Heated Pitot Installation Issues?
Posted: Fri Jan 07, 2022 4:29 am
Hello all,
Recently, I’ve been flying a couple of A model 170s. The first A model I flew was a 1949 that was/is essentially the same as my B model in terms of configuration, meaning pretty stock airplane, stock wing, etc.
The next A model I’ve flown has been a 1951 and has been largely the same as the ‘49 with the exception of a heated pitot tube installation in lieu of the standard pitot. Most recently, my former boss purchased a 1950 A model and asked me to teach him to fly it since he got 3-4 hours with me in my airplane to get his endorsement and then started flying his RV8 and has realized that he’s forgotten about flying the 170. His airplane is by far the heaviest (and by far the best equipped), and has a Horton STOL kit and a heated pitot.
For reference, I’ve flown a B model with a heated pitot/stock wing/home brew Lycoming O-360 install that had a similar issue, but it seems like (particularly the A models) the speed is way off from my B model for a given power setting. I’ve flown probably more different 170s than the average bear, and performance numbers have always been consistent, but the airplanes with the heated pitot have me stumped. It seems that the faster the airplane is moving, the larger the discrepancy is in what I expect for speed. I’m normally around 115 indicated at 2400 RPM in my own airplane, but these two are barely knocking on 95-100. I don’t think the prop is the issue as, without knowing specifics, I can tell aren’t that far off in pitch from mine because static RPM is around 2200 RPM and climb performance isn’t appreciably increased, if at all.
Is there some secret sauce for what I’m seeing? I’d be surprised if the airspeed indicators are the culprit in both cases. I can dissect static system inconsistencies in each airplane, but suffice to say the altimeter and VSI in each airplane is accurate and the boss’ airplane has a fresh IFR cert to go with the snazzy GTN650 in the panel.
I know there is a template for aligning the stock pitot tube properly, and I can’t imagine there being that big of an issue with misalignment of a heated pitot. Each A model has the pitot in a slightly different place; the 1951 has it close to the location of the original pitot, and the 1950 is further inboard and further aft along the chord of the wing.
Any insight? One of these days I’d like to fly my airplane in formation with each of them at the same power setting and observe the indicated speed of each. Until then, it’s hard to give target airspeeds to teach someone how to land the airplanes better when I don’t fully trust the airspeed indicator in each airplane.
Any and all advice is welcome.
Recently, I’ve been flying a couple of A model 170s. The first A model I flew was a 1949 that was/is essentially the same as my B model in terms of configuration, meaning pretty stock airplane, stock wing, etc.
The next A model I’ve flown has been a 1951 and has been largely the same as the ‘49 with the exception of a heated pitot tube installation in lieu of the standard pitot. Most recently, my former boss purchased a 1950 A model and asked me to teach him to fly it since he got 3-4 hours with me in my airplane to get his endorsement and then started flying his RV8 and has realized that he’s forgotten about flying the 170. His airplane is by far the heaviest (and by far the best equipped), and has a Horton STOL kit and a heated pitot.
For reference, I’ve flown a B model with a heated pitot/stock wing/home brew Lycoming O-360 install that had a similar issue, but it seems like (particularly the A models) the speed is way off from my B model for a given power setting. I’ve flown probably more different 170s than the average bear, and performance numbers have always been consistent, but the airplanes with the heated pitot have me stumped. It seems that the faster the airplane is moving, the larger the discrepancy is in what I expect for speed. I’m normally around 115 indicated at 2400 RPM in my own airplane, but these two are barely knocking on 95-100. I don’t think the prop is the issue as, without knowing specifics, I can tell aren’t that far off in pitch from mine because static RPM is around 2200 RPM and climb performance isn’t appreciably increased, if at all.
Is there some secret sauce for what I’m seeing? I’d be surprised if the airspeed indicators are the culprit in both cases. I can dissect static system inconsistencies in each airplane, but suffice to say the altimeter and VSI in each airplane is accurate and the boss’ airplane has a fresh IFR cert to go with the snazzy GTN650 in the panel.
I know there is a template for aligning the stock pitot tube properly, and I can’t imagine there being that big of an issue with misalignment of a heated pitot. Each A model has the pitot in a slightly different place; the 1951 has it close to the location of the original pitot, and the 1950 is further inboard and further aft along the chord of the wing.
Any insight? One of these days I’d like to fly my airplane in formation with each of them at the same power setting and observe the indicated speed of each. Until then, it’s hard to give target airspeeds to teach someone how to land the airplanes better when I don’t fully trust the airspeed indicator in each airplane.
Any and all advice is welcome.
