FOIA: A Study of Skirtless Hovercraft Design: A Thesis

FlyingSaucer.pdf
A Study of Skirtless Hovercraft Design: A Thesis
A Thesis submitted as part of Master's degree analysing the possibility of a working hybricraft.
Document date: 2004-05-01
Department: Air Force Institute of Technology
Author: Edward A. Kelleher, BS, Ensign, USNR
Document type: Master's Degree Thesis
pages: 70


Archivist's Notes: This is a very technical thesis examining the potential for developing a working hybricraft or skirtless hovercraft based upon William Walter's concepts using coanda nozzles. It is well laid and would be understandable for readers possessing relevant technical knowledge.

A study of a skirtless Hovercraft design – Thesis - by Edward A Kelleher in May 2004
Department of the Air Force Air University – Air Force Institude of Technology
Wright-Patterson Air Force Base, Ohio

Three designs of a hybricraft where analyzed with the following results:

The first design failed due to lack of the Coanda wing surfaces and ability to generate a solid pressure cushion.

The second and third designs repeatedly resulted in pressures on the lower surface of the craft to be above ambient pressure and higher than those produced on the upper surface of the craft.

For the first and second design there is a slight reduction in net force, more significantly for the second design than in the first.

The third design is the only one to show an increase in net force.

This study was too broad to bring about any real optimization of an operable hybricraft design.

Here are the Highlights:

PDF page 5 Three proposed skirtless hovercraft designs were analyzed via computational fluid dynamics to ascertain their lift generation capabilities.
The three designs were adaptations from William Walter’s hybricraft primer and his patent for a fan driven lift generation device.
Each design featured Coanda nozzles, or nozzles that utilize the Coanda effect, to redirect air flow to aid in the generation of an air curtain around a central air flow.
The designs also utilized a Coanda wing as a lifting body to aid in lift generation.
Each design was set at a height above ground of one foot and a radius of two feet.
The craft was assumed to be axisymmetric around a central axis for a perfectly circular craft, much like a flying saucer.



PDF page 12 In September 1998 inventor William Walter received a patent for a lift augmentation device that utilizes concentric nozzles to provide a central supercharged air cushion surrounded by an inner central air curtain and an outer or peripheral air cushion surrounded by a peripheral air curtain. The lift augmentation thus creates a hovercraft like vehicle that eliminates the skirt in modern hovercraft.
This craft differs from pervious attempts at skirt-less hovercraft in several ways. First, the jet stream producing source is positioned outside the main body in the form of rotor blades above the main body. The proposed design also claims to have the ability to navigate obstacles such as rivers, canyons, and other such natural barriers.


Henri Coanda would later produce multiple patents utilizing the effect he observed and studied to generate propulsion for aircraft. An experiment by Von Glahn found that placing curved and flat plates near a nozzle would result in a ratio of lift to undeflected thrust of about 0.8-0.9, depending on the total deflection angle.
Thus a Coanda nozzle could achieve a 90° deflection of the jet-stream and result in a vertical lifting force on the order of 0.8 of the undeflected thrust. This shows that Coanda nozzles can produce lift as well as maintain thrust.



The lift is created on the curved surface of the nozzle where the lower pressure regions form. Coanda attempted to use this idea with jet engines to generate flow over outer curved surfaces of crafts he designed. His patent for a lenticular craft give possible insight to the uses of the Coanda effect in the area of aircraft propulsion.
The generation of this lift principle can also be seen in the experimental work of Jean-Louis Naudin.
His Coanda saucer experiment using a simple concave object and high speed airflow over the top of the object shows that a low pressure region is generated above the craft. This low pressure region creates lift and causes the craft to hover. The high speed flow is able to create the low pressure region by remaining attached to the craft as it flows around it.

Recommendations:
A closer look needs to be taken in two areas.
The first is the Coanda wing and just how much lift one could generate with such a curved surface.
The second area is to look at the nozzles and how they can be adjusted to add to the air curtain and pressure cushion below the craft.

PDF page 56 Appendix A

Preliminary Study of a Skirtless Hovercraft

The intended purpose of this preliminary study was to look at the fluid flow of air in and around a purposed skirtless hovercraft design. The concept was created by William Walter in his Hybricraft Primer. The idea is to use blades to generate a downflow of air (much like a helicopter) into and around a body. The body is specially shaped to generate flow through Coanda Nozzles; nozzles that use the Coanda effect to direct air towards the center and below the craft to maintain an air cushion.

This study is a computational analysis of a few design cases of the craft. It will look at nozzles with varying opening distances and radius. These are important, for the t/r ration determines whether or not the flow follows the Coanda effect and remains attached to the nozzle shape.

Conclusions and Recommendations
The most significant conclusion is that the Coanda nozzle have not worked for these flow and design conditions. This study also reveals the necessity for the use of an unsteady solver and the probably use of inlet velocities of 100m/s or greater. The grids also need to be further refined to capture the flow properties at the bodies more effectively…..


[edit on 16-2-2008 by frozen_snowman]

Another detailed study for the possibility of inventing a hovercraft. I'm starting to like it

As I was expecting it starts with a description and picture of AVRO Car (ATS FOIA related link: FOIA: Avrocar Flight Test Plan) and as my fellow archivist described continues by analyzing the designs for three hybricrafts. Is a highly technical document but extremely interesting to read even for one who doesn't have the right educations.

The same document in pdf can be found at this military web page where all the designs and the pictures are in color, the same as the one posted here. Nice document indeed. Check the link: stinet.dtic.mil...