Aerotech Washer Purpose?

[Bruce]

For DMS motors, I found that Aerotech gives you this small washer that you are supposed to put in the ejection charge well before dumping in the black powder.

Does anyone know the purpose of this washer?

Won't the ejection charge be ignited by the delay column even without the washer being in place?

 

[prfesser]

The AT motors I've assembled have a rubber washer with a hole in the middle. It goes in the delay-grain recess before sliding delay grain, insulator, o-ring in place, and it helps prevent any flame from reaching the BP until the delay element has burned completely. Is that what you're talking about?

 

[Antares JS]

The AT motors I've assembled have a rubber washer with a hole in the middle. It goes in the delay-grain recess before sliding delay grain, insulator, o-ring in place, and it helps prevent any flame from reaching the BP until the delay element has burned completely. Is that what you're talking about?

No, he's referring to the little metal washer you put under the ejection charge in a DMS motor. Following because I'm curious too.

 

[bibbster]

Without the washer the motor ejection won't pressurize correctly which will prevent the chute, and possibly anything else forward of that, from ejecting.

 

[Antares JS]

Without the washer the motor ejection won't pressurize correctly which will prevent the chute, and possibly anything else forward of that, from ejecting.

Is the concern that the bottom of the ejection well would collapse and send a bunch of the pressure into the burned-out motor case?

 

[bibbster]

Is the concern that the bottom of the ejection well would collapse and send a bunch of the pressure into the burned-out motor case?

That is my understanding. Because the hole is the washer is smaller, it prevents that.

 

[Dan Griffing]

For DMS motors, I found that Aerotech gives you this small washer that you are supposed to put in the ejection charge well before dumping in the black powder.

Does anyone know the purpose of this washer?

Won't the ejection charge be ignited by the delay column even without the washer being in place?

The metal washer with the small center hole is to constrict the flow of the ejection charge BP back through the spent DMS rocket motor.

If you leave this out, the ejection charge pressure will likely not be sufficient to pop off the nosecone to deploy the parachute, and your rocket will turn into a lawn dart and be destroyed.

 

[rharshberger]

The metal washer with the small center hole is to constrict the flow of the ejection charge BP back through the spent DMS rocket motor.

If you leave this out, the ejection charge pressure will likely not be sufficient to pop off the nosecone to deploy the parachute, and your rocket will turn into a lawn dart and be destroyed.

DMS motors drill through the top of the chargewell, not through the bottom like RMS motors, 1/4" hole makes it easier for the ejection pressure to escape through the motor case rather than through the rocket, so the washer prevents that.

 

[racerRobert]

Good to know - I always wondered. Spraying metal washers all over the landscape not Green. Sure wish they would change the washer to something more green.

 

[Dan Griffing]

It’s such a small amount of metal (stainless steel I think) that it has no appreciable effect on the environment.

The effects of burning hundreds of pounds of ammonium perchlorate with its release of hydrochloric acid fumes probably has a much greater impact.

KNER or KNSU motors are much less toxic or harmful for the environment but they only have half of the total impulse as AP motors do.

 

[Rocketjunkie]

I don't know why there is even a reason for it. Back before reloads we used a 1/8 bit to drill through the touch hole. Since there are 2 different adjustment tools, why not use a smaller bit for the DMS tool?

 

[cls]

It’s such a small amount of metal (stainless steel I think) that it has no appreciable effect on the environment.

The effects of burning hundreds of pounds of ammonium perchlorate with its release of hydrochloric acid fumes probably has a much greater impact.

KNER or KNSU motors are much less toxic or harmful for the environment but they only have half of the total impulse as AP motors do.

... And all of that pales in comparison to the impact of all us driving 100s of miles for a launch day.

 

[Starfire73]

I just launched a LOC EZI-65 on an Aerotech H135W without that ejection baffle washer. My motor was missing one, so I went back to the vendor (who was on site for the launch) and asked him about it, and he said it would be fine to launch without one. I asked two or three other experienced club members and they all said the same thing; so I was confident in launching without one in place. I did launch without that ejection baffle washer in place, and the nose cone ejected just fine. DISCLAIMER - you’re launching at your own risk though if you launch without that washer in place.

 

[AeroTech]

I just launched a LOC EZI-65 on an Aerotech H135W without that ejection baffle washer. My motor was missing one, so I went back to the vendor (who was on site for the launch) and asked him about it, and he said it would be fine to launch without one. I asked two or three other experienced club members and they all said the same thing; so I was confident in launching without one in place. I did launch without that ejection baffle washer in place, and the nose cone ejected just fine. DISCLAIMER - you’re launching at your own risk though if you launch without that washer in place.

The risk is relatively low, but reduced ejection charge force occurred often enough that we came up with a solution to prevent it.

 

[Starfire73]

The risk is relatively low, but reduced ejection charge force occurred often enough that we came up with a solution to prevent it.

Is that a common sized washer I can pick up at the hardware store? I’d like to have a few in my range box just in case.

 

[Jim Green]

When the delay burns up in the current version of DMS motors there is a 1/4 inch hole left in the forward closure. When the black powder charge goes off the gases sometimes go down the motor and out the nozzle. The washer restricts that hole to 1/8 inch and causes the pressure to go more out of the top of the motor and eject the parachute better.

 

[ThirstyBarbarian]

It seems like the washer is relatively new. I have flown DMS motors in the past and they didn’t have them, and the first time my motor came with one, I wasn’t sure what it was. I followed the instructions and just used it without knowing what it was for. Thanks for the explanation.

 

[crossfire]

It seems like the washer is relatively new. I have flown DMS motors in the past and they didn’t have them, and the first time my motor came with one, I wasn’t sure what it was. I followed the instructions and just used it without knowing what it was for. Thanks for the explanation.

The washer has been around at least 3 years.

 

[ThirstyBarbarian]

The washer has been around at least 3 years.

I know. My first DMS motor was around 9 years ago, so there were a lot of years of flying for me before it was introduced.

 

[Rocketjunkie]

The risk is relatively low, but reduced ejection charge force occurred often enough that we came up with a solution to prevent it.

Why not use a 1/8" or 5/32" touch hole? You use a different DMS adjustment tool any way. Never had problems with adjusting delays in the time before RMS.

 

[AeroTech]

Why not use a 1/8" or 5/32" touch hole? You use a different DMS adjustment tool any way. Never had problems with adjusting delays in the time before RMS.

One reason was that we didn't want the tool used on our standard single use motors. Another was to have a common drill and knob with the RMS delay drilling tool so they could be used interchangeably.

 

[AeroTech]

Is that a common sized washer I can pick up at the hardware store? I’d like to have a few in my range box just in case.

Anything that fits the well and has about a 1/8" hole will work.

 

[BSNW]

Without the washer the motor ejection won't pressurize correctly which will prevent the chute, and possibly anything else forward of that, from ejecting.

GOLLY....for some reason "I told you so" doesn't quite cover it. Years ago I posted about the problem of that large hole in the charge well in these forums and got mildly piled on. Even by a vendor who said there was no problem with that large hole in the charge well. Now I see these little washers in the DMS motors....Golly I know it is gauche to say such a thing, but today I don't care....I told you so Aerotech and the others who said there was no problem...Wow (search DMS safety concern!).