To: (Separate email addresses with commas)
From: (Your email address)
Message: (Optional)
Send
Cancel

Thanks!

Close

Why The Stabilator On Your Cherokee Was The Secret To The F-86's Success

If you've flown any of the Piper Cherokee line of aircraft, you've noticed that their tail is different from most light aircraft. Instead of a horizontal stabilizer with a trailing elevator, Cherokees have an all-movable "stabilator."


Mark / Flickr

Piper Cherokee

cclark395 / Flickr

MiG-15 And Early Model F-86 (With Elevator) In Formation

Jay Swindle & Rain0975 / Flickr

Late Model F-86 Tail Showing A Stabilator

If you look at high-speed aircraft, like an F-15, you'll notice that they almost always have a stabilator - but why?

The answer stems from an elevator's effectiveness at transonic speeds. It's also the reason that the F-86E Sabre had an edge over the more powerful MiG-15.

It All Comes Down To Pressure

The traditional elevator sits on the trailing edge of a horizontal stabilizer. Normally, moving the elevator generates a pressure change which moves forward to cover the entire horizontal stabilizer. This generates a large force, allowing the tail to stabilize and control the aircraft's pitch.

The pressure change generated by the elevator moves forward at the speed of sound. At transonic and supersonic speeds, airflow over your tail moves faster than the speed of sound. That supersonic flow prevents the elevator's pressure change from moving forward and affecting the entire tail. In fact, the pressure waves form a shock wave at the elevator's hinge, and the only pressure change exists directly over the elevator itself. Your elevator essentially became a lot smaller - and less effective.


The Stabilator - More Effective At High Speeds

A stabilator moves as one piece, so pressure changes occur over the entire surface - even at supersonic speeds. Plus, you've eliminated the shock wave at the elevator hinge point, which significantly reduces drag.

By moving the entire stabilizer surface, you've increased controllability and decreased drag at high speeds.

The Drawback - No Control Feedback

Like everything in aviation, there is a drawback to a stabilator. Since the entire surface moves as a single unit and rotates around its aerodynamic center, there's very little control pressure acting against the pilot - the elevator moves without any resistance. Without a fly-by-wire system, this makes the elevator extremely touchy and difficult to control.

Mark / Flickr

You can create control feedback by adding an anti-servo tab to the rear of the stabilator. An anti-servo tab moves in the same the direction of the control surface - but it deflects even more. So, if you move the stabilator's trailing edge up, the anti-servo tab sticks up even further. Air flowing over the surface pushes back against you, adding control feel.

But Why Are They On Light Aircraft?

Why put a stabilator on a light aircraft? Piper wasn't concerned with supersonic airflow when designing the Cherokee's tail. A stabilator generates a large pitching moment without a lot of control force. They're a great alternative when an elevator would be too hard for a pilot to easily move. And, by adding a small anti-servo tab to the stabilator's trailing edge, you'll have just enough feedback to stay controllable.

Aleks Udris

Aleks is a Boldmethod co-founder and technical director. He's worked in safety and operations in the airline industry, and was a flight instructor and course manager for the University of North Dakota. You can reach him at aleks@boldmethod.com.

Images Courtesy:

Recommended Stories

Latest Stories

    Load More
    Share on Facebook Share on Twitter Share via Email