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  #21  
Old 12-23-2015, 06:05 PM
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Toobuilder Toobuilder is offline
 
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Quote:
Originally Posted by DanH View Post
That's right. First do a big pull to the lean side, then turn on the "lean" function and slowly push rich to find peak.
I don't think it matters when you turn on the lean find function if you do the BMP, because you pass through so fast it will re establish a new peak from the lean side.
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  #22  
Old 12-23-2015, 07:16 PM
gear1 gear1 is offline
 
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Default LOP operation

David,

Thank you for republishing the "Red Box" table. It is a valuable tool to stay out of trouble. LOP operation in my RV8 increases range by about 25% and only costs 5-7 KTAS at 11,000 to 13,000.

Several "Luddites" at our airfield, including a very experienced A&P, have chastised me for flying LOP. They are convinced that I will "burn up" my engine. Charles Lindberg taught bomber crews to extend their range by running LOP during WWII. The doubters are still at it 70 years later!

What will it take to convince them?
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  #23  
Old 12-24-2015, 05:37 AM
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rzbill rzbill is offline
 
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Quote:
Originally Posted by Toobuilder View Post
I don't think it matters when you turn on the lean find function if you do the BMP, because you pass through so fast it will re establish a new peak from the lean side.
Exactly. Done it too. I have tested the lean find function from both sides on the GRT and find no difference if done slowly. While I have never flown the other EFISeseses (EFII?) I don't see why they would not be just as accurate.


Quote:
Originally Posted by gear1 View Post
David,
What will it take to convince them?
In the scientific world it is a historical fact that a serious challenge to the status quo does not become dogma until the persons of power unwilling to change or see the evidence pass from the earth.
Don't waste your energy on them. Just fly with a grin on your face and let the A&P work on red box damaged engines.
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  #24  
Old 12-24-2015, 08:03 AM
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DanH DanH is offline
 
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Quote:
Originally Posted by gear1 View Post
Thank you for republishing the "Red Box" table. It is a valuable tool to stay out of trouble.
Do keep in mind that much of the underlying concept behind those numbers goes right out the window with variable ignition timing.

Quote:
Originally Posted by rzbill View Post
In the scientific world it is a historical fact that a serious challenge to the status quo does not become dogma until the persons of power unwilling to change or see the evidence pass from the earth.
Why just yesterday I had a nice conversation with a Baron owner who told me that electronic ignition and variable timing made no sense at all.

Of course he does own a well-known magneto overhaul facility
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  #25  
Old 12-24-2015, 08:59 AM
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Saville Saville is offline
 
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Default SI 1094D vs SI 1497A

This is a very interesting thread and I've captured some of the Lycoming Service Instructions. I notice there's one called "Fuel Mixture Leaning Procedures" and another called "Engine Procedures for Flight Training Operations"

Does one supersede the other?

What would be different with respect to Flight Training as opposed to normal ops?

Thanks!
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  #26  
Old 12-24-2015, 09:03 AM
StuBob StuBob is offline
 
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Quote:
Originally Posted by DanH View Post
Do keep in mind that much of the underlying concept behind those numbers goes right out the window with variable ignition timing.
In what way? Guessing, I'd think maybe the Red Box is much smaller, maybe nonexistent?
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  #27  
Old 12-24-2015, 10:04 AM
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skylor skylor is offline
 
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Default Red box

Quote:
Originally Posted by StuBob View Post
In what way? Guessing, I'd think maybe the Red Box is much smaller, maybe nonexistent?
Actually, it'll be bigger. For the red box to be smaller, the EI's out there would have to reduce spark advance over stock magneto values. Im not aware of any that do (except maybe the EFII programmed with a custom ignition curve)

The more conservative EI's such as light speed do not add any spark advance at high manifold pressures, thus in this case the red box would be mostly unchanged. At reduced manifold pressures however, the EI's do increase spark advance over stock values because this is where the biggest efficiency gains result. However, increasing spark advance increases internal cylinder pressures (ICP) and also causes the peak pressure to a occur at fewer degrees of crankshaft rotation (this angle is known as Theta-PP) past piston Top Dead Center (TDC). This results in increased CHT and reduced detonation margin. Therefore, the red box does not shrink as much at reduced manifold pressures with electronic ignition as it would with fixed-timing mags.

Skylor
RV-8
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  #28  
Old 12-24-2015, 12:59 PM
StuBob StuBob is offline
 
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Excellent. Thanks.

Makes me wonder what the implications are as far as required detonation margin, reduced octane fuels, MOGAS, turbos.........Everything affects everything else, doesn't it.
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  #29  
Old 12-24-2015, 01:41 PM
Bicyclops Bicyclops is offline
 
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Location: LA, California
Posts: 323
Default Timing advance

At low manifold pressure and high RPM, (where Lightspeed advances the most), the flame spread is slower than it would be at higher MAP/(lower altitude). The high RPM gives the slower flame spread less time to meet up with the one from the other spark plug and the peak cylinder pressure occurs later than the optimum timing of around 17 degrees after TDC where the connecting rod has the best leverage on the crank. The ignition advance is intended to bring the max pressure back to the place where it can do the most work rather than wasting much of the burning gases on a rapidly retreating piston and a rapidly increasing cylinder volume. True that if the timing advance is too aggressive, it could happen too early causing pressures and temperatures to be higher than what is good for the engine.

High compression pistons have the effect of increasing burn rate and that's why we retard the timing on those engines. It's all about getting max pressure at the point where the rod can transfer the most power to the crank without hammering.

If you base your red box on CHT rather than degrees EGT rich or lean of peak, it will still be easy to lean even when the ignition timing is advanced. The actual size of the red box doesn't matter much. If your CHTs are high, pull throttle and/or mixture. Unless, of course, you are ROP. In that case push mixture and/or pull throttle and/or lower the nose until you've got a handle on it.

Ed Holyoke

Quote:
Originally Posted by skylor View Post
Actually, it'll be bigger. For the red box to be smaller, the EI's out there would have to reduce spark advance over stock magneto values. Im not aware of any that do (except maybe the EFII programmed with a custom ignition curve)

The more conservative EI's such as light speed do not add any spark advance at high manifold pressures, thus in this case the red box would be mostly unchanged. At reduced manifold pressures however, the EI's do increase spark advance over stock values because this is where the biggest efficiency gains result. However, increasing spark advance increases internal cylinder pressures (ICP) and also causes the peak pressure to a occur at fewer degrees of crankshaft rotation (this angle is known as Theta-PP) past piston Top Dead Center (TDC). This results in increased CHT and reduced detonation margin. Therefore, the red box does not shrink as much at reduced manifold pressures with electronic ignition as it would with fixed-timing mags.

Skylor
RV-8
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  #30  
Old 12-24-2015, 01:58 PM
StuBob StuBob is offline
 
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Ok, so the idea is to advance timing in order to optimize theta-PP? If that's the case, what effect is there on detonation margin?
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