Helicopters are sufficiently different
that they merit a FAQ page (at least) on their own. Most of the
on the page is based on a series of postings in the Tech List from guys
serious helicopter experience that know what they're talking about.
Special thanks go to Jim McNeill, Norm Lagasse, and Todd Fredricks.
Based on comments from those who know,
it's very good. The significant helo effects, such as the fundamental
instability, interaction of control inputs, ground effect, transition
between hovering and forward flight, etc., are all done accurately.
No. Your stick becomes the cyclic
control and the pedals (or stick twist grip or whatever) control the
tail rotor. Your throttle becomes the collective but it works
Full forward is minimum collective and you pull back to increase. Note
to self: While your helicopter is loading up in X-Plane, push the
throttle all the way forward (minimum collective) so that when the
flight model starts you stay on the ground. Starting with maximum
collective usually makes for a very short and violent flight.
You can get away without pedals if you
check the "Auto-coordinate" box in the Joystick setup menu, Center
tab (called Null Zone in earlier versions). X-Plane will automatically
adjust the tail rotor to keep you
straight. There's just some things you won't be able to do, such as
in place in a hover.
OK - that's the basics. How let's hear
from the experts.
The rest of this material is taken from various postings on the subject
in the Tech list. I haven't done a lot of editing here - treat it as
pieces of an ongoing conversation.
These words from my first helicopter instructor have served me well for
the last 22 years: Small, Frequent Inputs. It doesn't matter if you're
flying a fully manual heli (Bell 47), a UH-1 or AH-1 (hydraulic boost)
or a Sea King or Blackhawk (Automatic Flight Control System with
Without a stabilization system in the helicopter (i.e., full manual
controls) every movement of one control (cyclic or collective) will in
fact require an adjustment to another control (cyclic, collective or
Once you discover the hover "bug" you'll truly enjoy the flying and the
challenges. Just keep this in mind; Flying a normal approach to landing
is one of the hardest things to learn to do well in helo flying. When
you master that you'll be able to land the helos on oil platforms,
building tops and mountain ridges.
The short answer to your basic question is that x-plane does a very
decent job of replicating helo flight. The biggest limitation is the
limited field of view (FOV) that one monitor provides. In real life
peripheral vision is very important in maintaining slow speed/hovering
flight, and that is lacking in X-Plane for the most part.
- No real helicopter pilot in his or her right mind would attempt
hovering flight solely by reference to instruments unless he/she was
using a coupled autopilot with hover hold capability... it just ain't
possible to do.
- When you're making a visual approach in a helicopter, don't try
to fly it down to the ground with a constant forward airspeed, like you
would in an airplane, and then rapidly decelerate into the hover...
that's why it's getting "squirrelly" on you. From the time you lower
collective to begin the final approach, you should be slowly
decelerating so that you gradually go through the translational lift
point into hovering flight as you reach hover height (normally 2 - 3'
skid height above the ground).
Jim hit the high points on the difference. Helo flying is a lot of seat
of the pants flying. The only time you really look at the gauges is for
quick cross-check of altitude (radar altimeter), airspeed and power
setting (torque). The limited FOV IS the real limitation for normal
flying. When you're flying approaches to landing or hover, you start at
known parameters like 500'AGL and 70 knots. Reduce power (torque) to
(try 15-20% torque or 5" manifold pressure) establish a 500 fpm rate of
descent and then set pitch to bleed airspeed to maintain that "sink"
rate. At 100' AGL you're looking for a sink rate of about 300 fpm and
about 40 knots on the airspeed indicator. Just realize that once you
to about 30 knots or so the airspeed indicator isn't reading all that
accurately (unless you have an advanced flight director/air data
computer/navigation system interlink).
This is where that peripheral vision is key. The rate of closure to
your intended landing spot is about the pace you would "walk your dog".
The rate is determined by looking out to the side about 45-60 degrees
the right (for a right seater pilot). The other important cue that
you're missing in the sim is the seat of the pants feel of when you're
transitioning from forward flight to translational lift (about 15-25
knots) to hover. In the real helos you can feel the "burble" as the
vortex ring (generated by lift generation within the rotor system)
translates through the disc and you feel the support of ground effect
hover. As Jim pointed out you're looking to reach hover just as you
To challenge your flying skills and learn to shoot power managed
approaches you should determine the power it takes to hover. Reduce
power about 5% torque or 2" or manifold pressure and use that setting
your "not to exceed" power for the normal approach to a touchdown. If
you can consistently fly that approach without pulling in a bunch of
torque at the end to "save it", then you're ready for landing on
building tops and mountain peaks.
From a simulation hardware perspective I would recommend a separate
throttle placed at your left side in a slightly declined position
(leaned forward about 60 degrees). This will provide a more natural
to increasing and decreasing power settings, i.e. pull up for more
power, push down for less. Pedals would certainly help "decouple" the
hand and control inputs for yaw control (tail rotor). For US made
you'll need a touch of left pedal and slight right cyclic for hovering.
In European helos, it'll take a touch of right pedal since their blades
tend to rotate in the opposite direction.
There's great fun to be had maneuvering a helo at low altitude in close
quarters. Have fun!!
It has also been great hearing from people who have flown real
helicopters, my guess is that a desktop joystick doesn't give an
accurate feel for what it would be like to use the real controls of a
helicopter, a slight nudge of the joystick can throw the helo into a
spin where I'm sure there would be more subtle feedback in a helicopter.
Kerry, there is feedback, but if anything the joysticks we use with XP
are much *less* sensitive than real cyclics. The major difference is
that the helicopter hydraulic systems, and some specialized
force-feedback systems, can generate an artificial feel. The basic rule
that we used to teach new students was to "think" the move... the mere
thought of making a move induces enough muscle contractions to create
the proper input without over-controlling. Collective levers, by their
very nature, generally require more muscle but still demand a delicate
I think Kerry is referring to the short throws of today's PC joysticks.
Real helos are probably more "sensitive" in the sense that you make a
whole lot more tiny corrections... i.e., ideally you would be making as
small a correction as practical (hence "thinking" the move instead of
waiting until the necessary correction becomes large enough to require
signficant cyclic movement). Short-throw PC sticks don't exactly lend
themselves to high precision... a correction that seems like barely a
movement of the PC joystick is likely to equate to a comparatively
and wandering deflection of the controls in the real helo/plane. So you
*can't* achieve this level of control on a typical PC joystick.
Fully concur with short throw controls. Having normal length controls
(both cyclic and collective) achieves a couple of things for you. For
the cyclic you're able to rest your right arm across your right leg to
support the arm and that leaves your control touch to just fingertips
for movement. It is significantly easier to finesse the control inputs
when you're not supporting your arm with the grip of the stick. As for
the collective, having a console just to the left of the collective
allows you to rest your left pinky & ring finger on a horizontal
surface and now you can flex the remaining fingers on the collective.
Very easy to make small inputs and corrections that way.
Kerry, sounds like you've been working the hover mode extensively. The
pitch up around 20 knots is very accurate and easily detectable in an
actual helo. It does take forward cyclic to overcome the pitch up in
disk. If you care to understand why it does this, drop me a line and
I'll exceed the layman's language slightly to explain it.
Anyway, here's an exercise to use that hover & transition practice
and take it a step further. If you're flying a skid equipped helo, get
the bird stabilized in a 4-5' hover. Note your power setting. Now
accelerate forward without changing power and accelerate through trans
lift and get about 50 knots on the A/S indicator. Now ease the cyclic
back to climb at 50 knots with hover power and clear a 100' obstacle.
Start a good ways back initially and work your way closer and closer to
the obstacle. This technique is excellent practice for Max gross weight
takeoffs from confined areas. When you've worked your way very close to
the obstacle and can consistently clear it, move in a little closer and
try applying right pedal in the climb.
If you're flying a wheeled helo, take the hover power minus 10% torque
or 2" of manifold pressure. Start the helo rolling on the ground with
that adjusted power setting and accelerate past trans lift to about 30
knots. The bird will lift off a little after that and then you can
continue accelerating to 50 knots. The remainder of the maneuver is the
same. This exercise provides good training for taking an wheeled helo
off a runway at max gross weight and high DA. (Not enough power
available to hover).
I'll add one thing to your dissertation, Norm. You can do the same
running takeoff exercise with skid-mounted helicopters. Raise the
collective just enough that the helicopter gets light on the skids then
maintain that amount of power with the collective and veeeeery slowly
feed in forward cyclic. As the helicopter accelerates it will start to
climb. Feed in enough forward cyclic to prevent the climb without
descending back into ground contact.
The helicopter may occasionally skip off the ground but that's ok. At
somewhere between 15 and 20 knots you'll begin feeling the
lift shudder and nose pitch at which time you will accelerate into
forward flight. With practice you'll find that you can make takeoffs at
power settings as much as 5 pounds below hover torque. And one nice
thing about doing it in sim... you don't wear out skid shoes ;-)
Norm's absolutely correct about getting a good "weld" with your cyclic
forearm. It's a major problem for most new helo pilots, and because of
differences in pilot stature and seat position, etc, there's no one
position that works for everybody... you have to experiment to find a
position that works for you.
You can also do this exercise on the water with amphibious helos, Sea
King, Jolly Green Giant, Jet Ranger on Floats. Some of the best fun
had was making water landings in H-3's (AF version of Sea Kings with
retractable trike gear and rear ramp). I need to go drop the XP version
in the water and see if I can shut it down. The two 360's during
shutdown are always a treat!
Ground effect has the same effect on rotary wing aircraft as it does on
fixed wing ones. Helo pilots talk of HIGE, Hover In Ground Effect, and
HOGE, Hover Out of Ground Effect, power to describe it. In essence,
translational lift is the point at which the helo "translates" from
requiring HIGE to HOGE power due to it's accelerating off the high
pressure "bubble" or, more accurately, vortex ring of air it's been
riding on. It's at this point that the vortex starts to flow up through
the rotor rather than remaining under it; and that is what causes the
shudder and pitch change. There is also an accompanying yaw change that
occurs at this point.
Norm, did I leave anything out?
Pretty close. The vortex ring is actually on the outside of edge of the
rotor disk. The vortex ring encased, ground effect "cushion" can be
thought of in simple terms with the dynamics of an air hockey puck. The
edge lip would be the vortex ring and the air trapped in the center of
the puck the lift air affected by decreased downwash due to ground
effect. As you said Jim, the shudder is in fact caused by the vortex
ring translating through the rotor disk. Think of it as wingtip
sliding through the rotor disk and causing turbulence on each "wing" as
it passes through. The pitch up is actually a function of the rotor
blades in the forward half of the disk being affected by the induced
airflow over the "wing" (combination of rotational airflow plus forward
motion induced airflow). On the advancing blade, increased airflow - on
the retreating blade decreased airflow. Due to rotational dynamics the
force is applied at the 3 & 9 o'clock positions and manifests
90 degrees beyond in the rotation. This results in the disk lifting in
the front and lowering in the back. The aircraft will follow due to the
pendulum action. Ok, now does anyone's brain hurt this early in the
Is there any correlation between the change of power required or the
change of lift resulting, from the transition out of and into ground
effect, and the change of lift and power required, at the 20 kt
transitional speed discussed earlier in this thread which gave rise to
my original query? Are they interlinked, different manifestations of
same effect, or completely un-connected (I'm assuming the helo is
out of ground effect my increasing its forward speed at a low height
above ground - the situation relevant ot he previous discussions)?
Also, am I correct in inferring from your explanation, that when the
helo moves out of ground effect, MORE power is required to maintain
height or upward velocity because it is no longer resting on a bubble
what is in effect compressed air?
I guess the best way to think of it is that they're different
manifestations of the same thing. Read Norm's last post. The vortex
surrounds the "air cushion" As long as your directional flight speed --
forward, lateral, or aftward -- stays below translational lift speed
you'll require HIGE power to hover. If you climb vertically you'll
require increasingly more power to remain at the hover until, at about
one rotor span off the ground, you'll be totally out of ground effect
and need HOGE power to hover. At that point, if you set up a relatively
high rate of descent with a low directional speed and try to arrest the
descent by adding power (collective) all you do is to accelerate the
vortex ring and rapidly increase the rate of descent. This is called
"settling with power" and has caused many helo crashes.
As you accelerate directionally, you start to outrun that high pressure
bubble of air and it takes less power to maintain altitude and
accelerate because the relative wind (caused by the aircraft's motion)
is providing "fresh" air through the rotor which is contributing more
lift and less to drag (the vortex ring). If you decelerate at that
you return to the hover. IF you continue to accelerate you have excess
power available to climb and increase speed.
If the wind is blowing strongly enough, it's possible to be in
translational lift while still sitting on the ground.
Since helos can operate out of remote locations, it's important to
understand the dynamics of hovering the helo and the associated power
requirements. If you end up on a small pinnacle pad (less than 1 rotor
disk in diameter) or on a significantly sloped area like the side of a
hill, you're ability to hover may be hampered if there is insufficient
power available to hover OGE. Slope or small ground space under the
will prevent the IGE cushion from developing.
As Jim pointed out the wind can certainly affect your ability to hover.
5-10 knots of wind can "disturb" the vortex ring and prevent IGE
hovering due to insufficient cushion and power limitations. 15-25 knots
of wind puts you right into trans lift and your power requirements are
That's why helo flying is always a challenge and usually a blast!!
FYI, the FAA publishes an excellent training manual that will give you
much more detailed insight into helicopter flight. It's a pdf so you'll
need Adobe Acrobat or the reader and is available at
I think Jim has covered it well, but I would add this wisdom from an
Army Warrant IP that I was learning from.
The situation was that I was in an OH-58C and I had maybe 5 hours total
time in helicopters (I had oodles of fixed wing but it wasn't helping
that day) and the task was try and keep the thing within a two rotor
disc circle. Well I had the thing everywhere but in the circle and
finally I tried to swap tail for nose and with a quiet but firm "I have
the flight controls." the warrant took over and the helicopter settled
down to a 3 foot hover that couldn't have been more stable had the
thing been welded to the ground.
I sat there, rotors spinning, frustrated as all get out, wondering how
I was ever going to get the thing to work for me and the warrant said,
"Quit thinking about what you need to do and just make it do what you
want it too."
I was trying to think about which pedal to push with power inputs and
when to raise and lower collective in which turns etc, but in a
helicopter with that big spinning gyroscope above everything happens 90
degrees from point of input and so by the time you try and think
through what you need to do you are already behind the machine and the
example of this is watching a young helo pilot (or myself at that time)
oscillate and gyrate all over the place. The pilot is trying to think
while they fly. You stop thinking and just push or pull whatever you
need to to make the machine stay where you
want it. Small inputs if you please. Input, wait, input, wait.
The easiest way for me to "get it" was to understand that a helicopter
flies in two ways; it pushes a lot of air down and in response to
Newtonian physics the machine lifts off the ground (not really flying
just thrust over matter although the rotor is flying through the air in
a hover and creating lift) and the second is in forward flight when the
rotor disk itself begins to act like a fixed wing through the cruise
envelope and then it is just like flying a fixed wing save for pedal
input which is never like rudder...AHEM...but forget that and also
forget about retreating blade stall which we can talk about at some
Once I realized that the only 'new' flying that I needed to get a
handle on was the air pushing down part and that that type of flying
had nothing to do with cruise (which is just like flying an airplane
but different...is this making sense yet) it got much easier.
I just realized that as I started my approach, long before passing ETL
(Effective Translational Lift) my ONLY job was to pick a touch down
point and do whatever it took to make that point coincide with my
achieving a 3 foot hover over it. So there is the key, the touchdown
point. You need to clearly see it and you need to have some visual (not
instrument) cues as to your rate of closure because unlike an airplane
where you fly an approach at 1.2-1.3 of your stall speed for your
configuration and then you roundout/flare with the knowledge that you
will touchdown at stall but never with NO velocity, in a helicopter you
are going to land with 0 forward velocity (roll on landings
This is why you cannot 'think' about what you are doing. You simply
cannot think fast enough. You have to 'see' what you are doing because
it is your eyes and butt which tell you if your rate of closure is too
fast and if the two vectors, those of vertical and forward velocity are
trending smoothing down toward 0. A good helicopter approach should
look like a straight line to the touchdown point.
ETL is not as dramatic as you might think, but what will happen is that
you will need to add a bit of collective (throttle) because the sink
rate will increase as the machine shifts from flying by means of the
physics of the rotor disk to depending upon a lot of air being pushed
down. And ETL passage is not an instantaneous thing, you will feel it
build as you decelerate and then shudder and then smooth again so as
you start to feel the vibration, you will have glanced at the airspeed
indicator on take-off and know about where to anticipate it on
approach, you just pull in a bit of collective and continue. From then
on down it is smooth, small inputs as you adjust rates of closure to
arrive at a hover.
Now having a penchant for words and not wanting to drag this out
forever but wanting to be helpful I would add one more thing. You might
find that a way to master hovers is to practice roll ons. The one thing
I like about Blackhawks (I like a lot of things about Blackhawks,
namely a bunch of redundant power) is that they have wheels. So what
you can do is a roll on landing which means that if you can't quite get
a hover at 0 airspeed, practice landing a Blackhawk on a runway at
slower and slower airspeeds until you feel comfortable with control
inputs to just make the landing speed 0.
You will find that a touchdown of about 30 knots works best.
Another good exercise for budding helo pilots is to sit in your lazy
boy recliner and just mentally visualize the rotor disk and the thrust
vector on the disc depending upon orientation. The reason why this is
valuable is that you are not just changing power in a helicopter
approach but you are actually changing the thrust vector of the 'wing'
itself by pulling back on the cyclic. The end result is that the
horizontal component of lift in the equation is reduced while the
vertical component is increased. This means you will need less power to
maintain altitude and so you need to be able to move both hands
independently without thinking. Roll-ons allow you to do this gradually
as you develop the skill.
You can do 'roll-ons' with skids it just makes things more exciting
what with the sparks and all. Very fun at night.
Nice description and a very valid point about the thinking too much
The old adage about just thinking the movement you want, rather than
trying to physically move the controls is still valid. When you think
about making the movement, your muscles move just enough to move the
control the amount you need. Anything else is over-controlling. That's
probably the hardest thing that airplane pilots making the transition
have to learn: Except in certain emergencies, the best thing to do is
often nothing at all. Just sit there, relax and you'll find that you'll
have just the amount of control authority that you need....anti-torque
pedal control excepted. Right, Todd :-)
Can I make one more request, a bit like talking me through a standard
approach and landing and what I would expect to experience in a real
helo. I'd like to practice it until I'm on cue. Say I'm approaching a
landing pad at 1,000' above ground, how far from the pad would I start
my descent, what speed would I be doing, Jim says an approach of 10
degrees is about right? What height would I go through the transition
assuming 20 knots transitional speed?
Well, here is the rub, all and any approaches are okay. The approach to
a carrier might be to match speed along side the thing, then translate
laterally til you are over the deck and then set it down. To an oil rig
to you might start the approach as a circle around the rig to recon
obstacles and as you come around bleed off speed until you are moving
at 5-10 knots and fly into the wind if possible over the pad and then
set down. To a runway, more like a fixed wing. A building top will be
start at 500 to 1000 feet above the level of the pad and orient into
the wind and fly it down to the touchdown. The only real reason to
start at any altitude that is much higher is so you have the
opportunity to stabilize your approach. As you gain confidence and
skill you will know how to configure your aircraft at any altitude to
successfully arrive where you want and need to be. Just practice with
runways for a while, then move to buildings and then oil rigs and
finally the USS Laminar underway in heavy seas.
I couldn't have said it better, Todd.
Kezza, just remember that the steeper the approach angle is, the slower
airspeed and rate of descent you need to keep it stable.
Once you initiate the final approach, the military way is to make the
approach a constant angle with a constant, gradual deceleration so that
you zero out the airspeed at a stable 3 foot hover over the landing
spot. With practice, you can do it every time, regardless of the type
of spot to which you're landing.
Don't worry about ETL. If the winds are strong enough you may never
reach it until after you shut the fuel off and the rotor RPM is winding
down; or if it's a very steep approach you may go through ETL as soon
as you start the collective coming down on final approach. Like Todd
says, every approach is unique.
All the helo drivers I've talked to have said that they prefer high
wind conditions for flight over calmer conditions. They would rather
fly in 20+ knot winds than calm. However, I've never been able to get
an satisfactory explanation of WHY.
Sure. The wind hides their mistakes :-)
Seriously, the big thing is that they are constantly in ETL which means
that they don't have to worry about an Out-of-Ground Effect Hover
(called HOGE) which takes *much* more power than a HIGE does; and that
translated into being able to carry a larger load, more fuel, or having
more power in reserve if needed.
The problem with many approaches is that the wind speed decreases and
changes direction as you descend below any barriers on approach (unless
you're landing to a totally exposed pinnacle) so good pilots never
count on making a wind-aided approach....it's just an additional bonus
if it occurs.
I would add that due to the nature of the rotor/lift system in a
helicopter, while the disk does act like a big wing, in situations of
unstable air, read turbulence, the system is much less susceptible to
the bouncing and uncomfortable attitude changes that occur with low
wing loading airplanes. So in winds, unless you have a lot of surface
shear (which can make landings interesting
you will find that circumstances which would be downright "I want to
land and go home right now" in a light airplane, are a non-event and
another day at work in a helicopter. Again, nothing worse than gusts
and a pinnacle landing site.
Good point, Todd, although that's a double-edged sword, especially for
older fully articulated or semi-rigid rotor systems. The problem is
that although the occupants don't feel the turbulence the rotor system
is reacting to it and is flapping (wobbling) ever closer to the mast.
Mast bumping is not
you want to encounter, as the smallest bump can deform the mast
resulting in catastrophic failure.
And people wonder why helo pilots are pessimistic introverts :-)
The point was directed as an illustration of the differences we feel in
helos over fixed wing in situations of gusts and wind. We have not even
yet discussed PIOs and mast bumping. Part of the MTP return to service
checklist on the OH-58 is rapid and abrupt cyclic inputs to test the
dampeners. The first time I experienced that it was enough of a shock
to know that I never wanted to experience full cyclic inputs and test
the integrity of the system.
Having never experienced blew blade syndrome after a bump I can say
that you can fly a UH-1 in some pretty stiff stuff and that was my
point, the kind of air that would really make a person not want to be
in a 172, and still be perfectly safe.
Point well taken.