Best rocket-stopping method

[Flyboy]

For flights on the same day, I think the biggest driver in different apogees will probably be the motors. They’re cheap and simple, but there’s going to be some minor variation. Shouldn’t be too much of a difference in apogee, though. Bit of a wild-ass guess, but at that height and weight of the rocket… +/-10-15 feet, tops? Not sure if production batches are labeled, but getting motors from the same batch would be my suggestion for matching performance.

That said, differences in temperature, humidity, altitude, and wind will absolutely make changes to the rocket performance and will need to be accounted for.

 

[mfb]

The altitude goal is we lose one point for every foot we go over 790 feet, so this is why I am asking and for the time limit the faster we can start going back down the better because we have to up and down within 44 seconds.

Quick comparison:
* Accelerate quickly to 70 m/s, then be in free fall to reach 241 m: 7 seconds
* Accelerate quickly to 100 m/s, then be in free fall to reach 241 m: 2.8 seconds but you reach that altitude at 70 m/s that you now need to cancel.
(neglecting drag in both cases here)

There isn't much time you can save on ascent. Deploying a parachute while still ascending could give you better control over the altitude, however.

 

[Vanadium 50]

For flights on the same day, I think the biggest driver in different apogees will probably be the motors.

The point is not for us to lecture him. The point is for him to get out there measuring sruff so he can see what influences what and by how much.

 

[Vanadium 50]

Honestly, there is a simple solution. You want the rocket on the ground sooner? Open the chute later,

Obviously, there are limits.

 

[boneh3ad]

It sure seems like stopping in midair is a lot harder (more complex, less reliable) than selecting the right size engine for the mass of your rocket.

The hard part of that is knowing what the thrust profile of model rocket engines is, but I bet someone has measured that.

 

[Vanadium 50]

The hard part of that is knowing what the thrust profile of model rocket engines is,

The manufacturer has a sheet.

 

[Rocket Maker]

Thank you for all of the suggestions I will be talking with my team and looking through the thrust profiles of different rockets.

 

[boneh3ad]

The manufacturer has a sheet.

Sure, but how repeatable is it? And at what level of detail?

 

[erobz]

Sure, but how repeatable is it? And at what level of detail?

It looks like they do get fairly detailed in the specs.

 

[boneh3ad]

View attachment 353248

It looks like they do get fairly detailed in the specs.

Yeah, that's pretty nice. I wonder if they would give you the actual data so you could use it in a numerical model. If so, you could get a pretty decently accurate estimate of altitude based on a pretty simple $\sum F = ma$ model that incorporates thrust and drag in real time. Just tweak the overall mass until you get the height you want. The issue would be repeatability of the motor, i.e., what's the uncertainty band on those curves?

 

[Vanadium 50]

Sure, but how repeatable is it?

Which is why I friggin' asked him. Lordy.