Electric thermal soarer
|Pete B - Moderator||03/06/2014 17:01:43|
7625 forum posts
Since my old Ripmax Nebula disappeared into a cloud last July, never to reappear, I've hankered for a bit of performance in marginal conditions. Now the Nebula, being what it was, was never going to be anywhere in the performance league but it was enough for what I wanted.
'Hook a boomer' and thermal soaring can be all too easy, so scraping 20 mins in marginal conditions can be just as, or even more, satisfying. My Phoenix P2000 is OK-ish when the lift is good but flights often tend to be straight up and down - a foamie will never really 'cut the mustard' for thermal soaring, IMHO.
I've been browsing the Net for a while and, reassured by Andy's thread over here, by reading a few German and Dutch forums and prompted by an early season sale, I bit the bullet on a Reichard Champion from Staufenbiel.
The spec was right with a GRP fuselage, built-up 2.74m span wings, about 10oz/sqft wing loading and the reported ability to penetrate a moderate breeze.
The package was duly delivered promptly and the contents, whilst not perfect in every respect, certainly didn't disappoint. The wings are a thing of beauty, with an attractive tapering planform and a tad of dihedral introduced by the elliptical tips;
Nicely finished wings, with the translucent Oracover well-finished and not a wrinkle or bubble in sight. The ailerons are already top-hinged with Oracover, as is the elevator. The fuselage has a rather noticeable seam but it doesn't detract too much from the appearance and is reinforced with a 1cm wide CF tape running the full length on each side of the fuselage.
A fairly comprehensive hardware kit is included:
Propulsion-wise, I couldn't bring myself to invest in an MVVS but a while back I had pushed the button on the HK Turnigy Gliderdrive 840Kv canned brushless, which I'm proposing to pair with a 14x8 folding prop and a Hobbywing Pentium 60A ESC, running on 3S.
The motor bears a remarkable likeness to the MVVS offering, admittedly - now whether it delivers the goods remains to be seen.....
The Champion is a later development of the Ellipsoid, which dates, I believe from the early 2000's and which is a mid/shoulder wing design. The Champion was essentially the same but has the wings mounted on top of the fuselage, which neatly avoids the head-scratching and contortions in getting a pair of wings to neatly and securely butt up to the fuselage. In short, it's simpler to get it right!
In either case, being from the NiMh era, the battery arrangements are designed around an 8 or 10 cell pack, with an angled bay extending from the rear of the cockpit to about mid-chord of the wings, the intention being that in the event of a heavy landing, the pack would be ejected through the cockpit to minimise the damage - yes, of course....
Anyway, in the LiPo era, things have changed, so to use one of the LiPo advantages - weight reduction - it is necessary to have a re-think about component location and adapt the cockpit fit to suit. Moving the pack forward will eliminate, or at least reduce, extra noseweight to set the correct C of G.
More on how I'm going about this in the next post.....
|Biggles' Elder Brother - Moderator||03/06/2014 18:25:38|
15748 forum posts
A very cool looking glider Pete!
|Pete B - Moderator||03/06/2014 18:29:11|
7625 forum posts
OK, let's start from the pointy end and the motor mount has to be the first item on the list. I was a bit surprised to find just a disc of GRP board supplied - surely that alone wouldn't cope with the rigours encountered around the motor and prop? Apart from that, it would probably require some additional reinforcement from within the fuselage to ensure it remains attached to the hull. At just 1.5mm thick, it doesn't present much gluing area on the edge.
My solution was to add a disc of 3mm birch ply to the disc, which significantly added to its strength and vastly increased the glued area of the mount. The GRP mount was pre-drilled in all the right places for my motor, which was a bonus but it was quite a bit oversize for the hole at the front of the fuselage.
One solution would have been simply to fit the mount in the fuselage as supplied and cut off the excess material but this would shorten the nose, increasing the weight needed to set the C of G. Prior to bonding the ply to the GRP, I mounted the GRP disc on some 12mm studding, fitted it in the pillar drill and sanded it down to a diameter which almost reached the edge of the nose aperture. I had to bear in mind that there would be side- and down-thrust set, so 2-3mm shy of the opening was about right. Once bonded, the sandwich was then turned so that the ply was slightly chamfered to follow the contour of the fuselage. The cooling holes were also drilled and Dremelled through the ply as well.
Satisfied with this, it was time to fit the mount to the fuselage. 2 deg right thrust seemed about right but reports on various forums suggested 2 deg downthrust was insufficent to minimise the tendency for the model to nose-up on full throttle. I decided to make it nearer 3 or 4 deg - yes, it's easy enough to program in some down elevator if necessary - but if it can be done mechanically in the first place....
30 min epoxy with micro-balloons provided the necessary stiction - and the studding was ideal for eyeballing the offset required - it's not quite as extreme as the photo may suggest!. Once dry, the studding was removed and the excess material sanded away, leaving a nice flush face for the spinner. I'm happy that I've now got a very sturdy mount, well-capable of handling the forces of a rotating 14" prop. The ears either side have been Dremelled out too, to provide some ventilation to the motor.
I had decided to discard the supplied ply NiMh mounting tray shown just above the nose in the first pic of the thread and instead fit a ply floor in the cockpit, screwed to four beech blocks epoxied to the fuselage sides, to hold the LiPo pack:
The ply tray was set high enough in the fuselage to allow the ESC to be fitted beneath, leaving about 15mm or so of free space below the ESC for cooling air to pass. The red wire on the heatsink is a Spektrum temperature sensor for telemetry feedback. I haven't cut lightening holes in the ply tray as I felt it would possibly weaken the tray and the small amount of weight saved would be of no value:
Moving back a little further, the rudder and elevator servo mount ply had been supplied and was used. I'd have been happy to use a mini-sized rather than standard servo but I had a couple of Towerpro SG-5010's to hand, so they'll be going in. Immediately in front of the servos, I fitted a ply tray, at half fuselage height for easy access, which will hold the Rx, telemetry module, altimeter and variometer:
That'll do for now - the gentle waft of chicken Bunha from the slow-cooker tells me dinner is ready.....
|Pete B - Moderator||03/06/2014 21:50:09|
7625 forum posts
Inner man refreshed with the chicken Bhuna, I'll move on....
Time to fit the rudder and elevator linkages. Nylon snakes are supplied in the kit and despite them being quite slippy, by the time the inevitable bend was induced at the tail, the friction had increased to the point where it was noticeable, so I adopted my usual practice of binning the inners in favour of 22SWG piano wire. Not frictionless but rather better than most snake inners, I've found, and sufficiently rigid at the outer ends to avoid any lost motion through bending. The ends are well cleaned and soldered to M2 threaded connectors, allowing clevises to be fitted.
I also had to consider the rudder and elevator horns. The elevator system, employing a bent wire in a piece of tubing attached with covering film to the elevator, didn't seem that clever to me, so in common with many other builders, I substituted it with a conventional horn. Not having a suitable ball-link, I aligned the horn and used a standard steel clevis, once again discarding the supplied plastic clevis. The supplied rudder horn, from GRP sheet, was also discarded in favour of a commercial horn.
First of all the outers were fitted, with lots of filing to give as straight an exit through the fuselage as possible. The snakes were roughened where they contacted the fuselage and epoxied in place, some masking tape being used to keep the surrounding surface clean:
The finished result:
Next stage was fitting the rudder post. As with Andy's build, the tailplane platform induced a significant tilt - mine was such that the tailplane was noticeably leaning to the left compared to the wing. Efforts to induce a correction by clamping just didn't work for me and the fin was correct otherwise so I went ahead and epoxied the rudder post in place, using plenty of clamps:
Once dry, I added a strip of 1/32" ply to the left side of the tailplane platform, which has resulted in everything ending up straight and true:
|Pete B - Moderator||03/06/2014 23:12:09|
7625 forum posts
One day I'm going to have a radio installation to be proud of.... I always seem to end up with odd wires looking untidy - and this installation is no exception
I'm using an AR9300 Rx, rather overkill for this model, which is just using throttle, ailerons, spoilerons, rudder and elevator but it's what I have available and suitable at present. That is coupled to a TM1000 telemetry module, providing the downlink to the DX9. A Spekky altimeter will provide height information and a Winged Shadow Thermal Scout provides the variometer function. I hope to replace these two modules with a Spekky variometer once it arrives from the States. As mentioned earlier, ESC temperature will be monitored, as will Rx volts and fade/hold events.
The rudder and elevator servos have been installed and one EZ connector fitted. I know they don't find favour with everyone but provided they are fitted with care and threadlock used where appropriate, I've found them completely reliable - and they make installation and adjustment very straightforward. The satellite Rx is mounted on the far wall with the aerial extending into the rear of the fuselage. Below that is the altimeter with the AR9300 to the right. These are all mounted using Velcro pads. The two cables disappearing over the far side are 10cm extension leads from the Rx, to make connection to the aileron leads a simpler process when assembling the model:
Looking from the other side, the TM1000 module is mounted on the floor, with the Thermal Scout module on the side wall above. The Ar9300 Rx is designed for carbon fuselages, with the option to mount the aerials externally on fairings. Given the limited amount of carbon in this fuselage, I've resisted the temptation to start drilling holes just yet and I've settled for one aerial facing fore and aft in the cockpit and the second laterally on the floor under the C of G position. If range tests show any issues, I'll mount them externally.
The next job is to install the aileron servos and leads....
|Biggles' Elder Brother - Moderator||03/06/2014 23:44:32|
15748 forum posts
Nice work Pete. Quite crowded in there isn't it. I think under the circumstances you'd done well with the wiring.
I was just going to ask about the CF tape and the aerials - but your excellent and thorough blog forestalled me!
Edited By Biggles' Elder Brother - Moderator on 03/06/2014 23:45:00
|ken anderson.||04/06/2014 07:47:24|
8544 forum posts
very nice pete.....thanks for sharing your put together with us...
ken Anderson ne..1...... sharing dept.
|David Ashby - Moderator||04/06/2014 12:43:58|
10948 forum posts
Looks good to me Pete
|Pete B - Moderator||08/06/2014 00:38:01|
7625 forum posts
On with the aileron servos. Staufenbiel recommend their D 260 2.8Kgcm 20g MG servos (similar in size and spec to the HS-82MG) but, considering the ailerons are not particularly large on the Champion and encouraged by positive reports, I've used HK939MG servos - a tad less powerful at 2.5Kgcm but metal-geared and only 12.5g.
The aileron servo mounting system, in common with many sailplane installations, is relatively simple - just glue the servo into the recess in the wing. Well, of course, it isn't quite that simple - it never is!
Slender as the wing is, there's not a lot of room for spare cable within the wing and the small size of the cable aperture in the ribs precluded using an extension lead connector, threaded through the wing, so the servo and extension leads were cut and soldered to a suitable continuous length.
Reichard helpfully supply some nylon monofilament pre-threaded through the wing D section and tape it to the root rib and servo bay, with a loop at the bay end. The plastic moulding of the JST plug was removed from the end of the extension and the monofil loop, with a bit of masking tape, was connected to the JST pins and pulled through. Even with the narrower section, it required a bit of patient shuffling before the pins appeared at the root.
The second wing would have been done the same way - but the monofil came away from the tape and disappeared inside the wing.... Now, my normal method is to tie an M3 nut to a bit of thread and drop it through the wing from root to bay - easy! That wasn't going to work this time, so, after a couple of minutes head-scratching, I attached some thread to the end of a length of piano wire, poked it down the wing to the bay and hooked the thread out with another bit of wire - success!
Now I was back in business. The servo bay base is the inside of the top sheeting - just a single skin of 1.5mm balsa - so I decided to reinforce the sheet with a rectangle of glass cloth epoxied to it. This makes a much sturdier mount for the servo and hopefully reduces any chance of the glue joint failing in service. This bay had already been done - the cloth is for the other:
I'll tidy up that messy bit of ironing, I promise! I was trying to do three other, non-modelling-related, jobs at the time..
Once that was dry, it was relatively simple job to wrap the servos in masking tape, roughed-up, and then mix up some 5min epoxy with micro-balloons and snug the servo into place - remembering to check the servo for serviceability, enlarge the arm hole for the 2mm pushrod, centre the servo and fit the arm retaining screw first! Looking at how that 31mm high micro servo fits in the bay, I'm sure anything larger would be a bit of a squeeze:
I've not used the supplied GRP servo arms - they were slightly oversize for the depth of the aileron, anyway. I've used Radio Active Small Control Horns which I had in the bits box.
The servo cover will be taped on once final setting-up is done.
|Pete B - Moderator||08/06/2014 00:40:12|
7625 forum posts
Now, back to the elevator horn arrangement. Once I'd connected everything up, things were not good. The moulded snake exit on the side of the fin was calculated for the designed connector - the bent wire in tube arrangement. As a result, using the outermost hole on the horn to minimise throw to +/- 6mm meant a fairly significant deflection of the 22SWG snake inner.
The effect was that I had two neutrals, depending on which way I moved the elevator - and they were about 3 mm different.... Clearly this is undesirable, so more head-scratching....
Eventually I came up with the following solution. I cut down a spare horn to a crescent shape, making a single clevis hole with sufficient clearance for the clevis movement. This was fitted further rearwards on the elevator, well behind the normal hinge-line. I also increased the snake inner gauge to 20SWG to reduce the risk of flexing with that unsupported length:
The net result is that I've reduced the disparity to negligible, fortunately - although it's far from the most satisfactory installation I've ever made...
We'll see how it goes.....
|Pete B - Moderator||28/06/2014 13:32:22|
7625 forum posts
Apart from taping on the servo covers (no photos) that was the Champ effectively finished - and very pretty she looks too
Terry came up for a day's flying a week or so ago, so with all pre-flight checks done and with 428W and 37A on the 14x8 prop, with a 3S 4000mAh Zippy Compact, putting the C of G at 60mm from the l/edge, I had no choice but to maiden it, which was a rather shorter flight than anticipated:
11637 forum posts
I cannot see any airbrakes or the possibility of crow braking, am I wrong?
Nice looking model though!
|Pete B - Moderator||28/06/2014 22:44:56|
7625 forum posts
No, you are correct, Erf. Just ailerons on this one, which have been set up as spoilerons to kill a bit of lift when necessary.
There are few English threads about this model - most are on the German and Dutch forums - and the general concensus is that the spoilerons are adequate. Given a long low approach, I didn't find landing a problem the other evening, so once the spoilerons are properly set up, it should improve further
I've got a flapped sailplane nearing completion at present and I was looking for a straightforward replacement for the Nebula, which would give me some relaxed thermalling - I think I've found it!
11637 forum posts
I have been pondering this assembly over a few days now.
It has struck me that it was more of a build than a simple assembly.
The other aspect that is exciting me, is the motor, I will be considering one myself for my Erfolg glider which at present has a Vector canned outrunner (rated max of 40 amp), which has to date provided a very lack lustre performance, particularly at this moment, where expectations have moved a lot in the past 7 or so years.
I do hope to read more about the motor performance as you experience the model.
With respect to air brakes, these days I will not go very high without them, but then again I never get high.
I guess being a modern model, the camber is very low, to provide a good speed range without ballasting. Is it this that will be used to get down? Reflexed draggy tips and high speed, shallow dive?
Edited By Erfolg on 29/06/2014 12:10:49
|Pete B - Moderator||29/06/2014 13:38:36|
7625 forum posts
Yes, Erf, it's a bit more than 'Plug and Play'
Fitting out a GRP fus is rather different from a balsa/ply construction and requires a bit of imaginative thinking sometimes.
Early days for the motor so far. There seems to be plenty of power but I don't think it sounds quite as smooth as I would expect an MVVS to sound - there's a trace of harshness at at one point in the throttle range.
The spoilerons should help with encouraging a descent but on the occasions when I've encountered massive lift, where no amount of braking will bring it down, I've found the only guaranteed way of getting out of the lift is to put in a couple of clicks of down elevator trim and fly in a straight line, upwind. I clean up the wing to speed up the process - the quicker you get out of the lift, the better. As you know, steep diving is a no-no with thermallers!
4318 forum posts
Spinning is probably the best, safe method of bringing down a glider, that's not equipped with dedicated spoilers of some type, when it's got too high for comfort. Spinning is more effective than spoilerons & of course can also be used with R/E only models.
I find side-slipping a very good method of landing in restricted spaces. Again often more effective than spoilerons & possible to do with R/E models.
Edited By PatMc on 29/06/2014 21:21:04
11637 forum posts
I certainly agree that S3021 is a good section, my own EMP 3m Algebra uses the section. I had not thought of reflexing the ailerons to increase drag, limiting speed and reducing the effective lift. Txs just did not have the functions available today on quite low cost RC equipment. My Algebra does have trailing edge training edge plate type airbrakes. The trouble is that the brakes are operated via fishing wire trace wire, works, yet is not particularly engineered.
I used to like E205, although the speed range is not as good, without ballasting and you cannot do that once launched.
These days I like MH 32, low camber thin and really has a good speed range, it is only in totally dead air that a floater can compete. Allthough by flapping, just 1 or 2 mm, it becomes a pseudo floater section
I know that there many who believe that spinning is the answer, my own opinion is, I cannot be sure that it is a true spin when at a great height, Just as possible is that I would be in a spiral dive, from which in the past I have seen models break up. I have also heard the argument, go inverted, the higher drag will bring you down. Again, when you cannot see the model clearly, getting the most thermal gliders inverted and keeping it there is a lot easier to say, than i can do.
One of the problems I used to encounter is that once at height, the width of a thermal was often massive. Just simply cruising out of the thermal often just did not happen. You had to get the speed up and shift possibly 1/2 a mile to be confident you were not in good air. To do that a section like S3021 permitted made this viable. The real issue (back then) you needed to have marked your trim with a fast cruise mark. Or if you did what i did the once, lean on the stick, more often and not, you became aware that your model was not there any more, oh, the wings are fluttering down and what is that screaming noise, did the earth move then and the subsequent sentence, I cannot get the fuselage out of the ground, which becomes, well that CF and Kevlar really is strong.
It will be very interesting to read about how you have set the model up, and how it gas performed.
|John Norman||30/06/2014 14:22:00|
|5 forum posts|
Splendid machine Pete......you moved the aerials so they end up outside the fuz.......are those little plastic supporting thingies purchasable bits of kit, or did you make them? The angled plastic bits supporting the aerial ends I mean
|Pete B - Moderator||30/06/2014 15:16:58|
7625 forum posts
They come with the AR9300 Rx, which has extended aerials for carbon fuselages, John. That Rx has now been replaced by the AR9310. The antenna exit guides can be purchased separately. I'm sure, with a bit of Googling, similar can be found in the wider RC market.
I'd agree with Pat that a properly developed spin is probably likely to cause least stress on an airframe. However, particularly at a distance and with a conservative C of G, it is much more likely to become a spiral dive, which will surely re-kit the model long before it reaches anything hard and unforgiving, as Erf points out....
I'd rather fly purposefully upwind, with just a touch of down trim (not 'leaning on the stick', Erf!) and at some point the lift will become sink. If it's not happening, then just fly crosswind until it does. All the time, the model is descending and, most importantly, it is in one piece. Sooner or later you'll be out of the lift - and then you can let the old ticker slow down...
|Andy Butler||30/06/2014 16:00:01|
455 forum posts
Good thread Pete. Mine needs fitting with a new X8R receiver and I have a vario and voltage sensor to go in too. Interesting that the motor is not so smooth. I did baulk at paying out for the MVVS but I have to say it was well worth it, it is exceptionally smooth and eerily quiet on a 12 x 8 folder. I see you have gone for the next size up - mine is the 3.6 960 and she climbs very well on that so yours should be very spirited. I had the same issue with the actuation of the elevator and ended up fitting a ball link as there was a little sideways movement which seems to be working well. As you have found, it has a very flat glide and getting down from height or at least out of lift can be a problem. The only time I have had it scarily high, I used the throttle trim to start the motor at just a few rpm's as the extra drag seemed to help along with the spoilerons and a very small amount of down had her in sink and down fairly swiftly.
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