What Did Kenneth Arnold Really Witness In 1947?
Liberation Times Insight
Written by Condorman - 2 September 2024
Insight from a senior level aerospace engineer.
On June 24, 1947, private pilot Kenneth Arnold claimed he saw a group of nine, reflective unidentified flying objects flying past Mount Rainier at speeds greater than 1200 mph.
There are many depictions of the craft he saw floating around in the media.
The one I had seen in the past was shaped like a crescent and looked like something out of a Batman comic so I never gave it a second thought. You can see the image further above.
I have since learned new information that piqued my interest. I am an avid follower of author Graeme Rendall and a reader of his books.
And Mr. Rendall has pointed out several times that in Mr. Arnold’s original submission to investigators shortly after the sighting, he wrote a nine-page letter with an original drawing depicting a heel-shaped craft. Here are a couple of excerpts from Mr. Rendall:
The following image shows the last page of Kenneth Arnold’s nine-page letter (posted on X by Mr. Rendall) with the original drawing of the vehicles he witnessed. Note that there is also a depiction of the side view which will become important later.
The heel shape seems to be the correct shape that Mr. Arnold observed and initially documented.
As to why Mr. Arnold changed his mind about the shape and posed for the crescent picture, I suspect someone tried to make the craft sexier and more sensational to market a potential book or movie. But my guess is as good as yours.
The following figure shows a model that approximates the heel shape and side view drawing from the letter.
This model is more interesting to me than the crescent, as it resembles a design I have actually worked with before, a hypersonic waverider.
Modern waverider design involves capturing a conical shockwave generated by the vehicle’s nose between the leading edges of the fuselage.
The trapped shockwave increases the pressure on the underside of the fuselage, generating lift.
Waveriders have much higher lift to drag ratios than wing-body designs, though they are typically optimized for a specific Mach number, altitude, and angle of attack, meaning the shockwave only attaches to the leading edge of the fuselage under those conditions. Below is an illustration of a waverider riding a conical shockwave.
And this is what a typical hypersonic waverider looks like. The bottom figure of the front cross section shows the shockwave attached to the leading edges of the fuselage.
The shape from Mr. Arnold’s letter is more blunt than the ones shown here, but the craft were not flying hypersonic and the optimization parameters used for waverider design can yield vastly different results in shape for the same Mach number.
This allows the designer to tune the geometry for different requirements and ease of manufacturing. The waveriders shown in the following figure are all optimized for Mach 5 with vastly different results.
One of the main difficulties of waverider design is that they need to get to their optimized Mach number and altitude to achieve their high lift to drag ratio.
With missiles this is easily done by strapping the waverider to a rocket.
But it is much harder to do for reusable vehicles. These typically require a set of wings strapped to the back of the waverider for takeoff, landing, and low speed flight.
The wings add weight and drag, reducing the lift to drag ratio and the overall efficiency and maneuverability of the waverider. This is one of my early attempts at a hypersonic waverider with wings.
This difficulty can be overcome with several design factors. Novel propulsion methods could get the waverider to the design speed quicker. Advanced lightweight materials would drastically lower the weight and reduce the need for wings as well as enable quicker acceleration.
And variable-geometry structures could be employed to continuously capture the shockwave as the craft accelerated supersonically to its cruising speed.
A combination of these design factors could account for the craft that Kenneth Arnold witnessed on June 24, 1947. Based on his description, the vehicles were traveling at over 1200 mph which translates to a range of Mach 1.8 to Mach 2.0.
I ran an optimization for a Mach 2 waverider that I’m not going to publish here because I used proprietary software and the result is definitely blunter and more like a heel than a hypersonic design.
Obviously, there is a lot less lift from a Mach 2 shockwave so the craft would need to be very light, but the hypothesis that this is a variable-geometry waverider that was optimized for Mach 2 at the time of the encounter fits well.
The side view also matches the waverider hypothesis as I mentioned earlier. An actual vehicle cannot be wedge shaped with a flat perpendicular back, as optimized waveriders look like.
The drag generated by the flat backside of such a shape would instantly eliminate any benefit of the design. A real-world craft has to gently bend the air to create an expansion wave so the air passes around the vehicle and exits with an oblique shock.
The image below depicts a NASA X-43 hypersonic demonstrator. And the one below it is the model of Kenneth Arnold's hand drawing. The resemblance is remarkable.
The one glaring omission from Mr. Arnold’s notes is a propulsion system.
You can see the prominent scramjet engine in the image of the X-43. Any type of jet technology employing air inlets and exhaust nozzles would have been visible on a craft with such clean lines, but there was no mention by Mr. Arnold of any visible propulsion systems.
So it’s very likely the vehicle employed a more exotic means of propulsion such as negative matter, which I have proposed on other occasions. See Can Tic Tacs Fly? for a description.
Why would a craft with exotic propulsion need a waverider design to generate lift? I can think of a couple of reasons.
Their propulsion system, while exotic, may not provide enough lift in some scenarios, perhaps when fully loaded with cargo.
The second reason may be that the waverider design allows the vehicle to conserve the power of the propulsion system by not making it do all the work to lift the vehicle. A combination of the two also makes sense.
There’s one more piece of evidence to support the waverider hypothesis. Mr. Arnold compared the craft’s motion to “a saucer if you skip it across water.”
An interesting behavior of a waverider is that if you go below your optimized speed, the shockwave detaches and the waverider loses lift and begins to drop.
As it drops, the waverider gains speed and the shockwave reattaches, generating more lift and thrusting the vehicle up. From a distance, this behavior would mimic a saucer skipping over water.
So, could Kenneth Arnold have seen a group of shiny variable-geometry waveriders traveling at Mach 2 without observable propulsion and playfully dropping in and out of their design speed to generate the up and down motion?
If he did, then he saw something completely anomalous. We haven’t built those yet, so they absolutely were not ours in 1947.
