DHC-3 Otter Archive Master Index

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DHC-3 Technical and Historical Notes

Karl E. Hayes © 2005

OTTER - DEVELOPMENT AND PRODUCTION - DE HAVILLAND CANADA

In 1928 the De Havilland Aircraft Company of England established a Canadian subsidiary, realising the potential for aircraft in the exploitation of Canada's natural resources. The formation of De Havilland Aircraft of Canada Ltd (DHC) was officially announced in March 1928 and the following year a seventy acre property was purchased at Downsview, near Toronto and a plant established there.

During the 1930s DHC assembled aircraft which had been manufactured by the English parent company and which had been crated to Downsview, aircraft such as the Puss Moth, Fox Moth, Dragon etc. In 1937 DHC manufactured its first aircraft (as distinct from assembling aircraft already made in England) in the shape of twenty five DH82A Tiger Moth trainers for the RCAF.

The company went into large scale production during the second World War, building many more Tiger Moths, 375 Avro Ansons and more than 1,100 Mosquito bombers. The ending of the war brought a period of adjustment, as such large scale production was no longer required. To start to fill the gap, DHC produced 53 of the DH83C, a Canadian version of the Fox Moth, which proved ideal for exploration of the northern bush country. These were followed by the first of DHC's own designs, the DHC-1 Chipmunk, a training aircraft to replace the Tiger Moth.

DHC-2 BEAVER

With the ending of the second World War, Canada was ready for the greatest northern development boom in her history. Worldwide, there was a shortage of minerals, oil, timber. Canada had all these in her northern hinterland, but lacked adequate transport facilities to get at them. Dog teams in winter and small boats and spur line railroads were the main means of transportation along with modified military aircraft, such as Stinsons and Norsemen. These in most cases were either too large and cumbersome for utilization in many areas or too limited in payload capacity. Aircraft were needed to explore for the hidden mineral resources and to move personnel, equipment and supplies economically and safely to the wilderness mine sites, to patrol and protect the forests, and generally to support the isolated communities throughout northern Canada.

With its first aircraft successfully behind it, DHC's design team turned their attentions to an aircraft which would serve the Canadian northlands, an idea they had long cherished. They saw both the need and the possibilities for an aircraft tailored to meet their country's bush flying requirements. The specifications for the new plane were based on the results of a questionnaire sent to all Canadian bush pilots from coast to coast. The information they provided produced a clear picture of what was required, a picture which was in accordance with DHC's own concept. Work started on the aircraft in September 1946. It was designated the DHC-2 and named the “Beaver” after the most industrious animal of that name whose habitat was the Canadian outback.

With Beaver production well established and the aircraft achieving good sales, the DHC design team decided on their next aircraft. It would be similar to the Beaver but larger and would provide double the Beaver's capacity and payload but with the same performance. It too would be a single-engined high-wing type, capable of operating on wheels, skis or floats. To emphasise its development from the DHC-2 it was originally named the “King Beaver”, although the name was changed to the Otter before the aircraft's first flight.

Factory Instruction Number 390 was issued on 29 November 1950 to authorize the construction of a prototype. There was none of the agonizing over the choice of engine that had occurred with the Beaver, as the Engineering Department had their eye on the Pratt & Whitney R-1340 Wasp engine of 600 horse power, which was of proven reliability and in good supply. The choice of engine did present some challenges to the design team, as there was only 30% more power over the Beaver's R-985 of 450 horse power to achieve their objectives.

On 12th December 1951, Chief Test Pilot George Neal taxied the prototype Otter CFDYK- X onto the runway at Downsview and took off from the same 600 feet stretch of runway that the Beaver normally used to become airborne, indicating that the design team had been successful in their efforts. The Otter was used on flight test work over the months that followed and was joined in the test programme by the second Otter built CF-GCV-X, which made its first flight on 2nd May 1952 and was used to test the Otter on floats. Both of these Otters had been constructed with quite a pointed vertical fin. In the course of the trials, the aircraft was found to have some stability problems, and in September 1952 the fins on both these aircraft were changed to what became the standard production fin, of a more rounded design. This change cured the stability problem, and the Otter was certified for commercial use, on both wheels and floats, on 5th November 1952.

Certification enabled deliveries to customers to proceed and the first Otter delivered was in fact the fourth aircraft built, CF-GBX, delivered to Hudson Bay Air Transport on 11th November 1952. This was followed by number six to Imperial Oil on 19th December 1952 registered CF-IOD and the other Otter delivery that year was number three, CF-ODH, to Arthur Fecteau on 29th December 1952. The two prototypes continued in use by DHC for some time, and were used to certify the Otter at an increased gross weight of 8,000 lbs, up from 7,200 lbs as originally certified. Initial production rate of the Otter was one aircraft a month, but in 1953 that rose to four a month. Otters rolled off the production line at Downsview and would continue to do so for sixteen years. The Otter was in production from 1951 until 1967, during which time 466 aircraft were built. The Otter sold well, principally as a military aircraft, as the following summary of deliveries illustrates:-

Military customers 350

Civilian operators 69

Government 36

Corporate 11

Total 466

POWER FOR THE OTTER

To power the Otter, DHC selected the Pratt & Whitney R-1340 Wasp, an engine of proven reliability which had been in production since 1926. A 600 horse power radial piston engine, it had powered combat aircraft during the war and was still widely used, in such aircraft as the Norseman, Harvard / Texan and Mallard. The R-1340 continued in production from 1926 until 1952 and during this period a total of 34,966 Wasps (both direct drive and geared types) were manufactured by Pratt & Whitney and its licensees. Included in this total were 1,149 engines built by P&W Aircraft of Canada Ltd at their Longeuil plant. They also manufactured a conversion kit while the Otter was in production which contained all parts required to convert a direct drive R-1340 to a geared type at time of overhaul.

This choice of engine did present some challenges to the design team. The Otter, originally known as the King Beaver, was essentially a scaled-up Beaver with the same take-off performance but twice the payload. The Beaver was powered by a P&W R-985 engine of 450 horse power, so there was only a third more power to achieve this greatly increased payload in the Otter. The geared version of the Wasp was selected for the Otter so that it could swing a larger propeller, which would improve performance. The Wasp thus drove a three-blade Hamilton Standard 3D40 Hydromatric propeller ten feet ten inches in diameter. The standard engine was designated as the R-1340-S3H1 and it had a blower ratio of 10:1. An optional S1H1-G was available, which had a blower ratio of 12:1, the so-called “mountain engine”, as it gave better performance at higher altitudes.

The Wasp engine as fitted to the Otter had a special exhaust system with four augmentor stacks. In these stacks, exhaust gases produce suction strong enough to pull cooling air through the engine. The engine is effectively cooled during steep climbs when forward airspeed is low and engine output near its maximum. Some controversy exists as to whether these augmentor stacks produced a measurable amount of thrust, as some claimed they did. They must produce some thrust, however small. They are also quite large and must have some drag. The speed was the same with or without the stacks, so it was argued that the drag was offset by the thrust.

Having chosen the R-1340 for the Otter, it was then a question of obtaining a sufficient quantity of the engines to commence production of the DHC-3. Relatively few geared Wasps had been manufactured, as compared with the direct drive version. After a search, fifty such engines were found in Sweden. Although it was not enough for a production programme, it was sufficient for a start. From then on, Pratt & Whitney Canada would overhaul used R-1340s and fabricate gearbox conversion kits to add to those Wasp engines to be installed on the Otters rolling down the production line at Downsview.

More than 50 years after the type's first flight, and having operated throughout this period in the demanding outback environment, the Otter is still providing yeoman service in the bush. Alongside the Beaver, it has proved its credentials as one of the ultimate bush planes. Its most criticised feature

however has been its engine. There have been many cases of engine failure. The Otter also proved somewhat underpowered for bush operations, particularly when over-loaded, as was frequently the case. As one operator said: “It would get off the ground right away, but then it would not climb. You would stand there and watch this thing struggle off toward the horizon, wondering if it was ever going to clear the trees at the end of the field”. Many times it didn't!

In the early 1970s the search started for a solution to the problem, motivated also by rising maintenance costs of the radial engine. There was no replacement for the Otter in sight, which led those interested in the problem to the only conclusion possible - they would have to convert the existing Otters by installing a turbine engine. Otter N3904 (54) was tested by Western Rotorcraft of Seattle in 1972 with a Garrett AiResearch TPE-331 engine but the project did not proceed and the aircraft had its radial engine re-installed.

In or about 1975, as a result of customer pressure, DHC did look at a turbo Otter project and considered re-engining existing Otters as well as production of new aircraft. It appears however that they were never very enthusiastic about the project, realising that the price of the finished product would be very high, probably too high for the market. They were also influenced by their Turbo Beaver, which with sales of only 60 aircraft was not considered a great commercial success. They decided not to proceed.

COX DHC-3T TURBO OTTER

The next exponent of the Turbo Otter was Cox Air Resources of Edmonton, Alberta, a company formed by Mr. Ray Cox to develop the aircraft. He was an aircraft mechanic and pilot, with many years experience in the Arctic. Since 1969 he had specialised in recovering crashed aircraft from remote locations, with more than fifty to his credit. His idea came from extensive work with Otters in the Arctic. He appreciated that they were a fine aircraft, with hardly any life limit to the airframe, but also realised that the Otter would eventually be driven into retirement by the economics of the operation and maintenance of its piston engine. He saw the solution to the problem with the P&W PT-6A-27 turboprop, the engine which powered the DHC-6 Twin Otter.

He teamed up with an aeronautical engineer named Aimo Pitkanen and set about designing and building a Turbo Otter. They saw their aircraft as the only replacement for the piston engined Otter, and as there was no-one else working on such a proposal, saw themselves in a “no competition” situation. Their aircraft would (a) reduce maintenance costs and the number of engine replacements (b) achieve greater productivity through higher cruising speed and increased payload, with improved crew and passenger comfort through decreased noise levels and (c) overcome any problems of availability of 80/87 avgas by changing to jet turbo fuel, as well as (d) increase utilization and profitability. This increased profitability (which would be achieved by lower expenditure on maintenance man hours, longer Time Between Overhauls, greater payload for short hauls, higher cruising speed, improved climb characteristics making operations in restricted areas safer and more profitable) would appeal to the bush operators, and there were a considerable number of Otters still operating in Canada which were likely candidates for conversion. They received enquiries from many parts of the world, as well as from Canada, which convinced them of the need for such a conversion, which they estimated to cost 200,000 Canadian dollars in 1977. It was considered that at the very least 40 aircraft would be converted, which would give them an extra ten to fifteen years service at competitive operating costs.

The Otter chosen as the prototype turbo conversion was number 421, which had been delivered to McMurray Air Services in 1961 as CF-MES. It was subsequently sold to Gateway Aviation of Edmonton. On 24th August 1973 it met with a bad accident at Cambridge Bay, Northwest Territories as a result of engine failure and was officially classified as “destroyed”. This however overlooked Ray Cox's considerable talents at salvaging and restoring aircraft. It was brought back to Edmonton and rebuilt as the prototype Cox Turbo Otter. Many problems were encountered during the conversion, mostly to do with weight and balance. The 42 gallon rear tank was relocated forward of the bulkhead, under the cockpit floor. A new 40 gallon hopper tank was installed forward of the firewall, which helped solve the centre of gravity problem caused by the much lighter engine up front, and which would sustain flight for one hour in the event of electrical systems failure.

The powerplant was the Pratt & Whitney PT-6A-27 turbine, developing 662 shp and driving a four bladed Hartzell 109.5 inch diameter propeller, which was fully reversible for water and land use and could be locked in zero-thrust configuration for engine starts on water. This would greatly improve the Otter's water-handling characteristics. A new electrical system was installed and a new instrument panel. As the avionics would be to each individual customer's requirements, racking was provided to accommodate whatever systems were required. A standard package was prepared incorporating state-of-the-art navigation and communications equipment.

The Turbo Otter was envisaged as being able to operate with the same wheel, float and ski arrangements as the standard Otter. The aircraft would have the same gross weight as the Otter (8000 pounds) but empty weight would be reduced by approximately 700 pounds, thus enabling increased payloads to be carried over 100 nautical mile ranges. Projected cruising speed was 125 knots with wheels (116 knots with floats), range 750 nautical miles, endurance six hours and a rate of climb one thousand feet per minute. These details were announced at a press conference held in Edmonton in November 1977. The prototype was to have flown in September 1977, but the project was delayed and funding proved problematical. As its own resources were inadequate, the company had to find external financing. This is a difficult matter at the best of times but none of the conventional sources would consider an unproved concept such as the Turbo Otter. The project did however continue with assistance from the Alberta Opportunities Corporation, the provincial lending agency.

By the time the prototype, registered C-FMES-X, made its first flight from Edmonton on 26th September 1978, more than a million dollars had been invested in the programme. Certification was expected to follow shortly thereafter, at which stage a plant was to be opened at Vegreville near Edmonton, to convert Otters at a rate of 18 per year. However, despite the successful first flight, continued funding for the Canadian certification became impossible to obtain, and the operation was moved south of the border. A new company, Cox Aircraft Corporation, continued with the work, based at Renton Airport, Seattle, Washington. The Turbo Otter was placed on the US civil aircraft register as N4247A in June 1981, and was tested with a higher powered PT-6A-135. US and Canadian certification was undertaken in parallel. Both engines would be on offer, the higher powered PT-6A- 135 appealing to the hot-and-high operator.

According to a magazine interview in April 1982, the company's president Ray Cox said that it had received to that date 30 orders for the conversion from commercial operators. He added that there had also been considerable interest in the performance improvements from military operators of the Otter. To quote from the article, which appeared in Aviation Week & Space Technology magazine: “Cox's timetable for starting the conversion program depends on obtaining the required financing, but under current plans the first Otter with a PT-6A-27 engine is scheduled for completion in September1982. Cox estimates it will take 90 days to produce the next two re-engined Otters, and then the Renton facility should be able to accomplish each conversion in 30 days. Three to five aircraft could be converted in the facility at any one time”.

“The $410,000 conversion price for the Otter includes the PT-6A-27 engine, zero timing the airframe and new electrical and fuel system components. Updated avionics would also be included in the standard package. Options being offered at an additional price include a larger cargo door, an additional two windows and three passenger seats and a leading-edge wing fuel tank. The eleven to fourteen passenger Cox conversion without the optional fuel increases the range of the aircraft to 750 miles with reserves. Cox says he has received expressions of interest from operators in South America, India, Kenya and Germany”. As well as the prototype Cox Turbo Otter, number 421, Cox also acquired Otter number 126, which was intended as the second conversion. It was damaged in a crash at Lynn Lake, Manitoba in May 1976 but was transported to Seattle to be rebuilt. Otter number 158 was intended as the third conversion. A former US Navy aircraft, it had been transported to Calgary in January 1981, where it was worked on by Kimba Air Services prior to going by road to Seattle for the turbo conversion. In the event, that never happened, and the aircraft was destroyed in a hangar fire in Calgary in May 1983. Otter number 380, a former RCAF aircraft which had crashed, was also acquired by Mr Cox with a view to being converted to turbine power as soon as certification was achieved.

The certification of the Cox Turbo Otter proved to be a lengthy one, and the prototype was still engaged in test flying when disaster struck the project on 19th December 1984. On that day, N4247A crashed at Alki Point, five miles from Boeing Field, Seattle, where by that stage the project was based. No one was killed in the crash, but the Otter came down in a residential neighbourhood and was badly damaged. The wreck of the Otter was brought back to Boeing Field. The Cox Turbo Otter project had always been somewhat under-funded, and it never recovered from this set-back. The following month, January 1985, the aircraft was re-registered to the Cox Aircraft Company of Washington Inc., Seattle but was not repaired. It had never achieved certification and the project had run out of luck, and money. It was a sad end indeed after so much money and effort had been put into the venture.

VIKING TURBO OTTER

Viking Air Ltd., was formed in 1970 and is based at the Victoria International Airport on Vancouver Island, British Columbia. In its early days, it established a reputation for recovering and rebuilding Grumman Goose and Widgeon amphibian aircraft. By the early 1980s, that market was exhausted and in its search for new business, in 1983 Viking purchased from DHC the exclusive manufacturing and distribution rights for spare parts for both the DHC-2 Beaver and the DHC-3 Otter. The Beaver and Otter drawings and tooling were transferred to Victoria and ever since Viking Air has been the major supplier of spares to DHC's “Out of Production” aircraft. It also supports the DHC-6 Twin Otter and developed its own turbine conversion of the Beaver.

Viking Air also set its sights on its own turbine conversion of the Otter. It acquired the rights to the Cox Turbo Otter conversion but these had to be modified to deal with the difficulties that Cox had experienced. Otter 393, which in November 1987 had crashed in the mountains near Wrangell, Alaska and which had been brought to Victoria for repair, was acquired, intended as the prototype of the Viking Turbo Otter. It lay at Victoria for some years, and in October 1995 was joined by Otter 307, intended as the second conversion. Both of these Otters were damaged in December 1996 when the roof of the hangar they were in at Victoria collapsed under a weight of snow. The following year, work commenced on repairing both aircraft and on converting 393 as the first Viking Turbo Otter.

The project proceeded slowly, as Viking Air had many other projects on-going as well, but by 2001 was taking shape. The conversion involved the installation of a Pratt & Whitney PT-6A-27 or - 34 turboprop engine driving a three blade Hartzell propeller, a new engine mount, composite nacelle and aluminium forward fuselage structure. The lower fuselage structure is replaced and a new forward belly fuel tank installed. This increased fuel capacity from 216 US gallons on the standard Otter to 326 US gallons on the Viking conversion.

On 22nd March 2001 Otter 393 was registered as C-GVTO, the last three letters of the registration standing for Viking Turbo Otter. It was painted gloss white overhaul and made its first flight as a turbine from Victoria on 9th May 2002. Over the months that followed, flight trials continued towards certification of the conversion, which were still on-going in October 2002, when Viking Air hosted a DHC “Out-of-Production Aircraft” conference at Victoria, which also celebrated the Otter's 50th anniversary. C-GVTO was one of a number of Otters present, still in the all-white colour scheme, with test equipment fitted inside the cabin. It carried an Air Wemindji logo on the fuselage side, having reportedly been sold to that company, subject to receiving certification which was expected in the not too distant future.

Delegates to the conference were given a tour of the Viking facility, and in the workshop was to be seen the fuselage of Otter 307 with wings detached, work not having yet started on its conversion. Another Otter to be seen at the conference was number 59, registered C-GIWQ, which was suspended from the roof of the hangar where the conference was taking place. This Otter had also been acquired by Viking Air, intended as their third turbine conversion. However, after the conference, due to other business pressures, the project was put on hold and Otter C-GVTO put into storage at Victoria, parked in one of Viking's hangars. Early in 2004, Viking Air obtained a contract to supply two turbine Otters to Trans Maldivian Airways. They acquired Otter C-FJUH (214) from Québec and it and C-GVTO were converted at Victoria as Vazar turbine Otters and exported to the Maldives. That left Otters 307 and 59, both still in storage at Victoria, for conversion to Viking Turbo Otters when the project was resurrected. Otter 307 (N8510T) had received its turbine engine by September 2004 and completion as a Viking Turbo Otter was expected during summer 2005. In November 2004, Viking Air acquired Otter C-FDNK (385) from Air Kipawa in Québec and it was flown to Victoria where during January 2005 work was underway to convert it to a Viking Turbo Otter with a PT6A-35 engine.

VAZAR DASH 3 TURBO OTTER

The Cox Turbo Otter, in its original form at least, failed to achieve success as it was too complicated. Many modifications had to be made to the basic Otter, particularly to the fuel system. The expense and time needed to test and verify these modifications, and to rectify difficulties encountered, caused the project to founder. The problem with the Otter remained, however, how to modernise the aircraft to give it the extra power it needed and improve its engine reliability. The next attempt at a solution adopted a much simpler approach, and got it right.

Dara Wilder was a pilot, inventor and manufacturer of mining and oil-extraction equipment. He knew the value of a big aircraft such as the Otter, able to transport men and heavy machinery out to the mines, and he could see that the solution was to replace the radial engine with a turboprop. He set some stringent, but realistic, requirements which were to ensure the success of his idea. The conversion had to be in the form of a bolt-on modular unit that would require no airframe modifications aft of the firewall. The conversion kit had to be simple enough to install in the field. Like the original Otter, the turbine-powered version had to be certified on wheels, floats and skis, as well as for commercial IFR operations.

Interestingly, Dara Wilder's project got going in 1984, the year the Cox Turbo Otter “bit the dust”, literally. The engine installation was designed by Floyd Perry of Salinas, California who was a veteran of turbine conversions. The engine selected was the Pratt & Whitney PT-6A-135, the same 750 shaft horse power turbine used in the Beech F90 KingAir. Since the engine was several hundred pounds lighter than the radial it replaced, it had to be hung quite a distance forward of the firewall to keep the aircraft's centre of gravity envelope in the right place. The result was the long, pointy nose which is characteristic of all turbine conversions of the Otter. To keep the conversion as simple as possible, the new engine mount attaches to the same four mounting points used by the Otter's original engine.

One of the things Wilder and Perry had to do during the certification process was to prove to the satisfaction of the FAA that the Otter's airframe would hold up under the additional torque loads imposed by the more powerful turbine engine. They had acquired Otter C-FDIV (453) which had crashed in 1982 and which had been brought to the Serv-Aero Engineering facility at Salinas, California where it was in use as the non-flying prototype, on which the engine installation was first performed and tested. This airframe was jigged up and instrumented, and then carefully monitored twisting forces were applied to simulate the torque loads of different power settings. The results were impressive, the airframe going not merely to the engine's 750 shaft horse power, but to over 1,200 horse power without flinching. As a result the engine mount can also accommodate the more powerful PT-6A-145 engine, which develops 1,150 shp. The fuselage of C-FDIV was later transferred to the Aero Flite Industries facility in Vancouver, where many of the turbine conversions were to be performed. It was used there as a ground instructional airframe, engineering trainer and demonstrator.

The flying prototype of the Vazar Turbo Otter, as this conversion was called, was Otter number 22. A one-time RCAF aircraft, it was subsequently operated by Gateway Aviation and then by Turn Air. It was advertised for sale in May 1985 with 10,800 hours on the airframe. Registered N9707B, it was converted to a turbine by Serv-Aero Engineering at their Salinas, California facility during 1987. In August 1988, N9707B flew from Bellingham, Washington to Ketchikan and Wrangell, Alaska where it was demonstrated to local operators. Four years after the project started, the Vazar received its certification on floats in the United States in November 1988. Canadian float certification followed in June 1989.

Most devotees of the Otter prefer the look of the original. The round, radial engine is much more attractive than the long, pointy nose of the turbine. The piston engine original also sounds like what an Otter should sound like. It should not sound like a King Air! Points like this aside, it has to be said that the turbine conversion has greatly improved the DHC-3 where it matters, in its performance. The lighter engine, giving a weight saving of 730 pounds, provides a payload increase of the same amount. An increase of 150 horse power enhances all areas of performance. Cruising speed is 805 increased by 43 mph, rate of climb is increased and take off and landing distances reduced. The engine gives much greater reliability and the TBO has increased to 3,500 hours. The Vazar is certified for IFR, allowing it to be operated at night and in the short days of the northern winters. It provides a much more dependable operation in severe weather and a much improved economy of operation. The Vazar is certified to carry 16 passengers.

Commercial development of the turbine Otter was undertaken by Dara Wilder's company, Vardax, based at Bellingham in Washington State. The company formed its Vazar Aerospace Division for the project. The Bellingham location is however only an administrative and marketing office. Operators of Otters wishing to convert their aircraft to Vazar dash 3s can either purchase a conversion kit and undertake the work themselves at their own base, or have the work performed by any contractor who specialises in the conversion. Many such conversions have been undertaken by Aero Flite Industries at the Vancouver International Airport. As John Hill of Aero Flite explained, the engine comes from P&W Canada in Montréal, Serv-Aero builds the conversion kit at Salinas and Aero Flite mates the engine and the kit to the Otter in Vancouver, to produce the DHC-3T Vazar Turbo Otter. Other companies specialising in this conversion are T.C.Aviation in Saskatoon, Saskatchewan and Recon Air in Geraldton, Ontario.

As at March 2019, 87 Vazar conversions had been completed, making this by far the most successful of the Otter turbine conversions.

THE POLISH OTTER

A different approach to the Otter's engine problem was taken by Airtech Canada of Peterborough, Ontario who replaced the P&W R-1340 radial engine with a Polish-built radial. The company's founder and president, Bogdan Wolski, a naturalised Canadian citizen who had emigrated from Poland in 1965, recognised that the supply of piston engines for the Otter would eventually dry up. Familiar with Poland's gigantic aviation industry, he knew that the only replacement radials which were still available were those in production behind the Iron Curtain, as it then was. He arranged with the Polish aircraft and engine manufacturer Polski Zaklady Lotnicze (PZL) for a supply of their engines, but before the project could proceed, the Canadian Department of Transport had to give their approval. A lengthy interchange between the Polish authorities and the DoT resulted in a bilateral certification agreement between the two countries. This facilitated several other certification procedures and significantly improved communications between Poland and Canada.

Airtech's first Otter conversion was a straight exchange of the 600 horse power R-1340 engine for a PZL-3S unit of the same power. The new engine was 528 pounds lighter, used less fuel and gave improved performance. Canadian certification for the engine was received on 11th June 1980 and the first Otter to be converted was CF-WJB (183) in the latter part of that year. Cost of the conversion was $98,500 Canadian. In all, eight Otters were converted to the PZL-3S engine, all the conversions taking place at Airtech's Peterborough, Ontario facility:

16 C-FEYO Newfoundland Labrador Air Transport

69 C-FCZP Raecom Air

73 C-FIFP Silver Pine Air Service

81 C-FIKT Newfoundland Labrador Air Transport

183 C-FWJB Sold to Cargair Ltee

310 C-GLJH Newfoundland Labrador Air Transport

329 C-GLFL Airgava Ltee

400 C-FAGM Newfoundland Labrador Air Transport

Sadly to relate, this conversion did not prove a great success. Of the eight Otters converted, five of them (the four Newfoundland Labrador Air Transport aircraft and the one Raecom machine) had their original R-1340 engines re-installed. The other three upgraded to a more powerful Polish engine. To quote from a frank Airtech assessment of the situation: “The PZL-3S conversion cannot be considered a success. Its appeal was based on improved payload, better fuel economy, improved reliability and equivelant take-off and climb performance. As experience was gained, operators had trouble achieving the benefits expected. Also, the engine and propeller were plagued with technical problems. The first version used a Dowty Rotol propeller, which has since been declared incompatible with the engine. Eventually all propellers were changed to a Polish design. This marriage has also not been without problems. Ultimately, all operators gave up on this conversion for the advantage of the 1,000 horse power conversion, or for the known problems of the R-1340”. Realizing the problems that were being experienced, Airtech introduced a much more powerful Polish engine, the ASz-621R-M18, which generated 1,000 horse power, four hundred more than the original P&W engine. 18,000 of these engines had been built, with production of new engines continuing in Poland at the rate of 800 a year, thus guaranteeing supplies. Thus converted, the aircraft became known as the DHC-3/1000 hp Otter. The first aircraft to be converted with the more powerful engine was C-FIFP (73), for Silver Pine Air Service, which previously had the PZL-3S engine installed. It made its first flight with the new engine on 25th August 1983 and was delivered to Silver Pine in the fall of that year, after the test flying to certify the conversion had been completed. In contrast to the unhappy experience with the PZL-3S, the 1,000 horse power conversion met with great operator satisfaction. The engine and propeller were both well-established products which worked together without teething pains. Take-off and climb performance were dramatically improved, although there was a loss of useful load of about 300 pounds. TBO went up to 1,550 hours. Fuel consumption was higher, but as Airtech pointed out the corresponding increase in cruise speed and the ability to climb quickly for improved True Air Speed and winds aloft compensated for this. The engine was specifically adapted for the Otter and gave the aircraft a distinct appearance. From an aesthetic point of view, it is not as ugly as the turbine's pointy nose, but it is no improvement on the original either. The Otter's distinctive exhaust and augmentor tubes are removed and replaced by a single stack exhaust manifold. The engine mount and cowlings are new. The engine drove a four-bladed propeller, although three-bladed props were also available. Another major advantage this conversion had over the turbine was price, with the 1998 conversion price being US$136,000.

Further conversions followed as operators saw the benefits of the new engine.

All of the early conversions were carried out at Airtech's facility at Peterborough, Ontario as the process was not then sufficiently refined to enable others to convert from a kit. The one exception was the prototype Polish Otter, C-FWJB. After it had its PZL-3S engine installed and was delivered to Cargair in 1981, it was sold by them the following year to Alas de Esperanza (Wings of Hope), who were performing charitable relief work in Peru. The Otter was flown all the way from Peterborough to its new base at Satipo in Peru. When the PZL-3S engine was replaced, as it was a bit far to travel all the way back to Canada, the 1,000 horse power engine was installed in Iquitos, Peru.

The conversion later became available in kit form, for use by authorized installers. The first such conversion was Otter N3125N for 40 Mile Air of Tok, Alaska, which was carried out by Victoria Air Maintenance at Sidney on Vancouver Island. The second, in 1995, was C-GCDX, carried out by its owners Selkirk Air at their Selkirk, Manitoba base. During 1998, Katmai Air of Alaska's Otter N491K became the fifteenth DHC-3/1000 conversion. As at 2001, the 1,000 hp engine had accumulated 45,000 hours on the Otter airframe, well establishing the combination.

One commentator described the Polish Otter in action: “The Silver Pine Air Service's Otter taxied away from a weathered grey dock at Pauingassi in central Manitoba. The Cree Indian residents of this isolated community stood watching with hands in pockets and short stubs of hand rolled cigarettes clamped between their lips. They had seen Otters before. The pilot eased in the throttle. As usual, the huge bush plane leapt into the air but this time, climbed away at an amazingly steep angle. Even the noise of the engine sounded different as the Otter roared upwards at 2,000 feet per minute, instead of the characteristic 400 fpm”. The Indians had never seen an Otter like that before!

At that stage, in 1986, Silver Pine Air Services had three DHC-3/1000s flying from their Pine Falls,Manitoba base, C-FIFP, C-GKYG and C-GSUV. Used as freighters, the Otters hauled cargo to Indian reserves, tourist lodges and fishing camps throughout Manitoba and Ontario.

As of summer 2001, the number of Otters equipped with the PZL 1,000 horse power engine had increased to 18, these being:

14 C-FODJ Green Airways

43 C-GQDU Air Saguenay

67 CF-HXY Lac Seul Airways

73 C-FIFP Blue Water Aviation

130 C-FKOA Sioux Narrows Airways

166 C-GGSL Selkirk Air

183 OB-1253 Alas de Esperanza

209 C-GBTU Blue Water Aviation

261 C-GKYG Big River Air

286 C-FLEA Green Airways

310 N21PG John P. Gerken

314 C-GCDX Selkirk Air

329 C-GLFL Air Saguenay

363 C-GSMG Sioux Narrows Airways

376 C-GSUV Black Sheep Aviation

386 C-GHYB South Peace Services

394 N3125N 40 Mile Air

434 N491K Katmai Air

There have been no further conversions to date. The fact that payload was not increased and the availability of many other engine options, most of them modern turbines, has led customers to go for the turbine option. Indeed, some of the Polish-engined Otters have been re-engined as turbines. As mentioned above, Otters KOA and SMG are operated by Sioux Narrows Airways, a company owned by Warren Plummer. In June 2001 Mr Plummer received an STC to convert the PZL factoryinstalled four-bladed propeller to a DC-3 type three-bladed propeller, this conversion being known as the 'Plummer Prop'. Most of these conversions are carried out on PZL-powered M-18 Dromader agricultural aircraft, but 9 of the PZL-powered Otters, including KOA and SMG, have been converted to the Plummer Prop. The conversion gives performance increases, fuel savings and economic benefits.

THE ORENDA ENGINE

Another piston-powered Otter re-engine program Magellan Aerospace Corporation to develop and manufacture this engine, which was intended as a replacement engine for a number of different aircraft. The prototype Orenda-powered Otter C-FEYY (19) made its first flight on 9th November 1998 from Peterborough Municipal Airport, Ontario and initial test flight for the Supplemental Type Certificate (STC) for this retrofit were successfull completed during that month.

The promoter of this project was Air Wilga Inc, an Otter leasing company and aircraft maintenance organisation based at Laval, Québec. It had three Otters in its fleet at that time, C-FEYY, C-FKLC and C-FAZX. Prompted by concerns that the original Otter engines were becoming too costly to operate and too hard to repair and find parts for, Air Wilga chose the liquid-cooled V8 engine for their project, not wishing to incur the expense of a turbine engine. Other benefits included increased speed, fuel economy and range, as well as lower operational and maintenance costs. The conversion trimmed 300 pounds off the standard floatplane empty weight. The replacement powerplant, Orenda Recip's OE-600, was the only in-production V8 aero engine capable of producing 600 horse power, and was also in use for re-engining programmes for other aircraft types, including the Beech KingAir, Air Tractor 401 agricultural aircraft, DHC-2 Beaver and Rockwell Twin Commander. The engines were manufactured at Orenda Recip's factory at Debert, Nova Scotia. In the Otter, the V8 resulted in a more dynamic nacelle profile.

Air Wilga commissioned Airtech Canada Aircraft Services of Peterborough, Ontario to carry out the engineering for the project, this company having already been involved with installing the Polish engines into the Otter. Throughout 1999 testing and development continued on the new engine installation. At Mille-Îlles, the Orenda-powered Otter C-FEYY was flown on floats, using a standard Otter as a chase plane. “It was no contest”, declared the test pilot, the Orenda-powered Otter “walked away from the 1340 Pratt”. It also demonstrated superior manoeuvrability and performance, and in terms of cabin sound levels, it was “comparable to a turbine modification, no vibration, no mind-numbing exhaust stack blasting at the pilot side door”. There were a number of incidents during the testing phase (see under C-FEYY(19) in the Production List) but all were overcome and on 17th January 2000 the STC was awarded by Transport Canada for the Orenda-powered Otter for floats, skis and wheels. Two months later, CFEYY entered commercial service with Johnny May's Air Charter based at Kuujjuaq in northern Québec, on lease from Air Wilga. That same month, work commenced on re-engining C-FAZX (458) as the second Otter with the Orenda engine and Air Wilga prepared to sell conversion kits to customers later in the year.

Meanwhile, C-FEYY in its attractive yellow and blue colour scheme, on wheel-skis, began an aggressive commercial schedule in the rugged bush country of northern Quebec. Veteran pilot of 37 years flying experience Johnny May stated “the Orenda powered single Otter should be re-named because it performs like a Twin Otter. Compared to the R-1340, I get to altitude in one third less time, the engine burns significantly less fuel and there is much less pilot fatigue due to less noise and vibration compared to the round engine”. EYY went on lease to Aero Golfe of Havre St.Pierre, Québec for summer 2001 before returning to Air Wilga. It was exhibited at the Oshkosh airshow that July. It was advertised as “The world's most affordable and advanced high power reciprocating engine. Complete firewall forward kit for US$229,000. Turbine power for piston price”. A lease of EYY was arranged to Waasheshkun Airways of Mistassini, Québec in February 2003.

The second Orenda Otter conversion C-FAZX went on lease to Air Saguenay during the summer of 2002. As one report noted: “Air Saguenay's maintenance crew, more accustomed to working on the traditional R-1340 powered Otters, is often pleasantly surprised to open the cowls on the Orenda to discover that, though everything is accessible, nothing needs to be done. And best of all, there is no oil on the firewall or inside the cowls”. However, only these two Otters, C-FEYY and C-FAZX, were converted with the Orenda engine, and despite a number of leases to different operators, it appeared that potential customers were more inclined to go with one of the turbine engine options. In any event, disaster struck the programme when in December 2002 it was announced that Orenda Recip Inc was closing down. It was not proving a commercial success, and its parent company was no longer willing to continue funding the venture. As a result, there being no manufacturer to accept on-going responsibility for the engine, certification of the Orenda engine for use in the Otter was withdrawn, and Otters EYY and AZX were grounded, pending being re-engined with another engine type.

TEXAS TURBINE CONVERSIONS INC

Based at Decatur, Texas this company is a family concern of the Bishop family. It began with a Pilatus Porter conversion to a Garrett engine, before deciding to convert the Otter to Garrett power. Their first aircraft was Otter 115, purchased in May 1998. Work started immediately on converting the aircraft with a Garrett TPE-331 turbine engine, with a choice of either the -10 or -12 version. The -10 is a 1,000 hp engine, while the -12 is a 1,200 hp. Both are de-rated to 900 hp but the -12 can retain this power to higher altitudes, making it better for hot and high operations. This conversion work was carried out at the company's facility at Decatur. In July 1998 the company announced its project, stating that it intended to achieve certification by early 1999. The “Super Otter”, as it is known, was registered on 15th April 1999 as N120BA to Bishop Aviation Inc and flight testing commenced. As the company's advertisements proclaimed: “While the airframe is limited to a 125 knot airspeed, the additional juice helps the Otter climb better and fly at max speeds to much higher altitudes than it could with the radial. As a bonus, the engine swap saves 400 pounds, which translates into a better useful load and gives operators a greatly increased TBO, up to 5,400 hours, over the P&W radial”.

The company offered the first five conversion kits at a price of US$175,000 installed at their Decatur facility. That price included all items necessary to turbine engine operation, but not the engine itself. The customer had the option of buying a new or overhauled engine. The TPE-331 engine drove a Hartzell four-bladed propeller. Certification in the US was achieved during 2000 and N120BA was put to use on the Bishop family's own sky-diving operation at Decatur. A second Otter was acquired, number 226, which would be used for the Canadian certification, expected in early 2001. The first conversion, N120BA, crashed at Decatur while taking off with 21 sky-divers on board, on 31st March 2001. Fortunately there were no serious injuries, but the Otter was severely damaged and the wreck was later sold.

The company thus acquired another Otter in June 2001, which was number 15 and was registered N150BA to Texas Air Cargo Inc, Decatur on 3rd July 2001. It was to be used for float approval of the Wipline 8000 floats. By the winter of 2002, five Otters had been converted at Decatur in the following order:

115 N120BA Bishop Aviation. Prototype. Crashed 31st March 2001

226 N226UT Ultima Thule Outfitters, Alaska

15 N150BA Bishop Aviation. Demonstrator

287 C-GYKO River Air Ltd, Ontario

252 N252TA Talon Air Service, Alaska

Kal-Air of Vernon, British Columbia were appointed by Texas Turbine Conversions Inc as an authorised conversion agency, this location conversion to C-GMCW (108) for Black Sheep Aviation of the Yukon during May/June 2002 and this aircraft was demonstrated at the Viking Air/Bombardier “DHC Out-of-Production Aircraft” conference held in Victoria, BC in October 2002. Kal Air have converted the following Otters as Texas Turbines up to December 2004:

108 C-GMCW Black Sheep Aviation, Yukon

118 N104BM Bald Mountain Air Services, Homer, Alaska

144 N93356 Ward Air, Juneau, Alaska

174 C-GFTZ Alpine Lakes Air, Smithers, BC

262 N338AK Wings of Alaska, Juneau, Alaska

361 N361TT Renew Air, Dillingham, Alaska

439 C-FPEN Fast Air, Winnipeg, Manitoba

454 N339AK Wings of Alaska, Juneau, Alaska

N338AK and N339AK were shipped to Kal Air conversion was carried out by Wings of Alaska themselves in their hangar at Juneau. In addition, they also converted N336AK and N337AK at their Juneau base, with the assistance of personnel from Texas Turbines who travelled from Texas to Juneau for the task.

WALTER TURBINE

The first Otter to be converted with this engine was C-FIOF (24) of Eagle Aviation of Pine Falls, Manitoba. In 1998 it was flown to McGregor, Texas where Eagle Aviation had arranged for the aircraft to be converted with the Walter engine, a powerplant very similar to the PT-6. The Otter flew back to Silver Falls in September 1999, converted with its new turbine, for test flying before returning to McGregor for further test work as part of the certification process. With certification achieved, it returned to its base at Pine Falls.

AOG Air Support Inc of Kelowna, BC became involved in the project. During December 2001 / January 2002, C-FIOF was at the company's Kelowna facility for technology refinement and maintenance work. In February 2002, AOG commenced work at Kelowna on converting a second Otter to a Walter turbine, this being Eagle Aviation's C-FVQD. This aircraft featured at the Viking Air “DHC Out-of-Production Aircraft” conference at Victoria, BC in October 2002 on amphibious floats, giving an impressive display. It then went on lease from Eagle Aviation to Inland Air at Prince Rupert, BC.

The Walter M601 is a 751 horse power engine, same as the PT-6 and with a comparable fuel burn. On the Otter it drives a five blade AVIA propeller. As the brochure proclaims: “The Walter M601 was originally designed in the Czech Republic to match Russian conditions of heavy climate and lack of qualified engineers on site. This is why the engine is specific by its install-and-go philosophy. This means there are no 'hot section' inspections, as with other products. These excellent features are making the M601 more and more popular outside the original target market”.

The third Walter conversion was C-GOFF (65) of Huron Air, which arrived at Kelowna for the work to be done in October 2002. Over the winter of 2003 / 2004, Eagle Aviation arranged for their other two Otters, C-GKYG and C-GSUV, also to be converted to Walter turbines at Kelowna. N103SY (296) of Mavrik Aire arrived at the Kelowna facility in April 2004, where it became the sixth Walter conversion. That was the position as at December 2004, at which stage there had been the six Walter Turbine Otter Conversions, which are referred to as WTOCs. During January 2005, work started at Silver Falls, Manitoba to convert C-GBTU (209) of Blue Water Aviation as a WTOC, and C-GBNA (125) of Voyage Air arrived at AOG Air Support's Kelowna, BC facility, also to receive a Walter engine.

OTHER ENGINES

Although not intended as Otter engine replacements for the general market, there were two one off projects to re-engine the Otter which are worthy of mention. The first involved Otter number 338, an original United States Army aircraft which went on to serve with Northern Thunderbird Air of Prince George, BC as C-GLES, before being acquired by Wayne C.Alsworth of Port Alsworth, Alaska, registered N338D in 1985.

Wayne Alsworth operated a general cargo and aircraft salvage business known as “Wayne's Aircraft Salvage” based at Port Alsworth. This frequently involved landing in remote bush locations with heavy loads, and he was concerned with the lack of adequate power for this work from the 600 horse power R-1340 Wasp engine. He decided to re-engine his aircraft with a Wright Cyclone R- 1820 engine, rated at 1,200 horse power, the same engine which powers the DC-3. The work was undertaken at Merrill Field, Anchorage during the early part of 1987. All the design, planning and actual conversion was undertaken by Mr.Alsworth himself. The engine mount was custom built. The cowling came from a Lockheed Lodestar. The cowl flaps came from a DC-3 and were modified to fit the installation. The propeller came from a Grumman Albatross. The Otter's trademark exhaust augmentor system was completely revamped and there was a huge, single exhaust port on the right side that “resembled a grenade launcher for cantaloupes”, as one observer described it. The propeller spinner came from an aviation surplus house in Canada but neither Mr Alsworth nor the proprietor had any inkling where it came from originally.

There were some control modifications in the cockpit, but perhaps the most significant was the change in weight and balance. The new engine was 400 pounds heavier than the old one, requiring the engine to be recessed closer to the firewall and the battery box to be relocated in the tail, to preserve the balance. There was no hydraulic accessory pump, so the flaps and skis would have to be hand pumped. Mr Alsworth was aiming for experimental status first, and after he had flown several hundred hours, he would review matters and decide then whether to go for full certification. Exactly how far he got in all this is not known, but perhaps not surprisingly his ambitious but somewhat makeshift conversion was not certificated, and the Otter was converted back to its original R-1340 powerplant.

The second conversion involved Otter 465, flown for many years by Air Fecteau of Quebec as CFVQI, and later by Temsco Airlines of Ketchikan, Alaska as N19TH. In July 1994 it was purchased by the Soloy Corporation of Olympia, Washington and in August of that year was registered as N5010Y to Soloy Dual Pac Inc. The Otter was acquired by the Soloy Corporation for use as flying test-bed for the certification of their Dual Pac powerplant, which they were developing in co-operation with Pratt & Whitney Canada. Back in the 1980s, Soloy held discussions with Otter operators looking for a lowcost twin-engine retrofit to increase the aircraft's capabilities. Nothing came of those discussions as such, but they did unofficially launch the Dual Pac concept, which was implemented years later when aircraft such as the Cessna 208 Caravan, the French TBM-700 and Switzerland's Pilatus PC-12 came along.

All of these types were powered by a single turbine engine but would not be cleared for use carrying passengers at night or in IFR conditions, as they only had one engine, and aviation authorities such as the FAA required twin-engined aircraft for that purpose. The Dual Pac concept was to join together two engines, which drove a single propeller through a combining gearbox. Thus, if one engine failed, the other would continue to power the aircraft. Soloy intended to sell its twin pack to Cessna, Pilatus etc but first had to get it certified. The Otter was acquired as the test-bed, i being somewhat more cost-effective to use the elderly Otter rather than a new and very expensive Cessna Caravan.

The Otter was taken from Ketchikan, where it had lain out of use for some time, to Soloy's facility at Olympia Airport, Washington. It was not in the best of shape. The paperwork revealed that it had been partially submerged in an incident while flying for Air Fecteau. It had been repaired by Propair at their Rouyn facility in July 1988, total time on the airframe at that stage being 14,230 hours. It had then been sold to Temsco Airlines and flew for them based at Ketchikan until they ceased operations in November 1991, after which it lay idle.

Between July and September 1994 the Otter was completely stripped down and refurbished by Soloy and the twin pack installed, comprising two Pratt & Whitney Canada PT-6A-114 turbines. It emerged from the hangar in pristine condition, in a gleaming all-white scheme, featuring a large 'Soloy Dual Pac' logo. It made its first flight in this configuration from Olympia on 29th September 1994, a flight of 32 minutes duration which, according to the accompanying press release, demonstrated its simple and safe handling characteristics. The press release explained that the Dual Pac was being developed to provide aircraft manufacturers and modifiers with a “safer and more efficient alternative to wing mounted twin-engined installations…The FAA has determined that the Dual Pac powerplant with its unique redundancy and separation of systems satisfies the requirements for classification as a twin-engine power system. When it is properly installed in an aircraft, the aircraft can be certified as multi-engine and approved for commercial transport of passengers in IFR conditions”.

The Otter continued its test work into 1995, flying for several hundred hours to build up in-service time for the powerplant and related systems. In July 1995 it was re-registered N32910 and in November of that year, its test work with Soloy complete, it was sold to Ketchum Air Service Inc., of Anchorage and converted to a Vazar Turbo Otter, registered N342KA.