FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1948
1948 - 2049.PDF
DECEMBER 2ND, 194? FLIGHT 90 140 Merlins. Mr. Shapiro thought that the twin-engined version would be used in future for all but special duties. His in- vestigations of econ- omic efficiency was, therefore, based on the twin - engined machine. Other con- tributions to safety, which were being developed, included automatic limitation of rotor r.p.m. and automatic conversion to autorotation. Having ensured maximum safety, the next subject for discussion was speed. The value of speed to the customer increased in large steps and not gradually. As an example, a reduction of travelling time to the Midlands from i\ hours to 50 minutes allowed a full day's work to be done, but a further reduction of 25 minutes was of little con- sequence. All helicopters under development had about the same cruising speed, 115 m.p.h., and the Air Horse promised -to attain this with economical cruising power. He thought no m.p.h. a minimum for passenger transport. In examining costs, Mr. Shapiro confined himself to direct 1OO 11O 12O 13O CRUISING SPEED M.P.H. Air Horse passenger carrier. All-up weight 17,500 Ib. Stage length 100 miles. Utilization 2,400 hours per annum. 3 4 "5 NO. OF ROTORS Variation of disposable loadj all-up weight ratio with num- ber of rotors. Power 2,500 f.p. Tip speed 550 ftisec. Disc loading 3.3. Minimum solidity and minimum under- carriage travel. --•''• • •""' ^»^^^^^^ The all-wood blades for the Air Horse were manufacturtifhy H. Morris of Glasgow. They have a length of 21ft, and each blade weighs 125 Ib. Same 1,500 piects of wood go into the construction of one moulded blade: '""'"'"' _ costs. The helicopter scored in the matter of indirect costs by virtue of the simplicity of ground installations. Aspects dealt with were: effect of size, configuration, and design para- meters. A graph, published herewith, showed that up to the size of the Air Horse and beyond, the effect of size on cost was pre- dominant. It includes the twin-engined Air Horse. Size had a far less pronounced effect on percentage of disposable load. After admitting that .comparisons based on hypothetical heli- copters of equal size but different configurations were built on slender foundations, Mr Shapiro simplified the problem of CIERVA W.ll PRINCIPAL DATA All-up weight Empty weight (freight carrier) Rotors ' Number * Diameter 47t* Number of blades per rotor Vincoo Nominal solidity ••• °:059° Nominal twist II deg -45 mm Nominal taper : MAVA ™iJ Blade profile N-A-C'A-™' Nominal r.p.m. • Performance Maxi rate of vertical climb I.C.A.N. Sea Level conditions—900ft min Level flight speed for max. continuous power I.C.A.N. Sea Level conditions— 125 m.p.h. Engine r I Rolls-Royce Merlin Mk.24. Single stage two speed supercharger, l^eai ratios : 8.15 : I and 9.49 : I. Max. power (5 min) Climb power (1 hour) Max. continuous power Boost + 18 + 12 + 9 R.P.M. 2,850 2,850 2,850 I.C.A.N. Sea Level h.p. 1,620 1.290 1.120 effect of configuration by con- centrating on percentage dis- posable load. For machines of equal size that criterion almost entirely determined the cost per ton-mile when speed, utilization and load were assumed constant. Compari- sons which expressed real trends could be made between helicopters with different num- bers of rotors. One of the illus- trations shows that a very con- siderable improvement results from increasing the number from two to three. He thought the best alternative system, the tandem machine, was only marginally better than the side- by-side twin-rotor, machine, and therefore probably inferior to the three-rotor. The safety feature of rotors on outriggers was actually found to be more economical in weight than the best alternative. Aerodynamic interference between rotors in for- ward flight had been found negligible in the Air Horse. Inter- ference in hovering, which would determine the aerodynamic lifting efficiency, still had to be measured full scale for reliable results. Turning to the choice of parameters, Mr. Shapiro explained that the design approach was made in the following steps: Definition of permissible all-up weight; determination of truly independent parameters; sub-division of component weights into groups depend- ing on , individual parameters and their combinations. All-up weight was limited to that which could be lifted vertically at a rate of 6 ft/sec by maximum engine power. Once the configuration had been settled and the power unit chosen, there were four major design parameters: Disc- loading ; tip speed ; blade solidity; and undercarriage stroke. The only two truly independent parameters were disc loading and tip speed. The effect of disc loading flattened out and remained stationary over a considerable region. Air Horse disc loadings were near the .. •... maximum, but solidity was adjusted to •*•"':• avoid tip stall, and undercarriage stroke increased to absorb the energy of unaided vertical descent without power. Low disc loadings meant low forward speeds owing to power limitations, until, at disc loading of around 3, power no longer limited forward speed. When it came to detail design, Mr. Shapiro stated that the value of weight-saving in a helicopter was greater than in a fixed-wing machine. On a basis of 2,400 hours' utiliza- tion, one pound of weight in the Air Horse was worth ^25 in selling price. Summariz- ing this part ot the Paper, Mr. Shapiro said that the Air Horse constituted a most im- portant advance in economic efficiency due to its size, made possible by multiplica- tion of rotors. The three- rotor configuration compared favourably with the best alternatives, and its many advantages were not bought at a sacrifice in economics. The Air Horse represented a choice of design parameters approaching the-optimum in all but tip speed. One important feature ot the Cierva Air Horse is the long-travel undercarriage. Mr. Shapiro explained in consider- able detail the reasons and arguments which have led to its adoption in preference to a more orthodox type. The rate of vertical descent of the machine was estimated at 41ft/sec, so that the energy absorption was approximately 12 times that corresponding to minimum A.R.B. requirements. It was considered in planning the design that a feature such as the ability to make an emergency landing without demand- ing great skill of the pilot was preferable from a safety point 30.000 5OOO I5OOOA.U W LB. 25.000 Direct flying costs of passenger- carrying helicopters. Stage length about ICO miles. Load factor ICO per cent. Utilization 2,4C0 hours per annum. B 10
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
