Ejection charge testing

Too much or just right? This is right at 2g. Thoughts?

[video=youtube;n0Z-4v2oMiU]https://www.youtube.com/watch?v=n0Z-4v2oMiU[/video]

Looks a little energetic to me - I would consider trying 1.6g
. If your booster does the same thing this may be so energetic the nose could separate deploying main at Appogee.

Im a big fan of the blow it apart or blow it up theory but that may have crossed the line.

Is that with the harness taped in intervals?

I'll be honest and I never even thought of this before, but try testing it on a table and on a support of some kind having it horizontally to simulate the apogee event.

Having it facing straight up could be less violent then having it horizontally like how it occurs on an actual flight.

The way it looks in the video looked just about right, but it occured to me that, because it is just a few degrees off vertically that could be the reason why the deployment looked less violent.

I would try it that way and do 1.5 grams. Did it have shear pins?

I would not use less. Others may think different, but I would get the chute closer to the payload bay....maybe about 3' - 4' from it.

I'll take back the part about straight up, still even at half ways it can look less violent.

Ya I've been going back and forth on this. The vent hole was "plugged" with the speaker wire I used to ignite the charge so there's a little leakage there not present in this test and the harness was rubber banded a single time (I would prefer to do multiples). You're right the chute does look awfully far from the bay but it's 1/3 of the distance. I'll triple check and adjust and give 1.75g a whirl. This was honestly a lot more energetic than I was expecting but my first time using blastcaps. Shear pins on the nose only.

One suggestion I've heard is to start high (which I'd think is this case here since the nose jerked back everything including the booster) and work down until failure...that way you know the range you have to work with.

Possibly pertinent questions: Is the rocket prepped just as it would be for actual launch? Is the nose weight and pins all in? How many pins and what diameter?

I prefer my main chute attached to the same quicklink as the nose cone. The main harness is a 2-loop and the drogue is a 3-loop OneBadHawk style with the mid loop closest to the AvBay this seems to allow the booster section to fall slightly below the upper payload bay with a properly sized drogue. As for starting charge weights, there are a number of spreadsheets and online calulators that will give a good starting point. Overdoing the initial charge test could damage/overstress the recovery harness or attachment points leading to a flight failure. I start with the recommended charge per the calculator then work up from there. I also use shear pins on all my HPR rockets specifically for consistency reasons, shear pins are always the same force, friction fits can be variable. To loose a friction fit and the main deploys at apogee, to tight and the main may not deploy at all.

If you were truly simulating the conditions in flight (same config, shear pins, etc), then I would say that was right on target. It separated cleanly, but did not 'yank' at recovery harness full extension on the far side. The angle you used somewhat simulated a less the vertical apogee event too. Personally, I would not go lower than the 2gr you used.

Having two altimeters makes this a little easier. Set the primary for 2gr and the secondary for 2.5+gr and don't worry about it--laundry is coming out one way or the other.

Be cafeful backing down to failure. When a charge fails to separate, I've burned the SNOT out of the recovery gear. It's also why I used "dummy" harnesses and tshirts to approximate recovery gear volume....and save burning my chutes up on the ground.

Oh, and that looks good to me.

+1 to using dummy recovery gear for testing, even starting with a recommended charge I occasionally get failures to eject during ground testing and that can fry a chute and nylon harness, kevlar seems to generally be okay. Usually the charge calculators give me a successful ejection first time which may or may not need to be adjusted upwards to get the results I like to see which is 75-90% extension of my recovery harness.

That looked good to me - I don't see anything "too" energetic about that.

IMO it was too energetic as the harness was blown to full extension plus it tried to drag the fincan along for the ride.

I like it. I would not reduce the charge.

The charge looks good. Get the laundry out of the tube!

mlrtime99 said:

Too much or just right? This is right at 2g. Thoughts?

[video=youtube;n0Z-4v2oMiU]https://www.youtube.com/watch?v=n0Z-4v2oMiU[/video]

Click to expand...

If that's the Madcow/Apogee Level-2, I would suggest 1.3g for both drogue and main. Worked perfectly for me. I hate having too much of an ejection charge, makes me think the shock cord will snap.

What's the length of the shock cord on this?

Looks good. I would rather have a bit too much than a bit too little.

I think part of the reason it dragged the booster up on to the chair was due to the angle of the trajectory combined with the mass and momentum of the payload tube/nosecone. I would guess that if the angle was closer to the horizontal that it may of landed on the ground sooner and bled off some of the forward momentum, reducing the effect of dragging the booster up on to the chair.

It's 15'.

That's a great point mpitfield... I just realized everyone usually tests with the nose/ebay dragging along the ground. I think that combined with the plugged vent for testing probably means 2 grams is perfect for flight. I'll be testing the nose cone with 1.4g tonight.

mpitfield said:

Looks good. I would rather have a bit too much than a bit too little.

I think part of the reason it dragged the booster up on to the chair was due to the angle of the trajectory combined with the mass and momentum of the payload tube/nosecone. I would guess that if the angle was closer to the horizontal that it may of landed on the ground sooner and bled off some of the forward momentum, reducing the effect of dragging the booster up on to the chair.

Click to expand...

During flight, there won't be any ground to bleed off momentum so there will be some shock loading on the recovery system from that size charge.

I'm not sure the charge is too large, I wouldn't go bigger, but I would try it with the full recovery system in place, chutes, chute protectors, dog barf, whatever you plan to put in there during a flight. Remember, the order you pack things can also affect how well the recovery deploys. You only need to get the main into the air stream and it will open and work. Slamming the nose cone to the end of the shock cord only adds wear and tear to the rocket.

Handeman said:

During flight, there won't be any ground to bleed off momentum so there will be some shock loading on the recovery system from that size charge.

I'm not sure the charge is too large, I wouldn't go bigger, but I would try it with the full recovery system in place, chutes, chute protectors, dog barf, whatever you plan to put in there during a flight. Remember, the order you pack things can also affect how well the recovery deploys. You only need to get the main into the air stream and it will open and work. Slamming the nose cone to the end of the shock cord only adds wear and tear to the rocket.

Click to expand...

Hey Handeman, I agree with your point. I was possibly not as clear as I thought I was while posting that. I was trying to explain why it appeared to look "exaggerated" as far as pulling the booster up on to the chair for this drogue test. One thing to keep in mind is the rocket is usually traveling in the same direction as the ejection trajectory, so not standing still. As you pointed out packing order, organization, z-folding and taping of shock cords, etc. is all part of the equation. Most of my rockets use different amounts of BP depending on whether I am deploying the main or drogue and some are so closet that I just use the same amount. I am sure once he tests his main he will have a better idea on if 2g is the right amount or too much.

I see nothing wrong with that charge at all, I would make the first flight without any changes.

Piling on, I think it is fine.

All the 54mm motors I fly have 2.0g charges; any time I fly a rocket that would take 54mm motors I throw in the full two grams and do not think twice about it.

watermelonman said:

Piling on, I think it is fine.

All the 54mm motors I fly have 2.0g charges; any time I fly a rocket that would take 54mm motors I throw in the full two grams and do not think twice about it.

Click to expand...

What? The size of the deployment charge required depends on the volume of the tube being pressurized by the charge, not the diameter of the motor. Not all 54mm motor rockets will require the same deployment charge.

Nathan said:

What? The size of the deployment charge required depends on the volume of the tube being pressurized by the charge, not the diameter of the motor. Not all 54mm motor rockets will require the same deployment charge.

Click to expand...

I'm with you, bro. My Dark Star 2.6" has a 54 mm MMT, but it is so close to minD that I am only using 0.5g charge wells.

Nathan said:

What? The size of the deployment charge required depends on the volume of the tube being pressurized by the charge, not the diameter of the motor. Not all 54mm motor rockets will require the same deployment charge.

Click to expand...

Of course not. However, the motor charges in the 54mm motors I buy have 2.0 grams. When I use electronic deployment on that same rocket I mimic the motor charge and leave it at that. Simple and effective.

watermelonman said:

Of course not. However, the motor charges in the 54mm motors I buy have 2.0 grams. When I use electronic deployment on that same rocket I mimic the motor charge and leave it at that. Simple and effective.

Click to expand...

As long as you don't max out your shock cord, get bounce back, or blow it up, sure. But we're simply suggesting that luck may not be the best way to go forward. And you may be wasting a lot of BP, which isn't cheap and is getting harder and harder to get.

....And the payload with 1.4 grams. Again my testing wires ran in through a vent that will be open during flight so I expect it to be fractionally less energetic. 12' shock cord, 48" main, dog barf on top of the charges and the chute (and as much of the shock cord as I can get) wrapped in a 12" nomex protector.

[video=youtube;_MYXX0pdaeM]https://www.youtube.com/watch?v=_MYXX0pdaeM[/video]

I would use 2 g at a minimum.

Bob

Very cool