INTRODUCTION.

The goal of this text is to provide a comprehensive set of 'operating strategies' for simulating the Fairchild F-27A Friendship within FS2004. They give you an insight into the role of pilot flying (PF) in an aircraft powered by early series Rolls Royce Dart engines during the classic era. Today with turbine overhaul facilities everywhere, forty-five extra years of experience, and some engine modifications along the way, higher rpm limits apply. This is all about experiencing the first decade or so of turbo prop engine operations.

Unfortunately the accuracy of the simulation is constrained by the capabilities of FS2004.

Contrary to popular opinion FS2004 does not contain 'a turboprop flight model'. It just contains a flight model for one particular concept of turboprop engine, (the P&W PT-6A). This third generation turboprop engine allows the pilot to vary airscrew rpm independently from fuel flow. First generation turboprop engines like the Rolls Royce Dart lacked that capability. The power and thrust output of early generation turboprops can be simulated correctly within FS2004, but the airscrew inputs cannot.

Aircraft powered by the Rolls Royce Dart have power levers, which control both fuel flow and engine rpm together. This can be simulated up to a point in FS2004, but only at the expense of suffering inaccurate rpm output as a consequence of the rpm linking to fuel flow.

The Rolls Royce Dart is not flat rated. As it climbs through the atmosphere, and air density falls, the power produced falls in step. In FS2004 the turbine rpm will also fall in step. This is not realistic, but it is the price you have to pay for elimination of the non-existent rpm levers whilst maintaining realistic power (and thrust) output.

In addition some aspects of Rolls Royce Dart operation conducted manually by the flight crew have been omitted, combined, or automated because they would be undertaken by pilot not flying (PNF).

The engines are tough, and only significant abuse in flight would cause them to fail. In the commercial world however aircrew must operate to much more restrictive engine limits, imposed by the engine manufacturer and airline, which ensure that the engines need maintenance as infrequently as possible. Turbine overhauls are very expensive.

Unlike a piston engine, the power that a turboprop produces varies considerably with outside air temperature. Many later turboprop engines had automatic temp trim to take care of the problem, but the Rolls Royce Dart, which has been in airline service since 1949 does not. Pilot not flying will take care of most of the manual temp trimming with the temp trimming switches. In FS2004 acting as pilot flying you must limit Turbine Gas Temperature (TGT) using your joystick throttle. If you never fly with real weather, or with high temperatures selected from the weather menu, this may not be much of an issue, but you will never really get the most from this (Bonanza Airlines) flight model if you do not explore Dart operation in desert temperatures.

Here is a phase-by-phase strategy guide for simulating the role of pilot flying in an F-27A within the limitations of FS2004.

OPERATING STRATEGIES.

1) The take off

The Dart 528-7E has water methanol injection. Invented in Germany during WW2 it was originally a means of adding war emergency power to piston engines. When employed with turboprop engines its usage is rather different. Whilst it always adds some extra power, its purpose is to restore the rated power of the engine in high outside air temperatures, but only for the duration of the take off. In principle it allows the gasses to enter the most critical parts of the engine at higher temperatures, because it provides additional cooling. It is not a form of reheat or rocket boost.

It is standard operating procedure to use it when available. Selection of water methanol injection for take off has therefore been incorporated in the flight model by default. The injectors will operate as the TGT exceeds the normal limits. The TGT does not fall. The point is to allow it to be higher. If you *choose* to not use ADI you will need to limit your TGT to 810C with the throttle.

When you make a wet take off the TGT can rise safely to 860C. Whether TGT ever gets near 860C will depend on the outside air temperature (OAT). The OAT will have to be very high for the limit to be breached. You will almost always be able to use full throttle for a wet take off. At sea level you will obtain about 1,870 SHP, but less at altitude. Water methanol injection 'cancels' high outside temperatures, but as deployed in the 528-7E it does not significantly compensate for thin air on high runways.

Some airlines fly from A to B. Others fly A - B - C - D without refuelling or topping up the water methanol tanks at B and C. You have enough water methanol for one, or perhaps two, wet take offs and one go around. On a bus stop route one or two of the three take offs will have to be made dry.

Without the benefit of water methanol injection the TGT limit is only 810C. When performing a dry take off with an OAT above about 20C, advance your joystick throttle much more carefully to temp trim the engines to less than 810C. It is a limit not a target.

The lower the engine limits the less power you can generate and the longer the take off run. If flying for a bus stop airline, from runways at high temperatures, choose which of the runways at A, B and C will be favoured with wet take offs with care. Practice dry take offs at < 810C in high OATs as well as wet take offs at < 860C, but make sure the runway is long enough.

2) The climb

Since you do not have enough water methanol to use during the climb, (water is very heavy and the airline would rather fill seats), all your climbs have to be made in dry power. Even if you made a wet take off you must get the TGT back to < 785C after the take off. If it is cold enough outside the TGT may already be below 785C. Turn off the ADI switch(es) to avoid the ADI tanks going dry.

It would be perfectly safe to climb the aircraft all the way to cruising level at full throttle and 810C. The engines would however need frequent expensive overhauls and you would soon need to look for alternative employment. As soon as you have complied with the noise abatement rules in force you must reduce to a profit maximising rpm setting and observe a lower TGT limit.

Until the end of noise abatement flight safety and excessive engine wear have been the only considerations, but now you must also take into account fuel economy. From this point onwards achieving the target RPM for fuel economy has priority over engine wear considerations unless the TGT limit may be breached. Breaching of the TGT limit implies that your pursuit of fuel economy is costing too much in engine wear.

Reduce to 13,800 rpm, but if TGT exceeds 760C you must reduce further.

As you climb the amount of oxygen in the air reduces and the engine produces less and less power. In FS2004 you must gradually advance the throttle to sustain 13,800 rpm, but eventually air density will be too low to sustain 13,800 rpm in FS2004 at full throttle.

This altitude is the lowest cruising altitude consistent with sustained economic operation of the aircraft, but unless you are flying a very short stage you will always want to climb higher. Thereafter in FS2004 you climb at full throttle and in FS2004 rpm will fall steadily. Whenever Dart engine revolutions fall below 13,000 rpm you must limit TGT to no more than 730C. This will only be a problem in a hot atmosphere.

Although the loss of rpm is a function of the limitations of FS2004, the accompanying loss of power as you climb into less dense air is entirely real. Your rate of climb will fall as you sustain 140 KIAS.

3) The cruise

Whilst a Dart 528-7E would not fail within the duration of a single flight, even if run continuously and dry at 850 C and 15,000 rpm, some aspects of the Rolls Royce guarantee concerning time between overhauls became void in the classic era if the aircraft was cruised continuously at more than 13,300 rpm. Designated 'normal cruise power' by the manufacturer this sets 'maximum cruise power' as far as the airline is concerned.

When conducting maximum cruise at > 13,000 rpm you are also limited to 760C TGT. In hot air max cruise may have to be conducted at less than 13,300 rpm. Hot air is associated with low altitudes. To cruise at maximum cruise power you must climb high enough to find cold enough air.

There is a profit maximising altitude for maximum cruise. It varies from day to day and place to place, but if expressed as a flight level it is usually close to FL160. It is the level at which you can set 13,300 rpm at the lowest possible TGT. It is much easier to find in FS2004, than in real life, as it will be the highest altitude at which you can sustain 13,300rpm. That combination produces the guaranteed maximum cruising speed.

In the case of the F-27A that is 264 KTAS (@ FL160). You will burn about 1600lbs of AVTUR per hour to achieve that.

In common with most turbine engined aircraft application of maximum cruise power may accelerate the aircraft beyond its safe structural limit at lower altitudes. The F-27A does not need a Machmeter or a barber pole ASI, but you must not exceed 224 KIAS as a result of applying max cruise power at too low an altitude.

However you should only use maximum cruise power if absolutely necessary, to make up time and get back on schedule. Otherwise you should operate the aircraft using the economical cruise power setting.

For the F-27A this is 12,600 rpm. In principle fuel economy will suffer, but the savings in engine wear more than make up for the extra fuel burned. This condition is economical cruise. Since it is conducted below 13,000 rpm you are limited to 730C TGT. This TGT limit will only be a problem on hot days.

Fortunately there is also a remedy for the higher specific fuel consumption arising from running at lower rpm. Simply climb to higher altitude until the gain in TAS in thinner air offsets the higher fuel burn. On a typical day somewhere around FL200. Again it is easy to determine in FS2004 as it will be the highest level at which you can sustain 12,600 rpm.

This is defined as the economical cruising level and produces the best economical cruising speed. In the case of the F-27A that is 258 KTAS (@ FL200). You will only burn about 1300lbs of AVTUR per hour to achieve that. Compare this fuel burn to 1600 PPH to achieve 264 KTAS at FL160 and it should not be hard to see why the airline you work for pays you to seek out profit maximising strategies rather than performance maximising strategies.

Performance maximising strategies are only appropriate to combat flying. Make the mind switch when using FS2004 to simulate different types of aircraft.

As these aircraft aged they were relegated to shorter and shorter stages until it was not worth climbing to FL160 let alone FL200. High altitude economical cruise was still 12,600 rpm, but old equipment needs nursing and on short hops at low level it may be sensible to cruise at only 12,000 rpm. Below 12,000 rpm specific fuel consumption is so high that it becomes impossible to make a profit. This therefore represents the lowest rpm you can sensibly apply for cruise. It is therefore also inappropriate to climb to extreme altitudes where you could not apply 12,000 rpm, even though it is possible on long haul flights.

If you suffer an engine failure, airline policy and the manufacturers guarantee on the other engine are of no consequence. In emergency you may divert with up to 15,000 rpm and up to 850C TGT applied to the good engine for as long as you need. It will have to be removed and overhauled after landing, but so what.

4) Descent

Reducing to less than 12,000 rpm for the duration of the descent is OK because you minimise fuel burn by staying high as long as possible. A cruise descent at say 12,000 rpm wastes fuel. Descend fast and late if ATC will allow, but make sure you make the mandatory levels in the standard arrival.

In descent your attention must switch to the PSI gauges. You must sustain sufficient power lever advance to avoid the yellow arc at the low end of the PSI range. If the needle enters that arc you will not have enough power to maintain pressurisation of the cabin, or to run the hot air de-icing systems.

Once you are low enough to depressurise the cabin and also have an outside air temperature above 5C, you should still avoid it to avoid undue wear of the propeller's reduction gear layshafts.

5) Approach

The Friendship was the most successful of the many aircraft offered as DC-3 replacements. Ex DC-3 pilots loved it. They were impressed by the permissive structural limits. It could cruise or descend safely at up to 224 KIAS compared to just 160 KIAS in the DC-3 / C-47. Full flap could be extended at an incredible 125 KIAS, as fast as a C-54. The DC-3 / C-47 limit is just 87 KIAS.

However few FS2004 users have been DC-3 pilots, and it is no longer 1959. If you are used to flying swept wing jets in FS2004, or simple flight dynamics with no structural limits in them, the idea that flaps cannot be used as air brakes may come as a shock.

When the F-27As were brand new it was permissible to extend the gear at up to 224 KIAS. This was subsequently found to be unsafe and the limit was reduced to 168 KIAS. This lower safety limit applies to these flight dynamics. If you plan ahead it will never be a problem.

When flying turbine engined aircraft always aim for a stable powered approach. Use the rpm gauge to make about 11,150 rpm. Set this rpm before you enter the holding pattern, (up to thirty minutes before landing), and do not attempt to change it until two mile final.

Unless subjected to speed control by ATC do not play around with the power levers during an instrument approach.

A couple of minutes before you intercept a 3 degree glide path, extend the gear. When you are below 135 KIAS extend FLAP 1. You are now ready to begin the descent to land. Maintain a 3 degree glide path. Your speed will be well below the 125 KIAS approach flap limit. When appropriate add further stages of flap to achieve the reference speed at the airfield boundary.

Practice flying the approach until you have learned to drop the gear at just the right moment to bleed your speed to 135 KIAS just before Glideslope intercept, so that you can extend FLAP 1 as late as possible and just before the Glideslope.

Depending on the strength of the headwind you may need to add or subtract a sliver of power over the last two miles, but sometimes the same power setting will be good for the last thirty minutes of the flight. If you do need to vary power from 11,150 rpm after you are cleared for the approach make slow small changes only to hold the 3 degree glide path and achieve your reference speed. The lighter you are the lower your reference speed.

Always use the abbreviated pilot's handling notes, called by pressing F10 and selecting the reference tab, from take off to landing, until you have accumulated enough hours in the F-27A to know them off by heart. Then you can use the Pilot's Notepad as a reminder.

That way you will have a realistic flight simulation experience and the aircraft will remain under control.

Do not attempt VFR approaches or visual circuits in turbine engined aircraft until you have mastered the stable approach technique in that aircraft type. When you are finally ready to attempt an unstable visual approach give yourself lots of room. Never attempt to fly a visual approach in FS2004 with a zoom setting of less than 1.0 (0.75 on a 16:9 wide screen monitor with the outside view stretched across the entire monitor) as human perspective will be so distorted that you will find it impossible to judge the glide path and will always wind up with a rushed approach.

6) Landing

When you land, the Dart has another trick up its sleeve. If you have the throttles sufficiently retarded microswitches in the main gear will detect weight on the wheels and will withdraw the flight fine stop lock from the airscrew shaft. The airscrews will fine to zero degrees (ground fine pitch) and will become pure air brakes even though the props are still turning.

This has nothing to do with reverse pitch or reverse thrust. They are not pushing any air forward, just adding drag. However since the effect is almost instant it is enough to ensure that the F-27A does not need reverse pitch. The aircraft will slow almost as quickly in ground fine pitch. Raise the flaps (no restriction as there is no reverse thrust to hammer them), and when below 55 knots start to add wheel braking as required.

To exit ground fine pitch simply advance the throttles, but remember ground fine pitch will not invoke if you forget to retard the throttles after landing.

7) On the ground

This flight model does not attempt to replicate Rolls Royce Dart 'ground condition' operations in full. The rpm gauges will over read on the ground. Nevertheless ground pitch settings including ground fine pitch are simulated by alternative means and the net thrust produced versus joystick throttle position is 'realistic' during ground handling. Unlike the real aircraft you can switch from ground to flight condition simply by advancing the throttle. It's a small compromise.

8) In flight

Use the abbreviated handling notes FK27_ref.txt. Press the F10 key and select the reference tab whilst flying and use them as a phase-by-phase and step-by-step checklist.

FSAviator May 2003. Modified by Tom Gibson June 2013.