As visible in the following picture

C-2A Greyhound

the left inboard stabilizer doesn't have a rudder but the right one does.

Wikipedia on the C-2 describes it as:

The C-2 has four vertical stabilizers, of which three are fitted with rudders. A single vertical stabilizer large enough for adequate directional control would have made the aircraft too tall to fit on an aircraft carrier hangar deck. The four-stabilizer configuration has the advantage of placing the outboard rudder surfaces directly in line with the propeller wash, providing effective yaw control down to low airspeeds, such as during takeoff and landing. The inner-left stabilizer lacks a rudder, and has been called the "executive tail", as it has nothing to do compared to the other three.

The rationale explains the primary design, but no explanation for the "executive" tail. Can anyone explain why the C-2 is designed this way?

  • 2
    $\begingroup$ What side is the critical engine on? $\endgroup$ – Ron Beyer Jan 17 '18 at 2:27
  • $\begingroup$ Port side engine (#1) is the critical engine. $\endgroup$ – Scooter Jan 17 '18 at 2:31
  • $\begingroup$ If I have to guess, that one has a fixed angle to counter act the engines. $\endgroup$ – user3528438 Jan 17 '18 at 2:41
  • $\begingroup$ I'm guessing that this is to maintain directional control when the critical engine fails. With the critical engine running, not as much directional control is needed on that side. I can't find anything to support my theory though. $\endgroup$ – Ron Beyer Jan 17 '18 at 16:44
  • $\begingroup$ @ymb1 So the issue was 2 rudders are insufficient, but under what conditions? If it is limited to critical engine out, Ron Beyer may have a valid argument. Otherwise it may just be a cost/weight/efficiency decision, adding just the one additional rudder is the cheapest, lightest, and least complex solution. The critical engine may just drive which side it's on. $\endgroup$ – Gerry Jan 17 '18 at 17:55

The C-2 was developed from the E-2 Hawkeye (the one with the big radome).

The radome disrupts the airflow behind, hence the need for the inboard fins (source), they help stabilize the airflow and act as fences for the outboard fins.

Those inboard fins were not needed for the streamlined radome of the earlier E-1 (shown below).

enter image description here

Alternatively they could have extended the fuselage length, but they didn't go that way. The three rudders provide sufficient control in single engine operation, yet are overpowering when both engines are working, which caused early control problems and stability augmentation had to be implemented (source: University of Tennessee, MS thesis, 2002).

The E-2 and C-2 feature rudder authority limiter as part of that augmentation (C-2A flight manual).

And apparently the rudder authority is sufficient enough that the E-2 can turn (to remain in orbit) while keeping the radome fairly level (source).

As to why the right one is the one with the rudder, I don't know. The engines are not handed (video). But as far as I know, a normal force on a laterally placed fin does not change the moment arm around the yaw axis, but I'm happy to be corrected.

Development information on the E-2/C-2 is scarce, so I hope that's sufficient for the time being, I tried to find as good sources as possible.

  • 1
    $\begingroup$ Yaw moment in proportion to the lateral displacement of the rudder will result from drag induced by the operation of the rudder. Presumably less of a factor here, with the rudder far aft of the CG, than on something like a Long EZ. $\endgroup$ – Erin Anne Jan 18 '18 at 6:23
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    $\begingroup$ Good research. I agree info is sparse. My primary question was more about the 'why 3 rudders?' more than 'why is the 3rd rudder on the right?' but I think the clues are in the thesis you linked. It comes down to the combination of P-factor and the tunneling effect of the E-2 dome which would create a greater slipstream over the right inboard rudder. This was important to get the lateral control at low air speeds. $\endgroup$ – Gerry Jan 18 '18 at 14:16

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