“Bad Start,” Greg’s May, 2015 Flying Carpet column

Beach vacation on the rocks…

PatrickShielsC182Cockpit-ILS21LfinalApproachPRC-FredGibbs_0409eSmw1200 Each spring Jean and I look forward to flying to our annual beach retreat with friends in southern California. That was still a few weeks away when I arrived at the airport one chilly morning for a local flight. Having preheated the engine overnight, I primed it as usual and turned the key.

The Flying Carpet, an older Cessna 182, has always been a terrific starter, rarely requiring more than half a turn to waken the engine. But this morning the engine barely cranked – it just groaned to first compression, and stopped. I wasn’t particularly alarmed as today’s mission was minor, and starting problems are usually easily resolved. I first suspected a weak battery. However, the voltmeter showed the battery fully charged to 24 volts, indicating outstanding health and plenty of power to start the engine.

This airplane’s battery is located back behind the baggage compartment. Thinking there might be a faulty connection or ground between it and the starter, I requested a GPU (ground power unit) start from Flagstaff’s Wiseman Aviation. However their battery cart fared no better. That the engine turned at all absolved the ignition switch and starter solenoid. “Obviously,” the problem must be the starter itself…

Mechanics Rory Goforth and Mike Clever towed the airplane to Wiseman Aviation, checked connections, and installed a new starter. But to everyone’s surprise, the engine still wouldn’t crank adequately to start.

GregBrownFT515_2713-starter adaptor calloutsSmw1200Rory explained that the only possible remaining culprit in this simple system was the “starter adaptor.” This clutch-like device mechanically connects the starter to turn the engine, and then disconnects it when the engine starts.

I’d heard of starter adaptors occasionally failing to disengage so the engine drags and burns out the starter, but never one that wouldn’t start the engine. However mine was apparently slipping internally so the spinning starter wouldn’t fully engage the engine

READ THIS MONTH’S ENTIRE COLUMN, BAD START.” (Allow a moment for the article to load.)

Top photo: Hitching a ride down the ILS to Prescott, Arizona, with instrument student Patrick Shiels and flight instructor Fred Gibbs. Lower photo: Arizona Air-Craftsman mechanic Leroy Dufresne examines the Flying Carpet after releasing it back to service.

(This column first appeared in AOPA Flight Training magazine.)

Greg

©2015 Gregory N.Brown

How to operate a constant-speed propeller

fc-cover-photo-smI’m often asked by pilots moving up to complex airplanes, what the real-world operational procedures are for a constant-speed propeller.

I like to compare using a constant-speed prop to riding a multi-speed bike. In each case you control performance via two variables:
1. rpm / how fast you’re pedaling, and
2. “oomph”/how hard you’re pedaling.

First, the rpm:

  • Flat pitch/high rpm/prop-control-forward in plane corresponds to low gear on the bike: hence better acceleration and (hill)climb performance, but limited cruise speed.
  • Coarse pitch/low rpm/prop-control-pulled-back corresponds to high gear on a bike: reduced acceleration and climb but faster on the flat and downhill/descending. Pitch is correlated to rpm through a governor, and managed by prop control.

Now for the “oomph” part. (Ie, how hard you’re pedaling.) In piston airplanes that’s controlled by throttle and measured by manifold pressure (MP). As with a bike, there are various combinations of oomph (manifold pressure) and rpm that can all result in the same speed. In aircraft the ratio is designed so changing MP up 1″ corresponds to changing rpm down 100rpm, and vice versa. So 22″ MP/ 2200 rpm = 21″ MP / 2300 rpm = 23″/2100 rpm. Consult your cruise performance charts for options.

From an operations standpoint, think bike. You’ll use high rpm/flat pitch/control full forward (think “low gear”) for takeoff, climb, and pre-landing in case you need to go around.

So on a normal flight:
1. max MP and max rpm (prop full forward) for takeoff;
2. adjust prop and MP to climb power after takeoff (if different than takeoff power)
3. reduce rpm and adjust power when leveling in cruise, and leave it there throughout the flight and descent. (Unless you need to climb en route; then you’ll increase rpm for that purpose.)
4. Increase rpm to full, pre-landing.

One thing you’ll love about this arrangement compared to the fixed pitch prop in, say a 172, is that the RPM won’t change by itself, so when flying in up- and downdrafts you needn’t constantly adjust power to keep RPM within range.

©2014, 2017 Gregory N. Brown

Announcing “The Turbine Pilot’s Flight Manual Third Edition”

TURB-PLT3_HiResI’m pleased to announce the new 3rd Edition of my book The Turbine Pilot’s Flight Manual, coauthored with my good buddy Mark Holt.

When the first edition of this book came out in 1995, it was the first publication to cover all the essentials of turbine aircraft in one book. It remains very popular to this day; I’m guessing that by now the vast majority of aspiring, personal, and professional corporate and airline pilots have copies on their bookshelves.

Along with updated contents reflecting the latest in turbine aircraft and cockpit technology, this edition for the first time includes selected color illustrations, and is newly available in ebook formats as well as print. The previously-included Aircraft Systems CD-ROM has been replaced with an included online resource page containing the same animations.

Finally, I hold a good deal of personal fondness for this book because it started me on my writing career, and has thus led to innumerable wonderful professional opportunities.

Many thanks to my coauthor Mark, and to the fine folks at our publisher ASA. Thanks especially to you readers for your lasting support and patronage of my books over all these years!

Greg

©2012 Gregory N. Brown

how it works: roll spoilers

On many jets and turboprops, roll spoilers are used to assist the ailerons in banking and thereby turning the plane. Roll spoilers are flat panels mounted on the upper wing surfaces, which deploy upward into the slipstream on the down wing only, disturbing lift and thereby aiding the down-wing aileron in effecting the turn.

Roll spoilers are interconnected with the ailerons, so as to perform in harmony with them. In many aircraft roll spoilers deploy as a function of airspeed. For example, on the de Havilland Dash-8, two roll spoilers deploy on each wing with the aileron below 140 knots, but only one operates per wing above that airspeed.

The reason roll spoilers are often required on high-speed aircraft is because they operate across such great speed ranges — such planes must resolve high-speed aerodynamics with the slow flight required for safe takeoffs and landings. Planes fly fastest with small, thin wings and high wing loading. Safe take-offs and landings, on the other hand, require high-camber, high-lift wings, with low wing loading. In essence, two different airplanes are required: one that can go fast, and one that can get everybody off the ground in less than ten miles of runway!

This challenge is resolved through extensive use of big flaps and leading edge devices (LEDs) like you see on jetliners, which effectively convert the wing from a high-speed shape to a low-speed, takeoff-and-landing shape. The problem is that in order to make wing size (and drag) small for optimum cruise speeds, the flaps must extend across as much of the wingspan as possible for adequate low-speed effectiveness. With all those flaps installed, there’s little room left on the wing for ailerons. Small ailerons may be fine for high speed cruise, but they’re often too small for adequate roll response at low airspeeds, like when taking off and landing. One solution to this problem is to put multiple ailerons on each wing, separately activated as a function of airspeed. The other solution is to install roll spoilers to help the ailerons. (The Boeing 767 utilizes roll spoilers AND two ailerons per wing — the outboard ones are locked above 240 kts).

On a few aircraft with very small wings, such as the Mitsubishi MU-2, the flaps must be so big to achieve reasonable landing speeds that there’s no room left for ailerons at all! So on MU-2s, all roll control is accomplished by spoilers. Since spoilers effect roll by destroying lift, crosswind techniques for such aircraft must be modified under marginal take-off and landing situations.

Incidentally, Transport Category Airplanes must be equipped with redundant or separated primary flight controls in order to overcome any control jams. So on planes that have them, the roll spoilers usually connect to one pilot’s flight controls, while the ailerons connect to the the other. The two control yokes are mechanically linked so ailerons and spoilers work together when turning either yoke. But if either the roll spoilers or the ailerons were to jam, a clutch connecting the two systems can be released or overcome, allowing one pilot to fly via the one that still works. Pretty cool, eh?!!

 To learn more about turbine aircraft and how they work, see The Turbine Pilot’s Flight Manual and included Aircraft Systems CD-ROM. ©2009 Gregory N. Brown

how it works: auxiliary power unit (APU)

Ever wondered about those little exhaust pipes protruding from the tails of many jets and turboprops? Well, your eyes aren’t deceiving you— in many cases those are indeed jet engine exhausts, from small “extra” jet engines known as “APUs.”

An “APU” (Auxiliary Power Unit) is a small turbine engine installed to provide supplementary power. Often found in the tails of larger jets and turboprops, APUs serve several useful purposes.

APU generators provide auxiliary electrical power for running aircraft systems on the ground when the main engines aren’t running and no ground electrical power is available. Applications include powering environmental systems for pre-cooling or preheating the cabin, and providing power for crew functions such as preflight, cabin cleanup, and galley (kitchen) operation. Many aircraft APUs can also be operated in flight, providing backup power for the main engine generators.

On larger aircraft, APUs also generate auxiliary “bleed air”, referring to pneumatic pressure drawn from the engine’s compressor section. That’s because large jet engines like those on airliners must be started using pneumatic power. Unless a ground pneumatic source is available, the only way to start large turbine engines is from an operating APU (unless another engine is already running, of course). To accomplish this, the small APU engine is first started using an electric motor (often doing double duty as the generator). Once up and running, APU bleed air is routed to pneumatic starters on the plane’s main engines. Those, in turn, spin up the engine compressors for starting.

This schematic shows a typical APU installation. Along with providing ground power, APUs often provide backup pneumatic power for pressurization in flight, and back up environmental systems on the ground and in the air.

To learn more about turbine aircraft and how they work, see Greg’s book, The Turbine Pilot’s Flight Manual. The material is easy for any aviation enthusiast to understand, and interesting!

©2013 Gregory N. Brown

how it works: “glass cockpit” vs. “steam gauges”

At first glance, the “glass cockpits” found in modern aircraft may look like they come from a different planet than the round “steam gauge” instruments found in older general aviation cockpits.

But upon closer examination you can see that most primary flight displays (PFDs) actually conform closely to the “standard T” layout of round flight instruments found in older cockpits. Look closely at the illustration and you’ll see the similarities in layout.

For those who are not familiar, note that the HSI (horizontal situation indicator) may be found in both round-instrument and “glass” cockpits — it’s simply a combination instrument including both heading indicator and CDI (course deviation indicator) needles.

To learn more about how turbine aircraft work, pick up a copy of my book The Turbine Pilot’s Flight Manual. You’ll find it enjoyable and interesting!

©2009, 2015 Gregory N. Brown

how jet engines work

While the reciprocating (or piston) engines that power cars and most light airplanes have a few commonalities with gas turbine (jet) engines, the two types are very different in most respects.

recipengBoth piston (left) and turbine (below) engines have somewhat similar stages of operation: intake, compression, combustion, and exhaust. But the similarities largely end there, the biggest difference being that in reciprocating engines those stages happen one at a time, while in turbine engines they are continuous.

Instead of compressing intake air with a piston, turbine engines use a series of wheels at the front of the engine known as compressors. Another set of wheels, known as turbines, is driven by exhaust gases departing the combustion section. Both compressor and turbine wheels are essentially sophisticated “fans,” composed of high-tolerance blades spinning at very high speeds inside a tightly-ducted cowl.

turbengMuch like a turbocharger, a turbine engine’s compressor and turbine sections are mounted on a common shaft. Intake air is compressed by the compressors, and forced into the combustion chamber. Fuel is continuously sprayed into the combustion chamber and ignited, generating expanding exhaust gases that drive the turbines. The turbines, through their shafts, drive the compressors, sustaining the process. The turbines also harness energy to drive accessories such as electrical generators and hydraulic pumps. Finally, the exhausting gases are accelerated through a nozzle at the back of the engine, producing thrust somewhat like the way air escaping the “nozzle” of an untied balloon propels it across the room.

enginecomparisonfig-webIn piston-powered airplanes the engine always turns a propeller to pull it through the air, but turbine engines can either operate as jets or drive propellers themselves. A turbine engine driving a propeller is known as a turboprop.

The basic gas turbine engine we’ve described is sometimes called a “gas generator,” or “core turbine engine.” Depending on how the exhaust gases are harnessed, the core turbine engine may be applied to turbojet, turbofan, or turboprop engines.

While most reciprocating aircraft engines burn gasoline, turbine engines consume kerosene. Turbine engines produce much more power for their weight than piston engines, but they burn more fuel and are far more expensive to manufacture. To learn more about turbine aircraft, see Greg’s book, The Turbine Pilot’s Flight Manual©2012 Gregory N. Brown