Quiz time

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    • #11168
      Steven SnyderSteven Snyder
      Participant

        Question 1: For a coordinated 30º banked turn, for any glider, if flown at the minimum SINK SPEED for the angle of bank, how much does the glider SINK RATE increase over the level flight minimum SINK RATE?

        A. 8% more than the level flight minimum sink rate

        B. 16% more than the level flight minimum sink rate

        C. 24% more than the level flight minimum sink rate

        D. 32% more than the level flight minimum sink rate

        E. 40% more than the level flight minimum sink rate

        F. I do not have a clue

      • #11169
        Greg PalmerGreg Palmer
        Participant

          Greg Palmer


          BSAT LLC

          847-922-1234

        • #11170
          Steven SnyderSteven Snyder
          Participant

            Greg, your comments are missing. Try again. Might be your signature.

            Steven Snyder224-628-2871
          • #11171
            ANDRZEJ CHICEWICZANDRZEJ CHICEWICZ
            Participant
              answer is D:32%
              ANDY

              On Sunday, September 26, 2021, 09:12:46 AM CDT, Sky Soaring <webmaster@skysoaring.com> wrote:

            • #11173
              Steven SnyderSteven Snyder
              Participant

                Question 2: For a coordinated 30ºbanked turn, for any glider, by what percentage does the minimum SINK SPEED increase over the level flight minimum SINK SPEED?

                A. 0% the minimum sink speed is identical to the level flight minimum sink speed

                B. 3% more than the level flight minimum sink speed

                C. 7.5% more than the level flight minimum sink speed

                D. 10% more than the level flight minimum sink speed

                E. 15% more than the level flight minimum sink speed

                F. I do not have a clue

              • #11174
                Brendan StewartBrendan Stewart
                Participant

                  This is fun!

                  For #1, my vote is B. 16%.  

                  My reasoning:  In a 30% bank, load factor is 1.154Gs, or just about 16% more than the weight of the glider in level flight. As bank angle increases, the lift vector is shifted into the turn and away from direct opposition to gravity. Assuming a constant angle of attack through the turn, effective weight exceeds total lift by 16%, which would subsequently increase the sink *rate* by about 16%,

                  For #2, my vote is C. 7.5%.

                  My Reasoning: We know that stall speed increases proportionally to the square root of the load factor. As far as I can tell, this effect should be universal for ALL performance airspeeds (excluding structural limitations like Va, Vra, Vt, Vw, and Vne) Since we’re in a 30 degree bank, we know our load factor should be 1.16, and the square root of 1.16 is 1.077, or just about 7.5% increase over the reference airspeed in the POH.

                  So, in practice a glider with a minimum skink speed of 40kts at max gross should expect to use 43kts for a 30 degree banked turn.

                  How’d I do? 🙂

                • #11175
                  Dennis BurkeDennis Burke
                  Participant

                    For #1, a 16% increase in Sink Rate (=ft/min) seems high, for just a gentle 30deg bank.

                    For #2, stall speed increase by square root of load increase (ie, a verticle weight increase by banking)  would be ~7.5%.  The polar moves right, yes?

                  • #11176
                    Steven SnyderSteven Snyder
                    Participant

                      Some good answers so far.

                      Question 3: For a coordinated 45ºbanked turn, for any glider, if flown at the minimum SINK SPEED for the angle of bank, how much does the glider SINK RATE increase over the level flight minimum SINK RATE?

                      A. 9% more than the level flight minimum sink rate

                      B. 19% more than the level flight minimum sink rate

                      C. 29% more than the level flight minimum sink rate

                      D. 48% more than the level flight minimum sink rate

                      E. 68% more than the level flight minimum sink rate

                      F. I do not have a clue

                    • #11177
                      ANDRZEJ CHICEWICZANDRZEJ CHICEWICZ
                      Participant

                        answer is :68%

                        ANDY

                        On Monday, September 27, 2021, 04:45:06 PM CDT, Sky Soaring <webmaster@skysoaring.com> wrote:

                      • #11178
                        Laurentiu NicolaeLaurentiu Nicolae
                        Participant
                          On Mon, Sep 27, 2021, 4:44 PM Sky Soaring <webmaster@skysoaring.com> wrote:
                        • #11184
                          Brendan StewartBrendan Stewart
                          Participant

                            I’ll go with B. 19%

                          • #11210
                            Steven SnyderSteven Snyder
                            Participant

                              Question 4: For a coordinated 45ºbanked turn, for any glider, by what percentage does the minimum SINK SPEED increase over the level flight minimum SINK SPEED?

                              A. 0% the minimum speed is identical to the level flight minimum sink speed

                              B. 4% more than the level flight minimum sink speed

                              C. 9% more than the level fl ight minimum sink speed

                              D. 19% more than the level fl ight minimum sink speed

                              E. 25% more than the level flight minimum sink speed

                              F. I do not have a clue

                            • #11211
                              Karl LandlKarl Landl
                              Participant
                                “D”

                                On Sunday, October 3, 2021, 05:30:33 PM CDT, Sky Soaring <webmaster@skysoaring.com> wrote:

                              • #11212
                                ANDRZEJ CHICEWICZANDRZEJ CHICEWICZ
                                Participant
                                  For question 4.
                                  answer is D: 19%
                                  ANDY

                                  On Sunday, October 3, 2021, 05:30:46 PM CDT, Sky Soaring <webmaster@skysoaring.com> wrote:

                                • #11213
                                  Steven SnyderSteven Snyder
                                  Participant

                                    Last but not least.

                                    Question 5: You need to reverse direction and you want to conserve energy … or, you are in a rope break scenario shortly after takeoff (above 200 ft AGL) and you have decided it is safe to make an approximately 210ºturn and return to the runway, what angle of bank and airspeed will lose the least amount of altitude for ALL gliders?

                                    A. 20º of bank and level flight minimum sink speed

                                    B. 30º of bank and level flight minimum sink speed plus 5%

                                    C. 35º of bank and level flight minimum sink speed plus 7.5%

                                    D. 45º of bank and level flight minimum sink speed plus 18.9%

                                    E. 60º of bank and level flight minimum sink speed plus 20%

                                    F. I do not have a clue

                                  • #11215
                                    Brendan StewartBrendan Stewart
                                    Participant

                                      Hmmm. I seem to recall a relatively steep bank angle during rope break practice. I’ll go with “D”

                                      It seems worth considering that rate and radius of turn factor into the equation. In a shallow turn, your sink *rate* is lower, but distance travelled is longer as is time to complete the turn. In a steep turn, the opposite is true: Sink rate is up, distance travelled is smaller and duration of turn is shorter.

                                      There’s a peak to this bell curve somewhere… 🙂

                                    • #11216
                                      Dennis BurkeDennis Burke
                                      Participant

                                        2 or 3 important Articles by Steve Platt, in Soaring Magazine, will clarify your analysis, radius, speed, downwind energy, etc:   “Turning Flight Performance”, April 2020, “Turning Efficiency”, Sept 2021,  “Rope Break”,  March 2019.

                                      • #11217
                                        Karl LandlKarl Landl
                                        Participant

                                          “D” of course because a 45º bank is always the most efficient one. Btw: I was at the field this morning to do some work on my trailer and upon arriving at the entrance the gate was wide open! This was at 8:32. I left at 11:45 with no one else showing up.

                                          Karl

                                          On Wednesday, October 6, 2021, 12:13:32 PM CDT, Sky Soaring <webmaster@skysoaring.com> wrote:

                                        • #11218
                                          ANDRZEJ CHICEWICZANDRZEJ CHICEWICZ
                                          Participant
                                            ANSWER IS D:45 deg of bank and + 18.9% minimum speed sink

                                            On Tuesday, October 5, 2021, 03:12:34 PM CDT, Sky Soaring <webmaster@skysoaring.com> wrote:

                                          • #11219
                                            Steven SnyderSteven Snyder
                                            Participant

                                              You do read your Soaring Magazine, I hope?

                                              September issue. Answers are: Question 1: C; Question 2: C; Question 3: E; Question 4: D.

                                              Answer Question 5: D. Th e optimum bank angle and airspeed to lose the least amount of energy (altitude) in a completed turn for ALL gliders is 45º of bank and an airspeed equal to the level flight minimum sink speed (for the current operating weight) plus 18.9% ( approximately 20%).

                                              If you don’t still have your copy you can read it here. https://magazine.ssa.org/viewer?y=2021&m=9&p=38&o=0&q=

                                              Log in required.

                                              Stay tuned for more brain teasers to come.

                                              Steve

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