Saunders Severn

Saunders Severn hydravion trimoteur britannique par Wikipedia (en)

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The Saunders Severn was a three-engined biplane flying boat intended for maritime patrol duties.

It performed well but was fragile and unreliable. Only one was built.

Design and development


The Saunders A.7 Severn was the last flying boat designed by S.E. Saunders Ltd before the take-over by [Vous devez être inscrit et connecté pour voir ce lien] and John Lord late in 1928 that produced the [Vous devez être inscrit et connecté pour voir ce lien], or "Saro", company.

Its first flight was two years after this change of ownership and so it has been alternatively referred to as the
Saunders/Saro Severn, the Saunders-Roe A7 and the Saro A7.

It was designed to [Vous devez être inscrit et connecté pour voir ce lien] for a maritime patrol aircraft.

It was the second Saunders aircraft to use their patented "corrugated" structure for the hull, first trialled on the [Vous devez être inscrit et connecté pour voir ce lien], in which longitudinal external corrugations in the skin replaced internal riveted stringers.

Full trials of the A.14, revealing both the strengths and weaknesses of this technique were not made until after the
Severn had flown.

Like the A.14 the Severn's construction largely avoided doubly curved hull plating, so the planing bottom was strictly
V-shaped and the upper hull rather slab sided.

The hull was a two-step design with [Vous devez être inscrit et connecté pour voir ce lien] sides above the [Vous devez être inscrit et connecté pour voir ce lien].

There was a gunner's position in the nose and a side-by-side open cockpit for the pilots ahead of the engines and wing.

Behind the cockpit and within a windowed part of the hull were crew positions and accommodation and from which a dorsal gunner's position just aft of the wings could be accessed.

There was an isolated rear gunner's position in the extreme rear of the upswept rear fuselage, above the braced
tailplane and between the two braced fins.

Twin balanced elevators projected beyond the tailplane and the fins carried balanced rudders.

Early flight trials showed the Severn to be heavy on the rudder, so separate servo-rudders were soon fixed on struts behind the main rudder surfaces. It was also heavy on elevators, which were increased in area.

The Severn was a three-engined [Vous devez être inscrit et connecté pour voir ce lien], the lower wing having a span of only 58 % of the upper one and about
52% of the chord.

This small lower wing was mounted just below the hull decking.

Both wings were made of fabric-covered duralumin.

The upper wing, which carried the ailerons, was joined at its centre line to the upper edges of the fuselage by a tandem pair of inverted V-struts, the forward one supporting the central engine, which was faired into the underside of the wing.

Single vertical struts held the outer engines in similar positions, with single inward leaning struts at the rear.

There were outboard outwardly splayed interplane struts with the braced stabilising single stepped floats mounted below.

The three 490-hp (365 kW) [Vous devez être inscrit et connecté pour voir ce lien] XI radial engines each had their nine uncowled cylinders forward of the wing leading edge, driving two-bladed propellers.

Operational history


The Severn first flew in July 1930 and began a test programme with the [Vous devez être inscrit et connecté pour voir ce lien]
(MAEE) at Felixstowe in August.

Quite soon this led to a reduction in tailplane area to reduce the Severn's excessive longitudinal stability.

That apart, the Severn's handling in the air and on water were found good, as was its performance.

It was let down by a long series of faults, due to a combination of weight-saving design and a lack of attention to detail, which would have caused unacceptable serviceability problems in Service.

Some of the faults were serious, like the failure of the central engine mounting and multiple cracks that appeared in the
hull; others, like the breaking of brackets and the loss of wing inspection flaps were less serious but numerous.

To explore the balance between good air and water performance and behaviour versus the expanding fault list, MAEE decided the Severn should go on a proving flight to the Near East.

This took the Severn and an accompanying [Vous devez être inscrit et connecté pour voir ce lien] 6,530 miles via [Vous devez être inscrit et connecté pour voir ce lien] and included trials on [Vous devez être inscrit et connecté pour voir ce lien].

The conclusions were as before: the Severn performed well in the air and on the water, was seaworthy during a storm and returned without corrosion, but suffered from many problems both small and large.

The second category included broken ribs and a servo-rudder king post and the conclusion was that this was not a practical aircraft for Service use, so no orders followed.

Nonetheless, the sole Severn served for about five months with [Vous devez être inscrit et connecté pour voir ce lien] after the end of the MAEE trials before it was lost in the [Vous devez être inscrit et connecté pour voir ce lien].

Saro learned from the experience and their next aircraft, the [Vous devez être inscrit et connecté pour voir ce lien] was much more robust.[Vous devez être inscrit et connecté pour voir ce lien]

Specifications


Data from [Vous devez être inscrit et connecté pour voir ce lien], p. 85

General characteristics

• Crew: 5
  
• Length: 64 ft 6 in (19.66 m)
  
• Wingspan: 88 ft 0 in (26.82 m)
  
• Height: 19 ft 3 in (5.87 m)
  
• Wing area: 1,557 ft² (144.7 m²)
  
• Empty weight: 14,800 lb (6,713 kg)
  
• Gross weight: (normal) 22,000 lb (9,980 kg)
  
• Powerplant: 3 × [Vous devez être inscrit et connecté pour voir ce lien] XIFP 9-cylinder radials, 480 hp (358 kW) each