Hybrid 60" Plank

[PDB]

Is the fuselage printed in PLA? Are the wings finished with a film or something else?

[Mike Chantler]

Fuselage is ordinary PLA except for carbon ballast tube.

 

Wing is 75g laminating film on hotwired EPS (as I can't get EPP).

You have to be carefull with the temperature of the iron!!

 

Spars are double, full-length, 6mm carbon tube (top and bottom).

Has hardwood LE and balsa sub TE with correx ailerons. Tips have ply end-caps.

 

Think I'd change TE for thin hardwood, and swap ailerons for hard balsa. 

 

Plan and Fusion 360 model on Tim's GitHub pages (url at start I think).

 

My Fusion 360  mods are VERY untidy - would send only via PM as they are a bit embarrassing!!

 

 

 

 

Edited October 20, 2023 by Mike Chantler

[Mike Chantler]

Have been flying Mk3 for six months and again, it's always one of the planes I take up the slope as it never fails to bring a grin to may face, and I know I'll get a flight unless its <5mph.

 

Stuffed it into the hillside and managed to damage the fuselage a few weeks ago - could of simply glued it back together, but simply printed a couple of replacement parts instead 🙂

 

But it got me to thinking about the next version, as have got a bit bored with my spit (which I will return to).

I'd like it to go a little faster, and roll quicker, but still want it to be a quick and cheap build.

 

So small changes I intend for mk4:

 

1. Use the fuselage ballast tube and don't put one in the wing.
2. Use balsa elevons to help streamlining.
3. Make the linkages a bit more streamlined.
4. Use a PW51 airfoil (about 10% thinner than the MH45).
5. Use wing bolts rather than sticky tape to make access easier (!). (may put Rx in wing under fus)
6. Use 2 x 1oz glass rather than 75 micron laminating film covering  (the film gets a bit wrinkly after a while with the abuse that a slope model takes).

[Mike Chantler]

Modified fuselage for thinner PW51 by creating a liner in Fusion:

 

Took a lot longer than I expected - until I discovered that I could delete the old hole and then recut the Pw51.

Edited May 27, 2024 by Mike Chantler

[Mike Chantler]

Added holes for bolts fore and aft, and printed:

 

Edited May 27, 2024 by Mike Chantler

[Mike Chantler]

Cut PW51 cores:

 

 

 

LE went a bit strange with the downward cut so will need to put in more stops and maybe make the cut before the wing surfaces. Can sort LE with a bit of sanding and pos micro balloons so gave sanding stick present of smart new covering of p120 🙂

Edited May 28, 2024 by Mike Chantler

[Mike Chantler]

Rough idea of wing construction:

 

[Mike Chantler]

Sanded LE, TE and roots for good contact glue surfaces, then glued and taped beds:

Contact glue works well as has great grab but allows repositioning if still wet/tacky 

 

POR for beds, Technicoll for cores .

 

Dremmeled spars groves top and bottom:

 

 

Scrap for getting offset and depth got round trail and error messing around of last time 🙂

[Mike Chantler]

Found old blocks in scraps box that I've had from when I was a kid - and finally think they will get used (for the centre-section reinforcement 🙂  )

 

 

 

And  3d print failed when i wasn't looking 😮 

Edited May 29, 2024 by Mike Chantler

[Mike Chantler]

Two 6mm spars PU glued, 10mm TE balsa contact glued and shaped 🙂 

 

Carbon rods have slight bow so can spring out as one did a little during drying 😞 so needed sanded down at tip to be flush 😞 

[Mike Chantler]

Hmmm.... forgot I had intended to add 1/8th ply endcaps to wing before spars and TE so had to mess around with drill holes and shape. Imperfect fit meant that I wasn't confident of contact adhesive holding so used epoxy which was a right pain to sand down to shape. MUST remember to add endcaps first next time 🙄 

[GrumpyGnome]

Brown Gorilla Glue sticks REALLY well, and sands easily.... for next time.

[Mike Chantler]

3 hours ago, GrumpyGnome said:

Brown Gorilla Glue sticks REALLY well, and sands easily.... for next time.

Yes, great idea  - I did use it for the spars (or rather the 5-minute Everbuild version).

 

Why I didn't use PU for these endcaps I have no idea, 🤔🙄 😕😬 you can even see it on the spar under the red bottle of epoxy above!

I can only plead senility ...

[Mike Chantler]

Contact glued 3mm cedar LE and shaped. Cut hole & recess for/and glued in double 1/8th ply back plate and balsa front block - used PU and PVA  this time for the basa block 🙂

(didn't think that the fit of back of balsa bloc was good enough for PVA so used PU there)

 

I would of liked the grain on the balsa block to go longitudinally, as one of its main functions is to stop the LE caving in on  fast arrival 🙂 But it didn't quite reach to the carbon spars like that - so c'est la vie

Edited May 31, 2024 by Mike Chantler

[Mike Chantler]

For some reason  the square tips started to annoy me, with absolutely zero evidence I started to think they looked very draggy, so have added little XPS tips.

 

[Mike Chantler]

Thinnest aileron stock i could find was about 2mm too thick, microplaned it down which was a bit hairy as width of stock wider than micro-plane and it kept on skimming over the wood or digging in too much. And that was with a fresh blade.

 

 

Then sanded to final shape. 

 

LE of aileron and TE of 

Elevon LE and wing sub-TE took an age with sanding bar. Next time I think I'll bag the whole wing and then cut the ailerons out!!

 

[Mike Chantler]

Spent a while testing old servos. The cheaper wing servos seemed to have quite a lot of slop 😞 but I baulked at using the KSTs at £33 a pop for what is supposed to be a cheap model.  The MKS are also quite pricy so went with the old bluebird 105s from a previous model (and am now feeling like scrooge!!) 

[Mike Chantler]

Made up some servo boxes and did small mockup to see how an under/over linkage would work a while back - but including here to remind me as they worked ok but next time I'd be very tempted to 3D print the sevo housings (but keep the carbon tops and bottoms).

 

[Mike Chantler]

Balsa template for dremeling out servo holes did not work well 😧 🤥. Just prepping with scapple much quicker and more accurate.

 

Under and over servo linkages went in surprisingly easy 🙂as just dremmelled the channels and will cover with glass.

 

 

 Servos in with (yellow) drinking straws for leads 🙂

Edited June 17, 2024 by Mike Chantler

[Mike Chantler]

Added elevons with 25g/m2 aramid hinges, circa 10mm top, and 18mm bottom. May be a bit ott, but I hate sellotape hinges gradually coming apart 😬

 

Aramid was from offcut of old material that I had sprayed with 77spray glue a couple of years ago +  cheap transfer tape- made it much easier to handle. I'd been dreading it a bit but went on quite easily  with just the right gap.

[Mike Chantler]

Gave 2 quick coats of filler mix in places with big dings, covered top, bottom, elevons with 25g glass + one coat WBP.

 

The very fragile glass cloth went on surprisingly easy - but not to be attempted late at night after a couple of pints (!)

 

Now wish I had used the filler mix all over - as very easy and fast to put on smooth coating, and stops WBP soaking into EPS voids 😕

Edited June 20, 2024 by Mike Chantler

[Mike Chantler]

Quick weight check:

 

Weight of mk3 seems to have grown from original 860g to 927g. Only difference is I reprinted the fuselage in yellow - so suspect I forgot to set the fill to 0% for some of the components.

 

Mk4 at 874g not bad, but I'm going to add more glass to improve ding resistance and may paint top of wing - this will likely move the CoG aft a bit so will need increased nose weight. 

[Mike Chantler]

Added 50g/m2 glass to forward 4"-5" of wing, top and bottom with brushed over ultra-low viscosity epoxy:

 

 

This may seem a little crazy to put 50g/m2 on top of 25g/m2, but my idea was that light glass + wbp would 'seal' the EPS voids, while not adding too much weight, while the heavier glass + resin would add a reasonable ding resistance (I just didn't fancy the idea of all that very fluid epoxy going into all the voids 😞 )

 

Rollered off excess with foam roller on toweling - this combo worked really well so will definitely do this next time 🙂 

 

But had afterthought that I should of coated top of sevo boxes and esp. the screw heads in wax before covering in the glass 🤔

[Mike Chantler]

Gave quick sand with 120 grit mesh - surprised at the coarseness of sandpaper that I could use. Sprayed with high-build primmer to find bumps and lows - there are lots!! Saned with 120 and coated in Feddy B's sauce filler mix:

Hmmm... lots of specs of talc I think - must siv 50yr old talc first next time 🤔

 

Edited July 1, 2024 by Mike Chantler

[Mike Chantler]

Boob!

I meant to note that some of the deep fill primer must have got through the 25g glass/WBP combo and started dissolving the foam  EEK!

Not so bad, and only in one place, so coverup was quick.

BUT could of been a bit of a disaster, blush  😞

 

I think it was where I sprayed too much primer on an area with little filler - silly really, as I just wanted it to show high/low spots after sanding, and probably no need for the heavier deep fill at this stage 🤔