Wildman RB-05A Sport, L-1 Cert failure, and I need shock cord options.

[Andrew_ASC]

I flew this RB-05A at VAST the other day after a university launch, it's very stable at a stability margin of 1.73 in OR, it handles stiff crosswinds nicely, leaves pad at decent velocity, and it had an empty weight of 2.5 pounds. There is a pound of lead in the nosecone as a modification since the stock rocket kit had -0.33 stability. Fully loaded is 3.5 pounds. The I300T-14A punts this heavy little guy a mile high basically in windy conditions. It sims for apogee at 16.6s on a good day. RSO helped me install a 550 Paracord shock cord on the range at his advice for longer length and it snapped anyways on deployment and that heavy nosecone slammed into earth from 5,400ft. I think it needs a thicker shock cord, but I don't have the experience to know how thick. I've got an IRIS 24" drogue and a RMS 38/480 casing. Other motor option is a 1299N, but I'm afraid of using the WARP9 since destroying a multistage rocket already with one this year, and having a deployment charge electronically explode next to hand on packing. Kit survived fall with no damage and I got the pieces back so its flying again someday.

 

[dhbarr]

Go see Teddy at OBH, you're all set.

 

[ksaves2]

Go see Teddy at OBH, you're all set.

Can't go wrong with that. He'll steer you right. Kurt

 

[Andrew_ASC]

What does OBH mean?

 

[blackbrandt]

OneBadHawk recovery harnesses.

 

[dhbarr]

What does OBH mean?

OneBadHawk recovery harnesses.

Yup, my bad.
https://onebadhawk.com/kevlar-harnesses.html

 

[kevinkal]

it had an empty weight of 2.5 pounds. There is a pound of lead in the nosecone

RSO helped me install a 550 Paracord shock cord on the range at his advice for longer length and it snapped anyways on deployment and that heavy nosecone slammed into earth from 5,400ft.

It seems very unlikely that a nominal, even overcharged, deployment could have generated enough force to fail 550 lb rated paracord with this rocket. Assuming the nosecone weighed ~1 lb, it would need to see 550 G's to fail the cord in tension. Did the cord fail, or did some attachment point fail? Could you please post pictures of the rocket, recovery gear and attachment points? There might be something to see that will enable some better feedback for you.

 

[rharshberger]

It seems very unlikely that a nominal, even overcharged, deployment could have generated enough force to fail 550 lb rated paracord with this rocket. Assuming the nosecone weighed ~1 lb, it would need to see 550 G's to fail the cord in tension. Did the cord fail, or did some attachment point fail? Could you please post pictures of the rocket, recovery gear and attachment points? There might be something to see that will enable some better feedback for you.

Did the edge of the airframe possibly cut the 550 cord? As Kevin pointed out photos can tell all kinds of stories.

 

[Handeman]

It seems very unlikely that a nominal, even overcharged, deployment could have generated enough force to fail 550 lb rated paracord with this rocket. Assuming the nosecone weighed ~1 lb, it would need to see 550 G's to fail the cord in tension. Did the cord fail, or did some attachment point fail? Could you please post pictures of the rocket, recovery gear and attachment points? There might be something to see that will enable some better feedback for you.

It has been my experience that these types of failures are usually because of too strong of ejection charges. How much ground testing did you do?

550 para cord is very susceptible to heat damage. Was it protected from ejection gases?

I would recommend 1/8" tubular Kevlar for shock cord. It is as strong or stronger then the 550 para-cord and much more heat resistant.

 

[Andrew_ASC]

Thanks. I literally don't want any headaches from the rocket I named LeadHead. Tell me what you think about 3/16" or 11/32" kevlar options and bonding cord to sanded airframe. It might be fun to L-2 cert with the setup later and possibly a longer nose with a 38/720 if this works.

 

[markkoelsch]

11/32 is over kill. I use that on my 16.5 pound Wildman Extreme. I think the 3/16" as long as adequate in length should work. 25' should be ok.

I personally would not trust it bonded to the airframe.


Sent from my iPhone using Rocketry Forum

 

[Andrew_ASC]

It has been my experience that these types of failures are usually because of too strong of ejection charges. How much ground testing did you do?

550 para cord is very susceptible to heat damage. Was it protected from ejection gases?

Nomex square with edge length of the body tube diameter. This kit had more in common with a scratch because no manual was supplied. And to be honest the scratch build multistages I did for university were more stable naturally without needing a pound of freaking lead, because custom fin design. A scale missile kit legit needs a pound of lead. No one argues about 1.73 stability versus the alternate of flying it at -0.33. The bond was locktite 5min epoxy since rocketpoxy ripped. The nose is a softer material of some kind, I'm not sure what though, it didn't like bonding too well with rocketpoxy and a hair dryer. The bond was damaged by heat on ground inspection in fiberglass hull but the cord broke at halfway in a shearing motion of exceeding its properties. 0.6 grams of delay charge by a more experienced flyer as mentor. No ground tests that day due to limited time we had to drive home 8 hours. Charge worked perfectly. I wonder if momentum of nosecone destroyed the cord. It was doubled up and it sheared. Bonds didn't fail.

The chute was wrapped in nomex cloth with lines rolled around it. Cotronics 4700 bulkheads and rocketpoxy was used on fins.

 

[Handeman]

Thanks. I literally don't want any headaches from the rocket I named LeadHead. Tell me what you think about 3/16" or 11/32" kevlar options and bonding cord to sanded airframe. It might be fun to L-2 cert with the setup later and possibly a longer nose with a 38/720 if this works.

At 2.5 lbs total weight, the 1/8" tubular Kevlar should be great plenty for shock cord on that rocket. The key is don't use too large of deployment charges.

As for doing L2 with that rocket, I would highly recommend making sure you have 5 or more successful flight on L1 motors before you attempt an L2. BTW, if you got 5400 ft on an I300, you can expect +8000 on a J350.

 

[Andrew_ASC]

To my knowledge the edge of the airframe did not cut the chord because the chord failed at a length longer than the edge of the tube. Has anyone else seen a similar failure?

 

[djs]

I use a y harness and shock cord on mine, using very thin Kevlar. Y harness may fix any problems with the cord being cut.

Btw my Saab flies great on an I212SS motor. Also flew it once on a Loki H100, which flew ok, but a little wobbly.

 

[DavidMcCann]

Note: a lot of commerical 550 cord, isn't.

 

[Andrew_ASC]

Note: a lot of commerical 550 cord, isn't.

Yeah, it took a hammer and a chisel to remove the anchor points. The cord interestingly has a green fiber that isn't 550 paracord inside it. Not good. The exterior was easily confused for paracord. It was what we had in a team range box in quantity required and using it was a bad call that luckily didn't end worse.

If anyone wants to post attachment points without bonding or a thread to such techniques, I'll happy take notes. A 3 point harness Kevlar seems like a good idea at least 10 or 15ft, not certain if I'll bond it to airframe or try bolts/other methods.