Sonic-boom comes to models

[Ollie]

In dynamic soaring the models encounter two sonic-booms in a circuit. The sonic-booms kick every time the shear layer is pierced. Not with constant high air speed but momentary encounter of the gust.

My primitive knowledge of aerodynamics is sub-sonic. Please teach me.

Beyond Dynamic Soaring 101:
http://www.charlesriverrc.org/articles/flying/markdrela_ds.htm

[EagleOne]

Ollie
In my opinion is it possible , that the sound that you hear when going into and thru the shear layer on the up wind turn is the compression of the air flow over and under the airfoil, compressing the low, high pressures causing the accelerating of the wing, increasing pressures equals increased sound, aft of the high point to the trailing edge and with the sound that you hear after coming out of and under the shear layer is the release of pressures and with an high angle of attack is the separation of air flow over the foil, and I like to add, a good chance of slight stalling.
As far as sonic- booms, when you see a plane implode before your eyes for no reason, then I believes it will be the beginning of the process of breaking the sonic barrier.
John

[Sparky Paul]

The speed of sound, or even that of compressibility is still way past what the fastest DS planes can achieve.
The planes that "implode" are merely demonstrating their lack of structural ability to handle the extremely high g loads.
When DS planes begin to approach the SOS, we'll begin to see the shock waves typical of a near-sonic plane forming at the rear of the plane.
This is a plane -near- sonic speed..
The next is not.. that's merely condensation due to the compression of the air at the front of the plane as it accelerates over the curvy parts.

[Ollie]

Yes, John, I got it from "Wing Theory" by Robert T Jones, page 63 and Fig.4.6.
"In a real compessible fluid, such a start will generate sound waves that spread from upper and lower sides of the airfoil with velocity c."

My questions are how much sonic energy radiates from the aircraft, how much the aircraft changes the velocity, how abrubt the gust and how much strength of the gust.

See:
http://www.rcgroups.com/forums/showthread.php?t=101242&page=3&pp=20
Posts 58, 78 thru 97.

[EagleOne]

Ollie all good questions, I don’t have the mathematical equations that you are looking for, but I like the ideal that you are looking at the two different air densities and velocities as sub-sonic / sonic.
I hope I don’t ruffle the feathers of someone with the photo below

[Sparky Paul]

That -might- be possible, if there is a seriously large difference between the shear layers.. several hundred mph.. These don't exist.
Any model encountering such a phenomena would collapse.

[Ollie]

I'm quilty of using the dramatic words "Sonic-Boom." At about 200 to 250 MPH DS models give off a very strong "whomp" sound every time the shear layer is pierced.

Under conditions full scale jets have crashed in down burst when landing approch. Full scale aircraft avoid thunder clouds. What do we measure the gusts and their abrubt shearing?

DS models use very abrubt changes of 20 to 30 MPH air velocity within a few feet. How do we detail the conditions thru the shear layer interface for aerodynamic forces and structural loads and cope with design? If my questions are primitive, help we will better questions.