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While my own research makes plain that the Cub-owning community seems to consider the idea of installing even the most basic autopilot into a Cub a mortal sin, there are scattered accounts on the web of J-3 owners operating with installed autopilots (mostly for long-distance cross country flying).

But as I tried to determine what such a modification would cost, I quickly discovered that autopilots are expressly, explicitly, and strictly the realm of STCs (emhpasis added):

D.13h - Autopilots (AP), Flight Guidance Systems, and automatic flight control systems (AFCS) or flight directors (FD) - STC

Meaning that nothing less than a pre-existing Supplemental Type Certificate would make such an installation legal. Since STCs are pursued by the aircraft manufacturers (or the 3rd party vendor who wants to open the market for their product), I presume the costs of such are prohibitive (millions of dollars).

Are the folks claiming to have such equipment making it up? If not, how did they get around the lack of any existing autopilot-related STC for the J3?

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    $\begingroup$ The lack of an electrical system is a teeny tiny impediment for a J-3. But assuming you had an electrical system, there's nothing really stopping you except mental health laws against developing insane and pointless ideas. $\endgroup$
    – John K
    Apr 12 at 19:23
  • $\begingroup$ Part 43 (law.cornell.edu/cfr/text/14/appendix-A_to_part_43) seems to strongly disagree? $\endgroup$ Apr 12 at 19:37
  • $\begingroup$ The autopilot was invented in 1912, so it is possible a few got "grandfathered" in for cross country, perhaps for one person and a lot of additional fuel. $\endgroup$ Apr 12 at 20:10
  • $\begingroup$ No nothing to stop you if the airplane has an electrical system and you want to go to all the trouble. Only a crazy person would though. which was my point. And the J-3 doesn't have, you know, an electrical system. $\endgroup$
    – John K
    Apr 12 at 21:10
  • $\begingroup$ @JohnK I must completely misunderstand the whole point of Supplemental Type Certificates then, and regulations regarding major modifications to aircraft. Adding an electrical system (its own major modification) doesn't seem any harder than adding the autopilot itself. So if there's something I'm fundamentally missing about the law here, I'd love to have that clarified and would accept that as an answer. $\endgroup$ Apr 12 at 21:59

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Early Piper Cubs had no electrical system so an autopilot install, forgetting about certs for a minute, was simply not possible for a good chunk of the aircraft's history. But a lot has changed since the cubs first rolled out of Lock Haven over 80 years ago and electrical systems have been added to some aircraft.

Its been added successfully (it seems) to some Super Cubs and there are lots of aircraft that now fall under the "Cub" header.

If you are talking strictly about the early J3 Cubs which barely have the useful load for two modern sized adults, then adding an electrical system, servos, and the required avionics becomes a practical issue at some point. The new glass units that can drive autopilots make this more feasible.

I think it ultimately comes down to a limited use case and little drive for getting one certified by any major manufacturer. Most of the Cub owners I know are either flying low and slow, doing aerobatics (in some Cub variant), landing on river banks or mountain tops, or towing banners on clear days. These are not really autopilot-required situations as they are basically all VFR flying and some sort of special case at that. While I'm not saying you can't use an autopilot to fly VFR the real value (for the flying I do regularly) is a fully coupled IFR approach in hard IMC down to minimums, or reducing work load on a long XC flight, neither of which I really see people doing in Cubs. Again this may just be the Cub owners I have encountered, and with a top speed of ~83MPH in a J3 you may as well drive these days...

The companies that sink time and money into building certified units likely also have this view and the numbers just don't drive the certification of a unit for an aircraft no one will install it in and an airframe that may not even be able to support it in the first place.

So, urban myth, maybe, statistically unlikely, I think so.

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    $\begingroup$ "Its been added successfully (it seems) to some Super Cubs and there are lots of aircraft that now fall under the "Cub" header." This is probably where I'm running into confusion, the word 'Cub' has lost its meaning in a lot of ways. $\endgroup$ Apr 14 at 14:53
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I cannot say whether autopilots on J3 cubs are a real thing or not, but it is possible from a regulatory point of view because you only need an STC if you want your airplane to have a type certificate. If you make a modification which would require an STC where none exists then you invalidate your type certificate and your aircraft is unairworthy. You have two choices then (this is for FAA), you can remove the modification and make it conform to the standard, or you can apply for a special airworthiness certificate, making it an experimental aircraft.

An experimental category aircraft will be issued a special airworthiness certificate and still be flown, albeit with limitations, i.e. only day VFR over non-built-up areas. To get that certificate the airplane must be shown to be safe with the modifications. So, you can do all manner of weird stuff as long as it's not going to kill you or anyone else without having an STC. Regulations differ across the world but most regulations I've seen have a similar structure. For example in the UK you would look to fly it under a Certificate of Airworthiness (CofA).

STCs cost a great deal of money because of all of the testing that has to be done to obtain them, so there has to be a compelling finance case to be worth it. Not enough people would want or be able to pay for an autopilot on a J3 for it to make money, so there's no STC for it. This is likely because the cub is one of the worst possible options for long cross country flights due to its slow speed. However, there's nothing stopping you from doing it as long as it could be done safely.

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  • $\begingroup$ Both you, and some commenters, have made it sound like STCs are things that people can just do? The people who purportedly fly these things with APs and radios, don't exactly strike me as 1%ers so where could the millions of dollars in prototyping/engineering have come from in those cases? $\endgroup$ Apr 13 at 12:34
  • $\begingroup$ What I'm saying is that you don't need an STC for an experimental airplane @WilliamWalkerIII. While an individual could theoretically develop a STC, typically that would be a manufacturer. $\endgroup$
    – GdD
    Apr 13 at 13:09
  • $\begingroup$ @GbD Okay. The experimental status is interesting. How densely populated can you get away with? I'm not planning on buying a J-3, but I am planning on flying LSAs and experimental stuff seems to be restricted in the same ways... except I live in the Boston area, lots of B and C airspace, which is obviously out, but can I fly out of class D? $\endgroup$ Apr 13 at 13:20
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    $\begingroup$ You can fly in any class of airspace with an experimental airplane as long as it has the equipment required for that airspace. Why don't you read up on Part 91.319 of FAR/AIM. $\endgroup$
    – GdD
    Apr 13 at 13:26

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