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Composite staging?

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The EGE

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I'm wondering if it's possible to use a small reloadable motor as a booster motor, without electronics. I know that this is usually impossible, because they need a tight pressure seal at the top, and they don't (usually) burn from nozzle to delay. However, it occurs to me to drill out the delay grain - not enough to make the motor burn through, but enough that the effective delay time is under a second. That way, the ejection charge would ignite the sustainer - a BP motor - just after the booster's burnout.

1) Has anyone else ever tried this?

2) Would this actually work? Would the motor CATO from the thinner delay grain? Would the ejection charge actually ignite the BP motor?

3) Would this be legal and certified? I've seen varying opinions on whether drilling out delay grains is legal and certified.
 

troj

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2) Would this actually work? Would the motor CATO from the thinner delay grain? Would the ejection charge actually ignite the BP motor?
Premature burn through, resulting in the forward end of the motor becoming a nozzle would be more likely.

3) Would this be legal and certified? I've seen varying opinions on whether drilling out delay grains is legal and certified.
It's definitely a case of modifying the motor. I don't know of any motor manufacturer who recommends shortening a delay by that much.

-Kevin
 

bobkrech

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I'm wondering if it's possible to use a small reloadable motor as a booster motor, without electronics. I know that this is usually impossible, because they need a tight pressure seal at the top, and they don't (usually) burn from nozzle to delay. However, it occurs to me to drill out the delay grain - not enough to make the motor burn through, but enough that the effective delay time is under a second. That way, the ejection charge would ignite the sustainer - a BP motor - just after the booster's burnout.

1) Has anyone else ever tried this?

2) Would this actually work? Would the motor CATO from the thinner delay grain? Would the ejection charge actually ignite the BP motor?

3) Would this be legal and certified? I've seen varying opinions on whether drilling out delay grains is legal and certified.
1.) Many folks have successfully staged a BP sustainer motor using the ejection charge from an APCP motor as the sustainer ignition source.

2.) You don't have to modify the APCP booster motor internally to make it work.

3.) You need to select a high thrust APCP motor with the shortest ejection delay and sim the flight to make sure that here is enough airspeed at sustainer ignition so that the second stage will have a stable trajectory. For example a G motor with an average thrust of 60 N or greater with a 4 second delay will work as the booster motor provided the rocket is not too heavy. A rule of thumb is that it the loaded two stage rocket flown on the booster motor alone requires a 7 second or longer delay to reach apogee, you will have sufficient air speed to use the same motor with a 4 second delay as the first stage booster engine.

4.) The booster and sustainer do not have to be in contact with each other. Review how gap staging works in the Handbook of Model Rocketry, and be sure to vent the space between the top of the booster and the sustainer nozzle so that the cold air can be pushed out of the way by the hot BP ejection gases and ignite the BP sustainer before the staging separation occurs. The only change you need to make with a reload or loadable motor is to not use the supplied the plastic BP well cap and use a single layer of masking tape to cover the BP well on the forward closure which will burn up when the ejection charge fires.

Bob
 

shreadvector

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Drilling a delay to a time shorter than the shortest delay sold for that type is not recommended by the manufacturer, so it would be a non-approved motor modification. The reason they do not recommend it is that the minimum delay time (often 4 seconds, but sometimes 3 for some repload varieties) is necessary so that there is enough delay material to form a pressure bulkhead during the high pressure motor burn. if the delay is too short, there will be almost no material left near the end of the propellant burn and the delay will fail sending flaming death out the top of the motor casing.

That would be "bad".

I'm wondering if it's possible to use a small reloadable motor as a booster motor, without electronics. I know that this is usually impossible, because they need a tight pressure seal at the top, and they don't (usually) burn from nozzle to delay. However, it occurs to me to drill out the delay grain - not enough to make the motor burn through, but enough that the effective delay time is under a second. That way, the ejection charge would ignite the sustainer - a BP motor - just after the booster's burnout.

1) Has anyone else ever tried this?

2) Would this actually work? Would the motor CATO from the thinner delay grain? Would the ejection charge actually ignite the BP motor?

3) Would this be legal and certified? I've seen varying opinions on whether drilling out delay grains is legal and certified.
 

troj

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One man's "bad", another man's "WOOT! That looked AWESOME!!!!"
Having had to call a fire department because of just such an "awesome" flight, to me, there's nothing "awesome" about 'em.

-Kevin
 

bobkrech

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Having had to call a fire department because of just such an "awesome" flight, to me, there's nothing "awesome" about 'em.

-Kevin
Even when the fire department doesn't have to show up, the rocket get toasted when the forward closure fails and you loose everything inside the rocket. Ouch!

Bob
 

RangerStl

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Yeah, it's only seems to be "cool" when it happens to somebody else's stuff. :bangpan:

:(
 

Jon Craig

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My post was just meant to be funny, guys. Not a suggestion to set up an intentional CATO. :D
 
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