{"id":4106,"date":"2011-08-13T21:49:09","date_gmt":"2011-08-14T04:49:09","guid":{"rendered":"http:\/\/cafe.foundation\/blog\/?p=4106"},"modified":"2011-08-13T21:49:09","modified_gmt":"2011-08-14T04:49:09","slug":"a-comparison-too-far","status":"publish","type":"post","link":"http:\/\/cafe.foundation\/blog\/a-comparison-too-far\/","title":{"rendered":"A Comparison Too Far"},"content":{"rendered":"

A recent entry comparing the German Carplane\u00ae<\/a> and Burt Rutan\u2019s BiPod <\/a>has prompted a response from John Brown, who found the posting of concern for the misapprehensions it might cause in readers.<\/p>\n

He notes, for instance, \u201cYour current article portrays us as a large Govt. Co. (we got a small subsidy) going up against a ‘charity’ organization (Northrop-Grumman’s subsidiary, Scaled Composites) in whose name the BiPod is registered at the FAA – as a glider<\/span>;<\/em><\/p>\n

\u201cIt compares us to 1930s modular concepts where actually the BiPod’s wings are screw-on\/screw-off \u2018modular\u2019 and use that older concept;<\/p>\n

\"\"<\/a>

Carplane's Transformer-like, reported 15-second transition<\/p><\/div>\n

\u201cIt attributes a commuter \u2018pitch\u2019 to us where, in fact, we’re not aiming for that market at all. [Thanks for your apology. However, the world is still quoting your article.]<\/p>\n

\u201cIt implies we somehow responded to Burt Rutan (we disclosed 2008 – via patent).<\/p>\n

We’ve displayed at the world’s largest Trade Fair & Europe’s largest GA show – not at a desert strip. We’ve published stats, specs & numbers (i.e. “hard details”) whenever asked.<\/p>\n

\u201cOur LSA speed limit and honest numbers are portrayed as inferior performance (rather than questioning why Scaled Composites would claim an LSA could go 200mph).\u201d\u00a0 (Editor\u2019s note: the first blog entry on BiPod did question where that speed would come from with the limited power sources described. That would imply a flat plate drag area at least as good as Mike Arnold\u2019s AR-5<\/a>, a lighter single-seater which managed 213 mph on 65 horsepower.)<\/em><\/p>\n

\u201cIt calls aspects of our powerplant concept into question – misunderstandings we subsequently cleared up. [But again, the world is still quoting your original article]\u201d<\/p>\n

Seeking enlightenment rather than controversy, we present highlights from Brown\u2019s visual comparison of BiPod to Carplane and his detailed critique.\u00a0 If Terrafugia wishes to provide a similar comparison, we would be delighted to present it to our readers.\u00a0 If Burt Rutan wants to provide his insights, we would be equally delighted.<\/p>\n

Carplane\u2019s web site provides the full .pdf of the comparison, and gives an introduction to some design considerations and constraints that would seem to apply to almost any roadable airplane or flyable car.<\/p>\n

Brown compares, for instance, the highly automated extension and retraction of Carplane with the manual assembly and disassembly required for the transitions between ground\/air\/ground modes on BiPod.\u00a0 This takes about 15 seconds of automated transition for the Carplane, and about 10 minutes of labor that should be familiar to any sailplane pilot on the BiPod.<\/p>\n

A driver\/pilot can stay in the same seat during the transition in the Carplane: The BiPod is driven from one cockpit and driven from another.\u00a0 Pilot and passenger will have to swap places following a mode change.\u00a0 Convenience is certainly on Carplane\u2019s side here, although the driver\/pilot willing to pull wings and tail feathers and stow them will probably be unfazed by stepping over the side of a sailplane-like cockpit for entry.<\/p>\n

\"\"<\/a>

One of several images provided by Carplane - unverified as to scale<\/p><\/div>\n

Brown claims superior airflow over the Carplane in driving configuration, surmising problems with the BiPod\u2019s forward-facing wing roots in their stowed position and a possible lack of downforce\u00a0 compared to Carplane.<\/p>\n

He notes that longitudinal weight distribution, lack of flaps on BiPod and placement of wheels on the two vehicles would lead to better takeoff and landing characteristics for Carplane, although BiPod has \u201cflown\u201d with \u201cwheel-powered runway hops (\u2018wheelies\u2019)\u201d with one person on board.<\/p>\n

Brown also looks at elevator size and area for necessary rotational force to allow takeoff, and thinks propeller placement on BiPod\u2019s stabilizer might restrict that action.<\/p>\n

Where Carplane is designed to fit in a single car garage, BiPod is unable to be fully sheltered.\u00a0 Other configuration issues give the Carplane\u00a0an apparent\u00a0edge in crosswind landings.<\/p>\n

Brown clearly has an advantage in the consumer market with the cockpit and motive power \u201ctransparency\u201d of operation.\u00a0 Rutan\u2019s pilots and passengers might feel a bit cramped, according to Brown, with battery packs in front of them and motorcycle engines behind them in both cockpits.\u00a0 If nothing else, Carplane has more elbow room.\u00a0 Brown also notes the apparent current lack of cooling for BiPod\u2019s power sources, while Carplane has a liquid-cooled ground power system and liquid\/air cooling for its high-mounted aerial engine.\u00a0 However, we can only assume that Rutan and his engineers would address this issue in further development.<\/p>\n

Although both roadable aircraft (or flyable autos) are similar in their catamaran-like layouts, their design philosophies and structural approaches are extremely divergent.\u00a0 The full critique, from Carplane\u2019s point of view, can be found on the company\u2019s web site.<\/p>\n

A complex, sophisticated craft such as Carplane would require a lengthy development process, and it has been in creation since late 2007, with a patent application filed on July 28, 2008. \u00a0BiPod was
\nreputedly a four-month effort as a proof-of-concept vehicle for some of Rutan\u2019s theories and ideas.\u00a0 Few such POCs retain all their bugs or features by the time they reach a consumer, so we would expect changes over an additional development cycle.<\/p>\n

Obviously, Carplane is intended for a high-end market, not unlike Terrafugia\u2019s Transition<\/a>.\u00a0 Enough AirVenture attendees crowded Rutan\u2019s presentation on BiPod to show an intense interest in the possibility of a humbler, labor-intensive vehicle, though, that one can certainly envision homebuilt aviation enthusiasts who are already dreaming of how they can improve on Rutan\u2019s original.<\/p>\n

Thanks to John Brown for retaining a sense of humor and the willingness to advocate for his firm\u2019s machine.\u00a0We invite other\u00a0qualified parties to share their well-documented and illustrated viewpoints.\u00a0 All viewpoints are welcome.<\/p>\n