IO-540 / Whirlwind 330 combo RPM Rise on Takeoff (is this normal?)

[mulde35d]

On my RV-10 I am running a Barrett IO540 with 9:1 , Dual PMAG, and CAI that puts out 290hp. I have a Whirlwind 330-78" 3-blade prop. I have used Vic's video to set my blade pitch on the prop nut and confirmed the governor is not the limiting factor. On my takeoff roll the RPM rises drastically and I am wondering how normal it is or if others with this combo have the same results. I know this is not really an issue on the 2-blade Hartzell's.

Maximum power takeoff (27" Mp)
Static: 2250 RPM
40 KIAS: 2350 RPM
70 KIAS: 2550 RPM
95 KIAS: 2650 RPM (initial climbout speed)
100 KIAS: 2700 RPM
105 KIAS: Over 2700 RPM Redline without engaging the governor.

As you can see it is a 400 rpm rise from static to climb airspeed. My technique is to engage the governor on the initial climb before accelerating past 100 KIAS. I considered increasing the blade pitch to aerodynamically limit the RPM more and prevent RPM overspeed above 100 KIAS, but then my static RPM is dropping below 2200 RPM and increasing my takeoff distance.

Anyone else seeing similar results? Most other aircraft I have flow have a slight RPM rise from static, but not 400 RPM.

 

[justa6ereh]

What do you mean by engage the governor?

 

[TParker]

This indicates that you need to adjust both the low pitch on the propeller and the high RPM stop on the governor. The propeller low pitch setting is too high of an angle, which is why your static RPM is so low (2200) and why you see a large range of RPM change. Your governor max RPM stop is too high, which is why it's going over redline before you pull in the knob/lever. You want the governor and knob/lever set so that it will control at 2700 RPM without you having to touch it.

Start with the propeller, and adjust the nut so you get something like 2600 RPM at full power, static. Then, adjust your governor high RPM stop so that with the knob/lever all the way in, and in flight, it controls at 2700 RPM.

 

[justa6ereh]

I’ll go a step further here…what you are describing, is how a fixed pitch propellor functions. If you have set the low pitch stop, you should get 2700 rpm right from the point of full throttle application and the governor will keep it there as you accelerate, until you reduce the propellor rpm, with the prop control.


that doesn’t sound like what you have going on,

 

[mulde35d]

This indicates that you need to adjust both the low pitch on the propeller and the high RPM stop on the governor. The propeller low pitch setting is too high of an angle, which is why your static RPM is so low (2200) and why you see a large range of RPM change. Your governor max RPM stop is too high, which is why it's going over redline before you pull in the knob/lever. You want the governor and knob/lever set so that it will control at 2700 RPM without you having to touch it.

Start with the propeller, and adjust the nut so you get something like 2600 RPM at full power, static. Then, adjust your governor high RPM stop so that with the knob/lever all the way in, and in flight, it controls at 2700 RPM

While I agree that would do it, I thought the whole point of Vic's video on setting the propellor pitch nut stop was to prevent an extreme overspeed should the prop governor fail. By doing it the way you described, any failure of the prop governor to control the RPM would result in an extreme overspeed of the prop (likely over 3,000 RPM). Am I interpretting Vic's video improperly?

 

[justa6ereh]

Your low pitch stop needs to be set around 2650 static.
Then the governor holds it there, by coarsening the pitch as you accelerate.

 

[TParker]

While I agree that would do it, I thought the whole point of Vic's video on setting the propellor pitch nut stop was to prevent an extreme overspeed should the prop governor fail. By doing it the way you described, any failure of the prop governor to control the RPM would result in an extreme overspeed of the prop (likely over 3,000 RPM). Am I interpretting Vic's video improperly?

The low pitch stop should not be thought of as a means to protect against, or limit the amount of, overspeed across the entire flight envelope; you'll end up using it as a fixed pitch prop if you try to set it that way, negating the benefit of the constant speed prop. So you have to choose what part of the flight envelope you're trying to protect, and to what degree.

I'd recommend thinking of it as a means to give yourself a useable fixed pitch prop in an emergency situation; enough to keep the airplane in the air in level flight at low speeds and low altitude without an extreme overspeed. Because the low pitch setting also impacts the every day performance of the aircraft, and things like drag on approach and stall speeds, it's a compromise. How you balance those objectives for your aircraft is up to you as a homebuilder.

 

[justa6ereh]

Basically what you have done, is to increase your your low pitch stop, thereby increasing your blade pitch, to such a degree that your engine is bogging down, not letting your prop move to it’s low pitch setting.

Go back to Vic video…adjust your prop so that you flatten the blade angle till you get 2650 at full throttle, then adjust your governor so that at that low prop ( flat pitch setting) your governor is on the stop.

Now when you accelerate to full throttle, at the beginnning you will see 2650 and once you are moving the prop will coarsen it’s pitch to govern it to 2700 rpm’s, till you initiate an rpm reduction.

Hopefully that helps…I think you maybe mis-interpreted his video on the “runaway governor scenario…” during takeoff…if you’re engine were to overspeed, you’d pull the power back, until you got back on the ground to adjust it.


With a 540…I’d secure the airplane on the ground, to do my full power run up…

 

[andoman]

Or do the static check on the runway at the very start of the roll. Advance throttle smartly and note peak RPM before moving more than a few plane lengths.
For some, a tied down full throttle run is fraught with anxiety. Especially with a big prop and engine! And it’s a production compared to the takeoff roll method.

 

[kiwipete]

Jon

You need to break this process down into two separate parts.

1) static rpm (or as suggested above full throttle rpm on the start of the takeoff roll when the throttle is advanced quickly - say 2 seconds to full open) your aiming to get approximately 2650. I know on the IO540 that the difference between 2600 and 2700 rpm is only 10 hp so your only loosing 3-4% power for a couple of seconds
This is set using the propeller fine pitch stop.

2) governor max rpm. This is set once your airborne. The easiest way is if you need to pull the prop lever back to get it under 2700 then try to set it exactly for 2700 then don’t adjust it and land. Remove the cowls and you’ll notice a gap between the lever arm on the governor and the adjustable stop. Wind the stop in until it rests firmly against the lever arm. Then fly and check and adjust again if necessary. From memory one turn of the stop is approximately 25 rpm.

If you’re not 100% clear in this process it’s a good idea to seek some help from an experienced aircraft maintenance mechanic. It’s not something that you really want setup wrong as a prop over speed can destroy both the prop and engine.

Regards Peter

 

[mulde35d]

I appreciate everyone helping me see where I misinterpreted the video. Went out and adjusted my prop pitch so I am getting 2630 static. Adjusted the governor stop to where I think it is right. Will finish the fine adjustment tomorrow.