Hugh STONE, et al.


VTOL with fixed wings & small props, plus more speed, range & endurance than helicopters.

Anna Salleh : "Plane-helicopter combo takes to skies" ( ABC Science Online, 20 November 2006 )

UNIVERSITY OF SYDNEY   ( 13 NOV 2006 ) Unmanned UFO takes flight

T-Wing Aircraft Homepage


Hugh Stone : The T-Wing Tail-Sitter Research UAV

T-Wing Flight Test ( August 2006 ) Videos

P. Garcia, et al. : Modelling and Control of Mini-Flying Machines

T-Wing Documents ( PDF )
ABC Science Online
20 November 2006

Plane-helicopter combo takes to skies


Anna Salleh

The vehicle combines the best of a helicopter and fixed wing aircraft, say researchers. It stands 1.5 metres high and has a wingspan of 2.4 metres (Image: University of Sydney)

A new unmanned aerial vehicle (UAV) that takes off vertically like a helicopter and then flips over to fly forward like a conventional plane is being developed by Australian researchers.

The T-Wing could provide cheaper and more efficient surveillance and reconnaissance, says Dr Hugh Stone of the University of Sydney whose team has been carrying out test flights.

"It can take off and land like a helicopter," says Stone, an aeronautical engineer who began the research as a PhD project. "It doesn't need a runway."

While helicopters can take off and land vertically and can hover, they are not as efficient at forward flight as conventional aircraft, which means they don't tend to fly as fast or as far.

This is why 'convertiplanes' were developed, aerial vehicles that convert from helicopter to plane mode.

Other UAV convertiplanes use helicopter type propeller blades and more complex and expensive technology to control the movement of the vehicle, says Stone.

But the T-Wing uses fixed propellers, like a standard aircraft.

Moving flaps that sit in the airstream behind the propellers are responsible for changing the direction of the aircraft and allow it to hover.

These flaps are controlled by an onboard computer system that detects and changes the plane's location and orientation.

"We can basically tell it a set of points in space and we upload those to the vehicle and then it will fly through those points," says Stone. "It doesn't need any intervention from us."


Like other similar vehicles the T-Wing is quite unstable and the flaps have to move 50 times a second to keep the vehicle hovering.

While it is not possible to fly the aircraft by radio control from the ground, it is possible to communicate with the onboard computer system in an emergency.

"We can intervene if something starts to go wrong," says Stone.

So far the team has successfully tested a prototype that is 1.5 metres high with a 2.4-metre wingspan and weighs 30 kilograms.

In the tests, the aircraft flew autonomously, except while landing when it had some assistance from radio control on the ground. The team plan to do further testing in December.


Stone says UAVs are generally equipped with cameras and used for surveillance and reconnaissance.

The research has been funded by the Australian Research Council, the University of Sydney and a US$30,000 grant (A$39,000) from the US Air Force.

Stone says his team is working with Australian technology company Sonacom to develop a commercial version of the aircraft for surveillance applications.

13 NOV 2006
Unmanned UFO takes flight

In what feels like a homage to the 1950s UFO era, researchers in the University's School of Aerospace, Mechanical and Mechatronic Engineering have developed an aircraft that takes off vertically before flying off horizontally.

With a wing span of 2.4 metres, a height of 1.6 metres, and weighing 30 kilograms, the "T-Wing" unmanned aerial vehicle (UAV) blends properties of a helicopter with those of a conventional aircraft.

"Anything that takes off vertically and lands vertically has more operational flexibility because no runway is required. It takes off using propellers, but because it flies like a conventional aircraft - wing-born - it is faster, has more range, and more endurance than a helicopter," explains project-leader Hugh Stone.

While normal aircraft use runway speed to create wind over their wings to provide lift, the lift for take-off of the T-Wing is provided by propeller thrust. As the propellers spin, they blow air over the control surfaces of the wings - 'the propeller wash' - which in turn allows the vehicle to control itself during vertical flight.

The T-Wing, or "Adriano" as the researchers have named it, operates autonomously, communicating with the ground via a console. Operators program points in space - 'way points' - which are uploaded to the vehicle, directing it where to fly.

There is a big interest world-wide in unmanned aerial vehicles, according to Dr Stone. He and his team have been working closely with Sonacom, a company hoping to use the technology to deposit sonar buoys in the ocean.

"Because UAVs are not reliant on human pilots - people who need to eat and sleep - they can stay up longer. Also, no lives are lost if it crashes," he says.

However, unlike many other UAVs, Dr Stone's aircraft has a vertical take-off capability. "It can be placed on the back of a truck and can take off in a clearing almost anywhere," he explains.

Researchers in the United States and Korea have also developed "convertiplane" UAVs with vertical take-off, however according to Dr Stone, these are extremely mechanically complex and therefore very expensive.

"Our design blends the operational flexibility of a helicopter with the forward flight of a conventional aircraft, and it does so more simply than other vehicles," he says.

T-Wing Aircraft Homepage

Welcome to the T-Wing vehicle home page. The T-Wing is a tail-sitter technology demonstrator UAV that is being jointly developed by the University of Sydney and an Australian company, Sonacom Pty Ltd. The T-Wing vehicle concept grew out of vehicle optimization studies conducted at the University during 1995-1999 by Dr Hugh Stone, for his PhD dissertation. Although in some respects similar to the Boeing Heliwing vehicle of the early 1990's it is fundamentally different in a number of respects. Some of the differences are:

* The use of control surfaces submerged in the slipstream of the vehicle's twin propellers to provide control during vertical flight (similar to the tail-sitter vehicles of the 1950's) as opposed to the use of standard helicopter cyclic control;

* The use of a canard to balance the aft wing and allow greater freedom in CG positioning; and

* A different fin and landing gear arrangement.

The T-Wing has a wing-span of ~2.1m and a MTOW of ~30 Kg. It is powered by twin 78cc 3W 2-stroke engines that turn 23 inch diameter propellers. The vehicle is controlled by an onboard PC-104 computer stack that drives all the servos and accepts inputs from the GPS and IMU sensors. The vehicle communicates with the ground via Radio Modem Serial Data link. So far the T-Wing has been flown in hover mode both manually (very briefly!) and under automatic control using Command Augmentation System (CAS) controllers. For hover mode, these map pilot stick inputs to velocity commands:

* elevator and rudder stick inputs become translational velocity commands;

* aileron stick input is treated as a (vertical attitude) roll-rate command; and throttle stick input maps to a vertical velocity command.

Tethered hover testing has commenced on the second airframe and on Monday 6th August 2002, the T-Wing flew with autonomous guidance in all axes except the vertical. Vertical position was controlled via a vertical velocity controller commanded by a remote pilot. Pilot input for vertical position control is necessitated by vertical height limitations of the tether system and the imprecision of DGPS altitude measurements. Once tether testing is complete, all pilot input will be removed. Once this is done, all axes will be connected to an onboard guidance loop which generates appropriate velocity commands for the controllers to navigate between a set of waypoints.

Tethered Hover testing resumed on 1st March 2005, with a total of 4 tethered flights exploring different vertical flight control modes and testing the integration of a new more accurate GPS receiver, pressure sensor and upgraded flight and ground-station software. Besides the standard vertical velocity mode tested previously, the vehicle was also tested with vertical angle-based controllers as well as rate-based controllers.

As of November 2005 we have installed a new avionics system which gives ~ 20 times increase in accuracy for the vehicle position, velocity and angle states. This has allowed us to conduct fully autonomous vertical flight testing with the tether test-rig. We have also been able to successfully fly the vehicle in 10-15 knot winds in both autonomous and vertical velocity guidance modes.

From May 2006 we replaced the 3W-78CC engines with Desert Aircraft 100CC engines to counter weight growth with heavier avionics and deterioration (with age) in the 78CC engine performance.

Between 1st and 30th August/2006 we have performed three transition flights, each involving at least one set of transitions between vertical and horizontal flight.

Launch Transition
 Forward Flight  Landing

VIDEO : T-Wing Flight Test ( August 2006 )

Free Flight with Transitions: 30/August/2006

... Free flight performed with both transitions on 30/August 2006. The vehicle performed the first transition fully autonomously and navigated to the first horizontal waypoint and turned on to the second fully autonomously but was then put in a semi-autonomous mode due to excessive altitude loss in the turn (due to a small problem in the flight controller – since fixed). With the pilot supplying high-level guidance commands for the vehicle’s low-level controllers, the vehicle was transitioned back to vertical flight and recovered safely. In the video the following aspects are seen:

Vehicle climbs up to a waypoint at 100 ft; It then continues climbing to a further waypoint at 300 ft; It then transitions fully autonomously away from the wind in the correct attitude. During the transition it loses approximately 3 metres in altitude; It then navigates to the first horizontal waypoint and turns towards the second autonomously; During the turn the vehicle loses significant altitude due to a small control system error (excessively tight saturation limits on some integral states in the pitch-rate controller); The pilot takes over high-level guidance and brings the vehicle back towards the runway (supplying pitch angle, and bank-angle commands); The ground-pilot commands the vehicle to perform a horizontal to vertical transition which it does in about 50m of altitude. The video is also cut to shorten the time of the descent portion of the flight (about 2 minutes in the actual flight) The vehicle lands in a vertical attitude.

Free Flight with Transitions: 1/August/2006

...Free flight performed with both transitions on 1/August/2006. The vehicle was accidentally put into a fully manual mode [due to bad ground-station ergonomics] during the flight and lost control, but was recovered in a semi-manual mode and landed without a scratch. The video has been edited to delete the unintended control departure region. In the video the following things are seen:

Vehicle climbs up to a waypoint at 100 ft; It then continues climbing to a further waypoint at 300 ft; It then transitions into the wind on its back and rolls right way up while in autonomous mode; At this stage the manual switch was inadvertently hit and the vehicle departed controlled flight; The video resumes with the vehicle recovered in a semi-manual mode; The ground-pilot commands the vehicle to perform a horizontal to vertical transition which it does in about 50m of altitude. The video is also cut to shorten the time of the descent portion of the video (about 2 minutes in the actual flight) The vehicle then lands in a vertical attitude.

Model Predictive Control Flights 28/July/2006

On 28th July 2006 the vehicle completed its first 100% successful Model Predictive Control (MPC) Flights on the tether test-rig. During these flights the vehicle performed the standard “+” pattern while in hover-mode vertical flight. The vehicle used an MPC algorithm looking ~2.5 seconds into the future to determine the optimal control to apply at any given point in time. The particular manifestation of the MPC algorithm used here has been developed by Peter Anderson as part of his PhD studies and runs on the 400MHz Celeron flight computer. For some of the predictive flights the vehicle was flown with an ultrasonic wind-sensor to capture the relative wind-information.

Fully Autonomous Tethered Testing with New Avionics: November 2005

... Vehicle performing a fully autonomous flight from takeoff through to landing. During this flight the vehicle passes through a total of 26 way-points before landing autonomously. The waypoints consist of  the following maneuvers: Climb 10 ft and hover... Move in a Cross-Pattern (“+”) with 8 ft legs in North, then South, then East and then West directions with belly facing North. This demonstrates vertical translations in directions aligned with major vehicle axes... Reorient belly 45 degrees to point North-East... Repeat Cross-Pattern with 8 ft legs in North, South, East and West directions to demonstrate vertical translations at oblique angles to the normal vehicle axis system... Reorient Belly pointing North ... Perform clock-wise hesitation vertical role, stopping at each major compass point (NESW). ... Perform similar anti-clockwise hesitation vertical role... Climb to 12 ft altitude ... Descend to 4 ft ... Land.

Modelling and Control of Mini-Flying Machines


Pedro Castillo Garcia, Rogelio Lozano, Alejandro Enrique Dzul


T-Wing Documents
Stone, H., Wong, K.C. "Preliminary Design of a Tandem-Wing Tail-Sitter UAV Using Multi-Disciplinary Design Optimisation ",
 International Aerospace Congress, Sydney, February 1997, p707-720

[ PDF ]

Stone, H., Clarke, G. “The T-Wing: A VTOL UAV for Defense and Civilian Applications”,
 UAV Australia Conference, Melbourne, February2001.

[ PDF ]

Stone, H., Clarke, G. “Optimization of Transition Maneuvers for a Tail-Sitter Unmanned Air Vehicle (UAV)”,
 Australian International Aerospace Congress, Paper 105, Canberra, March 2001.

[ PDF ]

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