What RPM range should I get from my O.S. 46 fx? I just changed props from an 11x7 to a 12x4 and thought I'd run a ground tune on it. Went to max lean at full throttle and gave it 4 clicks rich. The pinch test on the fuel line seemed to work well ( slight increase in RPM then settled back ). Throttled down to idle and counted to 10. Advanced to full throttle and the transition was smooth. Back to idle and counted to 30. Back up to full throttle with only a little hesitation. Full throttle RPM was a consistent 11,200 RPM. Idle RPM would be around 3200 after 10 seconds and about 2800 after 30 seconds. Does that sound about what I should expect her at 7000 ft. altitude.

I don't know about what happens at your particular ground altitude, but all this sounds normal to me. Perhaps a little lower in the idle RPM.. but you can judge that by the way it responds on landing. If you want a little more RPM, you may go to 10-8 or so, should be as equal to the original prop you had on there.

Every situation is different. Trial and error is in order at most locations and for your particluar engine/plane combination. See what works well and stick with it. This may mean a trip to the LHS and buying 4 or 5 different props and seeing what one works well where you are and then, as I said, stick with that.

CGr.

Thanks CGr.
I was wondering about that idle speed, but if I try to idle down any more the thing quits. Does it sound like it may be too rich on the idle side? I do have problems getting my Kadet Senior to slow down on landing. I haven't been able to fly for the last few days because of high winds so I have not flown this prop yet. I was hoping the larger diameter, smaller pitch would help the plane slow down some. Do you think it will?

Thanks

Rufcut

Yes, that prop will drastically slow your plane. That prop at that rpm gives you a pitch speed of about 70kph, maybe 45mph. Your previous prop choice 11x7 probably turned similar rpms, for a pitch speed of about 80mph. You'll find your climbout and take off runs have more authority, and with a 4 pitch prop, your idle RPM's are probably low enough to land about anything. your idle pitch speed is about 18kph, 12mph.

J

Yeah. Think of pitch as the gears on a car transmission.

Lower gears, higher engine RPM, more power and less speed. Higher gears, lower RPM, less power, and more speed. When I say power, I mean pulling power. If you climb a steep hill with your car, the transmission (if automatic) shifs down a gear to help with mor pulling power to get up the hill, and the engine increases in RPM.

Same with props. If you down size the pitch, the RPM goes up as does the pulling power, but for a given RPM, the max speed will decrease (simple math.. a 5 inch per rev prop turning 10,000 rpm will travel 50,000 inches per minute.. or approx 48 miles per hour).

Increase the pitch and the same happens, only at 10 inch pitch (exaggerated for simplicity), you double the amount of travel and the speed per minute and double the speed.. to 96 mph. But it takes longer to get there because you are still dealing with the same engine power as before only using more to turn the prop than before as in the car engine and transmission.


CGr

Thanks for the responses.
Anything that helps my landing is a good thing! I always seem to balloon when I flare and my rollouts ( or ski-outs currently ) seem really long. The last resulted in some wing damage. Note to self: never land toward the airplane-eating fence no matter which way the wind is blowing. Fortunately, I had a spare set of wings and I'm ready to give this new prop a try as soon as the weather settles down. Hopefully tomorrow.

Rufcut

Just remember... and this is not only for when landing, but is a good thing to remember WHEN landing. Elevator controls airspeed. Throttle controls altitude. Think about your approach. Start by going upwind.. nose into the wind, and say, ok, I'm going to land. Go completly across the upwind length of the field (nose into the wind and headed across in front of you) and start to remove throttle. Make your first turn. Now you are going downwind (moving in the same direction as the wind is) and beginning to loose altitude. Control your altitude with little throttle inputs not the elevator. Be smooth, not jerky. Keep the altitude constant or slightly decreasing. About half way, think about the landing.

Begin to reduce the throttle. Your altitude will begin to drop. Make your turn to base, keep throttle on to keep your rate of descent constant or if you are satisfied with your altitude, add a little (a click or two) of throttle to maintain your altitude. Once on final, reduce the throttle a bit more, but not to idle. Watch the plane come in. It should not 'ballon'. If it does, then you are at to much throttle and are adding elevator which will cause it go head up and loose airspeed, and eventually stall. So, try to maintanin the constant rate of descent and watch the altitude. As said, throttle controls altitude. You should be slowly descending. Then once over the runway and ready to land, tweek remove the throttle (go to idle) and tweek your altitude with the elevator. Watch it come in, and when you are ready, slowly "tap" the elevator to slightly raise the nose. Airspeed will drop and the plane will settle in for a smooth landing.

Practice it over and over again.. doing touch and go's.... meaning after you have landed, and are rolling, add throttle slowly but LEAVE THE ELEVATOR ALONE. At a point, the plane will lift on it's own and begin flying. Adding elevator to soon then the plane becomes balistic and is not flying.. it is being dragged along in the air by brute power. Let the plane fly itself.. it will. After it lifts off, do a couple orbits and begin at step #1 at the beginning of the upwind side and begin your approach..

Upwind.. heading into the wind. Downwind leg.. going in the same direction as the wind, base.. you are going perpendicular with the runway, final, you are now headed into the wind again, but are decreasing altitude because your airspeed has dropped. Racetrack patterns should have square ends. You fly straight in front of you, turn 90 degrees, straighten out, turn 90 more degrees, now you are headed in the opposite direction. Do this again at the end of the runway to end up in the direction to land... you are on downwind leg, turn 90 degrees, straighten out, turn 90 more degrees and your should be lined up for the landing. Oval turns do not let you get properly lined up unless you are very lucky.. Square turns like described will allow you to judge when to turn that 90 degrees to get lined up. I do that ALL THE TIME.. make 90 degree turns like that, and I practice it all the time too.

CGr.

CG's got the way, for sure...

A way I've told my students, and it's worked so far, is don't try to flare, as such. Instead, on late final, continue your glideslope until the plane is about a foot off the runway. The engine is at idle, the plane gliding. Try to fly the plane in this condition as long as possible without adding elevator. You'll find that you need to feed more and more elevator, as teh plane sinks. This is flaring. Finally, your plane is in a plowing glide, an inch off the runway, nose up and the wing finally makes less lift than the plane weighs. You land, and as slow as possible for that plane.

Now, this technique works great for more docile planes, but there are those that cannot be flared in, due to a tendancy to tip stall. Warbirds, in general, are a prime example. They must be flown to the ground, and indeed "flown" until they stop rolling, in many cases.

With that prop, slowing enough to flare will be easy. Harder will be remembering to keep some power on so it doesn't sink too fast!

J

I like to come in full bore about 10 feet off the ground, chop the throttle to idle, make a quick 180 degree turn and the plane sits right down like a helicopter.

I don't recommend beginners to land like that though!