I am currently in the very early stages of developing an advanced, pressurized, streamlined hot air airship which is eventually expected to be standard type-certificated under FAA regulations. The process will likely take a number of years, but it is a necessary and grueling procedure for any aircraft which will be used in commercial flight operations.

Example of banner area size

Initial flight testing will be carried out with a remote-control 1/3 scale model airship before moving onto construction of the full-size airship prototype. There is no definitive timeline for the project, as it is merely a spare-time endeavor and no budget has yet been allocated. Private investors/benefactors gladly welcomed - contact me.

The large airship will either be a six-person 160,000 cubic foot design or an eight-person 220,000 cubic foot passenger variant. I'm still doing a personal study to determine which passenger configuration would be optimum to fulfill multiple roles.

Propulsion and fin pressure will be provided by a 1.3L, 90HP fuel injected, four-cylinder, liquid-cooled Geo/Suzuki G13B engine coupled with a custom planetary gear propeller speed reduction unit (PSRU). The 1.3L Geo/Suzuki has an equivalent power-to-weight ratio of the Rotax 503, a common two-stroke engine found in hot air airships and ultralight aircraft. While the 1.3L engine is heavier, it is also proportionally more powerful, but still manages to go through less than half the fuel that a comparably-powered two-stroke burns.

Geo Metro 1.3L G13BB engine as mounted similarly on a trike ultralight

Reasons for choosing an automobile engine rather than a purpose-built ultralight aircraft engine:

• High reliability and long lifetime - No two-stroke reliability problems
• Inexpensive in both initial cost, maintenance, and overhauls - Rotax parts are expensive!
• Automatic computer adjustment of air/fuel ratio to compensate for changes in altitude
• Electronic ignition and fuel injection; easy to start all year round
• Half the fuel consumption of a two-stroke
• Much quieter - no two-stroke "weedwacker" sound

L to R: Our custom-fabricated planetary gear propeller speed reduction unit (PSRU), coupler and heavy flywheel. The starter motor bolts onto the reverse side of the PSRU bellhousing. The PSRU is bolted securely to the engine block in the place where the auto transaxle once was.

A three-bladed 74"-diameter ground-adjustable composite propeller has been selected for initial engine testing. A prop shroud/duct is a possibility, to simultaneously lessen propeller noise while increasing thrust. A pair of optional manually-operated clamshell thrust reversers will act as air brakes - sometimes necessary when landing or maneuvering at low speeds in still air.

A unique design feature of the envelope is an internal system of inflatable fabric battens pressurized by the propulsion slipstream. These stiffeners are a relatively simple solution which will make the nose less likely to cave in at higher airspeeds, a problem all current hot air airships face to some degree (with the exception of Dan Nachbar's semi-rigid Personal Blimp). This system of pressure tubes also inflates the tail fins and rudder in the same manner. When the propulsion motor is turned off, one-way fabric check valves in the nose and tail hemispheres keep air from rushing back out of the fins and battens.

Pressurization system overview

I am considering experimenting with a separate internal tube system (not shown) which would have its own dedicated inlet at the air scoop behind the gondola. The air tube connected to this inlet will continue through the rear fin hemisphere and then branch off inside of the rudder to multiple rear-facing air exits spread evenly up the height of the rudder. These "jets" will direct propwash in line with the rudder's direction and should conceivably help increase slow-speed maneuvering with the engine at low or idle. The jets will be of slightly smaller diameter than the tubes to maintain positive internal tube pressure.

The main envelope will be fed fresh air for combustion by an electric fan running off of the engine's electrical system. This fan provides a constant supply of fresh air to the burners and helps provide some of the positive pressure necessary for the airship to maintain its proper shape. The scoop behind the propeller provides the majority of pressurization force, and the pressure is a function of propulsion engine throttle. This means higher pressure is available when operating at higher airspeeds.

Two fabric overpressure valves will be located at the bottom of the envelope, one fore and one aft of the gondola. The lowest point in the envelope is where exhaust gases from combusion settle, and these two overpressure vents are designed to expel this exhaust air in conjunction with the electric fan underneath the burners. This limits the possibility of burner pilot light flameouts due to oxygen deprivation.

An internal fabric bulkhead allows for pitch control using the two opposing fore and aft burners. This bulkhead also limits the internal air movement ("sloshing"), a problem witnessed in more than a couple early streamlined hot air airships.

Watch this space for updates. (Last update: August 23, 2007)