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Swearingen SA227 Merlin / Metro

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SA227 Metro III


The evolution of the Merlin started in the early 1960s, with an air-stair door and engine conversion for the Beech Twin Bonanza. Swearingen was also fitting bigger engines on Queen Airs, and the first Merlin strongly reflects his background with these two Beech conversions. The Merlins I and II consisted of a new fuselage mounted on modified Queen Air or Twin Bonanza wings and landing gear. The Merlin I was to be a pressurized piston-powered airplane, the Merlin II a turboprop. The model I was never produced because Swearingen couldn't find a piston engine that satisfied him. The II made its debut with Pratt & Whitney PT6 turboprops in 1969, but by the time it reached the IIB version, it was powered by Garrett AiResearch TPE 331s with a shaft horsepower of 665 each, and it had a takeoff weight of 10,000 pounds.

The next step had to be the development of a new wing. There just weren't that many Twin Bonanzas and Queen Airs out there, waiting to donate their wings to a Merlin. There may also have been some reluctance on the part of prospective buyers to consider a new airplane with used wings. Thus came the Merlins III and IV.

Dramatically improved performance, extended payload-range capability and a host of safety features transformed the Metro II into the Metro III. Providing the the improved performance is a 10 foot extension to the earlier model's wing, combined with an uprating of the twin Garrett AiResearch TPE turbo-props from 840 SHP to 1,100 SHP. Water methanol injection is standard for hot and high take-offs, as well as being available for power augmentation during normal take-offs. Rated at 1,100 SHP wet, 1,000 SHP dry, power is now absorbed by new four-bladed Dowty Rotol props. Turning at 1,590 rpm (compared with 2,000 rpm on the Metro II), the interior noise level has been dramatically reduced to about half that of the previous model about a 6 Db drop.

Fairchild was building the Merlin's wings under contract to Swearingen when the recession of 1970 squeezed the airplane business. Fairchild wound up with both an interest in the company and an interest in keeping the airplanes going. The Merlin III was under development at about the time the small jets were first coming to market; to be a viable offering, it had to offer something the jets lacked. This had to be range, for there was no way a turbo-prop could match the jets' speed. The first Merlin III had AiResearch 840-shp engines and a fuel capacity of 662 USG. The maximum range at economy cruise, with a 45-minute reserve, was 2,353 nautical.

Other changes to the Metro II include a cleaning up of the engine nacelle and improved fire containment. The gear doors now close when the wheels are lowered, which not only improves the single-engine gear-down performance, but also assists in lowering the Vmca to 5 knots slower than the series II aircraft. Cowlings are stainless steel for improved fire resistance, while all flammable fluid lines are physically isolated from electrical componentry and wiring. Fire exteinguishers are located in each engine nacelle.

In all there are some 1070 major engineering changes over the Metro II, mainly covering safety related items, and this effectively ups the new aircraft's empty weight by about 550 lbs.

The Metro III is certified to 14,000 pounds (6,350 Kg.) MAUW, with a 12,500 lb zero fuel weight. Approved by both F.A.A. under new SFAR 41 and by ICAO Annex 8.

The Merlin IIIB has 900-shp engines, four instead of three-blade props, and an extra gear in the reduction system that limits the prop to 1,591 rpm and makes the props turn to the left. Prop rpm for the III was 2,000, so this is a significant reduc-tion.

The Merlin IIIB is normally flown in the 25,000 to 28,000-foot range. At gross weight, it takes 17 or 18 minutes to reach 26,000 feet. Flight Level 260 is close to where the maximum-range and maximum-speed lines meet on the chart. The speed up there at 12,000 pounds is 269 knots at .52 nautical miles per pound of fuel burned, for a flow of about 530 pounds an hour. At 10,000 pounds, a more common mid-cruise weight, the specific range can be as high as .6 nautical miles per pound of fuel consumed, with a cruise speed still over 260 knots, at 30,000 or 31,000 feet.

The Merlin IIIB is a purpose-built, high capability executive aircraft. Powered by a brace of 900 s.h.p. Garrett AiResearch turboprops, the IIIB can wind out to a 300 knot cruise, carry eight passengers and crew of two for over a thousand miles. (Initial rate of climb at gross is 2,782 fpm, while over a thousand feet per minute can be averaged right on through to the service ceiling of 31,000 feet.) Single engine rate of climb at gross is 700 fpm; service ceiling with one out 16,500 feet. The Metro III also exists in an all-cargo configuration, known as the Expediter, with changes which permit payloads of 5,000 lb (2 268 kg). Fairchild, by 1990, had begun delivery of 13 C-26A versions to the US ANG.

The Merlin III is like the VI, only shorter, lighter and faster. It has a six-passenger cabin with a slide-out potty in the rear. An equipped III will weigh, 7,200 to 7,300 pounds empty, 12,500 at gross. It has a maximum cruise speed of 275 knots, nine knots faster than the IV. Both aircraft have a 12,560-pound ramp weight and a landing weight of 11,500 pounds.

The primary difference in the two airplanes is range. The IV will carry crew, three passengers and baggage 1,875 nm at 226 knots, or at high cruise it will take the three 1,390 nm at 265 knots. The III will carry three passengers 2,255 nm at 257 knots in economy cruise, or 1,610 nm at 275 knots in high cruise.

Sharing the same wing and fuselage section with that of its big brother the Metroliner, the 17 foot shorter Merlin fuselage is pressurised to 7 psi differential, allowing cabin pressure to remain at sea level during a 17,000 foot cruise, or a 7,300 foot cabin at 31,000 feet. Going hand in hand with the capable pressurisation system, interior sound levels too have been designed with comfort in mind. Big slow turning four-bladed props, coupled with increased sound-proofing over earlier models, results in remarkably low cabin noise levels — similar in fact to a jet, and with a silky, vibration-free smoothness in flight that would hardly ruffle the surface of the boss’s gin and tonic. Elbow room in the cabin too is excellent. Maximum cabin width is a generous 5.2 feet; headroom is 4.8 feet.

Range and payload combinations are flexible. With a crew of two and virtually no payload, range isbetter than 2,000 miles (this with 4,342 pounds of fuel total), while with a full payload of 1,770 pounds on board the Merlin achieves 1,100 miles at 288 knots, still retaining a 45 minute reserve. Fuel flow shows around 600 pph.

Fully reversing prop blades and powered anti-skid braking assist with the field performance. Low pressure tyres are fitted and the Garretts can be equipped with water-methanol injection as an optional extra.

Developed from the Metro II, the Metro III version is operated by several air forces as a utility transport. The US Air National Guard designates its variant the C-26A. Other models are the Metro III(H) with a 16,000-lb (7,258-kg) maximum take-off weight (ANG C-26B), and the Expediter all-freight model with a 4,780-lb (2,168-kg) payload.

For specialized military roles, the manufacturer provides the Metro III Special Missions Version - A Special Missions aircraft based on the Metro III airframe is available for various maritime patrol/surveillance and ASW duties. Mission equipment includes a Litton 360 deg scan APS-504(V) or AIL APS-128D search radar in an underfuselage radome for maritime surveillance, and a sonobuoy acoustic processor and a MAD tailboom for the ASW role. Optional equipment in both cases comprises low-light TV, infrared linescanner, Flir, Doppler radar, and a searchlight. Maximum take-off weight is 7,257kg (16,000lb), and endurance with auxiliary fuel tanks is ten hours. Also operated by the Swedish Air Force as Tp 88s.

The Merlin IV has the same basic airframe/engine combination as the Swearingen Metro commuter airliner, but there the similarity ends. The IV systems are so different from the Metro, and the capabilities of the airplanes are so distinct, that the two have separate type certificates.

The IV is a 10-passenger airplane in standard corporate configuration. It weighs 12,500 pounds maximum for takeoff and cruises at 265 knots. The design has what engineers sometimes call "maximum mission capability": that is, with full tanks, full avionics and miscellaneous equipment, it will accommodate only the crew for maximum-range ferry purposes. From this condition you trade off range for payload to a maximum of 2,800-2,900 pounds in passengers and baggage and 1,500 pounds of fuel.

Behind the rear cabin bulkhead is a pressurized, 136-cubic-foot, 500-pound limit baggage/cargo compartment accessible through a 53-inch-wide door on the left side of the fuselage. A second, unpressurized, 45-cubic-foot baggage compartment in the nose will hold up to 800 pounds, less the weight of avionics boxes. Cabin pressure differential is seven psi, which gives the IV a sea-level cabin at 16,000 feet, its maximum cruise speed altitude. There are dual pressurization, heat and air-conditioner systems.

The Swearingen Aviation Corporation, a subsidiary of Fairchild Industries, added 17 feet to the length of an executive turboprop fuselage to create an airplane for both airlines and corporate operators. The 1976 models of the long Swearingen were called the Merlin IVA and the Metro II. The former is a corporate airplane, the latter is used for airline operations. The Merlin and Metro 4 are air conditioned and pressurized. When it is used as an executive transport, the Merlin's passenger load is usually lower and larger fuel loads can handle much longer trips with the average executive load. When cargo-carrying missions are combined with passenger operations, a Metro II "Expediter" version of the airplane is available. Its movable bulkheads and removable interiors facilitate a quick change from passenger to cargo operations or to any mixture of the two. The Swearingen Metro II and Merlin IVA received a restricted category certification that will permit them to operate at gross weights of up to 14,000 pounds. Special-mission editions of the turboprops, designed for patrols or aerial photography, are able to carry 648 gallons of fuel, for up to 10 hours of endurance.

Fairchild Metro III
two/three-crew light transport
Engines: two l,000-shp (746-kW) Garrett TPE33I-l1U-611G turboprops
Maximum speed 320 mph (515 km/h) at 12,500 ft (3,810 m)
Initial climb rate 2,350 ft (716 m) per minute
Service ceiling 27,500 ft (8,380 m)
Range 1,000 miles (1,609 km) with maximum passenger payload
Empty weight 8,737 lb (3,963 kg)
Maximum take-off 14,500 lb (6,577 kg)
Wing span 57 ft 10 in (17.37 m)
Length 59 ft 4.25 in (18.09 m)
Height 16 ft 8 in (5.08 m)
Wing area 309.0 sq ft (28.71 sq.m)
Payload: 20 passengers or 4,880 lb (2,214 kg) of freight

Metro IIIA
Engines: Garrett, 840 shp
TBO: 2500 hr
Max cruise: 278 mph
Econ cruise: 244 mph
Stall: 83 mph
Fuel cap: 4342 lb
Service ceiling: 28,900 ft
SE service ceiling: 15,000 ft
ROC: 2530 fpm
SE ROC: 620 fpm
Min field length: 2150 ft
Payload with full fuel: 389 lb
Max range: 2487 sm
High speed range: 1953 sm
Max payload: 2060 lb
Range with max payload: 1154 sm
Pressurisation diff: 7.0 psi
Seats: 11
Gross wt: 12,500 lb
Equipped empty wt: 7769 lb
Useful load: 4731 lb

SA227-AC Metro III-41
Engines: 2 x Garrett TPE-331-IIU-601G, 1000 shp
Props: Dowty-Rotol 4-blade, 106-in
Seats: 22
Length: 59.4 ft
Height: 16.7 ft
Wingspan: 57 ft
Wing area: 309 sq.ft
Wing aspect ratio: 10.5
Maximum ramp weight: 14,100 lb
Maximum takeoff weight: 14,000 lb
Standard empty weight: 8397 lb
Maximum useful load: 5703 lb
Zero-fuel weight: 12,500 lbs
Maximum landing weight: 14,000 lb
Wing loading: 45.3 lbs/sq.ft
Power loading: 7 lbs/hp
Maximum usable fuel: 4342 lb
Best rate of climb: 2500 fpm
Certificated ceiling: 31,000 ft
Max pressurisation differential: 7 psi. 8000 ft cabin alt @: 32,400 ft
Maximum single-engine rate of climb: 760 fpm @ 133 kts
Single-engine climb gradient: 344 ft/nm
Single-engine ceiling: 16,000 ft
Maximum speed: 271 kts
Normal cruise @ 25,000ft: 264 kts
Fuel flow @ normal cruise: 509 pph
Endurance at normal cruise: 8 hrs
Stalling speed clean: 97 kts
Stalling speed gear/flaps down: 87 kts
Turbulent-air penetration speed: 174 kts

SA227-AC Metro III-41B
Engines: 2 x Garrett TPE-331-IIU-601G, 1000 shp
Props: Dowty-Rotol 4-blade, 106-in
Seats: 22
Length: 59.4 ft
Height: 16.7 ft
Wingspan: 57 ft
Wing area: 309 sq.ft
Wing aspect ratio: 10.5
Maximum ramp weight: 14,100 lb
Maximum takeoff weight: 14,000 lb
Standard empty weight: 8397 lb
Maximum useful load: 5703 lb
Zero-fuel weight: 12,500 lb
Maximum landing weight: 14,000 lb
Wing loading: 45.3 lbs/sq.ft
Power loading: 7 lbs/hp
Maximum usable fuel: 4342 lb
Best rate of climb: 2500 fpm
Certificated ceiling: 31,000 ft
Max pressurisation differential: 7 psi
8000 ft cabin alt @: 32,400 ft
Maximum single-engine rate of climb: 760 fpm @ 133 kts
Single-engine climb gradient: 344 ft/nm
Single-engine ceiling: 16,000 ft
Maximum speed: 271 kts
Normal cruise @ 25,000ft: 264 kts
Fuel flow @ normal cruise: 509 pph
Endurance at normal cruise: 8 hrs
Stalling speed clean: 97 kts
Stalling speed gear/flaps down: 87 kts
Turbulent-air penetration speed: 174 kts

Merlin IIIA
Engine: 2 x TPE 331-3U-303G, 840 hp
Seats: 11
Length: 42.159 ft / 12.85 m
Height: 16.732 ft / 5.1 m
Wingspan: 46.26 ft / 14.1 m
Wing area: 277.496 sq.ft / 25.78 sq.m
Wing loading: 45 lb/sq.ft  220.0 kg/sq.m
Pwr loading: 7.44 lb/hp
Gross wt: 12,500 lb / 5670.0 kg
Empty wt: 7600 lb
Equipped useful load: 4531 lb
Payload max fuel: 189 lb
Range max fuel/cruise: 1720nm/6.3hr
Range max fuel / range: 2266nm/9.3hr
Ceiling: 31,000 ft
Max cruise: 272 kt
Max range cruise: 245 kt
Vmc: 104 kt
Stall: 84-97 kt
1.3 Vso: 109 kt
ROC: 2530 fpm
SE ROC: 620 fpm @ 143 kt
SE ceiling: 13,500 ft
Min field length: 3075 ft
Take off distance: 3051 ft / 930 m
Landing distance: 2854 ft / 870 m
Fuel cap: 4342 lb
Cabin pressure: 7 psi
Crew: 2

Merlin IIIB
Engines: 2 x AiResearch TPE 331-1OU-501G, 900 shp
Props: Full-feathering, reversible, 106-in, dia
TBO: 3,000 hrs
Length: 42 ft. 1 in
Height: 16 ft. 9 in
Wingspan: 46 ft. 3 in
Wing area: 277.5 sq. ft
Max ramp wt: 12,600 lbs
Max takeoff wt: 12,500 lbs
Standard empty wt: 7,600 lbs
Max useful load: 4,900 lbs
Max landing wt: 11,500 lbs
Zero fuel wt: 10,000 lbs
Wing loading: 45 lb/sq.ft
Power loading: 6.9 lb/hp
Max usable fuel: 648 USG/4,342 lbs
Max rate of climb: 2,782 fpm
Service ceiling: 31,400 ft
Single-engine rate of climb: 700 fpm
Single-engine climb gradient: 304 ft/nm
Single-engine service ceiling: 16,500 ft
Max speed: 309 kts
Normal cruise (@ 22,000 ft. and 12,000 lbs.): 280 kts
Fuel flow at normal cruise: 600 pph
Endurance at normal cruise, no reserve: 7.2 hrs
Stalling speed, clean: 103 kts
Stalling speed, flaps down: 89 kts
Turbulent-air penetration speed: 190 kts
Max pressurization differential: 7 psi.
8,000-ft. cabin altitude @: 32,400 ft.

Merlin IVA
Engines: 2 x Garrett AiResearch TPE 331-3U-303G,840 shp
Prop: Hartzell 3-blade,constant-speed, full-feathering, reversing, 102-in. dia
Length: 59 ft. 4 in
Height: 16 ft, 8 in
Wingspan: 46 ft. 3 in
Airfoil: NACA 652A215 at root 642A425 at tip
Aspect ratio: 7.71
Wing area: 277.5 sq. ft
Wing loading: 45 lbs/sq.ft
Empty weight: 8,553 lbs
Useful load: 3,947 lbs
Payload with full fuel: 235 lbs
Ramp weight: 12,560 lbs
Maximum takeoff weight: 12,500 lb
Power loading: 7.44 lbs./hp
Usable fuel capacity: 554 gals/13,712 lbs
Baggage area: 143 cu. Ft
Minimum runway requirement: 2,050 ft
Rate of climb: 2,400 fpm
Single-engine rate of climb: 650fpm
Service ceiling: 27,000 ft
Single-engine service ceiling: 14,700 ft
Maximum cruise (@ 16,000 ft.): 269 knots
High altitude cruise (@ 24,000 ft.): 240 knots
Maximum range (45-minute reserve): 1,810 nm
Stall speed, clean: 97 knots
Stall speed, gear and flaps down: 86 knots

SA227-AT Merlin IVC-41
Engines: 2 x Garrett TPE-331-IIU-601G, 1000 shp
Props: Dowty-Rotol 4-blade, 106-in
Seats: 13/16
Length: 59.4 ft
Height: 16.7 ft
Wingspan: 57 ft
Wing area: 309 sq.ft
Wing aspect ratio: 10
Maximum ramp weight: 14,100 lbs
Maximum takeoff weight: 14,000 lbs
Standard empty weight: 9100 lbs
Maximum useful load: 5000 lbs
Zero-fuel weight: 12,500 lbs
Maximum landing weight: 14,000 lbs
Wing loading: 45.3 lbs/sq.ft
Power loading: 7 lbs/hp
Maximum usable fuel: 4342 lbs
Best rate of climb: 2500 fpm
Certificated ceiling: 31,000 ft
Max pressurisation differential: 7 psi.
8000 ft cabin alt @: 32,400 ft
Maximum single-engine rate of climb: 760 fpm @ 133 kts
Single-engine climb gradient: 344 ft/nm
Single-engine ceiling: 16,000 ft
Maximum speed: 297 kts
Normal cruise @ 25,000ft: 268 kts
Fuel flow @ normal cruise: 527 pph
Endurance at normal cruise: 7.7 hrs
Stalling speed clean: 97 kts
Stalling speed gear/flaps down: 87 kts
Turbulent-air penetration speed: 174 kts

SA227-AT Merlin IVC-41B
Engines: 2 x Garrett TPE-331-IIU-601G, 1000 shp
Props: Dowty-Rotol 4-blade, 106-in
Seats: 13/16
Length: 59.4 ft
Height: 16.7 ft
Wingspan: 57 ft
Wing area: 309 sq.ft
Wing aspect ratio: 10.5
Maximum ramp weight: 14,100 lbs
Maximum takeoff weight: 14,000 lbs
Standard empty weight: 9100 lbs
Maximum useful load: 5000 lbs
Zero-fuel weight: 12,500 lbs
Maximum landing weight: 14,000 lbs
Wing loading: 45.3 lbs/sq.ft
Power loading: 7 lbs/hp
Maximum usable fuel: 4342 lbs
Best rate of climb: 2500 fpm
Certificated ceiling: 31,000 ft
Max pressurisation differential: 7 psi.
8000 ft cabin alt @: 32,400 ft
Maximum single-engine rate of climb: 760 fpm @ 133 kts
Single-engine climb gradient: 344 ft/nm
Single-engine ceiling: 16,000 ft
Maximum speed: 297 kts
Normal cruise @ 25,000ft: 268 kts
Fuel flow @ normal cruise: 527 pph
Endurance at normal cruise: 7.7 hrs
Stalling speed clean: 97 kts
Stalling speed gear/flaps down: 87 kts
Turbulent-air penetration speed: 174 kts

SA227-TT Merlin IIIC-23
Engines: 2 x Garrett TPE-331-IOU-530G, 900 shp
Props: Dowty-Rotol 4-blade, 106-in
Seats: 8/11
Length: 42.2 ft
Height: 16.8 ft
Wingspan: 46.3ft
Wing area: 277.5 sq.ft
Wing aspect ratio: 7.7
Maximum ramp weight: 12,600 lbs
Maximum takeoff weight: 12,500 lbs
Standard empty weight: 8090 lbs
Maximum useful load: 4510 lbs
Zero-fuel weight: 12,500 lbs
Maximum landing weight: 12,500 lbs
Wing loading: 45.0 lbs/sq.ft
Power loading: 7 lbs/hp
Maximum usable fuel: 4342 lbs
Best rate of climb: 2800 fpm
Certificated ceiling: 31,000 ft
Max pressurisation differential: 5.5 psi
8000 ft cabin alt @: 32,400 ft
Maximum single-engine rate of climb: 780 fpm @ 135 kts
Single-engine climb gradient: 346 ft/nm
Single-engine ceiling: 16,500 ft
Maximum speed: 309 kts
Normal cruise @ 25,000ft: 290 kts
Fuel flow @ normal cruise: 525 pph
Endurance at normal cruise: 7.7 hrs
Stalling speed clean: 102 kts
Stalling speed gear/flaps down: 89 kts
Turbulent-air penetration speed: 189 kts

SA227-DC Metro 23
Engines: 2 x Garrett TPE-331-12
MTOW: 7484 kg

SA227-TT Merlin IIIC-41
Engines: 2 x Garrett TPE-331-IOU-530G, 900 shp
Props: Dowty-Rotol 4-blade, 106-in
Seats: 8/10
Length: 42.2 ft
Height: 16.8 ft
Wingspan: 46.3 ft
Wing area: 277.5 sq.ft
Wing aspect ratio: 7.7
Maximum ramp weight: 13,330 lb
Maximum takeoff weight: 13,230 lb
Standard empty weight: 8150 lb
Maximum useful load: 5180 lb
Zero-fuel weight: 12,500 lb
Maximum landing weight: 13,230 lb
Wing loading: 47.7 lbs/sq.ft
Power loading: 7.4 lbs/hp
Maximum usable fuel: 4342 lb
Best rate of climb: 2650 fpm
Certificated ceiling: 31,000 ft
Max pressurisation differential: 7 psi
8000 ft cabin alt @: 32,400 ft
Maximum single-engine rate of climb: 680 fpm @ 138 kt
Single-engine climb gradient: 296 ft/nm
Single-engine ceiling: 14,500 ft
Maximum speed: 309 kt
Normal cruise @ 25,000ft: 290 kt
Fuel flow @ normal cruise: 525 pph
Endurance at normal cruise: 7.7 hrs
Stalling speed clean: 104 kt
Stalling speed gear/flaps down: 92 kt
Turbulent-air penetration speed: 189 kts

Fairchild (Swearingen) C 26 Metroliner
Engines: 2 x TPE 331 11U, 809 shp
Length: 59.383 ft / 18.1 m
Height: 16.732 ft / 5.1 m
Wingspan: 57.087 ft / 17.4 m
Wing area: 308.927 sq.ft / 28.70 sq.m
Max take off weight: 14502.3 lb / 6577.0 kg
Weight empty: 9181.6 lb / 4164.0 kg
Max. payload weight: 5300.8 lb / 2404.0 kg
Max. speed: 278 kts / 515 km/h
Landing speed: 87 kts / 161 km/h
Cruising speed: 248 kts / 460 km/h
Initial climb rate: 2362.20 ft/min / 12.00 m/s
Service ceiling: 27428 ft / 8360 m
Wing loading: 46.95 lb/sq.ft / 229.00 kg/sq.m
Range: 575 nm / 1065 km
Crew: 2
Payload: 20 pax

C-26B
MTOW: 16,000 lbs (7258 kg)

 

 


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