How Long Do LPRs Last? (And Does Anyone Even Care?)

[Spitfire222]

I laugh when Nasa or whoever pushes rocketry as a ''science'' hobby that leads to engineering. Because it's mostly autobody dust bunny stuff.

Yeah! Because rocketry has nothing to do with applied engineering and the laws of physics, no siree!

 

[BEC]

Believe me Bernard is seriously into rockets, he flies more in a weekend that me and my three kids do in a year, and my kids rockets eat Estes 24packs faster than I like buying them....

Thanks, Rich..... I think.

 

[Sooner Boomer]

I think a lot of the potential longevity has to do with the design of the rocket. Long skinny surface mounted fins that hang below the aft of the body tube are likely to get broken off. On the other hand, spools rarely wear out, get broken, or thermal away under a parachute.

Next, how does one mean "last"? Below is my 20-something year old Fat Boy.

A friend once told me he had the exact same hatchet that George Washington used to cut down the cherry tree. "Of course", he said, "over time the head fell off and got lost, so a new one was put on. And a couple of handles rotted or split, or fell off, and they were replaced, too. But it's the same exact hatchet that George had".

 

[jflis]

I have many rockets that are over 30 yrs old that are flyable (and do fly from time to time). My best was an Astron Sprint I built in 1973 that flew its last, and 500th flight at NARAM back in the early 2000’s…

 

[4regt4]

Kevlar shock cords won't last longer, especially if you tie to it the motor mount. There it will burn through in anywhere from 2 to 30+ flights. If put in via a tri-fold, it will eventually get sawn through by the upper end of the body tube. I put a heat-shrink tube on kevlar shock cords where they rub against the top of the body now to alleviate that, but don't have enough flights on a model set up that way to be confident in saying that doing that solves the problem. The regular rubber shock cords actually will survive this longer, but they do dry out over time, so in part it will depend on the time frame over which this experiment is conducted.

Last week I had a failure of a hybrid Kevlar/rubber band shock cord. It failed right at the knot joining the two together, which was near the end of the body tube. But not how you might suspect! The Kevlar burned through, however, the rubber looked fine. No signs of scorching. The rubber knot was assembled with a smear of wood glue to (hopefully) keep it from coming undone. The knot was still holding the bit of Kevlar that went through it, the burn through point was about 1/4" away. The Kevlar was a bit light, 100lb. It's all I had at the time.

Hans.

 

[BEC]

I was wondering when @jflis was going to turn up in this thread and remind us about that Sprint.

Hans, I’ve seen a Kevlar/rubber shock cord fail that way.

I have a model that I built in Jr. High (in 1967) that is still flyable AND has the original rubber shock cord (made with 1/8 inch Sig contest rubber) but it has only been flown a few times. This is it just before its first flight in over 50 years (on the same Tilt-a-pad it flew from back then).

 

[smstachwick]

I think a lot of the potential longevity has to do with the design of the rocket. Long skinny surface mounted fins that hang below the aft of the body tube are likely to get broken off. On the other hand, spools rarely wear out, get broken, or thermal away under a parachute.

Next, how does one mean "last"? Below is my 20-something year old Fat Boy.

A friend once told me he had the exact same hatchet that George Washington used to cut down the cherry tree. "Of course", he said, "over time the head fell off and got lost, so a new one was put on. And a couple of handles rotted or split, or fell off, and they were replaced, too. But it's the same exact hatchet that George had".

View attachment 518117

Ship Rocket of Theseus @Sooner Boomer

Ship of Theseus - Wikipedia

en.m.wikipedia.org

 

[BEC]

Ship Rocket of Theseus @Sooner Boomer

Ship of Theseus - Wikipedia

en.m.wikipedia.org

Yeah. We had this discussion around my 104-flight-and-counting Alpha after a shock cord failure on flight 97 which led to the floating away of the nose cone and ‘chute (and a FireFly altimeter), subsequent lawn dart onto a hard packed surface of the body and rebuild, repaint and re-decal.

But the fins and motor mount and the bottom five inches or so of the body are all parts of the original build, so I still call it the same Alpha.

 

[Sooner Boomer]

Ship Rocket of Theseus @Sooner Boomer

Ship of Theseus - Wikipedia

en.m.wikipedia.org

Terry Pratchett's "Scone of Stone".

 

[Cape Byron]

Ship Rocket of Theseus @Sooner Boomer

Ship of Theseus - Wikipedia

en.m.wikipedia.org

I have this discussion all the time with the kids about my 'Grandfather's axe, chisel, hammer whatever tool they want to misuse'. They're about as interested in the discussion as a wet rock on a cold day.

 

[PDawg]

Today was my 10th launch and recovery of my Puck Futin C powered Rocket. It has landed in water and had a fin re-attached 4 times. The body tube is failing under the fins so I'm retiring it and re-using the nose cone, engine mount, and 2/3rds of the body t tube. Not bad for an under $10 scratch build. I was happy to get it back at all with the Rocket eating trees around.

 

[mo2872]

I have an Estes Sentinel, Recruiter, and Der V3 I built in the late 80's/early 90's that all have dozens of flights on them. Just for an anecdotal piece of evidence/information.

 

[GalantVR41062]

A gathering of rockets I have built as a BAR. 3 kits and a hand full of scratch builds.
The 2 on the far right have the most flights.

The black and blue is named Recon 1 1/2. It's my first mid power scratch build, the lower body tube is from a old Estes ASTRO cam. I did not know about simulation software, did a cardboard cutout CP and trial and error for a stable flight with revised smaller canards and new longer, heavier nose cone. Has been through the ringer:


Splash down on its 3rd flight, broken off 3 of the 4 fins, a couple times each, patched up shock cords and a couple different chutes, flown on 18mm C6-3 upto a econojet F44w. Still used as a test flight at parks 19 and counting (I do hash marks on my rockets and a notebook of most flights).



This short scratch build has a boat tail, 24mmt, small payload that has had a 808 side view cam, ARTS 2 flight computer, Raven 3 flight computer in it. It's 18th and last flight was with a EX rocket candy load for the 24/40 aerotech case. The hard landing was about it for the payload tube, tired of gluing, bracing, re-stringing recovery gear.

 

[Grog6]

No, but I didn't have anything with me to take it out, and I'm not quite crazy enough to go all crocodile hunter on it. I've been told since that I can shoot it if I see it again, as a public danger.

 

[DaHabes]

So I posted a thread recently and one of the topics that came up is how long LPRs (or certain components inside an LPR) can last. It seems like no one really knows, and there's any number of reasons: people don't keep count of their flights for a rocket, rockets gets lost, destroyed or eaten by trees, rockets that last a while eventually get retired and sit on a shelf, etc.

So here's my question: if I (or anyone else so inclined) were to take a generic BT-50 or BT-60 3FNC or 4FNC type of rocket and run a bunch of engines through it, how many people here would care about the results? For example, I might take an Estes Alpha and build it 100% stock (or with a few mods, like adding a baffle and using a Kevlar shock cord), then run 13mm and 18mm engines through it and see how long the rocket (or one of its components, like a shock cord) lasts until it can no longer fly without major repairs. And if the rocket survives the several dozen engines run through it (and I can no longer afford to buy more engines), I'll do an autopsy of what I find inside the rocket.

So if you'd be interested in such a "study," let me know. And if you have any suggestions or other thoughts, I'm all ears.

My original Little Joe II was 50 year old and had been flown 30+ times, repaired many times. I finally retired it after two erratic flights. Theoretically, there is no reason for any limit as long as you maintain the consumables (shock cord and chute). If upon inspection they are suspect they should be replaced rather than flown to failure, for safety reasons.