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LRI Probe Question

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pavel569

Joined: 21 Dec 2007
Posts: 77

Posted: Wed Jan 09, 2008 8:41 am Post subject: LRI Probe Question

There is probably more than 10 topics about LRI or AOA - yes or not, buy or make etc. I have a machine shop and being cheap means I want to make it myself. I went through all these discussions here to find a recommended drawing for a probe. 

http://www.ch601.org/resources/aoa/aoa.htm



If I look at the drawing it just doesn't give a sense to me. Both the holes opening are at the same angle - they are parallel so no matter what the angle of  the probe with a wing is, they will have to read the same pressure. I see that the opening is actually not round but oval so it will have more/less area for air to come in but is that difference enough to have the right impact on the gage? What my common sense is telling me is that I have to have to drill the hole at port openings at a different angle - 45% so higher angle of attack will increase the ram pressure in lower probe.

One more thing - sharp or round edges. In my opinion it doesn't matter. Most important thing would be to have the flowing air coming only into the hole area opening - not to cumulate more air going in from other surfaces like pouring water through a funnel. So if I keep the probe edge flat just around the inlet, I should be fine. I'll make a few extras, so it may be for grab, I guess.

Please, let me know what you think.

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_________________
Pavel
CA
Zodiac 601XL
Stratus Subaru EA-81
Tail, flaps, ailerons, wings, fuselage, canopy done ...
"do not archive"

dbortol

Joined: 02 Sep 2006
Posts: 46

Posted: Wed Jan 09, 2008 11:17 am Post subject: LRI Probe Question

The angle of the ports doesn't matter, within reason. It's the angle of the surfaces to the relative airflow that causes a differential pressure.



On Jan 9, 2008 11:41 AM, pavel569 < pm569(at)hotmail.com (pm569(at)hotmail.com)> wrote:

[quote]--> Zenith-List message posted by: "pavel569" < pm569(at)hotmail.com (pm569(at)hotmail.com)>



There is probably more than 10 topics about LRI or AOA - yes or not, buy or make etc. I have a machine shop and being cheap means I want to make it myself. I went through all these discussions here to find a recommended drawing for a probe. 

http://www.ch601.org/resources/aoa/aoa.htm



If I look at the drawing it just doesn't give a sense to me. Both the holes opening are at the same angle - they are parallel so no matter what the angle of  the probe with a wing is, they will have to read the same pressure. What my common sense is telling me is that I have to have to drill the hole at port openings at a different angle - 45% so higher angle of attack will increase the ram pressure in lower probe. 

One more thing - sharp or round edges. In my opinion it doesn't matter. Most important thing would be to have the flowing air coming only into the hole area opening - not to cumulate more air going in from other surfaces like pouring water through a funnel. So if I keep the probe edge flat just around the inlet, I should be fine. I'll make a few extras, so it may be for grab, I guess. 

Please, let me know what you think.



--------

Pavel

CA

Zodiac XL N581PM





Read this topic online here:



  [quote][b]

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japhillipsga(at)aol.com
Guest

Posted: Wed Jan 09, 2008 11:18 am Post subject: LRI Probe Question

Pavel, I understand your concern. I have a LRI proble mounted under my XL's left wing that was made to these plans and it works well. Use it every time I fly. The probe is an aluminum bar cut square. One hole comes out the end and the second hole out the side. The corner of the bar is the split line. To adjust it to the planes stall you adjust the probe up or down. Best of luck, Bill

 

 --

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psm(at)att.net
Guest

Posted: Wed Jan 09, 2008 11:20 am Post subject: LRI Probe Question

Hi Pavel,



I built my own LRI probe and bought a new gauge from the manufacturer.



My take on the holes is you drill them just as shown in the 

drawing.  I haven't flown it in my plane yet (slight lack of flying 

plane) but I did a little testing while holding it out the window of 

a moving car.  It works fine.



I think the part you might not be considering is the sharp corner 

between the two input holes.  This edge divides the air flow so a 

portion goes in the upper sense hole and a different portion goes in 

the lower hole.  I think it is important for this edge to be sharp 

and the space from the edge to the sense holes to be flat.



Have fun,



Paul

XL fuselage

At 08:41 AM 1/9/2008, you wrote:

 	  Quote: 	
		  There is probably more than 10 topics about LRI or AOA - yes or not, 

buy or make etc. I have a machine shop and being cheap means I want 

to make it myself. I went through all these discussions here to find 

a recommended drawing for a probe.

http://www.ch601.org/resources/aoa/aoa.htm



If I look at the drawing it just doesn't give a sense to me. Both 

the holes opening are at the same angle - they are parallel so no 

matter what the angle of  the probe with a wing is, they will have 

to read the same pressure. What my common sense is telling me is 

that I have to have to drill the hole at port openings at a 

different angle - 45% so higher angle of attack will increase the 

ram pressure in lower probe.

One more thing - sharp or round edges. In my opinion it doesn't 

matter. Most important thing would be to have the flowing air coming 

only into the hole area opening - not to cumulate more air going in 

from other surfaces like pouring water through a funnel. So if I 

keep the probe edge flat just around the inlet, I should be fine. 

I'll make a few extras, so it may be for grab, I guess.

Please, let me know what you think.



--------

Pavel

CA

Zodiac XL N581PM

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cookwithgas

Joined: 06 Nov 2007
Posts: 159

Posted: Thu Jan 10, 2008 7:44 am Post subject: Re: LRI Probe Question

Pavel:



I have one on my right wing mounted approximately where the pitot is mounted on the other wing.  I made it exactly to the drawings and it works.  I made one for Ron DeWeese in Georgia and he rounded everything off so it looks better and his works well also.  



I've only had one test flight but will be tweaking some things including the LRI system on Saturday if we don't get too much snow today.  It is pretty cool to watch the needle rise as you gain speed.  Here are a few pictures of my installation:



http://www.cooknwithgas.com/12_1_07_LRI_ASL2.JPG

http://www.cooknwithgas.com/12_1_07_LRI_ASL.JPG



I made probes for several other builders and some sent me pictures that I posted here:



http://www.cooknwithgas.com/LRI.html



You will notice that some are rounded off and some are not.  



I'll have more to report after some more flight testing. 



Scott Laughlin

601XL/Corvair

Omaha, Nebraska

www.cooknwithgas.com

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pavel569

Joined: 21 Dec 2007
Posts: 77

Posted: Fri Feb 22, 2008 11:18 am Post subject: Re: LRI Probe Question

Does anyone of you using a holes in the wing as a ports for AOA? IMHO it is the most accurate method. Any disadvantages, bugs - other than possibilities of insects or ice plugging the hole? They are really small - .060" so there shouldn't be too much problems with flies etc. And I really don't like the look of the probe protruding the wing.

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Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

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_________________
Pavel
CA
Zodiac 601XL
Stratus Subaru EA-81
Tail, flaps, ailerons, wings, fuselage, canopy done ...
"do not archive"

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