Car

Ed Haywood said:
I always left power untouched til I hit pattern altitude, then set to 25 squared for normal climb. No science behind that, just easy to remember and made sense. However, this thread made me check my POH, which says full power for normal climb, so I'll start doing that instead. Live and learn.
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25 squared is what I have been doing too, because that is what I was taught. There is nothing in the POH about power settings for normal climb. Look at page 28 in this POH (not our exact one, but the same POH for our serial number Arrow): http://aboveaviation.com/wp-content/uploads/2012/08/POH-77WE.pdf

It says:
Climb
The best rate of climb with gear down at gross weight will be obtained at 85 MPH and 95 MPG with gar up. The best angle of climb with gear down may be obtained at 81 MPH and 91 MPH with gear up. For climbing en route a speed of 110 MPH is recommended. This will produce better forward speed and increase visibility over the nose during the climb.

So what to do? Use 25 squared? Full throttle and RPM to cruise? Full throttle and 2500 RPM?

This is for a '69 Arrow with a Lycoming IO-360-C1C engine.
 
Ed Haywood said:
That's backwards, I believe. Reduce MP first, then RPM. Increase RPM first, then MP. Constant Speed Prop training 101, keep MP less than RPM.
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Unless the POH says otherwise.
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Deelee said:
So what to do? Use 25 squared? Full throttle and RPM to cruise? Full throttle and 2500 RPM?
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For how long is your MP above 25 if you leave it at full throttle in the climb. It will drop to 25 and less fairly quick anyway as you are climbing with a normaly aspirated engine. I leave it full throttle and just reduce RPM to 2500 due to noise myself. Also an IO-360.
 
Ed Haywood said:
Fair point. The old "keep MP under RPM" saw was just a general rule of thumb taught to help understand the principle.
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Very true. I do teach start on the right to add power (pushing knobs in) and start on the left to reduce power (pulling knobs out). I then can break them of the “oh my god, we’re oversquaring the engine! What about the children?” Kind of thing for continuous cruise. Like all things, depends on the plane/motor.


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Spinka said:
For how long is your MP above 25 if you leave it at full throttle in the climb. It will drop to 25 and less fairly quick anyway as you are climbing with a normaly aspirated engine. I leave it full throttle and just reduce RPM to 2500 due to noise myself. Also an IO-360.
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Yup. Let God take care of the MP as you climb...


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Ed Haywood said:
Closing the throttle reduces air flow. Opening the throttle increases air flow. Fuel is metered by air flow so the ratio stays constant. Mixture is a separate control.
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Opening the throttle fully riches the mixture more than “just a little below full throttle” in a lot of engines.
 
Stewartb said:
Reduce power why?
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  1. The POH says to.
  2. When I do so I burn less oil.
  3. Older Mooneys are known for high cylinder head temperatures and poor engine cooling. Not an uncommon problem in vintage aircraft. Best way to avoid that is to lower power (25 squared) and ascend at a faster airspeed, cooling the engine.
  4. Even at that power setting the thing usually climbs like a homesick angel.
 
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Shepherd said:
FYI: We are talking temperatures on the field of -7 degrees F and colder.
1. No idea what the problem is. Neither do any of the mechanics who have been working on it for the past 4 years.
2. You would think so, but when you pull the power to idle, the engine shuts down. It's exactly like flipping the mags off.
3. On the ground you keep it above 1,000 rpm below that, silence.
It's a really weird situation. They have replaced the carbs, throttle cable, carb heat cable (carb heat works fine, no carb ice, ever) inductor, mags, fuel tank.
Once again, we are waiting for cold weather to see what happens. If it still fails, time to upgrade to 85hp.
Nothing like a little mystery to add to the drama and excitement.
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Interesting, very perplexing..
 
Ed Haywood said:
Fun thing to ponder: why is it called a "throttle"?
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After the throttle plate in the carburetor, which controls how much air is permitted to enter the carb. "Throttle" means choking or strangling, which is essentially what that plate does. If you were going to run at full power all the time, you wouldn't need it.

Ron Wanttaja
 
So... I have never heard of this thing about the mixture being more rich at full throttle, my understanding was always that the throttle controls the plate regulating how much air passes through the carburetor.. in the carburetor there's a little Venturi were the fuel is "sucked" up through a tiny little hole coming from a fuel bowl in which the level of fuel in the bowl is controlled by a float

TLDR; the amount of fuel going into the air is directly proportional to the amount of air passing through that Venturi.. hence the ratio is constant..

Why would it become more rich at full throttle? short of there being some additional plumbing I don't understand why this would happen and is not something I've ever been told

*Fuel injected engines there's a metering device that I believe similarly replicates the above.. ie, keeps the ratio consistent

*accelerator pumps/carb heat not withstanding, which do effectively enrich the mixture but for different reasons

**In the carbureted airplanes I have flown you reduce power at a safe altitude and keep the mixture rich to help with cooling

**In turbo (and injected) stay at WOT and basically pour fuel into the engine to keep it cool and get to cruise altitude faster.. if c h t are an issue climb at a higher air speed or step climb if absolutely needed to cool down.. but I've never been told to reduce power for climb in a turbo'd airplane
 
Just browsed the POH for the other plane I am most familiar with, the Cessna 182P.

Normal Climb - 100-110 MPH, 23 inches MP, 2450 RPM, lean as required, cowl flaps as required.

Max Performance Climb - 89 MPH, full throttle, 2600 RPM, full rich, cowl flaps open.
 
23 inches?! So they're assuming a 75% power sitting throughout the climb?
 
"FYI: We are talking temperatures on the field of -7 degrees F and colder.
1. No idea what the problem is. Neither do any of the mechanics who have been working on it for the past 4 years.
2. You would think so, but when you pull the power to idle, the engine shuts down. It's exactly like flipping the mags off.
3. On the ground you keep it above 1,000 rpm below that, silence.
It's a really weird situation. They have replaced the carbs, throttle cable, carb heat cable (carb heat works fine, no carb ice, ever) inductor, mags, fuel tank."

Maybe an airleak in the intake manifold system? and a compensating idle mixture adjustment error?
 
nrpetersen said:
"FYI: We are talking temperatures on the field of -7 degrees F and colder.
1. No idea what the problem is. Neither do any of the mechanics who have been working on it for the past 4 years.
2. You would think so, but when you pull the power to idle, the engine shuts down. It's exactly like flipping the mags off.
3. On the ground you keep it above 1,000 rpm below that, silence.
It's a really weird situation. They have replaced the carbs, throttle cable, carb heat cable (carb heat works fine, no carb ice, ever) inductor, mags, fuel tank."

Maybe an airleak in the intake manifold system? and a compensating idle mixture adjustment error?
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It's a possibility, but it only happens in extreme cold conditions.
 
dmspilot said:
There is your problem. There's a lot of misinformation on YouTube presented as fact.
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I always tell students “Any idiot and his brother can post things on the internet, and many do”.

No particular attribution about this video intended, just a general observation.
 
wanttaja said:
After the throttle plate in the carburetor, which controls how much air is permitted to enter the carb. "Throttle" means choking or strangling, which is essentially what that plate does. If you were going to run at full power all the time, you wouldn't need it.

Ron Wanttaja
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And why is “full throttle” when the carb ISN’T throttling the airflow?
 
PeterNSteinmetz said:
I always tell students “Any idiot and his brother can post things on the internet, and many do”.

No particular attribution about this video intended, just a general observation.
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yes....you've just confirmed my suspicions. lol :D
 
Tantalum said:
Why would it become more rich at full throttle? short of there being some additional plumbing I don't understand why this would happen and is not something I've ever been told
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Some have an additional circuit that further enrichens the mixture at WOT.
 
MauleSkinner said:
Does it happen with carb heat on, off, or both?
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Both. Carb heat seems to make no difference. Even though the Cub's primary business is making carb ice in all kinds of conditions, it's very honest about it and gives you plenty of warning.
 
Tantalum said:
So... I have never heard of this thing about the mixture being more rich at full throttle, my understanding was always that the throttle controls the plate regulating how much air passes through the carburetor.. in the carburetor there's a little Venturi were the fuel is "sucked" up through a tiny little hole coming from a fuel bowl in which the level of fuel in the bowl is controlled by a float

TLDR; the amount of fuel going into the air is directly proportional to the amount of air passing through that Venturi.. hence the ratio is constant..

Why would it become more rich at full throttle? short of there being some additional plumbing I don't understand why this would happen and is not something I've ever been told

*Fuel injected engines there's a metering device that I believe similarly replicates the above.. ie, keeps the ratio consistent

*accelerator pumps/carb heat not withstanding, which do effectively enrich the mixture but for different reasons

**In the carbureted airplanes I have flown you reduce power at a safe altitude and keep the mixture rich to help with cooling

**In turbo (and injected) stay at WOT and basically pour fuel into the engine to keep it cool and get to cruise altitude faster.. if c h t are an issue climb at a higher air speed or step climb if absolutely needed to cool down.. but I've never been told to reduce power for climb in a turbo'd airplane
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Not so on the TCM IO520/550 engines. The shaft of the throttle body is connected to two interconnected arms that mechanically enrich the mixture at the full throttle position. When I had an EGT installed in my Bonanza, I noticed that the EGT went up when I reduced the throttle from full power to 25 inches. Always wondered why, that is because the mixture is significantly leaner. Ever notice that if you are in the pattern climbing to pattern altitude and pull the throttle back to level off, how far you have to move the throttle before the MP starts to decrease. It is because you are mostly just leaning the engine and you have a significant pull on the throttle before the MP starts to move lower. Here are some pictures of the throttle linkage, one at full power and the other at idle. So as the throttle rotates around the Throttle Plate Shaft, the linkage to fuel controller shaft is substantially less.
 

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John Collins said:
Not so on the TCM IO520/550 engines. The shaft of the throttle body is connected to two interconnected arms that mechanically enrich the mixture at the full throttle position. When I had an EGT installed in my Bonanza, I noticed that the EGT went up when I reduced the throttle from full power to 25 inches. Always wondered why, that is because the mixture is significantly leaner. Ever notice that if you are in the pattern climbing to pattern altitude and pull the throttle back to level off, how far you have to move the throttle before the MP starts to decrease. It is because you are mostly just leaning the engine and you have a significant pull on the throttle before the MP starts to move lower. Here are some pictures of the throttle linkage, one at full power and the other at idle. So as the throttle rotates around the Throttle Plate Shaft, the linkage to fuel controller shaft is substantially less.
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Interesting.. the geometry of the arm makes it so the adjustment in the fuel control and the throttle plate is not linear

I am aware of the MP change "rate" compared to the throttle position, but I am under the understanding that this occurs because of physics.. in other words, opening the throttle from 15% (say that's idle, because it's never fully closed) to 30% results in a 100% increase in airflow (twice as much space). But closing the throttle plate from 100% to 85% is only a 15% reduction in air flow despite the throttle moving the same distance in your hand, so the MP will appear to "not really change" - but, to your point, that still moves the fuel control so it will lean somewhat dramatically relative to the small change in MP

*On a side note, this is an interesting human factors design choice in the coding of contemporary cars "throttle by wire" design. In older cars tapping the gas pedal seems to give an immediate burst of power (for the same reason as above), this is especially relevant in manuals. On newer cars, it's more linear, IE, "smoother" since the computer moves the throttle plate for you based on how much power it thinks you want.. "does Tantalum really want twice the power or just a small increase?"

About 2:20 in to demonstrate my point
 
Tantalum said:
Interesting.. the geometry of the arm makes it so the adjustment in the fuel control and the throttle plate is not linear

I am aware of the MP change "rate" compared to the throttle position, but I am under the understanding that this occurs because of physics.. in other words, opening the throttle from 15% (say that's idle, because it's never fully closed) to 30% results in a 100% increase in airflow (twice as much space). But closing the throttle plate from 100% to 85% is only a 15% reduction in air flow despite the throttle moving the same distance in your hand, so the MP will appear to "not really change" - but, to your point, that still moves the fuel control so it will lean somewhat dramatically relative to the small change in MP
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The Lycoming injection systems do that too. Look at the difference in lever length of the air and fuel controls. The little wheel on the screw between the two machined clevises is the idle mixture adjustment.

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As far as the throttle plate, yes, it operates as a function of the sine. The first few degrees of opening make a much larger difference than the last few degrees.
 
My very first flight instructor gave me the same piece of advice to the effect that statistically a power failure was most likely to occur at the first reduction in power after take-off.

The best explanation I ever found was that reciprocating engines are more likely to fail when an rpm change is made, as it increases stress on the moving parts. In that context, it isn't that the first power reduction "causes" a failure, it just precipitates a failure that would happen anyway later in the flight, and the idea is make the most of the power you have left and gain enough altitude to make it back to the field before you reduce power after take-off.

There's also a related issue in terms of pilots babying an engine by pulling the throttle back during the initial climb. Many horizontally opposed Lycoming and Continental engines have an enrichment circuit at full throttle and the excess fuel helps cool the engine in climb. Pulling the power back in climb denies it the benefits of that additional cooling.
 
If the hundreds of thousands of hours of experience I have from running all sorts of tests on engines in test cells is any indicator, I've seen just the opposite of what is being suggested here. Every engine I can think of that I've seen blow up over the years did not come at a power transition, instead they occurred after the engine settled in and ran at the new setting for some time.

My suspicion is that outside causes that would occur regardless if there is a power reduction or not are the cause of what is perceived as the "failure after initial power reduction". Something like a blocked fuel tank vent is going to cause a problem eventually with either a full or partial power setting.
 
mondtster said:
If the hundreds of thousands of hours of experience I have from running all sorts of tests on engines in test cells is any indicator, I've seen just the opposite of what is being suggested here. Every engine I can think of that I've seen blow up over the years did not come at a power transition, instead they occurred after the engine settled in and ran at the new setting for some time.

My suspicion is that outside causes that would occur regardless if there is a power reduction or not are the cause of what is perceived as the "failure after initial power reduction". Something like a blocked fuel tank vent is going to cause a problem eventually with either a full or partial power setting.
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I have never seen any actual evidence that an engine failure occurs at the first power reduction. I consider it old instructor's wife tale.
 
mondtster said:
If the hundreds of thousands of hours of experience I have from running all sorts of tests on engines in test cells is any indicator, I've seen just the opposite of what is being suggested here. Every engine I can think of that I've seen blow up over the years did not come at a power transition, instead they occurred after the engine settled in and ran at the new setting for some time.

My suspicion is that outside causes that would occur regardless if there is a power reduction or not are the cause of what is perceived as the "failure after initial power reduction". Something like a blocked fuel tank vent is going to cause a problem eventually with either a full or partial power setting.
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My time spent at race tracks, where unlike airplane engines, the engines are constantly changing from WOT to heavy braking every lap, the majority of the engines I have seen that came from together did so while accelerating. And started giving warnings laps before actually coming apart. My thought, which has no scientific studies to back me up is, when the engine starts coming apart the pilot reduces throttle to see what that noise or vibration is and at that moment the engine destroys itself. Then the pilot will think it came apart because of the throttle reduction.

I have actually witnessed an engine coming apart while idling to warm up.

Again, just my thoughts.
 
My experience is that if it happens at a power change, it’s the last rather than the first.
 
mondtster said:
If the hundreds of thousands of hours of experience I have from running all sorts of tests on engines in test cells is any indicator, I've seen just the opposite of what is being suggested here. Every engine I can think of that I've seen blow up over the years did not come at a power transition, instead they occurred after the engine settled in and ran at the new setting for some time.

My suspicion is that outside causes that would occur regardless if there is a power reduction or not are the cause of what is perceived as the "failure after initial power reduction". Something like a blocked fuel tank vent is going to cause a problem eventually with either a full or partial power setting.
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Yup. Reducing power is not stressing the parts; it's relieving them of some stress. They're not trying to keep going at full RPM and torque and resisting a slowdown. The only places I could see a power reduction causing problems would be with certain propellers that have RPM ranges that must be transitioned through, not run within. Some airplanes have a brief yellow arc on the tach for that. Another place would be some gear reduction units, where the torsional resonances of the engine and prop coincide and tear the gearing apart. More yellow arcs.
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