I guess it bears asking. Are we talking about indicated airspeed or true airspeed?
In my circumstances, most of my flying is between 5 and 10 thousand feet. An indicated airspeed of 80 or 85 knots or so can be 100 knots true airspeed at those altitudes. I can't give specific numbers from flight as I am about 1000 miles away from my H36. But I can note that full throttle cruise is commonly about 98 knots. And full throttle at those altitudes is probably 75% powere or less. There used to be an old wives' tail about getting an airplane "on the step" for cruise by climbing a bit above cruising altitude and then accelerating in a shallow dive to level flight at that altitude. Engineers disparaged that notion. I am not sure it doesn't apply a bit to the Dimona though. I have found that by working very hard at it, I can sustain close to 102 knots in still air cruise. But if I am lax, I can find myself wallowing around at 90 to 95 knots. My suggestion is to check IAS vs TAS by bidirectional flights over known geographical fixes or with GPS to determine actual ground speed. And certainly test the pitot-static system for leaks. The airspeed indicator can be tested for calibration. As an aside, I added a Kanardia EFIS that provides IAS, TAS and GPS ground speed. I was astonished that the 1983 airspeed indicator and the Kanardia are within one knot of each other. Who would have guessed that the airspeed indicator would be that accurate after all these years? If the motorglider engine is producing normal power for takeoff or specified static RPM, it should continue to produce normal power during cruise, so I wonder if it would be the primary concern. Michael Stockhill Polson MT USA On Sun, Nov 3, 2019, 2:06 PM Jarek Steliga <[email protected]> wrote: > > > Hello, > > I noticed that at level flight with the prop at cruise angle I can hardly > reach the air speed of 150 km/h at RPM 2500 (full throttle). Is this > something to worry about? Should not the top speed be around 190 km/h at > RPM 3000? > > With the prop at "start" position the full throttle revs are 3000. > > Any comments please? > > Regards > Jarek > > >
