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Aviation History
1961
1961 - 0653.PDF
:> T, 18 May 1961 663 p, :-d at Woodley before departure for the Channel Islands is one s • •:• two Herald Series I OOs which Jersey will operate until the 200s slivered in the "late summer" this year. Flags on the noseart indicate the aircraft's go-anywhere capability au^'.ion to which minimum control speed tests provide an answer. Th'vc are two parts to this series of tests, the determination of yN';;-'A"—minimum control speed when the aircraft is airborne—and yN! Vl the minimum control speed of the aircraft on or near the gr( Hid. H definition of VMC is the minimum speed at which the aeroplane Ca'- be controlled after sudden and complete failure of one powerunit The aircraft is said not to be under control if it is no longer po«ible to keep it flying straight, so that VMC is the threshold control speed when full rudder is applied. Because it is during take- off that engine failure is most critical, tests are conducted in this configuration—flaps in the take-off position, undercarriage up and the iive engine at take-off power. Angle of bank must not exceed 5 and the pedal load must not be greater than 1801b. Handling is watched carefully during simulated engine failure and feathering, because BCARs require that the aircraft must not get into a dan- gerous attitude and the heading change following transition to asymmetric power must not exceed 20°. VMCA tests give a measure of fin, rudder and aileron power. Among all the tests carried out on the 200-series Herald, this is where any changes might have been expected to have shown up. In the normal way it is not possible to fully similate a failure of the Rolls-Royce Dart engine and Rotol propeller combination, so an autofeather over-ride switch is fitted in the cockpit for test purposes. When auto-feathering occurs, out-of-balance forces are reduced, so that the test case simulates a true condition. Few variations were found between the Series 100 and Series 200 aircraft during VMCA tests: maximum pedal load reaches 140-1501b before re-trimming, full aileron movement is not required and minimum single-engine control speed is 80-87kt. depending upon altitude. This speed, together with the stalling speed, decides the take-off safety spe;d. V2 (1.1 VMCA and 1.2 x stalling speed), which can then be written into the manual. The next stage of tests, determination of VMCG. presents the test pilot and his observers with some of their most difficult problems. There is also an element of risk, because what is being measured is the minimum speed at which the aircraft can be held on the runway should an engine fail on take-off. As in all test flying it is normal to start at a fairly high speed and to repeat the test at progressively lower speeds until critical conditions are reached. At first the air- craft is flown off the runway, the lateral deviation from the centre line due to out-of-balance yaw being measured. Next a series of tests is performed in which the live engine is throttled back and the aircraft braked to a stop. The limit is reached, and VM:X, IS deler- For obtaining position-error measurements, the Herald trails a static line and (just out of the picture) dart ERALD 200 be the Mainstay of Jersey Airlines' Fleet BY ALASTAIR PUGH ILLUSTRATED MAINLY WITH "FLIGHT" PHOTOGRAPHS J Stalls power-on in turning fight—BCAR Section D2.I I, paragraph 1.2.3 Determination of VMCA—minimum control speed in the air—&CAR Section D2.8, paragraph 4.1
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