Thread Tools
Sep 16, 2019, 12:46 PM
DavidsPlanes
doxilia's Avatar
Douglas,

in post #12 you uploaded the picture of the kit using the RCG picture upload function. You also "hard posted it" (inline with your comments as seen in my previous post above).

It's nice in a build thread to use the RCG upload function as it allows larger pictures to be viewed (rather than small inline pictures) and it also results in RCG keeping a log of the build in pictures only. This way, if someone wanted to view your build from start to finish in pictures, one can bring up the "show all pictures" function and see the build without having to go through each post page by page. If you bring up the show all pictures now, RCG shows only 5 pictures to the thread - two of yours and three of the Magic 20 scratch build posted by someone else.

Just a thought as you may not be fully familiar with the functionality of RCG.

David
Sign up now
to remove ads between posts
Sep 16, 2019, 12:52 PM
'Douglas' to his friends.
Thread OP


Not long to wait now, I hope, to receive the wood needed for continuing. We can mount the empennage, but will then be on standby. Come on, postie..!
Sep 16, 2019, 03:33 PM
DavidsPlanes
doxilia's Avatar
Douglas,

Are you an Englishman living in France?

Nice area you chose!

David
Sep 16, 2019, 04:13 PM
'Douglas' to his friends.
Thread OP
Indeed, and have been enjoying the area for over forty-five years. I sometimes think I even understand some of it..!
Sep 16, 2019, 04:13 PM
Registered User
Steve Merrill's Avatar
Nice choice! You have good taste in models. I built a Mini-Curare, Mark Ritinger design. Flies great! foam wing and balsa fuse, e-powered with about 200 watts. Flies like its on rails.... I got a picture or two of it somewhere on this site.
Sep 16, 2019, 04:59 PM
'Douglas' to his friends.
Thread OP
Sep 17, 2019, 06:56 PM
'Douglas' to his friends.
Thread OP
I've rubber-banded the parts in their respective positions, and glued 'em up...



Once set (tomorrow, probably...), I'll take the assembly off the fuselage and add the inner bracing struts. It'll be ready, as a module, to be offered back up to the fuselage once the turtle-deck is done, and carved to profile. I just need that 1/4" stick for that...

Sep 19, 2019, 06:22 PM
'Douglas' to his friends.
Thread OP
Here's the tailfin released from the bands, and the bracing struts glued in place...



Meanwhile... Good News, the blocks of balsa have arrived ...



... to be immediately rough-cut on the band-saw ...



By coincidence, the two parts (the chin and the nose hatch...) can be cut from the same piece, so very little waste.
Our Eldest sets to forming the tailfin TE, using the pillar drill as a spindle sander ...





...whilst I prepare a servo deck ...



...which gets glued to supperts, in turn glued to the flanks ...



Useful things, lump hammers ...

A trial fitting, and a test of the system to join the separate elevator control cables, using a stripped-down electrical domino ...



They're just test pieces of cable for now, the definitive ones will be installed a bit later, once the outer sheaths are in place (the blue tubes in the foreground...).
I think that that's all for this evening; it's been a long, but fruitful, day, but now I'm tired. 'Night, all.

Sep 22, 2019, 01:00 PM
'Douglas' to his friends.
Thread OP

Help with nose wheel retract, please..?


Good evening ...
Posted elsewhere, but as it's Curare related, I'll repeat the request here ...
I've received the chosen retracts for this 'plane (Turnigy MCR All Metal Retract System, Small...). I want to install 3mm legs, and had no problems removing the original 3mm 'leg' from the two wing units, by backing off the two grub screws 'hidden' in their bronze bushings.. Not so easy for the nose wheel unit, though. There are no grub screws in the bushings; the 'leg' is held in place by the steering collar. This I was able to remove easily enough, but the 'leg' still refuses to come out. It appears, from close inspection, as if the inner end of the 'leg' has a flange, which prevents forward movement, and therefore extraction.
I have seen photos of others that have succeeded in fitting a 3mm nose wheel leg, so I assume that it is possible to remove the original 'leg'. How does one do this..? Does everyone have the same issue of the inner flange preventing it from coming out..? I don't wish to start disassembly of this unit if it can be avoided, but will do so, if it's the only way of removing this 'leg'. Do I have to resort to such measures, or have I overlooked something..?
Thanks in advance for any information or assistance offered; meanwhile...

Have a nice day

Douglas
Sep 24, 2019, 09:07 PM
'Douglas' to his friends.
Thread OP
Not well, so slow progress. There's Good News, though : I've sorted out the retracts conundrum, and ordered a set of (I hope...) suitable legs for this 'plane, to be delivered in a couple of week's time. Now to see how to fit them; it's not a simple operation, at least, for a first-timer such as I. I'm trying to avoid pitfalls; another reason for slow progress.
Still, the system will have to be installed, so, to that end, I've made a simple mock-up of the nose-wheel, as 'proof of pudding' for the dimensions I've ordered, and also to see exactly what needs building to support all of this. Here's my nose retract in its extended position with a dummy leg (a carbon tube stuffed with a bamboo stick, drilled for a 2mm plastic 'axle' and a 45mm wheel, held on with a rubber band...)...



... and again, retracted ...



This shows me at what level I need to install a ply floor to which I attach the unit, and at the same time how much and where I have to gouge out the 'chin' block for passage of the retract motor, which protrudes forward. It confirms, retracted, that there is also adequate clearance for the wing LE. It has been a bit of a gamble, but it looks as if it may come off, unless I've overlooked something critical. I've not gone into positioning of the steering command as yet, for example, but I think it'll work out.
From these experiments, I've decided where to put the floor pan, and have jigsawn and formed a piece of 5mm ply for the job. Here it is, dry-fitted...



In the foreground is a balsa block, with the shape traced on it corresponding to the lower cheeks. Those supplied are too narrow, and slightly too short, so instead of trying to 'bodge' something, I'll ask Our Eldest to bandsaw fresh blocks from this piece. Maybe tomorrow..?
I'm still waiting for the 1/4" sticks for the dorsal spine, so as to get on with the turtle-deck. I've also ordered the covering film that Our Eldest had asked for. That'll take a week or so to come, too, and I need to have it so as to pre-iron film around the control rod exits and hinge points. These delays are just as well, really; that'll give me time, maybe, to find some more energy from somewhere..!
Sep 24, 2019, 11:28 PM
DavidsPlanes
doxilia's Avatar
Douglas,

Nice progress.

Given the lack of a fuel tank it’s nice that you can raise the nose gear floor in order to better accommodate the nose wheel. My quick reaction to your photos without actually seeing the retract unit is that this unit is oversized and designed for a larger 5-8 lb model. If you compare your unit to the mechanical retract shown on the plans, you’ll get a sense of scale comparison. The typical e-tracts used on 45-50” span models such as the MK series are those sold under the E-Flite 15-25 brand and the many clones also made in China sold on eBay, HobyKing and elsewhere. Struts and axles should be 3mm but no more than 3.5 mm. Anything thicker is simply adding unnecessary weight. The nose gear on those units is slightly larger than the MK mechanicals shown. Here’s a link to the nose unit:

https://www.towerhobbies.com/cgi-bin...?I=LXHPFW&P=ML

And the mains:

https://www.towerhobbies.com/cgi-bin...p?I=LXHPFJ&P=7

On the bottom nose block, note that you can save considerable amounts of wood by simply making two identical “sides” per the side view profile cut away from your block or from 1/2” (or perhaps 3/8”) stock. Note that if you cut an entire block that goes from side to side you’ll simply end up removing the material in the middle to provide access to the nose gear, the retract unit and it’s cylinder (if you use this unit) as well as for cooling the motor which I presume you’ll do from the bottom in order to better preserve the lines and appearance of the model from above. In short, it’s easiest to first install the gear (motor, retract, ESC) and then build “around it”, if you will. In fact, the formers are actually designed with this in mind whereby you attach the two side pieces and mate them flush up against the lower extensions of the formers. The plans show an optional “cover piece” of balsa to close off the bay between the lower mount plate and the wing LE former in case the fixed MK nose gear is used instead. If you need a small block to span in between the sides in the front to taper into the nose ring and aft of the former for wing LE support (it’s really for aesthetics as the wing is held by a LE dowel or two. Two dowels usually better where a nose wheel is found in the area when retracted.).

I also recommend you find a way to install the steering servo in the retract bay as it will make your life much easier than running a flexible pushrod from a remote servo. This is often best accomplished using a mini servo or a thin wing servo mounted on its side out of the way of the wheel in between the retract unit and the axle. Some folks will notch the ply plate to directly mount the servo vertically “into” the floor but this will probably adversely affect the space above reserved for the 4s (usually better than 3s on these models) LiPo.

Lastly, it appears as though you are allowing yourself a fair bit of prop clearance. 5.5” from thrust line to ground should be all you need as this provides a 1” clearance (enough for trike models flying off hard top) on a 9” prop. IMO you shouldn’t run a prop larger than a 9x6 on a model like this. Personally I’d probably run an 8x8 (so 5” total clearance needed) on an EF1 type (~1200 KV) motor on 4s, of course, you might have something else in mind.

Final comment. Be very mindful of weight gain on these small models particularly on the fuse as the overall weight is usually slightly higher for electric versions unless one is diligent in removing weight where it’s not necessary (given the lack of glow engine vibration). These little classics are a blast but keeping wing loading in check is a must. Ask me how I know this - school of hard knocks (building and flying wise!).

Just my 2c worth given my long-standing interest and passion for these 20 size classics.

David
Last edited by doxilia; Sep 24, 2019 at 11:46 PM.
Sep 25, 2019, 06:05 AM
'Douglas' to his friends.
Thread OP
Thanks, David, that's very encouraging, and helpful. I'd like to respond to a couple of your comments, if I could, though. Time, and Our Eldest's landing ability, will be the final test of these retracts; they're a 'first' for us, and rather experimental. I'd like it noted that these are, in fact, the 'small' version, smaller than the profile indicated on the plan I'm using (but not by much...). They are also four times less expensive than the ones linked to above, and are all metal in construction. Being the 'small' version, they will only accept 3mm struts, of which there are far fewer models to choose from. I finally ran down a set from a well-known Chinese supplier, but they took quite some researching..!
I've noted the remarks on steering servos, and was going to see how to reduce the length of control rods this evening. I'm assuming that there's not much effort required, and that a micro-servo will suffice. The photos I've seen of other builds have the steering physically linked to the rudder servo, but I'll be using a dedicated servo, locally mounted. I'm not sure, though whether to link to the rudder command on the Tx, or use a separate knob on the Tx for taxying, without the rudder being affected. That won't affect the Build, though, merely the Tx programming.
I like the remarks concerning the blocks around the nose, and will bear it all in mind when we get to that (soon..!). All the plans I've seen, of all versions of the Curare, use solid blocks around this region, much of which is carved away to create the streamlined profile. The all-up weight of the 'plane is targeted at around 1.5Kg (around 3 lbs...) or so, and the electronics and power system should be lighter than the equivalent IC original. I'm more concerned, for the moment, of keeping at least some weight 'up front', so as to keep the C of G in the right spot, but I'll be able to judge that better only when I get the wings built. Your Lipo and motor specs correspond to what I've prepared for the 'plane, so that's a comfort.
Similarly for the prop and ground clearance. According to E-Calc, the ideal prop will be a 9x4.7, so that's what I'm going for (maybe 9x4.5 or 9x5, though...). An 8x8 would be running towards the upper limits of the motor, but if the future pilot wants even more thrills, it's an option. Let's get her into the air first, then see what, if anything, needs improving.
Again, thanks for taking the time to recommend and add comments based on your experience, it'll doubtless save us from dropping down the wrong rabbit hole. Respect.

Douglas
Last edited by Dad3353; Sep 25, 2019 at 06:11 AM.
Sep 25, 2019, 09:37 PM
DavidsPlanes
doxilia's Avatar
Quote:
Originally Posted by Dad3353
Thanks, David, that's very encouraging, and helpful. I'd like to respond to a couple of your comments, if I could, though. Time, and Our Eldest's landing ability, will be the final test of these retracts; they're a 'first' for us, and rather experimental.
I might have discouraged you from entertaining a 25 size classic as a first retract model but that is not very helpful. Just be mindful that it might pose some challenges. Enjoy the process and your first model with retracts!

Quote:
I'd like it noted that these are, in fact, the 'small' version, smaller than the profile indicated on the plan I'm using (but not by much...). They are also four times less expensive than the ones linked to above, and are all metal in construction. Being the 'small' version, they will only accept 3mm struts, of which there are far fewer models to choose from. I finally ran down a set from a well-known Chinese supplier, but they took quite some researching..!
It is hard to accurately judge scale from pictures particularly if shot at an angle but it appeared that this nose unit was on the "larger side" for a model of this scale. But I stand corrected if that's not the case. Cost for e-tracts for these models is not often an issue as they can be sourced for about $10/unit or so on sites such as HobbyKing and eBay. I only linked the E-Flite units for reference but they are essentially a variation of a very common Chinese unit. The E-Flites come with niceties like struts and axles as well as Y-chords (double or triple) to wire all units to the retract channel - all things that can be handled after the fact by the builder if desired when purchasing low cost units.

While the "all metal" is generally preferable and does indeed provide a more solid retract unit, the additional weight compared to resin cased units may be substantial. Seeing this is perhaps what triggered my comments about being mindful of weight. This is especially so on the Curare 20 as it's among the smaller designs in the 20 size MK lineup. The Curare and Mattlas are the two designs which are what I'd consider true 20 size models (no need for power above a 25 size engine). In comparison, models like the Cosmos 20, Aurora 25 and Kingpin 30 are quite a bit larger and have more wing area and end up about a pound heavier so are also better suited to carry solid retracts. However, the only difference I would consider between these models retract units is the strut gauge. I would still use lighter weight resin retract case units with metal trunnions (well mounted to a solid structure) but would use 3 mm struts/axles on the smaller guys and 3.5 mm on the larger ones.

That said, I'm not familiar with your retract units so even though they may be all metal, they might be reasonable in weight for your C20 build.

Quote:
I've noted the remarks on steering servos, and was going to see how to reduce the length of control rods this evening. I'm assuming that there's not much effort required, and that a micro-servo will suffice. The photos I've seen of other builds have the steering physically linked to the rudder servo, but I'll be using a dedicated servo, locally mounted. I'm not sure, though whether to link to the rudder command on the Tx, or use a separate knob on the Tx for taxying, without the rudder being affected. That won't affect the Build, though, merely the Tx programming.
It's wise to use a separate servo for steering (if one is determined to have it) as it considerably simplifies the setup. It also allows you to setup a rudder/steering mix (provided you plugin each servo to a different channel and you have a capable radio) that engages the steering on rudder input when the LG is extended. Then, when retracted, the mix is turned off and the nose gear stays quiet while the model is flown and the rudder servo is being used. This has the side benefit of also not driving a servo unnecessarily (and its power consumption) while in flight as well as avoid any potential binding while steering the servo in its retracted position. The rudder/steering mix should be mapped to the retract switch: mix on when extended, mix off when retracted.

As for the servo choice, one thing to keep in mind is that while a micro servo is desirable due to size and weight, their relatively weak plastic gears can be broken by a rough landing. For this reason, folks often use a mini-servo with karbonite or metal gears. This is true on larger 40 and 60 size models as well.

Quote:

I like the remarks concerning the blocks around the nose, and will bear it all in mind when we get to that (soon..!). All the plans I've seen, of all versions of the Curare, use solid blocks around this region, much of which is carved away to create the streamlined profile.
Perhaps all plans except the one you're building from... The MK C20 actually doesn't use fuse spanning blocks from the wing LE to the nose ring. Instead it uses two long squarish blocks (a block can easily be made up from a stack of sheets glued together at lower cost) on either side of the forward formers. Note how the formers extend down on your fuse from the tank/lipo floor as well as what is shown on the plans. In this way, MK designs a kit with the needed wood parts for either retract or fixed nose gear. The fixed option simply adds an additional hard plywood plate close to the bottom of the fuse draft backed by a balsa sheet to close the retract bay. If using retracts, these two parts are omitted from the "kit build". and one simply needs a nose block spanning the fuse width forward of the FW. In your case, given the electric motors access desired as well as the need for space for the NG cylinder (motor), you will dispense with most of this block as well. For this reason, I was recommending that you first install your gear and then build around it keeping in mind what access you need for maintenance. If you build up the model you will then find yourself removing much of what you built, shaped and sanded simply to gain access to all the gear you will be installing up front. In short, plan for the equipment needed and build accordingly without too much concern for how "other Curare's" are or have been built. This is also illustrated by Mike's Atlas and Blue Angel 60 builds.

Quote:
The all-up weight of the 'plane is targeted at around 1.5Kg (around 3 lbs...) or so, and the electronics and power system should be lighter than the equivalent IC original.
In my experience you will be hard pressed to meet the 3 lbs AUW once you add a 4s2500 battery or larger, you use retracts and stick to the plans verbatim. You may meet this target if the model is covered, care is taken with the choice of wood and you power the model with a 3s setup. If the model is under 3 lbs, then 3s is a good option (usually involving a larger 9" prop). If the model exceeds 3 lbs, I would recommend a 4s setup on an 8x6" or 9x5" prop to start. The latter 4s setup will provide the power necessary to fly the model well at the slightly heavier weight. That said, the best solution is a 4s setup on a light model.

The reason for the additional weight, all other things kept constant, is that an EF1 motor, 4s lipo and ESC typically weigh more than a 25 size motor and 6 oz (make it 7 including the tank itself) of fuel and a small throttle servo. Of course, this has been my experience but you might have a setup which keeps weight under a comparable glow setup.

Quote:
I'm more concerned, for the moment, of keeping at least some weight 'up front', so as to keep the C of G in the right spot, but I'll be able to judge that better only when I get the wings built. Your Lipo and motor specs correspond to what I've prepared for the 'plane, so that's a comfort.
I don't think you'll have any forward CG issues if you will be putting a heavy 4s lipo behind the FW. In fact, you may need to move the Lipo back in order the achive CG so keep that in mind as a possible requirement. At undesirable added weight, another option is to use a small LiPo or Life battery to drive the radio (instead of a BEC or the ESC) and install this in the tail boom if needed to achieve CG.

Quote:
Similarly for the prop and ground clearance. According to E-Calc, the ideal prop will be a 9x4.7, so that's what I'm going for (maybe 9x4.5 or 9x5, though...). An 8x8 would be running towards the upper limits of the motor, but if the future pilot wants even more thrills, it's an option. Let's get her into the air first, then see what, if anything, needs improving.
Again, thanks for taking the time to recommend and add comments based on your experience, it'll doubtless save us from dropping down the wrong rabbit hole. Respect.

Douglas
Sounds good Douglas. Build on!

David
Sep 27, 2019, 06:05 PM
'Douglas' to his friends.
Thread OP
Remember that large block in the previous photo..? Well, here is what has become of it ...



These lower cheeks are now the right length and width, and will be slimmed down later (much later..!), when we get to streamlining the shape of the fuselage. For now, though, they indicate the space inside for the retracts and stuff. On with that, then.
The former F2 needs to be cut away to allow the forward-mounted motor of the retract unit to pass. I mark out the wood that needs to be removed, and employ a key-hole saw for the horizontal cut through the ply ...



Chain-drilling works better for the vertical cuts, to avoid straining the ply too much...



... and, after a clean-up with rasps and files, the unit can be placed for a dry-run ...



The lower cheeks have to be scultured to cater for the steering arm. It can't be seen in the photo, but I've now glued into the underside (well, it's top-side, really, but the 'plane is upside-down for now..!) a pair of triangle-stock rails for the nose-gear platform. Nothing else is fixed, yet; I'll wait for the oleo struts for that.
What next, then..? Hmm... Whilst I'm at the fore of the vessel, I can have a look at preparing for the motor mount. FIrstly, though, I have to establish the nose former. This is rectangular, and should fit between the very front of the fuselage cheeks. These are too far apart, though, and I'm wary of trying to bend them inwards to meet the former, as there's 3mm at each side to make up. Inspiration strikes; I decide to, rather than bend in the cheeks, to pad them out with a pair of 3mm squares glued to the inside of the cheeks. The former will then fit; any excess wood will, in any case, be sanded away to form the almost circular nose, to match the 45mm spinner to be used. Here the inner cheeks are glued and clamped...



In passing, the steering servo (a 5gr digital metal-geared one...) can be seen provisionally in place. I'll carry on with preparing the nose tomorrow...
Sep 29, 2019, 06:56 PM
'Douglas' to his friends.
Thread OP
Now that the gear unit has its place, it's time to hollow out the chin block. Some tracing and measuring, then a session with 'chisel' hobby blades gives this result ...



A 'dry run', to check that it'll all go together...



... and the chin is glued, pinned and clamped into place...



I'll leave it overnight, and check then that the gear still slides in position, then go on to the lower cheeks. More tomorrow, then.


Quick Reply
Message:

Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Build Log Curare build - Carolina Custom Kits jzanutto Classic Pattern Flying 682 Oct 30, 2017 07:25 PM