Bolted Flange Joint Analysis of the Saturn V F-1 Engine Nozzle
Bolted Flange Joint Analysis of the Saturn V F-1 Engine Nozzle
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F1 engine on display at National Air and Space Museum
Photograph by Mike Peel (www.mikepeel.net)
The Saturn V’s F-1 rocket engine used a bolted flange joint to connect its mid and lower nozzle segments. I performed a non-linear finite element analysis (FEA) in ANSYS to evaluate how this flange—and the bolts themselves—respond to internal pressure, bolt preload, and thermal effects. This is a very brief summary of the analysis, I am happy to share further if you are interested.
Analysis Overview
Geometry: The model includes the mid and lower nozzle sections and the bolted flange ring joining them. The upper nozzle is excluded, with its effect captured by an equivalent force.
Loads:
Gas Pressure: Varies from 12.17 psi at the exit plane up to 47.72 psi near the mid nozzle entrance.
Thermal: 700°F exhaust gas causes thermal strain, modelled with the respective coefficients of thermal expansion.
Bolt Preload: Set to 50% of the bolt’s breaking strength.
Materials:
Nozzle: 300 Series Stainless Steel (𝐸=2.9×10^7 psi, 𝜈=0.27).
Bolt/Nut: A-286 Steel (𝐸=2.9×10^7 psi, 𝜈=0.31).
Key Findings
Total Deformation:
Maximum deformation near the flange bolt holes (∼3.8×10^−5m), indicating the joint is quite stiff under these loads.
Stress Concentrations:
Highest equivalent (von Mises) stress of about 6.9×10^8 Pa.
Stress hotspots appear around bolt-to-flange contact regions and fillets—typical in bolted joints.
Joint Integrity:
The joint remains largely in contact, though small gaps may open at the flange edges away from bolts under peak load/temperature conditions.
Preliminary margins of safety can be evaluated by comparing the maximum stresses to the material allowable of A-286 and stainless steel.
The non-linear FEA reveals that, although the flange experiences localized high stresses around the bolts, the overall deformation of the joint is minimal. Proper preload, carefully selected materials, and robust bolt design are critical to ensuring reliability under the combined effects of exhaust gas pressure, thermal expansion, and mechanical loading. These results help guide design improvements and validate that the bolted connection can withstand the severe environment within the F-1 engine nozzle.
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