Monday, October 5, 2015


Ducted-Fan Powered Sport Plane Prototype.
A concept lightweight "cold jet" airplane.


This prototype is based on a research report, from the 24th International Congress of the Aeronautical Sciences.
The report is available for reading in this link to the PDF document:

General Information:
The VSKYLABS DFSP-39-A is a full-composite, light aircraft with maximum take-off weight of 2000 pounds. It's propulsion unit utilizes a 700 horse power piston engine, and a composite fan driven by a light aluminum alloy. A by-pass cooling duct for the engine radiators is part of it's inlet channel and nozzle design. It is different from the VSKYLABS Ultra Light DFSP-39 aircraft. It is heavier, larger and designed for cruise speeds of 200 knots. 

The successful realization of a ducted fan propelled aircraft is difficult. Many designs failed because of problems with fan efficiency and shorter life time due to vibrations induced by the flow distortion at the inlet section of the fan. There are also other problems, such as the aerodynamics of the inlet channel, complex design of the fan and its drive, the piston engine installation and it’s cooling and more. In a case of engine failure, additional drag caused by the choked inlet.

Modern ducted-fan propulsion unit designs utilize a gas turbine engine, known well as the Turbo-Fan engine, which is actually a ducted fan unit, driven by a small turbo-jet engine. The Turbo-Fan engine has a lot of advantages over the piston driven ducted fan unit. I'll discuss this issue on a different post.

The aircraft is not for the beginner pilot; It is under powered, sensitive to power changes, agile but violent when you exceed it's flight envelope limits. It's a true challenge to fly, and a good demonstrator for this concept and it's limits.

VSKYLABS DFSP-39-A specifications:
Type: Single seat lightweight Ducted Fan powered sport aircraft.
Powerplant: One 700HP reciprocating engine which drives 7 blades fan unit.
Wingspan: 20 feet
Length: 28 feet
Weight: empty - 1400 lbs, full - 1900 lbs
Flight ceiling: not available yet - project and plane under development. 
Internal fuel: 400 lbs
SFC: not available yet - project and plane under development.
Range of operation: not available yet - project and plane under development.
Cruise speed: 165 knots
Maximum speed: 250 knots
Stall speed: 80 knots

Flying tips for the DFSP-39-A on X-Plane:

In general:
The DFSP-39-A is small and light aircraft. Controls are sensitive but it's behavior is docile and very predictable. It looks like a fast and aerobatic Jet, but it isn't. It is a light plane that's flying "on it's wings". The DFSP-39-A is under powered. Mild vertical aerobatic maneuvers can be achieved by flying the plane above 180 knots.
The 700HP engine's torque affects the light aircraft very much. Use aileron trim in all phases of flight, since roll moments will be noticed on engine power setting changes.

Speed management: 
Acceleration is moderate. You will notice this fact upon take off, and whenever trying to reach it's fast-cruise speed (above 200 knots). Climb at 150-160 knots, make room for slowdown since this aircraft does not feature speed brakes.

Take off and landing: 
Apply full power, nose up at 90 knots, lift off at 100 knots. Lift off below 100 knots is dangerous due to severe roll moments.
Landing the plane is tricky because the aircraft is energetic and light, so you'll have to practically fly the touchdown at 90 knots. Remember not to fly the aircraft below 90 knots due to severe high-alpha stall characteristics.

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