What's to stop someone from flying a 6-grain motor one grain at a time?

[LiftoffLumberjack]

I just noticed that I can buy one 29mm 1-grain Cesaroni propellent kit for $30.98, or one 29mm 6-grain Cesaroni propellent kit for $60.65 ($10.10/grain).

What's to stop someone (me) from splitting up the 6-grains and flying each one individually in a 1-grain motor case?

I realize I'd have to buy an ignitor and all the other ancillary parts separately, but there seems to be enough margin for it to make financial sense.

Is there any reason why I couldn't do that?

 

[Steve Shannon]

I just noticed that I can buy one 29mm 1-grain Cesaroni propellent kit for $30.98, or one 29mm 6-grain Cesaroni propellent kit for $60.65 ($10.10/grain).

What's to stop someone (me) from splitting up the 6-grains and flying each one individually in a 1-grain motor case?

I realize I'd have to buy an ignitor and all the other ancillary parts separately, but there seems to be enough margin for it to make financial sense.

Is there any reason why I couldn't do that?

Well, having six motors that don’t work well probably doesn’t really make a lot of financial sense.

You could do what you’re suggesting if you knew how to design a rocket motor, had access to all the other motor parts, and had a place that would let you fly it as a Research motor. And as far as I know Cesaroni doesn’t sell its liners, forward closures, and nozzles separately.

 

[K'Tesh]

Once you use the nozzle, wouldn't that ruin it for subsequent flights? Then there's the pressure the nozzle is supposed to focus... Too little, and I'd be worried of it just chuffing, or providing too little thrust for the rocket, and it failing to have a safe flight, or at least one where you could reuse the equipment.

 

[prfesser]

Well, having six motors that don’t work well probably doesn’t really make a lot of financial sense.

You could do what you’re suggesting if you knew how to design a rocket motor, had access to all the other motor parts, and had a place that would let you fly it as a Research motor. And as far as I know Cesaroni doesn’t sell its liners, forward closures, and nozzles separately.

The nozzle is sized specifically for six grains. A single grain with that nozzle will simply chuff, if it ignites at all. Need a different nozzle; and since phenolic erodes with each use you'd need a new nozzle for each flight.

Even if CTI did sell the parts separately...prices would probably be similar to those at RCS. $3 for a 29mm nozzle, $6 for a liner tube, plus o-rings and the like. And a delay grain. Probably fifteen bucks of consumables per flight.

And as Steve says, it would be classed as a research motor.

 

[Maxwelljets]

I just noticed that I can buy one 29mm 1-grain Cesaroni propellent kit for $30.98, or one 29mm 6-grain Cesaroni propellent kit for $60.65 ($10.10/grain).

What's to stop someone (me) from splitting up the 6-grains and flying each one individually in a 1-grain motor case?

I realize I'd have to buy an ignitor and all the other ancillary parts separately, but there seems to be enough margin for it to make financial sense.

Is there any reason why I couldn't do that?

A 6 grain reload kit isn't just a bag of 6 propellant grains that they hand you. It also contains a nozzle (single use, sized for 6 grains), a forward closure (single use), and a liner (sized to fit 6 grains plus the couple inches of overlap needed to work with the nozzle and closure- it's not possible to chop into sixths and have something work).

To make this work, you'd need to purchase several 1 grain liners (not sure how many you can actually get out of a 6g liner), 6 properly sized nozzles (the correct throat size will be much smaller than the 6 grain compatible nozzle it came with), and 5 new forward closures. CTI doesn't even sell these spare parts on the open market, but even if they did it's quite clear that it would not be financially worth it.

I grabbed price data from Wildman for 29mm classic motors and graphed the price vs the number of grains:

From this, we can tell that the price of the forward closure, nozzle, and bits of liner that are longer than the propellant is about $21.

 

[Banzai88]

Let's not even mention the fact that not every 6g motor is 6 propellent grains of the same core diameter as it's 1g cousin! Start altering critical things like that without understanding burn characteristics and you can quickly change a certified rocket motor into a road flare or a bomb!

Nope, not gonna do it. And if YOU are, I'm standing behind your car when you light that thing!

 

[LiftoffLumberjack]

Cool. Thanks for the responses everyone. It seemed like it could work, but I figured if it did, everyone would probably already be doing it. So thanks for confirming my suspicions, I think I'll just stick to flying them as intended.

 

[tsmith1315]

Great question, @LiftoffLumberjack!

Welcome to the forum!

 

[Ez2cDave]

And as far as I know Cesaroni doesn’t sell its liners, forward closures, and nozzles separately.

AEROTECH does . . . https://www.rocketmotorparts.com

As for the nozzle throat size issue, a skilled person could machine an adapter, inserted from above, to reduce the throat size. Depending on the material chosen, it could be reusable. A spacer or two and virtually any hardware could be used.

 

[smstachwick]

This is what I love about the forum; outside-the-box thinking, intelligent discussion, conclusion. I learned something from it.

 

[Ez2cDave]

This is what I love about the forum; outside-the-box thinking, intelligent discussion, conclusion. I learned something from it.

My signature - "Adapt & Overcome . . . Failure is not an option !"