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Wing building technique: materials and tools

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I’ve had requests on tools and materials we use to build our wings, as well as a more detailed description on how we build them. I’ll be doing a detailed description on how to build the wings for my “how to” section on this website in the next few months. Here’s already the overview of tools and materials.

Materials

Tools

Diana 4: upper sides of the wings

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Today I bagged the 2nd upper side of the Diana4 wings, having done the first one earlier this week. Bagging the wing is not all that much work – less than an hour. It’s the preparations that take most time.

After preparing the foam cores (see previous post) comes the incredibly important work of drawing the layout of the wings onto the building board and positioning the foam shells. We build upside down (upper side first). Once all the measurements are done and double-checked I position the foam shells and glue them to the building board using painter’s tape. Then I apply thin brown packaging tape on the edges of the shell on the board as well as to the individual shells of the underside of the wing. It’s important to find a packaging tape that doesn’t stick to epoxy resin – the purpose is to avoid the shells sticking to the wing core or other shells.

Once the board and shells are prepared I prepare the ebechi (abachi) wood. We use 0.6mm ebechi, prepared by a carpenter friend or purchased through RIK Modellbau. This ebechi is cut to size using the plan of the wings – important is to make the ebechi for the upper side approximately 4mm longer (depending on wing profile). I then draw the layout of the carbon inserts onto each of the four ebechi sheets (so I know where to position the carbon when glueing it to the ebechi). We rarely do a full carbon layup – that’s not necessary and would only add weight to the wings. The carbon inserts are just big enough to cover the carbon D-box at the leading edge of the wing, the control surfaces at the back of the wing as well as the positions for the servos and the wing joiner. Once the layout of the carbon inserts is drawn onto all four sheets I carefully sand the inner side (where the epoxy is to be applied) of each sheet and clean off the dust. I then apply a transparent primer (“Hartgrund”), 50% diluted, to avoid the epoxy completely soaking the ebechi. Allow this to dry out and another quick sanding and the ebechi is ready to be used.

Once all that is done it’s time to prepare the resin. I used around 60 grams of resin for the upper side. It is possible to do it with 10-15 grams less for weight watchers. Using a small roller I apply the resin to the parts of the ebechi sheet where the carbon layup is coming. I then put the carbon layup onto the ebechi and push it on using the roller. Then I use the roller to apply most of the resin to the carbon layup. I leave a few grams of resin and add a few drops of foaming agent and let this rest a bit. I then use a hard rubber roller and kitchen paper to roll excess resin off the carbon layup. Then use the soft roller to apply the remaining resin with foaming agent to the parts of ebechi not covered with carbon.

Then put the ebechi with carbon layup onto the shells. I use six or so small bits of double sided tape on the shells to make sure that the ebechi doesn’t shift. Then put the wing cores onto the ebechi, fix the outer ends in the right position with a bit of wax tape and fix the cores together with a bit of the same tape. Then close the upper shells, lightly fixing them into place with painter’s tape. Then bag the entire building board, use a vacuum cleaner to remove most of the air of the vacuum bag and then start up the vacuum pump. Stabilise the vacuum pump at -1.5 bar and let it run for 12 hours. I use a cheap webcam to watch the pressure of the pump so that I can go do something else and occasionally check the webcam on my smartphone. The entire setup runs over a timer that automatically switches off after 12 hours.

When I was cleaning up after bagging the 2nd wing I noticed the appropriate newspaper article used to protect my workbench (see last picture :-)).


Ventus 2c: installing the wing servos (2)

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After glueing in the servo horns on the side of the control surfaces the next step was to prepare the 3mm threaded rods in the right length. Then I glued the Chocofly wood/carbon servo frames in place. To do this, I first installed the rods on the side of the control surfaces, allowing me to center the frames with servo in exactly the right place. I applied a few dots of 5 minute epoxy to fix the servo frames. Then I removed servos and rods and applied thickened 12hr epoxy around the servo frames. After allowing the epoxy to cure I could then do the final installation of the servos and rods.

The wiring I prepared earlier and was thus easy to install. I removed all the servo plugs and soldered the servos straight onto the wiring – for reasons of weight, space and reliability – I don’t intend to ever replace the servos :-). The servo openings I closed using the bits milled out earlier and white foil I plotted using my Cameo 3.

The new LDS system is amazingly robust and without any play whatsoever. Adding to that the much greater ease of installation compared to systems I used earlier, this is a great system to use. Even though more expensive than the earlier systems we’ve used, it’s definitely worth it’s money. I’ll also be using it on my next builds.

Ventus 2c: installing the wing servos (1)

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For the Ventus2c I will for the first time be using the new Chocofly LDS PRO system. The wood/carbon servo frames, as well as the perfectly fitting aluminium servo horns I already used for the Orlik. The carbon control horns and the aluminium/steel/brass connectors are new. Although heavier than the system I previously used, it’s also much more robust. Most importantly, it’s easier to install as you can shorten the 3mm threaded rod to the right length and slightly adjust it to the perfect centering position once the servos are installed.

Another important change compared to previous builds is that I prepared all the openings in the wing and wing control surfaces before setting the hinges and seals. In the past I’ve ended up damaging the seals or even the wings when making those openings afterwards. Doing it before makes the process much less risky and results in a cleaner build.



Ventus 2c: seals for the wing control surfaces

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I’m finally starting to get the hang of doing the seals for the wing control surfaces. In the past I tended to make the epoxy resin mix too thick, which resulted in uneven seals. The trick is to leave the epoxy resin mix relatively liquid – it should be thin enough to spread out evenly, but no so thin that it flows over the tape. Here’s how I do it:

  • make sure you clean the gap between the wing control surfaces and the wing – any dirt, especially carbon dust, risks leaving black dots in your seals;
  • apply a thick PET Tape (see for instance here – with thanks to Martin E.) to the control surface, leaving just enough space so that when the control surface is at around 20-30 degrees down deflection the seal is nicely underneath the overlap on the side of the wing;
  • position the wing in a position that you can apply the epoxy resin to the tape so that it flows a bit more towards the side of the control surface;
  • prepare epoxy resin, thickened with a bit of aerosil and lots of micro-balloons as well as a bit of colourant (I use white) – the resin should be thin enough to spread out evenly, but no so thin that it will run off the tape;
  • apply the resin to the tape using a syringe – I also use a thin pin or metal stick to make sure it spreads out evenly;
  • wait until the resin is cured enough so that it no longer runs off, but still soft enough so that you can mould it;
  • move each control surface upwards and carefully slide the PVC tape under the overlap on the side of the wing – I use a long ruler for this. The control surfaces should be in a down deflection of around 20-30 degrees, the tape will round itself and ensure a nice and even round seal;
  • allow the resin to fully cure;
  • once the resin is fully cured, sand it back to the correct depth so that you have the deflection that you require on each rudder, leaving enough so that there is no gap between the seal and the wing for normal downward deflection (of course this doesn’t apply to the downward deflection of the brake flaps in butterfly mode)

Below are some pictures that hopefully clarify the above.




Ventus 2c: assembly to check if all is ok

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With canopy and wingtips all done, it’s time to assemble my Ventus 2c to check if all is ok – and of course to admire the result of my work so far. I also weighed the glider. As in the picture it’s now at 2.71kg – this is without filler, paint and most of the electronics (except for elevator servo and cable, which are already in the fuselage). This means that it should be possible to get a final flying weight of less than 5kg – as planned. Fingers crossed.

Next step is to apply filler to the wings and control surfaces and give them a final sanding. Then I’ll need to prepare the plane for the paintshop.

Diana 4: motor bulkhead and cockpit cover

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Sometimes things don’t go quite as planned, even if you’ve done it plenty of times. Installing the motor bulkhead of the Diana4 was a pain. The carbon bulkhead was just a bit too big for the fuselage, and I was sloppy in making the first cut on the nose. I ended up having to remove the bulkhead (fortunately only fixed with a few dots of 5min epoxy) and sanding it down by mounting it on the drill and rotating it on a bit of 120 grain sandpaper. Even the second try wasn’t quite as good as I wanted it to be, but with a few corrections on the fuselage it will come out fine once the fuselage is painted.

In-between I produced two covers of the instrument panel. The first one in the mould that was spray painted, the second one using thickened epoxy as the “basis”. Making these small parts in the mould are good for using left over bits of glass. Two layers of 160gr, or a layer of 50gr, one of 100gr and one of 160gr are more than enough for a robust cover.

Diana 4: installing the landing gear

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The Diana 4 will get a retractable landing gear. We’re running low on the stock of landing gear made by our club ages ago and only have a smaller version left. It requires an 89mm wheel rather than the 103mm wheel we used for the JS3 (which uses the same fuselage as the Diana 4). It still looks nice enough though, and the difference will be hardly noticeable. To install the gear I cut out the doors from the fuselage using my dremel with a 0.8mm milling bit. To give the doors a bit of extra stiffness I covered them with a layer of carbon fibre (before cutting them out of the fuselage). The doors are then attached to the hinges, made of steel wires through a brass tube. The landing gear is attached to 4m plywood.

Chocofly JS3: FES Fuselage

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I’ve been mostly flying my Chocofly JS3 on the slope. For my club’s airfield I have my scratch-built JS3, which is lighter and has more wing-flexibility (allowing for awesome thermalling). But I’ve very much grown to like the Chocofly JS3 and am keen to give this one a go at our club’s airfield as well. Unfortunately, our club doesn’t allow the use of impellers or noisy motors – it’s in a very quiet and sensitive area. To enable me to fly the Chocofly JS3 at my favourite airfield I thus ordered a 2nd fuselage a (long) while ago.

The 2nd fuselage arrived a few weeks ago. It’s in the usual excellent quality. Initially I considered installing a landing gear, but in the end decided against it. The reason is that I’d like an even lighter version of the JS3 for situations where lift is very bad, especially in early spring or late autumn. My Chocofly JETEC JS3 weighs around 6.8kg, my scratch-built one around 6.6kg, the Chocofly FES Edition will hopefully end up under 6kg.

The fuselage didn’t need much work to finish. I installed the FES with my usual method. I used the outrunner and ESC combination that I’ve been using for just about every build in the last few years, a Dualsky XM5060EA-14SE with a Castle Lite 100 ESC. On recommendation of Dani (Chocofly) I went for an 18×10 GM scale Propeller and the usual Freudenthaler 43mm scale spinner. The result looks really good. The fuselage is now ready for its maiden flight – once I receive a new set of winglets (see previous post)….

Chocofly JS3: losing the winglets :-(

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We’ve had some really good slope conditions over the past few weeks and I’ve been mostly flying my Chocofly JS3. I just love this glider. It’s my favourite choice if the winds are weaker or, as often happens in summer, when you can expect sudden gaps in lift. The JS3 will allow you to battle through low-lift episodes much better than most of my other gliders.

The many hours on the slope however also showed that the JS3 does have an upper limit in terms of speed. I own an early production version of the lighter GPS edition. I prefer this version as the lower weight and somewhat more flexible wings give it better thermalling properties. But it’s not made for vertical drops, tight loopings and ultra-high speed passes – I own other planes that are (including my other favourite, the Chocofly Diana2!).

The slope conditions were at times however just too good not to test the JS3’s limits. We’ve done multiple high-speed passes at well over 260kmh, but noticed that the winglets were starting to get a bit “noisy”. Ever since I lost the winglets of my scratch-built JS3 in Autumn last year I’ve been keen not to push my JS3s too far. But due to a stupid combination of unfortunate circumstances (of which I am to blame) I ended up in a steep dive with a brief loss of signal. The speed of the dive (260kmh) and the sharp recovery turn out of the dive were a bit too much for my JS3. Upon landing, I noticed that I lost my winglets. I always attach them with a strip of tape over the top and nose of the wing, but they were literally “torn out” of the outer wing, damaging a few cm of the underside of the outer wing. Fixing this is not a big issue and a new set of winglets has been ordered, but I promised myself and my JS3 that I will behave in the future….really!

Chocofly JS3: testing the short wing version (4.28m)

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Although I built a short-wing (4.28m) version of my scratch-built JS3, somehow I never got around to flying it. The long version (5.14m) simply flies awesome so I’ve never seen the need to install the short outer wings. Plus the short version doesn’t quite look as good as the long-wing version.

Chocofly also offers its JS3 in the long and short outer wing version, but I only ordered the long outer wing version. A few weeks ago Dani (Chocofly) put his set of short outer wings in my hands and urged me to give them a try. We’ve had some awesome slope conditions in the past few weeks, so I did. My impressions confirmed what Dani told me: it’s a very different plane. The JS3 becomes very agile (rolls great 🙂 ) but at the same time doesn’t seem to lose much of it’s thermalling capabilities. It’s a nice addition to the JS3 that extends the range in which the glider can be used to conditions with stronger lift and wind and where the pilot wants a more agile plane.

For me, the JS3 already had the broadest range in which a glider is excellent to fly. I’ve never flown a scale glider that is so good to fly and so much fun in conditions with very little lift way up to good slope conditions. The short outer wings further extend this range upwards. Interestingly, I did notice that the JS3 accelerates faster, but I did not notice a large difference in the top flying speed (see my next post). Important to note however is that even in the short wing version it doesn’t match the Diana2, which is still my favourite plane for good to excellent lift conditions. This in partly because my JS3 is the lighter GPS edition (and thus not as robust and heavy as the Alpine or HG Editions – my Chocofly Diana2 is an early Alpine Edition), but also because of the winglets – which limit the top speed of the JS3 (the Chocofly Diana2 comes with a set of “tiplets” for when it really gets “hot”)(see my next post). That’s however no criticism of the JS3 – it’s an amazing plane for the slope, but not built as a slope racer. I very much enjoyed flying the short wing version and have ordered a set of short outer wings.

Below a few pictures of the short and long outer wing version side-by-side.

Scratch-built JS3 with new winglets

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Last year was not a good year for either of my JS3. After the incident with my Chocofly JS3, which is fortunately flying again, I also had some bad luck with my scratch-built JS3 in September. We were racing triangles at our airfield in some of the most amazing thermals I’ve ever encountered, with a thunderstorm and heavy clouds coming in. I misjudged the height of the cloud coverage as well as the strength of the thermals. My JS3 was literally sucked into a dark cloud. I instinctively gave down elevator, which caused my JS3 to reappear within seconds. Unfortunately it picked up speed massively (my GPS logger later told me I hit 265kmh) which caused the winglets to flutter and torn out of the wings. After a quick check that all control surfaces were still functional, I managed to land the plane safely. The winglets were never found, and there was quite a bit of damage to the end of the outer wings, but fortunately nothing that could not be fixed.

Chocofly kindly provided me with a set of moulded JS3 winglets, which fit perfectly, saving me the task of making them myself. Fitting them and fixing the outer wings took a bit more work. Two weeks ago I then also finally managed to get the wings spray painted and today my JS3 happily took to the skies again, flying as good as ever. I love this plane.

VT-16 Orlik: Maiden Flight

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Yesterday my VT-16 Orlik had its successful maiden flight.

The day proved to be quite eventful. As usual we do the maiden flight in aerotow – which again proved to be a good decision. Even though we did extensive pre-flight checks, we somehow oversaw that the elevator wasn’t quite neutral and slightly up. As soon as I released the Orlik from the towline at around 250m I had to give a LOT of downtrim, after which the plane was flying ok. Also challenging were the crow (butterfly) settings. I installed and programmed the inner wing control surface (brake flap) to allow it to come down by around 75 degrees. This proved to be a bit too much, as (unlike some of our other builds) the plane responds very well to crow. In addition to that, the Orlik also needs a lot more downrudder in butterfly/crow than with our other builds. This meant that the Orlik came in too slow for the first landing and stalled around 30cm above the landing strip, literally dropping out of the air. Fortunately nothing happened. A quick reprogramming and further finetuning during subsequent flights cleared all problems.

Unfortunately that wasn’t all the excitement of the day. During my 7th flight I lost the canopy after engaging the motor for a short climb. We found it back after a long search in the already high wheat and I could have a final good flight at the end of the day. To add to the events of the day, in the late afternoon Georg’s Orlik also had a really nasty looking mid-air collision with the glider of a colleague. Both gliders however landed safely with barely a scratch.

I like the Orlik. It’s the pleasant oldtimer that we hoped it to be. It thermals very well, responds very well to rudder and needs little aileron in curves. It also has excellent stall behaviour. Of course it’s not a racer – and wasn’t built for that – but does pick up speed nicely with negative camber. I plan to fly it a lot in the next few weeks and further finetune settings and the center of gravity.

 

VT-16 Orlik: Ready for maiden flight

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My VT-16 Orlik is ready for its maiden flight. Three rainy days off meant I had time to finish installing the wing servos and finalising the wiring and programming and getting the center of gravity right. Getting the CG right proved a bit harder than I hoped. The fuselage of the Orlik is very long, and the nose very short. I had hoped that my two larger 3S batteries (2x 3S 3700), a small backup battery and the Dualsky outrunner motor would be enough to get to the CG. Unfortunately I’ve had to add a bit over 200gr of weight to the nose. The surprise however came when I weighed the aircraft: 7kgs. I had feared I would end up a higher than that. With deep wings and a wingspan of 4.6m the wingload will still be very low. Georg’s VT-16 is a bit more than 6.7kgs, so I’m not too far off the weight of his. Fingers crossed that I can maiden the Orlik in the coming week. I’ll soon post a data sheet on the Orlik as well.

 

VT-16 Orlik: installing wing servos

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The resin on the seals of the wing control surfaces of the Orlik finally hardened out enough to sand the seals into shape (it takes 3-4 days to fully cure when you use white colourant and micro-balloons and your workshop is not that warm). Finally I had some time off and a few rainy days:  time to install the wing servos.

We’re using the usual setup for our Scale 1:3.5 gliders: Six control surfaces (3 on each wing), connected with an Integrated Drive System (IDS). We never use airbrakes on modern wing profiles – butterfly is better for landing on the slope and with modern profiles the ability to camber the full wing makes a much more performant glider.

As servos we use the Chocomotion FOX 10/10 and 8/6. We’ve used these servos on all our builds for the past few years and with many flying hours never had one fail on us. New for the Orlik are the IDS aluminium servo arms and the new glass/wood servo frames with ball-bearings kindly provided by Chocofly. The new frames are easier to install than the plastic ones we used earlier, and the aluminium servo arms are a perfect fit with the Chocomotion servos (unlike the plastic ones we used earlier) and also very robust. For the rest I used IDS pieces I still had left over from earlier builds. Rather than building the connectors on the control surfaces within the wing, I’ve placed them externally. The reason for this is that the control surfaces are quite large and I’d like to somewhat reduce the power required by the servos to move them.

Fitting all is a lot of work and careful filing all the openings. It almost took me two full days. After getting all openings and pieces to fit, I first fix all the bits with 5 minute fast-curing epoxy. At the end of the day I add slow-curing epoxy resin thickened with aerosil, to make sure that it all holds. The epoxy will cure overnight.

Next step is finishing the wiring in the wing and programming the plane….

Out on the slope – Photo session EB-29R

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We’ve been spoiled with quite a few fantastic slope days over the last few weeks. I’ve been mostly flying my Chocofly JS3 and this week also my EMB-400 Urupema. Both planes still require some fine tuning (elevator incidence, center of gravity).

The JS3 is just a dream to fly, but I need to work a bit on the aileron throw and differentiation still.

The Urupema was a bit too nervous for my liking (very aggressive on the elevator, especially at higher speeds), but with increasing the elevator incidence and moving the center of gravity forwards it seems to have improved a lot. I’ll need to do a bit more experimenting still. The plane still amazes me – it combines the characteristics of a number of my favourite planes. It has totally friendly stall behaviour (with a very low stall speed) and thermals very well. But it also accelerates immediately as soon as the nose tips down even slightly (even in full camber!) and has an almost scary speed retention.

Last Thursday Richie joined us at the slope with his EB-29R (8m, 8kg). He built the plane entirely from scratch, including plug and fuselage moulds. With 8m the wings have lots of flex in them and the plane is definitely not built for high speed flying. But it thermals incredibly well and easily does very tight turns. Due to the low wing load, it’s also a breeze to start by hand – Richie didn’t need much more than a flick with his wrist to get it airborne – so cool to see!

I took my Canon camera to the slope to do a bunch of pictures of the EB-29R for an upcoming journal article. Here you can find the best pictures from the photo shoot, as well as some earlier pictures, videos and more information on the EB-29R.

In-between: Harth Style wing twisting glider (97cm)

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While ordering some parts from the Hoellein Shop I couldn’t resist also adding a small in-between build: the 97cm Harth Style from Tim Wirth. It’s a very easy and good value kit for a glider with twisting wings. It was a very quick build – bridging the time I had to wait for the resin of the Orlik wing seals to fully cure. The Harth looks like a pretty fast and not easy to fly (and especially difficult to land) little glider, but it could be much fun on the slope and for morning and evening flights at our club’s annual Hahnenmoos excursion in June.

VT-16 Orlik: silicon hinges and seals of the control surfaces

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Finally time to get back to my VT-16 Orlik build again. First I set the silicon hinges. After leaving the silicon to cure for a few days, yesterday I added the seals for the wing control surfaces. Both were done using our “usual” method, already described in earlier builds. Now I need to wait for the epoxy resin of the seals to harden out, before sanding them into perfect shape. It usually takes a few days to fully harden out and become easier to sand due to the white colourant and large amount of micro-balloons (and the fairly low temperature in my workshop at the moment). While I waited for the silicon hinges to cure I also finished the decals on the fuselage, which now looks pretty neat.

Project VT-16 Orlik: maiden flight of the first Orlik

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We maidened the first of our three VT-16 Orlik, the one built by our chief designer Georg.

As usual we did this in aerotow, yours truly having the honour to be the tow pilot with my trusted Boomster. In our experience aerotow is the safest way to maiden a model where you’re not sure if you got all the settings right – a powerful towplane will at least get the model to a decent height, giving the pilot time to get to know the model and change some of the trim settings.

The first flight went very well, with only a few changes required to the butterfly settings and aileron differentials and some further fine-tuning in-between further flights in the afternoon. Georg will be further fine-tuning this over the next few weeks, giving Andi and myself the benefit of being able to copy his settings before the maiden flights of our Orliks.

The plane behaves as expected. With 6.7kg (4.6m wingspan) and a large wing surface, it’s a real floater and can be flown very slow. The thin wing profile and option of negative camber however also allows for higher speeds. It reacts very well to rudder and ailerons and has a friendly stall behaviour.

I’ve had some time at the sticks as well and immediately fell in love with the plane. It’s perfect for the type of conditions we have at our airfield, where light and well thermalling-friendly gliders are our preference. Can’t wait to maiden mine.

 

Alpine slope season start

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A spell of warm weather and a nice northerly means alpine slope season start! On Monday our shaper Richie and I spent the afternoon on our favourite slope. There’s still quite a bit of snow there, but the landing area was clear.

For me a chance to fly my Chocofly JS3 again. Richie was flying his wonderful 6m scratch-built JS1. We spent two hours non-stop in the air with endless lift – awesome conditions. I’m hoping for a next opportunity soon….