Installation of a legal internal fuel tank


In 2017 I completed a westbound circumnavigation of the world in my 2011 Cirrus SR 22. The route required several legs that were beyond the range of the SR22. Three legs, Merced, CA to Maui, a distance of 2,150 kt miles, Maui to Majuro, the Marshall Islands at 2,050 kt miles, and Majuro to Guam a distance of 1,700 kt miles, also required that the aircraft be over the certified gross takeoff weight of 3,400 lbs for the G3.

To accomplish this, two aluminum ferry tanks were fabricated. One 40 gallon tank was placed where the copilot seat would normally be located and the other 100 gallon tank was placed where the back seat would normally be located. This allowed for approximately 17 hours of total endurance and a maximum range of approximately 2,700 kt miles. It also required a Special Flight Permit (ferry permit) due to the fact that the aircraft was over its maximum takeoff weight. My flight time from Merced, CA to Maui was 13 hrs, 16 mins and I actually landed with 61 gallons of fuel.

Special Flight Permits are a bit cumbersome because they are limited to your route of flight and expire in 45 days. This means for example, that you cannot do any scenic flying, carry passengers or alter your route, other than for weather or other operational considerations. If the 45 days expires it is not extendable and you are required to have the system re-inspected by a DAR (designate airworthiness inspector). This could be difficult and very expensive to deal with if you are sitting somewhere like Thailand for example when the 45 days runs out.

My goal after completing the trip was to find an option that would give the SR22 greater range and not require a Special Flight Permit. An Australian company, Turtle-Pac PTY. Ltd. has been fabricating bladder type tanks for many years and for a variety of uses including aircraft. The tanks are collapsable, self venting and are made of a rugged rubberized material. The 66 gallon tank design allows it to sit right on top of the back seat in the Cirrus and is designed to be connected to the seat belt attach points. This is a huge break through as internal fuel tank installations are required to meet a 9g barrier requirement. Having the flexible tank anchored to the seat belt attach points meets this requirement


In my G3 at 3,400 lbs GTW, the 66 gallon tank is limited to approximately 50 gallons depending on how much baggage and survival equipment is being carried. This provides for 142 gallons of useable fuel. In a G5/6 at 3,600 lbs the total 66 gallons could be used providing for 158 gallons of useable. Endurance and range are dependent on a variety of factors. My plane also has installed an Electro Air Electronic Ignition System which under certain conditions can increase engine efficiency. The plane is also clean wing and normally aspirated.

For example 142 gallons useable: (with Electro Air EIS)

16,000’, ISA, TAS: 164 kts , fuel burn: 10.3 gph, efficiency: 15.9 mpg = 2,200 kt miles total range (adjusted for climb fuel), no reserve, zero wind. A little over 12 hours of total endurance.

10,000’ ISA, TAS: 159 kts , fuel burn: 11.1 gph, efficiency: 14.3 mpg = 1,900 kt miles total range (adjusted for climb fuel), no reserve, no wind. Approximately 10 hours of total endurance

Realistic zero wind flight plan range, depending on altitude and power settings, with two hour reserve: 1,580 to 1,918 kt miles. Note; on long range flights, or where there is no reasonable alternate, I plan two hours of reserve.

While this is not enough range to make Hawaii from California, it does extend the SR22 range out to a point that a circumnavigation would be comfortably possible using the North Atlantic and North Pacific routes. It also makes possible crossings such as: New Foundland to the Azores, Petropavlovsk to Anadyr, Russia and round trip to Bermuda from the East coast. It also would make it possible to fly from Punta Arenas, Chile to Marsh Air Base on Antartica and return without fueling, a round trip distance of approximately 1,200 its miles. This has been an unattainable goal of mine for the last couple of years


Although not TSO’d the Turtle-pac aircraft tanks are made to US TSO standards. So this is where it gets complicated. In order to install the tank legally in the US requires the completion of three 8110-3’s and a 337. An 81110-3 is a “Statement of Compliance with the Federal Aviation Regulations”. It is used to issue a DER (Designated Engineering Representative) approval for a design of a certain piece of equipment, material, etc. and indicates that the DER finds the subject in question to be in compliance with the FAA regulations. In this case 8110-3’s were issued for the following: Structures, Powerplant/Fuel Systems and Systems/ Equipment. This involved three different DER’s and their associated fees. You can see where this is going. After obtaining the 8110-3’ the system is then installed under a 337.

All of this is the brain child of David Mathiessen and Matt Pereira at Air-Mods & Repair, Inc. located at the scenic Trenton-Robbinsville Airport (N87) in Robbinsville, NJ. While the engineering and associated paper work are complicated the system itself is simple and easy to use. It basically involves the tank, a line from the tank to a control and fuel selector box, two 28V Holley transfer pumps, a low pressure light, a three way sector valve, lines from the control box to the left and right wing and the associated electrical system. All of the fuel lines and electrical components meet FAA specifications. The installation also includes a required Ferry Tank System Handbook that is specific to the plane.

The system is simple to remove and re-install and takes less than an hour either way, however; it does require a 337 to remove the system and another one to re-install.

66 Gallon Turtle-pac installed in the back seat of 2011 SR 22 N140BV

The tank runs approximately $2,000.00 including shipping from Australia. The installation including the DER fees which make up the largest amount of the installation ran $12,478.00 for a total of $14,478.00.

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