No change in RPM or OilP when cycling prop

[Hair_Helmet]

On 6/9/2021 at 6:36 PM, FlyingCanuck said:

Interesting. I have the Hartzell 3 blade Top Prop conversion on mine

Couple months of flying this MT has been interesting.  I've done a few 2 hour trips dialed back to 2000 rpm, gph drops 20% and 5-10 mph less depending on altitude. 

[cliffy]

HM Standard Hydromatic props have oil on both sides of the dome piston and the oil needs to be cycled out of both sides on run up hence the "3 pulls" (A&P school on big radials)

We have oil on one side only no need for 3 pulls  Only function check

Has anyone checked the "clocking" of the gov arm disc and or how far the prop control actually pulls the disc around to shut off the flow of oil

 to reduce RPM?  It may be just an adjustment of the gov segment disc. 

I'll bet you tried it in flight at a higher RPM than 2000 Right?

[A64Pilot]

I still do three pulls.

Why? because it’s a dead end, think like a syringe, you can only pull oil in and let it out of the same hole, so your best chance in flushing the system is with multiple cycles, like rinsing out a syringe.

I’ve pulled a few props and found a bunch of sludge there and want to try to prevent it building up. It’s actually sort of normal for there to be sludge.

[A64Pilot]

On 8/25/2021 at 8:27 PM, Hair_Helmet said:

Couple months of flying this MT has been interesting.  I've done a few 2 hour trips dialed back to 2000 rpm, gph drops 20% and 5-10 mph less depending on altitude. 

In theory the system becomes more efficient at lower RPM, prop is more efficient due to less drag and motor also has less drag. I say in theory because it’s not been enough for me to measure once you isolate RPM as the only variable.

Just the shade tree mechanic in me, but I believe an engine is “happiest” at the RPM it’s smoothest at, so I now pick one of the RPM’s it’s smooth at. 

Lower RPM is usually quieter so, if it’s smooth at 2000 go for it, mine however isn’t.

[Hair_Helmet]

On 9/4/2021 at 6:55 AM, A64Pilot said:

In theory the system becomes more efficient at lower RPM, prop is more efficient due to less drag and motor also has less drag. I say in theory because it’s not been enough for me to measure once you isolate RPM as the only variable.

Just the shade tree mechanic in me, but I believe an engine is “happiest” at the RPM it’s smoothest at, so I now pick one of the RPM’s it’s smooth at. 

Lower RPM is usually quieter so, if it’s smooth at 2000 go for it, mine however isn’t.

I've done a number of trips now at various rpm's, and have been a bit cautious about using higher manifold pressure than rpm; although some say sticking to the square method is an old wives' tale.  Maybe someone has some thoughts or guideline on this.

I seem to lose 5-10 mph at 2000 rpm depending on the manifold pressure with about 20% less fuel.  The sweet spot for speed is 2400 rpm.  Smoothness wise it's a great prop throughout the range, but I really need to try a number of settings and record the data.

[carusoam]

The challenge at altitude…

The slower the rpm… the less fuel can be burned… speed drops.

The faster the rpm… the more fuel can be burned… speed increases.

 

Vibration and sound can also be reasons to find a comfortable combination of MP and RPM…

PP thoughts only, not a mechanic…

Best regards,

-a-

[1964-M20E]

@FlyingCanuck 

  Did you ever figure out what happened?

I recently had mine hydraulicly lock.  That is oil on both sides of the piston.  Pull the grease fittings to see if there is motor oil in the hub.  If so that's your problem.  Supposedly this is a very rare occurrence.

 

 

 

[PT20J]

On 10/19/2021 at 9:21 PM, Hair_Helmet said:

I've done a number of trips now at various rpm's, and have been a bit cautious about using higher manifold pressure than rpm; although some say sticking to the square method is an old wives' tale.  Maybe someone has some thoughts or guideline on this.

I seem to lose 5-10 mph at 2000 rpm depending on the manifold pressure with about 20% less fuel.  The sweet spot for speed is 2400 rpm.  Smoothness wise it's a great prop throughout the range, but I really need to try a number of settings and record the data.

For a fixed airframe configuration and density altitude, true airspeed is a function of thrust horsepower. If you are going faster or slower with different rpm and MAP combinations, it is because the thrust horsepower is not the same for all settings.

Generally, higher MAP and lower rpm yields better engine efficiency. This primarily due to reduced friction horsepower losses internal to the engine, but it also allows more time for the combustion event to complete which increases thermal efficiency. For constant thrust horsepower, this shows up as a lower fuel flow, not a TAS increase.

Thrust horsepower is brake horsepower (engine output at the propeller shaft) multiplied by propeller efficiency. Propeller efficiency is generally greater at lower rpm, but not very much over the useful range of rpm available to get required power at altitude. Former Mooney factory test pilot Bob Kromer has stated that the M20J prop was optimized for 2500 rpm.

Any combination of MAP and rpm that is in the POH is safe to use.

Skip

[JamesMooney]

Update: problem solved.

When the engine control cables were inspected, the prop control cable was re-rigged incorrectly. It was set up too short, and therefore was not giving full range of movement. It was not hitting the forward stop. Thanks to excellent advice from Byam Propellers and Henry Weber, the problem was addressed quite quickly. The prop now cycles properly at 1,900-2,000 RPM and produces at least 2,600 RPM on the ground in static testing.