Peak and lean of peak horsepower?

[Gary0747]

Just wonder if anybody has any better way of calculating horsepower at peak and leaner?  The best I have found is 14.9 hp per gph.   Does anybody know what JPI uses in their EDM 900 when leaning?  Most power charts I have seen do not include fuel flow so it is not clear how they are accurate tools when used for leaning beyond best power?

[gsxrpilot]

(gph X 13.7 / 210) = HP%

13.7 has to do with the cylinder compression in my Continental TSIO360MB. You'd have to know what yours is for you Lyc IO360.

210 is the max rated HP for my engine. Yours would be 200.

This works for LOP.

[Gary0747]

That is interesting. My 14.9 hp per GPH was for a Lycoming IO360 and your 13.7 hp per gph is for a continental tsio360. If both numbers are accurate it suggests your continental is 8 percent less efficient.  I wonder where these numbers came from and how accurate they are?  I doubt they are really a constant through a wide range of lean of peak settings. As you get very lean you are using energy to heat a lot of excess air. At the point the air fuel mixture approaches the LOFL or lower flammability limit of gasoline the engine will quit and make zero power while still injesting some fuel.   So I suspect what ever the numbers actually are they are only linear in a specific range of LOP operation. 

Edited February 9, 2020 by Gary0747

[jetdriven]

It’s les efficient. mostly because of the lower compression ratio. 
I think the LOP HP numbers are only accurate to about 50 LOP. 

[Cruiser]

the formula for calculating the FF multiplier is based on EGTrend Inc. Inc. 2004 test data.

FF Multiplier = 1.1604 * Compression Ratio + 5.030

The formula is based on a best fit line on the known values of 14.9 for 8.5 CR, 13.7 for 7.5 CR and 13.53 for 7.3 CR

the actual calculations are a little more complicated using BSFC values

[MoonFlyer68]

While I can not speak to thier accuracy, there are a couple LOP HP calculators in the download section of Mooneyspace.

[carusoam]

good news...

We can simplify the question in the OP!

For Peak... Calculating %bhp is the same for LOP...

Why... because there are essentially no extra fuel molecules being used solely for CHT cooling...  just like LOP.
 

+1 for anyone that included the CR in the calculation...

+1 for anyone that included the knowledge of their peak HP...

-1 for anyone that only used CR as an indication of efficiency, without taking the TC or TN into the larger equation...

%bhp(LOP)=f(FF, CR, max HP)

Anyone using an IO550, max HP seems to be a moving target... sometimes 280, other times 310, in the experimental world it can be in the range of about 550...   and the original Eagle has the albatross temporarily hanging around it’s max HP number...

Most of our NA engines are using 8.5(?)  Read your POH to see exactly what your engines CR is for sure... probably in the early pages.  Some may be a decimal point or two, higher or lower...

The CR is calculated from the volume of the cylinder when the piston is at the bottom of the stroke, minus the volume at the top of the stroke... that includes all of the gaps, down the sides to the rings and funny shape of the piston head, and cylinder head with the valves and spark plug annomalies....

The TC’d engines intentionally use a lower CR... for stuffing more fuel and air in there...

The factory TN’d engines are somewhere in the middle, like the TN-IO550s...  call them lightly TC’d... 

The Acclaim actually got a different CR than the Ovation...

We have at least one MSer using the 10:1 CR in his NA Mooney... STC’d .

The higher the CR, the better the efficiency... mechanically speaking...

Keep in mind... the mechanical CR isn’t accounting for the TC’d compressed air being stuffed in the front... that counts too...

The TC’d engine using a lower CR, is still very efficient...

 

Ultimately, there is a third part of the discussion... that would be ignition timing...

 

Our engines are set up for max power for T/O and climb... to avoid detonation...  lots of excess fuel is being used for this...

There is more room for safety from detonation while the engine is no longer producing 100% power...   <65% bhp, out of the red box...

In this area, advancing the timing holds some additional interest... converting the last few % of the fuel to CO2... where possible...

 

There is lots of real world experience running an NA engine LOP, with really advanced timing...

And probably a fair amount for TC’d engines as well...

 

When striving for continuous high HP operations... We need to closely watch how things are running to avoid...

• The red box (piston crown holes have no compression)
• CHTs from going too high (surfaces missing their cross-hatches are bad)
• TITs from going too high (vanes turned into nubs are expensive)
• Raw EGTs from going too high (exhaust parts have limits too)

 

We can increase... %hp

• increased MP, while ROP
• increased FF, while LOP
• increased CR, While NA’d, TN’d, and CR’d (really tough to do while flying...)
• advanced timing, during cruise (get that electronic mag ready)

Pretty interesting that it leaves out prop efficiency...  for that you need to follow up with your prop’s manufacturer...

• With an NA engine... the faster we turn the prop, the higher the FF is... more HP, yay!
• Hartzell the mfg of the TopProp indicates 2550rpm as an efficient place to run the Acclaim prop...
• too fast is an efficiency challenge at the tips... an air compressibility challenge...

Something to look forward to... if you have an Electronic Mag and the ability to adjust the ignition timing...make sure it is reset during the Gumps checks... for GA/climb power...

 

Well, that isn’t very clear...  Mostly because my writing isn’t at the level it needs to be, for this complex of a subject...

But it does somewhat indicate why it is so difficult to advance the timing of a TC’d engine while looking at E-mags...

The future of efficiency will be a TC’d bird, running LOP, with the timing set further away from TDC...

Remember the topic is about %bhp, efficiency is about converting the fuel to exhaust while generating the bhp....

 

 

Anyone know thermodynamics better than this?

Let me know where I dropped the ball...  

PP thoughts only, not a mechanic or CFI...

I think I may have mixed the words advancing/retarding the timing...  I used advance to mean send further away from TDC...

Feel free to ask me for clarification... I like being part of the conversation... 

Seeing if @Sandman993 is stopping by?

 

Best regards,

-a-

 

[PT20J]

I always find these discussions interesting and slightly amusing. There seems to be a lot of interest among pilots to figure out how much horsepower your engine is developing. I wonder why? Do your ever calculate how much power the engine in your car is producing when cruising down the highway? Perhaps the reason is that we are conditioned since our earliest exposure to airplanes by the power charts in the POH. All that is really necessary is to find operating points -- i.e., combinations of MAP, rpm and FF -- that get you what your want (speed, economy) and won't damage the engine. If you look at the way the airlines operated the radials at the end of the piston era, you'll find that they cruised at low power (usually around 55%) and LOP for economy and engine longevity. If you cruise ROP, you get more speed and less economy and need to watch your CHTs. Some have found that they can cruise at 80%+ power when LOP with CHTs below 400F. There is a wide range of operating parameters and the horsepower produced is only part of the equation.

The only accurate way to determine horsepower produced is with some sort of direct measurement device. The big radials had built in torque meters (interestingly calibrated in BMEP - clearly designed for engineers). The power settings in the M20J POH may be the most accurate as LoPresti measured torque to determine the actual power for the 201. His goal was to get >200 mph on 200 hp and he didn't want to fudge the numbers. Anyway, the reason for this digression is to point out that all other methods of determining horsepower are approximations. So, there is no need to be super precise about something that fundamentally lacks accuracy.

If you look up the engine manufacturer's data for your engine you should find a Sea Level and Altitude Performance chart for the engine. This is the standard form for figuring out HP as a function of MAP and rpm. It is generally published at best power mixture. Note that this is for the engine in a test cell. It will overstate the power in your airplane because the induction and exhaust system of an actual installation will reduce the power by some (hopefully small) amount.

The power falls off somewhat when you lean to peak or lean of peak. Power curves are not generally available for these conditions. If you read John Deakin's writings, you'll find that his opinion -- and generally the position of the old APS team -- is that percent power is overrated as an operating condition. But, the APS folks made an interesting observation: Over a range from slightly lean of peak to perhaps 75F LOP, the BSFC (lbs of fuel per hour per horsepower) is very nearly constant. This leads to the observation that no matter the combination of MAP and rpm, the power can be determined by knowing the BSFC. So, if you can find a curve of BSFC for your engine, you can figure out the horsepower when LOP. If you don't have this data, the APS guys figured out a further approximation. Normally aspirated and turbonormalized engines (usually about 8.5:1 compression) they noted have a BSFC of about 0.39 lbs of fuel per hour per HP, ranging from 0.385 to 0.40. Factory turbocharged engines (usually with about a 7.5:1 compression) are less efficient, with a BSFC of about 0.42 to 0.43. The actual weight of 100LL is 5.85 lbs per gallon: 5.85 /0.39 = 15.0 hp/gph and 5.85/0.425 = 13.7 hp/gph. 

Note that the hp/gph is NOT directly related to compression ratio -- this is simply a means to (roughly) approximate BSFC based on observations of the performance for a number of engines.

Hope this helps.

Skip

[carusoam]

Skip,

There is a huge amount of interest %bhp during cruise...for one reason...

APS has done a great job of expounding on it’s (the HP calc’s) purpose...

For our engines...

We have one important guideline during operation...

1) Don’t break the engine!

 

1a) We can do this by avoiding the red box

1b) Where is the red box?  A fairly rough number... 65%bhp

1c) How do we know where 65%bhp is ROP and LOP?   Mapa printed the key numbers by engine... (an even greater approximation)

1d) Some engine mfgs have included bhp numbers in their power charts for both ROP/LOP... the Continental IO550 for one... Great for comparison to the Mapa key number calculations...

The APS guys did a great job of researching the 65% number... the MS community has done a great job of demonstrating and reporting that this number works pretty well...

Somebody also gave us a CHT to try and stay under, for best longevity... 380°F

Lots of good guidance, no real sharp limits...

 

So I see one real reason for the high interest when first setting up an engine monitor, or getting a new plane, or getting a new engine...

After that...  knowing max power for T/O and climb numbers... really rules!

Best regards,

-a-

[jlunseth]

7 hours ago, Gary0747 said:

That is interesting. My 14.9 hp per GPH was for a Lycoming IO360 and your 13.7 hp per gph is for a continental tsio360. If both numbers are accurate it suggests your continental is 8 percent less efficient.  I wonder where these numbers came from and how accurate they are?  I doubt they are really a constant through a wide range of lean of peak settings. As you get very lean you are using energy to heat a lot of excess air. At the point the air fuel mixture approaches the LOFL or lower flammability limit of gasoline the engine will quit and make zero power while still injesting some fuel.   So I suspect what ever the numbers actually are they are only linear in a specific range of LOP operation. 

The constant is 13.7 for turbocharged and 15 (14.9) for normally aspirated, according to my materials from the APS seminar.

[PT20J]

The red box is a concept. It has fuzzy edges that vary by engine. The APS folks have always been clear about that. But I often see fellow pilots missing the point, taking it as a fact passed from on high written in stone, and then trying to skirt around the red box with undo precision as one might narrowly avoid Class Bravo with GPS. I just think that’s missing the point.

A much better way is to understand the underlying principles and use them to figure out how to operate your engine safely and efficiently based on what you are trying to accomplish. 

I recently asked Mike Busch what power he sets for cruise, and he said he had no idea. He guessed it might be around 65% but he didn’t really care. He had figured out combinations of MAP, rpm and FF for climb, descent and cruise that balance his objectives of speed, efficiency and engine longevity and the actual horsepower produced was irrelevant. He also pointed out that people often comment when flying with him how little effort he expends setting power and mixture. 

Just another point of view...

Skip

[carusoam]

Mapa gives us a way to define operating conditions using MP, and RPM/100, they call these the key numbers...

Each Mooney has a defined sum of the key numbers to equal %bhp... for ROP...  Mapa has used the combined efforts of many people to fine tune their key number strategy...

The ones I had the most interest in were 65% and 75% bhp...

During the climb, I typically use max power and control EGT/CHTs with the blue box method... 200-300°F ROP... (ship’s EGT gauge has a blue box there...) G1000 owners get a white box...   and climb until MP is no longer a factor...

Mapa has also defined all the engine settings for each phase of flight...

They make great guidelines.  Give a great frame of reference....

But as Mike Bush would say... they are not that critical or set in stone...

But, if you are on the opposite end of the engine management spectrum from Mr. Bush... they are perfect guidance. If there is such a thing...

I expect people leaning more on this crutch are just less familiar with engine operations... or engine metallurgy...

What else can they do...?

What if they are new to flying?

What if they are new to Mooneys?

What if they are getting to the next level of IFR?

Use the guidelines until better experience is obtained.  
 

Or that other JPI number that gets brought in from the gps and FF instruments and displayed....   nmpg.

PP thoughts only, not a mechanic or CFI...

Best regards,

-a-

[Ibra]

I had the impression fro NA engines the % of power = (MP*RPM)/(max MP*max RPM) nothing more nothing less  it is a rule of thumb but seems to work very well, try it 65% = (23*23)/(27*29.92) or 70% = (24*24)/(27*29.92) !

Obviously, there are more more idiosyncratic elements in delivered max HP power of my specific engine (e.g. max MP*max RPM) vs the Lyco rated values (e.g. 200hp), as not all engines delivers 29.92*27 at sea level while on breaks and this involve specific engine/environment data: weather vs ISA, compression vs max ratio, fuel grade, injector (e.g. GAMI spread), fuel flow vs placard value and even quality of ignition timing

Now at 65% power, engine does deliver the same TAS speed whether you are best Economy/Power or high/low RPM, I just have a look at the POH of the M20J to notice this, so on same RPM*MP % power number, FF will be higher for ROP vs LOP (roughly 2GPH) and higher for high RPM low MP combinations on same product RPM*MP

Now the paradox is when you look at Lyco or EDM manuals, the % power is roughly the same when going from best power to best economy (including peak EGT), however, this will not hold that long in deep LOP region as Power/IAS will sharply drops vs FF (you can't keep flying at 65% power with zero FF )

Who is made enough to do the testing and publish the full extrapolated Power-vs-FF in deep LOP operations? A careful flyer on constant speed prop RPM may still use FF (or better IAS change) to guess his power adjustment in LOP, obviously higher IAS % changes will result in more noise aerodynamic power/drag curves but that is what matters after all compared to any values produced by engine manufacturers on power-FF while sitting on a testing bench...

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[Parker_Woodruff]

Regarding the multiplier - isn't it 15.1 for the angle valve IO-360s?

[jetdriven]

You lose 2-3kt going LOP from ROP, So if you look at the book power settings and fly them LOP you’ll be about 5% less. Personally I fly full throttle and 2500 RPM LOP all the time.   Higher is less HP, but I always use as much as I can get. 

[jetdriven]

You lose 2-3kt going LOP from ROP, So if you look at the book power settings and fly them LOP you’ll be about 5% less. Personally I fly full throttle and 2500 RPM LOP all the time.   Higher is less HP, but I always use as much as I can get. 

[PT20J]

47 minutes ago, jetdriven said:

You lose 2-3kt going LOP from ROP, So if you look at the book power settings and fly them LOP you’ll be about 5% less. Personally I fly full throttle and 2500 RPM LOP all the time.   Higher is less HP, but I always use as much as I can get. 

That's what I do. I use 2500 because Bob Kromer said that the 201 prop is most efficient at that rpm and I have no reason to doubt him. I can't find a propeller map for my McCauley prop, so I can't verify it. Out west if I need to fly high, I will run peak to get a couple of extra knots sometimes. I don't worry much about the extra fuel as the little four banger doesn't burn that much at altitude anyway.

Skip

[Sandman993]

I lose way more than 3kts LOP... and rarely go that way. Certain conditions make LOP a good option, like 30kt tailwinds for instance.

i don’t know if it’s because of the increased cr, the tuned power flow exhaust system, gami’s or simply being a fresh, properly broken in engine, but I’m not having issues with high egt’s or cht’s. Case in point, two days ago, flying to and from Dallas at 7,000 msl give or take, the ship was using 10gph at 2500rpm, 22/23” and 5C the egt’s were 1240’s and the cht’s were 330’s. The tas was 163 and That’s about where my math ends. Per phone tas app and gtn 750.

For the climb out, I pitch for 120 and she gets along pretty good... full fuel, two grown men, bags and it’s not a surprise to see 1100fpm climbs...I do need to underscore the importance of good airspeed in climbs in case there are new guys...the 120 speeds at climb power usually allow me to stay near under 370 degrees while let’s say 80mph climbs, I would expect 400 or slightly higher. The baffling is in good condition.

last year at Oshkosh I asked a bravo driver that was staying with us if he ever flew his ship lop... his response was, hell no! “I bought this race horse to go fast”! I said dang, don’t bite me! Lol... he didn’t seem to care about copious amounts of gas.

[gsxrpilot]

I bought my Mooney to go fast as well. But there is no doubt the best speed mod is the ability to skip a fuel stop. Therefore if I can go A to B without a fuel stop ROP, then I'm going ROP and to hell with the fuel costs. 

But there are plenty of times that 9.5 gph LOP will allow me to go non-stop while 14 gph ROP would require a fuel stop. In that case, LOP is actually quite a bit faster, A to B.

I'm always calculating the best speed for my Mooney for any trip. Sometimes that's ROP and sometimes that's LOP. 

[jlunseth]

On 2/9/2020 at 12:02 PM, Gary0747 said:

Just wonder if anybody has any better way of calculating horsepower at peak and leaner?  The best I have found is 14.9 hp per gph.   Does anybody know what JPI uses in their EDM 900 when leaning?  Most power charts I have seen do not include fuel flow so it is not clear how they are accurate tools when used for leaning beyond best power?

PS, the JPI percent horsepower algorithm is proprietary and JPI does not publish it, but on the lean side it gives the same result in my engine as the standard formula, 13.7 x FF/Total Rated HP.  On the rich side it produces what is in the POH tables and graphs.  Choosing LOP leaning vs. ROP leaning in the JPI, determines which power algorithm the unit uses.  I have not found the %HP to be particularly accurate on the rich side in my aircraft, it appears to overstate power by about 8 percentage points.  And it is too much effort to get an accurate peak on the lean side, so I don't use the LOP leaning function, I just lean to a power setting that I know and that works. JPI's LOP leaning would work better in your NA. I pretty much ignore whatever it is saying.

[Tim Jodice]

14 hours ago, PT20J said:

Note that the hp/gph is NOT directly related to compression ratio -- this is simply a means to (roughly) approximate BSFC based on observations of the performance for a number of engines.

Hope this helps.

Skip

HP/GPH is always directly related to compression ratio. A higher compression ratio extracts more energy out of the fuel. A 150HP to 160HP STC for a 172 with a O-320 simply increases the compression ratio to get the 10 hp. 

A downside is you can't run Mogas in the 160 HP

The not so popular 10:1 compression ratio stc for Mooneys makes more power because of the Compression ratio.

The lower compression ratio in turbo engines is mostly if not entirely for detonation margin.

A V35B and TC Bonanza came with a 520 making 285HP. The turbo model needed an extra 2.5" to make up for the lower compression ratio. 

[gsxrpilot]

3 hours ago, jlunseth said:

And it is too much effort to get an accurate peak on the lean side, so I don't use the LOP leaning function, I just lean to a power setting that I know and that works. JPI's LOP leaning would work better in your NA. I pretty much ignore whatever it is saying.

I think this is a common issue specific to the 231's. There's just too much going on back and forth between throttle and mixture. So better to just lean to a known power setting.

The Lean Find function works well with the 252. I set the throttle and then pull the mixture back to a target LOP setting. But I can reduce the mixture very slowly and see each cylinder peak and move LOP. 

I expect it would work well with the NA engines as well.

[Cruiser]

It is all about MPG.......... efficiency.

I can go 180 KTAS into a headwind

and I can go 160KTAS with a tailwind. The Mooney makes it easy to choose, I like speed but I like to fly too............ what's the hurry ? 

[Ibra]

5 hours ago, PT20J said:

I use 2500 because Bob Kromer said that the 201 prop is most efficient at that rpm and I have no reason to doubt him

I am not sure to understand why that is not at 2700rpm?

[PT20J]

11 minutes ago, Ibra said:

I am not sure to understand why that is not at 2700rpm?

Generally props are designed to me most efficient at climb or cruise. Mooney probably wanted to favor cruising which would normally be done at a lower rpm.