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Most commercially available FLYING WINGS (RC aircraft or UAVs) are battery powered. Why aren't there more with with gasoline engines?

PS: Sorry I edited. The question is specific about flying wings configuration.

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  • $\begingroup$ I assume you are talking about two stroke RC engines and not 4 stroke ones? $\endgroup$ – Ron Beyer Nov 13 '17 at 13:25
  • $\begingroup$ Why the downvotes? $\endgroup$ – Caterpillaraoz Nov 13 '17 at 14:35
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    $\begingroup$ @RonBeyer there are lots of 4 stroke rc engines, in a wide weight and power range, either gasoline or methanol, starting from 3cc single piston driving 10'x4' inches prop. $\endgroup$ – qq jkztd Nov 13 '17 at 17:44
  • $\begingroup$ @qqjkztd I never meant to imply that there weren't 4 stroke RC engines... I was getting at general glow-type engines for lower-end RC aircraft versus higher end stuff. $\endgroup$ – Ron Beyer Nov 13 '17 at 19:37
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    $\begingroup$ If you're talking small drones, they often carry cameras. If you've ever held a gas-powered RC aircraft while the engine's running, you'll notice quite a bit of vibration. Vibration + Video = Useless Video. Image stabilization won't help much, if at all, with the constant buzz of a small RC engine. $\endgroup$ – FreeMan Nov 15 '17 at 21:44
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Because electric is the best propulsion method available for small commercial UAVs and their mission profiles:

-Significantly quieter

-No smells involved

-No flammable liquid involved

-Way easier to operate: properly tuning an RC gas engine is not for everybody

-Much lower vibration and on frequencies easier to filter out

-More controllability, a BLDC (brushless DC) motor has near-instant response to the throttle and thus enables the actual, simple building scheme of quadcopters

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    $\begingroup$ Big UAV's (like military/intelligence ones) are usually powered by turbines, so jet fuel. $\endgroup$ – SnakeDoc Nov 13 '17 at 18:09
  • $\begingroup$ @SnakeDoc even the ones with a propeller? $\endgroup$ – Baldrickk Nov 14 '17 at 9:55
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    $\begingroup$ @Baldrickk Propelled-powered military UAVs designed for long range missions (i.e. not the ones to "take a look behind the hill") use gas engines, often with ultralight sportplanes origins. $\endgroup$ – Caterpillaraoz Nov 14 '17 at 10:18
  • $\begingroup$ @Baldrickk Yes, called a turbo-prop. The turbine powers the propeller, instead of pistons. Take a look: en.wikipedia.org/wiki/… and here's the turbine: en.wikipedia.org/wiki/Garrett_TPE331 $\endgroup$ – SnakeDoc Nov 14 '17 at 16:40
  • $\begingroup$ To sum it up: large (up to now mainly military) drones have mission profiles very similar to the "manned crafts we are used to" so the propulsion systems are basically the same, with electric still playing a marginal role $\endgroup$ – Caterpillaraoz Nov 15 '17 at 7:26
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Not so long ago, internal combustion engines were the standard for R/C aircraft. They had some big drawbacks though:

  • these engines used nitromethane fuel, which is a solvent that attacks many common materials used in RC aircraft, and leaves everything covered in a smelly film
  • they are loud and run at high temperatures
  • they need to be fiddled with to get them to run well
  • if you have multiple engines, you have the extra problem of having to match their power output

When electric motors + battery packs reached the point where their power/weight ratio was high enough for use in RC aircraft, many hobbyists switched to this (more convenient) option.

For larger aircraft, the square/cube law means higher demands on power/weight ratio, and electric systems still lag behind gas engines in this regard. So large UAVs will have internal combustion engines.

A large variety of R/C engines is still available, from single-cylinder two-stroke glowplug engines with less than 1 cm3 displacement, to 4-strokes, multi-cylinder engines, mini turbines, up to a 1/4 scale Rolls Royce Merlin.

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  • $\begingroup$ Thank you. the question is specific about flying wings. i highlited in the question. $\endgroup$ – Irsan Irsan Nov 17 '17 at 2:38
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Many UAVs do used internal combustion 2 or 4 stroke engines. Examples include the Scan Eagle, Integrator and RQ-21 Blackjack from Insitu/Boeing. The Scan Eagle has demonstrated flight of 29 hours nonstop. Electric motors are limited by their battery weight and size; internal combustion fuel has far more energy per unit weight or volume.

Of course, these have weights of 30 to 140 pounds (15 to 60 kg) and only need one motor each. For quadrotors and such, the complexity of getting the engine rotation to the multiple rotors and controlling same isn't worth the trouble for most realistic designs.

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  • $\begingroup$ Thank you. the question is specific about flying wings. i highlited in the question $\endgroup$ – Irsan Irsan Nov 17 '17 at 2:39
  • $\begingroup$ Much depends on the configuration. Flying wings generally have less yaw stability than conventional layouts with a larger moment arm to the vertical stabilizer and rudder. So if more than one engine is used, they need to be thrust balanced closely. That's more difficult to do well with internal combustion engines while servoing the power to electric motors is relatively trivial to ensure synchronization. Combined with the above mentioned quietness, ease of use, lack of oil spray and mess, exhaust noise and so on, the performance of modern battery powered motors makes them much more appealing. $\endgroup$ – Jim Horn Nov 18 '17 at 1:02
  • $\begingroup$ these are common problem to all fixed wing configurations. not specific to flying wings. $\endgroup$ – Irsan Irsan Nov 22 '17 at 4:06
  • $\begingroup$ The Scan Eagle (Insitu X-200) is a tailless aircraft, i.e. a flying wing with a cylindrical payload/body with all control surfaces on the wing and winglets. Is that close enough? And with a single engine, the synchronization mentioned doesn't arise. There are a number of flying wing UAVs with gasoline engines from other manufacturers as well, though the ScanEagle configuration allows low drag incorporation of a stabilized camera system on the nose, among other advantages. $\endgroup$ – Jim Horn Apr 22 at 19:21

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