Focus on: Cessna 150/152

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MY very first instructional sortie as an 18-year old student pilot was in a 1966, French-built Cessna 150F that was then only a year old. Also on the fleet at the Cumberland Flying Club in Carlisle were some older 150s, including the 1961, US-built 150B model that had no rear window and a decidedly upright tail fin. My third flight was in a Chipmunk and included some aerobatics, but that is another story.

Cessna did not produce the Aerobat version of the 150 until 1970 and this was designated the 150K. Unfortunately, it retained the 100hp Continental 0-200 engine and its performance was absolutely minimal. However, the aircraft were a commercial success and improvements came along in due course. By 1974, the French Cessna assembly plant in Reims was building the FRA 150L, which sported a Continental 0-240 engine of 130hp and this proved much more sprightly, as you might expect, with a 30% increase in puff and only a marginal increase in weight.

For this article, my description and data will be based around this 130hp variant. One of these, G-BLPH, is currently available for dual aerobatic instruction at West London Aero Club, though I am sure that there must be many others around the country.

WHAT IS IT FOR?
My articles over the next few months will be about a number of different aerobatic aircraft types. Clearly, it would be possible to compare one type directly with another, but this would be a particularly pointless exercise if it was the comparison of an Aerobat with an Extra 300, or some other such mismatch.

So my approach is to start with a very basic question, “What is it for?” This is really to ask something about marketing and also something about what was in the designer’s head. The answer in this case must surely revolve around pilot training at a very early stage, even during the initial PPL course or immediately after it is finished.

Here is an aeroplane that has been the mainstay of many ab initio training schools and yet it can say to the student, or to the recent graduate, “There is more to this flying lark than just going to another airfield for lunch.” The purpose of this aeroplane is to open the potential aviator’s mind to the further exploitation of three-dimensional movement without the need to remove them from the simple basic-trainer environment with which they have only just started to feel comfortable.

Just as my initial 35-hour course was punctuated with a single aerobatic flight in that Chipmunk, any current PPL can get a similar eye-opener in this aircraft without any of the stress associated with more advanced or complex machinery. For me, this is a very laudable aim. Too many pilots remain unaware of the real potential of using the full envelope available to them.

BASIC PRACTICALITIES
Once you take all the ‘loose articles’ out of this 150, so that it is a bare shell devoid of maps, fuel testers, flight manuals, control locks, luggage tie-downs and the like, put in about half fuel and two reasonably normal-sized people, the weight and balance sit somewhere near the maximum weight, but not frighteningly so, and well inside the aft limit. I get the impression that only with two very heavy pilots, or some ‘illegal’ baggage behind the seats, could you conspire to get the C of G scarily close to the rear end of the graph. Broad-shouldered hunks will have to accept that they will be rubbing elbows for a while, rather like eating dinner at a table not really designed for so many diners.

There is a harness that has a broad lap-strap and two rearmounted shoulder straps, but no crotch strap between your thighs. This said, the lap strap keeps you in place quite well when inverted and the shoulder straps will keep you from headbanging the dashboard in an off -field landing, so these have their function well sorted. I would prefer to see an additional lap-strap as a back-up system. It is just possible to conceive of a single harness coming undone when manoeuvring and this would be very exciting, to say the least. That single buckle should therefore be checked repeatedly.

The seats are adjustable fore and aft to enable feet to be in close proximity to the pedals at all times, while ailerons and elevator are operated by a yoke, not a stick. The yoke is a disadvantage, no doubt in my mind about that. As there is a fixed-pitch propeller and a rev limit at 2800rpm, it is necessary to throttle back whenever the aircraft exceeds about 130mph. Thus, most of the time only one hand is available for the yoke, meaning, for example, that pulling without inadvertently adding a little aileron is difficult.

Naturally, for a very basic training aircraft, the routine aspects of starting, taxying and getting airborne are all very straightforward. We did have an amusing couple of minutes, however, when we were about to start taxying on the rather soggy grass. I had quite some difficulty getting the aeroplane to move forward. We double-checked everything, inside and out.

There were no chocks, no tie-downs missed. Was the parking brake off ? Yes, the wheels weren’t locked. What had we forgotten? Nothing, except that with an aeroplane that hasn’t moved for several days, something like 2200rpm – almost full throttle – was needed to get out of the slight depressions made by standing on the sodden ground. Eventually, with something of a smile and a shrug we got moving.

Once in a steady climb, the 130hp Aerobat climbs at between 700 and 800 feet per minute and will transit level at 100 to 120mph, depending on how much of a hurry you are in. These figures are certainly a noticeable improvement on the basic 100hp aeroplane and fuel consumption is quite miserly at perhaps 30 to 35 litres per hour over a general handling sortie.

PERFORMANCE
The easiest performance characteristic to measure in any aeroplane is its maximum level speed. This gives a general picture of the way in which power, weight and drag are interacting. With this 150L the figure is 130mph, which is enough to facilitate ballistic (aileron) rolls. More speed is advisable for a barrel roll without height loss. Looping needs nearer 150mph for success. So it is fair to say that most figures exploiting the vertical plane need a diving entry.

Another valuable performance measurement is the height to be gained in a near-vertical zoom climb. This shows primarily power-to-weight ratio, but also incorporates a bit more of the induced drag characteristics during the pullup phase.

Starting at the maximum level speed of 130mph, with half fuel and about 150kg of humanity aboard, I was able to climb just over 500ft, reaching about 70 degrees nose-up, before lowering the nose back to the horizon, lowering flap at the same time to be able to fly off level at about 45mph indicated at full power.

These figures are modest by the standards of specialist aerobatic aircraft, but are a useful basis to keep in mind for comparison with similar basic machines. When I made the tests that derived these figures, the London QNH was 1033hpa and the surface temperature at White Waltham was about 10°C so the air was quite thick. Obviously, the thrust available would be a little less on hot days in the summer.

The other performance index helps broad comparisons is the time taken to roll through 360° in zero-G flight, with the airspeed indicator somewhere near the top of the green arc. Here I can quickly and safely apply full aileron deflection, without risk of damaging the control linkages or putting too much twist on the wings. The best I could achieve with this Aerobat was one roll in five seconds, or 72°/sec. Later, I will describe how the aeroplane can be induced to roll quite a bit quicker.

HANDLING
As fuel is supplied to the engine through a normal carburettor, power is lost when normal loading passes through zero into the negative g range. This is not to say that manoeuvres incorporating short period of inverted flight should not be flown, just that thrust in that attitude will be zero and speed will react accordingly.

Also, it is likely that one or more of the arm-rest mounted ash trays will leave their allocated position when inverted and come to rest in the roof lining. It is very useful to have a passenger on board to retrieve such items in a timely manner, although a well-trained dog would probably cope at least as well...

Once thrust has died, it is best to reduce the throttle setting to the normal engine-starting position. The motor reliably restarts as soon as positive g loads, hence fuel supply, return. During loops, however, positive g, and thus also thrust, are retained. Entering at 150mph, loop diameter is about 500ft with a peak g loading of +3g. This is well within the maximum +6g flight limit, which in practice would require a great deal of determination for a pilot to exceed. The elevator control loads are quite heavy, even at 3g, so it is unlikely that the aeroplane would ever be inadvertently over-stressed unless VNE were exceeded and panic set in.

Despite the effort needed on the elevator control, looping, barrel rolling and flying quarter-clovers are all pretty straight forward. The Aerobat copes well in these figures, all of which are great exercises for developing a new pilot’s spatial awareness and control co-ordination.

Similarly, ballistic (zero g) rolls are simple to execute, albeit taking the five seconds mentioned above to complete. Half-Cuban Eights also work well, with the aircraft rolling as it gains speed on the down line. Just remember to push a little during the rolling segment.

Rolling straight and level is achievable, as long as speed is kept above 140mph. Below this speed, the inability of the fuselage to generate enough lift in the knife-edge positions means that height loss becomes inevitable.

The last of the basic aerobatic figures to discuss is the stall turn. Here the main point of discussion is whether or not they are permitted by the Flight Manual. Stall turns per se are not included in the list of approved figures. But loops and turns are, and a stall turn is two quarter loops with a fl at turn in between. Definitely included in the Flight Manual are ‘Vertical Reversements’ (sic) which some might interpret as meaning a stall turn. Unfortunately, the quoted entry speed for a Vertical Reversement is 90mph, which is absolutely not enough for a stall turn. Add to this the knowledge that this manual was translated from the French and a ‘Renversement Verticale’ in France is a Split-S (half roll and half loop down) and you will be getting nearer the truth.

In practice, stall turns have been flown regularly by many aerobatics pilots, both in and out of competition at Beginners and Standard levels. By keeping a small positive load on the aeroplane throughout, it is even possible with care to keep the engine running throughout, albeit with some compromise to the purity of the geometry. So the British Aerobatic Association ‘Beginners’ sequence is quite within the abilities of this aeroplane type and can be flown safely above a 1500ft base height with a diving start from 3000ft.

SPINNING
All Cessna 150s, even the non-aerobatic ones of my PPL days, are cleared for spinning exercises. In common with several other basic training types, however, getting a good spin entry is somewhat hampered by reduced rudder and elevator effectiveness at or around the 1g stalling speed.

The old Air Force training technique was to enter the spin in a Chipmunk at 70 knots, throttle closed. This is noticeably above stalling speed and the resulting spin is initially climbing and passes through a somewhat disorientating inverted position after half a turn, much more like a flick roll.

Waiting longer for the spin entry, until at or just after a full stall, can lead to a spiral rather than a spin unless control application is aggressive and just at the right time. Competition spins have to be fl own in Standard Level events and the judging requirements mean that the spin has to be entered from a full stall.

My method of ensuring a good spin in these circumstances is to add a small amount of power with the full rudder at the point of the stall. This ensures a deeper stall of the wing and more yawing force from the rudder. You can then close the throttle for a conventional recovery, or you can recover with this small amount of power applied, in which case the recovery will be quicker and more positive, due to the increased control effectiveness. This is true when spinning right or left.

FLICK ROLLS
Rather surprisingly perhaps, the Aerobat Flight Manual permits
flick rolls (snap rolls, in the translation) at speeds not exceeding 90mph. How sporty of them! Initiation of the flick roll needs almost full-up elevator, applied very quickly. This will give approximately 3g once the inertia of the airframe has been overcome. Application of full rudder should be delayed, relative to the elevator input, to allow for the distinct time lag before the attitude change is achieved. There should be perhaps half a second after starting the elevator movement before making the sharp rudder input.

With the right amount of both controls, a rapid wing-drop will be induced and the aircraft will start to rotate. At this point, the elevator control should be moved forward towards the neutral point to accelerate the roll. Too far forward, and the stall will be lost. Rotation will cease. If the yoke is kept fully back, the roll will be slow and cumbersome. The best position is about half way between aft and neutral. The complete roll will then be completed in about half the time of an aileron roll: perhaps 150°/sec.

CONCLUSION
For a pilot at the conclusion of his initial PPL training, here is a machine that he can be completely familiar with in all respects, yet one that he can use to explore a whole new field of aviation.

With this simple aircraft, it is possible to experience all the joy of complete three-dimensional freedom in a familiar setting and at quite reasonable cost. As an aerobatic performer, the Aerobat won’t set any records, but it will set a few pulses racing. It is ubiquitous and cheap.
What excuse can anyone possibly have for not giving it a go?
Be safe and enjoy your flying. 

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