NC Mid, or Chute?

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dhbarr

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Consider a spherical model rocket in a vacuum...

Wait, no. Consider a typical BP 4FNC. Some manufacturers want the NC in the middle of the train, others on the end.

Has anyone done studies on successful deployment percentages, partial failure modes, etc?

Is this a .gif/.gif question, where I'll get roasted on both sides?

What's your personal preference? Is there anyone who's seen rocket mid?
 

SpaceManMat

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My preference is to put the chute at the end. With the NC on the end it is essentially unrestrained and can bounce back when the chute opens and strike the chute and/or cause tangles. By putting the chute at the end the weight of the main body and motor will act to restrain the NC from going too far. Figured that out on the shake down flight for my L1 and stuck to it ever since.
 

Banzai88

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I've always been a nose cone, length of line, then parachute, then rocket. Sometimes I would put the parachute attachment to the ring on the nose cone. I wasn't cognizant of any difference until recently. I started paying more attention to how my rockets acted under full canopy. What I found is that the 'best' depends on the rocket and parachute type combo as a system.

My fiberglass minis tend to helicopter (twirl around and around during descent, clearly around a center influenced by the nose cone)and land with a high lateral velocity/rolling on ground impact when going my old way. Placing the parachute attachment on the end of the line, no more twirling and only slight oscillations normal to parasheets.

One other thing I've noted since changing configurations is that a flat sheet, flat sheet with vent hole, and elliptical will all act differently under load for the different locations.

So, try it one way, if that doesn't work the way you want it, change location or change 'cute type. I think that the heavier the rocket, the less it matters.
 
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mccordmw

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I prefer to not attach the parachute to the nosecone. The reason being some of the plastic loops on the nosecone don't seem very sturdy. I'm looking at a LOC PNC3.00 right now on my scratch build, and the attachment loop seems really flimsy. I can bend it with my pinky finger. If I put the main on that, it's going to get a good jerk on deployment. Also, if something goes wrong with the drogue, the main might deploy under much higher speed. I'd be afraid of the nosecone loop breaking. Conversely, the strength of the tubular nylon shock cord is way way stronger. It can take a high speed deployment. The chute would shred first. That affords me some additional protection.

That being said, I don't put the chute very far down from the nosecone. About 2' from it, I put in a loop and tie in the chute. With that layout, the nosecone attachment only takes the weight of the cone itself.

My general measurement rules are 1/3 : 2/3 for harness attachment points for the chutes, and 1 rocket lenght : 2 rocket lengths for harness lengths. Like this...

recovery diagram.jpg

So for a typical 6 foot rocket, the harness length for the drogue is 12' (+about 4' for the length inside the booster airframe). The drogue is 4' from the payload bay. The harness for the main is 6' with the main chute attached 2' from the nosecone.
 
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blackbrandt

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I prefer to not attach the parachute to the nosecone. The reason being some of the plastic loops on the nosecone don't seem very sturdy. I'm looking at a LOC PNC3.00 right now on my scratch build, and the attachment loop seems really flimsy. I can bend it with my pinky finger. If I put the main on that, it's going to get a good jerk on deployment. Also, if something goes wrong with the drogue, the main might deploy under much higher speed. I'd be afraid of the nosecone loop breaking. Conversely, the strength of the tubular nylon shock cord is way way stronger. It can take a high speed deployment. The chute would shred first. That affords me some additional protection.

That being said, I don't put the chute very far down from the nosecone. About 2' from it, I put in a loop and tie in the chute. With that layout, the nosecone attachment only takes the weight of the cone itself.

My general measurement rules are 1/3 : 2/3 for harness attachment points for the chutes, and 1 rocket lenght : 2 rocket lengths for harness lengths. Like this...

View attachment 300590

So for a typical 6 foot rocket, the harness length for the drogue is 12' (+about 4' for the length inside the booster airframe). The drogue is 4' from the payload bay. The harness for the main is 6' with the main chute attached 2' from the nosecone.
Those shock cords are extremely short... I'd be worried about ripping out my harness attachment points. The minimum generally agreed upon standard is 4-5x the length of the rocket for drogue and 3-4x for main.
 

mccordmw

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Those shock cords are extremely short... I'd be worried about ripping out my harness attachment points. The minimum generally agreed upon standard is 4-5x the length of the rocket for drogue and 3-4x for main.
I haven't sent up any huge rockets yet. I've been living in the MPR realm so far. L1 is coming in a couple weeks (fingers crossed). I've found with the lighter MPR, a total of 3x rocket length worked fine and kept weight down enough to put up my bigger rockets on G motors. I always followed this newsletter: https://www.apogeerockets.com/education/downloads/Newsletter348.pdf

Then again, I'm sure the bigger L1-L3 rockets play by different rules. Has anyone done a study on force experienced vs length for heavier rockets?
 

rharshberger

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I prefer to not attach the parachute to the nosecone. The reason being some of the plastic loops on the nosecone don't seem very sturdy. I'm looking at a LOC PNC3.00 right now on my scratch build, and the attachment loop seems really flimsy. I can bend it with my pinky finger. If I put the main on that, it's going to get a good jerk on deployment. Also, if something goes wrong with the drogue, the main might deploy under much higher speed. I'd be afraid of the nosecone loop breaking. Conversely, the strength of the tubular nylon shock cord is way way stronger. It can take a high speed deployment. The chute would shred first. That affords me some additional protection.


+1 not attaching directly to nose cone loop, I use a short tether/leader to attach my chutes to the nose cone loop of the recovery harness, but not to the nosecones' plastic loop directly. That way I don't get a nosecone and chute separation from the rest of the rocket. Usually my rockets are large enough that a small quick link is used to connect the NC loop, the recovery harness and the chute all together.
 

mpitfield

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+1 not attaching directly to nose cone loop, I use a short tether/leader to attach my chutes to the nose cone loop of the recovery harness, but not to the nosecones' plastic loop directly. That way I don't get a nosecone and chute separation from the rest of the rocket. Usually my rockets are large enough that a small quick link is used to connect the NC loop, the recovery harness and the chute all together.
+2 I typically try to get the chute as close to the NC as possible. Keep in mind most of my rockets are HP and for the most part I use One Bad Hawk's 25' 3 loop harnesses between the sections. This results in the NC hanging about 3' below the swivel at the end of the bridle, give or take.
 

Banzai88

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The minimum generally agreed upon standard is 4-5x the length of the rocket for drogue and 3-4x for main.

Which has more to do with the profusion of "Blow it out or blow it up" than actual measured proper length.
 

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