Unanswered Questions Answered (Or: Lies I Told to High School Students)

Dear Mr. Lochhead,

Here are a few videos that I described in class on Monday. The real things are always better…

STS-123 Landing [YouTube] – You can start to see the APU plume in infrared at 5:05, a little bit in visible at 5:15, and very clearly near wheel stop at 6:05. The APU plume is normal, happens after every landing. It never looks this cool, though, usually it is invisible. For the flame to appear so clearly, there was a favorable combination of (1) a night landing and (2) very low wind. (The wind would blow the combustible gases away from the ignition source, sort of like trying to light a lighter in the wind.)

Boeing 777 Wing Load test [YouTube] – I was wrong about which aircraft I had seen the wing load test failure. I thought it was the Boeing 787 Dreamliner, but it was actually a Boeing 777. (In this case, think of failure as success — you want to break things in the lab, not in production or flight.)

Rolls Royce Trent 900 Bird Ingestion Test [YouTube] – The title says it all. Bird strike testing is required by the Federal Aviation for several components, including fan blades and windshields, so you can probably find more videos if you look for them.

Dear Ms. Franklin,

I got part of the story right about hydrazine combustion regarding ammonia, but I missed most of it. Now that I can cheat and use my notes, I can tell you that nitrogen and hydrogen products are also produced.

First off, I was wrong about one thing: the Auxiliary Power Unit [NASA] (APU) on the Space Shuttle Orbiter does not use monomethylhydrazine (CH3NHNH2) — it uses plain old liquid hydrazine, which is the composition I gave you, N2H4. (The Orbital Maneuvering System [NASA], another set of rocket engines on the Orbiter, uses monomethylhydrazine.)

Combustion of hydrazine in the APU occurs without oxygen In space, there is no atmosphere to provide oxygen; anyway, during launch in the atmosphere, combustion is isolated from the environment.

  1. 3 N2H4 –> 4 NH3 + N2
  2. N2H4 –> N2 + 2 H2
  3. 4 NH3 + N2H4 –> 3 N2 + 8 H2

I was wrong about the catalyst, as well. The catalyst is iridium on alumina, but it is called Shell 405, not Shell 104 — or if you want to be more specific, Shell Corporation stopped making this in 2002, so the new version produced by Aerojet is called S-405.

To both of you: thanks for letting me talk to your classes on Monday. It was fun. Engineers are good folks, but students are more interesting than engineers. I hope you found it useful. If you ever have any questions, email me at kirk.kittell@gmail.com. I can put you in touch with the smart folks that put their hands on this equipment, or can hook you up with more photos or videos, etc., which is even more interesting than listening to me describe it.

(To everyone else: My dad is a principal at Chester High School in southern Illinois. I was hanging out with a few of his teachers — Ms. Franklin and Mr. Lochhead — and students on Monday morning when I was in town.)

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