Pfalz Fokker or Albatross

[bristol scout]

Originally Posted by Cigogne

Chock,

Your joking, right, about the wings falling off of Fokker-built machines? I know of no reports of D.VIIs shedding their wings due to failure. I know that there were some instances of the rear portions of the ribs failing of the centre-section portions due to excessive stress from combat maneuvers, but not of spar or wing failure. The outer portions w/ the control surfaces did not fail. The the examples I am speaking of are seen on the ground after their pilots safely landed. The box spars were extremely strong. If an aircraft was damaged in combat due to gunfire or collision, that was another matter and not related to the integrity of the airframe.

The aircraft catching fire was due to faulty phosphorus ammunition and the high-temperatures in the summer heat. The Unseasonably warm summer temperatures of 1918 combined w/ the lack of ventilation to the ammunition boxes and the unstable nature of the Ph munition resulted in a number of fatal accidents due to the combustion of the ammo.
The summer weather was an unforeseen factor not related to the design of the aircraft. Removal of cowling panels and addition of cooling vents and louvres for adequate ventilation fixed the problem.

I don't know of any German pilots who complained of Fokker-built machines vs. Albatros or OAW-built ones. There are ample photos of many of Germany's top pilots w/ Fokker-built D.VIIs. I think you are spreading a myth here. Where are you getting your information? There were a few accidents after the war with surplus machines, but who knows how they were cared for or maintained by the occupying forces? Smells like the A.R. Weyl myth being perpetuated from his Fokker: The Creative Years book that needs a ton of salt while reading it.

The Mercedes D.III originally had 160 h.p. when it came out in 1915-16. The uprated versions of 170-175 h.p., 180-200 h.p., that added the D.IIIa and D.IIIaü to the nomenclature were improvements of the existing D.III design and not a totally new design. Hence, despite these improvements in much of the literature it was still referred to as the D.III 160 PS. (PS = h.p.)

Cheers!

Hi Cigogne
I could have used you some months ago when in a very acrimonious 'debate' because I dared to mention ---and support--the very severe limitations of 'Fokker-The Creative Years.....

[Dan_San_Abbott]

hi Chock:
Albatros did return to the two spar lower wing in in the Alb.D.IV with the geared version of the Mercedes D.III engine. Because of problems with the engine, the Alb.D.IV project was abandoned.
After the return to the single spar design in the Alb.D.V and D.Va, in August 1917, Albatros returned to the two spar lower wing in the Alb.D.VII powered with 195Ps Benz BzIIIbo V8 direct drive engine. The performance showed real promise, it performance was better than the Fok.D.VII of 1918. All the wrinkles had not yet been wrung out of the engine. Initial tests showed the airframe suffered from resonance vibrations. After some change to the airframe, the vibrations were corrected, however the machine failed in performance and the design was dropped.
All subsequent fighters design and developed at Albatros had two spar upper and lower wings.
Blue skies,
Dan-San

[bristol scout]

Dr. Martin O'Connor in his Austro-Hungarian Aircraft In W.W.1 mentions the fact that---

"When the Albatros D111 design was ready for license production, FLARS witheld combat clearence because of the sesquiplane design of the aircraft. Special wing loading tests were performed which led to the insistence on the part of FLARS that five specific changes be made in the construction of the wings to improve their strength. These changes, combined with the superior workmanship of the OEFFAG factory workers resulted in an aircraft free from the wing failure problems that plagued the German-built D111 and DV fighters"

It would seem that there is nothing intrinsically weak in the sesquiplane layout--I do not know what 'changes' were made--but it is apparent from photos (on clear doped ones) that the lower wing did not have any 'extra' spars.

Dave.

[Chock]

The thing with flutter is that extra spars are not always the solution, as the problem is not always related purely to wing bend, but also to wing twist, and spars in themselves will not always prevent wing from warping, but are rather likely to prevent wing bend. For example, on modern stressed skin aircraft, the solution to prevent flutter is often simply using thicker metal panels on the outer ends of the wing in order to give more compression resistance to wing twist.

Perhaps it will help to explain what flutter actually is: When a wing produces lift, it bends upwards as it takes the weight of the craft, but it also bends as the wing itself generates lift and the upper surface is sucked up by the low pressure over it and the high pressure under the wing. This can happen unevenly across the surface (front to rear) as the centre of lift shifts with speed. When the wing bends upwards with the lift, the wing material tends to want to bend it back to its normal static position, and at certain speeds this can set up a harmonic cycle, where the wing bends up with the lift, then bends back to its normal position, then then cycle begins again. In some cases this cycle can begin speeding up and it can cause twisting of the wing because the structure is thinner at the leading and trailing edges of the wing (twisting flutter is what happened with the Albatros), sometimes you can get both twist and bend happening. So depending on what kind of flutter you have, there are several solutions. On racing gliders and some jet fighters for example, the flaps often have negative settings of several degrees, so that you can dump lift in high speed dives to delay the onset of flutter by reducing the bend caused by the wing generating too much lift at high speed.

With the Albatros wing, and in actual fact also with the SE5 wing too, twisting was the problem as the speed increased, creating compression and expansion loads, and on the DIII and DV Albatros, this meant that the leading edge of the wing would fracture as the material was stretched beyond breaking point when the wing twisted too much, and then the weakened wing would occasionally break up completely. On the SE5, it would cause the strut to break away from the wing.

You can counter this twisting force by means other than adding spars, notably by adding webbing in between the spars. The webbing is zig-zagged tightly over and under the spars along the length of the wing to keep the wing from flexing too much by effectively 'tying the wing ribs together'. This is one of the modifications that was added to the SE5 when it became the SE5a (as well as more bracing wires. Another well known WW1 fighter feature you can see which is an aid to preventing wing twist, is the N-shaped interplane strut on the Fokker DVII, which effectively connects the front of the wing to the back and spreads the load, whereas with a V strut to the bottom wing, there is no such structure preventing that twist from occurring, which is why they added the little strut extension on the DVa and some additional bracing wires, to try and stop the wing twist.

Al