Systems ATPL question.

[Shaun-356]

Hi everyone, Im currently sitting CASA (Australia) systems & Aerodynamics ATPL. One question Im wrestling with is: "What is a thermal relief valve?
The exam is based on Boeing equipment. Mainly 767.

Many thanks.

[Keith.Williams.]

When (most) materials are heated they expand.

If you have a hydraulic system in which fluid is "locked in" such as a parking brake system, such expansion can create pressure sufficiently high to burst the pipes. A thermal relief valve is simply a pressure relieve valve that is used to relieve excess pressure before the pipes burst.

[Kyriakos]

Combined gas law says: (P1*V1)/T1 = Constant or = (P2*V2)/T2

Adding on Keith feedback, and looking at the formula above, when theres excess (increased) pressure, theres an increase in Temperature due to the faster moving molecules (assuming volume remains constant). To compensate for that engineers introduced various damping mechanisms/devices on pressurized systems (hydraulic & fuel pumps).
One of those mechanisms is the thermal relief valve.

[Shaun-356]

Hi everyone,

If I may trouble you lot with a few questions I'm :ugh: with!

1) With regards to asymmetric stall speed. An increase in the stall sped will be caused by;
a) An increase in the density altitude.
b) An increase in the ambiant temp.
(I thought both sounded pretty good!!)


2) The torque gauge in a gas turbine engine measures?
a) Power, in a turboprob
b) The torque acting through the torque links in the engine


3) With regards to Hydraulic braking systems on large jet transports. Power brakes are provides so;
a) The incorporation of anti-skid brakes is possible.
b) To assist in moving the large quantities of hydraucic fluid required for braking.
(Again, I thought both sounded good!!)


Many thanks.

[training wheels]

If I may trouble you lot with a few questions I'm :ugh: with.

If you're using the AFT notes, the answers are all at the back of the manual! :)

[Shaun-356]

No answers in the back of a book to these ones I'm afraid. Help!!

Many thanks.

[TheBeak]

The first question is a little strange because an increase in temperature gives an increased density altitude. So if assymetric stall speed varies with one then it has to vary with the other.

As for the second question for a fixed RPM the torque will give you an indication of power:

Power = Torque x RPM.

And for the third I would say the answer could be either again. An anti skid brake system can only be applied to a power brake sytem so answer a. Without power brakes on an a heavy jet one would become VERY tired VERY quickly and so power brakes are needed to 'assist in moving the large quantities of hydraucic fluid required for braking'. And so b is also correct.

At least that is what I remember, the finer points of ATPLs came and went with the exams.

[Shaun-356]

Thanks for your help everyone. Just one last question!

There are two quantities of fuel, both weighing 1kg.
One with a SG of 0.7, and a second with an SG 0f 0.8.
When comparing calorific values, which one will have the higher value?

(The answer is not "the same". Thats what I put and got it wrong!!)

Many thanks.

[Shaun-356]

Thanks for your help everyone. Just one last question!

There are two quantities of fuel, both weighing 1kg.
One with a SG of 0.7, and a second with an SG 0f 0.8.
When comparing calorific values, which one will have the higher value?

(The answer is not "the same". Thats what I put and got it wrong!!)

Many thanks.

[TheBeak]

The calorific value reperesents the energy released as heat when combusted.

0.7 S.G = 100LL and 0.8 = Jet A-1.

Jet A-1 has a higher calorific value as it has more hydrocarbon chains than 100LL.

Therefore the fuel with a specific gravity of 0.8 will have the higher calorific value.

[Regan]

Sorry thebeak you are incorrect. The fuel with SG of 0.7 (which is AVGAS) has a higher calorific value as the question said 1Kg. AVGAS has a higher calorific value per unit weight but AVTUR has a higher calorific value per uint volume.