Half a croissant, on a plate, with a sign in front of it saying '50c'
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Model Airplane Engines Drone

Lots of pollution and noise, but flies longer
  [vote for,

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.

Vernon, Apr 19 2016

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]


       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.   

       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.
MaxwellBuchanan, Apr 19 2016

       Someone is already planning on making hydrogen fuel-cells to replace drone batteries. A link to that is inside the article I linked.
Vernon, Apr 19 2016

       [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.
Vernon, Apr 19 2016

       But then how would you differentially control each rotor?
MaxwellBuchanan, Apr 19 2016

       Well, there are such things as adjustable Vbelt pulleys...used in some Continuously Variable Transmissions (yeah, more complexity and weight, alas).
Vernon, Apr 19 2016

       Gas turbines.   

       Throttlable, operate in any orientation, low maintainance, run on kerosene.   

       Little tiny gas turbines...
8th of 7, Apr 19 2016

       //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//   

       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.   

       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.   

       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.   

       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.   

       Electric motors avoid all this.
bs0u0155, Apr 19 2016

       //you can't get accurate RPM information//   

       Not true. A simple sensor on the output shaft can give you up-to-the-millisecond information on speed.
MaxwellBuchanan, Apr 19 2016

       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.   

       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.
bs0u0155, Apr 19 2016

       //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.   

       Actually (and somewhat off-topic) has anyone tried playing classical music on an array of motorbikes?
MaxwellBuchanan, Apr 19 2016

       F1 engines are close enough? <link>
bs0u0155, Apr 19 2016

       Baked & WKTE: Military UAVs.
notexactly, Apr 19 2016

       //Baked & WKTE: Military UAVs.//   

       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,
bs0u0155, Apr 19 2016

       Big issue is responsiveness. Multicopters with multiple gas engines have been tried, and generally are a control nightmatre.   

       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.   

       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.   

       Lots of things have been tried. Have a look at what's successful....
Custardguts, Apr 20 2016

       Use variable pitch rotors [link] with shaft or belt drive from a central engine.
TomP, Apr 20 2016


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