Level 2 in Style video

I just posted my latest how-to video on tips for taking your level-2 rocket beyond the basics.
jcrocket.com/certify-level-2.shtml

John,

Great video, with one caveat. I get the premise behind your dual deployment configuration, but doubt the applicability. The typical Dual Deployment, with main parachute in the payload bay, reduces the holding power of the shear pins at the nosecone/payload bay separation point. In that configuration, you're really only concerned with the inertia of the nosecone and main parachute when the cord pulls taught, which is a fairly low mass and easier to contain in the bay. Your alternative design has a lot more inertia in the tail end of the rocket and will require a significant amount of shear pins to resist that joint from separating.

Have you flown this rocket in this configuration several times and validated this arrangement? I'm not saying it can't be done, just that a lot more care is needed when sizing shear pins. My fear is that you will experience early main deployment more frequently than not.

patelldp said:

Have you flown this rocket in this configuration several times and validated this arrangement? I'm not saying it can't be done, just that a lot more care is needed when sizing shear pins. My fear is that you will experience early main deployment more frequently than not.

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No, the first flight we will in two weeks at XPRS. I normally do the other arrangement (drogue aft, main forward); and you do have an excellent point about the forces on the pins holding the break for the main.

Great video John. Truley one to watch.


Alexander Solis

Level 1 - Mariah 54 - CTI-I100 Red Lightning Longburn - 6,345 Feet

John, where did you get that motor retainer? Also I understand Binder recommends DD on his kits be set up this way. His theory is there is more weight on the payload section/av-bay to help pull out the main over the weight of the nosecone alone. Makes sense to me.

grouch said:

John, where did you get that motor retainer?

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That one was made by "Rowe's Retainers", but is very old so may no longer be available.

Another excellent tutorial!

JohnCoker said:

That one was made by "Rowe's Retainers", but is very old so may no longer be available.

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Think there gone price list is from 2006

chris m said:

Think there gone price list is from 2006

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I emailed them, but I agree. I think they are gone

Yeah, maybe I shouldn't have used a discontinued product in the video, but I'd had it laying in my box o' retention devices for a while and felt the need to finally use it.

Those who've seen my other pages have spied AeroPack and Giant Leap retainers as well.

Also, of course one can use the venerable Kaplow clips, as I did on my Aerobee, using Shapeways to make them of stainless steel:

With retainers if you have them use it . To bad the company is out of business . They had a bell shape retainer that would be very cool.

I'm sure that av-bay design will work, but I would never epoxy and av-bay into the payload tube. How do you access the top of the av-bay for the forward charge?

I prefer charge cups mounted to the av-bay and they would be impossible to do if the av-bay was epoxied to the payload bay.

I presume it's possible to only glue in the coupler and not the forward bulkhead.

Handeman said:

I'm sure that av-bay design will work, but I would never epoxy and av-bay into the payload tube. How do you access the top of the av-bay for the forward charge?

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The forward payload tube is very short, so it's no problem to reach in from the forward end.

matthew said:

I presume it's possible to only glue in the coupler and not the forward bulkhead.

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Sure, you could make both ends caps that fit into the coupler. You could also epoxy in a forward ring that a completely removable bay rests against.

JohnCoker said:

... I normally do the other arrangement (drogue aft, main forward); and you do have an excellent point about the forces on the pins holding the break for the main.

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Nice video as always. The HP rocket I'm currently finishing up (see https://www.rocketryforum.com/showthread.php?63897-Upscale-Fliskits-Flea-The-Tick-HPR-build) will also have the main located in the booster section. I'm using 3x shear pins at both the payload and booster separation points (2-56 nylon screws, screwed into brass inserts that are mounted in the av bay couplers). I have some small concern that the apogee charge and resultant force could be enough to not only separate the forward payload section, but also separate the booster section. I don't actually think this will happen, but it did cross my mind. Assuming it does not, then I have no concern that gravity will somehow shear the pins as the rocket is falling on the drogue.

The biggest reason I am configuring the rocket this way is that the booster section is nearly 5x as massive as the payload section. My preference is to have the larger chute closer to all that mass, and the smaller drogue handling the lesser mass of the payload bay. (I realize that because everything is tethered together, it is one big mass - but treating them as separate 'loosely coupled' sections allows me to go for that very cool effect where the main blossoms, slowing the booster down, and the drogue then inflates just enough to have the payload section match the descent speed of the now-slowed booster. You end up with that graceful 'everything gently floating down' effect, which is truly spectacular to watch.)

Well, the proof of the pudding is in the eating, and the modified EZI-65 flew twice perfectly at XPRS this weekend:
jcrocket.com/ezi-65.shtml

Note that I went with two #2 Nylon screws for shear pins on the main. Paper tube also has higher friction than harder materials, which I'm sure helped as well.