Frank FT-250涡喷发动机评测

超级盾

作者：COLIN STRAUS
图片：BOB PETRIE
原载《Radio Control Jet International》杂志2020年6-7月刊

The Frank FT-250 package is quite comprehensive, including almost everything required, the only addi ...

The Frank FT-250 package is quite comprehensive, including almost everything required, the only addition required being a 3 cell Li-Po battery. (ECU manual not shown)

Turbine Package Contents:
Frank FT-250 Turbine
HP-Tech Brushless Fuel Pump
Projet Hornet III ECU
(Electronic Control Unit)
Projet GSU (Ground Support Unit)
Leads
I/O Board
Hornet III Instruction Manual
Fuel Tubing
Servo Operated Fuel Valve

     In the almost ten years I have been carrying out turbine tests I had yet to run a turbine produced by the Frank Turbine company from Austria, so I was delighted to receive for test an example of their recently released FT-250 turbine, which as its name suggests, has a nominal thrust of 250 Newtons. Frank turbines first became available to buy back in the year 2000,the company being founded by Alfred Frank; more recently, in 2018 the company was bought by Mario Pasqualini, and more emphasis was placed on new engine development and international sales - currently Frank produce a total of four turbines,ranging from the smallest, the FT-180, through the FT-220 and the subject of this test, the FT-250, right up to the very powerful new FT-500, which is expected to be available some time in autumn 2020.
    Supplied in an aluminium carry case with foam inner packing,the FT-250 turbine package includes the turbine itself, Hornet III ECU, matching Projet GSU, HP-Tech brushless fuel pump,I/O board, leads and tubing etc, and a first for this tester, a neat servo operated fuel shutoff valve. Instructions for the Hornet ECU were provided in both English and German, but there was no separate turbine manual, and in common with most turbines these days, no battery was supplied, so a 3S 2500mAh Li-Po was used for all the test runs.

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     Starting with the turbine, which is quite distinctive in appearance,notable features including the moulded carbonfibre front cover and the scalloped rear of the exhaust cone, as well as the central rear cone itself with an unusual short parallel section at its very end. Weight saving has clearly been a target for Frank Turbines with the FT-250, the carbonfibre front cover being evidence of this, and the result is an overall weight of just under 1,900 grams, this being significantly lighter than other turbines of similar power, and this weight includes the supplied FOD guard. The aluminium starter mount is very nicely machined and proved to be very rigid indeed, whilst the engine mounts were fretted out, both to reduce weight and so that the Frank Turbine name can be included. As is becoming standard, the fuel and kerostart valves are under the front cover, so there is only a single fuel inlet connector, the second connector evident in the photos is a pressure output, in normal usage this is kept plugged.

Turbine sitting on the case it comes supplied in.

Turbine sitting on the case it comes supplied in.

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     There are two electrical connections between the turbine and ECU, one providing power, the other being for data. As would be expected, the visible components are all very nicely finished, with both the compressor and turbine wheel being of excellent quality. The keroplug is internally mounted, however the thermocouple is fitted externally apart from the final short section which projects into the exhaust gas flow.
     The HP-Tech brushless fuel pump is beautifully produced and superbly finished,whilst the separate servo operated fuel valve is supplied fully assembled and ready to use within its carbonfibre frame, the servo lead connecting to the ECU. The ECU itself is an example of the well known Projet Hornet III unit,produced specifically for FrankTurbines and being marked as such.

Note the heavily fretted out turbine mount and the unusual scalloped rear of the tailcone.

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    Compared to some of the latest ECU’s the Hornet is a substantial size, but it is surprisingly light for its size, keeping the overall turbine package weight to a minimum.It is a sophisticated and advanced ECU, which offers a great deal of adjustability if required – having said that we made no changes to the factory settings during the testing, and none appeared necessary. The GSU supplied is the established matching Projet unit, which has become well known for its reliability over the years.

Moulded carbonfibre front cover minimises weight, note also the very rigid machined alloy starter mo ...

Moulded carbonfibre front cover minimises weight, note also the very rigid machined alloy starter motor mounting.

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     Setup of the Hornet ECU is very straightforward,and with the engine firmly bolted to the test stand the fuel line was primed and the first start commanded.Cold starts proved rather extended at around 1 minute 40 seconds in total to go from the initial command to the engine running at idle and the throttle control being passed to the radio, whilst starts with the engine still warm were little faster, although this is an issue that Frank are working on at present to improve. The starts themselves were quite fuss free with just a couple of small flickers of flame being visible for a few seconds, this being quite normal.

Rear view showing the crisply cast turbine wheel and the cut off centre cone.

Rear view showing the crisply cast turbine wheel and the cut off centre cone.

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     Once past this stage the rest of the start procedure was completely clear of flames, and once the engine was at idle we were able to commence the testing process, this being quite straightforward,with the engine running smoothly and steadily throughout the rpm range, the various intermediate points where figures are taken being held very accurately. The full throttle thrust (corrected for temperature and pressure) was found to be 265 Newtons (27.0Kg or 59.6Lbs), this being well above the nominal thrust figure of 250 Newtons claimed by Frank Turbines.Idle thrust was also above the claimed figure of 8.0 Newtons, at a measured 9.5 Newtons, although this is commendably low when compared to the full thrust figure. Fuel consumption was measured at 948ml per minute at full throttle, this being some way above the 840ml claimed, but of course with the power level also being well above that claimed, this additional fuel consumption is unsurprising. It should of course be noted that the performance and fuel consumption figures were measured with the FOD guard fitted, so will be representative of the installed performance.

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     Acceleration and deceleration times matched each other almost exactly, at around 4.5 seconds, this being fractionally slower than the 3-4 seconds claimed,but even then, these slightly slower times are still very respectable, particularly for such a powerful turbine.

Beautifully finished brushless fuel pump is supplied with the FT-250.

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     We did have one unexpected issue during the testing procedure, when at the end of a just over one minute full power run the engine produced a momentary ball of flame from the tailcone,which provoked an immediate shutdown of the engine. No damage was done, and once the engine had cooled it was restarted and testing continued. It proved impossible to replicate the problem in further runs, and it is possible that some air was trapped in the fuel filter,which when ingested into the engine caused the ball of flame when the pump momentarily supplied excess fuel, as it tried to compensate for the sudden loss of rpm as the trapped air travelled through the engine.

Unusual servo operated fuel shut-off valve is supplied, this operating via the ECU.

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     Following the extensive testing we carried out, the FT-250 emerged looking like new, and ready to be installed in a suitable airframe. Overall the FT-250 is an impressive engine, producing substantial power, yet having a very light overall weight, giving an excellent power to weight ratio. With an increasing number of airframes requiring engines of this power level, I am sure that we will start to see more Frank turbines in use around the world over the coming months.

Hornet III ECU is produced specifically for Frank turbines, and is a very capable unit indeed.

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     It should be noted that Frank also offer a range of turbine tailpipes,both conventional and with vector thrust, suitable for their own and other turbines. The tailpipes they have developed can add up to 10% additional thrust, due to the increase in mass flow and the advanced design of the aerodynamics of the inlet. We hope in due course to be able to test an example of one of these tailpipes in RCJI.

WEBSITE:
www.frankturbines.com

FT-250 on the test rig and ready for its test running schedule.