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From: William R. Bayne [mailto:[EMAIL PROTECTED]
Sent: Sunday, December 25, 2005 3:47 PM
To: Ed Burkhead
Subject: WRB Re: [COUPERS-TECH] Leaning with Stromberg carb
RLYTECH
Hi John, all-
From: John Cooper [mailto:[EMAIL PROTECTED]
Sent: Monday, December 19, 2005 12:06 PM
To: [email protected]
Subject: Re: [COUPERS-TECH] Leaning with Stromberg carb
At 02:11 PM 12/16/2005, WRB wrote:
> There are many possible causes of preignition, very few of which wouldI made no mention of timing.
> be attributed to poor maintenance practices. Deposits accumulate,
> magneto distributor caps deteriorate, moisture gets into them, etc.
> However, the percentages are irrelevant. It only matters if the plane
> you are flying is right or not.
I strongly disagree. Most of us have a professional set our timing.
That's true, and of itself misleading in your apparent game of "Gotcha". You purposely ignored timing in our accumulating chain of thought to make it appear I was the one departing. Here is what you omitted-the "rest of the story, as Paul Harvey would say:
At 09:40 PM 12/13/2005, WRB wrote:
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"?
No. Nor is it realistic to assume that 95+% of coupes operating with
the A-65 and C-75-85 Continentals with compression ratios of 6.3:1 are
correctly timed, and are without significant cylinder chamber lead
(or carbon) deposits.
Well, at least I attempted to qualify my question to the "real world".
If your guess would be 90%, that wouldn't make a difference most of us would
quibble over. If your guess would be less than 50%, that would truly be a
remarkable (and poor) reflection as to the level of skills the average pilot
gets when he hires the average FAA-licensed mechanic.
Noun 2. - obfuscation - the activity of obscuring people's understanding, leaving them baffled or bewilderedLOL
More obfuscation.
"Use of leaded fuels" has not been a historicalNo, but it is now. The C75/85 was certified on 73 octane fuel which was lead free. 80 had a MAXIMUM lead content 25% of that found in 100LL. Lead fouling of plugs and lead deposits in the combustion chambers are real problems today if you use 100LL.
problem of significance in engines such as ours.
You apparently chose to omit that part of my response which completely agrees with your comment. In fact, I continued: "Burning 100LL, a grossly overleaded fuel, now is; particularly with rich or over-rich mixture ops." Was it honest to so phrase your comment as to infer a disagreement that you somehow "win"? I think not.
You are suggesting that well maintained enginesIf that's what you think I said, you misunderstood me.
properly operated are just as likely to have significant cylinder
deposits as poorly maintained engines operated by the less informed and
proficient, and that's neither logical nor credible.
Again, I said a lot more before this out-of context summary. You might be easier to understand if you stayed more "on subject".
You're right. We were all taught that. This discussion was not a "oneI thought I did. Use of partial carb heat reduces the amount of heat energy available should carb ice develop, sometimes to the point where it is insufficient. Also, I quote from the Ercoupe Owner's Manual: "Unless icing conditions in the carburetor are severe, do not cruise with the heat on."
size fits all", though. If there is a genuine danger in such careful
and minor application of carb heat in the manner described for the
purpose described, what is it?
And again, your "response" is not very responsive in that it presumes nothing of value has been learned since 1946 (with regard to the admittedly poor uniformity of mixture supplied to individual cylinders on small Continentals). That's simply not true. You imply that the better vaporization observed with use of partial carb heat is of no use today under any circumstance. I don't find that position a reasonable one, although further research may be in order before anyone sticks the practice in manuals. Your ending quote from the Ercoupe Manual again suggests that operational knowledge gained since 1946 has no place in one's powerplant management practices. You're certainly entitled to that opinion, but it doesn't suggest the open mind or objectivity associated with almost all progress.
> It is difficult to control ...No, that the temperature of the incoming air is difficult to control precisely. Full carb heat is a known quantity. Partial carb heat is not. Under some conditions partial carb heat can actually cause the formation of carb ice. Also, at high power levels, carb heat lowers the detonation margin.
Are you suggesting our simple push-pull knob moves untouched after
adjustment, or that we need a vernier?
But again, you lapse into "what if" generalities while avoiding my specific question, which was: "If there is a genuine danger in such careful and minor application of carb heat in the manner described for the purpose described, what is it?
> I thought this related back to leaning on the ground, hence theLeaning is not the point. We're talking about carb heat. Use of carb heat on the ground should be avoided due to the fact that it allows unfiltered air into the intake. The prop provides the dust storm.
> concern about unfiltered air.
Sorry. I assumed it obvious you don't lean on the ground to clear
plugs at run up in a dust storm.
No. YOU'RE off on carb heat. I said "Please explain how, only 1000 ft. lower this very same mixture control could be totally ineffective in leaning mixture for taxiing and/or running up to clear plugs?" So, at least in my mind, the point WAS leaning.
>> "...the mixture should be full rich unless the engine is rough dueYou may think that's what I said, but again, you misunderstood me.
>> to a too-rich mixture."
>
> Duh! However, if you have a Stromberg And you have to lean And you're
> below 5000' DA, something else is happening. Best look into it!
>
>> Per the Ercoupe Instruction Manual, p. 6 states: "For average
>> operations
>> below 5000 ft. altitude, the carburetor should be left in the
>> full-rich
>> position. When at part throttle, the fuel consumption may be
>> improved by
>> leaning the mixture, but in no case should the control be moved back
>> far
>> enough to decrease the engine rpm."
>
> Duh again. And again, if you're below 5000' DA and leaning DOESN'T
> decrease RPM, something else is going on. Best look into it.
You either didn't read the second sentence, or you disagree with Erco.
See my comment above as to my misunderstanding you.
The Erco text is somewhat ambiguous, too boot. Please clarify the operations below 5000' that are not "average" where you think leaning will be beneficial.
Here we go back to 1946. The Ercoupe Manual refers to altitude above sea level (which is a constant). I thought you and I agreed that today's "real world" dictates substitutation of density altitude in such recommendation. Clarified enough?
>> It would not require "any sort of a full throttle enrichment device"You said: "...if the large holes in said plates were sized in design to deliver excess fuel at full throttle." As I stated, the holes do not deliver fuel. For a given mixture control setting, the leaning effect increases as the throttle is opened, so sizing of the holes could not cause a richer mixture at full throttle. Large holes do nothing; smaller ones increase the leaning effect.
>> to
>> achieve extra richness at full throttle if the large holes in said
>> plates
>> were sized in design to deliver excess fuel at full throttle.
>
> Those holes regulate the amount of air (not fuel) at (approximately
> atmospheric) pressure vented to the float chamber.
Did I suggest otherwise?
In discussing operational versus non-operational Stromberg mixture controls, the subject was delivery of excess fuel by the carburetor. Yes, my phrasing COULD be interpreted as suggesting fuel delivery was through these holes; but such was not my intent. This assumption was yours. I attempted to stay with our main topic even as you range far and wide to blur such focus.
(following moved up from lower in your response as it relates to the above-WRB)
If the holes are of a size when mixture is at "Full Rich" to deliverAgain, the leaning effect of the mixture control increases with increased airflow through the venturi. At idle there is no effect and the full effect (moderated by the mixture control setting) is obtained at full power. There simply is no way that a richer mixture could be delivered at full throttle than at lower throttle settings.
more fuel to the engine than it can convert to power (as a "safety
factor" at take-off), they will do so.
The Stromberg NA-S3A1 carburetor does not have an "economizer" or full throttle enrichment feature. If you don't believe me, I refer you to an article in the January, 2006 issue of Light {Plane Maintenance which states "The NA-S2 and NA-S3 Models...are not fitted with an economizer, accelerator pump or mixture control. (Note: the NA-S3A1 does have a mixture control.)"
I don't have this article, and would appreciate a copy for my files. You may be correct (and my belief otherwise may be wrong), in which case I will certainly acknowledge same once independently verified. There is but one reality here, as I sadi before.
Gee, this is the third time. I apologize for being so dense. See my comment above as to my misunderstanding you.The cable controls are entirely separate. If you refer to what happensBy coupled I mean that the leaning effect of a given mixture control setting varies with changes in the throttle setting (air flow). If you thought I was referring to a mechanical connection between the two controls then you misunderstood what I said.
inside after leaning when the throttle is moved, more information would
seem necessary for clarity.
Since this is taking on the tone of a religious discussion rather than a technical one, this is my final post on the subject.
I agree the thread has probably reached the limits of benefit to our readers, but others may not agree; and that's fine too.
Well, each of your quotes above date from the forties, as evidenced by sea level reference (as opposed to density altitude).
From the Continental A & C Series Operator's Manual, Ground Running; Warmup "Leave Mixture at 'Full Rich'. (See 'Ground Operations at High Altitude Airports', Section V for exceptions.)" And Ground Operations at High Altitude Airports states "Prior to takeoff from fields above 5000 feet elevation, the mixture control should be leaned to give maximum RPM at full throttle, static runup."
From the section on Cruise: "At altitudes of more than 5000' above sea level adjust mixture control for best rich power by moving toward 'lean' position until maximum RPM is obtained with fixed throttle. Return control toward 'Full Rich' position until RPM drops just perceptibly.... Readjust the fuel-air mixture for each change in throttle setting or altitude."
(Here's the kicker.) "CAUTION . . . Do not lean the air fuel mixture, unless such adjustment results in a higher RPM. Excessively lean mixtures cause over-heating and may result in damage to the engine."
Finally, from the section on Descending and Landing "The mixture control must be in 'Full Rich' position during descent.
And finally, I leave you with this, from the Ercoupe 415 D flight manual :"Flight: Adjust mixture control for best RPM (above 5000 feet.)"
But what do they (Continental, Erco, LPM) know?
;)
John Cooper
You have offered no logical reason to disable the Stromberg mixture control or leave one that way. You seem to endorse such practice, although I must confess your "real" position on the subject is as clear as mud.
I have explained in exhaustive detail why I strongly urge all with inoperative mixture controls to put the plane back the way it was manufactured and learn to use this capability intelligently. I hope there is little doubt as to where I stand on this subject and why.
Have a very Merry Christmas,
William R. Bayne
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