Best rocket-stopping method

[Vanadium 50]

They run until empty.

You can, however, select how long they run when you buy them. This is one reason I advised the OP to fly a lot of rockets,

 

[Flyboy]

You generally have several options in a given “class” of motor to tune your performance.

Most of these motors are black powder derivative fuel grains that are pressed inside the cardboard body tube of the motor and use an end-burning design.

And the burn time is usually no more than 2-3 seconds even on the big motors. Tuning rocket apogee height will be much easier by adjusting the weight, not the motor.

 

[Rocket Maker]

Thank you for all of the suggestions.

@Rocket Maker you need to be a lot more forhcoming - peope are trying to help you and you're only willing to type terse, nearly information free answers.

I don't see how stopping a rocket in flight will help you reach altitude or duration goals. You should start by explaining that before moving on to the how.

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.

They run until empty.

You can, however, select how long they run when you buy them. This is one reason I advised the OP to fly a lot of rockets,

I have been flying Estes rocket kits so I have been using mostly C6-5s with the Riptide rocket kit.

 

[A.T.]

... must have sufficient inside diameter to hold an egg of up to 60mm length sideways ...

I wonder why the egg must be put in "sideways". It definitely doesn't help with keeping the center of mass on the axis.

 

[Vanadium 50]

It just says there needs to be space to hold it sideways. no?

Anyway, if you want less altitude, a sudden stop is bad for the egg. Better to use a smaller engine. One could also add weight.

So, what is the variation in height for "identical" launches? Seems you would want to know that.

 

[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.