Is this variance in these D12-3s a problem?

Hi all,

While going through my motors, I noticed that all three of my D12-3s have different "heights" of the clay cap. Is this anything to be concerned about or is it just normal motor variance? The top and rightmost motor are from the same package whereas the leftmost one, with the lowest cap, is not.

That is interesting.

For something like this, it's best to contact Estes directly. It may help them if you supplied the lot number and measured the heights of the clay caps to the end of the motor.

Greg

Definitely contact Estes, all my D12-3s have the clay cap right to the top of the casing.

Most interesting! I'll definitely contact Estes and see what they say. Thanks all!

Hmmm... it's not unheard of, but I'd be interested in hearing what they have to say...

Some batches of powder are "stronger" than others (thus requiring less powder to give a specific amount of impulse) and of course some may be pressed harder (hence denser) than others. Also, the clay nozzle and cap is pressed (rammed by a hydraulic tamper) when the motor is "pressed" and some motors end up with thicker caps (especially) than others...

I've had motors come back where the cap was SO thick that only a little pie-shaped fragment of them blew out-- the remainder of the clay cap was still intact in the upper end of the motor! I've also had a molten bit of clay (inclusion) ejected from a burning rocket motor, bounce off the blast deflector, and land on the aluminum bleacher I was sitting on and roll under my thigh, burning a hole through my shorts and my leg as big around and deep as a pencil eraser (and was still molten and bouncing around white hot on the aluminum bleacher like a drop of water dripped into a red-hot skillet after I jumped up with a yelp!). This was a result (most likely) of a bit of clay used to make the nozzle ending up mixed in with the BP when it was pressed into the solid slug that makes up the motor propellant grain...

Such things are RARE, but they DO HAPPEN! (though having one landing under your butt and burning a hole it is a million-to-one shot!)

Later! OL JR

Over the years, I've noticed this is many of my 24mm estes motors.

All (most?) of mine have a slight lip between the top of the cap, and the case, so that I can just barely seat an 18mm motor into the hole.

Nate

There is nothing at all uncommon about this. Look at any large sample of identical motor types, like C6-3, C6-5, C6-7, or the D12 motors. You will also notice that the nozzle may be slightly different distances from the end of the casing, so that can also affect the upper end.

Weigh them using a small digital scale, such as the scales you can get super cheap at harbor Freight that will weigh in .2 gram increments. If you see a large difference in weight, that can be slightly different amounts of propellant. Look at many of the NAR S&T data sheets for the weights and measured performance of various motors. There is variation.

Heck, look at the 29mm Estes motors on the hooks at Hobby Lobby - I have seen some with the nozzle not only flush with the end of the casing, but some have the nozzle actually protruding from the bottom of the casing. They worked perfectly.

MichaelRapp said:

Hi all,

While going through my motors, I noticed that all three of my D12-3s have different "heights" of the clay cap. Is this anything to be concerned about or is it just normal motor variance? The top and rightmost motor are from the same package whereas the leftmost one, with the lowest cap, is not.

View attachment 247312

Click to expand...