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I'm a student pilot at a flight school that primarily flies RV-12s as a trainer. We had one day that through a booking error meant that all the RV-12s were booked so we had to use their Ercoupe 415-C instead.

I was surprised at how easy the plane was to fly and asked my CFI about the "characteristically incapable of spinning" placard on the front panel. He explained that the rudder pedals weren't necessary because the plane maintains coordinated flight by connecting the ailerons to the rear rudder.

I think this is an amazing innovation for the Ercoupe and I'm surprised it's not a design that I can find on any modern small aircraft designs.

Maintaining coordinated flight with rudder pedals isn't a complicated task for a trained pilot but it is another task that the pilot needs to perform. It seems like removing flight tasks from the pilot would make for a safer aircraft so why do manufacturers not include designs similar to Ercoupe's models?

Is it a weight/cost/drag issue, or are spins not as huge of a killer as they were in the 40s-60s?

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    $\begingroup$ Because taking away the rudder pedals harms pilots' fragile egos. And as long as you have rudder pedals, you might as well have a spin-prone aircraft. That's good for pilots' egos as well. $\endgroup$ – quiet flyer Feb 13 at 20:40
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    $\begingroup$ Depending on speed, you need different ratios of aileron and rudder for coordinated flight. If you always fly at the same speed, coupling both is fine. However, you will not be able to sideslip into a tight field. And slipping is fun! $\endgroup$ – Peter Kämpf Feb 15 at 21:11
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    $\begingroup$ With regard to the portion of your question about modern small airplanes, Cirrus aircraft feature a rudder-aileron half-interconnect. Applying rudder will move the ailerons, but applying aileron will not move the rudder. And yes, the interconnect can be easily overridden with muscle for crosswind landings. $\endgroup$ – Steve V. Feb 17 at 4:33
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The coupling between the ailerons and rudder are designed such that they avoid uncoordinated turns as you described. However, this occurred at the expense of control in other flight conditions.

In fact, there are situations where you need to deflect the rudder without roll input, you need to deflect the rudder more than the preset coupling, or in a manner that is opposite to the preset configuration.

For example, if you turn right, the system will add right rudder to keep the airplane coordinated. But if you want to do a forward slip, you may perform a left hand roll, but with rudder all the way to the right. The system would be incapable of performing this maneuver, meaning you can't fly in high winds with the system installed. This is fine if you live in an imaginary place where the winds are always favourable.

As a result, a common modification on the Ercoupe is to disconnect the coupling between the rudder and ailerons...

Edit: I also wanted to add that spins are recoverable, within reason, by a trained pilot. For some planes, you are simply forbidden to intentionally enter a spin as a remedy to its inability to recover from a spin!

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    $\begingroup$ Very interesting! It makes sense that you couldn't do a slip landing in an Ercoupe. That is certainly a downside. $\endgroup$ – Burke9077 Feb 13 at 22:34
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    $\begingroup$ Also, one of the things most student pilots learn is how to avoid a stall or spin, unless you're practicing them. $\endgroup$ – jamesqf Feb 14 at 3:01
  • $\begingroup$ Sounds like you want pedals that offset/trim what the automatic system would do. $\endgroup$ – J.J Feb 15 at 12:11
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    $\begingroup$ "Inability to recover from a spin"? I was thinking that the FAA regulations require at least all civilian airplanes to be able to recover from a spin using the "standard" method? $\endgroup$ – Martin Rosenau Feb 16 at 9:18
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    $\begingroup$ Hey @Burke9077, having a twin tail can have bring benefits when it comes to aerodynamics and redundancy for a given aircraft, and is usually done to get a reduced footprint (height) for storage. I am not sure what the design priority was for the Ercoupe, perhaps that is another question to ask! Take a look at this thread: aviation.stackexchange.com/questions/35871/… $\endgroup$ – Gerry Feb 18 at 20:33
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Rudder pedals are used for more than keeping turns coordinated. Forward slips for crosswind landings, slips to increase drag during descents, and reducing the tendency to weather-vane during cross-wind taxiing are examples.

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The ercoupe was an advanced design for its time, but it represented a bunch of compromises and the inability to do a forward slip was one of them. The plane's designer made up for this by choosing the airfoil so the plane would descend steeply enough with power off so the pilot wouldn't have to bleed off altitude if he was high on final, and by making the landing gear stout enough to manage landing while severely crabbed.

Another compromise was the omission of flaps; this was to simplify both flight operation and maintenance but required an airfoil that yielded a flap-like descent with power off (as mentioned above) which is why the ercoupe glides like a brick.

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    $\begingroup$ It doesn't glide any worse than its contemporaries. The procedure for losing altitude on final was to S turn. $\endgroup$ – John K Feb 14 at 4:23
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    $\begingroup$ handbook value for 65HP Piper J-3 is 10:1, 6:1 for the ercoupe... $\endgroup$ – niels nielsen Feb 14 at 6:17
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    $\begingroup$ Yeah but lots of contemporaries, biplanes, the short wing Pipers, also glide like bricks and you still have to side slip them from time to time, and if you had interconnected controls, you'd be left with S turns. 6:1 or 10:1 L/D is neither here nor there. $\endgroup$ – John K Feb 14 at 14:17
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The usual way to make a plane 'spin proof' is to ensure the centre of the wing (near the fuselage) stalls before the tips, and to move the Centre of Gravity far enough forward that the elevator doesn't have the power to keep the nose up below stall speed.

The first is commonly done by twisting the wing tips up at the trailing edge, reducing their angle of attack relative to the rest of the wing. It could also be achieved with a change of aerofoil section, or turbulators.

Both of these cause drag and reduce efficiency, and the second limits your ability to flare for landing. I imagine those were sufficient reasons for designers not to 'stall proof' their designs.

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