Helicopters or Airplanes--Let the games begin

[Jean Loup]

forgive for intruding...but, isn't WEAR what brakes more aircraft than pilots do

Yes, wear and tear account for roughly 60% of our unscheduled maintenance, however the other 40% is human error, both the maintainer's and pilot's.  Then again, I work in a weird little sideshow of aviation where we have airframes and rebuilt parts that have a ridiculous amount of hours put on them being used and abused by mechanics and pilots who just got certified.

As for autopilots, some do, but most just have a stability control system to counteract outside forces (wing gusts, etc) of varying degrees of complexity.  The simplest ones being a stabilization bar that uses the gyroscopic effects of weights spinning around and around to dampen oscillations.  More complex varieties use electronic and hydraulic systems to keep the helicopter pointed in the same direction at the same altitude, but the effect is more like a trim system than a true autopilot.

I hope the blades are new...I remember hely rotor blades had a life span of 40 flight hours...before "fatigue" hit them! Here in México, a french Puma (well...we know the french!) colapsed at touch down because blades disintegrated! Next to President's Fox Puma...
SkidKid, thanks for autopilot info! donyan 

[Chopper Doc]

There are heli's with auto pilots, as well as the SCAS equipped types as described by SkidKid.

SCAS machines (like the Bell 214S) use a flight control system to stabilize the machine, the pilot's job being to unstabilize it.  In the 214 the SCAS cannot be turned doff; if it is the machine is uncontrollable and therefore unflyable.  An early operator of the type lost one of the first machines trying to see what would happen if they did turn the system off - TSB and Bell then lost another trying to recreate the accident.  Turns out the gyros in the SCAS take some time to spool up, and the system will not come on line until they are stable.  During that time the helicopter apparently crashes.

Autopilot equipped machines can have three or four axis systems - the three axis (yaw, pitch and roll) are similar to simple fixed wing systems; they will maintain the flight attitude at the time of engagement and can accept NAV inputs to adjust for steerage or waypoint course changes; four-axis systems include the collective (power) control and can translate from ground to hover to flight and back.  The most advanced four-axis systems, like the Bell 412SAR version, can fly a programmed course from takeoff to landing without any pilot input.  When in a hover just off the ground, you can push on a skid tube and the machine will push back at you to maintain position - stop pushing and the machine instantly stops to maintain position.  The SAR machines can also perform a Man Over Board maneuver: the pilot overflys a spot on the surface, even the surface of a moving body of water like storm-tossed seas, hits the MOB button, and lets the helicopter take over.  With inputs from GPS, RNAV, RadAlt, and air data computers, the AFCS will fly the machine around in a circle into a stable hover into wind in a position 200 yards downwind and fifteen degrees right of the nose from the projected drift position of the MOB.  From that position the winch operator can modify the hover position from his station in the right-aft side pocket using his own set of controls.

All this black magic is made more incredible when you consider that helicopters are inherently unstable: every control displacement has to be countered by the pilot (or AFCS) once the desired attitude is reached or the aircraft will quickly drop out of the sky.  The best analogy is the marble and bowl one: invert a bowl and place a marble on top, and then displace the marble from it's balance point at the exact center of the bowl.  The marble accelerates in the direction of displacement and drops off the bowl: this is a demonstration of negative stability and illustrates how helicopters work.  Now place the bowl right side up and place the marble in the center again.  Displace the marble and it will oscillate in decreasing amplitude until it reaches a stable position in the middle again: this is positive stability and illustrates how fixed wing aircraft work.

The newest generation of AutoFlight Control Systems use ring-laser or other solid state gyro technologies, so they virtually eliminate precession as well as the startup lag.  They are also more sensitive and faster to respond than the old inertial systems.

[Jean Loup]

There are heli's with auto pilots, as well as the SCAS equipped types as described by SkidKid.

SCAS machines (like the Bell 214S) use a flight control system to stabilize the machine, the pilot's job being to unstabilize it.  In the 214 the SCAS cannot be turned doff; if it is the machine is uncontrollable and therefore unflyable.  An early operator of the type lost one of the first machines trying to see what would happen if they did turn the system off - TSB and Bell then lost another trying to recreate the accident.  Turns out the gyros in the SCAS take some time to spool up, and the system will not come on line until they are stable.  During that time the helicopter apparently crashes.

Autopilot equipped machines can have three or four axis systems - the three axis (yaw, pitch and roll) are similar to simple fixed wing systems; they will maintain the flight attitude at the time of engagement and can accept NAV inputs to adjust for steerage or waypoint course changes; four-axis systems include the collective (power) control and can translate from ground to hover to flight and back.  The most advanced four-axis systems, like the Bell 412SAR version, can fly a programmed course from takeoff to landing without any pilot input.  When in a hover just off the ground, you can push on a skid tube and the machine will push back at you to maintain position - stop pushing and the machine instantly stops to maintain position.  The SAR machines can also perform a Man Over Board maneuver: the pilot overflys a spot on the surface, even the surface of a moving body of water like storm-tossed seas, hits the MOB button, and lets the helicopter take over.  With inputs from GPS, RNAV, RadAlt, and air data computers, the AFCS will fly the machine around in a circle into a stable hover into wind in a position 200 yards downwind and fifteen degrees right of the nose from the projected drift position of the MOB.  From that position the winch operator can modify the hover position from his station in the right-aft side pocket using his own set of controls.

All this black magic is made more incredible when you consider that helicopters are inherently unstable: every control displacement has to be countered by the pilot (or AFCS) once the desired attitude is reached or the aircraft will quickly drop out of the sky.  The best analogy is the marble and bowl one: invert a bowl and place a marble on top, and then displace the marble from it's balance point at the exact center of the bowl.  The marble accelerates in the direction of displacement and drops off the bowl: this is a demonstration of negative stability and illustrates how helicopters work.  Now place the bowl right side up and place the marble in the center again.  Displace the marble and it will oscillate in decreasing amplitude until it reaches a stable position in the middle again: this is positive stability and illustrates how fixed wing aircraft work.

The newest generation of AutoFlight Control Systems use ring-laser or other solid state gyro technologies, so they virtually eliminate precession as well as the startup lag.  They are also more sensitive and faster to respond than the old inertial systems.

Thank you for a very elaborate & ilustrative answer  you earned well the ChopperDoc name  The bowl example is tops !!!

[Chopper Doc]

Thanks.  I've had lots of practice explaining rotary-wing theory of fight; the bowl is the best illustration of stability I've found.

The bowl/instability illustration, with it's obvious demonstration of the pilot's workload, also explains the purpose of the main rotor: it's there to keep the pilot cool.  If it stops, the pilot really starts to sweat.

[Rooster Cruiser]

I've had lots of practice explaining rotary-wing theory of fight;

I too have had lots of practice explaining rotary-wing flight, but it boils down to just three basics;

1)  A Helicopter is so ugly the Earth repels it.

2)  Anything described as 1500 parts trying to shake themselves apart is inherently untrustable.

3)  Any aircraft whose wing moves faster than its fuselage is by definition rotary wing, inherently unstable, and therefore untrustable.

 

[Chopper Doc]

Actually, Rooster, it's closer to 15,000 parts - all flying in close formation.  Independent maneuvers not approved.

Ugly and unstable?  Maybe, but you never send a stiff-wing out into the boonies to recover a downed helicopter.  Ever try to rappel out of a welded-wing?  How about speeding a car-accident victim direct from the scene to the ER doctors without concern for traffic delays?

You know, Rooster, in the right light those fling-wings are downright beautiful.

[Oddball]

15,000 loose parts flying in loose formation?  are yousure you are talking about h*l*c*p*e*s or a Avro Shackelton? lol

[TheSoccerMom]

Sounds kinda like my old cars and trucks....  though, most of those loose parts just fell off on the way to the airport.   

  but you never send a stiff-wing out into the boonies to recover a downed helicopter. 

Well, the chances of that happening are about as miniscule as can be, BUT....

I do know of a light helicopter that crashed on approach to a horrid jungle strip, so they sent out a heavy helicopter to pick up the stranded crew.... 

The second machine crashed on TOP OF the first one, due to the rotten down air where the cliff dropped off....
 
Hmmm, now there were TWO crews calling for pickup on the radio.....

And, hard as it may be to imagine, the rescue came from a trusty Twin Otter....  the pilot had his choice of any machine in the inventory (light to heavy fixed- AND rotary-wing -- he was current, and highly skilled in ALL of them), and he took the Otter in....  planted it just past the heap of wreckage in a super-short landing, and flew both crews out.

So, yeah, it isn't the norm, but it HAS happened, and I personally wouldn't have believed it except I know the guy who did it.

 

P.S.....  and just ask Mikey and Gordy, I LOVE helicopters...  but many machines have done incredible things in the hands of real aviators.   

[Chopper Doc]

Twotters, Buffallos, and hercs are the best flying things with welded wings.

Twotters, in particular, can do some incredible things.  We work with them lots in the camps up north.  Pictured below is yours truly hitching a ride in one from Baker Lake to Yellowknife one winter.

[Jean Loup]

Twotters, Buffallos, and hercs are the best flying things with welded wings.

Twotters, in particular, can do some incredible things.  We work with them lots in the camps up north.  Pictured below is yours truly hitching a ride in one from Baker Lake to Yellowknife one winter.

¿Why the "incognito" Because you are not wearing your dark glasses A Chuck relative, maybe

[Oddball]

i think Chopper Doc was ashamed to be seen flying in a twotter 

[Jean Loup]

I've had lots of practice explaining rotary-wing theory of fight;

I too have had lots of practice explaining rotary-wing flight, but it boils down to just three basics;

1)  A Helicopter is so ugly the Earth repels it.

2)  Anything described as 1500 parts trying to shake themselves apart is inherently untrustable.

3)  Any aircraft whose wing moves faster than its fuselage is by definition rotary wing, inherently unstable, and therefore untrustable.

 

Apart from the 15000 parts mistake, you forgot NOISY !!! Real NOISY !!! But a skydive from a hely (a military Puma in my case...) is an awfully horrifing/interesting experience...like meeting with Frankestain monster in the flesh !!! I had never junped fron 15,000 feet above ground level before...interesting. But leaving the ship...HORROR !!! You are suddenly pulled down by much more than "just" gravity pull: that big fan keeping the pilot cool, moves ALL the air DOWN, really FAST !!!

[Chopper Doc]

Not ashamed, just maintaining a semblance of privacy.

I've never jumped from a heli, but I've done the longline rescue shtick.  I can vouch for the draft under the machine, for sure, donYan.  Not quite like leaving a fixed wing where you trade forward speed for vertical speed gradually - if you drop from a hover you can actually feel yourself falling!

Dope on a rope:

[TheSoccerMom]

i think Chopper Doc was ashamed to be seen flying in a twotter 

Haaaa, well, I never go ANYWHERE without my Rubber-Nose-and-Glasses disguise...  and keep a spare pair in the minivan, even!!

 

 

[Chopper Doc]

I haven't gone so far as to pack a disguise, but I have crossed over to the dark side and built my own aircraft.  I even (gasp) fly them for fun...

Just don't tell anyone - you'll spoil my street creds.  This is a Zenair 701, a two-seat STOL craft.  I've done solo takeoff and landing on grass, no wind, in a combined distance of under 100'.  Only a chopper can perform in shorter distances than that - if you plan to use the aircraft again.