RV-6A Real World Numbers

[dbier99]

Originally Posted by koupster

Building time? Fly max endurance speed.
Max range speed should be around 92 knots.
Watch oil temps at these lower speeds.
Need to get somewhere a little faster? Try Carson speed - 121 knots
Lean to max EGT (Lycoming recommendation for O-360)
Try 1900 rpm, if that's rough, try 2300 rpm - staying out of the Hartzell no-no range.
https://www.yumpu.com/en/document/re...afe-foundation

Thanks for the link. Any insight regarding how to set the manifold pressure for either the 92 or 121 knot suggestions? Honestly things were simpler with our flying club's fixed pitch prop planes that had fuel flow meters. I'm not convinced that the CS prop does much except give us a faster climb - which we really don't need. Wish we could easily add a fuel flow meter.

[Robert Sailor]

Your CS will give you faster takeoff and better climb and allows you infinite settings on cruise….. the downside is cost and long term maintenance

[tgmillso]

The short version is get that manifold pressure back to 22" or below, grab that big red knob, pull it out until the engine stumbles, then richen slightly until smooth.
I have essentially the same engine as you (but with injection and EI) in a similar airframe (-7) and leaned out at 8,000' it will do 163kTAS on 7.6GPH. With that red knob pushed in to 100deg ROP, it does 171kTAS for 11GPH. ROP is totally not worth it for cruise. May as well be throwing $100 bills out the window. Lean of peak your engine will run cooler and cleaner, and you'll make the oil barons poorer. What's not to like about that? For building time, the aircraft will still fly great back at 5.5GPH and 120kts, so long as it's LOP.

For more detail on all of this, you really need to read the Pelican's perch articles by guru John Deakin. Undoubtable the most comprehensive information you can find on this topic.

https://www.avweb.com/features/avweb...s-perch-index/

https://www.avweb.com/features/avweb...part-3-cruise/

https://www.avweb.com/features_old/p...mixture-magic/

If you're thinking along the old school 24 square lines, you're probably also running AVGAS still. I wouldn't let that stinking stuff near my engine. There's a reason you don't put it in your car anymore. Read the article below and go buy yourself some ethanol free high octane mogas.

https://www.avweb.com/features/pelic...n-the-hogwash/

Your engine is on this list somewhere, and approved for 93AKI. Just be ready to use your electric boost pump when climbing on hot days, especially if you leave your aircraft in the sun which may heat the fuel, as the vapor pressure of auto gas can be quite different to AVGAS. Another contributor to vapor issues can be high oil temperatures, as the mechanical pump is bolted to the engine and can heat the fuel before it reaches the mechanical pump. Either way, having the boost pump on hot days during high fuel flow events takes care of things.

https://www.lycoming.com/sites/defau...ed%20Fuels.pdf

Good luck.

Tom.
RV-7

[tgmillso]

You're totally overthinking the fuel flow meter. I have a stupid amount of money tied up in avionics and engine monitoring, but frankly now I just use the red knob and listen to the engine, and use the airspeed indicator. When you are LOP for a specific RPM, for a certain fuel burn, you will get a specific IAS, as all the fuel is getting converted into horsepower. Rich of peak, this is not the case, as a lot of fuel is going out the tailpipe unburnt, and the rate will be highly dependent on the mixture setting. If you run these engines below about 22" of MP, there's not a lot you can do to blow them up, so get up there and go fly LOP. Pretty soon you will know for what IAS how much fuel you will be burning, so your airspeed indicator will essentially become your fuel flow meter. If you keep your testing low, there will be bugger all time spent on climb and descent, so what you used on an hourly basis in cruise will pretty much reflect the burn rate you calculate at the pump at the end of the day. This will give you something as useful and more accurate than most fuel flow meters, not to mention that the off-the-shelf calibration of most fuel flow meters is terrible, so you have to calibrate them anyway, or not trust them. Regardless, your son has to build hours, so it may as well be spent doing something useful.

Tom. Again.

[jneves]

Originally Posted by tgmillso

You're totally overthinking the fuel flow meter. I have a stupid amount of money tied up in avionics and engine monitoring, but frankly now I just use the red knob and listen to the engine, and use the airspeed indicator. When you are LOP for a specific RPM, for a certain fuel burn, you will get a specific IAS, as all the fuel is getting converted into horsepower. Rich of peak, this is not the case, as a lot of fuel is going out the tailpipe unburnt, and the rate will be highly dependent on the mixture setting. If you run these engines below about 22" of MP, there's not a lot you can do to blow them up, so get up there and go fly LOP. Pretty soon you will know for what IAS how much fuel you will be burning, so your airspeed indicator will essentially become your fuel flow meter. If you keep your testing low, there will be bugger all time spent on climb and descent, so what you used on an hourly basis in cruise will pretty much reflect the burn rate you calculate at the pump at the end of the day. This will give you something as useful and more accurate than most fuel flow meters, not to mention that the off-the-shelf calibration of most fuel flow meters is terrible, so you have to calibrate them anyway, or not trust them. Regardless, your son has to build hours, so it may as well be spent doing something useful.

Tom. Again.

I agree with you Tom, with a slight twist. I'm in the same boat on being able to lean without FF or even EGTs. Pull the knob back, get the stumble, richen up to get a smooth running engine and you're good. The twist is without the engine monitor and having no idea what the engine was "feeling" I was worried about getting lean and ending up in the "red box". After using all the engine data and leaning for a dozen or so flights I'm now able to just pull the red knob back, set to a specific engine smoothness, RPM and speed and only use the engine data to verify things are good once speed, RPM and temps settle down.

[dbier99]

Originally Posted by tgmillso

ROP is totally not worth it for cruise. May as well be throwing $100 bills out the window. Lean of peak your engine will run cooler and cleaner, and you'll make the oil barons poorer. What's not to like about that? For building time, the aircraft will still fly great back at 5.5GPH and 120kts, so long as it's LOP.

I really appreciate the suggestion and links regarding running Lean of Peak. We'll read through them tonight. I'd always been taught with our previous flying club planes (Archer & 172) to use ROP and have always been worried about LOP from an engine damage standpoint - but am willing to give it a try since so many here appear to do it. Hope we get it right!

Originally Posted by tgmillso

Your engine is on this list somewhere, and approved for 93AKI.

None of the airports we use sell MOGAS (93AKI) so that likely isn't a option for us right now. However, I will see if our carbureted Lycoming 0-360 A1A is approved in case we ever have access to MOGAS - but does switching fuels require some modifications or can we move back and forth between MOGAS and 100LL if MOGAS availability is spotty? Obviously, I have a lot to learn as a first time plane owner!

[jneves]

[quote=dbier99;1634418]I really appreciate the suggestion and links regarding running Lean of Peak. We'll read through them tonight. I'd always been taught with our previous flying club planes (Archer & 172) to use ROP and have always been worried about LOP from an engine damage standpoint - but am willing to give it a try since so many here appear to do it. Hope we get it right!


Mike B has a great webinar on YouTube about lead of peak operations. Watch it a couple times, if you use an iPad in the cockpit you can download AircraftPower app for free and based on your engine model it will give you % of power based on altitude, OAT, RPM and MP. I use this to see where I end up on the Redbox scale, then lead enough to stay just outside the safe operating limits, then back that up with verifying my CHTs are within limits as well. After doing this a bunch, it now comes down to a big mixer pull to the far lean side then richen up to get the speed I want and the CHTs that keep the engine happy.

[dbier99]

I've started reading the linked articles and am quickly realizing why so many people just fly 24 squared - because honestly much of what the author is saying is going over my head - and I used to think I was somewhat mechanically inclined. Even if I could figure out the right way to use the LOP methodology I'm not even certain I can trust the CHT readings on our recently acquired RV6A enough to depend on them to do LOP without engine damage.

I'll continue reading but for the time being I think we'll just fly at the usual 24 squared settings that the previous owner and most people I've talked with recommend because nobody I've spoken with has been able to provide an alternate setting that is known for lower fuel burn (even at lower speeds).

[Sam Buchanan]

Originally Posted by dbier99

I've started reading the linked articles and am quickly realizing why so many people just fly 24 squared - because honestly much of what the author is saying is going over my head - and I used to think I was somewhat mechanically inclined. Even if I could figure out the right way to use the LOP methodology I'm not even certain I can trust the CHT readings on our recently acquired RV6A enough to depend on them to do LOP without engine damage.

I'll continue reading but for the time being I think we'll just fly at the usual 24 squared settings that the previous owner and most people I've talked with recommend because nobody I've spoken with has been able to provide an alternate setting that is known for lower fuel burn (even at lower speeds).

Most likely you will never achieve true LOP with your carbed engine, the fuel delivery to each cylinder is too inconsistent. I pull mixture to where rpm is ~10 lower than full rich and that has proved over the past 23 years to be a pretty good economy setting. I assume some of the cylinders are running a little LOP.

But this thread has drifted far away from the original poster's inquiry.

[tgmillso]

Hi Dave. I'm not giving up that easily. This is not rocket science. Infact rocket science and jet engines are likely the reason we lost a lot of this understanding for a generation. People like Lindbergh has this all worked out back in the 20's, then applied it again during WWII.

http://www.charleslindbergh.com/wwii/

I too was trained like you by some of my instructors. Set to 24 square and nervously pull the mixture back to some arbitrary point based on a totally garbage EGT gauge. It was absolute bollox.

Lycoming state that you can basically put the mixture anywhere you like at power settings less than 75% power. Most pilots use 65% as their limit just to give them an additional buffer, and this can be controlled by simply pulling the throttle back to get you to 22" of MP. If you want more margin when you are starting down this path, then take off a couple more inches. To address Sam's comment, with the MP so low, it doesn't even matter if the cylinders are unbalanced because your intake manifold distribution isn't perfect, because the power levels are so low the engine doesn't care if it's rich or lean.
There's a reason we no longer walk around behind cars smelling unburnt fuel fumes anymore. It's because they are running LOP almost entirely, except when they are pulling hard up a hill, ensuring that all that fuel is turned into HP.
I'm sure there's another RV pilot in your area that would be delighted to take you up for a fly and show you LOP operation in the real world. Once you see it run in person, you will realize there's nothing to it.
On the AVGAS side of things, the lead bromide biproduct of combustion is a salt and is the primary contributor to corrosion in aircraft engines. You are doing yourself a disservice running it. There's no fuel at the airport I'm based at, so I just fill drums and have my own rotary drum pump. Not hard, way better for your engine and way significantly cheaper. You can mix mogas with existing AVGAS, with no changes needed.

Tom.