Rocket Motors without Ejection Charges

[Caley]

I've been trying to find out if you can purchase motors without ejection charges. The reason is that I am interested in dual deployment recovery.

I can't figure out how you can have a motor that has a 5 second delay, and then also have a charge to deploy your drogue chute without interfering with each other.

The only thing I can think is that you purchase a casing that takes reloads, but you don't install the ejection charge.

I hope someone can tell me just how this dual deployment works if you have an ejection charge built into the motor. Caley Ann

 

[blackbrandt]

If you have a reload (AT or Loki), you just leave out the ejection charge.

On CTI motors, you can take off the paper cap above the ejection charge and dump out the BP.

On SU AT motors, I'm not sure.

 

[ksaves2]

For reloadable motors Caley one just uses a plugged forward closure. For single use motors one can order an overly long
delay that could then act as a backup for apogee deployment. Once the altimeter blows out the drogue at apogee,
the late motor charge blows out in a benign fashion. The key is to simulate one's flight in software and chose a
delay that is longer than the expected apogee time. If the SU motor delay is not long enough, will need to go with a reloadable motor system. Nice thing about the long delay is there is an excess of tracking smoke that makes visual tracking much easier. Might still get smoke coming out after the drogue has blown and rocket is on the way down.

There are single use motors one can modify the delay length but they are generally
for high powered rocketry.

There are motors with zero delay for boost gliders but the selection is generally limited. Kurt

 

[Zeus-cat]

Leave out the charge, but you put in the delay!!!!!!!!! If you leave out the delay you will have a very interesting flight!

 

[ksaves2]

If you have a reload (AT or Loki), you just leave out the ejection charge.

On CTI motors, you can take off the paper cap above the ejection charge and dump out the BP.

On SU AT motors, I'm not sure.

Oh yeah, some of the AT 24mm motors one can dump the powder but some that would be hard to do.

Technically, the motor wouldn't "be certified" anymore and would supposedly have to be flown under
TRA research rules. In reality, no one would be able to notice or tell. Might PO the NAR folks though.

I drilled out the plugs in Estes E9-0's to use as booster motors in a modroc and nobody batted an eye.
Didn't ask and I didn't tell! Kurt

 

[djs]

For single use motors one can order an overly long
delay that could then act as a backup for apogee deployment. Once the altimeter blows out the drogue at apogee,
the late motor charge blows out in a benign fashion.

I do this with reloadables too- especially CTI. Having an extra safety delay/charge is always good, especially when you are just starting out with dual deploy. I'll always leave it in, unless the motor delay isn't long enough for what's needed.

The one time I thought "yeah, I can trust my electronics", and didn't put powder in the H550ST motor, well.. let's say it was expensive..

 

[Caley]

I think I got a different opinion from each of you, but it sounds like the best route is to keep the ejection charge, making sure it is activated beyond the point when the charge blows at apogee.

Based on what I remember seeing in some videos, the smoke trail that I see emitted after drogue deployment might be that rocket motor ejection charge.

I am working on a Madcow Mini DX3. Someone suggested I go with dual deployment. They say it works just fine, even with the smaller diameter rocket. Unfortunately, the EBAY is not big enough to contain dual components in case one fails. I think I will be going back to this gentleman to have him help me through all of this.

Just to let you know, I still haven't flown a model rocket since 1971, so everything I am doing, I am learning as I go. Hopefully I get it all correct. Thanks Guys
Caley Ann

 

[djs]

Caley- 2 things:
1. the "smoke trail" is the remainder of the delay grain burning. Usually with a charge you'll only see just a small puff of smoke, not a trail
2. The mini DX3 doesn't seem to come stock with an av bay- did you get one for yours? Yes, you might have a problem squeezing two altimeters in there. I did my first DD with only one altimeter for a long time, and it worked for me. Obviously redundancy is the best, but sometimes you work with what you can.

 

[cerving]

Oh yeah, some of the AT 24mm motors one can dump the powder but some that would be hard to do.

Technically, the motor wouldn't "be certified" anymore and would supposedly have to be flown under
TRA research rules. In reality, no one would be able to notice or tell. Might PO the NAR folks though.

I drilled out the plugs in Estes E9-0's to use as booster motors in a modroc and nobody batted an eye.
Didn't ask and I didn't tell! Kurt

Removing (or not including) the powder in a motor that's designed for that doesn't change the certification, it's no different than drilling a delay. However, in the case of an Estes BP motor it WOULD void the certification because there's no provision for doing it. There's been an ongoing debate over whether plugging a -0 Estes motor affects the certification... if you just put a little dog barf in the cavity and tape it over, you're 100% legal. In fact, Estes used to tell you to do that with clustered 2-stage boosters, so that if a motor doesn't light the other motors won't light it from the top end at burnout and toast everything.

 

[rharshberger]

The powder charge on Aerotech SU motors can be removed iirc, by pulling the red plug over the BP and dumping the charge, then/or not add dog barf, then re-insert the plug. (hopefully my memory is still correct on those motors).

 

[tomsteve]

If you leave out the delay you will have a very interesting flight!

yes, flames from both ends might look cool for a second, but are costly.

 

[tomsteve]

Caley- 2 things:
1. the "smoke trail" is the remainder of the delay grain burning. Usually with a charge you'll only see just a small puff of smoke, not a trail.

if you've used a reload, you've seen the delay. they are basically the same in SU motors. the delay, if im not mistaken, is propellent with something added to slow down the burn?
as the motor burns, its not only burning the propellant and the gasses are coming out the nozzle, the delay grain is also burning- at a delayed burn rate.

I have flown 29mm SU composite clusters. still using motor ejection, but I had varying delays on the motors. removing the ejection charge from the motors with the delays I didn't want( and keeping the ec in the ones with the delay I wanted) and putting a little wadding in was all that was necessary to keep the shorter delay motors from poppin the chute out prematurely.

 

[Caley]

Well, now I am totally and overwhelmingly confused with all the answers here. I think I need to find a member of my club (ROC) and find out how he/she does things. I am very good and show and tell, and usually get things on the first go around. Right now I don't know which end is up after all these answers. Caley Ann

 

[djs]

Hi Caley,

It took me a while to understand everything and how it all works. Please keep asking questions if you are confused!

Also, this video may be pretty helpful in explaining some of the basics:

https://www.jcrocket.com/electronic-recovery.shtml

 

[samb]

Well, now I am totally and overwhelmingly confused with all the answers here. I think I need to find a member of my club (ROC) and find out how he/she does things. I am very good and show and tell, and usually get things on the first go around. Right now I don't know which end is up after all these answers. Caley Ann

+1 !!!!!!!!!!!!!!!!

TRF is a wonderful place but no substitute for my local rocket buddies.

 

[Caley]

I've watched this video before, and watched it again. It is very good. But it still doesn't address the fact that most model rocket motors come with an ejection charge, and what to do with them. I know a couple of you talked about that here, and the best I have read is that you purchase a motor with the thrust needed, and a very long delay. That allows your altimeter to trigger your prepared ejection charge, and the motor ejection charge at some point fires after that, but before the low altitude main chute ejection charge fires.

Too bad the motor manufacturers haven't addressed the fact that most people who fly Cert levels L1 and above really don't need those motor ejection charges. And because of that fact, manufacture motors with no ejection charge. Maybe they will eventually do that, unless NAR and Tripoli require ejection charges in the motor. Caley Ann

 

[djs]

Too bad the motor manufacturers haven't addressed the fact that most people who fly Cert levels L1 and above really don't need those motor ejection charges. And because of that fact, manufacture motors with no ejection charge. Maybe they will eventually do that, unless NAR and Tripoli require ejection charges in the motor. Caley Ann

Hi Caley- you're asking a good question here. The truth is, there are a good number of HPR fliers that do not use electronics, and would rather just deal with ejection charges from the motors. I would venture to say that you're probably looking at 50/50 up to J motors or so. The manufacturers are doing this because there's a market for it!

 

[ttabbal]

The safety codes don't require motor ejection. Most high power motors have an option, usually with plugged forward closures. L3 and some larger L2 motors typically don't include motor ejection charge capability at all.

With high power, it makes a lot of sense most of the time to use reloadable motors. There are a few single use out there, but they are pretty rare. And there are the Aerotech DMS, that are single use but you still have to build them. All of those you can easily just leave the BP out. Just to reiterate though, do NOT leave the delay grain, o-rings, etc out. Just the BP. And for Aerotech style delays, make certain you put them together properly. It's an expensive mistake.

If I have a motor with eject capability, I generally include the powder even with electronic deployment. The idea is to use it as a backup for the apogee charge. I usually use the longest delay grain without drilling. The only exception would be if the simulation says I should have a short delay, perhaps 2 seconds, while the long motor delay is 10. I generally try to make the motor delay go about 2 seconds past apogee when using it as a backup. So that if the altimeter charge fails to separate the rocket, there's a second chance to avoid a ballistic rocket. There are a number of things that can go wrong with electronic deployment. Most of them can be mitigated with careful prep, but we're all human and make mistakes. And sometimes things just fail. If you're doing dual-deploy, there's still the main charge, but while having the main deploy a ballistic rocket helps the possible damage to people/property on the ground, it shreds the rocket. On the up side, the motor case and electronics will generally survive the shock. This is one thing I like about the Eggtimer Quantum. If it detects the rocket accelerating too much after the apogee charge has fired, it will deploy the main as a safety.

I've also seen many L2 flights that use single motor deployment, no electronics. High power doesn't require electronics in general, but the greater altitudes do make it nice to have. This can change based on where your club flies though. You need to keep the rocket in the waiver area. If deploying the main at apogee creates a high risk that the rocket will drift out of the waiver, the local club may require it. But you could probably do something like the JL Chute Release to get the same effect.

As mentioned, there is nothing as useful as seeing things in person. Drop by a launch, even if you aren't going to fly, and chat with people. Most rocket people are happy to show you how they do things and explain why they do it that way. There's also no "one true way", there are a lot of possible ways to achieve the same goal. I would suggest focusing on one to start with. It's easy to lose sight of the goal if you get lost in the options.

 

[Flyfalcons]

I've watched this video before, and watched it again. It is very good. But it still doesn't address the fact that most model rocket motors come with an ejection charge, and what to do with them. I know a couple of you talked about that here, and the best I have read is that you purchase a motor with the thrust needed, and a very long delay. That allows your altimeter to trigger your prepared ejection charge, and the motor ejection charge at some point fires after that, but before the low altitude main chute ejection charge fires.

Too bad the motor manufacturers haven't addressed the fact that most people who fly Cert levels L1 and above really don't need those motor ejection charges. And because of that fact, manufacture motors with no ejection charge. Maybe they will eventually do that, unless NAR and Tripoli require ejection charges in the motor. Caley Ann

Aerotech covers this in their instructions. If no ejection charge is desired, then leave the black powder out and put some grease in the ejection charge well.

That said, there are still plenty of designs that can fly on bigger motors, using motor ejection for the parachute. My Sea Wolf is an example of this - it'll handle 38mm J motors and does not use electronics.

 

[blackbrandt]

Aerotech covers this in their instructions. If no ejection charge is desired, then leave the black powder out and put some grease in the ejection charge well.

That said, there are still plenty of designs that can fly on bigger motors, using motor ejection for the parachute. My Sea Wolf is an example of this - it'll handle 38mm J motors and does not use electronics.

The other option (what I do) is just to fly with a plugged closure instead. I haven't used motor eject for a rocket in 2 years now.

 

[Woody's Workshop]

Here's an option (I wonder why no one has suggested this yet)...
Use you engine ejection for your drouge chute.
Get a Jolly Logic Chute Release to deploy your main at an altitude of your choice.
This is what I intend to do this season.

 

[Bat-mite]

Well, now I am totally and overwhelmingly confused with all the answers here. I think I need to find a member of my club (ROC) and find out how he/she does things. I am very good and show and tell, and usually get things on the first go around. Right now I don't know which end is up after all these answers. Caley Ann

You're confused because you got answers to questions you weren't asking, and probably people using terms with which you are not familiar, and others asking questions of their own not related to your question.

Let me try to make it simple.

For black powder motors like Estes manufactures, you cannot (read should not) alter the delay or the deployment charge in any way. You buy the motor with the specs that most closely match your rocket's needs and go with it.

In dual deployment, you want your altimeter to deploy your chutes. The altimeter is more accurate than any guess at a delay time. Lots of things affect when the deployment should occur. A rocket that has flown successfully ten times with a 5-second delay may one day deploy too early or too late. The altimeter doesn't guess. It determines apogee in real time.

So in the simplest cases, you have one altimeter, a drogue charge, and a main charge. You don't want your motor to eject the drogue, so you cut/remove the end cap and pour out the black powder. Now your motor can't screw up what your altimeter is doing by firing too early, too late, or at the same time (double-sized charge!).

However, you may be noticing that in this case, you have no back-up if the altimeter fails. So, in order to avoid failure, you can either have a redundant system (two altimeters, total of four charges), or use the motor's charge as a back-up. Smaller rockets have no room for two systems, and thus motor back-up is a great option.

If using motor back-up, you need to make sure that the motor's charge does not deploy until after the altimeter by a second or two. To do this, if you expect your optimal delay to be five seconds, drill it to be seven seconds. if you expect it to be three seconds, drill it to five, etc.

In some cases, you may find that for a particular rocket/motor combo, you need a longer delay than what is provided by the manufacturer. IOW, if you have a motor with a 14-second delay, and you calculate that you need a 15-second delay to avoid firing before the altimeter, then you must dump out the powder. No choice there.

If in any case you have to remove the motor's deployment charge, you must plug the hole somehow so that the burning gasses from the propellant don't come out of the top of the motor. Some people fill the hole with epoxy, some stuff the hole with dog barf and tape it over.

In summary:

• Estes and SU motors with no DD: buy motor with delay to suit rocket
• Reloadable motors with no DD: drill to suit rocket
• Reloadable motors with DD: drill to fire 2 seconds after optimal delay
• Reloadable motors with DD with two altimeters: same as above, or remove BP and plug closure
• Reloadable motors with DD, but optimal delay is longer than supplied delay: remove BP and plug closure

I hope this helps and doesn't make you more confused. I agree that the best way to learn is at a launch. A picture really is worth 1000 words.

 

[Caley]

John S, I've been watching tons of videos, so I pretty much understood what others were saying on this thread. But like so many other hobbies, X# of people, will have X# of solutions due to personal preferences. Today I watched an Apogee video about building a reloadable motor. Tim mentioned the black powder charge, and showed how it was installed. That is all it took for me to grasp that if you don't pour in the charge, you don't have a motor ejection event.

Since I have trouble figuring out just how the rockets slow down due to drag and gravity, I figured I would go with "Apogee/low alititude" altimeter controlled ejection. I only know basic math, so I cannot do all that fancy math that would tell me exactly what I need.

I'm pretty much decided on what to do now. I purchased an EBAY that fits my Madcow Mini DX3. I am still limited by it size, so I won't have a back up system. But because of this models low weight, I doubt I want to add too much extra to cut down on the variety of motors available.

This model is for me to learn before I build a larger L1/L2 cert airframe. I figure if I can get things working in the smaller rocket, it might actually make things easier when I step up.

Anyway, I have been working on things for about two months, so I am not rushing things, and happy to do it that way.

Caley Ann last model rocket flown in 1971

 

[DavidMcCann]

I like photos.

If you have a single use aerotech you'd like to use, pull the red cap, dump the powder, stuff in wadding, replace the cap, and tape it down with electrical tape.

Some people will say this modifies the motor and makes it EX, blah blah blah. I disagree entirely with this view.

I wouldn't worry too much about having a second altimeter. Units these days are very reliable.

 

[Caley]

David, Thanks so much for the tip. Caley Ann

 

[Dave A]

I like photos.

If you have a single use aerotech you'd like to use, pull the red cap, dump the powder, stuff in wadding, replace the cap, and tape it down with electrical tape.

Some people will say this modifies the motor and makes it EX, blah blah blah. I disagree entirely with this view.

I wouldn't worry too much about having a second altimeter. Units these days are very reliable.

Yes, altimeters are real reliable but wires, batteries, switches and igniters are prone to fail.
If your rocket is moving into the price of hundreds or more plus many hours of work I like spending another $50 for a 2nd altimeter for full redundancy.
When something fails in a 1 altimeter system all you'll have left is a motor case and an accordion that won't play music.

Example: I prepped a huge rocket back in Oct. Both altimeters read full continuity in the trailer. Went to arm the altimeters and one igniter showed OPEN. It probably would have flown correctly anyway however I swapped it out and it flew.
Why do I do this?
I don't have a shovel in the trailer, ya'll know what I mean.

 

[DavidMcCann]

Yes, altimeters are real reliable but wires, batteries, switches and igniters are prone to fail.
If your rocket is moving into the price of hundreds or more plus many hours of work I like spending another $50 for a 2nd altimeter for full redundancy.
When something fails in a 1 altimeter system all you'll have left is a motor case and an accordion that won't play music.

I don't disagree. But first avbay being a 38mm? I'd focus on getting one right, not stuffing two in.

 

[Dave A]

You are correct.....
I do have a 7.5" BumperWac. The 38mm upper stage has 1 altimeter for dual deploy, I run the sim and add 5 sec delay time to the F motor for 1 backup at apogee. There's barely room for that!

 

[Steve Shannon]

I don't disagree. But first avbay being a 38mm? I'd focus on getting one right, not stuffing two in.

I think the OP would be less challenged and possibly less frustrated if she did her Level 1 with motor ejection and get some flights as experience. Then learned electronic single deployment using a larger body tube, such as 2.6. Then advance to dual deployment. Each step teaches lessons. Finally, apply lessons learned to do a 38 if she still wants to. Trying to do too much without a good foundation of knowledge can lead to expensive flights where multiple things fail simultaneously and are difficult to distinguish.

 

[DavidMcCann]

I think the OP would be less challenged and possibly less frustrated if she did her Level 1 with motor ejection and get some flights as experience. Then learned electronic single deployment using a larger body tube, such as 2.6. Then advance to dual deployment. Each step teaches lessons. Finally, apply lessons learned to do a 38 if she still wants to. Trying to do too much without a good foundation of knowledge can lead to expensive flights where multiple things fail simultaneously and are difficult to distinguish.

agreed, but she has a madcow mini kit, and is asking for advice on that kit.

I did my L1 in a 2.6" bird that flew to 1200'. That's how I'd do it, but she didn't ask for advice on that.