anti spining strake

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by sanjo, Mar 20, 2007.

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  1. Mar 20, 2007 #1

    sanjo

    sanjo

    sanjo

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    Hi , Im building one version of the emerauders planes

    I have read a report of one cp328 that have instaled "anti spining strakes"

    to improve the control in all class of spins.

    someone have a diaghram or explanations about this feature
    tanks:tired:
     
  2. Mar 20, 2007 #2

    Othman

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    I wouldn't really call them anti-spin strakes... if they are what I am thinking of... because they don't prevent spins from occurring, but rather they prevent them from flattening out.

    These are flat triangular plates (strakes) that fit to the aft part of the empannage and connect to the horizonatl stabilizer. I imagine they generate some good vorticies to keep the upper portion of the rudder useful and to give the horizontal stab more lift during the high angle-of-attack condition encountered during a flat spin, causing the nose to point down.

    I have also seen some vertitical plates mounted to the bottom a fuselage, forward of the wing, to help break the airflow around the fuselage which caused the aircraft to flatten out during a spin. Basically the forward fuselage was generating too much lift during a spin.
     
  3. Mar 20, 2007 #3

    sanjo

    sanjo

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    tanks sir,

    your soupoused is right, in the article the coments was above the improve for the exit from a flat spin when using aleiron in the reverse way as the spin turns.

    the get a fully positive recovery in all conditions .
     
  4. Mar 20, 2007 #4

    orion

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    There are several mechanisms available for improving controllability in a spin. One is as described above, where a triangular surface is placed (in a horizontal attitude) at the root of the horizontal stab. Practical examples of this can be seen on BD-5s and the Glastar. As was surmised above, for local angles of attack higher than normal, the strake creates a vortex which provides the airplane with additional stab and elevator control, helping the airplane maintain a nose low attitude for recovery.

    A similar and more common addition is the dorsal fin - a triangular strake placed in front of the vertical stab. This was an effective fix (although not a cure) for the spin characteristics of the Grumman line of airplanes, which also tended to flatten out. As the plane spins, this strake also generates a vortex flow that is imposed onto the stab and rudder, thus providing a force counter to the spin direction.

    The last option is rarely used but it is the addition of ventral fins at the aft end of the body. They serve two functions - they provide more aft body area thus resulting in slightly better yaw damping and stability and also, when in a spin they create countering lift, similar to that of the dorsal.

    None of these are fixes - they are aids for better control and for providing the pilot with more control authority for getting out of an established spin.
     
  5. Mar 20, 2007 #5

    sanjo

    sanjo

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    tanks for the information,

    I will check some photo of the plane you told to see it:)
     
  6. Apr 9, 2007 #6

    Othman

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    This months cover of EAA Sport Aviation shows a GlaStar with a good example of the anti-spin strakes on the horizontal stab.

    Also take a look at the wing root leading edge. Are those some sort of flow control devices?
     

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  7. Apr 9, 2007 #7

    orion

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    They're supposed to be some type of VG assembly for high aoa control. I have however never seen any publication describing what they do. Given that there is only one of these (there used to be one at the root of the aileron too) per side, I wonder if they somehow induce early separation thus providing the airplane with a stall burble before actual stall onset. But I don't know - if someone here has a technical paper or description of this assembly, its posting here would be appreciated.
     
  8. Apr 9, 2007 #8

    sanjo

    sanjo

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    Tanks again,

    I will check the next issue ,
    I been watching the site of the planes , and watchig photos I see what are you talking about

    according to the installed in the root , i don't know

    Miguel
     
  9. Aug 1, 2018 #9

    Riggerrob

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    Similar triangular devices are installed - mid span - on Cessna 206 when Soloy converts them to turboprops. They are part of a STOL kit.
    I can understand how they create vortexes to re-energize top skin airflow at high angles of attack.
    I wonder if those vortexes also created invisible “fences” that prevent wing root turbulence (stalled airflow) from growing out to the ailerons.
     
  10. Aug 6, 2018 #10

    wktaylor

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    The X-T37 prototype was lost during spin flight-testing when the nose pitched-up/down and turn rate accelerated until the spin went 'flat'. The pilot successfully ejected and was able to describe the circumstances.

    After serious wind-tunnel testing 'two simple' solutions were derived...

    Cessna's solution was to (a) extend the aft fuselage ~2-ft which placed the stabilizers farther aft for greater moment/authority; and (b) a pair of strakes added were added on opposite sides of the wide/broad/smooth nose to destroy the unsteady vortex sheading which aggravated stall recovery. These mods made the aircraft a stable/reliable/'safe' jet trainer. See attached photos show the XT-37 and the T-37A final configurations.

    Cessna XT-37~prototype in-flight~c1954.jpg Cessna T-37A~Prdctn~With Nose Strakes.png
     
  11. Aug 6, 2018 #11

    Riggerrob

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    The Canadair Tutor jet trainer also added horizontal strokes alongside the nose to stall lift generated by the nose cone.
    RCAF Beechcraft Musketeers also added strokes to the top of their engine Rowling’s to improve spin recovery.
     
  12. Aug 7, 2018 #12

    wktaylor

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    S'more notes ref previous post.

    The T-37 [and Canadair Tutor] phenomena that was occurring is similar to the unsteady airflow about a smokestack... or whip antenna, etc... which any similar symmetrical/smooth/widebody perpendicular to airflow experiences. They experience airflow separation-vortex alternating [oscillating] side-to-side... resulting in a hard-to-break phenomena.

    The added the sharp-edge nose-body strakes on the T-37 [and A-37]... carefully positioned/oriented, based on wind-tunnel tests... cause the vortex to form/break/consistently/symmetrically resulting in predictable airflow pattern... as opposed to the unpredictable/shifting nature of unstable0vortex shedding around a rounded-smooth bodies.

    The nose strakes, combined with the lengthened aft fuselage... which repositioned the stabilizers farther aft and farther away from the wing-stall turbulence... greatly enhanced T-37 control effectiveness in deep stall... making it a relatively docile and reliable jet trainer.

    NOTE.

    Smokestacks, whip antennas, 'fat turbofan engine cowls' etc all benefit from added strakes. The fan-cowl strakes are obvious in photos [and videos!]... but the smokestack and whip-antenna are less obvious.

    Look for the sharp-edge features [typically spiral wrapped-of] on smokestacks which stabilizes the smoke flow out the top... not swirling all-about erratically... and in some cases flowing downward!

    Most modern automotive whip antennas have a peculiar full-length spiral pattern embedded on the whip. That spiral shape is very important for stable airflow separation around the antenna! I have had my car whip-antennas ice-up and the effectiveness of the spiral degrade to the point that the antenna have gone into massive whirl and flutter modes where I thought they might break-off!

    NOTE.
    NASA studied the wing and its effect on stall/spin entry/stability/exit. There are issues there, also. Wing leading edge modifications... which often look like little sharp wedges fastened to the airfoil nose radius at discrete locations... help control stall/flow patterns, affecting deep-stall controllability.
     
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  13. Aug 7, 2018 #13

    jedi

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    Ref old post #7

    I have had a conversation with the designer and they are a vortex generator intended primarily to clean up the flow about the aft fuselage and improve the effectiveness of the vertical stabilizer.

    I did a search for a brief write up about them but no joy at present.
     

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