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  • Originally posted by Smack View Post
    Somewhere I read about someone who planned to be able to move the mast fore/aft to trim the machine's balance.
    Brian
    Hi,
    I have been working on just such a system. Basically, the mast is anchored to the keel by a second "teeter bolt", so that the mast can pivot fore/aft. All that is then required is a lever to adjust the angle.

    Perhaps either you or Vance could explain what you understand by "partially powered"? It seems my understanding if flawed.

    (On a side-note) I've realised why most gyros are pushers. It's mostly because (I think) designing a side-by-side tractor gyro requires black arts. The pilot/passenger are just too far from the CG. And even if you get the craft balanced for a single occupant, adding an extra 200lbs on a quite large moment arm is going to throw it off whack considerably. Hence the large number of tandem gyros, with the passenger seated on the CG. Gyros which do have side-by-side seating always have the engine in the rear, with the occupants as close to the engine as possible. In this arrangement, the mast now conveniently sits between the engine and the cabin, and any change to cabin occupants affects the CG far less.

    However, I only have eyes for tractors, so I think Tervamaki has the right idea. A tractor with a rear mounted engine. Sure, one has to contend with torsional vibration in the shaft which passes between the pilot and the passenger, but we've known about this issue for decades now, and have solved that problem in a number of ways. The underlying structure would still be the tried and trusted aluminum tubes - just like a pusher. In fact, what I'm suggesting is a pusher with a shaft to the nose for the prop. And a pretty fuselage to go with it.

    Something like the third drawing (nowhere near as good as Tervamaki's...), with stub wings for the fuel (and possibly about 100lbs of lift at cruise).

    So - back on topic - how do you see partially powered rotors working?

    Regards,
    Duncan
    Duncan Meyer
    Brisbane, Australia

    Comment


    • Originally posted by rtfm View Post
      Hi Vance,
      I'm not sure I follow. I thought that a "partially powered rotor" meant powering the rotor up to a point, and then allowing the airstream to complete the task. Is my understanding incorrect? I refer to the initial post in this thread by C. Beatty.

      Regards,
      Duncan


      In my opinion for a patricianly powered rotor to have value some percentage of power needs to be applied to the rotor in flight allowing a shallower angle for the disk requiring less horsepower to go a given speed.

      In my opinion having the rotor outrun the drive negates the value.

      Air is not very efficient way to drive the rotor and doing it mechanically has the potential to do it more efficiently.

      The Predator will fly level with a rotor rpm anywhere between 315 and 400 depending on conditions and load.

      The only time The Predator’s rotor is powered is during pre-rotation.
      Regards, Vance Breese Gyroplane CFI http://www.breeseaircraft.com/

      Comment


      • I'm not sure but I think Vance is agreeing with you.
        I encourage you to keep on keep'n on!! Cannot wait to hear about a test flight. I'm not an expert but I feel it should be able to obtain a faster cursing speed once you get the ratios figured out.
        Resistance is futile…… You will be compiled!
        Cheers,
        John Rountree

        PRA- Director
        PRA- Volunteer Coordinator

        PRA31 - Vice President of S.D. Rotorcraft Club
        http://www.Pra31.org

        U.S. Agent for Aviomania Aircraft... the most stable gyroplane on the market today.
        See: Aviomania USA http://www.AviomaniaUSA.com

        OEM Dealer for MGL Avionics - glass cockpit EFIS for Experimental aircraft Ask about DISCOUNTS for PRA MEMBERS

        Comment


        • Ducan, As I explained,
          1) without device of blades pitch setting in flight, the rotor partially powered will gives no fuel economy.
          2) powered or no, the drag rotor is Total weight * Tan(disc A.o.A ).
          So, in my example I reduced the rotor drag by halve, due to partially powered. This reduced of 5 degrees the rotor thrust angle.
          It is non neglectible on the pitch balance.
          3) If the mast is settible in flight, then ask yourself what effort it requires.

          Attached Files
          Last edited by Jean - Claude; 05-28-2017, 11:52 PM.

          Comment


          • Hi,
            I am not clear in my mind by what you mean by "partially powered". How do you achieve this? How much power do you give the rotor? What RRPM is possible with no help from the wind at all?
            Duncan
            Duncan Meyer
            Brisbane, Australia

            Comment


            • Duncan, As I said in my post #584, the engine add a torque ie 12.7 Hp on the described rotor shaft. Wich reduces the rotor drag of halve. This torque would give about 335 rpm with no wind but during the cruise the rrpm will be 413 rpm instead 353 rpm without torque added
              Last edited by Jean - Claude; 05-29-2017, 11:10 PM.

              Comment


              • A friend of mine (Dick) has found a way to send a percentage (18% if I remember correctly) of the engine power directly to the rotor in flight and in his opinion the gyroplane uses less power for a given cruise speed.

                It looks a little like a differential from an automobile and splits power according to demand.

                This is what I would refer to as a partially powered rotor.

                In my opinion the rotor on a gyroplane operates at some specific rotor rpm in unaccelerated flight to maintain one g and running engine power directly to the rotor doesn't change the rotor rpm required to maintain one g significantly. I feel a partially powered rotor does allow the disc to be operated at less angle for a specific speed and creates less drag. In my opinion this may save as much as 10% on fuel consumption particularly at minimum power required speed.

                I suspect it would be possible with enough power to spin a gyroplane rotor to destruction without any assistance from the wind.
                Last edited by Vance; 05-29-2017, 10:47 AM.
                Regards, Vance Breese Gyroplane CFI http://www.breeseaircraft.com/

                Comment


                • More precisely with the assumptions post #584:
                  With free rotor I find the rotor drag is 112 lbs, and the parasitic drag is 58 lbs
                  And total drag of 170 lbs requires 25 hp from the propeller, ie 35 hp from the engine.

                  Now, if you want to halve the rotor drag, then you must reduce disc A.o.A by half . ie 5.25 degrees.
                  In this conditions, I find you need 413 rpm for the same lift at the same forward speed, and 12.7 hp is required on the rotor shaft.
                  So, the total drag is no longer 114 lbs wich requires 16.7 hp from the propeller, ie 22.6 hp on his shaft (efficiency is a bit better with less thrust) . Added to the 12.7 hp for the rotor, it is 35.3 hp despite a supposedly perfect mechanics.

                  with powered rotor 18%, ie total drag only 149.6 N or rotor drag =149.6 - 58 = 91.6 lbs, this requires disc A.o.A = 8.59 degrees.
                  So, for the same weight at the same forward speed, I find 372 rrpm and a required torque of 82 Nm on the rotor shaft, ie 4.28 hp
                  On the other hand
                  149.6 lbs requires 22 hp from the prop. or 30.8 hp from the engine. Total power gives 4.28 hp + 30.8 = 35.1 hp
                  What else , except a placebo effect?

                  Now, keep the same rrpm as free rotor by a extra blades pitch I find 2.9 hp on the rotor shaft, ie a total 33.7 hp and therefore -4% on fuel consommation.
                  Last edited by Jean - Claude; 05-30-2017, 02:27 AM.

                  Comment


                  • Originally posted by Vance View Post
                    In my opinion the rotor on a gyroplane operates at some specific rotor rpm in unaccelerated flight to maintain one g and running engine power directly to the rotor doesn't change the rotor rpm required to maintain one g significantly
                    The tilt back of the disc at the same rpm increases the A.o.A of the blades and consequently increases their lift
                    So, less tilt back requires more rpm for the same lift.

                    Comment


                    • Originally posted by Vance View Post
                      In my opinion the rotor on a gyroplane operates at some specific rotor rpm in unaccelerated flight to maintain one g and running engine power directly to the rotor doesn't change the rotor rpm required to maintain one g significantly

                      Originally posted by Jean - Claude View Post

                      The tilt back of the disc at the same rpm increases the A.o.A of the blades and consequently increases their lift
                      So, less tilt back requires more rpm for the same lift.
                      Thank you for your participation in this thread Jean-Claude.

                      I have expressed my opinions based on my observations Jean-Claude and have not done extensive testing.I have not flown a gyroplane with a partially powered rotor.

                      The Predator weighs around 1,100 pounds solo with ten gallons of fuel on board.She has thirty foot eight and a half inch chord Sport Copter blades.

                      It is my observation flying The Predator that the rotor rpm goes from around 320 rrpm at 30kts indicated air speed to around 360 rrpm at 90kts indicated air speed.It has been a long time since I checked it so my numbers may be a little off.

                      I have not tried to measure the rotor disk angle in flight.A rough estimate of the rotor head angle would be around 20 degrees at 30kts and around 5 degrees at 90kts. She is quite nose high at 30kts indicated air speed and a little nose low at 90kts indicated air speed.

                      I don’t know if this observed performance fits your calculations.Thirteen percent rotor rpm change fits my use of the phrase “not significantly” for twenty five percent of the rotor head angle Jean-Claude.

                      I feel comfortable postulating based on observed performance that the rotor system has a third of the drag at 90kts as it does at 30kts.

                      In my opinion the wind is not a very efficient way to drive the rotor and finding a more efficient way would lead to lower power required to fly at a given air speed.

                      A partially powered rotor is sufficiently complex to be something I would not try.

                      My friend Dick feels a partially powered rotor has value.
                      Last edited by Vance; 05-30-2017, 08:30 AM.
                      Regards, Vance Breese Gyroplane CFI http://www.breeseaircraft.com/

                      Comment


                      • These pictures were supposed to be in the last post.
                        Last edited by Vance; 05-30-2017, 08:30 AM.
                        Regards, Vance Breese Gyroplane CFI http://www.breeseaircraft.com/

                        Comment


                        • Originally posted by Vance View Post
                          ]I don’t know if this observed performance fits your calculations.Thirteen percent rotor rpm change fits my use of the phrase “not significantly” for twenty five percent of the rotor head angle Jean-Claude
                          I even suspect that your rrpm would change much less if your blades were rigorously rigid in torsion.
                          It appears from your numbers that the pitch of the blades to tip decreases almost 1 degree between 30 and 90 kts
                          However, the correlation you are making here is irrelevant for know the rpm increase due to the add of torque on the shaft, in forward flight. And you can be sure that adding torque on the shaft increases the rrpm, when the lift is not changed. Unfortunately the benefit disappears, because the losses by blade friction in air incresases as rrpm^3,
                          improve appears only if you increase the pitch setting of blade for keep the same rrpm despite the torque added .
                          Note that it may be sometimes by the elastic torsion of the blades without the designer is aware of this.

                          My theorical results fits with the best documented measurements I read: Naca report 475 and 515
                          So, rpm, drag, longitudinal and lateral flapping, calculated from only blades shape, local pitch setting at rest, and elastic twisting, gives at 45 km/h
                          141.4 rpm instead 141.1rpm measured
                          27.1° disc A.o.A instead 26° measured
                          1.3° longitudinal flapping instead 1.1° measured
                          2.6° lateral flapping instead 2.6° measured
                          Last edited by Jean - Claude; 05-31-2017, 10:00 AM.

                          Comment


                          • Gyroplane rotor RPM stays nearly constant with partial power.

                            As mechanical drive is applied to the rotor, its disc angle of attack decreases so as keep total rotor power constant. A reduced rotor disc angle of attack extracts less power from the slipstream. Dick DeGraw’'s gyros fly with nearly a flat rotor disc in the upper speed ranges.

                            That said, partial power to the rotor is not simple. It must be via a soft coupling to the engine; a hard coupling would render a gyro nearly unflyable as a result of the throttle/yaw coupling.

                            Comment


                            • Originally posted by C. Beaty View Post
                              Gyroplane rotor RPM stays nearly constant with partial power.
                              Certainly. But whatever the partially power chosen, this little difference of rpm produced by the torque mecanically applyed on the rotor shaft absorbs all this extra-power.
                              Improving is true only if rpm keep unchanged, by correcting on the blades pitch setting. As probably makes by Dick DeGraw's gyros.

                              Last edited by Jean - Claude; 06-26-2017, 12:41 AM.

                              Comment


                              • Good post!!!
                                Thank you all for sharing
                                Resistance is futile…… You will be compiled!
                                Cheers,
                                John Rountree

                                PRA- Director
                                PRA- Volunteer Coordinator

                                PRA31 - Vice President of S.D. Rotorcraft Club
                                http://www.Pra31.org

                                U.S. Agent for Aviomania Aircraft... the most stable gyroplane on the market today.
                                See: Aviomania USA http://www.AviomaniaUSA.com

                                OEM Dealer for MGL Avionics - glass cockpit EFIS for Experimental aircraft Ask about DISCOUNTS for PRA MEMBERS

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