4130 Aircraft Tubing Size Guide
Procurement of 4130 Aircraft Tubing Size Guide requires exact specification of outside diameter, wall thickness, and material condition. Applicable standards determine the mechanical properties and certification requirements for this chromium-molybdenum alloy.
Condition N: The Aircraft Mandate
Before discussing size, aircraft builders must understand condition. For certificated aircraft, sizing is irrelevant if the condition is wrong. The tubing must meet AMS-T-6736, which explicitly requires Condition N (Normalized). As-drawn mechanical tubing (ASTM A519) does not meet this requirement, regardless of whether the physical dimensions are correct.
Fuselage Truss Sizing Logic
In a classic Warren truss welded steel fuselage, sizes change throughout the airframe based on the load path:
- Engine Mount & Forward Cabin: Heaviest tubing (e.g., 0.750" to 1.000" OD, 0.049" to 0.065" wall) to support the engine weight, torque, and landing gear loads.
- Tailcone / Aft Fuselage: Progressively lighter tubing (e.g., 0.500" to 0.625" OD, 0.035" wall) as loads decrease toward the tail, critical for maintaining the aircraft's center of gravity.
| Aircraft Structural Area | Typical 4130 Tube Dimensions |
|---|---|
| Engine Mount | 0.750" - 1.000" OD x 0.058" - 0.065" Wall |
| Forward Cabin Truss | 0.750" - 1.000" OD x 0.049" - 0.065" Wall |
| Aft Fuselage | 0.500" - 0.750" OD x 0.035" - 0.049" Wall |
| Control Surface Frames | 0.375" - 0.500" OD x 0.035" Wall |
| Required Condition | Normalized (AMS-T-6736) |
Frequently Asked Questions
Can I substitute a slightly thicker wall if the exact aircraft size is unavailable?
In experimental aviation, builders sometimes substitute the next wall thickness up (e.g., 0.049 instead of 0.035) if a size is unavailable. While structurally safe, this adds weight. In certificated aircraft repair, substitutions must be approved by the design authority or IA in accordance with AC 43.13-1B.
Order AMS-T-6736 Aircraft Tubing
Submit your aircraft cut list for Normalized AMS-T-6736 supply with full MTC documentation.
- List of OD & Wall sizes
- Standard: AMS-T-6736 Condition N
- Footage per size
- MTC 3.1 required