Too Darn Hot

Fire in flight! is one of the scariest things in aviation. An engine fire in a single-engine airplane turns you into a glider, since putting the fire out means shutting off the fuel. But an engine fire in a multi-engine airplane turns you into a brick. One of the axioms of multi-engine flying is that in case of wing fire you must put the airplane on the ground now, no matter where you are. There are tales of multis dropping like a rock on downwind.

I was taught that the reason for this was that the aluminum spar got "soft" when heated. This seemed plausible, so I believed it and passed it on. But that's superstition, which has not place in flight instruction.

So here is a graph from Dennis R. Jenkins's X_15: Extending the Frontiers of Flight, a NASA publication available free here.

The graph shows the strength response to temperature for several materials used in aviation: aluminum, magnesium, titanium, stainless steel, and Inconel X. Inconel X can handle amazing amounts of heat, which is why it was used in the X-15. (The Wikipedia article on Inconel seems pretty good.)
The vertical scale is Tensile Yield Stress, that is, how much stress does it take to make the material yield, "strength" in layman's terms. The horizontal scale is temperature.

The aluminum curve is pretty scary: at low temperatures the strength remains about constant, but at about 200F it starts to decline rapidly, and is halved by about 400F.

That's not very hot. As a cook, I regularly touch stuff nearly that hot (I often stir stuff with my hand rather than a spatula). French fries cook at 375F. Typical ITT temperature for a PT-6 engine is about 1350F, and piston EGTs are in the same ballpark.

Aluminum loses its strength at temperatures that are common in aviation!

So, if you are in an aluminum-sparred airplane and there is heat on the wing land right now. Don't try to reach the airport. Land right now on something that won't hurt anybody else.

A composite airplane like the Diamond DA-42, which I believe has a composite spar, might be different. If this is correct (don't take my advice unless you verify that the spar is composite) then the spar should be able to maintain its strength at much higher temperatures, and you have more options as to landing.

[revised 15 Aug 2011]

Attitude Check

A lot of flight instructors (CFIs) give advice on Twitter (I am @DrATP, by the way), and this week a lot of it was wrong. Well, not exacly wrong, but it was not helpful.

I teach Mathematics, Computer Science, and Flying. Only the last one involves muscles and only the last one can kill you (despite how you felt in any Math class you took). I take a different approach to each subject, and think hard about how to do each one better. Here's one big rule of flight instruction that I picked up along the way and adopted quickly:

Don't teach what to do: teach how to do it.

This means something different for each student. For a presolo student, it's "Don't pull so hard." Around solo, it becomes "The nose is too high." A Commercial student might hear "You're pitching up too quickly." For an ATP it could be "V2 is 121 knots." In flying, the instructor changes to accomodate the needs of the student, not vice-versa.

(This is part of what I like about Part 61 flight instruction. At the university, or in a more-structured Part 141 program, the student changes to accomodate the needs of the instructor, who represents the needs of the program. In a structured curriculum the instructor must move on, even if some students don't understand.)

So all of a sudden I'm reading a lot of CFI tweets about flying the right airspeed in an emergency: that's telling you what to do.

I teach my students to fly the right attitude in an emergency: that's how to do it, but it's also easier and safer. And more of interest to the instructor than the student is that the lesson transfers to other parts of flying: fly attitude, not airspeed. So when I teach a multiengine student about Vyse, the proper speed for best climb performance after one engine fails, I teach him or her to fly the right attitude, not the right airspeed.

Of course it would be irresponsible of me to stop there. First of all, it's difficult to nail the attitude exactly, although usually people are too fast (which has a minimal impact on performance) rather than a little too slow (which really hurts performance). So, at some point the pilot has to fine-tune the airspeed. In the meantime, he or she has started to look for a place to land (better yet, turned toward the place they picked out before the engine failed), or even started to troubleshoot the problem.

The alternative goes like this: I fail the engine. The student raises the nose and stares at the airspeed indicator, looking for 60. When the indicator says 60 the airspeed is more like 55. "Too slow!" they think, so lower the nose until it reads 60. But by then the speed is back to 65. "Too fast!" they think. This continues ad impacto.

---

The hard part about instructing is seeing that what is so blankety-blank-blank obvious to you is not at all obvious to the student. This one certainly applies in Mathematics! But it applies to flying, too. We instructors need to look at things through the student's eyes, not our.

I'll close with a funny dialog between me and a student I was training in a 182. He pulled the throttle back a loooooong way on descent.

"One inch a minute, remember?" I said. This is the desired change in manifold pressure.

"I did that," he replied.

"No, that was more like five inches."

"No, I pulled it back one inch!" he insisted, and mimed the throttle travel.

And he was right: there was only one inch of throttle travel. Ever since then, I tell pilots "One inch of manifold pressure a minute." You get the idea, I hope.

SPOT

I mentioned earlier that I have been fooling around with SPOT. SPOT makes a little device that includes a GPS receiver and a satellite transmitter. The receiver keeps track of your position; four buttons on the front control the transmitter. The unit has the footprint of an iphone and is about twice as thick, although it is lighter. It has a solid belt clip that seems to hold it in place well. (I have been clipping it to my shoulder harness in the glider, and it has not budged.)

With a receive-only module and a different transmit-only module, SPOT does not do much. But, that's plenty. If you press and hold the 911 button, SPOT sends your GPS coordinates (via satellite) to its headquarters. They take your GPS position, figure out where the nearest Search & Rescue facility is, and send them to get you. It's for life threatening situations. [For those of you outside the USA, 911 is the nationwide telephone number for contacting emergency services.]

The HELP button sends email and text message alerts to a group of people that you specify on the SPOT website. The path is the same, but instead of "calling 911," it calls your Mom. Or wife. Or glider buddies, who find out where you landed out and come get you.

The advantage here is that satellite coverage is much broader than cellphone coverage.

I am pleased to say that I have not needed these features.


But SPOT offers another service: tracking. When in track mode, the unit sends a message with your current location every ten minutes or so. These appear on a (password-protected, if you like) web page, so your buddies can get a good idea where you are.

We used this a lot during the recent Region 9 North SSA contest. The contest director had access to everyone's SPOT page, and therefore had a good idea where the gliders were and when to expect them back.

The picture on the left shows three of my tracks. The low-numbered fixes heading to the southwest were from a night cross country with a student. The clump to the southeast was a glider flight in weak conditions (so I never got away from the airport, although I flew 2.9 hours). The ones to the northeast were from Tuesday's flight home from our satellite campus.

Some people have complained that SPOT service is, well, spotty, and should not be relied on for rescue. I have noticed that a few times the tracking message was never received, so they may be right. But the vast majority of the messages got through. For now, I'm concluding that SPOT really improves the chances that you'll be found sooner.

Recently, a Stemme motorglider went missing after departing an airport in eastern Idaho headed back to California. I was peripherally involved in the search as one of the few glider pilots in eastern Idaho; the searchers were looking for advice on glider tactics. Another part of the search was a lot of calling around to see if he had a SPOT; that would have made the search much quicker. Alas, the pilot was killed.

The other "complaint" is that SPOT needs a clear view of the sky to reach the satellite. So, if you are upside-down in a wreck, or stuck in a slot canyon with a boulder on your arm, it will be difficult to get the rescue message out. But, again, difficult is better than impossible.

I'd choose difficult over impossible any day.

The company strikes me as a company of true believers. They believe, with good reason, that their product will save lives. they seem to believe this so strongly that they have frequent promotions in which they give the unit away! You have to buy the tracking and messaging services, of course, but you pay nothing for the hardware.

Seems like a good deal.

42

Fans of Douglas Adams and The Hitchhiker's Guide to the Galaxy recognize the number 42. It's one of our cultural memes, like the crash of the Hindenburg or King's "I have a dream" speech. It's the answer to "Life, the universe, and everything."

The fictional Hitchhiker's Guide... had two words on the cover: Don't Panic. The kind of solid but generic advice a hitchhiker needs.

And a pilot.

I was in the glider with a new student. He already has a commercial power license, and although this was our first day of real training he was making fast progress. On his second takeoff, I gave him the flight controls, and he tracked the towplane pretty well. (That may sound like an insult, but it's not. New students, even transition students, even yours truly, find following the towplane to be Very Hard.)

Our first landing had been on the runway but without enough energy to reach the launch point, but the second had us stopped exactly on the line. Cool! (And it was his landing, by the way, I only offered encouragement.) So we turned the glider around and got ready to launch again. I got in, redid my belt and shoulder harness, and locked and checked the canopy. Check. Check. Check. I wiggled the rudders, called "ready" to to the tow pilot, and started my stop watch.

We started to move, but something didn't feel right, and didn't sound right. Did the the tail come up a little too easily?

"Oh, no, we still have the tail dolly attached!" The tail dolly is a large fiberglass cuff with a large castering wheel that fits over the tail. It makes ground handling easier. Taking off with it attached would give us an aft CG, perhaps aft enough to negate or even reverse the glider's natural pitch stability. It would also hurt our glide ratio, in an unknown amount. Bad idea!

So I aborted. I was surprised how surely my eyes focused on the release handle and I pulled. The rope went with the towplane.

"Glider goes to the right, towplane goes to the left," I told Bill, steering rather gingerly toward the right side of the runway. I was really working the stick, keeping the wings level and the nose at the right attitude. We slowed, so I reached for the wheel brake and braked gently. With this much speed dragging a wingtip could lead to a groundloop, and pulling the brake too hard would dump the glider on its delicate nose.

But we stayed poised, balancing on that one big wheel, and came to a gentle stop at the side of the runway. I stopped the clock. The tail came down, on the tail wheel. The tail dolly was still at the launch point, where it belonged.

True confession: in all of my glider training (remember that I am still a newby) I had never done an abort on the runway. Oh, we talked about it, we prepared for it, we had low altitude "rope breaks" and landed straight ahead, we had "rope breaks" at 200' and turned around to land downwind, we had "rope breaks" on downwind and landed. In twins an "engine failure" on takeoff is a standard maneuver, so I've done it or taught it or evaluated it hundreds of times. But I had never actually aborted on the runway in a glider.

A glider on the runway is different from an airplane: there is only one point of contact, so there is less wheel drag, and the glider is more aerodynamically efficient, too. It takes more flying to stay in control. (I know; I tried it in a Cessna 172 this morning.)

I had done the right thing: decided to abort at a reasonable time, pulled the handle, made sure that the rope really released, and maintained control of the glider. The last one is the most important; losing control bends metal and breaks bones. So, following Douglas Adams's advice, don't panic!.

OK, "don't panic," there's the Douglas Adams connection. But where does 42 fit it?

I looked at my stopwatch. The elapsed time, in seconds, was...

...42.

Young Eagles Day

I am a long-time enthusiastic supporter of The Experimental Aircraft Association [EAA]. Their Young Eagles program gives kids an opportunity to fly.  For one reason or another I have never been able to participate until today.

I took the club Archer, accompanied by one of our chapter members, to Gooding, Idaho, the home of the Idaho School for the Deaf and Blind.  This is the third year that our chapter has given flights to the kids at the school.  As the name implies, most of the kids have some kind of developmental difficulty, but I still believe that everyone loves to fly. 

The airport was like a mini-Oshkosh, with planes continually taxiing out, launching, and returning.  We used Oshkosh call signs too, to keep the radio chatter under control.  I was the white Archer, Mike was the Red Cherokee, Austin was the Pulsar, and so on.  We kept the pattern pretty full, and it didn't take long to give something like 50 kids airplane rides.  (The rides were substantial; mine averaged 18 minutes.)

[By the way, everyone did a full 360 before taking the runway at this uncontrolled field. There have been way too many midair collisions in the pattern this year, with tragic consequences.]

When I taught computer science, I used to say that "a good computer scientist is interested in everything;" now I am beginning to think that "a good pilot is interested in everything," too.  For example, at some point I learned sign language letters.  My friends and I used this on multiple car road trips before there were cell phones.  "Next exit," we'd sign, and the like.  Today I flew two girls who were completely deaf, so the only way to communicate with them was by signing.  I felt inept: their signing is so graceful and fluid.  But mine worked.  The girl in front was fussing with her shoulder harness during the taxi out, and not wanting to get distracted during a "critical phase of flight," I stumbled through signing "W A I T."  Which she did.

So you may never fly with a passenger who cannot hear.  But think about this: two guys I knew were flying a King Air that lost a door in flight.  They kept it flying, and landed at an airport in one piece.  In their later talk about the incident, they said that one of their big problems was that it was too noisy to hear each other.  

A little bit of sign language would have helped.

Smoke in the Cockpit (almost)

Dennis has had some bad luck with the flying schedule. First we took off into what was supposed to have been a 1500 foot ceiling, which would have been plenty for ground reference maneuvers, but in fact the ceiling was at about 500 feet, so we flew the one pattern and called it good. I suppose that the ceiling was 1500 at the ASOS station behind us.

A few days later, we pulled the airplane out of the hangar after a quick check of the radar, because the forecast called for snow showers. There was one big shower that was clearly going to pass east of the field. By the time we got the doors open and the airplane pulled out, though, the sky to the southwest had become dark and swirly. We watched a little as the storm approached with the airport boresighted, and I made the decision to lickety-split put the airplane away. The line crew was tied up playing tiddlywinks, so I just muscled it in as the snow started to fly, big sideways flakes getting into my ears.    Now the radar showed that the shower really had passed to the east, but had expanded while it did so.

Today the weather was way better than forecast and the airplane was available, so I called Dennis and we hustled out the field. We had briefed this flight several times, so we got in the air pretty quickly. We started with a climb under the hood, then some turns and a good stretch of straight-and-level, which went pretty well. The most annoying part was a new loud buzz in the intercom until we passed the localizer antenna. You know the kind of buzz: It's the "alternator failure" buzz.  I made a mental note.

We're still exanding his stall envelope.  We did clearing turns and the first stall went pretty well, although he almost got a secondary stall.  But it didn't smell right. Something on the ground, I thought. since we were downwind of a town. A couple of more stalls; the smell reappeared when the power was pulled back. I did not like the smell but he didn't smell it yet. Whatever it was was coming from the airplane. I turned off the landing light, and then the heat, but as soon as the power went to idle the smell came back. We turned back to the airport and landed.

There was no smoke. I have seen smoke in a 172 cockpit, thankfully on the ground just before takeoff, and was pleased not to see it again. But I sure was looking for it!

So Dennis has had more than the usual exposure to what the FAA calls "Aeronautical Decision Making": several instances of weather worse than advertised and a genuine "system and equipment malfunction." We had a good discussion about instruments and systems and what you lose when you turn off the master, with the added sensory input of the burn in the back of our throats from the ozone.