Why Buy a Coupe?….part one

By Ed Burkhead                                                        Return to www.planesgalore.com

(copyrighted, used by permission)  Part one 

This article was originally prepared in response to letters from prospective Coupe buyers who wanted to know the safety history, problems to look for, model information and everything else in which a prospective buyer would be interested.  It does not try to be a complete source, though.

See Stanley Thomas’ excellent book The Ercoupe. See the Recommendations/Books tags at the left of the page for availability information.  You can also search for the Ercoupe on the used market from several sources.  In addition, the Univair book Specification, A.D. notes, S.T.C.s, (Univair product number ESS, $17.00) is a critical reference book that every Coupe owner or would-be owner should have.

Strong Recommendation

Over the years, I’ve seen several new Coupers buy planes with major problems.  A pre-purchase inspection would have prevented financial catastrophe for most of these people.  Several years ago, with good advisors, I made a pre-purchase inspection checklist to make a try at preventing these problems.  I’d personally urge buyers to take this list to your own mechanic and talk over what you want to do during your own pre-purchase inspection.  Personally, I wouldn’t buy any plane without it.  I’m donating this to the public section to assist all potential Coupers.  It was written as a service to the club, however, and I urge you to join and stay a member of the EOC – the EOC is our mutual assistance society and we need you.

Quick history

This plane is a member of the family of planes known as the Ercoupe or Aircoupe.  The Ercoupe was designed between 1936 and 1940, with the first flight of the prototype in 1937.  Before WW2, 112 were built and approximately 5,000 were made immediately after the war.   About 400 more were built between 1958 and 1969.  The original name was derived from the name of the company, ERCO, which stood for Engineering and Research Corporation.  When later companies manufactured the plane, it was called the Aircoupe.

Designed by Fred Weick and a small team, the Ercoupe was the first plane to incorporate much of the original research that Weick performed as the assistant chief of the NACA aerodynamics division.  These new features include the inability to be held in a spin, the tricycle landing gear to improve landing and take-off safety, the fully cowled engine, and a control system in which the rudders are linked to the ailerons to simplify controlling the airplane.  All these features were invented by Fred Weick and his team.

Basic flying characteristics are the same as modern aircraft with one exception.  In the Ercoupes with linked rudders/ailerons, in a cross-wind, the airplane is landed in a wing-level crab.  Though the main landing gear is sturdy, it is not abnormally strong and certainly doesn’t “swivel.” Yet, due to the natural geometry of a tricycle with a swiveling nose wheel, the airplane immediately lines up with the direction of travel after touchdown.  Two-control Ercoupes fly with a demonstrated cross-wind component of 25 mph.  Some Coupers regularly fly with even stronger cross-winds.

Engine comparison

The planes with 75 hp engines have pretty good performance.  They will generally fly between 98 and 106 miles an hour, depending on the pitch of the propeller.  This is a good benefit of the airplane’s designer being the time-period’s leading authority on propellers.

When comparing the following figures with your own plane (or the one you are about to buy) consider these factors:  The propeller pitch will greatly affect the cruise speed and climb performance.  For every inch of steeper pitch, there will be about two miles per hour gain in speed until you reach the point (very quickly) when the engine doesn’t have the horsepower to spin the prop up to speed.  As speed increases, horsepower required increases almost linearly until a certain speed is reached where much more power is required to effect each new increment in speed.  The speed at which this occurs depends on the shape of the object being pushed through the fluid, in this case, the airframe through the air.

At some point a steeper pitched prop will result in less thrust than would be obtained with a flatter pitched propeller.  Probably before this point is reached, the climb performance will be non-existent – climbing is done at slower speeds where the steeper pitched prop is even more inefficient!

Ercoupes with the 85 hp engines get better take-off and climb performance, and will cruise a bit faster, and will use a little bit more fuel than 75 hp planes.  But there’s not a lot of difference.  Cruising speeds with the 85 hp engine range from 104-112 mph.

Most of the 85 hp engines in service in C and D models have been converted from 75 hp engines.  This was done (as allowed in type certificate A-787 note4) per Continental Service Bulletin M47-16 dated June 7, 1948.  Mostly, this requires changing the carburetor fuel jet to allow more fuel flow, remarking the oil dip-stick to show 4.5 quarts as full, adding a couple of engine baffles to take care of increased heat production, and changing the propeller so it conforms to the requirements of the new engine.  The details are in the Ercoupe’s Aircraft Specification A-787 and the other documents mentioned.

There is some performance gain – about 2-3 mph according to Paul Prentice’s book Fly-About-Adventures and the Ercoupe.

The Forney Aircoupes have the C-90 engine with a well matched propeller.  They always out climb my C-85 which has a climb propeller and they have to throttle back quite a bit for me to stay with them in cruise.  Cruising speeds probably run from about 106-114 mph (again according to Paul).  The Alon Aircoupes, with their sleek bubble windshield and 90 hp engine often claim cruising speeds up to 124 mph.

With the 0-200 engine, climb improves again, but cruising speeds drop down because of the propeller that was STCed with the engine conversion.  In the absence of definitive data, estimate cruising speeds to be about 108 mph.  Someone who’d like to research alternate propeller lengths and pitches (and fight with the FAA for approval) may be able to trade some of that climb for somewhat better cruising performance.

Remember that, for each airframe, there is a natural “maximum” speed determined by the shape and drag.  To get to that speed, it doesn’t take much increase in power.  To go faster than that speed, it takes a lot more power.  So, putting a much bigger engine on a plane will make it climb much better and yet it may not fly much faster.

Thanks to Ed Burkhead for this informative article.    You can read more from Ed at http://edburkhead.com/ercoupe/index.htm

Watch for part two of Why Buy a Coupe?… coming soon.

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