Missing cruise performance data

[RobertGary1]

The poh cruise data that came with my f model only goes up to 12,500. Nearly all my flights are above that. I saw a 67 f model poh that includes 15,000. Why did they drop that with the 76??

Also see the 77 J only goes to 14,000. Was Mooney too lazy to take the planes up to cruise?

 

[WAFI]

My 77 J POH has a service ceiling of just over 23K at 2300lbs and just under 19K at 2740lbs.

In my opinion once you get above 12K there are a lot more variables to contend with to make a accurate Cruise Table for a generalized purpose. Even at low flight levels I see to much of a difference from what my POH C & R is saying.  So, I just created my own and its dynamically changing as I gain more experience in my Mooney, along with adding modern upgrades "JPI" to the plane.

I fly in Florida and what I have found is 8.5K is my sweet spot. Mainly because I like the free AC up there and I can usually catch a nice tail wind when i'm heading NNW.

I'm curious to know if others have a sweet spot or preferred alt they shoot for?

[A64Pilot]

55 minutes ago, WAFI said:

 

I fly in Florida and what I have found is 8.5K is my sweet spot. Mainly because I like the free AC up there and I can usually catch a nice tail wind when i'm heading NNW.

I'm curious to know if others have a sweet spot or preferred alt they shoot for?

Average for an N/A airplane it’s around 7500, of course as we climb drag is reduced as the air density decreases, but engine power also is reduced, up to about 7,500 drag reduction decreases faster than engine power, above 7,500 engine power degrades faster than drag, of course there are variables one airframe to the next. This is based on max power available, of course if you pick say 65% your faster at 65% the higher you climb, that’s what makes turbo aircraft so fast up high.

 My Maule the sweet spot was 10,000 to 12,000, but that was because the Maule in search of STOL performance had more wing area than average aircraft, our Mooney’s have a high aspect ratio wing as well as Laminar flow, not sure what effect those two have. I’d assume the more efficient wing would increase the altitude of the sweet spot

”Average” is a Cessna or Piper.

I define sweet spot as fastest vs fuel flow, descend and you may increase speed but you’ll increase fuel flow even more, reverse if you climb.

[RobertGary1]

Im nearly always in mid teens on cross countries in my F. Depends on terrain etc. i don’t often go over 16,000. 

[Shadrach]

5 hours ago, A64Pilot said:

Average for an N/A airplane it’s around 7500, of course as we climb drag is reduced as the air density decreases, but engine power also is reduced, up to about 7,500 drag reduction decreases faster than engine power, above 7,500 engine power degrades faster than drag, of course there are variables one airframe to the next. This is based on max power available, of course if you pick say 65% your faster at 65% the higher you climb, that’s what makes turbo aircraft so fast up high.

 My Maule the sweet spot was 10,000 to 12,000, but that was because the Maule in search of STOL performance had more wing area than average aircraft, our Mooney’s have a high aspect ratio wing as well as Laminar flow, not sure what effect those two have. I’d assume the more efficient wing would increase the altitude of the sweet spot

”Average” is a Cessna or Piper.

I define sweet spot as fastest vs fuel flow, descend and you may increase speed but you’ll increase fuel flow even more, reverse if you climb.

I fly between 10 and 12K unless I have a headwind component of 10kts of more. Little to no speed penalty and any Peak EGT setting is <10gph.  I've flown no other airframe in the same HP class that is as usable into the teens and some that do notably worse with more.

[jaylw314]

6 hours ago, A64Pilot said:

Average for an N/A airplane it’s around 7500, of course as we climb drag is reduced as the air density decreases, but engine power also is reduced, up to about 7,500 drag reduction decreases faster than engine power, above 7,500 engine power degrades faster than drag, of course there are variables one airframe to the next. This is based on max power available, of course if you pick say 65% your faster at 65% the higher you climb, that’s what makes turbo aircraft so fast up high.

 My Maule the sweet spot was 10,000 to 12,000, but that was because the Maule in search of STOL performance had more wing area than average aircraft, our Mooney’s have a high aspect ratio wing as well as Laminar flow, not sure what effect those two have. I’d assume the more efficient wing would increase the altitude of the sweet spot

”Average” is a Cessna or Piper.

I define sweet spot as fastest vs fuel flow, descend and you may increase speed but you’ll increase fuel flow even more, reverse if you climb.

My 86 J POH depicts a speed vs altitude/power chart; at low altitude is limited by 75% power for cruise, I'm not sure drag at low altitude is limiting factor.  I suspect if you were brave enough to run at 80-100% power below 7000' MSL, you could go even faster.

There's also a nice range chart that depicts max range at 65% being slightly better at 2400 RPM at 6000' MSL than 2700 RPM at 13000' MSL

Do all J's have these charts in the POH?  How far back to they go in the short-bodies?  I'm pretty sure they're not in the C POH's, right?

Edited September 22, 2022 by jaylw314

[M20F]

I advise making your own performance charts using 3 way GPS, recording weight, temp, etc. to extrapolate along with fuel flow & power settings.  
 

This allows to cross check against the book to see if you have large deviations that need investigation and gets you something reflective of 50-60yrs of change.

I realize as soon as I post this last paragraph the replies will light up, but my experience with factory charts is they are often a bit optimistic.  

[A64Pilot]

The Maule at that altitude running 50 ROP with an IO-540 would burn 10 GPH. It was a 235 HP 540 and max RPM wax 2400, I usually ran 2200.

Odd thing was at any altitude flying alongside the identical airframe with a 180 HP it’s fuel burn was slightly less as with more HP I could be a little more aggressive with leaning because I was at a lower % power.

[A64Pilot]

21 minutes ago, jaylw314 said:

My 86 J POH depicts a speed vs altitude/power chart; at low altitude is limited by 75% power for cruise, I'm not sure drag at low altitude is limiting factor.  I suspect if you were brave enough to run at 80-100% power below 7000' MSL, you could go even faster.

There's also a nice range chart that depicts max range at 65% being slightly better at 2400 RPM at 6000' MSL than 2700 RPM at 13000' MSL

Do all J's have these charts in the POH?  How far back to they go in the short-bodies?  I'm pretty sure they're not in the C POH's, right?

I don’t know about charts, but my J at 500 MSL and OAT in the 80’s with everything shoved forward got an average on a three way speed run of 168 KTS.  Full fuel two people and she’s not light , pre-buy test flt.

One skinny pilot and min equipment, min fuel and maybe just a pilots seat. I feel it might do 175 kts, which is the claimed 201 MPH. She is an 81 J. Stay in ground effect and I’m sure she would.

They will go faster down low because the power is so high, but in my case that’s burning 19 GPH too, and who would cruise at TO power? Somewhere I’m sure Lycoming has printed cruise should be 75% or lower.

Some would, we have one Bo pilot in the neighborhood that does when we travel as a group, but swears he’s running 23 squared or so when you call him on it.

[jaylw314]

1 hour ago, A64Pilot said:

I don’t know about charts, but my J at 500 MSL and OAT in the 80’s with everything shoved forward got an average on a three way speed run of 168 KTS.  Full fuel two people and she’s not light , pre-buy test flt.

One skinny pilot and min equipment, min fuel and maybe just a pilots seat. I feel it might do 175 kts, which is the claimed 201 MPH. She is an 81 J. Stay in ground effect and I’m sure she would.

They will go faster down low because the power is so high, but in my case that’s burning 19 GPH too, and who would cruise at TO power? Somewhere I’m sure Lycoming has printed cruise should be 75% or lower.

Some would, we have one Bo pilot in the neighborhood that does when we travel as a group, but swears he’s running 23 squared or so when you call him on it.

LOL, talk about balls to the wall! 

[A64Pilot]

15 minutes ago, jaylw314 said:

LOL, talk about balls to the wall! 

You know to get that 201, they probably weren’t cruising at altitude.

[Hank]

2 hours ago, jaylw314 said:

How far back to they go in the short-bodies?  I'm pretty sure they're not in the C POH's, right?

My Owners Manual, 1970 C, has performance tables up to 12,500 msl [tables by altitude in 2500' increments]. Max range is shown at 12,500, 16" / 2300 (1043 miles); max speed is at 2500', WOT (27") / 2700 (174 mph), surprisingly 3 mph faster than at sea level.

Leaving Tampa under the Bravo at 900', I was indicating > 165 mph with 2 souls, 5-1/2 hours fuel and my wife's "light" baggage (suitcase + 4).

[jaylw314]

59 minutes ago, Hank said:

my wife's "light" baggage (suitcase + 4).

LMAO, that sounds familiar! 

[carusoam]

Interesting things come and go in and out of POHs….

The O1s have soft field performance charts where the later Os don’t….

Soooo… if you want to fly an Ovation off a soft field… make sure you get an O1!
 

And… if you get the 310hp package…  this is O3 territory….

 

Older POHs we’re full of non-technical errors… in their engine charts…

Plenty of room for updates based on actual data…

Note for A64, how does a person update their POH data… without making a change to something that shouldn’t be changed…?

 

PP thoughts only, not a mechanic nor CFI…
 

Best regards,

-a-

[Shadrach]

4 hours ago, A64Pilot said:

I don’t know about charts, but my J at 500 MSL and OAT in the 80’s with everything shoved forward got an average on a three way speed run of 168 KTS.  Full fuel two people and she’s not light , pre-buy test flt.

One skinny pilot and min equipment, min fuel and maybe just a pilots seat. I feel it might do 175 kts, which is the claimed 201 MPH. She is an 81 J. Stay in ground effect and I’m sure she would.

They will go faster down low because the power is so high, but in my case that’s burning 19 GPH too, and who would cruise at TO power? Somewhere I’m sure Lycoming has printed cruise should be 75% or lower.

Some would, we have one Bo pilot in the neighborhood that does when we travel as a group, but swears he’s running 23 squared or so when you call him on it.

My POH shows max speed (158kts) is attained at 2500’ and is about 3kts faster than sea level DA speeds.

[Igor_U]

13 hours ago, Shadrach said:

My POH shows max speed (158kts) is attained at 2500’ and is about 3kts faster than sea level DA speeds.

Interesting,

PDF POH #1194 I have for 1967 M20F performance data starts at 2500" MSL where surpassingly max power is 97%. Max speeds are 191 mph (166 kt) at MTOW and 197mph (171 kt) at 2300 lb. I dodn't have access to POH in my plane but I believe it's the same.

I doubt I can reach those speeds with my modified F.

[Shadrach]

4 minutes ago, Igor_U said:

Interesting,

PDF POH #1194 I have for 1967 M20F performance data starts at 2500" MSL where surpassingly max power is 97%. Max speeds are 191 mph (166 kt) at MTOW and 197mph (171 kt) at 2300 lb. I dodn't have access to POH in my plane but I believe it's the same.

I doubt I can reach those speeds with my modified F.

As I’ve stated before, the POHs are good enough for baseline flight planning and little more.

I don’t think the 97% number is surprising. Normally aspirated IO360 is quite capable of making more than rated power at SL on a standard day, It was just require an abusive mixture setting to do so. Given the standard lapse rate of 5.4” per 1000’, the The corresponding temperature drop compared to the meager drop in map makes for a relatively minor loss in horsepower. That doesn’t mean I’m saying the POH power % numbers are correct, just that they’re not completely unbelievable. 
 

The table below is pulled from a POH I found online. I’m going to go fly for a bit and see what kind of numbers I get it 2500’. Conditions at my airport are currently about as close to standard as one can hope for (600’DA at a field elevation of 703’).

 

[Igor_U]

Your performance chart must be from the later model. 1967 POH was quite optimistic with speeds:

 

 

 

[Shadrach]

On 9/23/2022 at 11:41 AM, Igor_U said:

Your performance chart must be from the later model. 1967 POH was quite optimistic with speeds:

 

So I went out and flew at lunchtime for about 20 mins just because my office is across the street so why not... 57df and 30.09. DA 800' at 703' field elevation. It was too choppy to really get precise speed numbers but I would say that the numbers (180ish) from the POH that I posted are in the ballpark.  I was light (2200lbs) and it was windy (32017G24) when I departed. I averaged about 1150fpm from 700' to 2500' so a few 100 shy of book but it was choppy, I was above Vy and I shallowed my climb approaching my 2500'.  I did over shoot a bit to get on the step.  I was making 144 to 146kts GS westbound with a forecast headwind component at 2500' of about 14kts so I was probably truing in the upper, mid 150kt range. I turned to the north and reduced to 2500rpm. CHT on richest cylinder was 321, leanest was in the high 330s with mixture full rich and cowl flaps closed.
At 12:22 I leaned aggressively to deceleration (visible IAS and altitude loss in the data at 12:22:33) and then enrichened to peak (slightly past) from the lean side. In the 10 to 15 sec I took to find true peak, CHTs climbed into the low 330s.

The most interesting data point from the flight are that CHT on richest cylinder (#2) at about 20LOP was almost identical to CHT at full rich CHT. The IAS difference, if there was one, appeared to be a wash.  The other interesting thing is that the CHT on my richest cylinder (#2) and my leanest (#3) were less than 10 degrees apart and both under 330 (delta is usually larger). #1 was just under 300 and #4 just over 300.

What does all of this tell us about actual cruise performance?  Not much.  It does reinforce my experience that LOP ops are the kindest, fastest, cleanest and most efficient way to operate an engine at low DAs.  That and that I need to upgrade to an engine monitor with a modern data interface. 

Sorry for the thread hijack @RobertGary1, I hope you find what you need.

[Fly Boomer]

On 9/22/2022 at 5:20 PM, A64Pilot said:

You know to get that 201, they probably weren’t cruising at altitude.

On the other hand, Bob Kromer said he had to take the 252 up to 28,000 to get that speed.