I have suffered enough of my buddy Vince's constant, incessant harangue to design one of these. Certainly, the Sparviero is on my "85 favorite airplanes" list, but it is always tough to move one of these over to my "85 favorite projects" list. As such, this model is the one that's interrupting the one that was interrupting the one that was previously interrupted that I finally got back to. Read that again and it'll make sense. Furthermore, readers here may be in for a long post as who knows when I will be done with this thing.

Nevertheless, the model is about 85% designed in 2d CAD (DesignCAD) and have even begun to glue things together. But I digress - here are the specs and the goals for this one:

80" wingspan
Est 10-12lbs
Good fidelity to scale, but field friendly and flyable.
3/4 cockpit
Reasonably uncomplicated to build, plug in wings at root to fuselage.
Multiple operating features: the (4) usual functions plus flap, retracts, torpedo drop, nav and retractable landing light.
I will have to make glass nacelles, cowlings and the canopy area which will be a hatch to get to the batts.
I will probably also have to make my own retracts, prefer electronic but may do air.
Paint everything, no decals

Would like some input on servos, rt now looking at standard Fut 3004's for elev/rud. Need aileron, flap. Comments?

Motocalc tells me that (3) OS 30 size (OMA-3825-750) motors, (3) 12 something props, with (3) 54 amp esc and (3) 3s 3000 mAh lipos will give me over 100 watts per lb at 10 lbs so I have a cushion if it gets porkier. I have the motors, and they are very nice - top cabin as I don't want to screw around here.

Where I am: I have assembled the empennage and have cut some other mostly fuselage parts. I should be starting the fuselage this week. Hoping to have this thing framed by the new yr.

Right off the bat, specifically with the empennage, I am deviating from my own design goals of making this thing easy. The SM.79 (or S.79 as it should be) had a covered (ie: open) framework for its empennage. No simply making a balsa framework sanded to a teardrop profile and slapping some sheeing on it. The ribs, of which there are many, are exposed via their edges poking up into the covering for all to see - both fixed and movable surfaces. Although the fixed surfaces are supported with struts or cable, the challenge here is making stiff movable surfaces and having all the ribs of each line up properly. Plus this nightmare must align properly on the fuselage of course.

I did a capstripped ply rib framework having interlocking LE's for the fixed surfaces but there are really no such LE's for the movable surfaces. These feature interlocking TE's - to keep their LE's aligned I am using interlocking spars set back from the LE that pick up each little rib. The fin was fiddly to keep in alignment until I put the vertical capping on so, looking at (9) ribs for ea stab, I built a jig. Both the fin and stab have alum tubes into which will run CF tube from the fuselage.

I am also using a scale hinge arrangment since it is appropriate to do so at this scale. This necessitated forming 1/32 balsa over a "U" shaped jig for the LE sheeting for the movable surfaces. This in turn picks up the interlocking spar noted above and makes the surface very stiff since a "D" box is formed.

I tried to do sequential photos for each component, even with the

Where I was going with the last sentence of my last post, I will never know. I actually made two sets of stabs. Eagle-eyed viewers will note a change to smaller alum tubes in the finished structure (.300 to .157) as the .300 tubes were overkill and I could skimp anyway since the stab is suported with struts, which are probably not needed anyway....

This going to be nice, love your design lots of fragile pieces that when assembled contribute to each others strength, subbed to this one looking forward to seeing it develop.

Have you any pictures of the CAD design?

Originally Posted by heli_madken

This going to be nice, love your design lots of fragile pieces that when assembled contribute to each others strength, subbed to this one looking forward to seeing it develop.

Have you any pictures of the CAD design?

Yes, I made that very comment to Vince who calls me from Rhode Island every 15 mins for an update.....When I first cut all this stuff out, it looked like there was no way it was going to work. Ea pc relies on ea other pc.

The '79 had movable LE slats and I would really like to do them, but not much room out at the tip. Nevertheless attd is a rough design idea. G Whitehead's book (I love that guy) has a dual pivot walking beam mechanism that was nice, just no room.
Thanks for your comments.

Now get back to work on the 129.
Rob

Congrats on tackling this build Casor.
But sorry you weren't able to finish the others first so as to clear the way.
I can see you were already started when we 'spoke' on another thread... and why you thought your laser was limiting.

I can also see that my comments on spar design were on target.
Please forgive my restating it here, but I mean it from the point of view of saving you money and weight.
As a gratefully ex-architect I do know a little about beam design and urge you to move as much material as you can to either top or bottom of the spar for better effectiveness. (I won't repeat my earlier comments made elsewhere - and you may find my blog on 'mini-waste wings' helpful). All that carbon in the middle of the spar is almost totally wasted material put where it is.
The major stresses are at the top of the wing (compression stresses trying to buckle the material) and the bottom of the wing (tension stress trying to pull it apart) - and this remains true even when the model is inverted except of course that top and bottom are reversed.

It would help reduce the strength needed if you can accommodate batteries in the nacelles with the motors because the more weight you can put out where the lift is being produced the better as it reduces the stresses imposed at the fuselage where most strength is needed. I do realise that this may be difficult to do at this size though. Even my DH Dragonfly at 86" span (8.25 pounds) was too tight to get the duration I wanted (20 mins) into the nacelles - though the 112" Percival Q6 (12 pounds) was big enough for over half an hour flying!

All this is in the hope that I can help you save some weight - although I also realise that if that lovely tail end is adding weight any saving of weight further forward will be of limited benefit, only giving marginal benefits in slower flying and improved performance.

I hope my comments don't seem too negative to you - I only want to help you produce a model that flies as nicely as it deserves to seeing all the effort you are putting in.

Best wishes to you for a great build and happy flying.
Robin

I really need your help on this so thank you again. While I have designed a number of models, none of them have been this large and never a "triple". And also while my father was an mech engineer and alot of it "wore off" on me, I am not an engineer so I need your input on this design. What I didn't show on my orig drawing were the spar caps and have re-posted a more complete drawing. Hopefully this covers the spar tension issue you noted.

I would really like to retain the plug in wing design and I will revisit the nacelles with your idea of putting the batts there. This is a good idea although it violates my "field friendly" goal estab at the outset, plus my homemade LG needs to be there also. But you're right, putting (2) of the (3) 10oz batts in the wings would alleviate stress on the wing.

So please, if you are willing to take the time to look at this, please comment. While I am starting the fuselage this wk, the wing is still "on paper" only so I can do pretty much anything.
Rob

I'm more than willing to help all I can - though being an ocean away doesn't help clarity - even with all the internet can offer us!

I'm relieved that you didn't take umbrage at my comments. I thought you might have felt I was trying to teach my grandmother to suck eggs... stupid phrase - hope you know its meaning.

I tend to mistrust bonding different materials like metal or carbon fibre to softer materials like balsa, besides which Carbon is high-tech, energy hungry and therefore expensive. I have only just for the first time used some as wing joiners on my 115" Short Stirling - and then only because it was available and high-tensile steel wasn't (and was fractionally cheaper). The Stirling has two wing spars and the two wings join on the centre line of the fuselage using one strip of 2mm x 12mm carbon in a brass rectangular tube out only as far as the first wing rib past the fuselage connecting each spar.
The brass tube outer is connected to the top and bottom spars by vertical grained medium-hard balsa and does not need to be any longer once the stresses have been spread in this way.

So I would be looking to do something on similar lines if I was building the Sparviero.
I would think the 1/4" x 1/8" hard balsa would be fine as you show it for the outer wing beyond the nacelles but I would make it stand-alone and not even spar web it for the outer half (the last four or five ribs) of the wing. Inboard of that to the motor I would use spar webbing of 1/16" medium balsa (vertical grain) and increase the webbing to both sides of the spars inboard of the motors. I would also double the spar members in the inner section (gluing the extra inside the main ones) mainly because of the landing shocks but dispense with all other material. I would maybe use ply as the side boxing of the carbon joiners as you are showing (if the sizes you show are what you have, just one length should be enough). And again vertical grained solid hard balsa above and below to complete the box and connect to the spars.

If this is the biggest model you have designed to date what I have said will probably sound far too weak to do the job. If so remember that we have been building in huge safety margins for as long as the hobby has existed and this over-design has inevitably tended to impress us that this is the norm. But, particularly for electric power I reckon what we always used to do was at least four times too strong. Sure it made for strong models but over heavy and they therefore had to fly faster to stay in the air - which makes for a non-scale impression - which would be a shame for your model, which I am sure is going to have every care lavished upon it.

Also of course my comments on the wing have to be taken in context with the rest of the model. Ideally the same criteria used in building a light wing that uses its materials to best effect should also be applied to the fuselage and all the rest of the airframe.

Anyway I would be pleased to hear your reaction.
I think (IIRC) I included a couple of photos of the Q6 wing construction in my blog - and it did occur to me that it may be useful to others if I posted an 'after-build log' for that model as I did for my Dragonfly. There are loads of photos that didn't get used in the published article which I could put on it.
Would that be helpful?

I think I get it here - let me do some work in CAD tonight and come up with a different design and will post another PDF so you can see if I got it right. One clarifiying question however is your ref to using only a single length of 1/8x3/8 CF for the joiner spar in the center, versus my stack of (3). Is this correct? I kind of agree here as this stuff is seriously strong and I also do not want to add any excess weight if I don't have to. Cost is really not a consideration since I already have the stuff and I am used to working with it. I have also employed designs having open spars near the tips but was not sure I could use this on a heavier model. My other question is does your revision assume the (2) batts will be in the wings?

You're right about prevailing model airplane design, most if it is overbuilt which is why I design my own. Anyone can build a bridge to support a car, the key is to build the same bridge to "just" support a car.

My tailplane feels a bit heavy since there is alot of wood there, but I am not used to the larger scales so we'll see. The ratio is about 2.75:1 tail to nose on this model. The fuselage design is primarily 1/8 poplar ply skinned with 1/16 balsa for the fwd fuselage sides and balsa longerons and skinning top and bottom so this should not be too heavy. The sides will be a covered open framework with spruce stringers since this is scale.

Excellent subject casor, a favorite of mine. I will look forward to watching your progress and building "vicariously" through you since I doubt I will live long enough to build a Sparviero of my own. Just too many projects on the "to do" list ahead of it. I did build the item shown below for a customer's giant scale SM.79. You'll be doing something similar I imagine.

Originally Posted by Chad Veich

Excellent subject casor, a favorite of mine. I will look forward to watching your progress and building "vicariously" through you since I doubt I will live long enough to build a Sparviero of my own. Just too many projects on the "to do" list ahead of it. I did build the item shown below for a customer's giant scale SM.79. You'll be doing something similar I imagine.

Hey Chad thanks for chiming in. Yes I think the torpedo for mine measures 21" long or something and I am planning to have a torpedo drop . Not sure how the prototype's worked but I like the aerial fins on yours. What did you make that out of?
Rob

Comments?

Originally Posted by casor

Hey Chad thanks for chiming in. Yes I think the torpedo for mine measures 21" long or something and I am planning to have a torpedo drop . Not sure how the prototype's worked but I like the aerial fins on yours. What did you make that out of?
Rob

Rob, the main body of the torpedo is a cardboard tube while the tapered aft portion was vacuum formed in two half shells and the nose was made from half a styrofoam ball. The fins are built up from laser cut balsa, ply, and styrene plastic. The tough part of making it droppable will be getting it strong enough that the aerial fins do not break off every time you drop it. Not a lot of material back there to tie the fins to the rest of the torpedo. I have a CAD drawing of the torpedo you are welcome to have a copy of if you would like. I also made up some cockpit detail for this particular customer including an instrument panel. I can provide you with a graphic of all the instruments as seen below if you want it as well. I simply put the printed graphic behind a laser cut plastic panel and sandwiched some clear sheet in between the two. I can scale the graphic and CAD files to any size you want. Anyway, all this stuff is just sitting on my hard drive and I don't imagine I'll be needing it again so somebody might as well get some use from it. Just send me an email about it if interested.

cwveich@cwvmodels.com

Hi Rob,
Yes, that's pretty much it - except that you can dispense with the c/f backer to the spars and the wing joiner need only be half the length.
Once the stress is shifted to the spars there is no point having it longer. Okay it doesn't do any harm except for a little extra weight but it might make a difference to the decision about whether the joiner is fixed permanently in the fuselage, since less of it may be sticking out risking damage in transit or storage.
To have the joiner removable the fuselage needs to include the same sort of surround to support it as you have in the wings, which it would need anyway to stop it deforming under strain.

The alternative is to extend each wing one bay so that it passes right through the fuselage and the joint happens on the centre line. That way there is only one point at which it alone is taking all the stress instead of two and there is incidental support from contact with the fuselage sides. Within the fuselage the upper sheeting of the wing can be omitted and receiver and servos housed in the wings fully accessible once the fuselage (or the hatch) is removed. There may be enough room for these just ahead of the spar.

Whichever option you choose all electric connections can be made automatically as main parts are assembled on the field by including DIN plugs and sockets. That saves a lot of time and effort as you would otherwise have to make sure all the leads are plugged in the right way round before bolting parts together.

Subbed in. There is something charming in this uglyish Italian bird

raipe