Tag Archives: safety

Why Helicopters Don’t Normally Take Off Vertically

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Just because you can do something, doesn’t mean you should do it.

Every once in a while someone watching one of my YouTube videos or searching for answers on the web that bring them to this blog ask why helicopters don’t take off straight up. I guess these folks know that it’s possible and they’ve seen it often enough in the movies to think that it’s normal or at least okay. It’s neither.

I actually explain why in my much longer post about the Deadman’s Curve. But I’ll try to keep it simpler here.

The Basics

Let me start off by saying that helicopters can glide. Yes, if the engine fails, the pilot still has control over the helicopter and can fly it, using autorotation, to the ground. If conditions are right and the landing zone is appropriate and the pilot’s skills are sufficient, the pilot and passengers should be able to walk away and the helicopter might even be able to fly again.

Notice that I mentioned three ifs:

  • if the conditions are right
  • if the landing zone is appropriate
  • if the pilot’s skills are sufficient

Height-Velocity Diagram for R44 HelicopterIt’s that first if that the pilot usually has complete control over: the conditions of flight. That’s where the Height-Velocity Diagram comes into play. This diagram, which is part of the Pilot Operating Handbook (POH) that pilots are required to know inside and out (and even carry on board, as if we could consult it while flying), shows the flight profiles in which an autorotation is most likely to be completed successfully. By “flight profiles,” I’m referring to a combination of airspeed and altitude.

To meet the requirements of that first if — in other words, to fly the safest flight profile in the unlikely event of an engine failure — the pilot needs to stay out of the shaded area of the Height-Velocity Diagram. A recommended takeoff profile is shown on this chart by a dashed line that starts at 0 knots and less than 10 feet off the ground, accelerates through 45 knots while climbing less than 15 feet, and then climbs out at a speed greater than 50 knots.

Make a mental picture of that. If you’re not going to climb above 10 feet until you get to at least 30 or 40 knots, are you going to be flying straight up? No. You’re going to be taking off a lot like an airplane might, with a bunch of forward movement before you start climbing.

This is why a “normal takeoff” for a helicopter climbs out after gaining airspeed — instead of climbing straight up. It’s for safety reasons.

(This is only part of the reason why we don’t land straight down, but I’ll save that for another blog post if I get requests for it.)

FAA Guidance

The FAA has a wealth of free information about flying, including “handbooks” that explain exactly how to fly. I’ve linked to the Helicopter Flying Handbook many times; if you don’t have a copy of this excellent guide and are interested in flying helicopters, download it in PDF format here.

Here’s what it says about performing a normal takeoff from a hover (position 1 in the image that follows) on Page 9-12:

Start the helicopter moving by smoothly and slowly easing the cyclic forward (position 2). As the helicopter starts to move forward, increase the collective, as necessary, to prevent the helicopter from sinking and adjust the throttle to maintain rpm. The increase in power requires an increase in the proper antitorque pedal to maintain heading. Maintain a straight takeoff path throughout the takeoff.

While accelerating through effective translational lift (position 3), the helicopter begins to climb, and the nose tends to rise due to increased lift. At this point, adjust the collective to obtain normal climb power and apply enough forward cyclic to overcome the tendency of the nose to rise. At position 4, hold an attitude that allows a smooth acceleration toward climbing airspeed and a commensurate gain in altitude so that the takeoff profile does not take the helicopter through any of the cross-hatched or shaded areas of the height/velocity diagram. As airspeed increases (position 5), place the aircraft in trim and allow a crab to take place to maintain ground track and a more favorable climb configuration. As the helicopter continues to climb and accelerate to best rate-of-climb, apply aft cyclic pressure to raise the nose smoothly to the normal climb attitude.

Normal Takeoff
This is an exaggerated view. In reality, each position would be a lot farther apart horizontally.

In the above text, in an R44, effective translational lift (ETL) occurs between 15 and 25 knots, normal climb power is about 45 knots, and then climb out power (best rate of climb) is 60 knots. So you basically stay within 10 feet of the ground until you’re at 45 knots, then accelerate while climbing to 60 knots, and then climb out at 60. These numbers may be different for other aircraft but are likely similar.

Real Life Situations

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Of course, one of the benefits of helicopters in many operational situations is that it can fly straight up. For example, I can take off from a confined space — perhaps a forest clearing — by being able to climb up above obstacles (the trees around me) before picking up airspeed and flying away. Is this safe? Well, there isn’t any signifiant danger unless the engine quits. And although the chances of the engine quitting are very slim, it is possible.

Years ago, while doing a rides event at the local airport with some fellow pilots who were working with me for cherry season, I noticed that one of the pilots was departing our landing zone by climbing straight up for 20 or 30 or even 50 feet before gaining airspeed. He was putting the aircraft right in the shaded area of the Height-Velocity Diagram. In other words, he was adding risk to his flight by basically ignoring the recommended takeoff profile.

With passengers on board. At a crowded event.

I’ve got a pretty good imagination and was immediately able to “see” what could happen if his engine quit. The helicopter would drop down with its blades still spinning. Everyone on board would likely be killed or seriously injured. And when all those spinning parts hit the ground and started flinging off in every direction, they’d likely kill or injure dozens of onlookers.

What were the chances of his engine quitting? About as close to zero as you can get without being zero. But that isn’t zero. It could happen.

After seeing him do this at least four times and realizing he wasn’t going to stop, I got on the radio and told him to stop. He asked me why. Knowing that I was talking on a frequency that could be heard by his passengers, my passengers, any other aircraft flying around the area, and anyone monitoring on the ground, I kept it simple: “Just because you can do something doesn’t mean you should.” I let him think a bit about why he shouldn’t and he stopped. (If he didn’t, I would have kicked him out of the event.)

Over the following month or so, I got to know this pilot better and I didn’t like what I saw. I don’t need to go into details here, but I feel that he’s the kind of pilot who will likely get himself killed doing something dumb in a helicopter. I’m just glad I took steps to make sure it didn’t happen on my watch.

Question Answered?

If this doesn’t answer the question about why helicopters don’t take off vertically, I don’t know what could. Please don’t hesitate to share your questions, comments, and stories in the comments for this post. Thanks!

Leaving a Parked Helicopter with the Engine Running

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An explanation of something I said in one of my recent YouTube videos.

I recently published a video on the FlyingMAir YouTube channel where I flew from my cherry season landing zone to my house. I was going to do a much longer flight that day with a friend and, when I reached the helicopter, I realized I’d forgotten my iPad, which I use with Foreflight for situational awareness and detailed airport information in flight. Faced with a choice of taking 20 to 30 minutes to drive back home and get it or just making the one minute flight up to my house on my way to pick up my friend, I went with the quicker option.

In the video, as I’m coming in for landing, I lament that a helicopter isn’t like a car and I can’t just keep it running while I go inside the house. I never explained why. A helicopter pilot — and even an airplane pilot — should know, but I forget sometimes that my video audience isn’t always directly involved in aviation. I got several questions — and a good story — in the video comments about leaving an unattended helicopter with the engine running. I thought I’d take a moment to share and expand on what was said in those comments.

First, Understand How a Helicopter Flies

The main danger of leaving a helicopter running while unattended is the possibility of it become airborne enough to move and crash. Never fear — if it does get airborne at all, it’s not going to fly away by itself. It will crash and likely pretty damn quickly. More on that in a moment.

Dynamic Rollover
The usual outcome of a helicopter trying to take off by itself is something like dynamic rollover, which is shown here. The helicopter gets hooked on something on the ground and rolls over. (This photo by John Murphy is from Wikipedia and used under the Creative Commons Attribution-Share Alike 2.0 Generic license. (Thanks, John, for sharing photos to help bloggers illustrate things like this.))

For a helicopter to get light on its skids and airborne, it needs a two main things:

  • Rotor RPM. The main rotor(s) must be spinning. Theoretically, a Robinson can fly at 80% RPM plus 1% RPM per thousand feet of density altitude. So at my house on a warm summer day, I’d estimate 83% RPM would be enough to fly, although we always fly at 100% RPM (unless there’s some sort of in-flight problem that makes this impossible, in which case, we’d land as soon as possible). For this reason, it’s never a good idea to leave the rotors spinning at anywhere near 100% RPM unless the pilot is at the controls, paying attention and ready to fly.
  • Collective Pitch. The collective control in the pilot’s left hand changes the pitch on the rotor blades the same amount (collectively) when it’s pulled up. With the collective full down, the blades are “flat” (or close enough for argument’s sake) and should not be able to get the angle of attack they need to produce lift. (And yes, the collective does look quite a bit like a compact car’s parking break lever.)

It’s the pilot’s responsibility to throttle down to an appropriately low RPM when on the ground. A Robinson’s cool-down RPM is between 60% and 70%; far too low for the helicopter to fly. When I flew at Papillon years ago, we’d just throttle down to the stop, which I think left us at around 70% RPM (but don’t quote me on that; it’s been 16 years). There are a few reasons why a pilot might not do this, but we don’t need to split hairs here because all of those reasons involve a pilot staying in the cockpit.

All the helicopters I know provide safety controls to prevent the collective from creeping up by itself. This is usually in the form of a collective friction lever (or possibly knob?) that the pilot should secure as part of her shutdown process. It becomes automatic. You set down, you throttle down to a cool-down or idle RPM (depending on your needs), and set the friction. Half the time, I don’t even remember doing it, but when I look down, it’s set.

So Is It Safe to Leave the Engine Running without a Pilot on Board?

Doing both of these things — reducing RPM and securing the collective in a full down position — should prevent a helicopter from misbehaving when parked when the engine is running. And lots of pilots will actually walk away from a helicopter with the engine running. Let me elaborate.

Suppose I was sitting in the helicopter with the engine running and I realized I needed something out of the back seat storage area. I need to get out to fetch it. Would I shut down?

The answer is no. I’d start by confirming low RPM and secured collective. Then I’d take off my headset and seat belt, open my door, climb out, open the back door, fetch what I needed, close the back door, and get back into my seat. During that entire time, I’d be well within reach of the controls if I started to hear or feel something weird going on.

Likewise, when I worked at Papillon, they’d routinely land a Bell 206L in the Native American village of Supai at the bottom of the Grand Canyon. The pilot would throttle down and secure the collective, then get out, walk around the front (never back!) of the helicopter, open the luggage compartment, and pull out luggage for the departing passengers. (That was back in 2004; I have no idea if they still do this but assume they do. It makes sense given the possibility of restarting difficulties without a ground support crew/equipment.)

Meanwhile, up at the Grand Canyon South Rim base, if a pilot needed to use the bathroom between flights, he’d have to wait until another pilot came down and sat in his seat until he returned. No passengers would be loaded during this time. This was a smart safety measure that some folks might consider overkill. I don’t.

A friend of mine who owned an R44 started up his helicopter on the ramp of his home base airport, which, at the time, I believe was Salinas in California. As he was warming up the engine, he realized he was missing a chart. Rather than shutting down, he simply left the helicopter empty, idling on the ramp, while he went to the on-airport pilot shop and bought the needed chart. He got into a ton of trouble with airport management when an airplane pilot complained about it. Friend or not, I think he exercised poor judgement when he did that.

The Story in Comments

One of my YouTube channel’s commenters, George Reynolds, had this to say about my video:

Not like a car, leaving the engine running. Reminds me or a true accident report where the pilot landed beside a house to impress a friend and got out, leaving the 3 forestry workers in the helicopter with the engine running. One of them thought the “handbrake” ought to be applied and the consequences was a wreck, but fortunately no injuries….

My first thought was OMG, what a story! It’s a perfect example of what can happen when a pilot fails to properly brief his passengers.

Going back to my original situation, if I had a responsible adult passenger in the front seat when I landed at my house, I’d throttle down, secure the collective, and advise the passenger to leave the controls alone, especially the collective, which should not be raised under any situation. Then I’d feel comfortable enough leaving the engine running.

What Could Happen

George’s story sent me to the NTSB database to look for the accident in question. I searched using all kinds of key words based on his story: handbrake, brake, house, passengers, pulled collective. I did not find a single story that matched.

But I did find others. Here are a few summaries; emphasis added:

Accident report LAX97FA149 on April 7, 1997 in Los Angeles, CA tells this story:

The pilot exited the helicopter to escort a deplaning passenger. The student pilot rated passenger was left sitting in the helicopter with instructions not to touch the controls. While the pilot was standing nearby, the helicopter began bouncing up and down in a resonant mode. The pilot ran back to the helicopter and pulled the fuel flow control lever into the cut-off position. The helicopter yawed to the right and settled back on the deck. Investigation revealed the full down position of the collective was spring loaded to keep tension against the control lock. An inspection of the helicopter revealed that the collective was not down and locked, nor were the frictions tightly applied. The manufacturer reported instances in which the collective lock was not seated properly, and consequently, the collective became released while the engine was running. If the lock slips off collective, the spring’s tension could force the control to move upward. No malfunction or failure was found with the engine or rotor systems.

So either the pilot hadn’t locked the collective or the collective lock had released due to a known design flaw.

Accident report LAX07CA034 on November 11, 2006 in Boulder City, NV says:

The helicopter rolled over after the pilot exited with the engine running and rotors turning to disconnect and move the auxiliary power unit (APU) to a secure location. The pilot left the helicopter running at 100 percent because he was charging the battery. The pilot’s back was to the helicopter when he heard the engine sound change. He turned around, and saw the front skids lift off the ground. The helicopter started to move in a backwards direction, and rolled over and went down an embankment.

Sorry, folks, but this is a stupid pilot trick, plain and simple. Never leave the helicopter at 100% RPM when there’s no pilot at the controls.

Accident report LAX01FA252 on July 21, 2001 in Los Angeles, CA reports:

The pilot got out of the helicopter with the engines running and the rotors turning to check on the security of a cabin door, and the unmanned helicopter began moving on the helipad and rolled over. The pilot had completed a nightime, helicopter, air taxi flight, and was preparing to depart the elevated helipad to reposition the helicopter to the operator’s base. After deplaning his passengers the pilot returned to the cockpit and was preparing to depart when he noticed a door unsecured indication on the instrument panel for the left cabin door. The passengers had deplaned through the right-hand door and the left door annunciation had not been on during the inbound flight. He thought one of the passengers might have released the left door latch inadvertently while preparing to deplane. He idled the engines and exited the cockpit to check the door. He reclosed the door and returned to the cockpit; however, the door open annunciation came on again. He recalled leaving the cockpit “2 or 3 times” to deal with the door and said he was “frustrated with it.” He did not recall retarding the engine power control levers to ground idle before leaving the cockpit the final time. While out of the cockpit, the wheel-equipped helicopter started to move as the pilot was returning to the cockpit. He recalled it was moving toward the edge of the helipad. He returned to the cockpit; however, before he could regain control there was a confusing sequence of events and the next thing he knew the helicopter was on its side. The pilot reported there were no mechanical discrepancies with the helicopter up to the time of the event. He remarked that it was very light [weight] with no one else on board. On the deck of the helipad there was a tire skid pattern consistent with a dynamic rollover event. The engine power control levers were found in the “fly” position.

I really feel for this guy. Something is acting up, giving him grief, and he’s frustrated. Unfortunately, that can also make you sloppy. I don’t know much about Sikorsky S-76 helicopters and nothing about the “fly” position, but I have to think that a helicopter should be set to “fly” when the pilot intends to fly. Maybe someone reading this can fill in more details? Since the chances of me ever flying an S-76 are very slim, I’m not interested in researching it.

Why This Matters

I’m a student in the School of Thought that says the more you know about what could happen, the better equipped you are to make smarter safety-related decisions.

In my video, my landing zone was good, there was little or no wind, the collective friction on my helicopter works fine, and I could have throttled all the day down to 60% RPM if I wanted to. The chances of the helicopter moving an inch while I was in my house were nearly zero.

Nearly.

There’s always a chance that something unexpected will happen. Having lost one helicopter already, I’m not interested in losing another. So I do what I think is safe, even if other folks think it’s overly cautious.

If the folks in the four accident stories I shared here had been students in the same School of Thought I’m in, their stories wouldn’t need to be shared.

Drone Pilots: Beware of Bird Strikes!

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Just a quick warning, with photos.

Last week, I did a few photo missions with my Mavic Pro flying camera. For two of the msisions, I launched from an open area at the far east side of the Tyson Wells complex in Quartzsite, just south of Keuhn Road.

I’m in the habit of using the Return-to-Home feature of my Mavic to get it back to its launch point quickly and efficiently. In all honesty, I’m awed by its ability to land exactly on its takeoff spot nearly every single time. I like to watch, with my finger poised over the pause button on the control (just in case), as it comes to the right coordinates far overhead, turns to the direction in which it took off, and descends to the spot.

On one of the three missions I flew from that spot, a small flock of pigeons flew right past the Mavic. I watched in shock and a bit of horror as the five or six birds swooped around my fragile aircraft. I felt relief as the Mavic continued its descent unharmed, but the whole thing repeated itself when another flock — or the same flock? — swooped past. Again, the Mavic was unharmed.

I happened to have the video camera going when this was happening. Here are two screen grabs, one from each flight, that show the closest encounter. The first one was definitely closer.

Near Miss
This reminds me of a scene from The Birds.

Near Miss
The bird is a bit farther off in this one. Can you see it?

Of course, the camera can’t capture action in a direction it isn’t pointing. For all I know they could have come closer behind the camera.

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While this is all kind of cool in a weird sort of way, it wouldn’t have been so cool if one of those birds clipped a rotor. The Mavic has four independently powered rotors. If any one of them was destroyed, I’d have to think the whole thing would immediately go out of balance and crash. This is one good reason why we don’t fly drones over crowds of people. Even though the Mavic weighs in at less than 2 pounds, having one crash onto your head from 150 feet would definitely cause some injuries.

Honestly, I’m surprised this hasn’t happened yet. A matter of time?