TURBOPROP

Question 1

What is the simplest form of reduction gear?

Answer 1

Spur gear.

Question 2

What speed is the turbo-prop engine proved to be the most efficient at?

Answer 2

480-725 km/h (30 - 450 mph)

Question 3

What altitude do turbo-prop engines perform well at?

Answer 3

6000m above sea level (20 000 ft)

Question 4

How much of the total power can a turbo-prop engine extract?

Answer 4

95% to drive the propeller/reduction gearbox, compressor and accessories.

(Remaining used as residual fuel)

Question 5

What is the core engine commonly known as in a turbo-prop aircraft?

Answer 5

Gas generator or gas producer

Question 6

How is a gas coupled/free power turbine designed?

Answer 6

There is no mechanical connection between the gas generator and the free power turbine.

(Only common connection is gas flow)

Question 7

What are the advantages of free power turbine engines?

Answer 7

• vibration not transmitted to propeller/gearbox
• engine start easier in cold
• propeller held at low rpm during taxi
• propeller brake used to prevent propeller movement (gas gen can be used as APU)

Question 8

How do gear/direct coupled turbines differ from the free power turbine engines?

Answer 8

Gear/direct has extra turbine discs which maintain connected to the compressor and reduction gearbox

Question 9

Why do gear/coupled turbines generate increased power forwards?

Answer 9

Exhaust gases passing through the additional turbine stages

Question 10

If fuel flow changes on a gear/coupled turbine, what else must change to remain a constant speed?

Answer 10

Propeller pitch

Question 11

Why must a turbo-prop inlet lip be of a large radius?

Answer 11

Due to Relatively low air speeds and high engine speeds to separation of airflow due to severe directional changes.

Question 12

What method is used to reduce compressor blade erosion?

Answer 12

Particle separators on the inlets

Question 13

What high quality forging are the gears made from in reduction gear boxes?

Answer 13

Alloy-steel

Question 14

What viscosity is oil in turbo prop reduction gear system in comparison to a turbo-jet engine?

Answer 14

Much thicker as they take higher loads as the system is much heavier.

Question 15

Why do propellers use SPUR EPICYCLIC gears for reduction gears?

Answer 15

Normal spur gears would be too noisy and bulky to provide such a large reduction.

(Output drive on same axis as input shaft)

Question 16

What are bevel epicyclic (planet) gears only good on?

Answer 16

Piston engines because of weight and dimension required to provide reduction ratios.

Question 17

How is reduction ratio found on bevel epicyclic gears?

Answer 17

Number of teeth

Question 18

What can helically cut gears do?

Answer 18

Reduce noise and vibration whilst also providing a means of measuring torque.

Question 19

What is a compound spur epicyclic good for?

Answer 19

Greater speed reduction without making components bigger.

Question 20

How do the shafts move in a compound spur epicyclic gear?

Answer 20

Tend to move axially.

Question 21

How does a rotating annulus make the propeller rotate?

Answer 21

In the opposite direction to the engine.

Question 22

What is a 2 stage spur reduction gearbox made from?

Answer 22

Magnesium alloy.

Question 23

How is the temperature of gas flow into the turbine in a turbo prop controlled?

Answer 23

Varying fuel flow.

Question 24

How is the mass of gas flow into the turbine controlled on a turbo prop engine?

Answer 24

Varying engine speed through through a variable pitch propeller.

Question 25

What is the propeller conditioning level for on a twin lever?

Answer 25

Set the propeller rpm in a constant speed mode.

Question 26

How do over speed safety devices protect the propeller?

Answer 26

First instance to coarsen the blade angle.

If fails, reduce engine power.

(Engine governor, free power turbine governer, an over speed governer)