Martin Mars flying boat firebomber

I am watching from the tree-lined shore of the Oshkosh seaplane base, as a beautiful, twin-engined Grumman Goose follows a float-equipped Piper Cub out into the sheltered cove. The Goose is quite a big machine by most private pilot standards – I’m sure the Cub pilot would think that – but both are about to vanish from my view.

They’ve not taken off, but have both disappeared behind the red and white form of the lake’s biggest airborne visitor to date, the Hawaii Mars, one of two Martin Mars seaplanes owned and operated as fire bombers by Coulson Flying Tankers of Port Alberni, British Columbia.

It’s a few seconds before the smaller aircraft reappear, long enough to let you know that the Mars is one big aeroplane – a bit like going flying in the Albert Hall.

Firefighting certainly wasn’t what Glenn L Martin had in mind for the Martin Mars. Originally conceived as a patrol bomber for the US Navy, the first Mars flew in July 1942, sporting twin fins, mounted on the ends of the tailplane.

One year later, with testing complete, the bomber concept was considered obsolete, but a need for a large transport aircraft meant that an order was placed for 20 of the design, which now sported a giant single fin.

In the end, only six were completed, and while two were lost early on in accidents, the “Big Four”, as the remaining Navy Mars were known, were operated till 1956 amassing nearly 70,000 hours. During that time they collected a number of world records for airlift and endurance, all of which still stand today.

Martin Mars survivors

When the Mars were to be marked for salvage, they were saved from the scrapman by a consortium of forestry companies, who figured they could convert them for fire bombing to protect Canadian lumber trees.

One was lost early on, fighting a fire while flying uphill; the load wasn’t released and the Mars crashed into the hillside. Another was damaged in a storm while beached, which led to it being scrapped. But the remaining two, Hawaii Mars and Philippine Mars, have being fighting fires since 1962, based at Sproat Lake, British Columbia.

They’ve passed through the hands of various owners, ending up with their current operator, Coulson Flying Tankers, in 2007.

Super size seaplane

We head out to Hawaii Mars by boat and slowly circle the aircraft, moored on its buoy. Weighing 9,500lb, the buoy, along with a spare engine and other support equipment travels with the aircraft when it’s deployed away from base.

It’s impossible not to be struck by the sheer size of the machine, not least by the 40ft-high fin which blocks the morning’s sunshine as we pass through its shadow. The four-blade props are 15ft 2in in diameter, but the four 18-cylinder (nine in two rows) Wright Cyclone R3350 radials look implausibly small on the leading-edge of the 200ft-span wing; the wing root is tall enough to walk around inside. The four engines provide a combined 10,000hp.

Passing one of the tip-floats, it’s the same size as our boat; one float, together with its two huge vertical attachments, probably has more metal in it than you’d find in the airframe of a Cherokee 140.

Boarding the aircraft via a door below the flight deck, you’re confronted by enough structure, portholes and nautical-looking hatches that you’d be forgiven for thinking you were on a ship. A staircase takes you upstairs. Here, the aft section is dominated by the flight engineer’s panel. The Mars has two flight engineers, responsible for the control and care of the four engines. It’s a wide array of gauges and levers, even an oscilloscope to help fine tune the running of an engine, or detect a duff plug. When there are 144 of them, you need all the help you can get!

On the left of the engineer’s panel are the fuel system controls. The panel looks a bit like a London Underground map that’s been punctuated with levers and gauges. You’re not surprised to hear that one trainee flight engineer managed to shut off the supply to all four engines on one Mars delivery flight in 1959… an action that caused the flight engineer to come running from the toilet when he heard everything go quiet.

Walking forwards to the flight deck, there are substantial metal desks with solid timber tops on either side that would have been the domain of radio operator and navigator. Slipping into the pilot’s seat, the multi-pane glazing all around makes you think wartime bomber – but the panel, featuring twin Garmin G600s with synthetic vision, along with dual Garmin GNS430s, Garmin GTX330 transponder, radar altimeter and TCAS, could be a modern GA single if it weren’t for the two dual-needle rpm gauges placed at top centre.

Every take-off unique

Before taking the boat ride to the Mars, I’d sat down for a morning coffee with Dev Salkeld, one of the Mars pilots who flew the aircraft to Oshkosh. Having flown for Cathay Pacific, Dev joined the Mars crew in 2009 when he heard of the opportunity, and was trained by two captains who had been flying the Mars since 1977. He’s since gone on to log over 700 hours in the aircraft fighting wildfires.

“Water operations are similar to other flying boats such as a Mallard or a Goose. The biggest difference is the sheer size of the aircraft. The wake when performing a run-up is huge so you need to be mindful of people’s docks. For instance, if someone has a big boat tied to a dock, it is possible that the wake could pull the cleat right out of the dock. Also, there’s a lot of inertia when taxying up to a buoy so you need to start slowing the aircraft early. To help with that though, the propellers on engines number 2 and 3 are reversible. As there is no water rudder, steering is accomplished through the use of differential power. We don’t worry too much about cooling at low speed on the water, as there’s a 72-blade fan that’s bolted on with the propeller in the front of each cowling, forcing cooling air around the cylinders when the ram air effect is negligible.

“Taking off, probably the biggest thing is watching out for boat traffic on the lake. Normally they will see and hear you and adjust their path accordingly. Sometimes, because of the shape of the lake, you’ll start out and might round a corner. In that type of situation they might not see you coming until later in the take-off run. We’re always thinking about amount of lake that’s available and the climb rate and surrounding obstacles. Because of the age of the aircraft and the many variables associated with seaplane flying, every take-off can be considered unique with regards to direction of take-off, wind, elevation, temperature, the weight of the load and obstacle clearance.

“Lift-off speed varies with weight. If the aircraft is light, that’s around 70-75kt, and we’ll climb at 130 KIAS. That will give us about 1,000fpm. By comparison, later when we’re fully-loaded with water, we’ll climb at 120 KIAS. That will give us 200-300fpm.

“In the air, I’m not sure that I’ve flown any other aeroplane that I could compare to the Mars. The rudder and elevator have electric/hydraulic boost pumps and they’re fine, not particularly heavy. The ailerons on the other hand aren’t boosted and with that long, high-lift wing, and comparatively small ailerons, it takes a lot of muscle, a really big yolk input, to get it rolling. They only get heavier at higher weights and speeds, and the aeroplane likes some rudder too, if you want a nice co-ordinated turn. Apart from that, it doesn’t really have any quirks or vices. It’s big and cumbersome though, so taking into account how slow it is to respond, you have to remember to stay ahead of it.”

Flying the Mars cross-country at the typical cruising altitude of 9-10,000ft sees a true airspeed of 170-175 knots, with a fuel burn of around 400gph, though Dev tells me, “After a couple of hours we can get it back to about 365gph.” Don’t forget to pack some oil too; the Cyclones typically use a couple of gallons per hour, per engine.

Scooping water

“To scoop water, basically we make what is the beginning of a normal landing. We use full-flap landing, that’s 40° and an approach speed of 85-90kt. You have to remember that from the cockpit, when you make that touchdown, it can seem like you should still be flying – the bottom of the hull is around 20ft lower than where you’re sitting. After touching down, the First Officer retracts the flaps and I’ll slow the aircraft to 70kt. It’s at that point I’ll hand the power over to the flight engineer with the call, ‘Engineer, you have the power’, and he’ll reply, ‘I have the power.’”

“Then I’ll select the two 7-inch diameter scoops down and the First Officer will start the timing. The flight engineer tries to maintain a scooping speed of 70kt, which generally needs full take-off power. At this point, the water is coming on board at about a ton (2,000lb) a second. The timing depends on the fuel load, as we’re always trying to balance fuel and water to attain a normal load that’s a gross weight of 162,000lb. Of course, this also depends on the length of the lake. Less length means a shorter time to scoop. Scooping the maximum 6,000 imp. gallons takes around 30 seconds and 3 miles of lake. Once the scoop time is complete, the First Officer retracts the probes and states, ‘The probes are up and the lights are green.’ This is to let the rest of the crew know that the probes have fully retracted. After the aircraft accelerates through approximately 75kt I’ll call for flaps 20, and we’ll accelerate to 83kt to get airborne. I’ll make a call for climb power when accelerating through approximately 90kt and then request the First Officer to ‘Retract Flaps, Slow’ while we’re still accelerating in ground effect.”

Fragile flaps

“On a normal take-off or while scooping, the standard procedure is to keep the flaps retracted because they’re fabric covered and could be damaged by the spray,” says Dev. “Once the aircraft is on the step (in a normal normal take-off) and accelerating through 65-70kt, the flaps are extended. When the aircraft is scooping the flaps are not extended until scooping operations are complete.”

Inside the Mars, the water is automatically mixed with a polymer thermo gel that sticks to burning trees, increasing the drop’s effectiveness. The water tanks are around half of the original 13,200 gallon fuel tank capacity, located in the very bottom of the hull. Their location means there’s little shift in C of G when the series of 22 doors in the planing surface of the hull open for a drop, but the Mars will want to pitch up. To stop it doing that, you need to push the yoke just about to the panel. One Mars drop can cover four acres, and combinations of drop height and speed help vary the intensity at which the load arrives on the ground. 

“When it comes to making a drop, if you could fly every approach and keep everything constant – the same height above ground, airspeed and deck angle, it would make it much easier. However that would be an ideal world and that rarely turns out to be the case when you’re required to make a drop on the varied terrain we deal with. The drop is normally performed at 115 KIAS and 150ft above tree canopy. If you are dropping into wind this will affect the groundspeed and of course the opposite is true for a tailwind. Also, depending on the elevation of the drop, the TAS will be higher, which will also affect the groundspeed. 

“We never bomb uphill but there are times when you might be running downhill, which can change the deck angle (perspective) as well as the aircraft speed. Sometimes, working along a fire there can be considerable drift (crosswind) so we may also allow for that. It’s very much a process that’s plenty of hand/eye coordination along with seat of the pants in the attempt to do everything the same all the time. A point of note on the fuel burn, when we’re working a fire, the Mars is typically burning 785 imperial gallons per hour. When things are going just right, in a single six-hour sortie, the Mars can make a drop every 15 minutes. That’s over a quarter-of-a-million gallons helping to protect property and safeguard lives.”

World’s largest

Dev reminded me that, except for the brief 30 seconds in 1947 when Howard Hughes’ ill-fated H-4 Hercules, or Spruce Goose was airborne, the Martin Mars is still the largest flying boat in the world. While China builds the  amphibious AVIC AG-600 touted as the ‘world’s largest seaplane,’ that aircraft, a mere 121ft long and 127ft span, would be dwarfed by the Mars. For the crews who trained the earliest AG-600, it was realised that the best preparation would be to head to Port Alberni and get some Martin Mars time.

As the ultimate firebombing tool, the Martin Mars retires having no equal. I ask Dev if he’ll miss it. 

“Absolutely. Every time I fly it is special. It’s a unique airplane, you can’t sneak around with. Everywhere we go people come out to look at it.”

Footnote: FLYER dedicates this republished feature to Devery ‘Dev’ Salkeld, who died 29 February 2020.