Vintage Hatz project history



A life long dream started to become true when Sam told me in Spring 2004 about his strong desire to build a real aeroplane together with me. But how did he com to this idea, as during his youngster years he has not been that aviation minded, nor
did he build aircraft models like his dad? Sam always let his dad know, that in his mind building flying models was some sort
of playing....
However, he always showed some interest in aviation, as we both attended airshows from time to time and with eleven years Sam had his first airplane ride with the late and much appreciated friend Peter Flueckiger in his Luscombe 8F.
However, when Sam and his dad went the first time on a “faining Gipther and son journey” for a week to England, Sam really got hooked to aviation, especially vintage aviation, when we visited the Hendon Royal Air Force Museum, the Shuttleworth - Collection at Old Warden, Duxford museum and most important, Retrotec LTD, Guy Black’s Hawker aircraft restoration shop on the south coast and last, but not least De Havilland Moth restorer par excellence Ron Souch near Southampton.

So after negotiation with my wife (Sam’s mother) we decided to hit the chance and began looking for a suitable project.
As said before, we both had been excited about the Gipsy Moth with folding wings when we visited Ron Souch.
Plans are available for a replica D.H.60G Moth from Chris Tucker, Switzerland, Twenty five years ago, I managed to buy a bunch
of drawings for the DH60G Gispy Moth (not the complete set) when it was available from Bae for restoration work or model building purposes. When Chris Tucker bought the last remaining Gipsy Moth in Switzerland, I loaned him my drawings for the restoration work. His son redrew the design and the drawings are available under the name “Apus Melba”. In early 2004 we heared from an abandonned Gipsy Moth project based on these drawings and almost bought it. However, two reasons
prevented us from doing this: The almost unavailability of a DH Gipsy I or II upright inline engine and the fact, that BAE and especially the English D.H Moth. Club are prohibiting the building of De Havilland replicas. Stuart McKay told us that British authorities would ground such a replica when being flown into Great Britain. So, we had to look for another suitable design. For Sam a biplane would have been a must, but I would have preferred a vintage folding wing design. As we couldn’t find a suitable design, that would have been roadable when folded, we dropped that requirement and began looking for a rigid biplane.
Having known the Hatz biplane design for years, I presented this to Sam and he agreed right away. This is a design that flies on rel. low horsepower and can be handeled by a low time private pilot.
As registering an experimental aircraft in Switzerland is much more difficult than in the USA, we have been delighted by the fact, that Swiss aeronautical engineer (and EAS technical conselor) Juerg Mueller was already building a Hatz and had done the necessary stress analysis.
The decision was made that we will be building a Hatz biplane using the “Classic” as a base.
Then it was very clear, that a biplane needs a radial engine. However a vintage radial was out of scope due to the lack of spare parts and expensive maintenance (similar reasons as for the DH Gipsy engine).
We had great hope that the newly built Australian Rotec 7-cyl. Radial  would be feasible, but its 110HP at a rel. high 2400/min seemed us insufficient. With the release of the new 9-cyl. Rotec with 150HP that problem was solved.


Project diary

In summer 2004 we ordered a set of Hatz Classic plans from Makelan Corp. and began to prepare our shop by building a large flat and level building board as well as setting up special machines and tools.
After receipt of the plans we set to build comfortable rib building jigs, which enabled us a quick and accurate rib fabrication. Following that, Sam built all the ribs in a row, every day one!

Instead of building then the wings, which would have used to much store space during the long period of building the fuselage and tail feathers we continued with the fuselage. This is a straightforward task when the tubings can be assembled into two flat side frames on the plane table. Sam perfected his TIG-welding skills while being supervised by a retired certified master welder. The Hatz fuselage is an easy design and hence not difficult to be built. The fuselage basic frame is strictly to plans, however many additional details were added or changed to suit our requirements. E.g. we installed aluminium Hatz Bantam seats, which had to be differently attached than the standard Classic ones.

Next, we built the tailplane, fin and rudder. While maintaining the surface area, we redesigned the shape of the stabilizer, elevator, fin and made slight mods also to the rudder. This to achieve the Waco style look, which matches our personal taste.
Construction otherwise is to plans with design details borrowed from Mehlin Smith’s Warner Hatz.
For better rigidy of the stabilizer, 2 streamline leading edge struts have been added.
Also we incorporated both a static variable incidence devise for the stabilizer as well for the fin. Main reason for this is the necessary lowering of the thrust line to adapt the radial engine. This may have an influence on the incidence set up. Also the generous vortices generated by the large dia prop might call for a correction of the fin offset.
Due to the lower thrust line of the radial engine it is helpful to have the longer gear legs of the Hatz Classic design.

When it came to the task of the landing gear, wing and cabane struts, we bought those ready made from Makelan as we thought at the project’s beginning; it would not make sense to build jigs for a one-off airplane. However, with the experience gained during the project, we think, we would do it today ourselves. Together with those ready made parts we also bought the wing tank, as we cannot weld aluminium with our TIG welding unit.
A very nice feature are the replica Bendix high pressure wheels (16” rim) with Motorcycle tyres. We first saw those in the 16” size on Mehlin Smith’s Hatz. He named us the American source and we just had to have them.
They are expensive, but, wow - exciting! Those wheels give the airplane a higher angle of attack, which gives more prop clearance, allows stall landings and provide the real vintage look…..
To have the perfect match with the main wheels, we searched and found a rebuilt Scott 2000 tail wheel. Next task was the shaping of the fuselage with just two stringers on each side and bottom, a wooden turtledeck with headrest and aluminium panelling between stabilizer and fin. Right after the rear seat we built a wooden baggage compartment with a vintage style aluminium access door. Sam sewed himself a unique post sack attached to the bottom of the baggage compartment.
The square plan view look of the Hatz fuselage has been smoothed out by attaching a wooden former to the side of the top longerons. That really gives a smooth and more attractive fuselage profiling!

The above modifications called of course now for convex curved aluminium panelling, so just bending a sheet of aluminium with the roller brake is out of scope. An English wheel is hence needed to achieve the desired result, however, the art of working with this tool has first to be trained! However it’s a great joy, when a panel can be completed as desired.
Using a bead rolling machine we are adding the decorative and stiffening corrugations to the front fuselage panelling as was common in the 1930’s.
We also set the cockpit decking some higher like Mehlin’s, which adds much vintage character, but care has to be taken not to restrict the forward visibility, which has of course the main influence from the radial engine.
The instrument panels are made from birch plywood, simply period designed with added aluminum central panel.
In the front cockpit we added a glove box accessible through an aluminum cover with spring hatch. A filament net attached to the bottom of the glove box offers some more store space.

Forward of the firewall we are building a special bulkhead, whose purpose is to encover the Rotec engine’s collector ring in the same style as on a Boeing Stearman or a Waco QCF/UBF (they used the same Continental W-670 engine).
As soon as all necessary attachments are weldet to the fuselage and nothing has to be changed we will remove everthing to prime and coat the fuselage frame. Then, the inside of the tubular frame will be filled with dry nitrogen with slight pressure.
Over a special valve the inside pressure can be controlled and refilled if necessary.

As a change we went on to the designing the special shaped wing tip bows. As we prefere the Waco QCF wing tip planform and curvature, we simply adopted this to our Vintage Hatz. In order to achieve the beautiful slope of a QCF wing tip bow, it’s manufacture is more difficult than one that is a straight line (one, that can be laminated on a flat board). As our bow is “3-dimensional”, we had to build a special jig to be able to make the laminations. There are two symmetrical bow pairs, 1 pair for the left and the other for the right wing. Both are made with the same jig, the other is made “upside down”. The bow is a 7 layer laminate made from pine wood and the individual layers are made from two pieces glued together at scarf joint at an angle to have the grain running about parallel to the slope of the laminate. The laminations are cut then using a template and are all different when flat, however match when having the final form. Watch for pictures in the “custom work” section.

For the leading edge spar we decided to have made our own machine router knive and made them ourself similar to the Makelan design. We wanted to have a bit more resistance at the leading edge and we think that way it’s easier to cover the leading edge in two parts. For covering the convex part of the leading edge in the region of the wing tip bow, we are building a special press moulding to fabricate a three layer birch plywood forming. That the project state in winter 2008/2009 and the history will be continued as progress allows.

Written by Hans U. Gautschi





Hans.U have a innumerable time contributed for investigations!




Video film presentation of our project by the Swiss federal television

January 2008


Following the sad crash of Hans Georg Schmid at the start of his flight to Oshkosh prior to his attempt to set an around the world record over the poles as well as other accidents where experimental aircraft have been envolved, the Swiss Experimental Association (EAS) wanted to present some positive promotion to the experimental movement. The idea was to publish a video filmed by the Swiss federal television showing a well guided project. EAS approached us to present our Hatz project. That’s why this video was born.





On the occasion of the Aeroexpo at Buochs Switzerland 09, we exposed our fuselage & empennage paired with the wings from Jürg Müller

August 2009


click for enlarge




The swiss Experimental Association release, issued 2012






The Airline Edelweiss from Switzerland published beside others our project at there flight brochure 2013






Aero-Revue, issued 2013