I've always been intrigued by the M10 Cadet, as it's seemed an accessible, fairly-affordable way to fly, with the pleasures of an open canopy and sociable side-by-side seating, and presumably better-than-Ercoupe flying characteristics due to Alon & Mooney mods. But after researching Ercoupes for an article I wrote years ago, and discovering the shocking truth about their actual fatality rates, any Ercoupe-derivative looks suspicious.
As memory serves (sometimes poorly), the M10 had some key differences from the original Ercoupe:
1.) Stallable/spinnable (the Ercoupe -- despite false advertising -- was, too; just not nearly as readily). This M10 "advance" was done, IIRC, by adding stall strips to the leading edges of the wings, and a more powerful (and different) horizontal tail, allowing more downforce, and thus higher angles of attack.
2.) Engine: the C-90 of the Alon version, vs. the orig. 75-hp of the Ercoupe 415C
3.) Vertical tail: The Mooney-style single vertical tail.
4.) Rudder pedals (though most Alons and many late Ercoupes had them, already)
5.) A nicer panel (derived from the Beech-related Alon?) somewhat akin to the Beech Musketeer.
6.) Different main gear: Spring-steel torsion bars in place of the Ercoupe's trailing-link mains.
While the various "improvements" made significant changes, serious problems remained:
A.) The Ercoupe wing. Very poor glide performance, given the weight and drag of the aircraft. Reflecting the 'Coupe's brick-like glide path, An NTSB report, comparing various light planes, showed 'Coupes to be THE worst in undershoot accidents of the 33 aircraft models in common use then -- double or triple that of such notorious sinkers as Grumman's Yankee and Piper's TriPacer -- and quadruple that of other noted sinkers by Piper (Cherokee) and Grumman (AA-5).
B.) Fuel tank - I can't recall if it was in a header tank (obviously dangerous in a crash) or the leading edges of the wings (also quite dangerous in a crash). Hopefully I'm wrong on both counts, and the M10 had conventional wing tanks behind the spar, but I doubt it.
C.) Shock absorption: Unlike contemporary Cessna's, for instance, there was little "crush space" under the Ercoupe pilot's butt to absorb otherwise-fatal impacts in minor/moderate crashes. Note that this is also a distinguishing fault of Piper Cherokees, when compared to Cessna 150/152/172/182. and the fatal crash rates strongly reflect the difference. Add in the rock-hard seat of the M10, and you'd better not smack it in, if you don't want your spine jammed into your brain.
It's very important to note that the M10 was based on the Ercoupe, which -- despite blatantly false advertising, and resulting popular myth -- was NOT a safe airplane by any stretch of the imagination, with a FATAL crash rate MUCH higher than, say, the more conventional, leading competitor of the period, the Cessna 120/140. (NEVER confuse "easy-to-fly" with "SAFE-to-fly".)
Flying Magazine's safety-issues editor, as I recall, once described it as having one of the worst fatal rates of any modern aircraft, per seat-mile. The NTSB's accident study of 33 most commonly used light plane families of the 1970s backed that up, with 'Coupes showing shockingly bad crash rates due to causes they should have been immune to, including stall/spin accidents (50% worse than traditional Mooneys!) and ground loops (worse than Cubs!) -- and a FATAL crash rate 2/3rds higher than regular M20-series planes.
See: https://close1d2.org/wp-content/uploads/2017/11/BewareTheSafeAirplane.pdf
...and Tables 3 and 11 in NTSB report at:
https://libraryonline.erau.edu/online-full-text/ntsb/aviation-special-studies/AAS79-01.pdf
Consequently -- as the courts, in the 1970s, began to more strictly apply crash liability to manufacturers of planes with design defects -- the M10 and its crash rate (which I have NOT yet separately researched), or its long-term expected crash rate, may have made it essential for Mooney to discontinue the model.
That may also help to explain why -- unlike the Champ, Cub, SuperCub, and Luscombe (none of which have good safety records, either, but are popular sporty taildraggers) -- nobody has revived or imitated the Ercoupe since the M10.
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