With Wings As Eagles: Craig P. Steffen's Blog

carb heat: the neglected control

2008 December 31 09:08

So far, in my very brief flying career, I haven't thought much about carburetor ice or carburetor heat, other than as it pertains to decent and landing procedures (any time you reduce throttle in a C-150, or any time the engine is running below 2000 rpm, turn carb heat on).

And there was the various written materials and the tests, which contain questions like "what is the sign of carburetor ice in an airplane with a fixed-pitch prop", the correct answer to which is "a drop in engine rpm".

Those things provide one side of the equation; how to find carburetor ice if you know you're looking for it. After my flying experience yesterday, I think the other half of the equation should be added to flight training with a little more emphasis. That is, what should you do as a pilot to make sure that carburetor ice doesn't sneak up on you? The reason for this post is that I almost had an engine fail yesterday, and I'm pretty sure it was because I had bad carburetor icing and I didn't realize it until almost too late.

My new rule in flying: If the engine does something unexpected, particularly if it runs rough or the rpm drops unexpectedly, turn the carburetor heat on and leave it on for at least a minute or two. Codicils to this rule are as follows: - This is especially true when flying and airplane with a carburetor (not fuel injection). - This is especially true when flying and airplane powered by a Continental engine. - carb heat enrichens the mixture going into the engine. Therefore the one exception to this if you've flown from low to high altitude and forgot to lean the engine, it will already be running too rich, in which case carb heat will make the problem worse.

It takes several seconds for carb heat to take full effect. You can tell if you had carb ice because when the heat is applied, after a few seconds, the rpm drops a LOT but then climbs back up (after the ice is all melted).

Along with the last point: part of the run-up procedure for any piston-powered airplane is to test the carb heat by turning it on and making sure that the carb heat control works. I did that yesterday, and I definitely got a respose. However, thinking back, I think the rpm may have decreased more than usual--in retrospect, the airplane may have already been developing carb ice on the ground.

So as with most things, it's mostly a matter of being aware. For pilots, one thing to be very very aware of; the engine doing funny things can be a sign of carb ice, to which there is one and only one reasponse: pull the carb heat control and leave it there long enough to clear any ice.

And since I like pictures, here's my friend from yesterday:

leaving the cradle for the first time

2008 December 25 09:59

Forty years ago this week, the crew of Apollo 8 were the first humans to go into orbit around another body besides the earth. The three astronauts, Jim Lovell, Frank Borman and William Anders remembered the mission this week.

The mission was a very big step in the Apollo program. It was the first use of the Saturn 5 rocket for a manned launch. The Saturn was necessary to provide the trans-lunar injection maneuver to fling the spacecraft from earth orbit to lunar orbit. Along with those physical capabilities, there were several orbital navigation tasks that all had to be performed correctly to get the spacecraft to the moon and back.

Apollo 8 also had a large cultural significance. The crew made a television broadcast from lunar orbit and read from the first chapter of Genesis, the bit that begins "In the beginning...". They also took a very famous series of photographs taken, some of which were the "earthrise" photos:

By the way, the Apollo 8 Command module is in the Museum of Science and Industry in Chicago, Illinois.

breathe in, breathe out

2008 December 23 13:04

In September, I wrote a very long text-heavy post about the process of internal combustion engines and what things can be adjusted.

I'm getting back to that, so I've attempted to produce a diagram that partially illustrates the process here:

Each thing in parentheses can be adjusted; some things only as part of the design of the engine, others are adjusted when the engine is running. If any of the items fails to work, the engine will not run.

Adjusting the performance of an engine (of given displacement) involves changing one or more of the items in the diagram. The engineering challenge is that such a change also requires you to change other aspects of the engine to compensate.

For instance, the ignition timing and mixture are intimately involved with each other; they need to change in relation to each other for the engine to keep running. If you stomp on the gas and the engine hesitates, it means that when the throttle opens quickly (increase in the effective volumetric efficiency), the mixture and ignition timing aren't changing properly to compensate.

I put in the mechanical removal of heat because that's a critical (and limiting) parameter of the Volkswagen air-cooled engine (like in my beetle). It's essentially a function of the fin area of the cylinder heads and the airflow around the engine. There are lots of ways to increase the power being developed by a VW engine. You can, for instance, make the intake and exhaust system much less restrictive to make the engine breathe better. However, that only increases the load on the cooling system and so makes it easier to overload and overheat the engine.

My next task with my engine is to decrease the compression ratio of the cylinders down to what it should be. I think it's been increased by accident, by people adding used heads without adjusting things properly. That will decrease the burden on the engine's cooling system and allow me to adjust the ignition and carburetion systems correctly, and hopefully stop the exhaust valve from stretching.

football season

2008 December 23 12:52

Our third cat (Thrice) arrived Thanksgiving day a year ago. Thrice and Pangur are only now relatively Ok with being around each other, sometimes. However, we had a real breakthrough the other day watching football. Here's Jasper, Pangur, and Thrice all together with us watching football the other night.

Jasper in the orange cat at the bottom. Of the grey cats, Pangur is to the right and Thrice is to the left.

I have the power

2008 December 19 09:24

On my recent trip to South Africa, I wanted to be able to power my laptop from the plane's power jacks during my flights if possible. I'd heard that there was such a type of power supply, but I didn't know what it was, and I didn't end up trying to get the right supply until right before I left.

The most common power jack on aircraft is called an "Empower Plug". It's a special jack that supplies up to 75W of 15V DC electricity to your portable device. Here's a photo of one of mine:

A common accessory for laptops is to have a power supply that runs on a cigarette lighter plug, so that you car run it from a car power jack. However, the Asus Eee doesn't seem to have one, so the only way to power it from a DC vehicle source is to have an inverter that takes DC power and produces AC wall power, and then you power the Eee from the normal wall power supply. Although this adds a step, I guess this is the only way to power my laptop on an airplane. So I went shopping, at the stores that I had available to me.

Wal-mart did have an inverter:

I tested it out on my battery pack; it ceased to work immediately without ever successfully powering my laptop.

I also ran across one at the local auto-parts store:

This one worked fine, but it had a really noisy fan in it. I took out the fan (another blog post), and it still worked Ok from my battery pack. I took it along on my trip. It did NOT work on the flight from Philadelphia to Heathrow. I'm not sure why; maybe the connector was the wrong shape (it seemed like it never did fit right).

After leaving South Africa again, I bought another inverter in Heathrow:

which worked on the flight back to the US. Yay! Having bought it in Heathrow, of course, it puts out 240V AC and has a UK/EU power jack, rather than a US power jack:

(I think that this is the US power jack equivalent).

Fortunately, I also have a Yung-Li power adapter from the old South Africa plug standard to a US outlet

which then converts the inverter to one that effectively has a US outlet:

By the way, before heading to South Africa, I did manage to get the right plug adapters to power my laptop and such:

These are of the very excellent Taiwaneese "Yung Li" adapter series. The South Africa adapter is the YL-8015. It's tough to find a place that sells them; I finally bought mine at Signal and Power Delivery Systems. (It's tough to find in their catalog, but they have them, and they will sell in small quantities.)

Will he prove his worth

2008 December 17 07:51

I just got back from teaching a one-week class in Cape Town, South Africa. Between preparing for the class, and the usual work stuff in October and November, and Thanksgiving, I haven't blogged here as much as I ought. That will change. My challenge to myself: at least two blog posts per day from now until January 1.

My report to my work colleagues about my trip to South Africa: it rained all the time, the people were mean, and it wasn't pretty at all. No need to subject anyone else to the experience; I'll be sure to go back next time to save you the the trouble and trauma.

Here are a few initial photos just pulled off the camera:

Me on top of the "Lion's Head", one of the mountains overlooking the city of Cape Town. This was taken Saturday December 13.

Sunset looking west from Lion's head.

(I would just like to state for the record that the hike up and then down the mountain left me fairly sore the next day.)

An earlier photo; the weekend before the class, my hosts took me out sight-seeing aroun the Cape Town area. This was taken at a vinyard. From left to right, this is Nick, myself, Jane and Andrew, who were among those doing the logistical work of hosting my stay. The other student, Drew, is taking this photo (and will appear here at some point).

Neil Gaiman and the defending of icky speech

2008 December 02 04:03

Some words yesterday from Neil Gaiman about defending the freedom of speech that you find personally objectionable. A very good read from someone who's very smart and grew up in a country without first amendment protection.

I promise this blog isn't going to fall into just having links, but this is a good one.