Modelling > Engineering Dept.

Medium Air Tanker concept

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Okay, this might be more of a 'scenario' but I've posted it here because I'm looking for more of a engineering critique.

In a nutshell (spoiler alert!), the concept is to revive the concept of land-based Medium Air Tankers (MATs) using the growing number of now-redundant early-model Dash 8 regional airliners. The idea is to use greater numbers of landing-based MATs capable of operating out of rural airstrips close to the action.

My sense is that the size of air tankers is being driven up, in part, by budgetary considerations - ie: if firefighting agencies lease small numbers of Large Air Tankers, it makes it more difficult for Government to cut their operational budgets.

A second component of the proposal is finding 'gainful employment' for these Medium Air Tankers outside of fire season. Surplus early-model Dash 8s are already being converted into cargo carriers. That seems a nature fit for work during the off-season.

The point of that 'extracurricular employment' is making the concept more fiscally palatable to both Government and wildfire response agencies. In this scheme for a Common Medium Air Transport, the agencies of Australia, Western Canada, and the Western US would be able to share interchangeable retardant tanks and ancillary air tank gear during their local fire seasons (although I'm aware that the respective fire seasons are beginning to merge).

I am hoping that this just might turn into an actual RW proposal. So, if you see any holes in the concept, let 'er rip!


Oversight of Firebombing in Australia - Fixed-Wing Air Tankers

For those who aren't familiar, waterbombers in Oz fall under the umbrella of the National Aerial Firefighting Centre (NAFC) but it is the Governments of each Australian State and Territory which is directly responsible for fighting bushfires. As NAFC puts it, "the aim is to facilitate resource sharing and cooperation between agencies across the country."

Up here in the Great White North, there is a similar arrangement through the Canadian Interagency Forest Fire Centre in Winnipeg. As with NAFC, CIFFC began with a mandate primarily concerned with coordinating equipment-sharing among local wildfire firefighting organizations in Canada. The dissemination of fire management information naturally followed. And then, in common with any centralized bureaucracy, the dictating of 'standards' inevitably begins. This could be helpful but such organizations drop into following the latest in bureaucratic fads.

What if the bureaucracy is just wrong? According to NAFC: "Fixed-wing aircraft that are used for firebombing tend to be of the larger agricultural-style, specially modified for firebombing. These aircraft are sometimes referred to as SEATs (Single-Engined Air Tankers).
This type of aircraft particularly suits the conditions most often encountered in Australia where there are relatively few long paved runways, but plenty of agricultural airstrips." One follow-on sentence covers all other classed of air tanker, saying: "Larger fixed-wing aircraft have been used where appropriate and cost-effective." Really?

"Rum: Opinion is divided on the subject." - or Size Matters

That NSW just bought a 737 Fireliner suggests that the NAFC conclusion is far from universally accepted. A quick scan of the Aussie press and social media posts, reveals a lively debate about the appropriate size of fixed-wing air tankers for Australia. In the last federal election, the Labor Party advocated buying "six Large or Very Large Air Tankers". No aircraft types were mentioned but NSW refers to its Coulson 737 conversion as a Large Air Tanker (LAT) whereas 10 Tanker's borrowed DC-10s are considered Very Large Air Tankers (VLAT). Both are impressive - the LAT carrying more than 15,000 litres of retardant, the VLAT having more than twice that capacity at just over 35,500 litres. Indeed, one drop by a DC-10 Air Tanker is said to be "equivalent to 12 drops" by a propeller-driven Firecat. And that's the part that has me wondering about an air tanker category which is altogether missing in this debate.

What about the Medium Air Tanker category? In a 03 January 2020 radio interview, former NSW Fire Commissioner, Greg Mullins, said "... large aircraft don't put out fires ... if you had 20 to 30 of these medium-sized aircraft, that have rapid turn-around, you could make a material difference ...". Mullins' point about large aircraft is true of all air tankers. The purpose of firebombing is to "give firefighters on the ground an edge". The medium-sized aircraft Mullins refers to are the Canadair and Bombardier 415 'Superscooper' flying boats. But there is also a case to be made for land-based Medium Air Tanker.

Australia uses US aerial firefighting terminology and classifications. Under the latter, a mid-sized or Medium Air Tanker is classed as one capable of carrying 2,000-to-3,000 US gallons (7,500-to-11,500 litres) of fire retardant or water. So, what ever happened to the medium air tanker category? It seems to have been overshadowed by those smaller SEATs. A typical small air tanker - the AT-802F - carries 3,104 litres (the float-fitted Fire Boss is reduced to 3.028L). That compares well with typical old-school medium air tanker - the Conair Turbo Firecat conversion which could only carry 3,296L despite having almost twice the power. [1] According to Conair Group, the natural replacement for their old Firecat series is the Q400-MR. [2] France decided to bite and their Securite Civile now fields Q400-MRs to replace its Turbo Firecats. [3]

So, an airframe with a wing area of 64.00 m² instead of 45.06 m²; twin 5,071 shp turboprops instead of 1,220 shp; and an empty weight of 39,284 lbs/17,819 kg instead of 15,000 lbs/6,803 kg. I get it, Conair had to work with Bombardier and Bombardier was pushing its then-current production Q400 airframe (and offering a trade-in programme for older Q400s had obvious benefits for new Bombardier production). Fortunately, Bombardier has since pulled itself out of the equation. [4] I'm thinking that this may free up another airframe which Bombardier wanted to downplay.

The Conair/Cascade Q400-MR air tanker can carry 10,000 liters of retardant. It earns its 'Multi-Role' suffix by being about to revert to a passenger- (or cargo-) carrying role in a few hours. Of course, that long Q400-MR fuselage is mainly empty while firefighting. In other words, while acting as an air tanker, the Q400 airframe represents a lot of dead. That wouldn't be the case were air tanker conversions based upon the earlier-model Dash 8 airframes - what Bombardier redubbed the Q100 and Q200. [5] Those earlier Dash 8 fuselages are 10.26 metres shorter than the Q400. Eliminating added-on fuselage sections reduces airframe empty weight by 6,700 kg. [6]

(Caption: The sideview, below, shows a Securite Civile Q400-MR dropping water. The inset is to help give a better sense of the 'extra' airframe for the stretched Q400 series.)

(To be continued ...)


[1] The AT-802F has a 1,350 shp PT6A-67AG, the Fire Boss a 1,600 shp PT6A-67F. The Conair Turbo Firecat needed two 1,220 shp PT6A-67AFs to carry a similar load.

[2] The actual Q400-MR conversions were performed by a former Conair division - Cascade Aerospace (bought by IMP in 2012). As a result, Conair's Q400-MR is closely related to the Cascade Aerospace Q400-PF (Package Freighter) conversion.

[3] The 'FireGuard' package (retardant tank and associated plumbing) can be removed from the Q400-MR in a few hours. This is to allow the Securite Civile to employ its aircraft as passenger carriers in the off-season.

[4] Bombardier sold the rights for the Q400 to Longview/Viking in November 2018. Back in May of 2009, Bombardier had ended Q200 and Q300 production (which will not be revived in production, DH/Viking said in December 2019).

[5] Q100 and Q200 were marketing names, the proper designations remain DHC-8-100 and DHC-8-200 series. Simplified ICAO codes are DH4A and DH4B (with DH4C and DH4D being the longer Q300 and Q400, respectively). CASA sometimes just refers to these aircraft as an '8Q'.

[6] The airframe empty weight difference is based on 17,819 kg for the base Q400 versus 10,477 kg for the Q100/Q200 less the ~635 kg difference in dry weight between a of pair of PW123 and PW150A turboprops.

Common Medium Air Tanker - "... extracting happiness from common things"

All air tankers face the same 'business-model' conundrum - what to do in the off-season? An obvious answer is find other gainful employment. The Securite Civile Q400-MRs are used as agency transports outside of fire season. Meanwhile, the dismounted 'bulges' go into storage until next year. That's fine for agencies with enough transport work (and the wherewithal) but the retardant tanks sit idle while wildfires burn in the Southern Hemisphere. That need not be the case.

Large Air Tankers are already shared between Australia, Canada, and the western United States. That will continue but increased cooperation could benefit a new class of Medium Air Tankers. What if these three regions could agree upon a common aircraft type? Instead of air tankers transiting the entire Pacific Ocean, only their retardant tanks would need to make the trip. A point in favour of adopting early-model Dash 8s as the basis for a Common Medium Air Tanker is availability. Many air carriers - including QantasLink - are phasing out most of their short-bodied Dash 8s. [1] Were that choice of 'platform' agreed, all that would needed a decision on uniform modifications so that the same retardant tanks can be mounted on the Common Medium Air Tankers in any of the three jurisdictions.

That leaves the question of what role such a Common Medium Air Tanker could fill outside of fire season. One possibility is suggested by the early-model Dash 8's ability to land on shorter, unpaved runways. This makes it ideal for servicing smaller, remote destinations. If passenger services are in decline to more remote Australian towns, what about an air cargo service for such communities?

Couldn't Common Medium Air Tankers Carry Cargo to Communities?

Air freight opportunities can provide broader economic benefits to smaller communities. An increase in aerial freight services - perhaps in 'combi' passenger/freight form - would serve to back up Federal Government pledges of "reasonable access to services for regional communities." (Indeed, such flights would probably qualify for funding under Canberra's Remote Air Service Subsidy Scheme.) This would provide a raison d'être for our conceptual Australian Dash 8 air tanker outside of fire season. And, fortunately, cargo conversion kits for early-model Dash 8s are available.

Voyageur Aerotech of North Bay, ON, is producing a dedicated cargo conversion - the Dash 8-100PF. This is a windowless cargo conversion which uses the Dash 8's original baggage door - a 1.52 m x 1.27 m up-and-over type door on the portside [2] Collins Aerospace is marketing a similar concept as their 'Class E' freighter. This is based on a cargo conversion kit developed by a Collin's subsidiary, B/E Canada of Winnipeg . [3] The latter's large cargo door kit provides a Dash 8 with a 1.73 m x 2.75 m clear opening suitable for oversized freight. That allows Collins to market a 'Class F' combi-freighter with palletized passenger seat which can roll-on and roll-off.

A degree of co-ordination would be required on which cargo conversions to adopt for each jurisdiction's Dash 8s. After all, if internal retardant tanks were chosen, their installation would likely dictate the adoption of enlarged cargo doors for all Common Medium Air Tanker 'platforms'. (More on retardant tanks to follow.)

(Caption: The sideview, below, shows a hypothetical Common Medium Air Tanker in the 'off-season' operating as a Voyageur-style 'Package Freighter'. Original rear baggage door - and forward 'air stairs' - are shown open.)

(To be continued ...)

[1] QantasLink’s contractor Eastern Australia Airlines continues to operate Q200s (and Q300s) where smaller passenger loads dictate. For some destinations - such as Lord Howe Island - shorter runways dictate the use of Q200s.

[2] There is also a smaller opening on the starboard side - the former 'galley services' door set just forward of the baggage door.

[3] The Winnipeg firm is subsidiary of Florida-based B/E Aerospace, Inc. which was bought by Rockwell Collins in 2017.

"And a dash of common sense!" - Smaller DHC-8-based Medium Air Tankers

Basing a Medium Air Tanker conversion on 'short' Dash 8 aircraft has two key advantages. First, as previously mentioned, an empty Q100 and Q200 airframes weighs 6.7 tonnes less than the larger Q400. Since the added fuselage space is irrelevant to the air tanker mission, why carry that dead weight? Second is availability since many air carriers - are phasing out short-bodied Dash 8s. [1] Ironically, it is the efficiency of the Q400 as a regional airliner which has prompted the retirement of the earlier-model Dash 8s. However, that Q400 efficiency depends upon flying higher and faster - hardly an apt description of typical air tanker operations.

'Big Sky Country' - An Almost-Was Air Tanker from Montana

The idea of turning early-model Dash 8s into air tankers isn't new. In 2004, Neptune Aviation of Missoula, MT, began exploring conversions of Q200s and Q300s to replace its aged Lockheed P-2 air tankers. (Neptune saw a slightly smaller retardant load as a reasonable trade-off for the Dash 8's superior stalling speed.) A single Q300 was bought to act as a prototype in 2005 but the project seems to have died as a result of cancelled US Forest Service  contracts. [2] Although details are sketchy, the planned Neptune Q300 air tanker was to carry around 6,050 litres (1,600 US gallons) of retardant. So, Neptune's planned retardant load was just over half the capacity of Conair's Q400-MR air tanker.

Although there are few available details, the Neptune conversion presumably involved a tank inside the fuselage (as per Neptune's later BAe 146 air tankers). That has two implications. First, this would be a permanent modification - involving drop doors being cut into the bottom of the fuselage. Second, it would require an enlarged cargo door to install that big fuselage tank in the first place. That does not preclude removing the tank at the end of fire season - as demonstrated by Coulson's larger C-130Q Hercules conversion with its roll-on/roll-off retardant tank. If the cost of installing a cargo door is a downside to the Neptune scheme, the obvious upside is that the fully-internal retardant tank adds no drag to the Dash 8 airframe.

As noted before, fitting a single 6,050 litre retardant tank into the former passenger cabin of a Dash 8 would require the fitting of an enlarged cargo door. That may not been seen as excessive if 'off-season' employment was likely to include over-sized freight. It would also make the Common Medium Air Tanker capable of moving bulkier firefighting equipment in the lead-up to brushfire season. Operationally, it means that there is no major added on the airframe when the retardant tank is fitted.

Of course, there are alternatives to internal retardant tanks. That will be covered in the next post.

(Caption: The sideview, below shows a hypothetical Common Medium Air Tanker fitted with an internal retardant tank. Enlarged B/E Canada-style cargo door - handy for 'off-season' freighting - is shown in the open position.)

(To be continued ...)

[1] Aside from the Lord Howe Island route mentioned in the previous post, QantasLink’s contractor Eastern Australia Airlines still operates out of some regional centres - such as Armidale - with a Q200-based air service.

[2] Neptune has since turned its attention to jet-powered RJs - using eight BAe 146-200s and a single RJ100 provided by Tronos Aviation of Summerside, PEI. Compared with Conair RJ air tankers, the Tronos conversions featured completely internal retardant tanks.

"And [Another] dash of common sense!" - DHC-8-based Medium Air Tankers

Bringing about something akin to Neptune's proposed Q300-based air tanker has its challenges. It is easy to imagine such an aircraft with a scaled-down version of the system used on the BAe 146 air tankers devised by Neptune and Tronos Aviation. But that is not quite the same thing as having a proven example on a similar airframe. But, of course, there is a proven air tanker system in use on a Q-series airframe - the Conair Q400-MR that we opened with. True, compared with the Q100 and Q200, the Q400 is much more powerful (perhaps too much so). And, to our mind, the Q400 suffers from an excess of airframe for the air tanker role. But, it exists.

'Strap-On' - Conair's Midriff Bulge Approach to Retardant Tanks

By contrast with the Neptune Aviation approach, the Conair/Cascade Q400-MR reveals a portly waistline. One advantage is that no enlarged freight door modifications are required. Nor is any cabin floor reinforcements needed to support a heavy internal retardant tank. And this add-on tank is easily removable - the Securite Civile using their 'de-bulged' Q400s to move personnel and equipment around at the conclusion of each fire season.

A similar approach could be used for the shorter Dash 8s. However, mounting a full-length Q400-MR tank on a Q100 or Q200 is probably a non-starter due to ground clearance issues. (To permit its extra long fuselage, the Q400 has a taller main undercarriage to match.) Total weight of a loaded, full-sized Q400-MR tank might also be a problem for the less powerful early-model Dash 8s. But that Conair tank has fore and aft sets of drop doors. What if Conair shortened their system to feature only a single set of drop doors?

Shortening the Q400-MR tank would better suit Q100 and Q200 airframes. A shortened tank gets around any weight issues or ground clearance problems - especially during take-off rotation. On that subject, early Dash 8s were specifically designed to operate from shorter, unpaved runways typical of more remote locations. This can be enhanced by add-on rough-field kits similar to those fitted to Dash 8 patrol aircraft being flown by Surveillance Australia Pty Ltd on behalf of the Australian Border Force. So, flying out of semi-prepared gravel airstrips would be no problem for Q100/Q200-based Common Air Tankers. This means that our conceptual Dash 8 air tanker doesn't need the higher transit speed of the Q400 - the short Dash 8 can stay closer to the action.

That gravel airfield performance would also be a boon outside of fire season. More remote airstrips are very unlikely to possess sophisticated cargo handling equipment. Using the original baggage door, non-palletized freight can simply be handed out to loaders at pickup (or 'ute') bed height and driven away.

(Caption: The sideview, shows a hypothetical Common Medium Air Tanker based on a Q100 or Q200 airframe fitted with a Conair-style 'midriff' external retardant tanks.)

The object here is not to advocate either of the retardant tank approaches. Both have their advantages and drawbacks. With either approach, rapid progress is key. The duration and intensity of wildfires is increasing in Australia and the West Coast of North America. Budgets are going to be strained but air tankers need to be built. As Greg Mullins said, the whole point of firebombing is to "give firefighters on the ground an edge".

I love the idea but I think it makes way too much sense for governments to go with it (particularly the state government of California, IMHO).  I could see a standardized airframe configuration with shared specialty gear as each area needs it.

An approach I could see for the US would be to take early LRIP MV-22Bs, bring them up to a common standard (much as the USMC is already doing), and outfit them with a downsized version of the MAFSS fitted to C-130's.  Using the belly hatch, they could even reload from lakes or rivers in hover.

Having said that, your approach seems much more economically sound and practical; I suspect bureaucrats will hate it just for that reason.


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