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AEROSCRAFT - An Industry Game Changer?

 

Impressive is the only word that can describe the DRAGON’S DREAM – ML866. After the impact of seeing one’s first rigid airship, the airship itself, with its modern technology and innovative features, reinforces the impression.

The ML866 is the proof-of-concept vehicle for the larger ML66. It features almost all of the systems and technologies of the larger airship, which as its name suggests, will have a payload of sixty-six tons.

The ML866 is 275 feet long, 96 feet wide and 45 feet high. Its total hull volume is 750,000 cubic feet. It is a 50% liner scale version of the ML66 production airship.

The hull is comprised of two main structures; the load bearing main frame constructed from triangular section girders assembled from composite longeron tubes with aluminium cross members, and the support frame for the aeroshell which is fabricated from components made from aluminium honeycomb. The engines, flight controls and other load generating items are mounted to the main frame. The frame for the aeroshell is complete on the ML866 but due to weight restrictions resulting from the airship’s small size, a helium-tight outer envelope has been fitted in place of the honeycomb panels planned for the ML66. The decision to incorporate a fully designed aeroshell support frame, which is identical to that planned for the ML66 (baring improvements suggested by testing) is in keeping with the philosophy of designing, manufacturing and testing as many components as possible that will be used in the larger production airship.

The entire hull is inflated with helium but is not pressurized. (In the ML66, gas cells will be used.)

Housed inside the hull are nine High Pressure Envelopes – referred to as ‘HPEs’  - into which helium is compressed or released for buoyancy control. Six HPE’s are located forward and three at the rear of the airship. Each HPE can be pressurised up to nine psi and combined the nine envelopes can change the buoyancy of the airship by approximately 3000lbs.

(The loud ‘bang’ emanating from the hangar some months ago and reported by the ever-inaccurate general media as a ‘failed blimp test’ was a HPE being tested to destruction.)

Four air-filled ‘compensation cells’ are installed inside the hull. Fulfilling a similar purpose to a ballonet in a traditional non-rigid airship, they are used to maintain a constant hull pressure as helium is pumped into and released from the HPE’s, and to compensate for the effects of altitude and temperature changes. Because the hull is not pressurized, the compensation cells are vented directly to atmosphere and do not require the valves and dampers associated with traditional ballonets. The ML66 will use gas cells, negating the need for the compensation cells.

The outer envelope, HPE’s and Compensation Cells are manufactured in-house using techniques developed for the manufacture of non-rigid airships.

The outer envelope is assembled from a number of large sections (the top comprises just two sections) made using longitudinal gores in traditional airship envelope fashion. It is silver on the outside to reflect sunlight and reduce superheat, and black inside to highlight any pinpoint holes. The sections are laced onto the hull and then sealing strips applied to make it gastight. Gastight fabric ‘boots’ are installed in locations were hardware needs to pass through the envelope such as at the engines and control surfaces. The top half of the envelope had largely been installed at the time of my visit and work was underway on the fitting the forward bottom sections.

A series of helium valves are installed on top of the envelope.

Three 230hp Continental IO-470 engines are installed on the ship, two amidships and one on the tail. The two centre engines can vector at any angle up to 90° up or down, and the thrust from the rear engine is directed in both pitch and yaw using a combination of engine vectoring and vanes to provide low speed control. The two centre engines turn three bladed propellers behind which is a ring of much smaller blades designed to provide cooling airflow over the engine at low airspeeds.

The fuel system consists of two main tanks, one forward and one aft, and smaller feeder tanks at each engine location. Fuel transfer between the two main tanks is used for trim, with the fuel system designed to take equal amounts from both main tanks to preserves trim throughout a flight.

The modern and spacious gondola sits midway on the underside of hull and is accessed via a built in stairway that forms part of the door. In concept and execution, the gondola embodies what a modern airship gondola should be and is designed to service the need of an airship pilot rather than simply adapt available heavier-than-air equipment and design philosophies. It has stations for two pilots, although the airship is designed for single pilot operation, and four passenger seats at the rear. Flight information and airship instrumentation is all included on two flat screen displays. The display on the pilots left is an off the shelf unit that provides flight, terrain and navigation information, while the larger right hand display provides aircraft systems information on a number of different pilot selected screens. A caution and warning system indicates which screen the pilot should select in the event of a problem.

A large centre mounted screen mounted on an eyebrow panel displays video feeds from six locations inside the airship and will also provide external views. The lack of a traditional instrument panel gives the pilot excellent visibility.

The pilot has three input devices, two joysticks and a third that more closely resembles the collective control from a helicopter. The joystick on the left of the pilot controls pitch, bank and yaw; the first – inside - control on the pilots right controls throttle once underway and the collective provides vertical control for take-off and landing and houses the engine vector controls.

The wrap-around windows provide excellent visibility in all directions, and the pilots seats actually swivel to provide the occupant with an enhanced view in any direction when required. (This feature will be particularly useful in the M66 and will allow one of the flight crew to monitor cargo operations without leaving his or her seat.)

The gondola partially retracts into the hull for ground operations. A ladder provides access into a roomy viewing area made helium tight in the ML866 using a heavy transparent material. In the M66 the ladder will lead directly into the hull.

The gondola is suspended from the top of the envelope using the same catenary system developed for the Dragon series of non-rigid airships. It consists of hundreds of individual envelope attachment points, each with its own cable, that gradually reduce down to six cables that connect to and support the gondola.

The flight controls consist of conventional stabilizers, elevators and rudders, with each control surface consisting of two parts for redundancy. Conventional rib and spar construction with fabric covering is used. The horizontal stabilizers and control surfaces are set at a downward slant and the verticals at an outward angle with all having cable bracing.

Distinctive all-moving canards are fitted at the bow to assist with pitch trim.

The flight controls utilises a fly-by-light system with a double fibre-optic loop to provide redundancy. The main flight control computer in the gondola processes pilot inputs and transmits signals to one of a number of terminals located around the airship from where they are directed to the item being controlled. The time from pilot input to system activation is measured in fractions of a second. The flight control system has been developed in-house to automatically monitor and control most on-board systems, greatly reducing the pilot’s workload and allowing him to focus on core flying activities. If a system becomes ‘off nominal’ the flight control system automatically flags it to the pilot who can assume full manual control of any system should the need arise.

For part of my tour I was escorted by Aeros indefatigable president, Igor Pasternak. Rightly proud of what has been achieved to date he points out that the key focus has to build a craft that customers wants, and more importantly can make money with. “Most of us” he says “came to airship industry because we love airships. But unless they make money there will be no industry to speak of.” He points out that the average age of the ML866 development team is around 25 and to date just $40,000,000 has been spent on the prototype with another two million dollars going to NASA who are managing the programme. “Having a tight budget makes you creative and efficient” Pasternak says, pointing out that they have developed a revolutionary airship on less than half the budget of other recent airship programmes that have delivered far less. The prototype is under budget and a year ahead of schedule.

The greatest development challenge has been the relatively small size of the airship and keeping its weight under control. Inevitably, there is always upward pressure on both weight and budget with any new aircraft, and especially one as revolutionary as the ML866.

Pasternak is proud of the fact that the company is “breaking all the rules” of accepted airship design and operation with the ML866, referring to the estimated three dozen new systems on the airship and proposed concept of operations. It’s a bold claim but the evidence to support him is taking shape in a very impressive manner.

The ML866 will undertake its flight operations at the Tustin base and it is planned that the ML66 will also be assembled and flown from the site. Development on the former marine base has left little room for airship operations (this was a definite oversight when plans for the development of the sight were drawn up: editor) but Pasternak is confident that the VTOL capability and excellent low speed handling of both the ML866 and ML66 will make operations safe and routine.

There was a high level of activity during my visit with individual groups working on the installation of bottom envelope sections, the rear engine instillation and the flight controls. It is hoped that the airship will be helium inflated and floating in the hangar, ready to demonstrate it buoyancy control system around the end of year. We hope to report on those tests.

There is no question that the ML866 is an exciting programme and the aircraft itself impressive. It is thoroughly modern and incorporates many of the materials, systems and technologies that airship proponents have long said will make the airship a viable mode of transportation in the modern world. Its potential is great and to that end this is an extremely important programme that could be a game changer for the industry. 

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