Practical Electric and Gasoline Powered Aircraft

kbd512 · 2023-10-28 13:57:58

First, apologies to tahanson43206 for going far off-topic multiple times. I don't think of things the same way, because I see all the tech as flight-related, but useful in different scenarios. I removed these posts from a topic created by tahanson43206 on "electric airplanes", because they're not purely in keeping with his topic, and because discussion of various aviation-related power sources are made, with some comparing and contrasting. It's not solely focused on electric flight due to the present limitations of such technology.

This topic was created to both stop obscuring his topic and because everything critical of plainly observable physical reality is anathema to the green religion, as it relates to how or even if it's possible to completely or mostly transition away from combustion to electrical power. I think their fantasy world at least appears superficially "better" than what we have now, if only it was possible from a raw materials / embodied energy / monetary cost perspective, but I don't see us getting there in my lifetime. I've laid out the reasons in my diatribe against what we're doing now, and how it's not helpful to achieving this cleaner / greener future. I also despise the ideological and technological blinders people wear when discussing their favorite tech. For example, a gasoline chainsaw is an absolute pain in the rear compared to any decent electric saw, and it's obvious to people who have extensively used both. Electric vs gas chainsaws aside, a battery powered airliner is an absurdity.

Rather than go so far afield from the theme of tahanson43206's topic, which is what I felt was doing, with posts he or others may find objectionable, I created a brand new topic purely comprised of my response posts, by moving all of the posts I made into his topic, because there was quite a lot of non-electric flight related content included.

The first set of posts pertain to a more recent discussions about powering a Mars aircraft with electrical power (new-ish Aluminum-air battery and CNT composite tech, which is very promising), followed by a diatribe against modern gas turbine aircraft engine technology, followed by another diatribe against electric aircraft (because they all look like publicity stunts to me, rather than an honest attempt to build dependable workhorse short-range electric aircraft).

I view the F-22 vs F-35 arguments the same way. People "ooh and ahh" over one aircraft because it can fly a bit faster or turn a bit tighter, while utterly ignoring the fact that it can't carry internally or even use (incompatibility with the software, or software never written to use them) any of the more devastating strike weapons in our military's inventory. Blasting the enemy to bit from the air is the starting point to all modern warfare. The F-22 was the publicity stunt. The F-35 is the first practical / mass-produced stealth fighter, and there are lots of questions about how practical and sustainable the F-35 has been or will be.

I'm not greatly enamored with any given engine or fuel technology. They all have severe limitations and use cases where one technology will work very well, whereas others may not work at all.

kbd512 · 2023-10-28 13:59:16

tahanson43206,

The wing cavity isn't that large, in terms of total volume. The lift you'd generate from filling it with Helium, even heated Helium, is negligible. 6mb of pressure is a good bit of nothing. It's a high-lift / high-speed motor-glider at the end of the day. It has the same engine power for cruise that the Pipistrel Taurus Electro has. There are ways of making the plane lighter that would yield better results.

The greatest advantages will come from increasing CL (Coefficient of Lift) and decreasing weight. A practical Mars manned aircraft is a materials / structures / CL combination problem. Assuming the stated cruise power figure is correct, then a thin film photovoltaic array would yield a drastically better result than filling the wing with Helium, because it could supply more than 100% of the power required if the array is 35% efficient.

All of these eVTOL designs use goofy multi-engine arrangements that attempt to circumvent basic physics and aerodynamics. At the end of the day, traditional designs are very hard to beat in terms of efficiency. The traditional designs were designed from a "first principles" standpoint before complex computer analysis was available. Well-understood and easily demonstrable aerodynamics principles were applied. The designers accepted that any time you go to extremes, as with this design, you create the very problems you're attempting to solve in any aircraft design.

In real airplanes, you typically have 1-4 engines, typically 1-2 engines. Dr Raymer's design has 4 engines, which is fine, but 1 motor with more propeller blades is how you generate more thrust, at the expense of drag, which is not a major problem here. Stall speed is 115kts and cruise speed is 150kts. Over that very narrow operating speed range, thrust density is more important than drag.

The E-2D Advanced Hawkeye now uses 8-bladed propellers. They did that to produce enough thrust on takeoff from the carrier, at low speed, to enhance safety when getting airborne. It hurts cruise speed a little, but makes engine failure on takeoff a less threatening proposition.

I would rather have 2 engines with 4 blades, vs 4 engines with 2 blades. To be perfectly frank, I'd rather have 1 "engine", even if it's actually 4 electric motors providing torque on the same output shaft, delivering power to 8 blades. This eliminates asymmetric thrust / engine-out issues. Using the engines to provide control authority is a bad idea, even if it's possible. The yaw and pitch stability problems should be resolved by a longer fuselage extension with larger vertical and horizontal stabilizers father aft of the wing. If you did rolling takeoffs and had less than half of that 345ft wingspan by switching to a biplane / box wing design, this is far less problematic. C-130s takeoff from rough fields above 100kts, at almost the exact same speed as this motor-glider, when fully laden, as a matter of fact. C-130J's stall speed is around 100kts, so the wingspan of a biplane would be similar to that of a C-130.

In this case, it makes far more sense to use shorter biplane or even triplane wings, accept the drag / speed / range penalty, employ conventional rolling takeoff using wheels, and design the gear to soak up landing loads. Trying to eliminate the use a ladder to embark / disembark seems a little bizarre. Lots of aircraft use at least handholds and footholds to disembark. If you put "bush wheels" and outrigger skids to prevent the wingtips from striking the ground, this is how the U-2 landing problem was solved. All gliders do this and 100% of their landings are rough field.

Airframes Alaska's "BushWheels" use Kevlar sidewall / tread area reinforcement of thin / light rubber inflated to low pressure tires, with no tread pattern / completely smooth so it doesn't kick up rocks into the tail or propeller. We would use CNT for its drastically greater puncture resistance and lower weight, an even lower inflation pressure using N2 or CO2 to account for lower weight on Mars, and a specialty cryogenic-capable rubber compound, which was developed for NASA for cryogen storage in rubberized "balloon tanks". Said wheels are not like other aircraft tires. A fully inflated "BushWheel" tire can be removed from the wheel / hub, because it's a completely enclosed rubber donut, unlike a normal car / truck / aircraft tire that uses either an inner tube or a bead seal to the sidewall of the wheel / hub. Thus, the complete inflated tire can rotate around the wheel / hub when the pilot stomps on the brakes during a rough field landing, without losing air pressure. There's no inner tube to pinch and no bead seal to break.

For the airframe, we also need CNT-based composites and CNT / mylar fabric coverings. This material is extremely pliable and nearly impossible to cut, even at cryogenic temperatures, without exotic and very sharp ceramic blades. Repeatedly throwing an axe at CNT fabric thinner than human hair, burying it in the wood backstop, failed to cut it. This process had to be done about a half dozen times before the fabric started to fray. Any other material that thin would've been split in half. This level of strength and durability negates the need to transport quite so many large hard composite structures to Mars. Maybe your Helium inflation idea could be used to add bending stiffness to the wing, now that I think about it. Airframes for colonist use can be shipped in kit form to Mars, then assembled on Mars, or at least stowed in a more compact form.

The very high energy density Aluminum-air battery is an existing tech item, partially developed by Israel, and tested in the US in a small fleet of passenger motor vehicle. Someone here posted links about it years ago. Recharging the battery requires a lot of energy, but it's doable. I guess you could think of this battery as a simple solid state fuel cell with oxidizer being the only reactant that must be supplied to generate electricity. You get somewhere between 1.2kW/kg and 1.5kW/kg energy density, but then you need 12kW to 15kW/kg to recharge it, so 10X more energy input for a recharge, which is a very unfavorable energy trade, much worse than hydrocarbon fuel synthesis. It's "rechargeable" in the same way that Aluminum smelting is "reversible". That's why it's never going to be practical for powering the world's passenger cars. The battery lasts for a month or two, and then it gets shipped back to the factory for "recharging" (un-oxidizing the Alumina (Aluminum Oxide).

Dr Raymer stated that there's no present need for such a large aircraft on Mars. I disagree. Imagine how much more science we could accomplish if we had an aircraft that could transport Spirit / Opportunity-sized rovers around to different locations on Mars, retrieve samples, and then fly them back to a lander with sample return capsules and rockets.

kbd512 · 2023-10-28 13:59:54

I've often spoken about the use of CNT-based fabrics, which are now being mass-manufactured here in the US and elsewhere, primarily for aerospace applications, though sometimes as a reasonably low-cost strengthening agent for construction materials like concrete under railway stations.

At the present time, in rough general terms, a CNT-based fabric is about twice as strong as Carbon Fiber (CF), for a given weight. Theory and perfect lab-grown samples aside, the bulk properties of materials we can actually mass manufacture allows for about this much strength-to-weight. This is critical for an aircraft on Mars, because weight is critical. The Martian atmosphere is also a feedstock for local manufacture of CNT. They have another unique material property that is very unlike CF. The fibers have been subjected to 1M+ bending cycles where the fiber is literally folded in half, as-in creased like a sheet of folded paper, then folded in the opposite direction in the same manner, without catastrophic failure or visible wear. If you did this to a strand of CF, it would snap like a piece of spaghetti before you cook it.

You can flex Glass Fiber (GF) or Carbon Fiber (CF) composite structure only so much before the strands of fibers embedded into the resin matrix begin to snap like glass rods. CNT is dramatically different. It can be flexed in ways that would destroy any GF or CF composite structure. You can still have composite structures that tolerate some flexing using GF and CF, but the limits are much more restrictive. This is not to suggest that if you flexed the structure enough that the GF / CF / CNT / BNNT fibers wouldn't pull away from the resin matrix, but that the fiber damage CNT or BNNT would suffer is almost non-existent. Your flexibility limit is the resin matrix bond to the CNT fiber. Kevlar is famous for being stronger than CF, but of the tendency to pull away from the matrix and suffer fiber buckling inside the matrix during compressive loading.

Net net is that new material technologies like CNT and Aluminum-air batteries are very important for enabling practical aircraft to fly on Mars.

Our ability to reduce structural weight by half makes the difference between 115kts takeoff speeds and more manageable 58kts takeoff speeds. A heavy bush plane like the DHC-2 Beaver stalls at 52kts, while the Pilatus Porter stalls between 52kts and 58kts. Both aircraft are still used to this day by civilian and military operators. The Porter has a range of 870 nautical miles, which is quite good. Dr Raymer's Mars plane concept had a range of 1,738 nautical miles, but this is atypical of light aircraft built as STOL or "bush planes". If that range is acceptable for the Porter, then it should also be acceptable for a similar "Mars bush plane".

A PT-6A powered Pilatus Porter is a good Earth-bound facsimile to Dr Raymer's (6,000lbs max gross) Mars plane, because the Porter (6,173lbs max gross) operates at similar speeds (cruise: 115kts; max level flight: 125kts; never exceed: 150kts). If we built a "Mars Porter" to be similarly capable, by halving the Mars Porter's structural weight, tripling the battery energy density, and removing all retro-rockets and fuel, that would give us a similarly capable Mars aircraft with a much larger wing. Both planes are radically different in terms of power plant / fabrication materials used / structural mass fraction / wing and tail area, but could carry approximately the same useful load at the same speeds and over the same distances. Each airframe is optimized for its intended operating environment, yet both would deliver comparable performance, so they can be thought of as 1960s vs 2020s aircraft design and technology for fulfilling the same mission on two different planets.

This is part of what makes the entire Mars plane design concept so interesting and compelling to me. We could apply some of the new tech to Earth-bound aircraft to reduce power requirements, but whereas we may be perfectly willing to devote 10X more energy to infrequent flights on Mars, we're going to need a different energy solution here on Earth, or a new way to drastically reduce the energy required to convert Alumina into Aluminum going into these Aluminum-air batteries.

It's not as if the tech doesn't exist, it's a question of how practical the tech is for any given role. Most people probably think the Lithium-ion rechargeable batteries are the most energy dense batteries we have, but they're not even close. Nobody has figured out how to reduce the energy requirement to recharge these "Metal-air" (O2, actually) oxidation-based batteries that fall somewhere between primary batteries and fuel cells in terms of operating characteristics. State-of-the-art is 1,300Wh/kg for Aluminum-air. It actually looks like and functions a bit like a fuel cell stack. Theoretical is 6,000Wh/kg to 8,000Wh/kg.

Aluminum-air batteries have a limited lifespan because the aluminum anode is consumed in the reaction with oxygen.

It's not "consumed", it's turned back into Alumina (Aluminum Oxide), which then must be converted back into Aluminum to "recharge" the battery, at fantastic energy cost, as Aluminum won't easily release its bond with Oxygen.

kbd512 · 2023-10-28 14:00:30

The propeller shown below is the type I would use, rather than multiple engines with separate propellers and the potential for highly asymmetric thrust. I don't hold a very high opinion of using engines to provide control authority or to enhance the maneuvering characteristics of a light aircraft. If engine power is lost, then control authority is also lost. This is indicative of a poor control strategy. It's been tried before, many times, but has never made its way into a production aircraft that passed FAA certification.

Propfan Front:

Propfan Rear Quarter:
propfan-jet-engine-_8_fa0f6034-628b-41a8-9c21-96f5efd61640.jpg

Propfan Front Quarter:
propfan-jet-engine-_9_bbbe4483-5ace-4745-ae6b-2ec567cff838.jpg

Propfan Side:

Safran CFM-56 Derivative Propfan:
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The propeller blade shape / style shown above is what I call a paddle-bladed scimitar prop. The scimitar / scythe shape delays localized breaking of the sound barrier and the associated wave drag, while the very broad blade takes a big bite out of the air (generates more thrust per unit area). The densely packed blades also increase thrust per unit area, at the expense of top speed or fuel economy- the prop will actually generate more thrust at lower rpm, which is critical in this application, but after speed increases past a certain point the prop will also function somewhat like an air brake.

kbd512 · 2023-10-28 14:01:11

Calliban,

I'm not skeptical that electric aircraft can work, but I am skeptical of all the ridiculous nonsense that I see related to how they're implemented, which does nothing to help develop a practical all-electric single-engine land plane or helicopter.

I see "electric aircraft" with a dozen engines and propellers to lift 2 to 4 people into the air, instead of more practical designs like the Bye Aerospace / Arion Lightning design. Why are these monstrosities being developed? To spend good money without a practical / usable result, which is most of what the "green energy" religion is all about. They soak up enormous amounts of captial, labor, and energy resources while producing very little energy.

I see Lithium-ion batteries that are an absurdity for anything other than a single very short flight. There's very little development of Aluminum-air batteries that achieve 5X to 6X the energy density of Lithium-ion. What do you need for practical flight? Oh, that's right, a lot of energy in a small / light package.

So, what do I see as "the solution"?

Develop practical 2-seat to 8-seat STOL electric short-range single-engine land planes and helicotper type aircraft that prove out all the basic design concepts and hone them to a razor's edge.

Create an electric "Piper Cub" and "Cessna 172 / 182" (the most widely produced and generally useful light aircraft designs on the planet) derivative that uses 1 electric motor, 1 propeller, and 1 battery in each wing.

Create an electric "Robinson R44" (the most produced light helicopter on the planet) and "Hughes 500" (the OH-6 / LOACH) and derivative that uses 1 electric motor (powering the rotor and tail rotor), with 1 battery in the fuselage.

It's obvious that these new technology aircraft won't fly as long as their gasoline-powered analogs, but that's not the point. The point is to create practical / affordable / well-designed / generally useful alternatives to gasoline, which remain some of the most popular training and general utility aircraft in the skies.

The Arion Lightning is a slick little 2-seater sport / utility aircraft, but it was designed for 820lbs empty weight, 1,320lbs to 1,530lbs max gross. Most are operated as LSAs (Light Sport Aircraft), below 1,320lbs, which is what the airframe was designed for. The Bye Aerospace "eFlyer 2" facsimile (airframe is based upon the Arion Lightning, just like the AeroComp VM-1 Esqual) is 1,460lbs empty weight, 1900lbs at max gross. Unfortunately, eFlyer 2's wing area was only increased by 25ft^2, a 24% increase, whereas the empty weight increased by 78%.

What's that mean for a light sport pilot? It means it's going to stall at a significantly higher speed, due to simple physics. That's not the end of the world. The Cessnas I fly stall at significantly higher speeds. At the end of the day, what was previously a light and nimble low-wing LSA / trainer, is now something that requires a PPL and experience flying larger / heavier / higher stall speed single-engine land planes. Loading up the wing a bit more for better stability in turbulence is not a bad thing, but it also comes with higher takeoff and landing speeds. The Piper Cub is similarly light and docile to fly. After you soup-up one of those and add a bunch of weight (more powerful and heavier engine / bush wheels / cargo pod / etc), then once again, you'd better know what you're doing. The cost of the eFlyer 2 is well into new-ish (less than 5 years old) Cessna 172 territory, so why would a new pilot buy something that expensive, which will only ever be a short-range trainer?

Where I see electrical aircraft really taking off, is in providing low-cost training and currency for new pilots. The promise is dramatic reduction in cost-per-flight-hour (CPFH). At the same time, the airframe can't become so expensive that CPFH improvements are immediately erased by the purchase price.

Imagine for a moment that we manage to make these things truly affordable by foregoing a lot of what I call "Gucci-gear". We could make said plane out of CFRP for absolute performance, but if we can make it out of GFRP or Aluminum for a fraction of the cost, then why spend so much more money on a plane intended to serve as a low-cost training aid?

This is where we admit to the limitations of batteries and decide that we're not going to spend unlimited money chasing after fantasies which have no hope of ever working, so long as the basic technology they're dependent upon remains hopelessly limited by gravimetric energy density. In the end, we know that there are physics limitations involved imposing severe constraints on workable solutions. No matter how light the aircraft's structure becomes, it will never overcome a 42X gravimetric energy density deficit over what's pushing it through the air.

kbd512 · 2023-10-28 14:01:45

In 1946, Republic's all-Aluminum XF-12 Rainbow could cruise at 400mph using 4 Pratt & Whitney R-4360 engines, and can fly 4,500 miles. It carried 5,000 gallons of gasoline, so 1.11 gallons per mile. If this aircraft was made from CFRP, as all modern airliners are, then it could also carry 90 passengers. Empty weight was 65,000lbs.

The De Havilland Canada DHC-8 Q-400 aircraft, which first entered service in 2000, which carries a maximum of 90 passengers, is powered by 2 Pratt & Whitney Canada PW150 engines, and can fly up to 1,300 miles using 1,724 gallons of fuel, at speeds of up to 400mph, so 1.33 gallons per mile. Empty weight is 39,284lbs.

What's been the "great fuel economy achievement" of the past 50 years of commercial aviation technological development?

Apart from electronics and sensors and airframe materials, all of which improved dramatically as a result of computerization and FEA, it's resulted in burning a little more fuel to travel at almost identical practical speeds. You can always burn more fuel to generate more thrust to fly a bit faster. That's what all rockets do.

With the benefit of 50 years of hindsight, I can say that very little has changed in the realm of gas turbine engine efficiency vs piston engine efficiency, as it relates to subsonic flight. The piston engine remains more fuel efficient, albeit by a much smaller margin.

Source for 1946 Average Engine Cost - USAAF Statistical Cost Analysis 1946
5,071hp PW150 was $1,300,000 USD in 2010.
3,700hp R-4360 was $40,638 USD in 1946, $454,429 USD in 2010.
3,700hp R-3350 was $24,496 USD in 1946, $273,923 USD in 2010.
2,250hp R-2800 was $20,441 USD in 1946, $228,579 USD in 2010.

4 R-4360s burned 444.44 gallons / 2,667lbs of fuel per hour.
2 PW150s burn 531 gallons / 3,609lbs of fuel per hour (and it's a considerably heavier fuel).

2 R-4360s weigh 7,440lbs; 1,333.5lbs per hour
2 R-3350s weight 5,340lbs
2 PW150s weigh 3,166lbs; 1,804.5lbs per hour

The break-even on weight is 9hrs, but the XF-12 could actually stay in the air for 11.25hrs.

The Speed-of-Air piston design has repeatedly saved about 30% on fuel burn, and resulted in drastically cleaner engine oil. The burn is so much cleaner that almost no soot generation is observed, to the point that their diesel engines will pass a 2007 California diesel engine emissions test without any engine exhaust treatments. Our re-pistoned pair of R-4360 engines could be burning 311.11gph / 1,867lbs per hour. No our fuel burn differential is up to 1,742lbs/hr. Now we achieve weight break-even with a pair of PW150s in less than 2.5hrs. The DHC-8 can stay in the air for 3.25hrs. We're adding engine weight, but saving quite a lot of fuel weight. R-3350s are considerably lighter at 2,670lbs while producing the same rated power as the R-4360s, which is why the commercial aviation world of the 1950s primarily used the much cheaper / lighter / smaller R-3350s. We're going to end up with a fuel weight equivalent advantage with R-3350s inside of 1.5hrs, and very few flights in regional airliners are shorter than that.

The R-4360s are obviously generating more power as well, because they can. Gas turbines lose power with altitude immediately. Piston engines with both turbochargers and superchargers can produce sea level power from 20,000ft to 30,000ft. I'd also like to point out that PW150s have FADEC. If the radials had FADEC, it's probable that they'd achieve even greater fuel economy. We could combine FADEC with Speed-of-Air piston technology and Mazda's compression ignition direct injection, we could probably get fuel burn per engine below 100gph, in a plane that can go from New York to LA and back on a single tank of fuel.

The difference in cost is extreme, yet performance is not. The R-4360 produced up to 4,300hp in some versions, while R-3350s produced up to 4,000hp. There's no argument about the reliability of modern gas turbine engines, but piston engine reliability is dramatically better than it was during the 1950s. We can say with certainty that all gas turbine engines are inordinately more expensive than piston engines producing equivalent power. Gas turbines are much lighter for the power produced, but not lighter than the quantity of additional fuel they consume. The comparably fuel efficient gas turbines in stationary electric power plants are drastically heavier than aircraft engines or aero-derivatives.

kbd512 · 2023-10-28 14:06:20

The following series of posts relate back to a prior discussion about electric aircraft and the absurdity of trying to achieve performance parity with gasoline, but I've moved it here because I believe it adequately illustrates why electric and gasoline aircraft should target different markets and be used for different purposes:

kbd512 · 2023-10-28 14:07:02

From the article:

Created for the US recreational sport-vehicle market, Blackfly operates under Part 103 of the federal air regulations. That comes with a few restrictions. As an ultralight, Blackfly can weigh no more than 254 pounds and may not be flown at night or anywhere near populated areas.

Another functionally useless toy for people with more money and obsession over futurism than practicality or uncommon sense. It "only" costs as much as a luxury SUV. Well, for that amount of money you could actually have a luxury SUV, or a real certificated airplane capable of more "recreational flying" than any user of the "BlackFly" will ever be capable of.

For people who want a functional airplane, a guy built one using scrap materials from the junkyard for $6,500 total, including the engine and avionics, although it's one of those "evil" gas burners. It can fly for at least several hours on a few gallons of gas and it seats two people, much like any other real airplane.

Affordable Flying: Building an Airplane for Less than $6,500

Maybe some people in our government could learn something from him, but that'd require minimally functional grey matter between their ears.

I don't want debts. I can't afford them. - Tim Buttles

Now, the labor doesn't pay anything, but watching TV doesn't pay anything, either. So, you have a choice. Either you're watching TV or you're gonna build an airplane. - Tim Buttles

Actually, the lack of money has been... I call it "good education". And if I did have a dollar, I'd still be doing the same things because I enjoy it so well. - Tim Buttles

The dude used spoons with tabs welded onto them to make latches for his engine cowling.

Tim Buttles is a member of EAA Chapter 183981, of Ogdensburg, WI.

My favorite comment on it:

There must have been one hell of a conversation when he got this thing inspected with the FAA.

My favorite comment that shows how little people know of aviation:

R V The other alternative, is not to crash into another plane, or someone else’s hanger. You would only be liable if you damaged somebody else’s property. Otherwise, if you crashed, and you walked away from the crash, you would just build another $6000 aircraft, or rebuild the one you’ve got. And if you didn’t walk away from the crash, well insurance can’t bring people back from the dead so it doesn’t really matter. Pretty unlikely, but you get the picture. Bottom line, insurance is not required in less you’re an idiot. It would be much more likely to be required on a car then on a plane. Cars are much closer to each other on the road, where is your supposed to have a 100 meter gap between aircraft while flying.

A "100 meter gap", huh?

Apart from formation flying with a very communicative lead, if I was ever that close to any other aircraft, even at the leisurely 140kts that that 172RG cruises at, I think I'd have a coronary. Dependent upon direction, with two aircraft flying that speed, that could easily result in a mid-air in less than a second. I think ATC woke up my flight instructor when we passed within about 500m of some Cessna or Piper heading in the other direction. I was shocked at how fast we crossed paths, and he was flying at a different altitude, not directly towards us, and was in no particular hurry. There's a good reason why you're not allowed to fly faster than 250 knots below 10,000. Cleetus and Billy Bob may never even see each other with a closure rate that's the better part of Mach 1.

My absolute favorite was that old country boy who built his bird using "nothing but what you can pick up from the Home Deppo". That old hayseed is an absolute hoot. Jack "Everything's Home Deppo" Harper. You couldn't come up with another one of him if you tried.

Home Depot ultralight aircraft, Jack Harper and his Home Depot plans built ultralight aircraft kit!

kbd512 · 2023-10-28 14:08:03

SpaceNut,

Now we know why electric aircraft are toys for rich people who don't intend to do much flying, and workfare for aerospace and electrical engineers not otherwise gainfully employed. They should rename that thing "Spirit of Never Going to Production". The only "innovation" that occurred was spending a lot of money for no useful result.

This is the biggest joke of all:

The project was half funded by the Aerospace Technology Institute and UK government, with the aim of eventually creating all-electric passenger planes. "This is not only about breaking a world record; the advanced battery and propulsion technology developed for this programme has exciting applications for the Urban Air Mobility market and can help make ‘jet zero’ a reality," said Rolls-Royce CEO Warren East.

People who want to design passenger carrying airplanes, actually design passenger carrying airplanes, not functionally useless and insanely expensive electronic gadgets intended to dazzle the uneducated with bovine excrement. Rolls-Royce has invested £80 million in electric aircraft battery technology alone, and maybe a century from now when AI designs a battery that stores an order of magnitude more energy than the laptop batteries in this toy, you might have a functional airplane, at least until the battery shorts out and achieves arc welding to surface-of-the-Sun temperatures, at the speed of light.

A better question to ask is what world record was actually broken by this waste of tax payer time and money.

The world record for the greatest amount of money spent to make a single-seat and functionally useless airplane go 300mph?

People routinely make airplanes go 300mph at the Reno Air Races, and while their planes are certainly not cheap, they're nowhere near the cost of this idiocy.

A Glassair III cruises at around 280mph and can easily break 300mph with the throttle firewalled. The airframe is around $100K, the engine is around $120K, the prop is $15K, and most of them have at least $30K worth of avionics in them. So, for $275K, you can cruise near 300mph and travel up to 1,300 miles with a single pilot and full fuel, or around 1,000 miles with a passenger and baggage.

The guy in the comments section must be unaware that if 100% of the airframe was covered with 100% efficient solar panels, flying at high noon over a desert would not provide enough power to remain above stall speed.

Modern electric motors are absolutely golden, in my opinion, and fully capable of delivering reliable power and lots of it, no "ifs", "and", or "buts". Unfortunately, that revolutionary new battery technology is "just" 10 years away, and always will be, at least until AI takes over, then it could be a day or a week or the AI may simply conclude that it's a waste of computing power, because no known electro-chemical reactions come within an order of magnitude of simple chemical reactions, so far as power output is concerned.

kbd512 · 2023-10-28 14:09:23

The World's Fastest Electric Airplane

This is the Rolls Royce assembled Sharp Nemesis NXT kit airframe that they're operating at or above max takeoff weight for that design, at all times, with a single pilot aboard. Adding a passenger, which the airframe was originally designed to have aboard, added too much extra weight. The internal combustion engine powered NXT seats 2 people. Rolls Royce's electric variant can produce up to 1,000hp for a few seconds, but then has to revert back to 280hp due to overheating issues with the motors and batteries.

The real Nemesis NXT's powerplant is a 350hp Lycoming TIO-540 that produces 300hp continuously. The Rolls Royce "Battery Weight Is My Nemesis" NXT can drain its 450kg / 216kWh battery pack in about 13 minutes in an utterly pointless attempt to attain 400mph, which it has yet to do. The real Nemesis NXT has gone over 400mph in numerous air races with far less power available, and cruises at 325mph for 4 hours, burning 20 gallons per hour at 325mph, and has a 90 gallon fuel tank capacity.

Given a 30 minute reserve, a real NXT can fly approximately 1,300 miles. The Rolls Royce NXT has never left its home airfield because it drains the battery so fast. 216kWh is not enough to maintain 300hp for 1 hour, never mind 4. To fly for 4 hours, the battery pack's energy density would have to increase from 168Wh/kg (at the pack level) to 672Wh/kg. To equal the real NXT's 4 hour endurance, at reduced speed, the battery pack level capacity would have to rise to 756Wh/kg. To equal the real NXT in every respect, the battery pack capacity would have to rise to 1,007Wh/kg. The electric motors are said to be 95% efficient, so the Rolls Royce variant can effectively maintain 275hp output for 1 hour.

216kWh available battery capacity * 0.95% electric motor efficiency * 1.341 kWh to hp/h = 275.1732hp for 1 hour (zero reserve)

This is starting to look a lot like that equally pointless waste of money on the solar powered aircraft that flew around the world over the better part of a year vs a week for the win Continental O-200 powered Voyager piloted by Dick Rutan and Jeana Yeager, but was then condemned to never to fly again because it was deemed structurally unsound after its single flight, just like the Voyager airframe that preceded it. Rolls Royce could've spent all those millions on the Karl brothers from Dark Aero and ended their program with an aircraft design that would be useful for more than virtue signaling stunts to appease people with no comprehension of basic math.

We have a team of brothers here in America, the Karl brothers, who formed the Dark Aero Corporation. They are using their engineering and fabrication skills to build a two seater capable of cruising at 275mph for 1,700 miles or 255mph for 2,450 miles, using about half as much horsepower as the Nemesis NXT. It burns that evil icky dino juice that mathematically challenged people have been taught to hate. The upside is that you can fly to your destination at 255mph for equivalent fuel economy of 32mpg- about as good as a Toyota Camry but about 4 times faster than driving.

The Rolls Royce NXT supposedly set a time-to-climb record (3,000m / 9,842.5ft) in 202 seconds, for an effective climb rate of 2,923.5 feet per minute. The actual FAI world record for a non-turbine-powered propeller driven aircraft (10,000ft / 3,048m) in 100 seconds was set on April 19th, 2018 in Oxnard, CA, using a 650hp turbocharged Mazda Wankel rotary engine stuffed into a Harmon Rocket IIA airframe, for an effective climb rate of 6,000 feet per minute. 100 seconds means the time from parking brake release on the runway to 10,000ft.

Both record attempts are equally silly since they confer no practical application of the propulsion technology to General Aviation aircraft. The service life of both "engines" is severely limited at the power output levels demanded of them. However, we can see how little value the 1,000hp of the electric motor powered Rolls Royce NXT actually helps it to go after similar record attempts.

The normal legal speed limit for all civil aircraft operated below 10,000 feet is 250knots Indicated Air Speed (IAS) or 287.695mph. If you fly any faster, then you're breaking the law without special arrangements made before-hand with the FAA to hold an air race event or to attempt to break a world speed record. The same speed rule applies in Europe and most other countries with civil aircraft operations. If you routinely fly higher than 10,000 feet, then you need to add pressurization or an Oxygen supply. The Dark Aero airframe can already fly at the maximum legal speed limit in cruise flight for hours on end, using its considerable 77 gallon "wet wing" fuel tank capacity and much lighter / highly optimized airframe design.

Rolls Royce has admitted that every test flight damages the battery, which is essentially 3 72kWh Tesla battery modules that were repackaged to make them light enough for the plane to lift into the air. They estimate 500 to 1,500 flights before the batteries are so degraded that there's an unacceptable risk of battery fires and explosions. Ignoring the money they dumped into lighter packaging and cooling, each 72kWh battery pack is $20,000 from Tesla or $60,000 in total, so you could fly this thing for 500 to 1,500 hours before you dump another $60K into a new battery pack.

If the Rolls Royce NXT's battery pack actually lasts for 1,500hrs, then it costs $40 per flight hour. If you fly economy cruise in the Dark Aero, you burn 8 gallons per hour, and at $5 per gallon (I pay $5.04 per gallon of 100LL at KDWH for that "thirsty" 180hp Cessna 172RG that I fly), then you're spending $40 per flight hour there, too, except that you can carry a passenger or fly for 2,450 miles in the Dark Aero. On top of that, you can expect 25 hour oil changes, so factor in another $2,400 spent over 1,500 hours. If you merely factor in the cost of electricity to fly for 1,500 hours, at $0.10/kWh (never achieved in Europe, where they pay 3X as much as we do here in the US by using a greater percentage of unreliable wind and solar energy), then that's an additional $32,400 for the electric NXT or $97,200 for Europeans who can't do basic math whenever their "green ideology" is involved. All people who are not mathematically challenged will clearly see how wrong the claim is that you will ever "save money" using batteries instead of gasoline / 100LL or kerosene / Jet-A, for equivalent performance aircraft. That's why they focus so much effort on banning gasoline / diesel / kerosene, instead of producing a viable battery product. They know they don't have a viable product unless it's the only product anyone can buy. Pilots don't care what powers their plane, so long as it's reliable. I need no convincing that electric motors are better than piston engines, and potentially better than gas turbines for many applications. That's self-evident. All aviation electric motors reliably crap out power like there's no tomorrow, for less weight than a piston or gas turbine engine- and if you want more there's always more. What's not evident at all is that batteries will ever match gasoline or kerosene for sustained power output within our lifetimes, which only derives from Watt-hours per kg / Watt-hours per Liter metrics. Batteries have been dutifully compared and found to be woefully lacking in the Watt-hours per kilogram department. Real pilots only care about cost per flight hour / range / endurance / payload. Power is power. It doesn't matter what provides it, so long as it works reliably.

If actual battery pack life is closer to 500hrs than 1,500hrs, then that's $120 per flight hour for electric, ignoring electricity cost, so then you're deep into Lycoming IO-540 territory. Electric is then considerably more expensive than the IO-540, even after fuel / oil changes / engine overhaul costs per flight hour are included in the bottom line CPFH figure. In return for signaling to everyone else that you have plenty of money but no basic math skills, you're "rewarded" with none of the range or endurance benefits of any other type of aircraft power plant, but have endless "virtue signaling" bragging rights over the other serfs who can't count but still worship at the altar of "green ideology". The bottom line is that the Rolls Royce NXT is a functionally useless aircraft for anything other than flying solo training flights in the pattern to get a high performance aircraft endorsement in your logbook, which is not possible without an instructor aboard, at greater cost than the existing Continental IO-550 powered Cessna 182s, which have a CPFH of $180 to $200 (engine / airframe / avionics / insurance). Yay "progress in the other direction"!

kbd512 · 2023-10-28 14:10:29

Apart from spending money on pet projects or class-limited air racing, I'm starting to question the rationality of doing stuff like this. There is absolutely zero practical use case for the original Sharp Nemesis NXT, yet somehow this version managed to become even less practical. The only thing I've seen them prove at this point is that ideology has overcome all reasoning and critical thinking skills.

There are literally dozens of aerospace design startups that have collectively squandered billions of dollars on battery technology that can't keep a practical passenger carrying aircraft in the air for 4 hours. I've already illustrated why solar powered aircraft can't be scaled up- if the power-to-weight isn't there, then it doesn't matter how much you try to scale it up because it still won't work. If anything, the problems will become more severe. The same is true of battery technology. Merely attempting to "build it bigger" is a non-workable strategy.

The Sharp Nemesis NXT is basically a bullet with wings and tail fins. If you can't get that thing to fly for at least 2 hours, then you have little hope of making larger / heavier / less aerodynamic designs fly for significantly longer. All of the aspirational battery gravimetric energy density targets have yet to be met by any commercial product. If you want a practical airliner that flies for 4+ hours and carries the same payload as existing turboprop and turbofan powered aircraft, then that means using a fuel cell rather than a battery, period and end of story, because there is no other story that doesn't devolve into the realm of pure fantasy. Airline services don't run on fantasy-based thinking.

There are a literal handful of niche use cases for 15 minute flights, like the "across the bay" runs in Canada, but the time makes battery powered passenger airliners functionally useless to any for-profit operation, such as Part 23 operators (aircraft weighing 19,000lbs or less, 19 passenger seats or less). You can't land a helicopter on a rooftop in a city without a pilot's license, so putting batteries and dozens of electric motors changes nothing. All that wasted money could have been devoted towards improving the reliability, aerodynamics and thus fuel economy of new airframe designs using existing engines. Instead, it was squandered on projects that have no practical reason to exist, because the technology to use them simply doesn't exist and nothing we have in our labs right now can allow them to exist in the next 5 to 10 years.

One-by-one, these otherwise highly innovative electric aviation companies that could have produced practical fuel cell powered aircraft, go under as it becomes apparent to the investors that there is no real progress on the battery technology front, no practical / general use case for aircraft that can't fly for 4 hours, and almost no paying customers who can afford to experiment with something that fundamentally doesn't work well enough to ever become a like-kind replacement.

SpaceNut · 2023-11-28 19:16:18

Flying taxi startup soars to new heights with latest design approval

SpaceNut · 2024-01-23 08:25:38

All-electric 'Seaglider' will island-hop to boost Hawaii connectivity

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In a significant development for water-based transportation, seagliders to be supplied by Regent Craft offer all-electric, zero-emission vessels designed for exclusive operation over water at impressive speeds of up to 180 miles per hour (289 kilometers per hour). This innovative technology promises to significantly reduce the time and cost of transporting people and freight between coastal communities.
Regent's flagship seaglider, the Viceroy, accommodates 12 passengers and operates solely over water, seamlessly transitioning between three modes: hull, hydrofoil, and ground effect flight, with a 160 nautical mile (184 miles) range utilizing current battery technology, which is expandable to over 400 nautical miles (460 miles) with advanced batteries.

tahanson43206 · 2024-03-15 20:56:36

The title of this topic includes the word "practical" as well as "aircraft"

The aircraft described at the link below is at the far extreme of "practical".

It is definitely an aircraft !!! It is designed to ship large wind turbine blades.

It will require a runway 6000 feet long, if built.

I think this application might be worth evaluation by lighter than air vehicles.

https://www.msn.com/en-us/travel/articl … 731b&ei=23

(th)

kbd512 · 2024-03-16 18:40:15

For all kinds of aircraft, the weight of its "fuel source"- be it H2, CNG, gasoline, kerosene, or batteries, dwarves the weight of the engine. Fuel weight is the limiting factor. Engine weight is a non-issue for gas turbines and electric motors. There is no such thing as a gas turbine or electric motor that limits the performance of the aircraft, relative to the weight of its fuel supply.

Current PEM fuel cell technology is 2.5kW/kg to 4kW/kg. A 1MW / 1,341hp fuel cell would thus weigh 250kg to 400kg. This is about the same weight as a 1MW gas turbine engine. A 1,271hp Pratt & Whitney PT6A-67D turboprop engine has a dry weight of 234kg, and SFC is 0.332g/kWh. After you add the exhaust ducting, lube oil, and additional engine accessories such as a vacuum pump for instrumentation, you're looking at 250kg, easily, and probably a bit more. Engine dry weight is not an acceptable analog for all-up / ready-to-fly engine installation weight. Even small engines with all fluids and accessories weigh a good bit more than dry weight suggests. At 10kW/kg, a 1MW electric motor weighs 100kg. Assume 0.4kg of 700 bar H2 storage tank weight per Liter of volume, and H2 is 3W/L, so 2.1kWh/L at 700 bar. Assume the PEM fuel cell is 60% efficient, so you only get 1.8W/L of H2 at STP. Assume Lithium-ion batteries are 200Wh/kg at the pack level, after most of the cell isolation safety features have been removed. This tracks well with British experience regarding their flight weight Lithium-ion batteries, during their development program that involved flying a modified Tesla battery powered Sharp Nemesis NXT racer.

Now let's do an apples-to-apples weight comparison for 4 hours of flight with gas turbines, H2 fuel cells and electric motors, and Lithium-ion batteries with electric motors. Assume all engines provide 1MW of continuous power output. An aircraft of this classification / description is a light commuter type commercial aircraft capable of carrying a dozen or more people.

1MW class are some of the lightest aircraft in common commercial use. Smaller specialist commercial aircraft do exist and see regular service, but 1MW+ would be typical of something flown by a regional passenger air transport service provider. Cessna 206s are much smaller / lighter / cheaper to operate, for example, but only short-hop ferry flights in places like Alaska are real use cases for them. In practice, Cessna 208 Grand Caravan or Quest / Daher Kodiak aircraft, carrying 8 to 19 people, are far more commonly used. You need enough butts in seats to keep prices under control.

250kg PT6A-67D, 332kg/hr * 4hrs = 1,328kg (about 431 gallons): 1,578kg total
100kg electric motor, 250kg 60% efficient H2 PEMFC, 200kg of H2 at 700 bar, 1,270kg of CFRP tank: 1,820kg
100kg electric motor, 4MWh battery pack at 200Wh/kg is 20,000kg: 20,100kg total

The fuel cell is 15% heavier than the gas turbine and jet fuel.
The batteries are 1,331% heavier than the gas turbine and jet fuel.

Even if batteries and electricity were 10X cheaper than jet fuel, it's not possible to make a 13.3X heavier aircraft 10X cheaper. That is not possible. Commercial aircraft purchase prices correlate very closely with weight, and there are no exceptions to that rule. If you see a very cheap but heavy aircraft for sale, that's because it's uneconomical to repair.

With that explanation complete, let's move on to analysis of what we need to compete with gas turbines and jet fuel:

A 10% increase in fuel cell efficiency makes the total weight 1,638kg. That means the fuel cell is 3.8% heavier than the gas turbine and jet fuel. If the fuel cell achieves 5kW/kg in terms of output, then it becomes 10kg heavier than the gas turbine and jet fuel, in terms of total weight. After you add in the fuel pumps, lines, and filters for the jet fuel, the weight becomes a wash between both types of aircraft. That means parity with gas turbines and jet fuel requires 10kW/kg electric motors, which already power existing large electric aircraft, 5kW/kg PEM fuel cells with 70% efficiency. We have 4kW/kg PEMFCs. We have 70% efficient PEMFCs. We need 5kW/kg PEMFCs with 70% overall efficiency. Hysata has 95% efficient commercial water electrolyzers. It takes 1.35kW of energy to compress H2 gas at STP to 700 bar.

Electric motors could have even better power-to-weight ratios, but they're already twice as power-dense as gas turbine engines. Only rocket engines have them beat. A 50kg electric motor vs 100kg means nothing to this application. If you can make the electric motor 50kg lighter for roughly equal cost, then yes, go ahead and do that, because every little bit helps. Recognize that a suitably strong and stiff engine mount to prevent whirl-mode oscillations and propeller vibrations from the prop, transferring into and ruining the motor or shearing the engine mount, is probably going to weigh more than the motor at that point. The 1MW capable propeller also weighs more than the electric motor it's attached to, by a good amount. This is potentially very dangerous, as in the prop and motor depart from the aircraft dangerous. Having some engine mass is a good thing for stability and absorption of vibration and asymmetric thrust loads on the propeller.

Lithium-ion batteries have to increase their kWh/kg to 2,706Wh/kg, ignoring the weight of power inverters entirely. In practice, I would assert that 3kWh/kg at the battery pack level is the minimum acceptable power-to-weight for any kind of battery powered manned aircraft. That means batteries have to improve their power-to-weight ratio / gravimetric energy density by 15X to become acceptable. For all kinds of reasons, it's highly improbable that such a thing will happen during the next 50 years. I hope I'm wrong, but history shows that using the lightest metal on the periodic table, we now have 400Wh/kg batteries and 200Wh/kg at the pack level. Batteries can and no doubt will continue to improve, but there won't be any 15X weight reduction.

kbd512 · 2024-03-17 02:06:40

Take a look at what this chart shows us about the efficiency of propellers vs ducted fans (turbofans) vs turbojet engines:

What you will notice is that ducted fans, essentially turbofans, have a very narrow flight regime where they happen to be efficient. This flight regime corresponds with the cruising speed of commercial airliners on long haul flights, as well as most military aircraft, which can go supersonic, but only at the cost of greatly increased fuel burn.

You can tweak the design of propellers, ducted fans, and turbojets, but at the end of the day the engine's overall propulsive efficiency is still greatly affected by flight speed. Certain kinds of designs are most suitable for specific cruising speeds.

Anyone who tells me they have some magical new Mach 2 propeller design is going to have to display convincing evidence indicating counter-factuals to a lot of fundamental aerodynamics to convince me that they have something worth investing money in.

That's where all this electric aircraft design silliness loses me. There is no valid counter-factual to the argument that aircraft weight and power requirements are very tightly coupled. Anyone who claims otherwise is either talking about an incredibly specific flight application, which is probably not generally useful, or they're talking out their rear end. NASA's X-57 Maxwell distributed electric propulsion manned aircraft demonstrator was cancelled last year because of problems with its battery electric propulsion system.

The way forward for electric aviation is 5kWh/kg PEMFCs with 70% fuel efficiency. That provides weight parity with gas turbine engines and jet fuel, using existing Type IV CFRP H2 storage tanks. There are no practical battery electric aircraft that can fly for 4 hours at weights comparable to existing aircraft. None. Absent some sort of minor miracle in battery technology, there won't be any such machines in the near future, either. The words "revolutionary" and "game-changing", when applied to electro-chemical battery technology, should be reserved for 3kWh/kg batteries made from common and low-cost materials.

I'm a little sick of hearing about people squandering perfectly good money on battery powered experimental aircraft that have no hope of ever competing with existing commercial aircraft using any known battery technology. It's all ideologically-driven vaporware. If money ever becomes a real concept to investors, they will immediately pull the plug on funding all battery powered aircraft larger / heavier than a bowling ball. What we're left is yet another pointlessly asinine engineering experiment intended to provide workfare for electrical engineers.

None of this means electric aircraft are not viable or something worth pursing! It means manned battery powered aircraft are not economically viable nor comparable in performance to piston engines, gas turbines, or fuel cells.

Batteries for transportation purposes appeal to people with near-zero demonstrated knowledge of basic engineering principles. They will spout off meaningless talking points about efficiency, but contribute little of substance when you point out that gasoline as an energy source is 60 TIMES more energy dense than a Tesla's battery pack, per unit weight, which is why being less energy efficient is far less problematic in the engineering sense, for internal combustion engines. Mass efficiency is a very real form of efficiency. Ask anyone who's been forced to carry something needlessly heavy how much weight matters. A Tesla carries a 625kg battery pack. If you had a 30mpg car carrying 625kg of fuel, it could travel 6,870 miles before it needed to refuel. The 45mpg Mazda cars could travel 10,305 miles before refueling. If the engine was 60% efficient rather than 30% efficient, then it could travel 13,740 miles- literally halfway around the world. It's easy to illustrate how absurd the argument gets about efficiency. The question should be, efficient relative to what?

Hydrogen fuel cell aircraft, with comparatively minor weight and/or efficiency improvements from material substitutions, will at least meet, or even grossly exceed, the mass efficiency of gas turbines and jet fuel. The moment this is pointed out, you won't get any intellectual arguments from our battery advocates about which energy source to use, because they have none. All street legal production motor vehicles can tolerate weight increases, however poorly, that would otherwise be instant show-stoppers when applied to any type of aircraft.

2024 Toyota Mirai

Toyota has a 5.4kW/kg PEMFC in a 2024 model of a production motor vehicle that doesn't cost more than a Tesla with equivalent range. Max output is only 128kWe, so we'd need 8 of them to provide 1,024kWe, each complete fuel cell module weighs 32kg, so 256kg in total, and all 8 would occupy 1.138m^3 in volume, remarkably similar to the PT6A. Toyota can simply hand you a fuel cell from a street car that causes it to only be 11% over the weight of a gas turbine and kerosene. An optimized 1MWe Toyota Mirai fuel cell would theoretically weigh 185kg, but let's ignore theory so we can purchase off-the-shelf hardware.

Ultra Lightweight High Pressure Hydrogen Fuel Tanks Reinforced with Carbon Nanotubes

This research was conducted over 10 years ago. They were able to reduce the weight of 700 bar H2 tanks by over 40% using a modest amount of CNT fiber, 0.5% by weight, mixed into the epoxy resin holding the CFRP tank together. The CF used was Toray T700 high modulus carbon fiber. A US DOT approved / "road legal" Mirai H2 tank weighs 87.5kg. This is not strictly necessary to contain the pressure, meaning it's over 2X stronger than it needs to be, by design. CNT increased the bursting pressure to 25,000psi+. That means a 40% weight reduction was achieved for equivalent strength to then-available CFRP 350 bar and 700 bar H2 tanks. That means DOT legal tanks for 1,890kg. For full CNTRP tanks, a 75% weight reduction over CFRP was achieved by other researchers for high pressure air tanks for firefighters. IIRC, their equipment is also DOT rated because it's transported over the road in fire trucks. With Toyota US DOT approved PEMFCs, US DOT approved CNTRP tanks, and our 10kW/kg electric motor, our H2 fueled aircraft's all-up propulsion system weight is 1,343.5kg. This is LIGHTER THAN our PT6A-67D and its 431 gallon load of JET-A by a meaningful margin- enough to compensate for any possible weight increases related to the fuel cells and electric motors and electric power cables, power inverters / conditioners if required, etc. That's what practical electric flight looks like, at a lighter total weight than gas turbines and kerosene. We did not have to invoke superconductors, graphene, space alien technology, or any other technology that doesn't exist, such as 3kWh/kg electro-chemical batteries. We went to Toyota or Doosan or Emrax or Wright Electric, plunked down cold hard cash, and walked away with a complete 1MW propulsion system. It took a lot of tech to get here, obviously, but that is what a "real deal" electric aircraft looks like. If it doesn't provide our battery enthusiasts with the gee whiz factor they crave, then maybe they can try walking or sailing from Los Angeles to Tokyo. I wish them good luck with that, because they'll need it.

If someone started making CNTRP 700 bar H2 storage tanks, which will literally halve the weight of the gas tanks when compared to CFRP, no improvement to fuel cell energy efficiency or power density is required to immediately and dramatically beat gas turbines and kerosene by 25%. That's a walloping weight reduction. If you also increase PEMFC efficiency by 10% and gravimetric energy density, the performance gap becomes too substantial to ignore, so an organic transition to H2 takes place when gas turbines and jet fuel can no longer compete on weight. No government regulation or artificial scarcity has to be concocted to get airline services to switch. If the tech is available, they'll start using it to enhance their bottom line. Recall that all airliners are now primarily fabricated from CFRP. This is not just some of them, it's all of them, regardless of who makes them. Anyone who wants to build a cost-competitive product uses composites. CNTRP 700 bar tanks with existing 10kW/kg electric motors and 4kW/kg PEMFCs, will be 25% lighter in weight than existing gas turbines for a 4 hour flight. As flight duration increases, the performance advantage of H2 will become increasingly significant.

In aerospace engineering projects that typically succeed, aircraft are designed around their engine and fuel source. After you decide what payload the aircraft must carry, to what distance, and at what nominal cruising speed, you then select an engine and fuel delivery system capable of providing the power to deliver the desired weight / range / cruising speed combination. When that design task has been completed, you design an airframe to carry all that weight as efficiently as it can, typically with concessions made to the practical operation of the aircraft in its intended operational environment. Jet airliners typically don't operate from grass runways with fuel carried onto the airstrip by hand in jerry cans, for example, so a concession is made as to when and where the aircraft may be operated. That implies airports with concrete runways, refueling trucks, fire trucks, and equipment to load passengers and cargo.

kbd512 · 2024-03-18 01:39:13

Something like what's shown here is very possible to design and build, but only using a single large and reliable electric motor, a single large and reliable fuel cell, and redundant electronic motor and fuel cell controls:

game-changing-all-electric-seaglider-gearing-up-for-first-crewed-flight-next-year_3.jpg

Adding a half dozen or more electric motors and dozens of propeller blades is the makings of an expensive maintenance nightmare.

As a basic design safety and passenger comfort feature, I do not want 24 spindly CFRP blades operating at high rpm, mere feet away from paper thin windows. If one of these numerous blades strikes a random seagull or other large bird during flight, it could be removed from the prop hub and thrown through the cabin like an oversized dagger.

I would much rather have a large, sturdy, centrally mounted propeller, with the top of the cabin protected by kevlar fabric, like so:

In addition to the safety of flight enhancement afforded to the passengers, there's no possibility of asymmetric thrust loads, you get a blown tail for improved rudder and elevator effectiveness during critical phases of flight, and the propeller is as far away from the water as it can possibly be.

Ignoring the absurdly bad hydrofoil idea, the rest of the Electric SeaGlider airframe design looks like a traditional seaplane, and should provide excellent handling qualities in flight and on the water. Prudent aircraft design does not endlessly seek out novelty or marketing gimmicks. There are no hydrofoils mounted to the hulls of wing-in-ground-effect aircraft because it's a dangerous design feature with no practical use case. I can already envision one of those hydrofoil devices either getting ripped off the hull after striking a coral reef or kevlar fishing net or other submerged hazard, and potentially opening up a hole in the fuselage or stuffing the entire plane into the ocean, nose-first, while the aircraft is on-step. Either way, that's an entirely avoidable disaster.

Being "different" is only a good thing when there are valid engineering reasons behind it.

Calliban · 2024-03-18 07:02:35

Kbd512, that is very impressive. There is ongoing research into high pressure electrolysis, which will generate hydrogen gas at a pressure of 700bar. So the energy needed for compression will disappear, aside from that needed to pump water into the electrolysis stack. But water is incompressible, so that energy loss should be modest. The energy density numbers suggest that compressed hydrogen could compete with kerosene and GTs on a weight and range basis. The only questions remaining concern capital costs, maintenance costs and reliability.

Diesel costs about $1/litre. That is $1 for 10kWh of stored energy. If electricity can be sourced at $0.1/kWh, then hydrogen should approach cost competitiveness with diesel.

Last edited by Calliban (2024-03-18 07:14:45)

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