Hi everyone.

I've been reading BCP for a two or three years now, I almost even posted a couple times . I occasionally fly a 206/207, but unfortunately my training wasn't exactly thorough when it came to the engines and how to treat them properly (a sad result of not having very experienced pilots training the new guys). Engine operation was covered quickly: full throttle/prop on take off, back off to 25 squared about 500', 23 squared in cruise. From what I've read about IO-520s here and elsewhere that's reasonable. The leaning was also taught in a simplified manner, rich for take off (near sea level), back to 18-20 gph at 25 squared, 14 gph in cruise then modify for the conditions.

My big concern is that we have one 206 with an IO-550 engine conversion. There have been no changes to the above procedures that are used for the IO-520s. I was trying to find more information about the 550 and I came across a post by MTV (I believe) on the Super Cub or 180/185 forums awhile back that said that the IO-550 is a different beast than the IO-520s, and for one thing they should never be leaned above 75% power if I recall correctly (and a pretty important difference). When I am at the main hangar I'll be seeing if there is an operating manual I could read, but in the meantime what differences should I be aware of when I am flying the IO-550?

Another engine question for all the guys with a pile of time on pistons I have is about oil. The generally accepted procedure taught to new pilots is to run the 206/7s at 9-10 quarts of oil. The reasoning provided is that anything more is just dumped over the side. Reading what information Continental has on their website:

The oil level should be maintained near the full level. A reduced oil quantity means the remaining oil is handling an increased heat load. Oil cooler baffle sealing should always be checked to provide proper cooling.

Is running the planes at the reduced oil level a reasonable thing to do?

Marc,

The IO-550 engine is quite a different beast than the 520. One of the reasons that you hear quite varying opinions on the durability of that engine, I believe, is that many pilots have not learned to run the 550, and as a consequence have fried quite a few cylinders over the years.

The 550 runs at 2700 rpm maximum, compared to 2850 for the 520. The 550 is approved to run at that power setting all day, whereas the 520 is limited to five minutes at max rpm. So, that's one difference.

First power reduction on a 520 SHOULD be to roll the rpm back to 2700 right after takeoff. That takes the engine from ~300 hp to ~285 hp.

First power reduction on the 550 is generally to roll the rpm back to ~2500 to 2600 rpm and climb at full throttle (which burns a lot of gas), or come back to 25 square.

Fuel flows on takeoff are critical in both engines, because you're using fuel for cooling. We set fuel flows for takeoff up as prescribed by Continental (and the placard on the instrument panel) for the IO 520, but in the 550, I wanted to see 29 GPH indicated at takeoff power. Again, its a big engine, and cooling during max power is critical. Your mechanics may argue that's too high, but we found out the hard way that 29 gph at takeoff power keeps the cylinders happy.

As to leaning, I believe Continental prohibits leaning at power settings higher than 75%. Check your AFM Supplement.

Which conversion does this 206 have--Atlantic Aero, Wipline, or??

If you can find someone with an Atlantic Aero conversion, ask them to copy the power charts for that engine. They are really nice, and aren't a direct fit for the IO 550 R or others (AA uses the N model 550, which is rated at 310 hp, and has a tuned induction-a very sweet engine).

In any case, do a little math. This is where pilots get in trouble with these engines. Here's the kicker:

You are trying to set, say 75 % power. In the IO 550 engine that would be 225 horsepower (75% of 300 bhp). In the 520, though, 75% power would only be 214 hp (75% of 285 CONTINUOUS bhp).

So, most people used to running 520's run them in cruise at, say 24 square, which may put you somewhere around 75% or so.

In the 550, though, if you run at 24 square, you are up around 85%, and if you lean at that setting, you are violating the manufacturers recommendations.

The 550 makes horsepower at much lower rpm than does the 520 in other words. Consider that the 520 has to turn up 2850 to make 300 hp for takeoff, while the 550 can do 300 at 150 rpm less.

Also note that, because Continental changed the method used to rate engine horsepower between the times they built these two engines, the 520's rarely make 300 honest hp for takeoff. They were rated at +- 5 %. The 550 is rated at +5 -0, so every 550 MUST make rated hp. As a consequence, they all make more like 305 to 310 to ensure they pass inspection.

Bottom line is that they are different engines. Treat them VERY differently. The AFM supplements should give you recommended power settings and leaning procedures for the 550.

I ran a 550 D all the time at 2300 rpm, 21 inches of manifold pressure (variable with altitude, but generally low level) and leaned to 50 LOP for a fuel flow of just over 13 gph.

I think one of the problems with these engines is pilots are not taking the time to learn the different operating procedures, and as a consequence, the engines early on ate a lot of cylinders. I was told that the cylinder design has also been changed, but in any case, these are great engines, just dont abuse them.

As to oil quantity, I always look for ~11 quarts in these engines at the start of a day. Some engines are a little more prone to throw a quart than others, so there is some difference in individual engines. In any case, I wouldn't start a day of flying with 9 quarts in one of these engines myself.

MTV

I gotta agree with MTV and would follow that advice. I also have run the 550 on several airplanes and have had fantastic results. It needs to be run at higher fuel flows to get the cooling and power. You should not have any problems if you do this.

Every same size engine I have flown behind is a bit different with how much oil they blow out. I did run one that was similar to yours, at 11 quarts it would blow a quart, but at 10 it would stay there for a full 25 hours. That was on a 206 on amphibs so I think the tail low position it sat in the water gave a slight false reading. Similar to a well used 207 sitting on the ramp.



But what MTV says is right, too many pilots are not operating the 550's correctly. I take bad engine rumors with a grain of salt. I flew a O-320-H2AD (which everyone avoided like the plague) on a 172 on floats with a prop pitched at redline at 59 kts for 2100 hours, most of that time over that because students wouldn't pull the power back quick enough.

Bottom line, the 550 a great engine like most, just operate it correctly. $10 of extra fuel burn will save you $$$$$$ of engine repairs.

Thanks for the reply MTV, I definitely have some homework to do. Luckily I won't be flying the IO-550 206 for a few weeks so I have time to learn

mtv wrote:As to leaning, I believe Continental prohibits leaning at power settings higher than 75%. Check your AFM Supplement.

Which conversion does this 206 have--Atlantic Aero, Wipline, or??

I belive it is a conversion by Bonaire. When I was about to start flying the 206s I looked through the POHs for STC information, but I think I only found the STC for the 550 with all the various propeller options and their operating limitations. I'll need to have a second look to see if there is any other information.

Hi Marc,
I have the Bonaire io550d conversion in my plane. I have all the manuals and info so let me know if you have trouble obtaining them and I'll see what I can do. BTW-MTV's post is on the mark.