Mooney bravo fuel burn at low power settings

[Ripley98]

This may be a thread somewhere but what kind of fuel burn numbers should one expect from a bravo at lower power settings? Let’s say a speed of 140-150ktas, 8-10k ft(something along the lines of where my f reaches). Considering options from my f model again but fuel burn,weight and range is always a factor and seems a little difficult to match the F in those terms. An eagle or encore I know is the answer but a little pricey now.

[A64Pilot]

I don’t know, but suspect not much more than your F, it’s carrying a lot more weight but may be a little slicker so one may somewhat cancel the other. BSFC is likely a little lower in the B. However it’s my understanding that isn’t an inexpensive engine to maintain, fuel burn may not be the issue? Speed is usually what costs fuel, because it takes HP. I could fly in formation with my 235HP Maule with a 180 and fuel burn if anything was lower in my 235 because I could lean more aggressively and lose the HP where the 180 couldn’t.

But it sound like a J mission or keep your F?

[Schllc]

@LANCECASPER or @donkaye can answer this question accurately  

they are well versed on this subject. 
fuel burn per hour alone isn’t a fair comparison. You are flying considerably faster. 
I haven’t owned a bravo but I’ve owned ovations and acclaims, and the maintenance and operating costs are not different enough to be a deciding factor. 
a turbo provides options beyond simply speed. 
I can’t imagine it being ore than say 20% more annually to own and maybe 10% more fuel. 

[philiplane]

If you fly 100 hours per year, the difference between a 10 GPH F and a 19 GPH Bravo is what, $4000? It's the smallest part of the overall budget. And you go 4000 NM further in the Bravo. Why pull the power back? You're still putting hours on the engine, and for what it costs to maintain and overhaul, you want to go as far as you can every hour. Or look at it this way- you only have to fly the Bravo 78 hours to go the same distance as 100 hours in the F. So the extra fuel is not as much as you think.

[Niko182]

2 hours ago, A64Pilot said:

I don’t know, but suspect not much more than your F, it’s carrying a lot more weight but may be a little slicker so one may somewhat cancel the other. BSFC is likely a little lower in the B. However it’s my understanding that isn’t an inexpensive engine to maintain, fuel burn may not be the issue? Speed is usually what costs fuel, because it takes HP. I could fly in formation with my 235HP Maule with a 180 and fuel burn if anything was lower in my 235 because I could lean more aggressively and lose the HP where the 180 couldn’t.

But it sound like a J mission or keep your F?

I believe the bravo doesn't usually have the benefit of running LOP, therefor the fuel flow tends to be quite a bit higher than the rest of the Mooney fleet with the exception of the rocket. I believe the fuel flow will be considerable higher than the 8 to 8.5gph hes seeing in his F. I'd guess maybe 14gph give or take to get 150 knots at 10k but that's just a guess.

[A64Pilot]

10 hours ago, Niko182 said:

I believe the bravo doesn't usually have the benefit of running LOP, therefor the fuel flow tends to be quite a bit higher than the rest of the Mooney fleet with the exception of the rocket. I believe the fuel flow will be considerable higher than the 8 to 8.5gph hes seeing in his F. I'd guess maybe 14gph give or take to get 150 knots at 10k but that's just a guess.

I don’t believe I can get 150 kts at 10,000 LOP in my J, more like peak LOP I’m probably closer to 140
At 10,000 all I can get according to my app is between 62% and 65% at best power, which is about 125 HP.

Only real answer is for someone with a Bravo to go out and fly 10,000 and 140ish kts true and as they don’t need big HP to do it, turn the RPM down and see what their fuel burn is.

[Shadrach]

4 hours ago, A64Pilot said:

I don’t believe I can get 150 kts at 10,000 LOP in my J, more like peak LOP I’m probably closer to 140
At 10,000 all I can get according to my app is between 62% and 65% at best power, which is about 125 HP.

Only real answer is for someone with a Bravo to go out and fly 10,000 and 140ish kts true and as they don’t need big HP to do it, turn the RPM down and see what their fuel burn is.

What does LOP mean? It could be anything leaner than peak. Peak EGT is in the best BFSC range, what’s the advantage to leaning further when at 10,000msl? 
 

 

[Fly Boomer]

14 hours ago, Niko182 said:

I believe the bravo doesn't usually have the benefit of running LOP, therefor the fuel flow tends to be quite a bit higher than the rest of the Mooney fleet with the exception of the rocket.

Why the Rocket exception?

[Niko182]

1 hour ago, Fly Boomer said:

Why the Rocket exception?

Because the Rocket and the Bravo burn around 18 to 19gph in flight and usually aren't flown LOP. Therefor I don't think the fuel burn differences are that apparent between the rocket and Bravo.

[Shadrach]

The TIO540 AF series engines are more thermally efficient (8:1CR) than most turbocharged aero engines but they are not as efficient as an IO360.  A Bravo simply cannot make as much power per volume of fuel as a 201.  That being said, the difference is probably not earth shattering.

As to the engine's LOP manners. Has anyone managed to get a TIO540 to run smoothly LOP?

[Rick Junkin]

1 hour ago, Shadrach said:

Has anyone managed to get a TIO540 to run smoothly LOP?

Yes indeed. There are several threads from @DVA and @Awful_Charlie that detail how to do it. I posted my JPI data from a typical sortie running ~40df LOP at 13.7GPH, 30/2200. I don’t remember the true airspeed but it was something north of 170. I’ll find it and add the link to that thread here.

Cheers,
Rick

As promised - my post with the JPI data is about half way down the page. This was from cruise at 8,000' and 160KTAS.

 

 

[A64Pilot]

On 12/12/2022 at 12:04 PM, Shadrach said:

What does LOP mean? It could be anything leaner than peak. Peak EGT is in the best BFSC range, what’s the advantage to leaning further when at 10,000msl? 
 

 

Sort of my point, but I think to get the HP to get that speed at that altitude would require ROP, so no theoretical gain from LOP fuel burn. I say theoretical because I don’t think I can get those numbers and be say -25 LOP.

When people say LOP without giving a number my assumption is they mean most efficient mixture, especially when they are talking about lowering fuel consumption as the post above was by saying the B can’t run LOP and therefore will have a higher fuel burn.

[A64Pilot]

Only Bravo numbers that make sense in this question is what’s the fuel burn to true out at 140isk kts between 8 to 10K, so yes your pulled way back to 360 power levels.

That was his question, what you burn at 170 etc will of course be way higher than 30 kts slower

I’ll fly around at 6.5 to 8 GPH often when I’m just out flying and not in a hurry, so I guess he’s asking how low can he get he fuel burn if he’s not in a hurry in a Bravo.

[A64Pilot]

On 12/12/2022 at 2:40 PM, Rick Junkin said:

Yes indeed. There are several threads from @DVA and @Awful_Charlie that detail how to do it. I posted my JPI data from a typical sortie running ~40df LOP at 13.7GPH, 30/2200. I don’t remember the true airspeed but it was something north of 170. I’ll find it and add the link to that thread here.

Cheers,
Rick

As promised - my post with the JPI data is about half way down the page. This was from cruise at 8,000' and 160KTAS.

 

 

See I’m thinking if he can make 170+ at 13 GPH, then he can make 140 ish at 10+ GPH. He’s getting 13 MPG at 170, that’s not far off 140 ish kts at 10 GPH.

‘Original poster didn’t state fuel burn, but I’m thinking it’s not less than 10 GPH.

‘In other words you can slow a Bravo down to F speeds if you chose to and fuel burn difference isn’t much different