Static RPM

Robert Dant wrote:

Thanks Roger. My numbers are comparing Static WOT on the ground (5200) with WOT in low altitude cruise (5400). Static=ground, WOT=in air. If I were to set 4800 static WOT, I’ll get about 5000 WOT in cruise. To get 5650 WOT in the air, I’ll likely have to set 5450 static on the ground. Like I said, something is odd in Denmark. BTW, new UMA tach, confirmed with TruTrak.

Somethings wrong with those numbers. There is far more than a 200 rpm difference between static on the ground WOT and cruise WOT. Maybe the instruments?

Yeah, I cannot figure it out. I have a new tach that I have confirmed with TruTach II. I’m wondering if there might be other factors. What if the engine wasn’t producing full power for some reason. I wonder if that might narrow the range. I’m stumped. Others on the forum has claimed a narrow range for Warp props, too, so I don’t think I’m alone.

BTW, this is on a seaplane, so I believe that I‘m OK to favor a higher RPM settting for takeoff performance.

Robert Dant wrote:

Yeah, I cannot figure it out. I have a new tach that I have confirmed with TruTach II. I’m wondering if there might be other factors. What if the engine wasn’t producing full power for some reason. I wonder if that might narrow the range. I’m stumped. Others on the forum has claimed a narrow range for Warp props, too, so I don’t think I’m alone.

BTW, this is on a seaplane, so I believe that I‘m OK to favor a higher RPM settting for takeoff performance.

Ahh! unlimited runway length and only the occasional yacht/ocean liner to climb over/avoid.

You will still have temperature related influence (density altitude) but I guess you can fly in ground (water) effect until some fuel has bunt off ?

Robert Dant wrote:

Now, Warp Drive 70” 3-blade remounted on 912ULS with new mounting hardware and repitched, trying to get 5650 WOT. I don’t know if the Warp prop is just strange or something else is happening, but I get 5400 static and 5600 WOT sea level. And with warmer weather, it’s more like 5200 static, 5400 WOT. Very little difference. How can this be such a small range? Some days, it’s seems the range is actually 0 (5400/5400).

So, I’m wondering if I’m dealing with a prop issue or something else.

Robert,

You won't see much change unless you have a high airspeed. In my case, no change untill above 100 KTS.

My fixed pitch 64" x 81 pitch is very over propped. I have only flown it once but I saw 4700 RPM on take off roll  at 2000'ASL (temp 12C) and as low as 4600 on climb at 5000' ASL. It didn't really increase at all on climb out even if I climbed at 100KTS. Once I levelled off it unloaded to 5100 RPM at 140 KTS. I know of one other person that has the exact same engine/ prop/ plane combination and he gets about 100RPM more than me but he is at sea level so without comparing DA the 2 might have the same figures. 

Being fixed pitch wood/composite, my only choice to change this propellers performance is to take a chain saw to it and cut the tips back a bit....

Interesting. You seem to get about 400RPM Range between static and WOT. If you tried WOT down low, you might be getting more than that. I suspect 800 is more typical for most applications. I have a seaplane, so 100knots is only a dream, but I get 100mph flat out at sea level.