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

all engineering mockups should have duct tape

2008 September 30 19:55

My art class continues. It's continuing to be fun and cool.

Our first project of the semester must involve "motion", either literal or thematically. I've been thinking about building a concealed James-Bond-style instrument panel for my Beetle. The reason I want more instruments is to be able to monitor more things about the engine and the electrical system. However, I also admire the extreme austerity of the Beetle's instrument panel. Two gauges, speedometer and fuel gauge, and two warning lights, generator and oil pressure. So I'm torn, so I want to have both.

So for my motion project for class, I'm going to build my concealed instrument panel. It embodies motion literally, by extending and retracting in response to the drive flipping a concealed switch, possibly in the ashtray or under the seat. It will go under the dashboard on the passenger's side beneath the glove box.

I won't have the panel entirely filled with gauges when I present the project, because I don't want to buy that much stuff for the car all at once, but I do want to have a couple of gauges mounted. I have everything for the first version of the panel on order, and the first gauge arrived today, an oil pressure gauge:

Here's the back of the gauge. The bottom three terminals are for the gauge itself. They are power, ground, and then the sense wire that comes from the oil temperature sensor. The black thing at the top with two terminals is the internal gauge light, which I will connect to the lighting circuit in the car so that the gauge is lit when the lights are on.

I was concerned that with the instruments over on the other side of the car, they'll be hard to read properly because of the angle. I got the gauge today, so I made a cardboard (and duct tape) mock-up of the panel in its extended position so that I could look at the gauge in the car to see how easy it is to read.



Here's the panel mock-up with gauge in the car. Having seen this, I think it'll be fine. Oil temp is the indication that will change the least, and so I think it's fine if it's the farthest gauge away from the driver. Basically, if the needle is straight up, then the engine is as hot as it needs to get.


clarification on flaps

2008 September 29 19:04

In my last post, I slightly oversimplified the situation about extending flaps and reducing throttle. Obviously, anything I say here is merely explanatory, and if you're learning to fly, you of course take your instructors advice and that of the airplane's flight manual, and anything here is supplemental information for your edification. [Further disclaimer: I have never formally studied aerodynamics, so this is an amateur explanation.]

Flaps are devices that extend the chord of the wing (make it longer from front to back) and increase its camber (curviness). These changes increase the amount of lift that the wing makes and also increase the amount of drag it experiences under a given set of circumstances. The increased lift means that the wing can support the airplane at a slower airspeed, and thus the stall speed gets lower. The increased drag means that you can bleed off energy faster (you can descend more rapidly without a dangerous build-up of speed).

Flaps are surfaces at the back part of the wing that swing down and/or extend (depending on their design). The position of flaps are their angle from their retracted position, sometimes spoken of in degrees. So "zero degrees of flaps" == "no flaps" == "flaps retracted", then as they are extended, "ten degrees of flaps", "full flaps", etc. The IMPORTANT THING that I ignored yesterday: As the flaps are extended, at first there's lots more lift and just a little more drag. As they're extended farther, the lift doesn't increase as much but the drag increases much more.

Operationally, what I should have said in yesterdays post, as far as flaps:

There are standard procedures for beginning a descent to landing. The Cessna 150 is the one I know: on downwind opposite the landing end of the runway: carb heat on, throttle down to 1700 RPM, flaps down to 10 degrees turning base: flaps down to 20 degrees, on the rest of the approach: lower throttle and add flaps as needed.

That's the standard procedure. What I was reminded of on Saturday was during the "as needed" phase, drop throttle first and then add more flaps when the throttle is at idle.


signed up and signed off

2008 September 28 07:46

I flew a small airplane yesterday for the first time since December. It was my familiarization flight in a new aircraft, and flying in and out of a new airport.

The flight went superbly well. I made a few mistakes, but I corrected them with one exception without the instructor mentioning it, and alltogether without the instructor having to touch the controls. In fact, he signed me off, so now I can go flying in that airplane by myself. Whoo-hoo!

After the flight, I did something pretty bone-headed which I will talk about here in the fullness of time.

Lessons on the day:

* a question can be the most effective way to correct someone "What is your target speed for this part of the approach?"

* power down, then flaps down Landing an aircraft is a pratical (as opposed to theoretical) exercise in dynamic energy conservation. You want to bleed off your two forms of energy (speed and altitude) in a controlled fashion so that you end up minimum speed as you touch down on the runway. The procedure for doing this is the pilot has an approach speed that they maintain by adjusting the pitch of the aircraft. To start the approach, the pilot adjusts the engine and flaps such that the airplane will bleed altitude at a reasonable rate (say, 500 feet per minute). The flaps and engine are adjusted (while keeping speed constant) to make the decending glide path of the aircraft end up at the end of the runway.

The engine adds energy, flaps subtract it. As you adjust your approach, it makes more sense to first decrease throttle, and after its at idle, add flaps to continue to bleed energy faster. The wrong way to do it is to start adding lots of flaps when the engine is still running above idle, so you have the engine producing energy and the flaps subtractng it. One thing that's wrong with this is that it's easy to adjust throttle, up or down. Once you've added flaps, it's dangerous to retract them too fast because they change the pitch and stall characteristics of the airplane. So once you have the runway made, drop power to idle and then add flaps to make the approach right. [Of course, this is all within the context of following the established procedure. See my next post for more.]

* on a grass field, you want full flaps on every landing Full flaps means slower stall speed, which means less energy available as you touch down, which is easier on the airplane. I forgot to put on full flaps on my second landing, and fixing that for the third landing got me mixed up and I ended up dropping a bunch of flaps with the engine above idle. Which brings me to:

* if you think you need power, you do Historically, my approaches tend to be high and fast. I guess just a residual fear of trying not to pile into the ground, but when I go flying for the first time in a while, my first couple of approaches will be high and fast until I get into the rhythm of a proper approach. Yesterday was no exception (there were also mountains that I was trying not to hit). However, the third approach I made, having added full flaps too soon, I ended up too low and too slow. I realized the problem in time, and fixed the landing without the instructor having to intervene, but finding myself too low on approach with full flaps (meaning the engine is less effective in trying to climb) is something very firmly in the category of "something to not do". In this situation, don't be bashful about adding power. You can always remove it once you're high enough.

By the way, on a grass field, you always taxi with the yoke pulled back all the way, to relieve the nose gear and tire. You just sort of pretend that you're in a taildragger.

Hopefully more flying stories soon.


expensive keys

2008 September 22 09:04

Saturday I participated in a transaction that was a new one for my young life; I joined a flying club. I wrote big check and what I got back was a set of keys:

and of course, privileges of club airplane rental.

I got my medical in August, so I'm all certified again. I now have access to airplanes, the second major ingredient. The third and final requirement to go flying is currency. I haven't flown since December, so I need to go up with a flight instructor, get comfortable in the airplane, and have the instructor sign me off that I'm allow to fly the club's planes solo.

So of the three major requirements to be able to go flying: paperwork: check airplane: check currency: as soon as I can schedule it.

So this blog might actually be somewhat about flying again. Yay!


machining without a license

2008 September 16 23:49

Now that I have my Beetle's engine apart, there are two problems that I'm going to deal with as I put it back together. The first is that the cylinder heads were machined without re-adjusting the chamber volume, so the engine has been running at too high of a compression ratio. This I'm going to solve by replacing one of the heads and getting all the chambers back in balance.

The other problem is that oil pressure tends to run low; the oil light flickers pretty strongly when the engine is idling after it's been warmed up. I did a check of the oil pressure specification right before I pulled the engine out of the car, and the pressur was definitely sub-par. Low oil pressure is sometimes an indication that the car is nearing needing to have the engine overhauled. I bought the car assuming that I'd be overhauling the engine in a couple of years. However, the other symptom of a worn engine is oil usage and oil smoke in the exahust, and neither of those is present.

However, it's also possible that oil pressure is low because the oil pump isn't entirely doing its job. Or some of both, for that matter. As a diagnostic, I took the oil pump apart. Some parts of it are pretty badly worn, and the last time it was assembled it was done by an idiot who used the wrong gasket and gooped it up with sealing compound. So I ordered a new pump.

The new pump came yesterday:

To get optimal efficiency out of the pump, certain clearances need to be exactly right. The gears in the pump have to be exactly the same height as the body, and the cover needs to be completely flat so it doesn't let oil by. To finely adjust those clearances, you can sand whatever part needs to be smaller and slowly remove material. This is essentially machining without having to have machine tools.

However, I've never done this. I don't know how long or how much effort it's going to take to remove a certain amount of material. So I decided to start with a practice run. I took the idler gear out of the oil pump that's in the engine and decided to see what it took to shave off metal. I also decided to work in flattening the oil pump cover, since it was pretty badly scored. Here's the gear and the oil pump cover:

So I worked on the pump gear for a while. The material comes off slowly enough so it's easy to control the rate. Here's the end of the gear with a little bit of material taken off; you can see the ends of the gear teeth have been sanded smooth:

Then I made the mistake of trying to work on the cover plate. It was going well at first. I could take off material. But then I wanted to just finish it up and get back to working on the gears. Well, the round gouge marks were deeper than I expected. So at this point, I realized this wasn't being easy and I need to get coarser sandpaper:

At that point, I figured I was 80 percent done. No way. I wasn't half way. The quarter-circle of gouges in that photo are pretty deep.

So finally, after 3 hours plus of sanding, my shoulders and hands are very tired, but the cover plate is on the right:

The one on the left is out of a pile of VW parts that I bought one time. It sort-of makes a before/after picture.

So the next few steps for working on the car are: - match oil pump parts - install oil pump - equalize combustion chamber volume After that, it's a matter of assembly and re-installing the motor.


holy hyperbaric chamber Batman!

2008 September 14 09:08

[WARNING: Long explanatory post. For those of you who already know about compression ratios: I think the reason my #1 valve was having problems was the CR on that cylinder was 8.2. A known good cylinder was 7.6. Spec for the engine is 7.3.]

In discussions of fire and fire prevention, it's common to talk about the required ingredients for starting fire: air, fuel, and an ignition source. Remove at least one, and you won't have a fire.

An four-stroke, internal-combustion engine (most car engines) is a little more complicated than that. I've heard people use the same three ingredients to talk about what can fail and make a car not run right, and that's useful, but it's an oversimplification if you want to understand what's going on inside the car.

The equivalent list for an internal-combustion engine are: - air intake - mix fuel with air (carburetion system) - compress the mixture - ignition to ignite the mixture - a place for the exhaust to go

All of these items must be present for the engine to run at all. However necessary, the following relationships are also required to be somewhat correct for the engine to run: - amount of fuel per air (called the "mixture") - when the ignition spark happens in time compared to the peak of compression (called "timing" or sometimes "spark advance") - amount of compression (called "compression ratio")

Further complicating matters, if any of the parameters changes rapidly, then there must be a mechanism to re-adjust the other parameters to keep the engine running. If this doensn't happen, then engine can stop.

When people think about running and adjusting engines, the mixture and the timing both at constant engine speed and as the engine changes speed are very important. If the mixture or the timing get far enough off, the engine quits and you know it. In the engine in my Beetle, the carburetor controlls the mixture and it has various mechanisms to set the mixture correctly and different engine speeds and loads. There is a vacuum port in the carburetor that's connected to the distributor; the distributor uses a combination of this vacuum signal and the engine rpm to set the spark timing.

I've spent a lot of time getting the distributor and the carburetor right in my engine. It's easy to tell when they're not working right; the car dies as I try to pull away from a stop sign or stumbles when I push on the gas or makes funny noises when I take my foot off the gas. When you get those adjustments wrong, it's easy to tell, because the car does something that you notice.

HOWEVER--there's a third adjustment in the above list. COMPRESSION RATIO (abbreviated CR). CR is the ratio of the inital to final volume of the fuel-air charge just before its ignited. It's a very important parameter for the running of the engine. The higher the CR, the more mechanical energy can be extracted from the fuel and so the more efficiently the engine will run. However, higher CR also means the engine will run HOTTER, which is very important in an air-cooled engine like mine.

It's easy to overlook CR because it's not something you can adjust from outside the engine, it's a function of the geometry of the insides of the cylinders. However, it's very important that it be set to a known, correct value for the engine to run correctly. Since CR is a function of the geometry of the cylinder/piston/head combination, it's physically possible that it's DIFFERENT for different cylinders (although that's almost certainly not what you want).

Compression ratio is measured by measuring the volume of the combustion chamber and the volume that the piston displaces in its motion, and plugging those into the compression ratio formula. The shape of the combustion chamber is very complicated, so it's measured with a liquid after using disk to form a top to the chamber with a small hole in the middle:

(This chamber isn't ready for volume measurement, obviously; one of the valves isn't installed. This is to illustrate how the plate fits over the chamber.)

I used water for the fluid, which isn't ideal, but it's readily available and easy to replace. Once I dry the chamber out with paper towels, here's my final drying method:

I measured the chamber volume of cylinder #1, which is the one that had been having problems, and cylinders #3 and #4, which had always been working right. One thing I discovered that the head on the right side of the engine had been machined so much that it had a ridge around the inside of the chamber:

that sticks up higher than the sealing surface (the shiny bit to the left of the ridge). My measurement of the volume of the combustion chamber for cylinder 1 was significantly different than for that of 3 and 4.

My best measurement for the CR of cylinder #4 is 7.6. My measurement for #1 is 8.2! By the way, the specification for the engine was 7.5 earlier in the 1600 engine, and 7.3 for the year of my engine.

So cylinder #1 has a CR of 8.2 instead of 7.3 (which means running hotter) and I also had air leaking into that side of the engine (means running leaner and thus hotter). I believe those two factors in combination are the cause of the stretching exhaust valve that has been my long-term problem with my car.

What to do about it? News at 11. :-D


there was much shininess

2008 September 12 08:57

The bookmark assignment is almost due in my art class. I've been polishing using my Craftsman rotary tool:

I'm not quite there yet, but it's getting fairly shiny:

The plan is to get it finished and protected this weekend so I can move on to the next project.


by the cut of his jib

2008 September 12 08:12

I got to play with computer hardware. Whoo! Not professionally, just my own.

When I bought the HP machine that I play Flight Simulator on, I bought a nice new Geforce 6600 graphics card to go with it. For purely lazy reasons, I didn't install the graphics card. However, I decided that to go along with my updated real-world flight status, I want to be able to fly virtually without having the simulation bog down because it's trying to render too much detail.

So I finally bit the bullet and got the graphics card out:

In addition to increased 3-D graphics rendering capability, the card has outputs for two monitors and component video:

The other reason to do the upgrade is to have a computer hooked to the TV in the family room, to be able to watch things like Rifftrax.

To package for the card recommended at least a 350 watt power supply, and the machine came with just a 300, so when I bought the system and the card, I also bought a 430 watt power supply. So the first task was to install that.

The patient open for surgery:

The old power supply:

and the new

Interestingly, the higher power supply is rated for less output on 5V. However, it has a total rating of 32A of 12V, vs. 19A for the old one.

Here's the flight simulator rig for the moment. Not ideal placement of the monitor, but I'll give it a better layout when I have all the software stuff sorted out.

And here's Jasper contemplating the old power supply:


pump it up

2008 September 10 00:33

I got the engine out of my beetle a while back; I guess a month now. I've been busy with other things, but now I'm trying to get back to it.

To make sure my work bench could support the weight of the engine, I put on some diagonal bracing and built a "cradle" to distribute the weight to the main beams of the work bench. The cradle is the box that's sitting on the near end of the bench:

The engine's finally up in the air:

and ready to work on:

In addition to the cylinder head problem (which is the main reason I pulled the engine), the oil pressure in the engine has fallen below spec. This is partially because the internal parts are worn, but it's also possible that the oil pump itself:

is worn beyond what it should be. I've ordered another one; while I have the engine out I'll replace the pump with a known good one and see if that helps the oil pressure enough.


bookmarks and gussets

2008 September 07 09:29

I seem to be in an art class. On the instructor's invitation, I enrolled in a local school in a jewelry making class, which teaches basic metalworking.

Our first project is a bookmark. We started with drawings, then made a paper template:

(this is supposed to be a depiction of our cat Jasper in his bed).

At the left here is the metal piece with the template traced on it. On the right is the metal saw that I'm using to cut out the piece. In the middle is what's called a "bench pin"; it's used as a back stop for the saw to brace the piece against.

Here's the piece with the outside edges cut. The inside shapes are cut by drilling holes and then uncoupling the saw blade from one end, inserting it through the drilled hole, and then re-setting the saw and cutting from there. The bench pin is particularly useful when doing this, because it braces the flat material all the way around the blade.



Here's the subject. You can decide if my drawing is a good depiction.

Now I'm not likely to start making sheet metal book marks for a living, or jewelry for that matter. However, knowing how to work with metal is definitely something that I want to be able to do better than I can now. Finishing metal surfaces is something that I particularly want to know how to do better. As I file and sand and finish this bookmark, I'm starting to learn that. Finishing is, I think, the specific skill that I will take away the most from the class.

However, there are certainly things that are directly related to things that I've at least thought about doing. In Jim Bede's book on "Build your own Airplane":

here are two pages of patterns for the fuselage gussets for Jim's BD-4 design:

with my bookmark for size comparison. The process of producing the gussets is exactly the same as the bookmark. The templates are supplied with the plans. You transfer the template and cut and file the part to shape. The final part doesn't have to be polished to a mirror shine like the bookmark, but it definitely needs to be smoothed all the way around.


back to basics with paperwork

2008 September 07 08:39

The point of this blog from the beginning was to talk about flying. I haven't flown an airplane since last December, so there really wasn't anything to talk about on the flying front. Part of that was because I thought I was going to get access to a very local airplane to fly, which didn't happen. My medical expired in March, and since I didn't practically have access to an airplane to fly, I didn't get it renewed right then.

HOWEVER...there is actually movement on the flying front. I August, I got a shiny new medical certificate, so I'm now officially legal to fly for three years

I'm also getting other things updated, like installing updates to my Flight Guides:

And in other news, I have an application in to a local Flying Club, and I have a meeting coming up in a couple of weeks to get that going. So perhaps, by October, I'll be flying again. Yay!


diamond in the rough

2008 September 06 20:22

I like reading Scott Adams' blog. He has a fairly ascerbic sense of humor which I mostly enjoy. Sometimes he says things just to yank people's chains, I think. Somtimes he comes up with some very interesting insightful comments.

He has a recent post about energy independence (going off the grid and so on) and how he doesn't think that it's going to be driven by government incentives. He thinks independence will be driven by cost ultimately because living that way will be so much more efficient.

He makes a great point, but it's just a lead-in without the rest of the argument. In discussions like this, about what are better for the world and what people should be doing, I often feel that the discussions should have much more facts. I honestly don't know the facts are about this issue, but presumably someone does. If I were going to become politically active, I think my thrust would be to inject as much quantitative analysis into lawmaking and legal proceedings as possible.

For instance, in talking about going off the grid, and interesting quantity would be measure what area of solar panels would be required to do that. That would be a moving number, depending on the efficiency of energy storage and solar panels and the time of year. Or even less than that, what's the area of solar panel required to run 100 Watts (one bright light bulb) 24 hours a day. For people interested in that technology, that would give them a ballpark idea of how much solar power would be required for them to run which appliances off-grid.

The other end of this equation is to set a number of the maximum sustainable population density given a certain technology level and latitude.

I wonder how hard it would be to find these numbers. I should try to look some of this up.