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    #46
    Originally posted by Babylon5
    Sorry I disagree, Although the taper thrust tube help to force the air at higher velocity allowing the plane to fly the plane at higher speed due to increase in dynamic thrust at "level flight." It won't help in the speed if you are flying in a tight circle .


    However from the physics point , the tapered cone constriction will cause a back pressure to built up inside the EDF chamber, causing the blade to stall. This will reduce the static thrust.




    Take a look at the link of the twin GWS50mmEDF setup, there is no thrust tube at the end of the 50mm EDF just the cone attached to the end of the motor and the intake ring


    See my other thread link thread #30


    Here is the extract from the thread 30

    "Hi Jeff, coming back to this topic. The cut down 3 blade offer some advantage and some disadvantage. According to my observation, the speed of the Jet on EDF do not always rely on thrust although most of the time it does.


    1.)more thrust=higher flying speed--->generally true

    2.)More thrust does not necessary translated to higher flying speed.
    Some multiblade EDF are design at lower rpm like the Super Flying Model is spec at 25,000rpm max. To improve the jet level flying speed in some practice, a hollow taper cone is delibrately place at the exhause to reduce or act to constrict and force the air out at a higher speed thereby increasing the jet flying speed. (There is a limit you can reduce the exhause opening and improve the level flying speed before flowback air pressure reduces efficiencies . )
    The tail cone /tube do not increase the static thrust but actually decreases static thrust..
    In this case you have the following:
    When constricting the exhause air opening....
    Lower Thrust=higher exit air speed=faster flying speed

    This is a situation where not all the thrust develop by the EDF is translated to higher level flying speed."

    I have mentioned this phenomenon many times in my other thread.
    I don't think I contradict myself.

    Cheers
    Like I mentioned before, the exhaust duct AKA thrust tube is not designed to increase thrust or velocity. It's simple designed to restore the lost efflux velocity. I mentioned before that the useful work is only produced after the air leaves the duct, so for nacelled duct fan, like those top mounted DF units or scale airliner designs, that do not have a thrust tube, the air exits right after the nacelles and work is directly being produced, and does not have the chance to expand and slow down like those jetfighter designs. As such these units only need a straight fairing and only start to taper off right after the point where the fan air leaves the shroud. Do not get confused between these 2 kinds of DF configurations.

    Comment


      #47
      Well... after reading all the expert view.. I guess only less than 10% of us (hope I am wrong) understand it or I should said able to translate it to practical use of those info into our EDF model world. I do believe theory and practical is a very different world. Every plane will produce very diff result with the same power plant.

      Like Votices said, why not help by list out what are the test you have done or the setup you have done and comments on the result.

      Example:
      Test done so all of us are having some idea about the power plant:
      Fan spec & $ / Motor & Spec & $ / ESC / Battery / Amp / Watt / static thrust if you have the no.

      Real setup:
      Plane Model/Brand / Fan / Motor / ESC / Bettry / Comments on setup like ROG ok, light hand launch etc..

      This way I guess we can relate better.

      Maybe Baby5 you can start posting some of your best setup picture so we can share it.

      For me, I realy like to see your setup of very low Amp yet very good thrust that you have done. I remember you have done one that is somewhere around 11A?? but yield a very good thrust. that will be the dream of EDF if I can have that same setup.

      Comment


        #48
        Hi DT8666,
        I am new in EDF world and also one who do not quite understand babylon's theory sometimes.
        For example those small EDF set up, by cutting off some blades can lower the amp draw(I agreed) and will increase the top speed and perforamce of the plane.(??? )
        I was thinking why can't we upgrade the motor to a suitable one instead of cutting off those blades?
        Anyway, I really appreciate all his effort and would love to see how his EDF jet perforamce.

        No doubt we have to learn the theory of how things work but for someone like me I would still prefer to know the set up of the plane which someone had infact tested and flew before. Therefore I like Votices idea of posting suitable edf set up for different kind of plane just for a quick reference.

        Babylon, may I know where are you flying your EDF jet or do you have any video to share with us? I would really love to see it.

        I am really keen in getting into some scale edf jet with proper ducting rather than those DIY or outboard edf set up jet someday (after seeing someone flew his big EDF jet awhile ago.)

        Comment


          #49
          The differences between theory and practical is only in the actual figures you are getting, due to losses here and there. As far as in the world of engineering and science, theory is where things get started anyway and designers just have to compensate for the losses in the practical world.

          My approach is not to really go into figures which can be too much for a hassle for hobbyist, but knowing the theories, at least people like us who experiments by trial and error ,we will know which direction to do things. If not we might be spending hundreds and thousands of dollars just to yield the little or no gains.

          Comment


            #50
            I promised that I wouldn't comment on his setup but for info, I maidened the Multiplex Twister with the stock fan and motor. The thrust is nowhere 1:1 ( I don't think it's even 1:0.5) but what the heck, I asked my kakis to launch it. It flew ok after gaining airspeed. It's slow compared to normal pusher or puller planes.

            Comment


              #51
              Originally posted by joe yap
              The differences between theory and practical is only in the actual figures you are getting, due to losses here and there. As far as in the world of engineering and science, theory is where things get started anyway and designers just have to compensate for the losses in the practical world.

              My approach is not to really go into figures which can be too much for a hassle for hobbyist, but knowing the theories, at least people like us who experiments by trial and error ,we will know which direction to do things. If not we might be spending hundreds and thousands of dollars just to yield the little or no gains.
              Fully agreed wiht you Joe. Knowing the theory sure help us to prepare better. Just it is too complicated sometime and most (may be) do not have the time and expertise to experience it. So the end result may cause the guy to spend tons of dollar to get it fix or may make the guy feel sad and say thats all and QUIT!

              The maybe expert here can help by putting up those end result and sample setup so we can just follow. That will sure save most of us some $$ and time and make the EDF highly possible instead of restricted to a few.

              Good work guys. Only if we can start the next step of posting the workable setup so all can follow/copy and improve further.

              Comment


                #52
                Originally posted by Alvin Roger
                Hi DT8666,
                I am new in EDF world and also one who do not quite understand babylon's theory sometimes.
                For example those small EDF set up, by cutting off some blades can lower the amp draw(I agreed) and will increase the top speed and perforamce of the plane.(??? )
                I was thinking why can't we upgrade the motor to a suitable one instead of cutting off those blades?
                Anyway, I really appreciate all his effort and would love to see how his EDF jet perforamce.

                No doubt we have to learn the theory of how things work but for someone like me I would still prefer to know the set up of the plane which someone had infact tested and flew before. Therefore I like Votices idea of posting suitable edf set up for different kind of plane just for a quick reference.

                Babylon, may I know where are you flying your EDF jet or do you have any video to share with us? I would really love to see it.

                I am really keen in getting into some scale edf jet with proper ducting rather than those DIY or outboard edf set up jet someday (after seeing someone flew his big EDF jet awhile ago.)
                Hi Alwin, agree you can upgrade or change to a better motor for better performance ,other Kv , more cells arrangements and other variables. ...but each new motor could set you as high a few hundred bucks while a propeller or impeller is only a few bucks. Purely from economics sense I would chose the later.

                Performance = higher power or more efficient or faster flying speed or longer flying time . Agree with Joe Yap that we look at all overall outcome , debate on issues and learn from each other. Most of the time we rely on theory and on text book but at times we got to think out of the box. .. be creative.


                It is up to the user to choose which performance is most important in his setup.


                Reducing the number of balde count and able to make the plane fly faster is well documented on the internet , with videos data and people who have experiment with.

                Why the lesser blade arrangement could propel the plane faster is subjected to debate.
                I have a teory but am not saying anything until I find out more.

                I did pose a video of the micro jet that misses the tree ...well almost . That plane uses a 3 blade arrangement. It is very short due to limited length allow for attachment. I use a camera so the video is not so clear.
                see link http://www.daddyhobby.com/forum/show...3&page=3&pp=15

                Thread 39


                I fly at Jurong West but may go elsewhere to fly where there is a proper runway. I am planning another twin EDF experimental plane .

                More next time.


                Cheers

                Comment


                  #53
                  Originally posted by $h@d0w
                  I promised that I wouldn't comment on his setup but for info, I maidened the Multiplex Twister with the stock fan and motor. The thrust is nowhere 1:1 ( I don't think it's even 1:0.5) but what the heck, I asked my kakis to launch it. It flew ok after gaining airspeed. It's slow compared to normal pusher or puller planes.
                  Hi Shadow, congratulation on your maiden flight of the twister.
                  By the way this evening , two twister flying had a mid air collision during low level formation flying. One twister went down with a flat spin. Surprising the twister that went down did not have any visible damage.
                  Multiplex model are one tough cookie.


                  Cheers

                  Comment


                    #54
                    Thanks for the link. Hope you enjoy your testing.

                    Originally posted by Babylon5
                    Hi Alwin, agree you can upgrade or change to a better motor for better performance ,other Kv , more cells arrangements and other variables. ...but each new motor could set you as high a few hundred bucks while a propeller or impeller is only a few bucks. Purely from economics sense I would chose the later.

                    Performance = higher power or more efficient or faster flying speed or longer flying time . Agree with Joe Yap that we look at all overall outcome , debate on issues and learn from each other. Most of the time we rely on theory and on text book but at times we got to think out of the box. .. be creative.


                    It is up to the user to choose which performance is most important in his setup.


                    Reducing the number of balde count and able to make the plane fly faster is well documented on the internet , with videos data and people who have experiment with.

                    Why the lesser blade arrangement could propel the plane faster is subjected to debate.
                    I have a teory but am not saying anything until I find out more.

                    I did pose a video of the micro jet that misses the tree ...well almost . That plane uses a 3 blade arrangement. It is very short due to limited length allow for attachment. I use a camera so the video is not so clear.
                    see link http://www.daddyhobby.com/forum/show...3&page=3&pp=15

                    Thread 39


                    I fly at Jurong West but may go elsewhere to fly where there is a proper runway. I am planning another twin EDF experimental plane .

                    More next time.


                    Cheers

                    Comment


                      #55
                      Originally posted by Babylon5
                      I fly at Jurong West but may go elsewhere to fly where there is a proper runway. I am planning another twin EDF experimental plane .

                      Cheers
                      Sorry to ask this, does belly landing plane need a runway for it? I thought it is hand launch and is better to land on grass?

                      Comment


                        #56
                        Originally posted by Babylon5


                        Reducing the number of balde count and able to make the plane fly faster is well documented on the internet , with videos data and people who have experiment with.

                        Why the lesser blade arrangement could propel the plane faster is subjected to debate.
                        I have a teory but am not saying anything until I find out more.

                        Cheers
                        This kind of thing can happen mainly because the motor has been overloaded in the first place. If your motor is not overloaded and you starts chopping some blades off, you'll reduce the amp draw but at the same time, you'll also reduce the work output of the fan drastically. By reducing the blade counts, you'll be reducing the power needed to drive the rotor and so the RPM will be allowed to picked up. Thus, the airplane top speed will be increased. However, static thrust can drop drastically if more blades are being removed further. If enough static thrust is lost in the process and unable to cope with the airframe drag, the top speed of the airplane will also be compromised.

                        For every individual design of the motor, there is a point where the maximum ELECTRICAL effieciency occurs at a certain wattage ( power). Beyond that, the motor can draws tonnes of current and yet only produce much lesser work, which most of the energy has turned into heat. The motor can be considered as overloaded and the rotor RPM will be restricted. So, in order to get the best of your setup, matching the load on your motor is vey important.

                        Other than reducing the number of fan blades, you can also try using fan with lower pitch to reduce the current draw.

                        Be creative and think out of the box in your designs, but remember the Law of Physics never lies, unless proven otherwise.

                        Comment


                          #57
                          now i know why my o lvl teachers said it is always safe to follow the ten year series no mater what sort of subject or matter your working on... hahahhaa
                          DUCT DUCT DUCT GO!!!!

                          Comment


                            #58
                            Originally posted by joe yap
                            This kind of thing can happen mainly because the motor has been overloaded in the first place. If your motor is not overloaded and you starts chopping some blades off, you'll reduce the amp draw but at the same time, you'll also reduce the work output of the fan drastically. By reducing the blade counts, you'll be reducing the power needed to drive the rotor and so the RPM will be allowed to picked up. Thus, the airplane top speed will be increased. However, static thrust can drop drastically if more blades are being removed further. If enough static thrust is lost in the process and unable to cope with the airframe drag, the top speed of the airplane will also be compromised.

                            For every individual design of the motor, there is a point where the maximum ELECTRICAL effieciency occurs at a certain wattage ( power). Beyond that, the motor can draws tonnes of current and yet only produce much lesser work, which most of the energy has turned into heat. The motor can be considered as overloaded and the rotor RPM will be restricted. So, in order to get the best of your setup, matching the load on your motor is vey important.

                            Other than reducing the number of fan blades, you can also try using fan with lower pitch to reduce the current draw.

                            Be creative and think out of the box in your designs, but remember the Law of Physics never lies, unless proven otherwise.
                            Hi Joe with regards to number of fan blades , maybe interesting to look at the pictures and the blade arrangement of this electric ducted fan.
                            see link.



                            There are some measurement data in German. Maybe of intetest to look into this as well.


                            BTW their fastest EDF plane setup has the EDF top mounted.


                            I am still wishing that someone will present this EDF complete with the plane for my birthday....just kidding


                            Cheers and happy readings

                            Comment


                              #59
                              Originally posted by Alvin Roger
                              Sorry to ask this, does belly landing plane need a runway for it? I thought it is hand launch and is better to land on grass?
                              Sorry, I miss out my last posting on this . That experimental plane has complete fix landing gear. Grass landing especially tall grass is very bad for the servo that controls the nose gear, not to mention potential nose over situation. The grass terrain at Jurong west is not exactly short and even.

                              Cheers and I hope to have answer your qery.

                              Comment


                                #60
                                Not surprising at all. I have even seen a 2 bladed fan design. You can also see that the fan blades are much broader to absorb the power of the motor, unlike the skinny GWS fans.

                                Don't get confused again. In the previous issue, we are discussing cutting down on the number of blades alone, and assuming that no change in pitch and blade designs. In your link, you are looking at purposefully designed fans designed for it's purpose. You must understand what you are comparing and do so fairly.

                                All these goes back what we have said before, the fan and the motor must match. Only when the motor is loaded to it's most efficient way, and the fan is producing the desired thrust and velocity, you'll get the best out of the whole setup.

                                Top mounted DF has nothing to do with speed directly. It does not impede you top speed of the airframe when flown in level flight or low alpha. The only problem comes in during high-alpha manouevers when the fuselage and wings blankets off the air into the inlet.

                                Comment

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