Greg’s YouTube channel showing attempts to make Estes motors fail:

Tubing that Greg used:

Tubing suggested by Ethan for motor mount tube:

Link from J for later use:

Estes motor brochure from Greg:

Estes motor thrust chart:

Motor mount link from Ethan:

Suitcase Rocket Motor Stand:

Ethan’s Chat Notes









Ethan Chew

10:33 PM

I agree with Greg.

There is only so much safety needed on this stand.

And pretty much just having the standard shield and tube is sufficient without needed probability failure rates.

I would say having a safety factor of at least equal to the commercial rating of the product is sufficient.

Needing probabilities would only be necessary if you are pushing the commercial limit.

Industry example;

For the pressure ratings of our piping and pressure vessels, we have our expected operating pressure equal to or less than the commercial rating.

If we intend to go above that commercial rating, we hydro test the pipes/vessels to twice what we are operating.

Test operations.

Cat failure.

The commercial rating is pretty high.

So if you stay within in, it can definitely take cat failure.

Here is a case in point on your situation with Project HALO.

We have blown up motors before.

But not in plug failure mode.

We first built a battleship heavy-wall cased motor as a test article.

That was a heavy steel pipe that had a commercial rating at 4 times the maximum normal operating chamber pressure.


10:34 PM

Ethan Chew

10:35 PM

During a plug type failure where a chunk of propellant broke off and plugged the nozzle, the nozzle was designed to blow out the back end.

Given that there was already a zone of exclusion around the back cone, that was sufficiently safe.

But the walls were able to hold the explosion.

Because we have a safety breakaway out the back nozzle.


10:36 PM

Ethan Chew

10:37 PM

The second time we blew up a motor was when we did a flight weight motor firing.

This used a thin-walled aluminum tube.

The failure occurred because the heat of the combustion weakened the motor case and caused it to rupture.

But that was with a safety factor of 1.5 standard.


10:37 PM

Ethan Chew

10:45 PM

Just a data point of exploding motor cases.

And good design practices that helped make them safe.


I recommend using tubing instead.

Those are an industry standard and have been pressure rated.

Check it out:

(P.S. Note on the alumiunm motor case failure. We had a shipping container between us and the motor for safety. It was able to deflect any debris from the burst).

What do you need?

Oh. It is listed everywhere.

What is the tube size you need? I assume this is for the motor case?

Oh, okay.

Recommendation, design for SF 4 to account for change of material strength due to increased temperature of burn.

Greg Moran joined group chat.

Ezri Clarke

10:48 PM

Greg Moran

10:48 PM

Greg Moran left group chat.

Ethan Chew

10:55 PM

If I may have an overview of the project, but your objective for Shepard is to test Estes motors for the purposes of Education and then future rocket motor development?


Is this why the design must be conservative due to its purpose?

Ah, okay.

I was thinking that if you were to first intend to fire with Commercial products such as Estes motors, you could do the test stand without the protections, just a simple hold-down.

The commercial case would be rated and approved for the use.

To me, having the SF 4 metal case would make sense for a development motor that had not been proven.

I would think if you are firing proven stock motors, the stand would be overdesigned.

Something such as what hold an estes motor to the flight rocket.

It is usually a simple bracket and cardboard or other material tube.


The most engineering you would need for a stock-fire setup would be to know the max thrust so that you can design the hold down appropriately.

Ezri Clarke

10:56 PM

Ethan Chew

10:56 PM

The exclusion zones would be to the back fire cone and front release path.

As well as the flank 10' sections (Estes standard).

Ethan Chew

11:00 PM

P.S. Recommended safety for the stock fire setup would be similar to the Suitcase Hybrid; 1/4" acrylic all-around flank and front shield.

Ezri Clarke invited people into the hangout.

Ethan Chew

11:05 PM

The apparatus that holds the rocket motor to the rocket.

What is provided by Estes.

Lemme get a pic.

I would recommend getting a thrust reading by mounting the green ring to a furniture drawer rail.

And having a strain gauge on the rail to get the thrust?



That was what we did in DBF.

(Ref a month ago on the propellor thrust test stand)

You invited people into the hangout.

Ethan Chew

11:14 PM


We had a simple metal block with a strain gauge attached.

Oh, if I may, I have found some photos and videos of Project HALO in case failure.

Usually as the movement is so little due to the static nature of the stand, friction does not have much play.

Project Halo Motor Test Setup (Hybrid motor with solid fuel grain and liquid nitrous feed):

Results of the motor case failure:

Battleship case motor with pressure tap:

I think this may download a video of the case failure:,r:6,s:50,i:252

But it gives an idea of the force involved (400 lbs thurst).

Ethan Chew

11:18 PM

You are welcome.