The International Cessna 170 Association

I have a heated pitot tube on my 170A is there anything I can help you with It was on the aircraft when I purchased it.
Bob

GO TO WEBSITE FOR SURPLUS: strube@ptdprolog.net
John - n3833v

In every photo of a 170A or B that has a heated pitot tube, they all appear to be the conventional type that exit down in a pylon of sorts and then make a 90 degree turn to face the relative wind....standard C-150 stuff. I have yet to see a 170 with the Kolsman tube pointed straight out of the leading edge. I have the drawing from the Association, but it is not clear as to whether the pitot exits straight out of the leading edge of the wing, or is mounted on a "conventional" pylon.

John, I think you are referring to the AN 5812-12 pitot head, which usually is mated to a short mast beneath the wing, commonly found on Cessna 172's.
The Drawing 0511051 is a straight mast Kollsman 518B-01 that exits the leading edge in a straight forward manner, such as on a Cessna 190/195.

You must be right George. There is no horizontal plan view on the drawings, but it does look as if the tube exits the leading edge, which is OK I suppose. I just have never seen one. All the 170s with heated pitots that I have seen have the convetional type hung from the underside of the wing. Does the 518B-01 have a drain hole to prevent moisture from running back along the line? How about current draw? With a 25 amp generator, I don't have a lot of, if any excess current supply. Which tube draws the least current?

The Kollsman 518B-01 is only a 75 watt heater. Go to strube.ptdprolog.net to check. It is the shark fin style.
John-n3833v

This is a revisit to this topic, both as a request and a offer to anyone interested. First the request, does anyone have the installation instructions for installing the Cessna Accessory kit SK 175-23B? This is the kit covering the installation of the heated pitot system for early 172's S/N 28000-50572. I would like to find a copy of that to look over.
Now for the offer. I would like the drawing to use as a referance, however it is not required since I have gotten a Field Approval to install a heated Pitot on a 54 170B. Reading thru this topic there had been some interest in installations like this so thought I would see if anyone is still interested and I could send a copy of this one to whoever had interest. Brian

If you have a need for a heated pitot tube, you must be contemplating instrument flight in IMC. If your airplane is presently equipped with a twenty five ampere generator, I would suggest that your first installation should be a sixty ampere alternator system. The twenty five amp system will hardly carry the lights you ought to have on during instrument conditions.

Indopilot wrote:This is a revisit to this topic, both as a request and a offer to anyone interested. First the request, does anyone have the installation instructions for installing the Cessna Accessory kit SK 175-23B? This is the kit covering the installation of the heated pitot system for early 172's S/N 28000-50572. I would like to find a copy of that to look over.
Now for the offer. I would like the drawing to use as a referance, however it is not required since I have gotten a Field Approval to install a heated Pitot on a 54 170B. Reading thru this topic there had been some interest in installations like this so thought I would see if anyone is still interested and I could send a copy of this one to whoever had interest. Brian

Hi
I have a copy of AK175-23D . It is dated Nov. 5 1975 . It applies
to C 172 -175 P 172.

If you want copy I can fax , or try to scan and send .

John

blueldr wrote:If you have a need for a heated pitot tube, you must be contemplating instrument flight in IMC. If your airplane is presently equipped with a twenty five ampere generator, I would suggest that your first installation should be a sixty ampere alternator system. The twenty five amp system will hardly carry the lights you ought to have on during instrument conditions.

and if you get close enough in IMC, that all the lights are seen by the other pilot, its probably too late.

Jatkins,

if you still have a copy of the AK175-23D to install the heated pitot...I sure could use a copy! I have a C175 and have been trying to nail this down for a while.
Please let me know and many thanks!
John

When I rebuilt my aircraft in the late 80's to early 90's I put in a stock Cessna heated pitot in the wing. I questioned my then PMI about approval and he told me at the time that since that was the way Cessna went with pitots from a tube sticking out to a heated mast and tube, he saw no reason to look at it as more then a product improvement. As such he said that I was just replacing one Cessna part with another and to make sure my 60 amp alternator couldhandle the load...he was just kidding. For mine it was a sanctioned logbook entry. More later on those type of entries, if you can reference parts manuals and certain parts of the service manuals you can do a lot that does not require 337's or STC's. If you look at AC23-27 and certain parts are not available for pre 1980 aircraft then you are allowed to use after market newer parts that meet the mission.

I cringe to think that this may be another can of worms but lets not make some of these safety and common sense upgrades turn into a mammoth event. I would think a letter from Cessna that one member mentioned earlier and a log book entry detailing the work would suffice for any Fed or IA.

marathonrunner wrote:..., if you can reference parts manuals and certain parts of the service manuals you can do a lot that does not require 337's or STC's. ....

I agree that installing a heated pitot per later Cessna designs is not a big deal, but it does require approval basis.

Just to clarify something tho'.... the source of the parts, or the fact that other models service manuals describe similar modifications.... is NOT what determines if a Form 337 or STC is required. Keep in mind that the TITLE of the Form 337 is "Major Alteration or Repair". If it's a minor alteration...then all is required is a logbook entry. If it's a MAJOR alteration (per FAR 43) then it requires a Form 337. All STC's I can think of require Form 337's.....It makes no difference where the parts came from or what other models they have been found on, or what service manuals they've been described in.

(While it's fun to add capability and equipment/improvements to our airplanes, ...a heated pitot is not high on my list. By the time a heated pitot is needed...far more serious matters will have my attention.....like weight of the ice, and lift capbility of the wings, horrible propeller-performance/vibrations, and handling characteristics of the airplane, ...not to mention visibility thru that iced-up windshield.... )

This airplane is NOT approved for flight in condiitons that require a heated pitot. If you find yourself in icing conditions you should EXIT immediately or land. (I'd rather spend my money on wx briefings and perhaps a GPS with XM radio/WX.) Then, of course, there's the issue of instrument venturiis.....

In my experience, the venturis ice up before the pitot tube.

In my experience, (rented Cessna 210) the little "trap-door" pitot-tube cover builds up a ball-of-ice and flops forward and blocks the tube. If you have a heated pitot...for goodness sakes...don't install one of those automatic pitot-covers.