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smoon

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I just finished a Madcow 4 inch Nike Smoke and am getting prepared to launch it for the first time in a couple of weeks.

The loaded weight of this rocket will hover just above 7 pounds, so I really don't want anything to go wrong and destroy the rocket or anyone's property or worse.

I have plenty of experience with lighter, smaller diameter rockets and some with a Binder Excel and have no ejection failures to date on these bigger rockets. I would like to keep it that way.

I will be using AT 38mm I motors (for starters) with motor eject, as this is a single deploy rocket with no electronics, for now.

I have 217 cubic inches of space inside the rocket to pressurize, so the nose cone will eject and take my recovery gear with it. When I calculate the size of the expected ejection charge, should I take into account the space the parachute bundle and shock cord bundle take up in the airframe?

The calculators tell me I need about 1.5 grams of BP to create 14 psi of pressure inside the rocket, and since I will not be able to ground test, using motor eject, I want to make sure I use enough (more than enough) BP to get the job done. Up until now, I have followed the manufacturers guidelines for how much BP to use, but this time, I want to be doubly sure I am using enough.

Any help from those that have been where I am is greatly appreciated.

Steve
 

smoon

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I Would ground test, but I am using motor eject, so I don't see a valid way to ground test that.
 

rharshberger

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What moto? If its a reloadable motor the ejection charge can usually be adjusted.
 

MikeyDSlagle

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Find out how much bp is in the charge for the motor you want to use. I am sure there is someone who knows or there is a table somewhere. You can find 12 packs of Aerotech Ejection Charges that come in sealed vials at 1.4 grams. Says they are a replacement for lost charges. Not sure, never used em. Nothing else, open up the motor you plan to use and measure the charge included. Then go from there. Not sure if modifying the ejection charge makes it a modified motor and gets into the experimental/research or not. I don't know enough of about such things.
 

smoon

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I will be launching it on Aerotech 38mm I reloads to start with, and I know they say to fill the well all the way for four inch rockets. This is what I did for my Binder Excel, and it ejected just fine.

That is a light, cardboard rocket, and this is a heavy FG rocket, so I am just being extra careful with this one.
 

rharshberger

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Find out how much bp is in the charge for the motor you want to use. I am sure there is someone who knows or there is a table somewhere. You can find 12 packs of Aerotech Ejection Charges that come in sealed vials at 1.4 grams. Says they are a replacement for lost charges. Not sure, never used em. Nothing else, open up the motor you plan to use and measure the charge included. Then go from there. Not sure if modifying the ejection charge makes it a modified motor and gets into the experimental/research or not. I don't know enough of about such things.
Adjusting the ejection charge has nothing to do with the certfication and is not a modification of the motor. Altering the delay or the propellant would be a modification.
 

MikeyDSlagle

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Adjusting the ejection charge has nothing to do with the certfication and is not a modification of the motor. Altering the delay or the propellant would be a modification.
Roger that. Good to know. Like I said, didn't know.
 

Bat-mite

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My :2:.

Don't try to account for the chute and blanket in your volume calcs. Even if it is packed really tightly, gas can escape thru the nooks and crannies. For length, use the space between the upper CR and the NC shoulder cap or bulkplate.

If you want to ground test, you probably can, even though you aren't using electronic deployment. You might have to buy some stuff.

Lots of people put their charges in the fingertips of surgical gloves. Shove in an e-match and tape it tightly together. Put your rocket in flight-ready condition, but stuff the MMT with rags. You don't want your test charge to light your motor charge!

Very likely you have a pressure relief vent to prevent premature separation. If not, drill one. Pull the e-match leads out through the vent hole. Hook up a launch controller and deploy your charge. See what you get. You can several glove-tip charges in differing amounts prepared beforehand to speed testing.

Remember that you want your chute completely out, but you do not want to overstress your harness. Find a happy medium. How long is your harness, BTW?

P.S. - if you use an Estes launch controller, be advised that the continuity test voltage is sufficient to light your match. The amount of current needed to light up the continuity bulb is way higher than you'll get with any higher-grade launch controller, like at a club.

If you don't want to do all of that, 1.5g sounds about right to me. I think my RW X-Celerator was using 1.3g.
 

Rex R

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IMO unless you're using sheer pins 14 psi is excessive, 10 psi is probably more than enough (even with a pair of 2-56 sheer pins). 14 psi equates to just under 167 pounds of force acting to separate the nose and airframe, 10 psi about 119 pounds.
Rex
 

smoon

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Thanks Rex.

Reading the info on the spreadsheet I was using to figure this out, I thought 14 PSI was kind of high, given it says that the force needed to break three shear pins is only 85 pounds (or something close to that, I don't have it near me). I thought I read somewhere 14 PSI was about what I should use.

Being single deploy, I won't be using any shear pins, but I do have a small vent hole in the airframe. If 10 PSI will do me, then I will shoot for that and not overstress anything.

Steve
 

rharshberger

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For ground testing I have used Estes igniters in the past (before I had a supply of ematches).
 

Buckeye

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I Would ground test, but I am using motor eject, so I don't see a valid way to ground test that.
Sure you can. Make a deployment charge with an ematch, igniter, etc. Mount this charge on the top of an empty motor casing (just like it would be on a live motor) with tape, hot glue, etc. Run the leads through the motor casing and out the nozzle end. Secure the motor casing with retention. Fire the charge with your Estes launch controller or similar.
 

ksaves2

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DO NOT use a substitute canister for a ground test on a motor ejection rocket!! Let me explain. I thought in a short rocket with motor ejection I'd be "certain" I had the right amount of powder to blow the shearpins for an apogee only rocket.
I used an ultracentrifuge canister with an ematch epoxied in place through a hole in the bottom of the canister and thread the match wires through the forward ejection charge well for the ground test. Put a measured amount of powder in the canister and did the ground test. Nosecone comes off with a nice force and rocket jerks forward. Okay, that looks good. Soooooo, I poured the SAME measured amount of 4f into the motor charge well, make the flight and the nosecone stays on! Postmortem showed the charge blew but failed to pop the nosecone.

What happened? I surmise some of the powder invariably goes into the motor through the well hole and isn't available to apply the necessary force forward. The amount I used was .5gm less than what is provided with the motor. My compatriots implored to just use what's provided with the motor and don't worry about it. I did on a second flight and the nosecone blows off nicely. Was a glass rocket so I just had to replace the nosecone and rocket was flyable again. The astute advice I received was after the fact.

Yeah, if a rocket is long and large there might not be enough provided and one needs to consider something else but my rocket was short.

If going to do a ground test for motor ejection, I'd use the charge well and put a small cardboard plate with a hole for the igniter or ematch to simulate the presence of a delay grain. That way one will be able to test for the powder that invariably falls through the hole more accurately. But then again, I'd still toss in extra. Please don't repeat my mistake. Kurt
 

Rex R

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the kit designers at MC are pretty good at designing kits to fly with the amount of bp supplied with the reloads, or at least that is my impression.
Rex
 

woferry

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For the first two flights of my Madcow 4" FG Nike Smoke I've used motor eject, I'll be moving to electronic eject in preparation for a VMAX flight in the future (TCC's Nike Smoke K2045 drag race). But I've flown an AT H550ST (the DMS version) and a CTI I125W-LB, both 38mm motors, both run with only the stock vendor BP and both flights were fine. My NC fit is quite tight, it takes some effort for me to install or remove the NC (and that's after a good bit of sanding, also). I have a single vent hole in the airframe to avoid pressure separation (forget the size of the hole and I'm on the opposite side of the planet from the rocket right now so I won't be able to check for a few days).
 

smoon

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Thanks for all the replies. I won't be able to address each one, but be sure I have read them all and taken everything into consideration, even if it is for future dual deploy use.

Kurt - your advice seems sound and mirrors what I have read in a couple of other places. I am glad your rocket sustained minimal damage and was able to be repaired. I have flown my Binder Excel following Aerotech's advice on powder usage in the instructions, and it ejected just fine. It has a longer airframe, so I would guess the same practice should yield the same results with the Nike Smoke, which has a much shorter airframe. I built an AV bay into the nose cone, so all that space is not to be accounted for during ejection.

Thanks Rex. This is my biggest Madcow kit. All my others are minis and a 2.6" DX3 that I modded for night launch, so I have nothing to compare this to in their lineup.

Will - I appreciate the information, since you have the same rocket. You don't have to tell me about sanding the nose cone shoulder. I have spent more time sanding it than the rest of the construction, and I am not done yet. I have what I think is the perfect fit now. I can pick up the rocket by the nose cone, but a little shake and it comes free. My work now is to sand the area where it steps out to match the airframe diameter. I had about a 1/16" gap and have managed to get it to about 1/32". With the shape of the nose cone, I am sure this will not affect aerodynamics much, if at all. I just want to make it look pretty. My vent hole is 1/8", as that is what the instructions say to use.

Steve
 

Bat-mite

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DO NOT use a substitute canister for a ground test on a motor ejection rocket!! Let me explain. I thought in a short rocket with motor ejection I'd be "certain" I had the right amount of powder to blow the shearpins for an apogee only rocket.
I used an ultracentrifuge canister with an ematch epoxied in place through a hole in the bottom of the canister and thread the match wires through the forward ejection charge well for the ground test. Put a measured amount of powder in the canister and did the ground test. Nosecone comes off with a nice force and rocket jerks forward. Okay, that looks good. Soooooo, I poured the SAME measured amount of 4f into the motor charge well, make the flight and the nosecone stays on! Postmortem showed the charge blew but failed to pop the nosecone.

What happened? I surmise some of the powder invariably goes into the motor through the well hole and isn't available to apply the necessary force forward. The amount I used was .5gm less than what is provided with the motor. My compatriots implored to just use what's provided with the motor and don't worry about it. I did on a second flight and the nosecone blows off nicely. Was a glass rocket so I just had to replace the nosecone and rocket was flyable again. The astute advice I received was after the fact.

Yeah, if a rocket is long and large there might not be enough provided and one needs to consider something else but my rocket was short.

If going to do a ground test for motor ejection, I'd use the charge well and put a small cardboard plate with a hole for the igniter or ematch to simulate the presence of a delay grain. That way one will be able to test for the powder that invariably falls through the hole more accurately. But then again, I'd still toss in extra. Please don't repeat my mistake. Kurt
Good to know. Thanks for sharing.
 

smoon

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I completely agree John.

That personal experience Kurt had can help all like me who are mulling these questions over.

Steve
 

ksaves2

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Yeah, I stumbled into that mistake. When using canisters for DD rockets I haven't had a failure yet with an adequate ground test. Bottom line is to simulate with the exact type of setup being flown. On small rockets I'd just use
what's given with the motor. If flying a long neck or large single deploy with motor ejection, ground test with the motor well and throw in a little extra. Kurt
 

soopirV

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Adjusting the ejection charge has nothing to do with the certfication and is not a modification of the motor. Altering the delay or the propellant would be a modification.
This caught my eye, and I wanted to make sure I understood- you aren't referring to delay timing, which is, I thought, a common and accepted practice? I would imagine altering the delay composition would qualify as a modification...
 

rharshberger

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This caught my eye, and I wanted to make sure I understood- you aren't referring to delay timing, which is, I thought, a common and accepted practice? I would imagine altering the delay composition would qualify as a modification...
Correct, I was not referring to drilling the delay, which is an accepted/planned practice. I should have just left the last sentence as altering the propellent would constitute a modification.
 

soopirV

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Correct, I was not referring to drilling the delay, which is an accepted/planned practice. I should have just left the last sentence as altering the propellent would constitute a modification.
That's what I thought you meant, but I'm pretty new to HP so wanted to be sure, thanks for the clarification!
 

Buckeye

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DO NOT use a substitute canister for a ground test on a motor ejection rocket!! Let me explain. I thought in a short rocket with motor ejection I'd be "certain" I had the right amount of powder to blow the shearpins for an apogee only rocket.
I used an ultracentrifuge canister with an ematch epoxied in place through a hole in the bottom of the canister and thread the match wires through the forward ejection charge well for the ground test. Put a measured amount of powder in the canister and did the ground test. Nosecone comes off with a nice force and rocket jerks forward. Okay, that looks good. Soooooo, I poured the SAME measured amount of 4f into the motor charge well, make the flight and the nosecone stays on! Postmortem showed the charge blew but failed to pop the nosecone.

What happened? I surmise some of the powder invariably goes into the motor through the well hole and isn't available to apply the necessary force forward. The amount I used was .5gm less than what is provided with the motor. My compatriots implored to just use what's provided with the motor and don't worry about it. I did on a second flight and the nosecone blows off nicely. Was a glass rocket so I just had to replace the nosecone and rocket was flyable again. The astute advice I received was after the fact.

Yeah, if a rocket is long and large there might not be enough provided and one needs to consider something else but my rocket was short.

If going to do a ground test for motor ejection, I'd use the charge well and put a small cardboard plate with a hole for the igniter or ematch to simulate the presence of a delay grain. That way one will be able to test for the powder that invariably falls through the hole more accurately. But then again, I'd still toss in extra. Please don't repeat my mistake. Kurt
Perhaps more data is needed to draw a conclusion.

Why are you using shear pins on a single deploy rocket? I assume for drag separation, but that is pretty rare. Shear pins invite lawn darts on simple rockets. Nothing but coupler friction has been good enough for me all the way through Level 2. Argument for another thread/day, I guess.

How does a short rocket increase the "certainty" of anything? Ground testing is ground testing, no matter the design.

Any BP that falls through the well hole will rest on the delay grain. It doesn't disappear. As soon as the delay grain burns through, it ignites any and all BP in the vicinity. Yes, the BP is a little more spread out, but the total quantity is still there to be consumed, and 4FG goes fast. I am no pyrotechnician, but this effect seems small to me.

Overall, I agree with your recommendation. Ground test, then add a pinch more for good measure.
 

ksaves2

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Perhaps more data is needed to draw a conclusion.

Why are you using shear pins on a single deploy rocket? I assume for drag separation, but that is pretty rare. Shear pins invite lawn darts on simple rockets. Nothing but coupler friction has been good enough for me all the way through Level 2. Argument for another thread/day, I guess.

How does a short rocket increase the "certainty" of anything? Ground testing is ground testing, no matter the design.

Any BP that falls through the well hole will rest on the delay grain. It doesn't disappear. As soon as the delay grain burns through, it ignites any and all BP in the vicinity. Yes, the BP is a little more spread out, but the total quantity is still there to be consumed, and 4FG goes fast. I am no pyrotechnician, but this effect seems small to me.

Overall, I agree with your recommendation. Ground test, then add a pinch more for good measure.
I want positive closure hence use the shearpins on a glass rocket with a floppy nosecone. Yeah, I can dink with tape, CA, epoxy, sanding the heck out of the buildup but I like a loose fit and shearpins. Sorry I disagree, but I suspect the powder that falls through the hole takes the path of least resistance. It blows backwards down the spent motor casing. I was using .5gms less than what was provided with the motor. A sealed canister in the test had enough force to blow the nosecone shearpins. Enough of my measured charge fell in the hole and effectively wasn't available to blast forward through the restriction/hole. It was critical in that wasn't enough force to shear the pins when the same amount used in a canister was simply dumped into the well.
Next flight I took the advice and just dumped the entire charge provided in the well. Popped the nosecone fine but the forward closure burned through on the CATO. A little higher and the chute would have had a chance to deploy.
Bottom line is to run one's simulation as close to the "real deal" as possible or just screw it and dump all the BP in that's provided with the motor and call it good! Kurt
 

DavidMcCann

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I want positive closure hence use the shearpins on a glass rocket with a floppy nosecone. Yeah, I can dink with tape, CA, epoxy, sanding the heck out of the buildup but I like a loose fit and shearpins. Sorry I disagree, but I suspect the powder that falls through the hole takes the path of least resistance. It blows backwards down the spent motor casing. I was using .5gms less than what was provided with the motor. A sealed canister in the test had enough force to blow the nosecone shearpins. Enough of my measured charge fell in the hole and effectively wasn't available to blast forward through the restriction/hole. It was critical in that wasn't enough force to shear the pins when the same amount used in a canister was simply dumped into the well.
Next flight I took the advice and just dumped the entire charge provided in the well. Popped the nosecone fine but the forward closure burned through on the CATO. A little higher and the chute would have had a chance to deploy.
Bottom line is to run one's simulation as close to the "real deal" as possible or just screw it and dump all the BP in that's provided with the motor and call it good! Kurt

I would guess the type of containment and breaking force had more to do with the failure than the BP in the touch hole. Vials would tend to hold more in and you get a nice contained burn, fast and hard. The open end of the bulkhead leads to some BP getting blown around and a slightly slower burn, and less of a pressure spike.

Conclusion is the same though... Test as close as possible to how it's going to fly.
 
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Handeman

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I would guess the type of containment and breaking force had more to do with the failure than the BP in the touch hole. Vials would tend to hold more in and you get a nice contained burn, fast and hard. The open end of the bulkhead leads to some BP getting blown around and a slightly slower burn, and less of a pressure spike.

Conclusion is the same though... Test as close as possible to how it's going to fly.
I agree with David on this one. I don't thing the amount of powder was the issue as much as the different types of containment on the ground test vs. flight. The reason I say that is when I started DD, I poured my powder on a strip of duct tape, laid the ematch on it and folded the tape to seal everything in place. When I modified the av-bay to use a charge well and sealed the powder in with dog barf and masking tape, I got a stronger ejection with the same amount of powder. It was all 4F BP, but the containment did make a difference.
 

rharshberger

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I would guess the type of containment and breaking force had more to do with the failure than the BP in the touch hole. Vials would tend to hold more in and you get a nice contained burn, fast and hard. The open end of the bulkhead leads to some BP getting blown around and a slightly slower burn, and less of a pressure spike.

Conclusion is the same though... Test as close as possible to how it's going to fly.
I agree with David on this one. I don't thing the amount of powder was the issue as much as the different types of containment on the ground test vs. flight. The reason I say that is when I started DD, I poured my powder on a strip of duct tape, laid the ematch on it and folded the tape to seal everything in place. When I modified the av-bay to use a charge well and sealed the powder in with dog barf and masking tape, I got a stronger ejection with the same amount of powder. It was all 4F BP, but the containment did make a difference.
Add to these two fine gentlemans advice, Consistency, if you don't do the charge the same way every time no matter what method you choose the results will vary.
 

watermelonman

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Ground test but make it vigorous or add extra powder for margin.

I cannot tell you how many deployment failures I have seen after watching a successful ground test where the builder thought they would use minimal powder for separation. I lost count long ago.
 
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