Allow the tank to be filled to the rules-defined level, and be removable.
An aluminium neck welded to the tophat. If the neck attaches at the bottom of the tank it needs a breather tube from the top of the tank to the top of the neck so air can escape while filling.
No part-specific design process is documented. The Fuel subsystem design process applies: 1. Set tank volume from endurance consumption plus margin, with the HydraMat area and the tank CG as constraints. CR26: 1.4 gal cell, 1.56 gal effective system. 2. Design the sump to the acceleration cases: 1.42 g at 45 deg from vertical under acceleration against a rear wall 30 deg from vertical, and 2.51 g at 66.5 deg from vertical under braking against a vertical front wall. 3. Lay up the sump: 1 layer of Kevlar over 5 layers of stitched carbon twill on HIPS dissolvable molds, bonded with 3M DP420, sealed with Caswell epoxy gas tank sealer. 4. Design the top plate: -4 AN weld bungs instead of fittings, stud bulkhead terminals so no fuel path runs through wire, an aluminium terminal block for proper bulkhead seating. 5. Leak test the assembled system before it goes in the car.
Rules govern the fill level and the venting. The recorded goal is a removable filler neck, compliant with all rules and out of the driver's view to reduce the number of firewalls needed. From the design reports and one-pagers: Rules define this part almost completely. IC.5.4.1: minimum 35 mm inner diameter at any point between the tank and the filler cap. IC.5.4.2: the portion nearest the cap must be a minimum 125 mm vertical height above the top of the tank and angled no more than 30 degrees from vertical. IC.5.4.3: an accompanying clear fuel-resistant sight tube with 125 mm minimum visible vertical height, 6 mm minimum inside diameter, above the top surface of the tank. A permanent, non-movable fuel level line must sit 12 to 25 mm below the top of the visible sight tube; that line is the fill line for the tilt test and for measuring endurance fuel use. IC.5.4.6: the sight tube and level line must be clearly visible to two people without artificial lighting, magnifiers or removing parts. IC.5.4.7: the filler must be directly accessible with a standard two gallon can (25 cm wide x 25 cm deep x 35 cm high with a 25 cm spout). IC.5.4.8: the cap must withstand severe vibration or high pressure such as in a rollover.
Al 6061. From the cost report drawings and CAD: From the cost report drawings: 6061 ALUMINUM (Filler Neck).
Fault Vault, 2026-06-07, CR26I: threads in the top hat failed after repeated removal and installation, with initial torque specs set too high. At competition multiple threads slipped and the tank leaked after endurance. Corrective action: do not overtorque, use antiseize, size up the bolt.
CAD mass, CR26I master assembly: 0.285 lb (0.130 kg). CG at X 61.82 in, Y -11.01 in, Z 11.49 in in vehicle coordinates. CAD mass, CR25 master assembly: 0.285 lb (0.130 kg). CG at X 61.82 in, Y -11.01 in, Z 11.49 in in vehicle coordinates. CAD mass, CR22 master assembly: 0.283 lb (0.128 kg), 2 instances, 0.565 lb total. CG at X 61.83 in, Y -10.53 in, Z 11.22 in in vehicle coordinates. Dimensions called out on the cost report drawings. These are the figures printed on the drawing, not a labelled specification; open the drawing itself for what each one refers to. Filler Neck (as drawn): 38.10, 34.90, 6.35 3.18, 254.00, 146.05 Filler Neck (as drawn): 1.90, 5.08, 25.40, R0.16, R0.32 Source: SolidWorks mass model exports: CR22 (5 May 2024), CR25 (4 Jul 2025), CR26I (30 Jul 2025), CR26E (22 Mar 2026) | Cost report drawings: CR22/Powertrain/Design/X - Cost Report Drawings/Fuel Drawings/Filler Neck.pdf; CR25/Powertrain/Design/Y - Cost Report Drawings/Fuel/Filler Neck.pdf; CR26i/Powertrain - IC/Design/Y - Cost Report Drawings/Fuel/Filler Neck.pdf; CR27i/.Powertrain/Design/Y - Cost Report Drawings/Fuel/Archive/Filler Neck.pdf Quantity per car, as costed: 1
Nothing in CrimsonStorage covers these yet.