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rsrandazzo(at)precisionma
Guest

Posted: Mon May 22, 2006 10:01 am Post subject: Advice from Gear-Heads...

Gents-



I've finished reading the entire list-archive history finally- and have

cultivated a tremendous amount of information (some good...some not-so-good

hahahah) that will help me in my effort to learn all there is to know about

our AC685...



I have a question to a reference that comes up a few times in conversations-

and was hoping someone could elaborate more in order to expand my general

fund of knowledge!



-> In a few conversations, some fellows have referred to keeping the props

loaded.  In the conversation- they seem to infer that you can tell when you

have unloaded the props.   How can you tell?   Obviously we don't have a

Torque gauge- so I'm assuming it's an experience factor here- but what am I

sensing-for/looking-for?



-> When operating on the ground, is there a preferred idle speed during that

serves the need to allow for oil heating/lubrication while also keeping the

torque working in the right direction?



-> On the same line of thought-  any thought to be given to adjusting idle

speed on the ground in gusty conditions to prevent negative torque?

N414C has a newly overhauled prop on the left side- and freshly overhauled

engine/prop going on the right side starting this week (FINALLY!) and it'll

still be a few weeks before I get a chance to worry about running the

engines- but I'm still learning....



Robert

CloudCraft(at)aol.com
Guest

Posted: Mon May 22, 2006 10:38 am Post subject: Advice from Gear-Heads...

In a message dated 22-May-06 11:02:23 Pacific Daylight Time, 

rsrandazzo(at)precisionmanuals.com writes:

-> In a few conversations, some fellows have referred to keeping the props

loaded.  In the conversation- they seem to infer that you can tell when you

have unloaded the props.   How can you tell?   Obviously we don't have a

Torque gauge- so I'm assuming it's an experience factor here- but what am I

sensing-for/looking-for?

A loaded prop has glassy, blood shot eyes, can't taxi in a straight line and 

is always hungry.   The last two symptoms are very typical of Commanders with 

geared engines.   Sorry  ... couldn't resist.



On the ground, with geared Lycomings, it's pretty obvious in that you can 

hear lots of clatter in the gear box.  I don't think the Continental gear box 

clatters as much, but both engines like an idle of 1000 to 1200 RPMs, not 800 

RPMs as with direct drive engines.



In flight there is no way to tell if the crank is driving the prop and not 

vice versa (without a torque meter, you're correct) but by NOT bringing the 

props to high RPMs (or Fine Pitch if you're British), is how to keep them "loaded."



You can keep your cruise RPMs set all the way from top of descent to touch 

down and you'll be fine.



This rattles lots of pilots as it goes against the traditional wisdom and 

training done in direct drive powered aircraft.



Look at the power curves of your geared Lycoming or Continental and you can 

see that with props at cruise, one can add MAP to about 60%  power or more, to 

get the go-around or missed approach going and not have to worry about lots of 

lever management in those first few moments.



Wing Commander Gordon

PS:Robert,  I have not forgotten about scanning the trends from N414C -- it's 

just that my day job has kept me from getting to them.  



Life is not simple anywhere. Probably less so elsewhere.

n395v

Joined: 10 Jan 2006
Posts: 450

Posted: Mon May 22, 2006 11:02 am Post subject: Re: Advice from Gear-Heads...

 	  Quote: 	
		  keeping the props loaded 	




A little truth, a little OWT, and a little knowledge frequently leads to perpetuated misunderstanding.



#1 Let's define keeping the "props loaded" also known as keep the engine driving the prop and never let the prop drive the engine.



This implies that the engine is always trying to turn faster than the prop and positive contact is maintained between the driving face of the gears.



This just isn't possible. As you note in idle, a vigorous wind gust can often "unload" the props as will every power reduction no matter how gentle or slowly it is made.



These gears are case hardened primarily on the driving surface and less so on the "backside of each tooth. They are also lapped during manufacture so the drive surfaces in a set more closely match than the non drive side of the gear.



This does NOT mean the non driving surface is soft nor is it fragile. It is just wears more quickly when used in an unloaded condition.



Your props are going to unload when you reduce power just accept that as fact. Just limit the duration of these unloaded periods as much as possible and limit them to low power settings.



Also consider moving your levers in the sequence opposite from what we have always learned   Reduce RPM then reduce MP. When making small adjustments advance MP then advance RPM.



Abrupt reduction inMP will backlash (unload the props) for longer than is probably healthy. Gradual reductions unload the props briefly but they will quickly equilibrate.



The time where loading is most prolonged and noticable is approach to landing, landing, and roll out. These are times of significantly reduced power and cause no real harm as long as you are smooth and gradual.

Get out of the habit of advancing RPM on final approach if you are comfortable in the knowledge a go around will not be required.



Next time you fly and are in cruise do a rapid 5"MP reduction or shove the props full forward. You will see and hear the "unloaded" condition. Useyour ears and butt as your torque meter.



Damage is done based on total duration of the unloaded condition as well as the quantitative sum of effective horsepower during the time you are unloaded. Un loading rarely causes catastrophic failure mostly justv accelerated wear. Extensive wear increases backlash (the distance you can rotate the prop between contact with the front gear face to the rear gearface) and if this becomes large enough a drastic power deduction may result in abrupt failure but part of every annual involves measurement of backlash. 



Use common sense, smooth control inputs and you have nothing to worry about. Do not sweat the approach to landing or Taxi phase. The gears are precision pieces of industrial metal they are not fragile.

Did you get the info on the SBs?



If you ever do find it necessary to make a rapid power reduction pull the RPM back 1st as far as you are comfortable with.

_________________
Milt

rsrandazzo(at)precisionma
Guest

Posted: Mon May 22, 2006 12:15 pm Post subject: Advice from Gear-Heads...

WCG:



No worries on the scans-  they can wait until you have ABSOLUTELY nothing

else to do some afternoon.... 



You and Milt have both taken time to find old records on this airplane- and

the effort is greatly appreciated.  Great community.

So now-  in order to have loaded props, based upon your definition-  I

should tear off the electric heating pads and use alcohol instead, right?

:-p  Who knew it would be so easy.  hahahahahah



Robert Randazzo



--

rsrandazzo(at)precisionma
Guest

Posted: Mon May 22, 2006 12:35 pm Post subject: Advice from Gear-Heads...

Milt-



Okay- thanks- this is helpful information.  Seems that the 520Ks are a bit

like the garrets on the J31s I flew years ago when it comes to their dislike

of negative torque...  The 31 hated negative torque- and the engineers had

developed this fancy negative torque sensing system that would tinker with

the fuel flow in order to keep the prop from driving the engine- and it

would cause the airplane to shudder like crazy if you loaded the props- so

you because pretty proficient at avoiding it.



The techniques learned there will be very easy to apply to the 520Ks...  It

isn't hard to avoid loading the props if you plan ahead and aren't afraid to

tell ATC when their plan won't work.



My experience with the N414C prior to putting it in the hangar for this

overhaul was that the airplane was very capable of managing the first/second

stage climbout of a go-around without adjusting the prop speeds on approach.

The only area where I think it might be more urgent to get the prop speeds

up is in a rejected landing....  But that is the rarest of of events,

fortunately.



Thanks for the comments, Milt- you are correct that it is easy to begin

thinking that the gears were made of sub-standard material after reading all

the "conventional wisdom" out there.  Sure- these engines are more

complicated than most-  and they are at the outter limits of power

production for this type of mechanical setup-  but if flown procedurally

with care to respect their limits- they will operate just like any other

powerplant out there.  Heck, most turboprop/jet engines will destroy

themselves if you don't manage them effectively...  It's all about

procedures and minding the limits and capabilities.  Difference is that you

generally get some pretty intensive training before you get to tinker with

stuff like that.  Not so in GA- so I imagine it's easy for a new guy to get

in over his head with some engines.



I received the docs you sent and they have been married to all the rest of

the information we have on the airplane.  I'm embarrased that I neglected to

send you a "thank you!" email....    You saved me a tremendous amount of

hassle having to dredge up those items on my own.  No doubt Felix had some

headaches finding them for you-  so please pass along our thanks to him as

well!



Robert Randazzo

--

BobsV35B(at)aol.com
Guest

Posted: Mon May 22, 2006 12:59 pm Post subject: Advice from Gear-Heads...

In a message dated 5/22/2006 2:03:31 P.M. Central Standard Time,  

n395v(at)hughes.net writes:



Get out  of the habit of advancing RPM on final approach if you are 

comfortable in the  knowledge a go around will not be required.



Good Afternoon Milt,

 

I agree with everything you say, but why not just keep the props back all  of 

the time during the approach whether there is a go around planned or  not?

 

Any of the Continental and Lycoming engines are approved for a pretty  

healthy dose of MP at the very lowest cruising RPMs. Some of them are even  approved 

for full throttle at minimum  recommended cruising RPM.   Since there is 

always a possibility that an emergency go around will have to be  conducted, why 

not plan on adding half or three quarters of the MP available,  then run the 

props up, followed by adding the rest of the MP. If that is trained  to as the 

normal operation, an emergency becomes the same as any other go around  and 

there is never any need to shove the props up before a considerable amount  of 

power has been added.

 

I don't know how any other airline handled it, but that is the way it was  

done at UAL and I carried that technique over to all my GA flying. 

 

It is the way I have taught and the way I have flown for most of  the sixty 

years I have been flying.

 

Works for me!

 

Happy  Skies,



Old Bob

AKA

Bob Siegfried

Ancient Aviator

Stearman  N3977A

Brookeridge Air Park LL22

Downers Grove, IL 60516

630  985-8503

n395v

Joined: 10 Jan 2006
Posts: 450

Posted: Mon May 22, 2006 2:00 pm Post subject: Re: Advice from Gear-Heads...

 	  Quote: 	
		   why not just keep the props back all of 

the time during the approach whether there is a go around planned or not? 	




No good reason to not do as you suggest.



 Just in the past have found it difficult to convince those transitioning to geared enginse to view power management a little differently especially if they have never flown blown engines. They easily learn to move the levers differently, oversquare is difficult for them to embrace and the last thing they seem willing to give up is shoving the props forward and making that God awful noise on approach because they were afraid it would grow hair on their knuckles if they didn't.

_________________
Milt

BobsV35B(at)aol.com
Guest

Posted: Mon May 22, 2006 3:13 pm Post subject: Advice from Gear-Heads...

In a message dated 5/22/2006 5:01:39 P.M. Central Standard Time,  

n395v(at)hughes.net writes:



No good  reason to not do as you suggest.



Just in the past have found it to  convince those transitioning to geared 

engines to view power management a  little differently especially if they have 

never flown blown engines. They  easily learn to move the levers differently, 

oversquare is difficult for them  to embrace and the last thing they seem 

willing to give up is shoving the  props forward and making that God awful noise on 

approach because they were  afraid it would grow hair on their knuckles if 

they  didn't.



--------

Milt

N395V

F1  Rocket





My Kinda Guy!!

 

Do Not Archive!

 

Happy  Skies,



Old Bob

AKA

Bob Siegfried

Ancient Aviator

Stearman  N3977A

Brookeridge Air Park LL22

Downers Grove, IL 60516

630  985-8503

BillLeff1(at)aol.com
Guest

Posted: Mon May 22, 2006 7:25 pm Post subject: Advice from Gear-Heads...

The bottom line is that you never want to let the props drive the engine  

while in flight. That does not mean you can't close the throttles on touchdown. 

 

One of the best ways to tell when this is happening is by the sound of the  

props. They make a distinct sound as they start to push the engine. It is  not 

a catastrophic condition but the damaging effects are  cumulative. 

 

You can't set the idle to prevent it.

 

I have flown at least half of the fleet or more of the 685's (including  

N414C) It is a great airplane but there is no substitute for proper  training.

 

One of my customers liked their 685 so well, they bought a second one!  

(please no jokes about having two because one is always in the shop)! They fly  the 

heck out of them.

 

Have fun

 

Bill Leff

tfisher(at)commandergroup
Guest

Posted: Tue May 23, 2006 7:26 am Post subject: Advice from Gear-Heads...

Just a quick comment,

When I taxi by people on the ground in my 680FLP (Mr.RPM) I see them

sticking their fingers in their ears due to my prop noise so at times I

increase the pitch to a coarse setting (not letting it go into feather)

until I am by them, any comments regarding stress on using this practice?



Tom F.



---

nico(at)cybersuperstore.c
Guest

Posted: Tue May 23, 2006 7:34 am Post subject: Advice from Gear-Heads...

Tom,

There is a solution to the hearing sensitivity of your audience, though. Get

a Paris Jet and taxi by them a couple of times and they would wave in

delight when you next taxi by in the Commander.

Nico

--

n395v

Joined: 10 Jan 2006
Posts: 450

Posted: Tue May 23, 2006 8:20 am Post subject: Re: Advice from Gear-Heads...

 	  Quote: 	
		  any comments regarding stress on using this practice? 

	




Tom,



In my opinion the answer is no problem.



You might read this thread for further opinion...........

http://forums.matronics.com/viewtopic.php?t=8485



I also wouldn't worry about the audience your taxi by is of short duration, they are at an airport and noise happens.



I never have seen corporate types worry about opthers ears when they let the APU run for an hour on the ramp to cool the plane irrespective of the fact that nobody withi 100yards can think because of the racket.

_________________
Milt

n395v

Joined: 10 Jan 2006
Posts: 450

Posted: Tue May 23, 2006 8:58 am Post subject: Re: Advice from Gear-Heads...

At the risk of generating spirited debate and controversy here is something for you big bore turboed gear heads to consider.



http://avweb.com/news/reviews/182501-1.html



I have never been a proponent of LOP solely for fuel savings but given $4/gal is probably here to stay it has moved up on my list of reasons to operate LOP.

_________________
Milt

BillLeff1(at)aol.com
Guest

Posted: Tue May 23, 2006 12:08 pm Post subject: Advice from Gear-Heads...

I think they think you are a Turbo Commander and are automatically  expecting 

a lot of noise. The Mr RPM is very quiet on the ground except at  lift off.

 

Bill

rsrandazzo(at)precisionma
Guest

Posted: Tue May 23, 2006 12:30 pm Post subject: Advice from Gear-Heads...

Bill-



Well now... Sometimes I like having people confuse me with a turbo

commander.  All the mystique and half the fuel burn.  



Robert Randazzo 



--

rsrandazzo(at)precisionma
Guest

Posted: Tue May 23, 2006 1:34 pm Post subject: Advice from Gear-Heads...

Bill-



We put 414C in the shop for a pretty intensive inspection immediately after

bringing her west.  It was pretty clear that we had a gem- but she'd been

subjected to "lowest bidder maintenance" for a while-  a suspicion which is

more-or-less confirmed now that I've exchanged email with Milt...



The process has been slow- but it's beginning to accelerate toward the

finish line.



I'm fortunate that our maintenance team is also the team conducting the

overhaul-  so they are very well invested in the airplane.  They've taken

great pride in pointing out some of the little details that they have looked

after "just because."



Hope to have her flying again during the next few months... Parts are going

back in- which is nice.



Rob

 



--

bowing74(at)earthlink.net
Guest

Posted: Tue May 23, 2006 5:22 pm Post subject: Advice from Gear-Heads...

Perfect!



bilbo



--

tylor.hall(at)sbcglobal.n
Guest

Posted: Tue May 23, 2006 5:51 pm Post subject: Advice from Gear-Heads...

Gear Heads,

I have a question about checking the props to see if they will go  

into feather.



I have been flying with my boss in a 421 and he does not like it  

since he says he can not test the props to feather mode with out  

causing a problem with the gear box.



In the 500B that I had access to, pulling the props back to feather  

for a brief moment was a standard thing, but it is a direct drive  

engine.



My Boss is down on  the 421, because he feels that if there is an  

engine problem and the prop does not go into feather, there will be  

an off airport landing since the aircraft can not maintain altitude  

unless the prop feathers.  He feels that there is a 50-50 chance that  

the prop will not feather.  He does cycle the prop, but not to feather.



How does one test the props to feather on a geared engine with out  

causing damage to the gear box???

Does unloading the prop at low RPM cause a gear backlash??



Pondering minds would like to know.

Tylor Hall



On May 23, 2006, at 3:33 PM, Robert S. Randazzo wrote:



[quote] 

 <rsrandazzo(at)precisionmanuals.com>



 Bill-



 We put 414C in the shop for a pretty intensive inspection  

 immediately after

 bringing her west.  It was pretty clear that we had a gem- but  

 she'd been

 subjected to "lowest bidder maintenance" for a while-  a suspicion  

 which is

 more-or-less confirmed now that I've exchanged email with Milt...



 The process has been slow- but it's beginning to accelerate toward the

 finish line.



 I'm fortunate that our maintenance team is also the team conducting  

 the

 overhaul-  so they are very well invested in the airplane.  They've  

 taken

 great pride in pointing out some of the little details that they  

 have looked

 after "just because."



 Hope to have her flying again during the next few months... Parts  

 are going

 back in- which is nice.



 Rob

 --

n395v

Joined: 10 Jan 2006
Posts: 450

Posted: Tue May 23, 2006 6:06 pm Post subject: Re: Advice from Gear-Heads...

Shut one down at a time in flight and feather it.

_________________
Milt

rsrandazzo(at)precisionma
Guest

Posted: Tue May 23, 2006 6:08 pm Post subject: Advice from Gear-Heads...

Tylor-



What is it that makes him think feathering the prop on a GTSIO is a 50/50

proposition?  I have read this supposition in a few less-informed discussion

groups- but I have never seen anyone substantiate it with facts.



A quick scan of NTSB findings doesn't provide any data that would appear to

substantiate any concerns about feathering...  (Aside from which- if there

were an actual trend on this- we'd have half a dozen SB's and AD's to

contend with on the issue and it would have been resolved by now.... I have

enough faith in the FAA to believe in that- but not much more faith than

that. ;-p )



I've NEVER found it to be a good idea to run a piston engine into feather

just for the fun of it-  generally a single swing of the prop pitch levers

to ensure that you have control of prop pitch is sufficient.



I can see the practical application of making a single test-to-feather after

major engine work and/or hanging a new prop/engine combination-  but once

validate as working I'm not so certain there is value in this test whether

the engine is geared or not...



Just my opinion- and not based upon any specific engineering information...



Robert Randazzo



 



--

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