PTS pitot comparison...

[slracer]

John, My wife is using the cattle prode right now! I'll see if she can spare it! (I hope!) -- Doug

[Tony]

There is a "theoretical" problem we all have when using a Pitot tube in a port subjected to a high test pressure.

It is just not possible to measure both impact pressure and static pressure at the exact same physical point within the port.
When the port is subjected to a high test pressure to achieve the high flow velocities we wish to test at, there will be a rather large pressure gradient along the length of the port, and at various positions within the port.

This very high pressure gradient is going to cause us a problem when comparing the impact pressure to the static port pressure. The differential pressure is going to vary depending upon the position, orientation, and unique design of the probe.

None of this happens when using a Pitot tube to measure airspeed in an aircraft or an airconditioning duct. In both cases the static air pressure either does not change, or changes minutely with major changes in static port position.
This is certainly not going to be true in a fast flowing cylinder head port subjected to a massive pressure gradient.

I don't see this as being a problem, because we are looking for trends, and looking for airspeed differences across the port cross section rather than trying to make absolutely accurate airspeed measurements.

But it does mean that the results are going to be different for probes that have physical differences in construction, particularly the location of the static pressure holes.

[ivanhoew]

good point tony ,almost worth using a ''lambda'' sort of scale .

[slracer]

Hi Tony, Very well put! As you might have surmised from my rather abstract comments, I have not given up on my revised pitot probe design, but studied the problem somewhat and arrived at a conclusion similar to yours. I made a couple more probes for John to have a whack at which should reduce some of the previous "perturbations". As you stated, it is not possible to read both static and dynamic at the same place, so the revisions I made were aimed at reducing the physical differences while trying to minimize "disturbances" in the flow. John suggested that he had a couple of ideas that we will also have to take a look at. Due to my continuing "work" with small displacement engines, I am also working on a smaller physical size probe (you might remember that my "oversized" intake valves are 27mm). I was also in the process of adding a probe capability to my "dark side" machine when I moved to new home in a new state. Maybe with some continued development the head of PTS International could get interested! -- Doug

PS - John, I am currently planning on returning to Wendover for the World Finals, Oct 2-6. Maybe I can sneak out of that one sometime and we could have dinner and talk a bit? Due to the later sunrises and earlier sunsets (along with a smaller number of competitors), the day is much more relaxed.

[Brucepts]

I was also in the process of adding a probe capability to my "dark side" machine when I moved to new home in a new state. Maybe with some continued development the head of PTS International could get interested! -- Doug

So what you are saying is . . . you'd like a probe bend smaller than .5"?

We are already exploring the "dark-side" with pitot flow elements (this is nothing new to me though as I already had a design in hand from the old days), Rick has to work on the programming to make it work with the DM and I have to do the testing. The end goal is to offer something similar to the FP "vacuum cleaner" product at about half the cost!

[jfholm]

PS - John, I am currently planning on returning to Wendover for the World Finals, Oct 2-6. Maybe I can sneak out of that one sometime and we could have dinner and talk a bit? Due to the later sunrises and earlier sunsets (along with a smaller number of competitors), the day is much more relaxed.

I would love to meet you some place to have dinner or whatever. btw I don't think I would let everybody know that you have a small probe

Our contract is over on October 6 so maybe I will be out the door by then we only haved about a third as many Union workers as we used to so this year will be interesting. Companies just do not want to pay any wages or do benefits anymore so we will see what happens. Just let me know Doug what you want to do.

John