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.
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.
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….
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.
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.
There is still a lot of work that needs to be done once a plane comes back from the paintshop. Most frustrating is that after the big “wow” of putting it together, the next steps are barely visible and yet there’s a risk of really messing things up. Probably the scariest thing is cutting out the control surfaces on the wings. If that goes wrong (not a straight line, wrong place), you at least have a very visible mistake and even risk ruining all the work and having to start again.
A crucial step for cutting the control surfaceds is always made during the building of the wings, where we drill small holes in the abachi between the two spars that mark the division between the control surface and the wing. These holes need to be kept open during all subsequent steps, so that you can find them back! With these holes you know that you’ll be cutting in the right place.
For the actual cutting we use two different methods. The first is an adapted Dremel with a 0.8mm mill bit, that’s pulled along an aluminium ruler which is in turn stuck to the wings with bits of double sided tape. I used this method for the Urupema wings. The second is a nifty little gadget with a small motor running on a 2S LiPO battery, running on an aluminium “track” (see picture below), which Andi and I used for the Orlik wings. Both methods require a steady hand and double-checking before you cut. Fortunately Andi is an expert in this and perfectly cut our control surfaces. Using wooden templates we also cut out the openings for the servos.
Following this there’s a lot of work cleaning out the foam. Then we sand back the upper part of the wing so that the gap between control surface and wing is around 2 to 3mm wide. Then we sand the part where the control surface goes under the main wing back so that you have a sharp edge. Finally, we apply 49gr glass inside the main wing so that it’s protected against humidity and slightly reinforced.
We spent three half-days painting the various colours on our Orlik (and Andi three more by himself). This wasn’t without challenges. It’s the first time that we spray-painted surfaces covered with Koverall (always a bit of a gamble to see if the solvents are compatible), and the first time that we applied so many different colours. The masking of surfaces takes a lot of time, and we needed to wait at least 12 hours between different colours to let the paint harden out. It all went relatively well, albeit with a few mishaps. The elevator and rudder covered with Koverall were very static and attracted every bit of dust, and the Koverall in some spots shows pinholes and stood up a bit. Most of this was easy to correct with a bit of sanding. Although not perfect, the surfaces look very good. We also made a mistake leaving two fuselages too close to the painting which resulted in some excess spray landing on them – the lower part is now a bit textured. But without these mistakes the planes would have looked too perfect – it’s an oldtimer that needs a few flaws :-).
This morning Andi went to pick up the fuselages and I just couldn’t wait to put my Orlik together. The edge of the canopy still needs to be painted (you now only see the epoxy used to glue the canopy to the frame), but I think it looks awesome.
Now comes some really difficult and precise work: cutting out the control surfaces, setting the hinges and seals, and then installing the servos. We’ll be doing this in parallel to finishing the electronics in the fuselage.
We’re incredibly lucky to have a “master painter” (malermeister) in our building team. Andi is an absolute expert in paint types, spray painting model aircraft and also has enough connections to secure a slot in a friendly paintshop that allows us to use their professionally equipped space to spray paint our Orliks. Today was the “white” day, where Andi spray painted the white base coat on our three Orliks (and I provided an extra pair of hands to help secure and transport all the bits). We’ll need another few visits to the paintshop though, as we’re going to put a few more colours on :-).
The general view among builders I know is that fitting the canopy is their least favourite (most hated?) task in building a model aircraft. The canopy frame is not too hard to build (see earlier post), but cutting and sanding the canopy to a perfect fit, and then glueing it on is a real pain. It takes a lot of time and patience and very few things are so visible and ruin a build like a badly fitted canopy.
I use a pair of Tamiya curved lexan cutters and a Permagrit sanding block to cut and sand the canopy to size. Important is to mark the center both at the front and rear of the canopy as well as the fuselage to make sure that you always place the canopy in the same position. I do a first a “rough” cut using the Tamiya cutters and then using the Permagrit to sand it into perfect shape (being VERY careful that you don’t slip and scratch the canopy!!). Then it’s try, sand, try, sand…..repeat. It took me a bit over two hours on the VT-16 Orlik to get to an acceptable cut.
I then wax the seat of the canopy frame in the fuselage (three times, using liquid wax, slightly rubbing it with some soft cloth in-between coats). I then prepared epoxy mixed with micro-balloons and aerosil, fairly thick, but thin enough so that I could apply it using a syringe. Using the syringe I applied the epoxy evenly to the canopy frame and gently placed the canopy onto the frame. Using pieces of waste wood with double-sided tape as well as lots of wax tape I made sure that the canopy is in the right position and nice and even with the edge of the fuselage. Now it’s time to let the epoxy cure. Fingers crossed that it will come out well tomorrow….
Today I finished covering elevator and rudder and applied the final (3rd) layer of dope. The rudder came out very well, but I will need to check a few things on the elevator’s fitting to the fuselage still (there’s a small difference in the throw of the two sides) before it can go off to the paintshop. I also installed the rudder and towhook servos, as well as the plate for the bungee hook (we usually start using a bungee on our airfield). Both rudder and towhook are the usual setup, with the rudder using the nifty adjustable wheel developed by our club, in a pull-pull setup using a kevlar cord. Now I’m looking for the right moment to cut the canopy to shape – a very tedious job which I’ve been putting off and for which I need to be in the right mood ;-).
I’ve used many different methods for covering aircraft in the past. Among my favourites are Oralight and Oratex. Both are relatively easy to apply, with Oratex being very robust and oralight very light. Most recently I used Oralight for my Inside F5J and Oratex for my EcoBoomster Towplane. Both however have as a disadvantage that the surface tension is good but not brilliant, and you regularly need to do another pass with the hot air gun or iron to iron out new wrinkles – especially when you store your planes in an unheated room like I do.
When building my Moswey III, I was shown another method by Georg, the designer in our building team, and an experienced builder. This method not only gives great surface tension (love to drum my fingers on it :-), it’s also very light and, importantly, doesn’t require you to regularly straigthen out wrinkles. For the VT-16 Orlik we decided to use the same method again.
I’m sure that there are many different ways to cover a glider. This is the one we use for the Orlik. Materials to use: SIG KOVERALL covering fabric; Dope (we use Fuller-MZ), UHU Hart glue, nitro thinner and acetone. Method: 1) make a mix of 50% (by weight) UHU Hart and Dope and use a brush to apply one or two coats to all areas that the Koverall tissue need to stick to, allow this to dry; 2) cut Koverall into rough shape; 3) put the Koverall on the area you want to cover and fix the edges (not inner parts!) of the cloth to the wood using a small cloth with acetone (the UHU Hart/Dope mix will dissolve and the Koverall will stick to the wood); 4) use a hot air gun to carefully tighten the Koverall and remove any wrinkles; 5) using the cloth with acetone attach the rest of the Koverall to the inner ribs/surfaces; 6) apply two or three coats of dope, letting it dry out in-between and making sure that the covered surfaces stay straight.
While the Moswey III was hand-painted (to get that Oldie look), the intention is to spray-paint the rudder and elevator of the Orlik. More on that later.
The rudder is now installed in the fuselage. Georg kindly prepared a balsa plate, with a coat of carbon on each side, in which the hinges (3 (bottom) and 2mm (middle and top) epoxy plate) were glued. After sanding everything into shape, the whole “cassette”, including 16mm balsa separators between the baseplate and rudder, was then glued into the tailfin (before inserting I used a syringe to apply slightly thickened epoxy just a bit before the location of the carbon coated baseplate). I clamped two bits of wood to the side of the tailplane to ensure a straight and tight fit. After allowing the epoxy to cure the rudder was sanded into its final shape, also to allow sufficient throw to each side.
The Orlik wings now perfectly fit the fuselage and are ready for the paintshop.
Fitting the wings to the fuselage is alway a bit of a torturous process, with lots of trying and correcting. Andi and I spent a whole afternoon for each of our planes, before glueing in the 6mm aluminium pins and letting the epoxy cure overnight – and hoping that the wings release again (we liberally applied wax to the fuselage to avoid this) and the fit is correct. Fortunately all went well.
Next step was to make the perfect fit between the wings and the fuselage. I used epoxy thickened with microballoons in a syringe, pressed in the space between the wings and the fuselage (after waxing the fuselage to avoid the epoxy sticking to the fuselage rather than to the wings). Then I spent hours sanding down the abachi on the wings, to get a nice and even surface, leading edge and trailing edge.
After making some corrections to the leading edge (there were some minor holes that needed filling with epoxy and micro balloons) the wings were covered in 49gr. glass, one side at a time. The glass was applied diagonally (for extra torsional stiffness of the wings). It was fixed with whitened epoxy, thinned down significantly with alcohol to allow the epoxy to be applied with a foam paint roller. The wings were left to cure hanging with the trailing edge down to avoid deformations.
Once cured, the wings were lightly sanded (220 grain). We then applied two coats of primer. The first coat with a spatula, pushing it into the glass structure (to avoid visible pinholes after spray painting), the second coat using a foam roller. Once the primer hardened out we spent some awful hours sanding it down again, almost onto the glass. For sanding we first used a machine with 220 grain paper, then finished the sanding by hand, using wet 400 grain paper.
A few minor flaws were corrected with spray primer, the wings are now ready to go off to the paintshop.
One of the things I like least is building the canopy frame and fitting the canopy. It’s a lot of work and so much can go wrong. The canopy frame is now done and ready to fit the canopy. The frame was built on the fuselage, as follows: 1) prepare the front pin, so that it can be epoxied straight into the frame (3mm steel, bent at the end); 2) carefully wax the fuselage on the area where the frame is built up – I use three coats of wax, slightly polished in-between; 3) apply thickened epoxy resin on the area where the frame is built up, let this cure a few hours; 4) prepare 10 carbon rovings (24K, 1600tex) for the full length of the canopy frame (around the entire frame) and soak with epox; 5) build the frame with the carbon rovings on the thickened epoxy (I apply two rovings at the same time) and let the epoxy cure again for a few hours (so that the rovings don’t “swim away” during the next step); 6) build up the rest of the frame using epoxy thickened with lots of micro balloons (and also a bit of colorant if you wish); 7) let the whole thing cure for 12 hours at least.
Important: after curing, but before releasing the frame from the fuselage, I drill the hole for the canopy lock. The canopy lock I made with a 1.5mm pin, soldered with a brass tube to a 1.5mm steel wire.
After this, it’s lots of sanding the frame to shape, then painting it, before glueing on the canopy. More on that later.
In-between other tasks I’ve been working on the instrument panel. I’m grateful to some of the colleagues on Facebook, who helped me with pictures and details, such as the text on the compass deviation table. I’ll attach the panel to the fuselage using velcro, so that it can be removed for access to motor and ESC. While looking for the correct instruments for the panel, I came across the excellent website retroplane.net, which has full instrument panels as well as vectorised instruments available for download.
I finally got to put most of the bits of my VT-16 Orlik together.
Unfortunately I had a mishap with the wings. When cutting the foam cores we forgot to cut the angle to the fuselage, leaving it at 90 degrees. As we started building the wings before we had the first fuselage, we didn’t notice this mistake until we tried to fit the wings to the fuselage and had a 12mm gap at the trailing edge on both wings. Fortunately this wasn’t too difficult to solve (with a big saw), but did take a few hours of unnecessary work.
A lot of work to do still, but it’s always very motivating to see the result of so many hours of work.
In-between working on the wings with Andi, I also installed the motor bulkhead and the landing gear into the fuselage of my Orlik. The bulkhead and landing gear frame were cut out of 4mm plywood and fixed with thickened epoxy resin. The motor bulkhead has a ring of carbon roving around it for extra safety. The bulkhead is installed at a 3.5 degree downward angle to avoid the plane pulling up excessively on full throttle.
For the motor we will be using the Dualsky XM5060EA-14SE. We’ve used this motor or its predecessor in most of our previous builds (the Urupema, JS3, and also my SZD-54). I really like this motor. It is sufficiently powerful for our use and especially also very quiet. We will be running it on our usual 6S setup (either with a 2x3S 3300 or a 3700mAh battery, depending on how much weight we will need in the nose). If all goes well the weight of the motor and batteries will be enough to avoid having to add much further weight to the nose.
Over the past few weeks Andi and I have been building the second and third pair of wings. We built them in the usual manner: foam cores, with carbon wing spar and carbon D-Box and carbon inserts over the control surfaces and a kevlar triangle over the area with the wing joiner. Andi built the upper sides of all four wings (we always build them “upside down”). We then “closed” the lower side together, after cutting the wiring channels and inserting the various carbon spars. The wings spent 12 hours in vacuum (-1.5 Bar) to cure. The result looks good, especially after an afternoon “sanding session”, where we sanded down the abachi wood on the wings to get an even surface and nice leading and trailing edges.
Today we release fuselage nr.2 (mine!) from the mould. Cracking open the mould and checking the result of almost a full day of work (the 2nd fuselage took us 6 hrs) is always an exciting moment. It came out without any major flaws and is 20gr lighter than the first fuselage. Nr.3 is due to be built on Monday. After that we’ll finish work on the 2nd and 3rd pair of wings – the upper sides are already done, but we’ll need four half-days to insert spars and close the lower side of the remaining wings. More on that later.
Yesterday we built the second Orlik fuselage. We’ll take it out of the mould tomorrow (we usually let it cure for around 48 hours). While waiting for the fuselage to cure I’ve assembled the landing gear and started preparing the electronics for the fuselage.
The landing gear will be very similar to the one we built for the Urupema, two glass boards held by aluminium rods, a 100m wheel, hinge up front and suspension with rubber bands at the rear. Georg arranged for one of his contacts to cut the 3mm glass board on his CNC milling machine.
As for the electronics in the fuselage, we’ll be using the usual components: an MKS HV6130H Servo for the elevator and a Chocomotion/Fox 12/9.5 for the rudder and towhook. The rudder will be operated using our usual pull-pull system with a kevlar wire. The towhook is the well tested self-built version. I’ve also prepared the plate and screw for the bungee hook, also standard equipment on all our gliders (we launch our larger gliders using a bungee system on our airfield).