Denemarken Fokker D.XXI project.

[Mathieu]

Hi,

Some days ago I sent a message to Orla Kragh Jensen, the man behind the Fokker D.XXI project in Denmark. he gave me so much infoprmation together with photos that I deceided to make a seperat thread about this project, even it is not a project in the Netherlands I place it under this part of the forum. If you want to reply, please do it in English so Orla and other Danish can read it aswell. I am very impressed with the progress so far and hope it will be finished in a few years!



Mathieu.

In February 2013, I was granted a homebuilder’s permission to build a Fokker D.XXI replica by the Danish Ministry of Transport, governed by the KZ&V (Veteranflyver Klubben, EAA Chapter 665). The permission is to g build a flyable Fokker D.XXI replica based on original drawings and information.

For the last approx. 30 years or so, I have had an interest I the Danish Army and Navy air forces prior to WW2 with a preference for the Army, “Hærens Flyvertropper”, and their widely use of Fokker aircraft. Initially I was planning for the Danish designed O-Machine, a design build on experience from the Fokker C1 recon plane but ended up with a huge number of pictures and documentations and a pile of drawings of the Fokker D.XXI making it the plane to build.

In my research, I have had the pleasure of visiting the museum in Soesterberg (The old one) on a Monday, having the Fokker D.XXI replica all for my selves and a friend (photographer) for a full day without limitations. The Dutch replica was measured, photographed, documented all over to support my project.

I also had the pleasure of being able to do the same thing with the semi original Fokker D.XXI, FR-110, in the museum at Jyvaskyla in central Finland, where I also had a day to investigate a more original version of the Fokker.


With the two research tours, several afternoons at the Danish National Archive, and I found my selves ready to file an application to build a homebuilt plane under the EAA homebuilder and national government approval.

I filed the application documented with an almost complete set of drawings, especially to support the fuselage steel structure as it had to be designed following modern rules for steel frames in airplanes. The rules are very well documented in the book “Construction of Tubular Steel Fuselages” published by the Aircraft Technical Book Company.
Well, I filed the application, it took a while to be approved as it was not the average homebuilders project, but I got my permission in February 2013.

Now, with the paperwork in place, the practical work could be started. Practical work meant that I had to use 14 days of my vacation to attend a TIC Welding school ad passing the exam to be allowed to weld my own plane. I did that, and went out looking for a suitable location for the building project. I found a location close to home and rented 1/3 of approx. 190 square meters in a work shop. Early 2015 I moved in and planned the project start. I needed quite a lot of tools and equipment and in April I received the first of many shipments of 4130 steel tubing from Aircraft Spruce in Germany. In May 2015, I started the welding the first main section of the fuselage, the cockpit section. The second main section was the tail fin and rudder post with the third main section being the rudder. In the autumn, I received a big load of steel tubes and took a week off from work to build the “Jig” for the complete fuselage, preparing the tubes by cutting, shaping them to fit the design. Within that week, I had the complete fuselage welded together and pre-painted to protect the metal.



During the spring og 2016, I have added details, flanges etc. to the fuselage frame and started on the rear wing arrangement and the elevator. I also added the last of the internal structure in the fore end of the fuselage.




At the moment, I am working on a tailwheel, as the original tailwheel I have in my possession does not lie up to the standard needed. So, I have to build a new one based on the drawings and measurements I have gathered.


The rear wing mounting flanges has been added and the basic structure frame for the rear wing has been mounted together with the lover strut support.
The elevator main tube has been added and mounted on the ball bearings after original specifications.

I waiting for a load of ¼” and 5/16” steel tubes for the profiling of the rear wings and elevator. When they arrive, the work of patience starts as welding the structure together with metal of that size and thickness, 0,71 mm wall thickness, really demands patience when working.

During the winter month, I have planned to start working on the Aluminum parts, the seat, panels etc. as they are riveted together and as it will be too cold for welding in the workshop. Also, the profiling of the fuselage is in the plan as that is mostly “bolt on” flanges to hold the shaped steel tubes and wooden parts.

As you have noticed, I have not been doing much work, Firewall forward, as I have not yet decided what engine to use. The original engine for the Danish built Fokker fighters was the Bristol Mercury VIII rated at 840HP, an engine that is very hard to find and most likely very expensive as it is so rare. I have been looking at the following substitutes: The Shvetsov ASh-62, very powerful rated at 1.000HP and on the heavy site. The Pratt & Whitney R-1340 Wasp rated at 600HP but almost the correct weight. The Wright R-1820 with a verity of HP output and a little to heavy. The Alvis Leonides 503 rated at 550HP is very small but with a suitable weight. All other alternatives seem too rare, too light or too underpowered and one thing that has to be considered is the center of gravity.

Until now I have only been doing research, construction and drawings for the main wing. I was involved with the ”reverse engineering” of the Fokker wing headed by Frank van Dalen and Theo van Wierst from Fokker Technologies for the PH-XXI, Jack van Egmont’s Fokker D.XXI. There was a lot of missing information on the main wing, as the Fokker drawings did not “fit” the specification for the Clack-Y or Clark-YH airfoil. The ”reverse engineering” project shoved that Fokker actually did construct a specific airfoil for the D.XXI fighter.

The main wing is a wooden wonder, stretching 15 meters from end to end and constructed around two box spars. For my wing, I have to have it stress tested before any approval for flying can be granted.

Overview over the main sections that I have been working on.




As last a photo of the genuine, under licence built, fuselage of the J-49.