Audio annunciator?

Hello all,

I'm thinking of building an audio annunciator kind of like the P2 but modern and better (theirs was designed in the mid-90s). Would there be any interest in this kind of thing? It would annunciate:

* Overspeed
* Underspeed (e.g. climbing at < Vx, too slow on base to final, etc)
* An analog "slow horn" increasing in volume as you get closer to stall speed (say, Vs to Vs+10kts)
* Low oil pressure
* Low vacuum (for gyros, etc)
* Hobbs output to track time in service instead of tach time (which gets you lower hours for longer overhaul intervals)

The underspeed and graduated stall warnings are the most useful I think. Stall horns on most aircraft tell you when you're already in a stall, which is just a bit too late in most cases when you're really in a dangerous spot (e.g. base to final turns).

All these speeds would have parameters you could set via USB, enable/disable them, etc.

It would be designed to DO-160 and DO-254 standards for possible later STC certification, so it won't be a bare PCB with ribbon cable, etc.

Any thoughts? Do you guys/gals see a place for this in the experimental market?

Thanks,
Ray

Hello,

Anybody trying this based on Arduino?
https://www.arduino.cc/

Tach time on many aircraft increases slower than hobbs. Flight schools bill on hobbs for that very reason.

It's a good idea but a little late - some (many?) of the EFIS boxes (I have GRT, it's one) already have annunciated warnings, progressive AOA warnings, etc. So I'm not sure how big the potential market is.

RayA said:

The underspeed and graduated stall warnings are the most useful I think. Stall horns on most aircraft tell you when you're already in a stall, which is just a bit too late in most cases when you're really in a dangerous spot (e.g. base to final turns).

Click to expand...

To be of any practical use here, you need to trigger off AOA, not speed. I do agree that traditional stall warning (horns, etc) trigger too close to stall to be actually useful. A graduated tone starting right about at approach AOA would probably work really well, but as others have noted it's already built into a lot of the EFIS products available.

A standalone progressive audio AOA (or progressive audio with display) might be more useful for the certified side, where most aircraft are older and don't have an EFIS.

It may be a fun project, but there are already a number of actual "ACU's" (Annunciator Control Units) on the market with multi channel capability visual and aural capability (like the AN21 16+5 channel unit from Flight Data Systems).

To that end, it's the input you still need to come up with, either as a feed from something, or utilizing a sensor/switch/input of some sort. Once you do that, you can pretty much take the General Purpose or Discrete inputs on most EFIS systems out there currently and program those channels to do any number of different functions as indicated.

I guess what I'm saying in the end from a standpoint of someone who sells a whole lot of avionics and electrical goodies that it may be a fun project, but to be blunt there is virtually no reasonable space/need for an additional unit in the market (in my opinion)....or not enough to make it really commercially viable - though you may be able to support a number of units on a hobby sort of basis.

Just my 2 cents as usual!

Cheers,
Stein

Audio response



Now for $2.73 ea, buy about 10 of these boards. Build a box, each has a mic, so record (10 sec) messages. Take each output and feed into a 600 ohm resistor, then to aux input on the audio panel. Now record whatever you like and trigger each module as needed. Better yet; have your wife record the messages so you would be sure to "PAY ATTENTION (insert her favorite response) YOUR ABOUT TO STALL"
John

RayA said:

Stall horns on most aircraft tell you when you're already in a stall, which is just a bit too late in most cases when you're really in a dangerous spot (e.g. base to final turns).

Click to expand...

This isn't true for certified aircraft:

Sec. 23.207 Stall warning.

(c) During the stall tests required by Sec. 23.201(b) and Sec. 23.203(a)(1), the stall warning must begin at a speed exceeding the stalling speed by a margin of not less than 5 knots and must continue until the stall occurs.

(e) During the stall tests required by Sec. 23.203(a)(2), the stall warning must begin sufficiently in advance of the stall for the stall to be averted by pilot action taken after the stall warning first occurs.

Click to expand...

Jordan1976 said:

This isn't true for certified aircraft:

Sec. 23.207 Stall warning.

(c) During the stall tests required by Sec. 23.201(b) and Sec. 23.203(a)(1), the stall warning must begin at a speed exceeding the stalling speed by a margin of not less than 5 knots and must continue until the stall occurs.

(e) During the stall tests required by Sec. 23.203(a)(2), the stall warning must begin sufficiently in advance of the stall for the stall to be averted by pilot action taken after the stall warning first occurs.

Click to expand...

Click to expand...

I'd argue it's still not enough. A stall warning that only kicks in on the verge of stall and provides only enough warning to be effective if action is "taken after the stall warning first occurs" doesn't provide the pilot enough time to recognize that he's in a pickle. Condition (c) requires 5kt warning in a 1g stall decelerating at 1kt/sec. That's 5 seconds' warning. Condition (e) only specifies that stall must not occur if the pilot takes immediate, decisive action-i.e. much less than 5 seconds' warning. But this is where most people get themselves in trouble. Almost nobody stalls and spins from level 1g flight; rather it almost all happens during turns and maneuvering flight. And I think the biggest reason for that is that pilots eat up their AOA margin above stall without realizing it; they don't know what their AOA is nor what it's doing until the stall warning sounds.

Check out this graph, which shows normalized AOA as a function of speed:

The red line is Vs. The yellow line is the onset of stall buffet in the RV-6 I sometimes fly. The gray line is the normalized AOA equivalent of a stick shaker activation in a large aircraft, and coincidentally is about 5kt above Vs in this example. The blue line is Vref.

Assuming the aircraft maintains Vref, notice how the 30 degree bank level turn leaves you at about the same AOA as level flight at 1.2Vs (about 6-7kt slow), and a 45 degree level bank leaves you at the same AOA as level flight at 1.1Vs. Especially in the latter case, you're operating right on the verge of a stall warning and yet there are no overt signs, no warning. Most pilots have no idea just how much closer they'd be to stalling in that situation.

That's why I don't think the solution is to make the warning louder or make it verbal or add a stick shaker, especially if all we do is keep the same activation points. To be effective, a stall warning would need to anticipate the rate of AOA change and fire early in cases of accelerated stalls or rapid deceleration; but I think a better approach is to use the indicators and audio tones to give pilots trend information and a better idea of exactly where they are on that curve to the left of the blue line, not only the gray or yellow ones. The idea is to have an accurate gas gauge, not just a "running on fumes" light.