The EPU - how does it work and why hydrazine?

Sorry if this seems like a simple question or something I should already know, but I keep reading about the F-16's EPU and its use of hydrazine. I was able to find out in the glossary that it stands for Emergency Power Unit.

I have several questions, actually.

1 Why is it there? Isn't there a Ram Air Turbine to provide electrical power in the event of an engine or generator failure?

2 How does it work?

3 Why use hydrazine? I assume it's the fuel for the EPU, but if that's the case, couldn't something less toxic be used?

4 What is meant by "firing" the EPU and how is it pinned safe? Is it similar to an ejection seat in that way?

Thanks for helping guys!

1 Why is it there? Isn't there a Ram Air Turbine to provide electrical power in the event of an engine or generator failure?

It's there for the stated name - An emergency and it provides power. No there is not a RAM air turbine to provide electrical power.

2 How does it work?

It provides power in modes. Bleed Air (that is it is augmented by bleed air from the engine) Or Hydrazine in this mode it uses the Hydrazine (H-70) from the tank located in the right strake, there is a process that uses nitrogen to turn the liquid H-70 into a gas and turn the turbine as the gas is expelled out the right lower strake. In the Bleed air mode the operation of the EPU is greatly extened, however if hydraulic pressure falls below a predetermined pressure the H-70 will begin to flow at greater amounts and provide the needed hydraulic and electrical power in order to fly the jet. In the H-70 only mode you have approximatly 10 minutes of operation from the EPU.

4 What is meant by "firing" the EPU and how is it pinned safe? Is it similar to an ejection seat in that way?

Firing the EPU is accomplish by two means, manually and automaticly. Manuall selection is done by the pilot, and this activates the H-70 only mode and can be terminated manually as well, operation time in this mode is the same as automatic H-70 mode. Automatic H-70 mode is actuated by loss of both hydraulic systems pressure falling below a predetermined pressure, or loss of electrical power. The EPU is safed with a saftey pin on the righ side of the inlet, it's particular location depends on what block you are refering to.

Thank you for a very clear answer to my question IDCrewDawg!

You're welcome!

3 Why use hydrazine? I assume it's the fuel for the EPU, but if that's the case, couldn't something less toxic be used?

Because it burns like you would not believe, The temp gets up to around 1800dec.

Is there an alternative, im not sure, yea its pretty toxic, I have had a few bleached shirts from it, but I prolly wont see the effects for another 10 years

Hydrazine in this mode it uses the Hydrazine (H-70) from the tank located in the right strake, there is a process that uses nitrogen to turn the liquid H-70 into a gas and turn the turbine as the gas is expelled out the right lower strake.

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3 Why use hydrazine? I assume it's the fuel for the EPU, but if that's the case, couldn't something less toxic be used?

Because it burns like you would not believe, The temp gets up to around 1800dec.

IDCrewDawg gives me the impression that the H70 is merely converted to a gas (H2?), thereby expanding and using the resulting pressurized gas to turn the turbine. Tankrat says the H70 burns like there's no tomorrow. I'm not doubting either of you and you're probably both right, I'm just a bit confused.

It is a chemical reaction between H-70 and nitrogen that leads to an explosive expansion of the resulting gas. This gas then drives a turbine. I seem to remember that it will spin up the turbine to its RPM of around 30,000 in a second. H-70 is also used by the Russians to power all their space launchers, including the SeaLaunch (Boeing) offshore platform rockets (Russian SS-19 first stage) docked in San Diego (I think)

yea its pretty toxic, I have had a few bleached shirts from it, but I prolly wont see the effects for another 10 years

During thraining we were told that if you can smell H-70 (amonia like) you are as good as dead so is there anything we all can do for you now...

It's a chemical reaction to the Iridium in the decomposition chamber. It rapidly breaks down into hot gases (1600 degrees) that are ported over a turbine (much like a water wheel).The nitrogen is used to pressurize the H-70 fuel tank, it never mixes with the H-70 (there is a piston separating the two). The speed is roughly regulated to 75,000 rpms. Hydrazine has been used as a rocket fuel for over 40 years now. I would more leary of some of the other chemicals used in fuel system sealing than H-70. Its an old wives tale that "if you smell it your dead".

During thraining we were told that if you can smell H-70 (amonia like) you are as good as dead so is there anything we all can do for you now...

I have personally known several people who have had the EPU fire directly onto them, yes its hot, but you won't die from it instantly. What are the long term effects, they don't tell us that.

Thanks guys - I think I understand now. Funny story about hydrazine - Back in the days of launching Corona surveillance satellites, they were having a big problem with fuel leaks, and they needed a leak detector. So some guy volunteered to go up and around the rocket on the launch pad and use HIS OWN NOSE to sniff for any H70 leaks! Well, he didn't smell any and the rocket launched successfully. Thanks again, you've all cleared that one up for me.

Funny thing about H-70, unburned its more hazardous than the stuff that comes out of the exhaust. Once it has been through the decomposition chamber its just steam and ammonia. There is a tiny bit of H-70 still in the gases but not enough the affect your limits over an 8 hour period.

I know H70 is toxic, but what are the effects of exposure? Just how bad is it?

Its a "suspected carcinogen",although no known cancer cases have ever been attributed to exposure to H-70. The primary hazard with H-70 is its ability to damage the liver and the kidneys (but then a long TDY could do that )

A long TDY? From some of the guys I know, I think a short one would do it with no problem!

Thanx for the info.