VSKYLABS Pulse Jet Concept Prototype 'Firefly'
Original Design Valveless Pulse Jet Powered concept  aircraft

NEW UPDATE (4.3.2016): V2016-001
(a free download link was sent to all the former Firefly buyers)

This package contains TWO aircraft:
- 'Firefly-1' (X-Plane 10.45)
- 'Firefly Delta dart' (X-Plane 10.45)
  • Flight model improvements for both aircraft, so they are more stable.
  • 'Delta Dart' external fuel tanks are now empty (without the extra fuel). In the next update these tanks will be filled-up again, once some stability issues in the design will be solved. 
  • Both models are for X-Plane 10.45


Scroll down to read important and useful information

Valveless Pulse jet engine demonstration
(from YouTube):

VSKYLABS 'Firefly 1' + 'Firefly Delta Dart' prototypes features and characteristics:

I have updated the 'Firefly 1' Pulse Jet aircraft. The original version suffered from some stability issues, as for being a tailless aircraft. It's vertical wing tips/stabilizers and small rudders limited it's cross-wind performance and reduced it's lateral stability qualities, and it's high aspect-ratio, tailless wing layout limited it's weight and balance and center of gravity aspects, as it narrowed it's flight envelope and it's flexibility.

When I first started it's design refurbish, I was planning to enlarge the vertical stabilizers/rudders, and to add a tail or canards for more comfortable longitudinal control. I didn't want to divert the design into an obvious design (which will look like a traditional glider, and will perform perfectly with the low-thrust pulse jet propulsion). So...I've decided to go with the delta wing design, which could be perfect for expanding the 'Firefly 1' flight envelope and it's optional payload (just like the F-16XL aircraft). Although the 'Firefly Delta Dart' is a low sub-sonic aircraft, the Delta wing layout offers some good advantages for it's low-speed performance. (I will write about it soon in this page).

This Update includes:
  • Two different aircraft inside.
  • A new version of the 'firefly 1' - the 'Firefly Delta Dart'.
  • Authentic pulse jet sounds update for both 'Firefly 1' and 'Firefly Delta Dart'.



Here are some general details regarding the 'Firefly' prototypes:

General flying tips for the 'Firefly Delta Dart':

  • The aircraft is setup in a way which will let you get it out of control, if you fly it out of it's comfort zone. It's an experimental aircraft and this is all the fun! :)
  • You can select to unload the ferry drop tanks from X-Plane's Aircraft/weight and balance window. Without these fuel tanks, the aircraft will be much more energetic, and you'll have to give attention to high angle of attack operations.
  • High angle of attack (Alpha) warning alert will sound as you will get close to it's limit. ease on the stick when you hear it. You are close to a pitch-up situation.
  • Rotation speed with the ferry drop tanks is about 110 knots. Final landing speed ~130 knots. Touch down at ~ 110 knots. Without the ferry tanks you can reduce these speeds by ~15 knots.

('Firefly 1') Lightweight fuselage is based on common Sailplanes fuselage size and construction.

Internal fuel tank is located inside the fuselage, behind the cockpit and below the wing. Internal fuel capacity is up to 420 lbs.

Retractable landing gears are electrically operated and retracts into an aerodynamic portable tank. Wheel base is 4.60 feet. The portable tank is attached to the bottom of the fuselage and it is not droppable inflight. There is a strorage compartment in the tank for utility equipment and personal use. Battery for extraction/retraction is located inside the tank.

('Firefly 1') Main wing features leading edge slats and trailing edge elevons. Wing tips are equipped with rudder control. The FireFly is controlled by a fly-by-wire system that corporates artificial stabillity. The FireFly is flyable without artifical assitance. Leading edge slats are automatic operated and extended below 130 knots. 

('Firefly 1') Canard surfaces are positioned in front of the fuselage. The canard surfaces are a low aspect-ratio fixed wing planforms that increases the FireFly stability at all speeds and reduces pitch-trim forces. 

Twin valveless pulse jet engines are attached to the wing symmetrically close to the fuselage. Throttle control system is electronic and located inside the fuselage. The engine constructed without any moving parts and an integrated air-pressure system allows static startup and ignition, as well as in flight. The air-pressure system is located in a compartment in front of the cockpit and it's electrically operated.

Electrical power for the FireFly is supplied by two aviation batteries and a ram-air generator that is located on top of the wing. When airborne, the ram air generator produces power for avionics and flight control systems. There is a battery for ground operations and backup. Power for landing gear retraction is supplied by a separate battery that is located inside the portable landing gear tank. 

('Firefly Delta Dart') Two external ferry fuel tanks can be added (they are not drop tanks, but in X-Plane they can be dropped by using the "Drop all drop tanks" button), containing 200 lbs of usable fuel each. Complete flight can be executed with the external fuel tank attached and full. Sport and aerobatic flight is better done without the external ferry fuel tanks, or when it's empty.

General specifications:
Type: Single seat lightweight pulse jet powered sport jet aircraft.
Power plant: Two Lockwood-Hiller valveless pulse jet engines, producing 420 lbs of thrust (each) at sea level.
Wingspan: 25.8 feet
Length: 20.8 feet
Height: 8.9 feet
Weight: empty - 850 lbs, full - 1400 lbs
Flight ceiling: 24,000 feet
Internal fuel: 420 lbs
External fuel: Up to 400 lbs in two drop-tanks
SFC: 1.7/hr.
Range of operation: 250 - 400 miles (internal fuel only) / 500 - 800 miles (with external fuel tanks)
Cruise speed: 160 knots / 170 knots ('Firefly Delta Dart')
Maximum speed: 300 knots
Stall speed: 70 - 90 knots

Engine simulation:
X-Plane does not simulate Pulse jet engines. Pulse jet engines built without any moving parts, there are no turbines and compressors, so engine response to addition of fuel is immediate, similar to liquid fuel rocket engines. The Pulse jets engines of the 'Firefly' are simulated in X-Plane as a throttled rocket engines, with loss of thrust as they go up in the atmosphere. Above 20,000 feet, the simulated pulse jets produces about half of it's maximum thrust at sea level.

External fuel tanks:
External fuel tanks are not drop-tanks. It can be setup for sport flying without the external tanks via the weight and balance setup window in the simulation. It can be dropped in flight as drop-tanks using joystick button assignment via the joystick button setup window in the simulation.

The cockpit is located in the backseat of the FireFly. It is a glass cockpit type with 3 Multi Function Display screens. Controlling the aircraft is done with a conventional centered stick, rudder pedals and twin throttle lever on the left side.

The cockpit is divided to three: Front panel, Left panel and Right panel. 

Front panel layout:

Front panel includes (left to right): 
Artificial stability switch, Landing gears handle and mechanic indicator, Battery, Fuel and Ignition switches for engines startup and operations, Moving map display with multiple zoom and layers (switches are clickable around the MFD), Fuel meter, Chevron (angle of attack indicator for landing assist), Internal lights panel no.1 (on the wooden panel), Below it there is an artificial horizon, Indicated airspeed, altitude and compas digital display (center MFD), Avionics master switch, Right MFD for engine, fuel flow data and digital HSI. On the right there is the parking brake handle (yellow "T" handle). On the lower right side there is the warning lights panel.

Special features:
Quick Field Of View Setting: There is a yellow tab on the right, located on the glare-shield, signed:"FOV". Push this Tab for switching to recommended Field Of View setting for the FireFly. It is a clickable Tab that switches between 75 to 95 Degrees of lateral field of view.

Quick time of day setting: Left to the FOV tab there is a round button. Push and hold this button to change the time setting from day to night. It is cyclic.

Right Panel Layout:

Right panel includes (front to aft): 
Pitot heat and AOA heat switches, Garmin GPS, COM 1 panel, COM 2 panel, External and internal lights panel and NAV 1 panel. On the right side of the cockpit there is a quick RIGHT engine shut down red colored handle.

Left Panel Layout (front to aft):
Generator and inverter switches, Twin throttle lever and a quick LEFT engine shut down red colored handle.

Please read the COPYRIGHT and DISCLAIMER information which can be found at and also within the package archive.