Siemens-Schuckert Werke D.III - Marek - 1:33

[Golden Bear]

Good choice of models, Ron. This is my adorable wife's favorite and it is parked over by her chair in the living room. I really like the lozenge on it.

Nice clean build too! I read that the engine and the prop actually counter rotate, so that will be a neat set of detail to see you implement.


Carl

[Don Boose]

Superb craftsmanship, Ron! And a fascinating airplane (a lot of those showing up in this Forum). Don

[member_3]

Carl - I haven't completed the engine and prop yet but when I do I'll put them on the kitchen counter and see if they rotate - that's the only way they will! I am considering trying to get one or both to at least rotate separately. My wife is still in birthday mode so I will have to wait a few more hours to get back to work on the D.III.

Thanks for the kind words, all.

[Clashster]

Great looking work, Ron! And quick, too! Here I am still looking at the same model for the past couple of months... (key word is looking) Great job!

[Golden Bear]

I wimped out on the rotating prop thing... I was worried about the fragility of the cowling and all. But I'm more of a risk taker now.

[shrike]

Originally Posted by Golden Bear

Nice clean build too! I read that the engine and the prop actually counter rotate, so that will be a neat set of detail to see you implement.


Carl

Yup. The engine spins one direction and the prop the other way.

The practical limit on a propeller is tip speed. Tip speed must be less than Mach, or bad things happen. Horsepower of an engine however tends to increase with rpm (as evidenced by 1700hp 1.5 litre F1 engines of the 80's) In order to harness that extra power you have to gear the engine output back down to keep the tip speed below the speed of sound. Then go with wider blades and/or more of them to absorb the power.

The Oberuesel got it's 'gearing' by spinning prop and engine in opposite directions effectively doubling engine RPM without increasing prop RPM beyond limits. That how it's output is so high compared to it's contemporaries, and why it's swinging a 4 bladed prop rather than 2 like everyone else.

[CharlieC]

Originally Posted by Golden Bear

I read that the engine and the prop actually counter rotate, so that will be a neat set of detail to see you implement.


Carl

Slightly different take.....

Rotary engines had the unfortunate property of making the aircraft quick to turn in the direction of the engine rotation (i.e. with the torque) but pigs in the other direction. Also if you got into a spin in the direction of the engine rotation it was difficult (if not impossible) to recover. The Siemens-Schuckert design was an elegant solution to reducing the torque effects of the rotary engine on handling and still get the benefits of the high power to weight ratio of the rotary engine. I remember reading somewhere that the S-S was the fastest climbing fighter of WW1 so it seems to have worked.

Regards,

Charlie

[shrike]

It's more complex than just torque, it's gryoscopic precession with the engine being a 150kg flywheel. A sharp turn to the right induced an upward vector ( in most engines at least) allowing the turn to be tighter without losing lift and stalling. A turn to the left induced a downward vector that required a slower turn to avoid a stall.
The S-S still has the gyroscope, although the prop might counter act some of that, it's only 25kg or so.

[CharlieC]

The Siemens-Halske engine was a bit more complex than a simple gearbox arrangement - the crankshaft, rods and pistons rotated in one direction (clockwise from the front), the propeller, crankcase and cylinders in the other. The gearbox was at the back of the engine bolted to the firewall and the propeller was geared down to half speed. I haven't been able to find any numbers on the residual torque of the engine assembly but it must have been quite low.

Apparently the 4 bladed prop was a solution to an earlier Siemens-Schuckert design problem where a 2-bladed prop made the undercarriage legs excessively long.

Regards,

Charlie

[member_3]

My love affair with this build got a little shaky lately. First, the engine. This uses standard radial/rotary engine construction with various size tubes with a disk at each end and rolled cylinders with a disk on the bottom and a cylinder head piece on top. I had assembled the crankcase with the pushrods and then started adding the cylinders. As it turned out the cylinders were a tad too tall so the pushrods do not quite reach the lifters on the cylinder head. When I do the next one I will leave off the disk at the bottom of each cylinder and just glue the cylinder directly to the crankcase.



The next issue was the cowling front plate with the four openings. The side profile assembly diagram indicates that it should be installed inside the front of the cowling. In order to accomplish this I had to trim nearly 1mm around the outer edge to get everything to cooperate. I'm not sure where the problem lies here - maybe I "tightened" the cowling too much when assembling it. At any rate, I'll be aware of that when I do the next one.



Ah, the lower wing panels! These panels slide into airfoil-shaped cuts in the fuselage. These cuts extend fore and aft of bulkhead B-C so there are slots in the upper and lower surfaces of the wing at the root to accomodate the bulkhead. As designed/printed the slot locations are wrong. The upper one had to be trimmed on the forward edge and the lower one had to be severely enlarged on the forward edge to properly align with the bulkhead. In addition, the airfoil-shaped openings had to be enlarged to accomodate the thickness of the wing panel with the box spar installed. This just an inconvenience since the wing fairing will cover all this but it was the first serious design error I had encountered. In the following photos the wing tips have not been shaped and glued.



The wing fairing was the one that nearly had this project end in the trash! Not a thing wrong with the design but it requires patient and careful shaping -PATIENT and CAREFUL, not my strong suits! After much fumbling and frustration I decided the best approach would be to glue the bottom surface in place and then, using that as an anchor, do the final shaping and alignment of the upper surface. As you can see here, the bottom was pretty much a snap.



The upper surface of the fairing requires that it be folded back upon itself to get the proper fuselage contact while also curving it to match the airfoil and align with the bottom fairing. There are numerous small cuts made along the fuselage joining surface which allows the airfoil curve to be achieved. I dampened the back surface with the usual stuff and slowly "sculpted" the necessary curves in the fairing using a sculpting tool from my miniatures toolset. I was mostly successful except toward the trailing edge where I did not deepen the curve enough toward the fuselage. As a result the outer edge does not run chordwisde on the wing but splays outward a little toward the trailing edge. The overall appearance is not terrible but I could have done a better job of it. I couldn't proceed to the left wing because of the state my nerves were in - I'll do that when I'm settled back down. I seem to recall that Marek's Pfalz D.III models have a similar fairing and produced similar comments in a build thread in another galaxy, far, far away. I'm glad I didn't install the machine guns; they would have been destroyed during the wing fairing struggles.