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Re: SF33 1/6 scale

Posted: 18 Apr 2019, 14:11
by Tonyw51
Yes I know the problem, I have just started building a bass guitar for my son which is receiving the attention and enthusiastic priority of my wife. I think modeling is on the back burner for a couple of weeks

Re: SF33 1/6 scale

Posted: 20 May 2019, 10:50
by Peter Balcombe
Just got back to the SF33 build, so have started on the LH wing.
The build is pretty much as for the 1st wing & I am currently notching the ribs for the aileron spars.
Once the upper hinge spar spar glue has set, it will be time to cut notches for the top aileron LE spar.

Re: SF33 1/6 scale

Posted: 20 May 2019, 19:11
by Peter Balcombe
And now with both wings fitted to fuselage to epoxy the carbon main joiner tube in place.

Re: SF33 1/6 scale

Posted: 20 May 2019, 23:39
by Tonyw51
G'day Peter, Good to see you back on this project. Could I ask you to put in a feed of detailed photos on the wing construction. Thanks, Tony

Re: SF33 1/6 scale

Posted: 21 May 2019, 10:50
by Peter Balcombe
Hi Tony.
Please look at the earlier part of this thread for photos taken during the 1st wing build, but I will add a few more as I put the 2nd one together.

As mentioned before, this plan is hand drawn and suffers from several inconsistencies & what I consider to be missing build info.
Thus it is not a good 'first build' model, but looks as if it can be made into a nice model with a little care and ingenuity.

As stated previously, I started my wing construction y laying down a pre-spliced lower main spar over the plan, spaced off the building board using 1/16" balsa spacers to simulate the bottom sheeting to be applied later. I also laid down a 1/4" wide strip of 1/16" balsa immediately forward of the TE section upon which to lay the rear of each rib.
Each rib can now be glued onto the main spar and TE strip after fettling to adjust the spar slot width and also the front edge to ensure a straight line at the front for fitting the dummy LE strip next. The most important ribs to get sorted out before assembly are the ply ones (R1 & R3), a these are harder to adjust in situ. I filled the spaces between each rib at the TE with balsa strip, sanded down flush with the tops of the ribs later.
Once a further 1/16" balsa strip is added, this gives a solid TE structure to fit the TE onto.

With all ribs in position (remember to angle the root rib & to fit a washout wedge under the TE from inner end of aileron), the dummy LE can be butt-jointed to each rib and then the 1/8" balsa root corner gussets added.

A length of 8mm ID carbon tube can now be inserted trough the holes in the root ribs & epoxied into position, followed by addition of the top spar (after fettling the rib slots to suit).

Now add the spruce top drag spar and the additional wedge behind the main spar over the joiner tube. The ribs are only cut for a wedge spar out to R4, but I took mine out to the drag spar intersection to give support for the webs to be fitted out to there. (I also added a cap to the joiner tube and filled the void between joiner tube & top/bottom spars/edges with hardwood/epoxy later, before the area was sealed with the webs).

There are no pre-cut notches for the aileron hinge & LE spars, this this has to be done manually. Bearing in mind the slimness of the ribs at this point, I decided to only fit the upper spars until the area had been sheeted in order to provide support whilst the lower notches were cut later. Hence i measured the spar locations & carefully notched & cut the ribs for the upper hinge spar only, fitted the spar & once secure, cut & fitted the 2 aileron end riblets, tack gluing these in place whilst spaced off the full ribs. Then the intermediate ribs can be very carefully notched and the top aileron LE spar fitted.

At this point, you are about ready to apply the upper sheeting once the dummy LE has been sanded flush to the top of the ribs & other areas prepared.
The rear incidence tube could be fitted before the top sheeting is added, but this can be easily done later before the lower sheeting is fitted. Holes are provide in the root ribs but when fitting, ensure that the incidence rod is parallel to a fitted main joiner in both front-rear & plan views.
The rear tubes could be also fitted using the fuselage as a iig as a single rod is used for each of the main joiner & rear incidence alignments.

A few detailed photos below may also be of use.

Re: SF33 1/6 scale

Posted: 23 May 2019, 10:04
by Tonyw51
G'day Peter,
Thank you for your post 21 May. You are so right with regards your comments about "first build". However, I am slowly muddling my way through and having a great deal of enjoyment in the process.

I really do appreciate your comments and instructions, they are a great help and confirm a great deal of what I have read into the plans, which is really comforting.

As a side, I was originally brought up using imperial measures, but when I started to play with European and Japanese motor bikes I built my workshop to metric and that was 40 years ago. Fortunately I still have fluency in "Imperial".

Cheers and thanks,


Re: SF33 1/6 scale

Posted: 27 May 2019, 20:04
by Peter Balcombe
Tony, we have to be fluent in both Imperial & metric in the UK :?

Moving swiftly on ... Once the top D box skin has been put on (with washout wedge in place), the rear edge of the balsa sandwich at the back of the wing ribs can now be straightened as required to fit the balsa TE stock.
At the root end, I now add the underside drag spar and joiner area sub spars to match those on the topside.
The front spar webs can be put in place over the first few rib bays & then the wing stood on its dummy LE to epoxy spruce infill around the joiner tube & firmly bond the tube to the main spars.
Once that has been done, the remaining spar webs can be added, including those behind the drag spar.

With both wing structures available I have also installed the rear incidence joiner tube into the fuselage and the 2nd wing, temporarily setting everything up with the fuselage to make sure that everything lines up & will subsequently rig easily.
Note; As far as I can see, the forward wing retention hook has to be fitted further forward of that shown on the plan due to a significant cable access hole forward of the main joiner. Moving it forward between 6-10mm should work.

Re: SF33 1/6 scale

Posted: 27 May 2019, 22:29
by Peter Balcombe
Front hook centre has been placed 30mm behind front of dummy LE, so 36mm behind LE at the root (which puts the rear edge of the doubler at the forward edge of the laser cut cable hole). I used 1/2”x1/4” Spruce strip doublers glued to inside of the root rib at the attachment points & will probably screw in small hooks at these points for use with elastic bands or similar through the fuselage.
Note that the rear attachment is directly beneath my rudder/elevator servos, so the band will need to be fished through each time, or left attached to pegs each side to ease rigging :o

Re: SF33 1/6 scale

Posted: 28 May 2019, 08:01
by Tonyw51
Hi Peter,
Yes I can see the rear hook will be well covered by the servo tray. I have a PA-22 model that uses a grub screw through the wing spar tube and it seems to work quite well. Maybe the same could happen in the rear incidence tube. Something to consider, I also shall consider a peg/hook mounted on a the bulkhead.

Looking at the vertical stabiliser I am not sure of the mounting strength of gluing it to the 6mm plate in the fuse. What have you done there?

What type of hinges are you using for the control surfaces? I am considering the hinged Du-Bro.


Re: SF33 1/6 scale

Posted: 28 May 2019, 08:56
by Peter Balcombe
Tail feathers are made but not yet attached until they have been covered.
I will almost certainly glue them on, making sure there is good clear contact between the wood on each side (covering overlaps removed as required).
(I have used this method on a 1/4 scale Mick Reeves Fournier RF4, so not a problem at 1/6 scale as long as you have wood/wood contact).

I have used Mylar strip hinges (approx 3/8” wide) on the tailplane & rudder (have previously also used this on up to 1/4 scale). I will also use this method on the ailerons to provide a basic hinge, using a full length Blenderm type tape gap seal.
I would have thought Du-bro hinges will be rather prominent & not really necessary for a smaller model of this type.