The Deutsches Forschungsinstitut für Segelflug (DFS) had proposed a design for a high altitude reconnaisance aircraft early in the war years. A glider design would have the advantage of being silent from the ground, of having a low ground speed for good photography and potentially the ability to loiter over target.

The DFS design, in common with many proposals which first saw the light of day in the early stages of the war was cancelled, only to be later resurrected. However, with insufficient time, the project was not completed by the war's end. Designed for cruising at altitudes of 80,000 feet, the pilot was protected by a sophisticated pressurised cabin. This could be used as a descent capsule with parachutes if the aircraft got into difficulties and had to be abandoned. Sealing and pressurising a conventionally designed, complex cabin would have been difficult, so a prone pilot position was adopted, with a simple, forward, armoured cabin window and oblique side windows fixed into the cockpit walls.

Taken up to launch height on the back of another aircraft, the DFS.228 would climb to high altitude for approach to target and then in common with other gliders, return to land on its ventral skid. With its rocket motor, the DFS.228's mission profile was to use power to climb, then glide down through its operating altitude, re-light the rocket motor to climb back again to height, glide down once more until starting the motor again, and in this manner operate a "Sägezahn" ("saw-tooth") flight pattern giving maximum range and maximum target coverage.

The DFS 228

The heavily retouched photograph here shows the DFS.228 prototype apparantly undergoing flight trials. The aircraft was carried aloft on the back of a parent aircraft (here a Dornier 217), released and then used its on-board Walter motor to carry it up to its full operating height.

This illustration shows the concept, although it has been suggested that this photograph is a photocomposite, with the DFS.228 "grafted" on top of a standard Dornier. In any event, it gives an idea of how the aircraft would appear on operations.

This photograph more clearly shows the DFS.228/Dornier combination. You can also see the "Sägefisch" or "Sawfish" logo on the nose of the glider. The arrangement of the observation windows is more clearly shown here.

DFS built three prototypes of the DFS.228 and the DFS.228 V1 took to the air a number of times. V1 had a conventional pilot's seat, inclined slightly to the rear and set on a pair of rails to be ejected from the cockpit section when that had descended to a height at which it was safe for the pilot to take to his own parachute, if required. The DFS.228 V2 had a re-worked cockpit with the prone pilot position, but was damaged in a landing accident. The DFS.228 V3 was a re-design but remained unfinished at the war's end. None of the prototypes was flown under rocket power, but the V1 was fitted with the HWK 109-509.D motor at DFS Ainring as part of the testing programme, and it was in this configuration that it was captured in a hangar by the Americans.

The DFS.228 V1 was captured in civilian markings "D-IBFQ" which were apparently applied so that the aircraft could be flown at a civilian flight proving ground without causing too much suspicion.

Captured was the V1 prototype with standard, seated pilot position. It is not known what became of the V2 prototype cabin with the prone pilot position after the war.

Walter HWK 109-509.D

The DFS.228 V1 was captured by the Americans at DFS Ainring. Pictured at, or around that time, it is shown complete and undamaged. The picture here is one of the most common of D-IBFQ, which shows it in a partly dismantled state at RAE Farnborough. This is discussed in a later paragraph: follow this link.

The design of the DFS.228 required it to be compact, light weight and yet climb to extreme altitudes under power. This would need a small, powerful motor and was a job ideally suited to the rocket power plant. Walterwerke in Kiel had plenty of experience in this type of motor, and had available tried and tested units. The rival BMW rocket motor designs were probably a good alternative, but the BMW team had yet to manufacture a reliable, working motor.

This photograph has appeared in print before, and my research shows it was listed in the RAE Farnborough archive, as negative No.69862 taken on 14^th June 1946. David Myhra's Schiffer Military History book "DFS 228" is ambivalent about the provenance, but Phil Butler's "War Prizes" places this airframe at RAE Farnborough and the RAE negative numbers co-incide with his date information, so I am confident in siting these photographs at the RAE Farnborough dump in 1946.

An HWK 109-509.A1 motor could have been applied "off the shelf" were it not for the slender, long design of the DFS.228 fuselage, and the need to bring the weight of the motor forward, close to the centre of gravity. Fitting the main body of the motor was possible in the rear fuselage behind the wing, but the rocket motor's thrust tube was then not long enough for the existing combustion chamber to reach the tail.

Therefore, Walterwerke modified a motor, the combustion chamber being suported by a small thrust N-frame attached to the reinforced fuselage frame near the tail, fitted to brackets welded onto the outer side of the combustion chamber. The C-Stoff and T-Stoff pipes had to be lengthened. Also visible in the photograph is a longitudinally running piece of metal, which Cobb describes as a thirteen feet, nine inch long thrust bearer.

Beeton's RAE Tech.Note Gas 12 (see References) is not very clear about the arrangement of the motor in the fuselage, although he states that considering the HWK 109-509.A2 and 109-509.D, "the components of the two motors were identical".

The illustration on the left is a photograph taken of the HWK 109-509.D in situ in the DFS.228 fuselage - to orientate you, this view is taken from the starboard side, looking across to the port side, with the nose to the right, and the tail to the left.

Although it is not at all clear from this picture, Walterwerke seem to have completely re-arranged a large number of components. That the motor is derived from an A.2 series is shown by the T-Stoff gravity starting tank, below which can be seen the top of the steam generator. However, the steam control valve, (just visible) is set in a different position, and the C-Stoff fuel filter -on the left of the picture- is tilted up.

Much of the interesting detail is obscured by a welded tube-framed cradle. Beeton makes no mention of it, but the author of the Foreign Aircraft Bulletin 23 "DFS 228 Stratospheric Reconnaissance Aircraft" says that the HWK 109-509.D had pressurised fuel tanks to drive the fuel to the fuel pump. He suggests that at the extreme altitude, the Walter screw pumps would not develop sufficient draw to bring fuels to the centrifugal outflow pumps. The cradle could be the correct shape for a cylinder of compressed gas for tank pressurisation - equally though, the bottle could just as easily be part of the environmental system for the pilot, in his pressurised cockpit.

Searching through a selction of UK archives, I have found two different reports on the DFS.228, one is a summary document, the other is a draft of RAE Tech.Note FA.280 and neither has any detailed illustrations of the aircraft's internal systems. However, Myhra's book reproduces an illustration of the rear section of the DFS 228 which seems to show the HWK 109-509.D arrangement.

This picture shows the general arrangement of the main motor body and the long mounting down to the combustion chamber. It seems to show the mountings welded onto the combustion chamber, so appears to have a reasonable degree of accuracy.

Shown here in more detailed close-up, the HWK 109-509.D arrangement seems to have a transverse fuel pump, with steam generator fed from a T-Stoff gravity starter tank.

The large cylinder above the main motor unit, for which there is a welded tube cradle in the photographs above, is shown in this diagramme, although the purpose is still no clearer.

The C-Stoff / T-Stoff fuel flow regulating valve seems to be in the portion of the picture towards the tail of the aircraft, just before the fuel pipes are seen heading towards the combustion chamber.

The other pipes are not shown with sufficient clarity to be able to tell whether they are part of the fuel/steam flow around the motor, or whether they form part of the supporting frame. Also not shown is the turbine pump steam exhaust pipe - although there must be one.

This is an interesting illustration, which does add to the photographs. However, a much clearer version would be an advantage. To date, I have been unable to find any clear illustrations. When these have been located, they might help to resolve some lack of detail.

Did RAE Damage D-IBFQ?

Pictured sitting damaged and open to the elements, it is not yet clear when D-IBFQ was transferred to the British, or when it was transferred back to Britain.

Unlike a number of German scientific developments, specifically sought out and taken back to England for evaluation, I have so far seen no other pictures of this airframe at RAE Farnborough. A number of large negatives of the aircraft park and hangar interiors at the Foreign Aircraft Exhibition at RAE in October 1945 do not show D-IBFQ.

I have heard it remarked that the British at RAE must have treated this airframe with disrespect. However, Tech.Note FA.280 by Cobb is at pains to point out that a number of his measurements and conclusions are problematic because of the extensive damage to the aircraft. Rough treatment would have been unusual for the thorough and painstaking analysis often undertaken at RAE, and would have impaired a proper evaluation of any new technology within.

To quote from FA.280, Cobb writes,

"The aircraft examined was the first prototype and was received from Germany in an extensively damaged condition."

"Unfortunately the cabin was very badly damaged when received and the information quoted below could not be verified ..."

What seems clear, is that the aircraft was not immediately shipped from Ainring to Britain after its capture, and may have been examined by a number of teams - American troops and/or members of the FIAT or CIOS teams moving through Germany at that time. British Air Intelligence had composed a document A.I.2(g) 2/46 (a copy of which has currently not yet been discovered for review) about the development and operation of the aircraft which must have been based on information gathered from some source; but the full movement history of D-IBFQ it is not yet known.

It would seem unlikely that the RAE wilfully damaged this airframe at Farnborough - but they almost certainly did dispose of it as scrap. If not before, most probably on 14^th August 1947, when most stored enemy airframes, no longer required for evaluation, were struck off charge and then scrapped.

Key References.

• Beeton, RAE Tech.Note Gas 12
• Cobb D.B., RAE Tech.Note FA.280
• Foreign Aircraft Bulletin No.23
• Myhra D., DFS 228

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