Power settings

[Brandt]

So, power is often expressed in percentages, yet Mooney doesn’t publish a percentage chart on power settings.  Am I to assume it’s the simple math e.g. 24 inches is roughly 72% of 33.5 inches and rpm doesn’t matter? Or am I missing something?

[N201MKTurbo]

My first question is, Why do you care?

If you are running it at best economy (LOP) you can use the fuel flow to compute %Power.

[PeteMc]

1 hour ago, Brandt said:

Or am I missing something?

Okay... am I missing something...  Or is that the M does not have %Power listed on the Cruise Power Schedule?

 

[Brandt]

46 minutes ago, N201MKTurbo said:

My first question is, Why do you care?

If you are running it at best economy (LOP) you can use the fuel flow to compute %Power.

Call me the curious type.

[Brandt]

15 minutes ago, PeteMc said:

Okay... am I missing something...  Or is that the M does not have %Power listed on the Cruise Power Schedule?

 

The POH does not.

[LANCECASPER]

3 hours ago, PeteMc said:

Okay... am I missing something...  Or is that the M does not have %Power listed on the Cruise Power Schedule?

 

@Brandt has an M20TN (Acclaim) not an M.

%Power is going to be a percentage of the rated horsepower not the Manifold Pressure.

[Brandt]

1 hour ago, LANCECASPER said:

@Brandt has an M20TN (Acclaim) not an M.

%Power is going to be a percentage of the rated horsepower not the Manifold Pressure.

Actually an M20V.  But close enough.  My question boiled down to whether MP was a suitable proxy for rated horsepower. At. 33.5 inches and 2500 rpm it should be producing 280 hp.  So can you extrapolate based on other MP settings?

[LANCECASPER]

37 minutes ago, Brandt said:

Actually an M20V.  But close enough.  My question boiled down to whether MP was a suitable proxy for rated horsepower. At. 33.5 inches and 2500 rpm it should be producing 280 hp.  So can you extrapolate based on other MP settings?

Oops sorry. Power settings are the same though.

I doubt that it's linear. Example, I doubt that at 16.75 inches that it's 140 hp, meaning 50% power. I think 50% would be a higher setting, but that's a guess.

[kortopates]

Power curves can be had by purchasing TCM’s Overhaul manual or Maintenance/Operations manual. Both have the same performance curves.

You may find an older version on the internet as well.


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[EarthboundMisfit]

Advanced Pilot Seminars teach the following formula to calculate HP when LOP:

Turbo'd: 13.75 x Fuel Flow = HP

NA: 15 x Fuel Flow = HP

So, use HP/Rated Max HP to get a percentage. 

Eg, Turbo @ 10USG/hr = 137.5 HP.  %= 137.5 / 280 = 49% power. 

I'm not sure about the calc for ROP.

[carusoam]

3 hours ago, EarthboundMisfit said:

Advanced Pilot Seminars teach the following formula to calculate HP when LOP:

Turbo'd: 13.75 x Fuel Flow = HP

NA: 15 x Fuel Flow = HP

So, use HP/Rated Max HP to get a percentage. 

Eg, Turbo @ 10USG/hr = 137.5 HP.  %= 137.5 / 280 = 49% power. 

I'm not sure about the calc for ROP.

One thing for sure… the compression ratio needs to be in there…

hence the differences between the TC’d and NA engines…

It helps to know what CR they used… to make sure it applies to our engines…

The TN’d Mooneys (Acclaim) will have a unique CR… its CR is neither NA or TC’d… it’s somewhere in between…

 

The same calc using ROP in place of LOP… swaps out Fuel Flow for Air Flow… done the same way…

Unfortunately… we don’t have air flow meters in our planes…

So we are kinda stuck using a chart to get AF from MP and RPM… since we are looking that up in a chart… we get the BHP direct from the chart instead of doing the calculation…

 

So….

Find the handbook from the MAPA PPP course… they simplify the look up part… so that %BHP can be directly determined from MP and RPM… for each Mooney, specifically…

It is worth taking the course… this is just one of the benefits…

Go MS!

Best regards,

-a-

[carusoam]

EBM,

Did you take the APS course in Australia?

APS has/had a guy in Australia… he is/was an MSer…

Not sure if they are still linked together…
 

Best regards,

-a-

[EarthboundMisfit]

Yes, sure did.  The APS course has been one of my favourites. 

Your CR point prompted me to pull out the course manual - the Turbo calc assumes 7.5:1CR, NA assumes 8.5:1CR. 

And there is a calc for ROP too.

[kortopates]

It helps to know what CR they used… to make sure it applies to our engines…
The TN’d Mooneys (Acclaim) will have a unique CR… its CR is neither NA or TC’d… it’s somewhere in between…
 

You’re perpetuating the big lie about the Acclaim engine! It’s not a TN’d engine at all. It’s CR is 7.5:1 like any other Turbo engine - since it is a real Turbo. it is essentially de-rated to 280HP but to suggest it’s TN’d has been a marketing myth since its inception.
Nor do TN engines use a CR somewhere in between NA and Turbo’since they began life as a NA engine, such as 8.5:1, and then added a STC for a turbo that is not boosted above sea level pressure, unlike the Acclaim.


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[EarthboundMisfit]

On 7/22/2022 at 4:35 AM, Brandt said:

Actually an M20V.  But close enough.  My question boiled down to whether MP was a suitable proxy for rated horsepower. At. 33.5 inches and 2500 rpm it should be producing 280 hp.  So can you extrapolate based on other MP settings?

According to APS, yes.  If full 280 HP = ROP 33 (-ish) inches MP 2500RPM, then each inch MP is approx 3% power change. 

[carusoam]

M20R, M20S, M20TN, M20U, M20V….  (Somebody thought it important enough to throw the N in here…) 

From a safety point of view…

When the turbo system fails… restarts from altitude can be extra challenging… especially over tall rocks…

 

With a TN’d engine that uses the NA engine’s CR….  A turbo normalized system failure has a much easier restart at altitude….

My bad… I’m unable to remember all the CRs of all Mooneys….

And… all the times the Marketing guys said one thing and meant something different…

But, it looks like Paul just simplified it for me…. 

 

We also have at least one M20J, with the 10:1 compression ratio pistons… around here…

Thanks Paul!

Go MS!

Best regards,

-a-

[carusoam]

10 minutes ago, EarthboundMisfit said:

According to APS, yes.  If full 280 HP = ROP 33 (-ish) inches MP 2500RPM, then each inch MP is approx 3% power change. 

Essentially the APS guys have given Air Flow and %BHP as a function of MP…

It would be cool to have an Air Flow meter… (very modern automotive )

It would be cool to have a fuelP gauge too….   (None found on the O1)

Best regards,

-a-

[jaylw314]

2 hours ago, carusoam said:

Unfortunately… we don’t have air flow meters in our planes…

Volume air flow is always proportional to MAP x RPM, right?  Mass air flow you can get by multiplying by air density, which itself just needs a fudge factor for inlet air temp.  Whether any motor is turbo or NA, or low or high compression shouldn't matter any.

I assume there's also a fudge factor for volumetric efficiency, but AFAIK that's a relatively small factor for our low RPM motors(?)

But at least in theory, you could calculate your % power by taking (MAP / MAP at max power) x (RPM / RPM at max power) / max power (x100%) if you're ROP.  In my M20J POH, that gives you a number about 4-5% above the listed % power in the cruise power schedule.

[kortopates]

11 hours ago, EarthboundMisfit said:

According to APS, yes.  If full 280 HP = ROP 33 (-ish) inches MP 2500RPM, then each inch MP is approx 3% power change. 

Yes, very good - actually 3.5% per the generic formula below: 

When ROP, mass airflow determines HP, therefore, %Hp:
%Hp = (100-(((Max RPM-RPM)/100)*2.5+(Max MAP-MAP)*3.5))/100
 

but redline MAP is 33.5" on the Acclaim at 2500 rpm or with the 310 STC 34" at 2700 rpm

[carusoam]

19 hours ago, jaylw314 said:

Volume air flow is always proportional to MAP x RPM, right?  Mass air flow you can get by multiplying by air density, which itself just needs a fudge factor for inlet air temp.  Whether any motor is turbo or NA, or low or high compression shouldn't matter any.

I assume there's also a fudge factor for volumetric efficiency, but AFAIK that's a relatively small factor for our low RPM motors(?)

But at least in theory, you could calculate your % power by taking (MAP / MAP at max power) x (RPM / RPM at max power) / max power (x100%) if you're ROP.  In my M20J POH, that gives you a number about 4-5% above the listed % power in the cruise power schedule.

Nothing like having a meter that reads to a tenth of a gallon…. Or a cubic foot per minute…

For accuracy and simplicity….  Modern cars use the hot wire MAF… (mass air flow) sensor.  If you have the ability to get data from its computer…

The challenge with MP… the data can’t be linear… the flow channels are so complex… as is the compressibility of the air itself…

 

Using the automotive example… it wouldn’t be too hard to use an MAF sensor… especially if interested in more complex electronic ignition…

Vote no on complexity… 

Best regards,

-a-

[carusoam]

8 hours ago, kortopates said:

Yes, very good - actually 3.5% per the generic formula below: 

When ROP, mass airflow determines HP, therefore, %Hp:
%Hp = (100-(((Max RPM-RPM)/100)*2.5+(Max MAP-MAP)*3.5))/100
 

but redline MAP is 33.5" on the Acclaim at 2500 rpm or with the 310 STC 34" at 2700 rpm

Interesting Factoid Paul!

The 310hp STC for the Acclaim is pure magic….

The excess HP for climb is great.  (From conversations with Joe Z…)

I didn’t know it came with 34” MAP to go with the 2700rpm…

 

Hanging out with Paul on MS… I get more knowledgable by the day!  
 

Thanks for sharing the details…

Best regards,

-a-

[rpcc]

Some good background reading on the tc vs tn comments above - https://taturbo.com/tnvtc.html

[carusoam]

14 hours ago, rpcc said:

Some good background reading on the tc vs tn comments above - https://taturbo.com/tnvtc.html

Nice reference and a quick read…

Thanks for sharing that one…

Best regards,

-a-

[SkyDriver]

Excellent talk, guys.

.
And after reading the article { https://taturbo.com/tnvtc.html } & realizing the meat of the article is within the final 2 paragraphs, got me to thinking / wondering how many dropped &/or bent valves were happening @ FL above-the-ground?
Also, octane # has put many a race plane (that survived) back into the shop so to lower compression ratio & to park while attorneys collected the evidence.

.
And today, some 50 years later, % power is the focus without even the mention of head temps coming up.  So I gotta figure we've become so digitally automated & trusting that we've released all liability to the winds.

.

Similar to strapping into a brand new Acclaim Ultra received 1 month ago & leaving the ground with a sputtering engine & not already knowing / having any touch-down options, relying entirely on digital (up to date?) intel.
Spooky.
.
Jim

.

On 9/27/2022 at 7:22 AM, rpcc said:

Some good background reading on the tc vs tn comments above - https://taturbo.com/tnvtc.html

 

[Schllc]

This article/paper is also describing the lop/rop arguments basis. 
All things about engine management, durability and longevity are primarily heat management. 
Its just physics….
I also completely agree about “conventional wisdom”, and the bad reputation turbos had embedded in a generation because of early problems. 
I have owned several TN planes, and aside from occasional turbo maintenance, have not found any difference in operating or maintenance cost between my ovations and acclaims. 
The fuel consumption on a 3hr trip is about 8% difference to save 30min travel time. 
It does beg the question of why Cont continues to reduce the compression of the TSIO-550 engine.  The bonanza TN system uses the 8.5/1 NA 550 engine and develops 300hp vs the acclaims 280, and I have not heard about premature failures, or detonation issues.