{"id":196,"date":"2012-10-16T05:17:35","date_gmt":"2012-10-16T05:17:35","guid":{"rendered":"http:\/\/openvsp.org\/blogs\/?page_id=196"},"modified":"2012-10-16T05:17:35","modified_gmt":"2012-10-16T05:17:35","slug":"aircraft-designed-for-a-10x-reduction-in-operating-cost","status":"publish","type":"post","link":"https:\/\/openvsp.org\/blogs\/mark-moore\/2012\/10\/16\/aircraft-designed-for-a-10x-reduction-in-operating-cost","title":{"rendered":"Aircraft Designed for a 10x Reduction in Operating Cost?"},"content":{"rendered":"

VSP is incredibly effective at putting together advanced aircraft concepts that can ask fundamental \u201cWhat if?\u201d questions<\/strong> \u2013 and help to quickly get answers whether it\u2019s worth continuing a new line of thought.\u00a0 A recent conceptual design study that we conducted at NASA Langley asked the question \u201cIs it possible to reduce the operating costs of an advanced General Aviation (GA) aircraft by a factor of 10?\u201d\u00a0 Asking such a question requires establishing a good baseline model (such as the Cirrus SR-20\/22), and then putting together a good conceptual geometric representation of the proposed solution to compare to that State-of-the-Art (SOA) reference.\u00a0 So I thought you\u2019d like see one of the VSP model concepts we came up with to meet this question, and a few of the key results. So why ask this question?<\/p>\n

The average price of 100LL right now is $6.10 per gallon, and a typical GA aircraft gets 12 mpg; this means fuel cost is about half the total operating cost and this problem is only going to get worse<\/strong>.\u00a0 100LL is going to have to go away, it is the major source of lead pollution.\u00a0 It\u2019s not a reasonable fuel to be using going forward, and specialty replacement fuels that are manufactured just for the GA market are likely to be even more expensive once the EPA and FAA finally get rid of 100LL.\u00a0 The Single Engine Piston market is going to die a slow death unless we can provide new technology solutions that are environmentally friendly and economically sustainable.<\/p>\n

Using electric propulsion is an incredible new degree of freedom for aircraft designers to radically alter how an aircraft performs<\/strong>, especially in terms of efficiency and operating costs.\u00a0 But right now electric propulsion is fundamentally limited by electric energy storage such as batteries, and for this reason the skeptics refuse to consider it a viable solution.\u00a0 At around 200 Watt hours\/kg, they are correct that the specific energy is about 60 times better for AvGas at 34,700 Whrs\/gallon.\u00a0 But you\u2019ve got to look beyond this simple comparison.\u00a0 Even a modern GA aircraft engine like the IO-550, the thermal efficiency is 28% and the specific power is about .5 hp\/lb; versus the electric motors that we have available today at 93% with 3 hp\/lb (including controller, with the motors we\u2019re developing now are 96% efficient at 5 hp\/lb).\u00a0 So that factor of 60 is immediately decreased by a factor of 3.3 based on the efficiency (energy required) alone.\u00a0 If you do a detailed accounting of the SR-22 propulsion system, you can save 498 lbs by replacing the reciprocating engine with an electric motor; which can go straight into added weight for batteries.\u00a0 Next consider the real range required for a typical GA flight, where a 200 to 300 mile range would be sufficient.\u00a0 Last, flying around with an Lift to Drag ratio of 12 just isn\u2019t going to cut it anymore (yes, that\u2019s what the SR-22 gets at its cruise speed of ~200 mph, but a much more respectable L\/D of 18 at 150 mph.\u00a0 Achieving higher L\/D\u2019s is clearly possible as we go to motor glider concepts, and electric propulsion dramatically cuts down on installation losses such as cooling drag (6 to 9% on the SR-22), scrubbing drag (about 2%), and propeller blockage which drops installed propeller efficiency (which can be alleviated by compact electric, lightweight motors that can be positioned just about anywhere on the airframe).\u00a0 Put this together with advanced batteries, like Envia, that have already demonstrated 400 Whr\/kg in the lab, and very reasonable electric aircraft solutions can be achieved.<\/p>\n

Baseline vs Advanced Concept:<\/strong>\u00a0 We did our comparisons to the SR-20\/22 because it is a good representation of the SOA in performance and operating costs, we started our advanced concept development based on a concept that offered a much higher efficiency starting point.\u00a0 I selected the SWIFT (Sweep Wing with Inboard Flap Trimming) concept developed by Steve Morris and Ilan Kroo (Stanford) as my concept starting point.\u00a0 It is an extremely efficient (L\/D > 26) and lightweight (420 lb) motor glider solution that Aeriane fabricates in France.\u00a0 But it\u2019s only a single person, low speed motor glider that required substantial changes to turn into a 4 place.\u00a0 We wanted to make an electric SWIFT concept into as efficient of a GA aircraft as possible, and maintain that high L\/D ratio (but with a substantially larger fuselage) at a much higher speed (150 mph), so we incorporated several advanced technologies we have been developing \u2013 such as a Boundary Layer Ingestion Inlet for fuselage drag reduction, and wingtip vortex propeller interaction for induced drag reduction.<\/p>\n

Attachments:\u00a0<\/strong> I\u2019ve attached a few slides that show the approach, and assumptions that went into this simplified analysis.\u00a0 I\u2019ve also placed the resulting concept geometry into the VSP Hanger.\u00a0 VSP permitted us to do a good internal layout to insure a fair cabin volume comparison \u2013 this was important since the bulky reciprocating engine was removed and permitted a fuselage wetted area reduction.\u00a0 We chose back to back seating because flying wing concepts have a very limited pitch trim capability, so we needed to keep the CG excursion as small as possible.\u00a0 But as you\u2019ll see if you look at the slides, we needed even more pitch trim capability so we adapted the SWIFT to a C-wing configuration (which also helped get us to a higher CLmax, which also is fundamentally limited with flying wings).\u00a0 Only tail volume coefficients were used for tail sizing, and no control analysis was performed \u2013 and with flying wings, this is an important simplification that needs to be further considered.\u00a0 But the results indicated that as long as ranges of about 200 miles are acceptable (including a 30 min reserve), that weights comparable to other 4 place aircraft can be achieved.\u00a0 Our analysis including directly exporting VSP wetted areas (from the tsv drag buildup file format) into an Excel spreadsheet that lets us quickly and easily understand the parasite drag.\u00a0 Coupled to a vortex lattice analysis (such as Vorlax or AVL), we were able to have a good understanding of the induced drag as well.\u00a0 We then used empirical methods to account for the change in fuselage drag from the BLI propulsor, and the induced drag from the wingtip wake vortex propeller.\u00a0 Vortex lattice codes do a great job of capturing the non-planar induced drag benefit of the C-wing layout, so there wasn\u2019t much uncertainty from this unconventional configuration.\u00a0 We didn\u2019t do a structural analysis, but those are the next steps we\u2019ll be taking as we go into further depth towards understanding this concept, and others.<\/p>\n

So what was the resulting conclusion?<\/strong>\u00a0 You can look at the attached slides to see more details (or read the attached AIAA paper that explains why we\u2019re looking at such concepts).\u00a0 But relating to the original question, the total energy required for the SR-20 (the slower, lower power version of the SR-22) is about 382 kW hrs.\u00a0 The total energy required for the electric Swift is 65 kW hrs.\u00a0 Using the average electric utility rate of $.115 \/kW hr and AvGas cost of $6.10 \/gal, the resulting difference in energy cost to fly 200 miles is $67.40 for the SR-20, and $6.14 for the eSWIFT \u2013 an 11 times difference in energy cost.\u00a0 Certainly a more complete life cycle analysis is required to amortize the batteries over their typical 2000 cycle life and take into account the difference in maintenance costs of essentially care-free electric motors versus reciprocating engines.\u00a0 But even at current electric motor and battery costs, the propulsion system is less expensive than using existing aircraft engine solutions.\u00a0 Even ridiculously expensive batteries appear to be a good deal compared to a Teledyne Continental IO-550N costing $60,000 for 310 hp.\u00a0 So it does appear possible to achieve an order of magnitude reduction in operating costs, and this isn\u2019t even taking into account electricity rates as low as $.06 \/kWhr for commercial users at off peak hours if batteries were to be charged at night.\u00a0 Personally, I believe there are exciting opportunities for dramatic improvements with electric aircraft over the next 10 years \u2013 and it\u2019s great to have tools like VSP to help understand these differences.\u00a0 Now if someone would just give me a vortex lattice method that\u2019s coupled to a propeller lifting line or actuator disk method I\u2019d be in even better shape to analyze such concepts as the eSWIFT.<\/p>\n","protected":false},"excerpt":{"rendered":"

VSP is incredibly effective at putting together advanced aircraft concepts that can ask fundamental \u201cWhat if?\u201d questions \u2013 and help to quickly get answers whether it\u2019s worth continuing a new line of thought.\u00a0 A recent conceptual design study that we … Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":19,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-196","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/openvsp.org\/blogs\/wp-json\/wp\/v2\/posts\/196","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/openvsp.org\/blogs\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/openvsp.org\/blogs\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/openvsp.org\/blogs\/wp-json\/wp\/v2\/users\/19"}],"replies":[{"embeddable":true,"href":"https:\/\/openvsp.org\/blogs\/wp-json\/wp\/v2\/comments?post=196"}],"version-history":[{"count":10,"href":"https:\/\/openvsp.org\/blogs\/wp-json\/wp\/v2\/posts\/196\/revisions"}],"predecessor-version":[{"id":215,"href":"https:\/\/openvsp.org\/blogs\/wp-json\/wp\/v2\/posts\/196\/revisions\/215"}],"wp:attachment":[{"href":"https:\/\/openvsp.org\/blogs\/wp-json\/wp\/v2\/media?parent=196"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/openvsp.org\/blogs\/wp-json\/wp\/v2\/categories?post=196"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/openvsp.org\/blogs\/wp-json\/wp\/v2\/tags?post=196"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}