Rick Junkin

I’m with you. I’m a simpleton when it comes to power management. I did the research and experimentation to find a cruise power setting I like and that’s the one I use. The numbers are always the same for the most part and it takes less brain bytes to plan and manage.

Hmm. Mine appears opposite that, where LOP %HP is overestimated by the G3X. I set the LOP fuel flow that yields 70% and the G3X shows 73%. I haven’t experimented with ROP settings yet.

Haha! Great minds and all that.

Those will be good data points, thanks! In the Bravo community we have the issue of the POH not speaking in terms of % power. Actually this is a non-issue as far as general aircraft operation; it only becomes an issue when we want to do something like the comparison you are about to do with pre-determined power parameters. Then we have to get into the charts in the Lycoming manual and do the calculations, because it doesn’t speak directly to % power either. Not a big deal, just requires some chart reading and math. The other way for us to do it is to set LOP power, see what airspeed it gives us, and then go ROP and search for the power setting that results in the same airspeed. Using this method requires no book work.

What’s the easiest way to remove the tail pipe on a Bravo? It’s looking like I need to either remove the firewall heat shielding so I can rotate the pipe and pull it out through the engine mount to the aft, or remove the turbo so I can pull it forward. It just dawned on me that I could give myself more maneuvering room if I put it up on jacks and retract the gear, getting the nose gear door out of the way. But then the jack is in the way? How have you guys done this?

Yeah that's what I said . I crack myself up.

@kortopates Ok, that's kind of what I was getting at, but you lost me with the part I bolded. How can I set my LOP fuel flow (13.2 in my case) and still be running ROP? Are you saying to initially set MP so low that 13.2gph is still ROP? Maybe an example will help me understand. I climb full rich at 34/2400. My standard LOP cruise setting is 30/2200, 13.2gph. At top of climb after I've accelerated out to 140KIAS I set 28" and dial the RPM back to 2200RPM while still full rich, watching the MP climb to 30" as I reduce RPM. Once the CHTs start to drop I do a BMP straight to 13.2gph. Using the method you described, would I initially set my cruise setting of 2200RPM after pulling the MP back to something like 20-25", set the FF to 13.2, and then increase the MP to 30" while adjusting the mixture to keep a constant 13.2gph fuel flow?

I thought you were too, but at first blush I had the RCA dog look on my face.

That's lost on me in this context. I'm sorry, I don't know what point you're trying to make.

I remember reading something like, "Set your lean of peak FF and then regain the power you lost by dialing the MP up 2 inches." All well and good, but only if you accept the fuel flow increase that occurs when you increase the MP. I believe Tom Haines even did a video demonstrating this in his Bonanza; unfortunately a quick google search for said video failed me. Everyone understood ROP operations so a lot of the early techniques of setting LOP were developed with a ROP mindset, if you will. Since there were no published power charts for LOP the only direct comparison power metric between ROP and LOP was airspeed. That's still true today for a lot of airplanes. As I've come to understand it, power output when LOP is tied directly to fuel flow, agnostic of MP and RPM. As an example, I get 70% in my Bravo at about 35dF LOP with 13.2gph and 30"/2200RPM. If I dialed the MP up to 32" and didn't touch anything else, the fuel flow would also increase (to about 14.2gph), giving me more power (75% according to the LOPvsHP spreadsheet) and still about 35dF LOP, only with a higher peak EGT/TIT reference and commensurate higher CHTs. BUT, if I then dialed the fuel flow back to my original 13.2gph I would be back to 70% only now at 32"/2200RPM and closer to 60dF LOP. I think what was happening when people advocated for this (adding back 2" MP) is they were starting with a known ROP power setting, pulling the mixture to the desired LOP value, then adding 2" of MP and accepting the fuel flow they got at that point and declaring equivalent power. So in reality what happens when you do this, you increase where the EGT/TIT value peaks because you're at a higher power setting, and you end up with a higher fuel flow while still maintaining about the same LOP offset. Nothing wrong with that, as long as the temperatures stay within limits and you're far enough LOP for the power you have set. This post may have been a Mr MOTO thing, but I see folks say, without further explanation, that you can regain power LOP by adding MP. That's true, but only if you allow the fuel flow to increase with the MP. In simplistic terms, when operating LOP, power output is driven solely by fuel flow. As I understand it.

Just in case this post goes away someday, I've also uploaded this file to the Performance Data category in the Downloads section of the site. Cheers, Junkman

Here's a link to the post from @Awful_Charlie where I believe I originally got the file, but the link to egtrends.com isn't working for me. So here's a copy of the .xls file I have, noting THIS IS NOT MY ORIGINAL WORK. I've converted it to Numbers format for my personal use on my Mac, but I THINK this is the original .xls file I downloaded from the egtrends.com site. LOPFFvsHP.xls

Yes, it’s the same spreadsheet, I just did some highlighting with my engine data entered. I think it’s already in he downloads section of this site. If not I can share it with appropriate credit to the original author.

I am able to run at 70% 35dF LOP as calculated at 13.2gph with all temps well within limits. I've posted this before; unfortunately it's a low altitude example but it shows all the important parameters. CHTs increase modestly at altitude but remain well below 380dF. I can run at 14.2gph / 75% but the TIT goes to about 1610 and I'd rather keep it below that. I accept the 8-10 knot hit on airspeed and cruise at about 175KTAS in the mid - upper teens. Again, it isn't fuel economy I'm looking for, it's cleaner and cooler engine operation. One of these days I'll remember to grab a screen shot at altitude. EDIT: Added screen shot of LOP % power spreadsheet.

I know I’m an outlier with a Bravo that runs well LOP. I do run Tempest fine wires and GAMIjectors with a 0.3gph spread, and work at staying on top of the ignition system condition and timing. Running at 2200 RPM also helps with LOP ops and I’m happy with the speeds I get. As was said, to each his own. For me it isn’t the fuel savings as much as it is the cleaner running and the lower CHTs. The plugs are always clean and the cylinders and valves always look great through the borescope at oil changes. Time will tell on the engine longevity but all indications are good and I’m optimistic.