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IO-520-D Engine Management on Takeoff and Climb

gkm

MEMBER
Question about engine management on takeoff and climb especially as it pertains to noise abatement. I tried searching the Cessna forums but didn't find much information. Thought I would post on Supercub.org to see if there are any cessna drivers willing to discuss.

I have an 88" three-bladed Mac and it is very noisy on takeoff. Normally I take off with the prop pulled back to 2700 RPM and full throttle. Then after climb established and flaps up, I go to 25" and 2550 RPM as per the book.

Someone suggested to me that I should keep full throttle and the prop at 2700 RPM for fuel flow and cooling, so the next few flights were exactly that - full throttle and RPM at 2700 all the way up to cruise altitude. Very noisy.

Then a friend said he typically uses full throttle and 2700 RPM on takeoff until off the ground and immediately pulls the prop back to 2500 RPM while keeping the throttle set full forward. However, I was under the impression that you should not bring the prop back to 2500 RPM under high MP conditions in these IO-520s. I certainly would love to operate it that way since it would be way quieter and still give me power for the climb.

My priority is to protect the engine first and consider noise abatement second unless mandated. Is there a good way to accomplish both?

Consider a sea-level takeoff with a climb to 4500 feet on a standard temperature and pressure day. What would you do? What is best for the IO-520?
 
Sounds like a fire breathing 180 to me... Air Plains or Texas Skyways conversion? Post a picture.
 
Does a carbed 520 count? I take off at full throttle and flat prop, retract flaps once airborne, dial down the prop a couple of turns while still over the runway, then re-trim and establish a steady climb. Once obstacles are cleared and I have maneuvering space I reduce to 25-26 squared but I level off at 1200' max for most flights (24 sq). At least for several minutes. My 0-520 romps along at 25 sq with the cowl flaps closed and sees CHTs in the 405* range. I'm comfortable in a cruise climb with those conditions but I usually leave partial cowl flaps open. 399* seems so much better than 400*. The only time I use extended full throttle for departure is when I'm at or near Vx speeds but its power I'm looking for, not temps.

Interesting question. I'm looking forward to more replies.
 
Sorry but can't figure out how to post a photo from my IPad.
And while I wish it were a fire-breathing 180, it is just a regular heavy 185.
Typical takeoff weights are between 2700-3100 lbs.
Vy basically 100mph
 
"...Someone suggested to me that I should keep full throttle and the prop at 2700 RPM for fuel flow and cooling, so the next few flights were exactly that - full throttle and RPM at 2700 all the way up to cruise altitude. Very noisy..."

More RPM more heat, more wear, more fuel/oil! Dial your prop back ASAP after take-off...Unless you are heavy and low.

The IO-540 can take a good beating, but does not always have too?
 
I think that pulling prop back to 2500 RPM under high MP settings (27-28") is acceptable in the IO-550 (?), but maybe not good for the IO-520? Not sure how this relates to the O-520 series.
My manual says max power is full MP with 2850 for 5 min.
Max continuous high power is full MP with 2700 rpm.
Max cruise power is 25" and 2550 rpm.
Doesn't specify whether or not full MP with 2500 rpm is a bad idea.
I haven't operated my engine this way but have heard from others that they do this routinely.
 
I would use 25-24 RPM/> 25" MP for all climbs "normal" ops. Don't use a flat prop for climb "unless your back is against the wall"
 
Sorry but can't figure out how to post a photo from my IPad.

Try the tap-a-talk app. I don't prefer browsing with it but it allows photo uploads from your mobile devices. like this one from my iPhone, mostly to remind myself how to do it.
 

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Suggest if you have the runway legth use 24 to 2500 for t/o and about 25 inches.Our strip is 2000 feet ,1000ASL .It is extremely noise sensitive and we regularly takeoff using this power at weights up to about 2900 lbs.CHT stay very low.On initial T/O set the pitch about one inch back from the firewall ,then adjust as necessary once constant speeding.
 
I ran 185's for quite a few hours. I always took off using 2850 rpm, as suggested by Cessna, then first power reduction after takeoff came at positive rate, by winding the prop back to 2700 rpm, wide open throttle (WOT). 2700 rpm and WOT is maximum continuous power for this engine.

After I had things cleaned up, and well clear of all obstacles, I always rolled the power back to 2500 rpm and 25 inches for climb. I never had a cooling problem, and I regularly ran engines to tbo with minimal top end work. And, often the airplane was loaded to 3350 and on floats. On floats, the temps were often in the 80's and sometimes in the 90's. Again, never had a cooling problem.

With that big prop, I suspect takeoff at 2700 rpm and WOT may be just fine. If it's working for you, and you don't want all the noise associated with 2850 (and there is some), I'd stick with that for takeoff, then with positive rate and clear of obstacles and a good climb speed, reduce to 2500 and 25 inches for climb.

If you are having cooling problems, or if the airplane is going through cylinders, (or even if it's not) take a VERY close look at your engine baffling. This is the single thing that kills cylinders on these big Continentals: Baffles with leaks, holes, etc. Tighten up the baffling, and most of your temperature related issues should go away.

MTV
 
I've been preaching "wide open throttle" in the climb for years. Old pilots and believers of old wives tales think high manifold pressures are bad for these engines. Bunk!!

Wide open throttle sets a throttle-plate/fuel-control relationship where you have maximum fuel for cooling at the high power setting. FUEL is what the engine WANTS and NEEDS at higher settings. As soon as you retard the throttle, the fuel control allows less fuel. .......the same goes for carbureted engines.

Please look at the manufacturers reccomendations, and give that engine the fuel it needs. Thanks.
 
I've been preaching "wide open throttle" in the climb for years. Old pilots and believers of old wives tales think high manifold pressures are bad for these engines. Bunk!!

Wide open throttle sets a throttle-plate/fuel-control relationship where you have maximum fuel for cooling at the high power setting. FUEL is what the engine WANTS and NEEDS at higher settings. As soon as you retard the throttle, the fuel control allows less fuel. .......the same goes for carbureted engines.

Please look at the manufacturers reccomendations, and give that engine the fuel it needs. Thanks.

But, bring the RPMs down to 2500?
 
Thank you 8GCBC! WOT at 2850, 2700, 2500......?
Using Dave's suggestion you would go 2850 for 5 min and then 2700 after that if still climbing. That would use the most fuel. I don't know many guys who operate like this. Any other 180/185 IO-520 drivers out there?
 
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Ditto what MTV says above.

sierra bravo, if that 405* CHT is in cruise, then you had better take a good look at your baffles. There is some air leaking by where it should not be. I have found when temps are that high that the cylinders do not last.
 
I've been preaching "wide open throttle" in the climb for years. Old pilots and believers of old wives tales think high manifold pressures are bad for these engines. Bunk!!

Wide open throttle sets a throttle-plate/fuel-control relationship where you have maximum fuel for cooling at the high power setting. FUEL is what the engine WANTS and NEEDS at higher settings. As soon as you retard the throttle, the fuel control allows less fuel. .......the same goes for carbureted engines.

Please look at the manufacturers reccomendations, and give that engine the fuel it needs. Thanks.

Dave, the power settings that you're recommending are acceptable, but there are few instances where its really necessary to burn that much gas in a climb. Cooling should not be an issue in this regard, if the plane is properly set up. I've climbed out in a fully loaded 185 on floats on a 96 degree F day using the procedure I described above and with a fully instrumented airplane and no cooling issues.

Here's the recommendation direct from the 185 POH:

"A cruising climb at 25 inches of manifold pressure, 2550 RPM (approximately 75% power) and 90-100 KIAS is normally recommended. This type of climb provides an optimum combination of performance, visibility ahead and passenger comfort (due to lower noise levels). Cruising climbs should be conducted at 18 GPH up to 4000 feet and then at the fuel flow shown on the normal climb chart in Section 5 for higher altitudes. If it is necessary to climb rapidly to clear mountains or reach favorable winds or better weather at high altitudes, the best rate-of-climb speed should be used with maximum continuous power. This speed is 90 KIAS at sea level, decreasing uniformly to 84 KIAS at 10,000 feet. The mixture should be leaned as shown by the 2700 RPM line on the fuel flow placard, located on the instrument panel."

In my experience, most if not all cooling issues on these engines relate to either crappy baffle seals OR failure of maintenance to PROPERLY set up fuel flows in the injection system.

If the fuel flows are set up right, you should be able to climb all day at 2500 and 25 inches without overheating. One additional thing: I never trusted the Cessna "fuel flow gauge", which is in fact a fuel pressure gauge, calibrated to read in gph. I much prefer a good fuel flow instrument, using a transducer in the fuel line to measure fuel flows more precisely. On takeoff, fuel flow is one thing that tells you you're making power and a reliable instrument is a good investment.

MTV
 
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sierra bravo, if that 405* CHT is in cruise, then you had better take a good look at your baffles. There is some air leaking by where it should not be. I have found when temps are that high that the cylinders do not last.

405* at a little better than 25 square for an extended time with the cowl flaps closed on a carbureted 520 is dandy. My baffles are fine. Typical 24 square cruise with cowl flaps closed temps run 360-370.
 
Back on topic, gkm should visit PPonks prop speed calculator and run a spread sheet of ideal prop speeds at his typical ambient temps. I ran one quick calculation with an 88" prop spinning in 70* OAT and 2700 RPM is the ideal prop speed. In fact even with my 86" prop 2700 RPM is the target speed for my typical Alaskan summer temps. More revs than that and the prop loses efficiency and gets really noisy. Noisy for no reason since the prop's thrust is better in the .88-.92 mach target range. Run the calculator at winter temps and get a load of the ideal prop speeds. I don't recall Cessna ever addressing temp variations and prop speeds but I may be wrong. In any event Steve Knopp is the guy I look to for engine and prop speed info. His prop speed calculator is a valuable tool for guys with big constant speed props that come with that little adjustment knob on the panel. A tach check with an optical tachometer would be a good idea, too. Your panel tach may be lying to you. Another thing to consider, prop tip erosion and gravel dings are reduced with lower prop speeds. That alone is reason to look at the Pponk target speeds.

http://www.pponk.com/HTML PAGES/propcalc.html

If this evening's temps reach the high 40s as expected my take-off RPM should be around 2650. I'll use that speed at full throttle with no hesitation.
 
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It could be the Vernatherm. I bet it is! Pull it: if there are any bent springs etc, and/or it does not open in hot water, order new!

Also, what is TT on oil cooler. Overhaul (clean)?
 
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Lycoming (T)IO-540 lore....

I found on Navajos (turbo), Aztecs (injected), Twin Commanders (turbo) if I wanted to cool the engines the RPM made a huge difference!! 2300 was best. My check pilot taught me that. I think WOT is about 40" on a Navajo/Chieftain?
 
Stewart,

The PPonk prop speed calculator is probably an okay indicator to compare props. That said, that calculator, like any computer program, is making a lot of assumptions, and those assumptions are not always valid.

Somewhat like the notion of attaching the tail of the plane to a scale and go to full throttle to evaluate prop pull. Problem is, the prop blades are only at that Angle of attack while static, and the AOA on the blades is constantly changing as the airplane accelerates.

Point is, these things aren't perfect, nor can they be relied upon to tell the whole story.

It's interesting that someone would buy a longer prop, then reduce the rpm to keep the noise down....:roll: Presumably, the manufacturer rated that engine's horsepower at maximum rated rpm. At 2700 rpm, for example, the IO-520 is rated at 285 hp, not 300 hp, which is the rating at 2850.

Interesting..

MTV
 
It is interesting and I don't know enough about it to speak with authority but the most important "zone" for prop performance is at the tips, at least as I understand it. The prop speed calculator corrects for air temp so that the tips aren't travelling faster than the speed at which they can produce thrust. If the tips are cavitating, if that's the proper description, the speed is excessive and the prop's performance is improved by reducing the speed. The temperature (air density) is the key. A guy operating in 90*F has a different condition than he would in 10*F. I don't think there's any question that the prop calculator is intended for operations, not static thrust tests.

Spinning the prop at 2850 on a 0* winter day has the tips going supersonic. It is crazy loud and the "bite" of the prop is improved by dialing down the speed. I believe the more efficient speed for the prop in that temp is about 2550. While its clear the total power of the engine is reduced the total thrust is at the prop is maximized. I suppose there may be a curve for the efficiency as prop effectiveness diminishes at faster speeds but engine power increases. There's probably a range where it doesn't change performance much, but if the slower prop speed provides equal thrust with less noise, its a good setting to choose.
 
Stick and rudder....

Sometimes just listening to the engine(s), prop(s), and airframe gives me a good idea of where to set power. It varies. Experience helps me.

My Scout with a MT prop starts talking back (vibration) in low MP descents. I have to bring it all back (MP and RPMs) or keep light power coming down.

BTW TC show no descent restrictions with MT prop.
 
I haven't heard anyone mention Mach number. It is the high Mach number which creates the high noise levels and high drag rise at the tips which results in a loss of thrust. It is generally considered that any tip speed number above Mach .80-.85 at the tips is a total waste. This is the speed which is considered to be the maximum for efficiency of a propeller. You may get more thrust at the standing start but once you start moving and adding airspeed you would be better off with a shorter prop to maintain the Mach limit numbers. If you were to look at a drag curve you would find that the drag component abruptly rises as the speed of sound is approached. Sort of like approaching a stone wall.

This is why you will likely notice that a IO-520 Cessna 185 will climb a little better when the prop is turned back to 2700 after takeoff. The 2850 rpm will get you moving quicker but looses it's advantage once you lift off.
 
8a, mach has been discussed relative to prop tip speeds as referenced on Pponks prop speed calculator. Bounce up about 7 posts to catch up. Your comments are interesting.

MTV, for your reference. Here's an excerpt from Wikipedia. Their page on mach speeds is pretty comprehensive.

[h=2]Overview[/h]The Mach number is commonly used both with objects traveling at high speed in a fluid, and with high-speed fluid flows inside channels such as nozzles, diffusers or wind tunnels. As it is defined as a ratio of two speeds, it is a dimensionless number. At Standard Sea Level conditions (corresponding to a temperature of 15 degrees Celsius), the speed of sound is 340.3 m/s[SUP][5][/SUP] (1225 km/h, or 761.2 mph, or 661.5 knots, or 1116 ft/s) in the Earth's atmosphere. The speed represented by Mach 1 is not a constant; for example, it is mostly dependent on temperature and atmospheric composition and largely independent of pressure. Since the speed of sound increases as the temperature increases, the actual speed of an object traveling at Mach 1 will depend on the fluid temperature around it. Mach number is useful because the fluid behaves in a similar way at the same Mach number. So, an aircraft traveling at Mach 1 at 20°C or 68°F, at sea level, will experience shock waves in much the same manner as when it is traveling at Mach 1 at 11,000 m (36,000 ft) at -50°C or -58F, even though it is traveling at only 86% of its speed at higher temperature like 20°C or 68°F.[SUP][6][/SUP]
 
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I am running a PPonk O-470-50 (carb'd 520) in my 180 and have been using the recommendations from Texas Skyways:

Take-off: Not only do you want to "Check Density Altitude", you may want to "Lean for
Best Power".
Apply full throttle. Use 3-4 seconds for full throttle from idle. Remember, the mixture is deliberately set rich, to keep the engine cool. Keep the throttle fully open while you are taking off and any time you are climbing. Retarding the throttle will close an enrichment valve in the carburetor. This enriched fuel mixture helps keep the engine cool. Leave the throttle open, all the way. Retard the throttle if you are going too fast.
When the engine becomes too rich during your climb, remember you probably have full rich mixture and the throttle fully open, use the mixture control to achieve smooth operation. Too rich is when the engine "stumbles" or looses power because it is too rich.
Again, the engine operates and is controlled the same as a 0-470, only more so.
After Take-off Climb: The airplane will probably climb best at about 100 KIAS or 115-MPH IAS. No, that isn't what the POH said, but give it a try. Also, this will change with different flight conditions and gross weight. You will also be able to see over the nose much better.
The take-off and initial climb should be made at 2700 RPM. After a comfortable and safe altitude is reached, reduce the RPM to 2600. Stay with full throttle. Remember; climb with full throttle for better cooling. After more speed and altitude is attained, reduce RPM to 2550 and later 2500.
Cruise: The engine RPM should be from 2400 to 2500 for normal cruise. If you want to fly slower, reduce the power with the throttle. Maximum engine efficiency and "torque" is achieved at 2400-2500 RPM.
Lower RPM means greater propeller blade angle. This gives greater blasts of air against the airframe. Sometimes these blasts "puffs" of air against the airframe causes undesirable harmonic vibrations. Higher RPM "less blade angle" usually gives smoother operation.
 
One engine parameter nobody discusses frequently is the torque curve. Recip engines are best understood using torque to meassure efficiency, NOT HP. A recip will get more HP with more RPM but the torque will go flat.

Diesels engines live on the torque curve and HP is rarely meassured/discussed (unless a newbie shows up).
 
I ran 185's for quite a few hours. I always took off using 2850 rpm, as suggested by Cessna, then first power reduction after takeoff came at positive rate, by winding the prop back to 2700 rpm, wide open throttle (WOT). 2700 rpm and WOT is maximum continuous power for this engine.

After I had things cleaned up, and well clear of all obstacles, I always rolled the power back to 2500 rpm and 25 inches for climb. I never had a cooling problem, and I regularly ran engines to tbo with minimal top end work.

MTV

This is how my employer does it on its fleet. According to the Maintenance Department, the engines routinely make it to TBO.

My employer is very particular about cooling the engine. We do it this way:
1. Descend at 500 fpm at 24/24 (requires adjusting the throttle every 500 feet or so)
2. Reduce MP 1" per minute until reaching 18" (this usually puts the airspeed in the white arc)

A descent from 3,500' to pattern altitude at 1,000' would look like this:
5 minutes for descent
6 minutes for engine cooling
Total: 11 minutes from start of descent to pattern entry
 
Stewart,

The problem with the plonk calculator is that it does not take into consideration the constantly changing aoa of the prop blades as you accelerate. That can be done, presumably, but not by a very simplistic calculator like that on plonks site.

Again, that's an okay place to start, but it doesnt tell the whole story.

In my opinion, you'd be better off with a well designed but much smaller diameter prop and actually use the power the engine can deliver.

As speedo notes, I learned my io 520 operating procedures from 135 operators in Kodiak, and those folks ran them like that day in and day out, with minimal problems.

Mtv
 
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