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Constant Speed Prop Power Settings

VF84Sluggo

Well Known Member
Folks,

For those running an IO-360, what power settings do you use? What are your nominal TAS cruise speeds and fuel burn?

I realize this will vary with cruise altitude, OAT, etc. Just looking for "ballpark" settings for cross-country planning purposes.

Thanks in adevance.
 
There is a graph in the operators manual, takes into consideration density altitude.
A quick and dirty rule of thumb is RPM in hundreds and manifold pressure:

43 - 55% 45=65% 48 = 75%
Most run 65%; your engine at 22" 2300 RPM leaned to peak should burn 8.2 to 8.5 gph depending on the injector balance. or full throttle and 2300 at 9000' density altitude. depending on propeller, should see 175-183 mph.
 
I have an O360 converted to FI with the Airflow Performance system. Hartzell CS prop (wide blade). Electronic ignition. For economy cruise I use 2280RPM 23.5” and LOP -30 or so. Depending on altitude which for me is mostly below 6,000 MSL, yields 6.8 gph or so. According to Dynon it is somewhere around 55% power and 150 kts true.
Above 5,000 if I am in a hurry, I cruise at 2300 RPM, WOT, which yields about 70% and 7.5gph and a bit more than 160 kts true. I can usually go LOP -40 in this condition. The go fast mode would be 2450 RPM, WOT above 5,000 ft. I rarely go there for an extra 5 to 8 kts.
As Lindberg proved during WW II, if you can go over square or better yet, WOT you reduce the engine pumping losses and generally get better economy.

Stay out of the Red box. If you don’t know what that is search the forum and you should find a lot.
 
I use a similar formula. I cruise 21x21 until I can't get 21" Hg then increase RPM to get 42. I indicate around 165 mph which trues out around 200 mph at 10,000. Burn is around 8 gph.
 
I don’t know how to post a link to a thread, but search in the forum for “lean red box”, and you will find several threads on it.
 
It is not Mike Busch's red box actually, but anyway.

The simple answer is Wide Open throttle all the time unless you need to slow down.

Prop.....anywhere in the 2300-2500 range, that is smooth and happy, most find the 2350-2450 area works well.

Red Knob..... Full rich for take off, WOT/2700 in the climb, lean occasionally to keep your EGT's in the 1280-1320 range. Once at cruise altitude do a big mixture pull, then fly LOP to destination.

IO360 will burn about 7.9USGPH in the 8-9,000 feet range, more down low, less up higher. I can give you a rough number but you just need to refine the BMP technique.

John Deakins articles make this easy to read and understand. Read articles 63-66 here https://www.avweb.com/features/avweb-classics/pelicans-perch/pelicans-perch-index/

Read the rest too.

https://www.advancedpilot.com/onlinecourse.html
 
Great info.

Staying at WOT is something new to me. I was taught the ol' "keep it square" rule from my early days. I'm going to have to get my mind around all this, that's for sure.
 
Great info.

Staying at WOT is something new to me. I was taught the ol' "keep it square" rule from my early days. I'm going to have to get my mind around all this, that's for sure.

That is an OWT that started back in the radial days. If Im going somewhere cross country the throttle is advanced to the stop on takeoff and not touched again until on the descent. Power is managed with RPM and mixture, just as David suggests.
 
That is an OWT that started back in the radial days. If Im going somewhere cross country the throttle is advanced to the stop on takeoff and not touched again until on the descent. Power is managed with RPM and mixture, just as David suggests.

We fly our fuel injected airplanes the same way - and the only difference with the carbed ones is that we pull the throttle back just a smidge to make for better atomization in the fuel/air charge due to the tilted throttle plate. But for all intents and purposes, that’s WOT as well.

Interesting results of some prop testing I have been doing regarding RPM. If you are looking for the best SPEED while the throttle is WOT, I have found that the higher you go, the more our props (both two and three blade) like 2500 rpm for attaining the best TAS. Above that, or below that, speed drops off by a few knots. AT the standard 8,000’ DA that Van’s uses for airplane comparisons, the two blade BA prop tends to keep goign faster (by just a little bit) at higher RPM’s until you hit redline (I have no idea what it does above that!). The three blades peak speed is still found at about 2500 RPM however.

I’m working on getting the data ready for publishing in the near future.

Paul
 
SNIP

Interesting results of some prop testing I have been doing regarding RPM. If you are looking for the best SPEED while the throttle is WOT, I have found that the higher you go, the more our props (both two and three blade) like 2500 rpm for attaining the best TAS. SNIP
Paul

+1. Above 8K’ or so I find 2500 RPM, WOT, 10-20 degrees LOP to be the sweet spot (RV-8, IO-360-M1B, Hartzell BA prop). Typical economy cruise is 173kts TAS, 7.5 GPH. During the winter I found running at this point the CHTs are to cold - below the 350 degree target to minimize stuck valve issues. To compensate and keep CHT up 350-360 degrees I tend to run at PEAK, burning 8.5 GPH but bumping up speed to ~180kts TAS.

Carl
 
This is an interesting thread. I’m new to CS prop operation, and I was told that the power lever, should never be forward of the prop lever. I’m learning some things after reading this thread, and the linked articles.

I understand what has been said for climb, cruise power/prop settings, but what about aerobatics? I’ve been using 26” mp, 2600rpm, and full rich. Any suggestions on where power and prop should be set for aerobatics from 2-3000’?
 
Am I the only one oversquare?

Ed Holyoke

I understand the lower RPM reduces engine pumping losses - so the engine is more efficient. My experience however is that the plane is slower at lower RPM for the same fuel burn. I equate this to propeller efficiency not being constant across air speed, altitude and RPM ranges.

For the Hartzell BA prop, my experience is that at altitude the prop/engine “system” seems to like 2480-2500 RPM as an operating spot where the power put into the prop produces the most thrust (or for the system the fuel burned yields the highest MPG for a given speed). Perhaps others have different experiences.

I’ve flown behind constant speed props that take all the engine power but are not great at converting that power to thrust. Props are a blend of science and art.

Carl
 
I understand the lower RPM reduces engine pumping losses - so the engine is more efficient. My experience however is that the plane is slower at lower RPM for the same fuel burn. I equate this to propeller efficiency not being constant across air speed, altitude and RPM ranges.

For the Hartzell BA prop, my experience is that at altitude the prop/engine “system” seems to like 2480-2500 RPM as an operating spot where the power put into the prop produces the most thrust (or for the system the fuel burned yields the highest MPG for a given speed). Perhaps others have different experiences.

I’ve flown behind constant speed props that take all the engine power but are not great at converting that power to thrust. Props are a blend of science and art.

Carl

I can't find a screenshot, but the same day I was seeing the same airspeed, same altitude, same fuel flow, similar CHTs at 2400RPM. The only difference I could see was that I was spinning the engine faster. Perhaps the prop was slightly more efficient at that RPM and was being offset by increased pumping loss.

I rarely set cruise power for max airspeed, mostly going for LOP and CHTs under control. Mine is a Whirlwind 74RV on a 10:1 parallel valve IO-360 in an RV-6 for reference.

Ed
 
During the winter I found running at this point the CHTs are to cold - below the 350 degree target to minimize stuck valve issues. To compensate and keep CHT up 350-360 degrees I tend to run at PEAK


This is how OWT's are born.

There is no logic nor science behind such a claim. I would not only suggest you just forget this and fly LOP all year round, but strongly urge you not to promote more OWT's.

My mate Mr Deakin and co, will surely be having a fit. Walters ashes will be churning in his urn too. ;)
 
Interesting results of some prop testing I have been doing regarding RPM. If you are looking for the best SPEED while the throttle is WOT, I have found that the higher you go, the more our props (both two and three blade) like 2500 rpm for attaining the best TAS. Above that, or below that, speed drops off by a few knots. AT the standard 8,000’ DA that Van’s uses for airplane comparisons, the two blade BA prop tends to keep goign faster (by just a little bit) at higher RPM’s until you hit redline (I have no idea what it does above that!). The three blades peak speed is still found at about 2500 RPM however.

I’m working on getting the data ready for publishing in the near future.

Paul

Paul, you are not alone here. I have found that to be true also, and with the 2 blade BA props, one VAF member whose name I can't recall (RV10 owner and ag pilot from Georgia) told me in a PM once that in his racing around the countryside he found that something like 2650-2675 he gained the best from his prop.

No doubt you will be more precise in data collection.

Something I am not happy about, recently doing side by side comparison with a Whirlwind 2 blade, the other pilot who must have been cheating somehow :rolleyes: he was 6 knots faster on GS given the same air, same everything. SO the WW guys have pulled some speed out of the -10 for their efforts.

I can't wait to see what you come up with.
 
This is how OWT's are born.

There is no logic nor science behind such a claim. I would not only suggest you just forget this and fly LOP all year round, but strongly urge you not to promote more OWT's.

My mate Mr Deakin and co, will surely be having a fit. Walters ashes will be churning in his urn too. ;)

David,

Sorry, but you are dead wrong.

I suggest you watch this Mike Busch video on why valves stick. It provides clear explanation as to why we should strive to maintain CHTs between 350 and 400 degrees.

https://youtu.be/7ohsVvYbAaQ

Carl
 
RV7 with IO-360/180HP. I take off full throttle and 2700. When I get all obstacles cleared, I reduce RPM to 2500, leaving the throttle full in ( if this hurts the engine, everyone with a fixed prop is in trouble, also the CHT's are cooler).

For cruise I go LOP with 25.8 HG and 2350RPM/7.5 GPH giving 155kts TAS down low, Up high; full throttle, LOP and 2500RPM/8GPH above 8000 giving 165kts TAS.
 
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David,

Sorry, but you are dead wrong.

I suggest you watch this Mike Busch video on why valves stick. It provides clear explanation as to why we should strive to maintain CHTs between 350 and 400 degrees.

https://youtu.be/7ohsVvYbAaQ

Carl
A couple of slides from this video:

Busch - why valves stick - 1.png

Busch - why valves stick - 2.png

I'm not clear on one thing - will running CHTs at 300 or 350 make that big of a difference on the valve stem temp? Seems like the 50 F difference there would not be that significant when it comes to the valve stem temperature. I'm certainly not qualified to challenge his numbers, but it's not clear how these were measured or how the CHT temp change impacts valve stem temp.

If I understand him correctly, this is not an issue if you run mogas or unleaded avgas.
 
I’ve been using this app to set and program power settings on my O-360-A1A powered RV4. The interactive app simulates the power charts from Lycoming, and can be set up for various types of Lycoming engines in the setup program (click on the ‘I’ in the lower right corner for instruction. I’ve programmed power charts in my GRT EFIS, and I can check it against the app on my iPad in flight to see if it’s accurate. It seems to be accurate.


https://apps.apple.com/us/app/aircraftpower/id718023187
 
Mike Bush's assumption is that you are using leaded fuel, not an issue for me since I use a non-leaded 93 octane fuel.

As an aside I have freed quite a few sticking valves, by dropping the valve into the cylinder : I have never seen one that had lead residual baked on to it (operating with leaded fuel), all of the stems were coated with coked on oil....
 
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Ok, I finished reading the suggested AVweb articles, watched the YouTube vid....man, looks like all this time I didn't know how to operate an IO-360.

WOT ALL the time? REALLY? Wow. Even if just local "sightseeing" at 1000 ft, not going anywhere in particular or in any particular amount of time?

Setting, say, 24" and 2400 RPM on a cross-country is bad juju?

Leaving prop RPM back and mixture leaned when landing?

Man...
 
Power

I looked at Lyc power software Scott referenced but it is only accurate at best power mixture! Since so many of us run exclusively lean of peak, is there any software than also takes fuel flow into consideration? I would like to have it available on my iPad for quick calculations.
Cheers
db
 
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