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Date: Wed, 13 Jan 2010 11:07:58 -0500
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From: Hamid Wasti <hwasti@lm50.com>
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Subject: Re: [LML] Re: Do-it-yourself AOA Project
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Wolfgang,

Unless you have access to a secret source of information not available 
to the rest of us, your comments are completely baseless. Have you 
actually looked at the schematic posted on BakerAircraft.com's website 
at http://www.barkeraircraft.com/files/AOA_rDisplay.pdf ? Have you 
actually understood it?

If you actually study the circuit on page 6, you will see that the LEDs 
are connected to the "+14V In" input voltage and they are set up to run 
at 24mA not the "typical 10mA" that you pulled out of thin air.  At 
13.8V input and a drop of 2.2V on the LEDs, the chip has to dissipate 
11.6V at 24mA or 278mW. At a Theta-J-A of 55C/W, this leads to a 15C 
increase per LED that is actually on.

Next time please study the subject matter before posting.

Regards,

Hamid

Wolfgang wrote:
> The home made AoA indicator from BarkerAircraft.com has a 5V 
> regulator. With that running the electronics and a 2.2V typical 
> forward V @ 10ma on the LED's, that leaves 2.8V at 100ma total 
> dissipated by the chip with all LED's illuminated. The total 
> dissipation of the chip comes out to about 0.28W. I don't see that 
> raising the chip temperature to any where neat a 100C limit.
>  
> Wolfgang
> ------------------------------------------------------------------------
> From: 	Hamid Wasti <hwasti@lm50.com>
> Sender: 	<marv@lancaironline.net>
> Subject: 	Re: [LML] Do-it-yourself AOA Project
> Date: 	Mon, 11 Jan 2010 19:41:18 -0500
> To: 	lml@lancaironline.net
>
> 	
>
>  
>
> It is an interesting product with some clever ideas, but a very poor 
> implementation. It is unlikely that it will keep working reliably for 
> long in the real-world/real-aircraft environment.
>
> The system does not take into account flap deployment. Anyone here use 
> flaps?
>
> The "normal" position of the probe is with the Hall sensor at the zero 
> point of the magnet. Anyone concerned about the fact that the system 
> could report "normal" output if the probe or the magnet falls off?
>
> Even the most rudimentary analysis of the Hall sensor's output as its 
> temperature varies from -20C to +50C would reveal a potential for some 
> worrisome inaccuracies. You could stall several LEDs before you expect 
> to, or you could be several LEDs away from a stall when the system 
> says you should be stalling. Would you be more or less likely to 
> actually stall in these situations?
>
> The design does not take into account the fact that each LED that is 
> on will cause the main IC's temperature to rise by about 15C. A little 
> slow flight practice with a 6 LEDs on and the IC is well past its 100C 
> limit, generating a burning smell and possibly smoke. Same would 
> happen after an engine out as you glide down at best glide speed. Can 
> you think of a worse time to find smoke in the cockpit?
>
> This is just a partial list of issues, but I think it gets the picture 
> across. The only thing worse than not having something is having 
> something that is not reliable.
>
> Regards,
>
> Hamid
>
> Gary Fitzgerald wrote:
>
>     /He has an article on this project in the Dec. 2008 edition of Sport
>     Aviation. Interesting use of a Hall Effect sensor./
>