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I did do a Google search before posting this, and the only thing I
found
was a single prototype associated with a Kickstarter project.
At least
it is not yet WKTE, and I did independently think of this.
The "lots of pollution" comes from the typical 2-stroke model
airplane engine. I'm
not sure a 4-stroke engine would be
practical over the long term, because the vertical drive shaft*
means the oil crankcase is horizontal with respect to the piston.
Sure, lawn mowers typically have that arrangement, but oil
leaks into the combustion area as the piston-seals wear. It can
be more polluting than a 2-stroke engine, if you don't replace
the seals regularly. And adding a gearbox to change a
horizontal crankshaft into a vertical propeller-drive shaft just
adds weight and complexity.
Which kind-of means this drone will need significantly more
maintenance than a regular electric drone. Well, what else is
the HalfBakery for, than Ideas like this?
*Since a 2-stroke engine mixes oil with the gasoline, and all of
it flows through the crankcase to lubricate stuff, it doesn't
matter what orientation is the crank shaft.
Prototype
http://www.digitalt...-drone-kickstarter/
As mentioned in the main text. [Vernon, Apr 19 2016]
F1 engine song
https://www.youtube...watch?v=1JPBdBIFGNQ
[bs0u0155, Apr 19 2016]
Variable pitch quadcopter
https://www.youtube...watch?v=Vy5Ky50eGJs
Simple solution to control [TomP, Apr 20 2016]
Goliath gas-powered quadcopter project
http://hackaday.io/project/1230
Alright then, if this is about quadcopters [notexactly, Apr 20 2016]
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Yes, I've often wondered why small IC engines aren't
used in drones. I guess one problem, as you noted, is
the noise; another might be the responsiveness of IC
engines compared to motors. |
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I think the most effective option would be a single IC
engine driving a small generator to run multiple
motors. The extra weight would be offset by not
needing batteries. |
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Someone is already planning on making hydrogen fuel-cells
to replace drone batteries. A link to that is inside the
article I linked. |
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[MaxwellBuchanan], I wonder if a vertical-piston engine
could have pulleys and belts to drive the drone rotors.
That might weigh rather less than a generator and multiple
electric motors, but I'm not sure how power-efficient it
would be. |
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But then how would you differentially control each
rotor? |
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Well, there are such things as adjustable Vbelt
pulleys...used in some Continuously Variable
Transmissions (yeah, more complexity and weight, alas). |
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Throttlable, operate in any orientation, low maintainance, run on kerosene. |
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Little tiny gas turbines... |
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//I'm not sure a 4-stroke engine would be practical over
the long term, because the vertical drive shaft* means
the oil crankcase is horizontal// |
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This is a solved problem. All orientations of 4 stroke
engines have been made to work reliably with tweaks to
the oiling. The most extreme examples in aviation are
probably the inverted V engines. Examples include the
engines fitted to the BF109. They have good scavenge
pumps and just sort of fling the oil about. |
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There's no problem with response either, idle to full
power can happen in very short periods of time. This is
especially easy with small engines. Even relatively large
engines on dirt bikes can throttle up and down in time to
hop between logs, for example. |
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Model aircraft engines, at least the small common ones,
are usually 2-stroke diesel engines running on a mix of
methanol and nitromethane. As a positive, they give
pretty phenomenal power density. |
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Now, the problems. The principle problem is control. The
variation between 4 brushless electric motors is going to
be small. You can also control the RPM directly, and scale
it up and down exactly. You can do that quite cheaply.
With the sort of IC engines fitted to model aircraft, you
can't get accurate RPM information. You can only
modulate their air supply and subsequent fuel supply
from the mini carburetor. This is inexact, will vary from
engine to engine. Worse, it will vary as the engines heat
up/cool down, with air pressure (which is going to be
changed by the prop it's spinning) with the cycles of the
moon etc. They also put out a cloud of nasty smoke.
Normally, this just trails behind the plane. In a hovering
scenario, you're going to get the engines ingesting that,
which will mess with their power output. You could
control your way around this, but you'd need precise
sensing of RPM, fuel injection and other heavy stuff. |
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Electric motors avoid all this. |
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//you can't get accurate RPM information// |
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Not true. A simple sensor on the output shaft can
give you up-to-the-millisecond information on speed. |
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True, you can add that. But the relationships between RPM,
fuel flow & air flow are all horribly messy. You have to build
complex maps. You can't simply have X throttle opening = Y
RPM. |
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Millisecond sensing is a bit last week for simple RPM, fuel
flow is a bit of a bugger, especially at the sort of rates these
engines consume. |
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//You can't simply have X throttle opening = Y
RPM.// No, but if the feedback loop is fast, you just
open the throttle until you reach Y r.p.m. |
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Actually (and somewhat off-topic) has anyone tried
playing classical music on an array of motorbikes? |
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F1 engines are close enough? <link> |
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Baked & WKTE: Military UAVs. |
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//Baked & WKTE: Military UAVs.// |
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I think what is meant by "drone" here, is quadcopter.
Although now I come to google it, gas-powered quadcopter
is also a baked thing, |
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Big issue is responsiveness. Multicopters with multiple gas engines have been tried, and generally are a control nightmatre. |
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And there's also a prototype hybrid quadcopter that's either on the market or about to be, with an IC engine running a generator, powering a bank of batteries and the normal arrangement of electric motors. |
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Also people have experimented with multiple gas engines, but using variable blade pitch to give fine control, also one crackpot design which had one central engine driving mutliple drive shafts (or was it belts?), with variable blade pitch used for fine control. |
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Lots of things have been tried. Have a look at what's successful.... |
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Use variable pitch rotors [link] with shaft or belt drive from a central engine. |
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