I entered the Local Motors and ARPA-E contest for the Lightweight Sedan challenge and proposed a three part method to reduce weight: Revised chassis, bio-composite materials, and a hybrid drivetrain using micro-turbines to produce electricity to power the vehicle. The contest parameters stressed that the proposal should be "research for the next 10 years." So, I cited the efficiency and extremely light-weight of micro turbines to piston engines, and postulated that increasing technology in battery / KERS systems would compliment the real-world application in time.

Needless to say, I was ridiculously mad when I saw that the winning entries were 1) an aerodynamic proposal based on an exoskeleton, 2) replacing body panels with a new metallurgy compound, and some other thing that I can't recall right now. None of them really addressed the contest parameters. It basically made me swear off any more Local Motors participation.

Anyway, the bright side is that I get to maintain all rights to my entry / materials, so one day, I just might have a chance to develop a concept based on these principles and show ARPA-E and Local Motors what they missed. I guess this is how Ferruccio Lamborghini must have felt at first. Sigh.

Exoskeleton? You mean monocoque construction (aka load bearing skin)?

No, I mean like the chassis components were on the outside of the car, like a bug. That was the crux of their entry, mollified by some talk of aerodynamic efficiency. From what I recall, the rendered images of their concept didn't even have a method of entry for the driver/passengers. No doors. It was...well, frustrating, as my tone probably conveyed.

Re: Monocoque - my entry cited that format to give additional strength to the chassis/panels mating. Bio-composites are approaching the tensile strength of carbon fiber, and could potentially be much easier to mass produce and at a lower price point. I thought the implication that in 10 years, with research, such an avenue would be viable. Instead, the second place entry was some proprietary kind of new metal that could be used to replace body panels...that's it. I remember calling that entry a "body kit" because that's what it reminded me of overall.

Ah, ok. I can definitely understand your frustration since exoskeleton and aerodynamic efficiency don't generally mix.

Thanks for being interested / opportunity to clarify. The rendering actually looked like I-Beams curved into some kind of egg-like shape. It was mathematically sound, sure, but at first glance coming up with an answer "Where can research go with this?" didn't seem apparent.

I tuned in to every Q&A session provided during the contest and time and again they reiterated certain principles for judging...when the results came in, yeah, pretty infuriating. Oh well...it did motivate me to finally meet with a Patent Attorney on a couple other ideas, so some lemonade did come out of it.

> The energy density of batteries sadly lags the energy density of gasoline or kerosene

Nitpick but the energy/mass density is usually called "specific energy" to differentiate it with the more usual energy/volume "energy density".

And while a battery's energy density is pretty bad, they pretty universally have a higher density than petroleum fuels and thus even worse specific energy: the best batteries have 2 orders of magnitude worse specific energy than petroleum fuels (Li-Ion or AgZn store 0.46 MJ/kg, kerosene stores 43 MJ/kg)

Thanks for that. Yes, I was concerned with "specific energy" (energy per kg, not per m^3).

> And while a battery's energy density is pretty bad, they pretty universally have a higher density than petroleum fuels and thus even worse specific energy

Is there a typo in there? Energy density (MJ/L) for batteries is lower than petroleum fuels by the same order of magnitude as the specific energy.

While batteries have very energy density compared to petroleum fuels, on average it's much better (compared to petroleum fuels) than their specific energy. Their energy density is 15 ~ 40 times lower than petroleum fuels whereas their energy density is 50 ~ >100 times lower.

I think we might see gasoline/jet-A over electric airplanes, perhaps with or without battery storage. That would allow a few neat optimizations. You'd have more control over CG. You could have a smaller high efficiency engine that always ran at peak efficiency (or an IC engine with several modes). You could have more control over noise in urban areas. With a battery for peak/boost power, you could have a tiny engine which could supply cruise plus accessory power and use battery-backed boost for takeoff/climb. Engines that are replaceable in a few hours. All kinds of good things could happen.

>Many airplanes are certified for a ramp, taxi, and takeoff weight higher than their approved landing weight.

Is that common in G/A aircraft?

In any case, I'd love to see a tech. revolution in GA powerplants. I've grown tired of having quaint old 1950's era tractor engines be the dominant technology.

Once you get past about the 6200#/3000kg MGTOW mark, it's very common to permit takeoff weight to exceed landing weight.

I suspect all GA turbojets and most GA turboprops are in this situation.

Even the Beech Baron (a light twin) has a 100# (~16 gallons) difference in max takeoff vs max landing weight.

There is little question that carbon-based flight power is here to stay for quite some time, but that isn't really the point - which is that electric flight is nevertheless a growth industry, and there are some markets where electric flight can make a lot of sense. If all you need to do is go up and fly for 2 hours or so, then an electric plane is a viable contender for the investment - maybe we're not at the tipping point, but we are approaching it, technologically at least, a few knots at a time.

It is a worthwhile goal, though. If we can somehow harness the suns' energy to get us around the world instead of using the world itself (and thus screwing it up), then we move closer to the cusp of a more viable long-term civilization. At the moment, every cheap flight to somewhere on a jet plane costs the Earth a great deal of survival potential...

Electric planes could stop GA poisoning everyone with lead. You could also choose a different fuel.

Toy planes (general aviation) are responsible for the majority of lead pollution:

www.emagazine.com/earth-talk/lead-in-aviation-fuel

The FAA certification process is the largest limiting factor for bringing an unleaded fuel to the market. There are about 9 different formulations of unleaded fuels flying in experimental aircraft right now. I have my own "favorite", but it's unclear when, if ever, that will be available for sale to non-experimental aircraft.

The magazine article you reference says that 70% of aircraft could use (a lower octane) unleaded fuel available today. That's true, but paints an incomplete picture. That's 70% by aircraft, not 70% by flight hours or fuel consumed.

Cape Air and similar and other turbocharged piston aircraft are the ones that can't use the available unleaded "mogas". Those are also the aircraft that fly the most hours and thereby use the most fuel. Fixing the 172s and Cherokees doesn't move the needle much on TEL emissions.

I want to get rid of the lead from my aviation fuel, both for environmental reasons and for practical reasons. (Practically, it's a pain to deal with on the supply chain side, is expensive, there's only one manufacturer of TEL worldwide, it tends to gunk and foul plugs, etc.)

The FAA is the regulatory body that is presiding over this, much more than the EPA. End running the FAA to get the EPA to make another "lead is bad" proclamation won't do any good, IMO.

My engines can't burn any available and certified unleaded fuel.

AOPA lobbies to delay unleaded fuel at every opportunity [1] [2] [5]. Unleaded fuel is available now [3], but 10% of owners would have to spend some money to stop poisoning 3 million children [4].

[1] http://www.aopa.org/News-and-Video/All-News/2015/April/01/Bi...

[2] http://www.agairupdate.com/article_detail.php?_kp_serial=000...

[3] http://www.flyingmag.com/blogs/flying-time/transition-unlead...

[4] the link in my GP post

[5] http://blog.aopa.org/vfr/?p=870

That UL fuel that's "available now" [3] is available now in Sweden only and doesn't work for the 10% of engines that require 100 octane fuel, those 10% of engines likely consuming >50% of the avgas sold.

If it was a matter of spending some reasonable (say mid 5 figure per airplane) sum of money to burn a readily available UL fuel, I'd do it. I literally can't do that.

There is no current path to certification for me to run that 91/96UL here in the US. It's a technical problem (maintaining adequate detonation margins on a high/hot takeoffs), a regulatory problem (getting the airframe and engine certified for the fuel), and a market problem (getting that fuel sold at airports here in the US). You have to solve the first to get to the second. I believe there are several viable compounds/blends now in testing and we're on to the second phase: getting one or more of them certified by the FAA. Only once that's done is it viable to talk about banning or curbing TEL use. If there's one clear winning fuel, the adoption by the industry will be swift (no pun intended, as SWIFT is one of the contenders, though I don't believe a leading contender).

I don't read any of those three AOPA links as AOPA trying to "delay unleaded fuel" in any way, shape, or form. One is an objection to an increase of tax on avgas (certainly one of the things I/we pay AOPA to lobby against), and the other two are presentations describing the technical reasons avgas contains lead now and the status of initiatives underway to create an alternative, unleaded fuel.

Surely the landing gear, wing spar attachments, and brakes all have to be able to cope with an unexpected turnback and landing with most of the original weight? (not to mention heavy landings in adverse weather conditions)

No see http://www.caa.co.uk/default.aspx?catid=60&pagetype=90&pagei... or http://www.boeing.com/commercial/aeromagazine/articles/qtr_3...

They are only certified to the maximum landing weight which typically is lower than the maximum takeoff weight. When an overweight landing (ie. the weight is higher then maximum landing weight) occurs engineers have to perform a thorough inspection of the plane structure - landing gear, spars, wings, wingbox

EDIT: thanks ForHackernews

> the maximum landing weight which typically is larger than the maximum takeoff weight.

I assume this was a typo and you mean that the max landing weight is typically less than the max takeoff weight.

I guess I was thinking more about smaller GA aircraft, but thanks for the detailed reply.

Planes usually fly around for a bit dumping fuel if they need to turn back.

I have not idea: But could this be why Planes will often dump fuel for a turn back.

If you could run cargo planes on beamed power, you wouldn't have to haul your power storage (fuel) to altitude. Also, given the extreme simplicity and reliability of electric motors, such an infrastructure would save huge amounts of money and also avoid externalities like atmospheric pollution.

The big question, of course, is the ability to build such an infrastructure with enough reliability.

Perhaps an orbiting network of solar powered satellites that can each manage large numbers of directed power beams. Though maybe that would be a non starter due to the large number of non-civilian applications.

Satellites? I doubt it. Too expensive. Long-duration high altitude aircraft, maybe?

A fuel cell that carries only hydrogen and harvests oxygen from the atmosphere ... is viable. *

*the whole membrane degradation thing excluded

metal-air fuel cells are in many respects even better. And with metal content around 50% they become weight comparable or better than 30% efficient ICE.

In that case you have lithium oxide to take care of and you have heavier plane with each second (of course most of the fuel is wasted on lifting the plane, so it may be better)

the electric planes, at least at first, isn't about just swapping ICE for electric. It is about building different planes. The current planes have evolved significantly under the limitations of ICE. The electric planes, at least initially, is about short-hoppers ("flying car" like functionality) where ICE is a no-go because of cost and noise. The electrics are well suited to build STOL and VTOL (multi-copters). With years the electrification can make its way through various hybrid schemes into much more efficient long-haulers.

How old are you? 50 years from now the world will be a lot different. It'll probably change as much as it did in the last 100, which to put into perspective:

http://www.aerofiles.com/gallaudet-c2-1915.jpg

45 years ago:

http://www.museumofflight.org/747

You probably should have gone with 46 years ago: https://upload.wikimedia.org/wikipedia/commons/1/11/Concorde...

What was your point? Here's a computer from 1965:

http://www.columbia.edu/cu/computinghistory/a10.jpg

Not all technology is increasing at the same rate. Adoption is another problem. Take this bullet train from 1964. Still won't find that in America.

http://cdn.gaijinpot.com/wp-content/uploads/sites/4/2014/10/...

Given your example, I thought you were talking about aircraft, so the diminishing returns in the recent 50 years seemed salient.

Nope, we were talking more about the ability to generate electricity for an electric plane, right? Battery technology, or something else that can deliver electricity.

Of course, 50 years from now we'll have commercial scramjets:

https://en.m.wikipedia.org/wiki/Scramjet

So, progress will be made on many fronts.

Battery technology isn't progressing at anywhere near the rate of computer technology.

It maybe isn't quite as bad as you think, as what really matters is the thrust for the combined weight of the engine and power source rather than just the energy density of the power source in joules per kilo. Combustion is generally pretty lousy, compared to electric, at converting joules into useful newtons.

Combustion is about 30% efficient, electric is about 95% efficient, so for the same energy input electric gets you 3 times (and a bit) the output.

Problem is, getting the same energy input via batteries weights 50~100 times as much as fuel does, and takes 15~40 times as much room. So your fuel still weighs 20~30 times as much, and takes 5~10 times as much room in your plane.

And while combustion is 30% efficient part of the energy loss can be used to heat up the cabin, because at 30000~40000ft you're not exactly at sauna temperatures outside, so now you need to spend part of your electricity to heat passengers and your batteries (because most of them don't like operating at 200K)