Jump to content

Boxing Clever


Tim Hooper
 Share

Recommended Posts

The brief is to create a viable RC model that can be drawn on two A3 sheets of paper. Obviously I have no idea what this design is to be used for. Mine is not to reason why, etc........

Using graph paper I sketched a reduced-size plan to get an idea of the proportions.

img_6377.jpg

img_6378.jpg

That done I set about sourcing the hardware, and gained this little lot....

img_6379.jpg

There's a 10 gramme 2000 kv motor, a 4x4 prop, 4 x 3.5 gramme servos, micro rx and 10A ESC.

img_6386.jpg

Here's the wing drawn full-size. A massive 22" span! The orange card contains the Profili printouts, using an E207 semi-symmetrical aerofoil. The lower wing skin is from 1/32 balsa.

img_6867.jpg


The lower skins, spars and ribs in place - all done with thin CA glue. The tips are raised to give 1/4" dihedral, and then the central joiner tubes are fitted. There's a central 3mm cf rod.

img_6871.jpg

Beneath the rod are two protruding 1/32 ply plates which will pass through the fusealge sides. These will be linked with a clip to prevent the wngs coming adrift in flight!

img_6872.jpg

The fronts of the lower skins are raised with tapered balsa wedges, prior to fitting the 1/4 leading edges.

img_6875.jpg

img_6876.jpg

So far, so good....... wink 2

Link to comment
Share on other sites

Posted by WolstonFlyer on 04/01/2015 21:37:58:

Very interesting, who set you the challenge?

That must remain a closely guarded secret. Let's just say the edict originated in South Essex......

All the gear weighs in at 96 grammes, leaving around 60 grammes for the airframe.

tim

Link to comment
Share on other sites

Tim

Beautiful work.

What size is the 2s battery?

I presume your target is a 160g (6 oz) all up weight?

I have a sneaking suspicion that at 22" span you wont need ailerons that big. wink 2

At these extreme small sizes is an 'exact' aerofoil actually going to make much difference?

I my experience anything much below 3" chord is so relatively inefficient (Reynolds number?) that its thickness becomes the dominating factor rather than its section in determining the 'power to fly'. It almost becomes a "thinner the better" scenario hence the remarkable performance that can be achieved by a flat plate wing.

I will watch with interest.

Link to comment
Share on other sites

Thanks all! smile

Vecchio, yes there's two aileron servos - one in each wing, which sort of answers Simon's comment about the inefficiency of such a time wing section - the wings are just there to hide the internal servos!

I have several 3S 450 packs in stock, so I'd like to utilise those if possible. If they're too heavy then I'll shell out for a smaller pack.

tim

Link to comment
Share on other sites

Here I've installed the tape-wrapped 3.5 gramme servos, using thin CA. Not an ideal way of doing things, but certainly the lightest!

img_6878.jpg

The servfo arms will emerge from their bays when the rx is connected and powered up.

img_6879.jpg

With the tops of the wings sanded to remove any high spots, the 1/32" tp skins are added and pinned overnight to let the PVA glue dry.

img_6881.jpg

The leading edges are radiussed and sanded smooth. I opted to fit 1/32 sheet facings over the root ribs - just to hide the exposed ends of the spars. Each panel weighs in at 21 grammes.

img_6884.jpg

img_6885.jpg

The tail surfaces are cut from light 1/16 sheet, with crossgrain end pieces to prevent warping, The elevator joiner is a length of wooden cocktail stick.

Just for fun I've built a little canaliser too.....

img_6886.jpg

Link to comment
Share on other sites

Vecchio, Netty and I have been flying a pair of Hitec Zippers. These little 24" ARTFs are certainly quite rapid, but quite smooth in flight. The ailerons are positive, but not ridiculously so. The elevator does need to be treated with respect though!

You're quite right lads - I'll need to make a custom box.

tim

Link to comment
Share on other sites

Blimey, the modelling pins alone will cost more than the build and fit out - I've never used even remotely that many on wings several times the size.  You must have needed a truckload for that 80" Quad laugh

On reflection, that could of course quite probably be where I've been going wrong all these years enlightened

Following this with interest

 

Edited By IanN on 07/01/2015 23:37:01

Edited By IanN on 07/01/2015 23:45:17

Link to comment
Share on other sites

Well I cannot think of a publisher here in South Essex ........we have a large Rc retailer here, a large balsa supplier and a glow fuel maker but nobody publishing plans that I know of! So who could it be? Seems we have to wait......

Link to comment
Share on other sites

Posted by cymaz on 08/01/2015 06:57:35:

Just a thought, it might have a detachable tail section. That way it could sit in a suitcase or hand luggage.

Plane for going on Hols with ??

Cymaz,

You're spot on! I'm hoping to have a threaded stud protruding from the base of the fin that will pass vertically through the rear fuselage (trappping the tailplane in the process), and then secure by a nut underneath. It's a system I've used before successfully.

Work has started on the fuselage. I've drawn the basic outline....

img_6888.jpg

The fus sides are cut from 1/32 sheet, with internal 1/16 doublers and longerons at the rear.

img_6890.jpg

F2 and F3 are simple frames, from firm 3/16 x 1/16 balsa strip. Making them as a single unit, and then cutting them free afterwards helps keep the sides parallel.

tim

PS. Ian, you can never have too many pins!

img_6892.jpg

Link to comment
Share on other sites

Posted by kc on 09/01/2015 11:51:34:

Tim, can you explain that last photo. Is it a neat way of making identical built up formers which are then sawn apart?

Exactly! As long as the longest two sticks are set absolutely parallel to each other, the the fuselage sides should be equidistant apart too.

Here're the two sides, together with F1,2 and 3.

img_6894.jpg

The formers in close up. F1 is cut from 1/16 ply, and is marked out for the motor mount. The hole below is to allow passage of the cables.

Oh.....that's a 5p piece inside F2.

img_6895.jpg

The sides are assembled (inverted) to the formers over a drawn centreline, pinned and clamped as necessary. I've added two pieces of the 1/16 bottom sheeting just to stiffen up the assembly.

img_6897.jpg

The front former F1 protrudes above the fuselage sides, so I positioned the front ends of the fus sides to overhang the building board. Two bits of scrap ply stop the clamps from marking the balsa beneath.

img_6898.jpg

The sternpost is lightly clamped. The little piece of 1/32 ply will, hopefully, line up with the protruding stud from beneath the fin.

img_6899.jpg

Link to comment
Share on other sites

The high winds have meant lots of workshop time this weekend!

The wing panels have incidence pins added (bits of cocktail stick). The actual joiner is a 140mm length of 3mm carbon fibre rod, whilst the piece of bent wire above it is the clip that holds the wings tight to the fuselage, as the two short ends pass through those ply lugs that protrude from the root ribs.

img_6900.jpg

The servo leads pass through slots in the fuselage sides. There's a length of plastic tube glued across the fuselage.

img_6903.jpg

You can see the wire clip holding the wing panel in situ. Seems to work so far!

img_6905.jpg

I've installed a length of 2mm threaded pushrod into the base of the fin. The stud lines up with holes in both the tailplane and its seat on the fuselage.

img_6907.jpg

The assembled tail set. Needs a bit of fine tuning, but the principle is sound.

img_6909.jpg

The airframe so far!

img_6911.jpg

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...