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lcottrell
Joined: 29 May 2006
Posts: 1494
Location: Jordan Valley, Or
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 Posted: Wed May 09, 2012 10:15 am Post subject: Pitot tubes and air speed Plus Wind on the Alvord |
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You may remember that I posted an email about the difference made in indicated airspeed due to the angle of cut on the pitot tube some time ago. To recap the idea came from John H about cutting the pitot tube at an angle to allow a correct reading when landing in a three point stance. I thought the idea had merit, and cut mine at about a 20 degree angle. I found that angle was too much and lowered my ASI reading by about 10 MPH. I decided that I would decrease the angle to see if that would better reflect what I see on my GPS. I cut it to about 40 degrees this morning and went for a flight to the Alvord and found that it read within about 2 MPH of what I was seeing on my GPS. Much better, much nicer.
My conclusion is that your ASI can be adjusted by how much air pressure you allow into your pitot tube. Perfectly round uncut tube allows the least airpressure due to the overall smaller size of the opening. Longer the angle, more opening to push air into the tube. Of course I could be wrong about the airpressure, but I am not wrong that the angle affects the reading on your ASI. Now of course I have a commercial static tube fitting mounted on the side of my plane.
If your ASI is not reading correctly, give it a try. If you don't like it you can always cut it back to square and not lose more than 1/4 inch off the overall length.
As I said I visited the Alvord Desert this morning. We have had a greatly reduced rain fall here in the High Desert this fall. So far here at the house we have only had 3.25 inches of rain so far since November. That may seem insignificant to most of you, but it is pretty close to normal here. The Water this spring is about where it was last year in September. After I made a circle of the Lake bed and was heading home I saw that someone had tossed out a tire on the Lake bed. After cussing pilgrims in general I noticed that there was visible evidence of the wind this spring.
Larry
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neilsenrm(at)gmail.com
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| Posted: Wed May 09, 2012 12:57 pm Post subject: Pitot tubes and air speed Plus Wind on the Alvord |
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Larry
As always great photos and the videos you share with us are wonderful.
The photo of the tire is impressive but I suspect that the tire was floating during most of its journey.
do not archive
Rick Neilsen
Redrive VW Powered MKIIIC
On Wed, May 9, 2012 at 2:14 PM, Larry Cottrell <lcottrell1020(at)gmail.com (lcottrell1020(at)gmail.com)> wrote:
[quote]You may remember that I posted an email about the difference made in indicated airspeed due to the angle of cut on the pitot tube some time ago. To recap the idea came from John H about cutting the pitot tube at an angle to allow a correct reading when landing in a three point stance. I thought the idea had merit, and cut mine at about a 20 degree angle. I found that angle was too much and lowered my ASI reading by about 10 MPH. I decided that I would decrease the angle to see if that would better reflect what I see on my GPS. I cut it to about 40 degrees this morning and went for a flight to the Alvord and found that it read within about 2 MPH of what I was seeing on my GPS. Much better, much nicer.
My conclusion is that your ASI can be adjusted by how much air pressure you allow into your pitot tube. Perfectly round uncut tube allows the least airpressure due to the overall smaller size of the opening. Longer the angle, more opening to push air into the tube. Of course I could be wrong about the airpressure, but I am not wrong that the angle affects the reading on your ASI. Now of course I have a commercial static tube fitting mounted on the side of my plane.
If your ASI is not reading correctly, give it a try. If you don't like it you can always cut it back to square and not lose more than 1/4 inch off the overall length.
As I said I visited the Alvord Desert this morning. We have had a greatly reduced rain fall here in the High Desert this fall. So far here at the house we have only had 3.25 inches of rain so far since November. That may seem insignificant to most of you, but it is pretty close to normal here. The Water this spring is about where it was last year in September. After I made a circle of the Lake bed and was heading home I saw that someone had tossed out a tire on the Lake bed. After cussing pilgrims in general I noticed that there was visible evidence of the wind this spring.
Larry
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If you forward this email, or any part of it, please remove my email address before sending.
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lcottrell
Joined: 29 May 2006
Posts: 1494
Location: Jordan Valley, Or
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| Posted: Wed May 09, 2012 1:18 pm Post subject: Pitot tubes and air speed Plus Wind on the Alvord |
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I wouldn't bet on the floating part at all. If you blow it up and look at it closely You will see that there is mud pushed up for about 10 inches on either side. Here at the house, 36 miles away, we had several days with wind as high as 69 MPH for an extended period.
Larry
On Wed, May 9, 2012 at 2:56 PM, Rick Neilsen <neilsenrm(at)gmail.com (neilsenrm(at)gmail.com)> wrote:
| Quote: | Larry
As always great photos and the videos you share with us are wonderful.
The photo of the tire is impressive but I suspect that the tire was floating during most of its journey.
do not archive
Rick Neilsen
Redrive VW Powered MKIIIC -Matt Dralle, List Admin. _blank">http://www.matronics.com/contribution
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Jason Omelchuck
Joined: 07 May 2009
Posts: 120
Location: Portland Oregon
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| Posted: Thu May 10, 2012 7:25 pm Post subject: Re: Pitot tubes and air speed Plus Wind on the Alvord |
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My guess is the tire was not floating but sliding on a film of goo when it rained. There are rocks in the Mojave that do the same thing
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