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Gyro-Tech US dealer and Modified Airfoil blades

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  • Gyro-Tech US dealer and Modified Airfoil blades

    In asking about a US distributor in another thread I was able to get ahold of Carlos at Helicopters International in Florida. What a nice gentleman. He happens to have a new set of 23' GT blades and hub bar that we are in discussion about currently. But I wanted to consult the Forum before making any big decisions of this importance.

    They are the "Modified Airfoil" design, which has a slightly smaller chord than their standard 8H12 blades (GT recommended the larger Standard blades for my Bee). When I went to GT's site to refresh my memory of the differences between the two blades it appears the Modified airfoil blades have been removed from the site.

    When I first learned of Gyro-Tech I thought the smaller Modified shape would have been best suited, since I don't see many light single-place ships slinging 8-1/4" chord blades. But GT recommended otherwise when assessing my needs.

    Nonetheless, I may get a great deal on the other style since these are already in stock in Florida, and apparently not being pushed anymore by GT if their absence on their site is any indication. So now I have to consider what performance hit there might be as opposed to the standard blades... if there is a trailing edge reflex that would make manual pre-rotation more difficult (a-la Dragon Wings), and if there would be any negatives to using this blade for reasons I don't yet understand as a newbie.

    If the fine folks here have an opinion I would be grateful for any feedback before proceeding further. Thanks in advance.

    Brian Jackson

  • #2
    Brian I don't have a clue,try to get in touch with Chuck beaty he will know.
    Best Regards,
    Eddie Sigman,Polvadera,nm
    (575) 835-4921

    Comment


    • #3
      Well, let’s see, Brian:

      The tip speed of a rotor is roughly equal to 66 x square root of blade loading.

      The rotor limited top speed of a rotor is roughly equal to 35% of tip speed.

      The power consumed by profile drag of a rotor varies as the cube of tip speed.

      So: Blade area = chord x diameter = 8.25/12 x 22 = 15.125 square feet (22 ft dia).

      Therefore, if AUW =500 lbs, tip speed = 66 x (500/15.125)^0.5 = 379 ft/sec = 258 mph and 35% of that = 90 mph. Horrors; top speed limited to 90 mph.

      Drag will be substantially less than it would be with 7 inch blades if pitched appropriately.

      And of course, there are other important considerations; coning angle, rotor shake, etc, etc.

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      • #4
        Brian,

        I was able to pull up a cached page of the Modified blades and screen capture it if it helps.

        Comment


        • #5
          Interesting their page says the rotorblades have a maximum speed to be flown is between 120kph-130kph (75mph-81mph).

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          • #6
            It should raise alarm bells when a blade manufacturer says “modified” 8H12 airfoil. In general, modifying a standard NACA airfoil degrades performance.
            For instance, removing the TE reflex from an 8H12 slightly increases maximum lift before stall but the resulting negative pitching moment is dangerous.
            Last edited by C. Beaty; 07-27-2018, 11:20 PM.

            Comment


            • #7
              Originally posted by C. Beaty View Post
              [SIZE=3]
              The power consumed by profile drag of a rotor varies as the cube of tip speed.
              Drag will be substantially less than it would be with 7 inch blades if pitched appropriately.
              Yes Chuck, the power consumed by the profile of a rotor varies with the cube of tip speed. But the power consumed by the profile of a rotor blade also varies with the area blades, So a 7" rope gives almost the same drag as 8.5", despite higher rrpm.
              Last edited by Jean Claude; 07-28-2018, 08:00 AM.

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              • #8
                You’re correct, JC. I should have said; “an 8.25” blade has slightly less drag than a 7” blade.”

                If my arithmetic is correct, the 8.25” blade has 8.6% less profile drag than the 7” blade, all else equal.






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                • #9
                  It appears that Gyro Tech is no longer making the smaller gyro blades just the larger 8H12 with the 8 1/2" cord.
                  Best Regards,
                  Eddie Sigman,Polvadera,nm
                  (575) 835-4921

                  Comment


                  • #10



                    Here you go in a bigger form
                    I'm a gyro Dude now! Bensen FTW

                    FRANK

                    Comment


                    • #11
                      Frank go look at the gyrotech web site again it stills shows pictures of the modified blade,but when you try to open that

                      page it says that they are no longer available. your information is out of date,I was there 10:00 PM MST. tonight.
                      Best Regards,
                      Eddie Sigman,Polvadera,nm
                      (575) 835-4921

                      Comment


                      • #12
                        All Frank did was re-post my screen capture but in bigger form.

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                        • #13
                          Originally posted by C. Beaty View Post
                          You’re correct, JC. I should have said; “an 8.25” blade has slightly less drag than a 7” blade.”

                          If my arithmetic is correct, the 8.25” blade has 8.6% less profile drag than the 7” blade, all else equal.
                          Yes, Chuck
                          And certainly even less difference, if we take into account the tip losses when the chord increases

                          Comment


                          • #14
                            Thank you all very much for the enlightening responses. It's always a welcome education. While I'm digesting all of this, may I ask if it's worth considering these other blades (assuming there's a substantial cost savings) as opposed to just buying GT's current offering?

                            Comment


                            • #15
                              Brian,

                              Your're not likely to get an educated response as I've not heard of anyone who has flown the modified blades. We don't even know in detail what the "modified airfoil" is, perhaps you could find out from the dealer or manufacturer.

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