Hydrazine APUs?
03-22-2018, 04:08 PM
#1
Day puke
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Joined APC: Feb 2006
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Hydrazine APUs?
Wandering through Youtube I found cockpit video of an F-16 dead stick landing. As he was rolling out, his wingman advised the tower to roll the trucks and advised tower he probably had a running APU with HYDRAZINE?
Do F-16s really use Hydrazine? If so, WHY?
Do F-16s really use Hydrazine? If so, WHY?
03-22-2018, 04:50 PM
#2
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Joined APC: Mar 2017
Posts: 176
Originally Posted by FlyJSH
Wandering through Youtube I found cockpit video of an F-16 dead stick landing. As he was rolling out, his wingman advised the tower to roll the trucks and advised tower he probably had a running APU with HYDRAZINE?
Do F-16s really use Hydrazine? If so, WHY?
Do F-16s really use Hydrazine? If so, WHY?
Google is your friend....
"The EPU, using hydrazine spins up to approximately 75,000 rpm in 2-3 seconds (The F-16 EPU starts within 2 sec.). It would take a much greater time if another fuel, like JP-8 were used. When required (EPU runs normally on engine bleed air), hydrazine is forced into decomposition chamber by nitrogen pressure, where the above reactions produce the gases to run the turbine/gearbox. The decomposition of hydrazine produces enough pressure, eliminating the need for a compressor, thus saving weight and also eliminating the need for an igniter, reducing complexity.
For the given weight, it provides continuous operation for the required time. In F-16, the EPU carries ~25l of hydrazine, which permits operation for about 10 minutes under normal load conditions and 15 minutes if the loads are less (i.e. in ground). If any other form, (like battery or cartridge) were used, it would be difficult to have a long operational time without heavy increase in mass.
For a combat aircraft, RAT is not an option. Also, a hydrazine powered EPU would work in any altitude or during maneuvering as it does not need an external oxidizer supply."
03-22-2018, 04:53 PM
#3
All is fine at .79
Joined APC: Sep 2016
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I love this answer :
Hydrazine use is related to aircraft stability. Without power to the computers, the F-16's preferred flight attitude is flying tail first. The basic aircraft design is aerodynamically unstable, intentionally, to achieve high performance. The flight control computers maintain stability.
If electrical power goes down, the pilot suddenly needs wading boots. To prevent such unfortunate circumstances, the APU was specified to be on-line at full power 0.25 seconds after power failure.
Apparently, in the late 60's to early 70's (design years) nothing else could meet the rapid start, weight, and power endurance requirements.
If electrical power goes down, the pilot suddenly needs wading boots. To prevent such unfortunate circumstances, the APU was specified to be on-line at full power 0.25 seconds after power failure.
Apparently, in the late 60's to early 70's (design years) nothing else could meet the rapid start, weight, and power endurance requirements.
03-22-2018, 05:43 PM
#5
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Originally Posted by ZippyNH
https://aviation.stackexchange.com/q...-the-f-16s-epu
Google is your friend....
"The EPU, using hydrazine spins up to approximately 75,000 rpm in 2-3 seconds (The F-16 EPU starts within 2 sec.). It would take a much greater time if another fuel, like JP-8 were used. When required (EPU runs normally on engine bleed air), hydrazine is forced into decomposition chamber by nitrogen pressure, where the above reactions produce the gases to run the turbine/gearbox. The decomposition of hydrazine produces enough pressure, eliminating the need for a compressor, thus saving weight and also eliminating the need for an igniter, reducing complexity.
For the given weight, it provides continuous operation for the required time. In F-16, the EPU carries ~25l of hydrazine, which permits operation for about 10 minutes under normal load conditions and 15 minutes if the loads are less (i.e. in ground). If any other form, (like battery or cartridge) were used, it would be difficult to have a long operational time without heavy increase in mass.
For a combat aircraft, RAT is not an option. Also, a hydrazine powered EPU would work in any altitude or during maneuvering as it does not need an external oxidizer supply."
Google is your friend....
"The EPU, using hydrazine spins up to approximately 75,000 rpm in 2-3 seconds (The F-16 EPU starts within 2 sec.). It would take a much greater time if another fuel, like JP-8 were used. When required (EPU runs normally on engine bleed air), hydrazine is forced into decomposition chamber by nitrogen pressure, where the above reactions produce the gases to run the turbine/gearbox. The decomposition of hydrazine produces enough pressure, eliminating the need for a compressor, thus saving weight and also eliminating the need for an igniter, reducing complexity.
For the given weight, it provides continuous operation for the required time. In F-16, the EPU carries ~25l of hydrazine, which permits operation for about 10 minutes under normal load conditions and 15 minutes if the loads are less (i.e. in ground). If any other form, (like battery or cartridge) were used, it would be difficult to have a long operational time without heavy increase in mass.
For a combat aircraft, RAT is not an option. Also, a hydrazine powered EPU would work in any altitude or during maneuvering as it does not need an external oxidizer supply."
Unless you mean specifically for the F-16 and not just any combat aircraft.
03-23-2018, 05:59 AM
#7
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The main reason: weight and space. Fighterrs have very little unused space; weight is the anethma of a fighter.
It was the smallest and lighest APU they could put in such a small jet.
F-15? Bigger...has a jet-fuel starter (I think).
F-4?
My starter was a 2-ton unit on the ground...kind of limited the places you would intentionally land (ie, they needed to have one).
It was the smallest and lighest APU they could put in such a small jet.
F-15? Bigger...has a jet-fuel starter (I think).
F-4?
My starter was a 2-ton unit on the ground...kind of limited the places you would intentionally land (ie, they needed to have one).
03-23-2018, 07:32 AM
#8
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Joined APC: Oct 2006
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Originally Posted by UAL T38 Phlyer
The main reason: weight and space. Fighterrs have very little unused space; weight is the anethma of a fighter.
It was the smallest and lighest APU they could put in such a small jet.
F-15? Bigger...has a jet-fuel starter (I think).
F-4?
My starter was a 2-ton unit on the ground...kind of limited the places you would intentionally land (ie, they needed to have one).
It was the smallest and lighest APU they could put in such a small jet.
F-15? Bigger...has a jet-fuel starter (I think).
F-4?
My starter was a 2-ton unit on the ground...kind of limited the places you would intentionally land (ie, they needed to have one).
Actually they were kind of fun. Smoke everywhere!
03-23-2018, 07:33 AM
#9
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Joined APC: Jul 2007
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Originally Posted by ZippyNH
For a combat aircraft, RAT is not an option.
F-105 RAT
