HP formula for LOP operations

[A64Pilot]

What is the formula for determine HP when LOP for an IO-360?

I’ve seen it quoted but can’t find it.

Edited August 9, 2021 by A64Pilot

[KSMooniac]

Jim is correct. That's for our 8.7:1 engines. 13.7 is the multiplier for 7.5:1 engines... Typical turbo versions, but not TN.


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[A64Pilot]

Thanks,

So at 7 GPH LOP I’m at 105 HP, that’s about what I guessed.

‘Interesting, ROP at the same MP and RPM I’m only 116 HP, I woud have thought I’d lose more LOP.

Edited August 9, 2021 by A64Pilot

[Hank]

8 minutes ago, A64Pilot said:

Thanks,

So at 7 GPH LOP I’m at 105 HP, that’s about what I guessed.

‘Interesting, ROP at the same MP and RPM I’m only 116 HP, I woud have thought I’d lose more LOP.

That formula only works for LOP. For ROP power, see your Performance Tables.

[Hank]

Just now, bluehighwayflyer said:

LOP ops is what I miss most about my old 201.   Truly.   It was just so easy.

What's difficult about setting power for our Cs? Key Number = 46 is pretty simple, and I usually use only three combinations depending on altitude.

[KLRDMD]

LOPFFvsHP calculator.xls

[PT20J]

There are many ways to calculate approximate power. Here is the best resource I've found. Written by a professional test pilot, it lists pretty much every method, discusses errors, and provides a list of resources including some spreadsheets to automate the calculations. The Lycoming paper showing how to calculate power from fuel flow both LOP and ROP is fascinating.

Skip

Determining Engine Power.pdf

[A64Pilot]

11 hours ago, Hank said:

That formula only works for LOP. For ROP power, see your Performance Tables.

I know, I downloaded a calculator for ROP HP, close some good enough for me, I just want to be sure I’m low enough power wise or not hurt anything.

[A64Pilot]

11 hours ago, bluehighwayflyer said:

Go deeper LOP and you will.  

LOP ops is what I miss most about my old 201.   Truly.   It was just so easy.

Jim

 

I setup at 22 squared, then lean to 7 GPH, that gives me 135 kts and is close to 50C LOP, so real LOP, but it’s still smooth. Factory single EGT probe, but that low of fuel, I’m sure everybody is LOP but at 50ish percent power, it doesn’t matter if they aren’t.

That gives me 19.29 MPG zero wind. 

It will run smoothly down to 6 GPH still 22 squared, but it slows to 120 kts and only gives me 20 MPG, so I gain only a tiny bit on MPG, but speed drops way off, and she will stumble, a bit from time to time, not bad but it’s there.

I don’t want to get fanatical about it, there probably are power settings that will work better, but 22 squared, 135 kts and over 19 MPG is good enough for me.

‘I got fanatical about it in my Maule with a multipoint calibrated MVP-50, Gami injectors and fine wire plugs, but first the 540 wouldn’t run near as smooth near as deep LOP as the 360 will with massive plugs and factory injectors, and I think the Maule was just too draggy.  Difference in fuel consumption on the Maule between LOP and 50 ROP if you corrected the MP to maintain the same exact airspeed was insignificant, not even close to 1 GPH. but it wouldn’t go deep LOP, power just went away and it would stumble, and yes it was a high compression motor, but parallel not angle valve, so maybe that’s why?

Just for comparison, the C-210L with an IO-520 and my Maule with its IO-540 gave about 11 MPG cruise. The 210 would carry a load though like a pick up truck.

I have not yet pulled the power back on my Mooney to run the same speed as LOP while ROP to see what the actual fuel savings are, I’ll run LOP just for the cleaner plugs etc.

‘I’ll eventually get a monitor but have other things that need to come first, just got back from testing to get my IA back, that cost about $3,000 all in, and on the 23rd my left knee is getting replaced, followed in 90 days by the right knee. 

Maybe after buying Christmas for the kids I’ll be moving around well enough to install a monitor?

Edited August 9, 2021 by A64Pilot

[carusoam]

How old are the kids?

-a-

[A64Pilot]

6 hours ago, carusoam said:

How old are the kids?

-a-

Youngest is 22, oldest is 36

but they are still our kids,and it’s just a saying.

End of last year we moved off of the boat, sold it, bought a house and had to buy a whole lot of “stuff” for the house that we got rid of when we moved aboard, the plan was to cruise for five years, but my knees didn’t last that long and the Pandemic sort of killed cruising the Caribbean anyway, we we only got three years. May sound silly, but I miss the Nomadic lifestyle of waking up in the morning and deciding if you want to find a different anchorage or just go Lobstering where you are, or just go sailing for the heck of it. Bought the Mooney and of course it took some cash and work to get it where I wanted it, it will always be a work in progress, nature of the beast, but so was the boat.

If my knees had held out I think we would have stayed on the boat, but I couldn’t see living aboard with knee surgeries as you have to climb onto and off of a boat. Besides living in a Marina just isn’t the same at all, all the disadvantages, but none of the advantages.

 

[Tom 4536]

On 8/8/2021 at 6:42 PM, Hank said:

That formula only works for LOP. For ROP power, see your Performance Tables.

So, on my 231 if I am at 55% LOP and want to increase to 60%LOP do I change the FF with mixture control or by increasing MP?

[jaylw314]

1 hour ago, Tom 4536 said:

So, on my 231 if I am at 55% LOP and want to increase to 60%LOP do I change the FF with mixture control or by increasing MP?

In theory, either one.  However, increasing mixture too much might put you ROP, but if you watch your EGT's, you'll be able to see that.  Likewise, increasing throttle may lean out your mixture and cause some roughness, but you'll notice that,too.

In my 201, I'm usually WOT when LOP, so I don't get a choice.

[carusoam]

Turbo ops are an interesting technical challenge…

They are a touch more complex than NA Ops…  mostly because any change you make or adjust… Cycles a change in the exhaust and then the turbo, resulting in a change if MP… and/or airflow…

Lets see if @jlunseth is around… to discuss mixture setting and bhp% setting in a 231…

Best regards,

-a-

[jlunseth]

9 hours ago, Tom 4536 said:

So, on my 231 if I am at 55% LOP and want to increase to 60%LOP do I change the FF with mixture control or by increasing MP?

The simple answer is that if you are really 55% LOP and want to increase to 60%, the best way to do it in the 231 is to increase MP until the fuel flow is 9.2 - or so. Fuel flow is not stable to the tenth, at least not in my aircraft, so if it is varying a couple of tenths, but varying around 9.2, you should be good. As you already know, the 231 is unique even among turbo aircraft in that when you change the MP, the fuel flow changes with it trying to keep the same fuel/air ratio. That mechanism isn’t perfect, but you have two things going for you in the change you propose. First, what you propose is not a big MP move so although the fuel/air ratio may not be exactly the same, it will be pretty close. Second, as long as you operate under 65% HP the GAMI people and Mike Busch both tell us that we can’t hurt the engine. so as long as the engine is happy (not running rough) you are not hurting anything at that power setting.