Low Manifold Pressure on Take Off in Mooney Bravo

[rocketman]

My 1910 TT TIO-540 AF1B Lycoming engine on my TLS/Bravo only gets 36 MAP on TO. RPM is 2575. All compressions 76 or better. No oil burn - normal oil analysis and no metal in filter.

 

What would be the likely cause of low MAP?

[Awful_Charlie]

It all depends on the temperature of the air coming out of the intercooler.  There is a page in the MM and the Lycoming operators manual about what to expect, but if the ambient is not hot, it sounds as though what you have is in the right ballpark.  If it needs adjusting, there is a square head on the left side of the intercooler that alters the absolute density controller - beware though, it is *very* sensitive, you'll be looking at less than 1/8th of a turn to move it an inch of MP

[johnggreen]

Turbochargers wear.  I had to bump my MP up twice or three times in the 800 hours I flew it.  Even then, I never let it get over 36.5".  Didn't need it and felt like I was helping the engine.

 

Jgreen

[rocketman]

Welcome back John. Good to hear you chime in again. Always appreciate your input.

 

At least I know I am not hurting anything at 36 MAP

[Tony Armour]

Raise an old topic. The manual says 1/8 turn for 2" of manifold pressure, mine was turned almost 1/4 turn and I only picked up 1". What has everyone seen in actual experience ? I have been at 33" max for quite some time but never really worried about it. We have checked tightness of bolts etc a few years back and recently my IA pressure checked the intake and exhaust. Maybe until you get near the book levels it takes more movement, ie not a linear curve. 1875 TT with a top at 1350. One quart oil for every 25 hours at most. I don't remember it being this low when we changed turbos around 1450 but it was lower, after a reasonable break-in time it may have gotten down there. The IA says that's when it started and we just never adjusted for it.

[AndyFromCB]

Raise an old topic. The manual says 1/8 turn for 2" of manifold pressure, mine was turned almost 1/4 turn and I only picked up 1". What has everyone seen in actual experience ? I have been at 33" max for quite some time but never really worried about it. We have checked tightness of bolts etc a few years back and recently my IA pressure checked the intake and exhaust. Maybe until you get near the book levels it takes more movement, ie not a linear curve. 1875 TT with a top at 1350. One quart oil for every 25 hours at most. I don't remember it being this low when we changed turbos around 1450 but it was lower, after a reasonable break-in time it may have gotten down there. The IA says that's when it started and we just never adjusted for it.

 

I'm from a different school of thought but I fly out west quite a bit, high and hot. Primary reason I got a Bravo over the Ovation. at 33" you are only making about 90% power, so all performance numbers from the book go out of the window. I think it's one thing to be making 36 but 33? That's below cruise climb. There has to be either something wrong with the system or something wrong with your gauge. Either case, I'd investigate more. One day, on a short runway, on a hot day, you might need all the power the Bravo can muster.

 

I kind of agree with John, on longer runways, clear on the end, I tend not to exceed 34 on take off, but it's nice knowing extra 4 inches and 20hp is available if the trees start looking too big too quickly or I'm loaded to the max.

[carqwik]

The Bravo is not a good initial climber when hot and heavy - has something to do with the prop design as I was told by Bob Kromer.  The Bravo prop is optimized for cruise.  They did try out a prop that made the climb better but had a speed penalty in cruise so.... 

 

My MP maxes at 36.5" too...I asked Tom Rouch about it and he told me why it's set that way...and that was 14 years ago so I don't recall his explanation.

[AndyFromCB]

The Bravo is not a good initial climber when hot and heavy - has something to do with the prop design as I was told by Bob Kromer.  The Bravo prop is optimized for cruise.  They did try out a prop that made the climb better but had a speed penalty in cruise so.... 

 

My MP maxes at 36.5" too...I asked Tom Rouch about it and he told me why it's set that way...and that was 14 years ago so I don't recall his explanation.

 

I've never seen less than 900fpm at 105knots below 12,000feet and I'm fairly "liberal" with my gross weight calculations...Never had issues meeting climb gradients out of KJAC...

 

Now, I agree about Bravos prop. It actually appears not to be optimized for anything. I would love for Hartzell to come out with a Top Prop for Bravo. Like they did for the later Ovations.

[rbp]

my M climb profile is 120kias @~500fpm.  keeps the CHTs cooler, better traffic visibility, and more comfortable deck angle

[Tony Armour]

I'm not sure we are thinking differently Andy.......i "am" trying to raise it ;-) But no, it hasn't been a big concern on the east coast and plenty of runway. I like the prop comment "not optimized for anything" :-)

[AndyFromCB]

my M climb profile is 120kias @~500fpm.  keeps the CHTs cooler, better traffic visibility, and more comfortable deck angle

 

I have never seen 500fpm at 120knots until well, well into the teens. Usually closer to 800fpm at gross at 120, 34/2400 slowly dropping of to 500fpm by about FL180. But I usually climb to 1000 AGL at 105knot, at my take off power and then point the nose down. So my initial rate of climb is often 1100fpm or so, which is pretty damn good. Not as good an 310hp Acclaim, but then what is. 

[Awful_Charlie]

Raise an old topic. The manual says 1/8 turn for 2" of manifold pressure, mine was turned almost 1/4 turn and I only picked up 1". What has everyone seen in actual experience ? I have been at 33" max for quite some time but never really worried about it. We have checked tightness of bolts etc a few years back and recently my IA pressure checked the intake and exhaust. Maybe until you get near the book levels it takes more movement, ie not a linear curve. 1875 TT with a top at 1350. One quart oil for every 25 hours at most. I don't remember it being this low when we changed turbos around 1450 but it was lower, after a reasonable break-in time it may have gotten down there. The IA says that's when it started and we just never adjusted for it.

 

1875 TIT is *waaaay* to high - maybe someone else can chime n here, but on the basis most turbos have a TIT limit of1650, and the AF1B is already "overrated" with a redline at 1750, I wonder if your outlet is toast and some of the vanes have melted or disappeared. To me it really sounds like you have an induction leak or there is something not right in the turbo. Do you have any other instrumentation to back up the factory gauges, such as an EDM (with it's own independent MP and TIT), or have you had the factory gauges checked? The one time I made an adjustment it took me three or four runs to get the setting nailed, and then the next run with my A&P before he would sign it, it had moved 1/2" by wiring and cowling up. Less than 1" of movement on the end of a 6" long spanner made a very measurable difference.

 

I've never seen less than 900fpm at 105knots below 12,000feet and I'm fairly "liberal" with my gross weight calculations...Never had issues meeting climb gradients out of KJAC...

 

Now, I agree about Bravos prop. It actually appears not to be optimized for anything. I would love for Hartzell to come out with a Top Prop for Bravo. Like they did for the later Ovations.

 

I'm considering the MT next time I come up for prop o/h - I like the idea of less weight, 1" more prop clearance and a short take off roll and better cruise. I'd like to hear from someone who has done it first, before committing to a 10+AMU job though

 

I have never seen 500fpm at 120knots until well, well into the teens. Usually closer to 800fpm at gross at 120, 34/2400 slowly dropping of to 500fpm by about FL180. But I usually climb to 1000 AGL at 105knot, at my take off power and then point the nose down. So my initial rate of climb is often 1100fpm or so, which is pretty damn good. Not as good an 310hp Acclaim, but then what is. 

I'm with Andy here. My standard (ie not runway length or obstacle clearance limited) SOP is

rotate at POH +3/+5 (I don't mean to teach you to suck eggs here, but you do realise Vr varies with TOW don't you?)

wait for 80-85KIAS, brakes on & off, gear up, hold the attitude. ~1000fpm depending on temps and altitude

wait for 100-105KIAS, flaps up, hold the attitude

wait for 120 KIAS, reduce to 34" 2400, trim nose down and lean to 1400 TIT (about 22GPH). 1000fpm (light and cool) to 600fpm (hot and heavy)

hold this until ToC, when it's cowl flaps closed, wait a minute of so, and reduce to cruise (normally 30" 200 for me), then lean to 15-25 LOP

[AndyFromCB]

1875 TIT is *waaaay* to high - maybe someone else can chime n here, but on the basis most turbos have a TIT limit of1650, and the AF1B is already "overrated" with a redline at 1750, I wonder if your outlet is toast and some of the vanes have melted or disappeared. To me it really sounds like you have an induction leak or there is something not right in the turbo. Do you have any other instrumentation to back up the factory gauges, such as an EDM (with it's own independent MP and TIT), or have you had the factory gauges checked? The one time I made an adjustment it took me three or four runs to get the setting nailed, and then the next run with my A&P before he would sign it, it had moved 1/2" by wiring and cowling up. Less than 1" of movement on the end of a 6" long spanner made a very measurable difference.

 

 

I'm considering the MT next time I come up for prop o/h - I like the idea of less weight, 1" more prop clearance and a short take off roll and better cruise. I'd like to hear from someone who has done it first, before committing to a 10+AMU job though

 

I'm with Andy here. My standard (ie not runway length or obstacle clearance limited) SOP is

rotate at POH +3/+5 (I don't mean to teach you to suck eggs here, but you do realise Vr varies with TOW don't you?)

wait for 80-85KIAS, brakes on & off, gear up, hold the attitude. ~1000fpm depending on temps and altitude

wait for 100-105KIAS, flaps up, hold the attitude

wait for 120 KIAS, reduce to 34" 2400, trim nose down and lean to 1400 TIT (about 22GPH). 1000fpm (light and cool) to 600fpm (hot and heavy)

hold this until ToC, when it's cowl flaps closed, wait a minute of so, and reduce to cruise (normally 30" 200 for me), then lean to 15-25 LOP

 

I think he was referring to his engine total time and not TIT.

[carusoam]

It is important for a Bravo to meet known performance / book numbers...

If it is not achieving them, you want to know why...

It is one thing to have worn turbine blades.

Completely different to have an exhaust leak.

Running out of HP is bad.

Especially if you only have 270 to begin with...

Not a knock on the Bravo, just a nudge to find the answer of something that can be really important...

Best regards,

-a-

[AndyFromCB]

It is important for a Bravo to meet known performance / book numbers...

If it is not achieving them, you want to know why...

It is one thing to have worn turbine blades.

Completely different to have an exhaust leak.

Running out of HP is bad.

Especially if you only have 260 to begin with...

Not a knock on the Bravo, just a nudge to find the answer of something that can be really important...

Best regards,

-a-

 

Anthony,

 

Is it only 260? I thought it was 270? I better check my book. I never really felt the Bravo was lacking for power. I casually went around few weeks ago at 24/2400, with gear and flaps hanging out and still managed to get back up to pattern altitude. Granted it was only me and 20 gallons of fuel. Never retracted anything.

 

But yes, good point on exhaust leaks. Exhaust leaks and broken clamps kills Bravo pilots. 3 dead so far. That's 1 in 100 chance.

[carusoam]

Andy,

According to MooneyPilots.com it is 270hp

Correction made to my post...

For my long body...

200 rpm + FF = 30 additional hp...

The T/O distance is reduced 30% by going from 2500 rpm to 2700 rpm.

The 270 hp is not terrible, but I would be affraid to unknowingly have it get worse...

For additional comparison (for anyone else that may be interested)...

Other Long Body Mooneys...

M20L(PFM) 217 HP

M20S(1) 244 HP

Best regards,

-a-

[JohnB]

Great topic guys, and topical! My Bravo previously maxed out between 36" and 38"MP. Over the last several months, I started noticing oscillations of mp at full power requiring me to throttle down to avoid redlining. . Had a bunch of things replaced (turbo, density controllers, wastegate) So now its set at 34" MP peak with no more oscillations. This apparently changes as atmospheric conditions change. in reading through the Lycoming tips...

 

  http://lycoming.com/Portals/0/techpublications/TechTips/Key%20Operations.pdf    ( Look at page 57  through 60 and pg. 61, para 3.)

 

a lower peak MP may improve engine life, but how low is too low? Does anyone know if there a MP that's so low that useful load and high altitude airport takeoffs will be affected?

[FoxMike]

Just some food for thought/dreams.  McCauley showed up at MAPA this year with a carbon prop.  The specifications callout a 45lb installed weight.  They were probably thinking of the Acclaim, but knows maybe they would adapt one to the Lycoming Engines.  McCauley and Lycoming are both Textron companies.

[JohnB]

Did some more research and found out on our Lycoming 540s, we get our full 270 HP at 35" MP. Anything above that is just extra, and 34" would be only slightly less than 270.

I'm getting 35.3" or so on my take offs. (Discrepancy solved was my factory mp gauge that was off a bit)

[carusoam]

Nice follow-up John.

Thanks,

-a-

[Tony Armour]

Remember 1/8 turn for 2" of boost, so says the manual. Look under the engine from the drivers side. 

That is on a vertical plane, the square head will be facing you out to the side, That is the gear door behind it painted maroon/gold

 

 

Edited February 22, 2016 by Tony Armour

[Awful_Charlie]

On 04/06/2015 at 3:43 PM, JohnB said:

Did some more research and found out on our Lycoming 540s, we get our full 270 HP at 35" MP. Anything above that is just extra, and 34" would be only slightly less than 270.

It depends on the IAT (or IOT in the manual) - check the engine OM Figure 5-16 on page 5-25 (Curve 13495-A) - it could be as low as 34.25" and as high as 37.25" for the 'Normal' line (70-170dF. The lower end of that would be an OAT around 40-50dF at sea level I think)

Yes, it is very sensitive - after several attempts, me & my A&P lockwired the adjuster for both rotations, and then gradually tightened one or the other and snugged the adjuster with a spanner against them until we got it nailed - it took us all afternoon.

Great picture Tony - but sorry, I don't like your lockwiring - there's nothing to stop the adjuster working anti-clockwise, and the bottom right screw doesn't look properly 'in safety' (although the effect might be trivial if just the one comes out, but then it you're going to the bother of putting wire through it, it might as well do something!)

[Tony Armour]

17 hours ago, Awful_Charlie said:

It depends on the IAT (or IOT in the manual) - check the engine OM Figure 5-16 on page 5-25 (Curve 13495-A) - it could be as low as 34.25" and as high as 37.25" for the 'Normal' line (70-170dF. The lower end of that would be an OAT around 40-50dF at sea level I think)

Yes, it is very sensitive - after several attempts, me & my A&P lockwired the adjuster for both rotations, and then gradually tightened one or the other and snugged the adjuster with a spanner against them until we got it nailed - it took us all afternoon.

Great picture Tony - but sorry, I don't like your lockwiring - there's nothing to stop the adjuster working anti-clockwise, and the bottom right screw doesn't look properly 'in safety' (although the effect might be trivial if just the one comes out, but then it you're going to the bother of putting wire through it, it might as well do something!)

I think that picture is before I adusted, but, I probably wired it back exactly the same. It would have to push against two different strands of twisted wire to go clockwise so I don't think it could move much. I would be interested in seeing how others are wired. I see the bottom right screw, maybe I corrected that :-)

[ArtVandelay]

Great picture Tony - but sorry, I don't like your lockwiring - there's nothing to stop the adjuster working anti-clockwise, and the bottom right screw doesn't look properly 'in safety' (although the effect might be trivial if just the one comes out, but then it you're going to the bother of putting wire through it, it might as well do something!)

This is why I don't do much work on my plane, but I don't see anything wrong with the bottom right screw.

I do see what you mean about the adjuster.

[LANCECASPER]

9 minutes ago, IrishTiger said:

Thanks Tony!! I'll have to get to it when I have another set of two hands because removing and putting that bottom cowling back on is a challenge!!! 

No kidding! Bottom cowl is definitely two person job and even then can be a pain.

Edited February 25, 2016 by LANCECASPER