The multiengine height-velocity diagram

February 6, 2015 by Markus Lavenson

The last two blogs provided great explanations of the height-velocity diagram as it pertains to single engine helicopters. So, let’s now take it a little further into the multiengine helicopter realm.

Just as with singles, you will typically find a H-V diagram for multiengine helicopters in the flight manual. However, unlike the singles, the H-V diagram for the multi is to insure a safe landing OEI (one engine inoperative), and not from an autorotation. Furthermore, whether or not the H-V diagram even applies is dependent on how well the aircraft can perform OEI. This performance is defined in a series of categories. If the multi is full-time Category B (as are all singles), or a part-time Cat B, then a H-V diagram limitation will apply; whereas, if Category A it will not. Basically, Cat A is where OEI performance is so good that the H-V is not applicable. Comparing three very different multiengine helicopters to highlights these differences.

The BO105CBS is full-time Cat B, with marginal OEI performance. Even in ideal conditions (light weight and low density altitude), it can barely hold altitude on one engine. Varying airspeed from Vy just a couple knots results in a descent. Approach and departure profiles AEO (all engines operating) need to be such that a quick transition can be made in accordance with the H-V diagram, in the event of an engine failure.

The Bell 412 is an example of a multi that can be operated Cat A or Cat B, depending on the weight, altitude, and temperature. At lower weights, altitudes, and temperatures it will have good enough OEI performance to qualify as a Cat A aircraft. However, in most day-to-day operations it is typically a Cat B aircraft, which means the H-V diagram would apply.

 

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Bell 412 H-V diagram

 

The AgustaWestland 139 is a true Cat A aircraft, although as with many other Cat A aircraft it is possible to find conditions that will push it into Cat B. The AW139 was largely designed to operate Cat A, in an offshore petroleum support environment with a high useful load (passengers, cargo, and fuel). It is capable of landing and taking off from helipads, while carrying up to 15 passengers, with Cat A performance.

 

AW139 height-velocity chart

AW139 H-V diagram

 

So, what is Cat A?  Cat A is where the aircraft has adequate performance capability for continued safe flight in the event of an engine failure, no matter when that failure occurs. While single engine and Cat B multiengine helicopters have no such assurances, the Cat A aircraft is able to ensure that a safe and normal landing can be made OEI at an airport or heliport.

In the event of an engine failure, different types or categories of helicopters dictate different courses of action in order to do the same thing: preserve rotor RPM. No matter the helicopter and its’ number of engines, Nr is the wing and it must be maintained. The single must obviously enter an autorotation. The Cat B multi must fly at or above Vy (best rate of climb OEI) in order to maintain or increase altitude, and then fly to an area where a safe landing can be made. During takeoff and landing while close to the ground and below Vy, an engine failure in a Cat B will likely result in a forced landing. Though not as dire as an autorotation, it is more of an event than the Cat A helicopter. The difference with the Cat A is that engine failure doesn’t dictate a forced landing. In the event of an engine failure during takeoff, a Cat A has the ability to either return to and safely stop at the takeoff area or to continue takeoff, climb and establish forward flight. In the event of an engine failure during landing, the Cat A can either land at the intended landing area or abort the approach and reestablish forward flight. Unlike Cat B, there is no exposure to the possibility of a forced landing, hence no H-V diagram.

(These views and opinions are my own and do not necessarily reflect the views of Era.)

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Maximum performance takeoffs and judgement calls

January 21, 2015 by Maria Langer

Ed note: In the last post we covered the mechanics of the Height-Velocity Diagram. Here author Maria Langer discusses an application of its use. 

This past summer, I was part of a helicopter rides gig at an airport event. There were three of us in Robinson R44 helicopters, working out of the same rather small landing zone, surrounded on three sides by parked planes and spectators. We timed our rides so that only one of us was on the ground at a time, sharing a 3-person ground crew consisting of a money person and two loaders. Yes, we did hot loading. (Techniques for doing that safely is fodder for an entirely different blog post.) The landing zone was secure so we didn’t need to worry about people wandering into our flight path or behind an idling helicopter.

The landing zone opened out into the airport taxiway, so there was a perfect departure path for textbook takeoffs: 5-10 feet off the ground to 45 knots, pitch to 60, and climb out. It was an almost ideal setup for rides and we did quite a few.

One of the pilots, however, was consulting a different page of the textbook: the one for maximum performance takeoffs. Rather than turning back to the taxiway and departing over it, he pulled pitch right over the landing zone, climbed straight up, and then took off toward the taxiway, over parked planes and some spectators. Each time he did it, he climbed straight up a little higher before moving out.

I was on my way in each time he departed and I witnessed him do this at least four times before I told him to stop. (I was the point of contact for the gig so I was in charge.) His immediate response on the radio was a simple “Okay.” But then he came back and asked why he couldn’t do a maximum performance takeoff.

It boggled my mind that he didn’t understand why what he was doing was not a good idea. The radio was busy and I kept it brief: “Because there’s no reason to.”

The Purpose

The Advanced Flight Maneuvers chapter of the FAA’s Helicopter Flying Handbook (FAA-H-8083-21A; download for free from the FAA) describes a maximum performance takeoff as follows:

A maximum performance takeoff is used to climb at a steep angle to clear barriers in the flightpath. It can be used when taking off from small areas surrounded by high obstacles. Allow for a vertical takeoff, although not preferred, if obstruction clearance could be in doubt. Before attempting a maximum performance takeoff, know thoroughly the capabilities and limitations of the equipment. Also consider the wind velocity, temperature, density altitude, gross weight, center of gravity (CG) location, and other factors affecting pilot technique and the performance of the helicopter.

This type of takeoff has a specific purpose: to clear barriers in the flight path. A pilot might use it when departing from a confined landing zone or if tailwind and load conditions make a departure away from obstacles unsafe.

The Risks

This is an “advanced” maneuver not only because it requires more skill than a normal takeoff but because it has additional risks. The Helicopter Flying Handbook goes on to say:

In light or no wind conditions, it might be necessary to operate in the crosshatched or shaded areas of the height/velocity diagram during the beginning of this maneuver. Therefore, be aware of the calculated risk when operating in these areas. An engine failure at a low altitude and airspeed could place the helicopter in a dangerous position, requiring a high degree of skill in making a safe autorotative landing.

And this is what my problem was. The pilot had purposely and unnecessarily decided to operate in the shaded area of the height velocity diagram with passengers on board over an airport ramp area filled with other aircraft and spectators.

Height Velocity diagram for a Robinson R44 Raven II. Flying straight up puts you right in the “Deadman’s Curve.”

Height Velocity diagram for a Robinson R44 Raven II. Flying straight up puts you right in the “Deadman’s Curve.”

Seeing what he was doing automatically put my brain into “what if” mode. If the engine failed when the helicopter was 50-75 feet off the ground with virtually no forward airspeed, that helicopter would come straight down, likely killing everyone on board. As moving parts came loose, they’d go flying through the air, striking aircraft and people. There were easily over 1,000 people, including many children, at the event. My imagination painted a very ugly picture of the aftermath.

What were the chances of such a thing happening? Admittedly very low. Engine failures in Robinson helicopters are rare.

But the risks inherent in this type of takeoff outweigh the risks associated with a normal takeoff that keeps the helicopter outside the shaded area of the height velocity diagram. Why take the risk?

Just Because You Can Do Something Doesn’t Mean You Should

This all comes back to one of the most important things we need to consider when flying: judgment.

I know why the pilot was doing the maximum performance takeoffs: he was putting on a show for the spectators. Everyone thinks helicopters are cool and everyone wants to see helicopters do something that airplanes can’t. Flying straight up is a good example. This pilot had decided to give the spectators a show.

While there’s nothing wrong with an experienced pilot showing off the capabilities of a helicopter, should that be done with passengers on board? In a crowded area? While performing a maneuver that puts the helicopter in a flight regime we’re taught to avoid?

A responsible pilot would say no.

A September 1999 article in AOPA’s Flight Training magazine by Robert N. Rossier discusses “Hazardous Attitudes.” In it, he describes the macho attitude. He says:

At the extreme end of the spectrum, people with a hazardous macho attitude will feel a need to continually prove that they are better pilots than others and will take foolish chances to demonstrate their superior ability.

Could this pilot’s desire to show off in front of spectators be a symptom of a macho attitude? Could it have affected his judgment? I think it is and it did.

Helicopters can perform a wide range of maneuvers that are simply impossible for other aircraft. As helicopter pilots, we’re often tempted to show off to others. But a responsible pilot knows how to ignore temptation and use good judgment when he flies. That’s the best way to stay safe.

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The mysteries of the height-velocity curve

December 17, 2014 by Matt Johnson

Call it what you want; height-velocity curve, dead-man’s curve or even limiting height-speed envelope for those who like sophisticated phrases. The “dead-man’s curve” is probably a carryover from our fixed-wing brethren while the industry generally accepts the simple reference of “H/V curve”. The inside of the curve is the area from which it will be difficult or nearly impossible to make a safe landing following an engine failure if you are in the same conditions depicted with respect to airspeed and altitude.

The H/V (height-velocity) diagram is a staple in the helicopter arena but sadly is often misunderstood by student and instructors alike. So, let’s take a look at what it is and how it is developed.

What is it?

The Height-Velocity diagram (curve) is a chart showing various heights above the ground with a combination of a velocity (indicated airspeed) where successful autorotation and landing is or is not possible. This magical combination of numbers yields two major regions on the chart; the area above the knee and the area below the knee. These areas are what actually plot much of the “curve”.  During initial helicopter certification, test pilots evaluate several characteristics of the helicopter that help determine the H/V curve. These factors include the helicopters initial response to a power loss, steady-state descent performance and power-off landing characteristics and capabilities.

Unknown to many, the development of the H/V curve and its associated number combinations is based on “pilot minimum skill level”. So, in a perfect world this means if the engine fails while I’m going this fast (KIAS) and at this height a pilot at a “minimum skill level” should be able to make a successful autorotation and hopefully some resemblance of a landing.

How do we define the pilot “minimum skill level?” That is a question I and many others can’t answer. Many will agree the current practical test standards are somewhat lacking and aren’t necessarily cultivating the “minimum skill level” necessary.

HVDiagramR44

No cookies for me please

To delve into this quandary let us recap the typical sequence of an autorotation training exercise. The instructor has the student line the helicopter up with the runway so that the power-recovery phase of the autorotation will occur as closely to the runway numbers as possible. Sound familiar? You know what I’m talking about, the “3, 2, 1, roll-off power” etc.

It’s the same thing with a 180-degree autorotation where the student is taught where to “fail” the engine based on tailwind strength and land at the “spot” within the practical test standard. Is there really anything practical about it?  Just what, if an engine failure occurs in the real world and the only spot you have is 600 feet directly below you? Could you get there? Safely? What about engine failures at night time with the same situation, the only place to go is directly below you or just out in front of you. If you remember anything from this article remember this, autorotations are like fingerprints in that no two are exactly the same.

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The dawn of the new Jet Ranger

December 4, 2014 by Ian Twombly

First flights of an aircraft design program are always a big milestone, but when the aircraft is one based on a machine that defined a generation, it becomes a big deal, indeed. Bell’s first flight of the 505 Jet Ranger X last month marks a significant event in the helicopter’s life cycle. The flight lasted only 30 minutes and included basic hover work and a few trips around the pattern at Bell’s Mirabel facility in Quebec, Canada.

Yet despite reaching a big milestone, it was arguably not even the biggest news to come out of the development program last month. What’s been much more fascinating to watch is the speed with which Bell has racked up orders for the next gen Jet Ranger. Officially launched at this year’s Heli-Expo in February, Bell has already signed 300 orders for the aircraft. Some 50 of those are from Chinese company Reignwood Investments. For sake of comparison, Robinson said earlier this year that it has produced 500 R66s since the aircraft was certified a few years ago.

image_nov10

If we assume the 300 orders for the Jet Ranger stick, it serves to validate the business case for the program. Some might say it shows the market was always there, which may be true. But often it takes an outside pressure, such as the R66, to drive demand for a segment. The fact that it gave Bell the opportunity to refresh the design doesn’t hurt either.

It’s easy to call the new Jet Ranger a clean sheet design, and absent any official definition, I suppose it’s a fair description. But it’s also not wrong to call it a significant refresh of an existing product. By using proven components, such as the drive system, Bell has smartly stuck to what it knows, and has helped to ensure the success of the product.

Expect to see the Jet Ranger certified in 2016, and absent any hiccups with the new plant in Louisiana, see them rolling out the door soon after.

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Plain and Simple: The Bell 206

October 20, 2014 by Neal Lanning

The Bell 206 Jet Ranger is what the non helicopter flying public pictures in its mind when you talk about vertical flight. It’s that iconic image of the Bell 206 “as seen on TV” all through the 1970’s – 1980’s and beyond.

Plain and simple, the 206 is one of the most reliable airframes ever built.  It is a workhorse in the helicopter industry and paved the way for many of the helicopter operations we rely on today, regardless of manufacturer, including the military.

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Advanced Helicopter has managed and operated a Bell 206 since 1997. It’s an older 1972 B converted to BIII specs, serial number 823, which is low in the 206 world. The helicopter is used in a specific operation for data collection and aerial photography now, but over its life has been a corporate helicopter, firefighter, aerial spray applicator, moviemaker, turbine transition instruction platform, and FAR 133 operations platform (long line).

I have somewhere between 600 and 800 hours flying that specific helicopter and over the years you build a relationship of trust and expectations from one another. I know when I’m working that helicopter what to expect from it and I would like to think it knows what I’m going to ask of it.

Most of the missions that helicopters do today were made possible by the Bell 206. It was the first to do many of them, which other manufactures, and Bell itself, later improved upon. It was born from the OH-58 Kiowa developed for the Army around 1962, and introduced around 1967. There it has done all kinds of missions: transport, medical, VIP, and even combat. It has proven to be an invaluable asset to the military.

The reason the 206 is so good in so many different applications is because it’s big enough to get the job done yet small enough to have maneuverability in tight spaces; its payload strikes a good balance between crew, fuel, and range. It’s also easy and forgiving to fly and relatively simple to maintain.

There were about 7,300 manufactured, many still working ever day somewhere. Bell no longer produces the Bell 206. It was replaced by the Bell 407, another great helicopter, but another story for another day. (The recently announced Bell 505 will soon replace the original 206.)

I’ve had the honor to fly many types of helicopters over the years and the Bell Jet Ranger is still one of my favorites. It provides a near perfect balance…plain and simple.

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The little helicopter that could

September 11, 2014 by Ian Twombly

If you’ve ever flown a Mooney you know they are fast, responsive, and a great value in terms of speed for fuel. That the company has fallen and come back time and time again is as much a testament to the product as it is an indictment of the ownership.

Fly an Enstrom and look in to the company’s history and it’s clear it and Mooney are kindred spirits. The Chinese state-owned company that controls Enstrom is only the latest in a long and undulating path that includes everyone from the famous and quirky to the publicly anonymous venture capital firm. Yet, like Mooney, the products have been strong with an equally strong following. Fly one and it’s easy to see why.

The current line-up is much the same as its been for the past 10 years–the turbine 480B, and piston F-28F and 280FX. The F-28F and 280FX are essentially the same helicopter with the exception of the 280FX’s sleeker cockpit. With the infusion of money from the new owner the company has almost doubled the size of its factory and is on an ambitious plan to produce the TH180, a trainer aimed squarely at Sikorsky’s neglected S-300.

Enstrom's upcoming TH180 trainer

Enstrom’s upcoming TH180 trainer

CEO Tracy Biegler says the trainer’s certification program is a warm-up to an expanding line of products, one that probably goes up to bigger turbines. With the right strategy, and assuming the models stay true to Enstrom’s core values, they should see success.

We had the opportunity to fly both the 480B and the F-28F, both of which are quite impressive. The turbine is a bit underpowered, but it flies beautifully, and has enjoyed a great safety record. That focus on safety is part of why the company has won some important foreign military training contracts over the last five years, and what has allowed it to go from producing only five helicopters in 2012 to an anticipated 30 or so this year.

Meanwhile the turbocharged F-28F has power to spare, at least with two on board and a slightly above-standard day. We were shooting up at 1,500 feet a minute at best-climb speed. Both helicopters are rock solid to fly, have benign autorotation characteristics, and are clearly well built.

If Enstrom can stay true to its roots and the owners remain interested, the men and women of Menominee have a bright future.

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Slaying the dragon

August 26, 2014 by Neal Lanning

Regardless of what helicopter you are flying, whether it’s the Robinson R22, Bell JetRanger, or any helicopter for that matter, you need to be comfortable with autorotations. At our flight school we have broken the auto in to three flights. If you’re a CFI reading this, try it. If you’re the student or certificated pilot looking to get proficient, ask for it.

Start with talking on the ground, sitting in the helicopter, and going through the physical motions. Move the controls the way you would actually respond. If you are the CFI, play the whole thing down (mentally) and don’t let the student get beaten before they even lift off. If you are the client/student try to put past bad experiences with autos behind you.

First Flight: Auto-rotative decent. Climb to at least 3,000 feet. I like even higher. The only thing you want at first is RPM control. There is plenty of time to adjust airspeed. RPM is the constant in most cases. Climb back up and then try adjusting the airspeed all the way through the decent from 30-70 knots, noting what cyclic control movements do to the RPMs. Get comfortable with controlling RPM with mostly cyclic movement. The ONLY thing you want to achieve by the end of this lesson is comfort with RPM and airspeed control in the decent.

Second Flight: I like to start with quick stops from 50 feet and 60 knots, which is very similar to the flare in an autorotation. End this lesson with auto-rotative descents, followed by a flare (quick stop). Join the needles (rotor and engine RPM) very early so it seems just like the two maneuvers put together. By doing this you’ve learned to join the needles at 300 feet AGL, and not in the flare where most over-speeds occur. End this lesson being comfortable with descents and the flare.

Third Flight: Go over all three maneuvers and then combine them all together. Join the needles a little further down the line each time. Don’t be crazy about that; the auto looks the same regardless of where you join the needles.

If you want to accomplish full down autorotations, add a fourth lesson of hovering autos and run-on landings, which will be the same as a touch down from zero ground speed or from 15-20 knots if you are unable to zero out the ground speed.

This should build your confidence and make it fun, regardless of what helicopter you are flying.

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Oshkosh or bust

August 14, 2014 by Ian Twombly

I’m forever spoiled. Everyone talks about flying an airplane to EAA AirVenture in Oshkosh, Wisconsin, but arriving in a helicopter is a far better experience. I’m burdened with knowing this now, thanks to Sporty’s Pilot Shop’s John Zimmerman, my ride to the show this year.

 

John owns a beautiful R44 he flies for fun and the occasional work purpose. Being a gadget geek, his is kitted out with a Garmin 430, a handheld Garmin 496, and that day we were carrying two iPads, and Sporty’s new Iridium Go! satellite hotspot. It also has air conditioning, which is a luxury well worth having. So while many would scoff at the suggestion that a helicopter is a cross-country aircraft, with some nice instrumentation and create comforts, it turns out to be well suited to the task.

 

The trip started with an early morning airline flight to Cincinnati, where I met John. The first two miles were over the eerily quiet Cincinnati-Northern Kentucky International Airport. The helicopter proved to be a good vantage point to see the juxtaposition of miles upon miles of runways for the dozen or so regional jets parked at the various terminals.

 

From there it was another 348 miles on to Oshkosh, including two stops. Since helicopters and their pilots are most comfortable at lower altitudes, trips like this are a joy. The world isn’t going by very fast, which leaves that much more time for taking it all in. Lounging around at 75 knots groundspeed, the trip took more than four hours, but it felt like much less.

 

The best part of the trip, and what airplane pilots miss out on, is the arrival to the show. In an airplane there is a mass convergence on one spot southwest of the airport as everyone forms a line and heads in. You have to listen closely to air traffic control, respond quickly, and follow the controller’s directions precisely. The arrival procedures in a helicopter are much more civilized. Simply listen to ATIS, monitor the tower, maintain 1,800 feet, and land. Transients can park at Pioneer field, outside the main show site. From the time we shut down to the time our ride arrived was 10 minutes. There’s no walking, no humping heavy bags. They pulled off the main road and we jumped in and left. Clearly the folks at EAA know helicopter pilots, and the arrival suits them perfectly.

 

With the R44’s fuel-burn rate, and lackluster groundspeed in headwinds, it might not be the most efficient cross-country machine. It is, however, a lot of fun, which is all that matters when you are on your way to Oshkosh.

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Robinson R22: The good, the bad, and the ugly

July 15, 2014 by Neal Lanning

As the President of Advanced Helicopter Concepts, Inc. in Frederick, Maryland, a Robinson Dealer and Service Center for 27 years, we have learned a lot about the Robinson R22. Advanced Helicopter currently operates five R22s, including one instrument trainer, a 1983 Alpha, serial number 378, that is still going strong.

The Good: The R22 is hands-down the world’s leader in civil helicopter training. It is like the Cessna 152 of the fixed-wing world. The helicopter is reliable, cost effective and safe if operated within its guidelines. Like it or not Frank Robinson and the R22 created an entire new helicopter market. It services the recreational helicopter pilot and allows helicopter ownership. Before the R22 and R44 both were rare. The R22 is also able to feed the rapidly growing EMS and law enforcement pilot demand that was fueled by a large crop of retiring pilots. With the demand in the last 20 years, retiring military pilots could not keep pace. With that being said…

13_Helicopter Transition_0133

The Bad: The R22 does demand respect. Regardless of your experience in the helicopter, when you think you have it figured out, it will remind you that you that it demands respect. Like all helicopters, especially those with light inertia rotor systems, the recognition time during an engine failure or other emergency requiring an autorotation is critical. The trick is to get the helicopter into an autorotation in time. Once in the autorotation it does a good job and is predictable. As a pilot of the R22 you must always be aware that getting into an autorotation is the most critical time. As a CFI you must double your effort and just know at some point in the flight you may have to take the helicopter if there is a problem. If there’s no problem, great, but the awareness must always be heightened.

The Ugly: If you are not diligent, do not get the helicopter into an autorotation in the small window, and the rotor RPM get below about 75 percent you may never get it back. So it essential to just get the helicopter into autorotation and maintain RPM, deal with airspeed, and find a suitable place next. Stored energy in altitude is your best friend; continuous low operation is not a good idea. There are other problems, such as the rapid rollover rate if you stick a skid, and the helicopter can be very unforgiving. Practice your hovering and ground maneuvers with some space between you and the ground.

Despite the issues, it is still a great helicopter and we love ours. The way the average pilot can overcome any issues is to be prepared. Visit a competent helicopter company with reputable CFIs until you have slayed the dragon and an autorotation is another day at the office.

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Tiltrotor completes auto tests

May 22, 2014 by Ian Twombly

AgustaWestland announced late last month that its AW609 Tiltrotor has completed dual-engine failure autorotation tests. This is a big milestone in the long development process that will result in the world’s only civilian tiltrotor, planned for certification in 2017.

The aircraft’s massive prop rotors make it impossible to land and take off with the engines in airplane mode. Because the aircraft exists in the space somewhere between an airplane and a helicopter, AW had to work with the FAA to determine exactly how it would be tested. The result was a requirement to be able to land safely in the same way a helicopter does after a failure in either mode. For the testing program that meant a demonstrated ability to go from a worst case scenario of full aircraft mode to a safe landing in full helicopter mode.

The few people outside company test pilots who have flown the aircraft praise its automated systems management capability. That is on display during the autorotation, where the aircraft automatically maintains an angle of incidence that results in 100 percent rpm after an engine or drive system failure. As the aircraft descends it must at some point convert fully to helicopter mode, which the company said it does rapidly. The nacelles go to a full aft position of 95 degrees for a run-on landing.

Most interesting about the aircraft is what might lead to a failure. It’s powered by Pratt & Whitney PT6 engines, each with its own gearbox. Both are connected by a common drive shaft, so if one engine fails the other working engine will provide power to both. AW thinks a complete and simultaneous dual failure is highly improbable, and the only time they envision a subsequent failure is with fuel contamination. Either way, more than 70 tests over 10 flight hours appears to prove the aircraft has the ability to handle such a problem.

AW609 demo flight during HAI's 2014 Heli-Expo

AW609 demo flight during HAI’s 2014 Heli-Expo

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