Klemm Kl 153 "Späher" (Scout)

[Jemiba]

First steps :
I started with a pure reconstruction of the mock-up, as it is shown on those photos.
The next step, which is more or less already done, is estimation of the span, and then
I'll try to estimate, what the "real thing" could have looked like.
Here are the results so far, in the pdf you'll find an explanation of the why and wherefore,
clues and discussions welcome.

 

[hesham]

Wow,looks great,amazing my dear Jemiba.

 

[lark]

After years of searching and trying the Klemm "Späher" at last comes to it's own..
Thanks a lot for the work Jens!

 

[Grzesio]

Shouldn't the fins have a little bit more rounded corners? It seems to me (although without any geometric analysis ), the radius is approx. 1/4 of the fin height...

 

[Jemiba]

You may be right, though with the upper left and lower right vs. the lower left and upper right corners,
it's a draw, I think, and the fin in the background is bit too pixelated. But I noticed, that I got the junction
from the boom to the fin wrong.

 

[Kuno]

I struggle a bit with the two tail-skids... does not appear to me as if it could have worked this way except maybe on a concrete-runway... else they may have "hooked in" quickly.

 

[Jemiba]

True, would probably have been more in the way of the skid of the Fi 156,
with more rounded undersides. Maybe even such a strut would have been necessary ?
(drawing via http://wp.scn.ru/en/ww2/o/217/2/2)

 

[Kuno]

Looking at the photos of the model it appears to me a rather crude one, little details...as the tail-skids did not get much attention. Anyhow - considered the time it was designed... were tail skids still adequate then?

 

[Arjen]

You can get a much bigger radius with a tailskid than with a tailwheel of the same weight, which can be quite helpful on a soft and/or rough airstrip. With aircraft operating more and more from hardened surfaces, that has become less and less of an advantage. At the time when the Kl 153 was designed, it was apparently still thought to be worthwhile to use a skid instead of a wheel.

 

[Kuno]

I do not understand how a "bigger radius" would be of benefit... and just none of the aircraft have a tailskid since decades, not even those operated on "rough strips". Tailskid is also very bad if you have to manouver the A/C in the hangar by hand etc.. Tailskid: No good!

 

[riggerrob]

Tail skids were easy to make from the same hardwoods as axe handles. Tail skids also served as brakes because they easily dig into grass airstrips. Before brakes on main wheels, there was no way to turn airplanes on the ground.
Same thing under the wingtips to reduce damage during ground loops.

Now that most runways are hard, the vast majority of antiques have been converted to tail wheels.

 

[Kuno]

Agree - that was about the time of WWI. A/C were very small and light and could be lifted up by a few men on the tail to turn them around. But even durign WWII when the majority of the airfields were still unpaved - tailskids were not instaleld anymore (although they may still have been found on some obsolete but still in service A/C).

I would not continue this discussion here - the model of the Kl 153 is rather crude and I could easily imagine that what we see now as some sort of (unsuitable as it is on the model) tail-skid.... if the aircraft would really have been built would have become tailwheels.

 

[Arjen]

I do not understand how a "bigger radius" would be of benefit...

Radius of the object's surface that touches the ground. A small radius wheel will sink deeper into soft ground than a bigger radius tailskid. Tailskids were vanishing from aircraft at the time of the Kl 153's design, so it is noteworthy that a tailskid is featured.

 

[Jemiba]

Judging photos of the Fieseler Fi 156 during the war, the majority still seems to have used skids
instead of tail wheels.

 

[Arjen]

Given the Fi 156's purpose - and the lightness of its construction - the Fi 156 using a tailskid makes sense to me.
I can't think of many other WW2 aircraft with tailskids.

 

[Jemiba]

I tried to translate the comparison table into an excel chart, but some parts are hardly readable.
Nevertheless, as planned, the Kl 153 only was heavier, than the Storch, when carrying a crew of 4,
whereas the Storch was limited to 3. Maybe a bit over optimistic ? The two Hirth engines alone would
have had a weight of about 310 kg, compared to about 230 kg for the Argus 10 engine of the Storch.

 

[Jemiba]

I tried to depict, what the real aircraft could have looked like, always open to discussion.

 

[Wurger]

I would say an excellent try ! Great work, Jens.

 

[Kuno]

I am still strugling with the design of that aircraft, considering that its name "Späher" (Scout) indicates that its was thought to be a recconnaissance-plane. It had already been stated that the number an the size of the windows would not really be suitable for the observer(s)...or was there a planned glazing in the floor of the aircraft to look down?

The gull wing also puzzles me a bit - normally a gull wing is arranged the opposite way to allow shorter legs for the undercarriage but enough ground clearance for the propeller. As it is for the "Späher" it may have been designed that way to lift the engines higher to allow the obeserver a beter view downwards/sidewards...

...which leads to the question on why the aircraft had two engines instead of one in the front? Two (rather weak) engines would only make sense in this case, if the observer would have been accommodated in a glazed nose - which apparently was not the intention.

It seems to me they had good reasons not to build this aircraft ;-)