I am changing acronyms starting with this post. Previously I was calling this an SAS for “Stability Augmentation System” but someone pointed out that this is technically more of a CAS for “Command Augmentation System”.
SAS implies a direct connection between pilot input and control surface deflection with some additional stability augmentation mixed in. CAS implies that a flight computer is translating pilot inputs into a “request” and the flight computer then tries to satisfy that request, but there is no immediate direct mapping between stick deflection and control surface deflection.
Just to review, the ATI “CAS” system internally tracks a target bank angle and a target pitch angle. The pilot is “flying” these target bank/pitch angles and the flight computer is doing it’s best to match up with the request. The pilot changes the target bank angle by deflecting the stick; the greater the stick deflection, the faster the target bank angle changes. This is similar for the target pitch angle. When the pilot centers the stick, the target bank or pitch angle is held steady.
If the pilot banks into a 15 degree turn (target bank angle) and centers the stick, then the flight computer will hold that 15 degree bank indefinitely or until the pilot deflects the stick again. Likewise with the target pitch angle, the pilot pulls the nose up or down with the stick, but when the stick is centered, the flight computer holds that pitch angle indefinitely (as best as is possible for the available throttle and airspeed and maximum control surface deflections.)
The system can limit that maximum bank and pitch angles to stay within “nice” limits. In addition, the system can limit that maximum control surface deflections to avoid abrupt and rapid attitude changes. Currently the system is rigged so that even if the pilot commands maximum pitch up angle (+15 degrees) and pulls the throttle to idle, there is not enough allowed elevator authority to stall the aircraft. This makes the aircraft very safe to fly and very predictable.
Here is some real world flight video from the same flights shown in the first video. The CAS system is active for all but the initial take off in both of these videos. You can see in some situations the system is working quite well, in some situations the flight computer cannot completely compensate for the natural airframe dynamics and environment effects (turbulence, etc.) and in a few situations additional tuning will be required:
1. We added some additional logic to slowly roll the wings to perfect level if the pilot puts the bank angle within +/- 10 degrees of level. It’s really hard to get it exact from a ground perspective, so the idea is to let the pilot get in the ball park and the system will take over and finish the job. Auto-leveling will only kick in after the pilot centers the stick so it doesn’t fight the pilot if the pilot is intending to bank the aircraft.
2. To mimic more natural flight behavior we automatically pitch the nose up by a few degrees when the pilot adds throttle and pitch the nose down by a few degrees when the pilot pulls the throttle back. This is much more “intuitive” for a pilot and makes the system more predictable and easy to fly.
This was unfortunately another windy day, and the telemaster is a self stable, “trainer” style airframe and thus roll and yaw are very coupled and the aircraft’s natural flight dynamics react quite a bit to even small wind gusts. This means the SAS isn’t shown yet in it’s best light. I guess I’ll keep apologizing for the weather and at some point move to a more stable airframe, or try to find nicer days to fly.
I will say one thing. Even when the aircraft is bobbing around on final approach in the turbulence, it’s nice to be able to fly hands off the aileron stick and trust the SAS system to immediately return the wings to level, even when we get knocked 10, 20, or even 30 degrees off kilter. I’m still fiddling and improving and I’m not totally in love with the system yet. But it’s good enough already that I miss it when I turn it off.
ATI has been developing a number of flight control system building blocks and we have been testing them on my Senior Telemeaster airframe. This week I decided to connect them up to create a simple SAS (stability augmentation system.)
Briefly, when flying with an SAS, the pilot is still 100% in manual control over the airplane, however we have inserted a flight computer in between the pilot control inputs and the control surface actuators. Rather than the pilot’s stick commands directly moving the control surfaces, the pilot stick commands are translated to roll and pitch “rate” requests. The flight computer keeps track of the target pitch and roll angles and adjusts these according to the pilot’s stick inputs. The more the pilot deflects the control stick, the faster the aircraft rolls or pitches in that direction. When the pilot centers the stick, the flight computer holds the current bank and pitch angles, even if there are throttle or speed changes, gusts and turbulence, etc.
Here is a video of my very first SAS test flight:
The first flight test went pretty much according to script. The basic mechanics of the SAS worked as planned and produced reasonably stable and smooth flight. Transition between direct manual control and SAS flight was smooth. After the flight I adjusted two things. First, my gains were set way too low. Even at full stick deflection, the system responded much too slow to be intuitive for an average pilot. Second, I had used an exponential control mapping. This means that near the stick centers, I have to move the sticks a lot to produce just a little bit of aircraft response, but as I near the extremes of the stick deflection range, the rates ramp up quickly and the aircraft responds at maximum (programmed) rates. Below are two plots that show the difference between linear and exponential input mapping.
I had a little fun on the first landing. I included it all in the video posted above. After a couple low slow approach passes followed by a go around, I figured I had enough confidence in the system to attempt a full landing. However, the combinations of gains being set way too low along with exponential input mapping meant my flare was way way way too slow and from the video you can’t even see any pitch up at all even though my stick was pulled all the way back. I hit so hard I sent the camera tumbling … sky / ground / sky / ground 🙂 Every thing was fine … I’ve had rougher landings once in a while even under pure direct manual control.
After this flight I tripled the gains and switched to linear input mapping and the result was something that is much more intuitive to fly and allowed me to do some nice landings on subsequent flights. The system still isn’t perfect and needs some more tuning and fiddling, but for the first day out in the field after a couple days of intensive coding, I am really happy with the results!
Here is some video from my last flight of the day:
One of the most challenging aspects of autopilot setup is tuning the gains for a particular airframe. When the gains are tuned poorly, the aircraft my oscillate excessively, it may lag way behind the target pitch angle or roll angle or velocity, it may never reach the target values. Poorly tuned gains could destroy an airframe in a worst case scenario, but often people just live with non-optimal gains that aren’t great but work well enough to get the aircraft around the sky. It’s hard to know what gains to tune and why and a person could play with the numbers all day and only manage to make things worse. It’s easy to spot a problem; often the aircraft will look like it is fighting itself even though it does make it’s way to where it should be, or it just may not do what you ask it to do.
Real World Experimentation
Today I did some test flying with one goal to improve the elevator / pitch gain. Previously my gains were set too low. The result was smooth pitch control, but the actual pitch lagged far behind the goal pitch and tended to oscillate slowly above and below the desired pitch angle. To fix this, I increased the proportional gain until the pitch became unstable, then reduced the gain by 50%. This doesn’t ensure optimal results, but works pretty well in practice.
Here is a short before and after movie
The first half of the movie shows a flight where the elevator gain has been increased until we have just crossed the threshold into an fast oscillating system. You will see it stabilizes from time to time, but any little gust or even a turn can excite the system and lead to oscillations. In the second half of the video the gains have been reduced by 1/2 and you can see the pitch is much more stable. One point to note is that both flights were flown in very windy/turbulent conditions. During the second flight I was seeing sustained winds at 20 kts, gusting to 25 kts. The aircraft was set to cruise at 28 kts for a portion of the flight and on one up wind leg, it just stopped in the sky. (28 kts = 32.2 mph)
Want to learn more?
If you are interested in more information on PID controllers and gain tuning, I wrote a tutorial several years ago explaining much of the basic theory that goes into a simple PID controller. I then discuss some specifics about the autopilot implementation used in the FlightGear flight simulator. This is interesting because my UAV autopilot uses the same basic FlightGear approach. In fact, it’s possible to develop an autopilot xml configuration file in the FightGear flight simulator, and then copy the config file over to the real UAV and run it with only a few small changes.
At the end of the tutorial I include several tips and strategies for tuning PID controllers.
My standard disclaimer is that my educational background is computer science; I do not present myself as a control theory expert; instead I’d just like to share what I have learned in a way that makes sense to me.
img_2637 Ahhh, green grass, blue skies, fair winds, and an R/C airplane …
May 21, 2008.
This winter I ripped out the old 4 stroke engine that was broke. That engine has been repaired, but I decided not to put it back in. Instead I decided that this light “stick built” airframe is crying to be electric powered. I bought an E-Flight 46 motor over the winter and installed it. Then when the bank balance rebounded a bit I bought a Castle Creations Phoenix 60 speed controller. Finally, yesterday, I scratched my head and worked out battery placement and installation. I have 2 x 8000 mAh 18.5v lipoly batteries from the telemaster project, and one of these seems to balance out the airframe perfectly when it is as far forward as I can put it.
Today I ran out to the field during my lunch break to try it out. I kept the original wood 12×6 prop I ran with the 4 stroke motor. No particular reason other than I like wood and nylon razor blades make me nervous.
Ok, so can you say way over powered? This combination will cruise nicely at just a few notches of throttle, and things start getting a little crazy above half throttle. Today was a really gusty swirly day, so I kept things slow and gentle and just tooled around the way a trainer should be flown. Plus I want to secure the big 2 lb battery just a little better before I start pulling too many g’s with it.
Two repair notes: (1) The tail wheel servo was partially stripped out when I got to the field today. That must have happened last year and went unnoticed. It really only affected how sharp I could steer to the left on the ground so I flew with it like that and didn’t worry too much about it. When I got home I dug out a replacement servo I had on the shelf and slapped it in. (2) When disconneting the deans connector after landing, I pulled a wire off. I can only blame myself for a bad solder joint, but it’s easy enough to solder up another bad joint and get flying again. 😉
It’s good to be out flying on a nice day, even if the winds are a bit gusty and swirly. After my flight, I sat and watched a dust devil blow across our field sucking up stuff and sending it at least 1000′ skyward … pretty cool but I guess I’m glad i didn’t try to fly through it with the Kadet Senior!
July 28, 2007.
I haven’t gotten EGN-1 out yet this year … too busy with other projects, so I loaded it the van and was going to get it running again today. I started up the engine and didn’t like the way it sounded, so I did a run up test and it died on me. From that point on I couldn’t get it running. I popped off the cowl and observed that it was spitting fuel out the carb as if it was running backwards or had really screwed up timing. After fiddling some more I dropped the valve cover and found that one of the valve adjuster screws along with the end of the adjustment rod and broke off and was floating around up there. It was all ground up and a mess. 🙁 So I think I need to write off this engine and find a replacement. It’s always something, but I’d rather discover these sorts of problems on the ground rather than in the air or just short of clearing the corn at the end of the runway. 🙂
May 20, 2006.
Conditions: Winds out of the E and light to start out with, switching more to the NNE and picking up to 10-15 mph by late afternoon. We had light showers come through in mid-day. Temps a bit tool cool for the shorts and t-shirt I decided to wear.
I made several flights. The one item of note is that I pulled the quick fueler off and piped the fuel direct. This had a *huge* affect and the engine suddenly became *way* rich to the point of not running. I had to go at least two turns in to get the engine running again. I think this was my last quick fuel valve I’ll ever use. It seems like a good idea, but I’ve had no end to fuel flow problems, unreliable engines that are impossible to tune across their whole rpm range. Hopefully I’m on a much better track now.
I also figured out that I can push the nose down on approach to lose altitude if I’m too high. In the past I’ve just let it float, but with such a high drag wing you can dive press down on the nose in your base and final legs and you don’t pick up a ton of speed. That which you do pick up quickly bleeds off. One of those “doh!” moments. Landings in the Sr. have now become much easier to spot and I have a lot less trouble floating by at 10′ agl.
April 10, 2006.
Conditions: Temps in the 70’s, winds out of the SSE at about 10mph. Sunny!
Results: We had several good flights and one dead stick from adjusting the idle a bit too low. Here are some pictures:
Novermber 26, 2005.
Objective: Winter flying.
Conditions: Temperature +18F, Wind chill +5F. Winds out of the ESE at 5-10 mph. Partly to mostly cloudy. About 1 inch of snow on the ground.
Results: I flew manually today with the co-pilot off; nothing other than a standard R/C airplane.
In the cold dense air, the Kadet had very nice performance. So nice in fact that I was unable to land with the engine running. Any amount of engine, no matter how slow was enough to keep the airplane puttering along with virtually no decent rate. I had to kill the engine in flight and dead stick it in for all my flights today. That worked fine, but this plane might need an extra lb. or two for ballast on these cold days!
Other than that there really wasn’t all that much to report. I dressed warm, the wheels handled the shallow snow just fine, the 90-degree cross wind didn’t seem to cause any problems. Just a very enjoyable day at the field. Oh, I did notice a significantly higher fuel burn in the cold weather which I guess makes sense. The denser air needs more fuel to maintain a proper ratio … (?)
September 10, 2005.
Objective: High wind handling tests.
Conditions: Temps in the high 80’s. Winds straight out of the south at 15-20, gusting to 25+.
Results: First off I cheated most of the time and flew with the FMA co-pilot enabled. This allowed me to worry more about ground tracking and less about keeping the wings level in the swirling gusting conditions.
Overall I had pretty good results. I actually had to tie up the plane when it was on the ground so it wouldn’t blow away. The biggest challenge I faced was getting the aircraft from the starting area to the runway. The winds were too strong to taxi (often they were higher than flight speed.) Even carrying the plane was tricky if you caught the wind wrong.
However, despite the challenging ground logistics the plane handles great in the air. I was fortunate that the wind was pretty much aligned with the runway so I didn’t have to deal with cross wind issues. The plane’s approach was very slow and at the higher wind speeds I needed to run up the throttle to 30-40% and push the nose down just to make headway towards the runway and not gain altitude. (The Kadet will climb with about 4 notches of throttle.) Once over the runway I was able to chop the throttle and land with virtually no forward ground speed.
Summary: In the hands of a moderately experienced flyer, the Kadet Senior can handle pretty fierce winds with little trouble. I wouldn’t recommend operating in a 20 mph cross wind, but a 20mph head wind is perfectly doable. If the wind grows beyond 20mph you need to be extra careful. The Kadet is so slow that I found that you will need substantial throttle just to make a small amount of headway into the wind. If you happen to lose your engine downwind in those sort of conditions, you are going to land even further down wind.
August 24, 2005.
Objective: I haven’t made much forward progress in hobby-uav land so I figured I’d take EGN-1 (in it’s current state) out for a few flights just for fun, and to make sure everything still worked fine.
Conditions: Temps in the low-to-mid 70’s. Winds were on the heavy side, 10-15 mph gusting to 20 and blowing in from the SE.
Results: The conditions forced cross wind take offs and landings which are always fun. For most of my activities I just turned on the co-pilot and let it do it’s best to keep the wings level in the gusts. It does a pretty good job as a wing leveler and allows me to pay more attention to my ground track and crab angle and decent path. I had a couple nice landings where I was crabbing 30 degrees into the wind as I approached and touched down.
The wind was blowing hard enough where I could emulate a kite. I turned on the wing leveler and trimmed it out so that it flew nearly motionless for several minutes. A click or two of elevator trim would control my forward back speed, and a notch or two of throttle would control my up/down. With very slight adjustments I was able to hold it close to motionless indefinitely. The winds were much lighter near the ground so I wasn’t able to do any kind of verticle take offs or landings.
I scuffed up a wing tip very slightly in one of the cross wind landings, but I suspect a little windex will make that all but go away.
June 16, 2005.
Objective: Accumulate flight time with and without the Co-Pilot.
Conditions: Near perfect. Temps in the middle 70’s, winds light and variable but mostly out of the north when there was any, zero clouds.
Results: I had several good flights, touch and goes, some aerobatics, and some nice relaxing meandering around the pattern. Here is a slow pass sequence …
img_2635 Take off. Can you spot the aircraft shadow? Notice the exhaust smoke …
img_2637 Another slow pass sequence. Turn to final, closer, closer, and then flying past …
img_2649 Short final …
img_2652 The grass is short so I tried a grass take off …
img_2654 Off into the wild blue yonder for another flight …
June 4, 2005.
Objective: Test my FMA Direct Co-Pilot (2-axis IR flight stabalization system)
Conditions: Temperature in the middle 70’s, wind from the S and SW varying between 5 – 10+ mph. Rain had just moved through so conditions were improving, but the wind was changing to be from the SW and increasing thoughout the tests. We had a couple little sprinkles for a short time but they passed through quickly.
Results: Again, I absolutely love to fly this airplane. It is such a delight to fly. Please see my description of the FMA Direct Co-Pilot in the Self Stabalization section of the EGN-1 project pages.
I think my tests were reasonably successful. I’m happy enough with the co-pilot to move forward and start looking at getting my flight computer running.
Other: I just wanted to mention again that I always have a lot of fun flying this airplane. I was the only one at the field tonight so no pictures, but one flight I took it up to a fairly high altitude. The cloud ceilings were still pretty low as the weather was still moving out. I stayed under the clouds so I know I didn’t got *that* high. 🙂 For some reason my engine killed on my after a couple minutes of running full throttle (heat?). This left me dead stick, but up high. My neck was getting sore from looking up so I layed down in the middle of the runway and just steered around above me as this stupid thing kept floating and floating seemingly forever … I probably glided for 10 minutes??? When I got lower I stood up, set up my approach, did a little slipping on final and touched down right at my feet. Very cool.
Another thing that is fun to do is overflair on landing and drag the tail wheel first for several feet before the mains touch down. I also am enjoying 1/3rd to 1/2 throttle take offs. At full throttle the plane leaps into the air quickly, but at reduced throttle take offs are much more “scale” like.
May 19, 2005.
Objective: Test and tune and continue to break in the engine.
Conditions: Temperature in the middle 60’s, wind from the from the north east at about 10mph. Overcast low clouds that looked a bit threatening, but we stayed dry.
Results: A bit mixed. I’m still not sure I have the engine exactly where I want it to be, but it’s *much* improved. I had the opportunity to execute a dead stick landing from high altitude. By slipping on the downwind and final legs of the approach I was able to plunk her down exactly where I wanted her … cool. Overall I had a fun and successful day with several flights, a “successful” dead stick landing and an engine that is getting closer to where I want it to be. I’m getting more comfortable flying this airplane and it’s becoming more intuitive to do slips on approach without wobbling all over the sky.
May 13, 2005.
Maiden flight! This afternoon I maidened my Kadet Senior ARF. I just can’t get over what an incredibly sweet flying airplane it is. I’m suddenly a huge SIG fan. 🙂
Objective: First flight. Get airborn, trim the aircraft, get a feel for the flight characteristics, and practice landings. Shake out any bugs before they get big enough to bite me.
Conditions: Temperature in the upper 50’s (F). 5-10 mph cross wind from the east.
Results: I was the only one at the field so I don’t have any new pictures, but the Kadet flies *really* well.
Engine: I found a good ebay deal on a brand new ASP 61 FS (which is the same as Magnum 61 FS.) I am just breaking in a brand new engine, so starting out it ran pretty tight and was very sensitive to the needle valve setting. As the engine ran a bit, it became much smoother at low and mid rpm ranges. At one point the engine died on the “go” part of a touch and go. I traced this down to a failing glow plug, replaced it, and was back in business.
Taxiing: I converted the Kadet to a tail dragger arrangement. I was a little unsure of the turning radius because I didn’t have much movement on the tailwheel. I found that I had just enough to do a 180 in the width of my club runway. The Kadet is very light, and the ASP 61 FS engine pulls it right along even at idle, so on a smooth surface it is always moving. With 1/2 – 3/4 throttle, the Kadet happily taxis through medium height grass.
Takeoff: My club runway is small enough so you don’t have a lot of space to monkey around. You pretty much have to gun-n-go and sort everything out in the air. This was no problem, the Kadet tail dragger tracks straight, has no ill tendencies, and will get airborn in just a few feet if you gun the throttle. Once in the air I needed a few clicks here and there of trim, but nothing too much. For future flights I want to play around with mid-throttle settings for takeoffs to get a longer take off run and more scale-like behavior. Once the tail comes up though you are basically above flying speed.
Climbout: At full throttle, the 61 FS will pull the Kadet up at a very steep climb angle, but not quite vertically. This could let you get airborn out of some pretty tight spaces … if you were so inclined. If you had a knowledgable pitcher, I suspect you could hand launch the kadet pretty easily.
Flying: The Kadet Senior is slow. Even at full throttle it’s slow. But it’s big and elegant. It will do loops and nice axial rolls easily and gracefully. I didn’t push things like spins or more violent maneuvers, maybe later. It will tool along at just a few clicks above idle throttle. I did try some vertical climbs and found I didn’t have enough power to go unlimited vertical. That’s probably a good thing. I suspect an overpowered Kadet could start fluttering and shedding important bits if you flew it too fast. But what a joy. If you are looking for something that is more towards the relaxing end of the spectrum (but still highly manueverable and controllable) and less on the white-knuckle end of the spectrum, this is the bird for you.
Approaches: One of the first things I do on a maiden flight is throttle back and start getting a feel for the approach characteristics of the airplane. In this case, the Kadet likes to float and float and float and float … and then float some more. On my first attempt I started my down wind at about 50′ AGL. I turned base and decended to about 25′ AGL … and I was a long way out when I turned final. I figured I was going to have to run a lot of throttle to make it to the touch down point, but no … it kept floating and floating, and floated right past me at eye level. I kicked in the throttle, executed a missed approach, then lowered the idle trim a bit and tried again …
I found that I could cross control the rudder and aileron, especially on my base leg to bleed off altitude. I’m not real smooth with this, but it works well and looks really good when done right. I need to practice this so I can get comfortable with a slip on final and have better control over the decent angle.
We had a bit of a cross wind this afternoon, but that was actually kind of fun because the Kadet lands so slowly, you really have to crab it a lot to hold the runway centerline in even a moderate cross wind.
Landing: All I can say is wow. This plane has the ability to land ever so gently. It floats outside ground effect, but get that big wing down close to the ground and you begin to worry about the buttered toast strapped to the back of a cat syndrome … is there some ill understood force that is keeping this thing perpetually airborn? After a few landings I begin to get better control of my touch down spot, and I could ease it in with out even flexing the soft gear. On my last landing of the day, I touched down on the left main (I could hear the wheel start to roll) it rolled a couple feet on one wheel, then lowered the right main (and could hear it beginning to roll) and rolled out the rest of the way dropping down below flight speed and finally slowing to a stop. If I hadn’t heard the wheels rolling I wouldn’t have know for sure if I was on the ground or not. This plane seems to give you enough control and moves slow enough so you can do those sorts of things with relative ease.
I had no tracking or stability problems with the tail dragger configuration in any phase of taxiing, takeoff or landing. The length and position of the gear seemed like it came out just about perfect for beautiful 3 point landings. I may want to beef up the gear at some point since it does flex a bit even when sitting still, but for now, you can land with so little additional load on the gear, it’s not a problem. If I start adding a camera, more fuel, or other payload options, I may need a bit stronger gear.
Summary: I am just really really really impressed with what a fun relaxing airplane this is to fly. I felt like I needed/wanted to use the rudder *much* more than your typical sport plane. I had to laugh at how slow it will fly. I was puttering around at just a couple clicks above idle throttle and the engine sounded like it wanted to quit at any time it was running so slow … landings are a dream. The gentleness of the landings are almost an out of body experience.
In terms of the objectives for the maiden flight, I was highly successful on all counts and was thoroughly impressed with the flight characteristics of this aircraft!
I hope to add a camera and do some aerial photography with this platform, so I’m very happy about how slow it will fly, and how much payload it should be able to easily carry.
(Sep 4, 2010 edit: I’ve moved way beyond this todo list, we are on our 2nd and 3rd gen autopilot hardware now. The software has been totally revamped. Still, kind of fun to look back to see where we were a few years ago. Never did clean the gummy residue off the load struts though …)
Setup a heading hold mode and implement waypoint following.
Setup auto-throttle control module.
Install secondary “tapped PPM signal” receiver.
Install MaxStream radio modem.
Low priority: clean gummy sticker residue off the aluminum load struts.
November 16, 2007
Today I logged about 50 minutes of fully autonomous flight. Since I fixed the MNAV firmware bug, I have not seen any servo glitching or problems. The (patched) system is starting to earn my confidence.
August 14, 2007
Today I did two test flights in some non-trivial wind.
On the first flight the gps gave me a couple sequential bogus readings so the aircraft thought it was -1000 MSL (i.e. below sea level.) This caused it to climb towards what it thought was target altitude, but in reality was way too high. So we shut down the motor and brought it back. I’ve never seen the gps glitch like this so I’m not sure what to make of it.
On the second flight we had good altitude readings, but I observed that I constructed my sequence of waypoints in a way that it was impossible to reach the 3rd waypoint from the 2nd waypoint given the existing wind conditions. I “cheated” and helped tighten that turn with the rudder and with that small amount of help, it was able to reliably negotiate the course.
July 28, 2007
Today I flew twice to collect airspeed data from the pitot tube. The data is noisier than I hoped, but seems to be pretty plausible and certainly usable if I filter/smooth it a bit.
July 27, 2007
Today I installed a pitot tube on the Telemaster and routed some flexible out the center section of the wing so I can plug it into the MNAV when I install the wing. I used a length of carbon fiber tube rather than metal. These pitot tubes take a lot of abuse, even when you know they are there and are trying to be careful. 🙂
July 13, 2007
Flight report: The goal of today’s flight was to excercise the altitude hold system after making a couple small tweaks to the gains. It was a beautiful morning, temps in the mid-60’s, not a cloud in the sky, wind out of the west at about 4-5 mph, nice smooth air.
Here is the plot of altitude vs. time. The red line is the target altitude of 426.72 meters MSL (or 1400′ MSL which is about 500′ AGL.) Altitude statistics for the flight: average altitude = 426.44m, min = 419.6m, max = 434.4m, standard deviation = 2.85m.
Here is a motor/battery plot from my eagle tree data logger:
Here is a movie of a synthetic replay of a portion of the flight:
June 23, 2007
I took the telemaster out and ran out the 8000 mAh battery over the course of two flights. I didn’t quite have a full charge on it to start with and ran it up at full throttle most of the time, so I only got about 22 minutes of motor on flight. It is a bit surreal to see such a large airplane fly so quietly, smoothly, gently, and slowly — but also very pretty to watch. The air was really smooth this evening and winds were light so the big telemaster was super stable and solid.
On the first flight the MNAV performed great. I saw one momentary servo glitch, but other than that, it tracked rock solid each time I activated the autopilot. I would fly down to one end of the field, turn around, line it up, and activate the autopilot. The autopilot would hold a pitch attitude and lock the wings level, so I could then steer with the rudder and fly a pass. At the other end of the field I’d flip back to manual control, wheel around, line her back up, and reactivate the AP again. I flew a dozen “long” passes like that and it worked well.
On the second flight, the MNAV servo output was in glitch mode the whole time. Each time I activated the AP, it drove the servos to full stop which puts the controls hard over. So I just flew it manually around the pattern, and checked periodically to see if the MNAV revived itself, which it never did. I should point out that I’m 95% sure the servo output glitch is something specific to this particular MNAV unit. It’s not a more general problem as far as I know. I should also point out that the sensors and flight computer runs fine during the time the servo output glitches out. Once I get the other MNAV back from Xbow, I will probably send this one in for service.
June 9, 2007
Today I flew two more flights with the MNAV involved. I activated the pitch angle hold and that seemed to work reasonably well to. I think the control outputs jitter more than the simulator and the plane reacts to turbulence more than the simulator, so the result is not a super smooth solid lock on the target values, but at the same time the bouncing seems really random like turbulence, not regular like an oscillating, not quite tuned, PID.
The flight control computer/mnav blipped out on me once and kept trying to put the controls hard over to full stop. I’m not sure what happened there, but it eventually recovered itself. I need to do some more ground testing to see if I can reproduce the problem.
June 8, 2007
First flight with the MNAV helping!
For the past weeks I have been battling one problem after another getting all the components together and working on this new airframe. The biggest problem has been interference and noise and a corresponding dangerous drop in range for manual control.
Ok, so tonight, I finally have everything together (I think — I hope! — it’s always those pesky oversights that can kill your airplane.) I pass my range check (not by a lot, but I pass), there is a 10 mph direct cross wind which I’m not especially fond of, but not too worried about. Skies are perfectly clear, temp is 70 degrees, I’m the only one at the field tonight, I need to be especially careful not to put my finger in the prop, I can’t dial 911 with out it! I power on the flight computer and verify it is up and running, I verify the borrowed IMU/GPS sensor is up and running, I verify I have gps lock, I double check all the controls are working and in the right direction, and finally I verify I can hand over control to the autopilot and yank it back reliably with a switch on my transmitter.
Tonight I only had the aileron channel routed through the flight computer, so when I hand off control, the AP is only going to do wing leveling, I still have manual control on all the other axes.
With everything in place, I took a deep breath and taxied out to the end of the runway and lined myself up. I took another deep breath and smoothly advanced the throttle. As the airspeed came up, the aircraft weathervaned strongly into the direct cross wind so I quickly shut down the motor and aborted the take off run. This was my first try at a cross wind take off in this aircraft so I didn’t have my thumb gains set right! 🙂 On the second try I pretty much held the runway center line, and after what seemed like an eternal take off run in the grass, the tail came up and I coaxed it off the ground. It climbed out more lethargically than I thought it should, but it was climbing … temps were warmer than when I’ve flown before and I had an extra battery pack on board … I’m not too worried just yet.
I circled the field for a couple minutes to gain some altitude and catch my breath. I was paying careful attention to whether or not I had solid manual control with no glitching. Flying this airplane manually is a no-brainer, so I’m not nervous about that. But this is the first time I’ve flown all the equipment plugged together and powered on. I’m very worried about the effect of noise and reduced range. If my receiver is overwhelmed with noise once the aircraft is at altitude, and I can’t control the airplane … it goes in hard and half my life for the past couple months goes home in a garbage bag (I did bring one just in case!) Failure at this critical point in the project could mean giving up all my UAV hopes and dreams. Success here is the gateway to all sorts of interesting future projects and fun. I’m usually not a highly dramatic type of guy, but for some reason, I felt a heavy weight that this was a very critical junction in my life. So I was *very* apprehensive about possible equipment failure or some oversight that would lead to the aircraft being destroyed.
But so far so good, I’m up and flying, control inputs feel solid, no glitches that I can see in my receiver. This was the main focus of my test flight, to validate the manual override board I have recently added to the whole system and to make sure I can fly the aircraft safely and reliably no matter what goofiness the flight computer might attempt.
So now I’m at altitude, tooling around, no more excuses … I flipped the autopilot switch to activate it and immediately my wings leveled out and stuck there. I wiggled the rudder back and forth to full stop in each direction. This aircraft has a lot of dihedral and strong roll coupling, so even though a good whack (sorry Bill) of rudder causes quite a bit of roll, and even though holding full rudder deflection puts a lot of pressure on the airframe to roll, the flight computer is able to bring the wings back to level again and hold them there.
This is the bonus part of the flight. I honestly didn’t care if the flight computer put the ailerons hard over and held them there, as long as I could recover manual control any time I wanted. But the nice bonus was that the roll angle estimation and wing leveling code worked great. The gains maybe weren’t exactly perfect, but they were ok, and did the job just fine.
I landed and then repeated everything again with a second flight. I figure anyone can hit the three point shot, but if you can do it twice in a row, maybe it wasn’t entirely dumb luck.
This UAV is running an almost exact copy of the FlightGear autopilot algorithm, it even has the same xml parser, property system, and almost the same autopilot config syntax.
The Rascal 110 dynamics model we have in flightgear is not perfect, but it’s not horrible either. I developed a bunch of flightgear autopilot modes to work with the Rascal 110 model, including a wing leveler, heading hold, pitch hold, altitude hold, speed hold, etc. etc. These autopilot configs were all developed entirely in FlightGear using a JSBSim dynamics model.
Now with this UAV I am developing, I can take the *exact* autopilot config file off the flight simulator (make a couple small syntax modifications) and the actual, real-life, real world uav autopilot can run the same algorithm on the real uav in real flight with the same gains. If the simulation model used to tune the gains is good enough, the real life UAV autopilot should work out of the box (maybe not optimally) but well enough to be stable and do the job.
In this case, the wing leveler config developed in simulation with JSBSim and FlightGear worked out of the box on the real UAV running the same algorithm. (The Rascal and the Telemaster aren’t exactly the same airframe so this isn’t a perfect conceived test case, but they are close enough …)
I hope to head out tomorrow and repeat everything with the pitch axis. So tomorrow night I could be easily be sobbing, but for tonight at least I am happy. 🙂
No pictures tonight … Ruth misplaced the digital camera …
May 28, 2007
Test flight with MNAV and GumStix collecting data
Today was really windy, but right down the pipe so I put in 3 flights on the telemaster. This weekend I mounted the Xbow MNAV connected to the GumStix flight computer. I can log about 60 hours of flight data on-board with the Gumstix’s 1Gb MMC card.
I can take that flight data and replay it in FlightGear to “visualize” the flight and also to get a sense of how well the sensors and flight computer estimate the location and attitude of the aircraft.
Here are some pictures of the initial installation of the equipment.
April 18, 2007
Temps were about 60F, clear sky, winds out of the East at 10-15 (runway is N/S.) The winds were very erratic, gusty, and changing directions. Not the nicest for flying but not insane either.
March 30, 2007
Today I tightened down the motor mounts, prop, and spinner. I plugged in the battery and fired up the motor. She seems like she generates plenty of thrust to fly. The speed controller seemed like it was getting a tiny bit warm in my short run tests, so just to be safe I moved it back out on the front of the firewall.
I installed the receiver and secured the antenna. I put a bit of effort into routing and securing all the wires so there wouldn’t be stuff flopping all over inside the cabin. With the power on, I setup all the servos to move the correct direction, and adjusted the linkages so all the surfaces start out centered. I think the current control throws look fine.
The aircraft balances pretty close, but is slightly tail heavy … I’m not sure it’s enough to worry about with this design. I think everything is just about ready for a maiden flight.
March 29, 2007
Installed the battery in the nose compartment and packed foam all around it so it can’t move or dislodge (I hope!) It’s a two pound battery. I moved the speed controller installation to just inside the front of the nose hatch.
I found a long tube to route the receiver wire through and stuck that down the tail. I’m not sure I’m happy with that, but it’s a start.
I’m to the point now where I need to finalize the receiver installation, balance, and I should be ready to fly.
March 28, 2007
Mounted the speed controller on the lower outside front of the firewall with double sided velcro tape. I found a 5/16″ washer laying around the lab for mounting the prop. Also, I ran the prop through a balancer and I think it is very close.
On the way home from work I stopped by the hobby shop and picked up a Y-harness for connecting the wing servos, a short servo extender for the throttle channel, and a packet of metal 4×40 x 1″ bolts for installing wing load struts.
March 26, 2007
Today I bent the load strut mounting tabs to the correct angles and glued the plugs into the aluminum tubes with the correct insertion distance. I “pinned” the struts for added structural security, i.e. drilled a hole through everything crossways and epoxied a wire pin in to make sure everything is solid.
I then drilled out the mounting holes and installed the blind nuts in the wings and fuselage.
Here are some various angles of everything assembled as far as I can right now:
March 23, 2007
Load struts: assembled plugs and straps that I will fit into the ends of the aluminum tubing. Sanded the wood plugs down to the inner shape of the tube for a nice snug fit … well, one is a little loose, but it will be ok.
“All” that is left is to glue the plugs into the tub ends, bend the tabs to be flush with the fuselage and wing, drill the mounting hole, feed the bolt through, and we are pretty much done.
The one small thing that I’m worried about is where I’m going to remove the wing covering in order to install the blind nut on the back side of the wood mounting block.
March 21, 2007
Today I fabricated and installed the aileron linkages. I also cut my wing load strut tubes to their proper size (aluminum tubing in a tear drop/airfoil shape.) I have brass strips to mount in each end which will bolt on to the fuselage and wing. I need to cut those and fit them into the ends of the aluminum tube.
March 19, 2007
Today I installed a light weight 1.75″ tail wheel with a collar. I also installed servo extension security clips between the aileron/elevator servos and their 24″ extension wires. This is a small added measure of security to make sure these never can pull, vibrate, or wiggle free.
This weekend I purchased short extension cables to facilitate plugging the wing servos into the receiver (so I don’t need to plug and unplug cables directly into the receiver every time I go to fly.)
Finally, I fabricated and installed a piece to re-enforce the wing leading edge mount.
Detail of tail wheel and rudder linkages …
Detail of elevator linkage …
Two shots of how the overall project is shaping up …
March 16, 2007
Progress made today:
Installed steerable tail wheel. I forgot a small step before I glued on the vertical stab. This forced me to go to the hobby shop to buy a slightly different tail wheel mount. The 2″ tail wheel is slightly too big, so I will probably need to get a 1.5″ wheel and a 3/32″ wheel collar.
Installed an elevator joiner wire. I bought something pre-bent from SIG and removed the nylon control horn. I cut a groove into both elevator halves and epoxied it in. I also notched the rudder in one spot for clearance. Note: this is another one that would have been good to do before gluing on the elevators.
Installed the elevator and rudder servos with their extension wires.
Installed the elevator and rudder control horns and linkages.
This is the elevator joiner I used …
IMG_4319 Low res cell phone shots …
March 15, 2007
Epoxied the tail surfaces onto the fuselage. Installed the main gear.
March 9, 2007
Pictures with the tail surfaces dry fitted …
After these pictures were taken, I ripped off most of the remaining yellow on the fuselage and replaced it with ferrari red.
March 6, 2007
Detail of tail servo mounting modification …
March 5, 2007
Detail of shipping damage (fixed) and re-covering plan …
While rummaging around my hard drive I stumbled on some early footage of our Senior Telemaster flying. This footage includes some of my earliest successful autonomous flight using the original MNAV sensor head (now discontinued.) There isn’t anything especially great about this footage, other than I love the way the Telemaster looks in the air, especially it’s “scale” take offs and landings. These videos date back to sometime in mid-summer 2007.
The following movie includes some take offs, landings, and some early autonomous flight. One thing that is purposely highlighted in this video is an MNAV firmware bug that would cause the servos to go hard over full stop and send the UAV spiraling out of the sky. Fortunately we could quickly flip back into manual mode and manually pilot the aircraft to safety. Eventually I personally tracked down the firmware bug and fixed it. (Now we no longer use the MNAV in our UAV work.)
Here is a second movie showing a segment of successful autonomous flight. The Telemaster is flying a bowtie — or figure 8 — pattern. This is interesting to me because it offers a visual reference for the “quality” of our early MNAV based autopilot system that we can compare our current system against.
Paw finalized the RxMux assembly after I verified everything worked.
March 3, 2007
Today I ground tested my RxMux manual override board and everything appeared to work great.
February 20, 2007
Flight testing the MNAV, Stargate, and Maxstream again.
In our test last November, we had problems with our gps antenna connection. We made an attempt to fix that issue, but have been waiting through about 40 days of brutally cold weather here in MN to find a flyable day. Finally today the weather and our schedules matched up so we put in 2 very nice test flights.
The MNAV worked well. The secured gps antenna connection held up well though all RPM ranges, taxiing, take offs, landings, and some relatively agressive in flight maneuvers. Everything seemed solid. That is great news because it lets us move on to more interesting things.
In addition to just collecting the data, I fed it into a running copy of FlightGear in real time so you could visualize a synthetic view of the real world flight on the computer. This includes the world position, attitude, and flight surface deflections. It’s very cool to see the virtual view on the computer match exactly what the real world airplane is doing as it happens.
This synthetic view will be useful for a number of things down the road. For example, we can click anywhere in the synthetic view and get back the real lon/lat/elevation of the ground point we clicked on. Now imagine that we have overlaid live video on top of the synthetic view in a way that matches the two views "conformally".
The synthetic view also gives us the ability to highlight obstacles, restricted airspace, target routes, approach paths, other uav’s in the air, etc.
Fly by …
Loop and Landing …
November 22, 2006
First flight with the MNAV, Stargate, and Maxstream on board
First, no crashes to report!
Here are some observations.
1. We powered everything on and it all worked at the field (including gps.) Then we did a test flight with the MNAV and radio modem *off*. We landed and then powered everything back on to do engine on tests. From that point on … with engine running or not running we were unable to get any gps lock. We were pushed into a corner with battery life so we couldn’t sit around and wait 30 minutes to see if the gps could find itself. So we flew without gps and collected attitude, airspeed, pressure altitude, and transmitter stick inputs; the gps never came to life in flight. Dang, no gps data. 🙁 We need to investigate this further, we don’t think it was an antenna connection issue since we *very* carefully secured that. I’ve observed in the past that the MNAV gps can be a bit persnickety, and the MNAV hides all the nmea strings so we can’t see if the gps is seeing zero satellites (antenna problem?) or seeing a few satellites but is lost and trying to find itself.
2. I was really underwhelmed with battery life for our maxstream radio modems and the MNAV/stargate. We were running standard 9v batteries for the maxstream and a 3.7v lipoly (1320mah) battery for the stargate. We got maybe 20 minutes out of everything before the batteries died. I’d really like a bit longer life for a better safety margin when we fly with the system in the critical control path.
So the two main technical issues for us to iron out are (a) figure out what happened with the gps … probably just needed to let it sit for a while longer to find itself and (b) we need longer battery life for a bit more comfortable safety margins. A 10-15 minute flight with 20 minute total battery life is pushing things a lot tighter than I’m comfortable with.
3. We did collect attitude data. I don’t have a very good sense as to the quality of the attitude data, and without location/gps to go along with it, it doesn’t really make sense to replay it in flightgear as a visual sanity check … that was what I was hoping to do. We don’t have an absolute truth reference, but when you replay the flight you can visually catch a lot of abnormal things that wouldn’t show up in the plots.
4. The pitot tube dynamic pressure system seemed to work and yield plausible results. Top speed for the day with our Rascal 110 was about 90mph. Throttled back cruise was maybe 35-45 mph. Approach speed was about 35 (makes sense since I didn’t change the elevator trim between cruise and approach so speed shouldn’t change too much if I’m flying hands off.) Touch down looked like in the neighborhood of 25 mph. (Units converted from m/s to mph indicated, not knots.) Sense since, not knots … how do I stumble into this clumsy english?
5. static pressure/altitude data seemed plausible. The minimum/ground value for the day was 738, max altitidue was 1230, so we kept it under 500′ AGL. Actual field elevation is close to 900′ so these values weren’t calibrated for local weather conditions and that is expected.
6. We updated the demo code to log transmitter stick inputs (and onboard battery voltage) as well. Those seemed pretty good overall, but there are several places where the servo channel data glitched out. The system didn’t register this as a complete transmitter off situation, but the data would get really noisy: 1-3 values at the high end, 1-3 values at the low end, 1-3 correct values, repeat. There is one particular stretch of about 7-8 seconds where the data got *really* noisy and bad. We never flew very far out, so I really didn’t want to see this kind of noise in my data. Makes me very nervous, makes me think that I could easily fly out of range and not be able to recover control in time to save the airplane, if the MNAV is in the critical control path. I didn’t try to fly especially far away, but at the same time we didn’t have gps working so I can’t know what the cutoff range is. We might be able to filter the transmitter data to help things out since there are clearly some good values in the midst of the noise, but still, not what I wanted to see. We’ll need to think very hard about a safe way to proceed. Aside from the one ugly 7-8 second stretch, the other drop outs seemed much more momentary and probably wouldn’t hurt us too bad.
So that’s where we are at. We need to figure out why our gps refused to work. We need to get some bigger capacity batteries. And we need to solve our MNAV interference/range issues before we can proceed on to autonomous flight.
This is the second Rascal 110 purchased by this project. It comes with a Zenoah G26 gas 2-stroke ignition engine. The engine seems to be a very nice match for the aircraft. With an 18×8 prop, it will idle at about 1800-2000 rpm and tops out at about 7000 rpm. This isn’t quite the 10k rpm that our OS 1.60FX would turn (with the same prop) on our first Rascal, but it is more than enough power for this aircraft.
October 25, 2006.
Pictures from our morning at Jensen field. We were flight testing to collect data from our 3-gps carrier phase differential attitude determination system.
Warmups on the ground …
Fly by’s …
Landing approaches …
Some of the ground crew helping out …
Closeups of the instrumentation …
Detail of one of the wing gps antennas mounted internally …
Today was a beautiful day. Temps in the upper 70’s. Wind about 5mph out of the N and NE. Our mission for today was to collect good MIDG data. We have had problems with our aerocomm radio modem link so Greg rigged up a little gumstix unit to record the data directly on board. We lose our real time link for this, but we get solid data with no drop outs. We want solid data for another little adventure.
This was our first outing of the season. We put in two flights today and the Rascal flew beautifully. The engine ran great and was rock solid. I even spotted my landings on the runway, although with the extra weight, she rolled out a little long onto the grassy area which is no big deal. The Rascal handles mowed grass with no problems.
Here are a couple new pictures of the Rascal with Greg and I.
December 12, 2005.
Here’s a word of explanation. On 10/26/05 we did a test flight and captured the live video stream from the onboard camera as well as the data stream from the onboard IMU/GPS/INS unit. (See the entry for 10/26 below.) We replayed the data stream in FlightGear with overlayed instruments (this can also be done in real time as the data is captured) and saved that out as a movie. Then we edited the two streams together in two different ways: side by side, and blended overlay. The result is interesting. You can see at the start of the flight where the IMU was pretty far out of whack … as much as 5-20 degrees off in yaw. But as the flight progresses you can see the error diminish and later in the flight the match can be quite good.
Both videos are about 50Mb to download. You will need DivX6 to play them. Linux or open source people might find they can play these with xine or mplayer. Windows people might need to go download the DivX6 runtime codec from http://www.free-codecs.com/download/DivX6.htm.
Side by Side
November 30, 2005.
Minnesota! This here is what we live for! We put up with above freezing temps, oppressively humid summers, terrible mosquitos for a few months of the year, and high taxes, but days like today are the payoff: Standing outside in +20F temps (and often colder) freezing our butts off or playing hockey, or both. 🙂
Today we flew Rascal #2 at Jenson field. Temps were about +20F. Winds were some where between calm and very light. We probably had about 2″ of snow on the ground … right on the borderline for operating with wheels. The first takeoff run was a little “S” shaped and we had one nose over on a landing (zero damage) but other than that everything worked fine as I adapted to the conditions. We also tested our new video capture hardware.
Just look at these picts and see what you folks in sunny warm climates are missing out on. Oh yeah, and these pictures look dark for good reason. The sun barely cracks the horizon up here this time of year. And when the sun is up (or not up) it’s usually cloudy.
November 11, 2005.
img_3142 Here is a diagram of some of the Rascal 110 dimensions.
October 26, 2005.
Today we flew Rascal #2 at Jensen Field. Weather was perfect, winds were light and out of the east. Our primary goal was to test the live video and live synthetic view right next to each other to verify they track each other as they should since both reflect live data. We also practiced flying over specific objects and buildings to see if we could recognize things from the live video in flight.
Here are two pictures taken nearly at the same time. The first is from the onboard video camera, the second is the FlightGear based synthetic view:
October 17, 2005.
Paw and Greg fixed our radio modem / RC system interference problem so now we get excellent range checks. We setup down at “Jensen field” in Rosemount, MN.
Here is a picture of the field and the row of hangars:
Our ground station is basically setting up our equipment on a picnic table in the shade:
Here are some pictures of our aircraft posing:
Our wireless video camera refused to work so we flew without that. Our primary objective though was to flight test our “synthetic visual system.” This consists of a MIDG-II IMU/GPS/INS transmitting data to the ground via an aerocom radio modem. On the ground we have some custom software that reads the MIDG-II binary data and sends the results over to FlightGear for real time rendering. Ted built us a “photo-real” model of the area that was compatible with FlightGear.
We were disappointed with the data rate we were getting (maybe 5hz.) This prevented us from doing any serious flying under the hood. But I think we validated our approach and when we track down our data rate issues we will have a very powerful remote piloting tool.
I made a short movie of an approach and touch down. I replayed the data on my laptop so it is smoother than in real time because the replay code can easily interpolate between data points. I pointed my little digital camera at the laptop’s screen and here is the result, low quality, but you can see things in action. Notice the live working instruments at the bottom of the display. We are landing to the west and have a pretty stiff turbulent wind coming from the NW and rolling over the hangers. I’m not showing off my piloting skills here, but the touch down was nice ad gentle. 🙂
Click on the following “text” link to view the movie:
All our instrumentation was moved over to Rascal #2 so today we flew a series of test flights to make sure the plane flew well with it’s payload. We couldn’t pass the range check test with our radio modem on so we scratched our heads for a while, but couldn’t come up with any clever ideas so we unplugged the power and grudgingly continued with no telemetry data.
We were very happy with the aircraft’s performance and handling with the load. We seemed to be getting solid video with our patch antenna. We also wanted to put more time on our buddy box/safety pilot system so we did one flight where we switched off control to each other.
Finally, happy with how everything was working, we walked over to the ground station and took turns flying “under the hood” with video only. Our camera points 45 degrees down which gives a good view of the ground, but not the horizon. We were able to hold a reasonably straight line via video alone, but turns were very difficult because you couldn’t see the horizon to get a good judge of bank angle and pitch angle. This is where the synthetic view would have been really nice … but no telemetry data.
Next up is to figure out our interference problems and get back to where we can fly with telemetry turned on.
September 26, 2005.
Friday and today we have been working on extracting our instrumentation from Rascal #1 and testing it to verify everything still works after our crash. We need to do a bit more testing, but we are reasonably confident at this point that everything survived intact (minus our radio modem which had it’s antenna sheared off.)
Today I continued to modify my MIDG-II replay software so I can read the live incoming data directly from the serial port and pass it to FlightGear. This gives us a live, real time, synthetic view that should match the real aircraft very closely. This should allow us to insert things like restricted airspace, important objects, mission goals, flight route, etc. into the synthetic view. We even have the capability of setting up a virtual ILS for our landing approach. Our sensors are not good enough to allow us to do a full stop landing, but they could assist us in lining up and flying most of the approach.
In addition, the synthetic display can be viewed from inside a live virtual cockpit with working instruments, from a chase plane, or from a tower view. This should be really cool!
September 21, 2005.
After crashing Rascal #1 we decided to take Rascal #2 up for it’s maiden flight. Everything worked great and the plane flies just as beautifully as Rascal #1. I think we get a lower idle and more braking action from the prop on approach, so Rascal #2 is easier to spot in on the landings. Also, there is much more fined grained precision on the low end of the throttle range with the G26 which means a notch up or down of power actually gives you a notch up or down of thrust. This makes controlling the rate of decent on approach work just like the text books say it should. (With smaller glow engines you typically have poor precision on the low end and seem to have not enough or too much power on approach with no fine grained control.)
One small bit of strangeness did occur in our 2nd flight. I think we had the idle set a little too low so when I pulled power for a slow fly by, the engine quit . I was downwind, but way to high to make a good approach to the runway. I kept the wings level and touched down on the extreme far end of our mowed grassy area. I bounced back up and sailed into the farm field (alfalfa???) bounced one more time in the field and the nosed over and went tail high. Zero damage, not a scratch, but it ended up *inches* from where Rascal