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RF Question on Hull Penetration (FAA Approval)?

iaw4

Well Known Member
dear colleagues---I know this idea has come up before, but maybe I can actually make it happen.

I am thinking about designing a sensor that tells you how many feet above the ground you are, with accuracy in inches from about 10-20' altitude. it then relays this altitude for display on an iPad or LED display or audio. I can design the sensor package to be very flat and very small, to come with a built-in battery, and to stick via Velcro safely to the bottom of an airplane even at 200mph.

I would not want to design it just for experimental use on Vans, but also for small single-engine certified airplanes (at flight schools). presumably sticking some velcro onto an aircraft is not illegal even for certified airplanes.

1. is my understanding correct that if something is portable and not permanently attached, then the FAA will not force me to certify it? (I assume that it would be too costly to get through an FAA certification. I have heard horror stories of a million dollars for a cough and years of bureaucratic delays.)

2. if I drilled a tiny hole into the hull, so that my sensor could stick a very small 2.4GHz antenna through the bottom when attached, would the FAA come calling?

3. alternatively, how could I get data into the cockpit? I am betting that Blutooth won't work because of the aluminum hull and short wavelength at 2.4GHz. would a 10 meter band signal make it around the hull into the cockpit, so that a gateway could then relay it to an iPad? has anyone experimented with something like it?

any advice would be highly appreciated. if you would want to get involved with the effort and/or have experience, please let me know. and, of course, if you already know of such a device, please let know, too.

sincerely, /iaw
 
You might want to take a look at the FAA's NORSEE policy. I think this would fall into that category, where approvals are a fair bit easier.

It would be some paperwork but even with a hull penetration I can't imagine it being horrible, as long as you're only talking unpressurized aircraft.
 
I can't imagine that a small hole would prompt an FAA problem for an EAB aircraft. After all, there are lots of different configurations for antennae locations, wiring routings, exterior lights, OAT probes, etc. What's wrong with one more hole?

For certified aircraft, you probably need to ask a better expert than me. But bear in mind that people do attach smoke systems, GoPro cameras, etc without major problems. It sounds like your thing isn't much worse than any of those.

My one question for you is whether you are reinventing the wheel. Radar altimeters already exist. I flew a Centurion once that had one. Pretty standard on military aircraft. I think they are standard on commercial planes, too. Not sure how your product differs, but getting something certified that then competes against the big boys in the avionics world might be some uphill battles.
 
"reinventing the wheel"...pun.

yes, indeed. however, I had not seen the $850 solution for small airplanes. in fact, this is pretty close to what I wanted to design, so there is no more need here.

mille grazie.
 
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