CG and baggage compartment

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Hartmut wrote:

I am by no means a specialist in approval procedures.

But I understand that original parts do not need approval , since the plane was licensed that way.

A logbook entry would be sufficient here. If you think about using parts from a Forney , that was using the flat shelf, then it is for the officials, similar to using parts from a Cessna, or a Harley - NOT APPROVED! And in need of a 337 at least.

So who ever that idiot was, that was cutting out those windows needs to be spanked first and then you might think about a way to live with the approved baggage compartment.

The tilting hat shelf was in there with a reason.

It disallows storage of items further aft CG than the canvas bag does.

The CG calculations of a Stock coupe allow to neglect any further CG calculations for flight when the empty CG of the plane falls into  a certain range.

Clearly spoken, as long as you do not overload the Coupe, you can not load it out of the proper CG range for flight.  The canvas bag is close enough to the CG that even loaded up to the allowed maximum will not bring the CG out of range.

This is another safety feature of the Coupe.  The large baggage compartment zeros all these thoughts of course and theoretically, ones you have it, you should calculate W&B before any flight. And a flat hat shelf should have a similar effect. Of course you could label it with a sign. No load here or so.

Bill Bayne responded:

With regard to luggage C.G., what you say is true for an Ercoupe with a wooden prop. BUT, there aren't many around.

A McCauley metal prop places 11 additional lbs. at the farthest forward moment (-32), which gives a measure of flexibility.  Those who choose to lug around a 35 amp battery add 5.3-8 lbs. at +55 (or so) which cancels this out ;<)

Let's look at this loading subject a little more thoroughly.

The 415-C "canvas bag" does concentrate baggage at +57. The (calculated) C.G. range of +26.4 to 30.3 remains the same for all models up to and including the M10 Cadet. The M10 allows up to 90 lbs. in its "large" baggage compartment, and the center of that load is still presumed located (by the pilot) at the same +57 arm. (no loose bowling balls in back ;<)

Ercoupe Models 415-C and CD dispense with the necessity to calculate C.G. when the "Empty wt. C.G. is between 25.2" and 26.6" with 40 lbs. baggage, and between 25.2" and 25.8" with the maximum 65 lbs. baggage and gross wt. of 1260 lbs.

For the 415-D, "Empty wt. C.G. is between 26.2" and 27.2" with the maximum 65 lbs. baggage, gross wt. of 1400 lbs., and 9 "up" elevator. For the 415-E, "Empty wt. C.G. is between 25.7" and 26.9" with the maximum 65 lbs. baggage, gross wt. of 1400 lbs., and 20 "up" (split) elevator.

For the 415-G, "Empty wt. C.G. is between 25.9 and 26.7" with the maximum 75 lbs. on "Kiddy Seat", gross wt. of 1400 lbs., and 20 "up" (split) elevator. Forney Models F-1 and F-1A retain the same "Empty wt. C.G." values as the 415-G.

Neither Alon nor Mooney lists a "Empty wt. C.G. range", probably because of the greater loading options in their larger baggage compartments. At the forward limit the plane is less responsive and slower. At the rearward limit the plane is faster and more responsive, but still stable and safe. The various STCs issued for large baggage compartments in Ercoupes are obviously the very sort of "non-standard arrangements" that nullify "Empty wt. C.G." ranges for each model.

Exceed these limits enough and the plane can become uncontrollable, as perhaps with two unsecured bowling balls in a "large" baggage compartment rotating rapidly upon liftoff. So, even an Ercoupe can not be considered "foolproof" in the hands of a genuinely determined fool.

I once calculated how much the C.G. varied from takeoff to landing at full gross starting with full fuel and landing with 1/2 hr. reserve, two occupants who each ate a sandwich with a soda, and burning a quart of oil. It's a real tribute to Fred Weick how very little the Ercoupe's C.G. changes without any action required on the part of pilot or passenger.