Fuel tanks installation of AW139

[twinbird]

Does anybody know the reason why fuel tanks of AW139 are located not under the cabin floor like other helicopters?
I found a regulation in Easy Access Rules for Large Rotorcraft (CS-29) (Amendment 4) as follows, but I couldn't find a regulation which cleary describes to prohibit fuel tank installation undert the cabin floor.

CS 29.952 Fuel system crash resistance
(e) Separation of fuel and ignition sources. To provide maximum crash resistance, fuel must be located as far as practicable from all occupiable areas and from all potential ignition sources.

[wrench1]

Does anybody know the reason why fuel tanks of AW139 are located not under the cabin floor like other helicopters?
I found a regulation in Easy Access Rules for Large Rotorcraft (CS-29) (Amendment 4) as follows, but I couldn't find a regulation which cleary describes to prohibit fuel tank installation undert the cabin floor.

CS 29.952 Fuel system crash resistance
(e) Separation of fuel and ignition sources. To provide maximum crash resistance, fuel must be located as far as practicable from all occupiable areas and from all potential ignition sources.

It is my understanding the certification requirements/costs to put fuel under the floor are considerably higher in a Part 29 aircraft than at other locations due to crashworthiness limits.

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The 139 fuel tanks are essentially bags within boxes, held in place so they can deform with a vertical deceleration and, not being in the floor, are further from the impact so less likely to puncture/rupture.

[rrekn]

There is no specific prohibition for location under 29.952, but all depends on the design. In the AW139 (much like the S-76) the fuel tanks are located aft of the passenger cabin to allow sufficient volume, and also provide easy installation of auxiliary tanks.

This same design is followed in the AW189, except that the 189 also has optional underfloor auxiliary tanks, or a belly tank.

[noooby]

The 76 has the fuel tanks inside the cabin. The people in the rear seat sit on top of the forward section of them. Fun times doing Keel Beam replacements. :ugh:

[ericferret]

The 139 tanks do go under the floor in the area between the baggage bay and the cabin.On SAR aircraft the area above the tanks is used as cabin extension.

[Encyclo]

A few factors we considered in the early design phase of the AB139 (BAAC):

1) Medical interior is no fun when tanks are under the 'body fluid' proof, sealed floor (think Bell 412).
2) CG control always a challenge when fuel is spread-out under the floor.
3) Risk of fuel cell puncture during off site landings (stumps & others)

Fly Safe, Always :ok:

[Sir Korsky]

The flange connector between the bladders is installed midway to ensure a nominal amount of fuel is available after a fuel cell puncture in the opposing tank. Gives you 30 mins-ish to get on the ground. Nice design, even considering the dreaded gray fuel on the schematic !

[Kulwin Park]

Does anyone have a schematic they could post up? I'd be interested to see it.

[Helifixa]

Does anyone have a schematic they could post up? I'd be interested to see it.

if you google it a good video comes up explaining the 139 fuel system. Not quite a schematic though.

[jimjim1]

if you google it a good video comes up explaining the 139 fuel system. Not quite a schematic though.

There is a very good looking video of the fuel system regarding it's operation.

https://www.youtube.com/watch?v=WGrl7SGIG0c

I cannot find anything that clearly shows the location of the tanks in the airframe or any description of the crash resistant features of it.

If anyone knows ... :-)

Thanks.

[Sir Korsky]

https://cimg6.ibsrv.net/gimg/pprune.org-vbulletin/872x511/fuel_84c543241b6460b4f23dba0f13ae8a06285fe664.png

all I can find - hope it helps. Tanks are rubber bladder type and resistant to tearing. They are held in place with Velcro strapping.

[noooby]

There are a couple pieces of velcro to help hold up the vertical leg of the tank but the tank is actually restrained in the fuselage with the tried and trusted method of lacing it in with para-cord.