Past Talks : May 2019
“C-7A Caribou Operations – Republic of Vietnam 1968-69” by Jack Froelich
The very mention of the name de Havilland Canada conjures up several really interesting and enduringly successful designs that have each made their mark worldwide: Chipmunk (or Chipfire as some have called it due to its manoeuvrability), Beaver, Otter, Twotter (Twin Otter), DH6, DH7, Buffalo and of course, the subject of tonight’s talk the Caribou. It is not a pretty aircraft and I suspect the Caribou is something of a Marmite design – you either love it or you don’t. For me, and no doubt the 70+ people that attend these evenings, the talks are always extremely entertaining, but the prospect of hearing about the Caribou was unmissable – yes, I like the Caribou. It is certainly not handsome, but it looks absolutely right for what it did so well. Our speaker Jack Froelich knew the aircraft first-hand as a pilot in the US Air Force. His job was to support the US Army in North Vietnam. Originally, the Caribou was operated by the US Army, but in 1967, Jack tells us, they were forbidden to fly any aircraft weighing over 12,500lb, so the Caribous and any other large aircraft were transferred to the USAF. The USAF meanwhile had to hand over its helicopters to the US Army in exchange.
So, what was the Caribou and what made it different? It was designed for Short Take-off and Landing (STOL) operations; it could carry up to 3 tons payload; it weighed 13 tons; in American operations it had a crew of two pilots and one Loadmaster. It was designed to operate from rough landing strips inaccessible to most other aircraft; it had a large ramp at the back to enable rapid loading and unloading of troops and cargo; and it needed around 1,000ft in which to take off. A typical cargo could be 32 Infantrymen, or 14 stretcher litters, plus 10 seats, or as frequently happened, animal transport! The DHC4, as it was first known, flew in 1958 and was the third STOL aircraft by DHC, preceded by the Beaver and the Otter. To achieve its very impressive performance, it was powered by two Pratt & Whitney Twin Wasp R-2000 7M2 radial engines producing 1450hp each from the 14 cylinders. The same engine had proven its reliability in the Douglas DC4 and Skymaster. What was different in this instance was that the engine cowlings had no cooling gills and the Hamilton Standard propellers were fully reversible. The engines also had two augmenter tubes extending backwards over the wing, which in theory helped to boost performance. However what did work was the flow of air blown over the flaps. The flaps were full-span, double slot (in effect two flaps – one hinged behind the other) Fowler flaps with an 80 degree droop. In addition, when the flaps were operated, the ailerons also drooped. All this, with the augmented air being blown over the wing meant that very high lift was achieved, enabling a typical approach speed of 60kts and touch down at 35/40kts. That is the equivalent of a typical small, light aircraft, rather than a 13 ton cargo carrier. Not only that, but it was a joy to fly, although it had to be flown 100% of the time – no casual hands-off flying while you fidgeted with the chart. In its original form the DHC4 was designed for single pilot operation, but that was not the American way of doing things, so two pilots it was.
The payload was less than that of a DC3, but the great benefit in many forward bases was its STOL performance. The fin and rudder are absolutely huge and they earned their keep on operations from small dirt airfields requiring a steep climb out. According to the operator’s handbook the minimum speed in these circumstances should be 80kts. However, it was soon discovered that on short fields just 75kts was feasible by holding the aircraft straight and steady using the enormous rudder until proper flying speed could be gained. Niceties are set aside when people are firing live bullets at you from just over the hedge. Small arms fire was effective up to about 3,000ft. To minimise the risk of small arms damage, crews either flew high, or as Jack preferred, very low. On these operations it was essential to ensure that at least 1,500lb of fuel was carried in the wing tanks to maintain their stiffness. Internally, the floor was made of plywood and could carry standard 4ft x 4ft pallets. Seats were built into each side of the aircraft facing each other, or two Jeeps could be carried instead. For comparison, it could carry more than a Chinook helicopter. The pilots’ cabin stood 3 to 4ft higher than the cargo deck. The instrument panel was quite basic and was designed for daytime, visual operations, where you check landmarks against a chart. It was not designed for night flying and instrument flying, but simple bush-flying. If you had the misfortune to fly through rain you got wet, because the Caribou leaked like a sieve. It was also very, very noisy. One luxury that USAF Caribous had that Royal Australian Airforce Caribous did not have, was weather radar. This enabled pilots to take some of the guess-work out of navigating by heading for the coast and following its contours and spotting rivers on the radar as they progressed.
The aircraft itself was reliable and so were the engines, which was fortunate, because all maintenance was conducted outside in sweltering heat and tropical storms. Engine access was helped greatly by the barn-door type engine cowlings. At the end of the Vietnam War around 50% of the Caribous went back to the USA and were used by the Reserve, while Australia kept theirs in ront line service until the 1990s and retired the last one in 2009. Operations were typically to move both military and civilian passengers (Jack openly acknowledged that they hadn’t a clue who most of the civilians were, because their travel passes were printed in Vietnamese and they could easily have been North Vietnamese soldiers going home on leave for all he knew). In addition they moved many cows. Most of these were dropped by keeping the aircraft at a steady 110kts at 300ft and then sliding out the crates containing the cows, to float down on two cargo parachutes to a soft landing. In all the time he was in Vietnam, Jack knew of only one cow to receive any form of injury, and that was a broken leg. As a change from dropping cows, they also dropped chickens in crates. The idea behind all this was keep the mountain tribesmen (Montagnards) on the side of the USA. The tribesmen were nomadic, but the intention was that by dropping cows to them, they would stay in one place to breed them and in due course the tribesmen could be trained as soldiers. That was the theory. The reality was that the cows and the chickens very quickly became the meal for the day. An expert also proposed that it was essential to drop trained German shepherd dogs, which the tribesmen were delighted to receive as a change in diet.
The Caribou often supported Special Forces into and out of forward bases, as well as such mundane, but important tasks as returning for reuse all the Chinook underslung cargo nets and slings deposited in the remote drop-off points. Finally, Caibous were used to provide occasional support for Air America’, the quasi civilian airline that conducted covert military operations in areas that the authorities preferred to not talk about.
Home base for Jack Froelich was Cam Ranh Bay. From there they would fly to places such as Dak Pek where special training was required before any pilot was allowed to attempt a landing. It was very tricky and touchdown had to be made in the first 10 ft of the runway to successfully get in. One thing it did demonstrate was the crashworthiness of the Caribou. It was a tough aircraft and of the relatively few that crashed, most occupants survived. Plei Me airfield was a Special Forces base frequently attacked by the North Vietnamese. The runway was only 1,100ft long which made full use of the STOL features and full reverse thrust; Lei Khe airfield near Saigon was surrounded by a Michelin rubber plantation still in full operation. The plant manager operated a Cessna 190 to enable him to do his job properly and to take the family shopping in Saigon. The fact that he was in the middle of a war zone appeared to be no problem to him; Man Buc airfield in the Central Highlands required nerves of steel and determination ‘to get it right’. The runway was surrounded by hills and the approach to land required a climb all the way up. At the last minute, at a set point a 90 degree turn was required before you dropped the aircraft onto the runway. By way of compensation, one of the bases had a Michelin Star chef and any run into that base was always welcomed.
Jack made comparisons with other similar aircraft, such as the C123 (Fairchild Provider) and DC3, both of which were much in use. In each case these aircraft could carry more cargo, but required long runways to operate. They could not do what the Caribou did so well on small, inhospitable airfields. I was interested to learn that South Korean troops were also involved in the Vietnam war, primarily to provide base security. From Jack’s experience, they were very hard people and genuinely took no prisoners. This was a very interesting, very lively and different talk about an unusual aircraft. I loved it. Thank you Jack Froelich for a most enjoyable and informative evening – and thank you to the backroom ‘boys’ of course for freshening us up halfway through.