Idea, but ...

[banjonate]

So I am a casual model rocketeer, definitely a LPR guy (LPR is cheaper per launch, easier to build, and go just as high even if they are harder to see!), but I have built a few bigger scratches lately and flown on D, and really like the idea of building bigger stuff (basically because the kids think it's more impressive).

I also am liking shaping my own balsa nose cones, which opens up the possibility of using ANY tube, either made myself or already existing, rather than just standard-size tubes. Which brings up...

I have an idea for a couple 2" mailing tubes ($1.99 at Meijer for a 24" tube). I have a 29mm scratch build that uses 18mm engines (it is two stage) that I would like to upscale. Problem is, F-15 Estes motors are awful heavy and not very punchy (this is all me looking at charts; I have never flown anything on more than D's!); the model I simmed had a velocity off the rod of about 12 m/s; I like myself some slow liftoffs, but that seems like it's pushing it.

I know that, as far as black powder motors go, the E12 is actually the highest initial thrust you can get (more than the E16). But, I also know that keeping acceleration down is key to achieving majesty, so...

Assuming I want to do a two-stage, what do you think about:

a) Using a longer-burning (with no delay) booster stage parallel with a couple of shorter-burning plugged or standard motors to help the first stage along, or

b) Reversing that, and using a shorter-burning standard (or composite?) engine with a delay as the booster with longer-burning parallel motors?

This is just in the "thinking about it" stage and definitely experimental (for me). So any feedback is appreciated.

 

[neil_w]

Two quick thoughts:

So I am a casual model rocketeer, definitely a LPR guy (LPR is cheaper per launch, easier to build, and go just as high even if they are harder to see!),

I'm also an LPR guy (with occasional MPR dabblings), for different reasons. Just to be clear, they most definitely do *not* go as high.

b) Reversing that, and using a shorter-burning standard (or composite?) engine with a delay as the booster with longer-burning parallel motors?

You cannot use a motor with a delay and ejection charge to start the sustainer. You must use either (a) a proper 0-delay BP booster motor to directly start a BP sustainer, or (b) use a plugged booster motor and do an electronically-controlled air start of the sustainer.

 

[Nytrunner]

a) Using a longer-burning (with no delay) booster stage parallel with a couple of shorter-burning plugged or standard motors to help the first stage along, or

This sounds like a good bet. Have an E16-0 (or E12-0) central with a couple D12's or C6's clustered with it.
*Note: This will make more aft end weight, so you have to carefully manage the CG-CP of the full stack, while making sure you have enough exit speed for stable flight

 

[banjonate]

The more I think about it, the more I like the idea of the E12-0 with 3 or 4 A10s around it, with a F15 in the sustainer (assuming it all fits).
What’s the word on the synchronized ignition of those vastly different sized motors? I can see this as the A10s being ignited much easier and leaving the pad before the E (or D or C?) motor does.

 

[Nytrunner]

BP motors should light near simultaneously. They don't have core volumes to pressurize like Composite motors

 

[dhbarr]

2x e9, CHADstaged from d12-0's

 

[jqavins]

[T]he model I simmed had a velocity off the rod of about 12 m/s; I like myself some slow liftoffs, but that seems like it's pushing it.

That's way beyond pushing it. That's already pushed it into the mud at the bottom of a ditch.

Make sure that the ignition system has enough oomph for a three motor cluster. If you're launching with club equipment that shouldn't be a problem. For launching on your own it's very doable, but you need to check.

Your idea gave me an idea. The E12 has a burn time of 2.4 seconds. The A10's time is 0.9 seconds, and it comes with a 3 second delay. It might work to have the sustainer light at 2.4 seconds, then parachutes pop out of the side boosters at 3.9 seconds. Depending on the height and speed at the moment of staging, 3.9 seconds may be too late to do any good. If it does work out then it would be really cool, imo.