Shock cooling

[Tom-D]

Pipeline and fish spotters "loitering" engines at low MP can have cylinder problems because the pressure created during the burn cycle isn't high enough to push the rings outward and keep them sealed up nice and tight to the oil film layer on the cylinder wall in some engines.

Idle power will do that...in any engine that has been run in properly.

Lots of blow-by, the cylinders don't like it, and the oil "scraper" ring ends up not doing its job, etc. Definitely a "known issue" with the O-470.

can you show the maintenance difficulty reports that show this problem?

Highest MP and lowest RPM that makes a BOOK power number that you want, is the best treatment for big "sloppy" engines like our 471 cubic inch beast. Worries about "oversquare" operation are unfounded in the O-470, unless you're "off the chart" in the POH, and most over-square worries in many engines are often left over from all the way back to bolted-on cylinder engines of yesteryear instead of our cylinders that are screwed on. You'd blow the bolts off with the higher pressures.

nuts on studs and thru case bolts are what all of our engines use today. I have never heard of a screwed on cylinder.

If it's in the POH table for on O-470, it's an approved power setting unless otherwise placarded. (Some installations of O-470 engines on some aircraft have a range where the prop governor or other components have problems and there's a "skip" in the green arc on the RPM gauge, where the engine shouldn't be operated continuously.)

Where does the POH set a minimum take off horse power?

Picking the percentage of power you want and then using the line in the table which has the highest MP and lowest RPM, has the ring seating benefit,

Rings are seated before it leaves the test cell or the completion of the test run called for in the overhaul manual, by both major engine manufacturers


as well as over the long-haul treats your bottom-end the best, in the O-470. Less revolutions of the crankshaft for the same power is always a good thing, wear-wise. Plus if you're paying by tach time as all owners are for maintenance, that's an indirect benefit to your wallet, too.

a fare point, but that is not authorization for you lug your engine at the most lowest power setting.

So, if you have to "loiter" at low MP with an O-470, you're going to be replacing jugs sooner than you expected to. The bottom-end will probably be fine, as long as you're not taxiing it around at low RPM without enough oil being "splashed" down from the galleys above onto the bottom-end.

You don't know the crank assembly is pressure fed, and that there is a minimum oil pressure at idle to sustain the engine?

Most of the lower half of the engine is oiled via whatever falls from above. 900 RPM with 55 lbs of oil pressure is a nice bath. Lower on either, stuff may or may not being adequately lubricated very well.

Really low idle is the worst. Oil pump can't regulate well turning that slow, the pressure falls, oil galleys just aren't getting as much oil, and less oil is being flung around to hit all the "stuff" in the low end and cool it as well as lubricate it all. Hot summer days, I see folks pull engines way back to super-low idle while waiting for takeoff clearance or prior to run-up, thinking they're "saving" the engine from heat, and instead, they've just starved it for oil flow.

I have come to the conclusion you have no clue as to the oil system operation, or its required pressure at idle, or that the only portion of the engine that gets splash lubricated is the accessory gears.

Anyway, you just have to know your specific gear and how it's built to do what it does. Much of that info is difficult to find, or buried in Service Bulletins and Service Letters that came out decades ago and aren't always readily accessible to people without some sort of "subscription" to them.

Both engine manufacturers have all their SB and manuals on line free of charge.

I've got piles of SB numbers I'd love to read, but can't find from Continental. Especially older superseded ones that had good info, but they don't want people reading and not knowing there's a newer version. The lawyers make them pull them down from public view. Old mechanics often have them in paper format on their bookshelf.

Pro airline pilots sit in hour after hour of "systems" training on their birds, but we little guys often have far fewer options to get the information. The type clubs usually gather this type of info into a single, usable, form... if your aircraft was popular enough to even have a strong type club.

The engine and aircraft manufacturers have placed all the service information on line rather than try to hide it, and get sued.

 

[denverpilot]

The engine and aircraft manufacturers have placed all the service information on line rather than try to hide it, and get sued.

Well, I could feed you some SB numbers I'm looking for and you could go hunt for them... And Service Letters are even harder, as sometimes they were just mailed once in the 70s and never seen from again.

They don't always make it abundantly clear where the even the SB's are... they're just in that mysterious "online" place somewhere-out-there. :wink2:

Their lawyers know where the links are, of course.

 

[Tom-D]

Well, I could feed you some SB numbers I'm looking for and you could go hunt for them... And Service Letters are even harder, as sometimes they were just mailed once in the 70s and never seen from again.

They don't always make it abundantly clear where the even the SB's are... they're just in that mysterious "online" place somewhere-out-there. :wink2:

Their lawyers know where the links are, of course.

They use Google search like I do.

http://www.tcmlink.com/servicebulletins.cfm

 

[denverpilot]

They use Google search like I do.

http://www.tcmlink.com/servicebulletins.cfm

Gosh, I would have never thought to use Google.

Note, right at the top of the page:

"This page provides access to a partial listing of some of the more commonly requested service bulletins. Complete access to all TCM Service Bulletins is available through Aviator Services and FBO Services."

(Emphasis added.)

It also doesn't contain all SBs or Service Information Letters (SIL) and some other useful "unobtanium" documents. I will assume two things, the copies and references I've seen were from the original paper versions from shops/mechanics who were "paying to play", and that TCM's lawyers would exercise Copyright if anyone just started posting them somewhere. Plus, they could have been superseded. There's no "master list" to check at that site, nor historical record.

Google searches for the specific, known, SB or SIL numbers directly, sometimes turn up discussions on aviation sites about them, but not the document being discussed.

 

[Tom-D]

Gosh, I would have never thought to use Google.

Note, right at the top of the page:

"This page provides access to a partial listing of some of the more commonly requested service bulletins. Complete access to all TCM Service Bulletins is available through Aviator Services and FBO Services."

(Emphasis added.)

It also doesn't contain all SBs or Service Information Letters (SIL) and some other useful "unobtanium" documents. I will assume two things, the copies and references I've seen were from the original paper versions from shops/mechanics who were "paying to play", and that TCM's lawyers would exercise Copyright if anyone just started posting them somewhere. Plus, they could have been superseded. There's no "master list" to check at that site, nor historical record.

Google searches for the specific, known, SB or SIL numbers directly, sometimes turn up discussions on aviation sites about them, but not the document being discussed.

When you have a SB number, plug it into the Google search window. It's on the web some where.

 

[Ted]

"This page provides access to a partial listing of some of the more commonly requested service bulletins. Complete access to all TCM Service Bulletins is available through Aviator Services and FBO Services."

That is correct. You won't end up finding a complete list online, at least not from the manufacturer. And really that's where you should get them from, because they get updated.

A quick phone call to the tech reps will usually get you not only the information you're looking for, but probably some more information that you didn't know to ask for.

 

[Tom-D]

That is correct. You won't end up finding a complete list online, at least not from the manufacturer. And really that's where you should get them from, because they get updated.

A quick phone call to the tech reps will usually get you not only the information you're looking for, but probably some more information that you didn't know to ask for.

That is why you won't get a full list, they don't post out dated Service info.

If the "C" version is current, why read the "A" version ?

Your wobble check is a primary example

 

[Ted]

That is why you won't get a full list, they don't post out dated Service info.

If the "C" version is current, why read the "A" version ?

Your wobble check is a primary example

Correct, but the manufacturers don't even always publish the complete batch of current SIs, SLs, and SBs online. There are a number that you'll need to call up directly to get. Not a matter of hiding anything, just the way it works.

And if you get it from another website, how do you know it's the most current?

 

[gismo]

were did the 25-50% come from ? 100# means a lot in that little aircraft.

when the empty weight is 1150# (most are lower than that) and the actual gross weight is 1650# you have 500# to work with. 1 pilot at 150, 12 gallons of fuel is all you need to fly 1 hour.

so do the math, 6.02pounds per gal X12 gallons = 72.24#
plus 150# pilot= 222.24#

Which is actually below your 50%

The "25%" (actually 25-50%) came from my post you replied to. I was pointing out the excess power available on most warbirds due to the fact that they are usually flown way, way below whatever the military calls MGW. With 50% less weight, a 25% power reduction provides substantially more performance than full power at max weight. While the same could be said of a 150, that would mean leaving much of the airframe behind. And as Trapper John pointed out your example has the plane loaded much heavier than 75% of MGW.

 

[gismo]

1,150 + 150 + 72 = 1,372

1,372 / 1,650 = 0.832, or 83.2% of MGW

Tom's one heck of a mechanic but sometimes his math skills appear to be a bit tarnished. (just pulling your chain Tom).

 

[Tom-D]

Tom's one heck of a mechanic but sometimes his math skills appear to be a bit tarnished. (just pulling your chain Tom).

do you want to talk useful load or gross weight.?

you'll never get a Warbird to 50% of its gross weight.

so all you can do is talk useful load, and 50% of 500 is a lot easier to obtain than 50% of 20,000#

If you would like to leave half the bomb load and fuel at home, I can do that in a C-150 too

 

[Tom-D]

Correct, but the manufacturers don't even always publish the complete batch of current SIs, SLs, and SBs online. There are a number that you'll need to call up directly to get. Not a matter of hiding anything, just the way it works.

And if you get it from another website, how do you know it's the most current?

Service instructions and letters usually get sent directly to the owner of the equipment.

 

[Ted]

Service instructions and letters usually get sent directly to the owner of the equipment.

That's when new ones are published, though, and still not always the case (especially for the engines). I've gotten some SBs for the Aztec and the 310, but I haven't gotten any for the IO-540s or IO-520s in the mail. I have go to searching for them.

Furthermore, if it's an old SI/SL/SB, I won't have it unless I go looking for it. And most owners aren't going to know that there's one available that addresses their problem.

A simple phone call will do the job very well...

 

[gismo]

do you want to talk useful load or gross weight.?

you'll never get a Warbird to 50% of its gross weight.

so all you can do is talk useful load, and 50% of 500 is a lot easier to obtain than 50% of 20,000#

If you would like to leave half the bomb load and fuel at home, I can do that in a C-150 too

Maybe not 50% but 75% is rather plausible I think. In a P-51 that's 1400 lbs of fuel plus a 175lb pilot. In a B25 I saw advertized that would be 9100 lbs of fuel and two 200 lb pilots.

But the point I was trying to make is that a lot of warbirds are typically flown (in the civilian world) at a much smaller percentage of their max weight than most (but not all) single GA piston airplanes.

 

[Tom-D]

But the point I was trying to make is that a lot of warbirds are typically flown (in the civilian world) at a much smaller percentage of their max weight than most (but not all) single GA piston airplanes.

How often do you fly at max gross?

The old war birds were designed to operate at a set take off weight, your general aviation aircraft was not. they are certified to be able to operate safely at a gross weight, but we all know flying it at the weight is not a good idea.

So, most of us operate at a weight less than that.

 

[Trapper John]

The old war birds were designed to operate at a set take off weight, your general aviation aircraft was not.

Care to elaborate?

 

[Dr. O]

Well, I guess it is up to me to be the grumpy, old, curmudgeon here... (wait, I resemble that remark)

Like Ted, my Piper factory gauges are just this side of useless for reading an actual number, especially the CHT... But they at least let me know the engine is still running!

OTOH, these gauges and these engines have been trucking along for some 54 years with total engine times of 6400 hours+ and nothing catastrophic has happened... Engines routinely make it to TBO and beyond... I don't need a pair of $4K gauges to know that on hot days I'm best off to lower the nose and add 10 or 12 knots to my climb speed <well, actually in my case 12 or 14 mph as we don't have no no stinking knots> and that when high and hot I probably shouldn't yank the throttle and dive straight down... A calibrated hand on the throttle works well and costs significantly less than expensive instrumentation...

I would cheerfully fly behind a gee-whiz glass panel, but I don't need one and neither do the engines...

denny-o

 

[Dr. O]

And to directly answer JohnH - if I need to descend "right now" without any preplanning, my answer to you would be to pull the throttle right back to idle without going rich on the mixture while simultaneously you pitch up and begin a 2 G turn to bleed off airspeed while milking the flaps down, when able drop the gear... At some point in this exercise you will need to push the throttle back in to keep the descent rate from hitting the peg, which will keep the cylinders warm... A mere 5 to 10 seconds of idle power will not damage your heads... If you maintain a hard turn - or S turns to keep ATC happy - with gear and flaps down you will need significant power to control the descent rate and the engine will be happy...

Just like Clint did in Space Cowboys, when the wet behind the ears engineer told him he couldn't get down to the runway from there - you are the pilot, you make it happen...

cheers
denny-o

 

[Ted]

The old war birds were designed to operate at a set take off weight, your general aviation aircraft was not. they are certified to be able to operate safely at a gross weight, but we all know flying it at the weight is not a good idea.

I think most people don't operate at gross weight, but that's typically because most people don't have a need to, not because it's "not a good idea."

I have no qualms operating the Aztec or 310 at max gross. Same goes for any other plane I've flown.

 

[Tom-D]

I think most people don't operate at gross weight, but that's typically because most people don't have a need to, not because it's "not a good idea."

I have no qualms operating the Aztec or 310 at max gross. Same goes for any other plane I've flown.

That's you, most of us think different and want a bit more safety factor.

 

[Trapper John]

That's you, most of us think different and want a bit more safety factor.

Who is "most of us" besides you?

Put 2 decent sized people and enough fuel to fly more than an hour in a C-150 and you'll be close to if not at MGW. And that's been done hundreds of thousands of times in training flights. Successfully.

 

[Ted]

That's you, most of us think different and want a bit more safety factor.

Really? Because most of the pilots that I know end up doing pretty similar when there's a need. We also use full power on takeoff.

 

[dmccormack]

As a demonstration, sure - But you're not doing it as a matter of regular procedure to try to extend the life of the engine, right?

Noooo.....

Best way to extend the life of these engine is WOT, period.

 

[Tom-D]

Really? Because most of the pilots that I know end up doing pretty similar when there's a need. We also use full power on takeoff.

Just like any other machine, work them hard and junk them early.

 

[Cap'n Jack]

That's you, most of us think different and want a bit more safety factor.

Tom- given no issues with density altitude and runway length, what is the problem with operating at gross weight?

 

[Trapper John]

Take a look at the Type Certificates for the C-172, C-182 & C-206. If it were bad to operate at MGW, why would Cessna (& FAA) allow this:

Special Ferry Flight Authorization. Flight Standards District Offices are authorized to issue Special overweight ferry flight authorizations. This airplane is structurally satisfactory for ferry flight if maintained within the following limits:
(1) Takeoff weight must not exceed 130% of the maximum weight for Normal Category, and
(2) The Never Exceed Airspeed (VNE) and Maximum Structural Cruising Speed (VC) must be reduced by 30%;
and (3) Forward and aft center of gravity limits may not be exceeded; and (4) Structural load factors of 2.5 g. to -1.0 g. may not be exceeded.

 

[jesse]

Who is "most of us" besides you?

Put 2 decent sized people and enough fuel to fly more than an hour in a C-150 and you'll be close to if not at MGW. And that's been done hundreds of thousands of times in training flights. Successfully.

All it takes is two 175 lb people and full fuel and you're at gross in a C150.

 

[Trapper John]

All it takes is two 175 lb people and full fuel and you're at gross in a C150.

Doesn't look like the C-162 is any better...costs a bunch more, though.

http://www.cessna.com/single-engine/skycatcher/skycatcher-weights.html

 

[Tom-D]

All it takes is two 175 lb people and full fuel and you're at gross in a C150.

Is it easier on the aircraft with 1, 110 pound person and half fuel?

 

[Tom-D]

Tom- given no issues with density altitude and runway length, what is the problem with operating at gross weight?

would you rather own an aircraft that is at 2000 TT with a new engine or one with 10,000 TT and a run out 2500 engine.....FBO rental.

the answer to why is what I am pointing out.

stuff wears out metal fatigue sets in faster when the aircraft is worked hard, it is no different with trucks and equipment.

 

[Ted]

The aircraft and engines are, in fact, designed to operate at their max gross and maximum power ratings. While I'm the first one to point out that limits are not goals, things like not using full power for takeoff on horizontally opposed engines is really just asking for trouble. Tom, you're the first person I've heard advocate that.

 

[jesse]

Is it easier on the aircraft with 1, 110 pound person and half fuel?

No. Not really.

Buy them both new.

Fly one properly with a 110 lb person
Fly the other one properly with two 175 lb people

The differences in the weight they were operated at isn't going to effect the useful sale value, ever. Other things may. That won't.

 

[Tom-D]

No. Not really.

Buy them both new.

Fly one properly with a 110 lb person
Fly the other one properly with two 175 lb people

The differences in the weight they were operated at isn't going to effect the useful sale value, ever. Other things may. That won't.

It isn't always about the money.

 

[jesse]

It isn't always about the money.

Okay then tell me what measurable difference to the airplane it would make.

 

[Trapper John]

would you rather own an aircraft that is at 2000 TT with a new engine or one with 10,000 TT and a run out 2500 engine.....FBO rental.

the answer to why is what I am pointing out.

stuff wears out metal fatigue sets in faster when the aircraft is worked hard, it is no different with trucks and equipment.

You might be able to say that a 10,000 hr 172 is "more worn out" than a 2,000 hour 172, but what is the useful life of a 172 airframe? Does Cessna publish a life limit? Do they require special inspections at a certain number of hours?

If you took a 2,000 hour 172 and a 10,000 hour 172 of the same vintage and did side-by-side annual inspections, what differences would you see? Could you tell the difference if you didn't know the number of hours on each before you started inspecting?

What if you inspected two 10,000 hour 172s, an A-model that racked up 200 hr/year for 50 years, and one that racked up 2,500 hr/yr for 4 years at a big flight school? What differences would you see? Which one is "more worn out"?

 

[Tom-D]

Okay then tell me what measurable difference to the airplane it would make.

Two aircraft setting side by side, one has 10,000 hours and the other has 2000, same make model and in the same condition, which will the common buy choose?

 

[Tom-D]

You might be able to say that a 10,000 hr 172 is "more worn out" than a 2,000 hour 172, but what is the useful life of a 172 airframe? Does Cessna publish a life limit? Do they require special inspections at a certain number of hours?

If you took a 2,000 hour 172 and a 10,000 hour 172 of the same vintage and did side-by-side annual inspections, what differences would you see? Could you tell the difference if you didn't know the number of hours on each before you started inspecting?

What if you inspected two 10,000 hour 172s, an A-model that racked up 200 hr/year for 50 years, and one that racked up 2,500 hr/yr for 4 years at a big flight school? What differences would you see? Which one is "more worn out"?

Why do you believe that Grumman and some other aircraft have a time life? Cessna didn't do that, does that mean fatigue does effect the aircraft in the same way?

""Could you tell the difference if you didn't know the number of hours on each before you started inspecting?""

Most defiantly, I cam spot an old aircraft with out seeing the logs. and I'm not alone.

 

[Ted]

The correct answer, like with anything else, is "It depends."

My Aztec has 10,000 hours on it - I wouldn't hesitate to buy another 10,000 hour airframe if the condition checked out.

 

[Dan Thomas]

You might be able to say that a 10,000 hr 172 is "more worn out" than a 2,000 hour 172, but what is the useful life of a 172 airframe? Does Cessna publish a life limit? Do they require special inspections at a certain number of hours?

If you took a 2,000 hour 172 and a 10,000 hour 172 of the same vintage and did side-by-side annual inspections, what differences would you see? Could you tell the difference if you didn't know the number of hours on each before you started inspecting?

What if you inspected two 10,000 hour 172s, an A-model that racked up 200 hr/year for 50 years, and one that racked up 2,500 hr/yr for 4 years at a big flight school? What differences would you see? Which one is "more worn out"?

Cessna has something called the Continuing Airworthiness Program (CAP) that applies to their singles. It's a program that most people have never heard of and even Transport Canada inspectors here had never seen it. There's a long list of items that they want checked at hourly or calendar intervals, most of them never appearing on Cessna's inspection sheets, and we've found it wise to take a look at them. Further, Cessna's Service Bulletins are words to the wise and usually have some merit. Cessna will eventually come out with an Aging Aircraft program that will demand removal of high-time airplanes from the fleet, and governments will probably endorse it.

Things we find as 172s and their cousins get old:

Cracking engine mounts (the CAP says check it initially at 12,000 hours. Much too late. We find them cracked at 4000.)

Cracked horizontal stabilizer forward spars (caused by pushing down on the stab to lift the nosewheel to turn the airplane).

Cracked aft lower doorposts (in the radius where the post transitions to the gear box. Gotta take the plastic out and look under the aileron cable pulley, right at floor level. Caused by taxiing over rough ground or landing in a crab). Most are busted by 5000 hours.

Cracked forward doorposts at the lower door hinge. Caused by that rotten hinge design that pulls the doorpost outward when you close the door.

Loose nosegear mounts. Caused by shimmy. Worn torque links, same cause. The shimmy damper can't control shimmy when this stuff is worn. Dynamically (not just statically) balancing the wheel and tire assembly is the real solution, just like on an automobile.

Cracked landing light mounts (cowl-mounted).

Cracked bulkhead at aft end of main baggage compartment. When the fin/rudder moves the tail this area flexes and the bulkead flange cracks.

Worn, cracked seat rails and worn seat locks, in spite of ADs against that. World's largest GA lawsuit was due to a crash after loss of control caused by worn seat rails and locks. The plaintiffs won $450 million even though the owner hadn't had those rails looked after, and the owner IS responsible to see that ADs are done. Go figure.

Worn flap tracks. Seized flap rollers that caused the wear. Flap support arms worn by shifted roller sleeves.

Worn rudder hinge brackets (on the rudder itself). Caused by misjgging at the factory that has the middle or top brackets resting on the aluminum fin brackets instead of the lower hinge resting on the bearing surface of the lower hinge. Aggravated by being parked outside in the wind with no gustlocks. The wind blows dirt into the hinges and wiggles the rudder and chews up the hinges. Even low-timers can have badly worn hardware.

Cracked rudder hinge brackets caused by tailstrikes on the runway. The lead weight at the rudder top drives the rudder downward at the strike and flexes the hinge brakes and cracks them.

Corrosion caused by mouse and bird droppings inside the airplane, including inside the wings and elevator, believe it or not.

Add the usual worn cables, pulleys, hinges, and so on, and it adds up.


So you can see, a good-looking 10,000-hour airplane might have a $10,000 paint job, while the one next to it has ugly original paint but that $10,000 was spent on maintenance of the above. Which one will sell the easiest?

Dan

 

[jesse]

Two aircraft setting side by side, one has 10,000 hours and the other has 2000, same make model and in the same condition, which will the common buy choose?

The question was aircraft with the same hours but flown with different passenger weights since you seemed to imply that flying a C150 at gross was bad.