Building My First Custom Rocket......Few Questions

FjStix

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I am designing and building this rocket based off of the best simulation results I can get in RockSim. It is a 66mm Tube which is 48" L, A 29mm Motor Mount with either an Aerotech F20 or F67 Motor. My main questions are as follows:

1) What's the threshold for Longitudinal G-Forces leaving the rail? I understand this comes down to build quality at a certain point. I am hovering around 25 G's @ 70-75 Ft/s within the first 48". Any concerns or is this well within norminal?

2) What is a High Ft/S Descent rate at chute deployment? I am using a 24" Nylon Chute and with the Chute Release drag, I am within 80-100 Ft/S at Deployment. Too Fast? Again, I understand if the shock cord isn't installed adequately then bad things will happen.

3) Piggy-Backing on the previous question. What is the max Ft/s @ Chute Deployment you would recommend. I am a champion at losing rockets and want to get this down as close as I can before releasing the main. I am factoring in the drag of the folded chute/chute release which is deployed near Apogee of 1,500 Ft.

4) Final question - If there was one thing you would warn a new rocketeer about for their first flight above a few hundred ft, what would it be? I am thinking of doing a build thread to gather as much information and guidance as possible.

Thanks All!
 

boatgeek

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1. 25G might be a little high if you're using low power/Estes tubing. If you're using thicker wall tube, then no problem.

2. For apogee deployment, you usually want to be within 2 seconds of apogee, or 60-ish ft/s. For main deployment (dual deploy or chute release), the usual rule of thumb is 80-100 ft/s.

3. It's probably a bad idea to put in an extra long delay to reduce drift. When the chute opens, the chute will shred or tear a zipper into the body tube. The extra few seconds of delay won't materially reduce your drift and dramatically increase chances of damage. Dual deploy using a chute release is the easiest way to reduce drift. I typically set the release at around 400-600 feet, but other people like to go higher or lower. The rocket will fall quickly to the release altitude and then open the main chute for a soft landing. A smaller chute can help with less walking if you have a soft field to fly on.

4a. Point at the rocket while it's in the air. That makes it easier for you to see, easier for others to spot it if they lose sight of it, and easier for you to pick it up again if you lose sight of it. If you're not on a smooth field, I like to wait until the rocket lands until I start walking for recovery. Less chance of tripping and/or losing the rocket when you look down. b. If you're using a chute release, practice ahead of time, both folding technique and making sure that the band isn't too loose (chute deploys at apogee and a long walk) or too tight (chute never deploys).
 

dpower

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4) Final question - If there was one thing you would warn a new rocketeer about for their first flight above a few hundred ft, what would it be? I am thinking of doing a build thread to gather as much information and guidance as possible.

Thanks All!
Recovery. It gets much easier to lose them, so think about the size of the recovery area, hazards (water, trees, cornfields, etc), and plan accordingly, using techniques to bring it down faster, and more easily locatable (tracker). Or for simple rockets like the Estes Goblin, just let ‘er rip, and, and realize you might not get it back.
 

teepot

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What is a High Ft/S Descent rate at chute deployment? I am using a 24" Nylon Chute and with the Chute Release drag, I am within 80-100 Ft/S at Deployment. Too Fast? Again, I understand if the shock cord isn't installed adequately then bad things will happen.
I like to come down under drouge or with the parachute held by a chute release at 50 fps. Land at 15fps or less.
 

FjStix

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I like to come down under drouge or with the parachute held by a chute release at 50 fps. Land at 15fps or less.

I am planning on using my Chute Release but according to RockSim It will be closer to 100FPS at deployment unless I deploy higher. Is it common to have a drogue deploy at my 6s ejection delay (Apogee) and still use a chute release. I feel like that would be an easy tangle situation if not done right.
 

boatgeek

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I am planning on using my Chute Release but according to RockSim It will be closer to 100FPS at deployment unless I deploy higher. Is it common to have a drogue deploy at my 6s ejection delay (Apogee) and still use a chute release. I feel like that would be an easy tangle situation if not done right.

I would suggest that you set your delay so that ejection is as close as possible to apogee, but definitely within 1-2 seconds. If you have a choice of going a little long or a little short on the delay, go with short. There's lots of things that make a rocket get less altitude than the sim, but not nearly as many that make it get more altitude.

After ejection, your chute balled up in the chute release will act as a drogue (there's a thread with descent speed data under JLCR on TRF somewhere...) and will keep the rocket falling at a fairly reasonable speed. Some people add another drogue or streamer as well, but I haven't found it necessary. On my flights, the shock cord stretched out pretty well for no tangling.

Then you can set the JLCR altitude to somewhere in the 500-foot range and have a soft landing.
 

FjStix

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Thanks All! If this thread Isn't gone when I launch I will post up my results.
 
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