Copyright ©2011 by Paul Niquette. All rights reserved.

Reminiscence Alert: Sharing technical features of flight with a first-timer in the cockpit provides great entertainment for every old-time pilot.  Excuse me for dropping into the first person singular here, but I especially enjoy giving elementary demonstrations aloft.  I always begin in straight and level flight, exulting about the cockpit's distinguished view of the world.  I gesture at the control wheel and gently pull back, raising the nose and making the passenger in the seat beside me feel momentarily heavier.  Pushing forward results in wide-eyed weightlessness.  Next, I bank the plane with the control wheel left and right; no surprises there.  Finally, I point at the rudder pedals on the floor and demonstrate left and right skids

“Go ahead, try it yourself,” I say with a smirk.  I ceremonially withdraw my hands from wheel and my feet from the pedals.

Parenthesis.  The first thing first-timers observe is that the flight controls seem to be interconnected in crazy ways.  Whereas the plane responds to the control wheel with banking as expected, at the same time, there is a surprising effect called adverse yaw.  It’s as if an invisible foot has mischievously trounced a rudder pedal.  Likewise for the rudder itself, which does indeed cause the plane to yaw as expected, but at the same time, the plane wants to bank the wrong way. 
Of course, during my little flight demonstrations, I cheat.  I deliberately coordinate aileron and rudder control pressures, concealing these strange doings in the sky and setting the stage for surprises for -- and discoveries by -- the hapless first-timer.

Pertinent to the question in the puzzle is the plane's counter-intuitive response to the rudder.  When one applies pressure on either pedal – the one on the right, say –  the rudder itself is moved toward the right, which makes the tail of the aircraft swing left, such that the nose yaws to the right as intended.  Are we on the same page here?  Meanwhile, without corrective action by the pilot, the aircraft incongruously banks toward the left.  Hey, and what if there is no pilot to do the corrective action?  Excuse me but I am getting ahead of my story.

The explanation is elementary: The conventional empennage is built upside down!  (Exclamatory punctuation merely signifies an astonishing assertion.) The rudder stands upright on top of the fuselage.  It should hang below the fuselage, where it would induce rolling motion consistent with yawing.  By the way, on the planes that have them, V-Tails  are likewise mounted atop the fuselage, where they can produce the same anomaly.

Except on the Predator.

Take a close look at the Predator's wings.  They are glider-like, slender and long.  High aspect ratio, it's called.  Great for efficient, long endurance flight, which is what the Predator is designed to do.  You will see a slightly curved camber line as well, which assures adequate lift at low speed.

What you do not see are ailerons! (Exclamatory punctuation merely signifies an astonishing observation.) 

Apparently with its underslung empennage, the Predator does not need draggy old ailerons near the wintips flapping up and down for routine coordination of turns.  The inverted V-Tail all by itself will naturally manage turns in both roll and yaw.  Orville and Wilbur would have admired that kind of systems integration, since it facilitates an exceptionally simple design for the Predator’s wings.  Lighter weight, too. 

With neither bladder nor bowels onboard to limit time aloft, our solution can be...
Sans ailerons, the Predator's wings have more room to hold fuel.
...which suggests a new, emphatic definition for the expression wet wing, plus...
Given les porte-manteaux for V-Tail's ruddervator (rudder+elevator) and for the delta-wing's elevon (elevator+aileron), our explanation for the Predator's inverted V-Tail appears to warrant a tripartite neologism: rudderlatoron (rudder+elevator+aileron).

Almost forgot, here is the response to my query...

We appreciate your interest in our aircraft, but the information you are seeking is not for public disclosure.

Kimberly Kasitz
Public Relations & Communications Manager
General Atomics Aeronautical Systems, Inc.

Reaper and Avenger

Not all models of UAVs built by General Atomics Aeronautical Systems feature the inverted V-Tail.  As can be seen in photographs of the Reaper and the Avenger, their ruddervators resemble butterfly-wings placed atop the fuselage.  Solvers will see something else, too: ailerons!  (Exclamatory punctuation merely signifies an apparent affirmation of our solution.) 

Both the Reaper and the Avenger are larger, heavier, and complexer than the Predator.  Their respective empennages feature separately hinged control surfaces.  Nota bene, the Reaper has an underslung rudder, but the Avenger does not.  For good reason.  One version is called the Sea Avenger, and it is designed to operate from an aircraft carrier. Tailhook, anybody?

Which reminds me: How does the Predator take-off and land with only 5.3 degrees of ground clearance?  First Principles coerce us to assume that for taking off fully loaded, the Predator must be given a long paved runway -- surely at least a couple thousand feet.  For landing with nobody on board, the Predator is apparently designed to be mashed onto the ground with essentially no flare, much like a wheel landing in a tail-dragger.

Epilog: Design Criteria for Unmanned Aircraft Systems
From: Paul Niquette 
Sent: Sunday, November 06, 2011 9:09 AM
To: 'Kasitz, Kimberly'
Subject: RE: Empennage of the MQ-1B Predator

Dear Kimberly Kasitz,

Relevant to your Tuesday, October 18, 2011 5:05 PM reply to my Monday, October 17, 2011 1:28 PM query, you will find a reference to an exceptionally pertinent Engineering Technical Letter (ETL 09-01)  dated 28 SEP 2009 published by Department of the Air Force Headquarters, Air Force Civil Engineering Support Agency, which is "APPROVED FOR PUBLIC RELEASE: DISTRIBUTION UNLIMITED." 

That document has been excerpted for an Epilog published in the Solution to the V-Tail entry at Puzzles in the Skies.  Moreover, in the next week or so, I shall be collaborating with others at…


…and technical explanations by AAS experts about the Predator’s ‘inverted V-tail’ would make welcome inclusions for the article. 

Best regards,
Paul Niquette

Solvers will find in ETL 09-01 more technical information than most people might ever want to know about the Predator, with its inverted V-Tail, along with confirmation of our obervations about other UAVs with upright V-tails (Fire Scout, Global Hawk, Reaper, Shadow, Warrior). 

Detailed technical specifications in the document for the Predator include (emphasis added)...

Wing Span ................... 48.7 ft
Length ......................... 27.0 ft
Height ............................ 6.9 ft
Vertical Clearance ........... 5.3 in
Tread ............................. 9.1ft
Wheel Base .................. 10.2 ft
Controlling Gear .............Main
Ground Turn  (180° ) .... 196 ft
Basic Empty Gross Weight ............... 1,680 lbs
Basic Mission Take-Off Weight ........ 2,250 lbs
Take-Off Distance, Ground Roll .... 1,800 ft
Take-Off Distance, to 50-ft ............ 2,500 ft
Landing Distance, Ground Roll ..... 1,150 ft
Landing Distance, from 50-ft ......... 1,700 ft
Gross Load of Assembly on Main ........ 90%
Tire Pressure, Nose Gear .................. 45±2 psig

...which seem to support our horseback estimate "for taking off fully loaded, the Predator must be given a long paved runway -- surely at least a couple thousand feet." 

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