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NARAM

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13 years 7 months ago #4319 by bobkrech
Replied by bobkrech on topic Re:NARAM
John

I simply can\'t believe >800 M on an E6. The the weight of the 2 eggs is 120 g and the motor is 48 g. I find it hard to believe the rocket would weigh less than 200 g. To get to 800 M on an E6 at that weight, the Cd has to be less than 0.2! To get to 889 M you need a Cd=0.15! Really?

Your previous 600 M flight on an E15, you present 440 M flight on an E9 and a possible 550 M flight on a C11/E9 are all believable.

I think the > 800 M altitude measurement needs to be looked at.

Bobj

jbuscaglia wrote:

billspad wrote:

jbuscaglia wrote:

To add insult to injury, our record was broken by nearly 250m.


Is that a typo or is it really almost 50% higher than your record?


No, it\'s not a typo, but it\'s only 42% higher. The Flying I-Beam Kids hit over 800m. I think that the actual number was 849m, but I\'m not certain. They used an Apogee E6. We had 421m on our second flight. They had over twice our altitude. Very sad.

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13 years 7 months ago #4320 by jbuscaglia
Replied by jbuscaglia on topic Re:NARAM
bobkrech wrote:

John

I simply can\'t believe >800 M on an E6. The the weight of the 2 eggs is 120 g and the motor is 48 g. I find it hard to believe the rocket would weigh less than 200 g. To get to 800 M on an E6 at that weight, the Cd has to be less than 0.2! To get to 889 M you need a Cd=0.15! Really?

Your previous 600 M flight on an E15, you present 440 M flight on an E9 and a possible 550 M flight on a C11/E9 are all believable.

I think the > 800 M altitude measurement needs to be looked at.

Bob


I didn\'t see their model, but high-performance egglofters do tend to have ridiculously low Cd\'s. The team in question are excellent modelers and they typically use a closed breach launcher which probably added a few percent more altitude, in a similar fashion as a piston launcher. Plus, it was in the thin air of Colorado. The last time NARAM is in Colorado, altitude records were falling left and right. I\'ve broken 900 meters with in E6 for single eggloft (at a regional in Indiana) in a model that wasn\'t all that special, so it doesn\'t completely shock me that they could get close with two eggs.

That said, there are places, especially over the baseline, where the altitude reduction equations will break down, so it\'s possible that they got a tracking anomaly. They had redundant trackers at each end of the baseline, so they would have computed 4 altitudes (one from each combination of trackers). I believe that they take the average of all the tracks with < 10% closure. Without seeing the raw angles, it\'d be tough to tell.

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