A Comparison Too Far

Dean Sigler Electric Powerplants, Feedback, Sustainable Aviation 7 Comments

A recent entry comparing the German Carplane® and Burt Rutan’s BiPod has prompted a response from John Brown, who found the posting of concern for the misapprehensions it might cause in readers.

He notes, for instance, “Your 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;

“It compares us to 1930s modular concepts where actually the BiPod’s wings are screw-on/screw-off ‘modular’ and use that older concept;

Carplane's Transformer-like, reported 15-second transition

“It attributes a commuter ‘pitch’ 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.]

“It implies we somehow responded to Burt Rutan (we disclosed 2008 – via patent).

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.

“Our LSA speed limit and honest numbers are portrayed as inferior performance (rather than questioning why Scaled Composites would claim an LSA could go 200mph).”  (Editor’s 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’s AR-5, a lighter single-seater which managed 213 mph on 65 horsepower.)

“It calls aspects of our powerplant concept into question – misunderstandings we subsequently cleared up. [But again, the world is still quoting your original article]”

Seeking enlightenment rather than controversy, we present highlights from Brown’s visual comparison of BiPod to Carplane and his detailed critique.  If Terrafugia wishes to provide a similar comparison, we would be delighted to present it to our readers.  If Burt Rutan wants to provide his insights, we would be equally delighted.

Carplane’s 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.

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.  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.

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.  Pilot and passenger will have to swap places following a mode change.  Convenience is certainly on Carplane’s 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.

One of several images provided by Carplane - unverified as to scale

Brown claims superior airflow over the Carplane in driving configuration, surmising problems with the BiPod’s forward-facing wing roots in their stowed position and a possible lack of downforce  compared to Carplane.

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 “flown” with “wheel-powered runway hops (‘wheelies’)” with one person on board.

Brown also looks at elevator size and area for necessary rotational force to allow takeoff, and thinks propeller placement on BiPod’s stabilizer might restrict that action.

Where Carplane is designed to fit in a single car garage, BiPod is unable to be fully sheltered.  Other configuration issues give the Carplane an apparent edge in crosswind landings.

Brown clearly has an advantage in the consumer market with the cockpit and motive power “transparency” of operation.  Rutan’s 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.  If nothing else, Carplane has more elbow room.  Brown also notes the apparent current lack of cooling for BiPod’s power sources, while Carplane has a liquid-cooled ground power system and liquid/air cooling for its high-mounted aerial engine.  However, we can only assume that Rutan and his engineers would address this issue in further development.

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

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.  BiPod was
reputedly a four-month effort as a proof-of-concept vehicle for some of Rutan’s theories and ideas.  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.

Obviously, Carplane is intended for a high-end market, not unlike Terrafugia’s Transition.  Enough AirVenture attendees crowded Rutan’s 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’s original.

Thanks to John Brown for retaining a sense of humor and the willingness to advocate for his firm’s machine. We invite other qualified parties to share their well-documented and illustrated viewpoints.  All viewpoints are welcome.

Comments 7

  1. Really, CAFE foundation? Why keep putting up articles that perpetuate this soap-opera? These are a couple of vehicles that aren’t in production, and likely never will be (if history is any guide)? The bottom-line is that BiPod is real working hardware (and should get a lot of credit for that) but its a proof-of-concept item only. Carplane exists only as drawings and pretty animations (something anyone with a computer can make these days). Since neither vehicle has been fully produced and tested, NEITHER is in a position to be making claims about what they can or can’t do; or what the “competition” can or can’t do. Please just let this die – we need solutions in efficiency, not bickering or needless drama.


    (Editor’s Note: I’m not interested in the emotions brought about in this set of non-issues, but rather putting out as much factual material as possible, without taking sides or taking a partisan approach. Obviously neither design has flown and Mr. Rutan has an actual object in hand – much to his credit. But this shouldn’t be a competition – and the two designs in question would never find the same market. The two roadable airplanes are two different approaches to a long-sought goal. Steve Saint’s Maverick is another. Terrafugia another. All have different potential clients and different performance ranges. We can learn from all of them.

    Rather than make this into a “soap opera,” let’s all try to be open to the tremendous creativity that is being exhibited here. I had the privilege of interviewing Molt Taylor years ago when he was experimenting with airplanes made from vinylester-reinforced liner board. He made two that actually flew, but were terribly controversial. He made a comment that may hinder or even doom all potential roadable airplanes, having built and sold at least one AeroCar. He believed that licensing would be the biggest hurdle to overcome. His AeroCar required a pilot’s license and medical, driver’s license, automobile license, aircraft registration and airworthiness certificate, trailer license, and back then a radiotelephone license. He counted nine licenses or certificates in all, perhaps too much of a bureaucratic nuisance for many.

    I say we cheer all these brilliant souls on, but raise questions in the hope of gaining understanding.)

  2. I’ve been watching the Carplane gain momentum since 2008. I know and have flown with John Brown, and I’ve been a fan of Burt Rutan’s since Voyager made it around the globe on a single tank. I applaud CAFE and Dean Sigler for the approach they have taken in handling this fascinating subject.

    I’ve been long dreaming of owning my own aircraft, and the idea of an aircraft that I can use to drive home from the airport and keep in my garage is exciting to say the least. Hangar fees are expensive in Australia! Not to mention the idea that I can fly somewhere for the weekend and drive home if adverse weather conditions might make flying a riskier option.

    Noel, you say the two vehicles aren’t in production, which of course they aren’t. Are you suggesting that the aviation press should avoid any discussion of the next generation of aircraft until they are on sale at the local aircraft showroom?? It strikes me this sort of innovation is precisely where the aviation press should be focusing its attention.

    Carplane has ticks in all the regulatory boxes. As John Brown has pointed out, Carplane complies with the size/shape/lift/performance requirements for registration as both car and plane. Bi-Pod is a concept vehicle at a MUCH earlier stage of development. I’m sure that Burt Rutan with his proven innovative talents is more than capable of solving the technical issues standing between Bi-Pod and a vehicle that would be registrable on road and in the air, but by the same token this isn’t just mud-slinging we’re seeing here. Have a look at http://www.carplane.de and inform yourself before you dismiss the discussion as premature.

  3. As an aviation enthusiast, albeit one that has been “out of the loop” for quite some time, about 30 years really, I was very excited to see that Mr. Rutan decided to focus (his alleged) final design in this particular area. The buzz generated by all the parties involved, drama included ; ), is making it a touch easier to point out to my renewable energy engineering obsessed teen-age son, that aviation technology deserves his attention. My dad made a point of informing me of Mr. Rutan’s endeavors in the 1970’s, along with John Monnett for that matter, and I can’t tell you how pleased and excited I am to see that after not being in-touch with goings on for such a long time, both Mr. Rutan and Mr. Monnett to varying degrees, have devoted significant resources to furthering the viability of the technology. Cafe Foundation is pretty cool too.



  4. This “controversy” is quite exciting. Getting people talking and expressive their views is the best to rapidly advance the development of PAV’s and to bypass less workeable technologies without spending too much money and time, and hopefully finding the real workable soultions. For my part I saw no controversy in the articles as I took each one approach on its own merits and the differences are perfectly clear.

    The main critique that I have for each (all) of the present roadables is that the risks of taking a flying machine on the road negates the advantages. Exposing a highly refined flying device to the risks of damage at ground level, how much damage can a vehicle sustain before it is unwise to leave the ground in, is too high a risk to safely take. In the design that I am working on I considered the benefits of roadability, and the Aerobile (the nearest like vehicle to mine) was a very successful roadable, of too little value to be worth the compromises. The only compromise that I will make in that regard is to power the main wheels with 4 kilowatt max motors so that the vehicle can move short distances with out using the propeller, and this for ground safety purposes.

    My main effort has been applied to reducing the takeoff and landing distances to very little, on the one hand, expanding the number of landing locations, on the other hand, and reducing drag. This is particularly significant for Australia where the number of airstrips is negligible. This is why I have chosen an amphibious solution to work on, and a three seating arrangement for user appeal. For me, the AirMax SeaMax is so far the front runner design solution, although the IconA5 is pretty cool.

    The other most exciting theme underway is in the development of electric power for aircraft. And what we really want to see is the convergence of all of the technologies into truly useable solutions that will fulfill the PAV dream. It is all getting so close. So this is where I feel that the roadable concept will struggle, electric powered flight (for the time being) requires truly minimum weight in order to achieve useful range, and the extra requirements for strength to cope with road forces work against that objective. But having said that, there is one tuly remarkable road vehicle concept that offers hope for good roadworthy but light weight solutions and that is the VW L1 concept vehicle, which should not be too difficult to add a wing to.

    Keep up the discussion people, this is all very exciting. And NASA how is that advanced aircraft control system of yours coming along? Is it going to be overtaken by autonomous flight solutions?

  5. Bill, funny you mention the VW-1-Liter car. The same engineer who worked on that project is also working on ours. (Note: we have no formal association with VW.)

  6. Well then, John, send him over to my project when he has finshed on yours.

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