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Understanding the H/V Curve: A Line Drive Analogy

Posted 7 years 275 days ago ago by Randy Rowles

The Height/Velocity Diagram indicates the combination of height above ground and air speed that should be avoided due to safety concerns related to emergency landings. For new helicopter pilots, the height-velocity (H/V) diagram can be confusing. From one Instructor to another, the understanding of the H/V diagram may differ, which will affect how the subject is taught. Even when referring to the FAA’s Helicopter Flying Handbook, the entire subject is covered in only two pages (FAA H-8083-21A Chapter 11 Pg. 11-8 & 11-9). 

Often during FAA examinations, applicants are unable to articulate the correct use of the H/V diagram and which flight profiles are relevant. Although the H/V diagram contains several sections, each with their own purpose and explanation, the intent of this article is limited to the H/V Curve or as it is also known…” The Deadman’s Curve”. In an effort to explain the H/V Curve, I will attempt to relate the topic in the form of a baseball analogy.

We’ve all seen it…the fastball pitch thrown with laser precision toward an awaiting catcher’s mitt. A steely-eyed batter cocked back with a piece of lumber crafted for the single purpose of connecting with a ball of cork, yarn, and cowhide. Crack! The perfect pitch met with the perfect swing. The ball is returned to the field with such force that no curve to the flight of the ball exists. It’s a line drive at the speed of a meteor sent directly back where it had originated: the pitcher’s mound. The pitcher, still leaning forward in the stretch has no time to react. A quick move of the glove in front of the body is the only hope of blocking this incoming white and red stitched missile.

In this scenario, the pitcher is living deep within the H/V Curve. No matter how long the pitcher held that position or experience gained through years of play, the only option is to ‘attempt’ to block from being hit by the ball. The physical limit of human reaction coupled with the time and opportunity of the situation leaves no other option for the player in this situation…other than luck!

The second baseman is the next position to receive the projectile, however this position has its own challenges when dealing with this situation. When covering second base, the player will position themselves toward first base in an attempt to close the gap that exists between the players of each respective base. Due to the second baseman’s distance from second base itself, the ability to react and get to this rapidly approaching ball will be determined by the individual player’s skill, agility, awareness, and reaction. In addition, the player’s physical stature may also have an affect. A taller player may be able to close the distance much faster than a shorter player.  

The second baseman lives on the fringe of the H/V Curve. In this area of the curve, an average pilot’s ability is considered. As an example, a helicopter pilot that practices autorotations daily may be able to perform a safe autorotation where a helicopter pilot that rarely practices this maneuver may not.

As the ball passes second base, the next position to engage the ball is center field.  The center fielder is there ready, waiting, and often running toward the ball. At the same time, scanning the field looking where the ball needs to be thrown. The center fielder is playing well outside of the H/V Curve. This fact provides the center fielder with a tremendous asset when dealing with such a difficult play…time! 

In this analogy, we see that the more [time] you have to deal with an autorotation provides for increased situational awareness, preparedness, and options. Your ability to react, stabilize, and navigate to a safe landing area depends on it.          

About Randy:
Randy Rowles has been a FAA pilot examiner for 20 years for all helicopter certificates and ratings. He holds a FAA Gold Seal Flight Instructor Certificate, NAFI Master Flight Instructor designation, and was the 2013 recipient of the HAI Flight Instructor of the Year Award.  Randy is currently  Director of Training at Epic Helicopters in Ft. Worth, Texas.