vmirv8bldr

vmirv8bldr

Well Known Member
I acquired a used Cessna pitot and modified it to fit the Gretz mounting kit. (Modifiecations were simply removing material with a file until it fit far enough to align the screw holes.)

At any rate, this is a heated pitot off of a 150. The electrical part is simple enough to figure out. But the pitot tubing part is causing me concern.

The aluminum pitot itself has a female threaded hole and is quite large, between a -4 and -6 size. Additionally, the tube arrived at my door with a nylon or plastic male - male fitting in the hole.

Questions:
1. Is this thing going to melt when heat is on? (I could test it, but then would have to clean melted stuff out of the tube.)

2. Should I replace this nylon or plastic fitting with an aluminum fitting, and if so, any idea what size / type fitting?

I tend to think that ideally I would want a non heat-conductive junction as close to the pitot tube as possible, to help retain heat in the tube itself rather than spreading through instrument tubing.

Thanks,

Thanks
 
Piper Pitot Experience....

B.P.

I can't tell you for sure about the Cessna pitot, but I used a Piper blade-style heated pitot that I had been carrying around in a box of parts for years. I wasn't sure how hot it would get, and had the same question you did about nylon or metal fittings - it had a barbed aluminum fitting screwed in. I slipped a nylon tube on, hooked it up to my power supply, and watched the nylon tube melt right off..... :eek:

I installed using aluminum tubing!! :rolleyes:

Paul
 
I'll second that

After I scorched my hand testing out my AN5812-clone pitot tube, I decided to run aluminum all the way to the wing root and make the transition to nylon there. Pretty easy and indestructible.

mcb
 
Cessna Pitot

I also have a Cessna pitot which came with a nylon fitting as well. The heating element is in the round part of course, and in my simple and fairly short test (with the fitting removed), the 'vertical' part of the unit did not warm up very much. Based on that, I'm planning to use the nylon fitting and currently have nylon tubing run to it. Whenever I've preflight tested Cessna pitot heat on A/C I've flown, I've only noticed the part near the opeining heating up much (which is what you'd expect...).
Based on Paul's report, I will do a longer test in the near future...
I believe the nylon fitting is a -5 (5/16) thread if memory serves (a chancy proposition).
 
My Cessna pitot came off a 172, but it's exactly as you describe.

The AN fitting part # I used is: AN816-4-4D. Took me several tries to get it right.

You can go here for more info. Note that in the picture the pipe threads are not fully inserted. Also, I have no idea why they drilled the hole in the top of the hole at an angle, but I figured it may be some aerodynamic voodoo or something.

BTW: Mine also came with nylon fittings, so it's apparantly what Cessna uses and I wouldn't think there would be a problem with it.
 
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Does anyone know if Cessna uses different part number heated pitot tubes on the various models? The amount of heat extracted by the air passing by will vary with airspeed, and I'm wondering if they might have pitot tubes with different wattage heaters for the various model Cessnas. If so, I would want one from a Cessna that cruises at RV speeds, to be sure to be getting enough heat.
 
In a perfect world there should be no air passing 'through' the pitot. The line should only pressurize and maintain a static pressure. If the air is going through, you have a leak somewhere in your pitot system.
 
Oh yeah, you're right. Out through a little hole in the aft end usually. The line though should remain pressurized.
 
BTW, I just test fired the Falcon unit. It gets CRANKIN hot real quick. Not all the way up to the fitting, but almost.

I arrived at the decision to install a 6" slice of AL tube before transitioning to the plastic stuff.

I figger that is prudent.

;) CJ
 
Thanks for the help

Although it may never be an issue, I think I'll install a little Al tubing then transition to nylon tubing.

Thanks,
 
Cessna Pitot

My pitot is exactly like Jamie's - angled thread and all. At least they're consistent :).

I hooked mine up to a fully charged battery last night for about 10 minutes. The vertical part eventually got pretty warm, but not too hot to hold. The tip was very hot of course, and given enough time the whole thing would eventually get that hot with no airflow. In the airstream (especially since it will be cold when in use) I don't think it will be an issue, so I'm sticking with the nylon fitting, for now anyway...
 
Cessna Pitot Tubes

The Nylon fitting is standard on all of the 150 through the 182 pitot tubes that I have ever seen and maybe on the 210's (but I have not checked them). The heating elements are also identical in size and shape for the 12 and 24 volt elements (they are interchangable). There is no difference between the wattage in the various planes based on speed of the plane. The air does "pass through" minimally where there is a small drain on the heel of the unit. The drain hole is about the size of a normal paper clip. A paper clip can be used to check to see if the hole is plugged. It should be checked at every annual and/or as a pre-flight item before flight in weather. If it is not draining then you start seeing water getting into the lines and get some wierd readings if you fly through rain much.
I am flying with a Cessna Pitot tube and put an aluminum fitting on where Cessna had the Nylon fitting. This was not done out of necessity. It was done because it is a homebuilt, so it is built to a higher standard than production aircraft. :)
 
gvgoff99 said:
The heating elements are also identical in size and shape for the 12 and 24 volt elements (they are interchangable). There is no difference between the wattage in the various planes based on speed of the plane. :)
Click to expand...

the above is true, but be careful how you read it. just because the size, shape, and wattage are the same for 12 and 24 volt elements does not mean that the elements are the same -- they're not. "interchangable" in the above i take to mean that one can be replaced by the other physically. if you took it to mean you could use one in place of the other on a 12-volt airplane, you'd be mis-reading it (imho.)

i ordered a cessna heated pitot from a salvage place, the ad said 12-volt. when i received it, i hooked it up to a fully-charged battery, and it got pretty hot, but the current draw was only about 1-1/2 amps. knowing that this was too low, i called the place, and they sent me another one. it got hotter quicker, and drew nearly 5 amps, so i'm convinced it is a 12-volt unit. i doubt the 28-volt unit would be effective in melting pitot ice on a 12-volt airplane. (bob nuckols has a good article on pitot heat efficiency on his website.)

btw, the salvage placed enclosed about $8 cash with the replacement, so i could return the original. i'd deal with them again (honest mistake.)
 
OOPS

John, I should have specified that the 12 and 24 volt heating elements are physically the same size. As you correctly pointed out the 12 and 24 volt elements are not the same current draw and the heating elements need to be the correct one for the voltage of the plane.
 
Installing Cessna pitot - how?

What is the procedure for installing a Cessna heated pitot tube? I only know where and how to mount the stainless tube pitot from Vans on my -10 wing, but... 3 questions:

1. Where would a heated pitot be located?
2. How would it be attached?
3. Where would one acquire the mounting bracket?

Doug Nebert
#40546
 
Gretz Aero

I spoke to Warren at Gretz Aero. The Mounting bracket he sells isn't quite perfect for the Cessna tube, but you can "modify" the Cessna tube to fit. I requires about 30 minutes of filing and test fitting, but is REALLY simple. I'm at work with no photos, or I'd send them to you. I got the unpainted version of Warren's bracket, then prepped and primed it. Filed and fit maybe 10 or 15 times. Now it looks like they were made for each other. As for mounting it to the plane, foolow the instructions that come with Warren's bracket. No problem.
 
ddnebert said:
What is the procedure for installing a Cessna heated pitot tube? I only know where and how to mount the stainless tube pitot from Vans on my -10 wing, but... 3 questions:

1. Where would a heated pitot be located?
2. How would it be attached?
3. Where would one acquire the mounting bracket?

Doug Nebert
#40546
Click to expand...

I also used the Gretz bracket and modified my Cessna pitot to fit the mount. It's really trivial. It just involves filing the flange of the pitot down a little.

See my procedure and results here:
http://rv.jpainter.org/?view=entry&date=2004-10-20
 
Cessna heated Pitot heads

Instructing pilots for too many years, checking the pitot head heat as part of a preflight check was mandatory.
Also mandatory was instrucing the student to make sure NEVER to leave it switched on while the a/c was stationary or on the ground as that will limit the life of the heating element within the pitot head severely.
Once airborne and flying in sub-zero temperatures, it will be impossible to melt any plastic line attached to the pitot head.
The fact that Cessna uses plastic tubes on the pitot head should indicate that they assume all pilots will have gotten the proper instructions on how to opertate them.
If you doubt my words, contact any Cessna service agent.
 
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