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Issue 74-The Propeller arrives.

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  • wonwinglo
    • Apr 2004
    • 5410

    #1

    Issue 74-The Propeller arrives.



    The long awaited propeller is a disappointment and the model deserves better,the propeller is far too thick at the hub outward of the blades because no helical pitch or undercamber has been added,as it stands the prop would struggle to even move the aircraft forward ! it is no good pretending that it is right because it falls far short of accuracy,however there is a solution but it will require some effort on the part of the builder,the idea is to get the blades thinner along the undersurface and to do this we will need to scrape in the undercamber taking into account the beautiful twist as any propeller has,think of this as a screw,which it is,the best example is a ships propeller,take a look and see what I mean or if you live close enough to an air museum that has a world war one aeroplane in the collection ( such as Old Warden) then you have your pattern in front of you.

    First of all place a ordinary glass milk bottle into an old towel and tie up the end so the bottle is enclosed inside,now with abandon simply smash the bottle against a concrete surface,now carefully lay out the debris ( what is this man on about,I can hear you saying ! ) and amongst the broken pieces you will see some curved very sharp pieces of the glass,carefully watching your hands ( wear gloves for this) sort out the useful curved sections,next take you propeller and turn it over in a vice with pieces of wood clamped to the sides,carefully and patiently scrape the full length of the blade gradually removing the surplus wood,at the same time observe how the pitch starts to take on a gradual curve working from the root to the tip,you will be emulating exactly the practises of the old propeller manufacturers from days gone by,these were men of great skill and passion for their job,the used hundreds of station templates to achieve the exact shape of the blade,and once this was finished they had to carefully balance the prop in a knife edge jig,just as we do with our flying model propellers.

    Once you are satisfied that the shape is correct,then start to use rough,medium and finally fine garnet grades of finishing paper,we will need to re-varnish the prop using some marine grade clear varnish,apply two coats with a soft brush rubbing down in between coats.

    The decals are stick on affairs,I would have preferred proper waterslide transfers but these are not bad and look good when in place,once on apply some Johnsons Klear,but not varnish as this goes straight through the sticker and looks awful !

    With a bit of extra care your prop will look a vast improvement from the lump supplied,almost forgot to mention that mine had wood that was of two similar a dark lamination,thus these do not show up as well as they should do,there is no answer to this except to carve a new propeller from scratch,this we will be dealing with in a future tutorial when time permits.

    The propeller is another important step towards the completion of the model,how it will bolt onto the short propeller boss will remain to be seen ? probably some type of insert.
  • wonwinglo
    • Apr 2004
    • 5410

    #2
    For those wondering why the use of glass ? well there are few materials as sharp that work on wood,the scraping action removes material at quite an alarming rate,but please be careful and wear some protection,once the glass wears down just discard and use another piece.

    Its an old pattern makers trick from the 1920's so nothing new.

    Comment

    • Guest

      #3
      propeller

      receved my propeller a fortnite a go well streching it a bit to call a lisher shaped bit of ply covered in green lacker a propeller but claening off the green lacker was an inprovment then filling the frunt of the blades flat it could be called a propeller but when i hollowed out the back of the blades it was pulling throue the air all by its self so if you are be hined in receving isses it one plus that can fined out the fullt befor hand and plan how to sort then out after raeding wonwinglo exalent tread

      Comment

      • wonwinglo
        • Apr 2004
        • 5410

        #4
        Hello Roman,glad that you at least managed to get your propeller as many never did ! it was always my intention to make a scratch built prop but for the moment that will have to wait as I have so many more pressing jobs,there are so many faults with that prop that a clean start is really what is needed,a simpler solution rather than carve from a solid block of wood,would be to laminate several pieces together held together at the centre hub with a bolt,before glueing up simply swing the fan of laminates,just like the full size manufacturer would have used,this way a true helical pitch is built into the hub/blades,for beginners to propeller building this is certainly the easiest solution,once properly cured then carving with a long knife blade and finishing with glasspaper would complete the job.

        Laminated scale preops look really good especially when finally varnished as the wood grain really shows through.

        Comment

        • Guest

          #5
          Hi Barry & Roman,

          Sounds like you are having fun with those Props, I was certainly interested to read the glass method for carving props and will cetrainly bear that in mind next time I have a go.

          Like Barry says, I would have been tempted to carve my own but they do take time...worth it though for the end result.

          Surely a quicker way to get a nice prop would be to use one of the ones intended for R/C Models, there are quite a few nice wooden props on the market now which will at least have the right sort of blade profile you are looking for. As it will be fitted to a non flying model you can always do any other modifications necessary without having to worry about shedding blades etc with an engine turning over at high rpm's

          Regards......Mark.

          Comment

          • Guest

            #6
            Hi

            All my bottels had been pot out for resicerling the day be for i carved out the back so used a cured carving cisel taking care of the way the crain ran it whent in to different dirrecshions by hand and then sanding . An ulterative is to use some spring steel fileed or ground to shape is good have use this method to make some small moldings.hold the steel vertcaly and pull to wardes you works like a small plane .

            Comment

            • wonwinglo
              • Apr 2004
              • 5410

              #7
              I like the sharpened spring steel idea,this is an ancient version of the spokeshave tool,to assist in use and avoid nasty cuts bend the ends over and sink into slots cut into a piece of hardwood,the spring steel will take a natural curve adjustable by the amount of spring tension,you could even sharpen up one of those vegetable scrapers,the type with a circle ?

              Comment

              • Guest

                #8
                Varnishing the Prop

                Hi, I've just bought a Hasegawa Fokker DR1 1:8th and saw you have been building something similar. I'm trying to gert some ideas for the varnish of the prop. The prop is a light wood with good grain and I was wondering if you stained it darker before varnishing? What varnish or any other products did you use?

                Thanks in advance!

                Nuvolari

                Comment

                • wonwinglo
                  • Apr 2004
                  • 5410

                  #9
                  You could always use a Blackfriers brand wood stain ? similar products will be available in your country,check out the colour charts in the shop before purchase.

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