How much lift is too much?

[braddsn]

I have my lift dialed in perfectly (I think) with my 4" shells now. However, I have nothing to compare them to, because I have never been at ground zero watching 1.3g shells go up. They thunder when they leave the tubes, hit about 350 ft, and burst at apogee.. I am using 12% shell weight. But what would happen if a guy used 40%? Would the mortar give? Or would the shell flowerpot? I am only asking because I am curious. How would (or could) a guy ever know if he is using "too much" lift? Has anyone experimented with large amounts of lift just to see what would happen?

[nater]

The shell could flowerpot from too much lift. If the shell is strong enough, there is a point where no additional height will be gained. There is also a point where additional BP will simply burn and not contribute to any pressure gains.

 

Commercial 4" shells have a decent thump to them as they lift. Sound can be deceptive since the shell shape, mortar type, and weather all effect the sound waves.They are probably my favorite size for a commercial shell since they can come in a variety of effects at a good price. 4" and 5" shells make the bulk of the average body of a show as well.

[enanthate]

How long fuse are you using for your 4"?

 

I'm using 3,5 seconds, and it bursts at ~apogee everytime. Using 10-12% lift.

I think that 4" should have 4 seconds though, not quite sure. Correct me if I'm wrong. I imagine my 4" would be slowly (and barely) on it's way down after 4 seconds (if not perfectly at apogee).

 

Been suspecting that I could have more lift though, maybe I should try 15-17% to see? Might fire one today, so might try that. Don't fully trust my fiberglassmortar with reinforced bottom though, any inputs would be great.

[ddewees]

You'd be surprised what those mortars can handle...

 

I remember in my early days, using outrageous amounts of lift... with ground-shaking results. Not once have I ever destroyed a mortar from the lift alone. I've blown up plenty of mortars (and racks), but never from just the lift... no matter how much I've used.

 

 

It sounds like you're doing fine though... since you claim "and it bursts at ~apogee everytime". So unless you think apogee is too low for the shells you're using, not sure why you'd want to almost double your lift amount.

[enanthate]

Was thinking the apogee is a bit too low, yes. Don't really know for sure, got nothing to compare it to.

When I film a break, I'm looking straight up with my iPhone, and the stars fly outside of the image. Now I'm walking 2-300 meters back to get the whole thing on camera. I didn't think the break should be that big (close) ?

Not using booster. Still talking 4".

Have fired a 6" that visually appeared quite alot smaller than a 4", due to it's distance when breaking. Was standing within 50meters of the mortar. Haven't bothered me really, but would be nice to have a comparison to see whether it's actually breaking at the right altitude or not.

[gregh]

I think as long as the apogee is at least a safe minimum, anywhere from that point to the stratosphere is fine as long as you are happy with it. It's all about your personal preference. In reality, we are artists, and what we do is art. We ultimately create these for our own enjoyment and often other people get to enjoy the fruits of our labor too. Granted throughout history, many artists have worked for commission, but until somebody is paying me to make my 4" apogee at a certain height... I will break them where I want, and so should you. There is no right or wrong...