Tag: Idaflieg

Everything related to Idaflieg or Akaflieg.

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Project Hobbes: Evaluation in Stendal

After months of learning to design PCBAs, going through numerous iterations, design changes, getting loads of interesting feedback and suggestions, software bugs and bugfixes… I was finally here: I arrived at Stendal.

Armed with a crate full of equipment, spare parts and some fresh clothes I was eager to get started. Let’s get my hardware in as many gliders as possible and start flying!

Neo Theo

The first glider to receive my system was FVA Aachen‘s DG-1001 “NeoTheo”. They had already generously agreed to have my system installed before the event. Great! With the help of one of their members, I installed my device on my second day in Stendal. Their beautiful glider is equipped with an LXNAV S100, which I initially designed my device for. The S100 is able to send both Indicated Airspeed and G-loading at 10Hz over a serial connection and it supplies 5Volts/1Amp for any device connected to it. More than enough for the Raspberry Pi Zero 2W that I use, which only needs 0.2Amps.

My device mounted in FVA’s NeoTheo. The white instrument is in the panel, the PushButton is mounted on the stick.

After installation everything seemed to work on the ground. So I updated the software to the latest version, verified that the device uploaded it’s logs after landing and I went for a CS-STAN technical checkout flight. Together with Kobo, Idaflieg’s current president, I towed to 1250 meters. Kobo had asked if my device would also support inverted flight, since his aerobatic students sometimes manage to stall the DG-1001 during inverted figures. The device does support inverted flight, so an inverted test was to be included too.

First we evaluated the device in normal flight, and below 850 meters altitude we rolled the DG inverted and stalled it. The device worked exactly as intended and signaled the pilot nicely before he would negatively stall the glider.

Kobo simulated a classical error: a student flying an un-coordinated base-to-final turn. These are especially dangerous, because there is very little room for spin-recovery.

Kobo simulates a slow base-to-final turn

The French connection

The day after my arrival, I suddenly saw a familiar face walk towards me: it was Matthieu Scherrer! I bought my last glider, my Ls6b, via him from his gliding club. Matthieu flies an Ls6 too, and performs research on gliders. Matthieu was eager to talk to DLR about the comparison flights, and he was attending the OSTIV Congress in Uvalde in the afternoons.

It turned out that Matthieu was also presenting a paper on estimating Angle of Attack (AoA) from accelerometer data. Off course this was very interesting to me, since I estimate AoA too. My method has a clear problem: I cannot deal with flapped gliders. Matthieu’s method should have a way to solve that issue. Matthieu and I talked a lot about his method, my device, and how the two could be combined. Long story short: I received an A4 paper with formulas to implement and will test those with Condor Soaring.

What about other gliders?

I had brought 5 pieces of my device to Stendal. Before visiting, I knew that my device could be mounted in “Neo Theo” and what hardware was present. About the other gliders, I had to make assumptions. I chose two assumptions, which were more or less false:

  • Most gliders will have recent LXNAV equipment. An S80 variometer or an LX8000/LX9000 device with PDA port.
  • The rest will have RJ45 IGC-compatible pinouts.

Both turned out to be wrong. I encountered gliders with older LX9000 devices, which did not feature a PDA port yet. I also encountered gliders with an XCVario, which looks RJ45 IGC-compatible but isn’t (it uses 3.3V UART instead of RS232). An LX7000 device that I encountered needed an RJ12 connector, which the local hardware-store didn’t have.

Even the simulator didn’t work, as the different WiFi clients were not allowed to exchange data. That meant my device couldn’t receive the simulator’s telemetry.

Taking a step back

This was all pretty frustrating. After the initial success of installing the first device, I now failed 4 times in a row. For reasons that were outside of my control in Stendal. With my departure closing, I was afraid that this was going to fail. Six months of work for nothing.

Then I remembered some of the wisdom that I had heard: it’s not reality that’s the problem, it’s how your relate to it. I decided to take a small step back, get out of my daily routine at the airport and have a good lunch in the city center of Stendal.

I then decided that I should put my money on NeoTheo and have as many people fly it as possible. I announced that I would donate to Idaflieg for every evaluated flight that took place on NeoTheo. That worked very well, and the next day four flights with NeoTheo took place, despite windy conditions.

Further evaluation

Two testpilots perform a skidded stall with the system

In total my system has now been evaluated 8 times. It has flown with experienced pilots, inexperienced pilots and even a test-pilot. My device has worked well: I see no bugs or crashes in the logs. The installation of the PushButton also worked well, as there were no accidental presses and it was never close to obstructing any flight controls.

Lessons learnt

Apart from the analysis of the evaluation, I think many lessons can be learnt from my experience. I’ll list a few here…

Optimize for change. This is also the first principle of eXtreme Manufacturing. The fact that I could see my logfiles after the landing of a glider and could build+test a new software-version within 5 minutes was hugely powerful. Several times have I made small improvements to the device, to make the experience a bit smoother. For example: I did not read 5 Volts from the LXNAV S100, but more like 4.6 Volts. That should not be enough for the Pi to run, but it still did. I could make the low-voltage warning go away with a simple change in software and continue testing.

The more generic an interface, the better. I falsely assumed that most of the gliders I would encounter would have either an LXNAV instrument with an RJ45 PDA port (5V + 3.3V TTL UART), or a RJ45 IGC-compatible port (12V + RS232). I was wrong in many ways. I encountered many gliders with either no external port or a (just slightly) incompatible port. This cost me many hours of trying to make things work, without any results. If I would have designed my system with simple screw-terminals instead of a fixed-pinout RJ45 connector, I would have been able to get more gliders to work.

Resilience is all about how you relate to the circumstances, and yourself. When I failed to do 4 installations in a row, I noticed my mood deteriorating pretty quickly. As soon as I stopped beating myself up and started to be kind to myself, the ideas started to flow and better outcomes followed quickly.

Speak up. A lot of days went by where not much happened. I was waiting for people to “discover” my project. It turned out they were busy with projects of their own. Only when I clearly stated that I wanted people to fly with my device, things started to happen. I had to speak up.

integration is crucial. Since I’m not the only instrument in the cockpit, it must co-exist with other instruments. It is vital that the pilot can distinguish between your instrument and all others, and that mental workload remains low. One pilot reported having issues managing their attention between my device and the variometer. Another thought it was difficult to determine if my device was beeping or if FLARM was warning about nearby traffic.

There is synergy between software and physics. Many of the people I spoke to were jealous of the level of software-engineering that has gone into my device. The fault-tolerance attempts that I made were clearly working. On the other hand, I was often very jealous of the amount of physics knowledge that these people have. I can hardly understand the physics behind AoA estimation, let alone improve upon it. The right software engineer and the right physicist can create something far greater and useful than each can on their own.

The value of feedback cannot be overstated. The amount of useful feedback I got from Idaflieg’s pilots was brilliant. No amount of development or thinking can replace this. If I would have had multiple days of testing, I’m sure I could have made tremendous improvements.

Results

I need some time to evaluate the results of the questionaire that the pilots filled in for me. This will feature in a separate post, and will be published at Idaflieg.

In general I think it can be said that the system as such proves valuable. There are some issues to work out, such as the integration with other instruments in the glider cockpit: FLARM, the variometer, the radio. All of these produce sounds too, and we need to be careful about where we direct the attention of the pilot. We also need to take care we do not overwhelm the pilot. In general my device was not loud enough when flying fast (especially in the backseat) and the LED was hard to see. Making it louder might make the integration with other devices more important.

The device appears to detect the approach-to-stall well in most cases. Dynamic stalls appear to be challenging, as the onset is too quick for my device to detect it in time.

Acknownledgements

I would like to thank these people for their invaluable assistance in my project:

  • Idaflieg and DLR, for allowing me to execute this project.
  • FVA Aachen, for trusting their glider with my home-built electronics.
  • My colleagues, for helping me learn PCB design and fixing mis-manufactured PCBs.
  • Roald, for helping me with 3D printing and mounting a PushButton on the stick.
  • Kim, for mental support and helping me out with the evaluation form.
  • The Idaflieg pilots, for their evaluation and suggestions.

There’s no greater thrill than seeing your ideas become reality. Thank you.

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The Zacher Protocol

As you might know, last summer I visited the Idaflieg Sommertreffen. In preparation I received training on the Zacher Protocol, Idaflieg’s method for systematic evaluation of aircraft handling.

Since the instructions were entirely in German, I decided to translate them to English. Today I’m glad to say, both the German and English versions of the Zacher protocol have been published by Idaflieg!

Behind the scenes Idaflieg has a database with the results from a few years of Sommertreffen. In the database is data from each individual flight on a glider. The data has been checked for plausibility and details like weight&balance are present. You can ask Idaflieg for specific results by emailing vorstand@idaflieg.de

I am convinced that the publication of this method is very valuable. It allows anyone with an interest in flight testing to get hands-on experience on the subject. For anyone aspiring to become a test pilot one day, it provides a peek into what flight testing is in practice. Both in flight and on the ground. I wholeheartedly hope this will one day become a standard part of any aerospace engineering track.

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The Akaflieg Braunschweig SB-14 – an exercise in minimalism

As a result of my education in embedded systems programming, I’ve come to respect minimalism. Perfection – for me – is found when there is nothing left to subtract.

Shortly after my arrival in Stendal, I made my way to the enormous glider hangar. I had never seen glider prototypes and I was keen to have a look at what the Akafliegs brought to Stendal this year. There I met the Akaflieg Berlin B-12, the FTAG Esslingen Apis Jet, but one glider stood out for me personally… the Akaflieg Braunschweig SB-14.

The SB-14 has to be one of the most slender composite sailplanes that has been produced so far! An exercise in minimalism. Function dictates form. I love it! During my visit the SB-14 regularly flew test flights, and I spoke to some people who designed parts of this sleek machine. So I just had to know more, and started to talk to Lars Samake, project leader for the current certification efforts.

The SB-14 in flight, Lars at the controls. Photo by Simeon Schmauß

In contrast to some other Akaflieg designs, the SB-14 was not designed to test a new concept. Instead the goal was to minimize the surface of the fuselage compared to other gliders. To further reduce drag a special wing profile was designed, where the transition from laminar to turbulent flow happens very late. The airflow is forced from laminar to turbulent using boundary layer blowout holes, similar to what some other gliders (DG-300, ASG-29 and others) use.

The SB-14 had it’s maiden flight already in 2003, and has flown under a Permit to Fly ever since. As with most Akaflieg projects, the goal is to create something which passes certification, so the intention has always been to finish certification. Certification to JAR-22 was started in the past, but never finished.

The flight tests during the Sommertreffen of 2023

In the past few years, the “high risk” tests for JAR-22 have already been performed. These include tests like extending the airbrakes at 1.05 times the intended Vne.

This year it was time for calibration of the airspeed indicator, checking stalling behavior, checking the air brake effectiveness, control forces, stability… you name it. The goal was to perform two certification flights per day.

Two flights per day doesn’t sound like that much, but each flight should be thoroughly prepared the evening before the flight. During the flight everything is filmed, so an additional one to two hours of evaluation takes place after the flight. During the first weeks of the Sommertreffen, Lars did all these tasks himself, but he was happy to leave the flying to another pilot once a more aft center of gravity was required. During the whole process, Lars was supported by the members of Akaflieg Braunschweig and pilot with extensive flight test experience, and the LBA is also present during the Sommertreffen.

Evaluation of the airflow over the fuselage using tufts. Source: Youtube/AkafliegBraunschweig

What’s next?

So what’s left for certification? The same tests that were performed this year should be performed with water ballast, in order to test the glider at the maximum take-off weight. These include tests evaluating stall speed, stall characteristics, general flying characteristics and take-off/landing behavior of the glider.

I can’t wait to see this beautiful glider back in the air next year. Hopefully for the last time with a Permit to Fly…

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Forschen, Bauen, Fliegen with Idaflieg in Stendal

Ever since I started my studies in Computer Science, I started to fiddle with electronics in gliders. I enjoy this very much, except for one small part: explaining this to other glider pilots. Most glider pilots I meet roll their eyes when I passionately talk about electronics in gliders, and mumble something like “But why?”.

Getting a bit tired of trying answer that question, I started to look online for like-minded people. And so around 2010 I found out about Idaflieg, the umbrella organisation of the German Academic flight clubs (Akafliegs), existed. Following their motto “Forschen – Bauen – Fliegen” (Researching – Building – Flying), they not only teach you to fly. They also perform research and build their own prototypes, quite successfully. It’s no surprise that most well-known glider manufacturers employ former Akaflieg members. Their prototypes also inspire these manufacturers. Perhaps the most recent example of this is the Mü31, whos influence can be seen on the high wing position of the Jonkers JS3.

Idaflieg collaborates with the German Aerospace Laboratory (DLR), which provides their beautiful Discus 2c DLR with instrumentation and personnel during the yearly summer meeting, the Sommertreffen. During 3 weeks, Idaflieg and DLR collaborate at Stendal airport to measure the performance and flight characteristics of gliders, perform their own experiments and certify their prototypes.

Visiting the Sommertreffen was on my wish list for about 10 years now, but I somehow never got around to it. Around new year of 2023 it started to hit me: I have to visit this event! No more postponing, this is the year. And so I drove via my club’s summer camp in Wilsche to Stendal.

Aftermovie Idaflieg Sommertreffen 2022 – Idaflieg e.V. / Lars Samake

The first night, I start to talk with Carlos of Akaflieg Stuttgart. He asks me who I am and why I am visiting. I expect the “why” question, but it doesn’t come. Carlos starts to tell me about his club’s project: fs36 – the first certified glider with fly-by-wire technology. Carlos tells me it’s pretty difficult, because none of the CS-22 regulations are written with fly-by-wire technology in mind. Therefore it’s up to Carlos and his club to prove their system is safe enough to be certified.

Zachering

The next day I receive my instruction in Zachering, a systematic method of evaluating the handling of gliders named after it’s original author: Hans Zacher. By flying prescribed maneuvers and using just a stopwatch, tape measure and protractor, one can evaluate many aspects of a glider’s handling. Carlos asks me to join him in the evaluation of a brand new DG-1001 Neo, an offer I can’t refuse since I regularly fly aerobatics on the DG-1000S with 18-meter tips. My club has the “old” 20 meter tips too, and I don’t like them.

We tow to 1800 meters and retract the electric landing gear. First we look at the stalling behavior of the glider. We stall the glider straight and level, with 10 degrees of side-slip and in a steady 30 degrees turn. I notice that the DG has become more docile with these new tips, especially compared to the old tips I don’t like. There are lots of warnings before the glider stalls, and with 10 degrees of side-slip there is a tendency to enter a stable turn with some shaking and mild rocking.

Carlos flies a 30 degrees turn.

Next up is the behavior related to adverse yaw. We roll a few times without using any rudder input and note for the time needed to reach 30 degrees of bank. We also estimate how much yaw is introduced as a side-effect of rolling. We also perform the inverse maneuver; from a stable 30 degrees turn we roll back to wings level using just the rudder. Finally we measure the time to perform a 45 degrees left to 45 degrees right turn. The DG seems more agile in 20 meters than I’m used to. I’m starting to be impressed with these new tips!

We enter a thermal together with the Akaflieg Darmstadt D-43, a side-by-side two-seater. The D-43 looks sleek when it flies over the iconic church of Stendal. Again I’m surprised by the low control forces of the DG.

The Akaflieg Darmstadt D-43. Photo by Simeon Schmauß

The next day we continue our program. Next up are maneuvers to determine the stability of the aircraft, which requires still air. We begin with the dynamic stability in the pitch axis. After we release the tow, the DG is trimmed to 115kph and slowly decelerated to 100kph. After the stick is released, the aircraft enters a phugoid. The DG dives down and lifts the nose up at 130kph. I start my stopwatch and Carlos writes down 130kph. The DG slows down and lowers the nose, and Carlos writes down the minimum speed. The DG picks up speed again, accelerates to about 130kph and starts to lift the nose again. I time 27 seconds and Carlos writes down the airspeed. We continue this 6 times, and conclude that since the speeds at the top and bottom of the oscillation do not diverge the DG is currently dynamically stable in pitch.

Finally we look at the forces needed to fly different airspeeds. While having the aircraft carefully trimmed at 115kph, we fly different speeds and note down how much force should be exerted to steadily maintain that speed. We also look at the required stick deflections.

After about 40 minutes we’re done with the program and land. Next up is an evaluation of the cockpit and checking our results with an experienced Zacher instructor. If our results are good enough, they will be entered into a central database. Using this database one can then compare our results of the DG with the results from other gliders.

Performance measurement

After evaluating the DG with Carlos, I help with preparing a Glasflügel 304 for performance measurements. This particular 304 has been measured already once in 1981, but using a different reference aircraft. Measuring it again can reveal differences between the two reference aircraft and their setups.

A complete day is spent cleaning, polishing, documenting (every little scratch and bubble in the gel coat is carefully described), instrumenting and finally weighing the glider. At the end of the day the 304 has been fitted with a very precise GPS received and a WiFi connection for communication with the reference plane. The plane is weighed with the pilot on board and parked in the front of the hangar.

The next day my alarm clock goes of at 05:20AM. This is when the decision is made: is the weather favorable for a turbulence-free performance measurement? The weather looks good, and at 05:45AM the Discus 2c DLR, the Glasflügel 304 and two tow planes are transported to the runway. Everything is set up on the runway of Stendal and the tow planes tow the gliders to 3000 meters. To prevent the pilots from getting bored, quality German music is played over the radio. The gliders are towed into formation and release. For each data point, they fly the same airspeed for a few minutes in formation. Meanwhile the measurement system records their vertical speed precisely at 10 times per second.

After about an hour the gliders fly over the airfield in formation and land. A DLR employee starts to extract the data from the Discus 2c DLR. He shows me a plot with the measurement from 1981 and today’s measurement. The data looks good: as expected there is a slight degradation in performance compared to 1981.

After a week I drive home extremely inspired. I’ve learned a lot, I’ve seen lots of awesome prototypes (more on those in separate posts) and I’ve even been able to help a little bit. I can’t wait for next year…