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Chris Williams 1/4 Scale T21**

Posted: 31 May 2019, 21:53
by Sean Fitzgibbon
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So my Ka3 build is finally about to leave the building board to be covered. That means the next project needs to be planned and it's going to be the 4.1mtr T21 from Mr Williams.(He did tell me at MW that he hadn't actually built one himself, this is a scaled down version of his 1:3.5 prototype).
Still just at the stage of making lists of materials and enjoying the anticipation of seeing it grow in the workshop, anyone that has built one , please chip in with advice!

Re: Chris Williams 1/4 Scale T21

Posted: 01 Jun 2019, 08:33
by Rich vale
I have built four of them!!

Re: Chris Williams 1/4 Scale T21

Posted: 01 Jun 2019, 08:39
by Rich vale
The build is straight forward. The only problem that needs care is the covering of the ailerons and wing TE which twist very easily.

Re: Chris Williams 1/4 Scale T21

Posted: 01 Jun 2019, 10:58
by Sean Fitzgibbon
Rich vale wrote: 01 Jun 2019, 08:33 I have built four of them!!
That's just showing off!!
I'm hoping to start building towards the end of this month once I've gathered together some of the timber required. I have the laser cut pack from Sarik, so it's mainly spruce strip by the look of it!

Re: Chris Williams 1/4 Scale T21

Posted: 01 Jun 2019, 11:40
by chris williams
As long as the 'D' section has top & bottom sheeting and full-length ply webbing, it should be impossible for the wing to twist, although TE's can sometimes distort

Re: Chris Williams 1/4 Scale T21

Posted: 01 Jun 2019, 23:28
by B Sharp
Just like full size machine Chris!
Brian :)

Re: Chris Williams 1/4 Scale T21

Posted: 06 Jun 2019, 19:37
by jack
nice easy build,just lots of it ;) ,your biggest concern will be getting enough of your local church roof in the nose :lol: :lol: ,l actually found that l could get a pair of six volt spill proof batteries in the nose,one either side of the keel,the aerotow release went in the middle-if you need weight it might as well be useful wieght ;) ;) .....keep the tail as light as possible,every gram counts,have fun :D :D

Re: Chris Williams 1/4 Scale T21

Posted: 26 Aug 2019, 21:56
by Sean Fitzgibbon
Had a great weekend at the Nationals, a spot of preplanning meant I had emailed a list to SLEC to pick up.
Very efficient service as always, I now have the bulk of the required timber to press on with the T21.🤗

Re: Chris Williams 1/4 Scale T21

Posted: 07 Sep 2019, 18:41
by Sean Fitzgibbon
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So, having glued together the parts to make up the stabiliser spar and the elevator leading edge, construction proper has commenced.
This began with adding the stabiliser ribs to the spar, which I decided to do vertically due the dihedral of the tailplane.

Re: Chris Williams 1/4 Scale T21

Posted: 18 Sep 2019, 21:57
by Sean Fitzgibbon
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Steady progress, just finished fitting the diagonal ribs in the tailplane. My aim is to try and put at least an hour a day into this build in an attempt to maintain momentum.

Re: Chris Williams 1/4 Scale T21

Posted: 14 Nov 2019, 09:24
by SedB
Looks good so far!
I just got my copy of the exact same model today, so will be looking forward to see the progress in this topic :D !

Daniel

Re: Chris Williams 1/4 Scale T21

Posted: 05 Jul 2020, 23:46
by Sean Fitzgibbon
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So, after declaring that I intended to invest at least one hour a day on this build, circumstances dictated that I didn't touch it for months!!
I am now back in the saddle and have rediscovered the motivation to press on with the project, having seriously considered packing up this hobby after over 30 years of building and flying.
Over a week or so of evenings in the workshop, the tailplane is pretty much completed and I'll probably move on to the fin and rudder this week.

Re: Chris Williams 1/4 Scale T21

Posted: 09 Jul 2020, 20:53
by Sean Fitzgibbon
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With the tailplane and elevators completed, I've moved on to the fin and rudder.
The upper forward ribs of the rudder balance aren't shown on the plan, but it's fairly straightforward to work the shapes out. As for the elevators, the rudder ribs are made from balsa triangles, again easy process of marking out and cutting.

Re: Chris Williams 1/4 Scale T21

Posted: 13 Jul 2020, 07:29
by Sean Fitzgibbon
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I'm really enjoying this build so far, the fin and rudder are now complete and put to one side with the tailplane and elevators. Next jib is to clear the board and set up to start the fuselage.

Re: Chris Williams 1/4 Scale T21

Posted: 13 Jul 2020, 13:08
by Jolly Roger
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Looks great Sean. You're really cracking on.

The T21 is one of those snub-nosed chubby-winged cartoon gliders you just want to pick up and cuddle!

We had the Yorkshire Gliding Club T21 crawling around the sky above our house all Saturday. It's going nowhere fast and at times just sits, parked in the sky. Adorable.

Re: Chris Williams 1/4 Scale T21

Posted: 13 Jul 2020, 14:50
by Sean Fitzgibbon
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Hi Roger,
I know what you mean, there's so much character in the vintage gliders. I popped down to our club field on Saturday after Frank Skilbeck told me that he and Dave Keen were going to try towing Dave's T21.
This is a 1/5th scale model, from the Mike Trew plan I believe, that Dave acquired second hand fairly recently.
Our field at Newent isn't the largest or exactly obstacle free, but they did a great job and managed three flights, although Frank's Laser 150 powered tug was operating at it's limit! Watching the T21 arcing around in the sky certainly gave me more incentive to crack on with mine.
Chris' design is very well thought out and although a lot of the tail end parts are not included in the short kit, it still has been a straightforward process so far.

Re: Chris Williams 1/4 Scale T21

Posted: 18 Jul 2020, 09:04
by Sean Fitzgibbon
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So, moving on to the start of laying down the fuselage sides, I was pondering the issue raised on a parallel thread by Sebd. This refers to the force required to pull in the longerons at the nose following a fairly dramatic curve. I also have the issue of not being able to source spruce strip long enough to make them in one piece.
So I decided to scarf the longerons in the area where they will be supported by doublers and then split them longitudinally from the nose back to just in front of F4.
Chris had commented that his preferred method now is to use doubled 3 x 6mm strip rather than one 6 x 6mm, so I'm hoping this hybrid method will address the problem.
I have to say that this process and then cutting in the diagonal strips is made so much easier with the little Proxxon table saw.

Re: Chris Williams 1/4 Scale T21

Posted: 18 Jul 2020, 11:08
by RobbieB
Sean,
I too use the 2 x half thickness method to wrap spruce longerons around difficult bends - so much easier than forcing or steaming and you end up with a structure just as strong. Just make sure that when you are scarfing, the joint faces mate accurately and are in the length to thickness ratio of 12:1 or thereabouts for a longeron, 15:1 for a wing spar flange; and as you say, preferably in the region of a former but most full size boys would say if the joint is done correctly that shouldn't matter.

Re: Chris Williams 1/4 Scale T21

Posted: 18 Jul 2020, 12:15
by Sean Fitzgibbon
RobbieB wrote: 18 Jul 2020, 11:08 Sean,
I too use the 2 x half thickness method to wrap spruce longerons around difficult bends - so much easier than forcing or steaming and you end up with a structure just as strong. Just make sure that when you are scarfing, the joint faces mate accurately and are in the length to thickness ratio of 15:1 or thereabouts; and as you say, preferably in the region of a former but most full size boys would say if the joint is done correctly that shouldn't matter.
Hi Robbie,
Good to hear that other people concur!
The scarf joints I made were about 80mm long for the 6mm section and cut on the Proxxon table saw before a light sanding with the Permagrit. I used the clear, non foaming Gorilla glue to form the joint and a test piece that I made failed outside of the glued area.
The design has a double longeron for a portion of the length of the fuselage, and the joint is completely covered by this for more security.
It's a very satisfying process to build this so far, lots of lovely traditional wood modelling.

Re: Chris Williams 1/4 Scale T21

Posted: 22 Jul 2020, 21:31
by Sean Fitzgibbon
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The formers are nearly finished and the fuselage sides just need the longeron doublers adding before I can start looking at starting putting the fuselage together.
The only slight modification I made was to infill the top of the pylon formers with 1/4 ply beneath the hardwood insert.

Re: Chris Williams 1/4 Scale T21

Posted: 23 Jul 2020, 14:14
by Sean Fitzgibbon
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First two of the fuselage longeron doublers added, ensuring a handed pair!

Re: Chris Williams 1/4 Scale T21

Posted: 26 Jul 2020, 09:09
by Sean Fitzgibbon
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Next step has been to dry fit the centre section formers and then think through how to go about the actual assembly.
I'm leaning towards building the rear section over the plan to create a straight, rigid structure before adding in the main formers and then pulling in the longerons to the nose area.

Re: Chris Williams 1/4 Scale T21

Posted: 26 Jul 2020, 18:45
by Sean Fitzgibbon
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More progress this afternoon, all of the cross bracing done, this project is eating spruce and balsa strip!

Re: Chris Williams 1/4 Scale T21

Posted: 02 Aug 2020, 17:55
by Sean Fitzgibbon
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I've found jigging the front end of the fuselage quite tricky, both physically and in terms of finding datums to work to because of the angled formers and large curves.
I've spent a session dry fitting and comparing to the plan and I think I'm happy with how I'm going to proceed.
The rear end is now clamped in the old trusty SLEC jig and the whole thing positioned over the plan to align the main centre formers.
I've glued in the lower keel and worked out it's vertical position at F1 to set it's height.
Once it's set I'll add in F1, F2 and F3 with the top keel to hopefully create a stable front end. Dry fitting did at least prove that slitting the front portion of the longerons eases the pressure required to form the bends significantly. I did find the lower keel is a little short which obviously puts F1 a tad out if position. I plan to compensate by making the nose block a little longer, more room for the inevitable lead! I also remade F4 in 1/4" ply, partly for strength and partly because the fit of the original wasn't great.

Re: Chris Williams 1/4 Scale T21

Posted: 09 Aug 2020, 15:20
by Sean Fitzgibbon
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Took some time to pull in the longerons at the nose, one at a time laminating them together to hold the curve.
Now adding the ply sheeting, I've used epoxy for this more added strength, figuring the weight is forward of the centre of gravity.
When the side panels are in position, I'll cut and fit the strut brackets. Plan is to cut them from hard aluminium, but long enough to be one piece right through the fuselage and epoxied to the former.

Re: Chris Williams 1/4 Scale T21**

Posted: 29 Oct 2020, 09:42
by SedB
Forming the longerons I found the hardest part so far. I really had issues lining all out and forming them to a proper fit. Looks very promising so far Sean!
Wondering how I can add strength to the front part of the glider, I'm curious how yo'll be making those strut brackets!

Daniel