PA-22-160 climb vs cruise prop and speed?

[DaleLindstrom]

I have attached a spreadsheet showing RPM vs Airspeed. Do I have it correct?
Just enter a new pitch to see the difference.

[krwill]

I have attached a spreadsheet showing RPM vs Airspeed. Do I have it correct?
Just enter a new pitch to see the difference.

Well it's dead on for me if I use 85%.

Sent from my LM-X210(G) using Tapatalk

[DaleLindstrom]

Or, how about an RPM/MPH = PITCH chart.

[Subsonic]

Pick your desired pitch and rpm and figure it out

Pitch x rpm x 0.0009 = miles per hour with no slip. Using my known numbers, 0.90 is a good efficiency number; 10% slip.

58 inch X 2700 rpm X .0009 = 140.9 x .90 = 127 mph which is what I would see down low.

Just adjust the pitch and rpm for what you want to do.

Theoretically at 2500 rpm, 58” prop the math shows I should true out 117 miles an hour.
That is exactly what I see.

If anyone wants to see where I got the .0009 I will be happy show you the computation.
inches x rev per min x 60 min per hour divided by (5280 ft per mile x 12 inches per ft.). The units then cancel to miles per hour. Hope you enjoy this as much as I did deriving it.

By the way 61 inch pitch would give you 133.4 with the same conditions. An increase of 6.4 miles per hour. My prop is new. That variable 0.90 will change slightly with prop condition. Bear in mind this is theoretical. Your mileage my vary.

I have doubts about many mph claims. I was getting 135 mph with a 54” prop until I redid my static system and calibrated it with a four course gps flight and some fancy math that camtom12 understands.

Gilbert thanks for this post. I found a similar condition - My AI was optimistic, my original mechanical tach was erratic, I had no static system...I also didn't have a 61" prop as I was told upon purchase of the plane, etc. Garbage in... So, in the last year I got a good calibrated AI, hooked up a real static system per Piper dwgs, bought/installed an EI digital tach. Got prop overhauled and measured - 58". Now I get just about exactly what your calc indicates using 90% efficiency with wheel pants, and 2-3 mph less with them off. Just ordered new 60" Sensenich from Univair. (74DM6-0-60) That should get me another 4 mph at cruise.

[Drake12321]

Thanks for the useful info.

[akflyer]

For anyone chasing issues with the flight performance.. Check your Tach. In doing some testing of props recently on multiple aircraft ranging from 150 HP to 220 HP my little 160 hp was pulling the same RPM numbers as the 180 HP guys but I was still lacking on performance. I bought a trutach optical tach and found that my mechanical dream-o-meter was off by a good bit. At RPM under about 1200 it is dead on with the optical but starts to go whacky from there. When the Dream-o-meter said I was turning 2650-2700 I was actually turning 2400-2425. In the blink of an eye I went from having the strongest 160 on the airport to just having a regular old plain 160.

When I was cruising by the dream-o-meter at 2400-2450 I was always tail low and not seeing the cruise speeds others have. I passed it off to the climb prop and the big tires. Now that I fly with the optical tach the tail flys level and the speeds are much better.

[CamTom12]

That's a really good point - I noticed hotter CHTs in cruise after I installed an electronic engine monitor, but also faster cruise speeds. I think that my old tach was reading high!