In response to a request made by the US Bureau of Aeronautics in 1945, the Piasecki Helicopter Corporation (Philadelphia, USA) started development of a helicopter that could carry out search and rescue missions and utility missions within a 150 km of its base. This base could be a small ship with a helicopter platform, large aircraft carriers (e.g. the USS Saratoga carrier with the HUP-2 Detachment in the Mediterranean and the North Atlantic) or coastal airports. The request resulted in the design by Piasecki Helicopters Corporation of the Model PV-18 helicopter, with user designations of HUP-1 Retriever (US Navy), UH-25B (HUP-2) Retriever (US and French Navy), UH-25A (H-25A) Army Mule (US Army) and the UH-25C (HUP-3) for the Royal Canadian Navy (Boeing Vertol Division, 1968. Missions and Milestones. Boeing Publ. SB 632B, USA, 28 p.). From 1949 until 1952, 32 HUP-1 tandem-rotor helicopters were designed and constructed to operate a dipping sonar, which would make these the Navy's first Anti-submarine Warfare (ASW) helicopters. However, as the HUPs proved to be underpowered for this task, the ASW equipment was soon removed. HUP-2 helicopters were used in the Korean war from 1950-1953.
The HUP-2 Retriever was constructed for the US Navy from 1952 onwards with a more powerful engine and was not used for anti-submarine warfare. Later versions incorporated a modified Sperry A-12 autopilot (indicators located at bottom center of the HUP-2 instrument panel shown below), which controlled the helicopter about the roll, pitch and yaw axis, but not altitude.
After 1951, the US Army also used this helicopter for transports. The Army HUP was designated as the H-25A Army Mule (70 of these were constructed). Only 19 HUP-3 helicopters of the total of 336 built were exported to France (Aeronavale) and Canada (Navy). HUP helicopter production stopped in 1954 and helicopters remained into service until 1964.
I would like to thank Ed Manuel, Robert (Bob) Morris and Albert (Al) Carrato (MCPO Retired, U.S. Navy) for providing me with information about the HUP-2, its navigation and communication equipment, and how it behaved in flight. During the Korean War Bob Morris was an electronics ground officer (ensign fresh out of OCS with an EE degree) assigned to HU-2 Lakehurst in 1952 as electronics maintenance officer. Ed Manuel was one of the pilots who flew the HUP-2 in the 1950s, whereas Al Carrato was an AT-2 and flew as a rescue crewman (and co-pilot) in the HUP-2 close to end of its service at NAAS Port Isabel in 1960-1961. He also flew the P4Y2 Privateer as a waist gunner.
Ed Manuel finished 19 months of flight training in 1953 and then had four options to choose from:
The last option seemed the most attractive and Ed went into a four-month training programme, starting in Bell HTL-4 helicopters at Ellyson Field in Pensacola. Later during his training he switched to the HUP-2, and briefly the HUP-1, which had hydraulic control boosts on the cyclic. The HUP-1 also had an autopilot installed, but pilots were prohibited from engaging it at elevations below 2000 or 3000 feet because it appeared to have failures that had caused deaths before at low altitudes. Because helicopters in training never flew at high altitudes anyway, the limitation meant that the autopilot could never be used. Ed only used it once (probably up to the instructor), when he was shown how easy flying a helicopter could be on autopilot in a near the ground hover. During training the pilots were also exposed to flying the HUP with the boost system turned off, which was not something anyone would want to do for any length of time.
Most of Ed's training flights were in the HUP-2, which had electric boosts and no autopilot at that time, in contrast to the HUP-1 helicopters. According to Ed, the hydraulic boost system of the HUP-1 performed great, but the electric boost of the HUP-2 was lousy. Bob Morris remembered that his squadron had a big HUP-2 retrofit sometime between 1953 and 1955 to put in some kind of electric boost (perhaps a linear actuator?). Bob left active duty in 1955, presumably before the poor results of the electric boost experienced by Ed became apparent.
After finishing training, Ed was assigned to the HU-2 squadron at NAS Lakehurst, N.J. All HUPs then, and for at least several years later, had wooden blades. Because of the low inertia of the wooden blades the HUP collective down stop was set below the position for recommended autorotation rotor rpm (to permit more rapid recovery of lost rotor rpm), which made the HUP different from all other helicopters. Just one more thing for the pilot to pay attention to in an emergency autorotation! According to Ed, emergency autorotations are always very different from practice autorotations. The following applies to helicopters with reciprocal engines without engine rpm stabilization. In a practice autorotation the pilot never loses rotor rpm as he enters autorotation. This is because as he lowers the collective to begin a practice autorotation, he maintains rotor rpm by reducing the throttle as required to maintain rpm, until the rotor and engine RPM needles on the dual tachometer (see image below) split and the helicopter is in full autorotation. The real world, where the pilot is not expecting to need autorotative flight, is very different. A finite time is required for the pilot to analyse what is happening, and then to take the required action of reducing the collective to the down stop on all other helicopters, and initially also there in a HUP. While analyzing what is going on (probably sudden engine silence), the rotor rpm is already very rapidly decaying. The Navy specifications for demonstrating autorotation characteristics in a new helicopter (into at least the 1960's) required the demonstration pilot to not move the collective from the flight position (prior to the simulated engine failure) for 2 seconds. Ed does not know about the HUP, but he does know that some helicopters had to get a deviation from that requirement to 1 second, which is not a lot of time for the pilot to act. The lower than usual collective down stop in the HUP did allow the rotor rpm to recover faster than other helicopters, which was necessary because the rpm decayed faster in a HUP because of the low inertia blades.
Ed left the Navy in September 1955 to become an engineer at Sperry. He is the second aircraft pilot ever to land on a nuclear submarine (see below).
The HUP-2 was also the first helicopter to land on a nuclear powered submarine (the famous Nautilus submarine). Prof. Ed Manuel was kind enough to send me a very interesting publication on this event titled The Forgotten First for America's first nuclear-powered ship (Acrobat PDF file). It was written for the celebration of the 50th anniversary of the landings of a HUP-2 helicopter on the Nautilus. A ceremony was held at the Nautilus museum to celebrate the event on August 4, 2005. The document can also be viewed in html at www.specialeventsremembered.com/nautilus. The pilots that carried out these daring landings were Marvin Alexander (first landing) and Ed Manuel (second landing). They were both accompanied by crewman John H. Fenlon, who therefore landed twice on the sub that same day. The challenge of landing on the sub's narrow deck was somewhat less difficult for Ed, because he already knew that the deck was wider than the HUP's landing gear.
Ed's squadron, the Helicopter Utility Squadron 2 (HU-2) was based at NAS Lakehurst, New Jersey, and furnished all helicopters and crews to the entire Atlantic Fleet. Their activities included plane guard rescue for aircraft carriers, ice breaker guidance through "leads" in the ice, cruisers, battleships, and anything else that needed a helicopter. Reading this document gives you a very nice impression what flying in a HUP-2 meant in these early days of helicopter development! The document also contains some nice pictures of the HUP-2 and of the Nautilus. Marvin Alexander, the pilot who made the first aircraft landing on a nuclear powered ship, made a career of the Navy (28 years) and flew every helicopter they had during that time. His tour following HU-2 at Lakehurst was as a helicopter instructor in Pensacola. Both Ed and Marvin now live on Jekyll Island, Georgia.
As an AT-2, Al Carrato was stationed at Naval Auxiliary Air Station (NAAS) Port Isabel, TX, from 1960 to 1961. He flew as a crewman in am International Orange coloured HUP-2 and had been assigned to this small naval auxiliary air base because he was an aviation electronics technician and also had "flight skins". So he could do the job that normally would have been assigned to two people. Apart from his HUP-2 crew duty, he was also in charge of maintenance of the IFF equipment, ARC-27 transceiver and all other navigation equipment used on aircraft that frequented the base for gunnery training. As crewman in the HUP-2 he fished several pilots out of the ocean and along the beaches of Padre Island.
Even though Al Carrato was enlisted, he flew as a co-pilot (handling everything control but the collective) and had about 1,000 hours in the HUP-2. He was probably the only enlisted co-pilot, although this was never a formal designation (wings and record entry). This was done out of necessity when the question arose, after a number of trips to bring home downed pilots, about crew safety when something happened to the pilot. Because the base Executive Officer was one of the two HUP-2 pilots (we had two crew members) he ordered Al to begin training to fly the helo. Initially he was not allowed to use the collective, but he ended up practicing with it during landings, which was only known to Al and the junior pilot. The idea was that if something happened to the pilot Al could get the HUP-2 down safely. The two HUP-2s at NAAS Port Isabel flew guard duty everyday, including weekends, when pilots were airborne in training aircraft flying over the Gulf and shooting at banner targets towed behind an aircraft.
Power to the HUP-1, HUP-2 and HUP-3 helicopters is supplied by Continental R-975-42, R-975-46 or R-975-46A air-cooled, nine cylinder radial engines (based on a Wright tank engine).
The engine is located within the fuselage aft of the fuel cell and firewall. It simultaneously drives two three-bladed rotors through drive shafts and reduction transmissions. The rotor blades of the HUP-2 are of either wood or metal (later versions) construction.
The fuselage is of all-metal, stressed skin construction. The
cockpit incorporates side-by-side pilot seating with the pilot seat on
the left for no reason other than that is where airplane pilot seats
are located. Presently, the command pilot's seat is on the right
because the pilot can release the collective stick for short periods
(unlike the cyclic). The HUP cabin can be fitted with troop seats or
litters. The minimum crew required to fly the helicopter safely, under
normal non-tactical conditions, is a pilot. A co-pilot, rescue hoist
operator, litter attendant or other crew members may be added.
Typical loading of the HUP-2 is 4300 pounds (basic weight), with a crew of two, one passenger and 100 gallons of fuel. According to Marvin Alexander, the HUP was by far the best-designed helicopter ever for rescue pickup by hoist. This because it was the only helicopter where the pilot could directly see the person being picked up (by looking down through the open hatch under the co-pilot-seat location). Normally the crewman in a HUP operated the hoist, but if required the pilot had a hoist switch on the cyclic. If needed to help someone into the hoist collar, the crewman could attach himself to the hoist cable and be lowered down by the pilot. In all other rescue helicopters, the pilot had to be told by the crewman operating the hoist (way behind him) where to move the helicopter just to stay over the rescuee. Ii is difficult to imagine how that would work for a rescue at sea when the pilot has absolutely no hover reference at all (because all he can see is water)!
The communication equipment listed in the NAVWEPS AN 01-250HCA-1 flight handbook for the HUP-1, HUP-2 and HUP-3 helicopters (1960) consists of radar, radio, interphone and navigation equipment. The following equipment was installed in the HUP-2:
Bob Morris was well aware of the serious weight constraints of the HUP-2. The air-cooled Wright tank engine in the HUP-2 was obviously not designed as a light-weight aircraft engine. Weight considerations also put pressure on the selection of the communication equipment. Bob Morris and his team were always under the gun to keep weight down because every pound of extra weight cost fuel and thus airtime on station. The standard radio was the ARC-1, VHF, 10-channel transceiver, which was not light-weight either. In 1953 the fleet was rapidly converting to UHF, with the standard radio being the ARC-27, a UHF, synthesized, 18 preset channels out of a possible 1750 channels. Bob remembers the ARC-27 being quite a bit bigger and heavier (80 lbs).
When Al Carrato flew the HUP-2 in 1960-1961, the ARC-27 was indeed installed at the aft end of the crew compartment (starboard side) of the HUP-2s at NAAS Port Isabel.
BUAER apparantly found a UHF set, ARC TYPE -12, in a warehouse. The NAVWEPS AN 01-250HCA-1 flight handbook for the HUP-1, HUP-2 and HUP-3 helicopters (1960) lists this set for being used in the H-25A model, but not in the HUP-2. It fit the ARC-1 rack and used the ARC-1 control box and made an easy conversion, except for the antenna. A tech rep brought some over and showed Bob's group how to align it. The team put one in a HUP-2, but after the first landing (most are not like silk, and Bob can visualise one in a fighter carrier landing) the thing went off frequency. It was swapped out for a different one but they all seemed not to like the jolt of landing. Bob thought he knew now why these radios were in the warehouse.
At the squadron, an ARC-27 was taken to Blimp overhaul metal shop, where Bob had them make a light-weight case for it. The ARC-1 and ARC-27 were both vacuum tube sets, thus requiring high voltage, which arcs at high altitude. It was necessary then to pressurise the case. The ARC-27 had a real heavy, hollow, cast case (for cooling airflow). It worked fine, but was still too heavy for the HUP-2. Bob's team was still using VHF when he left. Apparantly there was an official version of the ARC-27 that came along that was not pressurized, which would still have been too heavy. Of course in the late 50s with the advent of the transistor, new low voltage, compact, transceivers were developed. According to the NAVWEPS AN 01-250HCA-1 flight handbook for the HUP-1, HUP-2 and HUP-3 helicopters (1960) the ARC-27A UHF command set was installed in the HUP-1 helicopter replacing the AN/ARC-1 set, but was never installed in the HUP-2.
This page shows a US Navy Piasecki HUP-2 Retriever helicopter panel (see Joe Baughers search engine for BuNo numbers). A picture of a HUP-2 helicopter, now in a very poor state, can be found at AMARC Experience - Minden Scrapyard. Sid Nanson has access to USN and USMC records of aircraft and kindly provided me with the following information about the history of a particular Piasecki HUP-2 helicopter with BuNo 130027.
The HUP-2 helicopter with BuNo 130027 was taken on charge on 30 July 1953 from Piasecki Helicopters at Morton. It was received at the Overhaul and Repair (O&R) facility at Naval Air Station (NAS) Lakehurst, NJ, of the Bureau of Aeronautics (US Navy) (Buaer) Methods and Standards (M&S). It was then transferred to the HU-2 Helicopter Utility Detachment on January 7, 1954. This was Ed Manuel's squadron. On February 4, 1954, it was received by HU-2 Det. 39 aboard the USS Antietam, which took it to NAS Guantanamo Bay in Cuba where it was received on 26 March 1954. In 1956 the helicopter was overhauled at O&R Buaer Facility (FA) in Jacksonville (received 1 May 1956). The helicopter then went to NAS Naval Air Reserve Training (NART) unit in Oakland (received 27 October 1956). It got a second overhaul at O&R Buaer FA in San Diego (received 16 January 1958) and went to NAS Alameda where it was received on 19 June 1958. It served here until 17 November 1960 when it was transferred to the NAS Litchfield Park Storage Facility near Phoenix in Arizona, where the Navy initially stored their surplus aircraft. HUP-2 130027 was struck of charge on 28 March 1963, nearly ten years after it had been taken into service and had accumulated a total flight time of 1433 hours. At some stage 1963 and 2000, the helicopter received a civil registration in the USA as N91330 (see Rotorspot - Civil Rotor Files). HUP-2 130027 was later observed at several scrapyards in Tucson, Arizona, still carrying BuNo. 130027 on its skin. This included Bob's Air park (South Wilmot Road) and ARM/DMI (Dross Metals, East Nebraska), where it was last seen in August 2000. It was then moved to Minden Air Corporation (East Drexel) scrapyard where it was first seen in June 2001 and last reported on July 2002 (Source: Searchable Database - Tucson Scrapyards). Chris Slack (from AMARCExperience) was so kind to send me an image that he made of this helicopter at the Minden Air Corporation scrapyard in July 2002.
The helicopter is presently in a very poor state with part of the fuselage gone.
The images below show different instrument panel configurations and a typical instrument panel, as shown in the NAVWEPS AN 01-250HCA-1 flight handbook for the HUP-1, HUP-2 and HUP-3 helicopters (1960).
Typical Piasecki HUP-2 Retriever instrument panel configuration as shown in the flight manual, 1960.
Different HUP-2 instrument panel configurations as shown in the flight manual, July 1960.
Typical HUP-2 instrument panel, close-up from the 1953 flight manual (revised 1960)
The image below shows a restored instrument panel from Piasecki HUP-2 helicopter with BuNo 130027.
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