New Löfgren variometer

[krasw]

This is something that might interest this group, there are never too many new gadgets to fill our panels:

https://www.lofgren-electronics.fr/

I had a lenghty conversation with Niklas about this project and was impressed enough to order one to try out. There is some really new (and good old) thinking behind this variometer and new pressure probes. 

https://www.youtube.com/watch?v=se0CtRjJO_s

Obviously not gliding computer, nor inertial variometer, but something to supplement those and maybe replace that old mechanical vario (scary thought).

[Mark Mocho]

I know it is just a translation error, but it is amusing to note that "accurate" is consistently misspelled as "accurat."

Interesting device anyway.

[Tony Condon]

i like the built in speaker. a simple self contained audio vario thats been missing from the market for a while. Now if only it had the option to run on a 9V battery like the old Borgelt B40...

[Richard Pfiffner]

What about a LXNAV S3 builtin speaker and a plug for speaker and with a backup battery option . Been around for over 10 years.

https://www.craggyaero.com/lxnav_vario.htm

Richard

www.craggyaero.com

[Moshe Braner]

A lot of the modern devices are not picky about the supply voltage, it can be anything in a wide range.  For the Lofgren vario the manual says 9-16VDC, 25mA no sound, 55mA full sound.  Quite a low current.  So you could arrange a 9V backup battery and switch if you want to build that bit yourself.  Although if it really needs a full 9V then a weak "9V" battery (say down to 8V) may not work well.  Try it and see.

[Tom Seim]

So, what is the "innovative filtering" claimed for this vario? This is a very high bar to clear when compared to the Lx Nav Hawk vario.

Tom 2G

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[krasw]

I would be surprised if any variometer manufacturer discloses filter tech, as that is the essence what vario r&d is. Many problems with electric varios are related to predictive filtering of noisy signal, which for example causes familiar needle overshoot/undershoot behaviour, unless heavily damped with long time constant, and therefore loosing speed advantage over mechanical vario.

[cathartes]

a description of the technical underpinnings of the hawk system was published at the most recent OSTIV congress...

https://ostiv.org/congress/congress-events/congress-details/xxxvi-congress.html?_hash=MZ0HX1RSH9dE3l1VmQhSukmzjXovGZ6Shr3dkQ6bWiE%3D&ctx=a%3A1%3A%7Bs%3A2%3A%22id%22%3Bi%3A521%3B%7D&d=attachment&f=Ostiv_Congress_Proceedings-2024-12-06.pdf&p=ostiv-docs%2Fcongress%2F2024%2FOstiv_Congress_Proceedings-2024-12-06.pdf

[Dave Nadler]

Larus is open-source (In winning cockpit at Uvalde 18m).

[Steve Koerner]

Is there any other speed-to-fly system out there which is using this idea of displaying your effective McCready on cruise rather than using a dial to set it?  I haven't heard of that before. 

I think it's an excellent idea.  It simplifies the process; tacitly acknowledging that the most appropriate setting changes every few minutes in flight. No fooling with a dial is required.

[krasw]

I think the Hawk paper describes more the workings of inertial system (following Leutenegger study that produced original Butterfly variometer), not exact logic of TE signal filtering. Extended Kalman Filter is the standard predictive filter used everywhere in signal processing, variometers included, so the term itself does not tell much. 

[Eric Greenwell]

I've always read the MC setting to optimize your XC speed is based on the lift you expect to reach at end of your current glide. Changing it during the glide is specifically rejected. What are you optimizing by changing it every few minutes?

[Steve Koerner]

Yes Eric, "few minutes" maybe overstates my point.  Probably every ten minutes or so circumstances will have changed enough to matter - altitude, terrain, landing options, clouds etc.  The idea of setting McCready to next expected climb is an ideal that only works when the ground presents no threat; that's rarely the case.  There's lots of reasons that come up to fly varying degrees slower than that ideal.  Consider this for an example: it's more difficult to stop for a thermal when you're cruising at 110 kts than it is when cruising at 90.  At the top of the lift band when you do not need a thermal, it makes sense to fly closer to ideal MC than when you've dropped three thousand feet and do need a thermal.  That difference is preferably manifest as a reduction of McCready from perhaps a 4 setting to 3 say; a little lower and you might be wanting to fly at 2.5.

Anyway, that's all beside the point of this thread.  The speed-to-fly method that is disclosed seems like a clever idea. I wish my current instruments did that.

[Tom Seim]

They can do whatever they want, but if they want me to spend my hard-earned money on it there will have to a clear benefit cited, not "innovative filtering," which could mean anything. Hawk varios, OTOH, go into extensive detail on what their filtering is, and I spent a bunch of money for this upgrade.

Tom 2G

On Sun, Feb 2, 2025 at 5:01 AM krasw <kristia...@gmail.com> wrote:

I would be surprised if any variometer manufacturer discloses filter tech, as that is the essence what vario r&d is. Many problems with electric varios are related to predictive filtering of noisy signal, which for example causes familiar needle overshoot/undershoot behaviour, unless heavily damped with long time constant, and therefore loosing speed advantage over mechanical vario.

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[krasw]

Exactly, I have never heard anyone changing MC after every thermal to fine tune for expected next thermal, like theory says they should. On the other hand, most pilots would change gliding speed during glide to next thermal, based on their altitude and number of missed climbs under previous clouds. Instant displayed MC is certainly a fresh idea, why would you fiddle MC manually when just quick look at instrument tells you what MC are you doing at the moment. These ideas are the exact reason we need competition between gliding electronics manufacturers. 

[Ryszard Krolikowski]

Mc is not to follow. 

Mc is telling you if you planned ahead correctly.

For Blue, no clouds, like Arizona, steady freight train speed only. 

Ryszard

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[Nicholas Kennedy]

Most pilots and myself I believe use the Mc setting to vary the hypothetical range available displayed.

In my Oudie and my CAI 302/303  I vary the Mc setting to help keep me safe flying between known safe landing options, by giving me the speed= range distance number.

If I have airports in front on me I Dial up the Mc until the arrival height goes down to a comfortable level, and try to fly that speed.

Often times as high as 5-5.5

If the  nearest safe landing is way out there I'll go as low as 1.5, but almost never lower than this.

I don't like landing out, I'm a cautious XC pilot.

It's easy to vary the Mc setting and see your glide range go up and down

Does the above make sense?

The above vario looks interesting, as a back up for most, or a good option for the local casual flyer.

I believe Hawk is the benchmark for dedicated serious XC pilots

YMMV

Nick

A2

[Dave Nadler]

On Sunday, February 2, 2025 at 8:02:26 AM UTC-5 krasw wrote:

...Many problems with electric varios are related to predictive filtering of noisy signal, which for example causes familiar needle overshoot/undershoot behaviour, unless heavily damped with long time constant, and therefore loosing speed advantage over mechanical vario.

That's not where most of the problems come from.
For those interested in the technical aspects, you might find my presentation at the 2023 SSA convention interesting:
In search of the Perfect Vario

[cathartes]

At the risk of thread drift.

A problem with MC is that every tactical soaring decision gets stuffed into it. When people talk about it they often mean different things. I've regularly seen it to describe:

• forward looking expectation of the next thermal to optimize the current nominal cruise speed
• setting the nominal speed and shaping speed deviations for dolphin flying
• backward looking at the speed or conditions which have been experienced
• a nominal speed for task planning
  
• decision threshold for the strength of a thermal you should stop for
• glide ratio for arrival calculations
• a rough proxy for land out risk

No doubt, enterprising glider pilots have found uses for it beyond this list.

At a given time "the" "maccready number" for each of these considerations may be very different. This is not to knock the use of MC, it is very valuable and finds its way everywhere precisely because it can be used as at least a decent proxy, and at best a theoretically optimal solution for all of these things. What it does suggest though is that if we're going to call everything MC then we need to be more precise what we mean by it.

[*Eric Greenwell1*]

I use one MC value (typically 4) in my flight computer, which many years of flying has shown it generally can get me to a safe landing place.

I use a different one in my speed-to-fly vario, typically 0-4 range, with 2 or 3 being sort of average. Why stop at 4? Well, 4 on strong days, often indicates I should fly at a frightening speed in sink, well over "yellow line", and I'm not going there. Also, when I used to fly Nationals, the pilots that finished near the top flew fairly steadily, obviously not following a STF, and STF theory (and tests) indicate the MC setting has a small effect on task speed once you exceed 2.

Rule of Thumb: Looks Great ahead - 90 knots; looks Good ahead - 75 knots; looks Poor ahead - 60 knots.

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[krasw]

I finally found time to watch the presentation. Very interesting, thanks. I think it correctly outlines the need for inertial platform to show correct airmass movement while flying fast. Kalman filter slide gives the basis for the overshoot/undershoot problem. When you insert polynomial regression into noisy signal and extrapolate into future, that is exactly what happens.

We are still talking about different problems here. While thermalling (constant low speed), the need for inertial system is less. I have used TE and full inertial variometer for thermalling now for 1000+ hrs, side by side, and still think that TE is valuable source of information. Many of us would argue that you actually can take advantage of horizontal gusts while thermalling. Maybe you have tried straightening to upwind in very windy thermal, pulling up extract extra altitude from the horizontal gust, just before turning back at thermal windward edge? That is basically dynamic soaring, shown only by TE. 

[Dave Nadler]

On Tuesday, February 18, 2025 at 4:54:14 AM UTC-5 krasw wrote:

I finally found time to watch the presentation. Very interesting, thanks. I think it correctly outlines the need for inertial platform to show correct airmass movement while flying fast.

Actually, an inertial platform is not required, though that is how a few systems do it.
I don't have a public presentation yet on Dave's vario but I get the gust-free TEA/TEV and gust vector without the inertial platform.

 

Kalman filter slide gives the basis for the overshoot/undershoot problem. When you insert polynomial regression into noisy signal and extrapolate into future, that is exactly what happens.

Kalman is best-estimate of present, no extrapolation to future.
I'm not sure what you're referring to with overshoot/undershoot (hasn't been an issue at least for me in past);

primarily I'm discussing gust response.

 

We are still talking about different problems here. While thermalling (constant low speed), the need for inertial system is less. I have used TE and full inertial variometer for thermalling now for 1000+ hrs, side by side, and still think that TE is valuable source of information. Many of us would argue that you actually can take advantage of horizontal gusts while thermalling. Maybe you have tried straightening to upwind in very windy thermal, pulling up extract extra altitude from the horizontal gust, just before turning back at thermal windward edge? That is basically dynamic soaring, shown only by TE. 

The gust vector is indeed useful as it generally emanates from ~thermal center,
and can be measured by a variety of measurement systems.
Again, I'm currently measuring gust vector without the inertial platform.
I believe Mike Borgelt's latest is also doing this.

Leaving the thermal you can gain energy accelerating in the outflow gust.
Much more efficient than trying to speed up in the thermal prior exit.

Anyway, it will be a while before I've got a public presentation...

Thanks for your interest!
Best Regards, Dave

[krasw]

Installation ready and first test flight yesterday, here is some raw footage for variometer geeks:

https://youtu.be/eQtPKEbm4Ig

First impression: it is extremely fast and sensitive (can be set up slower), and at the same time totally readable. Speed of variometer is very close to my inertial netto with shortest possible time constant. Easily the best pressure sensing variometer I have flown with. For high speed flying inertial has obvious advantages, so I see use of both in a panel equipped to gliding perfection. But maybe the time of mechanical vario is over. Yikes did I say it out loud? 

[Matthew Scutter]

I have never seen an ASI jump around like that in any gliders I have flown, even in an LS8 (that's the glider we're looking at right?). Do you have some kind of pneumatic leak or incorrect plumbing?

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[Ian Molesworth]

Seems to match the bounce in the variometer?

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[krasw]

In video ASI is driven by nose pitot, and variometers use only tail pitot. The ASI pneumatic lines are basically 1 m of length from pressure port to ASI. This might lead to more jumpiness as there is not much damping in system and nose pitot is not optimally placed. Tail pitot is a bit smoother, the pitot probe is in smooth airstream, but this has a small effect on variometers as ASI aneroid is damping signal for variometers.

I wonder if you have flown more with 57 mm Winter ASI? It is like someone poured syrup inside, it tells you very accurately 10s average speed you had a long while ago. I had one previously in this glider and did not like it much.

[Niklas Löfgren]

Good day, Niklas here, the producer of the LÖFGREN variometer.

Our variometer is built to gain an advantage in competition flying, a lot of the concepts I wrote down after flying my last world championships in 2018. For example perfectly functioning electronic compensation (removing the TEC tube) reduces drag, saving roughly 10m for every hours of XC flight. The way it functions(less lag, better stability, less errors) simplifies the thermal selection and centering process. No fiddling with MC settings reduces mental energy spent on that. The simple nature of it reduces the mental energy needed to operate it, it’s very intentional. In high level competition you need all the mental energy you can get for tactical decision. What it does, it does exceptionally well.

The variometer can be driven from a 9V battery but without(or very low volume) sound since the 9V battery can not deliver enough current. Without sound it functions correctly down to 8V. It can also be driven from a small 12V solar cell. We decided to not have an internal battery since an external is cheaper, and more user friendly option, in the long term. Since there is no IGC logger inside a short interruption is no problem. Regarding long term, our variometer is built to last using high quality components.

The filtering is innovative in the sense that we have made two settings: Speed and Noise. This gives better flexibility to adapt it to your liking. We also have a guide in the manual how-to optimise it for you. The filtering is also innovative in that you can achieve a responsiveness comparable to a mechanical variometer but without the instability/over-shoot normally encountered, which I think is a world's first? Combine this with our tubes (pretty much perfecting total energy compensation) and you have something very exciting. The result is a very fast responding variometer(and sound!) which is still smooth, even in turbulent thermals / weather.

Regarding the MC discussion. I encourage everyone to do a calculation of “How much theoretic speed do I loose when flying on the wrong MC setting”. MC have a very flat optimal in normal conditions(less flat in weak conditions, and very flat in strong conditions), exact speed control is not needed, other factors dictate your XC speed more. Myself I try to stay close to the actual but never slower than 0,5 (m/s) and almost never more than 2 unless final glide. Something to keep in mind: Flying at a higher MC gives you better buffer towards speed-for-best-glide-ratio if you hit sink.

We have two versions of the variometer: With built in speaker or with connector(RCA) for external speaker.

For the next XCsoar release our variometer will be supported. Data output is roughly 4Hz including vario, ASI and temperature. The data output from our variometer is very accurate, and with minimal delay, with this in mind.

We have variometers in stock and from 2026 we ship world wide.

If you have any questions just send us an email at nik...@lofgren-electronics.fr or visit www.lofgren-electronics.fr…or ask here of course. We are always happy to help.