ODD prop question!

[wadeg]

Here is an odd prop question:
Of the 912s ground-adjust props available, which one creates the least thrust at idle?
Being that the 912s idles so high, on approach, its inability to slow a prop drives me nuts. It is always a battle to get a steep approach without burning up a lot of runway in a float.
Please keep focused with the question. I have already done the following:
-reduced pitch
-broken the 1.3x vso rule
-slipped hard
-reduced idle setting to compensate for windmilling.

My only beef with the series 7 is the battle to bring it down steep. After 6 yrs of flying it, I still grumble after every shallow approach. I am wondering if a prop other than my 3 blade warp drive taper tip would be worth a shot.

Anyone got pointers????

[n85ae]

This might be reciting what you just said you have done, BUT it works for me.

I have an IO-240B so mine is obviously different, but here's my experience

I used to have that problem, and I overcame it by learning to fly my plane
very slow on short final. It will get a good sink rate, AND with a safe margin
above stall, but it takes a lot of practice because it just feels much too slow.

Go up to altitude and practice power off descents, and stalls in descents. Not
stalls in level flight, but in practice landing approaches. This will help since
you will get more of a feel for controlling the plane while it's sinking. At least
that's what I have done, and it helped me a lot.

The plane will drop like a brick in a slow slip as well. How slow? Go up to altitude
and practice that as well. I have put mine in a full rudder slip at altitude, and
brought the nose up to the point of cross control stalling it, and it gets so
much buffeting over the turtledeck it's very easy to tell when it's about to
break. In any case slowing it way down is the key.

Mine rivals the best sailplanes out there if I come over the numbers with ANY
extra speed. However the nice thing is the plane handles very well going slow
and any impending stall is easily cured with just relaxing the stick or touch of
power.

Hope that helps.

Jeff

[Av8r3400]

Set your idle screws to give a 1200-1500 idle when on the ground. This is too slow to idle the motor, but is just fine if you manually give a little to keep the 1800-2000 for taxiing and warm up. What it will do is allow you to get 1800-2000 on final with some drag added from the windmilling prop.

After that keep your speed at or below 60 mph in final any you'll do fine.

[Danzer1]

I think what Jeff is trying to describe is a forward slip. Read this article: http://www.flyingmag.com/technique/t...g-forward-slip

Practice at altitude and/or find an "old school" CFI to practice with.

Greg

[jiott]

Also remember that if you set your idle at the minimum 1400 rpm that the prop speed is 1400/1.43=979 rpm due to the gear reduction; which is not that much different than a direct drive Lycoming, etc.

Float is not really a function of prop speed because you can adjust your
airspeed to as slow as you want with AOA. To minimize float you must be very close to stall at the time you flare. Its all a matter of AOA control and how close to stall you want to cut it on short final. After doing all this, the float is then just a matter of airplane design, ie. wing area, weight, flap configuration and drag. I have been experimenting with using full flaps on my SS7 and it does help with a steeper approach (more drag).

Getting back to the original question, there may be a prop out there that has less thrust at idle compared to higher speed, but I don't think it will make much difference because airspeed is still controlled by AOA and not throttle (thrust). I do agree that a prop with less thrust (more drag) at idle would steepen the approach angle at the same airspeed, but would only have a minor effect on float providing you control airspeed to just above stall. With the airplane design we are stuck with (a very good one IMHO) increasing drag is the only option we have to steepen our approach and I believe using full flaps will have much more effect that a slight difference in prop drag at idle.

Sorry for the long reply, but I have been struggling with the same issues and these are the conclusions I have come up with.

[jiott]

I have completely ignored slip in my previous post because it is a totally different technique in our toolbox (and a really good one to be sure). I believe the original question was addressing the basic physics on a stabilized approach.

[n85ae]

Yeah that thing you do when you cram the pedal all the way to the floor
and look out the side window to land. Exactly, that's what I meant. It's good,
plane falls from sky much better.

Jeff

I think what Jeff is trying to describe is a forward slip.

[wadeg]

Thanks for all the input! Had a very busy work week and came back to some great tips!
I especially take note of the mention about being just a tiny bit fast destroys a steep descent.

[N981MS]

Late to the party but I agree with the previous posts. Get comfortable with getting slow. No one mentioned something I have noticed, however. While on the approach and too high, I have an instinctual urge to put the nose down even with 700 Kitfox hours. The correct action is to keep the nose (AOA) up and thus the speed down. It is an unusual sensation and really takes some getting used to.

Keep us posted.