Fabricating velocity probes

[slracer]

John, I don't have a probe capability functional on the bench. It is in the upgrade I am doing right now. That is one reason I would like someone else to do the test. Other reasons include the fact that I don't have a "conventional" pitot probe to compare the results, nor have I ever done a velocity probe test.

I'll pack the prototype and the second version and send them to you. Do you have any thoughts on a single static hole on the inside of the larger tube "facing" the pitot pickup? I'm thinking that location would be the closet to the pitot in the same slipstream (as much as possible) and would keep the static port from getting into the boundary layer along the wall. When you test, maybe you can tape over all but the closest hole? Send me an email with your address and I can get out on Monday. Thanks! -- Doug

[jfholm]

btw, what the heck kind of penny is that? I don't recognize it.

John

[jfholm]

Thanks Ed,
I just went and corrected my spelling and noticed your reply. Cool penny.
John

[86rocco1]

You're welcome and what the heck happened to my post? That's the second one today that's disappeared.

[slracer]

For any of the rest of you who also "lost" Ed's reply, it is the new style 2009 US of A Lincoln penny. The reverse now shows ol' honest Abe sitting on a log and reading a book. It looks like the axe sitting next to him hasn't been used so I assume it is a book about politics! This is the first of these I have seen. Being an old numimatist, nummismatist, hmmm coin collector :p I always look at any coin that hits my hand. When I was 12, I found a relatively rare quarter in my change at the movie theater and had to choose between popcorn and collection. Having my brother tempt me clear through the movie didn't make it any easier to keep the coin!

Doug

Ed - What did you have to add? When I first made my last post, the pic was fitted to he screen. This time it was huge and ran off the screen!

[bruce]

[jfholm]

Yeah, the forum thought that picture of the penny Ed put on was porn

John

[86rocco1]

Nothing, I just edited the text of my reply and it disappeared.

BTW, here's another pic of that penny, it's one of four designed to commemorate the 200th anniversary of Lincoln's birth, if anyone's intersted you can read about them

[slracer]

Cool site Ed! I'll have to look for the other 3 "aspects" of Lincoln's life. I had a District of Columbia quarter the other day and wondered if the Congress was really going to give them a Senator (or make it a state)? Then I got a Puerto Rico version and knew something else was going on. The 2010 National Parks series should also be interesting. Does the Government make money on the coins that people take out of circulation. "Let's see, we make a million new quarters but collectors take 200,000 so we don't really have to pay for those that gives us $50,000 to play with! Hmmm" I personally have nearly $20 worth! :p -- Doug

[86rocco1]

I'm in no position to make comments on American electoral policy so I won't touch that but I do know a thing or two about coins. They wouldn't make any money on the pennies, undoubtedly why there haven't been a lot of commemorative pennies over the years but, I'm sure on higher denomination coins like the quarters, they make lots. You've got $20 worth of the state series quarters and I wouldn't be surprised if there are at least a million other people that do too so we're not talking ten of thousands of dollars to pay with, we're talking tens of millions, Hmmm.

[jsa]

[slracer]

Hi all, Latest update: the 2 versions of the probe went into the mail to John Holm on Monday. The PO said it would be 3 days so I expect them to arrive on Thursday or Friday (as our mail doesn't leave town until after 4PM). John will test in any way he sees fit and report back via this thread. If they work, I'm a hero! If not, it was another exercise in "learning"! :p (Read the "trailer" on John's posts to see if I am a "wise" man!) Either way, thanks for all the inputs! -- Doug

[jfholm]

The results of my post will be strongly influenced by whether you are buying breakfast Aug 5th or not

John

[larrycavan]

One potential issue with tiny diameter pitot tubes is the inability to recover when moved to a new location inside the port. That can be tested very easily.

Probe a location in the port with high velocity pressure and quickly remove the pitot tube while watching your guage.

Use it for CSA approximation while you're testing. Pretty handy for that sort of thing as well as local velocity numbers.

Average_CSA = ( Flow_CFM * 2.4) / FPS

[slracer]

Larry, Thanks for the input! But are you saying that pressure in the tube may stay high when you move it to a different location? I assume it will drop to the proper level after some time, but would it be better to remove it completely and then go back in? Hmmm, where is that primer of Do's and Don'ts?

Some dimensional data: with 1/16 OD K&S brass tubing, the wall thickness is .014 so the pitot hole is .0345. The wall thickness is a constant for all sizes I'm using so a 3/32 OD would be .066- ID (which is why it nests so well with the 1/16 OD). As a comparison, the Dwyer 166/167 pitot-static probe has a .047 ID. May have to make a 3/32 pitot and increase the size a bit if the results don't "behave" themselves. :p

The OD of the static tube is 1/8 so the ID is .097. There is no ID called out on the Dwyer drawing, but the OD is 0.120 inches. -- Doug

PS - I like the quotes after Bruce and John's name so I added the one I had on my wall when working. It seems to fit here!