How to compute HP from fuel flow, for 310 HP Ovation?

[THill182]

This confuses me:

When I fly LOP the horsepower of the engine should be a direct function of the fuel flow; presumably you just multiply the fuel flow (GpH) by 14.9. When I then divide that number by the max horsepower of the engine, then I should get % power.

These computations worked well and mapped to the power charts of my 270HP Ovation 2; but when I look at the 310HP Ovation 3 numbers (I have the conversion to 310HP), they don’t. For example, the 310HP power chart shows a fuel flow of 13.4 GpH to yield 217HP and 70% power. But 13.4*.14.9=199.66.

Why is that?

 

 

[carusoam]

Sharing some ideas...

There are two ways to develop the factor used for %hp...the 14.9 number was based on things like compression ratio of the engine. This seems to work pretty well.

the other way is to take the numbers in the chart and back out the factor.

With the 280hp IO550, you had one choice of rpm, 2500rpm.

With the 310hp, you get a couple of choices, 2700 and 2550 along with 2500.  The only thing that changed was FF in relation to the rpm.  You should have the same HP and FF at 2500 rpm as you had before.  Did that change?

@2700 rpm and full throttle that is 100% at SL and declining with MP as a function of altitude. Blue box ROP...

@2550 rpm, LOP.  The STC chart has FF and %hp

Then there is the MAPA method, adding MP + RPM/100

I still rely on the STC chart,

-a-

[THill182]

For reference, here are the charts; still not sure this compares 242HP for 310HP Ovation, at 78% and 2550RPM is 14.8 Gph; on the 270HP Ovation 14.5 GPH gets you 75% power; so 30HP difference at comparable fuel flows? Must be doing something wrong.PowerFFCharts.pdfPowerFFCharts.pdf

[Jeff_S]

I gave up trying to figure this out in the O3. I attended a webinar from Continental where their engineer said flat out, and repeated so everyone could hear it again, that as long as you stay at or below the max recommended cruise power setting, you cannot blow up that engine. From that point on, I find myself cruising either at peak or just slightly LOP, adjusting periodically for temps. Usually I find myself having to richen just a touch so #6 CHT doesn't get too low. It can creep down into the 250s which is also not real good for a cylinder (again, per the Continental Guy's advice).

Those webinars are at the Social Flight web site in their "university" section. They are very educational since he bases all his discussions on the IO-550.

[kmyfm20s]

11 hours ago, THill182 said:

This confuses me:

When I fly LOP the horsepower of the engine should be a direct function of the fuel flow; presumably you just multiply the fuel flow (GpH) by 14.9. When I then divide that number by the max horsepower of the engine, then I should get % power.

These computations worked well and mapped to the power charts of my 270HP Ovation 2; but when I look at the 310HP Ovation 3 numbers (I have the conversion to 310HP), they don’t. For example, the 310HP power chart shows a fuel flow of 13.4 GpH to yield 217HP and 70% power. But 13.4*.14.9=199.66.

Why is that?

 

 

If you look at the fine print on the bottom of the power chart is says subtract 8% for best economy. 217x.92=199.64

 

[THill182]

7 minutes ago, kmyfm20s said:

If you look at the fine print on the bottom of the power chart is says subtract 8% for best economy. 217x.92=199.64

 

Aha! (Ignoring the fine print has gotten me into more trouble!). That makes sense now. The horsepower and % figures on the 310 chart are for ROP, and I must subtract 8% for LOP operations.

I normally run at slightly below 13GpH (so, 12.6 to 12.8 GpH; about 50F LOP) at 8,000 or 9,000 ft. That would give me a fairly low power setting, which in my tests costs me roughly 8kts-9kts or so compared to ROP 75% power.

 

PS: I will also go to the Continental IO550 seminars on line as suggested by JEFF_S; thanks!

 

[kmyfm20s]

Yes, I usually run WOT, 2400rpm, 12.5gph at 8500' and get 173ktas.

[pinerunner]

Your starting assumptions are pretty good. Since fuel is the limiting reagent (chemist term) when you're lean of peak you can use a simple factor times fuel flow to get power output and 14.9 is pretty good for most of us 200 hp IO-360 flying types, if you've got your LOP conditions set up pretty well. The number is useless when you're flying rich of peak and then you should use the good old charts with MP and RPM which could easily be used to calculate how much air is flowing through (temperature has an effect too, but most don't fly in very extreme temperature conditions and ge away with ignoring it). From a physics point of view fuel flow with complete burn-up will give you how many calories of heat were generated but that heat can never be converted to horsepower with complete efficiency. Therefore expect a different conversion factor if you go to a different engine, especially higher compression or turbocharged.

Edited January 17, 2016 by pinerunner

[THill182]

OK; so for what it's worth:

I typically fly at 2600 RPM LOP; since the simple 14.9 (* FF) approach is a good approximation to HP when running LOP, here are then the power settings at finer granularity:

A few notes:

1. The first two columns have numbers from the power/FF table of the POH (or supplement)

2. The last 4 columns are computed; so that

2.1. For numbers from the POH, I subtracted 8% of power from the ROP operation as per the fine print (actually, if I compute them using the 14.9 multiplier, I get the same results)

2.2. For the computed numbers I used the 14.9 x FF formula

3. In the last two columns, I expressed the resulting HP as a percent of 310HP (post-conversion per STC on my Mooney) or 270HP (pre-conversion, i.e., Ovation 2)

I usually run at 12.4 to 12.8 GpH, so that keeps me below 70% power given the original 270HP rating. Hopefully, that will give me the longest expected lifetime of happy motoring before an overhaul...

[carusoam]

Great logic.  Longevity should work out.  

The max HP for the IO550 engine seems to be a sliding scale from 270 to 310 being 100%.  Realistically the engine has a design that is able to withstand a much higher number.  (Anyone know the design's max hp?)

Cylinders are the most susceptible to wear.  Many Os have had top OHs after the halfway point.  Running LOP and CHTs at 320°F it is going to be a long time...

Best regards,

-a-

 

 

[carusoam]

The IO550 has a CR of 8.5 according to my POH.

The Lycoming website lists various CRs for different IO360s.  The 200hp N/A engines use a CR of 8.7.

One discussion I read used 14.95 X FF based on the 8.5 CR.  It also mentioned the max rating for the engine being used.  TC'd engines use a lower CR like 7.5 , they use 13.7 for the factor...

 

So...

1) staying with the 14.9 number seems to be usable.

2) using 310 hp as the max design hp seems to be safe.

3) %BHP(LOP)= (FF X 14.9 ) / 310 

 

George Brailey from GAMI is probably a good resource for this kind of information.  I'm still looking for something to reference.

Mike Bush on the IO550...

https://www.savvyanalysis.com/articles/where-does-the-energy-go

Best regards,

-a-

Found it on the pelican's perch...

John Deakin

http://www.avweb.com/news/pelican/pelicans_perch_84_mixture_cht_194816-1.html

IO550, 8.5 CR, FFx14.9

Additional references to the red box theory including the charts are there, as well...

[Bob - S50]

On 1/16/2016 at 6:16 AM, THill182 said:

OK; so for what it's worth:

I typically fly at 2600 RPM LOP; since the simple 14.9 (* FF) approach is a good approximation to HP when running LOP, here are then the power settings at finer granularity:

A few notes:

1. The first two columns have numbers from the power/FF table of the POH (or supplement)

2. The last 4 columns are computed; so that

2.1. For numbers from the POH, I subtracted 8% of power from the ROP operation as per the fine print (actually, if I compute them using the 14.9 multiplier, I get the same results)

2.2. For the computed numbers I used the 14.9 x FF formula

3. In the last two columns, I expressed the resulting HP as a percent of 310HP (post-conversion per STC on my Mooney) or 270HP (pre-conversion, i.e., Ovation 2)

I usually run at 12.4 to 12.8 GpH, so that keeps me below 70% power given the original 270HP rating. Hopefully, that will give me the longest expected lifetime of happy motoring before an overhaul...

Logically, that chart does not make sense to me.  There must be some calculation error.  I suspect the error is the numbers given for the ROP settings.  Here's my reasoning:

When LOP, power is limited by fuel.  When ROP, power is limited by oxygen, and some fuel is wasted.  That is, when ROP, some fuel goes out the tail pipe unburned.  When LOP, you are getting as much energy as possible out of the fuel.  If I have the same fuel flow ROP as LOP, I'm burning less fuel ROP than LOP (because some of it goes unburned when ROP).  If I'm burning less fuel, how can the HP developed be higher (186 vs 171)?

I think what you needed to do was subtract that 8% power given in your POH differently.  That is, if you POH showed 11.5 GPH giving you 60% power, you were actually getting 52% power.  That would be less than the calculated 55% power and would make sense.  And remember, economy cruise power from your POH is probably peak EGT which is only a whisker away from LOP.  The difference being that at peak EGT some unburned fuel AND some unburned oxygen BOTH go out the pipe because they were not close enough to combine while in the cylinder.  310HP x 52% = 161HP, not 186 HP.

Just my 2 cents worth.

Bob

[carusoam]

Asside from the math...

The 310hp O3 STC single power chart is 50° ROP...

From the O's POH there are two separate charts. one is for ROP (best power) and the other is LOP (economy).

Maybe something can be gained by comparison there..?

Best regards,

-a-

 

[GeorgePerry]

On 1/15/2016 at 10:38 AM, THill182 said:

 

PS: I will also go to the Continental IO550 seminars on line as suggested by JEFF_S; thanks!

 

If you find out when they are please post...I'd like to sit through that as well

[carusoam]

GP,

The SocialFlight is a free app that can be obtained from the App Store.  It has a collection of presentations by Continental that are easy to find?  LOP ops Part 1 & 2 are dated May 2015.  Essentially they are YouTube videos collected in a nice GA package with other suppliers...

I sat through a Camguard presentation that was given live, once.  Fortunately their live presentations go right to recorded ones saved for later viewing.

Best regards,

-a-

[Awful_Charlie]

16 hours ago, Bob - S50 said:

Logically, that chart does not make sense to me.  There must be some calculation error.  I suspect the error is the numbers given for the ROP settings.  Here's my reasoning:

When LOP, power is limited by fuel.  When ROP, power is limited by oxygen, and some fuel is wasted.  That is, when ROP, some fuel goes out the tail pipe unburned.  When LOP, you are getting as much energy as possible out of the fuel.  If I have the same fuel flow ROP as LOP, I'm burning less fuel ROP than LOP (because some of it goes unburned when ROP).  If I'm burning less fuel, how can the HP developed be higher (186 vs 171)?

Not entirely true - remember the affect of mixture on BSFC, which rapidly *increases* again after going lean of the peak efficiency point. We could expand that statement a bit to say something like "when LOP the power produced is dependant on the fuel flow whilst the fuel/air mixture is maintained"

Consider these: (numbers plucked from thin air ;-)
2500 RPM, 25" MP, 12USG/hr. 10dLOP, BSFC 0.40lbs/BHP/Hr (say at max efficiency)
2500 RPM, 27" MP, 12USG/Hr, 100dLOP, BSFC 0.45lbs/BHP/Hr

Now you're burning the same fuel but the BSFC is worse, so you're making less power, but both are LOP

Does someone here have the BSFC curve for the engine in question?

[Jeff_S]

11 hours ago, GeorgePerry said:

If you find out when they are please post...I'd like to sit through that as well

Well, if you are using an iPad you have to get the Social Flight app. I just tried to hit the website on Safari and it wouldn't even let me open that page. Interesting. But either way, when you to get to Social Flight either through the web or app, look for the Social Flight University link, then go to the Aircraft Ownership and Operations section, and you will see several different webinars available from Continental. There is a two part series on LOP operations for your Continental engine. The first one is fairly general and meant for someone who has little experience or knowledge about LOP ops, but it's a good refresher. The second one is where he provides some good nitty gritty detail that you can really use.

There is an awesome graphical power calculator that the moderator uses in his seminar. He says that (I paraphrase) "we're still working with the lawyers to get approval to release this" but apparently the lawyers won, because it's not available anywhere I can find.

[kmyfm20s]

As previously mentioned there are archived webinars on Social Flight. Attached are TCM's upcoming webinars.