Cessna 150 pitot tube placement - bent?

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Matthew Rogers

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Matt R
Can anyone send me a diagram with measurements of the pitot tube of a 1966 Cessna 150F? Mine may have gotten bent out of place and I want to check to see if it is still in the correct orientation/angle/etc. I remember seeing a document diagraming the exact placement of the fuel vent, so I am looking for a diagram with measurements of the location of the end of the pitot tube and if there is a specific angle it should be at relative to the wing. Thanks.
 
Matthew Rogers said:
Mine may have gotten bent out of place
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FYI: most pitot tubes are an AN5812 P/N tube that, while possible to bend, it's usually the mount collar or underlying structure that is bent. Google the AN number for a picture.
 
On this era of Cessna 150, it is just a 90 degree bent aluminum tube that pokes out the under side of the wing. Nothing bolt on or fancy like the ones from later years.
 
I'm thinking his may be more like this:

main-qimg-4315df2ef0c315df8ca638932bd7f355
 
Page 16-13 of the Cessna 100 Series Service manual has a diagram. Per the instructions on page 16-11 you are supposed to trace the diagram on to a sheet of plastic/plywood/metal using carbon paper (can you get that any more?), and then make a template. If you don't have the manual find some one who does and make a 100% size copy.
 
flyingbrit said:
Page 16-13 of the Cessna 100 Series Service manual has a diagram. Per the instructions on page 16-11 you are supposed to trace the diagram on to a sheet of plastic/plywood/metal using carbon paper (can you get that any more?), and then make a template. If you don't have the manual find some one who does and make a 100% size copy.
Click to expand...

This
 
flyingbrit said:
Page 16-13 of the Cessna 100 Series Service manual has a diagram. Per the instructions on page 16-11 you are supposed to trace the diagram on to a sheet of plastic/plywood/metal using carbon paper (can you get that any more?), and then make a template. If you don't have the manual find some one who does and make a 100% size copy.
Click to expand...
I do have carbon paper! And that is the exact thing I was looking for. I'll bring this with me the next time I go over to the plane. But for a single use, the paper cut out will probably suffice if it is not windy. Paper does not stretch.

But when making templates these days in my woodshop, I often just use spray adhesive and glue the paper directly onto the plywood and use that to cut out the shape. It also preserves any marking that were on the diagrams.
 
Matthew Rogers said:
Paper does not stretch.
Click to expand...

No, but between the .pdf document and printing there are opportunities to get the size wrong. FWIW, the rectangular black border on my diagram measures 9-1/16" X 7". However it is a photocopy and thus not 100% trustworthy. An original Cessna manual would probably be best, but sometimes you have to make do.
 
I printed it out. If it is not the right size, it will be obvious because the wing profile will not fit. But it is a good idea I’ll stick it on the photocopier and make 80%, 90%, 110%, and 120% size copies to bring along.
 
To calibrate a pitot tube use a string to see where the air is going.
tie a string to the Pitot tube, then trim to 100 MHP, the string is should be straight with the tube.
 
Tom-D said:
To calibrate a pitot tube use a string to see where the air is going.
tie a string to the Pitot tube, then trim to 100 MHP, the string is should be straight with the tube.
Click to expand...
Cool trick, I’ll try that too after using the diagram to adjust to get as close as possible.

second question, why do the early 150s (G and earlier) have such a wide range between IAS and CAS at the low end of the range while the later models have less error between IAS and CAS. I am talking more than 10 mph at the low end or an error of 25%.
 
Matthew Rogers said:
Cool trick, I’ll try that too after using the diagram to adjust to get as close as possible.

second question, why do the early 150s (G and earlier) have such a wide range between IAS and CAS at the low end of the range while the later models have less error between IAS and CAS. I am talking more than 10 mph at the low end or an error of 25%.
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error due to location of static port ?
 
No, the POH values for IAS and CAS correction have a wide range. They even say that speeds below 40 mph the airspeed is completely unreliable. And tyo confound things, the stalling speeds are listed as CAS, not IAS, so they expect you to do these calculations while flying - or at least do the math before taking off. So power off stall at 20 degree flaps is listed as 49 mph CAS. You then plug that into the table and get 40 mph IAS.

For example for 1966 C150,
Flaps up
IAS is 40 mph and CAS is 51
IAS is 50 and CAS is 57
IAS is 60 and CAS is 65

Flaps Down
IAS is 40 and CAS is 49
IAS is 50 and CAS is 55
IAS is 60 and CAS is 63
 
If you had a real pitot tube instead of that trendy re-usable metal drinking straw, you'd have a better correlation, ya hippie! :) Now go get your bamboo spork and dip your fuel tanks before your next flight. Why aren't you getting good advice from the 150-152 club instead of this pack of hooligans? Now get off my lawn. (Anyone need another beer?)
 
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