What Would Happen if You Compressed a Model Rocket Engine?

Matt_The_RocketMan · Mar 22, 2019

Its a question i was think bout the other day, so what would actually happen? Would it crumble? would some magical ignition start to happen? or Nothing at all happens and the machine fails.... this concept if for both regular, composite, and large solid propellant engines....

Thanks for the info

midpower_madness · Mar 22, 2019

A team of testers ran these motors through bizzare and hazardous test situations. One test was to put a stress test Estes and AeroTech motors under 1 tonne of pressure. Nothing happened other than a broken motor. No ignition occured in any of the test samples.
APCP while extremely energetic is far more reliable than BP by factors.....

Rex R · Mar 22, 2019

I have seen a few videos on YT where various things were crushed by hydraulic press, a text book was interesting knowledge Is power

. try looking at the hydraulic press channel.
Rex

Matt_The_RocketMan · Mar 22, 2019

Rex R said:
I have seen a few videos on YT where various things were crushed by hydraulic press, a text book was interesting knowledge Is power . try looking at the hydraulic press channel.
Rex

thanks for that but i was just wondering if a composite/ or maybe larger motors higher than G class...

blackjack2564 · Mar 22, 2019

Large motors I have seen [M] coming in ballistic have auto ignited when front closure is forced into case causing extreme compression.
Yes it happens under certain conditions....looks like nuclear reaction complete with mushroom cloud.

solid_fuel · Mar 22, 2019

blackjack2564 said:
Large motors I have seen [M] coming in ballistic have auto ignited when front closure is forced into case causing extreme compression.
Yes it happens under certain conditions....looks like nuclear reaction complete with mushroom cloud.

How does that happen? An unlit motor coming in ballistic? Part of a cluster where not all motors lit?

Nytrunner · Mar 22, 2019

Methinks one of the conditions for this to occur is that you're flying "through the looking glass"

rharshberger · Mar 22, 2019

solid_fuel said:
How does that happen? An unlit motor coming in ballistic? Part of a cluster where not all motors lit?

Sustainer froma two stage project?

Matt_The_RocketMan · Mar 22, 2019

rharshberger said:
Sustainer froma two stage project?

no I was asking bout what would happen if you compressed a Engine higher than a G class

Andrew_ASC · Mar 22, 2019

Anything above Mach 0.3 is in compressible flow by advanced fluid dynamics theory. You need to define compressed better. I’m guessing by compress you mean crush it in a press. Jim is correct with his unique observation of a sustainer stage of a two stage project auto igniting. Fascinating observation, Jim.

Matt_The_RocketMan · Mar 22, 2019

Andrew_ASC said:
Anything above Mach 0.3 is in compressible flow by advanced fluid dynamics theory. You need to define compressed better. I’m guessing by compress you mean crush it in a press. Jim is correct with his unique observation of a sustainer stage of a two stage project auto igniting. Fascinating observation, Jim.

yeah thats what i meant , compressing high powered motors at pressures that would eventually cause explosions , ignition of some sort

Andrew_ASC · Mar 22, 2019

In the ballistic recovery mode the aerodynamic drag forces caused by pressure differences on the surface of the rocket are compressing the airframe structure with a severe flight load, the airframe when compressed may transmit this loading to the motor casing closure in Jim’s scenario. You can think of the Air exerting forces equal to a press if you wish.

midpower_madness · Mar 23, 2019

Yes, if AP is placed in a situation where it received significant shock - supersonic speeds - it could detonate. But simply through crushing I haven't seen it yet.

midpower_madness · Mar 23, 2019

Andrew_ASC said:
In the ballistic recovery mode the aerodynamic drag forces caused by pressure differences on the surface of the rocket are compressing the airframe structure with a severe flight load, the airframe when compressed may transmit this loading to the motor casing closure in Jim’s scenario. You can think of the Air exerting forces equal to a press if you wish.

Wow! That would be something to see.

Rex R · Mar 23, 2019

from a safe distance(100' or more)

Flyfalcons · Mar 23, 2019

Matt_The_RocketMan said:
no I was asking bout what would happen if you compressed a Engine higher than a G class

An M is generally considered to be larger than a G.

dhbarr · Mar 23, 2019

midpower_madness said:
Yes, if AP is placed in a situation where it received significant shock - supersonic speeds - it could detonate. But simply through crushing I haven't seen it yet.

[ citation needed ] Are you talking about loose powder or APCP grains? In either case, what do you propose the critical diameter to be?

midpower_madness · Apr 2, 2019

No idea. I just know that crushing an APCP fuel grain does not cause ignition at very velocities.

BDB · Apr 2, 2019

I have seen APCP detonate when it was on the receiving end of a supersonic shock wave caused by a C4 detonation. Short of that, it's stable and non-detonatable.

heada · Apr 2, 2019

dhbarr said:
[ citation needed ] Are you talking about loose powder or APCP grains? In either case, what do you propose the critical diameter to be?

Loose AP can and has detonated in the past which is why we have limits on AP particle size in formulations.

https://en.wikipedia.org/wiki/PEPCON_disaster

I'm not sure APCP has without being confined incorrectly (too small nozzle opening, etc.) or as Jim explained above. Even then, I think its more the vessel bursting due to over-pressure vs the APCP detonating.

dhbarr · Apr 2, 2019

Yes, I wasn't trying to contradict anybody; powdered oxidizers can be made to detonate, but once bound they can be made fairly stable.

Steve Shannon · Apr 2, 2019

dhbarr said:
Yes, I wasn't trying to contradict anybody; powdered oxidizers can be made to detonate, but once bound they can be made fairly stable.

One of the papers I found when looking for data that would support our court case a decade ago was an analysis done by NASA where they discussed the fact that they could not get the APCP used in the solid rocket boosters to detonate, which they wanted to be able to do in case a self destruct signal needed to be sent.

That’s not to say that a form of APCP cannot be designed which could be made to detonate, but the formula they wanted in the SRBs was difficult to destroy. I’ve looked and I no longer have that paper. Nor have I found it online. I don’t think it was needed or useful to the legal and technical team we had who actually worked on the case. I was just one of many who were probably sending unsolicited stuff.

TimothyG · Apr 3, 2019

Steve Shannon said:
One of the papers I found when looking for data that would support our court case a decade ago was an analysis done by NASA where they discussed the fact that they could not get the APCP used in the solid rocket boosters to detonate, which they wanted to be able to do in case a self destruct signal needed to be sent.

That’s not to say that a form of APCP cannot be designed which could be made to detonate, but the formula they wanted in the SRBs was difficult to destroy. I’ve looked and I no longer have that paper. Nor have I found it online. I don’t think it was needed or useful to the legal and technical team we had who actually worked on the case. I was just one of many who were probably sending unsolicited stuff.

From a university safety standpoint that paper would be wonderful to have when submitting requests. I’ve had a few teachers ask about propellant being an explosive and how we’d store it on campus. So far we’ve stored off campus for anything energetic but I’d prefer more oversight on our club motor storage not less.

Steve Shannon · Apr 3, 2019

TimothyG said:
From a university safety standpoint that paper would be wonderful to have when submitting requests. I’ve had a few teachers ask about propellant being an explosive and how we’d store it on campus. So far we’ve stored off campus for anything energetic but I’d prefer more oversight on our club motor storage not less.

Reference the lawsuit. If APCP could in any way have been classified as an explosive, ATF would have grasped it.

jadebox · Apr 5, 2019

Steve Shannon said:
....analysis done by NASA where they discussed the fact that they could not get the APCP used in the solid rocket boosters to detonate,

I suspect that it is mentioned that the propellent won't explode in descriptions of the SRB self-destruct system.

The system was designed to spit the motor case down most of its length causing a loss of pressure. The SRBs didn't explode during the Challenger accident when the main tank exploded or when the self-destruct opened up the motor cases.

blackjack2564 · Apr 5, 2019

solid_fuel said:
How does that happen? An unlit motor coming in ballistic? Part of a cluster where not all motors lit?

It was the unlit sustainer . 10ft deep crater only 2ft diameter, everything went up in air with mushroom cloud.
This was a totally freak situation where all the stars must align for it to happen.

All the black spots surrounding the hole for 30ft are where hunks of burning propellent spewed out of cloud ...scorching the playa
It was boosted by minimum diam. 98mm N-2800 to min diam. 75mm long burn something. Never separated whole thing came down in full stack. When we first found it, steam was wafting out hole like a volcano ...water table is only 2-3ft under playa.

Steve Shannon · Apr 5, 2019

blackjack2564 said:
It was the unlit sustainer . 10ft deep crater only 2ft diameter, everything went up in air with mushroom cloud.
This was a totally freak situation where all the stars must align for it to happen.

That makes sense to me, but it is nothing I know much about. The extreme compression of the air in the case could have superheated it, igniting the propellant. Because of the extremely high pressure in the case the propellant would have had a very high burn rate and likely suffered cracking or shattering and a significant increase in surface area exposure. It would be an interesting experiment to try to duplicate that set of circumstances.

midpower_madness · May 19, 2019

Powered AP is a different animal. There are various binary explosives that have used very specific NOx rich fuels to make something similar to Kinepak. VOD is said to be 9500 m/sec.

Matt_The_RocketMan · May 19, 2019

I would be most concerned about home made sugar rocket engines, potassium nitrate is super reactive

NateB · May 19, 2019

I have never made a sugar motor, but BP motors compressed with a hydraulic press perform better when pressed with higher pressures. Same thing applies to stronger oxidizes. I am sure there is a point of diminishing returns and possibly a point where too much pressure could be dangerous but I think the tooling would break before an ignition occured.

What Would Happen if You Compressed a Model Rocket Engine?

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