Raptor NG Discussion

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Well-Known Member
Aug 8, 2009
Sahuarita Arizona, Renton Washington, USA
Or you could hide the trash can in big barrel as proposed in "Could you design anything stranger?"post #8 Under Aerodynamics, Design ....etc.

"No drawings but reference the Williams X-jet variations incorporated as the core of a hybred 8 foot diameter ducted fan containing 6 or 8 electric fans quad copter style for additional thrust, range and control:

Williams X-Jet - Wikipedia

"Other VTOL systems developed by Williams International included a jet-powered flying belt, developed in 1969, which was powered by a Williams WR19 turbofan, and X-Jet's predecessor, the WASP I (Williams Aerial Systems Platform), which was developed in the 1970s and was powered by the more powerful WR19-9 BRP5, rated at 670 lbf (2.98 kN) thrust and a specific fuel consumption of 0.47 lb/lbf·h (13.31 g/kN·s)."

The 8 foot diameter is a limitation to keep the vehicle street legal and allow storage in a standard one car garage. The roadable requirement is to allow the vehicle to transition from the garage to a suitable VTOL or STOL takeoff and landing area. The duct also allows sufficient lifting area to transition to horizontal flight with a maximum forward cruise speed of 250 knots."


Well-Known Member
Jun 27, 2015
capital district NY
Ducted fan propulsion system will work only for slow flying aircraft(up to 200mph) and because thrust of Ducted fan based on "Mass flow" of the air pushing by fan, aircraft powered by this system can't fly at high altitude where air is thin and weight less. With Ducted fan aircraft will fly good only up to 12,000-15,000 feet of altitude. For PM picking this propulsion system - full utopia!!!...
I am under the impression from what I have read that ducted fan is good to around 100mph or maybe a little more, it is also good above around 200mph (turbofan jumbo jets) it is the middle area from around 100mph to 200mph that it sucks?


Well-Known Member
Jun 29, 2003
Thought I would interject some data from tests on an 11" diameter and 17" diameter fans set that I ran a few months ago. The test bed is a rolling vehicle now powered by a 35 hp 2si 2 cycle engine with a direct drive to the ducted fan. I monitor thrust, torque and rpm. When rolling I also monitor airspeed. The fans are bladded with jet engine compressor blades and the pitch is gound adjustable. Compressor blades aren't opyimized for this application so my results are below the theory predictions. Below is a plot of the 11 inch fan results at zero forward speed.

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11 inch fan Unit with 17 inch fan and 12 hp engine

Victor Bravo

Well-Known Member
Jul 30, 2014
KWHP, Los Angeles CA, USA
What exactly is the relationship between the Raptor, the Kasperwing, Dr. Sorokodum's flapping palm fronds, Manolis Pattakos' hand-held propeller/meat grinder, the Australian Wallaby, and nuclear submarines?

Apparently anything end everything being discussed here is rather enthusiastically brought into relevance with one or more of these items, regardless of the actual relevance.

Is this what Steely Dan meant by "Pretzel Logic"?


Well-Known Member
Jul 15, 2020
Cool test rig. So you're getting about 1 lb. of thrust per hp?
The big RC EDF motors are a little better than this.


SCHUBELER DS-215-DIA HST® with DSM10066-290

Sheath Inside Diameter: 195 mm
Geometrical Throughput Area: 215 cm²
Total Weight: 3400 g
Static Thrust Range: 215-250 N
Jet Speed: 84-98 m/s
Speed Range: 12,000-14,000 rpm
Input Power: 9.8-15.6 kW
Battery: 12-14S 20000 mAh
Efficiency: 78%

Test data is here:

250N static thrust on 14.6KW or 56# on 20HP. Around 2.8 pounds of static thrust per hp. Although when we input the electrical efficiency of the engine (78%) the fan itself puts out around 3.6 pounds of thrust per shaft hp.
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