Adjusting Max RPM

[DanH]

Tell me about adjusting the maximum RPM setting for a Hartzell CS prop.

Today I tied the airplane, pulled the spinner, and made a few full throttle runs, adjusting the low pitch stop screw each time as indicated in the prop manual. Took about two full turns to get the 2650-2700 RPM range static at WOT.

First takoff was fine, 2710 RPM. However, later when doing T&G's I looked down and saw 2800. Only idea I have is warmer oil, 185F vs 100-120F on the first takeoff with Phillips 20-50.

So what gives? Am I missing something?

[Hwood]

Dan......Congrats on getting airborne!

No expert here, but I had high rpms as well (IO-360/Hartselle/MT gov). I simply adjusted the MT gov so it would limit. Worked great.

[Andrew M]

On the certified engine, prop, governor installations, the low rpm stop (internal) is left alone. As long as the engine make rated rpm at minimum stall speed or there abouts I let it fly. I think it has something to do with the range that the governor can govern. Adjustments to the governor are with hot oil, because you are either adjusting oil in, or limiting oil out. (oil is flowing through). Another reason the low rpm stop is set at a flying speed is in the event of governor failure. You can get rated power at a flying speed without an overspeed.
I honestly can't say I know this for sure, It's one of those "tribal knowledge tidbits" the FAA is loath to acknowledge without something written from some authority, but it does make sense.
Andrew
AP IA
-9 preview

[Walt]

Originally Posted by DanH

Tell me about adjusting the maximum RPM setting for a Hartzell CS prop.

Today I tied the airplane, pulled the spinner, and made a few full throttle runs, adjusting the low pitch stop screw each time as indicated in the prop manual. Took about two full turns to get the 2650-2700 RPM range static at WOT.

First takoff was fine, 2710 RPM. However, later when doing T&G's I looked down and saw 2800. Only idea I have is warmer oil, 185F vs 100-120F on the first takeoff with Phillips 20-50.

So what gives? Am I missing something?

Sounds like you've done everthing correctly, now you just need to adjust your governor back to the 2700 limit. The low pitch stop is only for static RPM setting.

[Andy Hill]

Dan...

1. FPS. I'm not brave enough to do the FPS via tie-down / full power runs. For ours, and those I test fly, I do it incrementally with aborted takeoffs / short accel runs, and later just observations on takeoff. Look for Max Rpm achieved with an unusually sharp opening of throttle.

2. Governor - does not usually need adjusting.

If I had an aim, I would set 1 to 2600-2650 RPM, and 2 to 2680-2690. By setting 1 a little low, all it does is deny you full power at, say, <20KIAS, by 30KIAS the airflow will allow RPM to get to 2700+.

T&Gs will always be a problem, especially if you do not let IAS decay to almost zero. The rapid acceleraiton of the engine does not give the governor (and the MT ones are probably not the best) a chance to limit to 2700. Solutions are to:

1. Slow to almost a halt before applying power
2. Advance throttle more slowly, or in 2 stages - second stage more slowly
3. Accept there will be overswing, NB Lyc allow 10% (2970RPM) for 3s, check Prop as well.
4. Problem will be reduced by setting 1 to 2600-50 rather than 2650-2700

This is an area where our fancy EFIS systems do us no good - in the old days, where 2600-2700 was <1/4" on a gauge, usually viewed with parallax, we did not notice this all going on. Now get 2701RPM for 0.1s and red lights, bells, end of world is nigh declared

Andy
RV-8 G-HILZ

[Bob Axsom]

This is an interesting topic to me. You may know that I try to increase the speed of my RV-6A as much as I can. So far this has been accomplished mostly by drag reduction and thrust increases have been limited to buying a blended airfoil Hartzell C/S prop with F7496 blades to replace my older design with F7666 blades and backing out the prop governor control arm rotation limiting screw to where the arm travels all the way to the structure that the limit screw is mounted in. The prop change did increase the top speed at 6,000 ft density altitude by 3 kts as revealed by Van's tests reported in the RVator. The Governor limit screw adjustment allowed the rpm upper limit to be increased from 2600 rpm to 2720 rpm. I normally cruise at 2450 rpm but I would like to get the additional rpm for racing that is within the "no action required" rpm limit or upper rpm margin (for the prop it is a percentage above the aircraft manufacturer's specification as I recall - 2700 will be my base number). I have not had the time to research this yet but it is a "to do" item in the future.

Bob Axsom

[DanH]

I'm not brave enough to do the FPS via tie-down / full power runs.

FWIW, this rig seemed to work well....

Took a look at the tailwheel spring and rear bulkhead structure, and decided against tying to the tailwheel. First task was firing up a blower and cleaning the asphalt in front of my hangar....no rocks or grit. I have a very big textile strap with loop eye ends, formerly the ballistic parachute bridle for an Eastern Bloc twin-engine lightplane. Formed a noose at each end and cinched them at the top of the gear legs, then ran a large double rope from the bight to my truck. Good solid attach point and much higher than the wheels, the usual noseover pivot. For insurance I grabbed two good buddies and positioned them in front of the stabilizer to keep some meat on the tail. They said it was very windy

Back to the prop. Great comments, more please!

[rv9av8tr]

Hey Dan,
Were you only seeing the 2800 during throttle up doing T&G's, or were you also seeing 2800 during a normal TO? I found my Hartzell speed control to be a little unstable during the first couple hrs of initial ops, then it settled in and has been rock stable.
I also had to screw in my low pitch stop screw to limit static / T.O. to 2700. All said and done, I was getting 2690 static. The first couple flights I saw it go to 2710 during climbout, but now it's turning ~2680 during climbout and has remained stable. Airborne, it takes about 1 turn on the Prop knob to get the governor to kick in.

[DanH]

Originally Posted by rv9av8tr

Hey Dan,
Were you only seeing the 2800 during throttle up doing T&G's, or were you also seeing 2800 during a normal TO?.

Good question. Saturday's two departures from rest showed around 2800, which is why I was adjusting the pitch stop on Sunday. The subsequent departure was in the low 2700 range. Exactly what I frankly don't recall; third flight, so right after liftoff I'm mentally busy as a one-armed paperhanger. The 2800 range showed up later after a touch and go.

Just dug out my A&P textbook; I need to read up on prop governing. Need to read up on GRT data logging too.

[Sid Lambert]

Dan, call Bill Woods about this. He had exactly the same issue in the first few hours.