MULTI-ENGINE AERODYNAMICS

OEI AERODYNAMICS

How do pitch, roll, and yaw forces change during an engine failure?

Pitch decreases, roll pulls toward the failed engine, and yaw swings toward the dead engine.

Which axis — pitch, roll, or yaw — usually gives the most obvious indication of an engine failure?

Yaw.

Why does lift change on one wing during an engine failure?

Because the loss of thrust causes a drop in the accelerated slipstream over that wing.

How would the aerodynamic forces be different if an engine failure occurred on the ground?

The roll moment would be weaker since the wheels are on the ground and lift is reduced; also, the slipstream may be dampened by ground interference.

Why is it so important that pilots practice the body movements required to compensate for changing aerodynamic forces during an engine failure?

Because a real engine failure demands a quick and correct reaction from the pilot.

OEI CLIMB PERFORMANCE

Why does a 50% reduction in power result in a far greater reduction in performance?

Performance depends on excess thrust. An engine failure both cuts thrust and adds drag, which severely reduces excess thrust.

Following an engine failure, how can performance be improved?

By cutting drag through establishing a zero sideslip condition and adjusting the airplane’s configuration appropriately.

What pilot actions distinguish the sideslip angle from the zero sideslip angle?

In a sideslip, the pilot uses rudder and aileron to keep wings level and maintain heading. In zero sideslip, the pilot banks slightly toward the operating engine and eases off rudder pressure until the airplane shows slight uncoordination (split ball).

APPLIED OEI CLIMB PERFORMANCE

How might a pilot plan differently for an engine failure after takeoff at sea level versus at a high-density altitude airport?

At high density altitude, there might not be enough excess thrust to climb or even maintain flight after an engine failure. Pilots should plan for a possible off-airport landing and consider delaying the flight until conditions improve.

What actions can a pilot take to increase single-engine performance before departure?

Reduce weight, use maximum available power, and configure the airplane for a maximum-performance (short field) takeoff.

VMC

What aerodynamic force makes VMC the minimum controllable airspeed?

Rudder force. Once yaw from engine failure overpowers full rudder deflection, VMC is reached.

Why is VMC so important during takeoff?

Flying below VMC after an engine failure on takeoff is often unrecoverable without sufficient altitude.

What are all the certifying criteria used to establish VMC?

• Critical engine inoperative and windmilling
• Operating engine at maximum power
• Most unfavorable gross weight and center of gravity
• Bank up to 5° toward the operating engine
• Maintain heading within +/- 20°
• Takeoff configuration (flaps, cowl flaps, trim set)
• Standard atmosphere at sea level (15°C and 29.92″ Hg)
• Out of ground effect
• Gear up
• 150 lbs maximum rudder force

What effect does landing gear have on VMC? On performance?

Lowering landing gear reduces VMC and also cuts performance.

Why is VMC determined with landing gear up?

Landing gear provides a stabilizing keel effect that lowers VMC. However, since the gear is usually retracted after an engine failure for better performance, VMC is certified gear up.

How does density altitude affect VMC? Performance?

High density altitude lowers VMC by decreasing engine power but also reduces overall aircraft performance.

CRITICAL ENGINE

What are the four factors that make an engine critical?

P-factor, accelerated slipstream, spiraling slipstream, and torque.

How does P-factor affect the critical engine?

P-factor causes more thrust on the descending blade (right side in most light twins). Since the right engine’s descending blade is farther from the CG, a left engine failure causes a bigger yaw force than a right engine failure.

How does accelerated slipstream affect the critical engine?

Accelerated slipstream boosts lift behind the propellers, with greater lift located behind descending blades. Because the right wing’s lift is farther from the CG, losing the left engine creates greater rolling asymmetry.

How does spiraling slipstream affect the critical engine?

The spiraling slipstream wraps under the engines and exits to the right. The critical engine’s slipstream hits the tail and counters yaw if the non-critical engine fails. If the critical engine fails, the tail gets no help resisting yaw.

How does torque affect the critical engine?

Engines spinning to the right produce a left-turning torque. If the non-critical engine fails, remaining engine torque slightly helps. If the critical engine fails, torque worsens the yaw problem.

Does an airplane with counter-rotating engines have a critical engine? Why or why not?

No. Counter-rotating engines cancel out the four factors, making both engines equally important.

MULTI-ENGINE SYSTEMS

GENERAL SYSTEMS

What is the major difference between the propeller governors in single-engine and multi-engine constant speed systems? Why are they designed differently?

Multi-engine airplanes have propellers that move to high pitch, low RPM if oil pressure fails, helping to feather and reduce drag. Single-engine airplanes move to low pitch, high RPM to help with windmilling and restart.

What is the purpose of an unfeathering accumulator?

It stores pressurized oil to push the propeller out of feather for restarting the engine.

What is the purpose of a propeller synchronizer/synchrophaser? How do pilots without either keep the propellers in sync?

Synchronizers or synchrophasers adjust RPM to lower vibration and noise. Without them, pilots match RPMs using the tachometer and fine-tune by ear and feel.

What is the difference between fuel cross-feed and fuel transfer systems?

Fuel cross-feed lets an engine draw fuel from the opposite tank. Fuel transfer moves fuel physically from one tank to another.

What is the difference between de-ice and anti-ice systems?

De-ice systems remove existing ice; anti-ice systems prevent ice from forming.

How do de-ice boots function? What improper use can cause them to stop working?

De-ice boots inflate with pneumatic pressure, cracking and shedding ice from the wing’s leading edge. If used too early, ice can stick to the inflated boots, trapping them and disabling the system.

How does a glycol bleed system work?

Glycol bleed systems prevent ice accumulation by forcing anti-ice fluid through a series of pores located on the wing surfaces. This coating of glycol inhibits the formation of ice.

What improper use can prevent it from working?

Glycol systems are preventive only. If ice is already present on the airfoil before activating the system, glycol cannot remove it. Allowing ice to form before system use is a common misuse that renders it ineffective.

Advantages and Risks of Heated Wing De-Ice/Anti-Ice Systems

A heated wing system provides both de-icing and anti-icing capabilities. Unlike glycol or pneumatic boot systems, heated wings can be activated at any time to either remove existing ice or prevent further buildup.

Primary hazard:

The heating air is extremely hot. A leak in the bleed duct system can lead to structural damage or even pose a fire risk.

Cessna 310 Fuel System

(Note: If you are not training in a Cessna 310, you may disregard this section.)

Fuel System Operations

Excess Fuel Handling:

Any excess fuel delivered to the engine-driven pump is routed back to the corresponding main (wingtip) tank.

Purpose of Internal Main Tank Pumps:

Internal pumps move fuel from the forward portion of the main tanks back toward the electric-driven pump. This is especially critical during steep descents to ensure continuous fuel feed.

Fuel Management Capabilities

Crossfeed:

The Cessna 310 can crossfeed between tanks but cannot transfer fuel directly from one main tank to the other.

However, fuel can be transferred from a wing locker tank to the corresponding main tank.

Number of Fuel Pumps:

Depends on configuration:

• 2 engine-driven pumps
• 2 auxiliary pumps
• 1 internal transfer pump per main tank
• 1 pump per locker tank

Thus:

• With 1 locker tank: 7 pumps total
• With 2 locker tanks: 8 pumps total

Number of Fuel Tanks:

5 or 6 tanks, depending on locker tank installation:

• 2 main tanks (wingtip)
• 2 auxiliary tanks (inboard wing)
• 1 or 2 locker tanks (optional)

Fuel Selectors:

2 fuel selectors (one for each engine).

Fuel Strainers:

2 fuel strainers (one for each engine).

Fuel Usage Procedures

When to Switch to Auxiliary Tanks:

After at least one hour of flight if starting with full main tanks.

Takeoff and Landing Fuel Tanks:

Always use main tanks for takeoff and landing.

The auxiliary fuel pumps (set to LOW) support the main tanks.

If an engine-driven pump fails, the auxiliary pump automatically switches to HIGH, maintaining fuel flow.

Note: When the auxiliary pump shifts to HIGH, you may need to lean the mixture to compensate for potential over-fueling.

Risk of Fuel Dumping:

Operating on auxiliary tanks with full or nearly full main tanks can cause fuel to vent overboard.

Multi-Engine Operations

Takeoff Speeds

Critical Speed:

The minimum speed published by the manufacturer at which the aircraft can continue flight on a single engine.

Aborting After Critical Speed:

Yes, it is acceptable to abort if runway length permits. It may even be preferable in certain scenarios.

Blue Line:

Vyse — the best rate of climb speed with one engine inoperative.

Red Line:

Vmc — the minimum controllable airspeed with an engine inoperative.

Important: Vmc is dynamic, affected by configuration, power output, and bank angle. The published Vmc represents the worst-case combination, summarized by the acronym COMBATSOG150.

Vxse vs. Vmc Proximity:

In many multi-engine aircraft, Vxse (single-engine best angle of climb) and Vmc are very close.

Safety Concern: Following an engine failure during a short-field takeoff, climbing at Vxse puts the aircraft close to Vmc, requiring precise flying to maintain control.

Accelerate-Stop and Accelerate-Go

Accelerate-Stop Distance:

The distance to accelerate to critical speed, abort the takeoff, and come to a complete stop.

Accelerate-Go Distance:

The distance to accelerate to critical speed, experience an engine failure, and continue takeoff to 50 feet AGL.

Balanced Field Condition:

When the accelerate-stop and accelerate-go distances are equal.

Relation to Runway Length:

None. Balanced field conditions are purely a performance planning concept, independent of actual runway length.

Takeoff Brief Importance

Why it Matters:

Engine failures during takeoff allow no time for indecision. A takeoff briefing ensures the pilot is mentally prepared to act immediately.

Three Critical Scenarios to Include:

• Engine failure before critical speed
• Engine failure after critical speed
• Normal two-engine departure

Visibility Near Minimums:

Considerations:

• Limited ability to return to the airport.
• Degraded situational awareness if engine fails.
• Risk of being invisible to other aircraft after aborting; ensure clear communications or runway exit plans.

Terrain-Specific Adjustments:

Example: If rising terrain is on the left and open water on the right, plan to turn right after an engine failure to maximize safety options.

Multi-Engine Maneuvers

Drag Demonstration (Drag Demo)

Purpose:

To demonstrate how different drag factors affect single-engine performance.

Key Drag Factors to Consider:

• Landing gear
• Flaps
• Cowl flaps

Vmc Demonstration (Vmc Demo)

Purpose:

To illustrate loss of directional control as the aircraft decelerates below Vmc during single-engine operations.

Deceleration Rate:

1 knot per second is the standard rate during the demonstration.