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What is the blue range indicating on this manifold pressure gauge?

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What is the blue range indicating on this manifold pressure gauge?

Why don't airplane turbo piston engines have boost control?Why does the EGT gauge in 172s have no numbers on it?Why does manifold pressure increase when you turn on carb heat?Why did the manifold pressure gauge on the Ki-61 have negative values?What does the suction gauge actually show?Why does manifold pressure increase with power?What appears on EGT Gauge if the mixture is rich or lean?What are these lights above the panel in a Blue Angels cockpit?What does a helicopter “gas prod” gauge measure?What is Engine Pressure Ratio?What happens to manifold pressure reading following a reduction in both throttle and RPM?

3

$begingroup$

This is baffling me. Does anybody with experience with this type of indicator have any idea what the blue range of this gauge means?

It's mounted in a mock-up panel. I know nothing about where it originally came from, though it seems pretty clear that it's from a turbocharged piston twin.

flight-instruments piston-engine

share|improve this question

edited 1 hour ago

David Richerby

9,92033578

asked 5 hours ago

PugzPugz

2,609827

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  It would help to know what aircraft this gauge is in
  $endgroup$
  – DeepSpace
  5 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  @DeepSpace I'm sorry I have no idea. It is a standalone gauge we have just sitting around, but it looks pretty clearly to be from a turbocharged piston twin.
  $endgroup$
  – Pugz
  5 hours ago
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Related: Why don't airplane turbo piston engines have boost control?
  $endgroup$
  – ymb1
  5 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  For being a "standalone gauge we have just sitting around", it seems to be pretty well screwed into a panel of some sort.
  $endgroup$
  – FreeMan
  4 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  @FreeMan yes it is! Mock up panel.
  $endgroup$
  – Pugz
  2 hours ago
  

  
  
  
  

 | 
show 1 more comment

3

$begingroup$

This is baffling me. Does anybody with experience with this type of indicator have any idea what the blue range of this gauge means?

It's mounted in a mock-up panel. I know nothing about where it originally came from, though it seems pretty clear that it's from a turbocharged piston twin.

flight-instruments piston-engine

share|improve this question

edited 1 hour ago

David Richerby

9,92033578

asked 5 hours ago

PugzPugz

2,609827

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  It would help to know what aircraft this gauge is in
  $endgroup$
  – DeepSpace
  5 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  @DeepSpace I'm sorry I have no idea. It is a standalone gauge we have just sitting around, but it looks pretty clearly to be from a turbocharged piston twin.
  $endgroup$
  – Pugz
  5 hours ago
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Related: Why don't airplane turbo piston engines have boost control?
  $endgroup$
  – ymb1
  5 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  For being a "standalone gauge we have just sitting around", it seems to be pretty well screwed into a panel of some sort.
  $endgroup$
  – FreeMan
  4 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  @FreeMan yes it is! Mock up panel.
  $endgroup$
  – Pugz
  2 hours ago
  

  
  
  
  

 | 
show 1 more comment

$begingroup$

This is baffling me. Does anybody with experience with this type of indicator have any idea what the blue range of this gauge means?

It's mounted in a mock-up panel. I know nothing about where it originally came from, though it seems pretty clear that it's from a turbocharged piston twin.

flight-instruments piston-engine

share|improve this question

edited 1 hour ago

David Richerby

9,92033578

asked 5 hours ago

PugzPugz

2,609827

$endgroup$

share|improve this question

edited 1 hour ago

David Richerby

9,92033578

asked 5 hours ago

PugzPugz

2,609827

share|improve this question

edited 1 hour ago

David Richerby

9,92033578

asked 5 hours ago

PugzPugz

2,609827

edited 1 hour ago

David Richerby

9,92033578

edited 1 hour ago

David Richerby

9,92033578

asked 5 hours ago

PugzPugz

2,609827

asked 5 hours ago

PugzPugz

2,609827

2 Answers
2

active

oldest

votes

6

$begingroup$

It's a manifold pressure limit with altitude. It relates to a limitation on the differential between ambient and total manifold pressure at different altitudes with turbocharged or supercharged engines; a limit on the amount of actual boost with altitude in other words, not the total pressure.

At 30000 ft, standard atmospheric pressure is only just under 9 inches. 20 inches on the gauge is 11 inches of boost above atmospheric.

At 20000 ft, atmospheric pressure is just under 14 inches, and you're limited to 35 inches, which is about 21 inches of boost.

Between 16000 ft and sea level, with atmospheric pressure between roughly 16 and 30 inches, the limitation is the red line of 40, which is anywhere from 10 to 24 inches of boost above atmospheric.

The increasing limitation in maximum boost with altitude is usually related to the reduced cylinder cooling ability of the thinning air with altitude, and the potential for detonation.

share|improve this answer

answered 4 hours ago

John KJohn K

21k12862

$endgroup$

add a comment | 

5

$begingroup$

The blue scale indicates the maximum manifold pressure (MP) at a given altitude.

• from sea level (SL) to 16000 ft: the maximum MP is 40 inHg (inches of mercury).




• from 16000 ft to 30000 ft, the maximum MP goes down to 20 inHg.

The altitudes are barometric altitudes.

share|improve this answer

edited 4 hours ago

answered 5 hours ago

boglbogl

3,7871733

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Do you have a reference such as a POH that describes this? What type have you seen this in?
  $endgroup$
  – Pugz
  5 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  You beat me to it, one addition: it's SL→16,000 for the 40 inHg.
  $endgroup$
  – ymb1
  5 hours ago
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  @Pugz, no, unfortunately not, but it is written on the gauge itself.
  $endgroup$
  – bogl
  5 hours ago
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  So this is indicating the maximum possible given existing atmosphere at a given altitude, not any sort of limit, but just for pilot reference to to compare to the altimeter?
  $endgroup$
  – Pugz
  5 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  @bogl: I meant to say from SL to 16,000, the max is 40, it starts to go below 40 above 16,000 ft.
  $endgroup$
  – ymb1
  4 hours ago
  

  
  
  
  

 | 
show 1 more comment

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6

$begingroup$

It's a manifold pressure limit with altitude. It relates to a limitation on the differential between ambient and total manifold pressure at different altitudes with turbocharged or supercharged engines; a limit on the amount of actual boost with altitude in other words, not the total pressure.

At 30000 ft, standard atmospheric pressure is only just under 9 inches. 20 inches on the gauge is 11 inches of boost above atmospheric.

At 20000 ft, atmospheric pressure is just under 14 inches, and you're limited to 35 inches, which is about 21 inches of boost.

Between 16000 ft and sea level, with atmospheric pressure between roughly 16 and 30 inches, the limitation is the red line of 40, which is anywhere from 10 to 24 inches of boost above atmospheric.

The increasing limitation in maximum boost with altitude is usually related to the reduced cylinder cooling ability of the thinning air with altitude, and the potential for detonation.

share|improve this answer

answered 4 hours ago

John KJohn K

21k12862

$endgroup$

add a comment | 

6

$begingroup$

It's a manifold pressure limit with altitude. It relates to a limitation on the differential between ambient and total manifold pressure at different altitudes with turbocharged or supercharged engines; a limit on the amount of actual boost with altitude in other words, not the total pressure.

At 30000 ft, standard atmospheric pressure is only just under 9 inches. 20 inches on the gauge is 11 inches of boost above atmospheric.

At 20000 ft, atmospheric pressure is just under 14 inches, and you're limited to 35 inches, which is about 21 inches of boost.

Between 16000 ft and sea level, with atmospheric pressure between roughly 16 and 30 inches, the limitation is the red line of 40, which is anywhere from 10 to 24 inches of boost above atmospheric.

The increasing limitation in maximum boost with altitude is usually related to the reduced cylinder cooling ability of the thinning air with altitude, and the potential for detonation.

share|improve this answer

answered 4 hours ago

John KJohn K

21k12862

$endgroup$

add a comment | 

$begingroup$

It's a manifold pressure limit with altitude. It relates to a limitation on the differential between ambient and total manifold pressure at different altitudes with turbocharged or supercharged engines; a limit on the amount of actual boost with altitude in other words, not the total pressure.

At 30000 ft, standard atmospheric pressure is only just under 9 inches. 20 inches on the gauge is 11 inches of boost above atmospheric.

At 20000 ft, atmospheric pressure is just under 14 inches, and you're limited to 35 inches, which is about 21 inches of boost.

Between 16000 ft and sea level, with atmospheric pressure between roughly 16 and 30 inches, the limitation is the red line of 40, which is anywhere from 10 to 24 inches of boost above atmospheric.

The increasing limitation in maximum boost with altitude is usually related to the reduced cylinder cooling ability of the thinning air with altitude, and the potential for detonation.

share|improve this answer

answered 4 hours ago

John KJohn K

21k12862

$endgroup$

share|improve this answer

answered 4 hours ago

John KJohn K

21k12862

answered 4 hours ago

John KJohn K

21k12862

answered 4 hours ago

John KJohn K

21k12862

5

$begingroup$

The blue scale indicates the maximum manifold pressure (MP) at a given altitude.

• from sea level (SL) to 16000 ft: the maximum MP is 40 inHg (inches of mercury).




• from 16000 ft to 30000 ft, the maximum MP goes down to 20 inHg.

The altitudes are barometric altitudes.

share|improve this answer

edited 4 hours ago

answered 5 hours ago

boglbogl

3,7871733

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Do you have a reference such as a POH that describes this? What type have you seen this in?
  $endgroup$
  – Pugz
  5 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  You beat me to it, one addition: it's SL→16,000 for the 40 inHg.
  $endgroup$
  – ymb1
  5 hours ago
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  @Pugz, no, unfortunately not, but it is written on the gauge itself.
  $endgroup$
  – bogl
  5 hours ago
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  So this is indicating the maximum possible given existing atmosphere at a given altitude, not any sort of limit, but just for pilot reference to to compare to the altimeter?
  $endgroup$
  – Pugz
  5 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  @bogl: I meant to say from SL to 16,000, the max is 40, it starts to go below 40 above 16,000 ft.
  $endgroup$
  – ymb1
  4 hours ago
  

  
  
  
  

 | 
show 1 more comment

5

$begingroup$

The blue scale indicates the maximum manifold pressure (MP) at a given altitude.

• from sea level (SL) to 16000 ft: the maximum MP is 40 inHg (inches of mercury).




• from 16000 ft to 30000 ft, the maximum MP goes down to 20 inHg.

The altitudes are barometric altitudes.

share|improve this answer

edited 4 hours ago

answered 5 hours ago

boglbogl

3,7871733

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Do you have a reference such as a POH that describes this? What type have you seen this in?
  $endgroup$
  – Pugz
  5 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  You beat me to it, one addition: it's SL→16,000 for the 40 inHg.
  $endgroup$
  – ymb1
  5 hours ago
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  @Pugz, no, unfortunately not, but it is written on the gauge itself.
  $endgroup$
  – bogl
  5 hours ago
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  So this is indicating the maximum possible given existing atmosphere at a given altitude, not any sort of limit, but just for pilot reference to to compare to the altimeter?
  $endgroup$
  – Pugz
  5 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  @bogl: I meant to say from SL to 16,000, the max is 40, it starts to go below 40 above 16,000 ft.
  $endgroup$
  – ymb1
  4 hours ago
  

  
  
  
  

 | 
show 1 more comment

$begingroup$

The blue scale indicates the maximum manifold pressure (MP) at a given altitude.

• from sea level (SL) to 16000 ft: the maximum MP is 40 inHg (inches of mercury).




• from 16000 ft to 30000 ft, the maximum MP goes down to 20 inHg.

The altitudes are barometric altitudes.

share|improve this answer

edited 4 hours ago

answered 5 hours ago

boglbogl

3,7871733

$endgroup$

share|improve this answer

edited 4 hours ago

answered 5 hours ago

boglbogl

3,7871733

answered 5 hours ago

boglbogl

3,7871733

answered 5 hours ago

boglbogl

3,7871733