Cierva W 11 Air Horse

My dear Jemiba,

the Cierva W-11T was enlarge version of W-11 with two 1620 hp Rolls-Royce
Merlin 502 engines,and W-12 project was to be fitted with Rolls-Royce Dart
turboprops .

Sorry, Derek Wood describes the W.11T as powered by" Mamaba or Dart". The
Merlim was used for the W.11 Airhorse and the "T" in the W.11T probably stands
for turbine. And the model clearly shows turbo engines on a heli, larger than the
W.11 ... but is it identical to the W.12 ?

Dear Jemiba,

in my source the Cieva W-11T and W-12 were a different projects.

Stumbled upon this one in one of the Flight archives then did a little searching for it:


http://www.aviastar.org/helicopters_eng/west_w11.php


Never knew there was a three-rotor helicopter before!

An interesting machine, indeed. BTW, in Derek Woods "Project Cancelled", the W.11T
is described as the Mamba or Dart powered variant, contrary to aviastar.org. But I don't
know which source is right.

That would have taken some seriously spectacular gearing. Recall that in the early 1960's that the mighty CH-47 was having a difficult time keeping two rotors synchronized. On the positive side the helicopter would have had a very decent center of gravity range.

Hi,

a little different Air Horse.

I wonder how significant the weight of the dynamic components was toward the aircrafts lift capability (circa 1949?). Of course in the new picture there is no rotor overlap so there would be no synchronization gear.

From THE AMERICAN HELICOPTER VOLUME V, NO.II, January 1947

Model of the SPRAYING MANTIS or AIR HORSE designed by Pest Control Ltd. and the Cierva Autogiro Co., Ltd., and claimed to be exclusively for agricultural work. Photo shows model's full compliment of one hundred nozzles across a ninety foot span, capable of spraying 50 gallons of insecticide or fungicide per acre. Capable of carrying 3 to 4 tons from field to field at 80 m.p.h. it will cover 400 to 500 fields a day. Model incorporates 8 patents.

Click to expand...

Now at least we know a little better what that strange helo had been designed for!

M.R.H.Uttley,Westland & the Br. Helicopter Industry, 45-60,Cass,2001 explores what was in MAP's mind when embarking on rotor proof-vehicles, 1944/45. W.11 began as heavylifter/casevac; crop spraying for the African groundnut scheme's ample funding may have served simply to relieve the Defence budget.

Much more information to be found in 'Cierva's Triple Rotor Chopper', 'Aeroplane Monthly', January 1978, pp.4-10.

Quick and dirty summary, Cierva company re-formed in 1944 by Weirs, under c.g.Pullin as MD. Decided that project should be large 'bulk transport machine'.
This because complexity of helicopter made economical operation difficult if payload less than 1 1/4 tons.
Ministry of Ag. then became involved, causing design revision as 'Spaying Mantis' to CAOR 3/46, issued June 28, 1946. At this stage, the aircraft had two rotors at front, one at rear.
CAOR 3/46 superseded by spec. E19/46, and order for one prototype, now to revised layout with single rotor at front, and deep fuselage for cargo/passengers.
Second prototype ordered in early 1947. Flight testing revealed need to increase vertical fin area, and some resonance problems.
On the drawing board at this time was the W.11T, a version powered by two RR Merlins mounted on stub wings, able to be exchanged later for turboprops, and allowing for the use of auxiliary propellers for forward flight.
On June 13, 1950, the prototype crashed, killing all three on board, due to fatigue failure in the front rotor head.
As a result of this, both the Ministry and Weirs withdrew their financial support, effectively killing the project. The second prototype did some tethered testing in support of the crash investigation, where it was discovered the the fatigue was due to a particular vibration experienced only by the front rotor head. After further testing, it was dismantled and stored, before being scrapped in 1960.


cheers,
Robin.

Some more pictures of the Air Horse

Two more photos of the W.11 Air Horse:

From The Helicopter Museum

From Flightglobal 1949,

here is a Model for W.11T,but the engines was different in its configuration ?.

Harrier's post shows the twin Merlin version.
Hesham's post shows the Mamba (or Dart) version.

Chris

hesham said:

a little different Air Horse.

http://www.flightglobal.com/pdfarchive/view/1949/1949 - 0383.html

Click to expand...

I repeat sending this drawing,but I add the caption which was not appeared in the earlier,just to know it.

From Flightglobal 1947.

An earlier post mentions the weight problem with the drive train comparing it to the CH-47’s problems with its synchronization problem but then states the new drawings show no over lap. The W11 never had overlap, the rotor diameter limited by that criteria. A twin rotor can overlap with the rotors turning in opposite directions. I challenge anyone to explain how you have an over lapping three rotor helicopter. The earliest drawings showed over lap due to lack of information. The reason for the extreme out riggers is thus evident.

Is there anything to stop the design from having the rear ramp of the Chinook rather than the clamshell doors....would this have even been more useful?

PMN1 said:

Is there anything to stop the design from having the rear ramp of the Chinook rather than the clamshell doors....would this have even been more useful?

Click to expand...

The ramp creates more drag in flight (I am told) than does the clamshell doors. The ramp is more practical for off loading quickly in combat and can be lowered while still in flight. Opening the clamshell in flight might be problematic. I think the Mi-8/17/171 would be a more practical discussion point as they have been built with both clamshell and ramp. The weight and moment arm discussion I will leave to those more fluent in things aerodynamic.

The clamshells could not be opened in flight. If you wanted to drop stuff out the back, not only through the doors, then you just removed the clamshells before take-off.

Jemiba said:

An interesting machine, indeed. BTW, in Derek Woods "Project Cancelled", the W.11T
is described as the Mamba or Dart powered variant, contrary to aviastar.org. But I don't
know which source is right.

Click to expand...

Is there any free body diagram illustration on how anti torque is achieved?

If I remember correctly the rotor heads were all angled so as to provide a small amount of lateral thrust to counteract torque.

Zeb

Weir rotorcraft,from Aeroplane monthly 1990.

View: https://www.youtube.com/watch?v=2zIX3ZK_HkI
https://militarymatters.online/forgotten-aircraft/cierva-w-11-air-horse-the-triple-rotor-heavy/

The following may be of interest.

The saga of the Air Horse, a large multi-role heavy lift helicopter, or flying crane, began in 1945. This giant was to be used in the United Kingdom and in many areas within the British Empire. The engineers had decided upon this path after noting that, since a small helicopter had almost as many components as a large one, the cost of helicopters did not increase as fast as their weight. In turn, believing that the main factor limiting helicopter size was the diameter of the rotor(s), Cierva Autogiro came up with a most unusual and ambitious design. Equipped with three pylon-mounted rotors located at the points of a triangle, one on each side and a third at the rear, the Air Horse would weigh approximately 14,000 pounds when loaded – an unprecedented figure for a helicopter.

In August 1945, Pest Control, a pioneering aerial application firm based in England, requested that Cierva Autogiro alter its project to take an agricultural role into account, thus turning the new design into one of the first, if not the first helicopter to be conceived at least partly for aerial application. Given this, Cierva Autogiro and Pest Control asked for government support. In spite of some misgivings, the Colonial Office and the Ministry of Agriculture and Fisheries agreed to help. The Ministry of Civil Aviation issued an operational requirement in late June 1946. In July, this requirement was rewritten and issued as a specification by the Ministry of Supply, the department responsible for the purchase of government equipment. Cierva Autogiro received a development contract for a single prototype, which received a Royal Air Force (RAF) serial number. It signed a contract for a second prototype in early 1947.

A full-size mock-up of the W.11 Air Horse, with a Rolls-Royce Merlin engine on board, had been completed by the middle of 1946. Pest Control’s spraying gear was just as impressive as the helicopter itself. Dominating it was a 600 Imperial gallon (720 U.S. gallon) stainless steel tank carried underneath the fuselage. A special pump located inside could deliver up to 120 Imperial gallons (144 U.S. gallons) of pesticides per minute to a gigantic spray gear. Thus equipped, the Air Horse or Spraying Mantis, as Pest Control called it in all seriousness, might be able to treat 400 to 500 acres of land a day. Cierva Autogiro and Pest Control displayed a model of the agricultural Air Horse as early as mid-1946.

As time went by, the design of the Air Horse was modified. Having realized that a beefier structure was needed to support the pylons and larger rotors needed to lift the spray gear, Cierva Autogiro provided its helicopter with a large fuselage. This, in turn, meant that the new Air Horse could carry a sizeable load (up to 3,750 pounds of freight with a maximum fuel load or up to 24 passengers). Bulky loads could be loaded through a pair of clamshell doors at the rear of the fuselage. Pest Control’s suggestion that the spray tank not be enclosed to help disperse the chemical fumes as quickly as possible was not followed. Even though the unique three-rotor configuration remained, the triangle it formed now pointed toward the front and not the back. Designed to be statically and aerodynamically stable, the Air Horse had a landing gear designed to absorb the shock of an emergency landing caused by an engine failure at an altitude of up to 150 feet.

Through it all, Pest Control remained confident that the Air Horse would be of great use for aerial application in many areas. After all, the agricultural version of this helicopter would lift 600 Imperial gallons (720 U.S. gallons) of liquid pesticides or 5,600 pounds of powdered pesticides. A 70 foot wide spray gear would provide huge spray coverage. By then, Pest Control had an option on a few Air Horses. If the trial flights of the prototype went well, construction of a small force might proceed.

As part of an earlier agreement with a small British aircraft manufacturer, Cunliffe-Owen Aircraft, construction of the Air Horse prototype began in 1947. Cierva Autogiro was to supervise the technical and financial side of the project. Sadly enough, Cunliffe-Owen soon went out of business. Cierva Autogiro thus had to provide the factory space needed to continue the work, on top of the added managerial responsibilities. Topping this up, it had to deal with delays in the delivery of materials, financial difficulties and a shortage of technical drawings.

The first prototype of the Air Horse was completed in time for display at 1948 edition of the annual airshow organized by the Society of British Aircraft Constructors, at Farnborough. It went there by truck. Observers were most impressed by the giant helicopter, which carried a civil registration for the occasion. Ground runs and tethered hovering flights began in October. The Air Horse made its first untethered flight on December 7th, 1948. The test program of this machine, the heaviest, largest and most powerful helicopter in the world, continued throughout the following year and into 1950. There were minor issues but the Air Horse performed rather well.

Intrigued by the potential of the Air Horse as a flying crane, the British Army followed the trials. As well, the authorities in Southern Rhodesia (now Zimbabwe) kept abreast of all developments. Indeed, the Colonial Office was intrigued enough by the role the Air Horse could play overseas, especially in that self-governing colony in Central Africa, that it added to the sum it had already invested in the project. The enthusiasm within Cierva Autogiro was such that some people began to consider the possibility of taking the Air Horse to North America. In addition, Pest Control may have been considering the possibility of asking Cierva Autogiro to press forward with the development of the W.11T, an even larger machine powered by two Merlin engines mounted on stub wings. Twin-engine safety was deemed necessary when operating in remote areas within the British Empire. Weighing up to 30,000 pounds, the huge machine would be able to carry up to 36 passengers or lift an 11,200 pound payload. Some engineers suggested that turboprop engines be installed as replacement for the Merlin engines.

In June 1950, an experienced RAF pilot showed up to begin a series of evaluation flights before the Air Horse made its way to the Aircraft and Armament Experimental Establishment where it would undergo serious testing. Squadron Leader Frederick John “Jeep” Cable, an experienced pilot who had flown only rotary-winged aircraft during his career, was at the controls when the Air Horse crashed, on June 13th. He, Cierva Autogiro’s manager and chief test pilot, Alan Henry Marsh, and a company flight test engineer, Joseph Unsworth, perished. The second prototype, which had performed some ground runs, was grounded. A thorough investigation revealed that a vital component in the front rotor head had failed in mid-air.

With the second prototype stripped down to help with the investigation, Cierva Autogiro, Pest Control, the Colonial Office and the Ministry of Supply began to consider what to do next. A feeling at the Ministry of Supply that the Air Horse was too big a jump a size in helicopter development, coupled with the need to provide funding for the Bristol Type 173, a tandem rotor helicopter under development for freight carrying and passenger flights to city centers, led to a gradual disengagement. The loss of the money it had spent so far on the Air Horse project would have to be accepted as the price to pay to develop modern helicopters in the United Kingdom. In turn, the grandiose plans of the Colonial Office to grow certain crops in the Empire had pretty much evaporated. The final nail in the coffin of the Air Horse, and of Cierva Autogiro, came when James George Weir, the engineer and industrialist who had supported the company since day one, decided to pull out. In need of factory space to develop a giant flying boat airliner, the SR.45 Princess, Saunders-Roe took over the Cierva Autogiro facilities – as well as the W.14 Skeeter, a light helicopter test flown in October 1948.

The second Air Horse prototype was eventually put back together and used for tethered flights intended to find the cause of the structural failure that befell the first prototype. It was later used as a test rig. The now unique machine left the factory in June 1954. Stored in a Ministry of Supply depot, it was scrapped in 1960.

Ironically, Pest Control’s interest for the Air Horse had begun to cool well before the 1950 tragedy. New spraying methods made it possible to use smaller and cheaper helicopters. In fact, trials had been conducted as early as the spring of 1948, using a U.S-made Sikorsky S-51 equipped with a spray gear designed by both Pest Control and Westland Aircraft, the British representative of the helicopter’s maker, the Sikorsky Aircraft Division of United Aircraft. Pest Control’s experience in ground spraying and the design of ground spraying equipment proved highly useful. It is worth noting that the S-51 was apparently delivered as early as August 1947.

From Air Pictorial 1949.