At what point does model rocketry have to morph into HPR?

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Imagine if you will that scene rewritten with Andrew as the black knight.

Better casting: This new learning amazes me Sir Bedevere. Explain to me again how sheep’s bladders may be employed to prevent earthquakes.

(linked for Drax)

I don't think anyone has yet answered the OPS's question -- except maybe for G-T in post #68

I was wondering...

At what point is it nearly impossible to hold a rocket together made of paper, plastic, and wood? J? K? L?

"Nearly impossible" is nearly impossible to quantify, and it seems obvious (to me) that if you use enough paper and wood -- and if you were only interested in having the rocket survive the flight -- you could launch it on an O.

Set some other constraints. Which is to say, under what circumstance should the RSO say "no" because the risk of a hardened projectile falling behind the flight-line is greater than the risk posed by a rocket disintegrating under thrust?

This, I think, would require a flow-chart. A long one.
 
I've been in the hobby since 1973. I grew up on Estes and Centuri. Back then it was all paper, plastic, and wood.

But the last few kits I bought were fiberglass, carbon fiber, and metal tipped nosecones. Some of these "indestructible" kits are even designed for short-thrust E, F, and G motors.

I was wondering...

At what point is it nearly impossible to hold a rocket together made of paper, plastic, and wood? J? K? L?

Why I'm asking...

I've seen too many over-engineered and under-executed, "indestructible" rockets plant themselves balls-deep into the ground. I have to think that if that same lawn-dart hit an RV, car, or person it wouldn't be pretty.

And I've been thinking...

Why use "deadly force" instead of "reasonable force"? Why use a gun when you could use a taser? Why use fiberglass instead of paper tubing? Why use a metal-tipped nosecone instead of a plastic cone?

Then again...

I have to admit that I have no data behind my thoughts. I mean, if you jump into water from a meter it's fun. If you jump into water from 18 stories up, it's deadly. Maybe a balsa nosecone with an "E" bounces off your car... but with a "K" it pierces the roof. I don't know.

What are your thoughts?

Properly designed (with stress calculations and knowledge of materials) rockets of impulse up through at least M have been constructed.
The only fatal accident in rocketry involved a model rocket, not a high power rocket. That’s not to say high power rockets are safer of course; they have more mass and more energy. But the Safety Codes help manage the greater risks by imposing greater safe distances.
However, launch directors also need to be proactive in range operations. The safe distances are only a starting point. Ranges need to be set up with considerations for prevailing winds. Pads should always be vertical or tilted slightly away from the spectators (never towards).
If rockets are flying over the crowds during ascent there’s a problem with the range design. Operations should be halted until that is corrected.
 
[video=youtube;M_FCQ550770]https://www.youtube.com/watch?v=M_FCQ550770[/video]
Let the flutter do the talking.

That is a great video of fin flutter.

To answer the OP's question with my Captain Technicality hat on, LPR becomes MPR when you put an E motor in, and HPR when you put an H motor in (yeah, yeah, or anything over 80N average thrust). As far as construction methods, I've seen cardboard and 1/8" plywood with epoxy fly to ~M1.5, 54mm airframe on a 38mm J. Faster could probably be done, with thicker fins and good gluing techniques. One potential issue is that the larger the body tube, the larger the fin span needs to be, and the more likely flutter becomes. It's possible that you'd be better off at high speeds with a smaller diameter. I think this calls for testing with the Loki Doomsday 38mm. :dark:
 
always dangerous after four pages of replies but going back to original post which has been partially answered

1. At what point is it nearly impossible to hold a rocket together made of paper, plastic, and wood? J? K? L?

Has nothing directly due to engine size. Has everything to do with rocket velocity, of which the factors include rocket size, rocket mass, rocket aerodynamics (drag coefficient), and not just motor size but also motor output and burn time. An improperly built rocket can shred on an A motor. A balsa finned Rocket can break Mach if built right (may need to paper fins.). At some point in fin size and rocket velocity wood fins without fiberglass become impractical, but not directly dependent on motor choice.

2. Why I'm asking...

I've seen too many over-engineered and under-executed, "indestructible" rockets plant themselves balls-deep into the ground. I have to think that if that same lawn-dart hit an RV, car, or person it wouldn't be pretty.

Major misconception here. No rocket under the safety code can nor should be engineered to survive a ballistic recovery. Not high power, not mid power, not low power. This is one reason high power qualification flights require the rocket after recovery to be re-fly-able.

3. And I've been thinking...

Why use "deadly force" instead of "reasonable force"? Why use a gun when you could use a taser? Why use fiberglass instead of paper tubing? Why use a metal-tipped nosecone instead of a plastic cone?

Fiberglassing is used for strength to handle higher velocities and for cosmetic reasons. Metal tipping of nose cones (and some fancy ablative materials on fins) is used to help rocket survive higher velocities. Neither fiberglass nor metal nose cones are used to help a rocket survive a bad landing, in fact one of the key points in model Rocketry is to AVOID bad landings.

4..Maybe a balsa nosecone with an "E" bounces off your car... but with a "K" it pierces the roof. I don't know.

Carelessness and stupidity in combination with model Rocketry is dangerous with any motor size. You can poke your eye out bending over a launch pad prepping a A4-3T motor rocket. As mentioned, a relatively recent death was caused by a non high power rocket. While the safety code forbids trying to catch a high power rocket on descent (kind of a Darwin Award IMO) otherwise the rules are fairly similar.

Model Rocketry remains safe because those who practice it (for the most part) continue to emphasize safety in all aspects of the hobby from MicroMaxx to 3/4 scale Mercury Redstone rockets.
 
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always dangerous after four pages of replies but going back to original post which has been partially answered

1. At what point is it nearly impossible to hold a rocket together made of paper, plastic, and wood? J? K? L?

Has nothing directly due to engine size. Has everything to do with rocket velocity, of which the factors include rocket size, rocket mass, rocket aerodynamics (drag coefficient), and not just motor size but also motor output and burn time. An improperly built rocket can shred on an A motor. A balsa finned Rocket can break Mach if built right (may need to paper fins.). At some point in fin size and rocket velocity wood fins without fiberglass become impractical, but not directly dependent on motor choice.

2. Why I'm asking...

I've seen too many over-engineered and under-executed, "indestructible" rockets plant themselves balls-deep into the ground. I have to think that if that same lawn-dart hit an RV, car, or person it wouldn't be pretty.

Major misconception here. No rocket under the safety code can nor should be engineered to survive a ballistic recovery. Not high power, not mid power, not low power. This is one reason high power qualification flights require the rocket after recovery to be re-fly-able.

3. And I've been thinking...

Why use "deadly force" instead of "reasonable force"? Why use a gun when you could use a taser? Why use fiberglass instead of paper tubing? Why use a metal-tipped nosecone instead of a plastic cone?

Fiberglassing is used for strength to handle higher velocities and for cosmetic reasons. Metal tipping of nose cones (and some fancy ablative materials on fins) is used to help rocket survive higher velocities. Neither fiberglass nor metal nose cones are used to help a rocket survive a bad landing, in fact one of the key points in model Rocketry is to AVOID bad landings.

4..Maybe a balsa nosecone with an "E" bounces off your car... but with a "K" it pierces the roof. I don't know.

Carelessness and stupidity in combination with model Rocketry is dangerous with any motor size. You can poke your eye out bending over a launch pad prepping a A4-3T motor rocket. As mentioned, a relatively recent death was caused by a non high power rocket. While the safety code forbids trying to catch a high power rocket on descent (kind of a Darwin Award IMO) otherwise the rules are fairly similar.

Model Rocketry remains safe because those who practice it (for the most part) continue to emphasize safety in all aspects of the hobby from MicroMaxx to 3/4 scale Mercury Redstone rockets.

Great reply!
 
Why I'm asking...

I've seen too many over-engineered and under-executed, "indestructible" rockets plant themselves balls-deep into the ground. I have to think that if that same lawn-dart hit an RV, car, or person it wouldn't be pretty.

Major misconception here. No rocket under the safety code can nor should be engineered to survive a ballistic recovery. Not high power, not mid power, not low power. This is one reason high power qualification flights require the rocket after recovery to be re-fly-able.

What is the misconception, and who's?

It may be that rockets are supposed to crumple if they come down nose-first and heavy -- but the OP reports seeing rockets do otherwise.
 
. . . Why use fiberglass instead of paper tubing? . . .

After getting a big zipper on the first flight of a cardboard rocket that I spent many weeks building and painting, I no longer build cardboard rockets.
 
After getting a big zipper on the first flight of a cardboard rocket that I spent many weeks building and painting, I no longer build cardboard rockets.

Please don’t take this the wrong way, but you may be making the point for the original poster. By building using fiberglass you avoid the end result of opening a parachute at high speed (zippering) but you may not have figured out how to prevent the root problem, high speed deployments.
 
I'm a little late to this party, but I'm always particularly fascinated by the level of response loaded question threads such as the OP's receive.

E=MC^2.... the speed, not the weight, is the major component of the rockets "potential" to do serious damage.

Equally as intriguing is why hobby level rocket fliers are debating Einstein's field equations and relativity as they apply to the related field of the physics of a vehicle in flight when the more relevant equation F=ma by Newton, the guy whom without we would not have rocket science is not instead discussed by those (and those certified to presumably have a fundamental knowledge of his three laws as they apply to rocketry) seeking answers concerning the amount of destruction said vehicle has the potential to create?
 
Please don’t take this the wrong way, but you may be making the point for the original poster. By building using fiberglass you avoid the end result of opening a parachute at high speed (zippering) but you may not have figured out how to prevent the root problem, high speed deployments.

It was a dual deploy cardboard Der Red Max with altimeter apogee deployment and a Jolly Logic Chute Release. It zippered when the JLCR released.
 
I have seen ballistic fiberglass rockets fly again the same day. The OP was accurate. People like fiberglass for the durability factor. This forum is filled with post where people state they didn't have a main deploy and the rocket tumbled in from apogee separation only to bounce off the ground with nary a scratch. Doesn't seem safe to me.
 
I'm a little late to this party, but I'm always particularly fascinated by the level of response loaded question threads such as the OP's receive.

E=MC^2.... the speed, not the weight, is the major component of the rockets "potential" to do serious damage.

Equally as intriguing is why hobby level rocket fliers are debating Einstein's field equations and relativity as they apply to the related field of the physics of a vehicle in flight when the more relevant equation F=ma by Newton, the guy whom without we would not have rocket science is not instead discussed by those (and those certified to presumably have a fundamental knowledge of his three laws as they apply to rocketry) seeking answers concerning the amount of destruction said vehicle has the potential to create?

Yadda.. yadda.. yadda. Being late to the party means you have the benefit of reading everyone else’s comments… and then bloviating.

Newton.. he’s the guy that hung out with Johnny Appleseed, right?

It’s an interesting thread.

Most of us are here to have fun and learn from others. As for me... I just like to design and build low powered rockets…

I'm a retired M.E. / CWI, never implied I was a rocket scientist, and certification as such isn’t a pre-requisite on this forum.

Leading with my chin, is something I do often. No fear I guess.

When I waded into this thread I remembered a discussion, 4 decades ago, about velocity being squared and its impact on the energy being more so than weight.

And I picked the wrong equation…. As Steve was kind enough to clarify

You’re correct that the kinetic energy is proportional to the square of the velocity, but the equation for kinetic energy at any of the velocities we’ll ever achieve is e = 1/2 m * v^2.
Conservation of energy and conservation of momentum must both be considered when analyzing the potential for damage.

And for the record.. we would still have "rocket science" even if Newton had never been born.

Albert-Einstein-quotes-Education1.jpg
 
It was a dual deploy cardboard Der Red Max with altimeter apogee deployment and a Jolly Logic Chute Release. It zippered when the JLCR released.

In order to zipper, it would seem that the fin section was falling forward end down even though the nosecone and chute bundle were out. Was the rocket greatly overstable?
Or perhaps it was falling flat and the chute opening was very fast. In either case there are ways to prevent zippering. A drogue chute is one of the best ways because it will result in the body section being aligned forward end up. Different folding methods for the chute bundle reduce the shock of opening.
Another thing that contributes to zippering are small diameter Kevlar shock cords. That’s one of the reasons I prefer wide tubular nylon straps. Kevlar has its place also, but wider is better.
Changing to a fiberglass body helps prevent zippering, but if you have done nothing to prevent the high speed deployment then the force that pulled the shock cord through the body tube still exists. The sharp edge of the body tube is going to be causing stress within the shock cord at that point. Eventually something will break.
 
I'm a retired M.E. / CWI, never implied I was a rocket scientist, and certification as such isn’t a pre-requisite on this forum.

CWI? Товарищ!

There has been awful abuse of physics in this thread.

For instance, for a rocket falling as a single rigid object, kinetic energy and momentum are not really separable -- so the advice that both need to be taken into account when estimating the destructive potential of such a body isn't wrong, but neither is it especially useful.

And the folks who remembered the factoid that Galileo demonstrated something about the rate of descent of a falling body being independent of the weight of the object, missed the important detail that the lincean academician was arguing against the prevailing view of gravity based on the (very sound) observation that falling feathers descend more slowly than falling bricks.

These are folks who very likely have ideas about how to size parachutes for rockets of different weights, but who -- for whatever reason -- did not make the connection to ballistic descent.


I ask again, how much physics should we require of an L2 -- given that L2 means "Certified to work at the RSO table"?

I am not asking to be provocative. I am planning (hoping, really) to fly my L2 certification this season. While I am comfortable with the kinds of analysis I've posted here; I've shredded, lawn darted, and core-sampled a few rockets. My failures have been failures of craft, or failures of design. That is to say, I know why a rocket goes up, and I know why it will come down more or less rapidly; but, I am liable to use too little of the wrong kind of adhesive, or to overestimate the strength of some piece of the fabric of the rocket, or just to screw something up because there is so much that I just don't know.

And for the record.. we would still have "rocket science" even if Newton had never been born.

Duly recorded. While it is difficult to overstate the contributions of Newton, you might also have to erase Leibniz, Fermat, De Moivre, Maclaurin, Lambert, Descartes, Gauss ... while you are editing history to the minimum required to get to a rocket to the moon (for instance). Although it seems unlikely that Tsiolkovsky would have gotten very far without differential equations -- somebody was probably going to invent the calculus for him.
 
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Last edited by rhildinger; Today at 04:52 PM. Reason: snarky reply was unnecessary

That was very sensible of you. Welcome to a higher class. Who wags their finger at such an intelligent, well-spoken argument?

Aside from being behavior expected of children, I'll never understand the rationale behind the mocking of others for being intelligent. Furthermore, because not everyone is (amongst them being intelligent people), to possess the ability to be so articulate with their knowledge while so magnanimously sharing it with others is truly a gift we should all appreciate and strive towards.

Kudos for your reversal. I respect people like you.
 
If you go to the Golden Corral on Elm Street and tell Morty the night manager that CORZERO from TRF respects you, he'll let you comb his back hair for ten minutes.
 
I'm a little late to this party, but I'm always particularly fascinated by the level of response loaded question threads such as the OP's receive.



Equally as intriguing is why hobby level rocket fliers are debating Einstein's field equations and relativity as they apply to the related field of the physics of a vehicle in flight when the more relevant equation F=ma by Newton, the guy whom without we would not have rocket science is not instead discussed by those (and those certified to presumably have a fundamental knowledge of his three laws as they apply to rocketry) seeking answers concerning the amount of destruction said vehicle has the potential to create?


Probably because f=ma is no more relevant to this question than e=mc^2. Neither is the correct equation. F=ma tells you how fast your rocket will accelerate with given net force, it doesn't tell you how hard it will hit you on the head on the way down.
 
Probably because f=ma is no more relevant to this question than e=mc^2. Neither is the correct equation. F=ma tells you how fast your rocket will accelerate with given net force, it doesn't tell you how hard it will hit you on the head on the way down.

Actually it does. Your head causes the rocket to decelerate rather quickly.
 
Probably because f=ma is no more relevant to this question than e=mc^2. Neither is the correct equation. F=ma tells you how fast your rocket will accelerate with given net force, it doesn't tell you how hard it will hit you on the head on the way down.

I'm no mathematician, in fact, I'm math retarded, but I'm pretty sure if you want to solve for "a" then a=F/m. Isn't the "Force" of an impact is the solution to F=ma?
 
I'm no mathematician, in fact, I'm math retarded, but I'm pretty sure if you want to solve for "a" then a=F/m. Isn't the "Force" of an impact is the solution to F=ma?

No. I think what you're getting at is momentum, which is mass * velocity. Momentum and kinetic energy are the two things that matter in a collision.

F = ma describes the force required to accelerate the specified mass.
 
No. I think what you're getting at is momentum, which is mass * velocity. Momentum and kinetic energy are the two things that matter in a collision.

F = ma describes the force required to accelerate the specified mass.

Ok, thanks.

How then is the "Force" of an impact defined and calculated?
 
F = ma is certainly applicable, but since acceleration is defined as delta-v over delta-t, the "F = ma" equation displays asymptotic behavior as delta-t approaches zero. To put it more simply, as the time it takes for an object to decelerate approaches zero, the amount of force required to achieve that deceleration approaches infinity. If we modeled the behavior of an object falling at any velocity and hitting the ground as an instantaneous deceleration to zero, we would run into the infinite force issue. That's one of the reasons why that equation doesn't really help in determining what happens when a moving object hits something like the ground or a person's head.
 
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