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How a 4-Pound Engine Can Replace a 40-Pound Engine

149 points by ytNumbers 10y ago

whamlastxmas 10y ago
Clickbait. It's a 4 pound engine that makes 3 horsepower. Impressive, but the article says the 40 pound engine makes 6.5 horsepower. Also, one costs $50 and the other probably $50,000. And no information given about the 4 pounder.
- noir_lord 10y ago
  > LiquidPiston says that their X-mini is still in a testing phase, and they hope to get the weight down to 3 pounds and the power up to 5 hp. (The 40-pound piston engine produces about 6.5 hp.) That's an unkind reading, for many applications a 5hp 3lb engine would replace a 6.5hp 40lb engine (not least because you put two 3lb engines at 5hp in for a total of 10hp at 6lbs..). In any case it's a fascinating engine and the application for things like drones are pretty obvious.
  - dharma1 10y ago
    I wonder how it compares to fuel cells on drones, in terms of weight of the engine and energy density of the fuel
    - oofabz 10y ago
      The problem with fuel cells is power output. They are very efficient and reliable but they generate much less power than a mechanical engine of the same weight. Power/weight ratio is very important for aircraft engines.
      - dharma1 10y ago
        You are right, power/weight ratio is important. I've seen news pop up in the last 12 months of fuel cell powered drones with several hours flight time (compared to under an hour with li-ion batteries) so I'm assuming they can push out enough power for a multirotor for decent lift without weighing too much. Fixed wings should definitely see good gains, as it requires less power to fly than multirotors. I haven't followed it closely but 5-10x flight times vs li-ion sounds realistic considering the energy density of hydrogen. http://www.hes.sg/ http://www.hes.sg/
  - whamlastxmas 10y ago
    Having a conditional "they hope to" makes that information worthless. I hope be to be a billionaire for sitting on my ass, it doesn't mean it's likely or that I'm even working towards it.
- kbenson 10y ago
  > but the article says the 40 pound engine makes 6.5 horsepower. So? Every production car engine today weighs more than 40 pounds and makes more than 6.5 horsepower. That doesn't obviate the need to lighter engines, even if they are less powerful. > Also, one costs $50 and the other probably $50,000. Doubtful (and where are you getting $50k from?). You can see most of what goes into the engine in the video. Their advances seem to be mostly process and shape changes, not due to some space age material. It may cost $1000 in its current incarnation, but that's what you get when you manually machine all the parts instead of have them mass produced.
  - whamlastxmas 10y ago
    1. My point was that it wasn't a replacement. It's not even capable of getting half the power. Hence my claim that the title was clickbait, it's patently false. That's like saying I invented a replacement motor for the Bugatti Veyron at half the cost, oh by the way it makes 400 horsepower instead of 1000. 2. Again it's my demonstration of clickbait. A 40 pound engine that makes 6.5 horsepower will never be replaced by an engine featured in the article. At least, not in the next several decades. An engine that weighs 40 pounds and makes 6.5 horsepower is called a lawnmower engine. It's cheap to make and maintain and people use it because it's affordable. People aren't going to replace their $50 lawn mower engine with one that's $1000.
    - kbenson 10y ago
      I'm not sure why you think replacing an engine has to entail having the exact same performance as before. > That's like saying I invented a replacement motor for the Bugatti Veyron at half the cost, oh by the way it makes 400 horsepower instead of 1000. You can. What's wrong with that. Maybe there's something else about the engine that makes it noteworthy, such as it being electric? In this case, it's a way to showcase specific aspects of the engine, it's size and weight. > A 40 pound engine that makes 6.5 horsepower will never be replaced by an engine featured in the article. Might it be replaced by two 4 pound engines with a total of 6 horsepower for 8 pounds? Or maybe three for 9 horsepower for 12 pounds? Perhaps the efficiency can scale and they can do a single motor for ~9 horsepower and ~12 pounds? > It's cheap to make and maintain and people use it because it's affordable. It's cheap because it's mass produced. You can't compare how useful this engine is to existing engines without considering the cost when built at the expected scale. > People aren't going to replace their $50 lawn mower engine with one that's $1000. I'll just repeat myself with inflection: "It may cost $1000 in its current incarnation, but that's what you get when you manually machine all the parts instead of have them mass produced."
bryanlarsen 10y ago
Note that the 40 pound engine includes the tank, gearbox, muffler et al, while the 4 pound engine is just the core. Still an amazing demo, though.
alistairSH 10y ago
This is another take on the rotary/Wankel engine. Mazda and many others have tried to develop durable, efficient versions of this type for decades, with only limited success.
- phineastcat 10y ago
  The reason Mazda struggled with the rotary engine is due to what their application was. Rotaries work most efficiently and reliably when run for long periods of time (hours) at a consistent RPM. Vehicles with traditional manual or automatic transmissions (what most Mazda rotary cars had afaik) do anything but keep consistent RPM. Mazda subsequently struggled with keeping emissions down, and fuel economy up, while prolonging the life of the engine. If you tie a rotary to a generator, or true CVT transmission, they're much better suited to the task.
  - koolba 10y ago
    That sounds like a good choice for a hybrid that uses the rotary ICE to periodically charge the battery.
    - lttlrck 10y ago
      Or a range extender generator like in the BMW i3
      - thephilsproject 10y ago
        I first saw this on the Audi A1 e-tron concept; it was a 250cc wankel for the range extender. I thought that was the future when I saw it, and here I am now with a Vauxhall Ampera (Chevy Volt)!
      - phineastcat 10y ago
        Mazda actually had a Mazda2 EV prototype with a rotary range extender that they unveiled in 2013. Not sure what ever happened with it, though.
  - 10y ago
ar0b 10y ago
Pretty informative video about rotary engine dis-advantages. https://www.youtube.com/watch?v=v3uGJGzUYCI https://www.youtube.com/watch?v=v3uGJGzUYCI
- zfnsgmdydmy 10y ago
  Except this isn't a Wankel. I looked into this a while back, and they're able to get 50%+ thermal efficiencies by using their own modified thermodynamic cycle that promotes more complete fuel combustion, as well as arranging the engine components in such a way that the engine has low heat rejection qualities. Nearly doubling the efficiency of the typical ICE setup and doing so with large weight reductions far outweighs any issues with rotary seals. These things are so compact and simple that it would be feasible to simply drop an entirely new engine into your car and melt down the old one when the seals wear out. Not that it would come to that, but those are the kind of economics we're dealing with here. This is a legitimately nifty invention. t. mechanical engineer
  - johnward 10y ago
    Trying to understand what is different and found this: "The basic idea is similar to a Wankel rotary, but turned on its head. Where the rotor holds the seals in a normal Wankel, the housing does that job in the X1 engine. This allows significant reduction in oil consumption over a regular rotary motor. Other enhancements include direct injection, a high compression ratio at 18:1, and a dramatic change to the geometry of the combustion chamber, which maintains a constant volume during ignition. This change means the air-fuel mixture auto-ignites like a diesel, and can be burned much longer than normal. The result is a more complete combustion ending in low emissions and very high chamber pressures. This high pressure is allowed to act on the rotor until it reaches nearly atmospheric pressures, so almost all the available energy is extracted before the exhaust is physically pushed out. Again, this is different than a normal internal combustion engine, which releases very energetic, high-pressure exhaust gas." http://www.popularmechanics.com/cars/a8174/liquidpistons-hyper-efficient-engine-turning-the-rotary-inside-out-13817971/ http://www.popularmechanics.com/cars/a8174/liquidpistons-hyp...
tim333 10y ago
It might be fairer to compare to a state of the art piston engine. Brief googling finds a DeNardis 40cc engine weighing 11 lbs and producing 7hp. Still impressive though. http://www.denardisengines.com/40cc.html http://www.denardisengines.com/40cc.html
- VLM 10y ago
  Ouch. Note that the 4 pounder is only outputing 3 HP so at a pound and a third per hp a denardis equivalent would weigh a bit more than 9 lbs. Note that the denardis spec includes the accessories that make the engine work and the picture in the article does not. Likely an installed operating denardis would weigh less. There's a trick you can play with engines that only engineers really understand. A good engineer can fluidly trade economy, reliability, and mass. So if you want a couple ounce model airplane engine that outputs a couple HP and might run for ten hours before burning out at insane RPMs with awful fuel economy specs, those are widely available and fairly cheap. Or you can buy an inboard diesel that'll push a motorboat for insane cruising distances under hurricane conditions and maintained with a shoebox of cheap tools, but it'll be expensive and heavy, like 5 HP and it'll be 100+ pounds. I have no question someone can build a 4 pound engine that outputs 3 HP or an 11 pound engine that outputs 7 HP. The only question is how long, and how much gas it'll burn. Something tells me neither of them would run my commuter car for 200+K miles OR get 30+ MPG, which is pretty easy for my extremely high tech, but heavier engine, commuter car.
  - jws 10y ago
    The denardis 40cc 7hp engine says it burns 610g of fuel per kilometer driving a pocket bike. That is around 3 mpg for those of us with strange units. It's safe to say they traded away efficiency.
    - walrus01 10y ago
      It's a two stroke engine with oil mixed into the fuel, I don't think the intended users (there's such a thing as competition racing micro motorcycles??!) care too much about fuel efficiency...
sgnelson 10y ago
This article/company are misrepresenting the truth. Once you add the carburetor, a starter (watch the video, they use a drill to start the engine, obviously real small engines have pull starters, which add weight.), the exhaust, intake manifold, etc. This engine is much heavier than 4 pounds. This is almost the equivalent of me saying I've invented a 3 pound airplane, which is nothing but a carbon fiber tub. You just have to add wings, engines, cockpit, etc. etc. It's a small engine, yes, that's nice. But don't blow it's carbon emissions up my ass and expect me to believe the hype.
- JoeAltmaier 10y ago
  The starter may be a non-issue. E.g. starting a drone that way (with a drill) would be fine. Maybe even leave off the exhaust. Depends on the application, which they admit.
  - evan_ 10y ago
    This is true but the engines they're comparing to have all of these things. You could take the starter etc. off of those engines and it would weigh less, too- it's a misleading comparison.
    - GauntletWizard 10y ago
      You take off all those things, those engines still weigh 20 pounds. You put the mini-versions of all those things on theirs like they show in the video, and I doubt it breaks 10. It's probably overstated bragging, but they've got much to brag about.
  - runholm 10y ago
    Then don't cheat by comparing the weight of the motor with starter to the one without a starter. They are comparing two very different things to produce a spectacular head line.
kukx 10y ago
For those wondering how it works, here's a visualization: https://www.youtube.com/watch?v=0e785YnDmq0 https://www.youtube.com/watch?v=0e785YnDmq0
- King-Aaron 10y ago
  That's an extremely elegant design in terms of intake/exhaust flow.
ChuckMcM 10y ago
I saw this a couple of years ago, its a pretty nice rotary engine. As others have pointed out, rotary engines have their challenges but their advantage in weight and torque still makes them a good choice for aircraft. The "secret sauce" that the Liquid Piston folks bring to the party is the upgraded rotor shape. It doesn't need apex seals like the old Wankel version did. The news here is that they had reduced their experimental work into an actual functional engine. Unlike the Wankel, their cylinder design would really support a compact multi-rotor engine but presumably you could gang them together on the same crankshaft if you really wanted to. Other than the UAV and possibly the paramotor market I'm not sure where these guys are going to find customers though.
- sgt101 10y ago
  I'm going to get laughed at.. but the first thing I thought of was lawn tractor! A lighter tractor would be less of an issue to wrangle about a garden, it would consume less fuel shifting itself about, domestic ones get relatively few engine hour... a smaller engine might allow novel designs that get into tighter corners are simpler and cost less... You need ~10hp for a lawn tractor as is soooooo...
  - zodPod 10y ago
    The only problem that I could see there is that you actually kind of need weight on a tractor. You take a 500lb tractor and take out the 150lb engine you're getting a lot closer to the weight of the driver and you're upping the possibility of tipping over significantly.
    - serge2k 10y ago
      Couldn't you just adjust the driver/engine position to account for this?
      - zodPod 10y ago
        That's a good point!
FunctionalMan 10y ago
If they can get something big enough to be a backup engine on an otherwise Electric car....
carlob 10y ago
When I read it was 70 cc I was a little taken aback. In Italy there are a ton of people moving on scooters (mopeds) that are limited to 50 cc. It's true that they can't have more than 1.5 hp of power, but that's the law not the physical maximum for a piston engine.
hinkley 10y ago
A video with a slightly different design, including hollow cylinder head: https://vimeo.com/163543761 https://vimeo.com/163543761
userbinator 10y ago
0.75hp/lb is better than the 0.1625hp/lb engine they replaced with it, but doesn't seem so revolutionary compared to the power-to-weight of existing engines: https://en.wikipedia.org/wiki/Power-to-weight_ratio#Engines https://en.wikipedia.org/wiki/Power-to-weight_ratio#Engines Even the well-known Mazda rotary is slightly better at 0.92hp/lb, and various aviation engines have higher power-to-weight ratios still.
- walrus01 10y ago
  I think the big difference is this is really, really light weight and tiny compared to a small aviation engine. More in the category of something you would power a 100 kilogram drone with than an ultralight or LSA category aircraft.
walrus01 10y ago
This is potentially very interesting for medium sized drones that need 12+ hour endurance, as lithium ion/lipo batteries just don't have the energy density of gasoline... Even when you lose 50% to heat in a typical internal combustion engine the kilojoules per kilogram is so much greater in a liquid hydrocarbon fuel.

149 points by ytNumbers 10y ago

Clickbait. It's a 4 pound engine that makes 3 horsepower. Impressive, but the article says the 40 pound engine makes 6.5 horsepower. Also, one costs $50 and the other probably $50,000. And no information given about the 4 pounder.

noir_lord 10y ago
> LiquidPiston says that their X-mini is still in a testing phase, and they hope to get the weight down to 3 pounds and the power up to 5 hp. (The 40-pound piston engine produces about 6.5 hp.) That's an unkind reading, for many applications a 5hp 3lb engine would replace a 6.5hp 40lb engine (not least because you put two 3lb engines at 5hp in for a total of 10hp at 6lbs..). In any case it's a fascinating engine and the application for things like drones are pretty obvious.
- dharma1 10y ago
  I wonder how it compares to fuel cells on drones, in terms of weight of the engine and energy density of the fuel
  - oofabz 10y ago
    The problem with fuel cells is power output. They are very efficient and reliable but they generate much less power than a mechanical engine of the same weight. Power/weight ratio is very important for aircraft engines.
    - dharma1 10y ago
      You are right, power/weight ratio is important. I've seen news pop up in the last 12 months of fuel cell powered drones with several hours flight time (compared to under an hour with li-ion batteries) so I'm assuming they can push out enough power for a multirotor for decent lift without weighing too much. Fixed wings should definitely see good gains, as it requires less power to fly than multirotors. I haven't followed it closely but 5-10x flight times vs li-ion sounds realistic considering the energy density of hydrogen. http://www.hes.sg/ http://www.hes.sg/
- whamlastxmas 10y ago
  Having a conditional "they hope to" makes that information worthless. I hope be to be a billionaire for sitting on my ass, it doesn't mean it's likely or that I'm even working towards it.
kbenson 10y ago
> but the article says the 40 pound engine makes 6.5 horsepower. So? Every production car engine today weighs more than 40 pounds and makes more than 6.5 horsepower. That doesn't obviate the need to lighter engines, even if they are less powerful. > Also, one costs $50 and the other probably $50,000. Doubtful (and where are you getting $50k from?). You can see most of what goes into the engine in the video. Their advances seem to be mostly process and shape changes, not due to some space age material. It may cost $1000 in its current incarnation, but that's what you get when you manually machine all the parts instead of have them mass produced.
- whamlastxmas 10y ago
  1. My point was that it wasn't a replacement. It's not even capable of getting half the power. Hence my claim that the title was clickbait, it's patently false. That's like saying I invented a replacement motor for the Bugatti Veyron at half the cost, oh by the way it makes 400 horsepower instead of 1000. 2. Again it's my demonstration of clickbait. A 40 pound engine that makes 6.5 horsepower will never be replaced by an engine featured in the article. At least, not in the next several decades. An engine that weighs 40 pounds and makes 6.5 horsepower is called a lawnmower engine. It's cheap to make and maintain and people use it because it's affordable. People aren't going to replace their $50 lawn mower engine with one that's $1000.
  - kbenson 10y ago
    I'm not sure why you think replacing an engine has to entail having the exact same performance as before. > That's like saying I invented a replacement motor for the Bugatti Veyron at half the cost, oh by the way it makes 400 horsepower instead of 1000. You can. What's wrong with that. Maybe there's something else about the engine that makes it noteworthy, such as it being electric? In this case, it's a way to showcase specific aspects of the engine, it's size and weight. > A 40 pound engine that makes 6.5 horsepower will never be replaced by an engine featured in the article. Might it be replaced by two 4 pound engines with a total of 6 horsepower for 8 pounds? Or maybe three for 9 horsepower for 12 pounds? Perhaps the efficiency can scale and they can do a single motor for ~9 horsepower and ~12 pounds? > It's cheap to make and maintain and people use it because it's affordable. It's cheap because it's mass produced. You can't compare how useful this engine is to existing engines without considering the cost when built at the expected scale. > People aren't going to replace their $50 lawn mower engine with one that's $1000. I'll just repeat myself with inflection: "It may cost $1000 in its current incarnation, but that's what you get when you manually machine all the parts instead of have them mass produced."

bryanlarsen 10y ago

Note that the 40 pound engine includes the tank, gearbox, muffler et al, while the 4 pound engine is just the core. Still an amazing demo, though.

alistairSH 10y ago

This is another take on the rotary/Wankel engine. Mazda and many others have tried to develop durable, efficient versions of this type for decades, with only limited success.

phineastcat 10y ago
The reason Mazda struggled with the rotary engine is due to what their application was. Rotaries work most efficiently and reliably when run for long periods of time (hours) at a consistent RPM. Vehicles with traditional manual or automatic transmissions (what most Mazda rotary cars had afaik) do anything but keep consistent RPM. Mazda subsequently struggled with keeping emissions down, and fuel economy up, while prolonging the life of the engine. If you tie a rotary to a generator, or true CVT transmission, they're much better suited to the task.
- koolba 10y ago
  That sounds like a good choice for a hybrid that uses the rotary ICE to periodically charge the battery.
  - lttlrck 10y ago
    Or a range extender generator like in the BMW i3
    - thephilsproject 10y ago
      I first saw this on the Audi A1 e-tron concept; it was a 250cc wankel for the range extender. I thought that was the future when I saw it, and here I am now with a Vauxhall Ampera (Chevy Volt)!
    - phineastcat 10y ago
      Mazda actually had a Mazda2 EV prototype with a rotary range extender that they unveiled in 2013. Not sure what ever happened with it, though.
- 10y ago

ar0b 10y ago

Pretty informative video about rotary engine dis-advantages. https://www.youtube.com/watch?v=v3uGJGzUYCI https://www.youtube.com/watch?v=v3uGJGzUYCI

zfnsgmdydmy 10y ago
Except this isn't a Wankel. I looked into this a while back, and they're able to get 50%+ thermal efficiencies by using their own modified thermodynamic cycle that promotes more complete fuel combustion, as well as arranging the engine components in such a way that the engine has low heat rejection qualities. Nearly doubling the efficiency of the typical ICE setup and doing so with large weight reductions far outweighs any issues with rotary seals. These things are so compact and simple that it would be feasible to simply drop an entirely new engine into your car and melt down the old one when the seals wear out. Not that it would come to that, but those are the kind of economics we're dealing with here. This is a legitimately nifty invention. t. mechanical engineer
- johnward 10y ago
  Trying to understand what is different and found this: "The basic idea is similar to a Wankel rotary, but turned on its head. Where the rotor holds the seals in a normal Wankel, the housing does that job in the X1 engine. This allows significant reduction in oil consumption over a regular rotary motor. Other enhancements include direct injection, a high compression ratio at 18:1, and a dramatic change to the geometry of the combustion chamber, which maintains a constant volume during ignition. This change means the air-fuel mixture auto-ignites like a diesel, and can be burned much longer than normal. The result is a more complete combustion ending in low emissions and very high chamber pressures. This high pressure is allowed to act on the rotor until it reaches nearly atmospheric pressures, so almost all the available energy is extracted before the exhaust is physically pushed out. Again, this is different than a normal internal combustion engine, which releases very energetic, high-pressure exhaust gas." http://www.popularmechanics.com/cars/a8174/liquidpistons-hyper-efficient-engine-turning-the-rotary-inside-out-13817971/ http://www.popularmechanics.com/cars/a8174/liquidpistons-hyp...

tim333 10y ago

It might be fairer to compare to a state of the art piston engine. Brief googling finds a DeNardis 40cc engine weighing 11 lbs and producing 7hp. Still impressive though. http://www.denardisengines.com/40cc.html http://www.denardisengines.com/40cc.html

VLM 10y ago
Ouch. Note that the 4 pounder is only outputing 3 HP so at a pound and a third per hp a denardis equivalent would weigh a bit more than 9 lbs. Note that the denardis spec includes the accessories that make the engine work and the picture in the article does not. Likely an installed operating denardis would weigh less. There's a trick you can play with engines that only engineers really understand. A good engineer can fluidly trade economy, reliability, and mass. So if you want a couple ounce model airplane engine that outputs a couple HP and might run for ten hours before burning out at insane RPMs with awful fuel economy specs, those are widely available and fairly cheap. Or you can buy an inboard diesel that'll push a motorboat for insane cruising distances under hurricane conditions and maintained with a shoebox of cheap tools, but it'll be expensive and heavy, like 5 HP and it'll be 100+ pounds. I have no question someone can build a 4 pound engine that outputs 3 HP or an 11 pound engine that outputs 7 HP. The only question is how long, and how much gas it'll burn. Something tells me neither of them would run my commuter car for 200+K miles OR get 30+ MPG, which is pretty easy for my extremely high tech, but heavier engine, commuter car.
- jws 10y ago
  The denardis 40cc 7hp engine says it burns 610g of fuel per kilometer driving a pocket bike. That is around 3 mpg for those of us with strange units. It's safe to say they traded away efficiency.
  - walrus01 10y ago
    It's a two stroke engine with oil mixed into the fuel, I don't think the intended users (there's such a thing as competition racing micro motorcycles??!) care too much about fuel efficiency...

sgnelson 10y ago

This article/company are misrepresenting the truth. Once you add the carburetor, a starter (watch the video, they use a drill to start the engine, obviously real small engines have pull starters, which add weight.), the exhaust, intake manifold, etc. This engine is much heavier than 4 pounds. This is almost the equivalent of me saying I've invented a 3 pound airplane, which is nothing but a carbon fiber tub. You just have to add wings, engines, cockpit, etc. etc. It's a small engine, yes, that's nice. But don't blow it's carbon emissions up my ass and expect me to believe the hype.

JoeAltmaier 10y ago
The starter may be a non-issue. E.g. starting a drone that way (with a drill) would be fine. Maybe even leave off the exhaust. Depends on the application, which they admit.
- evan_ 10y ago
  This is true but the engines they're comparing to have all of these things. You could take the starter etc. off of those engines and it would weigh less, too- it's a misleading comparison.
  - GauntletWizard 10y ago
    You take off all those things, those engines still weigh 20 pounds. You put the mini-versions of all those things on theirs like they show in the video, and I doubt it breaks 10. It's probably overstated bragging, but they've got much to brag about.
- runholm 10y ago
  Then don't cheat by comparing the weight of the motor with starter to the one without a starter. They are comparing two very different things to produce a spectacular head line.

kukx 10y ago

For those wondering how it works, here's a visualization: https://www.youtube.com/watch?v=0e785YnDmq0 https://www.youtube.com/watch?v=0e785YnDmq0

King-Aaron 10y ago
That's an extremely elegant design in terms of intake/exhaust flow.

ChuckMcM 10y ago

I saw this a couple of years ago, its a pretty nice rotary engine. As others have pointed out, rotary engines have their challenges but their advantage in weight and torque still makes them a good choice for aircraft. The "secret sauce" that the Liquid Piston folks bring to the party is the upgraded rotor shape. It doesn't need apex seals like the old Wankel version did. The news here is that they had reduced their experimental work into an actual functional engine. Unlike the Wankel, their cylinder design would really support a compact multi-rotor engine but presumably you could gang them together on the same crankshaft if you really wanted to. Other than the UAV and possibly the paramotor market I'm not sure where these guys are going to find customers though.

sgt101 10y ago
I'm going to get laughed at.. but the first thing I thought of was lawn tractor! A lighter tractor would be less of an issue to wrangle about a garden, it would consume less fuel shifting itself about, domestic ones get relatively few engine hour... a smaller engine might allow novel designs that get into tighter corners are simpler and cost less... You need ~10hp for a lawn tractor as is soooooo...
- zodPod 10y ago
  The only problem that I could see there is that you actually kind of need weight on a tractor. You take a 500lb tractor and take out the 150lb engine you're getting a lot closer to the weight of the driver and you're upping the possibility of tipping over significantly.
  - serge2k 10y ago
    Couldn't you just adjust the driver/engine position to account for this?
    - zodPod 10y ago
      That's a good point!

FunctionalMan 10y ago

If they can get something big enough to be a backup engine on an otherwise Electric car....

carlob 10y ago

When I read it was 70 cc I was a little taken aback. In Italy there are a ton of people moving on scooters (mopeds) that are limited to 50 cc. It's true that they can't have more than 1.5 hp of power, but that's the law not the physical maximum for a piston engine.

hinkley 10y ago

A video with a slightly different design, including hollow cylinder head: https://vimeo.com/163543761 https://vimeo.com/163543761

userbinator 10y ago

0.75hp/lb is better than the 0.1625hp/lb engine they replaced with it, but doesn't seem so revolutionary compared to the power-to-weight of existing engines: https://en.wikipedia.org/wiki/Power-to-weight_ratio#Engines https://en.wikipedia.org/wiki/Power-to-weight_ratio#Engines Even the well-known Mazda rotary is slightly better at 0.92hp/lb, and various aviation engines have higher power-to-weight ratios still.

walrus01 10y ago
I think the big difference is this is really, really light weight and tiny compared to a small aviation engine. More in the category of something you would power a 100 kilogram drone with than an ultralight or LSA category aircraft.

walrus01 10y ago

This is potentially very interesting for medium sized drones that need 12+ hour endurance, as lithium ion/lipo batteries just don't have the energy density of gasoline... Even when you lose 50% to heat in a typical internal combustion engine the kilojoules per kilogram is so much greater in a liquid hydrocarbon fuel.