Announcement

Collapse
No announcement yet.

1926 RRG Prufling in 1:4 Scale

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • 1926 RRG Prufling in 1:4 Scale

    This model was built a few years ago as my first for aerotowing. I had never aerotowed before so presumed a secondary trainer would be appropriate enough! RRG in Germany made plans available for the construction of these across Europe and in other parts of the world. The Prufling (examinee or student) was of simple wood and ply construction that any one or group could build with minimal tools and experience. They were mostly bungee launched on hillsides but one was even slung beneath a dirigible to be the first glider to be released at altitude in this manner. There is a nice model of one at the soaring museum in Elmira, NY. The full scale version had a 10.50 meter span so mine is ~2.63m or around 105". The 3-view from Martin Simons' book 'Sailplanes: 1920-1945' was used to draw the plans. The airfoil in the book was used. Martin even provided a contemporary cockpit controls diagram for reference to me via e-mail communication. That was very generous of him. Thanks Martin! The 'build' appears reversed but the original thread was lost thus the re-post with pictures of the completed model first. That way you can see what it looks like before wading through posts to see the end result. This poor thing ain't no sleek and sexy flying machine! It is different and I love the beauty of wood!

    Click image for larger version

Name:	2014HSVAerotowDay2_0077.JPG
Views:	349
Size:	100.9 KB
ID:	6912 Click image for larger version

Name:	2014HSVAerotowDay2_0082.JPG
Views:	293
Size:	36.7 KB
ID:	6913

    Click image for larger version

Name:	DSC02550.JPG
Views:	321
Size:	84.7 KB
ID:	6914 Click image for larger version

Name:	DSC02699.JPG
Views:	304
Size:	83.8 KB
ID:	6915

    Drawing plans and starting construction with the rudder. It's a flat easy thing to make with sticks and 1/64 gussets.

    Click image for larger version

Name:	DSC02536.JPG
Views:	310
Size:	67.3 KB
ID:	6916 Click image for larger version

Name:	DSC02537.JPG
Views:	311
Size:	72.7 KB
ID:	6917

    Click image for larger version

Name:	DSC02538.JPG
Views:	299
Size:	76.4 KB
ID:	6918 Click image for larger version

Name:	DSC02539.JPG
Views:	319
Size:	68.3 KB
ID:	6919

    Click image for larger version

Name:	DSC02534.JPG
Views:	289
Size:	90.0 KB
ID:	6920 Click image for larger version

Name:	DSC02535.JPG
Views:	296
Size:	89.9 KB
ID:	6921

  • #2
    The fin will get built a little later after fuselage 'fleshed out'. A jig was made to match the side view curve of the lower nose bows. 1/16" balsa laminates 'keyed' into each other at their tips. When this assembly dried it was taken off the jig. The upper nose bow was built flat on the plan. These parts were used to make upper and lower fuselage crutches. The lower one was built over the upper one to maintain symmetry. These were then pulled off board and the cross members were added to build a basic box structure. A square was used to maintain alignment. Cabane supports were added. FG and epoxy added to the lower bow. The tow release will be in this area so might as well make it tough. It will need nose weight anyway!

    Click image for larger version

Name:	DSC02540.JPG
Views:	322
Size:	83.0 KB
ID:	6926 Click image for larger version

Name:	DSC02542.JPG
Views:	293
Size:	81.9 KB
ID:	6927

    Click image for larger version

Name:	DSC02543.JPG
Views:	292
Size:	62.8 KB
ID:	6928 Click image for larger version

Name:	DSC02546.JPG
Views:	304
Size:	80.7 KB
ID:	6929

    Click image for larger version

Name:	DSC02547.JPG
Views:	315
Size:	81.1 KB
ID:	6930 Click image for larger version

Name:	DSC02549.JPG
Views:	298
Size:	86.3 KB
ID:	6931

    Click image for larger version

Name:	DSC02551.JPG
Views:	302
Size:	84.1 KB
ID:	6932 Click image for larger version

Name:	DSC02552.JPG
Views:	320
Size:	80.0 KB
ID:	6933

    Comment


    • #3
      BTW... thanks to Andy Grose for the two photos shown above! Andy took many fine photos of my models flying! They are spectacular shots! Martin Simons provided the control system diagram so typical of these birds. This drawing was used as a starting point. The Prufling most likely(?) had a rudder bar in lieu of rudder 'paddles' as seen on the Primary types. I used artistic license to make everything functional. There was no way I could find pulleys small enough to loop the control cables as seen on the diagram. Compromises must be made. However, the control column and rudder bar will actually be connected via cables and pulleys elsewhere directly to the control surfaces. The servo will have links to drive the control column and rudder bar. In essence, if you can find a quarter scale pilot then the pilot would be able to fly this airplane if the servos were removed!

      Rudder bar components shown. Pivot tube slotted and cable passes through. A small fork (not shown) got soldered to the cable. The fork will engage end of control stick for elevator control. Pivot tube bushings with brackets fabricated from brass. The stick pivots on a bracket soldered to pivot tube. Lateral motion of stick will operate ailerons. That action will be transmitter via micarta tiller at end of pivot tube. All brass was painted black. The control stick is wood, stained and with cord wrap for the handle. Clevis soldered on each end of cable for elevator connectivity.

      Click image for larger version

Name:	DSC02580.JPG
Views:	314
Size:	74.0 KB
ID:	6936 Click image for larger version

Name:	DSC02554.JPG
Views:	308
Size:	64.7 KB
ID:	6937

      Click image for larger version

Name:	DSC02556.JPG
Views:	317
Size:	71.0 KB
ID:	6938 Click image for larger version

Name:	DSC02561.JPG
Views:	292
Size:	60.6 KB
ID:	6939

      Click image for larger version

Name:	DSC02562.JPG
Views:	277
Size:	79.0 KB
ID:	6940 Click image for larger version

Name:	DSC02564.JPG
Views:	284
Size:	61.1 KB
ID:	6941

      Click image for larger version

Name:	DSC02565.JPG
Views:	288
Size:	81.7 KB
ID:	6942 Click image for larger version

Name:	DSC02574.JPG
Views:	316
Size:	81.2 KB
ID:	6943

      Comment


      • #4
        The curved forward keel was added to the fuselage frame. Supports were added to the keel. A skid hard point can be seen near the front. Others will get added, later. Servo rails and rudder bar mount added. A skid was made from music wire, painted then mounted. The control column mounted to keel. The ex-WWI pilot got in for a test fit. He was good with it! Elevator tiller parts. Control column connected to the aileron servo. The last picture show how the length of the cable and clevis connection was determined. A previous picture showed it fullu assembled in a finished state. These scratch builds are all about putting stuff on then taking it off for tweaking.

        Click image for larger version

Name:	DSC02553.JPG
Views:	286
Size:	67.6 KB
ID:	6948 Click image for larger version

Name:	DSC02555.JPG
Views:	311
Size:	90.2 KB
ID:	6949

        Click image for larger version

Name:	DSC02557.JPG
Views:	293
Size:	90.4 KB
ID:	6950 Click image for larger version

Name:	DSC02559.JPG
Views:	299
Size:	64.7 KB
ID:	6951

        Click image for larger version

Name:	DSC02566.JPG
Views:	299
Size:	77.1 KB
ID:	6952 Click image for larger version

Name:	DSC02568.JPG
Views:	283
Size:	81.9 KB
ID:	6953

        Click image for larger version

Name:	DSC02569.JPG
Views:	312
Size:	78.0 KB
ID:	6954 Click image for larger version

Name:	DSC02571.JPG
Views:	331
Size:	83.9 KB
ID:	6955

        Comment


        • #5
          Oooops! Left off the 'test fit' pic with the ex-WWI pilot. Wings started. They will have pull-pull cables from cockpit to the ailerons. A balance cable will connect each wing to make the 'loop'. Root ends have a single pulley. An inner rib will have two pulleys. One for the 'up' cable and one for the 'down' cable. The root ribs were faced and reinforced with 1/64" ply. Waxed paper keeps pulleys from getting glued to their mounts and makes for a nice 'spacer'. Just rip waxed paper out after epoxy cures. The last pic shows how the tapered tip ribs were determined. Just measure from the stringer at the proper rib location, transfer the measurements the cut the rib. A little sanding to fair everything and you're good to go!

          Click image for larger version

Name:	DSC02567.JPG
Views:	312
Size:	87.5 KB
ID:	6957 Click image for larger version

Name:	DSC02575.JPG
Views:	316
Size:	82.0 KB
ID:	6958

          Click image for larger version

Name:	DSC02576.JPG
Views:	312
Size:	72.8 KB
ID:	6959 Click image for larger version

Name:	DSC02577.JPG
Views:	321
Size:	77.0 KB
ID:	6960

          Click image for larger version

Name:	DSC02578.JPG
Views:	292
Size:	79.3 KB
ID:	6961 Click image for larger version

Name:	DSC02579.JPG
Views:	287
Size:	82.6 KB
ID:	6962

          Click image for larger version

Name:	DSC02581.JPG
Views:	312
Size:	79.4 KB
ID:	6963 Click image for larger version

Name:	DSC02582.JPG
Views:	282
Size:	79.1 KB
ID:	6964

          Comment


          • #6
            The Prufling is a collection of parts connected via brackets, bolts and whatnot. Here are some fittings. They were cut from sheet steel, hammered flat, filed smooth, cleaned and painted. The wing strut attach carry thru 'beams' are 1/8" music wire. The ends were heated cherry red then hammered flat, drilled, tapped to receive 4-40 bolts, cleaned and painted. The sanding bar was placed thus to help align the upper spruce spar while glue dried. Here is a close up of aileron pulley rib.

            Click image for larger version

Name:	DSC02583.JPG
Views:	295
Size:	72.3 KB
ID:	6966 Click image for larger version

Name:	DSC02586.JPG
Views:	244
Size:	62.0 KB
ID:	6967

            Click image for larger version

Name:	DSC02609.JPG
Views:	228
Size:	61.7 KB
ID:	6968 Click image for larger version

Name:	DSC02610.JPG
Views:	230
Size:	81.5 KB
ID:	6969

            Click image for larger version

Name:	DSC02618.JPG
Views:	258
Size:	82.6 KB
ID:	6970 Click image for larger version

Name:	DSC02619.JPG
Views:	249
Size:	73.1 KB
ID:	6971

            Click image for larger version

Name:	DSC02584.JPG
Views:	251
Size:	78.0 KB
ID:	6972 Click image for larger version

Name:	DSC02585.JPG
Views:	252
Size:	75.0 KB
ID:	6973

            Comment


            • #7
              More wing stuff. Here is a close up of one of two spar sockets each root end. A 'stub spar' with appropriate wing inter-connect fittings will get added later. Drag and anti-drag members added. They are 1/8" spruce. A balsa fairing strip added to the top of the LE spruce spar to be sanded fair. Support added to aileron pulley ribs. This is not shown on the three view but I didn't want that rib flexing under load. Overkill??? Microlux table saw used to profile balsa LE.

              Click image for larger version

Name:	DSC02587.JPG
Views:	234
Size:	73.0 KB
ID:	6994 Click image for larger version

Name:	DSC02588.JPG
Views:	229
Size:	80.0 KB
ID:	6995

              Click image for larger version

Name:	DSC02589.JPG
Views:	234
Size:	76.3 KB
ID:	6996 Click image for larger version

Name:	DSC02590.JPG
Views:	237
Size:	72.4 KB
ID:	6997

              Click image for larger version

Name:	DSC02591.JPG
Views:	252
Size:	76.7 KB
ID:	6998 Click image for larger version

Name:	DSC02592.JPG
Views:	266
Size:	80.9 KB
ID:	6999

              Click image for larger version

Name:	DSC02593.JPG
Views:	212
Size:	77.7 KB
ID:	7000 Click image for larger version

Name:	DSC02594.JPG
Views:	232
Size:	84.1 KB
ID:	7001

              Comment


              • #8
                More profiling of LE. After the parts were cut to fit they were glued to the wings. The basic structure of wings are done. Just need to add 1/64" cladding and stain.

                Click image for larger version

Name:	DSC02595.JPG
Views:	223
Size:	74.1 KB
ID:	7003 Click image for larger version

Name:	DSC02596.JPG
Views:	228
Size:	79.3 KB
ID:	7004

                Click image for larger version

Name:	DSC02597.JPG
Views:	223
Size:	82.5 KB
ID:	7005 Click image for larger version

Name:	DSC02598.JPG
Views:	236
Size:	73.4 KB
ID:	7006

                Click image for larger version

Name:	DSC02599.JPG
Views:	220
Size:	62.9 KB
ID:	7007 Click image for larger version

Name:	DSC02600.JPG
Views:	218
Size:	92.4 KB
ID:	7008

                Click image for larger version

Name:	DSC02601.JPG
Views:	217
Size:	87.1 KB
ID:	7009 Click image for larger version

Name:	DSC02603.JPG
Views:	229
Size:	93.7 KB
ID:	7010

                Comment


                • #9
                  Can't have cables jumping off pulleys! Balsa and plastic tube segments added to help keep cables in place. The plastic tubes have their ends beveled in order to get a very close fit to the pulley cable grooves. The music wire was used to emulate the cable runs while glue dried. When the wings are disconnected and placed in storage the cables won't fall off the pulleys. Balsa infill added to fuselage edges then sanded fair. This is needed for 'purchase' when the 1/64" ply skinning added.

                  Click image for larger version

Name:	DSC02604.JPG
Views:	222
Size:	66.9 KB
ID:	7012 Click image for larger version

Name:	DSC02605.JPG
Views:	214
Size:	72.9 KB
ID:	7013

                  Click image for larger version

Name:	DSC02606.JPG
Views:	215
Size:	77.6 KB
ID:	7014 Click image for larger version

Name:	DSC02607.JPG
Views:	214
Size:	78.3 KB
ID:	7015

                  Click image for larger version

Name:	DSC02608.JPG
Views:	230
Size:	64.3 KB
ID:	7016 Click image for larger version

Name:	DSC02614.JPG
Views:	219
Size:	84.8 KB
ID:	7017

                  Click image for larger version

Name:	DSC02615.JPG
Views:	230
Size:	78.4 KB
ID:	7018 Click image for larger version

Name:	DSC02616.JPG
Views:	221
Size:	79.8 KB
ID:	7019

                  Comment


                  • #10
                    Hard points for tail feathers made using dowel and threaded rod. Ooops! The stab mount is too high so it got cut free, trimmed then re-attached. Once stabs set in place they were braced with scrap while the strut ends' epoxy cured. CF tow used to reinforce nose at tow release area.

                    Click image for larger version

Name:	DSC02623.JPG
Views:	238
Size:	76.4 KB
ID:	7021 Click image for larger version

Name:	DSC02624.JPG
Views:	239
Size:	73.9 KB
ID:	7022

                    Click image for larger version

Name:	DSC02627.JPG
Views:	212
Size:	85.5 KB
ID:	7023 Click image for larger version

Name:	DSC02629.JPG
Views:	211
Size:	83.6 KB
ID:	7024

                    Click image for larger version

Name:	DSC02631.JPG
Views:	219
Size:	84.1 KB
ID:	7025 Click image for larger version

Name:	DSC02636.JPG
Views:	217
Size:	77.6 KB
ID:	7026

                    Click image for larger version

Name:	DSC02635.JPG
Views:	220
Size:	63.7 KB
ID:	7027 Click image for larger version

Name:	DSC02630.JPG
Views:	233
Size:	80.0 KB
ID:	7028

                    Comment


                    • #11
                      Rear upper fuselage formers constructed. The rudder and elevator horn were made from music wire. They were bent to shape, soldered together and trimmed to length. Brass tubes were flattened one end, drilled for cable attachments, soldered to the music wire parts, cleaned and painted. These fuselage top stringer was taped to a brass tube then glued to the formers. This made sure it was dead straight. The front top hatch was constructed. The fin was constructed now that the fuselage plus rudder length known.

                      Click image for larger version

Name:	DSC02637.JPG
Views:	222
Size:	71.3 KB
ID:	7030 Click image for larger version

Name:	DSC02639.JPG
Views:	208
Size:	70.8 KB
ID:	7031

                      Click image for larger version

Name:	DSC02638.JPG
Views:	203
Size:	89.9 KB
ID:	7032 Click image for larger version

Name:	DSC02640.JPG
Views:	223
Size:	81.8 KB
ID:	7033

                      Click image for larger version

Name:	DSC02641.JPG
Views:	221
Size:	71.9 KB
ID:	7034 Click image for larger version

Name:	DSC02642.JPG
Views:	208
Size:	71.9 KB
ID:	7035

                      Click image for larger version

Name:	DSC02643.JPG
Views:	233
Size:	83.7 KB
ID:	7036 Click image for larger version

Name:	DSC02644.JPG
Views:	209
Size:	82.3 KB
ID:	7037

                      Comment


                      • #12
                        Titebond Contact Cement (Weldwood Contact Cement is the same) used to attach 1/64" ply to balsa structure. Brush the cement onto each part and let dry. A sheet of paper is placed between the parts so that the proper alignment can be made. Once satisfied ease the paper out and the parts will start to adhere to each other. You get one chance to get it right! Don't even breathe while doing this! You could build a model with this glue but you'd be on pins and needles the whole time! On the wing LE a triangular block of mahogany was use to 'burnish' the ply onto the structure and around the LE. No heat or water was needed. The hatch got the same treatment but it was a whole lot easier to cover!

                        Click image for larger version

Name:	DSC02661.JPG
Views:	205
Size:	80.9 KB
ID:	7039 Click image for larger version

Name:	DSC02655.JPG
Views:	209
Size:	74.8 KB
ID:	7040

                        Click image for larger version

Name:	DSC02656.JPG
Views:	190
Size:	82.2 KB
ID:	7041 Click image for larger version

Name:	DSC02657.JPG
Views:	220
Size:	83.3 KB
ID:	7042

                        Click image for larger version

Name:	DSC02658.JPG
Views:	196
Size:	74.8 KB
ID:	7043 Click image for larger version

Name:	DSC02660.JPG
Views:	187
Size:	79.8 KB
ID:	7045

                        Click image for larger version

Name:	image_2377.jpg
Views:	199
Size:	78.8 KB
ID:	7044 Click image for larger version

Name:	DSC02662.JPG
Views:	195
Size:	63.6 KB
ID:	7047

                        Comment


                        • #13
                          This should be post #14 and the above one #15 but I got it out of order while posting. Nothing wrong with site except for person using it! Cable attachment shackles made from coat hangar wire. A whole slew of 1/64" gussets and cap strip stock made ready. The structures were stained. 'The Digger' is a great little tool to make hinge slots. I like it so much that when it got misplaced for a spell I made a replacement from brass.

                          Click image for larger version

Name:	DSC02633.JPG
Views:	181
Size:	64.3 KB
ID:	7049 Click image for larger version

Name:	DSC02632.JPG
Views:	194
Size:	85.6 KB
ID:	7050

                          Click image for larger version

Name:	DSC02634.JPG
Views:	172
Size:	70.3 KB
ID:	7051 Click image for larger version

Name:	DSC02645.JPG
Views:	191
Size:	79.0 KB
ID:	7052

                          Click image for larger version

Name:	DSC02646.JPG
Views:	191
Size:	78.5 KB
ID:	7053 Click image for larger version

Name:	DSC02651.JPG
Views:	193
Size:	92.5 KB
ID:	7054

                          Click image for larger version

Name:	DSC02652.JPG
Views:	178
Size:	88.4 KB
ID:	7055 Click image for larger version

Name:	DSC02654.JPG
Views:	175
Size:	80.9 KB
ID:	7056

                          Comment


                          • #14
                            Ferrules cut from aluminum tubing. Their ends were flared so the cables don't chafe then they were painted black. The ferrules were let into the fuselage frame work and strengthened with CF and epoxy. A 1/64" ply cladding piece added. Card stock patterns made to size the 1/64" ply covering.

                            Click image for larger version

Name:	DSC02663.JPG
Views:	193
Size:	76.9 KB
ID:	7060 Click image for larger version

Name:	DSC02665.JPG
Views:	176
Size:	61.3 KB
ID:	7061

                            Click image for larger version

Name:	DSC02666.JPG
Views:	178
Size:	82.0 KB
ID:	7062 Click image for larger version

Name:	DSC02669.JPG
Views:	191
Size:	80.4 KB
ID:	7063

                            Click image for larger version

Name:	DSC02670.JPG
Views:	173
Size:	96.6 KB
ID:	7064 Click image for larger version

Name:	DSC02671.JPG
Views:	190
Size:	82.3 KB
ID:	7065

                            Click image for larger version

Name:	DSC02673.JPG
Views:	172
Size:	85.2 KB
ID:	7066 Click image for larger version

Name:	DSC02674.JPG
Views:	189
Size:	80.8 KB
ID:	7067

                            Comment


                            • #15
                              More skinning. Balsa sheet glued inside fuselage. This will form lead shot receptacle after the ply skin put in place. Shot mixed with epoxy will be poured into the opening at the top inside 'lip' of fuselage.

                              Click image for larger version

Name:	DSC02675.JPG
Views:	189
Size:	78.9 KB
ID:	7069 Click image for larger version

Name:	DSC02677.JPG
Views:	169
Size:	78.0 KB
ID:	7070

                              Click image for larger version

Name:	DSC02678.JPG
Views:	199
Size:	83.8 KB
ID:	7071 Click image for larger version

Name:	DSC02679.JPG
Views:	198
Size:	84.8 KB
ID:	7072

                              Click image for larger version

Name:	DSC02680.JPG
Views:	197
Size:	80.0 KB
ID:	7073 Click image for larger version

Name:	DSC02681.JPG
Views:	174
Size:	84.9 KB
ID:	7074

                              Click image for larger version

Name:	DSC02682.JPG
Views:	194
Size:	79.4 KB
ID:	7075 Click image for larger version

Name:	DSC02683.JPG
Views:	195
Size:	81.7 KB
ID:	7076

                              Comment

                              Working...
                              X