1921 Vampyr in 1:4 Scale

[ARUP]

This is my third scale sailplane. I like the unusual subject to replicate and the Vampyr is definitely a worthy candidate! The Vamyr is the FIRST aircraft to have a stressed skin 'D' tube wing. In the words of Martin Simons- "This was revolutionary". All other aircraft of this stressed skin configuration can trace their 'lineage' to the Vampyr! The three views were obtained from Martin's fantastic book, 'Sailplanes: 1920-1945'. If you really like the history and evolutionary process of sailplanes and their design then get these books by Martin Simons! The Vampyr was designed by George Madelung working under Professor Arthur Proell of Hannover Technical University. The wing had a 'D' tube forward of the main spar and aft was fabric covering. It had two small struts used to stabilize the attachment to the boxy ply covered fuselage. It had three soccer ball type wheels. These were found to create less drag than normal wheels. The Vampyr had three different configurations which gave a clue as to its handling. The 1921 version had ailerons. These didn't seem to be very effective but 'differential throw' as we know it today didn't seem to be understood then. Photos show the Vampyr with wildly deflected ailerons in both directions! The second version of 1922 had 'warperons' which shows the wing had increased area in plan view around the 'aileron' portion of the wing. An interesting mechanism drove the 'warperons' which I'll show later. The third version shows the Vampyr with 'warperons' and increased rudder height. It must have been a bit of a 'pig' handling wise!

The original thread was lost so this is another 'retread'. The Vampyr is a great flying sailplane (to me, anyway) and indicates the slightest lift with ease. Even I can make this one stay up! Its best thermal flights were at the inaugural Clover Creek Aerotow. It doesn't 'penetrate' very well due to its scale Gottingen 441 foil. I got caught at the Horizon Hobby Aerotow last year and had to make a huge 'walk of shame' but at least I had sense to land it on a rise so that my feet didn't get muddy like some others who landed in corn! Again, LenB. did the maiden which was at Jim Dolly's 'Cumberland Aerotow'. There was concern for the incidence of the full flying stab but the design stood the test of time and it flew pretty much 'off the board'! Thanks, Len! Andy Grose took these great pictures of the Vampyr flying at Epp's Field near Huntsville, AL. Thanks Andy!

[Asher Carmichael]

This is an amazing model, in flight or under inspection. Mike, we're glad you enjoy modeling these early types.

[ARUP]

Hey Asher, thanks! Somebody has to build these old timers... might as well be me! I was fascinated with the 'warperon' version so proceeded to build that wing. It didn't work out too well so regular aileron outer panels were built. The build will show how it initially progressed so fasten your seat belts! For storage and transportation I made it a three piece wing: a center section and two outer panels. A picture above shows how I enlarged the Go441 foil from the three view using the 'grid method'. I like 'old timey' methods, too! After drawing the wing plan I used the length at each rib station plus their respective thicknesses to cut some blue foam ribs. These got sandwiched between the Go441 foil template and the end rib template to 'rough in' the ribs. These were separated so that wood ribs could be made by tracing the blue foam ribs. These were cut a little large. Everything was put back between the templates to be sanded again so that the wood ribs would be more fair. They were given reference marks while still between the templates. That helps with alignment later. These were taken apart again and used as templates to make the 'real' ribs. As the wing progressed the warping mechanism had to be configured. You can see some of the structure in the photo taken from the book, above. There is another picture of this mechanism in the book but it is difficult to 'flesh it out'. I wanted to make sure the end result would appear as the 'real' version even if it wasn't exactly the same. I guess that's what is called 'artistic license'! In today's lexicon... 'fudging'! The warp cranks were made from music wire with brass tube bushings. The cranks will have a small lever at one end for the push rod connection. The ribs at the warp portion of the wing had to be flexible so their rear portions were made from bamboo skewers. The tail end of a rib resembles a triangle which is a rigid structure. Aluminum tubes with flattened ends act as receptacles for the 'free' end of the rib. When the wing flexes up and down the rib end is free to move fore and aft within the tube. You can see the flat end of the aluminum tube epoxied to the TE with the 'free end' of the bamboo inserted. The other rib portion (bamboo) is glued to the TE.

[ARUP]

The crank engages a 'slider'. The full scale may have crank in a fixed slot. The slider rides on two music wires that are attached to the bamboo portion of the ribs. You can just see the push rod connection to a horn on the crank. The slider is of brass tubes and sheet. Everything is at scale locations as far as can be discerned in photographs. The push rod is driven by a bell crank. I am almost certain cables from the cockpit drove the bell crank. I'll use a push rod from a servo in the wing. Bell crank and crank supports cut from 1/16" marine ply.

[ARUP]

Bell crank supported so no flexing here will occur. Both wings have their warping mechanisms in place. The LE, tips and root ends need finishing. The outer panel root ends get these 'push rod inter-wing connector' bell cranks. The tab on the bell crank will allow easier access for the push rod clevis from the center section's push rod. Wing joiners and their joiner boxes fabricated to fit between the spars. Epoxy will work just fine! Sheeting at the root end of the outer panels will stiffen things up.

[ARUP]

Starting the center section. It's just a big Hershey bar! The wing joiner slots were transferred to a rib after they were stacked, blocked up and slotted to receive spars. The spars were scarfed together from some scrap.

[ARUP]

Blocks were cut to fit at the center section's ends. This will stiffen the ends and be used to anchor the alignment pins. Had to make sure the center section and out panels align. Added TE. Shear webbing glued in place then bottom spar added.

[ARUP]

Here are the wing components together. I used my granite counter top surface for gluing the false LE and for getting the wing joiner glued in place. The wing was placed top surface down for this. You can see the angled packing filling the gap where the wing joiner fits between the spars. The lower 'D' tube sheeting glued in place. When ready the upper sheeting will get glued in place after the wings are jigged for proper washout.

[ARUP]

Wing alignment pins and tube were let into the wing panels. The tubes were put in first so that a drill bit could make the properly aligned hole while the panels were held together with clamps. The picture shows them apart. Sheeting was cut away so CF tow could be epoxied around joiner box and spars. This strengthens everything with minimal weight gain. Some scrap sheeting was glued and sanded to hide the 'surgery'. The picture depicts this still in an unfinished state.

[ARUP]

When the wings get put together for flight they need something to keep them from slipping apart. Bass blocks were let into the wings fore and aft so that metal clips can be used. 'D' tube and center section sheeting made up. I use Ambroid cement for this exclusively. I have a good stash of Ambroid thank goodness. It sands as easily as balsa so the join line just disappears. The 'sheeting' pics are a little out of order but you get the idea. Sheet steel drilled and cut then mounted to two ply plates that were 'sandwich' epoxied to the spars and shear webbing. This was made to engage a fixed pin in the fuselage. This 'hangar', two auxiliary struts and two brackets at rear of wing all connect wing to fuselage.

[ARUP]

Sheeting upper 'D' tube part of wings. The 'T' bar just holds the sheeting down while pinning progresses. Making skins for the outer panels. Cap strips with gussets detail picture.LE glued to wings. 1/64 ply used as guide for 'roughing-in' the profile.

[ARUP]

Masking tape put on as an ablative for some LE sanding. I didn't want to cut into the 'D' tube sheeting too much. Fitting servo rails. Each outer panel gets its own servo to drive the push rod to the 'warperon' mechanism. Balsa wingtips with bamboo portions fitted. The TE was flimsy with just 1/64" ply so balsa stock was glued to it, sanded fair then a strip of 1/64" was glued in place sandwiching the balsa. The TE is stiff, now! The wing is done. A hatch was made for the servos on the underside.. The 'warperon' mechanism works very well at this stage. Deflections of more than an inch each way are easily accomplished. Too bad I didn't (and still don't) know how to make a video of it in action.

[ARUP]

Fuselage construction begins. The plans were drawn in side and plan view. The all flying stabilator is hinged at the apex of the tapering fuselage. It is a real 'Jesus Joint' if there ever was one! Spruce was used for this area of construction. It was scarfed to balsa forward section stock. Logerons laid down then uprights and diagonals fitted. A pine block was carved for the nose area since the release and nose wheel are in close proximity to each other. The block had to be put through the band saw and table saw a few times to get proper angles and curves. I like to do the difficult construction and fabrication while interest is super keen! These kinds of parts are somewhat difficult to execute.

[ARUP]

Fuselage box being built. A form was made, its edge covered in film then the forward fuselage bows were laminated. Ply bulkhead fitted. This is essentially the pilots seat back. Bows get scarfed in place. The fuselage had to be tilted to get the upper bow scarfed in place at the correct angle.

[ARUP]

Formers built up then bow attached. Diagonal braces glued in place. The diagonal across cockpit opening gets removed later. It looks flimsy but the ply skin will really strengthen it. The stabilator was built 'clam shell' fashion.The other half gets built onto it for symmetry.