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Author Topic: deHavilland Technical School TK4  (Read 935 times)
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RalphS
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« on: December 18, 2020, 03:24:43 PM »

Although I don't need any new models I have to do something to alleviate this lockdown induced boredom.

After getting the foam Percival Provost to fly I decided to make another foam model using similar dimensions,
power train and r/c control components. The foam is very light so using the same types of components
should result in a similar performance to the Provost.  Looking for something interesting to make I
narrowed it down to the deHavilland Technical School TK4 or the Heston Napier Racer.  Both had short
lives with similar bad conclusions.  In the end I decided on the TK4 as it will be red and not another
silver coloured model - I have too many of them.  I had downloaded 4-view drawings of both aircraft and
with eyes half closed, the general shape is very similar. There is plenty of information about both planes
on the internet for people to read.

Like the Provost it is more nearly scale than true scale and should stand up to flying on our small
local site in a range of conditions.  I think it will be be too fast for indoor flying, for me anyway.

The general construction follows the Provost crutch design and is joined together using aliphatic
adhesive.  It looks like pva glue to me and I haven't bothered to try and find out any differences.
Because the foam is not closed cell it allows the glue to cure quite quickly.  Sanding, using a coarse
grit, removes material very quickly so the shaping process can be quite rapid.  I will try for a better
surface finish than on the Provost using micro balloons or talc mixed with water based acrylic varnish.

A few pictures show progress to date. 
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RalphS
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« Reply #1 on: December 18, 2020, 03:25:57 PM »

A few more pictures
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PeeTee
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« Reply #2 on: December 18, 2020, 04:40:54 PM »

Very nice too, Ralph !
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Squirrelnet
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« Reply #3 on: December 18, 2020, 04:53:43 PM »

Nice build Ralph. Its an unusual design I've not seen before , it should look great in red
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Yak 52
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« Reply #4 on: December 18, 2020, 05:19:26 PM »

Nice one Ralph. I always liked the creations of the Teknical Kollege Smiley

The TK4 was an extremely advanced machine for it's time too.
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Russ Lister
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« Reply #5 on: December 18, 2020, 05:52:27 PM »

It's a new one to me .... great subject, Ralph  Smiley
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Pete Fardell
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« Reply #6 on: December 18, 2020, 06:08:54 PM »

Always loved this beautiful little plane, Ralph, and you’ve really captured its lines. I’m trying to remember who did the plan for the gorgeous rubber version in (and on the cover of) AeroModeller in the ‘90s? Might have to dig it out.
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OZPAF
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« Reply #7 on: December 18, 2020, 06:15:16 PM »

Nice work Ralph. Those wing fairings look neat. It will be interesting to see how this flies.

Merry Christmas

John
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RalphS
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« Reply #8 on: January 04, 2021, 02:17:45 PM »

Slow progress.................  Covid/Christmas/Covid/New Year/Covid..and so it goes on with not
much chance of improving yet.  I have had my first jab and should have the booster on Saturday 9th Jan
but that now seems to be in doubt.  Reading between the lines, I doubt that we will be able to to be
completely safe to mix with others until some considerable time in the future.  No point in rushing
to complete the TK4 yet.
 
I was a bit surprised to see that some people were not aware of this little aircraft. Possibly due to its short life. 
I didn't know of the rubber powered version mentioned by Pete but did see a mention of it on the search engine but can't find it now!

So what have I done.  Well, the centre section lower fuselage has been glued in, carved and sanded to near final shape.
I have fixed the fin and tailplane to the fuselage.  Cut the rudder and elevators free and fitted the actuator arms
for them.  To keep the push rod exits below the tailplane level I have fitted a tiny plastic tube to the bottom edge
of the rudder that will be fed over the actuator arm (my description) so that there is nothing sticking out of the
rudder. Similar bent wire arms join the elevators using the same type of plastic tube glued to the inboard ends of
elevators. 

I may fit the elevator horn next, along with the wire pick up to be attached to the elevator push rod. I can then fit
the rear underside panel, carve and sand to blend with the rest of the underside. Still a lot to do - ailerons, form
spinner and canopy, make a pilot, turn up a prop and spinner mount.  Think about the paint work, do I use raised landing
gear or just draw it on? Make decals and get the Silhouette to cut decals leaving a white margin around the edge.

Thank goodness for a reasonably comfortable workshop.  Hope everyone is keeping Covid free.  Happy new year!
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Pete Fardell
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« Reply #9 on: January 04, 2021, 06:51:35 PM »

Looking very good, Ralph.
Just for the record... the rubber version plan I mentioned was in AeroModeller May 2000, and was by David G. Smith. I’ve just dug it out so here are a couple of snaps. He says he actually built two having lost the first OOS.
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OZPAF
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« Reply #10 on: January 04, 2021, 07:57:22 PM »

I like your detail design Ralph - very neat!

John
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RalphS
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« Reply #11 on: January 05, 2021, 09:36:55 AM »

Just for the record... the rubber version plan I mentioned was in AeroModeller May 2000, and was by David G. Smith.

Thanks Pete, you are a mine of information.  I found a copy of that issue - with plan - from Magazine Exchange so have ordered it.

I wasn't taking the AM at that date and have never heard of David Smith, the designer and builder.  The model illustrated looks very good.  Can't wait!

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RalphS
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« Reply #12 on: January 05, 2021, 09:40:32 AM »

I like your detail design Ralph - very neat!

Thanks John.  I like to use the KISS principle.  Kiss Grin   Years of simplify and combine with piece part reduction in manufacturing.
Ralph
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Yak 52
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« Reply #13 on: January 05, 2021, 10:34:15 AM »

Very nice Ralph  Smiley I really like the clean control system.

I'm struggling to judge the scale of it - what thickness depron are you using on the fuselage?


Jon
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RalphS
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« Reply #14 on: January 05, 2021, 11:39:12 AM »

I'm struggling to judge the scale of it - what thickness depron are you using on the fuselage?

Hi Jon, the thick bits are 6mm and the thinner parts are 3mm. The wingspan is about 19", the fuselage is about 12" (without measuring)

 The 6mm and 9mm (not used here) carve very cleanly with a new, sharp snap-off blade type knife fully extended.  A sanding block with rough and smoother abrasive shapes the 6mm thickness very quickly and smoothly. The 3mm can be carefully formed to single curvature shapes.  There are people who have made Lancaster and Halifax indoor r/c models in the NW producing excellent fully formed fuselages from 3mm Depron over wooden moulds and baked in their ovens.  I can't be bothered to make wooden moulds so have used 6mm sheet carved to whatever curves are necessary. 

Pity that Depron is no longer available from sellers.  My flying mate said that he has a few sheets remaining.

Ralph
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Yak 52
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« Reply #15 on: January 05, 2021, 01:47:17 PM »

Thanks Ralph. I've not done that much depron carving as such, mostly I've just designed models with flat panels and rounded corners so far. I generally cover with packing tape which doesn't like compound curves. I'd like to start some more scale/complex shapes in this style but need to work out a filler/painting method. Fortunately I have quite a stash of depron   Cool
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RalphS
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« Reply #16 on: January 08, 2021, 10:17:57 AM »

I have just received the May 2000 Aeromodeller (from "Magazine Exchange") with the rubber powered TK4 feature and plan.  I see that the designer, David G. Smith was from Columbia, SC 29206, USA.  How he managed to produce such a smooth looking finish to a stick and tissue model is amazing. The performance also appears to be excellent.  He was obviously as skilled a flier as a constructor.

Might make one when I finish my r/c version.  Won't be as good as the original though.

Still ploughing on with my foam model.  Dark, cold days don't help.
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RalphS
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« Reply #17 on: January 22, 2021, 03:13:00 PM »

A bit more done - but slowly.  There is no dead-line and the guy who wrote the book (Parkinson's Law) about industrial
organisation, that we all had read many years ago, made it clear that "work expands to fill the available time".  
He knew a thing or two did C. Northcote Parkinson.  

So, fit the aileron servo in a similar way to that in the Foam Provost.  Make the ailerons full length rather than
outboard of the flaps as on the full size - (There is only one person in my flying group who will know).  This
makes it easier to connect the control horn to the ailerons.

I did a trial fit of elevators, rudder, and ailerons and connected the radio to see if they move about as they should.
The actual movement will have to be dialled in later.  Experience on the Foam Provost will help in deciding that.

Think about the cockpit occupant who will be much larger than the Provost crew.  I have vacformed (badly) a cockpit
canopy from a supermarket excessive packaging plastic cover.  This is good enough for a trial fit so I may decide
to leave it that way.

Painting is the next big job.  Too cold and dank to do it outside so the Squirrelnet cardboard box spray booth will
have to be set up again.  All sensitive surfaces in the workshop will have to be protected with old sheets and my
anti-covid masks will be re-purposed for spray painting.

I have had my second vaccine injection - hope it works!
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Re: deHavilland Technical School TK4
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RalphS
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« Reply #18 on: January 29, 2021, 03:49:54 PM »

There is a need to fit a spinner to the TK4.  The motor is supplied with a rubber band-on prop mount.  I couldn't see how to fix a spinner to the mount.  Because the model will be quite light I think that a bolt-on prop fixing will be okay when it comes to flying it sometime. Our field has been under water for several weeks so what with that and Covid restrictions there does not seem to be any need to come up with a quick and cheerful solution - so back to the lathe!!!  Get a piece of 8mm dia alum, use my cross drilling device to drill through 1.6mm (M2 tapping drill). Tap M2 right through.  Turn one end down to 4mm diameter and thread half way with M4 die.  Reverse in the chuck and part off.  Clean up end and drill 1.5mm diameter to fit on the motor spindle.  Tidy up a bit where the cross drilling and the
mounting hole cross.  I will cut a 23mm dia disc from 0.5mm birch ply to fit between the end of the motor and the new prop mount to take the spinner using a similar technique to that used on my r/c Veron Hawker Fury. Took me most of the day but with warmer temperatures and the radio it was enjoyable. The people on the gardening programme said that in 30 days time it will be light until 6pm (London time) so there is hope yet.
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OZPAF
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« Reply #19 on: January 29, 2021, 07:05:54 PM »

You made that sound easy Ralph Smiley A nice bit of shed engineering! Good on you.

John
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RolandD6
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« Reply #20 on: January 30, 2021, 02:33:08 AM »

I notice you have protected the head stock thread but not the cross slide threads.

I use pieces of paper held on with magnets to keep chips and swarf out of the threads. Pieces of junk mail paper can be very handy for this purpose.

Paul
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Squirrelnet
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« Reply #21 on: January 30, 2021, 03:04:59 AM »

Nicely done prop mount Ralph. I share your enjoyment of listening to the radio while working away in the shed, sounds like a nice way to spend a day

Quote
I notice you have protected the head stock thread but not the cross slide threads.

I use pieces of paper held on with magnets to keep chips and swarf out of the threads. Pieces of junk mail paper can be very handy for this purpose.

Paul

Ahhh... so thats what the Nectar card is for ! good idea Ralph and Paul. My older Unimat has a central lead screw which lies directly under the chuck, it leads to constant brushing to keep the threads clear . I'll try a suitably placed bit of junk mail over it next time
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RalphS
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« Reply #22 on: January 30, 2021, 06:46:25 AM »

You made that sound easy Ralph Smiley A nice bit of shed engineering! Good on you.
John
Carving metal is good fun - with the correct, sharp tools.

I notice you have protected the head stock thread but not the cross slide threads.
I use pieces of paper held on with magnets to keep chips and swarf out of the threads. Pieces of junk mail paper can be very handy for this purpose.
Paul
I will try that - save using the high power vacuum cleaner to suck it off.  Thanks.

Ahhh... so thats what the Nectar card is for ! good idea Ralph and Paul. My older Unimat has a central lead screw which lies directly under the chuck, it leads to constant brushing to keep the threads clear . I'll try a suitably placed bit of junk mail over it next time
The Nectar card is there to stop swarf dropping into near impenetrable parts of the bed.  The thread protection is the piece of black unshrunk heat shrink tubing just pushed on.  I usually have the same on the tailstock thread but see it wasn't there this time.
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RalphS
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« Reply #23 on: February 21, 2021, 04:06:00 PM »

It is getting warmer, Covid seems to be retreating, starting to think about flying again.  So, must get on with completing the TK4.

The foam texture varies a bit due to the board thickness and if it has been cut away.  I haven't been able to get a smooth finish without adding a lot of filler.  I don't want to add weight so it will have to do. 

The fullsize was bright red with a tapered white speed line each side. I sprayed the whole model matt white as I was going to use Tamiya "Clear Red". Never having seen this before I assumed it would be okay over the white base coat and so it turned out with a hint of a shine - better for small models than a solid gloss red coat.

The pictures show

The fuselage painted white and masked.
 
The masked model given a light spray of white around the masking edges to attempt to stop bleeding when the red was applied.

Sprayed Clear Red and partly demasked.  No serious bleeding!

Fully demasked. Phew!

Then glued the pilots head to the cockpit interior structure and did a bit of painting to hint at his upper body.  Glued the canopy moulding using "Hypo Cement" and added some self adhesive pre-painted framing. 

Have to next think about making and cutting decals for the registration marks attempting to use the Silhouette cutter with
CAD generated letters.
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OZPAF
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« Reply #24 on: February 25, 2021, 03:11:59 AM »

That's neat Ralph! The canopy and pilot look great - boy it was small!

John
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