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First Flight in the RV-9A with the Constant Speed Prop

Ed_Wischmeyer

Well Known Member
When I bought my RV-9A, it had many things I wanted but not a constant speed prop. I had flown the factory demo quite some years ago with the same 160 HP and prop, and remembered that it had sparkling climbout, but remembered little else. After 237 hours in my -9A with the fixed pitch prop, I had my first flight today with the new prop.

On takeoff, the prop transforms the plane from a pussycat to a tigress. Takeoff power is now 160 HP, 100%, but with the fixed pitch, it was at best 80% as indicated on the Garmin. That's 32 HP more, or a 25% increase. It shows.

My technique is to take off with flaps 10 so that the plane lifts off in a less nose high attitude and the runway stays visible, particularly valuable on a narrow runway. With the fixed pitch prop, I retracted the flaps at 80 knots. On my first takeoff with the new prop, I was sitting there fat, dumb and happy, in no more of a hurry to retract the flaps than I had been with the fixed pitch prop. Quite promptly, the plane was at 100 knots and the flaps were still down. Oops! So now, as soon as the plane breaks ground, I start watching the airspeed and get the flaps up as the plane accelerates through 80. It happens quickly.

One quirk is that this governor (from Van's) allows the prop to overspeed to 2780 RPM unless you are glacial in advancing the throttle, and by the time you get to full throttle, you're already well off the ground. The prop quickly settles down to 2680 RPM at the max RPM setting, close enough.

In the pattern, all of the familiar aural cues of the fixed pitch prop are gone. I've got tons of constant speed prop time, but because the rest of the RV-9A was so familiar, I was expecting the former aural cues and tried to rely on them. There was lots more looking at the airspeed and manifold pressure on this flight than in previous flights.

I'd noticed on two high speed taxi tests (the first being the leak check) that the plane didn't seem to decelerate as I expected. This morning, I discovered that the idle was a high 1,000 RPM. Since we never touched the idle setting, this means that we were *almost* careful enough adjusting the throttle linkage for full throw in each direction. There's more descent rate and deceleration to be had once that's fixed. And although I'm normally pretty observant, there were enough distractions doing the high speed taxi tests that I completely missed that detail.

Other observations, including some foolers: the plane seems to need more nose up trim at low speeds (heavier prop); it's much, much easier to get the stall warning to go off in the flare than it used to be; and the mag drops were higher. Couldn't figure out that last but after a morning of flying, the mag drops decreased from 120 RPM back to 80 RPM; the #2 EGT seems lower relative to the other cylinders than I recall. I'll look at old recorded data to double check; and at the same fuel flow, the plane seems a few knots faster, but I have no hard data.

A friend actually did the first flight with the new prop two weeks ago for me (another story), and the engine seemed to have a minor ignition problem when taxiing out. I never observed that today, thankfully.

Takeaways:
* Below 110 KIAS, the extra power granted by the constant speed prop is transformational;
* The constant speed prop has a 2700 RPM limit instead of the 2600 RPM limit of the fixed pitch prop, so max cruise speed at high power should increase a bit;
* With the fixed pitch prop, I'd learned all the power settings for the traffic pattern, how much deceleration I could get on an ILS if ATC asked me to keep the speed up, etc. Have to start from scratch on all that;
* Descent and deceleration are TBD after the throttle linkage gets re-adjusted;
* The -9A did very well in high density altitude situations some years ago with the fixed pitch prop. It ought to sparkle now.

Perhaps the one detail that is rarely discussed in the never ending fixed pitch vs constant speed prop discussions is ease of flying. There's less workload with the fixed pitch prop, of course, but the aural cues of the fixed pitch prop also help make the RV-9A easier to fly.

On the first landing, the plane was exactly on centerline, stall warning on, very gentle touchdown one wheel at a time in the slight crosswind. And when I parked the airplane, the nosewheel was exactly, perfectly on the stripe. I've set the bar too high for future flights... But now to really learn the airplane. Five hours of Phase 1 is enough to learn what you need to test things and to learn to fly safely with the changes, but full experience will take more.
 
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go high, dial the RPM back to 2200, and lean it and you will be amazed at the fuel efficiency. have fun.
 
?One quirk is that this governor (from Van's) allows the prop to overspeed to 2780 RPM unless you are glacial in advancing the throttle, and by the time you get to full throttle, you're already well off the ground. The prop quickly settles down to 2680 RPM at the max RPM setting, close enough.?

Ed, it?s not a quirk. It?s indicative that the low pitch stop on the prop dome is not properly set. This is very common. Many people don?t have their low pitch stop set correctly. I cringe when I hear one surge on takeoff.

I?m assuming you have a Hartzell propeller. If so, reference the Hartzell Propeller Manual, p. 4-4 Operational Tests, Static RPM Check and p. 6-33, Maintenance Practices, Propeller Low Pitch Setting.

Basically, you?re removing the governor from the picture to allow you to adjust the minimum blade angle. This blade angle should be great enough so that at full throttle, the rpm can?t go above 2700 rpm in a static condition. I shoot for 2600-2700 rpm. After the the low pitch stop is set correctly you come back and adjust the high rpm stop on the governor. As soon as you get moving, the propeller unloads a bit and then the governor starts governing.

With the higher blade angle, it will get rid of the surging at takeoff and will increase your engine out glide performance. The improved engine out glide performance assumes a condition where you don?t have oil pressure and thus no control over the prop. The prop goes to low pitch without oil pressure. On takeoff, you can cob the power (although I don?t recommend the practice) without any fear of over speeding the engine and prop. Physics prevents it from doing so.

Good luck. Be careful doing full power engine runs.
 
What prop are you now using Ed? I swapped out the FP prop that came with my RV-9A project and have an MT CS installed. After flying CS prop on my RV-10, it was a no brainer to put one on the RV-9.
 
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