USB stick data recording, blackbox-like housing?

[bwilson4web]

Hi,

I was following the recent Seawind 3000 crash in DeLand FL and noted that the aircraft was pretty much consumed by the fire. For rebulding N19WT, I am planning to go with three, external, RS-232 serial output, data recording systems:

• Dynon 10A - electronic flight information system
• Grand Rapids Tech EIS 2000 - engine monitoring system
• fuel injection ECU - engine fuel injection system

My plan is to use one of my ordinary laptops to record the data to a USB stick but then I read about the fire destroying the Seawind 3000.

I'm now thinking the USB stick should be in a fire-resistant, water resistant, housing with just a USB extension cable to reach the laptop. As long as the data is saved to the USB stick and it is reasonably protected against fire and water, there would be a record of what happened. So I started looking for ruggedized, fireproof and water proof housings and there isn't much out there.

As a quick hack, I'm thinking a short, steel pipe with two caps. The cable would exit via a small slot cut into the pipe or one of the caps and everything inside wrapped in glass cloth possibly micro-epoxied. The idea is to have enough thermal protection to resist a short-lived fire. Adding a voice recording file, it would pretty much have everything found in a real blackbox.

Unknown is how much heat needs to be removed from a USB stick in normal operation . . . otherwise the housing becomes a fatal, oven for the USB stick. However, a thermal fuse (aka. low temperature solder) could provide a thermal path that in a fire would melt, reducing the heat flow to the USB stick. There are other one-way thermal systems (aka., bi-metal links) that could allow heat flow out but isolate fire generated, high-temperatures from cooking the USB stick. Without power, most electronics can handle fairly high temperatures.

Thoughts?

Bob Wilson

[cluttonfred]

Since weight is always a factor, I would think that lightweight metal box with ordinary loose fiberglass insulation and the drive itself wrapped in heat-resistant, heat-reflective tape would be a simple, rugged solution. You are right that the weak point would be the thermal bridge provided by the wire. Some sort of wireless set-up (a Bluetooth connection?) would be a way to avoid the wire altogether.

[steveinindy]

There are other one-way thermal systems (aka., bi-metal links) that could allow heat flow out but isolate fire generated, high-temperatures from cooking the USB stick. Without power, most electronics can handle fairly high temperatures.

So far as I am aware, the commercial variety use a coupling that shears the power at about 4 g of impact force.

Since weight is always a factor, I would think that lightweight metal box with ordinary loose fiberglass insulation and the drive itself wrapped in heat-resistant, heat-reflective tape would be a simple, rugged solution.

Yeah.....ever seen what happens to fiberglass at the temperatures seen in your standard GA post-crash fire? It melts (why do think so little is left of Cirrus and other composite aircraft after crashes?) and your suggestion . If I were going to do this (and the thought has crossed my mind on more than one occasion), honestly your best best is to copy the housing used on real FDRs and CVRs. The data unit is housed in a ceramic housing filled with water with a wax-sealed or thermoplastic-sealed vent hole to allow the water to boil off carrying some of the heat with it. Then you wrap the thing in a steel casing. Pretty much any other metal is going to wind up being destroyed in a post crash fire or by the impact itself.

No need to go reinventing the wheel when you can just reverse engineer what has already been done. In other words, just pretend you're working for a Chinese company.

I am planning to go with three, external, RS-232 serial output, data recording systems:

• Dynon 10A - electronic flight information system
• Grand Rapids Tech EIS 2000 - engine monitoring system
• fuel injection ECU - engine fuel injection system

I would strongly, strongly suggest adding a cockpit voice and/or video feed. The voice feed would be simple enough since you could simply add in an intercom system with an extra "line" and use that to feed the CVR.

Some sort of wireless set-up (a Bluetooth connection?) would be a way to avoid the wire altogether.

KISS. The wire problem is able to be overcome in much simpler and more reliable ways.

[Frank Giger]

My first thought is that the pipe isn't such a bad idea if it wasn't for fire.

So why not get it away from the aircraft?

Let's say it's positioned near the tail at the top of the fuselage in a recess that's fabric (or otherwise) covered, spring loaded with a ten foot coil of wire attached to it, and that the spring is held compressed by a temperature released material. This could be as un-exotic as a cable tie that would melt.

If the plane wrecks and no fire, recover the stick.

If the plane burns, the tail is the last to go, and the stick sproings towards the back, away from the aircraft. The cable to the usb disconnects and the wire keeps it easy to find.

In all metal aircraft, one would think positioning it near the tail would be enough to keep it cool enough not to need the Emergency Sproing Device (tm).

[cluttonfred]

I like Frank's spring-loaded disconnect idea a lot, seems very simple and doable. Even without having it actually spring away from the aircraft, it would break the thermal bridge at the wire. It wouldn't be hard to come up with an insulated metal box over the USB port, with spring-loaded covers. The top cover you open to add or remove the drive, the bottom cover would be propped open and spring shut if the cable tie melts and pops the box away from the surface.

[steveinindy]

In all metal aircraft, one would think positioning it near the tail would be enough to keep it cool enough not to need the Emergency Sproing Device (tm).

You'd be surprised. I do like the idea of the ESD though.

If the plane burns, the tail is the last to go, and the stick sproings towards the back, away from the aircraft. The cable to the usb disconnects and the wire keeps it easy to find.

Here's my thought though.....

You have an aircraft moving forward at say 70 knots that hits the ground. If the device is triggered to "sproing" on impact, you have to have enough force to propel it rearwards against that momentum. If you wait to deploy it until after the aircraft has stopped, you have a real chance of the trajectory being towards either the fire (plenty of aircraft tend to have their tails come "over the top" or pointed straight up as a result of the crash sequence) or having some form obstruction in the way that would minimize clearance.

My suggestion to make it easier to locate would be to not rely solely upon the wire but to have some form of really obnoxious sound device that could be easily shut off by first responders. Thing about a human hearing range version of the underwater pingers used to locate commercial data recorders when they wind up in water....

[martymayes]

Who is going to tell an investigator they should be looking for a data recording device?

[bwilson4web]

I like Frank's spring-loaded disconnect idea a lot, seems very simple and doable. Even without having it actually spring away from the aircraft, it would break the thermal bridge at the wire. It wouldn't be hard to come up with an insulated metal box over the USB port, with spring-loaded covers. The top cover you open to add or remove the drive, the bottom cover would be propped open and spring shut if the cable tie melts and pops the box away from the surface.

I had not thought of this but it is a good idea. There is no requirement that every data recorder survive every crash when most of the accidents (by gross numbers) are in light aviation. The performance specifications for a light aircraft data recorder are not the same for a +12,500 lb GW vehicle which tends to crash less than an order of magnitude than light aircraft.

So now I'm thinking 'ablative' coating and a rudder/tail mount. It doesn't have to survive every crash but enough that we can start to get a statistically significant sample. Did the Seawind have an engine failure? What were the engine metrics?

The only source would be the pilot in ICU and possibly the passenger. You don't suppose they might have been 'pre-occupied' during the emergency?

For my project, I have no problem with making two, ablative coated, USB sticks and mounting them on the tail-wheel spring. I don't even have to change them out unless I have a question about a recent flight and I'll have all of the early flights on that stick.

This is not a hard problem to solve.

Thanks,
Bob Wilson

[steveinindy]

Who is going to tell an investigator they should be looking for a data recording device?

Just mark the thing like is laid out in the AC/FAR regarding recorders. If you do that, it'll be identified most of the time.

I have no problem with making two, ablative coated, USB sticks and mounting them on the tail-wheel spring

You might not want to mount it somewhere prone to shock loading (inadvertent disconnection from the power source if you have a shear mechanism built in) or vibration as this can negatively affect data recording or device longevity. Given my choice in a small plane, I'd argue for either a mounting in the tip of the vertical stab or the tail cone.

[Frank Giger]

Of course we need to back up and think of what the design requirements are.

If it's to be a true "black box" that can stand everything but a nuke strike we're in trouble in a GA aircraft as it's going to weigh a ton and cost a fortune.

However, let's think more along the lines of the typical GA wreck, where the aircraft is largely intact first and then contemplate fire.

The ESD works great in the forced engine out, spin on turn to final, and CFIT wrecks where there is no fire.

For fire, how much does one need to design for? Fifteen hundred degrees? Twenty five hundred? And for how long?

Designing for 100% recovery seems like a dead end to me; a 70% recovery rate would be acceptable in my eyes as a production product for GA aircraft. If a plane were to crash into a building and the whole thing roast it I wouldn't expect recovery.