Historical information on the Zeppelin "R" Series:
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Without doubt the most remarkable aircraft built by the Germans during
the First World War were the "R" (Riesenflugzeug) type giant machines with
four, five or six engines. The eventual degree of reliability that was
attained was a noteworthy achievement when it is considered that
everything connected with these unique aircraft had to be developed and
produced from scratch. There was no previous experience in the design of
aircraft of such gargantuan proportions. As an example of just one of the
many difficulties, which had to be faced, that of engine failure may be
instanced. Many of the first engines fitted in the Giants had been used
with excellent reliability in airships, but in the aircraft they blew up
(often literally) with monotonous regularity. This failure was eventually
discovered to be due to the fact that the engines were called upon to
produce upwards of 1,200 r.p.m. for considerable periods on take-off and
climb, whereas in airship installation they were never-or rarely-called
upon for more than a steady 800 r.p.m.
The Zeppelin Staaken R types had been developed, with varying engine
permutations, from the V.G.O. I, which first flew in April 1915, to the R
VI, in which production version had four high compression engines mounted
in tandem pairs - first four 245 h.p. Maybach and later 260hp Mercedes.
The wings were all basically the same, with a 42.2 metre wingspan and a
332 sq metre area.
VGO-I and VGO-II, 1915
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In 1915, V.G.O. (Versuchsbau Gotha Ost) produced the VGO-I with 3 x 240Hp
Maybach engines (the engine from which the later high-compression 245hp
Maybach Mb.IVa engine was developed), having two pushers in wing nacelles
and one tractor in the nose, giving it a maximum speed of 110 km/h.
VGO-I : 9520 Kg and 720 Hp = 76% power loading.
The next model, VGO-II, was almost identical: 22 cm shorter, 40 cm higher
and 683 Kg heavier.
VGO-II: 10203 Kg and 720 Hp = 70% power loading.
These models, however, were very under-powered, requiring round 40 minutes
to reach 2000 metres, but as they were capable of payloads of upto 1 ton of
bombs, they did the job, and it didn´t matter how long the climb took them.
VGO-III
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The third version, V.G.O.III, was a six-engined machine, with two engines
in the nose, geared to one propeller, and four engines in tandem push-pull
pairs in the wing-nacelles. This model was later re-named R.III, and had
6 x 172 Hp Mercedes D.III engines - a total of 1,032 Hp.
VGO-III: 11600 kg and 1032 Hp = 89% power loading.
This model was still under-powered, but improving. It only took 30 minutes
to reach 2000 metres.
Staaken R.IV
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It was at this time that the Zeppelin Fluzeugbau had moved to Staaken, near
Berlin, in the summer of 1916, having transferred from Gotha-Ost, and it was
there the majority of the building and development work was carried out.
The next model was the R.IV, the first Staaken built model. This plane went
through several engine permutations.
As used to bomb England, it was the only production version with composite
engines: Two small 172hp Mercedes D.III in the nose driving the tractor prop,
and 4 large 230hp Benz IV in pairs, geared to one prop each in the wings.
Always 3 screws. The two Bz.IVs (460hp) were the most powerful engines that
the gearboxes could tolerate.
R.IV typically 13000Kg and 1264hp. Power loading = 97% (but only at sea level).
This model required 27 minutes to reach 2000 metres.
It was under-powered compared to the R.VI above about 1200M which is why this
more powerful version was dropped for the 'less powerful' 4 x Mercedes and then
for the 'even less powerful' 4 x Maybach. By 1918 there were lots of AA guns
and it was power at altitude not power at sea level that mattered.
Staaken R.V
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The next model was the R.V, with 5 x 245Hp Maybach MB.IVa high compression
engines and three tractor props - the wing-nacelles each had two engines geared
to one propeller, and one engine driving aprop in the nose. The gearboxes, however
could not cope with the power of these engines, and the model was re-designed
with independant propellers for each engine, becoming the R.XV, but was
produced too late to see any combat, and handed to Japan at the end of the war.
Staaken R.VI
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Series production switched to the R.VI, a simpler 4 engine and 4 prop
version first with Mercedes (1917) and later with Maybach (1918) High
Compression engines.
R.VI/28 weighed 11460Kg and had 4 x 267hp = 1068hp = 93% power loading
but it retained that power at altitude. 27 minutes to 2000M.
Behind the flight deck and cabin there were 10 cylindrical tanks with 3000
litres of petrol, and a pump to fill a 150 litre gravity-tank above the cabin.
The R.VI/30, had a fifth engine, inboard behind the cockpit, driving a
supercharger turbine, which could add 15 to 20hp per engine but since any
Mercedes D.IVa was limited to a maximum of 267hp and only above 1300 Metres,
the compressor would be used to rate them at 267hp at a greater altitude
probably 2000M. It would reduce rate of climb below 2000M due to its weight
and then boost the rate of climb above 2000M.
This may have been the last version with Mercedes engines, after which the
switch to Maybach engines took place. The Maybach was rated 245hp at 2500M
without the compressor and maybe 245hp at 3000M with it, so the 245hp Maybach
was substantially more powerful than the 267hp Mercedes.
It is also worth noting that control of the refineries at Ploesti
allowed Germany to control what was produced and optimise the production
for German aero engine needs. The reliability of an aero engine depends
on the quality of the oil you lubricate it with. All German engines
became more reliable after Germany controlled Ploesti and changed the
refining processes.
Of the eighteen R.VIs completed (R 25-39 and R 52-54), six were built
by Aviatik, seven by Schutte Lanz and four by O.A.W. All except R 30,
the experimental supercharged model, saw operational service with
Riesenflugzeugabteilungen 500 and 501 on the Western Front and operated
from the Ghent area.
Construction of these monster machines, which spanned almost 140 ft.,
was a complicated and lengthy process, and the total number of man-hours
must have been prodigious.
The fuselage was of wooden construction and basically a fabric-covered,
braced, box-girder. The upper longerons were in a horizontal plane on a
level with the airscrew axis for almost the whole of their length. The
lower longerons were parallel as far back as the gun position, where they
swept up in a straight taper to join the upper longerons in a horizontal
knife-edge. A gun position was provided in the extreme nose, and in this
cockpit the bomb- release gear was located. Aft of this position the two
pilots sat side by side with dual wheel controls, followed by the radio
operator's and navigator's compartments. On a level with the leading edges
of the wings, provision was made for a mechanic, who was mainly
responsible for controlling the emptying of the eight cylindrical fuel
tanks so that trim was not upset. The spacious dorsal cockpit accommodated
two gunners, who were also able to fire below the fuselage through a
ventral position in the floor. The section of space for stowage of
eighteen 100 kg. bombs with a through passageway in order to communicate
with the fore part of the fuselage.
Of vast proportions, the wings were otherwise of orthodox construction
and based on two main spars, which were of double box-girder section. The
center panel of both wings extended as far as the engine nacelles and was
without dihedral, as was the whole of the upper wing. The outer panels of
the lower wing had marked dihedral. Taper on the wings was slight and on
the leading edges only. Steel-tube compression members were positioned at
interplane strut locations. The ribs were closely spaced and built-up
lattice-girder structures, with top and bottom spruce flanges held
together by double-lath web strips disposed zig-zag fashion. Ailerons were
of steel-tube framework and, being unbalanced, must have demanded
considerable muscle power-small wonder two pilots were required. All wing
surfaces were fabric covered.
Streamlined engine nacelles of alloy stringers and panels were
supported by twin "A" frames of steel tube located at the spar stations,
to which, in turn, the engine bearers were attached by a complex frame of
sheet steel and wood. The tandem-mounted engines were fitted with
gear-boxes, and the airscrews of the rear engines were driven through
extension shafts. A small cockpit was located between the engines wherein
the flight mechanic endured his lonely vigil. All struts were of
circular-section steel tube faired off with three-ply sheet.
An unusual feature of the Zeppelin Staaken R.VI was the wide use of
aluminum in the construction of the tail. This was a huge biplane
structure, the size of a single-seat fighter, with a swept leading edge to
the tailplanes and inverse taper at the tips of the unbalanced elevators.
The tailplane section was of a reverse camber. The triple rudders were the
only control surfaces to be balanced, and all were fitted with fixed fin
surfaces.
Although no less than eighteen wheels were used in the undercarriage,
all three chassis were relatively simple vee-type structures. The axles of
the main chassis, located immediately under the engine nacelles, were
thicker than those of a railway wagon and supported two pairs of twin
wheels each end, which must have caused considerable drag. Axles were
bound to the steel-tube vees with elastic cord. The tailskid was a
conventional component fabricated from a single piece of ash and shod with
steel.
June 1917 saw the delivery of the first Staaken R.VI "R 25", soon to be
followed by "R 26" in July. Many and varied were the sorties made by these
Giant aeroplanes, including a considerable number of attacks on England,
the first being on 17th September 1917, and even a raid on Le Havre, which
involved a round trip of some 800 km. For a raid of this length a reduced
bomb load was carried, probably in the nature of 750 kg. All bomb loads
were in direct proportion to the fuel carried, which again was related to
the range required. For raids of short duration 2,000 kg. of bombs could
be carried, but the average load for a long-range sortie was about half
that weight. The 100 kg. bombs were stowed internally, but the larger 300
and 1,000 kg. bombs (which were the largest bombs to be dropped from any
aeroplane during the First World War) were carried under the belly, only
partially enclosed.
The R 25, the first of the Staaken R.VIs to be supplied, made an
intrepid solo raid upon London during the night of 17th/ 1 8th February
1918, and with considerable skill scored a direct hit upon St. Pancras
railway station. R 26 succeeded in making no less than twenty varied
sorties, during which a total of some 26,000 kg. of bombs was dropped.
The R.VI, R 39, was one of five Giants raiding England on the night of
16th - 17th February and dropped the first 1,000 kg. bomb on Britain,
hitting the Royal Hospital, Chelsea. The same aircraft dropped the second
1,000 kg. bomb on the night of 7th - 8th March 1918, destroying houses in
Warrington Crescent, Maida Vale.
Rfa 501 made a total of eleven raids on England between 18th December
1917 and 20th May 1918. They dropped 27,190 kg. of bombs (compared with
84,745 kg. dropped by Gothas in twenty-two raids) and lost no aircraft due
to Allied action.
A seaplane variant of the R.VI was built for the Navy, with
4 x 260 hp High compression Mercedes D.IVa, 6-cylinder in-line water-cooled.
They were among the first cannon armed German aircraft.
They came too late to see much wartime service but they flew in
'airline' operations along with the R type survivors for maybe a year
after the war. Their operational history is otherwise obscure.
Taken from the internet page, Pilots-n-planes-ww1.com:
Source: The German Giants by Haddow and Grosz,
Putnam Books ISBN 0 85177 812 7
Source: German Aircraft of World War I by Gray & Thetford,
Putnam Books, ISBN 0 85177 809 7
