Money in the Bank

February 18, 2009 by Tim McAdams

When I tell people that I fly helicopters the comment that I hear a lot is, “Isn’t that dangerous? If something happens to the engine you can’t glide like an airplane.” Well, I explain that is not true, helicopters do glide, it’s called autorotation. Without going into too much detail about the aerodynamics, I describe how it works with the concept of stored energy.

For discussion purposes, a helicopter on the ramp switched Off contains zero energy. However, when a pilot starts the engine, the fuel is converted to energy that is used to start spinning the rotor system. The rotor rpm is brought up to 100 percent; the pilot then lifts off and begins accelerating and climbing. Once established at cruise altitude and airspeed, the helicopter has two kinds of stored energy—Potential energy (energy because of position) in altitude, and kinetic energy (energy do to motion) in airspeed and rotor rpm. Essentially, this is money in the bank to be used in an emergency. It is the successful manipulation of this energy that will bring the helicopter and its occupants to a safe landing during a loss of power.

When a helicopter’s engine stops in flight, a freewheeling unit disconnects the engine from the rotor system to prevent the engine drag from slowing the rotor rpm. In addition, the pilot must immediately lower the collective pitch allowing the helicopter to start descending and forcing the airflow up through the rotor system. Basically, the helicopter begins consuming altitude energy to maintain rotor rpm. This is a very important step because waiting too long to lower the collective will allow drag to slow the rotor system and stall the blades. If this happens we destroy the helicopter’s ability to manipulate energy and it will simply fall out of the sky with fatal results.

Once established in autorotation the descent rate is normally 1,200 to 1,500 feet per minute and the pilot should maintain about 60 knots and maneuver the helicopter to the best landing area available. Approaching 50 to 75 feet agl, the pilot begins to rapidly decrease airspeed with a flare. Airspeed energy is used to arrest the descent rate. If timed correctly, the helicopter should momentarily end up about five feet above the ground with little to no airspeed. With all the altitude and airspeed energy gone, the only energy left is in the rotor system. The helicopter will start descending and the pilot should then raise the collective pitch control and use the rotor rpm energy for a gentle touchdown. As the rotor system slows to a stop the helicopter returns to a state of zero energy.

Of course all this assumes ideal conditions. We all know that in the real world it doesn’t always work that way. There are certain combinations of airspeed and altitude that simply do not have enough stored energy to make a safe landing. For example, hovering at 150 feet the pilot must rely mainly on rotor rpm to cushion the landing. The vast majority of helicopters do not have enough energy stored in the rotor system to completely stop the descent rate. Most likely the landing will damage the helicopter and injure its occupants. If a pilot is hovering higher, say 500 feet, there is enough altitude energy to trade for airspeed and complete a successful autorotation.

This explains why helicopter pilots prefer to take off by moving forward to gain airspeed first, instead of going straight up.

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14 Responses to “Money in the Bank”

  1. James E (Jim) Anderson Says:

    TIM, I AM THE GUY IN THE AOPA FLIGHT TRAINING MAG THAT SOLOED THE 300CB ON JULY 24 2008 AT THE AGE OF 70.5 YRS

    OF AGE. I AM FIXED WING W/13,000 + HOURS W/ATP MEL SEL SEA MEI CFII. I INTEND TO FINISH THE ADD-ON ROTORCRAFT

    RATING, HOPEFULLY THIS YEAR. IT’S JUST TAKING A LONG TIME BECAUSE OF THE EXPENSE AND TIME REQUIRED. I HAVE

    TWO A/C, A C-172 AND C-A152 THAT I USE FOR INSTRUCTING, ETC. I FLY OUT OF CEU (NEAR CLEMSON UNIV.). I JUST

    FINISHED A FIRC AND AM DUE A FLGHT PHYS NEXT MONTH. HOPE TO KEEP ON KEEPING ON FOR A FEW MORE YEARS.

    THANKS

    SKYKING1

  2. Cal Gray Says:

    I am only at about 500 hours and almost all of that in the R-22. I used to do a lot of low level photography work over water… and when I say low it was generally under 50′… always had that left hand ready to dump collective and flare it in.

    I just wanted to say that was a very well written and concise explanation of how we can “Glide” a helicopter. This is indeed the first question most people ask.

    I love that AOPA is finally showing the rotorcraft members a little more attention, it’s a fantastic organization and feels nice to be a little more a part of it.

    Cal Gray
    Annapolis, Maryland

  3. Gregory Beck Says:

    Tim,

    I’ll second the above thoughts about how nice it is to have more helicopter perspective coming from AOPA. As a 3 year member and helicopter pilot, I now like AOPA even more. It looks like your work will just add to the high-quality work they do. I look forward to more of your well written articles.

    Gregory Beck
    Paso Robles, CA

  4. Jacob Draisen Says:

    Tim,

    I’ll third the above thoughts about how nice it is to have more helicopter perspective coming from AOPA. I am a 4 year member, helicopter and fixed wing pilot. Please keep up the great quality articles.

    Jacob Draisen
    Marietta, GA

  5. Walter Fuller Says:

    Tim,
    I am really glad AOPA has finally added helicopter articles to the already fine magazine and you will add class and expertise to this section. I am a member that goes back to the begining who has fixed wing and helicopter rating.
    Buy the way I have a one of a Kind Jet Ranger that I fly for pleasure and enjoy very much. It has an all glass instrument panel by Sagem with autopilot and radar altimeter, a joy to fly for a youngster of 74.
    Keep up the good work.

    Walter Fuller
    Plano,TX

  6. Bill Kalivas Says:

    Tim,
    I have a question regarding icing in helicopters. Early in my training I was told that most helicopters could shed ice by the fact of the blades are spinning. After reading more general articles and the mention of helicopters needing anti-icing capabilities, I would
    like more information. I would appreciate some general guidelines in helicopters being flown into light, moderate, heavy icing conditons.

    Regards.

  7. Ernie Ehling Says:

    Tim,
    I too am happy to see articles on helicopters in AOPA. I obtained my private pilot airplane license back in 1983, and recently completed my instrument rating. In the late 1980’s I began training to add my helicopter rating. Initially I trained in an R22 and later flew Enstrom helicopters. I soloed the Enstrom and was well on my way to completing the rating when the helicopter operation I trained with had an unfortunate accident and closed (along with some of my pre-paid funds). I never completed the rating having run out of money and then entering law school. Now 20 years later I have a strong desire to complete my helicopter ratings. I remember my first autorotation in the Enstrom. As a fixed wing pilot used to generally mild descents following an engine failure, it definitely caught my full attention. I think the Enstrom is a great helicopter, and with three rotor blades there is a great deal of energy in the rotor system. This made auto’s much easier. I look forward to reading more of your articles.

    Ernie Ehling
    Freehold, New Jersey

  8. Terry Frost Says:

    just wanted to add my “BRAVO” to this article…I’ve been a member of APOA for over 25 years. I have about 30+ hours in fixed-wing but am strictly a rotorcraft pilot/CFI. Mostly doing commercial work part-time due to other career choice, and have about 500 hours. Learned to fly in the 80′s in a Bell 47 receiving my private certificate. Quit flying for 17 years and got back into it learning the R-22 and R-44 getting the commercial and then CFI…All that to say it’s great to see our new president (AOPA that is) at the Heli-Expo taking an interest in helicopters and AOPA finally appealing to us ‘Rotor Heads’

  9. Todd Dolihite Says:

    I have really enjoyed Tim McAdams articles and agree with the above comments. I fly both fixed wing and helicopters and am amazed to see how many helicopter pilots have had little exposure to AOPA. There is an untapped well of potential new members in the rotary world. We need as many voices as we can get to keep general aviation from being over regulated, over taxed, and under appreciated. Many thanks to Craig Fuller and his attendance at Heli-Expo as well as non-aviation events to spread the word about about G.A.

    Respectfully submitted,

    Todd Dolihite
    Maryland

  10. Slow Softball Says:

    Hey, is there a section just for latest news

  11. Tim McAdams Says:

    There is not a dedicated section; however, I am submitting helicopter news stories that will be included under “GA news” on the main page.

  12. kevin Says:

    I’m a rated fixed wing pilot and want to get a rotorcraft rating.

    Here’s my question. I run a small business but would like the opportunity to ferry helicopters or instruct part time. Do you guys think there are part time positions available for something like this?

    Become A Marine Pilot

  13. HRPufnstuf Says:

    I too am glad to see AOPA finally showing more attention to helicopters. I did a 20 minute intro flight in a Cessna, and was underwhelmed. However, one ride in a helicopter, and I said “I’ve got to do this!” Two years later, I have my Private certificate, rotorcraft only. But I’ve been an AOPA member from the start, and they helped me considerably dealing with Oklahoma City in getting my Medical Certificate (took a LONG time to get a waiver because of a heart condition). Thanks for all you do, AOPA. It’s sure been worth the cost of my membership.

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