Bravo Cruise Performance

[Jsavage3]

From the POH performance section, can you share what Mooney says the Bravo will do in cruise at 11k/12k for both ROP and LOP?  Both KTAS and FF please?  

[Fritz1]

The POH only gives cruise figures for peak TIT power settings which produce excessive CHT and TIT, I typically cruise at 30" 2300, about 78% power, 18.5 gph, 100 dF rich on 1st cylinder to peak which produces about 176 KT TAS at 12,000 ft, my aircraft has TKS, others may be 3-5 KT faster, going max cruise power 34" 2400, about 90% power typically increases cruise by 11-12 KT, flow goes to about 21.5 gph to keep TIT below 1580 dF, In a nutshell, the POH performance figures not realistic, engine durability requires higher fuel flows, to keep CHT below 480 and TIT below 1580, the sweet spot of the Bravo is around it's critical altitude of around 21000 ft, 188 KT TAS, 18.5-19 gph 78% power, she will reach 200 KT when pushed to max cruise power, about 22 gph, think when pushed to the limit at 25,000 ft the Bravo will reach 215 KT

[slowflyin]

I run similar power settings to @fritz1 and see similar results.  My commute has shortened so I don't fly as high as often with typical altitudes of 9-10K.   Most days at 75% I see 174-176 TAS.   Last time I took a longer trip it was summer time with 196 TAS at 75% at 18K.   I also have TKS.  I've been told TKS cost 10 kts.   I'd argue that only holds true if your not in ice.      I see an increase of about 2 kts per thousand feet over 8K.   I've also been told to expect 200 @ 18K  @ 75% in a non-tks Bravo.  

[Rick Junkin]

On the LOP side at 11-12,000’ I see 165-170KTAS at 13.2gph (70%) and 30”/2200RPM. I also have TKS.

For reference, here’s a screen shot of my G3X at 6,000’. Adding 2 KTAS per thousand feet up to 12,000’ the math shows 170KTAS, which of course will vary with OAT/ISA offset.

[PilotX]

Here is what I see, if I recall these were about 12500'

ROP

22/28” 16.6gph (137KIAS)

LOP

22/28” 11.5 (110)

22/30” 12.5 (125)

22/32” 13.5 (132)

22/34” 14.5 (137) ~ 170 True.

Edited January 7 by PilotX
Added altitude.

[hazek]

On 1/7/2025 at 5:55 PM, Rick Junkin said:

For reference, here’s a screen shot

Hot damn, those are some tight CHTs! How did you get there?

[Rick Junkin]

1 hour ago, hazek said:

Hot damn, those are some tight CHTs! How did you get there?

My airplane had all new baffles and baffles seals in 2014, and I keep a close eye out for keeping the seals in good shape and all of them folding the right direction when the cowling goes on. I had a small tear in the back seal at one point that caused about a 15 degree increase on #6 as I recall. Once it was repaired the temp came back down.

One thing I’ve noticed is my CHTs are tighter LOP than ROP. The ROP spread can be 30+ degrees while LOP is always less than about 15 degrees and usually around 10.

[hazek]

19 minutes ago, Rick Junkin said:

One thing I’ve noticed is my CHTs are tighter LOP than ROP.

Makes sense even on the face of it. If cooling efficiency is constant then the nominally higher temps will yield nominally bigger spreads.

But yeah, I need to talk my partner into fixing our baffles. And all the gaps. When the engine was last replaced they've done some pretty horrendous job.

Edited January 27 by hazek

[Fritz1]

baffles are the easiest fix on the Bravo, the right rubber material, a couple of pop rivets and RTV, the smallest leak and associated loss of ram air makes a big difference, there are typically big gaps in the factory baffling around the starter and around the alternators, fine wire plugs also appear to go well in the Bravo engine, I daresay they dropped the TIT by 15 degrees in my engine, feels like more complete combustion in the cylinder and less post-combustion in the exhaust

[Rick Junkin]

2 hours ago, Fritz1 said:

there are typically big gaps in the factory baffling around the starter and around the alternators

Ironically, I have those unsealed gaps around my starter and left alternator and yet my CHTs are even and well controlled. The right alternator has seals around it. In my case I'm not going to fix what isn't broken, but I can see how adding some seals in those areas could make a difference for an engine with cooling problems.

 

[hazek]

Our engine is decently cooled, so wouldn't say we have cooling problems but the temps are like this with a notably worse spread:

This was on a winter flight in cruise at 27"/22 ROP 1600TIT, and CHT3 I'm pretty sure it's actually more like 356.

[ddevito]

I have GAMI's, and fine wire plugs. Shortly after takeoff at I go to 2300 RPM and only back the throttle out enough to turn off the boost pump, so it runs around 34" WOT. I also go to 15 GPH and climb at 110 KIAS all the way to altitude. Cylinder Temps rarely exceed 400 on climb and settle out mid 350ish level flight. TIT never exceeds 1600. I never touch the throttle or mixture until my destination and then only the throttle. I rarely fly at low teens, usually low flight levels for any flights over 1.5 hr. or 6 to 9K for shorter trips. So I'm getting true at lower altitudes 175ish and 200 at the flight levels.