My Scratch MPR Crashed First Flight ) :

[[POW]Eagle159]

So I got out to launch in the morning, It was a calm day, but up 200 feet, there was moderate winds, I only flew 5 out of 8 rochets, with 1 crash and 1 MIA.

So here is the crash, it lawn darted from about 400 feet. This was my first Mid-Powered flight(other than my Saturn V), on an At E20-4w.

The take off was nice! and the ejection was a tad late, it was still pointing upwards but falling backwards.

Then the ejection charge went off...... The nose cone went shooting off annnnd kept on going. I attached the shock cord around the eyelet, but that failed.
Sense I am new to MPR, I thought my 24" estes Saturn V chute would be a good choice. Nope, poor chute had no chance, the shroud lines all ripped from the plastic and the rest of the chute floated away never to be seen again.

And then the inevitable lawn dart happened, The LOC 3in. tube didnt get damaged at all, no paint was hurt, But the tube stuck in the field 5 inches. The nose cone tumbled down and made a nice tip first landing. It did whistle a bit on the way down....


I do/dont know what went wrong after learning what happened from the crash site. I know now the attachment to the nose cone was weak and the plastic estes chute was WAY to weak.


I had 12 feet of kevlar shock cord, is that too short? It seemed like it. I still dont know if Im going to re-fly it or keep it grounded...
ALSO, I used cardboard centering rings, one rear, one above fin tabs and one at the front of the stuffer tube, when I looked down the tube the forward centering ring is gone! Did it get blown out?!? If so HOW? The card stock centering rings om my estes Saturn V survived 2 E20 flights and they were thinner!

Any input on my build/flight, any questions/comments? Thanks for reading.

 

[aditat2]

What a shame!! That's a pretty bird. Did you have your shock cord attached to the front centering ring? If so , that could have pulled it out. I understand that most centering ring/motor mount failures are usually due to failure of the glue joint, not the ring itself, so I'm not sure what the problem there could be unless I could actually see it. I'm pretty new to MPR myself, but everything I have learned has made me go for sturdier chutes and shock cords, not to mention attachment points, to give mine the best possible chance for survival on the way down. Standard wisdom is that your shock cord should be at least 3X the length of the rocket, so judging from the pictures I would say it was probably ok, but just barely. Since the damage was minimal I'd rebuild and try it again, but that's me.

 

[Rocketbuilder]

That's too bad. I would say 12ft of Kevlar might have been a little short, but that probably wasn't the main factor. You definitely need a nylon chute for heavier rockets that you don't know for certain will eject at apogee. I purchased a Top Flite nylon chute from my club's on-site vendor, and I love it. It just blows away the plastic Estes chutes. In fact, now that I've got snap swivels on all my rockets, I may just get a few nylon chutes and use them exclusively. Get one, trust me, you will like it. :2:
As for the centering ring, I had a similar experience when the top stage of my three-stager lawn-darted; the forward (fiber) centering ring and the standard Estes motor tube were nocked out, despite being very securely glued in. I guess those sorts of things have a lot more kinetic energy than we realize, when they get moving that fast.
But hey, it'll fly again. Or, if you decide to keep it grounded (cough, cough, DON'T DO IT! cough), plant something in it!

 

[tightwad]

I feel for you. Your photos brought back memories of my scratch built Atlas that took core samples 8 inches deep. No chute election on mine. These things happen. Fly her again with a nylon chute and a touch more shock cord...say, 15 feet or so, if you have the room.

 

[hornet driver]

That's a tough one! That was/ is a great looking bird. I have a feeling we'll see her in the air again.

 

[Rex R]

the fact that the eyelet on the nose ripped out would lead me to believe that the shock cord was too short. I make a point to not attach the chute to the nose directly (bout a foot down on the cord).
rex
edit
if you could see your way to mentioning the recovery weight, we could assist in chute selection.

 

[bill_s]

12 feet of Kevlar, or 100 feet, isn't going to stretch. The length gives a chance for the nose cone to slow down but that's it. You need some actual shock absorbation for a plastic chute on heavy rocket, at least. I ripped one shroud line out of an Estes 24" with a >100 ft/sec eject (x >1 lb.) and 12 feet of 1/2" elastic.

Seems impossible that the cone would become detached AND blow out the chute ...

 

[chadrog]

Try bundling and taping your kevlar cord. It's a nearly free way to absorb ejection shock. I do this on almost all of my rockets with kevlar cords, and none have sustained any damage with the cords prepped this way.

A wrap or two of masking tape around four or five bundles works wonders!

 

[azgreg]

Don't take this the wrong way, but this is a cool picture. As a matter of fact it will be my desk top for awhile.

 

[BABAR]

Ouch!

The most frustrating launches are not the ones that go south, but the ones that go south and you don't know WHY. In this case you've got some good ideas to make sure it doesn't happen next time, and it looks like you got the parts you needed to fly it again back relatively intact (concur with previous poster, nice looking bird.) Seems like a combo of Kevlar and Elastic makes sense (Kevlar on the rocket attachment end to weather the ejection blast, underwear or other elastic on the chute and nose end to soften the shock.) Nylon chute makes sense.

On the good side, you had a stable boost and a successful ejection mechanism, and what you recovered is flyable again.

Good luck on the next flight!

 

[[POW]Eagle159]

Thanks for the comments!

The rocket is quite fine, the nose cone is on rather tight but I can fix that.
I just have to cut out another centering ring, a little stronger this time. The ring was never recovered from the crash site so I still dont know what happened to it...

The shock cord is glued on to the side of the tube wall, like the estes kits but better.( that part is fine).

I will buy a nylon chute around 24" The rocket is 17 ounces. And I will add another 5 feet of shock cord, maybe elastic?

@azgreg, Yea my dad thought that was an awesome picture(I think he was proud of taking the shot).

 

[Green Jello]

Wow man, that really sucks. Sorry.

These pictures really show the difference between Florida where you are, and Nevada where I am. That thing would have been in a million pieces out here instead of 5 inches into the ground. So hey.....a bright side.

 

[qquake2k]

I've used both elastic and nylon webbing on rockets that size. I never use just Kevlar. Nylon webbing is *slightly* more stretchy than Kevlar. Probably not enough to matter, but it makes me feel better. When I use webbing, I always go at least 18ft or longer. I also bundle it with tiny rubber bands. Even with all that, I have had zippers. I think if you fly enough it's inevitable.

As for attaching to the nose cone, I never use the plastic loop on the cone. I drill two holes in it and tie a loop of cord through the holes to use as the attachment point.

https://www.rocketryforum.com/showt...tch-build-the-Plasma-Fart&p=309735#post309735

 

[Rocketjunkie]

If you want the best of both the strength of nylon or Kevlar and stretch try using both Take the elastic, stretch it fully and then reduce the length about 10%. Tie loops in your nylon or Kevlar this distance apart. Attach the elastic to these loops. On a strong ejection, the elastic will stretch but the nylon or Kevlar will take up the load before the elastic breaks.