"Burying your head like an ostrich in a pile of regulations (that remain substantially as they were) will not change that simple, unalterable fact. When a professional plays fast and loose with the truth, they betray the trust of everyone on this list; whether they (or the list) know it or not, and whether they (or the list) care or not."
When a self-proclaimed "expert" advises aircraft owners to knowingly ignore the regulations set by our governing body (the FAA) they are not only betraying trust, they are suggesting that person commit an unlawful act.
If you as a pilot knowingly operate your aircraft outside the limits of the TCDS or legal ammendments (STC,337s) you are liable for civil penality.
We A&P IAs are commited by law to make sure any aircraft we sign off as airworthy meets the TCDS or legal ammendments (STC,337s).
If you are commited to this goal get a STC (put up or shut up), until then don't advise us to operate our aircraft outside the FARs.
Sorry for getting on my high horse.
Bill Biggs
From: "Ed Burkhead" <[EMAIL PROTECTED]>
Reply-To: "Ed Burkhead" <[EMAIL PROTECTED]>
To: "'Coupe-Tech'" <[email protected]>
Subject: FW: [COUPERS-TECH] Why it might not be prudent to operate your C75 above red line
Date: Fri, 24 Feb 2006 23:17:30 -0600----[Please read http://ercoupers.com/disclaimer.htm before following any advice in this forum.]----This message was automatically forwarded on behalf of Bill Bayne. Please address any responses to the mail list or directly to Bill at: [EMAIL PROTECTED]
From: William R. Bayne [mailto:[EMAIL PROTECTED]
Sent: Friday, February 24, 2006 11:16 PM
To: Ed Burkhead
Subject: Re: [COUPERS-TECH] Why it might not be prudent to operate your C75 above red line
rlytech
On Feb 24, 2006, at 16:11, John Cooper wrote:
...The vast majority of Ercoupes with C75 engines are equipped today with the McCauley 1A/B90 prop.
That's confusing because one unfamiliar with the terminology can't look this "prop" up. You meant either the McCauley 1A90 or 1B90 prop.
The TCDS specifies max diameter 73 and minimum 71.
Yes, and apparently no one ever bother to update the TCDS per Ercoupe Service Memorandum No. 37, Note 2.:
"The C.A.A. has recently approved static RPM and diameter for fixed wood propellers for the Ercouope 415-C with the Continental C-75 engine as follows: Static RPM Maximum 2050 Minimum 1900, 72"-74" diameter. McCauley (Met-L-Prop) info. in the Univair Catalog shows a 74" prop for 75 hp Ercoupes.
Much has been made of the advantage of the longer (73") prop and most came that way, so likely most are nearer 73" than 71".
With good reason. Quoting from Fred Weick's book "Aircraft Propeller Design":
"With the relatively thin-bladed metal propellers the pitch and diameter giving the maximum rate of climb are approximately the same as those giving the greatest high speed."
"When a 'good climbing propeller' is ordered, what is almost always desired is a propeller which will give a short take-off run and a steep angle of climb and not a high rate of climb. It happens that with both wood and metal propellers, the ones having the largest diameters and the lowest pitches which will give a reasonable high speed give both the quickest take-off and the greatest angle of climb and not a high rate of climb."
For "all-around performance..." the "...compromise...propeller...will...have a larger diameter and smaller pitch than the best high-speed propeller but a smaller diameter and greater pitch than the propeller giving the shortest take-off and the steepest climb..." and "...operates at its maximum or peak efficiency at the high-speed condition of flight."
Point #1: If you aren't based at altitudes above 5,000' msl or at a short strip with obstacles one must clear, a "climb" prop (of smaller diameter and greater pitch) is not the best choice. So Fred specified a 73" diameter prop as "standard" for the 75 hp.
Point #2: Early 75 HP Ercoupes reaching 127 mph were NOT doing so at the TDCS "allowed" 2275 rpm". Fred knew it. Erco knew it. The CAA knew it. Owners using their extra power were not struck by lightning, and no mechanics or pilots lost their certificates. That's just the way it was. Everyone knew C-75 RPM "limits" were meaningless after the C-85. They were routinely ignored before our Johnny-come-lately would-be wizards started sounding like the Taliban of aviation!
Point #3: You say "Operation of a C75 in an Ercoupe in excess of 2275 RPM is prohibited by the type certificate. Period, end of statement." I say "John, when you catch some owner doing it, call 911".
Point #4: You said:
"...the TCDS specifies static RPM limits. These are certification requirements and any IA doing an annual inspection should verify the engine/prop combination meets these requirements. To not do so is to jeopardize your certificate and open yourself to our litigious society's dark side. That said, any prop combo that meets the requirements will not get you near 2575 RPM in level cruise".
I'll put it simply, John. You're wrong! Read Ercoupe Service Memorandum No. 37, Appendix A. and weep. It clearly shows that the standard wood Sensenich prop on a C-75 turned up to 2600 R.P.M. at "Maximum Speed". The McCauley 1-A-90 similarly turned up to 2500 R.P.M. To whatever extent anyone cared, these props "met" applicable static limits. Welcome to the "real" world.
Burying your head like an ostrich in a pile of regulations (that remain substantially as they were) will not change that simple, unalterable fact. When a professional plays fast and loose with the truth, they betray the trust of everyone on this list; whether they (or the list) know it or not, and whether they (or the list) care or not.
From the McCauley TCDS: [quote]
NOTE 9. Special Limits.
Table of Propeller-Engine Combinations Approved Vibrationwise for Use on Normal Category Single-Engine Aircraft
The maximum and minimum propeller diameters that can be used from a vibration standpoint are shown
below.
[end quote]
For the C75 a Maximum of 74" and a minimum of 69.5" is specified
For the C85 a Maximum of 71" and a minimum of 68.5" is specified
But, you say, there is no difference between the two engines, why different props? Simple. The 73" prop (actually any prop longer than 71") has been demonstrated to exhibit undesirable vibration characteristics when operated on that engine in excess of 2275 RPM. (The difference in the lower limit has to do with repair allowances on the various prop lengths.)
There you go again, pointing to PAPER limits instead of structural (real) ones (although you SUGGEST concern over structural limits). Your "truth" is not the "whole truth"! McCauley's position is that "No RPM restrictions are required on any Met-L-Props..." (those likely to be fitted to Ercoupes, et al).
The McCauley TCDS clearly shows, in the overall sense, that the 1A90/CF (elliptical tip) and 1B90/CM (square tip) propellers of 70" to 78" diameters (68"-38" pitch) are designed for 85 HP continuous operation up to 2600 RPM, and 71" to 75" diameters (72"-38 pitch) are good for 100 HP (0-200) continuous operation up to 2750 RPM. These are the very same mechanicals as the STC C-85 we were originally discussing. With NO evident aluminum prop vibration or stress problems in the operating range between 2275 RPM and 2575 RPM, the "point" of your subject line (above) becomes another of your "red herrings".
If you have never seen a C85 crank cracked through the middle journal, you're missing something.
There are a variety of possibilities that could cause such a failure, but operating at up to 2575 RPM would not likely make such a list if McCauley compiled it.
Also, you may recall that to convert a C75 to a C85 you have to increase the oil capacity.
Not true. You increase the oil QUANTITY in the existing tank by re-marking the dip stick (or buying one already "calibrated" for the 85 HP engine). The C-85 rewards its proud new owner for complying with such a SILLY PAPER REQUIREMENT by quickly blowing this excess oil out all over the coupe's belly. Many pilots choose to operate ILLEGALLY "low" on oil because they have found that making such a mess over and over again serves no useful purpose; but there I go again, wandering back into the "real world". Sorry.
This is because the engine will not meet it's certification requirements wrt. cooling when operated at that power level using the C75 oil capacity.
John, "Certification Requirements" are a one-time deal, sorta like marriage. Once done, it's up to the owner to keep temps under the red line. High oil temps are much more often caused by deteriorated baffling than too little oil. As a professional, you know that to be true, right.? Why the B.S.?
What else have we missed?
Some relevant facts would have been nice.
Read my excerpt from Fred's letter again. He reiterated his selection procedure AFTER metal props had become the "norm". Fred Weick is a bit beyond worrying whether or not YOU cut him "slack". ROFLOL!
One more thing, to cut Fred some slack, most early planes came from the factory with wooden props. Wooden props are notoriously free from vibration concerns.
John Cooper, A&P
Skyport Services
Enjoy "your" forum John. No one else stands a chance in a popularity contest with the owner of Skyport, and it appears that's what this forum has become. My apologies for irritating those of short attention spans with all these (final) facts.
William R. Bayne
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