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T.6296 hub and replica propeller

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  • #31
    Yesterday I shaped the underside of the patterns up to section BB. The shape is slightly oversized, and approximate at this stage. In the first photo you can see where I checked the blade shape and angle against the “extra” profile. It is very flat. Most RAF propellers have a curved underside until Section CC or DD. The T.6296 is unusual from the point of view that it seems to transition from a symmetrical section at Section AA to a flat underside approximately 2” outboard of Section AA. Although it does not seem possible, I was able to achieve this without any sharp bends or awkward transitions. It will be interesting to check the complete T.6296 to make sure that this is correct. I am very confident that my patterns will be very close. Unfortunately I have not been able to locate any photographs taken at the time. I suspect they are on an iPhone 4, which crashed. I have not been able to retrieve any data from this phone, but I will try to at least salvage the photos I took of the T.6296 blade.

    As a result of the lost data I do not have a record of the shapes of the top surface of the blade at Section BB. Starting from Section CC to the tip I have quite good measurements. The blade at Section BB was difficult to measure, so I was relying on photographic evidence. Still, I am very confident that I will be able to determine the shape of the blade out to Section CC. I will of course check these shapes and dimensions against the complete T.6296 at Narromine when I am able to get up there.

    The second photo shows the underside of the blade out to Section BB. The third photo shows how close I was able to get to pencil line on top of lamination 8, when I smoothed the laminations using information I had used to work upwards from laminations 1 through to 8. I am happy with the proximity to the pencil line. There is only a 3mm or so gap, which is about the amount I expect the original boss would have shrunk over the last century, hence the discrepancy. Closer to the boss the margin is much larger. I suspect I need to do a lot more sanding and shaping to obtain the correct shape. The fourth photo shows a quick check of the incidence at Section BB. The underside is slightly more shallow angle, which is ok because I will be able to rectify this with further sanding. Also, particularly towards the boss the leading edge radius tends to be larger than the trailing edge radius. As a result, the underside of the blade, even if it is flat tends to be at a shallower angle than the angle of incidence. The centreline is determined by the centres of the leading and trailing edge radii, not necessarily by the angle indicated by the underside of the propeller. When the leading edge radius is the same as the trailing edge radius, the flat underside is equivalent to the angle of incidence. It can be misleading if the principals used when designing these propellers are not known.
    Attached Files
    Last edited by Garuda; 03-01-2021, 08:31 AM. Reason: Grammatical error

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    • #32
      £550 now, bargain!!

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      • #33
        Originally posted by JR44 View Post
        £550 now, bargain!!
        For me the bargain might start at 60 GBP and go down from there.

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        • #34
          Yes exactly!

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          • #35
            Originally posted by JR44 View Post
            The seller seems to have doubled the buy it now price to £795 Plus £30 shipping.
            Dreamer!
            I just had another look at the listing, and besides the price the seller only offers postage within the UK. I am on the other side of the world! I know that postage for such a propeller boss is not cheap, since the owner of another T.6296 boss very generously offered to send it from the USA to Australia, until he went to the USPS and got a quote for shipping!

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            • #36
              Originally posted by Garuda View Post

              I just had another look at the listing, and besides the price the seller only offers postage within the UK. I am on the other side of the world! I know that postage for such a propeller boss is not cheap, since the owner of another T.6296 boss very generously offered to send it from the USA to Australia, until he went to the USPS and got a quote for shipping!
              Mostly for future reference, propellers can be shipped internationally by using IPS, which uses discounts from FedEx, UPS, etc and also handles the brokerage service. I have shipped a number of full sized props around the world with them and their prices and services have been very reasonable. When I sell a propeller I crate it myself at my expense and charge the buyer only what it costs based on the IPS quote.

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              • #37
                Since finding what I believe is an original T.6296 hub, which I have posted photos of in a new thread it has allowed me to check the patterns I have already made, and continue developing the patterns. Predictably the patterns I made from pine using the augmented reality app are very close but slightly distorted. They are within the “ballpark” and with a bit of sanding are close enough to integrate with the patterns I have made directly from the original hub. More recent pattens have been made from a timber which is relatively new to me. It is called Merbau and it is very stable, unlike the pine patterns I was using when I started this thread. If you look closely in the photographs of the pine patterns it’s possible to see quite a lot of movement. I helped a friend to build his deck and I realised that Merbau is very similar in appearance to Mahogany, which the original propellers were made from. I used some of the offcuts from his deck to fabricate the most up to date patterns. I will gradually replace the pine patterns with Merbau. The aim is to work from each end and integrate the data I have as accurately as possible. I have an original propeller tip, measurements from a blade and now access to an original hub. Once the patterns are complete I will check them against a complete, original T.6296.
                Attached Files
                Last edited by Garuda; 11-21-2022, 04:40 PM. Reason: Additional information

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                • #38
                  I have drilled four of the eight bolt holes into a piece of MDF and have traced the shape of the trailing edge onto the board. I noticed that there are two styles used to laminate the propeller and the angle and width of the half laps varies between the two construction styles. The blade I measured in Sydney in 2011 and the hub in the USA have all laminations half lapped. The hub in England, the hub I have found here in Canberra and the complete T.6296 in the museum at Narromine appear to have only the front and rear laminations (one and eight) half lapped. All other laminations appear to be butt jointed. I will take photos of both construction methods as I construct my patterns. I also traced the shape of the propeller blade tip and drew lines at the appropriate radii to check the location and appropriate rotation of the tip. Each peg was drilled in a radius from the centreline, and as a result they are very important reference points.
                  Attached Files

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                  • #39
                    Laminations one and eight (front and rear) showing how the angle of the half laps “creeps” clockwise, as the propeller is viewed from the front. I placed the jig I constructed from the T.6296 propeller blade in Sydney where it had broken deep inside the hub over my patterns. There is a few degrees difference between these two different construction methods, or perhaps the difference is due to inaccurate construction.
                    Attached Files

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                    • #41
                      I have marked the partial outline of lamination 6, using the same method shown in the third and sixth photos in the previous post. The pencil has been held at an angle which approximates the extra width of each particular lamination. When the shapes are cut I have been allowing a margin of a few extra millimeters. Once the shape of each lamination has been determined by measuring the original hub and sanding them to shape there are some points I am concerned will not sand out. If I had a scanner or a probe this job would be made so much easier. If it becomes necessary to manufacture further patterns I will have the ones I have already made as a very good starting point.
                      Attached Files

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                      • #42
                        The replica hub in its current form. I have still been having a lot of trouble determining how the blade blends with the hub but I’m getting much closer to working it out. Even when I have access to the original propeller this transition will not be easy to measure. Hopefully by that time I will have access to a hand held scanner. If not I’ve got a few ideas for some MDF patterns which will allow me to check the shapes and dimensions I have determined so far.
                        Attached Files
                        Last edited by Garuda; 12-26-2022, 11:28 PM.

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                        • #43
                          I traced the location of the row of pegs at Section GG. The previous row, which was scribed in an arc, as all pegs are at each section is Section FF. Some shrinkage is to be expected where a 105 year old timber propeller is concerned. I noted about 8% shrinkage in the thickness of the laminations in the hub. Shrinkage of the laminations in width is minimal, due to the fact that the underlying laminae are glued to them at 90 degrees. There is evidence of warpage and splitting in the hub due to the fact that the timber has not been allowed to shrink in the manner it would have shrunk if it had not been laminated. When I drew the outline of the blade onto the piece of MDF the tip was located about 10mm short of its predicted location. This can be accounted for by shrinkage in length of the laminations. Shrinkage at the leading edge of the blade appears to have occurred much more so than shrinkage at the trailing edge. For this reason the blade seems to have been brought forward at the tip, as shown in the photo, where I have lined the pegs up with the scribed radius. I will leave the shape of the blade “as found”, including the 10mm shortfall in length. Once the patterns are made I will compare the shape I have determined using the evidence I have so far had access to and compare the shapes and dimensions with those of the complete T.6296 in the museum. Once I have checked these shapes and dimensions I will correct for shrinkage. Unless I am able to find a copy of the original T.6296 drawing I won’t know the exact intended shapes and dimensions but I will be able to determine them within a few millimeters.
                          Attached Files
                          Last edited by Garuda; 12-31-2022, 11:30 PM.

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                          • #44
                            Shaping the components of laminations 7 and 8.
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