VFR as in flight in VMC.
Cloth over steel tube is probably OK, so long as lightning can’t go through the control cables.
bonding is not exactly expensive
Having seen some of the photography, the cost in € or other currency can indeed not be excessive, but the weight penalty may weigh down heavily on a max gross of 450 kg.
I am not having a go at any particular type of aircraft. I am just trying to understand the thinking process behind somebody building an aircraft which is so vulnerable to something which is rather common. And bonding is not exactly expensive.
There are a few things. I’m not an electrical engineer, so I am on thin ice here. But, as I understand it (electric stuff) this bonding, as shown in the pictures, cannot be nearly enough, or the correct “treatment” for lightening. Isn’t this a Faraday cage kind of thing? You will need a “cage” around the structure. On a plastic plane, the only way to do that is to actually build one, you have to have some mesh of metal on the outside, or at least around the main structure. A fine net of light weight pure (and very conductive) aluminium just beneath the paint would be my solution (from the top of my head).
This brings me to the other thing. Experimentals are experimentals. The builder must (or at least should) build the aircraft so it is fit for the correct fight. This is something everybody building experimentals knows. If it is going to be an IFR machine for “hard” IFR, then it must be built accordingly. I think any slightly serious builder would think about that, and think about it hard and long, until a solution is found. Just did a search at Aircraft Spruce, and what did I find? The correct product for the task, lightning strike protective meshes specifically designed for the task. Sold by the foot, both in copper and in aluminium.
This leads me to believe that plastic experimentals built for IFR actually has the correct protection. For VFR only, who cares, it is stupid to fly in thunderstorms in any case.
There are two separate issues:
Item 1 needs a large-area conductive mesh, or a conductive paint (spray-in zinc, etc – many solutions are used in electronics). This won’t give lightning protection unless very substantial and well bonded. But without this, VHF comms won’t work properly unless you are lucky, or some clever solution is found. Cirrus seem to have found a way without static dissipating wicks, but I don’t know how that works (it is not at all obvious how it could possibly work but it must work). The Spruce stuff you found would be great for this job.
Item 2 needs just a heavy cable to bypass the conductive items (control cables, or the pilot 
) which might otherwise end up conducting the 100,000 amps or whatever, and melt. You don’t need a complete “cage” – in the same way that a house just needs a rod on the roof, and the lightning bolt will head straight for that because it goes for a sharp point.
This leads me to believe that plastic experimentals built for IFR actually has the correct protection.
I doubt they do, in the USA where non-CofA planes can fly IFR subject to some equipment carriage requirements. But maybe a certified Lanc does have this?
I doubt they do, in the USA where non-CofA planes can fly IFR subject to some equipment carriage requirements. But maybe a certified Lanc does have this?
They are not non C of A. They receive a C of A. It’s the same in Norway and most other places. They receive a C of A in the experimental category, meaning it is not verified that the aircraft is airworthy according to the Normal category. But they are just as much airworthy (in the eyes of the authorities) as any other aircraft for personal use and receives a certificate to prove it.
I still don’t get this lightning stuff. A house is grounded, its just a part of the ground. An aircraft or a car is not, they are odd pieces of material in the air. Here is what DexMet, the producer of these mats, writes:
Aluminum has been the principle material used in aircraft and aerospace construction for the past 60 years. With the growing interest to construct more efficient aircraft, manufacturers are designing more components out of light-weight composite materials. Current composite structures include engine nacelles, flaps, wing tips, and even rotary blades on helicopters and wind turbines. Composites, however, are poor conductors of electrical current. Without proper protection, they are susceptible to severe damage in the event of a lightning strike. When Dexmet expanded aluminum and copper MicroGrid materials are incorporated into the surface of these composite structures, the lightning strike energy is dissipated over the surface of the component, which prevents damage to the composite material below.
Composite material when hit by lightening, it literally explodes, like trees when they are hit. I don’t understand what good the internal bonding of different pieces will do.
Anyway, they certainly do have lightning protection. Glasair did a research program with no less than NASA for their Glasair III kit to be used for IFR. This is probably the first real lightning tests done by any GA composite aircraft.
the lightning strike energy is dissipated over the surface of the component, which prevents damage to the composite material below.
That statement (from the seller of that mesh) is basically a total lack of understanding.
Lightning doesn’t just “dissipate” over the surface of a component. It has millions of volts driving it and the lightning bolt will continue its way along, through the aircraft and out the other side:
etc (many photos on the web)
The reason for bonding for lightning protection is to provide the passage through the airframe – same as the lightning conductor on a house (goes into the ground at the bottom).
For this to work, you can’t just put the metal mesh into the composite. You have to join all the bits of mesh with cables. This may happen through them being bolted to some sort of metal frame, or dedicated wires can be used. And exactly the same if you want static protection; they have to be joined up too, and the static wicks have to be connected to the same “circuit”.
That PDF link is dead right now, but maybe Glasair do the bonding as discussed.
NOTE: those pics were all in VMC
Composite material when hit by lightening, it literally explodes, like trees when they are hit. I don’t understand what good the internal bonding of different pieces will do.
As the aircraft isn’t grounded, the lightning bolt will pass through it. It will enter in one point and exit in another point. On its way through the aircraft it will heat the aircraft structure due to electrical resistance. The less the electrical resistance, the less the heating. If there is a particular point with higher electrical resistance, the heating will be concentrated in that point. Bonding will reduce electrical resistance and thus heating. It is not correct to say that “composites explode”. The explosions are caused by expansion of heated air (or moisture, in the case of trees).
Edit: Nice pics, Peter! (I started writing my message before Peter posted his.)
Peter, I have sent you the pdf on mail.
As I said, I have no practical engineering experience in this stuff, and maybe even less so in theoretical knowledge. But you have to remember this product is used by all composite Boeings and Ebraers. So please excuse me if I find it a bit conceptually difficult to agree with the notion they don’t know what they are talking about. I said difficult, not impossible. After all they are simply producing meshes spec’ed by Boeing.
It is not correct to say that “composites explode”. The explosions are caused by expansion of heated air (or moisture, in the case of trees).
Well, that’s pretty much the definition of explosion (I did not say detonation).
From that Glasair doc (many thanks for it BTW)
That’s exactly what I have been saying. This is a full-CofA plane so it needs to have the interconnecting bonding, plus mesh in the composite. But non-CofA “plastic” planes don’t have that (let’s forget the debate that some kind of “CofA” is issued to some homebuilts; I am talking an ICAO Part 23 (or preceeding) CofA). They are just fibreglass and that’s it. Any protection is going to be accidental only e.g. via there being a tubular frame.
One can “take a view” on the lightning risk (and I believe that is the general drift in the “IFR in homebuilts” projects going on in various CAAs) but if you get charged with static, the radio is not going to work. That’s unless there is some clever way to get around that… there might be an antenna location which works OK. When I had the bad bonding issue across the elevator hinges, I found the COM2 (antenna closer to the elevator) was near-useless but the COM1 (above the front seats, almost) was usable. But with a poor range: KX155A doing only about 20nm.
This stuff does make me seriously wonder why so much GA one hears on the radio has such poor comms. One tends to assume it’s because they are flying shagged 30 year old radios like this
or this model, still very popular in the UK and the bread and butter of one-man-band avionics repair shops
but maybe they are modern homebuilts where nobody thought about this, and because the “major demographic” doesn’t venture too far (or flies mostly non-radio – as many homebuilders I know do, exactly) nobody has seen a reason to put much effort into it.
