Saturday, January 28, 2017

Cold and windy...

Jurassic TARC readies Stripes for launch (click to enlarge).
Duane and I linked up with the Jurassic TARC team around 11 this morning - it was a chilly day, with temps in the low 40's, made even colder by a sustained 10 mile per hour wind out of the west-southwest. However, young people are quite hardy, and Jurassic TARC was determined to get in about 6 practice flights despite the cold.  I hate cold, so I watched them ready their "Stripes" rocket from my chair next to Duane's SUV, which I used to shield my carcass from the wind. In about 40 minutes, the bird was prepped and loaded on the pad, eager to blast off on its Aerotech E15 motor.

Turns out that the E15 was a bit too much - Stripes shot off the pad to over 960 feet, and the stiff wind carried the rocket very quickly to the east, outside the bounds of Pegasus field. The payload section containing the egg and altimeter was recovered; unfortunately, the lighter sustainer stayed aloft on its parachute for quite a bit longer, drifting beyond the line of trees on the east boundary of the field across the road. After a long search, it was given up for lost, and Jurassic TARC decided not to risk "Stars", their second rocket. Temporarily defeated by the wind, they decided to call it a day. The Falcon Rocketeers began arriving as Jurassic TARC was packing up; upon hearing the fate of Stripes' bottom, they too decided to waive off on their practice flights.

But the day's flying was not done. While Jurassic TARC was out searching for Stripes, I did the final prep on my Centuri RX-16 clone, which was the only rocket I brought to the field. It was "fully instrumented" - HD keychain camera strapped to the side, with the tiny Micropeak logging altimeter and Jolly Logic Altimeter Two loaded into the payload bay. This was a fair amount of weight, and I figured the C6-3 motor would not loft the model very high, which I regarded as a good thing given the wind. My expectation proved right - the RX-16 lumbered off the pad, straining to get some altitude. The parachute deployed just fine, and the model landed on the grass about 30 yards from the pad.

Other rockets would take to the air. One of the TARC team captains launched a naked Alpha on an A8-3, and Marc launched the "Alpha 5" - a rechristened Estes Make-It-Take-It - a couple of times on the same motor type. Allen put up his gold Crossfire, an Estes Amazon (the one with the "snake skin" finish due to crazed clear coat), and his Patriot with its unique decor. The most spectacular flight was made by his Mercury Redstone, which was loaded with an Estes altimeter and powered by a Quest C6-3. It did a little dance in the air and arced right into the ground; I felt great sympathy for Allen as he dug pieces of the escape tower out of the soft earth.

Allen's Crossfire leaves the pad (Click to enlarge).Allen readies his Mercury Redstone (Click to enlarge).

Marc and son hook up the Alpha 5 (Click to enlarge).The Alpha 5 streaks upward (Click to enlarge).

The Amazon lifts off (Click to enlarge).Allen's Patriot starts up the rod (Click to enlarge).

After a couple of hours, the wind-enhanced chill was getting a bit much, so we packed up and headed to our homes. Back in my warm apartment, I downloaded the data from the Micropeak and compared it to the results from the Altimeter Two. Looking at the table below, you will notice that the peak altitude, max speed, and time to apogee (boost + coast) are in pretty good agreement. However, the accelerations differ by quite a bit  - I am inclined to believe the Micro Peak values, as 7+ g's max acceleration is a bit hard to swallow given the relatively slow liftoff of the RX-16. I attribute these discrepancies to the algorithms used to calculate the acceleration from the altimeter data.

Altimeter data comparison (Click to enlarge).
The difference in descent rate and total flight time bothered me the most. However, a study of the plot of the Micropeak data has provided reasonable explanations. It clearly shows that the descent rate is not constant, starting out around -18 feet per second and slowing to around -12 feet per second at landing. There is a fair amount of fluctuation, so perhaps the difference in algorithms produced the different values. The shorter flight time reported by the Micropeak can be partially explained by the fact that landing is reported as having occurred at -4 feet. It appears that the Micropeak set zero altitude to correspond with the blast deflector on my tripod launcher, which is about 3 feet off the ground; it reported the total time to return to this level, which is higher than the actual ground. The Altimeter Two seems to calculate differently, as its time corresponds to actual contact with the grass. At 12 feet per second, it will take 0.33 seconds to fall the additional 4 feet - close enough to the reported difference.

Micropeak altimeter data for RX-16 flight (Click to enlarge).
With my rocket and data fixes satisfied for the day, I now am ready to watch the science-fi B movies on Svengoolie tonight.


  1. Hi Bill,
    Great launch report.
    Regarding the Quest C6 engines, I've seen the same thing happen at our local launches. If the Quest C6 is in a BT-20 or 50 minimum diameter model, things are fine. But in a BT-60 sized model it'll be on the ground before the ejection charge goes. The engines are long burn with not a strong enough sustaining thrust. I've seen two Dr. Zooch models nose in with the Quest C6. I do use a lot of Quest B6-4s. While they are sooty those seem to slightly outperform the Estes B6.

  2. Note that AltimeterTwo has a 3-axis accelerometer in it, and the MicroPeak's app is calculating everything from the altitude samples and the deltas between them. I don't know (or don't recall) what the sample rate is for AltimeterTwo. Also, the peak acceleration may happen at ejection. I see a pretty good spike in the data in your MicroPeak plot.....

    Benard Cawley