CRUSADER DUCTED FAN MODEL

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CRUSADER DUCTED FAN MODEL

Home Forums Scratch build CRUSADER DUCTED FAN MODEL

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  • #120808
    John W E
    Participant
      @johnwe

      445387446_769246818362450_5864905328179643304_n (1) (Medium)Been squirreling away; building the Crusader, this accompanies Bluebird which I previously built.

      This Crusader model is near enough 90% balsa wood.   The reason for this is to keep the weight down.   The fan I used is a 90mm diameter ducted fan and the power supply is 22 volt lipo batteries.

      I took her down on the lake for the 2nd time as the first time I tried it – it was a complete disaster.   The centre of gravity of the model was totally out on the 1st occasion.   It would not plane it just buried itself in the water  – plus the scale size rudder which is midships on the model had no affect whatsoever.

      Basically I spent the last 3 weeks drying the model out – shifting the centre of gravity – in other words placing the batteries in the model as far back as possible.

      I literally increased the size of the rudder 4 times.

      This morning, when I tried her on the lake – she did attempt to plane but the centre of gravity is still out and there is not sufficient power within the ducted fan.

      Yet again, that rudder did not make a ha’peth of difference and sadly just still wished to run on a straight line.   Glad my son was with me to catch the model – that is why I only have one pic of her on the water.

      Time for a rethink – and evaluate the model itself – is it worth pursuing financially?

      happy days.   This is exactly what modelling is all about.

       

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      #120809
      Colin Bishop
      Moderator
        @colinbishop34627

        Sounds like a job for Ashley, he’s the ducted fan expert!

        Colin

        #120816
        Len Morris 2
        Participant
          @lenmorris2

          Hi John,  that looks a really nice model and getting it right is half the fun.  Is it worth pursuing financially?,  No.  Is it worth pursuing for the ‘joi de vie’ ?, Absolutely!

          I would try getting your rudder well astern of the floats and COG to give it some leverage, maybe on the end of submerged blade.

          The hydroplanes on my model of Resurgam (submarine) sit exactly on the boats COG and have little effect when diving other than slowing her down.  The rudders at the stern although much smaller are well behind the COG and work very well.

          Len.

          #121319
          John W E
          Participant
            @johnwe

            videoframe_10175hi there, next instalment of the saga I have.    New alloy fan; new speed controller running on 12s batteries (roughly 48 volt) partial success.   I still cannot quite get this model onto the plane even though I altered the front spray defectors – I made them 3 times larger.   I added a rudder to the stern to make it manouverable until Joe Bloggs here steered the model into stationary paddle boats !  I think, you know, that it may be time for a sit back and a ponder about this model.

            Here are a couple of photographs from the video that my son took.   I have to add that I didnt wish to put the video on here because of the blue language.

            crusader at the pondgettin past go

            #121320
            Len Morris 2
            Participant
              @lenmorris2

              Hi John, it’s a splendid model and every time you post you seem to have solved one more problem.  Well done, do stick at it.

              I know nothing about boats like this but looking at the pictures she seems to have plenty of thrust.  At speed she looks bows up and I wonder about a rear trim tab at the stern (possibly on a servo)  and slightly lowered sponsons to help the hull clear.  I think you’re in the region of very small changes making a big difference.

              Len. 🙂

              #121323
              John W E
              Participant
                @johnwe

                hi ya there Len

                Thanks for the encouragement.   After trials this morning at the lake, we had a group meeting to discuss positives and negatives.   I am lucky because in our Club a guy called Don Walkenshaw he is a close friend of Ernie Lazenby – and Son – and they have both built a jet powered Crusader.   So I have been drawing heavily from their knowledge.

                The outcome of our discussion is, as you have suggested, put some form of ‘wedge’ at the rear of the sponsons and also try and increase the width of the centre planing wedge.

                The other thing I have thought of is playing around with the centre of gravity.  Although I have increased the power output by using a new fan, which is developing roughly 13 – 14 lb of thrust at 48 – 50 volt – it is the weight of the batteries I think I am losing out with.  So, I am toying with the idea of repositioning the batteries, so I slightly move the centre of gravity forward a little bit to see if this may improve.   If not, then I will go and start to alter the hull.

                I have increased the models weight in total to 10 lb or thereabouts.    That is all in.   Batteries, motor, speed controller, although the speed controller is capable of handling 150 amps, weighs next to nothing – believe it or not it is actually grams.   Same as with the EDF fan which is all alloy ad it is a JP Hobbies one.   Compared to the ‘placka’ one which was in there originally.

                So, I will let the model dry out – because it does draw in a lot of spray through the inlets – although even 90% does go out the back end with the fan jet – some of the water does end up in the hull.

                John

                 

                #121327
                Colin Bishop
                Moderator
                  @colinbishop34627

                  It must be frustrating trying to find that ‘sweet spot’ where everything comes together to  spark the maximum performance John. There are a lot of variables and the solution can only be found by empirical experiments. Still, that’s all part of the fun.

                  Makes a change from the problems that commonly affect the rest of us scale(ish) types in ensuring that the model doesn’t fall over from lack of stability.

                  Colin

                  #121386
                  ashley needham
                  Participant
                    @ashleyneedham69188

                    John. I too have a crusader and similarly it has been out a couple of times with no success, in fact it was pretty dire.

                    People I have spoken to say it’s a very very difficult thing to get right.

                    One of my issues is probably size, it’s too small at 20 ish inches, it leaves no room for big changes in c of g and so on. Like you I appear to need more power. It is a very wet boat until it starts planing which is the issue for a model. I am in two minds whether to scrap mine or continue…not sure I would prop it as its cheating.

                    One of our ex boating chaps built a water prop one and this ran very well however….??

                    Ashley

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