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Bus Load Analysis

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Jerry Grimmonpre'

Joined: 09 Jan 2006
Posts: 144
Location: Huntley, Illinois 60142

Posted: Mon Feb 06, 2006 8:24 pm Post subject: Bus Load Analysis

Hi all ...



I humbly ask for input on the following and maybe create new thought ...

Load analysis:  Pitot heat load vs. load of AOA (angle of attack) Sport 

instrument.

Rob are you here?



When considering the imbalance of the load effects of these two items ... it 

seems we squander a lot of amps on pitot heat when the AOA could substitute 

while using about .4 amps and include audible warnings, as well, while 

landing at any weight.



In my reading of the Lancair list, I've found there has been zero incidents 

of moisture problems in the  AOA ports in the outer wing D sections.  This 

included heavy rain with the airplane tied outside.  If this port is not 

affected by moisture, it seems to follow that icing may be less of a problem 

with this delta P port.   This applies to the AOA system called AOA Sport, 

where the pressure differential is measured at the outboard wing D section.



When considering pitot heat, as a 7.5A continuous load, it would increase 

most Continuous Bus loads by near 30-40%.  Powering-up an AOA system pales 

in comparison at only .4 amps.



Those of you with the AOA Sport ... have you found any moisture or frozen 

ports?

How many have found pitot heat cleared up their airspeed indications within 

moments of turning on the pitot heat?



What I'm trying to get at here is: do you think pitot heat should be listed 

as continuous amps used, considering the availability of AOA and it's low 

demand on amps?

Regards ...

Jerry Grimmonpre'

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brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Mon Feb 06, 2006 10:06 pm Post subject: Bus Load Analysis

Jerry Grimmonpre wrote:



 	  Quote: 	
		   I humbly ask for input on the following and maybe create new thought ...

 Load analysis:  Pitot heat load vs. load of AOA (angle of attack) Sport 

 instrument.

 Rob are you here?


	


I like AoA. It is one of the most useful instruments in an airplane. I

also know that neither AoA nor ASI are going to be much use when the

wing is iced up. Ice changes the airfoil shape and possibly the

effective angle of incidence. The wing will stall at a different

airspeed and probably a different angle of attack as separation of

airflow is likely to occur sooner.



So it doesn't much matter.



Well, there is one thing: if your ASI is working and you experience

stall buffet at some airspeed, at least the ASI will give you some idea

when you are in the ballpark again. In that it might be of some use if

the wing is iced up. And your AoA pressure ports will probably be

covered with the ice anyway.



But I still like that AoA instrument. I had one on my previous CJ6A and

verified its calibration from 1/4G all the way up to 5Gs. It made flying

acro a lot more comfortable because I could always just take the wing to

zero alpha and wait until I had more airspeed to recover. I never had to

deal with the airplane departing if I didn't want to.



-- 

Brian Lloyd                         361 Catterline Way

brian-yak at lloyd dot com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

- Antoine de Saint-Exupery

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_________________
Brian Lloyd
brian-yak at lloyd dot com
+1.916.367.2131 (voice) +1.270.912.0788 (fax)

I fly because it releases my mind from the tyranny of petty things . . .
- Antoine de Saint-Exupery

jschroeder(at)perigee.net
Guest

Posted: Tue Feb 07, 2006 5:50 am Post subject: Bus Load Analysis

Jerry -



I'm not sure what your point is. The AOA Sport relies on pitot and static  

pressure inputs. Therefore, in known or suspected icing, I would have the  

pitot heat on - to get both airspeed and the AOA. Why would one risk  

losing both by trying to save some juice in the weather?



I have installed this AOA in a Lancair ES. The AOA ports are on the right  

wing and the pitot tube is on the left wing.



Hope this helps.



John

On Mon, 6 Feb 2006 22:22:13 -0600, Jerry Grimmonpre <jerry(at)mc.net> wrote:



 	  Quote: 	
		   What I'm trying to get at here is: do you think pitot heat should be  

 listed

 as continuous amps used, considering the availability of AOA and it's low

 demand on amps?

 Regards ...

 Jerry Grimmonpre'


	


--

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Jerry Grimmonpre'

Joined: 09 Jan 2006
Posts: 144
Location: Huntley, Illinois 60142

Posted: Tue Feb 07, 2006 9:22 am Post subject: Bus Load Analysis

DO NOT ARCHIVE

Hi John ...

Thanks for your note, I was trying to make the point of declaring the 

"constant on" of the pitot heat to be an excessive "charge" to the account 

of bus demand.  Sort of like the "constant on" of a Com radio does not 

consider the moments of transmit to be considered demand on the bus because 

of the duration of transmit time.

I see, from your response, the that the AOA does require pitot/static and, 

of course, that can only come from a non iced system.  I had it in my mind 

that the AOA Sport only required inputs from the two ports on the wing D 

section.   Thanks for your enlightenment.

Regards ...

Jerry Grimmonpre'

 	  Quote: 	

 <jschroeder(at)perigee.net>

 Jerry -

 I'm not sure what your point is. The AOA Sport relies on pitot and static

 pressure inputs. Therefore, in known or suspected icing, I would have the

 pitot heat on - to get both airspeed and the AOA. Why would one risk

 losing both by trying to save some juice in the weather?

 I have installed this AOA in a Lancair ES. The AOA ports are on the right

 wing and the pitot tube is on the left wing.

 Hope this helps.

 John

 On Mon, 6 Feb 2006 22:22:13 -0600, Jerry Grimmonpre <jerry(at)mc.net> wrote:

> What I'm trying to get at here is: do you think pitot heat should be

> listed

> as continuous amps used, considering the availability of AOA and it's low

> demand on amps?

> Regards ...

> Jerry Grimmonpre'

 --

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mprather(at)spro.net
Guest

Posted: Tue Feb 07, 2006 12:46 pm Post subject: Bus Load Analysis

Hi Jerry,



Interesting question..  Comments embedded.



 	  Quote: 	
		   

 <jerry(at)mc.net>



 Hi all ...



 I humbly ask for input on the following and maybe create new thought ...

 Load analysis:  Pitot heat load vs. load of AOA (angle of attack) Sport

 instrument.

 Rob are you here?



 When considering the imbalance of the load effects of these two items

 ... it  seems we squander a lot of amps on pitot heat when the AOA could

 substitute  while using about .4 amps and include audible warnings, as

 well, while  landing at any weight.



 In my reading of the Lancair list, I've found there has been zero

 incidents  of moisture problems in the  AOA ports in the outer wing D

 sections.  This  included heavy rain with the airplane tied outside.  If

 this port is not  affected by moisture, it seems to follow that icing

 may be less of a problem  with this delta P port.   This applies to the

 AOA system called AOA Sport,  where the pressure differential is

 measured at the outboard wing D section.




	


I don't know that you could say that being impervious to rain has any

bearing on being impervious to ice.  Even if ice doesn't end up covering

either port, it changes the airflow over the wing, and lowers the angle of

attack of stall.  I had a fortunate opportunity to ride around in the

right seat of a Pilatus PC-12 last week..  The pilot was explaining to me

that when prop deice, and the engine inertial seperator were enabled, the

stick shaker/pusher would activate at 8deg less AoA(!).  The system

assumes that when you have both systems enabled, it's pretty likely you

are in icing conditions.



 	  Quote: 	
		   When considering pitot heat, as a 7.5A continuous load, it would

 increase  most Continuous Bus loads by near 30-40%.  Powering-up an AOA

 system pales  in comparison at only .4 amps.



 Those of you with the AOA Sport ... have you found any moisture or

 frozen  ports?

 How many have found pitot heat cleared up their airspeed indications

 within  moments of turning on the pitot heat?




	


Typical use of pitot heat is to power it up whenever you are in visible

moisture - the idea is that you don't want a dead ASI to be the indication

that the pitot heat should be turned on.



 	  Quote: 	
		   What I'm trying to get at here is: do you think pitot heat should be

 listed  as continuous amps used, considering the availability of AOA and

 it's low  demand on amps?


	


That's a slightly different question..  The pitot heat is a continuous

load - like nav lights.  Unlike flap motors and electric landing gear

equipment, which are momentary loads.  The real question I would ask is

whether either an AOA or the ASI is required in order to comfortably

complete any flight you intend to use the airplane for.



I don't know that this rationale is backed up by good statistics, but if I

were planning to use an airplane for lots of real IFR work, I'd probably

want a power budget that allowed me to run the pitot heat after the

failure of my primary engine driven electrical power source.  Especially

with a naturally aspirated (rather limited service ceiling) engine.  If

however, my airplane was going to be used for occasional scud avoidance -

punch through a layer in order to find some sunshine when it's cloudy on

the ground, I wouldn't worry about having pitot heat be supported by the

endurance bus.  I figure that the intersection of time when I have an

electrical failure, and when I can't comfortably complete a flight without

the ASI/AoA would be exceedingly low.

 	  Quote: 	
		   Regards ...

 Jerry Grimmonpre'




	


Matt-

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Jerry Grimmonpre'

Joined: 09 Jan 2006
Posts: 144
Location: Huntley, Illinois 60142

Posted: Tue Feb 07, 2006 5:02 pm Post subject: Bus Load Analysis

DO NOT ARCHIVE

Hi Matt ...



 	  Quote: 	
		   Typical use of pitot heat is to power it up whenever you are in visible

 moisture - the idea is that you don't want a dead ASI to be the indication

 that the pitot heat should be turned on.


	


There-in lies the problem.  AOA Sport will not indicate properly with an 

iced pitot/static because AOA Sport relies on those two to feed the computer 

creating the progressive decay indications of the AOA LED's.  It would seem 

great to have an AOA idicator impervious to icing but the reality is the 

wing's AOA and it's resultant lift reports the truth ... the wing demands 

clean airflow.  Therefore an iced pitot/static OR AOA ports will not report 

a reliable warning indication so plan to leave the pitot heat on when in 

icing conditions and forget the AOA as being ice proof.

 	  Quote: 	
		  

> What I'm trying to get at here is: do you think pitot heat should be

> listed  as continuous amps used, considering the availability of AOA and

> it's low  demand on amps?


	


I just answered my own question .... yes, leave pitot heat on continuously 

in icing conditions and therefore plan the bus load analysis for the 7.5 

amps required.

 	  Quote: 	
		  

  The real question I would ask is

 whether either an AOA or the ASI is required in order to comfortably

 complete any flight you intend to use the airplane for.


	


An aviator who knows the airplane will know what power/attitude/descent rate 

will result in getting to the end of the runway in a normal landing 

configuration.



 	  Quote: 	
		  

 I don't know that this rationale is backed up by good statistics, but if I

 were planning to use an airplane for lots of real IFR work, I'd probably

 want a power budget that allowed me to run the pitot heat after the

 failure of my primary engine driven electrical power source.  Especially

 with a naturally aspirated (rather limited service ceiling) engine.  If

 however, my airplane was going to be used for occasional scud avoidance -

 punch through a layer in order to find some sunshine when it's cloudy on

 the ground, I wouldn't worry about having pitot heat be supported by the

 endurance bus.  I figure that the intersection of time when I have an

 electrical failure, and when I can't comfortably complete a flight without

 the ASI/AoA would be exceedingly low.



 I agree.
	


 	  Quote: 	
		  >

>



 Matt-

Jerry Grimmonpre'

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