Prop governor

[jwx96]

What’s the lowest I can set my manifold pressure and expect to have the prop hold 2400 RPM. I recall being able to fly at 17/2400 but now I am seeing the prop follow the manifold pressure and start slow as I reduce the manifold pressure lower than 22 inches. 2003 DA40, Woodward governor - overhauled 350 hrs/ 2 years ago, MTV12B prop also overhauled at the same time. Oil pressure is normal. Oil temp is 159. OAT -15C. Thanks

[Rich]

This is not likely the governor. The governor can only constrain the prop's RPM by increasing pitch. The spring and aerodynamic forces should be the factors in reducing pitch to maintain the RPM.

The low temperature may be a factor, coupled with the fact that a few years ago MT went with tighter-fitting prop blade seals. One example is this has resulted in the prop being slow to return to the 2000 RPM when cycling the prop at runup. I speculate that the -15C is causing a further tightening of the seal/blade interface. Is this new behavior with the cold weather? As a test, try reducing the MP and lowering the nose to pick up airspeed which might be enough to cause RPM to come up again.

[jwx96]

Thanks Rich. I understand what you are saying about the role of the governor. Yes, the new behavior does seem to correlate with the cold weather, but I didn't have the same problem last winter. At my runups the prop returns quickly to 2000 RPM but everything is toasty then related to the plug-in engine heater and a good insulated cowing cover. The prop speed did not come back up to 2400 when I started my descent yesterday with the manifold pressure set at 17-18. I'll try your idea to see if I can get a faster descent to bring up the prop speed and I'll try things on a warmer day too, and I'll see if there is a difference the farther I get from my preheat. But, can you answer, should I be able to set the MP at 17 and the prop at 2400? That's what I recall using for instrument approaches, but this problem is causing me to question my memory. Thanks again.

[Rich]

Thanks Rich. I understand what you are saying about the role of the governor. Yes, the new behavior does seem to correlate with the cold weather, but I didn't have the same problem last winter. At my runups the prop returns quickly to 2000 RPM but everything is toasty then related to the plug-in engine heater and a good insulated cowing cover. The prop speed did not come back up to 2400 when I started my descent yesterday with the manifold pressure set at 17-18. I'll try your idea to see if I can get a faster descent to bring up the prop speed and I'll try things on a warmer day too, and I'll see if there is a difference the farther I get from my preheat. But, can you answer, should I be able to set the MP at 17 and the prop at 2400? That's what I recall using for instrument approaches, but this problem is causing me to question my memory. Thanks again.

My ordinary cruise descents are around at ~15" and it maintains 2400. Same with instrument descents at 10" and 90 KIAS. Level patterns are flown at 15" and 2400 (90 KIAS) is still there. But I haven't flown it this cold - ever. My prop was overhauled in late 2022 and still doesn't return to 2000 at runup.

The worst possible case is something I experienced in 2009. The blade bearings failed (actually broken into chunks) and the prop was all sort of wonky until it was rebuilt and this problem was discovered. This was thought to be a crappy grease MT used back then and no longer does.

Other than the small amount of engine oil that is used to push against the piston in the prop and maybe conduction from the crankshaft the prop is sitting out there exposed to the cold air. Grease congealing? Anyone else seeing this? How about our Canadian Brethren?

[jwx96]

My shop is making some phone call to to get some opinions. I talked to Jürgen ant MT and my shop is going to talk to him too. I talked to another shop and to Brandon at Savvy QA. The recommendations are varied and include working with the governor, the prop and also performing a Lycoming oil leak test. We removed the governor and I drove it to a nearby prop shop that bench tested it for free and it checked out ok.

If it’s likely the prop I may want to invest in a new prop rather continuing to work with this one. It’s been repaired 2x since its most recent overhaul in 2021 - 390 hrs ago. Can anyone provide me with the wt and balance numbers for a 2002-3 DA40 with the 2 blade Powerflow compatible Hartzel aluminum prop. My current W&B numbers are 1692 lbs and CG 95.8. Thanks!

To answer Rich’s question - yes when I put it into a dive the RPM increased from 2000 to 2300 but not back to 2400. Also, for each successive t/o the max RPM was 100 RPM lower starting at a normal 2680. And toward the end of the flight I couldn’t get more than 2460 RPM in cruise at 3000 ft with both levers full forward. The symptoms are somewhat intermittent. For example, for the first 30 min of my flight the prop behaved mostly normal, but with on occasional 15-30 sec lag before it found 2400 RPM after a throttle reduction. When I came in for my final landing the prop held 2400 RPM with a MP pressure of 12”.

[Rich]

Symptoms sound much like mine back in ‘09. Bearings all were shot, as well as the blade ferrules.

The Hartzell composite is a basically a wash with respect to W&B relative to the MT. The Hartzell aluminum will add 16 lb to your empty weight. I did the CG calculation for that aluminum prop some time back and CG moves forward by 1 or 2 tenths of an inch.

But the bad news? Hartzell has been sucked up by some investment firm pirates and according to AVWeb they have just announced major price increases (50% and above) across all products.

[mhoran]

Here's the W&B for our 2007. The G1000 and active traffic push the final CG rearward, but you should be able to use the raw numbers for your calculation.

[Rich]

I need to correct my earlier statement.

I just revisited my what-if spreadsheet, where I can add/remove things and test their effect on w&b. My plane is 1699/95.51 right now with the MT. Adding the Aluminum Hartzell makes it 1715/94.76. The CG moves by a whopping .75 inch.

The data open to question is not the relative prop weights, but the moment arm of the prop. I measured its location relative to the wing root reference defined in the POH W&B section and came up with a moment arm of 15 inches. (Calc: 86.4 minus 71-ish inches). Playing around with this and using 20 inches still gives a new CG of 94.81 - a movement of .70 inches. So it's not particularly sensitive to errors in this number.

[jwx96]

Thank you both! I’ll put the numbers into ForeFlight with my typical loads and see what I get. Yes, my shops here told me about what happened at Hartzell. Last year the price was around $6000 for the one I will consider. And I believe Hartzell also owns Syktech, PlanePower and Slick. Not good news.

[blsewardjr]

My 2003 DA40 with the Aluminum Hartzel PowerFlow Version prop is 1703 lb and 95.2. I've just replaced the aluminum prop with the Hartzel Composite. Awaiting the final numbers because the prop governor had to be overhauled when the new prop failed to make the required full power RPM. I am very glad I bought the new prop before Hartzell was sold.