Why battery-powered aircraft will never have significant range

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Kiwi303

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,
More common in hot rods is raising the compression to barely safe on pump gas, and running lots of boost, for both racing power, and limp home cruising. ( this takes self control. It's easy to build an engine that you can wreck if you get stupid )
Thats old tech... these days it's electronic wastegate linked to knock sensors... the sensors pick up pretetonation pulses long before they can damage the engine and crack the wastegate to lower boost on intake, Like wideband O2 sensors keeping fueling just on clean burn, knock sensors keep boost to maximum possible below grenade point.

Stick anything in the tank and the computer will work out how much boost to cram in as well as how much fuel to match that compressed air.
 

Sockmonkey

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But they were right. They had lived long enough to instantly spot malarkey that defied physics.
It's more that it defies economics.You could make something that could perform safely and well as a car and an aircraft, but the tech, materials, manufacturing and maintenance on something that complex would be horrific.

Anyhow, my personal take on how to do a VTOL would be to stick a system like the Harrier has into a lifting body like the Facetmobile. Then you have the option of high AOA vortex lift STOL for use when carrying heavier loads.
 

dog

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The eVTOL's in development must all be putting
a very significant effort into control mechanisms and circuits.
Some of them must be absolutely electric down to opening doors.
Given that the tech sector is now so large and that there would be a large comanality with other tech,EV's,robots,etc,etc,there are lots of
companys that can realy quickly put together
a design,web site,and strart atracting investors.
Also given public perception as supplied by the
media ,some of these companys are going to
get rich like Icon.
On the other hand some of these outfits are
completely level headed and going for a world
wide introduction of eVTOL taxis,and lemos.
One tweet from musky on a startup with a new
battery in a flying prototype and then there will
be plenty to critique.
 

Aesquire

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Thats old tech... these days it's electronic wastegate linked to knock sensors...

Stick anything in the tank and the computer will work out how much boost to cram in as well as how much fuel to match that compressed air.
Yep! For supercharged engines, & as you point out, adjustable waste gates on turbochargers allow pretty good control. My Caravan is naturally aspirated and uses variable valve timing & fuel injection.

But?/And that is New Tech and OEM Factory equipment. The Aftermarket is catching up.

Several automotive brands use hydraulics & computers to control the cams. And not being dumb, it's not a separate hydraulic system, it's engine oil under pressure. ( you've already got oil under pressure, why duplicate pumps, lines, reservoirs? ) The side effect is... Unless you are religious about both oil change intervals and running the proper synthetic oil, the valves on the solenoids will stick. The computer will flash error codes. The parts you need to replace ( including the seals where the wiring penetrates the valve covers, etc. ) are inside the oil spray seals. Inside the engine. ( again, not dumb from an engineering view! Minimize penetration and external leak sources. Mechanics get paid by the hour. )

That has led to a Lot of repair work being directly caused by letting the oil get dirty. The "I run synthetic and only have to change my cultish loved miracle fluids every 10,000 plus miles" is now stupid. ( and I'm a Synthetic oil cultist of the formerly heretical creed that loved the freedom from sludge, yet rejected the freedom from oil changes based on, honestly, olde school practices. Dirt in oil bad, ug. )

Honda, Ford, Chrysler, etc. all have oil related common repair issues, all valve train & dirty oil. Scores of videos with titles like "Why your (brand name) has ( cam/valve/turbo encabulator) problems!"

Then there's a whole category of unrelated to the above, brand specific engineering screw-ups like Nissan coolant leaks into transmissions & CVT chain shrapnel that are irrelevant to airplanes and don't need exploring here.
 

EzyBuildWing

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Archer Aviation's newly unveiled "MAKER" electric looks like it's got "battery breakthrough-technology" for increased range and speedier-charging.....
Check out their grand-unveiling here(happened just a few hours ago):

 

Dusan

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Anyhow, my personal take on how to do a VTOL would be to stick a system like the Harrier has into a lifting body like the Facetmobile. Then you have the option of high AOA vortex lift STOL for use when carrying heavier loads.
This is not that simple, the facetmobile has a 50hp rotax and able to cruise at 80kts. I think it has a 60 inch prop. Using momentum theory, a value of 0.75 for the figure of merit, the power needs to increase to 160hp to lift the whole 740lbs AGW, this is not counting any losses due to flow interferences. Simplistically, three times more power means three times more engine weight, consuming accordingly more fuel. The rotax503 weights 70lbs dry, the facetmobile has a 13 gal tank, 70lbs. You actually need more fuel for the same performance, but assuming you keep the fuel the same, you need to get rid of at least 140lbs from the airframe or passenger weight and do that somehow including all the ducts and nozzles needed for VTOL flight. You could try to increase the prop diameter - an 8 ft prop needs only 100hp to lift 740lbs, but now you need very large ducts. This is a loosing battle.

Using electric propulsion - things changes a bit. The power to weight ratio of electric motors is much higher than piston ICE. The EMRAX 268 weights 45lbs, 268hp peak, 145hp continuous, and happily provides 50hp cruise at 90+% efficiency. How much fuel an 160hp piston engine takes when it is choked to make only 50hp? Anyway, you have to spare about 100lbs to put the controller, cables, batteries, ducting and nozzles. This is not bright, but it is maybe doable for a short, 30 minute flight.
 

Dusan

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Archer Aviation's newly unveiled "MAKER" electric looks like it's got "battery breakthrough-technology" for increased range and speedier-charging.....
Check out their grand-unveiling here(happened just a few hours ago):

Nice show! I didn't learn anything.
 

Aesquire

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This does apply to Electrics, but it takes a minute to get there... ;)

Hot Rodding as a hobby is based on the principle that the manufacturer left performance on the table to pick up. For reliability, obviously, but also insurance and regulatory reasons. 1970s Chrysler products simply had false published horsepower numbers to keep insurance costs for the buyer down. In the 1980s a German law meant that every motorcycle maker's liter class bikes were all rated at no more than 100 ponies. Etc.

In the 1970-80s it was SOP with motorcycle nuts to change to a lower restriction exhaust & from an airbox to individual low restriction filter pods. ( or modification to the existing airbox ) often the minute a new bike got to their garage. Later, in the 1990s, the manufacturer built bikes much closer to their ultimate limits, and the easy extra power wasn't there. Still some, but not as cheap or easy to get out.

With electric motors, you have to carefully consider how close to optimized the manufacturer has designed. Pushing beyond spec with higher voltage etc. May be catastrophic.
 

Victor Bravo

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What I learned from that video is that the entire range aerospace engineering aspects of an aircraft are just so last-century, and that all of that rubbish is simply far less important than having a couple of cute girls actually banging on drums and high production values in an unveiling. Overly dramatic music and dark red lighting frees the mind from so many annoying details.

Urban Air Mobility is a very valid, good, needed concept. The Archer aircraft may very well work as advertised, I hope it does, and they certainly sounded like they paid attention to a lot of details.

They just totally missed the fact that their marketing and unveiling approach repels the critics that they should want to win over. Not that old fart critics are their intended market, we're not of course, but that if they had thought to make a presentation which addressed the things that us old farts get irritated by, their path to market (for people of all ages) would not be complicated by a bunch of loud old farts opposing it.
 

Sockmonkey

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This is not that simple, the facetmobile has a 50hp rotax and able to cruise at 80kts. I think it has a 60 inch prop. Using momentum theory, a value of 0.75 for the figure of merit, the power needs to increase to 160hp to lift the whole 740lbs AGW, this is not counting any losses due to flow interferences. Simplistically, three times more power means three times more engine weight, consuming accordingly more fuel. The rotax503 weights 70lbs dry, the facetmobile has a 13 gal tank, 70lbs. You actually need more fuel for the same performance, but assuming you keep the fuel the same, you need to get rid of at least 140lbs from the airframe or passenger weight and do that somehow including all the ducts and nozzles needed for VTOL flight. You could try to increase the prop diameter - an 8 ft prop needs only 100hp to lift 740lbs, but now you need very large ducts. This is a loosing battle.
When I said a system like the Harrier, I meant an actual jet engine.
 

Dan Thomas

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It's more that it defies economics.You could make something that could perform safely and well as a car and an aircraft, but the tech, materials, manufacturing and maintenance on something that complex would be
There wlll always be some crippling facts:
An airplane needs to be light. A light car gets blown off the road in high winds, and controllability in a crosswind would be badly compromised. Parking lot dings would be serious. The car's CG has to be somewhere between the front and rear wheels but not close to either. The airplane's CG has to be near the rear wheels or it won't rotate or land gently.
VTOL is one solution but it still has to be light. It takes much more energy to fly it than a fixed-wing, and electrics can't do it yet. Flying bathtub quadcopters have ridiculously short range and would never meet road standards.

The whole effort means compromises that are fatal to any practicality.
 

PiperCruisin

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They're the same shape they'd be if they had to fly on a 20-hp lawn tractor engine. Like a motorglider. Nothing new here at all, like you say.
With electric you can change the configuration significantly. Examples: distributed propulsion, easier span loading, rotating control cylinders, pusher props or prop on the tail, easier start/stop.
 

dog

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Messages
568
Yep! For supercharged engines, & as you point out, adjustable waste gates on turbochargers allow pretty good control. My Caravan is naturally aspirated and uses variable valve timing & fuel injection.

But?/And that is New Tech and OEM Factory equipment. The Aftermarket is catching up.

Several automotive brands use hydraulics & computers to control the cams. And not being dumb, it's not a separate hydraulic system, it's engine oil under pressure. ( you've already got oil under pressure, why duplicate pumps, lines, reservoirs? ) The side effect is... Unless you are religious about both oil change intervals and running the proper synthetic oil, the valves on the solenoids will stick. The computer will flash error codes. The parts you need to replace ( including the seals where the wiring penetrates the valve covers, etc. ) are inside the oil spray seals. Inside the engine. ( again, not dumb from an engineering view! Minimize penetration and external leak sources. Mechanics get paid by the hour. )

That has led to a Lot of repair work being directly caused by letting the oil get dirty. The "I run synthetic and only have to change my cultish loved miracle fluids every 10,000 plus miles" is now stupid. ( and I'm a Synthetic oil cultist of the formerly heretical creed that loved the freedom from sludge, yet rejected the freedom from oil changes based on, honestly, olde school practices. Dirt in oil bad, ug. )

Honda, Ford, Chrysler, etc. all have oil related common repair issues, all valve train & dirty oil. Scores of videos with titles like "Why your (brand name) has ( cam/valve/turbo encabulator) problems!"

Then there's a whole category of unrelated to the above, brand specific engineering screw-ups like Nissan coolant leaks into transmissions & CVT chain shrapnel that are irrelevant to airplanes and don't need exploring here.
Check your oil,Smell your oil,look at your oil,
and if you dont like how it looks or smells,then
plan to change your oil when its hot so it all
comes out of your levely parked car/truck,plane, and put in good oil and a good
filter.
Realy important with anything with lots of miles or time on it.
Motors are not cheap,good oil is.
And of course you can ask me how I know.
 

EzyBuildWing

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Sep 23, 2009
Messages
285
Location
Sydney NSW Australia
Joby Aviation claiming batteries of 235 Wh/kg...... over 100 start-ups now working on commuter-eVTOL's...........
Which/who will take home the glittering-prize?
Question is, which one's to go long on, and which one's to short.......?
 

Dan Thomas

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Sep 17, 2008
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Joby Aviation claiming.....
Yeah. Claiming. Aviation history is littered with claims that were never borne out. I wish you guys could see the problem here: companies looking for investors, some of them with less-than-honorable intentions. Truth is a scarce commodity these days.
 

Dusan

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Canada
When I said a system like the Harrier, I meant an actual jet engine.
Unfortunately smallish jet engines - able to provide 740lbs thrust - are rare, built for cruise missiles for 'one flight only' and have horrendous fuel consumption. You can try to use an j69, providing 880lbf and weighting 360lbs. It will use pretty fast the 13 gallons of fuel.
 

BBerson

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Port Townsend WA
Rolls Royce built some impressive small turbofan "lift jets" with 16 to 1 thrust/weight ratio. Just for lift, some bits were plastic.
 
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