Thread: was up with my prop pitch?

i'm loving the winter performance, 125-130kts tas is normal again.

i've had this argument with my a&p and assumed he was right. he claimed that due to denser air in winter that the winter pitch adjustment would be to a flatter pitch.

i see the opposite. i haven't had an adjustment for over a year, in the summer my max rpm was 5,500 but now it is close to 5,800.

i guess that while the air is denser the colder temps produce more power and more rpm. its more about temps then density.

Charlie Tango,
Mine is doing the exact same thing as for as RPM goes. At a cruise setting of 5200-5300 i'm seeing 117-120 tas @ 9500 - 10,500'. Not the 125-130 tas that your seeing. I can get 5700 RPM WOT also, but only 5100 at the 6200 airport elevation on take off. Whats your tako off RPM?

mike,

take off at 7,100' msl gives me 5,250.

i always cruise at 5,500 to keep my 912 happy.

sounds to me like you are still too flat and cruising too slow

btw i do have a warp drive prop

I too have a warp drive. After my flight yesteday afternoon I fueled up. I had 5.5 hrs on the tanks, took on 25.5 gals, that puts me at a very happy 4.64 gph. I'm not getting the takeoff rpm you are, but can achieve the 5700 WOT. I hate to set more pitch in and loose the takeoff rpm, but would like more tas. With your 5500 cruise setting what is your fuel burn, and whats your take on the prop setting on 89WD?

to compare wot rpm we would need to do it at the same density altitude. i think i'm flatter then you.

my fuel burn is higher then yours, the upside is engine wear. the 912 was designed to operate its entire life at 5,500.

max tas should come from 5,500 cruise @ wot but that is harder on the motor in take off and climb then a flatter pitch. i find the loss of speed from the flatter pitch to be pretty minimal. i notice the light planes at the reno air races use a climb prop vs a cruise.

tas readings are subject to error especially in light sport that might lack pito-static calibration. i find a good check on calibration to be winds aloft speed and direction. any pito-static error or even oat error should make your winds aloft read incorrectly.

if 9WD were mine and i was willing to adjust i would go a bit flatter and burn a bit more fuel. fuel provides cooling and is healthy, you can't control mixture so pitch is your best point of adjustment.

Hi Mike,

If you want a little better cruise then you should drop the WOT rpm down to 5550-5600. You are a little flat and using your prop right now has the edge of climb over cruise. OAT and flight elevation both play a part in this configuration. I just adjusted a prop from 5700 WOT at cruise bqack down to 5550. The owner likes it better. 1 degree more pitch will achieve what you want. The people I adjust props for usually see right about 5000 rpm on take off at 15 flaps and 60 knot climb. The rpm you see on climb out will depend on how you take off and your airport elevation. With an rpm of 5000 on take off a reduction for you of only 100 rpm you probably won't really be able to tell much difference, but you will see a little more speed on your instrument at WOT flat and level. Try adding 1 degree. I think it will be right where you want.

Originally Posted by N89WD

... At a cruise setting of 5200-5300 i'm seeing 117-120 tas @ 9500 - 10,500'. Not the 125-130 tas that your seeing...

117-120 tas isn't bad considering that you are developing about 60hp. the best you can do at 10,000' (continuous) is about 70hp but you would need to be pitched for 5,500 wot and fly wot.

cruising wot @ 10,000' in any normally aspirated aircraft makes sense unless you want less then 70% power for cruise. this may not seem intuitive to some.

Charlie Tango,

I don't think your prop pitch is the cause for the better performance.

Just a function of temperature and density with more O2 available for better performance by your 912.

This point was dramatically shown to me last year when I flew to the west coast and cruised along the Oregon coast at 500ft with 75% power and 128kts (mind you I have a VP prop but used the same notch setting as always).

So in my estimation it is strictly a function of available O2 for combustion to get better performance,

Being relatively new to these forums I have a question...what does WOT mean?

WOT = wide open throttle.

rpm alone don't tell the whole story, but a given rpm @ wot gives a better fix on power setting.