The International Cessna 170 Association

I’ve seen lots of discussion on the 8042 STC for the 170. Recently swapped my 7653 out for a new 8042. Climb improved tremendously…and as expected the cruise suffered a bit.

Has anyone done a 43 or 44 degree pitch change with real world performance numbers?

I’m getting 90-95 mph cruise at 2450 rpm on a less than 200 hour overhaul.

Should I expect 5 mph per degree on average in cruise?

Thanks in advance for any real world performance figures anyone may have.

I have a 8043 and see about 105-108 mph at 2450.

Joe
4518C

Joe Moilanen wrote:I have a 8043 and see about 105-108 mph at 2450.

Joe
4518C

Thanks Joe. Mind if I ask what size tires you are running? I’ve got desser 8.50’s,,,

If you run at 2650 you will see the same 105-108 that Joe does with his 8043 at 2450. The engine is rated at 145HP at 2700. I run at 2650 to give me some slight cushion if I start descending and can throttle back a bit. I didn't see a big change from 8.50's to 26's. Biggest change was the prop itself.

Propeller design theory is such a “black art” that I find it almost impossible to predict what a pitch-change will do other than to regurgitate what Cessna/McCauley claims. They had the money to research that and did it on a standardized airplane. But Your airplane and some other guys airplane may have so many differences as to make predictions really difficult.

Firstly, the two airplanes are using different Airspeed Indicators. They have different rigging and different damage histories. They have different operating weights. And the Old Prop had thinner blades nearing end-of-life…. or it was a 50 year old polished-thin blade (like my EM7655) and a different profile than your DM or MDM 7653 or whatever…that achieved the same indicated Airspeed…. even tho’ my Red paint job slowly pulled-away from your Green one.

My Airspeed Indicator was “Overhauled” and recertified and my static system was totally re-plumbed during restoration and my TACH was new…..and this nearly worn-out appearing polished prop pulls this airplane along at a GPS confirmed (triangular course) at 104 kts (119 mph) and burns 7.8 gph doing it at 2450 indicated RPM….. All of which is INCOMPARABLE on paper to another 70-year-old airplane in the fleet that uses its’ very different Instrumentation….. the two different results being achieved on Different Days with Different Atmospheres at Different Altitudes with Different Props on Different Engines dragging Different Airframes behind.

The way to make a true comparison without spending a fortune is to have a formation flight with another airplane that undergoes ZERO alterations between flight and both airplanes operated at WOT, side-by-side with the subject airplane having a before/after prop-change….and see if the subject airplane has an altered speed as compared to the control aircraft. Even so, it would be best to do it on subsequent days at the same time of day. (I don’t like flying formation at night.)

supercub04 wrote:

Joe Moilanen wrote:I have a 8043 and see about 105-108 mph at 2450.

Joe
4518C

Thanks Joe. Mind if I ask what size tires you are running? I’ve got desser 8.50’s,,,

I'm running 8.00's.
Joe
4518C

Thanks all for the replies. Always willing to learn...cheers.

I fly behind an 80/40, there are too speeds slow and slower. But on floats try to get off with a standard float prop 76/49........ good luck.

supercub04 wrote:I’ve seen lots of discussion on the 8042 STC for the 170. Recently swapped my 7653 out for a new 8042...

Would you mind posting where you got your 8042 and how much you paid for it? I've been on the hunt for a used one since I got my 170 but I am beginning to think I may just have to buy a new one!

Fishsticks wrote:

supercub04 wrote:I’ve seen lots of discussion on the 8042 STC for the 170. Recently swapped my 7653 out for a new 8042...

Would you mind posting where you got your 8042 and how much you paid for it? I've been on the hunt for a used one since I got my 170 but I am beginning to think I may just have to buy a new one!

I ended up buying a new one from Sensenich Propeller in Gainesville GA. About $5300.

supercub04 wrote:I ended up buying a new one from Sensenich Propeller in Gainesville GA. About $5300.

Awesome! Thank you!

Hi guys! where did you buy the stc for the 8042? And could you use the stock spinner and backplate? Thanks

Call Kenmore Air for the STC and tell them what you are looking for.

https://www.kenmoreairharbor.com/stcs.html