A Different look At Inerting in Flight Ivor Thomas – Chief Scientific and Technical Advisor to the FAA, Fuel System Design

A Different look At Inerting in Flight Current approach has been to look at how to get high quality NEA (>5% O 2 ). This leads to needing high bleed pressures and also results in lower efficiency ASM performance (30% NEA recovery).

A Different look At Inerting in flight New approach is to look at using the available bleed pressure and going to high flows of NEA and high O2 content (10% and above) during descent This also gives high ASM efficiency (60%) Very Simple System Architecture

Note: Efficiency is the ratio of NEA flow to Supply air flow

Concepts Concept 1 –Run with a low flow, NEA 2% O 2 during climb and cruise to keep up with fuel burn, air evolution, etc –Run in a constant high flow mode during descent, 1.0 to 1.5 lb/min, NEA 16% O 2 at top of descent, NEA 9% O 2 on final approach.

Concepts Concept 2 –Run with a low flow, NEA 2% O 2 during climb and cruise to keep up with fuel burn, air evolution, etc –Run in a constant NEA 12% O 2 mode during descent, gives 0.5 lb/min at top of descent, increasing to 2.5 lb/min on final approach.

Concepts Concept 3 –Run with a low flow, NEA 2% O 2 during climb and cruise to keep up with fuel burn, air evolution, etc using a small orifice to control flow –Run with a larger orifice during Descent, gives high flow 16% O2 NEA at Top of Descent, 9% O2 NEA flow at low altitudes.

Concept 1 Results Using 737 Classic CWT and a single ASM –Assumptions Bleed pressures from Boeing data ASM Performance Approximated from available data 16 minute descent profile, with no holds for traffic ASM flow held constant –O.3 lb/min in climb and cruise –1.75 lb/min in descent

Concept 1, Short flight- 15 minutes cruise duration

Concept 1, Long flight- 200 minutes cruise duration Peak due to fuel burn on TO and early climb

Concept 2 Results Using 737 Classic CWT and a single ASM –Assumptions Bleed pressures from Boeing data ASM data approximated from available data 16 minute descent profile, with no holds for traffic ASM NEA O2 level held constant –2% in climb and 1.5% O 2 cruise –12% O 2 in descent

Concept 2, Short flight- 15 minutes cruise duration

Concept 2, Long flight- 200 minutes cruise duration

Initial Conclusions Using a simple approach of taking the bleed air pressure available and running the ASM to produce high quality NEA in climb and cruise, and high volume, 10% O 2 or above NEA, in descent can provide an inerting system that keeps the CWT inert throughout flight, and doesn’t need ground running capability.

Initial Conclusions Benefits of this approach: –Very Simple system, no compressor –No ground running needed –High reliability, Only moving parts are cooling flow modulating valve, plus shut off valves, plus flow controller (Regulator or two position orifice) –Low weight 50 lb + manifold to tank –Minimum impact on airplane

Questions Need to verify ASM performance under low pressure/high altitude conditions Need to decide which mode is better, –constant flow, –constant NEA O 2 level. –Two position orifice control (one for Cruise and one for Descent) –Any other ideas?

Conceptual Test Program 1. Validate concept using current ASM’s 2. Validate analysis on ¼ scale 747 SP –Sea Level –Altitude/Descent cases 3.Optimize tank manifold with scale 737 tank 4.Ground and Flight tests

Summary Concept looks promising as a way of getting an effective, high reliability inerting system, with minimum effect of the airplane and no impact to ground operations. More work needed, and FAA is teaming with industry to continue effort.