Good morning, John ERCO did NOT "require the trim tab when installing the C-85". They first "installed" the C-85 in production airframes with the 415-E Model. The change to a separate trim tab had long been applied to all production Ercoupes after Serial No. 1622.
It was introduced, per Ercoupe Service Memorandum No. 19, because the relatively high tension required to trim the aircraft in cruise tended to restrict the elevator in reaching its intended maximum "up" movement of twelve to fourteen degrees. Specific pilot objections are set forth in paragraph 3 therein. The wider trim tab installed on the 415-D was likely intended to improve elevator efficiency since the CAA, in its infinite wisdom had restricted ERCO to a maximum "up" movement of approximately 9 degrees. This wider tab was then carried forward through 415-CD Model production because that model was nothing but 415-D airframes already rolling off the production line "re-rated" for the 1260 lb. gross weight of the 415-C under the original Aircraft Specification 718. Since all of these models came out of the factory with 75 hp, none of these modifications had anything relationship whatsoever to installation of the C-85 or the illusion of an additional ten more horsepower. It is also interesting to note that ATC 718 does not contain trim tab "up-down" information in the "Control surface movements" section, probably because such had no application to the first 1622 Ercoupes. There is no rational explanation as to why this information has not been added to one of the many later revisions of ATC 718, particularly since it is very conspicuously present for every model listed in ATC 787. If safety of flight or good engineering practice require it in Type Certificate, why not the other? When ERCO "installed" the C-85 in the 415-E Model, again it was NOT ERCO that "required" the additional cooling baffles around the oil tank, but the CAA. Apparently flight tests were not entirely satisfactory in terms of cooling (presumably at maximum angle of climb) with the split elevator. So, ERCO enjoyed increased revenue flow from the CAA mandate of extra cooling baffles for the C-85 in ATC 787 Ercoupes. Owners of earlier Ercoupes desirous of improved "feel" of elevator operation discussed at length in Ercoupe Service Memorandum No. 19 were forced by ERCO "policy" to replace perfectly servicable elevators lacking trim tabs with new ones incorporating a recessed articulated trim tab. This also increased ERCO's revenue flow. Selling an increased volume of parts already in production under such CAA mandates was clearly a "high profit margin" bonus for ERCO for which private owners had to foot the bill. The desire to own the "latest and greatest" is a human weakness exploited by manufacturers again and again to this very day for increased profit. It thus made no sense at all for ERCO to "go to bat" on behalf of owners on issues that would predictably reduce ERCO's revenue stream from the sale of related parts. Regards, William R. Bayne . |-(o)-| . (Copyright 2010) -- On Aug 30, 2010, at 06:04, John Cooper wrote: > On 8/30/2010 1:29 AM, William R. Bayne wrote: >> It is sometimes necessary to dig further into apparently "simple >> truths" to reach maximum enlightenment > OK, then why did Erco require the trim tab when installing the C-85 if > it is not necessary? For that matter, why did they introduce it at > all? > > -- > John Cooper > Skyport East > www.skyportservices.net > >
