet. Such a huge mismatch must be due to some cause, and according to the team, it is usually a bad batch of motors or lots of drag on the rail, which everyone knows is not accounted for in the simulations. And nearly 100% of the time, the team is wrong - it ain't the motor, and it ain't the rail.

It's the sims - they put too much faith in the altitude predictions.

Open Rocket and Rocksim are fabulous tools, and they are absolutely the things to use in designing hobby rockets in this day and age. However, both programs make some simplifications and assumptions, with the net result that they almost always overestimate the altitude the rocket is capable of achieving on a specific motor. I can prove this with a specific example - my Geezer TARC entry for this year, the Eggsploder. Here is the altimeter profile of its flight from September of last year:

Eggsploder PNUT altimeter data (Click to enlarge).

You will note that the peak altitude is around 840 feet, 40 feet off the 800 foot goal (not bad for the first flight, eh?). This is the actual performance; now let's pull up the Open Rocket simulations:

Open Rocket simulations for Eggsploder (Click to enlarge).

Take a gander at simulation 15, which is an exact match to the weight of the rocket as flown under zero wind conditions. It predicts a peak altitude of  976 feet, 136 feet higher than that of the actual flight. Simulations 16 and 17 are for wind conditions of 5 and 10 miles per hour; even they are over 75 feet higher than actual.

So Open Rocket over predicts... What about the other guy on the block, Rocksim?

Rocksim simulations for Eggsploder (Click to enlarge).

Note the last simulation - 1000 feet! This is what Rocksim predicts if I let the program calculate the drag coefficient, which is the default when you create a rocket in the software. This is not too different from the Open Rocket results (~30 feet difference) and still way higher than the model actually flew. However, Rocksim allows you to manually adjust the drag coefficient (You can somewhat do this in Open Rocket by changing the roughness of the surfaces, but this is very crude). This enables you to match the sim to the altimeter readings, which is what I tried to do in the first two sims. Sim #1 is for a drag coefficient of 0.63, and simulation #2 is for a drag coefficient of 0.65; both these numbers are higher than the Rocksim determined drag coefficient.

Bottom line - If I choose a motor combination for Eggsploder that gives simulated altitude of 800 feet, I would be very unhappy with the performance, as the rocket would struggle to make it to 700 feet, well short of the goal. This is why, year after year, I always tell the teams to sim high - you can always add weight to bring the altitude lower, but it is very hard to raise the altitude without changing to a more powerful motor, which can mess with stability (bigger motor = more weight in back = less stable).

So I write this post, hoping that next year's teams will read it and pay attention. Maybe next year will be the year.

But I'm not going to get my hopes up...

Decals and wraps in Open Rocket

Centuri Payloader from 1962 catalog (Click to enlarge).

HARA has received an email from Levi's (the clothing company) looking to do a late 1950's/early 1960's period photo shoot involving model rocketry in Huntsville. So yesterday, I started inventorying my retro clones and noted that I had plenty from the 1970's, but very few from the earliest days of our hobby. This realization planted my carcass in front of my computer, where I began a search of the early catalogs on Ninfinger's site, looking for some models that could be quickly cloned. The 1962 Centuri Payloader - a shorter, skinny ancestor of the popular Payloader II - caught my eye; simple 3FNC with a clear plastic payload section and white decor with a black roll pattern. Easy peasy, and there was a Rocksim file for this model posted on the Rocket Reviews web site.

However, I did not like the fins in the Rocksim simulation - they seemed to have too great a span, so I went back to the catalog image and made a few measurements, assuming a ST-7 (0.759" diameter) and a rocket length in the vicinity of 15". I then created a simulation in Open Rocket, which looked to be a much better match to the catalog, and dashed off a quick order to eRockets for the parts. This ought to have made me happy, except that a plain white rocket in Open Rocket is, well, blah. So how do I get that roll pattern into the sim?

Past attempts at incorporating decals into Open Rocket had failed miserably, leaving me to think those that could were possessed of some great arcane knowledge not dispensed to ordinary mortals. But last night a Google search turned up this thread on The Rocketry Forum, the second post of which was like reading the Rosetta Stone. All you have to do is:

• Use a paint program (MS Paint, Pixelmator, etc.) to create an image wrap for the body tube. This wrap should have dimensions length x (pi x diameter), scaled by a suitable factor to permit easy drawing. In my case, the body tube was 10" long, so the clipboard should be at least 10 x (0.759 x pi) or 10 x 2.38. This is way too small, so I converted to centimeters and multiplied everything by 50, yielding an image size of 1270 x 303. This is usable, and soon I had it drawn up in Pixelmator (see below). Rotate it 90 degrees, save it to a JPG file, et Voila! You are done with the hardest part.

Centuri Payloader wrap in Pixelmator (Click to enlarge)

• Now open the simulation in Open Rocket, select the body tube and click on edit.  Choose the appropriate color for the body tube (white in my case) and then change the "Repeat" option to "Clamp Edge Pixels". Under Texture, select From File, find and select the image wrap file, then click OK. Switch the view in Open Rocket to 3D Finished and you should see your rocket's body tube nicely decorated with your wrap,

Finished Payloader design in Open Rocket (Click to enlarge).

There's more stuff in the thread dealing with fins, but this was enough to get me started. I am pretty pleased that my designs and sims now will be a lot less plain!

Centuri Payloader in Open Rocket's Photo Studio (Click to enlarge).

Back to NARCON...

This past weekend I was in Houston for the National Association of Rocketry's annual convention, NARCON. It's a two day affair, filled with talks, vendor exhibits, and over a hundred rocket geeks - the perfect venue for an old geezer rocketeer like me to hang out and take in this sport we call rocketry. James Duffy and the Texas sections (rocket clubs) hosting the event did an outstanding job organizing and running things, and I can safely say that everyone present thoroughly enjoyed themselves. NARCONs are held in cities that sport some sort of space-related attraction, and this year's convention was held at the Hilton across the street from Johnson Space Center and just down the road from Space Center Houston. This presented mucho opportunity for the participants to experience some space program history, and many did. Who can pass up a chance to see one of the majestic Saturn V's or to climb into the Shuttle carrier aircraft and into a mock Shuttle cockpit?

James Duffy gives tips on how to build a scale Little Joe from scratch (Click to enlarge).

So what was special about this year's NARCON? There were many good talks; Trip Barber gave a presentation with tips on how to win at TARC and there was an excellent status on the Museum of Flight's G. Harry Stine collection. However, there were three that stood out in my mind:

1) Joe Barnard of BPS.space thrilled the audience with how he developed his thrust vector stability kits for finless model rockets. It was kinda like watching the old Wild World of Sports - there was the idea, the agony of defeat (over and over) in the beginning, then finally the thrill of victory. Joe's stuff ain't safety code legal, but it is cool as the dickens and the audience was incredibly stoked by his presentation. Check out his website for some neat video and details.

Waiting for John Beans' talk to begin (Click to enlarge).

2) John Beans of Jolly Logic gave a presentation on what he calls "Rocket 2.0." He pointed out that we have been using pyrotechnic charges to recover hobby rockets for 60 years, and that deployment charges, while fairly reliable and of extremely low weight, still have a big issue - we use delay time as a proxy for deployment at a specific altitude. Mess up the delay time, or if the ejection charge doesn't work, and it's disaster time. John is musing upon a low energy notion in which a parachute section separates like a fairing, letting the parachute fall outside the rocket. This parachute is then allowed to open by a Chute Release-style device. He produced a 3D printed concept to illustrate his point. Mr. Beans is quite an innovator - his Chute Release has transformed mid power and lower impulse classes of high power - and I really look forward to see what comes out of his shop in the next year or two. Exciting times are ahead!

Folks start to gather for Gary Rosenfeld's "History of High Power Rocketry" talk (Click to enlarge).

3) Gary Rosenfeld of Aerotech regaled us with the history of high power rocketry, taking us from its beginnings with Irv Wait of Rocket Development Corporation (which was bought by Centuri and became their Enerjet line) up to the Aerotech fire, which gave room for Cesaroni to grab a share of the composite motor market. There were lots of pictures, and a lot of good ancedotes (I was amused by the name of an early HPR rocket - the "E-legal", and stunned by the images of the Aerotech facility after the fire). Gary was quite the rocketeer in his younger days - it takes a wild man to cluster composite motors - and was present for many of the events that shaped the development and adoption of high power. The hour went by all too quickly.

Part of the vendor room (Click to enlarge).

There were no big announcements at the vendor forum Friday night, other than Aerotech announcing its 18 mm composite A and B motors, which will be available in 2 packs this month. As usual, I could not keep my money in my wallet - I ended up purchasing a Mercury Redstone skin from John Pursley and an Odd'l Rockets F-104 kit from JonRocket. Only the lack of luggage space prevented me from buying more.

The traditional banquet was held on Saturday night, with the speaker being astronaut Scott Parazynski, veteran of 5 Space Shuttle missions with 47 hours spent outside on EVAs. He recounted his experiences of orbiting Earth, and of climbing Mt. Everest (twice - he succeeded on the 2nd attempt). It was a fascinating presentation, and each of us was lucky enough to receive a free copy of his book "The Sky Below"; Scott kindly took the time to autograph the books people brought to him -   a true gentlemen.

Sunday morning I packed my things and headed off to the airport - it had been a very good NARCON. Good talks, cool rocket stuff to buy and poke at, and lots of people to talk to. The latter is perhaps the best aspect of NARCON; it gives us a chance to link up with old friends from distant parts of the country and to meet new entrants in the hobby, filled with enthusiasm and excitement. A hobby for just one is not very exciting, and I was reminded that there is more to rocketry than TARC launches at Pegasus field. I came back with new goals and with new energy.

My signed 1970 Estes catalog (click to enlarge).

I also got Vern and Gleda Estes to sign my 1970 Estes catalog. It is now right up there with my Centuri catalog signed by Lee Piester. One of my bucket list items is now checked - I have the autographs of the Rocket Royalty.