& the 'Phrog' by
Boeing's H-46 Sea Knight is a 'Cinderella' helicopter that nobody seems to know much about. Yet Boeing delivered more than six hundred to the US Marine Corps and Navy from 1964 through 1971, and most of them are still flying. It will be replaced in Marine Corps service by the V-22 Osprey tilt rotor but according to the latest reports the H-46 will be in use until 2012, a service life of forty-eight years. To put that in perspective the Spitfires first delivery was in 1938 and if it had the same service life as the H-46 it would still have been in service in 1986. The Marines joke "If it was good enough for my Father (by now occasionally Grandfather), its good enough for me."
Kawasaki in Japan built another 135 for use by the Japanese defence forces and it is also in service with Canada and Sweden. It was the primary transport helicopter used by the Marines in Vietnam. They used it for every conceivable purpose, plus a few not thought of when it was designed. Yet it is not nearly as well known as the Bell UH-1, the Huey, or even as well known as its stable-mate, the Boeing H-47 Chinook. It deserves better. Maybe because most of its service is at sea, 'over the horizon', it suffers from being out of sight, thus out of the minds of journalists. The films of Vietnam show nothing but Hueys. To be fair the US Army had lots and lots of Hueys. They were everywhere, but everywhere. A joke current at the time said if you wanted a photo of a Huey, close your eyes, point your camera anywhere, click and youll have at least one in the frame. Often true, I frequently see Hueys in the background of pictures I took in Vietnam of other things. But the Huey couldnt carry the loads that an H-46 could. In the temperatures in Vietnam, frequently over 35 degrees C, six was about the limit. The H-46 manual said twenty-four but in reality it was seventeen if they were American and twenty if South Vietnamese. The big advantage of the Huey was there were so many of them.
The Marines used the 'Phrog' in Vietnam and still today, to transport personnel and cargo, from ship to shore and point to point on land, landing troops for assault and resupplying them afterwards. It has been put to every possible use; VIP transport, SAR, and in Vietnam, medical evacuation (medevac), anything and everything the Marines needed it for. Among the toughest missions in Vietnam were medevacs under fire and they could be assigned to any Marine Corps helicopter at any time. Unlike the US Army, who had special "Dustoff" units for this mission, the Marines would divert the nearest helicopter. Likewise, the Navy uses it for many purposes, including SAR. But its predominant Navy use is to resupply ships underway at sea.
Developed for the US Marines from the V107, the H-46 was designed in the late fifties by the then Piasecki Helicopter Company, to an Army specification that eventually became the Chinook. Some of the first ones built were delivered to New York Airways who flew them between the New York airports and the top of the then Pan Am building in downtown Manhattan. They dont do that any more.
During the time it was being redesigned, Piasecki was purchased by Boeing, who renamed the Company Boeing-Vertol. Today its just Boeing. Frank Piasecki was one of the pioneers in helicopter design and like many others (Bristol come to mind) he was a firm believer in twin tandem rotors. The aircraft was completely redesigned for the Marines, its first designation being HRB-1 and following the American tradition of giving nicknames to every aeroplane, it was called Herby. After it became H-46 the nickname changed to "Phrog", because from the front, thats what it looks like. The American services give nicknames to all their aircraft. For a while the brass tried to stop it, but the present 'brass hats' grew up doing it themselves. I never could figure out why the F105 was named "Thud" until an F105 pilot told me it was the noise the airplane made when it hit the ground if you didn't keep up your airspeed making high 'G' turns at low level.
Delivery of the H-46 continued during 1965 to the Marines and eventually to the US Navy. The Marines always say that they get the Navys hand-me-downs but in this case they got to play first, maybe because the H-46 is a helicopter. The Navy likes the idea that the Marines fly the same aeroplane as they do. They knew that by the nature of the mission, the Marines fly their aeroplanes harder, "ride them hard and put them away wet", and if the aeroplane was ever going to break, the Marines would break it first. This happened in 1967, when in less than two months, six Marine H-46s disintegrated in mid air. Eyewitnesses to one crash saw the entire aft pylon break off. The problem was identified as Whirl Mode Flutter, the same problem that afflicted the Lockheed Electra, and when it happened there were no survivors. All aircraft were grounded until the problem was identified, then modified and put back into service as fast as possible. The aircrews eventually recovered their trust in the aeroplane enough to fly it hard, but it took some time.
The H-46 goes to Vietnam
In 1965, the war in Vietnam was heating up. The Marines were using the Sikorsky H-34 to implement their recently developed tactics of 'vertical envelopment', using helicopters to quickly transport troops to where they could do most good. The H-34 was probably the first helicopter the Marines had that could really do the job, but it was slow and powered by a big Pratt & Whitney radial engine, heavy and complex when compared with the gas turbine engines just coming into service. The P & W produced 1,525 hp from 2,000 plus lbs. The two GE T58 gas turbines in the H-46 weighed only 440 lbs total and produced a combined 2,500 hp, increasing over time to 3,540 hp. It was the gas turbine engine that made the helicopter into the practical vehicle it is today.
HMM-164, the first H-46 squadron, arrived in Vietnam (in country in the patois of the day) in March 1966. The H-34 squadrons were steadily replaced by the H-46, until by July 1969 the changeover was complete. Meanwhile, the Navy received their first H-46, to be used for resupplying ships underway at sea by vertical replenishment (VertRep in the argot of the Navy). The H-46 can transfer twice as much cargo per hour from ship to ship as can be transported between ships by using a high line. To high line, ships have to maintain station about a hundred feet apart, not always possible in bad weather. The H-46 can fly and deliver stores when the weather is too bad for ships to maintain station. The only thing it cant deliver is fuel oil.
Reflections on the war
War (and Vietnam was a war and a vicious "give no quarter, take no prisoners" type of war to boot) is a strange beast. It's unbearably sad when your friends get killed but most of the time, nothing out of the ordinary is happening, so life goes on much as usual. The Vietnamese learned not to stand up and fight the Americans in the conventional way, like they did against the French. They got their heads handed to them whenever they did, such as in the Au Shau Valley and the Tet Offensive, early 1968, when the Viet Cong came out of hiding and appealed to the South Vietnamese to rise up. They didn't, and the Viet Cong got slaughtered. But the American public considered Tet to be a defeat, especially when they saw pictures of the VC inside the Embassy compound. The North Vietnamese then proceeded to fight a guerrilla war and bleed the Americans steadily until they gave up. Against the South Vietnamese after the Americans left, the North again fought a conventional war.
There were no front lines as such, so things could go from normal to all hell breaking loose in a fraction of a second. The same thing could happen in the air, a cold Landing Zone (LZ) could turn instantly into a very hot one. Myth has it that the North Vietnamese were a bunch of ignorant peasants. They may have been peasants, but they werent ignorant. They well trained, very skilled riflemen who knew the vulnerable points on all the American helicopters and how to spring an ambush and disappear before the Americans could bring down artillery on them. If they couldnt get away, they stayed as close to the Americans as possible to negate the American artillery. They also knew to let a helicopter land in a zone and bottom the collective before they opened fire. It would take seconds for the aircraft to take off, an eternity when a bunch of AK47s are firing at you.
An interesting feature of war is the suspension of most of the normal rules. When I arrived in Saigon, at Tan Son Nhut, on a Boeing 727, I watched as two flights of F4s, laden to the gills with ordnance, did a routine formation takeoff. In the city, Hueys were flying everywhere, literally just above the rooftops. For an aviation enthusiast, Vietnam in the late 60s was paradise. There were aircraft everywhere, all the time.
They were interesting times, as I got a lot of flying. In Vietnam, the pilots were flying 100+ hours a month, often much more, so a volunteer to fly maintenance test hops was more than welcome. The squadron would put a junior HAC (helicopter aircraft commander) in the right seat, me in the left seat and I would do any flying necessary. The HAC could listen to Adrian Croneower (Good Morning Vietnam!) on American Forces network, Vietnam (AFVN) on the ADF, or go to sleep if he wanted to (and often did). Actually, Adrian had long left the Vietnam when I was there but his salutation had been adopted by all the DJs. Over the years I got over five hundred hours that way.
I got about 10 minutes training with a 50-calibre machine gun before I flew as a gunner. Actually, it was after I had flown a mission. The armaments Master Sergeant said if I was going to fly, I'd better know at least the minimum. Like how to load, cock and fire (dead easy), and how to clear a jam (much harder), something I never had to do, fortunately. The 50 cal was stone reliable.
The first time I fired the weapon was in anger. I was instructed to fire at a tree line to encourage Charlie to keep his head down. The rounds started hitting the trees and they started falling down. I was so startled I stopped firing. Everyone thought I'd been hit and it nearly caused the pilot to abandon the approach. When he realised I was okay, the language he used to encourage me not to do that again was most vivid. Loosely translated he said, "I say, John. Don't stop firing in the middle of an approach without saying something. It makes us think you have been hit and that would be most unfortunate."
When the H46 is light, it is a very sprightly bird. From cruise at 125 knots, full collective and some back cyclic will result in an immediate indicated rate of climb of more than 4,500 feet per minute. The Vertical Speed Indicator can peg. Very useful if you are flying along minding your own business, at fifty feet. That was the height we flew at in Vietnam, or less, preferably much less. You were in much more danger from midairs than you ever were from Charlie. Another reason to stay low, you stay more alert that way. And you were here and gone before 'Charlie' could draw a bead on you.
But as in all wars, compared with the rifle companies, the aviators had it easy. The riflemen liked having us around, for obvious reasons, but they walk everywhere, even today, with eighty plus pounds on their back, plus their weapons and ammunition, the same load that a Roman Legionnaire carried. That's why they are called 'grunts', because that's what they do as they walk along carrying well over one hundred lbs. To them we were 'REMFs' (Rear Echelon Mother F.....rs). The great Australian adjective/noun was in constant use, as a substitute for every conceivable thing. Of course, we thought those in Saigon were the REMFs and I am sure they had their own candidates for the honour. But a rifleman on patrol slept on the ground. No matter what we did during the day, we had a club to go back to, with happy hour when the drinks were fifteen cents, a can of beer five cents, and we slept in beds with sheets on them. The food was good and there was a movie every night, unless we got hit by rockets. I guess we were REMFs, after all. The heaviest thing I carried was my boots.
I was more scared of rockets than any other thing. They made no sound; the first time you knew one was there was when it landed. During an attack, the idea that there might be a rocket in the air, right now, with my name on it, was terrifying. Far worse than reality. In February 1969, we were attacked eight nights, one night in four. Mortar attacks didn't bother me nearly so much. You could hear the mortars being fired and you knew that the gooks would "shoot and scoot." They could fire six rounds, break down the mortar and be gone in less than a minute. So you knew how long you needed to be frightened. It took a minimum of seven seconds from the time you heard the round being fired until it landed. You always knew where the nearest bunker was and you got to know very quickly if you could reach it in time. If not, get flat and get as low as you can, on soft ground if you can make it, but never be standing up when the round explodes. I never believed the mortars would hit me, the gooks were aiming at the airplanes. But, the rockets were aimed at the whole base and being hit or not was a random thing.
Manoeuvres not in the manual
The military always say "Train like you fight, because youll fight like you train." But it is impossible to train like you fight. For a start, nobody is shooting at you, so you dont develop a survival mentality. Secondly, if you fly like you would in combat, there will be operational accidents. Politicians dont like accidents. Questions get asked in Parliament or in Congress, so the manoeuvres so painfully developed stop being flown and the capability is quickly lost. In peacetime, it's "Do it by the book, no matter how stupid that is". In wartime, all that changes. It's "Do what works" and "If the book is wrong, then don't do it, Stupid." Because if you continue to go by the book, you get killed. The freedom and the intense friendships that are formed with people you know would die for you, as you would for them, is what attracts some people to wars.
There were three manoeuvres that were developed quickly in Vietnam by the pilots flying the H-46 under the stress of combat that were never in any training manual. But every pilot flying H-46s knew how to do them, even the one that was strictly prohibited!
There is a one major difference between the tandem rotor helicopter and the single rotor helicopter. The two-contra rotating rotors cancel out the effects of torque, unlike the single rotor helo where any movement of the controls, and particularly power changes, produces yaw effects which can be quite large. The pilot quickly learns to make these corrections without thought but they can affect the aircrafts performance.
Most of the time, the H-46 was flown just like any other helicopter, especially if it was in formation with others. But if you were assigned a medevac, especially if the LZ might be hot, a manoeuvre called the Buttonhook was particularly useful. H-46 pilots claimed that by flying a Buttonhook approach, the Phrog could get into a LZ quicker than any single rotor helicopter. The less time the aircraft was exposed to hostile fire the better so it was a good idea to get into the landing zone, land, pick up the casualties and get out as quickly as possible. Doing a long straight in approach from altitude, gradually slowing into a hover would get you shot down very quickly. The Buttonhook was started directly from cruise speed and low level by setting up a high drag turn which resulted in rapidly decreasing speed and decreasing radius of turn which resulted in an increasing rate of turn. The aeroplane was never going in the direction it was pointing and it was rapidly decelerating.
H-46 pilots used the characteristics of the twin rotors to develop the 'Buttonhook', so called because from above, the manoeuvre traced a path over the ground that looked like an old fashioned buttonhook. It was most effective when the desired landing direction was 180 degrees from the initial heading, but the heading difference could be as low as 75 degrees. The aircraft appeared to start into a normal turn but as it slowed rapidly it rotated sharply, seeming to hang in space at the end before swivelling into position.
A Buttonhook is begun at an airspeed above 120 knots at an altitude no higher than one hundred feet. The start position is close abeam the intended point of landing/hover, one hundred meters but no more than two hundred. First reduce collective pitch to a minimum (trying not to disengage the sprague clutches and dropping the engines off line) then raise the nose of the aircraft from five to twenty degrees, thereby maintaining or reducing altitude slightly. Then roll the aircraft to bank angle not exceeding forty-five degrees while applying sufficient yaw input to maintain balanced flight. At the same time smoothly come back with the stick (full aft cyclic) and increase collective pitch which will cause the aircraft to "hook" around in the direction desired with no gain in altitude. The desired result is a controlled loss of altitude accompanied by a substantial loss of airspeed; usually dropping from 120 knots to below 40 knots in five seconds. The increase in collective pitch must be substantial to ensure engines are on line and spooling upwards, in preparation for landing power. Then as the aircraft rotates to the desired heading, roll out level and increase collective to full power if necessary. The aircraft is now almost stopped in a position to transition to a hover or a landing whichever is desired. This manoeuvre required practice to get right. Common mistakes were:
It wasn't taught in flight school but any pilot who got shot at, quickly learned it from the experienced pilots. The 'Phrog' had so much excess power most of the time, it was rarely at maximum weight, and would accelerate much quicker than a Huey. You could jink nicely with it since it had a very high crosswind component, thirty knots at least, so you could point somewhere other than the track you were making, at the expense of higher drag.
To learn a Buttonhook was not easy and there were many hard landings. But the typical pilot in Vietnam was flying most days, well over one hundred hours in the average month, sometimes more. When you fly that much, you get good. The aircraft seems to do what you want without any conscious thought. Yes, it was dangerous, but it saved lives. My friends from that era, all now retired, conclude that there is nobody left in the Marine Corps who can fly a buttonhook. I described the manoeuvre recently to a young Marine H-46 pilot, and I could tell that he found it hard to believe that people did such things. He certainly wasnt prepared to try one. And given the amount of time he flew, he was wise. But if he was being shot at, he might change his mind.
While the Marines were evolving their buttonhook, the Navy was learning how to do underway replenishment by helicopter. At full flight operations in 1969, the carriers on station off Vietnam would run out of everything in three days. To keep them supplied in these conditions, the aircraft assigned to Service Force ships were flying all day and every day, even at night, until pilot fatigue was a distinct worry. There was a big incentive to develop techniques to speed up operations. The faster the aircraft could fly the round trip, the sooner the replenishment would be finished and the more rest the pilots would get before they had to fly again. It got the carrier back on the line quicker too.
All the cargo was carried in cargo nets slung under the helicopter. The load was hooked on while the H-46 was hovering over the flight deck at a height of eight feet by a crewman who went beneath the airplane. The take off would be made vertically and when the load was clear of the deck, the pilot would then fly backward to clear the flight deck, as fast as thirty knots. When clear he would start turning towards the receiving ship while transitioning to forward flight. When the load had been deposited on the deck of the receiving ship, the pilot would then fly sideways at over thirty knots between the ships to get back to pick up the next load. To fly sideways, move the cyclic stick to bank the aeroplane towards where you want it to go and hold opposite yaw pedal to stop it from yawing into the bank. In a fixed wing aeroplane, this is the formula for a spin, but not in the H-46. This is an area of the flight envelope that the H-46 has it over any single rotor helicopter. To see two helicopters dipping and pirouetting between ships at sea was a sight not easily forgotten.
The other manoeuvre was strictly forbidden, but the pilots would do it in an emergency until Boeing put in an interlock to stop them. There is a trim feature called 'Hover Aft', which automatically tilts the whole rotor plane aft, depending on airspeed, to keep the fuselage as close to level as possible. Without it aircraft would get very nose high in a quick stop. When first installed, 'Hover Aft' could be engaged manually but was not supposed to be engaged above seventy knots. But some joker found that if it was engaged at the cruise speed of 120 knots, it acted like a speed brake slowing the aircraft down very quickly. Combined with a buttonhook, the result was an extremely rapid approach.
It also overstressed the airframe, although it didnt break it. The attitude of the pilots was they would use it if they needed it. The aircraft might disintegrate one day but they would probably be long gone by then whereas they were risking being shot down now. There was much wailing when the latest models arrived with much more power and no pilot ever has enough of that, but no manual 'Hover Aft'.
In the summer of 1969, I got an emergency bulletin from Boeing instructing me to brief the pilots not to engage 'Hover Aft' above seventy knots. I briefed an all pilots meeting, with full details of what it did to the airframe. First question was: "Will the tail come off if I do it?".. .."We..ell, no I don't think so, but it overstresses the airframe and it may fail later", was the reply. I already knew what was going to happen. Later in the club I was told "You're a nice guy John, and we know you have to follow the company line, but if I need it, I'll use it. F**k the airframe, it'll probably fail next year and by then I'll be a civilian."
When I got back to the factory and I was debriefed by the Engineering group, I was greeted with incredulity when I told them what the pilots said. "You mean to say they'll still do it, even after we've told them not to? Even when we put it in the pilot's manual? Don't they know what that does to the airframe?" They clearly did not understand combat pilots, that when you are being shot at, one's time horizon shortens immensely. The near future is the next twenty seconds and the far distant future is five minutes away. If they didn't want something to happen, then make it impossible. Thats why the interlock was installed. And thats why the Navy likes the Marines to fly the same aeroplanes.
After every war, new pilots do not learn the more dangerous techniques that the operational pilots know. There would be too many accidents if they did. To be fair, in peacetime, pilots dont get the chance to fly as much or in the same conditions as pilots do flying combat missions. In Vietnam helicopters routinely flew below fifty feet, an altitude that will have the MPs waiting for you if you do it in peacetime. But Second World War fighter-bomber pilots would have considered 50 feet to be in the stratosphere.
Common knowledge disappears fast. Within ten years, the last junior pilots with 'The Knowledge' are now field grade and moving out of flight operations and the new pilots dont know. After 20 years, they dont even know that they dont know.
In 1970 I flew ashore to Marble Mountain in Vietnam in a Navy CH-46, gleaming, polished and waxed, everything in place, shipshape and Bristol fashion. We had a hangar on board ship and our birds led a pampered life. As we taxied past the Marine H-46s, all oil stained, grimy, wrinkled and beat to death, the contrast was striking. To save weight, everything not necessary for the mission, including the windows, was stripped out. They looked totally clapped out. But most of those aircraft are still flying today, overhauled and rebuilt for sure, but still flying. The Phrog is a tough old bird, still doing the job it was designed to do.
Marine H-46 squadrons, including '261, are now based at New River, North Carolina and Miramar, California, where HMM-165 is based. I took part in a reunion there in August, which was a lot of fun. Visit the account at HMM-165's website here.