Current News
First of all, never flight test on Friday the 13th ... or just don't admit it aloud.
Yes the airplane is still in one piece after successfully carrying the Piccolo!
We flew a total of 9 flights (poor winch battery) and logged another 51 minutes in the air. The purpose of these flight session was to test the Piccolo air-data-link and ensure all was healthy in the air ... this is after ground test have shown that the Piccolo is happy being nestled away in the fuselage. I subscribe to the built-up approach.
As it stands, the coax running the 900MHz Piccolo antenna from ahead of the wing down the tail for the hidden antenna caused some interference on the servos. All of the servos had extra "jitter." We had full control over them, they just liked to vibrate by themselves over 1deg or so. I turned down the Piccolo transmit power to 0.1W and the vibrations went partially away. I moved the coax out of the servo wire bundle and taped it to the fuselage side by itself, which helped a whole lot more. We went through an extremely thorough 4-quadrant range check with the RC transmitter antenna collapsed. After 20 minutes and my arm getting tired of holding the plane, we called it safe to fly. Range antenna collapsed is 120 paces whereas without this extra transmitter we were seeing 150 paces. Other RC pilots at the field said most of their planes don't get near to 90 paces, so we are still comfortable with this range check.
We had two nice thermal flights, one of 12 minutes and the other of 17 minutes. We arrived to the field a bit later than normal, about 3pm, and the wind was slowly picking up, so we didn't expect to find very well-organized activity anyhow.
The data link was 99-100% the entire flight and I didn't note any data drop-outs. In fact, I collected 80.8Mb of data (compare this to the 50kb from the 105 minute flight from before)! Holy cow that's a lot of data ... Excel can't even plot half the rows of data we took!
I'm still plotting throught the new data format trying to get back to having all my plot utilities working correctly, so I don't have a good screenshot to show yet. However, I did take some general photos. You can see all of them in the Flight Test 4-13-07 gallery, but here is my favorite:
Next flight is this upcoming Friday!
For only two flights, we did quite well for ourselves at the field Friday. The first flight was a quick 2min checkout. The second flight lasted just over 105 minutes and included three climbs to over 1000m (3 280) with a peak to 1112m (3650ft) on the first trip up. Each decent was controlled with the massive flaps to get back to within seeing distance of the ground ... point here being we could have easily rode out another two hours if our eyes and batteries could last that long! I sized the servo and transmitter battery to run for 215min with a 1.5 safety factor, so we probably still had quite a ways to go duration-wise. Maybe for next time!
The datalogger battery was not so fortunate. I have a small 2-cell 650mah lipo that powered the GPS, microcontroller, and SD Datalogger. After the first ascent, the battery must have been getting low because the GPS sentence logged started accumulating, well, entropy. The data was more and more garbled with odd characters and line feeds. I cleaned everything up as well as possible, but only the first thermal is actually logged in any reasonable fashion.
Good news with the datalogger though: I got the new 2Hz method to work! I set up the uBlox SAM-LS to output only the UBX sentence at 4Hz and re-wrote the logger to record that sentence directly. The little microcontroller I'm using couldn't do everything at 4Hz, but it does keep up fairly well with a 2Hz rate. Since I moved away from storing on onboard eeprom to an external SD card, I can dump considerably more data without fear of filling the card (for example, we flew 1:45 and the file was ~500kb out of a 128mb card!). I have a plot of the big first thermal below:
The next step is to fly the same type of flight but with the Piccolo as a passive datalogger and sending data to the ground station. This will check that the wireless link does not interfere with the RC system or vice-versa and will give me some new type of flight data to learn how to plot. Once I have the new flight data, I'll start working out a parallel method for computing the vehicle energy rate as opposed to using the Skymeldoy variometer. I'm not sure which will work better, but surely I won't know unless I fly both and compare ;-)
Thanks for reading. I appreciate all those who send me random emails to say how you're keeping up with this project and wish me the best of luck. This news page is for all you guys & gals!
Great news! There is a shiny new Piccolo Plus inside ALOFT ... okay it's not actually shiny new at serial number 337, but it's new to me. I got a nice package from NASA Dryden yesterday about 3 that included a Piccolo and Ground Station. Thanks to Michael Allen for helping me through all the paperwork to make this possible. Now quite literally I am on a ticking 8 month clock.
Once I got the Piccolo home, I was able to get it mounted to a soft foam rubber vibration isolation mount in about five minutes. I don't expect the glider to see much vibration since there is no motor, but I made one anyway. I already had the 900MHz communication antenna installed, so that went fast. I hooked up a GPS antenna and ran it just outside the window. After reading, and re-reading the documentation, I powered up the system and watched everything boot up. Yay it all works!
I do have some hardware issues to work out, namely there are a few cables I need to make:
Now you know my good news. I promise I'll post some photos after this weekend when I get access to a digital camera again. Stay tuned!
Update: Jim Gray at Jim D. Gray & Associates, Inc. has donated a quad-helix antenna that should fix the GPS problems entirely. He was very kind in explaining how the antenna is produced by dipping a ceramic into copper, shooting the copper with a laser to activate it, then dipping the assembly into etchant to produce a 3-d PCB effectively. Some other specs he shared were that the patch antenna loses 3/4 of its coverage at only a 45deg bank. At 90deg bank the coverage is all but gone. With the quad-helix antenna, it has a total 120deg view of the sky, so even at 60deg bank, it can still see 30deg coverage directly above the aircraft. What's more, it is sensitive enough to pick up satellites only 5deg from horizon! I think we may have a winner :-) Thanks Jim for the info and donation!
A few images that better paint a picture about this antenna:
After a few days of looking at my flight data from Sunday, I have noticed the GPS position jumps around or predicts two consecutive positions with the same lat/lon even though the vehicle is moving. My theory is that the patch-style antenna I have been using has trouble maintaining a good sky view as the vehicle rotates through a 360deg heading turn at a 40deg bank. At this bank angle, the patch is already having trouble seeing 1/2 the sky. On top of that the heading is constantly rotating, so the sky view is changing rapidly too. I have the feeling this could be solved with the newer style quad-helix antennas that has a radiation pattern for better picking up satellites even at higher bank angles... I'm looking into options.
Today was quite a good advancement of the whole system!
Adam (my pilot) and I can now launch by ourselves. Brady gave some expert coaching about how to launch the larger airplanes ... Adam peddled up the first two launches while Brady tossed, then third launch and onward I did the honors heaving ALOFT skyward. Since Brady is unavailable for flying the next two weeks, he let me borrow his winch. Now that we can launch ourselves, we're taking on more responsibility :-)
I also added an SD Data Logger to the GPS/Vario logger hardware that flew last set of flights. It was a very stressful Friday and Saturday evening trying to integrate the Log-O-Matic from Spark Fun with the Basic-X. Unfortunately the BX debug messages have inverted logic whereas the logomatic reads non-inverted logic. Nothing is ever simple...
I planned to log data at 4Hz, but with the SD snafus described above, I was not able to integrate my code changes in time. I am using a uBlox Sam LS that will give a 4Hz update rate in the proprietary UBX format. I rewrote the GPS parser to accept UBX sentences and had that working beautifully during testing earlier this week. I imagine a future integration of the SD logger and higher data rate will be possible.
From looking at the flight data, I believe my GPS is having intermittent drop-outs while the vehicle is banked at 40deg or more. Since a GPS must have good satellite coverage and spread, by the high bank angles we are possibly switching sky coverage too quickly for the GPS engine to keep up. I have seen helical GPS antennas that have better coverage during high bank maneuvers; perhaps I should give them a call.
Last but certainly not least, the flight report itself. We flew 8 flights for a total of ~40minutes of air time. Adam and I are quite comfortable flying in a bit more wind, so we were able to get all 8 flights within 2.5hrs. We located 4 good thermals despite a cloud front that moved in and blocked the tremendously good early conditions. ALOFT finally broke 300m on Flight #7 in an odd thermal that simply stayed attached to the ground. The other three thermals we found were not strong enough or consistent enough to gain beyond 200m altitude; under different conditions, we feel these thermals would have been very easy to core and utilize.
Oh I should also mention my loaner Piccolo shipped on Friday and should be here this week! Adam and I already coordinated flying a passive data logging flight on Friday, so I have my integration work cut out for me.
So the saga continues ... manual flights are getting easier and more confident; data collection is getting increased capacity, but more temperamental; electronics components are really starting to fill up the fuselage!
PS: I'll be borrowing a camera after next Sunday, so I'll post some photos of the aircraft again. It has been a while, I know.
I had the chance to post a few new images from what I have been working on recently. First, you can see the 10-mile test cross-country course I'll be running with ALOFT to develop the XC algorithms at some point. This 10-mile course was developed by the Down East Soaring Society guys for manual XC flying. On a good day, it should only take ~15-45 minutes to go around the course at a top cruise speed of 45mph. With ALOFT, I'll be able to cruise much faster than 45mph if desired, so the 10 mile course may be a tad short for testing. I can make it harder and lower the max altitude limit to force the thermal searching algorithm to work harder.
I also posted a couple images from the recent hardware testing, such as a car driving test to confirm the GPS logger unit conversions are all correct. I literally taped my GPS logger payload tray to my car hood and drove around town. I was checking the lat/lon to x/y meters conversion especially, but it also confirmed that GPS velocity (ground track speed) was not terrible to use when you're going 70mph. Furthermore, it was a great systems test to get more familiar with the LED status indicators I set up. I think I need a better GPS backup battery because the little uBlox SAM-LS is still taking 5 minutes to re-acquire lock after being powered off. Anyhow, here is the result of the testing:
Last, I posted a screenshot of the first flight of the GPS & Vario logger that flew on 3-18-07. This officially marks the first time I have flown my own software, so I was super excited to see everything worked out like I designed. There is certainly room for improvement, such as adding an SD logger to allow more than 14 minutes of recording with the 48k eeprom. But, it worked, so it just will take some minor tweaking and things will continue to improve! I do just need to gather more flight data to test out the thermal finding algorithms...
Enjoy!
The 3-18-07 test flight went great!
The weather was blustery on Saturday as a cold front moved its way to Raleigh, so I decided to hold off flying until Sunday. As the weathermen predicted, Sunday was quite chilly cold with highs in the mid 40's.
The Down East Soaring Society brough their winch out to the field, along with Brady's 15ft XC ship, a 2.5m composite ship, and several DLG's (Discus Launch Gliders). I got a chance to fly my Bubble Dancer a while while we waited for the wind conditions to settle out better for flying ALOFT.
Around 3pm the conditions were looking good for putting ALOFT in the sky. Adam and I did a full range check to ensure the new GPS/Vario logger I had installed did not interfere with the RC system. We booted up the logger and moved the launch crew to the winch. After waiting a few minutes for the gusts to subside, we hooked the plane to the winch and started tapping the pedal. Once line tension built up, Brady let go and we were up!
We put in a total of 6 flights...
Flight 1: 3.7min
Flight 2: 8.2min
Flight 3: 6.8min
Flight 4: 8.2min
Flight 5: 2.0min
Flight 6: 3.7min
Total Flight time: 32.6min
The GPS/Vario logger worked wonderfully too! My software has finally flown! The microcontroller recorded GPS lat/lon from the uBlox receiver and vario signal from the Skymelody. So I have my first own flight data. After working through homework this week, I'll post a few flight paths so you can see for yourself.
In other news, I installed the 900MHz comm antenna for the Piccolo inside the tail, so there is no additional aero drag and we don't disrupt the glide performance. Boy it still looks slick!
Watch for more news in the near future!
The next ALOFT flight test is scheduled for Saturday, March 17th at 10am. While the schedule may be too tight for getting the autopilot onboard for some datalogging time, I think the GPS & Vario logger I wrote this past summer may get a chance to fly. This will be my first effort to getting aircraft performance numbers.
Aside from flight data, my pilot and I are going to get some more stick time; we'll specifically be getting familiar with how the plane thermals and try to get some good rates of climb. We want to spec the plane out and find the maximum comfortable altitude we can do the XC course while still being within visual range.
With regards to the airplane, a new 3000mah nimh servo battery has doubled the onboard servo supply. Also, a new 1650mah nimh transmitter promises around 4 hours of flight time (actual time tbd). Between these two, we should be able to get lots of good flight time this upcoming weekend.
In other hardware news, the Piccolo is nearing my doorstep. I think we're down to two signatures to complete the paperwork. Also, Phytek America LLC donated a USB-CANmodul for hardware-in-the-loop testing. This is an essential first step for determining the aircraft control gains, and the USB-CANmodul is the piece of hardware that makes the HWIL interface possible. Thanks Phytek! Also, Tri-M has donated two Micro Mouse GPS antennas to this project. One will be onboard for providing the autopilot GPS positioning while the second antenna will provide DGPS corrections via the groundstation. Thanks Tri-M!
I have been programming up a storm over spring break ... holding the details close until I have something to show for myself, but rest assured I'm making steady progress :-)
Look back after next weekend for an update about how the 2nd real flight test went!
-Dan
Pictures & Video at the end of this post. Description first:
I took ALOFT back out to Wilson to make sure she flies correctly before I try adding autopilot hardware. A couple guys from Down East Soaring Society came out again, Dick Proceus and Brady Baggs, to help with the maiden flight; both gentlemen have flown lots of XC in the past with large gliders, so I really appreciate their help. My pilot and I made the drive from Raleigh to Wilson a few hours before everyone else was to show up. Adam Propst and I set up ALOFT and then flew a few different personal airplanes to get our fingerns warmed up and assess the day's conditions. It was windy and turbulent low, but conditions were slowly improving.
After a complete 4-quadrant range check and voltage double-check, ALOFT was ready to go. The foursome debated how best to launch, ROG versus hand-launch, what launch preset to use, how much wind was too much wind, and so on. It was great discussion and I learned quite a bit about large-scale flying and setup. Onward to the good stuff...
We hooked up ALOFT to the winch line, Adam stood with the transmitter, Brady stood with the plane in hand, Dick managed the pedal, and I stood to the side with a big knot in my stomach. As a side-note, I decided not to be the pilot not because I think I will have my nose in a laptop for autonomous testing, so I have handed the responsibility to a great pilot buddy from school, Adam. Then we all gave the conditions our thumbs up, Dick started tapping the winch to build up line pressure, and Brady let go. ALOFT pulled forward and rotated nose-up. It flew up a good hundred feet or so and then the line broke! We noticed the plane and parachute went backwards, not where they were supposed to go! Adam calmly pushed back over and continued the test flight.
This plane absolutely floats. With an L/D near 30, even with the meager 100ft altitude from popping off the winch, Adam flew circles around getting the trim in check and getting used to the large aircraft turning performance. Finally after a long 30 seconds, he set up for a landing approach and put the plane on the ground softly. Yay, ALOFT flies!
We flew 6 more flights, adjusting the CG a bit more forward and changing the elevator trim. The winch line breaking problem was fixed, attributed simply to too much elevator up-trim on the first launch. We also had to get used to flying the airplane faster than we expected, but it sure moves nicely once up on step. Landing also were tricky at first, but are much nicer now with a new technique of using full flaps and holding the nose down on the approach and then easing off the flaps to stretch the glide as needed. It looks beautiful in the videos once I get them uploaded here.
So there is the story and the verdict: ALOFT flies just dandy. Next step, moving onward to the autopilot installation and tuning, once it arrives (nearly completed with the loan paperwork to get one in my hands!). Then, it's time to finish programming up the algorithms and start finding some thermals!
Pictures in the gallery ... follow this link
Well, I hauled the SBXC an hour down the road both Saturday and Sunday only to have mother nature make the decision for me: too windy.
Saturday was a chilly and breezy day. Despite the weather, thermal activity was very good. Several planes brought by members of the Down East Soaring Society went up, up, up! I even managed to spec out the Bubble Dancer on my own without the vario. Brady Baggs brought a winch for launching the SBXC. Unfortunately the two solenoids BOTH fused closed launching another large glider, so we switched to using the backup winch. In the meantime, my pilot and I did a thorough range check. Then, we did two toss-checks to ensure the CG and elevator trims were appropriate. The first went beautifully: the plane was trimmed and glided straight away for perhaps 150ft. The second throw was also good, except the landing was a bit more nose-down; the tail slapped the ground and the rudder hinges all sheared off. Perhaps the plastic was simply brittle from the cold and could not take a less-than-perfect landing. As a result, we packed up the SBXC for the day.
Fast forward 24 hours. Adam and I fixed the rudder hinges to be bomb-proof and crated the plane back to Wilson, NC. The weather was even winder and colder than the previous day. Brady replaced both solenoids, so his winch was ready to go. Another local member with over 40 years of glider experience flew a Psychos to test the winds and immediately said "this is not a good day for a maiden." Heeding experienced advice, we packed up yet again.
The next try is in two weeks, Feb 18th.
This weekend was actually quite a success though! The aircraft glides just fine and is trimmed out ready for a winch launch. I expect it to fly like any other SBXC: clean and smooth. Since the airplane flew on its own weight during the toss-check, I'll consider that a "successful maiden!" It was also extremely useful to do an outdoors range-check and go through the assembly/disassembly checklists a few times in earnest. Lastly, we identified the weak link of the rudder hinging and the old winch solenoids, both of which could have resulted in problems if not corrected before the maiden. All-in-all, this was a very succcessful weekend!
Believe it or not, I forgot to take pictures of the assembled airplane outside, but I did capture the hand-toss on video: see it here.
Check back after March 18th for hopefully more good news!
