Challenge Questions PPL/CPL Sec 5.

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Challenge Questions PPL/CPL Sec 5.

Post  Admin on Sat Dec 12, 2009 7:55 pm

Q 1. Explain in detail, the difference in operation/function of the following types of fire protection systems.

- Fenwall Resistance Type Detector

- Kiddie Resistance Type Detector

- Gavanier Firewire Capacitive Detector

- Systron Donner

- Photoelectric Cell Smoke Detector

Q 2. What are the chemical solutions used in high pressure charge fire extinguishers found in the engine nacelle and how do they work to extinguish the fire? Heres a clue - one type of chemical solution used as a high pressure charge fire extinguishers includes 'Bromochlorodiflurosulphate'. Now thats a mouthful!

Q 3. Referring to the reciprocating power plant/engine, what is 'bootstrapping' and what can be the cause of it?

Q 4. What is the difference between 'thermoswitches' and 'thermocouples'?

Q 5. What are the 2 vector quantities which determine the Aoa of a propeller or compressor blade? What happens when there is an imbalance between these vector quantities?
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Re: Challenge Questions PPL/CPL Sec 5.

Post  Binary10110 on Tue Feb 09, 2010 5:50 am

I'll start with Q4...

My guess would be that a thermal switch uses a bimetallic strip to bridge a gap in a circuit.
As the two metals warm up, they expand at different rates. This causes it to bend, breaking the circuit.
When it cools down, the metals contract and it bends back again, closing the circuit.

A Thermocouple, on the other hand, uses two metals connected together. A current is passed down a wire of one metal and returns via another. Where two metal wires join, there is a change in resistance. This resistance actually fluctuates depending on temperature.
This resistance can be measured and the temperature can be determined.

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Re: Challenge Questions PPL/CPL Sec 5.

Post  Admin on Tue Feb 09, 2010 6:44 am

Close, very close.

You're talking about the 'resistance/capacitance' systems, utilized in other models of fire detection technology, such as the Gravanier Firewire Capacitive Detector and Fenwall Resistance Type Detector. Thermal Couples however, do not use 'resistance/capacitance as part of its technology. At lest, not the ones found in most aircraft. Heres a clue - there are two parts or 'junctions' to a thermal couple.

As for the Thermal Switch, I'm sure theres not much to add. Different publications put it differently. Its such a basic system, its all the same. Its basically a single wire/loop, either made from some sort of eutectic material in an inconel tube or some other solid conductor with similar properties, capable of regaining its original form after exceeding its initial capacity (over heat warning). Basically how you put it. Thermal switches are used to detect overheating, more than actual engine fires. Thermal switches are like the first line of defense in a basic aircraft.
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