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From: William R. Bayne [mailto:[EMAIL PROTECTED]
Sent: Tuesday, December 13, 2005 8:39 PM
To: Ed Burkhead
Subject: WRB Re: [COUPERS-TECH] Leaning with Stromberg carb
RLYTECH
John,
OK, I'll bite! Could you please verify the accuracy of what you state here?
Your general statements are obviously true, but is it realistic to suggest that:
1. The 95+% of coupes operating with the A-65 and C-75-85 Continentals with compression ratios of 6.3:1, correctly timed, without significant cylinder chamber lead deposits (that would raise said ratio), and burning average fuel are capable of cylinder pressures high enough to endanger cylinders or induce actual "preignition/detonation" at their "high power levels"?
2. To infer by omission that deficiencies of single-cylinder sensing apply to multi-cylinder information (EGT and/or CHT)?
Can you reference any instances of engine damage on a coupe (or aircraft with the same engine/carburetor combination and similar performance) reasonably attributable to "misuse" of the mixture control? If so, do you personally consider such occurrence (or the "risk" thereof) to be of statistical significance to an Ercoupe owner/operator?
Do you agree that judiciously applied carburetor heat can improve (reduce) the "normal" (rather high) mixture ratio spread between cylinders on our little Continentals?
As a"point of order", per the Continental Operator's Manual, Form X30012 Dec. '80, a pilot is advised to lean "...at altitudes of more than 5,000 feet above sea level..." and "Prior to takeoff from fields above 5000 feet elevation...". While I entirely agree these references SHOULD be with reference to "density altitude" (which can be MUCH lower in summer), in fact they are not.
No one in my cockpit will argue with my choice to use the latter, nor will the engine. Should Continental correct their manual? I think so. Will they? Don't hold your breath. Which "should" be followed? Decide whether you want to please Continental's lawyer(s) or get the most efficient performance from your engine safely.
This is exactly why information offered on these lists should be "filtered" to the extent of being "real-world useful as specifically applicable to coupes (or certain models thereof)" as opposed to generic spam can wisdom (which may or may not apply to coupes). An amazing amount of the latter has ultimately proven more confusing than useful here when examined.
Even as I raise these issues it seems time again to acknowledge I do not hold nor have I held any type of FAA mechanical certification or license. As a Pilot I merely seek, to the best of my ability, to understand what I must to manage the considerable responsibilities and risks of aircraft operation under FAA scrutiny and keep insurance in force. That's rather daunting!
My compliments on your response to the "compass leak" thread. Legal and useful information clearly from one who knows.
Regards,
William R. Bayne
<____|-(o)-|____>
(Copyright 2004)
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On Dec 13, 2005, at 2:32 PM, John Cooper wrote:
At 02:08 PM 12/13/2005, you wrote:
I liked using an accurate EGT for leaning. It makes me happy.
Whatever makes you happy! ;)
Mixture distribution on C-series is crude at best. The spread between cylinders makes digital readout moot, IMHO. Note too that 50 degrees rich of peak at high power levels is the most dangerous as far as cylinder damage and preignition/detonation goes. Continental recommends no leaning below 5000' (density altitude). That way, you're forced out of the high-power operations window and nothing you can do will damage the engine.
Note that with a Stromberg, you must re-adjust the mixture every time you change the throttle setting.
John Cooper
Skyport Services
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