{"id":46420,"date":"2018-06-19T02:52:37","date_gmt":"2018-06-19T02:52:37","guid":{"rendered":"https:\/\/one.sightlinemg.com\/defensenews\/uncategorized\/2018\/06\/19\/quieter-military-drones-that-fly-farther-the-pentagon-thinks-this-engine-could-be-the-answer\/"},"modified":"2026-08-08T10:02:16","modified_gmt":"2026-08-08T10:02:16","slug":"quieter-military-drones-that-fly-farther-the-pentagon-thinks-this-engine-could-be-the-answer","status":"publish","type":"post","link":"https:\/\/one.sightlinemg.com\/defensenews\/air\/2018\/06\/19\/quieter-military-drones-that-fly-farther-the-pentagon-thinks-this-engine-could-be-the-answer\/","title":{"rendered":"Quieter military drones that fly farther? The Pentagon thinks this engine could be the answer"},"content":{"rendered":"\n<p class=\"wp-block-paragraph\">Most people haven\u2019t heard of the engine created by Felix Wankel in the 1960s, but its derivatives may end up powering the military\u2019s future <a href=\"https:\/\/www.airforcetimes.com\/air\/2017\/12\/30\/new-in-2018-air-force-will-officially-retire-mq-1-predator-drone\/\" title=\"\" target=\"_blank\">unmanned aerial vehicles<\/a>.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Despite a compact design that allows it to run at higher speeds and produce more power than conventional internal combustion engines, the Wankel engine never really caught on. <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">It\u2019s bad on fuel efficiency, and it burns too much oil. <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">But now, engine technology company LiquidPiston Inc. may have changed that, and they want to throw their new design into military drones.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Company CEO Alec Shkolnik has a Wankel engine design that\u2019s essentially been inverted, and he says it can increase<a href=\"https:\/\/www.airforcetimes.com\/news\/your-air-force\/2017\/06\/01\/air-force-malfunctions-caused-2016-predator-crash-in-iraq\/\"> flight endurance <\/a>by more than 50 percent \u2014 the maximum length of time that an aircraft can spend in cruising flight.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u201cWe developed what we call the X4 engine, which is like the old Wankel rotary engine, but flipped inside out,\u201d Shkolnik said. \u201cIt solved a lot of the challenges the Wankel used to have while giving it this new thermodynamic cycle upgrade.\u201d<br><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">In addition to the advanced flight time, LiquidPiston\u2019s propulsion can reportedly reduce a drone\u2019s engine heat signature and minimize vibration impact on sensitive<a href=\"https:\/\/www.airforcetimes.com\/flashpoints\/2017\/10\/22\/air-force-general-the-battle-against-isis-is-about-to-converge-in-the-euphrates-valley\/\" title=\"\" target=\"_blank\" data-original-title=\"\" aria-describedby=\"popover231879\" style=\"\"> intelligence, surveillance, and reconnaissance<\/a> equipment.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The <a href=\"https:\/\/www.militarytimes.com\/news\/your-military\/2018\/01\/22\/military-project-aims-to-combat-disease-outbreaks-protect-warfighters\/\" title=\"\" target=\"_blank\">Defense Advanced Research Projects Agency<\/a>, or DARPA, is certainly interested. The government agency just awarded LiquidPiston another $2.5 million to develop and refine its 30 kilowatt, 40 horsepower X4 rotary diesel engine prototype.<br><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u201cDARPA believes that there is potential for a family of high-efficiency, compact, lightweight heavy-fuel engines,\u201d Mark Gustafson, a DARPA program manager, said.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u201cIf fully successful, this project will provide proof of concept that our challenging objectives are achievable and pave the way for potential new capabilities in ground, air, and maritime applications,\u201d he added.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Combined with previous funds from 2016, DARPA has pushed $6 million into the new technology. <br><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Here\u2019s how it works: The regular Wankel engine replaces pistons with triangular rotors that follow an elliptical path around an oval-shaped chamber. Combustion then occurs in the space between the triangular and circular shapes. <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">LiquidPiston inverted that design. <\/p>\n\n\n\n<blockquote class=\"imgur-embed-pub\" lang=\"en\" data-id=\"a\/ztDUKkp\"><a href=\"\/\/imgur.com\/ztDUKkp\">LiquidPiston engine vs. conventional Wankel engine<\/a><\/blockquote><script async src=\"\/\/s.imgur.com\/min\/embed.js\" charset=\"utf-8\"><\/script>\n\n\n\n<p class=\"wp-block-paragraph\">The X4 engine uses an oval rotor in a triangular chamber. Combustion occurs at fixed points within the chamber, which makes it easier to lubricate without burning oil. <i><\/i><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">By doing it this way, the company says it has engineered the first new combustion engine and engine cycle in more than 80 years. LiquidPiston\u2019s design can be five to 10 times smaller than a normal piston engine \u2014 as small as an iPhone \u2014 lighter than a diesel engine, and two times more efficient than a gasoline engine. <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">On top of that, an electric vehicle using a LiquidPiston engine combined with a small battery pack could have a lower carbon dioxide footprint than plug-in electric vehicles.<br><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">DARPA gave the company the most recent investment after they proved the feasibility of their design.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u201cThe targets are extremely aggressive,\u201d Shkolnik said. \u201cThe engine should weigh 30 to 40 pounds and double the efficiency compared to other engines, for example the Army\u2019s Shadow UAV.\u201d<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1000\" height=\"706\" src=\"\/wp-content\/uploads\/2026\/08\/LiquidPiston-X2Engine-Comparison.jpg.jpg\" alt=\"\" class=\"wp-image-95463\" srcset=\"https:\/\/one.sightlinemg.com\/wp-content\/uploads\/2026\/08\/LiquidPiston-X2Engine-Comparison.jpg.jpg 1000w, https:\/\/one.sightlinemg.com\/wp-content\/uploads\/2026\/08\/LiquidPiston-X2Engine-Comparison.jpg.jpg?resize=300,212 300w, https:\/\/one.sightlinemg.com\/wp-content\/uploads\/2026\/08\/LiquidPiston-X2Engine-Comparison.jpg.jpg?resize=768,542 768w\" sizes=\"auto, (max-width: 1000px) 100vw, 1000px\" \/><figcaption class=\"wp-element-caption\">A standard 35 horsepower diesel engine, left, next to LiquidPiston\u2019s 40 horsepower diesel engine. (LiquidPiston)<\/figcaption><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">The <a href=\"https:\/\/www.defensenews.com\/digital-show-dailies\/aaaa\/2018\/04\/25\/these-two-drones-are-leaders-in-accident-rates-how-is-the-us-army-responding\/\" title=\"\" class=\"selected-link\" target=\"_blank\">Army\u2019s RQ-7 Shadow<\/a> \u2014 a drone with a 20-foot wingspan and 18,000-foot ceiling \u2014 currently uses a Wankel engine design and has a flight time of four to nine hours, depending on payload and variation.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Another important factor is that the X4 technology is scalable.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u201cWe have a 5 horsepower engine as well, which could fit in something like an Aerosonde [a 30-pound UAV],\u201d Shkolnik said. \u201cThis 40 horsepower one is more suited for the Shadow, or drones of similar size.\u201d<br><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u201cThe Shadow, though, is something we talked about with DARPA because it\u2019s a well-known platform, its got more than a million hours of operating time, and it\u2019s really not a good engine on that bird,\u201d Shkolnik added. \u201cIt\u2019s one of the big limiting factors for that platform.\u201d<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The Shadow\u2019s engine has had issues scattering the enemy due to the engine\u2019s excessive noise, which is like a \u201cflying lawn-mower,\u201d Shkolnik said.<\/p>\n\n\n\t<aside class=\"smg-interstitial-link wp-block-smg-interstitial-link\">\n\t\t<a href=\"https:\/\/one.sightlinemg.com\/airforcetimes\/news\/2018\/06\/01\/air-force-reapers-are-now-flying-isr-missions-from-poland\/\" class=\"smg-interstitial-link__inner\">\n\t\t\t\t\t\t\t<div class=\"smg-interstitial-link__media\">\n\t\t\t\t\t<img loading=\"lazy\" decoding=\"async\" width=\"300\" height=\"157\" src=\"https:\/\/one.sightlinemg.com\/wp-content\/uploads\/2026\/08\/3983196.jpg.jpg?w=300\" class=\"smg-interstitial-link__image wp-post-image\" alt=\"\" \/>\t\t\t\t<\/div>\n\t\t\t\t\t\t<div class=\"smg-interstitial-link__content\">\n\t\t\t\t<span class=\"smg-interstitial-link__kicker\">Related<\/span>\n\t\t\t\t<h3 class=\"smg-interstitial-link__title\">Air Force Reapers are now flying ISR missions from Poland<\/h3>\n\t\t\t\t\t\t\t\t\t<p class=\"smg-interstitial-link__excerpt\">The U.S. Air Force\u2019s MQ-9 Reaper drone quietly started flights from Miroslawiec Air Base, Poland, in May, but the service isn\u2019t exactly saying why.<\/p>\n\t\t\t\t\t\t\t<\/div>\n\t\t<\/a>\n\t<\/aside>\n\t\n\n\n<p class=\"wp-block-paragraph\">\u201cOur engine has the potential to be very quiet,\u201d he added. \u201cThere\u2019s no piston slap, for instance, so the only real noise is from the gears and combustion. So, it\u2019s relatively quiet.\u201d<br><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Because the X4 will be a pure diesel engine and not spark ignited, LiquidPiston can also design variants that have no electronics on board that could interfere with certain types of surveillance equipment. The rotary engine design also decreases engine vibration that could throw off measurements. <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">On top of that, because the engine is thermally more efficient, less heat goes into the exhaust, so it should have a lower heat signature to bypass an enemy\u2019s thermal imaging devices. <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u201cThe other thing I want to point out is the reliability and durability, because that\u2019s a big limiting factor for today\u2019s UAV engines,\u201d Shkolnik said.<br><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The Army\u2019s Shadow drones have difficulties starting and are often lost in mishaps, he said. Their current engine has to be serviced frequently. <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u201cBecause our engine is an inside-out version of the Wankel rotary, our seals aren\u2019t in the rotor, they\u2019re actually in the housing and they\u2019re much easier to lubricate,\u201d Shkolnik added.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The engine is entering its second phase of testing this year, which should wrap up around October. The objectives are to demonstrate the 30 kilowatts of power and to reach 45 percent fuel efficiency. That development will be executed at LiquidPiston\u2019s test facility in Connecticut.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">After the second phase, LiquidPiston plans to team up with a transition partner company that makes UAVs to bring the design to life. <\/p>\n","protected":false},"excerpt":{"rendered":"<p>Most people haven\u2019t heard of the engine created by Felix Wankel in 1960, but its derivatives may end up powering the military\u2019s future unmanned aerial vehicles, or UAVs.<\/p>\n","protected":false},"author":7,"featured_media":95459,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"_yoast_wpseo_meta-robots-noindex":"","_yoast_wpseo_meta-robots-nofollow":"","_yoast_wpseo_canonical":"","_acf":"","_yoast_wpseo_primary_category":7,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","_smg_distribution_targets":[]},"categories":[7,160,36,27,167],"tags":[],"coauthors":[3374],"class_list":["post-46420","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-air","category-daily-news-roundup","category-newsletters","category-unmanned","category-unmanned-systems"],"acf":{"subheadline":"","legacy_arc_id":"YG67EXTEAZH27KBOYEANG5J4ZY","arc_canonical_url":"\/news\/2018\/06\/19\/quieter-military-drones-that-fly-farther-the-pentagon-thinks-this-engine-could-be-the-answer\/","remove_feature_photo":false,"is_sponsored":false,"subtype":"","redirect_url":"","disable_inline_ads":false,"native_logo_pretext":"Presented By:"},"yoast_head":"<!-- This site is optimized with the Yoast SEO Premium plugin v26.0 (Yoast SEO v28.1) - https:\/\/yoast.com\/product\/yoast-seo-premium-wordpress\/ -->\n<title>Quieter military drones that fly farther? 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The Pentagon thinks this engine could be the answer\" \/>\n<meta property=\"og:description\" content=\"Most people haven\u2019t heard of the engine created by Felix Wankel in 1960, but its derivatives may end up powering the military\u2019s future unmanned aerial vehicles, or UAVs.\" \/>\n<meta property=\"og:url\" content=\"https:\/\/one.sightlinemg.com\/defensenews\/air\/2018\/06\/19\/quieter-military-drones-that-fly-farther-the-pentagon-thinks-this-engine-could-be-the-answer\/\" \/>\n<meta property=\"og:site_name\" content=\"Defense News\" \/>\n<meta property=\"article:published_time\" content=\"2018-06-19T02:52:37+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2026-08-08T10:02:16+00:00\" \/>\n<meta name=\"author\" content=\"Kyle Rempfer\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"Kyle Rempfer\" \/>\n\t<meta name=\"twitter:label2\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"5 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\n\t    \"@context\": \"https:\\\/\\\/schema.org\",\n\t    \"@graph\": [\n\t        {\n\t            \"@type\": \"Article\",\n\t            \"@id\": \"https:\\\/\\\/one.sightlinemg.com\\\/defensenews\\\/air\\\/2018\\\/06\\\/19\\\/quieter-military-drones-that-fly-farther-the-pentagon-thinks-this-engine-could-be-the-answer\\\/#article\",\n\t            \"isPartOf\": {\n\t                \"@id\": \"https:\\\/\\\/one.sightlinemg.com\\\/defensenews\\\/air\\\/2018\\\/06\\\/19\\\/quieter-military-drones-that-fly-farther-the-pentagon-thinks-this-engine-could-be-the-answer\\\/\"\n\t            },\n\t            \"author\": {\n\t                \"name\": \"migration\",\n\t                \"@id\": \"https:\\\/\\\/one.sightlinemg.com\\\/defensenews\\\/#\\\/schema\\\/person\\\/cc76c831bb37a926738c8391fca7a3b1\"\n\t            },\n\t            \"headline\": \"Quieter military drones that fly farther? 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