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So your static RPM is 2580.. that’s ok, but you will get a little better acceleration at 2600 to 2650 static. The next question I have, are you able to hit 2700 rpm in climb? If not, then your governor needs to be raised. (You do have 1/8 to 1/4 inch before the knob hits the panel, right? You want the engine controls to fully hit their full range before they hit the panel)
Yup.. I find it takes 2 and 1/3 turn to get it about right. Did you fly it yet? It’ll probably get to 2700 just about the time you lift off, and will glide better when you pull to idle..
Not yet, maybe a week or so!
Since governor adjustments should be tested in flight, I used another method. Before doing run up on ground to full throttle, loosen the jam nut of the governor just enough to allow you to turn the stop set screw out. (maybe 1/4 turn of jam nut). Then back out governor stop several turns. Enough to know for sure your governor is no longer slowing the RPM's down.
Thanks, that is what I was thinking too.
Vic, I bought an RV-9A some time ago with a CS prop. I’ve never had any issues with RPM (fortunately), but also never knew about the process of setting the low pitch limits. I just watched your video…it was very helpful. Many thanks for the continuing education for RV owners!
Yes, it can be useful, though you'll want to zoom in a bit closer. What you've shown would tend to indicate that the low pitch stop is set low, and you're getting an overshoot before the governor catches it. The amount of overshoot will vary based on throttle application rate, and how low the stop is set.
Looks like you can’t maintain 2700 rpm in the climb? Raise your governor setting be backing out the screw on the governor.. and adjusting the cable so the blue knob isn’t bottoming on the panel before the governor hits the stop. Then to get rid of the surge, adjust the propellor low pitch stops to provide 2650 static. If you can’t maintain 2700 in the climb, you are not using the full 180 hp..
Thanks for the feedback. Here is the data zoomed to 28 seconds of the takeoff role and climb. The RPM is on the left vertical axis and MP and fuel flow is on the right. It does look like the prop is overshooting and stays at 2670 in climb.
If you can’t dial in 2700 while you are climbing, you also need a governor adjustment
Stick back, tail tied down, flaps up, and chocked.
Flaps up, stick back, brakes held, if the tail starts to rise, release the brakes!! I would not chock it, because it removes an option for you to release the brakes. Heck, you could even do it on the runway and perform a takeoff with the check. If you don’t want to split your attention, either bring a passenger to video the tach or set up a GoPro aimed at the panel.
Bear with me as I get my mind around the low pitch stop setting and see if my logic is correct. I have a 0-360, Hartzell C2YK-1/7666A-4 Propeller and a MT P - 420 - 3 governor. On takeoff, my engine data shows RPM increasing to 2730 for 1 second then decreasing to 2650 - 2670 during the roll. I apply throttle slowly. The propeller never gets to 2700 RPM except for the brief surge. At rotation and during climb fuel flow settles in at 17 - 17.5 gals/hr and MP at 29. The data would indicate the low pitch stop is set too low preventing the prop from achieving full RPM or is the governor is limiting the prop RPM? How do I determine which one?
On initial power application, it takes a second for the oil pressure from the governor to ‘catch up’. During that time the mechanical fine pitch stop limits rpm. Yours is above 2700, suggesting you need to move that stop (adjust on the nose of the prop) slightly coarser, toward lower rpm. Once you’re going, the governor kicks in, and limits rpm to 2670, very slightly low. Adjust the governor stop for slightly more RPM. Re-do your test. Most prefer the mechanical stop to limit initial rpm to around 2650-2670, and the governor set to 2680 or so. That way on every takeoff you can verify the stop is set correctly (best glide in an engine out) and the governor works (it will kick in half way down the runway).
It sounds like you will want to adjust both the low pitch stop and the governor. The prop low pitch stop being too low is why you get the surge, you'd probably get more surge if you slammed the throttle. The governor being set too low is why the RPM is a bit low in climb, the low pitch stop isn't in play in this situation.
Understandable. You can do this as a series of takeoffs as well, it will take more time; I'll outline this below.
As mentioned, you have the ability, and responsibility, to determine this as the builder/integrator for your experimental aircraft.
No. You want to turn the low pitch stop in, because it sounds like your pitch stop is set too low. Hard to know how much too low it is, because it's not currently limiting the RPM and the governor is catching it.
Yep, this took several trials for me, even though Hartzell's docs tell you approximately how far to turn it in order to reduce RPM by a given amount. You have to loosen the nut, turn the pitch stop "a little", tighten the nut, and then go fly. Repeat until your RPM behaves correctly. It helped to mark on the spinner bulkhead with a magic marker how far I previously turned the stop, so I knew roughly how much more adjustment I needed.
That’s why I recommend 2 turns.. If you go only 90 degrees at a time, you’ll have to do it 8 or 9 tries. Most hartzell props need 2 and 1/3 turns.
If you get 2700 as soon as you firewall it, then it is NOT set correctly. You should be getting 2550-2650 statically. You say that you aren’t getting any surge, but could that be because you are applying power soft and gently (as you should) and that’s masking any surge? Try bringing it up to about 2000 then shoving the rest in quickly and see if there’s any surge, I bet it probably will.
Nope, I can add power very fast and no overshoot.
On my fixed pitch -4, I go from 2100 static to 2700+ at cruise. That’s a 600+ increase from zero knots to 170 knots. I’m pretty sure if a governor let go on any CS equipped RV in cruise, they are going to have a massive overspeed. I know about a -14 that had a governor failure on takeoff and his prop went to 3000+ at liftoff and had no thrust, so he chopped the throttle and landed straight ahead and melted his brake caliper O-rings. Thankfully, no fire. Since then, he sent the prop out for inspection, had the governor overhauled and corrected his low pitch stops.
Yes you are right that if a governor failed at cruise it would be a serious overspeed. I don't think it would matter much if the pitch stops were set at 2600 or 2700 static rpm, its going to go well above 3000.
