Standard booster engines have neither delay nor ejection charge, and when the engine burns through it ignites the next stage more or less immediately. Delayed staging, however it is achieved, allows the rocket to coast upward for some distance before igniting that next stage. Supposedly you can get higher altitude that way, but the delay before igniting the next stage needs to be short enough that the rocket is still going up when it happens. Otherwise, as gh said, the rocket might be pointing downward at that moment... a less than optimal situation.

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You don't have to be meticulous about getting every tiny bit of the ejection charge (black stuff) out. If a few grains of it stay stuck to the delay (dark gray stuff), it can improve reliability.

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To follow up on Solomoriah's description, I'll add visuals.

A booster has both the blue and red portions removed.

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With a standard booster motor - ie, with a -0 suffix - there is only the fuel grain - no delay, no ejection charge, no cap.

There have been some plugged motors which include the delay and plug while other plugged motors include only the plug. Some of these may include a 0 in the suffix, but they are NOT intended to be booster motors.

HTH.

Doug

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Plugged motors are supposed to be designated with a "-P" (P for plugged) to prevent them being inadvertantly used for booster motors... with the plug blocking all propellant gas and flaming bits blowing forward, there would be no upper stage ignition, and a guaranteed lawn dart of the upper stage...

Later! OL JR

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Back in the early 80's I tried launching my original Stiletto with an A8-3 to an A8-3. (They were the only engines I had at the time.) The park I was launching from was surrounded by canals on 3 sides. She took off, slowed down, and the ejection charge blew and ignited the upper stage when she was at about a 45 degree angle. I saw my prize bird take off like a missile an head for the water. The 2nd ejection charge blew a few feet above the water about 100 feet from shore. Bye bye birdie.

I found the sustainer, and one of the fins were missing. I couldn't find it near the landing site, so it must have happened at altitude when the 1st ejection charge blew. Granted, i was a kid back then, and I didn't put as much care into building a rocket back then as I do now.

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Thanks guys. I didn't realise -0 motors don't have a cap or ejection charge. I'm sure I have a pack of C6-0 here somewhere, but have never opened. I'll fish them out and have a look.

Those Stilettos look nice. Now I have an urge to build a two stager.

Understood, JR. I was pointing that out because at least one plugged motor - can't recall for sure which one - had a -0PT suffix IIRC. That is, while it had the 0 in the suffix, it was not suitable for staging

Also, I recall an early motor which had a delay, but was plugged. B4-4P maybe? So, while it didn't have an ejection charge, it did have a smoke trail.

That is, between pure boosters and ordinary motors, there were a couple of other (rare) configurations which some might confuse with boosters.

Doug

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In international competition, where motors are made to order, some countries use pulsed motors to attain higher altitudes. These A-impulse motors have a distinctive sound, a very short high thrust initial boost phase, then a short pause, then a very low thrust sustain phase, then a second delay, then ejection. These motors are used in parachute, streamer, and helicopter duration events. But, honestly, they haven't been effective at winning so you don't see many countries use them. This last summer I don't recall hearing any but I remember the Chinese using them 3 years ago in Slovakia.

For International two stage events, like altitude and scale altitude, many teams use a short delay between booster burnout and sustainer ignition for exactly the reason you mention. Since drag increases as the square of velocity, the lower your velocity the lower your drag. Allowing your rocket to slow down after the booster stage theoretically allows for lower second stage drag and higher flights. But obviously there is always a risk you will slow down too much and become more prone to tipping off which will decrease altitude. But most international competitors believe a short delay between booster burnout and sustainer ignition is helpful.

Delayed second stage ignition at FAI events is done a variety of ways.

International-style booster motors are almost always gap-staged, rarely taped directly to a sustainer motor. The booster motors have a tiny pinhole on their top and a small amount of loose black powder is placed on top of the booster by the flier. A "flash tube" which leads up to the sustainer nozzle is then placed on top of the booster motor to guide the flame to the sustainer. Since these booster motors do not depend on burn through to directly ignite the sustainer, it is possible to order booster motors with a short delay added above the propellant, which many countries do.

Another way some contestants create a pause before sustainer ignition is to ignite the booster directly and the sustainer with a timed fuse. Both are ignited at the same time on the pad with the sustainer fuse cut to a precise size that will allow it to burn just a bit longer than the booster motor. Our last two U.S. junior and senior Scale Altitude teams became quite adept at this very difficult technique.

Overall, most fliers competing in world class altitude events believe that a short delay between booster and sustainer really does yield higher altitudes. And you will almost always see high power altitude fliers here in the U.S. use a (sometimes lengthy) delay between stages when doing electronic ignition of upper stages.

Hope this helps,

Steve

Guys,

Could somebody talk me through the physics of the advantage of a slight delay between staging on our rockets?

I understand why some full-size sounding rockets do it to, for instance, to avoid melting fins or noses from friction heating or to generally minimize Max-Q, but this reasoning does not apply to model rockets.

Old G. Harry in the Handbook discusses why you would not want a delay; essentially max altitude is generated by maximum final burn-out velocity which would seem to argue against a coast phase of any kind.

What am I missing?

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