I'm sure you've answered this 1000 times but...

I've used engines that were stored correctly, that were 30 years old and they performed like new ones.

Randy

That's not necessarily a positive endorsement, you know...

David Erbas-White

True!

As most of us know, it mainly depends on how they have been stored. If you don't know for certain, then it's a gamble. I'd suggest trying one with a rocket you don't mind losing to see how it goes, before you cluster or stage one you really don't want to lose.

Randy

So...what is the "shelf life" of estes motors?

What, exactly (or even roughly), constitutes too much temperature cycling?

I store my engines in my garage. It is not heavily insulated, but 'somewhat' insulated. Since I live in southern California, not far from the coast, it only gets as low as the 40's in the winter (generally), and up to 100 in the summer (but not that hot in the garage). The temperature changes are relatively long (i.e., there is no 'rapid' cycling).

I (unfortunately) don't launch that often, so I don't have much data to determine if this is good/bad/indifferent to the engines, though I CAN say that I've never had a CATO (knock wood).

I don't want to store the engines in the house, not due to 'concerns' about them due to flammability or anything, but simply because of storage space issues.

Can anyone comment on this?

David Erbas-White

What, exactly (or even roughly), constitutes too much temperature cycling?

I store my engines in my garage. It is not heavily insulated, but 'somewhat' insulated. Since I live in southern California, not far from the coast, it only gets as low as the 40's in the winter (generally), and up to 100 in the summer (but not that hot in the garage). The temperature changes are relatively long (i.e., there is no 'rapid' cycling).

I don't want to store the engines in the house, not due to 'concerns' about them due to flammability or anything, but simply because of storage space issues.

Here is my cut & pasted standard response (no time limit for the temperature cycle time):

Here is why temperature cycling can cause Catastrophic failures (CATOs). The nozzle, propellant and the casing all expand and contract at different rates. Since the motors are so small, this is only a problem if the temperature that the motor "sees" swings between wide extremes. When this happens, we see several effects:

1) The propellant and the clay nozzle develop a crack at their interface. This actually results in *Lower* peak pressure and peak thrust because the motor can begin the end-burning earlier than it should (never forming the "big dome" of burning surface area that we should get at normal peak thrust).

2) The casing and the propellant can de-bond. They aren't really bonded in a "glue" sense, but the mechanical bond is weakened from the stretching and contraction. (For wet rammed motors, there may be a tiny glue-like "bonding", but the cycling will break that bond). The flame can propagate along the entire inside of the casing and propellant interface and result in a huge overpressure. This leads to a casing split (if the delay is still "grabbing" the casing tightly) or a "blow through" which is like a Roman Candle.

The two of these can combine to form different CATO scenarios:

a) Blow through at ignition or just after ignition (on the pad/rod). Clearly a sign of a nozzle/propellant interface crack allowing the flame front to reach the debonded casing to propellant interface at or just after ignition.

b) CATO above the pad (like 50 feet up). Clearly there was no crack along the propellant/nozzle interface and the flame front had to wait until it naturally reached the casing wall and then propagate up the de-bonded propellant/casing interface.

A final scenario is the cracked propellant grain. These can go BLAM (or KA-PLOW) quite spectacularly since they really overpressurize the casing big-time and can happen with a perfect casing to propellant bond. A defective tool used to form the centerbore of the propellant can cause these. The C5-3 had such a problem when a tool was mis-manufactured. I believe the root cause was a lack of radius on the tip, which formed a sharp edge, which led to cracking. Motors also could be cracked if any contaminant got on the tool or in the propellant during ramming, but dropping or rattling will not cause a crack!

As for the temperature cycling - avoid firing a motor at a temperature 75 degrees F lower than the highest temperature it has ever seen. If fired while too cold, the propellant will be contracted away from the casing and it will probably fail. Folks launching in cold weather can do so if they store their motors in their warn car or in their toasty parka inside pockets. (Is that an F100 in your pocket or are you just happy to see me?)

Why would a normally stable rocket fly unstable when using a motor that it flew stable with before?

Did you look at the nozzle? We have had several VERY scary "flights" where the rocket had little thrust and/or veered into cruise missile mode. After crashing and putting out the brush fire, we examine the nozzle and find that it is either too wide (wider than normal at the throat) or it is eroded asymmetrically. The asymmetric erosion is bad and you can clearly see the exhaust residue all over the missing area of the nozzle indicating that it disappeared at ignition or shortly thereafter.

All unstable flights with Estes motors from years "A" and "B" and maybe "C" need to be inspected and if the motor/nozzle is the cause, a M.E.S.S. form filled out and the manufacturer notified. The least that will happen is a package of replacement motors and a kit. The most that will happen is an improvement in materials used in manufacturing and a product that performs like we remember for decades and decades.

I hope this info helps folks.

-Fred Shecter NAR 20117

-- ""Remove "zorch" from address (2 places) to reply.

This should be in the FAQ.

This should be in the FAQ.

I knew you would say that and I almost added it to my sig for this post.....

hee, hee.

-- ""Remove "zorch" from address (2 places) to reply.

Thanks for the advice. I (unfortunately) do store many of them 'loose' in a tackle box, but have many others in a large Rubbermaid type box (and the ones in that box are still in their Estes/Aerotech packages.

Desiccant packages are a great idea, but where does one buy those?

BTW, when I say 'near' the coast, I'm 10 miles inland, and humidity is really not much of a problem (especially compared to the South...)

David Erbas-White

With all these tagged FAQ posts, someday we should actually make a FAQ with them. We ought to be up to a significant fraction of a gigabyte by now :)

Jerry

I have about a billion of them from AP drums :)

Just put the motors in Ziploc bags as a primary precaution.

Should I list them for sale on my website?

My response did not cover humidity. Humidity soak or cycling did not increase failure rates, BUT it did affect performance. A D12 would become a D7 (lower thrust for longer time) and the delay time could increase 2 or 3 fold. i.e. a D12-5 would become a D7-10 or D7-15.

This was in the days of good clay. If you had humidity soaked poopy-clay nozzle motors, the nozzles would undoubtedly erode a huge amount reducing thrust and total impulse.

-Fred Shecter NAR 20117

-- ""Remove "zorch" from address (2 places) to reply.

Your forgot to say:

This should be in the FAQ.

become a D7-10 or

R&D project ? create D7-10s and D5-15s using a humidifier ?

time the reciepe needed for each type of "evoluted" motor. would that be motor tampering , naw, it wold be motor evolution.

I'm trying to be funny not troll.

art

seriously, this would be very useful. In particular, making a contest certified A3-4t behave like an A3-6t or A2-6t.

Alan

I've flown motors over 30 years old that worked perfectly. Maybe even better than the current stuff. As long as they were never exposed to high temperature or humidity, they should be fine.

It's one of those stupiditys of the "system" that I've got 5 year old motors that are no longer certified, but 34 year old motors that are. All made by the same manufacturer.

Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD" >>> To reply, remove the TRABoD!

The critical parameter seems to be the difference between the maximum temperature that the motor has ever been exposed to and the internal temperature at ignition. I that is greater than about 70 degrees, you are very likely going to have a CATO.

If you've got some suspect motors, and all were stored together, test out a few, either static test, or in models you don't care about. Flying saucer type rockets make good motor test vehicles. Odds are that either most will fail, or none will fail.

There was one R&D project where they deliberately temperature cycled motor to induce failure. Then the motors were rewarmed back to their original peak temperature, and fired while still warm. They performed like normal motors. Do if you've got motors you think were baked, rebake them and fire while warm. As an R&D project of course :-)

Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD" >>> To reply, remove the TRABoD!

Suggestion: if you wnat to tag a post for the FAQ, rather than repost a 135 line message, and add one line saying "this should be in the FAQ" which results in other reading the whole post looking for your non content; instead repost the message with [FOR THE FAQ] or just [FAQ] appended to the subject. It's easier to search subjects for "FAQ]" than to search the whole message body.

Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD" >>> To reply, remove the TRABoD!