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1:4 1928 RRG Professor

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  • ARUP
    started a topic 1:4 1928 RRG Professor

    1:4 1928 RRG Professor

    It's time to start another build! I'm a sucker for antique aircraft and especially appreciate those with an historical significance. Alexander Lippisch designed the Professor which first flew on 06 August 1928. It was piloted by Robert Kronfeld, a brilliant pilot. (Kronfeld had to escape when Nazis came to power.) The Professor was to be a step up in performance from the primaries but was still simple in design and manufacture. Most importantly, it was the first sailplane to employ the use of a variometer! True soaring was born on this day!

    I am using three views from Martin Simons book: Sailplanes 1920-1945. I am going to build the prototype version named Rhongeist which was a nickname given to Lippisch. Lippisch spent a lot of time in the Rhon Mountains. It has a plywood skinned open cockpit fuselage, fabric covered flying surfaces, 'pendulum' elevator, struts and skid. It will span 4.025m (~159") with a chord of 0.375m (over 14") and the length will be 1.75m (~69"). The rudder and elevators will be removable to facilitate storage, along with the three piece wing, in a nice and cozy custom made box.The wing will be in three parts. I am waiting for the delivery of wing tube and socket joiners so the rib patterns can be finalized. I am still drawing the plans.

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    This picture is an internet grab of a Professor. Stay tuned!

  • Mark9
    commented on 's reply
    Darn now I need to build a work table on the patio....

    Rained another .7" here last night the fields are swamps!

  • ARUP
    commented on 's reply
    Mark9- get a belt sander... they're great! I can swap different grits easily. Mine is a DeWalt as are my other power tools.

    Al- Thanks! This stuff is done outdoors! Mother Nature sneezed and now it's raining! yuck!

  • Al Clark
    commented on 's reply
    Nice sanding! Bet your shop has a good coating of spruce dust now.

  • Mark9
    commented on 's reply
    Probably a little dusty too? I might need to get a hand belt sander too, but would need a bench on the patio...

  • ARUP
    replied
    Wow! This build is coming on a year since started. How 'tempus fugit'! The struts were sawn from spruce stock obtained from Aircraft Spruce and Specialty. Before sawing the board was clamped to the bench and a belt sander was run across each end each side to taper the ends properly. Before sanding, a line was penciled onto the ends dividing the upper side from the lower side equally. After cutting struts from the board they were roughly carved to an airfoil shape using a sharp knife. The belt sander was clamped to the bench this time then the struts were sanded to a finer shape free hand. Then they were hand sanded to 'finish grade'. I'm 'pooped' after all of this sanding work. Next, the wing will be offered to the fuselage so that the struts and their fittings can be set.

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    Good night!

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  • ARUP
    commented on 's reply
    Thanks, Gunny! I told my buddy about your PT-19. I'm trying to get some folks interested in sailplanes around here. I took buddy's Calypso glider and flew it for over 20 minutes without power. He was amazed!

  • ARUP
    commented on 's reply
    TJ, these sailplanes' control surfaces don't need much travel.

  • Tango Juliet
    commented on 's reply
    It surely won't happen this year. In fact, I may have to rebuild the Elevators. They're too narrow at the fuse to get full Down travel.

  • gunny11
    replied
    Nice work Mike! Finish is looking great.

    Leave a comment:


  • ARUP
    commented on 's reply
    Tj- keep plugging away. It would be cool if you had it ready for NARCA.

  • Tango Juliet
    commented on 's reply
    That's what I was thinking. Thanks for confirming. I set my project aside to do some smaller ones first. I'll get back to it this winter again.

  • ARUP
    commented on 's reply
    Hey TJ, the pic shows my left hand holding the tool. The big brush will be in the right. The brush is loaded with dope. Apply the lots of dope to the tool and as the dope seeps through the fabric of the tool (the same fabric with which you cover the air frame) it will get spread to the model's fabric as you drag the tool across the fabric. Surface tension and capillary forces are at work so the dope won't get pushed through the model's fabric to unreachable places!

  • Tango Juliet
    commented on 's reply
    I'm not sure I fully understand your Dope Spreading Tool, but the finished product looks great! Maiden should be soon, huh?

  • ARUP
    replied
    All the covering and nitrate doping is done! The fin was epoxied in place. A temporarily installed dowel segment sharpened in a pencil sharpener was used to locate where to drill for the peg that will secure the fin to the fuselage this end. Masking tape was used to delineate where Stix-It adhesive was applied. The bottom surface is concave so it is very important to get the fabric properly attached. The 'Dope Spreader Tool' is shown. Put a little dope onto the structure to 'prime', lay down the dope spreader tool then slather dope onto the tool as it is dragged across the fabric. The dope gets put onto the fabric really fast and none gets pushed through the fabric to pool. I put three coats of nitrate dope onto the model this way. Next to do is finishe the ply sheeting around the fin. Stay tuned!

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