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  #11  
Old 04-17-2017, 11:33 AM
rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by frghtdg View Post
Poor on the gas with a high pitch cruise setting forgotten during a distracted descent, could overstress the engine. Checklist.
Not really relevant to this discussion, but this is an old wives tale that is for the most part (in regards to how people commonly operate their engine) false.

Anyone with a fixed pitch prop is in this condition every time they take off.

BTW I set my fixed pitch airplane power with the MP also. That way I don't have to keep readjusting as the aircraft speed stabilizes. It is easy to do with any airplane (as long as it is equiped with a MP gauge) once you get to know the specific numbers of that airplane.
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Last edited by rvbuilder2002 : 04-17-2017 at 12:20 PM.
  #12  
Old 04-17-2017, 12:12 PM
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DanH DanH is offline
 
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Originally Posted by rvbuilder2002 View Post
Not really relevant to this discussion, but this is an old wives tale that is false.

Anyone with a fixed pitch prop is in this condition every time they take off.
Not so false, and not quite.

Consider the "Limiting Manifold Pressure For Continuous Operation" found on any Lycoming power chart. It clearly prohibits, for example, 2200 RPM at full throttle.

As for fixed pitch, note that the line allows full throttle at 2400.

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  #13  
Old 04-17-2017, 12:18 PM
rvbuilder2002 rvbuilder2002 is offline
 
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Originally Posted by DanH View Post
Not so false, and not quite.

Consider the "Limiting Manifold Pressure For Continuous Operation" found on any Lycoming power chart. It clearly prohibits, for example, 2200 RPM at full throttle.

As for fixed pitch, note that the line allows full throttle at 2400.

Figures....
As I wrote my post it initially said .... for the most part false, but I removed it (I am at home sick and didn't feel like expounding on the specifics).
So I will edit my post to say "for the most part in regards to how people commonly operate their engine".
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  #14  
Old 04-17-2017, 12:41 PM
BobTurner BobTurner is offline
 
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I vote with Scott! Note the table above says 'continuous' operation. Lots of certified 172s turn less than 2400 rpm at the start of a full throttle takeoff. The OP seemed to imply oversquare was always a bad idea. As is often the case, the truth is somewhere in between-some oversquare is allowed, but there are limits, both in time and settings.
  #15  
Old 04-17-2017, 03:04 PM
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cdeerinck cdeerinck is offline
 
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Question Don't want to try it

If you leave the CS control where it was during cruise, and go to full throttle, what does happen?

I am not suggesting anyone do this, but I am curious what happens when it is done.

You are giving the engine full gas, but not asking for much RPM in return. Does that mean you are running way too rich, and risk fouling your plugs or is it worse than that?

And does the answer change in any way if you are running with EFII?
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  #16  
Old 04-17-2017, 04:03 PM
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DanH DanH is offline
 
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Quote:
Originally Posted by cdeerinck View Post
If you leave the CS control where it was during cruise, and go to full throttle, what does happen?

I am not suggesting anyone do this, but I am curious what happens when it is done.

You are giving the engine full gas, but not asking for much RPM in return. Does that mean you are running way too rich, and risk fouling your plugs or is it worse than that?

And does the answer change in any way if you are running with EFII?
The issue is manifold pressure, not throttle position. Altitude dictates how much manifold pressure at full throttle. Down low you get a lot of MP. Up high you don't.

Lots of manifold pressure at some low RPM is one contributing factor in detonation. Others are F/A ratio, CHT, fuel octane, and inlet temperature. Give it a bad combination (say, 28.5" MP, 2400 RPM, leaned to just on the rich side of peak EGT using fuel barely meeting the 100LL standard, CHT at max on a hot day) and it will detonate.

Full throttle does not mean "full gas". In simplified terms, fuel metering is designed to match airflow in a proportional manner, by weight. For example, if the proportion is 12.5 lbs of air to 1 lb of fuel at some throttle position, it should be the same at any other throttle position. More air, more fuel, less air, less fuel, but always in proportion.

The mixture control varies the proportion.

The EFII-brand system is a fuel metering device. It delivers whatever it is set to deliver, as do carbs or constant flow injection. The metering components and method may be different, and accuracy is arguably better under many conditions, but a knothead can still put the knobs in the wrong places, just like the rest.
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  #17  
Old 04-17-2017, 04:05 PM
frghtdg frghtdg is online now
 
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Quote:
Originally Posted by rvbuilder2002 View Post
Not really relevant to this discussion, but this is an old wives tale that is for the most part (in regards to how people commonly operate their engine) false.

Anyone with a fixed pitch prop is in this condition every time they take off.

BTW I set my fixed pitch airplane power with the MP also. That way I don't have to keep readjusting as the aircraft speed stabilizes. It is easy to do with any airplane (as long as it is equiped with a MP gauge) once you get to know the specific numbers of that airplane.
Scott....I believe you to be up there with GOD in terms of knowledge, smarts, and wisdom. If you say I can have my RPM back at 2200 from a high altitude cruise, and shove the throttle forward to avoid hitting Sweet Pee crawling on the runway and not have a concern in the world, that it's an old myth....I believe you.
I was only passing on how I was trained to operate high powered turbocharged Cessna twins 400 series years ago.
"Keep the prop ahead of the throttle you knucklehead " the old geezer would yell.
Another thread, plus we're putting Bob to sleep.
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  #18  
Old 04-17-2017, 08:52 PM
rvbuilder2002 rvbuilder2002 is offline
 
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Originally Posted by frghtdg View Post
Scott....I believe you to be up there with GOD in terms of knowledge, smarts, and wisdom.
Far from it.
The God of this world has never made a mistake..... I make multiple ones per minute.

Quote:
Originally Posted by frghtdg View Post
If you say I can have my RPM back at 2200 from a high altitude cruise, and shove the throttle forward to avoid hitting Sweet Pee crawling on the runway and not have a concern in the world, that it's an old myth....I believe you.
I didn't say that, and if it is my edited post that you read (it likely was because I did that only minutes after writing it), you already know that.

You said
Quote:
Originally Posted by frghtdg View Post
rule never to break......always keep the prop ahead of the throttle (knobs)
I and many others break it every time we fly. The very first control I move after takeoff is the prop RPM control to reduce RPM to 2500 to be a bit more noise friendly (RV's are noisy).

This practice is fully within Lycomings recommendations in two ways (it is within the RPM limitation and is not a continuous operation condition).

If it is not yet obvious, my comment was in regards to your use of the word never.
__________________
Any opinions expressed in this message are my own and not necessarily those of my employer.

Scott McDaniels
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")

Last edited by rvbuilder2002 : 04-17-2017 at 11:04 PM.
  #19  
Old 04-17-2017, 09:49 PM
Plummit Plummit is offline
 
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Quote:
Originally Posted by rvbuilder2002 View Post

The very first control I move after takeoff is the prop RPM control to reduce RPM to 2500 to be a bit more noise friendly (RV's are noisy).

That's my M.O. too. As I'm climbing over the runway I start twisting the prop control back to 2500 RPM. At the end of the runway I'll bring the flaps up into reflex and then start pulling the throttle back to 25 inches for the climb. I also lower the nose to get some more speed (read cooling). I'll then bring the mixture back to somewhere around 16 GPH. This is at my home airport which is basically sea level.

-Marc
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  #20  
Old 04-18-2017, 06:15 AM
BillL BillL is offline
 
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Default Funny - everyone is right

Great discussion for about 1/2 way through the RV Social.
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