Captain Avgas
Well Known Member
In the Experimental category we are at liberty to put whatever materials we feel are appropriate into our aircraft cockpits. We are not bound by choosing materials in conformity with the flammability requirements of FAR Section 25 (Federal Aviation Regulations Section 25) as are the manufacturers of certificated aircraft.
And that is all very well as long as we realise what that means. Unfortunately the issue of flammability is complex and very few builders of amateur built aircraft have a good handle on the ramifications. This is not surprising when you consider that there are literally dozens of different relevant tests including, but not restricted to, flammability, smoke developed, and spread of flame. It can all become a bit bewildering.
Fortunately I was a director of an engineering consultancy that specialised in the design of large scale permanent fabric tensile structural roofs for public buildings (mostly from PTFE glass fabrics) and consequently I have a reasonable knowledge of flammability testing of fabrics.
Over the years I have seen many of my fellow builders fill their cockpits with highly combustible materials including seats, trims, carpets, sound insulation.....and even heat insulation.
The main problem in the Experimental category stems from builders choosing fabrics and trims that comply with motor vehicle standards for flammability rather than aviation standards. In essence most materials complying with motor vehicle standards (such as FMVSS 302 - Federal Motor Vehicle Safety Standards) are in fact highly combustible synthetics. Once ignited they tend to exhibit a rapid spread of flame and emit droplets of flaming resins that can rapidly cause horrific flesh burns.
Fortunately there is a way that even the uninitiated builder can make a safe decision on the trims he puts into his aircraft cockpit without having to be an expert in fabric flammability. He can get a sample piece of the material he is proposing to use and he can set it alight with a cigarette lighter. If the material continues to burn when the cigarette lighter is removed (the independent source of ignition is removed) then it is NOT suitable for use in a cockpit. If, on the other hand it self extinguishes when the independent source of ignition is removed...it is OK to use. It's that simple. No rocket science involved.
The most important thing to understand is the Oxygen Index of the material. The Oxygen Index of a material is that level of oxygen, as a percentage of the total gas mix, required to support the continued combustion of the material in the absence of an independent ignition source. Air has approximately 21% oxygen therefore materials with an Oxygen index of 21 and below will burn readily in air once ignited. Conversely those with an Oxygen Index above 21 will self extinguish once the initial ignition source is removed.
In other words the simple cigarette lighter test will indicate whether the material has an Oxygen index above (or below) 21.
The question may be asked as to why some fabricators of seats and trims for Experimental aircraft use fabrics conforming to FAR 25 and others use highly flammable motor vehicle fabrics. The answer to that lies in the cost and the availability of FAR 25 fabrics. As a rule of thumb aviation grade fabrics cost approximately three times that of motor vehicle fabrics. In addition motor vehicle fabrics can be readily purchased off-the-shelf from a myriad of vendors by the square metre in a huge range of textures and colours. On the other hand aviation grade fabrics are usually only sold by the roll (or multiple rolls). This means that a fabricator wishing to use aviation grade fabrics has to tie up a huge amount of capital to offer a modest range of colour and pattern options. Only fabricators turning over a LARGE VOLUME of aviation trims can generally afford to do this.
The issue of flammability in the cockpit is not about choosing fabrics and trims that are non-flammable.....there is no such thing. The issue is about choosing fabrics and trims that do not exhibit a rapid spread of flame in air. In the end it's all about buying a small amount of time....time to get on the ground...or simply time to just exit the aircraft.
I hope I've been able to throw some light on this topic so that builders can make a more informed decision.
And incidentally, regardless of what trims you opt for, don't forget to always have a Halon fire extinguisher on board.
And that is all very well as long as we realise what that means. Unfortunately the issue of flammability is complex and very few builders of amateur built aircraft have a good handle on the ramifications. This is not surprising when you consider that there are literally dozens of different relevant tests including, but not restricted to, flammability, smoke developed, and spread of flame. It can all become a bit bewildering.
Fortunately I was a director of an engineering consultancy that specialised in the design of large scale permanent fabric tensile structural roofs for public buildings (mostly from PTFE glass fabrics) and consequently I have a reasonable knowledge of flammability testing of fabrics.
Over the years I have seen many of my fellow builders fill their cockpits with highly combustible materials including seats, trims, carpets, sound insulation.....and even heat insulation.
The main problem in the Experimental category stems from builders choosing fabrics and trims that comply with motor vehicle standards for flammability rather than aviation standards. In essence most materials complying with motor vehicle standards (such as FMVSS 302 - Federal Motor Vehicle Safety Standards) are in fact highly combustible synthetics. Once ignited they tend to exhibit a rapid spread of flame and emit droplets of flaming resins that can rapidly cause horrific flesh burns.
Fortunately there is a way that even the uninitiated builder can make a safe decision on the trims he puts into his aircraft cockpit without having to be an expert in fabric flammability. He can get a sample piece of the material he is proposing to use and he can set it alight with a cigarette lighter. If the material continues to burn when the cigarette lighter is removed (the independent source of ignition is removed) then it is NOT suitable for use in a cockpit. If, on the other hand it self extinguishes when the independent source of ignition is removed...it is OK to use. It's that simple. No rocket science involved.
The most important thing to understand is the Oxygen Index of the material. The Oxygen Index of a material is that level of oxygen, as a percentage of the total gas mix, required to support the continued combustion of the material in the absence of an independent ignition source. Air has approximately 21% oxygen therefore materials with an Oxygen index of 21 and below will burn readily in air once ignited. Conversely those with an Oxygen Index above 21 will self extinguish once the initial ignition source is removed.
In other words the simple cigarette lighter test will indicate whether the material has an Oxygen index above (or below) 21.
The question may be asked as to why some fabricators of seats and trims for Experimental aircraft use fabrics conforming to FAR 25 and others use highly flammable motor vehicle fabrics. The answer to that lies in the cost and the availability of FAR 25 fabrics. As a rule of thumb aviation grade fabrics cost approximately three times that of motor vehicle fabrics. In addition motor vehicle fabrics can be readily purchased off-the-shelf from a myriad of vendors by the square metre in a huge range of textures and colours. On the other hand aviation grade fabrics are usually only sold by the roll (or multiple rolls). This means that a fabricator wishing to use aviation grade fabrics has to tie up a huge amount of capital to offer a modest range of colour and pattern options. Only fabricators turning over a LARGE VOLUME of aviation trims can generally afford to do this.
The issue of flammability in the cockpit is not about choosing fabrics and trims that are non-flammable.....there is no such thing. The issue is about choosing fabrics and trims that do not exhibit a rapid spread of flame in air. In the end it's all about buying a small amount of time....time to get on the ground...or simply time to just exit the aircraft.
I hope I've been able to throw some light on this topic so that builders can make a more informed decision.
And incidentally, regardless of what trims you opt for, don't forget to always have a Halon fire extinguisher on board.
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