Coanda or Bernouli, which describes lift?

In summary, during experiments with a pulse jet, different methods were attempted to increase its performance while keeping its weight low. One method involved introducing a larger diameter pipe into the jet and partially allowing it to find its natural location, resulting in the discovery of the Coanda effect. However, there are conflicting opinions on the role of the Coanda effect in lift. The Bernoulli principle was found to be the foundation, with the Coanda effect having a minimal impact. The observed effect was similar to the attraction of two magnets and occurred consistently at the midpoint of the length of the pipe. Data on the pulse jet's dimensions and output are provided, and the possibility of scaling for increased output is mentioned. The experiment was conducted in 1993
  • #1
MR. P
When firing my pulse jet I tried various approaches at increasing its' performance without significantly increasing its' weight. When (while holding a piece of larger diameter pipe with channel locks) introducing a larger diameter than the jet diameter pipe into and partially allowing the larger dia, pipe to find its' natural location I discovered (felt) something that was described as 'the Coanda Effect' . A database search reveals disagreements among 'people in the know' regarding the mechanism for describing 'LIFT'.Is there a definitive answer??

frank MR. P
 
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  • #2
While Bernouli doesn't tell the whole story, it does form the foundation. The Coanda effect has a minimal impact on lift. For one thing, that cohesion force doesn't increase with flow velocity. Its essentially a static force.

Also, your description of what you observed isn't all that clear, but it sounds like normal aerodynamic forces - not the Coanda effect.
 
  • #3
russ_watters said:
While Bernouli doesn't tell the whole story, it does form the foundation. The Coanda effect has a minimal impact on lift. For one thing, that cohesion force doesn't increase with flow velocity. Its essentially a static force.

Also, your description of what you observed isn't all that clear, but it sounds like normal aerodynamic forces - not the Coanda effect.

thank you for your responce russ...The effect I felt was simiar to the feel you sense when two magnets are in close proximity to each other when attracting. I also noted that by keeping the larger diameter constant, the effect always appeared at the midpoint of the length i was using here's some data:

Pulse jet tail pipe diameter 1 1/8"
Pulse jet length 27"
pulse jet inlet diameter 2 1/2"
length of inlet & combustion chamber 6 1/2"
length of reducer 2 1/2" to 1 1/8" 1 1/2"
stand alone operating frequency ~230 pulses/sec
reflected standing wave frequency ~365 pulses/sec
normal acoustic output >120 db
augmented/ducted acoustic output <100 db with a 3 1/8" X 4" duct

I was firing this thing at my friends' subaru repair shop in Monrovia Ca. in 1993
way before 9-11 even then the police would come by and shut me down after 15 min of continuous operation each time I fired it. In totality I managed to get 10 firings in 10 days to discover whatever. When I started ,it produced ~6 lbs of thrust when I finished I was producing close to 60 lbs mostly due to the increased operating frequency. These machines posess a doubling cubing relationship or thereabouts in that dubling the operating frequency cubes the output power. This was the most rewarding engine and experience I've ever had and I'm still looking for another.
I'd be a rich man if scaling worked, however, it was the unique combination and the physics of the mass flows that produced the high thrust and a yet unresolved observation during the last firing of a 'reflected standing wave' that I believe affected the higher operating frequency in combination with the reduced acoustic output.


frank MR. P
 

1. What is the Coanda effect?

The Coanda effect is a phenomenon in fluid dynamics where a fluid flowing close to a curved surface will follow the curvature of the surface rather than continuing in a straight line. This effect is important in understanding lift generation in airfoils.

2. What is Bernoulli's principle?

Bernoulli's principle states that as the speed of a fluid increases, its pressure decreases. This principle is often used to explain the lift generation in airfoils, where the curved shape of the airfoil causes the air to move faster over the top surface, resulting in lower pressure and thus lift.

3. Which one better describes lift: Coanda or Bernoulli?

Both the Coanda effect and Bernoulli's principle play important roles in lift generation. The Coanda effect helps to explain the shape of the airfoil and how the air follows the curve, while Bernoulli's principle explains how the pressure difference between the top and bottom surfaces of the airfoil creates lift. Therefore, both are necessary to fully understand lift.

4. Can the Coanda effect and Bernoulli's principle be separated in lift generation?

No, the Coanda effect and Bernoulli's principle are interdependent and cannot be separated when it comes to lift generation. They both work together to create lift in airfoils and cannot be considered in isolation.

5. How does the angle of attack affect the Coanda effect and Bernoulli's principle in lift generation?

The angle of attack, which is the angle between the airfoil and the oncoming air, affects both the Coanda effect and Bernoulli's principle in lift generation. As the angle of attack increases, the air must flow over the curved surface of the airfoil at a greater angle, resulting in a stronger Coanda effect and a larger pressure difference between the top and bottom surfaces of the airfoil, leading to increased lift.

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