A friend of mine has a 182 with a Ponk 470/520 conversion, and he's been experimenting with (and asking people about) cruise power settings. He's getting everything from "always run 23 squared" to "25 inches and 2100" to "20 inches & 2300". I was curious what the 180/185 guys here like to run theirs at?

Eric

Simple answer is to go to the airplane/engine cruise and range performance charts, and set power accordingly. You're not going to hurt anything as long as you keep things in spec. And to me, most important is how the airplane feels for the load I'm flying.

Gross weight and a short trip I'll keep it at high RPM/MP settings so I'm not wallowing through the air. Long trip, pushing into fuel reserves with crap weather where I'm going, I'll pull way back into the higher gas mileage range. Covered in ice and airspeed going to hell in a handbasket, I shove everything full forward and hope it doesn't blow up before I whack the ground.

Gump

For my 182 I cruise at MP= 21 inches. RPM= 2300 RPM. I have a O470 and not a 520 in my plane, however. Bob

skybobb wrote:For my 182 I cruise at MP= 21 inches. RPM= 2300 RPM. I have a O470

At what altitude? At 10,000 feet you're not going to get 21 inches out of an O-470.

You have to customize your power settings for the mission you're flying. It's like saying, "I drive my Buick at 1,500 RPM." OK, where? On the freeway, down Main Street, in a school zone? There is no one answer.

Gump

Gump, you are showing your age...nobody drives Buicks anymore

whee wrote:Gump, you are showing your age...nobody drives Buicks anymore

Studebaker????

Gump

I have the 520 in my 180. I usually run my prop around 2300. That seems to be the "sweet spot" for it. 88" C66. My sight seeing cruise is usually around 15"MP giving me around 9 gph. and 100kts. or so. If I'm going somewhere, I keep the same rpm. but run the power upto 18-19". Usually flying at 8-9K' giving me around 130kts and 12-13 gph.

Geez, you guy's baby them. I run the IO-520 after takeoff at 25 squared until altitude decreases the manifold press. I leave it at 2500 RPM though for the flight. I think it likes it. It will honestly use 1gt. of oil in 50 hours. That is in a C-210.

Not a thing of babying it. It's a thing of economics. I can only afford so much gas. The less gas I burn, the longer I can fly. I just fly for fun, so the longer I can do it, the better I like it.

Plus I'm little dirty, so you reach a point where you can add power , but don't gain a proportional amount of speed so why waste precious gas(for me).

I change my oil and filter around 35 hrs. with no appreciable oil consumption.

I have a PPonk O-520 in my 180. After takeoff I climb at full throttle and 2600rpms all the way up to cruise. Leave the throttle wide open. Then back to 2500 for a short flight or high altitude, and 2400 for longer flights. The WOT MP is whatever it is at the altitude I am at. Steve Knapp recommends full throttle for climbs for cooling and I haven't had any problems. The only time I bring the MP back in cruise is when the turbulence is kicking my a#$ down low. The cruise AS is in the mid yellow otherwise. This is with a 86" Mac 401 prop.

At 8500' I can expect 160KTS true at 14gph at WOT(which is about 21" anyway) and 2500. I lean to 1475 EGT on the highest cylinder. That is about 50 rich of peak. In 400 hours never had issue or problem, nice clean exhaust and plugs.

Use whatever you like, if its a PPonk O520, I would be surprised if you ever have a problem with any combination. To get a fuel burn equal to a stock O-470 at 3-6K MSL, just fly the O-520 at 18-20"MP and 2300. No magic, the O-470/520 are great honest engines.

By the way, in the years of flying different planes but not always knowing what to expect on fuel burns there is a simple calculation you can do to figure it out. It varies a GPH or so but is rather close for an average cruise. Take the engine HP drop the last number and divide by 2. Ex. a 230hp engine== 23 / 2 = 12.5 gph. Cessna 172 with a O-320 150hp. 15 / 2= 7.5 gph. The only bigger variations I have found are in turbocharged engines but even then just err on the higher side 1 GPH. Its pretty close.

Call Steve Knapp at PPonk. He will tell you just fly it at the speed and fuel burn you want. The O-520 is just a nice simple big liter engine.

Have fun!

Oops, after a couple of glasses of wine my math goes to sh#$. A little math correction on my last post.

230 hp engine 23 divided by 2 is gonna burn about 11.5 to 12gph on an average. 12.5 is safe.

a64pilot wrote:Geez, you guy's baby them.

"Babying" an engine is not your friend. Betting that what you save on fuel, you lose on early overhaul and cylinder repair costs.

We used to get IO-520's new in the crate, bolt 'em on our 207's, and a year later swap 'em out for new ones. In a whole lot more than 10K hours behind the IO-520's myself, as long as an engine was trouble free during the first 20-30 hours, I never had an engine not go to TBO completely trouble free. There's always the occasional pilot or mechanic induced failure, but fortunately those are rare (or should be).

We ran them hard. Full throttle/prop on takeoff. Crank the prop back to 2650 after turn-around altitude, climb at 25 square, and then 23 or 24 squared for cruise depending on weight. Never worked above 3,500 feet, so all power was at full rich. Secret was that they ran 5+ hours a day, most every day, and we were really fussy about keeping temps in the middle.

I do the same in my own airplanes. If I have the horsepower, I'm gonna use it. I like the feel of a healthy engine pulling hard and a crisp airplane going as fast as it can. Screw the gas bill, that's what credit cards are for!!!!!

Gump

For all the talk about fuel, it's really the cheapest thing about aviation, even at today's prices. However, it is the easiest thing to complain about.

Ya'll need to do the math based on cost per mile including maintenance ( I know it's a strain ). It's pretty easy to fool yourself into thinking a low fuel burn = inexpensive miles but at some point you get behind the curve and more hours towards tbo's, oil changes, yada yada yada. It gets complicated, especially when you try to quantify longevity of components at different power settings and drag based on different loads.

Find numbers for your average operation and work from there. an hour with a calculator, some extrapolation and you can sorta' graph where the curve starts to get whacked.

Or just ask some crusty ol' buzzard (no offense Gump) with k's of hours in type and he'll probably get ya' pretty close.

N6EA wrote:Or just ask some crusty ol' buzzard (no offense Gump)

Hey... No offense taken. Most everyone I know nowdays is a crusty ol' buzzard.

Gump

IO-520 in an Ag Truck working; 25 squared @17-18 gph all day.
IO-520 in a 206 hauling jumpers; 25 squared to whatever 2500 in the climb and bottom of the green and 2300 rpm coming down.
IO-520 in a 185 cruising around, 23 2400
O-470 in my 180 cruising around; 22 2300 (no gump, not where it won't give it to me).
On floats; in a Kenmore 180, IO-520 185 or IO-550 185; I usually look out at the bottom of the wing and see how she's "plowin". Sometimes another inch or two (yes gump, where it'll give it to me) makes the difference in getting on the air "step" or not. Since being on the step can mean 5-7 mph increase I feel that the difference between 22-23 inches is worth it. Of course in the 550 pwered sled you've got to be gettin' "gross" on the weight to make it plow! And I don't mean gross weight.

lowflyin'G3 wrote:(yes gump, where it'll give it to me) .

Sorry guys if I came across as being an old grump or something. I'm just saying that you can't run an O/IO-470 or 520 with a constant speed prop like you do an engine with fixed pitch prop. It's comparing apples and oranges.

Gump

GumpAir wrote:

skybobb wrote:For my 182 I cruise at MP= 21 inches. RPM= 2300 RPM. I have a O470

At what altitude? At 10,000 feet you're not going to get 21 inches out of an O-470.

You have to customize your power settings for the mission you're flying. It's like saying, "I drive my Buick at 1,500 RPM." OK, where? On the freeway, down Main Street, in a school zone? There is no one answer.

Gump

You are quite right. I was thinking of an altitude lower that 5000 feet. But I didn't indicate any altitude. I can't pull that kind of MP at 10,000 Ft.

GumpAir wrote:Sorry guys if I came across as being an old grump or something. I'm just saying that you can't run an O/IO-470 or 520 with a constant speed prop like you do an engine with fixed pitch prop. It's comparing apples and oranges.

Gump

As opposed to comparing GRUMPS & GUMPS ?

Hows the joke go ? " What's the difference between a grump and a gump ?"

Gump wrote:"Babying" an engine is not your friend.

I know it is very different but am I hurting my C-85 when I run around at 2100RPM? Cruise is 2250. When I'm not going anywhere I sometimes pull it back and just bum along. I don't really save much gas I just ain't in a hurry and why not burn 3 gph if I can. But if you tell me it is doing harm then I'll throttle up and spend that extra 5 bucks per hour

zero.one.victor wrote:I was curious what the 180/185 guys here like to run theirs at?

Eric

I've had my 180 15 years now, it has a 470-U, so it's limited to 2400 redline. (theoretically )

I've found 2300 to 2350 to be smooth, so below 7500 I'll run 23 squared or 23/2350 for flights over 100 miles so I'm getting 140 kts. Above that, usually WOT (minus 1/2 inch for a little burble to even out the EGT's) at 2300. above 12,000 she gets a little too slow, so I might use 2400 up there.

With avgas going through the roof, I've taken to running 22 squared if I'm only going 100 miles or less, or if I've got a tailwind.

John Frank of CPA always said: Find the smoothest RPM at cruise and square up the MP to it...or maybe 1 inch over for normally aspirated engines. Every engine/prop/airframe combo is a little different. Lot's of 185 guys like 2450 with the three blades, but if you square that up down low you're getting about 80% at 18-20 gph, too expensive for my tastes.

Another thing to think about is how lean do you want to run it? If you use lower rpm/mp combos when you're not in a hurry, you can usually lean to peak....in my 180 at 22 square I get about 125 kts @ 10gph instead of 140kts @ 13gph, where I have to run 125-150 degrees ROP.

One caveat about extended low power ops: running several inches undersquare ALL the time isn't too good for your ring sealing. If I'm going to be running 55% or less I might take the RPM all the way down to 2000 so I can have the MP around 18 to 20. That's only down low...if I have to go up to 15,000 I have no choice but to run way undersquare or I'm only going to go 90 kts!

After mulling all this over for 15 years, I basically have two cruise settings....high 23/2350 and low 22/2200! Above 9000 I can lean the high setting to peak and it becomes the only cruise setting.

Hope this helps you find what's right for you.

Rocky