Keeping it real

Let's consider some actual present day small aircraft and motorcycles to see how realistic this crazy idea is.

A low weight target and one of the oldest and best planes around (many still flying today!), is the Piper Cub. The slightly larger Cessna 150M is probably a bit closer in final weight to what a flying motorcycle would be. As of this writing, the most produced small aircraft in the world was the Cessna 172, with over 43000 built by 2010. These aircraft have the following general specifications for comparison:

Model	Piper J-3 Cub	Cessna 150M 1977	Cessna 172R
Length	6.83m	7.3m	8.28m
Wingspan	10.7m	10.2m	11m
Height	2m	2.6m	2.72m
Wing area	16.6m2	15m2	16.2m2
Empty weight	345kg	504kg	767kg
Max takeoff weight	550kg	730kg	1111kg
Powerplant	48kW	75kW	120kW
Power/weight	0.139kW/kg	0.149kW/kg	0.156kW/kg
Propeller diameter	?	1.8m	?
Cruise speed	121km/h	198km/h	226km/h
Stall speed	61km/h	78km/h	87km/h
Range	354km	678km	1289km
Fuel consumption	?	23L/h	?
Lift to drag	?	7 minimum	?

So now that we have some planes on the table, let's consider some motorcycles from most common to most exotic/awesome. The Honda CBR1000RR is a common screamer, and not too heavy. While the company started out making aircraft, BMW's motorcycle line has strayed quite far from that original task, weighing in at the heaviest of our presently considered bikes, and less power than the Honda. The next two bikes are substantially lighter, and probably reflect the lowest possible weights since they were developed for racing.  While the Norton only has a 588cc engine, it sports a Wankel engine which generally produces roughly twice the power per cc as a four stroke engine while also being lighter and having less moving parts to fail, all bonuses for flying machines. The last in our lineup is the Britten V-1000, a famous feather-light carbon fiber and kevlar framed racing motorcycle, which just screams of the 80's including (unfortunately) the lowest power engine of all our motorcycles.

Model	Honda CBR1000RR	BMW K1300R	Norton NRV588	Britten V1000 (1989)
Engine type	999cc liquid-cooled inline four-cylinder	1293cc liquid-cooled inline four-cylinder	588cc twin-rotor Wankel type	Water-cooled 999 cc 60 deg V-Twin quad cam 4-stroke
Wheelbase	1410mm	905mm	?	?
Seat height	820mm	820mm	?	?
Fuel capacity	17.8L	19L	?	24L
Curb Weight	199kg, road ready, fully fueled	243kg, road ready, fully fuelled	150kg guess with fluids (reported 130kg dry)	138kg with fluids
Power output	133kW @12000 rpm	129kW @9250rpm	126kW @11500RPM	101kW@9500RPM
Power/weight	0.668kW/kg	0.531kW/kg	0.84kW/kg	0.732kW/kg

An interesting point to make from these comparisons is that almost all of the motorcycles have more power than even the largest plane, except for the Britten which had an inferior engine from the 80's and probably made more smog than the whole lot. While the motorcycles are all of course much lighter than the planes, it seems reasonable at first glance that we should be able to fix a pair of wings, a tail, and a prop onto one for a cost of around 100kg, which would still make them lighter than the lightest plane up the page. Now for aerodynamics, probably the motorcycles are a bit shy of optimum, but just about everyone around has seen a motorcyclist hauling down the highway at 100mph (~160kph), and with some appropriately molded fairings, a motorcycle could probably rival a typical small plane for aerodynamics.

After all this talk about flying things, I think I'm going to buy myself a Great Planes Spirit 2 meter balsa sailplane kit for my birthday, to complement the 1hr flying lesson Deborah got me. It's sort of a pain that the online hobby shop says you need 'covering tools' (ie a heat gun and/or iron) and '2+ rolls covering' (ie lightweight shrinkwrap), and these things aren't obvious purchases on the webpage. Good thing my favorite online hardware store ever, McMaster-Carr (seriously that's not a paid advert, they just kick ass, like you buy something in the morning and it's on your doorstep that afternoon style ass kicking), sells polyolefin heat shrink wrap and heat guns. A 500ft roll is probably way more than I need (for the first plane anyway...), but it costs as much as the small folds that hobby stores sell. Hopefully that's all I need! 

a Great Planes Spirit 2 meter balsa sailplane

Heat shrink wrap and a heat gun as depicted by McMaster-Carr

After this one's finished maybe I'll do a replica in carbon fiber to beef up my composite materials experience. More on that next time.

UPDATE: Polyolefin heat shrink doesn't seem to be well suited to structural wrapping due to its low elasticity and general weakness of heat welds. I'm going to pick up some of the PVC heat shrink which will hopefully work better.

Homework

Now that you know about my dream, I want to spell out some of the background work I've done. I'd rather not get too bogged down in the details so I'll just list off some classes I've taken and titles of books I've found useful:

• For a general understanding of aerodynamics and fluid behavior, the graduate fluid mechanics series at UCSD's Mechanical & Aerospace Engineering department was excellent, and used the textbook 'Fluid Mechanics' by Kundu and Cohen. I also found a second text by the author T. E. Faber titled 'Fluid Mechanics for Physicists' useful during the class.
• For an aircraft engineering background and more flight oriented aerodynamics, I turned to the texts 'Introduction to Flight' and 'Fundamentals of Aerodynamics' by John D. Anderson.
• To think of this project from more of a business oriented side, I took the graduate technology ventures course at UCSD's Physics department taught (in winter 2008) by Michael Lutz of the Tech Coast Angels, where we used the text 'The Art of the Start' by Guy Kawasaki, among others.
• To familiarize myself with the process of applying for patents on how I've solved some of the problems with flying a motorcycle, I read the book 'Patent it yourself' by David Pressman.
• I've also used the book 'Limited Liability Companies for Dummies' to look into different paths through which this project might be commercialized.

All of this happened in my off hours at various libraries and coffee shops in the San Diego area while I completed graduate school. 

In addition to the extra-curricular reading from above, I ran through a couple of exercises as well. I studied airfoil properties in Matlab through the Joukowsky transform (possibly a future post?), and started porting a fortran code for 2D Navier-Stokes cylinder flow (from a computational physics class I took as an undergrad) to Matlab so that I could more realistically model airflow over foils of arbitrary shape (ie NACA airfoils) and arbitrary mach flows. I also used the open source software Blender 3D to render models of what I thought a flying motorcycle might look like, which I used for the logo of this blog.

An NACA 0015 airfoil, which can be closely approximated by a Joukowsky transform

Plots of fluid velocity around a cylinder and test stream density from a Navier-Stokes code

Another rendering of the Blender 3D model I assembled of a flying motorcycle

For future exercises, I would like to move away from the 2D modeling and 3D rendering toward an integrated engineering platform such as Solidworks and Fluent by Ansys or Abaqus by Simulia, but these are expensive suites and this project has zero income so unless someone wants to donate me a license (!) that may take a while. Alternatives such as OpenFOAM, or CAFFA from the book 'Computational Methods for Fluid Dynamics' by Ferziger and Peric, may be more realistic in the near term.

Getting away from the drawing board is something I need to work on in the near future. I'm also pretty excited about some of the great services extended through my new Experimental Aircraft Association membership, including the composite construction class offered during the aircraft builders workshop in Virginia this February. I've been hoping to build a small remote controlled glider or powered plane out of carbon fiber composite as a preliminary to the full blown motorcycle (AND to actually use the Spektrum DX6i radio/receiver/servo combo I bought a while back...). While the books, classes, and computers I've engaged with so far have been some excellent background material, these steps will help me to finally make some of this real.

UPDATE: I should have also added the text 'Motorcycle handling and chassis design, the art and science' by  Tony Foale, which is an excellent reference for the relevant physics and engineering principles.