Hmmmm.... a “Trip-ping” point (pun intended) is that the duration is based on the time until first part of the rocket touches down. Judge could very well say that if the line is attached to the ground at launch and never departs the ground that your time for the event would be 40 minus zero, which would be a big penalty. So you are going to have to have either a chute or streamer that LEAVES the ground, activates your deployment sequence at the 800 foot altitude, and gets retracted or otherwise lifted into the air, and does not touch the ground for the 40 seconds. Starts to get a little Rube Goldberg-ish. Still fun to think about.
Taking advantage of the loopholes in the rules,
streamer on the ground, 780 feet of cord, only the first 5 or 10 feet need to be flame proof. Rest is just strong enough not to break when rocket hits 780 feet.
Single stage rocket, with “Dart” configuration (unpowered Upper section, which can contain nearly the entire rocket, including the fins and motor casing, but does NOT contain the altimeter, which is in a pod that gets released by a trip device when the 800 foot tether length is reached. Maybe put a chute or more likely a streamer on this, so when deployed, it basically goes maybe 20 feet to get to 800 feet.
Two sections attached by another elastic shock cord plus say 100 feet of Kevlar thread, long enough to allow a safe deceleration of the egg payload compartment (which is now dragging the streamer), strong enough to support the weight off the altimeter pod, 780 feet of cord, and streamer and streamer drag.
Launch rocket.
At 780 feet the string, still attached to the Dart, trips something that separates the motor AND altimeter pod. This segment is unstable (or has a VERY strong shroud line chute) and almost immediately stops. This is your altimeter reading. Yes, the rest of the rocket is still ascending, in reality the apogee maybe 850 to 900 feet depending on length of “daisy chained” shock cord, but you are scored on the ALTIMETER reading. So if you can figure a way to deploy your altimeter at 800 feet AND keep it attached to the rest of the rocket, you have hopefully nailed altitude assuming a vertical rocket launch.
Okay, so we have deployed the altimeter pod at 780 feet, assume inertia combined with chute or streamer gets you to 800 feet.
I attached the ground streamer to the Dart. Why? Because if HAVE TO GET THE STREAMER OFF THE GROUND AND UP INTO THE AIR, otherwise if it it never leaves the ground it counts as the first part of the airframe to touch down, so time is zero. Dart keeps going up, slowing but taking the streamer up off the ground with it, I am hoping to get another 50 -100 feet, as I think a thick streamer with NO Weight attached will likely take about 30 seconds or more to drift to the ground (remember, START time is when rocket starts its first motion, NOT when last part leaves the ground. So the LATER it leaves the ground, and the longer it floats, the less likely the streamer or string is going to be the first touch down part.)
(Another loophole in the rules about first part to touch the GROUND or TREE, put the STREAMER AND STRING on the side of PAD. This doesn’t count as the “ground” or a “tree.” You still need to get it into the air, otherwise your dangling string will be the first part of the rocket to touch the ground. But the judge CAN’T legitimately say that it was touching down from the moment of launch and give you a 40-zero penalty.)
Okay, now for the DOWN part (timing). Your altimeter pod section Also deploys a parachute with a weight and a string say 400 feet long (I am thinking the main body of the rocket is gonna deploy pretty soon and start descending so you won’t need 800 feet.). This can be a very lightweight string.
You can predict to about 1 second the time from launch to deployment, and within say 40 feet of the altitude. Using experience you should be able to come pretty close to appropriately sizing your parachute to hit your target impact time. The beauty of it is you can use a larger chute for your payload for a gentler landing of your egg, since it can land many seconds later.
In an attempt to “un-hijack” your thread, Oscar, we need more information on your rules, which sound much less restrictive than TARC. If the rules are, who can get closest to 240 foot reading on an Alpha with an onboard altimeter, I am thinking if you build the altimeter into a side pod released by a 240 foot string (and attached with an eyelet hook so it slides down the string) and there are no rules regarding attaching the string to the ground, it could be done safely.
YAMV (Your Altitude May Vary.)
