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SpaceNut,

450bar to 850bar Type IV CFRP high-pressure H2 tanks are quite real, even if most people don't normally see them in their daily lives.  A Type IV pressure vessel is a very specific US Department of Transportation H2 / CNG storage container rating that comes with safety and testing requirements attached to it, because rated pressure vessels are used for transportation of compressed gases.  Type IV works equally well for air and most other high pressure gases.  There are highly acidic or basic chemicals for which CFRP is not a good storage container, but they are typically compatible with air, Oxygen, Hydrogen, Methane, Helium, Nitrogen, Argon, and other common gases.  For gases such as Chlorine and Fluorine, you're better off using stainless steel, potentially with a fluoropolymer liner, and accepting reduced storage pressures.  Composite tanks with fluoropolymer liners can store Chlorine and Fluorine gases, but that's not how it's typically done.  I assume there are good engineering and economic reasons for continuing to use stainless steels and reduced pressures for such aggressively oxidizing chemicals.

A 450bar tank with a water storage capacity of 250L / 0.25m^3 can safely contain 112.5m^3 of air, while an 850bar tank can be charged with 212.5m^3 of compressed air.  The 850bar tank will be heavier than the 450bar tank, but not in terms of equivalent storage capacity.  For example, a pair of 450bar tanks can hold about the same amount of air as a single 850bar tank, but the weight of both tanks will exceed the weight of the single 850bar tank by a considerable amount.  If you double the capacity of a singular 450bar tank, then it still ends up weighing a little bit more than the smaller 850bar tank.  More importantly, 0.5m^3 is nearing the limit of what a vehicle with the same exterior dimensions as a standard compact car can reasonably carry, which is why the 850bar tank makes more sense for this application.  If volume was not as constrained, then it might be possible to make that 450bar 0.5m^3 tank for less money than the 850bar tank because the processing steps are less costly, but it still requires more fiber and resin, so the materials cost will likely remain similar to that of the 850bar tank.

I see the chassis materials and design as 4 major types with various cost, durability, and recyclability trade-offs:

1. CFRP monocoque
A. lightest possible total vehicle weight
B. highest possible specific strength
C. highest possible cost (purely based upon structural materials cost, not cosmetics; apart from CNT and BNNT fibers, Carbon Fiber is the highest energy input fiber, which is reflected in its cost, followed closely by S2 Glass Fiber and Aramid fibers such as Kevlar, followed by the much more commonly used but much weaker E Glass Fiber and Basalt Fiber, which can be quite close to common grades of Carbon Fiber on tensile strength, and the various natural fibers- flax, hemp, cotton, etc)
D. greatest absolute performance (greatest "fuel economy", due to lightest possible weight, which implies less power required, lighter powerplant, etc)
E. most difficult to repair and recycle

Specialty grades of Glass Fiber, Basalt Fiber, and Kevlar can all come remarkably close to Carbon Fiber on specific strength, but not stiffness, so all other composites will be significantly heavier to achieve the same mix of material properties.  No natural or synthetic fiber replicates all the mechanical properties of the others, which is why all of them have their own unique roles as structural materials.

As GW pointed out, accurately evaluating potential impact-related structural damage to CFRP and GFRP is exceptionally difficult.  All impact damage is cumulative, and structural degradation is not linear in nature.  If you beat on Aluminum, applying a given amount of force with each impact (below the point at which it yields, obviously), then its ability to resist future impacts without failure is linear up to a point.  This has never been the case with CFRP and GFRP composites.  One heavy impact might reduce structural integrity by 50%, while successive impacts might do very little additional damage, or the composite may fail completely.  As a general purpose fabrication material, it's a significant compromise compared to steel or Aluminum.  It will never corrode the way a metal would, and won't suffer from stress-corrosion cracking the way Aluminum does, but if you ever impact it in any serious way, the entire structure is probably trash, structurally-speaking.  It may not outwardly look like it's junk, but appearances can be deceiving.  The fibers can and will crack within the resin matrix.  As far as absorbing a singular hard impact, CFRP does that better than almost any other material, for a given weight.  However, accidents will leave razor-sharp shards of composite on the roadway that will puncture tires and injure occupants or bystanders unless Kevlar liners are applied to the interior and exterior of the parts.  It's a mess to clean up, but would allow people to walk away from otherwise unsurvivable accidents.

2. Steel or plastic sandwich cored steel monocoque
A. lightest possible weight amongst metal options using high strength steel
B. lowest total cost
C. least durable due to corrosion and denting
D. simplest and cheapest to repair and recycle, but still high energy

Steel crumple zones do a fantastic job of absorbing hard impacts.  Modern FEA has allowed automotive engineers to deliberately design sacrificial vehicle structures to fold up like an accordian, absorbing most of the force of the impact in the process, while a structural "strong box" prevents intrusion into the cabin of the vehicle.  Steel is very easy to work with, and modern hydroforming allows incredibly complex shapes to be formed into a single sheet of metal, work-hardening the metal to the degree of hardness required in the process.  The latest sandwich core steels use thermoplastic cores so that very thin sheets with a flexible plastic core can be formed into the desired shapes, and then electrically welded together without affecting the core material.

3. Aluminum monocoque
A. Strength comparable to lower grades of mild steel, but not high-strength steel, ease of fabrication is part geometry-dependent
B. highest cost amongst metal options, similar materials cost to GFRP
C. more durable than steel if modest corrosion protection is applied, less prone to denting for the same weight as steel, but fatigue life strictly limits ultimate durability
D. Repair is possible and no more labor-intensive than steel, but not stress-corrosion damage is non-repairable, easiest and cheapest to recycle of all available options

Giant pressure casting machines such as Tesla's GigaPress allow automotive manufacturers to press Aluminum into very complex near-net shapes, with very little subsequent machining required.

4. Flax composite monocoque
A. Strength comparable to lower grades of CFRP, especially CFRP cloth / fabrics commonly used in automotive applications, about 5X better than CFRP at noise and vibration dampening
B. Fabrication and materials cost comparable to much less costly GFRP- easier to work with than GFRP and CFRP, less of a health hazard, doesn't shatter in quite the same way as CFRP in a high-speed impact, so less of a cleanup hazard and won't puncture tires
C. Overall performance comparable to a high grade GFRP, total cost is on-par with GFRP, meaning similar to Aluminum
D. FFRP repair options are as limited as CFRP and GFRP, but markedly easier to recycle into fiber boards, so less total environmental impact, and flax crops absorb CO2

A passenger vehicle for the masses is going to be of monocoque or semi-monocoque construction.  It won't be a body-on-frame design, which always costs more to produce, is markedly heavier since two different crash energy absorbing structures must be designed and fabricated, less passenger-friendly (reduced ride quality and overall handling), typically doesn't protect occupants as well in a major crash, despite what people "feel" about the protection offered by a truck or SUV vs a car (personal belief or marketing and salesmanship vs actual NHTSA testing results which don't paint a pretty picture of large truck and SUV survivability, especially in rollover accidents), and always requires more power to move down the road.  In practice, trucks and SUVs are typically body-on-frame designs, and they're great for towing / hauling, but not-so-great for passenger transport safety.  Body-on-frame is almost necessary for off-road applications, because monocoques tend to beat themselves to death, or rather, inadequate suspension systems beat monocoques to death.

All that said, those are the practical body designs.  Steel will probably be cheapest and easiest to work with, because we already do.  Aluminum will be or at least could be exceptionally easy and energy-favorable to recycle.  Composites will provide the most efficiency and performance.

What trades are we willing to make?

This WILL work, and it won't burn a single drop of hydrocarbon fuel.  That's not even a question mark, at least in my mind.  They will not accelerate any faster than economy cars, and EVs will always easily beat them in acceleration performance, but they will run down the road at 75mph and they will take you from Point A to Point B with efficiency similar to an electro-chemical battery after all infrastructure and operational costs are factored in.  Air powered cars will be cheaper to operate than electro-chemical batteries or combustion engines.

We had compressed air locomotives which powered ore hauling trains used in coal mines 100 years ago, because there was no danger of fuel-air explosions without coal-fired steam engines.  It worked using the tech of 100 years ago, and they only quit using compressed air after they shut the mines down.  The modern replacements in new mines were either diesel engines with special modifications to suppress open flame or external electrically powered.

A YouTube video of a compressed air locomotive in action, from 2015:
Lea Bailey Light Railway Running on Air Part 1, May 2015

These devices exist, they're real, if they didn't work we wouldn't have had our industrial revolution since they powered coal mines and iron foundries, and we can achieve excellent overall energy utilization efficiency by consuming the heat from air compression as hot water or steam, perhaps to power locomotives or power plants, so that we get two or even three different uses out of the energy consumption process.  A solar thermal or geothermal power plant can drive the air compressors.  While we're pulling heat out, from deep beneath the Earth, we can use solar thermal to inject heat back into the rock so we don't cause any problems for the mantle or core.  That is what a real circular energy system and economy looks like.  It's simple, it uses natural processes, it's far more cost-effective than short-lived electronics, and the materials and manufacturing processes to make that happen are all in abundant supply and it doesn't take any advanced education to use or maintain them.

The compressed air locomotive is an ancient device using 110psi compressed air stored in an Iron cylinder.  A modern air powered car is storing its air at 10,290psi in a linerless or HDPE-lined CFRP cylinder.  That means it contains 93.5X more air per unit of cylinder volume.  A 250L tank weighs about 182kg.  If the tank was made from high strength steel, it would weigh somewhere between 910kg using 250ksi steel and 1,820kg using 125ksi steel.  Modern materials therefore have an outsized effect on the practicality of air powered vehicles.  Put another way, that air powered locomotive would have 93.5X greater range on a single tank of compressed air, with approximately 1/5th to 1/10th of the weight devoted to its compressed air cylinder for the same volume of compressed air.

We can validly assert that a rubber tire motor vehicle, irrespective of weight, consumes 9X to 10X more power than steel wheels on steel rails due to rolling resistance, but that still means we can go at least 10X further than that old 110psi locomotive if both vehicles required the same amount of power to move their respective payloads.  It's hard to do a complete apples-to-apples comparison of two very different vehicle designs and different weights, but that's accurate enough to illustrate how drastically modern materials technology has evolved from 150 years ago.

For kbd512 re Post #364

Thanks for a thoughtful review of the comparison between technology options.

Your observation about not buying equipment before a complete system is designed is certainly valid, as experience has shown. I was trying to create a psychological framework for members of this group to solve the problems of creating a small scale compressed air energy storage system. No one asked me to do anything!  Calliban specifically asked that no one spend any money on anything.

Had my gambit been successfully we would now have a working compressed air energy storage system able to light a set of 12 volt bulbs.

Now we will remain as we were, just a forum with ideas and plenty of interesting information, but there will be no demonstration of capability in our archives. 

The resources available to throw at a problem are certainly a factor in success vs failure.

If you look at Calliban's member text, you'll see a mantra that argues against thinking about how to do something, vs acting to make it happen.

My guess is that you'd find that most entrepreneurs do NOT know how to do something that is new, and many fail, but a few succeed, and our vibrant civilization thrives because of their willingness to take the risk.

Elon Musk is a reasonably good example of an entrepreneur who has the risk tolerance to address an opportunity, whether it is business or a technology or a combination.  Losses go with that boldness, and by observation, I deduce that he has the ability to accept the early failures as the price for eventual success.

In any case, the inspiration you and Calliban have provided to forum readers remains available, and it may yet inspire someone to attempt to create a viable compress air energy storage system beyond known capabilities.

(th)

SpinLaunch is developing a kinetic energy space launch system that reduces dependency on traditional chemical rockets, with the goal of significantly lowering the cost of access to space while increasing launch frequency. The technology uses a vacuum-sealed centrifuge to spin a rocket and then hurl it to space at up to 4,700 mph (7,500 km/h; 2.1 km/s). The rocket then ignites its engines at an altitude of roughly 200,000 ft (60 km) to reach orbital speed of 17,150 mph (27,600 km/h; 7.666 km/s) with a payload of up to 200kg. Peak acceleration would be approximately 10,000 g. If successful, the acceleration concept is projected to lower the cost of launches and to use much less power, with the price of a single space launch reduced by a factor of 20 to under US$500,000.

At Spaceport America in New Mexico on 22 October 2021, SpinLaunch conducted the first vertical test of their accelerator at 20% of its full power capacity, hurling a 10-foot-long (3.0 m) passive projectile to an altitude of "tens of thousands of feet." This test accelerator is 108 ft (33 m) in diameter, which makes it a one-third scale of the operational system that is being designed. The company's first 10 test flights reached as much as 30,000 feet (9,100 m) in altitude.

For SpaceNut re addition to SpinLaunch topic ...

Thanks for bringing over the images and text from earlier work on the payload delivery procedure.

The high ellipse method does not seem possible for the SpinLaunch system, at this point.  It would be challenging for the gas gun method, at it's present state of development.

Major advances would be needed in both systems to permit the use of the high ellipse concept.  However, if it ** can ** be achieved, then it provides a way for mission planners to manage flights with greater control and much longer windows.  The payloads in high ellipse will remain in orbit until a suitable delivery window can be arranged, while the low ellipse method will have one and only one chance to reach the fuel depot.  Failure in that case will result in loss of the payload.

(th)

Beryl’s center is forecast to pass about 26 miles (45 kilometers) south of Barbados, said Sabu Best, director of the island’s meteorological service’s director.

On Saturday, Beryl was located about 820 miles (1,320 kilometers) east-southeast of Barbados, with maximum sustained winds of 65 mph (100 kph). It was moving west at 23 mph (37 kph).A major hurricane is considered a Category 3 or higher, with winds of at least 111 mph (178 kph). Hurricane watches were in effect for Barbados, St. Lucia, Grenada, and St. Vincent and the Grenadines, while a tropical storm watch was issued for Martinique and Tobago.

Hot water, salt, or rock could potentially damage the road surface or vehicles or burn people involved in the accident, but compressed air becomes cold air during an accidental release.  700bar H2 tanks struck by bullets will release their stored H2, but they don't burn or explode, so compressed air stored in the same manner would result in a lot of nothing happening.

The CFRP Type IV (HDPE liner or liner-less) H2 tank that US DoE is evaluating at has a 253L water storage capacity, operates at 700bar, and weighs 182kg.  That would provide 177.1m^3 of compressed air (0.253 * 700 = 177.1m^3 or 6254.2275ft^3).

A 1hp air motor regulated at 90psi is equal to a volumetric flow rate of 12scfm to 15scfm.  Actual flow rate depends upon the type of air motor involved.  Turbines tend to be more efficient than pistons and gerotors, because pistons have more friction and starting torque to overcome.  They provide more torque, but not more power per volume of air flowed through them.

6,254ft^3 / 12ft^3 per minute = 521 minutes of operation at 1hp, or 8.68hp-hrs
6,254ft^3 / 15ft^3 per minute = 417 minutes of operation at 1hp, or 6.95hp-hrs

That's not very much, but the horsepower required to move a vehicle at a given speed is a function of aerodynamic drag and rolling resistance.  As speed increases, aerodynamic drag force becomes the limiting factor.

Force(drag) = 0.5 * Density(air) * velocity^2 * Area * Cd (drag force coefficient)
F = 0.5 * rho * V^2 * A * Cd
rho = 0.07647lbs/ft^3 (sea level "standard atmospheric density")
V = 55mph
A = 8ft^2 (standard full size passenger car frontal area)
Cd = 0.31 (Toyota Corolla drag coefficient used, most passenger cars fall between 0.25 and 0.3, 0.35 to 0.45 for most trucks and SUVs)

F = 0.5 * 0.07647 * 3,025 * 8 * 0.31
F = 286.84ft-lbs

That means aerodynamic drag requires 0.522hp to overcome at 55mph.

Coefficient of rolling resistance (Crr) is mass, gravity, and surface-dependent.  On a concrete roadway, which is what we have here in Houston and in many other major cities, the following is what your rolling resistance looks like for a 1,000kg total vehicle weight and "grippy" tires rather than absolute minimum coefficient of friction tires:

F = mass * gravitational acceleration * Crr
F = 1,000kg × 9.81m/s^2 × 0.015 = 147.15N
F = 108.54ft-lbs

In total, 395.38ft-lbs of force needs to be produced by the drive system to maintain 55mph, or 641.92ft-lbs to maintain 75mph.