98mm N5800 MD rocket for BALLS

What are your preparations for the worst case where it shreds? How will you keep track of the parts? Do you care? (after all you are doing single deeply fast descent and you are launching at BALLS)

CarVac said:

What are your preparations for the worst case where it shreds? How will you keep track of the parts? Do you care? (after all you are doing single deeply fast descent and you are launching at BALLS)

Click to expand...

Honestly, at that point, it's visual tracking and picking up everything I can find. To respond to your statement in parentheses - I'm doing dual deploy (I'm still on the fence between a 12 inch chute at apogee to guarantee that it is unstable or droguless), with only a moderately fast descent (28 fps at last estimate). Granted, it's a nonstandard dual deploy profile, with the main around 5000 feet, but it's definitely not single deploy, since a chute of this size would almost definitely carry it out of the waiver cylinder if deployed at 120k (descent would take well over 20 minutes). If it comes apart, I'd definitely love to pick up as much as I can, both to avoid littering, and to have the best possible chance of diagnosing the failure point. That having been said, I'm not explicitly designing anything to survive a failure - I don't have the mass or volume margins for that.

Best of luck with the launch. I look forward to a report of a successful flight.

To the thread starter, do you have a Youtube Channel? I'd like to see the video as soon as it launches. Reminds me of Qu8ke

Don: I do indeed, and I'll post any video that I have here. I'm expecting two pad cameras plus whatever video I can get from other people who are at the launch.

Also, I'm just about ready - I'm leaving for BALLS in the morning, and the rocket is basically complete. Here are the beauty shots:

Good luck Chris!

Cj

I second that Chris... good luck. I've followed this thread and you've definitely done your homework.
See you at Oktoberfest perhaps.

Jim

Very nice looking rocket, Chris. Looking forward to seeing it fly (on video). Good luck!

Jeroen

That's a sweet lookin' rocket!

I hope that you meet or exceed your goals.

Greg

Looks great Chris. Good luck!


Matt

So what happened with the test fin? What was the test apparatus and loading when it failed?

Am I correct in my assumption that you decided not to tip to tip? :gavel:

Good luck at Balls

I did not tip to tip, and as for the test fin, I didn't have any extremely scientific method of testing (sadly), but it was easily able to withstand all of my weight on the tip of the fin, with the body tube clamped in place. I still haven't broken it, but that test was sufficient to convince me that it should be strong enough. Of course, that's all based on the assumption that the fins will never see a significant angle of attack. If something caused the rocket to pitch over a bit at high speed, all bets are off.

Chris, so long as your fins are glued from the very tip of the fin you should be fine. What resin did you use to adhere the fins to the tube?

Cotronics 4461.

Best of Luck Chris!!!

Best of luck Chris! I really want to see this one make it. It's so beautiful! Good Luck!

Go get 'em tiger. Looks great!

I'm rootin' for ya Chris.

And that'll be the last time we see that rocket with that nice of a paint job. Whether or not the flight is successful.

Im excited to see this fly, I hope you all the best.

Just curious, and I have not worked with L3 motors so my experience is admittedly minimal. However, the problem seems to be that at the beginning of the launch you need larger fins for stability, but then as the rocket gains speed, those larger fins become obstacles. There needs to be a way to have large fins at launch when you need them, and smaller fins at speed when you don't.

I am thinking that perhaps the best approach with an N5800 is to make it the second stage of a min. dia. 2-stage attempt. The first stage would be done with 2-3 V-max motors to get the rocket up to speed, then 1 second after launch you airstart the N5800. This way the need for large fins on the N5800 stage is negated. The rocket is moving fast enough at that point that you don't need that much stability. The smaller the fin, the less likely it will be destroyed and result in a shred. The larger fins would be on the first stage. This would not break the N record you are attempting, but it would truly live up to the spirit of "Balls."

Another thought would be to figure out how to make "breakaway fins" where the outer sections would break off (or be ejected?) at a certain velocity.

edwinshap1 said:

Chris, so long as your fins are glued from the very tip of the fin you should be fine.

Click to expand...

Has it ever been done before?

EeebeeE said:

Just curious, and I have not worked with L3 motors so my experience is admittedly minimal. However, the problem seems to be that at the beginning of the launch you need larger fins for stability, but then as the rocket gains speed, those larger fins become obstacles. There needs to be a way to have large fins at launch when you need them, and smaller fins at speed when you don't.

I am thinking that perhaps the best approach with an N5800 is to make it the second stage of a min. dia. 2-stage attempt. The first stage would be done with 2-3 V-max motors to get the rocket up to speed, then 1 second after launch you airstart the N5800. This way the need for large fins on the N5800 stage is negated. The rocket is moving fast enough at that point that you don't need that much stability. The smaller the fin, the less likely it will be destroyed and result in a shred. The larger fins would be on the first stage. This would not break the N record you are attempting, but it would truly live up to the spirit of "Balls."

Click to expand...

Evan: Check the thrust curve for the N5800. Initial thrust is like 6800 newtons, waay more then enough to take small fins to a fast speed on a minimum diameter rocket. The issue with this rocket is that if it yaws or cones, shreds will occur....

EeebeeE said:

Just curious, and I have not worked with L3 motors so my experience is admittedly minimal. However, the problem seems to be that at the beginning of the launch you need larger fins for stability, but then as the rocket gains speed, those larger fins become obstacles. There needs to be a way to have large fins at launch when you need them, and smaller fins at speed when you don't.

Click to expand...

Interestingly enough, as you start going really fast (mach 3+ or so), the cp actually starts to shift forwards, so the stability is most marginal on this rocket at burnout. Because of this, the fins really couldn't be any smaller unless I added noseweight. There is some merit to your idea though - not so much for the smaller fins, but simply because the higher you can get it before lighting the N5800, the less dense the air you have to push through, and therefore the lower the forces on the rocket.

I obviously have more to learn before I get to this level. But I appreciate the feedback and your letting me into the conversation. It is a beautiful rocket, and II am looking forward to seeing flights of it on youtube.

The only suggestion I might offer is to find room for an MD-80 micro video camera on board. The camera only weighs 0.6 oz. with battery, is about 1.75" long, x 0.75" wide and 0.75" tall. With an 8gig micro SD card, it will record for a couple hours. Mount it inside facing the horizon and cover the opening with a small piece of glass. I have used this configuration and the peeop hole I use is 1/8" in diameter. You could go down to 1/16"but your alignment needs to be perfect.

It would be a low quality video (720 x 480) and it might skip a couple frames because of the speed, but a video nonetheless. If I was going to send something up into the darkness of space, I would want to see what my rocket saw. Onboard HD cameras are larger and weigh more, and would need a larger peep hole to see out of.

Best of luck to you.

Really looking forward to seeing how the rocket looks after your successful flight. I love that scorched paint from high-supersonic flight look!

I really want to see this one succeed. What a clean and purposeful looking design, best of luck Chris.

Yes, that sounds good. Also the 808 #16 or #18 camera from eBay. About the same weight (weighs 19 grams) but records in high def (1280x720p) $39
I used the older version on my rockets (the #11) for $11


Edit: I just read your message that you left for BALLS. I hope u got to include an onboard camera!

Good Luck, Chris!

I would love to hear what happens. I'm sure one of these threads will have the results. There will be a large audience of interested followers.

Good luck Chris! We're rooting for you. The rocket looks great.

Want this to succeed VERY badly...it would just be a shame to shred...