EAC Viper Iris

The Viper: A '70s kit offered to Estes Aerospace Club (EAC) members. It uses smaller T motors. It is a good, economical flier with parachute recovery. The small 12-inch parachute is a good choice for this rocket, since it is limited to A-power only.




I wouldn't waste the time using 1/4A motors unless it's extremely windy or you have an extremely small field, the larger motors are so much more satisfying.  This rocket was later given my Iris* modification, which extends the body tube about 5 inches above the parachute bay, and allows for a payload with an altimeter to measure altitudes.

With its most powerful A-motor, I can’t seem to get this above the 200-foot mark.  This rocket has flown higher than the Cape Hatteras Lighthouse in NC, the tallest lighthouse in the USA.  (* Iris is named after the Greek god of the rainbow. She is a messenger of the gods, linking the gods with humanity.)



I learned to like this model imensely, it's simplicity, styling, and absolutely reliable flying in windy weather has won me over, and the motor costs are insignificant. Its light weight is very forgiving of faulty parachutes, and its limited altitude nearly ensures it will not get lost. The Viper has in many ways been my second 'Alpha' rocket.

SPECIFICATIONS

Series Number: 2
Number of Stages: 1
Stock Length: 13.75"
Diameter: 0.976"
Iris Payload Length: 4.5"
Modified Length: 18.25"
Payload Internal Length: 3.56"
Payload Internal Diameter: 0.95"
Payload Volume: 2.525 cubic inches
Number of Fins: 4+4 cannards
Fin Span: 4.976" diameter
Cannard Fin Span: 1.35" diameter
Stock Weight: 28 grams
Payload Section additional Weight: 7.5 grams
Total Empty Weight: 35.5 grams
Liftoff Weight Range: 48 - 50.3 grams
Motor Diameter: 13 mm
Motor Length: 45 mm
Motor Retention Method: Clip
Recovery: 10" Plastic Parachute
Recovery Protection: Wadding
Shock Cord Elastic Length: 14"
Shock Cord Mount: Paper
Altimeter Capable: Yes
Nosecone Material: Balsa Wood
Fin Material: Balsa Wood
Paint Used: Pactra Aero Gloss Dope
Launch Lug Size: 1/8"
Kit Brand: Estes
Completed: about 1975

FLIGHT LOGS

(Estimated about 12 flights on this rocket back in the 1970's)

2010, November 13: Tanguy Soccer Field, Light wind

A3-4T: Good Flight & Recovery.  200’ altitude is an estimate, there was no altimeter onboard.

2011, July 3: Indiantown Gap, Light wind

A3-4T: First test flight with altimeter payload. It was a perfect flight and recovery.  The altimeter came back with a reading of 183 feet.




2011, September 3: Indiantown Gap, Light wind

A3-4T: Good test flight and a perfect recovery. I launched it to see how winds were behaving a few hundred feet up before I sent up higher flights. Winds were a bit breezy and erratic, so C-engine flights were scrubbed for the day.  This flight measured 176 feet apogee.




2011, November 6: Penn Manor, Breezy

A3-4T: Good flight & Recovery. The breezy winds had little effect on the flight, went up fairly straight and true. Altimeter read 199 feet. This is a record high. It also reached 66 mph which was also a record. After apogee it descended 30 feet before the parachute ejected at 169 feet (delay was just 2/10 seconds slow), and came back at 7 mph. Duration was 19.7 seconds.

2011, November 25: Penn Manor, Moderate wind

A10-3T: Another good flight of the Estes EAC Viper with an Iris payload and an Altimeter 2 on board. Though I know the A3 motor is an excellent choice for this rocket, I tried an A10-3T motor this time. Just like the A3 motor, the wind didn't affect the flight much as it went straight up to 155 feet, about 30 feet less than an A3 would do. It reached a top speed of 52 mph (14 mph slower than an A3 would do) with a peak of 17.6G's (about 10Gs more than an A3 would do). Ejection was 0.8 seconds past apogee, at 140 feet, where it began its descent at 6 mph. Flight time was 20 seconds.

2012, February 5: Penn Manor, 5-10mph winds

A3-4T: Yet another sport flight for the Viper. It was cold and a bit windy. I didn't know if the chute would open in the 40-degree weather, but I didn't care since this is a small model. I knew this model will fly straight in windy conditions so I chose it for the first flight of this February day.


The A3-4T motor burned for a full second and accelerated the rocket at 7.1 Gs, averaging 2.8 Gs for the burn. It reached a speed of 61 mph and had an apogee of 179 feet. It then coasted for 1.3 seconds and fell to 148 feet before ejection, and descended with a partially deployed but somewhat inside-out parachute. It descended fast at 14 mph and landed 18.9 seconds later. Good flight!




2012, April 1: Penn Manor, 5-10mph winds, gusty

A10-3T: First flight of the day. Weather was cool, cloudy and a bit breezy. The Viper flies well in winds, but I chose the A10 over the A3 to get up quickly before the winds could affect the flight too much. The one-second burn accelerated the rocket rapidly straight up, with the highest recorded peak Gs for this rocket ever at 19.7 Gs. Average acceleration for the burn was 2.4Gs. It reached a speed of 51 mph and coasted for 2.2 seconds to an apogee of 146 feet.

After descending 22 feet in another 1.2 seconds the ejection charge fired to deploy the parachute, which was left inside-out on one shroud line, so it descended a bit fast although safely at 12 mph.  It landed after a duration of 11.3 seconds within a hundred feet or so. Good first test flight. As usual, the Estes A10 produced about 33 feet less in altitude and flew about 12 mph slower than the A3, because it has only about 90% total Ns power of the A3.

2012, June 30: Indiantown Gap, Erratic winds

A3-4T: Pulled this ol’ bird out because it’s a nice straight flyer in any kind of winds.  I even chose the A3 motor over the A10 - even though the A10 is better for winds - because I wanted to defy the winds again. It did not disappoint me. Mostly I wanted to compare the A3 and A10 motors for a third time.
It took off and went straight up, and was back down on the ground in 15 seconds or so and still within the launch area only maybe 20 feet from the pad. Typically on this motor it will go 60-65 mph and reach 185 feet, but the rather sensitive launch-detecting accelerometer was prematurely triggered while loading it on the pad, so I have no data on this flight. I could have repeated the flight, but it was late afternoon on a really hot day and I needed a rest after 8 flights. Some other time.

No, it did not explode. That's the ejection charge firing and releasing the parachute.

2012, Sept 1: Indiantown Gap, 12mph winds

A10-3T: The strong winds made me take out the Viper again, one of the best windy fliers I have. With the A10 motor’s impulse, it would be up before the wind could find out.  The parachute was still the original ‘70’s plastic, and was feeling a bit sticky and melty, so last-minute I replaced it with another 70’s era ‘chute in better condition.

This A10 burned for a measured 9/10th second. Acceleration peaked at 20.1 Gs, highest I ever recorded for this rocket.  The average Gs was also higher than ever recorded at 2.6 Gs. This was a powerful motor! It reached the fastest speed for an A10 motor too, at 53 mph.After that it coasted for 2.3 seconds, still going straight up, and hit an apogee of 148 feet.  It turned over after apogee and with a slightly long delay of 3.2 seconds it descended 10 feet in 9/10ths second.  The parachute deployed and it descended the final 138 feet at 10 mph, ending the flight in 13.3 seconds.  It landed only about 30 feet from the launch pad.  It was a satisfyingly successful flight.



A3-4T: This was another good opportunity to compare the A3 and A10 motors.  In general, the A10 is faster, but because of the higher drag forces at higher speed, doesn’t go as high – just like the theory goes.
This motor burned for 8/10ths second, peaking the acceleration at 10.6 Gs (half of the previous A10). The average G force was 3.6 (more than the previous A10).  This got the Viper going to 65 mph (12 mph faster).  By going slower for a longer time, it reached an apogee of 182 feet after a 2.8 second coast. As predicted, it was 34 feet higher than the “faster” A10.

The ejection was a tad early at 3.3 seconds, and during the last ½ second it fell 5 feet before ejection at 177 feet.  With the well-deployed parachute it came back at 8 mph and landed 18.5 seconds later within 40 feet from the launch pad. I almost caught it in the air one-handed but a last-minute wind shift just over my head made me look like an un-coordinated nerd.