Best RPM for Mooney 20 F

[Guitarmaster]

Ok. After reading Mike Busch's article,  I ran oversquare on the way to work yesterday.  3500ft, OAT 25F, 24"/2000.  Roughly 63%.  My observations....
 

1.  A bit strange.  Very quiet.  Mostly wind noise.  Sounds a lot like a turboprop.  I kept having to look at the airspeed to make sure I was still flying.

2.  IAS = 130 KIAS.  Slightly faster than 72% running 22"/2500.  Interesting.

3.  A little vibration.  No more than high RPM, but more low frequency.  Overall, the engine seemed to purr.  Zero sign of detonation.

4.  I don't have an engine monitor, but the CHT was NOTICEABLY lower.  See attached pic.  Again, interesting.  

5.  I think the ability to keep the power up in the descent should be really good in regard to "shock" cooling during descent and not unwinding the engine.

6.  Although there is no measurement, there is clearly increased torque on the crank.  Is this bad?  Don't know.  Mike Busch's experience would say no.

7.  No FF for me, but i would guess based on fuel added, burn is around 8.5 GPH.  Interesting.  Of course, lower RPM would equal lower FF.

I guess time will tell, but so far I can't really see a downside.  A majority of my flights are low altitude.  Anything above about 4000ft will probably see diminishing returns due to the red arc on the tach and so lower % power as MP decreases with altitude.

[bonal]

1 hour ago, Guitarmaster said:

I wish... nope, it's a Windsor.

Well if your making 400hp out of a Windsor your doing OK

[Shadrach]

8 hours ago, Guitarmaster said:

OK. After reading Mike Busch's article,  I ran oversquare on the way to work yesterday.  3500ft, OAT 25F, 24"/2000.  Roughly 63%.  My observations....
 

1.  A bit strange.  Very quiet.  Mostly wind noise.  Sounds a lot like a turboprop.  I kept having to look at the airspeed to make sure I was still flying.

2.  IAS = 130 KIAS.  Slightly faster than 72% running 22"/2500.  Interesting.

3.  A little vibration.  No more than high RPM, but more low frequency.  Overall, the engine seemed to purr.  Zero sign of detonation.

4.  I don't have an engine monitor, but the CHT was NOTICEABLY lower.  See attached pic.  Again, interesting.  

5.  I think the ability to keep the power up in the descent should be really good in regard to "shock" cooling during descent and not unwinding the engine.

6.  Although there is no measurement, there is clearly increased torque on the crank.  Is this bad?  Don't know.  Mike Busch's experience would say no.

7.  No FF for me, but i would guess based on fuel added, burn is around 8.5 GPH.  Interesting.  Of course, lower RPM would equal lower FF.

I guess time will tell, but so far I can't really see a downside.  A majority of my flights are low altitude.  Anything above about 4000ft will probably see diminishing returns due to the red arc on the tach and so lower % power as MP decreases with altitude.

Just so you can compare and contrast how I was running under similar conditions this past Sat in the same make and model (though JPI equipped) on a quick run to a neighboring airport.

Departure airport conditions - elevation 703', OAT 7C, Barometric pressure 30.04"

Cruise setting - 2500', 2500RPM, Full Throttle with Ram-Air open (~28.5" this time of year), mixture LOP adjusted to keep hottest CHTs in the 330 range (~30LOP), I don't currently have FF, but I'd guess it was a bit over 10gph @ 155KIAS (DA at alt was probably around 1000')

On the 24NM flight home, a King Air that I had departed ahead of called 15 to the SE of the field at 4000. I had just made my 10 mile call (I had no idea that we were heading to the same place). What's interesting about this is that tower called my speed over ground at 140Kts and the King Air at 190kts both heading into a >10kt head wind, I offered to let the gal in the King Air pass but tower sequenced me #1 and asked me to keep my speed up until 3 miles out. The Beech was on about a 2 mile final when I left the runway.

I'm not suggesting that everyone should run their plane the way I run mine. I will say that 20kts matters even more when running against the wind or in controlled airspace when blending with faster traffic.  Controllers will treat you differently. A plus is later running into pilots on the ground that were on freq earlier and their surprise when they see the vintage split windshield and guppy mouth, as almost all of them expected something newer with 2 more cylinders.

[Marauder]

Ok. After reading Mike Busch's article,  I ran oversquare on the way to work yesterday.  3500ft, OAT 25F, 24"/2000.  Roughly 63%.  My observations....

 

1.  A bit strange.  Very quiet.  Mostly wind noise.  Sounds a lot like a turboprop.  I kept having to look at the airspeed to make sure I was still flying.

2.  IAS = 130 KIAS.  Slightly faster than 72% running 22"/2500.  Interesting.

3.  A little vibration.  No more than high RPM, but more low frequency.  Overall, the engine seemed to purr.  Zero sign of detonation.

4.  I don't have an engine monitor, but the CHT was NOTICEABLY lower.  See attached pic.  Again, interesting.  

5.  I think the ability to keep the power up in the descent should be really good in regard to "shock" cooling during descent and not unwinding the engine.

6.  Although there is no measurement, there is clearly increased torque on the crank.  Is this bad?  Don't know.  Mike Busch's experience would say no.

7.  No FF for me, but i would guess based on fuel added, burn is around 8.5 GPH.  Interesting.  Of course, lower RPM would equal lower FF.

I guess time will tell, but so far I can't really see a downside.  A majority of my flights are low altitude.  Anything above about 4000ft will probably see diminishing returns due to the red arc on the tach and so lower % power as MP decreases with altitude.

BTW -- the cylinder temps you are seeing at that power setting is what I would see with full power on a cold winter day.

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[Guitarmaster]

3 hours ago, Shadrach said:

Just so you can compare and contrast how I was running under similar conditions this past Sat in the same make and model (though JPI equipped) on a quick run to a neighboring airport.

Departure airport conditions - elevation 703', OAT 7C, Barometric pressure 30.04"

Cruise setting - 2500', 2500RPM, Full Throttle with Ram-Air open (~28.5" this time of year), mixture LOP adjusted to keep hottest CHTs in the 330 range (~30LOP), I don't currently have FF, but I'd guess it was a bit over 10gph @ 155KIAS (DA at alt was probably around 1000')

On the 24NM flight home, a King Air that I had departed ahead of called 15 to the SE of the field at 4000. I had just made my 10 mile call (I had no idea that we were heading to the same place). What's interesting about this is that tower called my speed over ground at 140Kts and the King Air at 190kts both heading into a >10kt head wind, I offered to let the gal in the King Air pass but tower sequenced me #1 and asked me to keep my speed up until 3 miles out. The Beech was on about a 2 mile final when I left the runway.

I'm not suggesting that everyone should run their plane the way I run mine. I will say that 20kts matters even more when running against the wind or in controlled airspace when blending with faster traffic.  Controllers will treat you differently. A plus is later running into pilots on the ground that were on freq earlier and their surprise when they see the vintage split windshield and guppy mouth, as almost all of them expected something newer with 2 more cylinders.

10GPH @ 155KIAS.  That great!  

With that power setting and LOP, doesn't that put you in the "red box?"  I need to go back and look at this.

[Guitarmaster]

1 minute ago, Marauder said:

BTW -- the cylinder temps you are seeing at that power setting is what I would see with full power on a cold winter day.

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No doubt the cold air has much to do with it.  It is cooler than last year running the same power % "undersquare" with the same conditions.  Of course, I have never had a problem with cooling of the engine in my airplane.
What I though the most interesting was the increase in IAS.  it's only a knot or two, but it is there.

[Shadrach]

2 hours ago, Guitarmaster said:

10GPH @ 155KIAS.  That great!  

With that power setting and LOP, doesn't that put you in the "red box?"  I need to go back and look at this.

I know it was more than 10, but I don't know how much more than 10 (probably close to 11 +/-). No way, I was going that fast on 75% power. 

As any propulsion engineer will tell you, the red box is a "fuzzy box" (no jokes please, Chris)...  At 30LOP with an OAT in the low 40s (cowl flaps closed) my CHTs were in the range below:

#1) 297

#2) 332  

#3) 326

#4) 294

Oil temp 176 (almost time to winterize)

No way my engine is anywhere close to detonating with temps like that. I should have gone full rich "per the POH" to see what CHTs that would yield.  The notable thing is that my CHTs run closer together LOP than ROP.  I have seen my internals after running this way for 880hrs (split case because of crank case crack). I have enough of my own data to know that given the choice, I will never run a NA injected engine in low altitude cruise on the rich side of peak ever again.

APS is very conservative with their definition of the red box (as they should be).  They are supplying information to folks flying all sorts of engines O, IO, TIO, TNIO, TSIO, GTSIO, etc... They all have different temperaments, but if the engine is well instrumented and the operator has a fundamental understanding combustion science, they can be run at optimal efficiency ratios.  

I wish I was TN'd and intercooled, If I could get my airplane to run at this setting at say 17,500' I think it would be a truly impressive performer.

[Marauder]

1 minute ago, Marauder said: BTW -- the cylinder temps you are seeing at that power setting is what I would see with full power on a cold winter day.

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No doubt the cold air has much to do with it.  It is cooler than last year running the same power % "undersquare" with the same conditions.  Of course, I have never had a problem with cooling of the engine in my airplane.

What I though the most interesting was the increase in IAS.  it's only a knot or two, but it is there.

I often wondered how linear the factory CHT was. When I compare my JPI CHT against the factory value, the JPI always seems to run a bit warmer.

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