Descent Procedure

[n454mw]

Hi, I love the 182, just fantastic, and I didn't even know it was coming until this morning.

I haven't found ANY issues at all to date. I have 1.6 or 1.7 hours on the tach so far and I have found this bird easier to hand fly than the 172. It just seems smoother and easier to handle, both in the air and on the ground.

Would some kind soul out there with RW experience in a high proformance plane please take me step by step through the prep for descent and the actual descent?
For example, which should be changed first the throttle or the prop rpm?
Except for priming the engine when should the fuel pump be used?
And last but not least which is better for low altitude flying, the two blade or the three blade prop?

[Wolfie25]

The 182 is a fantastic aircraft, credit to A2A. I've never a 182 for real but I believe the power changes should be as follows: to power down, manifold first then rpm, to power up, rpm first then manifold. If it's just to descend, just slowly reduce manifold to establish desired rate of descent. To level out again, just slowly increase the manifold to desired setting.

I believe the fuel pump on cessnas is primarily just for priming unless engine driven pump fails.

The difference between the props is: the 3 blade will have a slightly better climb performance, but a slower top speed. 2 blade will have slightly lower climb but higher top speed. At low alt where the air is thicker the 2 blade would give great performance whereas up high I think the 3 blade would give better performance (pls correct me if I'm wrong there).

I've never flown a high performance aircraft myself, only pa28-181 and 152's/172's but I have though collected some CSU/RG theory papers, that's all I know/understand

[Great Ozzie]

Hi Mark,

For Descents:

Have a look at Pelican's Perch #19: Putting It All Together and checkout the section Descents and the OWT of "Shock Cooling" (I think Esa posted this link in another thread btw).

For Moving the Controls:

•Applying Power: Mixture, Prop, Throttle

•Decreasing Power: Throttle, Prop, Mixture

One doesn't want to lug the engine i.e. a lot of MAP (throttle) with little prop. Not good. And just like a fixed pitch, you want mixture RICH when you go to apply power, and you pull power THEN mixture.

Also, have a look at this Flying Magazine's Constant Speed Prop Basics

Link to a Hartzell FAQ Technical Questions. Check the questions:

•If 2-blade propellers are more efficient, then why don’t all propellers have 2 blades?
•Will a 3-blade prop make my airplane quieter inside?

------------------------------------------------------------

Below from New England Propeller website:

"Article by Nicholas E Silitch of Private Pilot Magazine":

The most popular reason for converting from a two-blade to a three-blade propeller is that it looks better. but in addition to the esthetics, there are some other differences that can make a switch attractive. Three-blade propellers generally have a slightly better climb and slightly slower cruise than their two-blade equivalents. hut these differences are seldom large enough to be really noticeable. The most noticeable difference is the three-blade's distinct advantage in smoothness and noise reduction. This is coupled with improved ground clearance in installations, which means less propeller damage from stones and less chance of a ground strike.

Another practical advantage of the three- blade is reduced maintenance. This comes from the reduced rotational stresses from the shorter blades, which can make a real difference, particularly if the conversion is replacing one of those troublesome 'dreaded threaded" two-blade propellers with blades more than 82 inches long. These blades have had a history of problems and a three-blade replacement (either in a threaded or new style) can result in real long-term savings. Particular installations can have even more advantages. The reduced diameter of the three-blade conversion on a Cessna 185 floatplane eliminates water damage due to the reduction in diameter and eliminates the noise problems associated with water-borne 185s by reducing the tip speeds. This keeps the blade tips from going supersonic at takeoff horsepower. which is what causes the infamous 185 whine. In addition, the increased climb performance, however marginal, is always appreciated in a water airplane.


"Article from Dec 91 Flying Magazine Written BY J. MAC MCCLELLAN":

Most PILOTS KNOW THE ADVANTAGES OF a three or four-blade prop over a two- blader. The extra blades add static thrust, which improves takeoff acceleration and climb. A three-bladed prop lessens-or at least greatly changes the vibration and noise levels in the airplane in a way most people find more comfortable. And a three-blade prop looks better on the ramp. Any airplane looks more powerful, fast and capable with an extra blade. But these are not the reasons U.S. Propeller Service began offering three-blade prop conversions. The real reason is maintainability. The other three-blade prop benefits are a bonus. U.S. Propeller's primary business is prop overhaul at its shops in Connecticut, North Carolina and Florida. Prop overhaul is a business best suited for technical zealots. Props-even on light airplanes are so highly stressed that any corrosion, nick or slight imperfection can lead to failure of the blades or hub. And a prop failure is usually fatal because the severe imbalance of the engine turning with only part of a prop jerks the engine out of its mounts. Once the engine departs, an airplane is usually beyond the bounds of its flyable CG range and cannot continue with a controlled glide.

[n454mw]

Thanks for the replies guys. Ozzie those articles were very helpful.


Mark

[mike10]

Hi Mark,

For Descents:

Have a look at Pelican's Perch #19: Putting It All Together and checkout the section Descents and the OWT of "Shock Cooling" (I think Esa posted this link in another thread btw).

For Moving the Controls:

•Applying Power: Mixture, Prop, Throttle

•Decreasing Power: Throttle, Prop, Mixture

One doesn't want to lug the engine i.e. a lot of MAP (throttle) with little prop. Not good. And just like a fixed pitch, you want mixture RICH when you go to apply power, and you pull power THEN mixture.

Also, have a look at this Flying Magazine's Constant Speed Prop Basics

Link to a Hartzell FAQ Technical Questions. Check the questions:

•If 2-blade propellers are more efficient, then why don’t all propellers have 2 blades?
•Will a 3-blade prop make my airplane quieter inside?

------------------------------------------------------------

Below from New England Propeller website:

"Article by Nicholas E Silitch of Private Pilot Magazine":

The most popular reason for converting from a two-blade to a three-blade propeller is that it looks better. but in addition to the esthetics, there are some other differences that can make a switch attractive. Three-blade propellers generally have a slightly better climb and slightly slower cruise than their two-blade equivalents. hut these differences are seldom large enough to be really noticeable. The most noticeable difference is the three-blade's distinct advantage in smoothness and noise reduction. This is coupled with improved ground clearance in installations, which means less propeller damage from stones and less chance of a ground strike.

Another practical advantage of the three- blade is reduced maintenance. This comes from the reduced rotational stresses from the shorter blades, which can make a real difference, particularly if the conversion is replacing one of those troublesome 'dreaded threaded" two-blade propellers with blades more than 82 inches long. These blades have had a history of problems and a three-blade replacement (either in a threaded or new style) can result in real long-term savings. Particular installations can have even more advantages. The reduced diameter of the three-blade conversion on a Cessna 185 floatplane eliminates water damage due to the reduction in diameter and eliminates the noise problems associated with water-borne 185s by reducing the tip speeds. This keeps the blade tips from going supersonic at takeoff horsepower. which is what causes the infamous 185 whine. In addition, the increased climb performance, however marginal, is always appreciated in a water airplane.


"Article from Dec 91 Flying Magazine Written BY J. MAC MCCLELLAN":

Most PILOTS KNOW THE ADVANTAGES OF a three or four-blade prop over a two- blader. The extra blades add static thrust, which improves takeoff acceleration and climb. A three-bladed prop lessens-or at least greatly changes the vibration and noise levels in the airplane in a way most people find more comfortable. And a three-blade prop looks better on the ramp. Any airplane looks more powerful, fast and capable with an extra blade. But these are not the reasons U.S. Propeller Service began offering three-blade prop conversions. The real reason is maintainability. The other three-blade prop benefits are a bonus. U.S. Propeller's primary business is prop overhaul at its shops in Connecticut, North Carolina and Florida. Prop overhaul is a business best suited for technical zealots. Props-even on light airplanes are so highly stressed that any corrosion, nick or slight imperfection can lead to failure of the blades or hub. And a prop failure is usually fatal because the severe imbalance of the engine turning with only part of a prop jerks the engine out of its mounts. Once the engine departs, an airplane is usually beyond the bounds of its flyable CG range and cannot continue with a controlled glide.

This is not really on topic but I was wondering what your take is on LOP operations. I have no real world experience in planes with a constant speed prop but as a mechanic with lots of engine building experience in racing applications I find some of the stuff I read people doing downright crazy. Am I wrong on this? I have read on pilot forums of people setting RPM at the bottom of the green arc ignoring the manifold pressure with the throttle wide open and running the mixture extremely lean to reduce power!!!!

A combination of high load/ low rpm and very lean mixture is not at all good I would be really reluctant to play around with that with a 40k engine.

[Great Ozzie]

I have read on pilot forums of people setting RPM at the bottom of the green arc ignoring the manifold pressure with the throttle wide open and running the mixture extremely lean to reduce power!!!!

A combination of high load/ low rpm and very lean mixture is not at all good I would be really reluctant to play around with that with a 40k engine.

Hi Mike,

Constant speed or not, I was a "Best Power" person when it came to setting the mixture. That just seemed to be the safest thing to do wrt treating the engine "right".

That said, having read some of Mike Busch's articles e.g. this one - The Savvy Aviator #59: EGT, CHT and Leaning - I think given certain parameters & equipment, it would be "ok" i.e. I could easily see myself using his procedure if I owned an airplane.

I would want to have (like him) a "GPS-coupled fuel totalizer", "tuned fuel-injector nozzles" & some sort of digital engine monitor where you get CHTs & EGTs for all cylinders. Mike says he uses a max CHT value of 380°F and mentions that once you get below about 60% power, "you can run the mixture pretty much anywhere you please without over-temping or over-stressing anything".

If you have a look at Lycoming's "Fuel Mixture Leaning Procedures", you can see Busch's advice (above) is in line with Lycoming's (below), albeit a bit more conservative:

For maximum service life, maintain the following recommended limits for continuous cruise operation:
(a) Engine Power Setting - 65% of rated or less.
(b) Cylinder head temperatures - 400°F. or below.
(c) Oil temperature - 165°F. - 220°F.

(Lycoming Service Instruction No. 1094D)

So again, it's the Goldilocks' advice - not to run the engine too hot or too cold (e.g. he mentions extend periods of CHTs below the mid-200s). Not too hard or too soft (power setting wise)... but "just right" to get max longevity.

-Rob

[mike10]

I have read on pilot forums of people setting RPM at the bottom of the green arc ignoring the manifold pressure with the throttle wide open and running the mixture extremely lean to reduce power!!!!

A combination of high load/ low rpm and very lean mixture is not at all good I would be really reluctant to play around with that with a 40k engine.

Hi Mike,

Constant speed or not, I was a "Best Power" person when it came to setting the mixture. That just seemed to be the safest thing to do wrt treating the engine "right".

That said, having read some of Mike Busch's articles e.g. this one - The Savvy Aviator #59: EGT, CHT and Leaning - I think given certain parameters & equipment, it would be "ok" i.e. I could easily see myself using his procedure if I owned an airplane.





I would want to have (like him) a "GPS-coupled fuel totalizer", "tuned fuel-injector nozzles" & some sort of digital engine monitor where you get CHTs & EGTs for all cylinders. Mike says he uses a max CHT value of 380°F and mentions that once you get below about 60% power, "you can run the mixture pretty much anywhere you please without over-temping or over-stressing anything".

If you have a look at Lycoming's "Fuel Mixture Leaning Procedures", you can see Busch's advice (above) is in line with Lycoming's (below), albeit a bit more conservative:

For maximum service life, maintain the following recommended limits for continuous cruise operation:
(a) Engine Power Setting - 65% of rated or less.
(b) Cylinder head temperatures - 400°F. or below.
(c) Oil temperature - 165°F. - 220°F.

(Lycoming Service Instruction No. 1094D)

So again, it's the Goldilocks' advice - not to run the engine too hot or too cold (e.g. he mentions extend periods of CHTs below the mid-200s). Not too hard or too soft (power setting wise)... but "just right" to get max longevity.

-Rob

Yeah that all sounds good I will read that article.

It just seems to me that some guys are taking crazy risks with having just enough knowledge to be dangerous.