Saturday, April 11, 2015

Ultralight Pulse Jet

Valveless Pulse Jet engines as an Ultralight aircraft plausible propulsion?

JetManHuss experimental prototype: The PJSP-2 Seaplane version.

This is a modified Seaplane model of the PJSP-2 land version (which can be found in the 'Prototype' section in this website). The PJSP-2 prototype is a 'low-tech' experimental aircraft. Originally I developed this model to test the plausible configurations of a lightweight and tailless aircraft regarding it's lateral controllability and stability characteristics during take off and it's effect on the vertical stabilizer size and landing gears layout.  

The valveless Pulse Jet engine is one of the most simplest jet propulsion device ever designed, and is the simplest form of jet engine that does not require forward motion or ram air flow to run continuously. Simple air blower and initial spark are required for engine start-up, and a self resonance mechanism 'inhales' clear air and 'exhales' combusted, energetic gas flow in frequencies of up to 50 cycles per second. 

Pulse Jet engines operation is limited to low - mid subsonic speeds and altitude, mainly because of internal to ambient pressure ratio issues, to maintain it's resonance. These limitations are within a lightweight or ultralight aircraft flight envelope, therefore theoretically suitable for this kind of propulsion. 

Valved Pulse Jet engine design (such as in the German V-1 flying bomb) produces more power, and proved itself as a possible light aircraft propulsion, although being mechanically more complex and limited in continuous operation because of the life-span of it's Reed valves mechanism. I chose The 'Lockwood-Hiller' design Pulse Jets for my designs, being the most commonly built by amateurs (During the 1950's and 60's, some development work was done on the valveless pulse jet concept in the USA by Hiller and Lockwood). 

Up to these days, besides using small valveless Pulse Jet engines in small sized UAV's and experimental Go-karts, no actual use in full-scale aircraft has been recorded. Although this kind of propulsion is primitive and thrust limited, the idea of using it as a lightweight aircraft propulsion device got me trying to visualize it as a part of an actual aircraft.

A 'Lockwood-Hiller' Valveless Pulse Jets engine powers an amateur Go-Kart

I designed several prototypes of lightweight aircraft with a theoretic valveless Pulse Jet propulsion, and "wind-tunnel' tested it in X-Plane flight simulator. The exterior features of my Pulse Jet aircraft prototypes was initially for testing various experimental concepts and designs, other than actual Pulse Jet propelled concepts. The valveless Pulse Jet propulsion systems in my designs is just a 'bonus', more like a red-line of thrust and weight limitations for the designs, and mostly for inspiration. 

Valveless Pulse Jets engines on two of my experimental designs

Playing with valveless Pulse Jet engines was simple because I decided to 'deal' only with the limitations of thrust and it's best possible location around the aircraft. Because X-Plane doesn't simulate Pulse Jet engines, I configured the Pulse Jet engines in my prototypes as 'rocket' engines, with predicted thrust and fuel consumption similar to a designated Pulse Jet engine (with a thrust drop-down as altitude rising). The size of the 'Lockwood-Hiller' Pulse jet engine I've implemented in my designs is based on existing amateur engines I found over the social networks, which can produce up to 250 pounds of thrust. A practical issue in real life design would be the ability to restart the engine during flight, or after a flame-out (a small ram-air or compressed air starter device could be used for start-up during flight).

I hope you'll find it interesting, educational and fun to fly.


Now, let's fly some Pulse Jets !

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