New member of the fleet and pics from the last HARA launch of the season...

So I finished the Skylance - it turned out AOK. Now to apply primer to the Centuri Sabre and move on to the next project - whatever that is.

Finished Skylance (Click to enlarge).

HARA held its last launch of the 2021-2022 flying season back on April 9. I had to pass because of work, but the skies were mostly clear and the temps comfortable. However, the wind sucked; 3 high power rockets (level 1 certification models) were hung high in the trees, and so far we only have been able to retrieve one. Make that most of one - a part of it is still hanging in the tree. 

Anyway, Patrick and others passed on some pictures for the launch album on the HARA FaceBook page and I thought I would share a few below. Next time I expect to fly is Memorial Day weekend - I am going to launch more than my usual 4 or 5, I think. Have to come out of this dry spell properly.

A Student Launch team watches the sky while waiting for RSO check
(Photo by Patrick Morrison - Click to enlarge).

Top of Patrick's umbrella rocket (Photo by
Doug Aguilar - Click to enlarge).

The backside of the umbrella rocket (Photo by
Doug Aguilar - Click to enlarge).

The umbrella rocket under power (Photo by Patrick Morrison - Click to enlarge).

R2D2 pops his top (Photo by Patrick
Morrison - Click to enlarge).

The 18mm motor inside an Estes Long Ranger
CATOs (Photo by Patrick Morrison - Click to enlarge).

Student Launch rocket heads skyward
(Photo by Patrick Morrison - Click to enlarge).

Nice shot of a mid-power Crayon rocket
(Photo by Patrick Morrison - Click to enlarge).

Flyer posing by his Level 3 cert rocket
(Photo by Vince huegele - Click to enlarge).

On its way to a successful Level 3 cert flight
(Photo by Patrick Morrison - Click to enlarge).

Level 1 rocket hanging in tree (Photo by Patrick Morrison - Click to enlarge).

Estes Olympus falling out of the sky (Photo by Patrick Morrison - Click to enlarge).

Sometimes Estes parachutes do work... (Photo by Patrick Morrison - Click to enlarge).

The Estes MaxTrax rocket...

Estes MaxTrax starter set (Click to enlarge).

I recently acquired an Estes MaxTrax starter set (now out of production). The MaxTrax was a ready-to-fly BT-56 based rocket featuring an "altitude tracking capsule" that separated from the rocket at ejection. Slowed by a small streamer, it would fall to the ground at a constant speed; impact would stop the internal timer - which was triggered by a spring loaded switch at ejection - and the capsule would display the altitude, which was simply time of fall multiplied by the speed.

A 1990's application of an old idea based on some simple physics - first proposed in mid-1970, as rocketeers searched for an easier way to get the altitudes of their birds without having to use theodolites, which were cumbersome and hard to maintain. Back in 1974, Stephen Fentress suggested that ping pong balls might be a good option, as they were standardized as far as size and weight. His data and calculations showed that a ping pong ball fell at about 28.5 feet per second, so timing the ball's fall and multiplying that number by 28.5 would produce the altitude in feet. The experiments for the RX-16 rocket in Centuri's Power System outfit also suggested using a ping pong ball to get the altitude, except that the manual rounded 28.5 to 30 feet per second (page 17). The MaxTrax was the latest rocket to use the concept, creating a capsule with an internal timer to eliminate the need to time the fall with a stop watch. It's also probably the last time this will be used in a commercial rocket - accurate, small and cheap electronic altimeters have eliminated the other methods used in rocketry for many decades. 

Note - I wrote a bit more detail about this in a blog post 8 years ago. It was intended to be the first of a two-parter, but me being me, I never wrote the second piece.

My MaxTrax (Click to enlarge).

The altitude capsule (Click to enlarge).

So what to do with the MaxTrax? It's pretty obvious - stick an altimeter in the rocket body and compare its altitude at ejection (which we shall take as the "truth") to the reading on the MaxTrax capsule. Easy, and it will produces some numbers to play with. I was stoked until I happened to glance at the MaxTrax reviews on the various forums, which revealed a very important reason why the Estes concept never really worked out.

The darn thing didn't work most of the time.

It all has to do with stopping the internal electronic timer, which is started when the capsule is ejected from the body. There is a "bounce switch" in the nose, which consists of a small spring that on impact with the ground is supposed to travel forward and complete a circuit, stopping the timer. One problem is that there is too much space between the spring and the metal contact, requiring a hard impact to stop the timer. The other is that the capsule is fairly light, so it can land on its side - the bounce switch requires a nose-on impact with the ground.

Estes acknowledged the problem in a note packaged with the rocket:

Click to enlarge.

This can't be good. Still, I'm going to give it a try at my next launch. Some have suggested removing the foam around the nose cone to help close the bounce switch, so I'll start with that. I guess I can afford to waste a few B6-4 motors.

Stay tuned...

This TARC season is over...

Girl Scout team poses with their rocket (Click to enlarge).

Another TARC season has passed - and once again, no team from the Huntsville area made it to the Finals up in Virginia. I have some thoughts on why this keeps happening, which I will share later. But first, let's consider the good things that came out of this year's TARC:

• We had 2 new Girl Scout teams, who went from totally inexperienced to making 3 qualification flights in just three months. This is quite an accomplishment, especially when you consider that one group of scouts had the best scores, beating even the John Paul II teams. One cannot help being impressed, and I sincerely hope that these young ladies will be back next year.
• All teams made qualification flights.
• All rockets flew straight, though we had a few problems with fins popping off. So often, in fact, that it became a running joke.

So one can be pleased that the teams crossed the finish line, which is indeed something to be happy about. We just didn't do well enough to place.

Redstone Composite Squadron team member poses
with the rocket (Click to enlarge).

Girl scouts prep their rocket (Click to enlarge). 

So what went wrong? The Huntsville teams can obviously build stable rockets that meet the competition goals, and they certainly put in the practice time - these are not the issues. The problem is not in the building and the flying. It's what comes after the flying, in the analysis of the data from the practice flights.  Therein lies the difference between making so-so qualification flights and qualification flights good enough to make the TARC top 100.

The local teams simply do not bother to analyze their flight data. There are no plots, no analysis of the altitude versus mass, no accounting for weather conditions - even though these numbers are recorded for each flight. The strategy used by the teams in recent years is based on luck, i.e., let's practice until we get a flight that has a low score, then attempt the qualification flights immediately afterward. They are essentially making random guesses until the rocket makes a good flight. The specs of that flight - mass, motor, ballast, etc. - are then duplicated for the qualification flights, even when the weather conditions have changed significantly. The outcome is predictable - lacking compensations for the wind and temperature, the qualification flights have scores in the 40's, 50's and 60's, even though the good flight had a score of 10 or less.

Girl scout rocket takes to the air (Click to enlarge).

JurassicTARC team member retrieves the rocket
(Click to enlarge).

But you can't compensate by guessing. You have to look at the practice flight data to get those numbers. Unfortunately, that requires the local teams to put forth an effort beyond what they are currently willing to do. So they trust to luck. And sooner or later, that strategy will pay off for someone. On a rare day, Fortune will smile upon a team who will string together two decent qualification flights, setting them on a path to the TARC Finals. But to win in Virginia, you have to fly to a different altitude on a different field, and even Fortune can't help against those odds. Placing in the top 10 requires that you understand how to adjust the rocket to meet a different goal.

John Paul II teams hard at work (Click to enlarge).

We are planning to hold a TARC workshop early in the coming season - maybe there will be a team that will listen and realize that looking at the flight data is just as important as designing the rocket. 

I keep hoping.