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user9253
Joined: 28 Mar 2008
Posts: 1938
Location: Riley TWP Michigan
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 Posted: Thu May 22, 2025 10:46 am Post subject: AOA LIMITER |
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Many fatal aircraft accidents are caused by stalling and spinning into the ground.
Why not make airplanes stall proof? This is not a unique idea. Aircraft have been
built with limited control stick travel which prevented stalling. That idea never caught on.
Maybe landing speed was too high. Boeing patented an AOA limiting system.
As far as I know, no such system exists for general aviation. The attached
drawing shows a wedge intended to move upward to limit how far the control
stick can be pulled back, thus preventing a stall. This system would not prevent
the pilot from flaring and landing normally. In fact the pilot would not even
realize that an anti-stall system existed unless he leveled off too high above the
runway and kept trying to pull the stick back further. The AOA Limiter would prevent
stalling and the airplane would mush and fall onto to the runway, landing hard on its main gear.
Compare that to no AOA Limiter installed. The pilot levels off too high above
the runway. Then the plane stalls and noses into the runway. Either way is not desired.
The AOA Limiter system would monitor the AOA information coming from
either an existing EFIS or from a stand alone AOA device. That data would
be sent to a microcontroller which would command a servomotor to drive the
wedge. A cam could be used instead of a wedge.
Many aircraft builders have the skills and smarts to install an AOA Limiter
system in their homebuilt aircraft. We need an electronics guru to design the
circuit and program the microcontroller. Eric?
Comments anyone?
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Eric Page
Joined: 15 Feb 2017
Posts: 257
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| Posted: Thu May 22, 2025 11:07 am Post subject: Re: AOA LIMITER |
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| user9253 wrote: | | Many aircraft builders have the skills and smarts to install an AOA Limiter system in their homebuilt aircraft. We need an electronics guru to design the circuit and program the microcontroller. Eric? Comments anyone? |
That's a very clever idea, Joe. I'm flattered, but I'm afraid that I know virtually nothing about microcontroller programming. I've fiddled around with a system called PICAXE (developed for use in UK schools), primarily because it's programmed in BASIC and I learned a little of that when I was a kid, but even that's a struggle. There was another user here who's a cool hand at programming -- he's helped with other projects -- but I'm ashamed to admit that his name escapes me at the moment...
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dj_theis
Joined: 28 Aug 2017
Posts: 59
Location: Minnesota
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| Posted: Fri May 23, 2025 3:43 am Post subject: Re: AOA LIMITER |
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Just a few thoughts on the concept.
A fail safe software solution is a challenge but “doable.”
A fail safe hardware implementation might be a larger challenge but still achievable.
What would you think of adding a “stick shaker” instead of inserting a mechanical interference?
Dan T.
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Scratch building Sonex #1362
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user9253
Joined: 28 Mar 2008
Posts: 1938
Location: Riley TWP Michigan
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| Posted: Fri May 23, 2025 9:16 am Post subject: Re: AOA LIMITER |
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Dan T.
Thanks for your suggestion.
Anything that will help prevent the pilot from stalling the airplane is beneficial.
But pilots have been known to ignore blaring stall warning horns and stick shakers
and still manage to stall and spin in. A stall proof aircraft will save lives.
The challenge will be designing an AOL Limiter system that will not create
a dangerous situation when it fails.
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alec(at)alecmyers.com
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| Posted: Wed May 28, 2025 2:41 am Post subject: AOA LIMITER |
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The DA42 has (or had - I think it can be removed) a stick limiter to prevent overrotation during a go-around. It was engaged when the flaps were lowered.
How will your system distinguish when it’s safe to allow the AoA to increase for landing, and when it isn’t?
Sent from my iPhone
| Quote: | On May 23, 2025, at 13:17, user9253 <fransew(at)gmail.com> wrote:
Dan T.
Thanks for your suggestion.
Anything that will help prevent the pilot from stalling the airplane is beneficial.
But pilots have been known to ignore blaring stall warning horns and stick shakers
and still manage to stall and spin in. A stall proof aircraft will save lives.
The challenge will be designing an AOL Limiter system that will not create
a dangerous situation when it fails.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=515427#515427
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user9253
Joined: 28 Mar 2008
Posts: 1938
Location: Riley TWP Michigan
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| Posted: Wed May 28, 2025 6:41 am Post subject: Re: AOA LIMITER |
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The AOA Limiter that I envision would not limit the stick to a fixed position.
The aft limit of stick position would contently change and be determined by the AOA.
Think of it as an autopilot, not for heading, but for AOA. The automatic system
would do the same thing that a human does on approach to landing on a short runway.
It would allow the pilot to pull the stick back as far as possible without actually stalling the wings.
If the pilot pulls the stick back too far, then just before the wings stall, the AOA
Limiter would push the stick forward just enough to prevent the stall while still
allowing the plane to fly as slowly as possible.
Think of the AOA Limiter as a muscular flight instructor teaching a student to land
as short as possible while approaching over obstacles. The student is about to
stall right over the trees when the flight instructor overpowers the student
and pushes the stick slightly forward.
The AOA Limiter would allow the pilot to move the stick as normal except it
would not allow the pilot to stall the wings.
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