M20J cruise settings

[ArtVandelay]

Speed depends on density altitude and humidity. For those of us in Florida are at a disadvantage when bragging about our speed.

[Ibra]

51 minutes ago, ArtVandelay said:

For those of us in Florida are at a disadvantage when bragging about our speed.

C'mon, near equator & earth spin? you should get some decent TAS numbers (vs earth center) on west-to-east routes 

https://www.nasa.gov/pdf/142825main_Bobsled_Launch.pdf

[skykrawler]

When travelling I use  22" and 2400 - to lower the noise.   ROP 10.o down low.  Peak or LOP up high.    Of course at altitude this is WOT.

If the temps climb I richen.

Down low this nets ~148kts,  increasing to 150 to 155 up high.

Fly high to stay away from the Indians.

 

[Shadrach]

35 minutes ago, skykrawler said:

When travelling I use  22" and 2400 - to lower the noise.   ROP 10.o down low.  Peak or LOP up high.    Of course at altitude this is WOT.

If the temps climb I richen.

Down low this nets ~148kts,  increasing to 150 to 155 up high.

Fly high to stay away from the Indians.

 

Interesting post. Your SOP is the precise opposite of mine.   Air and therefore power is available in greater quantities at low altitude so cooling with air (LOP) has less impact on cruise performance and a higher impact on reducing FF.  At high DAs there is less air available and therefore less power available it seems intuitive that the best course of action is to use all of the available air for combustion and use fuel for cooling (ROP).  My cruise ops are simple. I cruise at 2500 and as close to peak EGT as possible. Whether that's lean (down low) or Rich (up high) depends on altitude.

Your advice seems counter intuitive. Can you expound on your logic?  Also, seems highly unlikely that a J would 155KTS on 22" and 2400 LOP

[Shadrach]

On 1/10/2021 at 8:19 PM, larrynimmo said:

Most of my flights are under 50 nautical miles away...and some are in restrictive airspace.

when I fly greater distances then I do between 6k and 9k depending on winds

You should try WOT, 2500 and 40-50 LOP at 2000.   My stock F model turns about 155KIAS on ~11gph at that setting with nice cool CHTs. YOu;d likely do better.   If I ran 2450/24, 30LOP at 2000ft all of my CHTs would be well below 300.

[mike_elliott]

2 hours ago, ArtVandelay said:

Speed depends on density altitude and humidity. For those of us in Florida are at a disadvantage when bragging about our speed.

No were not

[skykrawler]

1 hour ago, Shadrach said:

 

Your advice seems counter intuitive. Can you expound on your logic?  Also, seems highly unlikely that a J would 155KTS on 22" and 2400 LOP

I didn't really offer as advice, just what I do.    My thinking is down low the %hp is higher and I want to avoid the critical pressures.    At higher altitudes the %hp is lower and its unlikely to end up where you can hurt the engine.   I rarely cruise low unless its a short trip and the winds are miserable (recent 100nm excursion was 30+kt headwind above 2500).   My engine monitor is older and doesn't have the digital values,  just the bars.

The true airspeed can be computed from the picture.

[PT20J]

12 hours ago, skykrawler said:

My thinking is down low the %hp is higher and I want to avoid the critical pressures.

22"/2400 at sea level is only about 60% power, so you can run the mixture anywhere you want without fear. Not saying what you do is wrong -- at such low power it could make sense to run at best power mixture to get the most out of the engine. But, it would be more efficient to run LOP at a higher MAP and you might go a few knots faster on less fuel. Might be something to experiment with. I presume that the concern about pressures is concern about detonation. Detonation requires high temperatures and high pressures. The FAA detonation margin tests for certification are run high power and at redline CHT. If you keep the CHT under control on a normally aspirated Lycoming at 75% power or less you will be fine. 

Skip

[moosebreath]

2600 rpm / WOT. 100 deg ROP.  I did not pay all that money to go slow.

[dsking001]

I normally cruise 6-8k. At that altitude I run 2500 RPM, WOT, and 75-50 ROP. This yield a consistent 153 KTAS at 10.3-10.8 GPH. If I see something different than those numbers I start checking things. At altitudes >9 I usually run 2600 RPM, WOT and 30-50 ROP. I usually see about the same 153 KTAS (maybe a knot or two less if it's bumpy) and 9.8-10.2 GPH. At low altitude (I rarely cruise at this altitude) I pull the MP back to 25" and still run 2500 RPM. I will get 153 plus a knot or two, but I will keep the mixture rich. I usually burn closer to 12 GPH in this case and typically am sight seeing rather than cruising.

Hope this provides some insight.

[ArtVandelay]

The true airspeed can be computed from the picture.

Not without OAT.

[N201MKTurbo]

27in/2400 LOP 1550 TIT 155 KTS 9 GPH

[ZuluZulu]

Went up today and tried 2500 RPM at 6500.  MP was 23.7.  CHT: 355/362/357/346.  11.8 GPH.  139 KIAS, 159 KTAS, 157 KT GS (right quartering headwind at 7 KT).  The OAT seemed to be bathed in sunlight: 82ºF indicated, with surface temperatures around 50ºF.

[Marauder]

23 minutes ago, ZuluZulu said:

Went up today and tried 2500 RPM at 6500.  MP was 23.7.  CHT: 355/362/357/346.  11.8 GPH.  139 KIAS, 159 KTAS, 157 KT GS (right quartering headwind at 7 KT).  The OAT seemed to be bathed in sunlight: 82ºF indicated, with surface temperatures around 50ºF.

The outside air temp has always been an interesting observation for me. I have the pilot side mechanical and electronic ones on the left wing (JPI 900) and rear fuselage (Aspen RSM). The wing and window one are usually within a degree or two but the fuselage one is typical 3 or 4 degrees C different.

[ZuluZulu]

11 minutes ago, Marauder said:

The outside air temp has always been an interesting observation for me. I have the pilot side mechanical and electronic ones on the left wing (JPI 900) and rear fuselage (Aspen RSM). The wing and window one are usually within a degree or two but the fuselage one is typical 3 or 4 degrees C different.

I've been thinking similar things since the G5s and OAT went in.  Rarely do I think, "yeah that sounds right."  Most of the time my reaction is, "there's no possible way that's right."  And it's almost always hotter than I expect, never cooler.  I need to figure out where mine is actually installed.  Could it be breathing hot exhaust in the slipstream maybe?

[Ragsf15e]

3 hours ago, ZuluZulu said:

I've been thinking similar things since the G5s and OAT went in.  Rarely do I think, "yeah that sounds right."  Most of the time my reaction is, "there's no possible way that's right."  And it's almost always hotter than I expect, never cooler.  I need to figure out where mine is actually installed.  Could it be breathing hot exhaust in the slipstream maybe?

Some installers go the easy route and stick it in a cabin fresh air intake somewhere on your cowl (pilot side on older airframes).  It should be outside the slipstream and shaded.  Typically under the wing, a foot or two outboard.  My jpi probe is a under the wing, pilot side.

[laytonl]

In my ‘92 J model I use 2500 Rpm and WOT. Based on my experience I use a chart for FF vs altitude and then adjust as needed to maintain CHTs at 360F.  This yields 160kts.  I have to keep the cowl flaps partially open during the summer in Georgia when below 8,000’.  Lee

[ArtVandelay]

The outside air temp has always been an interesting observation for me. I have the pilot side mechanical and electronic ones on the left wing (JPI 900) and rear fuselage (Aspen RSM). The wing and window one are usually within a degree or two but the fuselage one is typical 3 or 4 degrees C different.

You can adjust the JPI oat if it’s off, because it’s mounted in the cowling.

[jetdriven]

its not off by the same amount all the time.

[Electro]

On 1/10/2021 at 6:32 PM, EricJ said:

I'm usually at 8k-10k feet, always wot/2500, usually 100 ROP.   Gives a reliable 150 kts at about ~10.2 gph.

 

Just about exactly what I get.

[bradp]

I just flew today - LOP WOT 2500 at 6k 20 degrees LOP.  9.2 GPH. that gave me 150 Kts true.  CHTs 330-360.  Descended to 2000 on a vector and had 40 or 50 LOP, same setting 10. Something LOP and same 150 kts true.  My gami spread is a bit off since annual. 

[carusoam]

Congrats on the first post, Electro!

Don’t wait so long for the next one.

Best regards,

-a-