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MINIMOA 1/4 SCALE

Posted: 17 Nov 2020, 09:47
by chris williams
My personal history with the Minimoa goes back a long way. The b/w pic shows my 2nd version in the early 1980’s, scaled up from the Bob Banks plan, which was my 1st. (The gentleman holding that one is the Proto-Wookie version of Motley)
Unlike today, there was little around in the way of 3-views, so the accuracy of the models was not great. The recent ¼ scale version this log, (this time based on Vince's excellent 3-view) will describe is still not my last, as I have subsequently built a fifth scale version based on the same plan.
So, down to business…

Re: MINIMOA 1/4 SCALE

Posted: 17 Nov 2020, 11:25
by chris williams
Let’s start with the wings, as there’s a common misconception that gull wings are difficult to build. In the past, I have always built the wing in two parts, glueing them together at the gull join. As I have discovered with the smaller models, 5mm sq instead of 6mm spars are much easier to steam into a bend (applies to fuselage construction, too). So, the wing is built in one piece over a simple set of jig supports with single 5mm sq spars top and bottom. After the ply webbing is added to the front of spars, a secondary sub-spar is retro fitted in front, thus achieving a gull shaped I-beam, which is both strong and light…

Re: MINIMOA 1/4 SCALE

Posted: 18 Nov 2020, 11:23
by chris williams
With the top spar and aileron spar added, a handful of web plates are added to lock the main spars in place. At the same time, the 0.8mm ply triangles can be applied to reinforce the rear of the ribs. Note: the ribs are set at right angles to the lower spar...

Re: MINIMOA 1/4 SCALE

Posted: 18 Nov 2020, 13:05
by Christian Baron
I follow your build with interest.
Chris, airfoils are HQ35/xx I think?
When will the plan be available?
Regards,
Christian

Re: MINIMOA 1/4 SCALE

Posted: 18 Nov 2020, 14:42
by chris williams
Yes, inner panel HQ35/14, outer panel transitions to 35/12. Email me, Christian, and I will send you all the stuff... (Cliff is going to do a kit)

c_williams30@sky.com


cw

Re: MINIMOA 1/4 SCALE

Posted: 19 Nov 2020, 12:35
by chris williams
Once enough ply plates have been added to lock up the spars, the wing can come of the lateral jigs and the 15mm brass wing joiner box fitted, followed by the remaining ply webs ...

Re: MINIMOA 1/4 SCALE

Posted: 20 Nov 2020, 10:11
by chris williams
Retro-fitting 5mm sq spruce sub-spars in front of the web plates is a simple 10-15 minute job. The 1.5mm sheeting for the gull break is applied separately: the bottom sheeting is simple, but the top needs a little water and gentle persuasion. Note that the TE is clamped to a straight-edge to ensure that the spars remain straight as the rest of the sheeting is applied...

Re: MINIMOA 1/4 SCALE

Posted: 20 Nov 2020, 11:32
by Adam C
Chris,

Do your plans show the lateral jigs you set up?

Adam

Re: MINIMOA 1/4 SCALE

Posted: 20 Nov 2020, 16:09
by chris williams
Yes, Adam, the details are on the plan...

Re: MINIMOA 1/4 SCALE

Posted: 20 Nov 2020, 16:21
by Adam C
Excellent. You have thought of everything!

Out of interest, I fly a heavy 7kg artf kirby kite with its gull wings. I was shocked to find the joint at the bend was just vertical grain balsa. Still very strong despite being enough to make me wince.

Re: MINIMOA 1/4 SCALE

Posted: 20 Nov 2020, 20:52
by RobbieB
Ah, but it's not a cantilever wing and the strut attachment points are outboard of the gull break.

Re: MINIMOA 1/4 SCALE

Posted: 21 Nov 2020, 09:34
by chris williams
With the lower sheeting completed, the wing can be laid on the transverse jigs, weighed down, and the upper sheeting added. This time the straight edge is there to help ensure the inner panel TE is nice and flat...

Re: MINIMOA 1/4 SCALE

Posted: 22 Nov 2020, 09:24
by chris williams
With the basic wing structure completed, it's time to get back to the beginning...The fuselage is constructed via the traditional half-shell method. The difference is that in place of the 6mm materials used in the past, 5mm has been used instead because it is adequately strong and, in the case of the spruce, easier to bend.

Re: MINIMOA 1/4 SCALE

Posted: 23 Nov 2020, 09:16
by chris williams
For more years than I can remember, I have utilised 1.5mm ply planking for the front of my fuselages simply because it's so strong & ding-proof when subjected to rigours of slopeside landings. Applied in fairly large sizes, with three planks scored out and cracked into a curve to follow the contours of the fuselage, the only downside lies in the physical effort to cut the wood with Box Cutter style knife. The problem is holding the straight edge in place without it moving as you apply the cut. Tape or pins go some way to solving the prob, but recently I've come up with a wheeze using clamps and an A2 cutting mat. The pic should be self explanatory: all you need to do is release the clamps one at a time and manoeuvre the wood into position for the next cut. If, like me, you have high-mileage hands, they will thank you for it...
Meanwhile, when enough planking has been added to front of the fuselage, the half-shell can be removed from the board and the other side built up...

Re: MINIMOA 1/4 SCALE

Posted: 23 Nov 2020, 09:59
by Barry_Cole
Or you could simply cut it with your circular saw???

:D :D :D :D

BC

Re: MINIMOA 1/4 SCALE

Posted: 23 Nov 2020, 12:42
by chris williams
Not really... it's two scored cuts halfway through and then a full one: the whole thing with a slight taper.

Re: MINIMOA 1/4 SCALE

Posted: 23 Nov 2020, 13:32
by Barry_Cole
Oh yes, I forgot about your 3 for the price of one, offer....

:shock: :shock: :shock: :shock:

BC

Re: MINIMOA 1/4 SCALE

Posted: 25 Nov 2020, 09:07
by chris williams
The basic tail mount is set up in the pic. Once the diagonals have been fitted, and the planking completed, the filling process at the front can begin...

Re: MINIMOA 1/4 SCALE

Posted: 26 Nov 2020, 08:12
by chris williams
With the front end filled and shaped up, the next task will be to remove the temporary formers...

Re: MINIMOA 1/4 SCALE

Posted: 27 Nov 2020, 09:14
by chris williams
With the temporary formers removed, the interior of the front of the fuselage can be glassed; this time with chopped mat and polyester resin. The fuselage is placed on its nose to allow the surplus resin to congregate at the front...

Re: MINIMOA 1/4 SCALE

Posted: 27 Nov 2020, 16:48
by Adam C
Watching, learning and enjoying.

Re: MINIMOA 1/4 SCALE

Posted: 28 Nov 2020, 09:07
by chris williams
With the interior of the fuselage cleared out, F5a can be installed and the top sheeting applied. A card template is useful for determining the rough shape of the top decking, which is wetted up, taped into a curve, and ironed dry before fitting. I used 0.8mm ply on the prototype, but these days I would now recommend 0.6mm ply...

Re: MINIMOA 1/4 SCALE

Posted: 29 Nov 2020, 08:23
by chris williams
Before the rear of the fuselage can be finalised, the tailplane must be put together. The basic frame has the top sheeting added first (because the tailplane tapers in thickness underneath); then the jig supports are spot-glued to it and the tailplane put inverted on the board whilst the bottom sheeting is applied. Both top and bottom sheeting overlap the rear spar to from a shroud for the elevator. The elevator's false LE is offered up at this stage to synchronise the holes for the Robart style hinges...

Re: MINIMOA 1/4 SCALE

Posted: 30 Nov 2020, 08:14
by chris williams
Once the elevator false LE is hinged up, the TE & ribs can be added. Once complete, the elevator is sanded flush to the tailplane.

Re: MINIMOA 1/4 SCALE

Posted: 01 Dec 2020, 08:21
by chris williams
Now it's time for the elevator actuation arrangement: Hopefully, the pics should be self-explanatory. Because the servos are difficult to access, they are mounted on a removable plate should any maintenance be required.

Re: MINIMOA 1/4 SCALE

Posted: 02 Dec 2020, 08:17
by chris williams
Now the rear end of the fuselage can be closed up. Note the rudder cable guides that will be embedded inside the ply outer covering...

Re: MINIMOA 1/4 SCALE

Posted: 03 Dec 2020, 10:05
by chris williams
Time now to put the rudder together: as I don't seem to have any pics of the process, I've used the ones from the 5th scale build, which, apart from the size, is pretty much identical...

Re: MINIMOA 1/4 SCALE

Posted: 04 Dec 2020, 09:49
by chris williams
On the full-size, the gap between the rudder and the fuselage was covered by hinged plates on either side. In this instance, they are sprung-loaded to keep them flush to the rudder. As usual, card templates are used to make up the lower ply covering on the fuselage...

Re: MINIMOA 1/4 SCALE

Posted: 04 Dec 2020, 13:43
by tjarko
Nice scale details!
Is the rudder counter weight functional?

Re: MINIMOA 1/4 SCALE

Posted: 04 Dec 2020, 15:05
by chris williams
No, the model doesn't fly fast enough for it to matter...

Re: MINIMOA 1/4 SCALE

Posted: 04 Dec 2020, 15:38
by Barry_Cole
chris williams wrote:
04 Dec 2020, 15:05
No, the model doesn't fly fast enough for it to matter...
Usually...... :shock: :shock: :shock: :shock:

BC

Re: MINIMOA 1/4 SCALE

Posted: 04 Dec 2020, 20:34
by SedB
I really enjoy looking at your builds, quit jealous of your pace (I think balsa shortage as a result of building windmills is a hoax, it's you building gliders 24/7 not!?) :lol:

I'm looking forward to see this model come along!

Re: MINIMOA 1/4 SCALE

Posted: 05 Dec 2020, 08:16
by chris williams
A quick tidy up of the wheel mount...

Re: MINIMOA 1/4 SCALE

Posted: 06 Dec 2020, 08:32
by chris williams
The wing joiner box is set behind the main bulkhead, and packed out at the top to align with the angle of the wings...

Re: MINIMOA 1/4 SCALE

Posted: 07 Dec 2020, 05:47
by Paul Neville
Hi Chris, is this new plan available to purchase yet?

Re: MINIMOA 1/4 SCALE

Posted: 07 Dec 2020, 08:23
by chris williams
It's being donated to the forum, Paul: you can get a copy plus the parts PDF's from me...



c_williams30@sky.com

Re: MINIMOA 1/4 SCALE

Posted: 07 Dec 2020, 10:09
by chris williams
The crescent shaped ply part on the rear cockpit bulkhead performs the twin duties of tying the two former halves together, and providing an edge to which the canopy can be glued.
The canopy frame is built up in place, with the starboard rail first being hinged up with brass doll's house hinges

Re: MINIMOA 1/4 SCALE

Posted: 08 Dec 2020, 12:24
by chris williams
When adding the ply sheeting, I always find it easy to apply it in two halves, with the join in the middle, over the short longeron...
Where possible, the joints are reinforced with short lengths of fine piano wire, inserted via the drill...

Re: MINIMOA 1/4 SCALE

Posted: 09 Dec 2020, 13:35
by Adam C
This is the bit I loath, canopies. Not the party snack version, the annoying glueing and making a mess variety.

Re: MINIMOA 1/4 SCALE

Posted: 10 Dec 2020, 08:08
by chris williams
The aileron shrouds are made up from 0.6mm ply, grain cross-wise, and 1.5mm balsa sheet. The balsa will be later sanded flush to the cap strips

Re: MINIMOA 1/4 SCALE

Posted: 11 Dec 2020, 08:17
by chris williams
The ailerons are built flat to the board...

Re: MINIMOA 1/4 SCALE

Posted: 12 Dec 2020, 10:01
by chris williams
The ailerons are hinged with Robart style hinges. The final LE is rounded off in order for it to rotate within the aileron shrouds on the wing. The hinges are supported in the wing with 9mm dowel, and the hinge knuckle set back in the aileron to allow for correct rotation. The servo is mounted on 3 x 6mm spruce rails...

Re: MINIMOA 1/4 SCALE

Posted: 13 Dec 2020, 08:24
by chris williams
With the fuselage now fully sheeted, it's time for the tricky business of setting up the wings in their rightful place...

Re: MINIMOA 1/4 SCALE

Posted: 14 Dec 2020, 08:00
by chris williams
The 1.5mm ply wing fairing plates are set up flush to the wing, and the space in between filled with balsa, then finished with polyester filler...

Re: MINIMOA 1/4 SCALE

Posted: 14 Dec 2020, 10:05
by Adam C
What do you use for a datum line for the incidence on the wing? Or are you simply taking a zero reading off the wings to set the tail?

Re: MINIMOA 1/4 SCALE

Posted: 14 Dec 2020, 22:15
by chris williams
Adam, although the HQ section is different to the Gottingen 681 section of the full-size, the wings are set at the same relative angle to the fuselage. The tailplane is then set 1.2 to 2 degrees negative to the wing. Of course, manually attaching the wing to the fuselage can be slightly hit & miss if you're not careful, but the incidence gauge keeps you on the straight an narrow...

Re: MINIMOA 1/4 SCALE

Posted: 15 Dec 2020, 08:11
by chris williams
Once the the gaps have been filled with balsa, the fairings are finished off with filler...

Re: MINIMOA 1/4 SCALE

Posted: 16 Dec 2020, 10:15
by chris williams
Now to set up the spoilers...

Re: MINIMOA 1/4 SCALE

Posted: 17 Dec 2020, 10:16
by chris williams
Time for gritted teeth...The Canopy

The small compound curved part at the front is achieved with the use of a clear plastic lemonade bottle, but if I was to do it again, I'd use the one-piece top segment, as I did with the 5th scale version. I suspect that the moulding I had made at Sarik for the MO2a would do the job nicely...

Re: MINIMOA 1/4 SCALE

Posted: 18 Dec 2020, 09:57
by chris williams
Just a few details left, now...

Note: the servo aperture is covered with a patch of vinyl that is colour-matched to that part of the wing:
Note: The TE gussets on the ribs were not originally fitted, but were retro-fitted when the opaque film covering was removed and replaced with the matt clear

Re: MINIMOA 1/4 SCALE

Posted: 19 Dec 2020, 10:04
by chris williams
A few details of the finished airframe...

Re: MINIMOA 1/4 SCALE

Posted: 21 Dec 2020, 15:08
by chris williams
The current state of the Minimoa with its translucent finish... (The 5th scale version is shown for comparison)

Re: MINIMOA 1/4 SCALE

Posted: 21 Dec 2020, 18:07
by terry white
Chris, That's absolutely superb mate. I followed your build with interest.
A good build thread, with lots of pici's and a great model at the end. can't wait to see it fly.

Re: MINIMOA 1/4 SCALE

Posted: 22 Dec 2020, 09:54
by john greenfield
Hi Chris

What do you do to "prime" the HK film before painting.

AEB

Re: MINIMOA 1/4 SCALE

Posted: 22 Dec 2020, 10:57
by Barry_Cole
I think it is all film on the wings....

BC

Re: MINIMOA 1/4 SCALE

Posted: 22 Dec 2020, 11:41
by chris williams
Thanks for the kind words, Terry...hopefully, normal service will be resumed some time next year ;)

Yes, John, all the flying surfaces are film covered with film providing the trim colour as well... (The fuz is Solartexed and 2-pack painted)

Re: MINIMOA 1/4 SCALE

Posted: 23 Dec 2020, 09:45
by chris williams
The plan has been donated to the forum...You can get a copy from there, or directly from me, where I can also provide the build pics in convenient digital folders...

Re: MINIMOA 1/4 SCALE

Posted: 23 Dec 2020, 11:17
by Bovin
Hi Chris, thats looks suberb and what a pace.... :D

Vincent

Re: MINIMOA 1/4 SCALE

Posted: 23 Dec 2020, 11:30
by Peter Balcombe
Bovin wrote:
23 Dec 2020, 11:17
Hi Chris, thats looks suberb and what a pace.... :D

Vincent
Just as well he doesn’t often have a Carpal Tunnel Op. 8-)
Perhaps he will slow down as he recovers :lol: :lol:

Re: MINIMOA 1/4 SCALE

Posted: 23 Dec 2020, 12:44
by chris williams
Don't be fooled, Vincent, this model first flew back at the end of 2018... It comes under the heading: 'Here's one I made earlier' ;)

Re: MINIMOA 1/4 SCALE

Posted: 23 Dec 2020, 13:24
by Bovin
I was fooled.... :D
Vincent

Re: MINIMOA 1/4 SCALE

Posted: 23 Dec 2020, 22:53
by SedB
This one looks stunning, congrats!!