Wednesday, June 28, 2017

It fell, daddy!

"It fell, daddy" - These words were the comment made by a little girl after witnessing a very heavy model of a Blue Origin (I think) spacecraft arc right into the the ground at Southern Thunder. It was an all too common occurrence during the two days of the launch, and is becoming increasingly more frequent at every launch. Rocketeers - inexperienced and veteran - are forgetting a very basic rule of rocket flight...

Weight is everything

Consider this YouTube video:

Obviously underpowered, eh? If you look at the video description, you will find that the motor used in this flight was an Aerotech E23-8T; E impulse is not even on the Leviathan list of recommended motors (F26-6FJ, F50-6T, G40-7W, G80-7T). If the flyers had done a little math or simulation beforehand, they would have realized that the max altitude on this motor - assuming the rocket weighed 17.5 ounces as stated on the kit art - was only 300 or so feet, with a coast time of 3 seconds. The 8 second delay they used was waaaaay too long; no wonder the rocket plowed into the ground.

The moral of this story? Stick to the recommended motors unless you are prepared to do some sims or math - after weighing the built and finished rocket, of course. Unless you are these folks, who used trial and error to arrive at the right motor (yes, I am being sarcastic):

A simple glance at the kit instructions would have told them that an A motor was not on the recommended motor list for the Amazon; the lowest usable impulse was B. But I suppose they had to find out for themselves. Fortunately, the Estes Amazon is a hardy beast, or its first flight would have been its last.

However, the Blue Origin model I mentioned at the beginning of the post wasn't a kit, so there is no list of recommended motors. So what do you do with scratch builds? Well, we have wonderful computer programs like Open Rocket and RockSim that you can use to fairly accurately estimate the performance of these rockets, enabling one to choose the right motor/delay combination. To be fair, there are some model types - like saucers - that these codes can't handle, forcing a bit of internet searching to discover the motor types used in similar models that have been flown by others. After you weigh the rocket, of course - the simulations are no good unless you have a weight match. This is especially true of those who tend to overbuild - all that epoxy and stuff can add considerable weight to the model, which isn't automatically factored into the simulation programs.

At a launch, I like to use an iOS app called Rocket Calculator, which does all sorts of nifty rocket math, including estimating altitude, coast time, and thrust-to-weight ratio. The numbers it produces are usually within 10-20% of those of Open Rocket or RockSim, making it an excellent tool for deciding proper motor/delay combinations.

Rocket Calculator main menu
(Click to enlarge)
Rocket Calculator Altitude
Prediction (Click to enlarge).
I know that some may think I am being a bit of a curmudgeon (or "tightass", "stick-in-the-mud", etc., etc.). However, our hobby survives because rocketeers fly their models safely; rockets arcing into the ground ain't safe. Fly smart - stick to recommended motors or use the results of valid simulations/calculations.

I am now leaving the soapbox.

Tuesday, June 27, 2017

I survived Southern Thunder 2017


Just a few minutes after arrival, I slipped in the very muddy ground along the tent line and created a big new mud puddle when my huge carcass hit the ground. Fortunately, my pride was the only thing to suffer damage - if you discount the fact that I went through Saturday covered in mud like a sewer worker. Nonetheless, I soldiered on and managed to enjoy Southern Thunder 2017 very much, especially on Sunday when I stayed a good deal cleaner.

Lining up at the RSO tent for pre-flight checks (Click to enlarge).
For those of you who don't know, Southern Thunder is the big annual launch for the Music City Missile Club (MC2) and my club HARA. Traditionally held in June, this year we were joined by a new co-host, the SoAR (Southern Area Rocketry) club out of north Georgia. This is a good thing, as SOAR brings to the event some very experienced folks and some nice launch equipment to augment MC2 and HARA's already awesome capabilities. The Birmingham Rocket Boys also came north and joined in on the fun by conducting a night launch on Saturday night. I haven't seen the official numbers for Sunday, but there were about 227 flights on Saturday, which is lower than in past Southern Thunders. The cause was obvious - a smaller attendance, no doubt caused by the monsoon rains that blew through the area Thursday and Friday, creating the treacherous quagmire that led to my fall. The weather was so bad that I was doubtful it would improve by launch day, and I am sure many potential attendees were put off by the iffy forecast. Their loss, because those of us at ST2017 had a great time flying rockets with all sorts of motors, from 1/4 A all the way up to M's.

Looking south from the middle of the tent line (Click to enlarge).
My Estes Orange Crush on the pad (Click to enlarge).
I flew 7 rockets during the two day launch - not great, but hey, at least I got a few birds in the air. Here's the list:
  • Estes Orange Crush on a C11-5 (Saturday)
  • Estes Mammoth on an Estes F15-6 (Saturday)
  • Aerotech Initiator on a G74-9W (Sunday)
  • Downscale Enerjet 2250 clone on 3xB6-4 (Sunday)
  • MPC Pioneer 1 on a Quest A6-4 (Sunday)
  • Estes Marauder clone on a B4-4 (Sunday)
  • Estes Alpha on an A8-3 (Sunday)
All flights went well, with soft landings in the drier parts of the field. I got some ribbing from members of my club about the Mammoth and Initiator flights, which were considered to be a significant deviation from my norm. I guess they are right - I rarely fly anything with more impulse than an E, even in Geezer TARC. The Initiator flight was my favorite; I love the fire and sound of the brilliant Aerotech White Lightning motors, and the G really put the rocket way up there.

My Enerjet downscale awaits its turn (Click to enlarge).Racking up mod rocs (Click to enlarge).
Allen accompanied me and Duane to the field, and his modified Madcow Patriot put in a very nice flight on an H motor. I gave him considerable grief about sticking a G118 into an Estes Ventris, which I figured would shred the rocket, but it held together nicely, with the electronics in the modified payload section executing a perfect dual deploy. I also enjoyed the flight of his finless induction rocket, which flew (mostly) straight on an C6 motor - to the amazement of the onlookers.

Allen's induction rocket on the pad (Click to enlarge).And in the air (Click to enlarge).
And Duane? He flew nothing - nada, zilch, bumpkus. Perhaps I shouldn't criticize, because he may have been the smartest of our trio. With no prepping and waiting in lines, he was completely free to watch the flights, some of which were rather spectacular in a NASCAR fashion. I was oblivious to quite a bit of the action while doing flight preps. Lots of things go on at a Southern Thunder, with the launches, raffles, and special events. Blink and you can easily miss something quite neat.

Southern Thunder 2017 sponsors - there were lots of goodies given away! (Click to enlarge).

Monday, June 12, 2017

Motivated by the written word...

The monotony of all the flying done during my spring work travel season has been broken by reading Wes Oleszewski's "Growing Up with Spaceflight" series. Wes - aka the infamous Dr. Zooch of scale rocket fame - spins pretty good yarns about growing up with the space program, starting with a wee lad watching Mercury shots and progressing on through Gemini, Apollo, and the Shuttle. I have just finished reading "Project Apollo Part 1", and I had to laugh when at the end of the book Wes describes getting into model rocketry. Consider this short excerpt:

"A few months earlier I had gotten an MPC "Pioneer One" model rocket for my 13th birthday. Of course just flying it and watching it come down on its parachute was something for regular kids and not for the insane spaceflight lunatic who lived at 3324 Lexington Drive. No indeed - I had to heavily modify it and add stuff that would certainly get me thrown out of the National Association of Rocketry - had I been a member. Today I had assembled a kludge the likes of which was so dangerous that it was a miracle that Vern Estes himself did not come to my house and slap me up-side my head; it was perfect."

Wouldn't be fair to Wes to go further; if you want to know what the kludge involving the Pioneer One was, buy the book - it's only a few bucks on Amazon, and there is a lot of great stuff on the early Apollo missions presented in a fun, leisurely manner. However, I think you can guess that things did not go well. Most of the "spaceflight lunatics" who grew up in the 60's did stupid stuff with rockets - my ill-considered schemes were so crazy bad that I dare not speak of them with current rocketeers, lest I be called accursed and cast from their company. So I admire Wes for putting some of his exploits in print. As for me, I'm gonna keep quiet.

MPC Pioneer 1 (Click to enlarge).
MPC ad showing the Moon-Go at right (Click to enlarge).
As a kid, I also owned a few MPC kits, and liked them very much - they looked cool and had plastic fin units and detail parts. These passed into oblivion decades ago, but I have managed to gather a few for the kit stash, including a Moon-Go, which was one of my favorites. Anyway, the book's description of the Pioneer One incident reminded me of my past model, and I realized that I have enough original MPC parts in the bins to build one. And, so this weekend, I started work on a Pioneer One - it goes together quickly and I should have it finished and painted by Southern Thunder, where it shall make an appearance, involving "just flying and coming down on its parachute."

Old rocketeers have no desire to tempt the fates - we cannot dodge quickly anymore.

Note: There is a short history of MPC rockets and some catalog images posted here, should you have the interest. Wes' first rocket was a Flare Patriot, btw.