A Philosophical Question - How Much of a Rocket Can You Replace

Advertise with us
the rocketry show
The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
jadebox

jadebox

Roger Smith
TRF Sponsor
Joined
Jan 18, 2009
Messages
5,943
Reaction score
584
Okay ... here's a question that just came to mind. How much of a rocket can you replace and still have the rocket?

For example, I'm rebuilding parts of my "YouBee" for the third or fourth time. After the first flight, I replaced the shock cords and parachute. After the second flight, I replaced the electronics bay and main parachute section. After the third flight, I rebuilt the rear (fin) section of the rocket. Now, after the fourth flight, I am replacing the middle sections.

All that will remain of the rocket I originally built and flew will be the nose cone, parachute protector, camera cradle, and a few quick-links.

So, when I get done with this latest rebuild, will it still be the same rocket? How much of a rocket can you replace and have it still be the same rocket? :)

-- Roger
 
Last edited:
jadebox said:
Okay ... here's a question that just came to mind. How much of a rocket can you replace and still have the rocket?

For example, I'm rebuilding parts of my "YouBee" for the third or forth time. After the first flight, I replaced the shock cords and parachute. After the second flight, I replaced the electronics bay and main parachute section. After the third flight, I rebuilt the rear (fin) section of the rocket. Now, after the fourth flight, I am replacing the middle sections.

All that will remain of the rocket I originally built and flew will be the nose cone, parachute protector, camera cradle, and a few quick-links.

So, when I get done with this latest rebuild, will it still be the same rocket? How much of a rocket can you replace and have it still be the same rocket? :)

-- Roger
Click to expand...
I'd say LCD (Lowest Common Denominator) Nose cone, engine clip or launch lug. I have VERY low standards.....I'm cheep, too!
 
WillMarchant said:
https://en.wikipedia.org/wiki/Ship_of_Theseus
Click to expand...

Pretty much like Abraham Lincoln's axe, with X number of new handles and Y number of new blades. I have replaced the entire top half of a (small, cardstock) rocket, but that's as far as I got.

If I ever do end up having to gradually replace every component of a rocket, I think Abraham Lincoln's Axe will be a fine name indeed. :)
 
That's like a story my grandpa used to tell. Guy claimed to own the actual ax that George Washington used to chop down the cherry tree. When questioned further the man confessed that the head had been replaced twice and the handle 5 times but it was still the same ax ;)

LOL at Rocketbuilder!!! Same basic story at nearly the same time :D
 
Last edited:
We rebuilt my son's Quest Gamma Ray, from only the plastic parts that were left (nose cone/payload tube/transition). Lost it on a thermal, and then it was found many months later (and much worse for wear).
 
Antique airplanes are rebuilt and the only “Real Part” from the original plane is the manufactures ID plate.

Mark
 
MClark said:
Antique airplanes are rebuilt and the only “Real Part” from the original plane is the manufactures ID plate.

Mark
Click to expand...
One of my buddies claims to have rebuilt a classic Harley 'from an oil stain'....it's still reproducing today....
 
In the aviation business the rule is that as long as you use at least one part from the unit that was sent in to be repaired you can call it a repair and use the same part number and serial number. Every time it gets repaired you can apply the same rule; even if that means that during a subsequent repair the one "original" part gets replaced. So you could still call it by the same part number and serial number.

If I do a fairly major repair I tend to rename the rocket. When I repaired my Loc Isis, I renamed it Isis II.
 
Zeus-cat said:
In the aviation business the rule is that as long as you use at least one part from the unit that was sent in to be repaired you can call it a repair and use the same part number and serial number. Every time it gets repaired you can apply the same rule; even if that means that during a subsequent repair the one "original" part gets replaced. So you could still call it by the same part number and serial number.
Click to expand...

The keyword you're looking for is "data plate." You can start from a data plate and build a whole new airplane around it, and it's legally the same airplane, conforming to the same airworthiness certificate and all. There are businesses (mostly in Southern California) that build P-51s more or less form scratch to customers' specifications (want an extra seat in the back? no problem) and bolt old data plates onto them. I recall the story of a perfectly fliable airplane that moved countries a lot in its youth and had no US airworthiness certificate and therefore didn't exist as an airplane in FAA's eyes--at most they would register it as experimental. The story is about the owner buying a wreck of an identical model and throwing away everything except the data plate. Legally, he'd repaired the wreck with spare parts from the manufacturer. In practice, he bolted the wreck's data plate onto his existing airplane.

Here in Calif., a constitutional amendment ("Prop 13") limits property tax growth to 2% per year. However selling a house, or building a new one, forces reassessment at market value. Remodeling has no such tax implications. It's very common to see construction sites that tear down an entire building but leave a couple of feet of a side wall standing. The state considers what you build around this wall an alternation to the original building rather than new construction.

Ari.
 
I have a 1980s Estes Bomarc. 1st rebuild in 1990 was replacing all the sheet balsa, a new main tube, and replacing the plastic 'spine' with one built up from more sheet balsa. 2nd rebuild a few months ago replaced everything except the original 'ramjet' nose cones and the 'spine' from the first rebuild, using all new body tubes and basswood.

Can I say I'm flying an almost 30 year old kit at that point?

FC
 
Fun topic - As long as there's at least one part from the original, sure! I saved a couple bits from a maxi x-wing I received from a deceased friends estate, then subsequently totalled; I plan to build a new one around these bits, with parts from an open-box kit. It'll be the *same* rocket, sentimentally. Interesting paradox "The Ship Of Theseus", hadn't seen that before.
 
https://www.nytimes.com/2005/08/02/science/02cell.html?pagewanted=all&_r=0

"Whatever your age, your body is many years younger. In fact, even if you're middle aged, most of you may be just 10 years old or less."
(snip)
"Other tissues have lifetimes measured in years, not days, but are still far from permanent. Even the bones endure nonstop makeover. The entire human skeleton is thought to be replaced every 10 years or so in adults, as twin construction crews of bone-dissolving and bone-rebuilding cells combine to remodel it.

About the only pieces of the body that last a lifetime, on present evidence, seem to be the neurons of the cerebral cortex, the inner lens cells of the eye and perhaps the muscle cells of the heart. "

I'd say you can replace just about everything and still call it the same rocket. We have essentially universal precedent for that kind of claim.
 
Bare Necessities is being modified. Every single part we made except literally six (two nose tip parts, three fins, and the fincan) is being replaced, but the hardest part is being kept intact so we count it as the same.
 
No matter what, it is the same rocket that you have worked on and poured your energy / heart into building. If rockets have souls, the soul of the rocket is still there and begging to be shot off at least one more time.

Evolution in rocketry seems to be a thing on so many levels. You are just doing it on the same rocket. Well done BTW.
 
iter said:
The keyword you're looking for is "data plate." You can start from a data plate and build a whole new airplane around it, and it's legally the same airplane, conforming to the same airworthiness certificate and all. There are businesses (mostly in Southern California) that build P-51s more or less form scratch to customers' specifications (want an extra seat in the back? no problem) and bolt old data plates onto them. I recall the story of a perfectly fliable airplane that moved countries a lot in its youth and had no US airworthiness certificate and therefore didn't exist as an airplane in FAA's eyes--at most they would register it as experimental. The story is about the owner buying a wreck of an identical model and throwing away everything except the data plate. Legally, he'd repaired the wreck with spare parts from the manufacturer. In practice, he bolted the wreck's data plate onto his existing airplane.


Ari.
Click to expand...

When I worked at the helicopter shop, we did that frequently. If the bird was destroyed in a crash, the one part we would go out of our way to acquire would be the data plate. Even if the data plate was unrecognizable, it would be enough. We would just get a new blank data plate to replace the old one and fill it out with metal stamps. Same helicopter.

There are places here in Fort Collins that build new aircraft that way also, including P-51s.
 
BEAR said:
When I worked at the helicopter shop, we did that frequently. If the bird was destroyed in a crash, the one part we would go out of our way to acquire would be the data plate. Even if the data plate was unrecognizable, it would be enough. We would just get a new blank data plate to replace the old one and fill it out with metal stamps. Same helicopter.
Click to expand...

So wait, then the helicopter contains no parts from the original, not even the data plate! Crazy.

Ari.
 
Eventually, with use, every part on an aircraft is going to be replaced. Whether it wears out or it times out (only allowed so many cycles of use or hours of use before it is rebuilt or replaced), so why not the data plate. If it was damaged and the rest of the aircraft was OK, why would you not change out the data plate? That said, change out the worn out data plate for a new one and it is still the same, according to FAA regulations. Put a data plate on your rocket and call it good.
 
iter said:
The keyword you're looking for is "data plate." You can start from a data plate and build a whole new airplane around it, and it's legally the same airplane, conforming to the same airworthiness certificate and all. There are businesses (mostly in Southern California) that build P-51s more or less form scratch to customers' specifications (want an extra seat in the back? no problem) and bolt old data plates onto them. I recall the story of a perfectly fliable airplane that moved countries a lot in its youth and had no US airworthiness certificate and therefore didn't exist as an airplane in FAA's eyes--at most they would register it as experimental. The story is about the owner buying a wreck of an identical model and throwing away everything except the data plate. Legally, he'd repaired the wreck with spare parts from the manufacturer. In practice, he bolted the wreck's data plate onto his existing airplane.

Here in Calif., a constitutional amendment ("Prop 13") limits property tax growth to 2% per year. However selling a house, or building a new one, forces reassessment at market value. Remodeling has no such tax implications. It's very common to see construction sites that tear down an entire building but leave a couple of feet of a side wall standing. The state considers what you build around this wall an alternation to the original building rather than new construction.

Ari.
Click to expand...

Actually I wasn't referring to a data plate; aircraft components can be repaired the way I stated. If you reuse one part, even a screw, the unit can techinically be built up from there and the unit labeled as a repaired part. As neither of these situations really refers to model rockets I think it is up to the individual how they want to deal with it.
 
I'm reminded of the old puzzler "How far can you walk into the woods?"

For those who don't know, the correct answer is "Halfway". Once you reach the center, you're walking out of the woods.
 
Just to stir things up...

You have a rocket which is designed to break apart in the middle - there's a lower half with motor mount, fins and half the body, plus an upper half with nose cone and payload bay accounting for the other half of the body. The two halves are joined together by the usual shock cord. And then one day the shock cord breaks.

You repair the rocket by building a new nose cone, payload bay and shock cord, and then attach these to the original lower half.

You repair the rocket by building a new motor mount, fin can and shock cord, and then attach these to the original upper half.

Which of these repaired rockets is the original?
 
Both? Neither? The idea was original!
FAA would allow it to all be the same aircraft without any original parts. Do you have the "data plate"? Every rocket should have a data plate so we do not have to go through this again.
GEE, I think I bit my tongue. It was in my cheek.

BEAR
 
FAA is a federal government agency. Government laws and regulations have no relation to intelligence, consistency or common sense.
My rockets: If I say it's the same (repaired) rocket, it's the same rocket. If I say it's a new rocket made (partially) from used paets, it's a new rocket.
With your rockets, you decide.
My fingers ar starting to twitch. Therefore, I'm going out to the shop and either repair or build a new rocket.

Mike
 
Apropos regulations. NAR rules say you must wait for L3CC approval before you may start construction of your L3 rocket. Imagine you're an L2, and have an L3-capable rocket that you're flying on K and L motors. How many of that rocket's parts can you reuse in your L3 ship and still claim you started construction after L3CC approval?

Ari.
 
mikemech said:
FAA is a federal government agency. Government laws and regulations have no relation to intelligence, consistency or common sense.
My rockets: If I say it's the same (repaired) rocket, it's the same rocket. If I say it's a new rocket made (partially) from used paets, it's a new rocket.
With your rockets, you decide.
My fingers ar starting to twitch. Therefore, I'm going out to the shop and either repair or build a new rocket.

Mike
Click to expand...

I disagree. I have dealt with both the FSDO and MIDO sides of the FAA at my job and found the inspectors to use a lot of common sense when dealing with issues. The regulations are a bit loose in many areas with wide discretion to the FAA inspector. Get a good inspector and things run smoothly. There was this one time we had screwed up big time and the inspector... well, probably shouldn't tell you about that.
 
iter said:
Apropos regulations. NAR rules say you must wait for L3CC approval before you may start construction of your L3 rocket. Imagine you're an L2, and have an L3-capable rocket that you're flying on K and L motors. How many of that rocket's parts can you reuse in your L3 ship and still claim you started construction after L3CC approval?
Click to expand...

You took my flippant question and made it into a serious one. Humph!!!!!


I think it would be up to the L3CC/Tap to make the call. I doubt there would be any concern about reusing basic components from previous rockets such as a parachute or altimeter. But, larger components, which are usually assembled from smaller ones, like a fin assembly built for a previous rocket, would probably not be okay to reuse. It's the things in between, like the sled for the altimeter, which could go either way. It isn't a significant component, but also isn't usually something usually bought as a "part."

-- Roger
 
Maybe it could depend on the relationship between the potential L3 and the L3CC/TAP. If they knew you, they knew the rocket, they knew you were the builder, and they were comfortable with your skill level, then possibly some of the rules and regulations might get stretched a bit or come under new interpretations. I mean, these rules are part of a living document, aren't they?:wink:
 

Similar threads

J
Questions after an ‘almost’ perfect Boosted Bertha launch. W/video
Replies
12
Views
725
bjphoenix
B
WizardOfBoz
How do fins fail?
Replies
22
Views
739
ksaves2
ksaves2
SuperNova-Rocketry
2 parachutes exiting from the nose cone
Replies
15
Views
642
SolarYellow
SolarYellow
N
Premature Drogue Chute Deployment Diagnosis
Replies
7
Views
281
cwbullet
cwbullet
MarsLander
"Flying the field"....Broad Experience Input from YOU!
Replies
2
Views
215
Voyager1
Voyager1

Latest posts

Back
Top