Questions about Fokker D.VIII wing

I'm looking for information about the wing dimensions and airfoil shape for the Fokker D.VIII. I was under the impression that the D.VIII wing was a direct decendent of the Fokker D.VII's upper wing. However, the aerodrome's aircraft data indicates that the D.VII had a greater wing span, 29'3.5" vs 27'6.75". My interest in the D.VIII's wing is related to it's historical significance in the development of the field of aeroelasticity. For example, a quote from the book Aeroelasticity by Bisplinghoff, Ashley and Halfman describes one of the first documented cases of torsional divergence. Since the D.VIII saw only brief combat service at the end of the war, who were the pilots that were killed in the high-speed dives described by the authors in the quote?"As an early example of this kind arose during World War I in the development of the Fokker D-8 airplane shown in Fig. 1-3. In the initial design of this airplane, which was a high-wing cantilever monoplane, the torsional stiffness was determined by a criterion which had been applied to biplanes. The D-8 was put into production because of its superior performance, and was not in combat more than a few days before wing failures repeatedly occurred in high-speed dives. Since the best pilots and squadrons were receiving them first, it appeared possible that the flower of the German Air Corps would be wiped out. After a period in which the Army engineers and the Fokker Company each tried to place the responsibility on the other, the Army conducted static strength tests on half a dozen wings and found them sufficiently strong to support the required ultimate factor of 6. This produced a serious dilemma, and it was clearly up to Anthony Fokker to discover the cause or cease production on the D-8. Static tests were undertaken by the Fokker Company, and this time, deflections were carefully measured from tip to tip. In Fokker’s words (Ref. 1-6), the following conclusions were drawn: “I discovered that with increasing load, the angle of incidence at the wing tips increased perceptibly. It suddenly dawned on me that this increasing angle of incidence was the cause of the wing’s collapse, as logically the load resulting from the air pressure in a steep dive would increase faster at the wing tips than at the middle. The resulting torsion caused the wings to collapse under the strain of combat maneuvers.” This seems to be the first documented case where static aeroelastic effects at a fairly high speed produced a redistribution in airload such that failure resulted."

[Cigogne]

NiedHF,

It was not the Fokker D.VIII that was the subject of the tests, but rather the E.V, which with reinforced wings was RENAMED the D.VIII when it was to be released back into service. Idflieg dispensed with the "E" classification and all new fighters, regardless of how many wings they had, were considered "D" types. What source are you getting your information from?

The problems with the structure were due to a subsidiary assembling the wings incorrectly and sloppy quality control. Idflieg's Sturzkommission believed there were other faults and Fokker had to make concessions to them in his redesign.

The E.V (and D.VIII) wing structure was a decendant of the Fokker V.1 and V.2 prototypes that first used this structure. All other Fokker cantilever designs are decendants of these two aircraft. They, in turn, were influenced (outwardly at least) by the thick wing designs of Dr. Hugo Junkers. It is clear that Fokker was influenced by them when seeing them in Dec. 1916. His cantilever wings only appeared after being influenced upon seeing the Junkers aircraft. Fokker's V.1 and V.2 wings, which were entirely wooden structures (including the outer skinning) was due to contact with another fellow named Forssman who ran a patent office and was a rep for the large German plywood manufacturer Brüning und Sohn.

The D.VII wing differed in many ways, one was that is was fabric covered. The E.V/D.VIII wings were covered with plywood skinning, making them more rigid. I am not certain that "high-speed dives" were the cause of the problem either. That seems suspect as it was a requirement that aircraft be able to dive. The aircraft proved this in the Fighter Trials. It was only after being produced and released to the Front where the problems manifested themselves. The rush to production and problems at the wing assembly facility where the original specs WERE NOT FOLLOWED were the causes of the problems. Not the design per se. Much has been written of this.

Cigogne

[greenknight]

NiedHF,

If you're still looking for information on the Fokker EV/DVIII wing, The May 1980 issue of World War I Aeroplanes (Issue #79) has a fair bit of material devoted just to the wing. See the link:

http://www.ww1aeroplanesinc.org/docs/back_issues.htm

I also read of the divergence issue, perhaps also in Bisplinghoff, Ashley, and Halfman some years ago. Back when I was doing my graduate work (late '80s) I remember my professor recieving a report that originated in Germany that contained a history of aeroelasticity and/or unsteady aerodynamics. It may have come from one of the German Univs., but the text was in English. To the best of my recollection the author's name was Bublitz, and report was written in the 80's. I was fascinated with some accounts of possible aeroelastic problems with some WWI aircraft. I remember Albatros fighters and Handley-Page bombers mentioned, probably the Fokker cantilever wing also.

I did a quick Google search using the words "Bublitz" and "Aeroelasticity" and got reference to a report by Dr. Peter Bublitz in a discussion at a technical meeting. Not too much to go on, but perhaps a start.

What you're researching sounds interesting. If I can be of help we can take this discussion offline.

Best Regards.

The book "Aeroelasticity", by Bisplinghoff, Ashley, and Halfman (BAH), Addison-Wesley Publishing, 1957, is a highly respected textbook on aeroelasticity and it would be surprising if their description of torsional divergence in the Fokker DVIII were completely inaccurate. My assumptions about the DVIII wing being related to the DVII wing came from a figure caption at another web site. Thanks to Cigogne for setting me straight on this. Since BAH directly quotes Fokker ref. [1-6] - Fokker, A. H. G., "The Flying Dutchman, " Henry Holt and Co., Inc., 1931, perhaps some of the BAH claims can be easily verified. Unfortunately, I don't have a copy of this book. Perhaps someone in this forum who has the book can check the quote? If the reference is correct, then it would be surprising if Fokker would have admitted to a design error if it really was an issue of sloppy fabrication as claimed by Cigogne. Of course, aeroelastic effects were not well understood in 1918, so Fokker should be credited with discovering this phenomena on his own! Also, no mention is made in BAH as to how Fokker corrected the problem, though he must have come up with a fix. What was the fix?

If the BAH quote is accurate, who were the pilots that were killed in the DVIII? I doubt that a mono-wing could fail in a dive without killing the pilot!

Torsional divergence is usually associated with high aspect ratio wings with insufficient torsional stiffness. I am not familiar with the DVIII wing, but if the wing had a plywood covering as stated by Cigogne, it seems as though the DVIII wing would have had a relatively high torsional stiffness. The Bublitz reference given by greenknight sounds interesting. I would be surprised if the torsional behavior of the DVIII was not examined more closely in the post-war period, since aeronautical engineers would have been very interested in understanding aeroelastic problems associated with the transition from the biplane to monoplanes. For example, BAH state: "In later experience with the D-8, subsequent to the war, U. S. Army Air Corps engineers at McCook Field, Dayton, Ohio, observed a violent but nondestructive case of wing bending-aileron flutter. This was cured by statically balancing the ailerons about the hinge line, a technique which seems to have been pointed out first by Baumhauer and Koning (Ref. 1-7) in 1922."

[Cigogne]

The book "The Flying Dutchman," Henry Holt and Co., Inc., 1931 on Anthony Fokker has been found to contain a lot of "colorful" stories that aren't true. Peter Grosz, Alex Imrie, and others have unearthed a lot of information that comes directly from Fokker company archives and from correspondence/interviews with surviving engineering staff, etc. to back it up.

Fokker "dictated" the book to a writer named Gould but didn't rely on a lot of hard evidence, it being more of a memoir.

So even though the other BAH book is quoting the Fokker/Gould "Flying Dutchman" book, the source material is flawed. While an interesting book, it needs to be taken with more than a grain of salt and weighed with other research.

The WWI Aero research, Imrie and Grosz material would be good to reference to get a more balanced picture.

Cigogne