Roadable aicraft discusssion on the News Letter. June 30 2005
Roadable airplanes ARE flyable. There are no technological break throughs required. The vast majority of the parts are off the shelf.
The main challenge is minimizing the weight penalty of the required roadable components. Most roadable aircraft designs use twin booms for the tail but the Rutan Canard configuration is a better fit with roadable requirements IMHO. To my knowledge nobody has flown the canard configuration yet.
I had a brain storm on a roadable aircraft based on Herb Adam's canard configuration. Here are some shots of his configuration.
I realized one of the unique features of the rotary is its very simple e-shaft. If one makes it longer and larger in diameter on the front end one can get power out of both ends. One end is mated to a stock VW transmission and the other end uses one of Ken Welters 3:1 cog belt reduction drives.
You take off in first gear and get much better acceleration to flying speed. This is due to the traction you get out of tires as opposed to a highly slipping prop. As soon as you run out of RPM in first gear you push in the clutch and shift into neutral. The prop then takes over. The only drawback here is the weight of the stock VW gear box and drive shafts.
Its a motor cycle on the ground as that circumvents a load of EPA and DOT rules.
The large wheels also give you a bit more ground clearance for suspension travel when landing. Suspension is on the down stops when lowered for landing. Also the rotary gets better gas millage just like any other ICE if you keep the road cruise RPM as low as possible using the stock VW gear box and final drive.
With the gear retracted there will be near zero aerodynamic penalties.
One of the design parameters one needs to pay a lot of attention to on a roadable is the weight of the wheels and tires. I suggest dragster forged aluminum front wheels and tires at 15 by 3 1/2 for the rear. You need diameter as the cruise RPM on the ground using the VW tx requires a rather large diameter tire. The front tire can be a light weight motorcycle wheel and tire. Motor cycle disc brakes will also keep the weight down.
This is my layout for the front suspension. It is based on a design I did for Craig Breedlove's 3 wheel rocket powered land speed record car 35 years ago. Went 400 mph in the quarter mile using a surplus TRW lunar landing module rocket motor. Craig was asked how he could possible steer such a fast car and he said he did not really steer. He lined it up with the race track and then held the steering wheel still while the rocket motor fired. The drag runs were quite spectacular.
When he fired the rocket the car disappeared with a loud bang in a huge cloud of smoke. The crowd gasped and thought he blew up in a zillion pieces. If you immediately looked down the strip you could see the braking parachute open. Needless to say one or two exhibition runs and the sanctioning body outlawed the car as being too dangerous for the spectators.
Craig ran it at Bonneville without breaking the record as he was running out of rocket fuel around 400 MPH. He decided to remove the wings between the rear wheels and the large laminar flow wheel pants that I had designed. He did this to save weight. The car was stable until the rocket motor shut off and then it went into a Lomchevak at 400 MPH. Needless to say Craig survived because of the robustly designed cockpit done by Margie Smith. It was two concentric tubes of .065" thick 7075 T6 riveted to .065" thick 7075 T6 hat sections every 10 or 15 degrees and was about two feet in diameter. Front and rear 4130 steel tubing sub frames where torn off.
This quote from a web site is inaccurate as the rocket car actually ran at Bonneville and crashed as I outlined above. That is why you won't see the actual car in a museum. Just a mock up.
"During the 1970's, Craig campaigned a rocket dragster powered with a lunar module motor fueled by hydrazine. This led to this consideration of a new rocket-powered land speed record car, but U.S. government restrictions on the use of rocket engines and fuels became too stringent to successfully continue the program, and he had to abandon his rocket car project in the mid-1980s. The full-size, 41 foot mock-up for that intended rocket car is now exhibited at various museums and is the design forerunner to his newest Spirit of America land speed record car."
Anyway the two down tubes control the camber of the front wheel as it turns left or right. The pivot axis is a virtual axis formed at the convergence of the lateral links and the upper convergence of the down links. Since they are parallel they converge at infinity in outer space some place so the pivot axis is near vertical. To add rake angle or caster to the pivot axis you move the top ball joint in towards each other which makes them converge at a finite distance above the fuselage. The yoke is made out of half a dozen layers of carbon fiber. Craig's was made from thick wall square steel tubing. The link below and in back of the yoke is the steering link. The steering box and steering arm are not shown. Nor are the pneumatic cylinders that support the suspension on the road and retract the front wheel in flight. Nor are the various required suspension attach brackets shown.
The aluminum links and aluminum ball joints are all stock sprint car parts. I was at the Ventura dirt track on Saturday night when my 73 year old friend John Richards was racing his 650 HP sprint car in the senior's race. Dirt track sprint cars take a lot of abuse. That is where I got the idea for the light weight suspension links. Almost all sprint car suspension parts are aluminum and very reasonably priced because of the volume manufacturing.
The rational for this design is it widely distributes the suspension loads into the structure unlike a traditional motor cycle fork design. Therefore it is much lighter than a motor cycle fork arrangement.
For road work you remove the canard and main wings and tow them behind you.
Trailer configuration. You build narrow wheels and part of the hitch into the leading edge of the wings and strap the canard to one of them. Hinge the tip vertical stabilizers to lie flat (more or less) on top of the wings.
Perry Micks response on when you need the trailer and when you don't.
In most cases would you even need to trailer the wings? You keep the car at home and the wings at your local airport. Drive to airport, put on wings. Fly to your destination. Leave wings at that airport. Drive locally around that airport. When you are ready to go home, drive back to destination airport and put the wings back on. Takeoff and fly back to home airport. Take wings off and drive home, leaving wings at local airport.
Vance Jaqua's structural comments and sketchs.
Here is a rough sketch of the structural concept in the basic envelope of a roadible canard. The foam filled sills with BID shells act like large chassis side rails and the seat structure fulfills a central X section effect . End box sections close out the frame. The seat back forms a roll over structure and main wing connect point. Non structral panels provide access to the drive line.
I would be tempted to integrate the engine, trans, and portions of the suspension into a single unit carried in a sort of tube engine mount bed mount. this would be tied into hard points tabbed and ribbed into the "side rails" simple swing axle - airbag suspension - vacuum pump to pull up the wheels, The belt redrive may or may not be a structural part of the package. The whole unit to drop down after a non structural aero shell is removed from the bottom. The suspension loads dumped into the mount - much as on nose wheel struts to bed mount engines. The rough sketch gives a general view of this type of layout. Numerous other options are also available. The roadible airplane is not a daunting engineering problem, but mostly one of logistics, marketing, and operation under the existing systems. Vance
Jeff Spitzers roadable airplane. Rear wheels are driven.