Monthly Archives: June 2008

Flight School Day 21

Today we flew the required night cross-country flight to Murfreesboro, Tennessee.  If you knew what you were looking for you could probably see all the way to Murfreesboro once we got to 5,500 feet.  The cities on the way were lit up pretty good and the sky was pretty clear.  I flared too high (compensating for yesterday when I kept landing too early) and we dropped about a foot to the ground in the hardest landing I’ve made so far.  We kept rolling and took off and headed back south.

Aaron had me do hood flying on the way back so I couldn’t see out the window.  He let me use the GPS to navigate and we made it back alright.  In the 10 miles or so I started having trouble keeping lined up with the GPS as I descended, so when I took the hood off I wasn’t pointed directly to the airport.  There is very little lighting to the North of the airport so it looks like a sea of nothingness with some airport lights at the end.  This made me really careful about my slip (we were a little high) as it seemed without reference to the horizon, keeping the nose sufficiently low to prevent a stall would be tricky.  It turned out to be one of my better slips though probably because of how careful I was being.

We used flight following both ways and talked to Huntsville, Memphis, and Nashville controllers.

Flight School Day 20

Today was my first night flight, but when I arrived it was still pretty light outside, so I flew the plane around the pattern solo for 4 landings (all wheel landings).  They got progressively better each time.  Then Aaron got on the radio and had me pick him up at the ramp.  After we got airborne, it was still light, so we flew around looking at all there was to see.  We found a valley where fog was beginning to form by the trees giving it a white-carpeted look.  We flew down the valley over the fog and he showed me places where he hunts.

Once it started getting dark we headed over to Moontown and I keyed the radio to get the lights to turn on.  On my first landing, I came close to not turning sharp enough to line up with the runway, but I got it lined up.  The wind was calm so we let the airplane roll to the end of the grass strip and then we turned around and took off the other way.  It was a little bit disorienting not seeing the usual landmarks and only having the runway edge lights to go by.  We probably did around 10 landings there before heading back to Madison County.  For some reason my landings at Madison County weren’t as good.  I kept thinking I was higher than I actually was and touching down earlier than I expected.

The air was completely still, but on my takeoffs I was still working the rudders like I am used to flying in the afternoon so he told me I was using them too much.  After that all my takeoffs were pretty smooth.

Flight School Day 19

Today I learned how to fly by only watching the instruments.  This was supposed to simulate what would happen if I lost visibility by flying into a cloud or something.  First I got to buy my somewhat expensive “blinders” that clip over my glasses and only allow me to see the instrument panel… I should get into that business… ~$30 for a piece of plastic that clips on your glasses.

Anyway… I took off from the airport and after climbing a thousand feet or so, he had me start wearing the blinders.  He would then tell me to do things like climb to a specific altitude or head a certain direction.  This is a little trickier than it might seem as no one instrument really gives you enough information, but you have to combine readings from all of them.  Then he had me turn while climbing and descending.  At one point I flew almost 100 feet below the altitude I was supposed to be at because I got distracted trying to fix my heading.  He said never get too low… a little too high is okay, but never get too low.  So after flying around a while he had me lift my visor and I realized he had me flying all over the top of a hill.  We saw an irregularity in some trees and flew close to investigate and saw a big cave opening on the hill.  It seemed like somewhere impossible to accidentally hike to and hard to see from anywhere except where we were.

Then he had me climb to about 4000 feet and we practiced “unusual attitude recovery” where I would close my eyes (while wearing the blinders) so I couldn’t see the instruments or otherwise surmise what was happening and he would put the airplane in an unusual attitude like climbing really steep and banked crazily off to the side.  He would then have me open my eyes and “fix it” only looking at the instruments.  We did this about three times then he had me follow a bunch of headings again and flip my visor up and find the airport.  Turns out he had me lined up perfectly on downwind parallel to the runway.  We tried a wheel landing that turned into a bouncy 3-point landing, took off, and tried another one.  This time it worked perfectly.  The wheels touched exactly when I wanted them to and I was able to apply just enough pressure to keep them on the ground.  I lowered the tail just right and it was probably my smoothest landing so far.  The very calm winds helped.

Flight School Day 18

Today was my first cross-country solo.  I flew to Muscle Shoals (about 53 miles).  The wind was stronger this time than when I flew with Aaron last time, so I needed a 10 degree wind correction in order to fly a direct course to Muscle Shoals.

I requested flight following from Huntsville International approach on the way there and the trip went smoothly.  I landed on runway 36 at Muscle Shoals and while I was taxiing back a plane was coming in on the crossing runway.  I waited for him to land and decided it would be a good opportunity to figure out how to use the GPS.  I followed the GPS route back to Madison County Airport and requested flight following again.  This time they informed me of two aircraft on my path.  I saw each of them and made it back safely.

Flight School Day 17

I wasn’t planning on flying today, but the weather was nice and I had an hour or so before I had to go pick up my companion to go home teaching, so I decided to do my 3 solo landings at a class C airport at Huntsville International.

It was pretty hazy once I got to about 2000 feet and the sun was just right to really light up the haze.  I decided to fly straight west rather than southwest which would have taken me directly to the airfield so I would have time to listen to the radio and talk to approach control.  Approach told me to expect a straight in approach on runway 18L, but didn’t give me a vector to fly like they did the day before.  So I turned in towards the airfield, but it was still out of my sight.  I probably should have asked him for a vector, but I didn’t.  After a few minutes I realized I had passed 18L when he told me to expect 18R instead and turn left heading 170 (I had flown a bit west of the whole airport).  Anyway, once I could see the airport I got lined up really nice and realized the wind was stronger than I was hoping for, so I performed a wheel landing and ended up putting both wheels down earlier than I should have and the wind blew the plane like a weather vane so I was pointed slightly into the wind, but I was able to compensate with the rudders and came to a nice stop.

Then I took off and my next two landings were great.  Before my last landing, I told tower that it would be my last one and they asked if I was going to do a full-stop landing.  I know what that means, but in the embarrassment of landing on their nice huge runway meant for jumbo jets and coming to a complete stop right in the middle of it (in my mind possibly annoying everyone in the tower) I answered that yes, it would be a full-stop landing.  So they were trying to figure out what terminal I wanted to use or if I wanted to go to the FBO when I realized what they meant and said that no, I would be stopping on the runway before taking off and flying back to madison county :-)  That’s probably when they realized I needed all the help I could get :-)

After the final takeoff, they cleared me to turn left back to Madison county as soon as it was safe and so I ended up flying over the air traffic control tower.  Departure asked me my altitude and I mistakenly read ~1500 feet as 2500 feet and he double checked and then told me what he was reading and I apologized and said his reading was correct :-)  About that time Departure probably cleared the whole airspace around the airfield so I could make it back without any further incidents.

That’s about the time I looked at my watch and realized I had 25 minutes to pick up my home teaching companion.  So I flew straight back to madison county, crossed midfield with my engines already idling so I could lose 1000 feet to get down to pattern altitude and then turned and landed the plane.  This was my only full-stall landing of the flight as the winds were pretty calm.  I also decided to find a better technique than that as it involved a lot of crazy maneuvering and didn’t give me as much time on downwind as I would like to contemplate and prepare for the landing.

Flight School Day 16

This was the first of the cross-country flights.  Aaron had me plan a flight to Muscle shoals (54 miles away) and calculate the direction we should fly corrected for the wind.  I also chose a few checkpoints on the map and calculated how long it should take to fly to each checkpoint.  The wind was not very strong so our wind correction was just a couple of degrees.

We got to our checkpoints almost exactly when we expected to and were very close to each one of them.  Aaron had me do a wheel landing and once my tail touched the ground he let me add throttle and take off.  Then he took the controls and flew me to where they get the parachutes packed for aerobatic flight.  The runway was incredibly narrow–it was basically in some guy’s backyard.  He was out on his lawnmower cutting the grass, so we flew over and waved our wings at him.

Then I flew back towards muscle shoals airport and flew us back to Madison county using the same checkpoints in reverse.  The whole flight took about an hour.  When we got to Madison county I did another wheel landing.

Flight School Day 15

Today was my first flight into class C airspace for landings at Huntsville International.

The airport is about 2 miles from restricted airspace at Redstone arsenal, so I had to watch for that.  We took off and flew west until approach told us to turn towards the airfield.  First they cleared us for runway 36R and we did about 3-4 landings there before they told us to fly left downwind for 36L, so we used the huge runway for a couple landings before they gave us the option to return to 36R.  After one of my takeoffs on 36R when I keyed the microphone, the radio turned off, so we pushed the radio in (it seems to have vibrated forward).  That solved the problem until we were leaving the airport and I keyed the microphone again while talking to departure and the same thing happened with the same solution.

We did all wheel landings today.  They are getting better, but probably still not good enough where I would feel comfortable doing them solo (I am wondering if it was the landings that jarred the radio out :-)  Really the landings were gentle but the airplane wasn’t pinned to the ground so it would hop around and as soon as Aaron touched the stick the airplane would be perfect :-)

He said I did a great job on the radio and he signed me off to land at Huntsville international.  I need to do three landings solo there to get signed off.  He said to go early in the morning when traffic isn’t as bad–apparently traffic while we were there was pretty busy but it seemed less busy than I imagined.

The other problem I had was I felt like I was too high all the time because the runway is so huge, so I almost always had to add power on final to make it to the runway.

Flight School Day 14

I am sending this about a week late, so just read it a week back in time…

Today I rented the plane and explored the region around Huntsville.  First I flew north to Fayetteville to see if I could find the airport.  It was pretty easy to find.  Then I turned around and flew down the east side of the parkway over south huntsville until I was a few miles from the river.  Then I turned east and flew over the hills (Monte Sano, Green Mountain, etc).  I flew around there for a while seeing what there was to be seen.  Then I flew North and found Moontown.  I landed there once and then decided to fly back to Fayetteville and try some landings there.  There was a bit of a crosswind and I landed twice.  Both landings were a little crooked because of the crosswind and myself not compensating enough or in sync with the gusts, so I felt the wheels screech a bit, but there wasn’t any bounce.  Then I flew back to Madison county and landed there.  I flew for 2 hours.  There was very little traffic–the only airplane I saw was also at Madison county.  I took off without setting my transponder to altitude because I got distracted by getting my heading indicator aligned with the runway–I got it set about 5 minutes after takeoff, hopefully nobody was worried.

Robotic Inverted Pendulum

A friend and I decided to build a two-wheeled balancing robot similar to the Segway transport vehicle for our Electrical Engineering senior design project.  A professor mentioned an inverted pendulum would be a very impressive senior design project. Years previously, a student of his did his master’s thesis on the inverted pendulum problem and built an impressive robot using analog circuitry–we thought it would be fun to build the modern equivalent.  We obviously drew inspiration from the Segway transporter and other robotic inverted pendulums that had been appearing with the arrival of inexpensive MEMS gyroscopes and accelerometers.

A two-wheeled inverted pendulum is somewhat more challenging to stabilize than a four-wheeled moving platform with an inverted pendulum and seems to typically require the use of wheel encoders. One of my primary goals was to make the robot as inexpensively as possible and forgo the use of encoders. I used two accelerometers at right angles to each other (in-fact there are three inside a small MEMS chip) and basic trigonometry to sense the robot’s angle to vertical. This angle will have error any time the robot is accelerating–I compensate for this by using a angular rate gyro.  The rate gyro cannot be used alone because it is subject to drift and would require manual calibration, but combined, the two sensors work great.

Jude Collins hacked a Nintendo 64 controller with a bluetooth transmitter to control the robot. Previous to this the robot was ridiculously boring as it just stood there. It turns out if an inverted pendulum stands doing absolutely nothing it is totally unimpressive. Here is the earliest video with remote-control.

Another design-goal was the ability for the robot to stand itself up. Previously to this we had not seen this done and a lot of robots seem to require to be placed in the upright position to calibrate–ours self calibrates in any position.

The robot has been crashed plenty of times and somehow has not been significantly damaged. In part to see how well the robot balances itself in free-fall we staged a mini robot high dive:

Driving this inverted pendulum can take a little practice. Braking has to be done by leaning backwards. This means when the robot is moving forwards the wheels have to speed up enough to cause the robot to lean backwards and then slow down. This is all done automatically of course but seems a little tricky for new drivers. I suspect the addition of wheel encoders could make this easier, but after 5-10 minutes driving becomes almost second-nature. Turning is very sensitive/easy and can be skillfully used to do some impressive drifting.