Pitot static static

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PhilW

New member
I have a most wonderous cruisemaster. At 23 square my airspeed generally hovers about 180 mph (I've heard there are some that even go faster). It usually flies 300 feet higher than my GPS and NAVCANs radar shows. It is a marvelous aircraft indeed!

Well so much for fantasy...obviously I have a static issue...pulling a little vacuum perhaps. I have an original pitot static probe...that's the long one with a collar just in front of 4 small static holes. That design seems the perfect set-up to create turbulence (and a vacuum) over the static holes...and the problem I have.

Has anyone else had this issue...if so how did you solve it?

Phil
 
My 14-19-2 had a rotted out static hose. It was not all that hard to run a new hose next to the old one. I wish I could go 180 at 23^2. That is almost as fast as the book numbers!
 
I do SAT checks in WPA. On my crate I have Viking static ports both sides aft fuselage. I also have the heated pitot head so my airspeed reflects perfectly what my static test set says it should be. Not nearly what Bellanca claimed. You can test your pitot static lines by blocking them before the instruments and applying pressure to see if it holds. You might find as previously stated by Ralph the hose has rotted or partially blocked by insects. Lynn
 
I found a photo of my Pitot tube. I have the heated tube with the static ports about the middle of the tube. It works at high speed but not at low speed. Below 120 the air speed indicates slower than you are going, getting worse the slower you go. The wing stalls just as the air speed reaches 0.
 
Thanks to all for the comments and suggestions.

The system isn't leaking, nor is it blocked; we checked. It's interesting that my issue is the mirror image of Ralphs...at cruise, my airspeed is 20-25 mph high and the altitude is about 300' high; below 120 mph the speed and altitude are close to correct and the approach speed is near dead-on.

I'm quite certain the problem lies with the collar in front of the static holes. I suspect the turbulence behind the collar is creating a slight vacuum (which is more intense at higher speeds) causing an error in the read-out. We machined a sleeve that fits snugly over the collar and covers the static holes, that is we blocked off the static system. Well, not really because we drilled 4 small holes in the sleeve. The idea was to avoid the turbulence of the collar...the result was interesting...the airspeed and altimeter were sluggish and both read low throughout the speed range. Indeed on approach the airspeed was about 40 mph. Not a number I'm comfortable with considering the circuit here is 600' with a curving approach. We opened the holes up a bit more and have come quite close to solving the problem. My AME figures the sleeve is not a very elegant solution and is proposing that we grind off the collar.

Phil
 
My guess is that the collar is to trip the airflow and reduce the “siphon effect”. Removing the collar may make the error worse not better.
I fly my approaches at 60 but 50 is ok for short final, you may need a touch of power in the flare. If I fly the approach at 75 or 80 it will float forever. At low speed my ASI is measuring angle of attack more than air speed. It is possible to cycle the ASI between 0 and 60 by pulling on and releasing the yoke. The behavior of the ASI is very consistent with changing aircraft weight and balance.

My Cruisair 14-13-2 had a heated pitot with a band around it in front of the static port and it behaved exactly the same as the 14-19-2 without the band does. (well that wasn’t much help was it.) :roll:

Ralph
 
We had the same collar problem on the Spartan. Removed the collar and that was the fix. The collar is an attempt to supply a source of dead air.You might try moving the static to the fuselage like the Viking. Lynn
 
My 14-19-2 is the same with pitot static errors. Before GPS it was easy to impress others with my excellent performance. I assume that a couple of hundred feet of altitude error will cut my chances for a mid air.
 
So does the study that Lambros and Raspet did on the Cruisair apply to the Cruisemaster? They found a significant airspeed error way back in the early '50s.
You could always do what the previous owner did to mine, and put that big pig sticker pitot that I have. May be ugly, but VERY accurate...also good for hanging out your laundry at fly ins too!
 
I'm with Larry.

I was wondrously dissatisfied with the accuracy of my airspeed when I bought the Cruiser in 1987 but lived with it for over 10 years. I rationalized that the newer airplanes, including the Viking series, had gone to dual static ports at an approximate 2/3 point on the fuselage. Left and right side going to a "T" and water trap. Simple and inexpensive for the materials. Indirect chatting with my FSDO of the time showed that my feeling was correct, the inspector agreed that what I proposed was a minor alteration and other than flight testing the installation (and mentioning it in the sign off) I was merely copying an approved installation on later Bellancas. He and i both ignored the Aircraft Specification vs. Type Certificate Data Sheet train of thought; me for convenience and he because he felt it was a safety of flight improvement comparable to installing shoulder harnesses.

Flight tests using a pre-marked triangle course and GPS verification confirmed that the static location induced error was all but gone from stall buffet to a "high speed (cruise) descent. I'm VERY happy with it.
 
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