ZEPPELIN-STAAKEN R-XVII

[delcyros]

While writing down a booklet for a friend, I was wondering about the Zeppelin Staaken R-VI successor.
The original Zeppelin Staaken R-VI is well known for it´s unparalleled size, beeing the first bomber with enclosed cockpits and supercharged engines.
What perhaps is less well known is that Zeppelin-Staaken was working on a number of modifications to the plane (R-XII to R- XVI) until it started a general new conception in 1918, whiches resulting Zeppelin-Staaken R-XVII was nothing short than a quantum leap in bomber design in general appearance. The end of world war one closed the files but Zeppelin Staaken was eager to modify the R-XVII into a purely civil version. Small parts construction on the so called "1000 hp" plane started in may 1919 at Berlin-Staaken.
Designed by Baumann and Rohrbach, who favored thick-wing cantilever monoplanes, but unlike Junkers, who used tubes and ribs covered with corrugated sheet, Rohrbach used dural stressed skin employing a single torsion-box spar running from wingtip to wingtip, its smooth top and bottom serving as the wing’s upper and lower surfaces. Leading- and trailing-edge ribs, attached to the front and back faces of this box and covered with thin dural sheet, gave the wing its shape. His E.4/20 of 1920 was a streamlined, all-dural design powered by four engines, weighing 18,700 pounds loaded. Only large wheels and landing gear struts marred its lines, and its high-placed, tapered, cantilever wing spanned 102 feet. It had a cabin that seated up to 18, as well as a lavatory and generous mail and luggage space.
The fuselage was completed in june, 1920 and the allied controll commission allowed testflights under supervision of french and british officers with Maybach IVa-engines. The maiden flight was on sept. 30th with Carl Kuring.
At its first flight, in 1920, both its design and performance—cruising more than 130 mph at less than full power, and ranging nearly 850 miles—were a good dozen years beyond what any other airliner had attained.
The allied controll commission regarded the legend performance as to high to be considered as a civil plane (top speed in excess of allied fighter top speeds) and Zeppelin had to deliver the engines back to ILÜK while it could keep but was forbidden to sell the fuselage and wings.
But though never itself produced, many of its features—stressed skin, torsion-box spar, leading edge engines, and gracefully tapered wing—became standard elements of long-range aircraft, as did its general configuration.
The USA sent two engeneerers to Zeppelin in order to negotiate with and perhaps buy licenses from Zeppelin Staaken but Reinhart and Deeds arrived only to be informed that the plane had to be scrapped by orders of the allied controll commission.

The ILÜK decision to scrap the prototype has to be seen in relation with early allied high altitude trials, such as the french Villacoublay trials of 1918 where the max. speed of a turbocharged fighter was 205 Km/h @ 4.500m (very comparable to the 205 Km/h at this altitude of the actual performance projection for the E4/20).

Further reading:
A. K. Rohrbach, “Das 1000-PS Verkehrsflugzeug der Zeppelin-Werke, Staaken,” Zeitschrift für Flugtechnik und Motorluftschiffahrt, vol. 12, no. 1 (15 Jan. 1921);
E. Offermann, W. G. Noack, and A. R. Weyl, Riesenflugzeuge, in: Handbuch der Flugzeugkunde (Richard Carl Schmidt & Co., 1927).
Peter W. Brooks, article in Air Pictorial (June 1986). [thanks, Graeme!]

[delcyros]

The performaces were considered to be:

official designation: E4/20 (designation given by ILÜK)
company intern designation: 1000PS plane

engines: four Maybach IVa supercharged 6 cyl. engines (245 hp each), rated altitude: 8.275 ft. / 2.500m
Crew: 3
passengers: 12-18
max. payload: 3.970 lbs / 1.800 Kg (incl. passengers, 628 Kg fuel)
payload at max. range: 2.600lbs / 1.180 Kg (incl. passengers, 1.250 Kg fuel)
take of weight: 18.740 lbs / 8.500 Kg
structure weight: 9.540 lbs / 4.372 Kg
span: 101.8ft
wing area: 1141 ft^2
aspect ratio: 9.08
length: 54.6ft.
height: 14.9ft.

range: 740 mls (design)
speed: 140 mp/h / 225 Km/h at Sea level
cruise speed: 130 mp/h / 200 Km/h at Sea level
stall speed: 68 mp/h / 110 Km/h -at 7.500 Kg-gross weight
Cl-max: 1.20
service ceiling: 19.500 ft.

statistics (NACA TM 5):
50 ltr. needed for 100 Kg payload (design)
1000 Km distance may be covered with 300 Marks (design, 1922 state german currency)

performance estimation (see below for details):
best speed: 152 mp/h / 245 Km/h @ rated altitude (2.500m)


The wings were of a particluarely thick airfoil, which allowed the construction of access tunnels to the engine nacelles to be embedded into the wings structure. The planform was slightly tapered to the ends with a very high -esspeccially for the 20´s- aspect ratio, allowing for an unpredecented low induced drag which in return significantly improved the performance. Not all of these figures may have been design intentional but the combination of a thick airfoiled but braceless and struttless wing construction in combination with a high aspect ratio, a large span and tapered planform must be considered as a radical and progressive departure from earlier Zeppelin-Staaken giant wing conceptions.

[B-17engineer]

If it is a Bomber why does it need passengers? or was that before it got converted into the bomber

[delcyros]

Germany was not allowed to build military planes in accordance to the Treaty of Versailles. The only possibility to try to continue running aircraft companies was in the civil sector. Zeppelin tried in this case and the plane eventually was transformed into a civil plane but as with many other companies (LVG, Hansa Brandenburg, Albatros), the allied controll commission prevented civil certification until the companies went into liquidation.

The military version sure would have less payload but the documentation for this is lost. Just for those of You who want to know how a strategic bomber in 1920 might have looked like.

[Graeme]

Thanks Delcyros. Interesting aircraft.

It had a novel passenger entrance...

Originally Posted by delcyros

the allied controll commission prevented civil certification until the companies went into liquidation.

Bill Gunston points out that the Inter-Allied Control Commission disallowed the E-4250 but deemed the Junkers F13 (developed at the same time) "to have no military potential" and so construction was allowed. Lucky for Junkers.

[delcyros]

Thank You, Graeme.

I have traced down the original image for Gunstons drawing:
(source: Booklet from Zeppelin exhibition Friedrichshafen 2006, Deutsches Museum, Ulf Essers, Peter M. Grosz)

Bill Gunston points out that the Inter-Allied Control Commission disallowed the E-4250 but deemed the Junkers F13 (developed at the same time) "to have no military potential" and so construction was allowed.

The Inter-Allied Controll Commission allowed construction and test flights of this plane. But once they realised after test flights that only two fighter-types could reasonably match the speed of this giant they
demanded the plane to be scrapped. Junkers was clever enough not to quest for extreme performances.

Another novel figure was the washing room in the stern and the bord toilet.

[Graeme]

Originally Posted by delcyros

But once they realised after test flights that only two fighter-types could reasonably match the speed of this giant they
demanded the plane to be scrapped.

Hi Delcyros.

There is a very detailed assessment of the E.4/20 in an issue of Air Pictorial (June 1986) by Peter W. Brooks. Brooks points out that there was also Allied resentment at rumours of a possible trans-Atlantic attempt with the aircraft that hastened its demise. The 'planned' flight was to be piloted by Captain Hesse and Lieutenant Lehmann. Since the E.4/20 burned about 1 Kg of fuel per Km it was estimated that 3,500kg of fuel would be enough to make the flight against the prevailing winds. With a projected production gross weight of 9,180kg this was considered "just possible".

In late 1920 there was a projected scaled down version (effectively half size) of the E.4/20 called the E.2/21, designed to carry six passengers with two leading edge engines it was abandoned in late 1921.

Compared to the Handley Page 0/10 and DC-2...



More characteristics...





(Profile from "Conquerors of the Air" by Carlo Demand abd Heiner Emide - 1968)

[delcyros]

Graeme,

I owe You a beer if You can shed more light on this plane! That´s fantastic info, indeed.
Brooks article was unknown to me & I will try hard to get a copy but I am afraid that Air pictorial isn´t aviable in central europe libraries.
I am still searching for a fuel consumption curve of the Maybach IVa engine. I am somehow surprised by the legend performances. Just questioning because it even compares with the four engined Armstrong Withworth A.W. XV (maiden flight 1932) and Fokker F XXXVI (maiden flight 1934), altough both enjoy the advantage of more advanced engines as well as more streamlining.

There is an excellent picture of the scrapping works on the prototype E 4/20 from the collection Koos in the recent issue of Flieger Revue extra, showing the cockpit and the acess tunnels in the wingroots. I may post it later (have to ask firstly).

best regards & many thanks!


Edit: The lower profile drawing is likely in error wrt the nose. I can make a good case of it with the Koos photo. The profile shows the state of the E4/20 from the very first picture (compare above), where the cockpit is covered by textiles to prevent excessive cockpit heating caused by direct sun exposure. This artificial textile cover makes the nose looking that smooth. The nose curve is a bit deeper, on about the line of the lower spinner.

Other details of interest are the undercarriege and the camouflage pattern. The undercarriege consisted of four (not two!) main wheels, each 1600mm diamter. Two of the wheels were paired each. The load carrying capacity must have been considerable (Staakens 800 mm tires had a load taking capacity of 4000 Kg per wheel). A half embedded nose wheel and a sporn completed the gear system (compare picture below).

Not all of the plane was left in silver-metallic. The outer wings indeed were produced partly in wartimes and still showed the typical night bomber camouflage (compare details).

[HoHun]

Hi Delcyros,

>I am still searching for a fuel consumption curve of the Maybach IVa engine.

Hm, I don't have any curves, but here is some data from Kroschel/Stützer's "Die Deutschen Militärflugzeuge 1910 - 1918":

Maybach
Friedr.-
hafen
Mb IVa
1917
6ZylR
Wasserkühlung (water cooling)
245 PS Nennleistung (rated power)
245 PS bis 2,5 km (up to 2.5 km)
1400 U/Min Nenndrehzahl (rpm rated speed)
165 mm Bohrung (bore)
180 mm Hub (stroke)
23 L Hubraum (displacement)
1:4,94 Verdichtung (compression)
1759 mm Länge (length)
554 mm Breite (width)
993 mm Höhe (height)
403 kg Gewicht (weight)
215 g/PS/h Verbrauch Benzin (consumption gasoline)
10 g/PS/h Verbrauch Öl (consumption oil)

Maybe it's a beginning ...

Regards,

Henning (HoHun)

[delcyros]

Thanks HoHun, that helps.

The question is whether or not 215 gPsh (ca. 277 l/PS/h) specific fuel consumption are related to cruise or max poweroutput?

It would compare well with

Argus AS III (6 cyl. inline, 1916):
0.229 l/hp/h @ 140 hp (78% powerload out of 180 hp max)
or 177 g/PS/h @ 140 hp -rated power is at sealevel

BMW IIIa (6cyl. watercooled, 1917):
0.225 l/hp/h @ 160 hp (86% powerload out of 185 hp max)
or 174 g/PS/h @ 160 hp -rated power is from sealevel to 2000m

Benz IV (6 cyl. watercooled, 1916):
0.230 l/hp/h @ 200 hp (87% powerload out of 230 hp max)
or 178 g/PS/h @ 200 hp -rated power is sealevel

Maybach IVa (6cyl. watercooled 1917):
0.277 l/hp/h @ ??? hp (out of 245 hp max)
or 215 g/PS/h @ ???hp -rated power is from sealevel to 1800 (early) and 2500m (late) altitude, respectively.
also:
0.258 l/hp/h @ ??? hp
or 0.200 g/PS/h @ ???hp

More datas are necessary to draw a specific fuel consumption curve related to power but the suggested datas are at least in the same ballpark.
The most economic power is usually on the left side of the curve, this means that a more economic flight is able at higher specific fuel consumption but lower power, one reason why multi engined planes are significantly more fuel efficient than single engined ones.

best regards,

[HoHun]

Hi Delcyros,

>More datas are necessary to draw a specific fuel consumption curve related to power but the suggested datas are at least in the same ballpark.

Hm, I believe your figures for the rest engines are somewhat on the low side - are you sure that there is not some accidental confusion between L and g in the original source?

Do you have von Gersdorf et al.'s "Deutsche Flugmotoren und Strahltriebwerke", by the way? It might be worth checking for consumption figures, too ...

Regards,

Henning (HoHun)

[delcyros]

I admit that I have only limited information of period propulsion. The figures derive from the virtual aircraft museum and are correlated between "Reiseleistung" and "Reiseverbrauch" (but You are right that they appear to be in the range of automobile rather than aircraft specific fuel consumptions):

Das Virtuelle Luftfahrtmuseum - BMW III a

I would not be surprised to see a figure of 215 g/PS/h at ca. 90-95% or 30-35% powerload.
The Maybach IVa was also rated at 200 g/PS/h specific fuel consumption (again without respective powerload) in:
Peter Kleinheins, Wolfgang Meighörner (Hrsg.), Die großen Zeppeline (2004), p. 94.

Kyrill v. Gersdorf also has some figures in his progresses in aeronautical research articles.

Only about 810 hp (82.6% powerload) are necessary to establish the suggested cruise speed of 200 Km/h at sea level. The trial speed of 200 Km/h continous & 225 Km/h max derive from sea level conditions, where the Maybach IVa delivered about 235PS at 1400 rpm according to Gersdorf. The Maybach IVa was overcompressed and could deliver the max. nominal (for 1400 rpm) outptut of 245 PS at 8.275ft., which would be the altitude for best performance & most economical cruise, too.
The most economical flight regime cannot be fixed without a proper specific fuel consumption curve of the engine in question. I have pretty well curves for Hispano and Merlin but none for Maybach.
These curves are often quite similar for each family but significant changes might occur when compression rate and fuel quality changes.
An often repeated mistake is to use the figure for specific fuel consumption for all powersettings as a fixed value.

From the aforementioned datas I have tried to compile a performance chart. The speed curves are estimations, but they appear to be reasonable (top speed at rated altitude is 152 mp/h / 245 Km/h @ 250+ PS under the assumption that best speed at about Sea level was 225 Km/h@245PS), the poweroutput curve for the Maybach is a correlated projection from performance drop of various Benz, Daimler and BMW engines from NACA-reports and might be subject to errors above rated altitude. The service ceiling with the geometrical method is quite high, ca. 5.780m. Gross weight was assumed to be G(f)= 7.500Kg.

best regards,

[delcyros]

Another interesting find unearthed in W.G. Noacks NACA technical note 48, dating to may 1921. The appendix includes the original barographic readings of the E4/20 testflights with & without supercharger from late 1920.

The service ceiling of this airplane appeared to be 3.800m (ca. 12.600 ft.) without supercharger and 5.900m (ca. 19.500ft.) with in the service ceiling trials. Heureka! That is pretty close to my guessed figures.

Note that only the graph with "II" (supercharged) is actually a flown barographic reading. The graph with "I" (without supercharger) appears to be a projection without supercharger (the Maybach IVa was "supercharged" by overcompression).

best regards,

[HoHun]

Hi Delcyros,

Looks like a really good estimate! Did you actually extrapolate it graphically (outstanding job then!), or did you calculate it?

My calculated result is generally in quite good agreement, though I'm not sure about all of the parameters - for example, were the Maybach engines direct drive? I noticed that Kroschel/Stützer mention a geared version with one of the Zeppelin-Staaken bombers. What was the propeller diameter? (I can only calculate constant speed propellers anyway, so my results are not so accurate. If you have an idea how to approach constant speed props, I'd like to learn how it's done - I'm always looking for help! :-)

Regards,

Henning (HoHun)

[delcyros]

Hi HoHun,

I happen to use a program for stall speeds for the estimates (it includes, Cl-max, air density, wing area, weight and g with the simpliefied formula developed in NACA-reports) There was some kind of back & fore correlation necessary but stall speed, altitude (and thus air density), Cl-max and weight was aviable from the datas provided by Graeme´s valuable excerpt from the Air Pictorial Series. In this way I matched the figures and calculated the change rate at increasing altitude (I used standart atmossphere conditions for air density). The rest was done graphically as to few inforamtions are aviable (basically only the power at rated altitude) for computation.

The Maybach IVa was used in connection with 3.20m and 3.60m props. The latter were typically used for R-planes, while the former was used on G-planes (except floats). My cdr- measurements adjusted from a more detailed picture give two values for the prop diameter: Compared via wheel diamter (1600mm) I get a prop diamter of 3.67m and compared with height (4500mm) cdr gives a prop diamter of 3.60m. Both figures are in good agreement with the aforementioned 3.60 m standart prop diameter for R-planes

I cannot say whether or not the engine was geared (a simple reduction gearing would be desirable for large props) and have forewarded the question to the Zeppelin Museum in Friedrichshafen. They had a quite accurate scale model of the E4/20 on display . It misses the auxilary nose wheel & has single main wheels instead of twins but otherwise it´s very good, note the fully closed cockpit.
[this picture has bee posted here
RC-Network Modellbau Magazin
]



hope this helps,