If you had to choose one - Ejection, before or after optimal delay?

[bjphoenix]

If the rocket goes vertical, isn't the velocity the same at 1 second before or 1 second after?
If the rocket weathercocks you probably want sooner rather than later so the rocket isn't as far from the pad, and there is less chance that the rocket will be too close to the ground.

 

[Tom Flint]

With low power rockets I prefer too long a delay and an ejection past apogee. High power rockets tend to die if they are allowed to go much past apogee and start pointing straight down, and they often are flown in suboptimal wind conditions where they do not follow a nominal (vertical) trajectory, which most sims for delay time do not take into account. Therefore for high powered rockets I'd prefer to deploy a bit early.

 

[Steve Shannon]

If the rocket goes vertical, isn't the velocity the same at 1 second before or 1 second after?
If the rocket weathercocks you probably want sooner rather than later so the rocket isn't as far from the pad, and there is less chance that the rocket will be too close to the ground.

Even if not vertical the (vertical) velocity is the same one second before vs one second after. But, it takes time to eject the parachute and it takes time for the parachute to unfurl. During that time, what’s happening? If you chose to eject before apogee, the rocket is slowing down. If you chose to eject afterwards, the rocket is gaining speed.

 

[jmasterj]

You really don't need to 3D print a washer. Most gift cards are 1/32" thick, you can pretty easily cut one out of that.

There's no reason to not try to get closer to the optimal time, but as many have said, there can be relatively large discrepancies from the target time.

 

[waltr]

You really don't need to 3D print a washer. Most gift cards are 1/32" thick, you can pretty easily cut one out of that.

There's no reason to not try to get closer to the optimal time, but as many have said, there can be relatively large discrepancies from the target time.

There are many materials that are 1/32" thick. I made some 1sec delay washers from G10 epoxy-fiberglass and some from polystyrene. Both work.

I do drill to a 1second time but have had many delays off by more than 1sec.
As has been said in above posts--- Electronics is the most reliable to eject at apogee.

 

[Bill S]

I've always opted for the 'slightly early' since you can reasonably predict the orientation of the rocket (pointing up or not quite pointing down yet) and slowing down when the nose pops. That way the laundry is sent into a path that is clear of rocket parts and will aid in slowing the rocket down if it hasn't already.

With the 'slightly late' option, the rocket is often pointed down enough that you risk the body of the rocket falling through the deploying laundry and while the whole assembly is post-apogee and gaining speed toward the ground. Too risky for me, and I've seen more than a few go through just this very thing and end up with tangled recovery gear.

I've tried slightly early (.25 to .5 second), and nearly every time, the nosecone has hit and damaged the fins. When I go with slightly after apogee (up to about a second), I don't see nosecones damaging the fins anywhere near as much. Once in a while I'll see a tangled up parachute, but it isn't very often. Your mileage may vary of course.

 

[overklock]

I've tried slightly early (.25 to .5 second), and nearly every time, the nosecone has hit and damaged the fins. When I go with slightly after apogee (up to about a second), I don't see nosecones damaging the fins anywhere near as much. Once in a while I'll see a tangled up parachute, but it isn't very often. Your mileage may vary of course.

This is my thought as well. Deploying in a pre-apogee position also means you're working against both the force of gravity, as well as wind resistance.

 

[Banzai88]

This is my thought as well. Deploying in a pre-apogee position also means you're working against both the force of gravity, as well as wind resistance.

Velocity is velocity, air resistance is air resistance, UP or DOWN. The difference is EARLY you're pointed up and you're slowing down (and thus experiencing reducing wind resistance), LATE you're usually pointed down and you're speeding up (and thus experiencing increasing wind resistance).

Gravity is gravity, the force of the ejection should, in a properly designed and pressurized system, be ejecting the nose cone with sufficient force to drag the recovery gear out with it. In any case you're gonna have that whole 'equal and opposite reaction' thing going for you as well.....in the air, both pieces are separating away from each other to some extent.

If things are snapping back and hitting fins, that's a function of too short or too elastic (or both) of a recovery harness material.

 

[RocketTree]

If you are looking for 9 seconds, and the drilling tool has options to achieve 8 & 10 sec... Drill it down to 10 seconds. Then set the drilling tool to the next step (8 seconds) and drill out half of that remaining step (1/32"). That should give you 9 seconds, plus normal allowable variance.

 

[dhbarr]

Velocity is velocity, air resistance is air resistance, UP or DOWN. The difference is EARLY you're pointed up and you're slowing down (and thus experiencing reducing wind resistance), LATE you're usually pointed down and you're speeding up (and thus experiencing increasing wind resistance).

Gravity is gravity, the force of the ejection should, in a properly designed and pressurized system, be ejecting the nose cone with sufficient force to drag the recovery gear out with it. In any case you're gonna have that whole 'equal and opposite reaction' thing going for you as well.....in the air, both pieces are separating away from each other to some extent.

If things are snapping back and hitting fins, that's a function of too short or too elastic (or both) of a recovery harness material.

It may also matter if most of the mass is above or below the break.

 

[4regt4]

You really don't need to 3D print a washer. Most gift cards are 1/32" thick, you can pretty easily cut one out of that.

There's no reason to not try to get closer to the optimal time, but as many have said, there can be relatively large discrepancies from the target time.

I just folded some ordinary printer paper enough times so that my calipers said it was 0.031" thick. Cut it into a square, punched a hole in the middle with a paper punch. I didn't try to overthink it.

Hans.

 

[Joekeyo]

I take all simulation programs as being just a guideline, not gospel. I'd rather have the rocket pointing down so that the nose cone is pointing down as if it will be easy to naturally fall off.

Simulation programs as guidelines as well as the delay times - printed, drilled, or otherwise. Lots of variance to hold down to get a consistent ejection on top.

 

[SDramstad]

On the way up both gravity and wind resistance are slowing the rocket. On the way down only gravity is accelerating the rocket and wind resistance is slowing it down. so 1 second before apogee you are going faster then you are 1 second after apogee. I prefer slightly long delays.

 

[overklock]

On the way up both gravity and wind resistance are slowing the rocket. On the way down only gravity is accelerating the rocket and wind resistance is slowing it down. so 1 second before apogee you are going faster then you are 1 second after apogee. I prefer slightly long delays.

Well thought out and said

 

[neil_w]

On the way up both gravity and wind resistance are slowing the rocket. On the way down only gravity is accelerating the rocket and wind resistance is slowing it down. so 1 second before apogee you are going faster then you are 1 second after apogee. I prefer slightly long delays.

I would posit that the effect of drag at the low velocities right around apogee is pretty small. It may be true that velocity 1 second before apogee is *slightly* higher than 1 second after, but that would be secondary to the other differences between before and after.

 

[SDramstad]

I would posit that the effect of drag at the low velocities right around apogee is pretty small. It may be true that velocity 1 second before apogee is *slightly* higher than 1 second after, but that would be secondary to the other differences between before and after.

Yup, at one second the difference is minimal. At 2 to 3 seconds not so much.