Fabricating velocity probes

[larrycavan]

"It is a wise man that learns from his mistakes, but it is a wiser man that learns from the mistakes of others. "

We can all learn plenty from each other

[slracer]

Ok John, Neat trick! The header says you made the last post at 10:30AM, but it doesn't show up on my computer. How did you do that? :p :p -- Doug

[jfholm]

If it is the post I am thinking about I had mad some spelling errors and went back to correct them. I did not want to show how dumb I really am. But when I hit add modified post it disappeared and gave me an error message. I did a screen pop of the error message and was going to post it so Bruce could see it. This has happened a couple of times to me and I think it happened to Ed last week.

John

[bruce]

Seems there was a problem with the forum host this morning could be why the post disappeared.

A loss of one or two posts from time to time is a small price to pay as apposed to me losing all the posts to a forum upgrade . . . so I keep plugging along with the software I am currently running.

[slracer]

John, Better that the gremlins get you than that they get hjbvcwoiuyv5i87qvcwnungviv8hoij8hj3987vthom5vgu!

Doug :p

[jfholm]

Bruce, believe me I am not complaining. It was not an important post anyway. Maybe it was just God watching over your forum :;):

John

[bruce]

Oh my! I can't imagine you two in the same room together LOL

[slracer]

Bruce, Have one of your old spy buddies , oops, I meant work mates, put a satellite camera over Salt Lake on Aug 5. I'll be passing through on a road trip on my way to Bonneville and plan on meeting John. Shouldn't be hard to find us as I will be in my pickup with one partially complete race bike and a pit bike in the back! -- Doug

[bruce]

You guys better take some pics to post here!!

[jfholm]

I see what you mean Doug - I just saw this blank deal how weird is that?
John

[jfholm]

Well here is the day of reckoning on Doug's pitot tubes. Now all you start humming the Jeopardy tune for 30 seconds and then I will post . . . . . :;):

I built a calibration tube which I will post pictures of at the bottom. This was so I could make sure I was repeating and accurate and could verify the results.

I used Three ways to calculate. The readings in Port Flow Analyzer from Performance Trends, a math formula that I happen to get from an older post by Larry Cavanaugh, thanks Larry, and the velocity spreadsheet that Larry had posted.

Doug, are you sweating it yet? Hee Hee.

The test tube is 1.600" in diameter for a CSA of 2.011 sq inches. I did my tests at an actual 10" H2O. The tube was flowing 141 CFM @ 10" H2O.
With my conventional pitot tube, 1/8" outer tube and 1/16" inner tube the reading was 9.5" H2O and PFA said it was getting 202 fps. Using the math and Larry's spreadsheet it said it was getting 204 fps.

Now with Doug's pitot with the longer shephard's crook it gave a reading of 9.58" H2O and PFA said a little above 202 fps and the calculation and Larry's spreadsheet said 204.9 fps.

For the last test I used Doug's pitot with the shorter smaller shephard's crook and it gave a reading of 9.54" H2O and PFA stated 202 fps and the math and Larry's spreadsheet stated 204.5 fps.

Doug's probe with the shorter smaller crook on the end was pretty stable and worked very well. They all worked very well but I liked the smallness of this one of Doug's as you could get it into some very small places.

Great Job! Doug. I am going to test them in a real head now and see how they act.

John

Test apparatus:

[jfholm]

I played around for a while longer and in reality the most stable of the two of Doug's is the one with the longer shephard's crook. It is equal to or more stable than my regular pitot tube. They all basically get the same reading.

John

[slracer]

John, So far I feel pretty good! I told both of them that they had to behave or it was off to the crusher! But the real question is do the numbers vary when you fix the location of the tip and move the large tube closer to or further away from a wall? Or if you hold the pitot tip in the center of the port and rotate the outer tube around it? You will probably be able to check that better in a "real" port. Thanks for the fast response, maybe I'll be able to sleep tonight! :p :p

Doug

[jfholm]

This little fixture I made was easy and fairly cheap. Yet it is a very educational tool as you can tell what the air is doing in the tube. The velocity "DOES" slow down when you get right up against the wall and is fastest right down the center.

On your probes if I hold them right in the center of the tube and rotate them it makes no differrence.

I do want to get them in a "real" port instead of and "ideal" port and see what will happen. My probe is so much bigger on the shephard's crook end and it is hard to use is some of the ports. I am going to be making some new probes and they will have a much smaller radius.

Also we need to make one for the exhaust which will just be a straight one and does not need the radius.

John

[49-1183904562]

Great work John and Awsome work Doug,

I do have to say the picture of the test setup was a little unnerving I kept thinking the stuff on the shelf was going to fall on me .

Rick