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1/5 Scale Slingsby T51 Dart 17.

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B Sharp
Posts: 723
Joined: 19 Mar 2015, 17:18
Location: Perthshire

Re: 1/5 Scale Slingsby T51 Dart 17.

Post by B Sharp »

Rog, what I think I will do is to extend the hinge line of the fin rearwards by 23mm and remove the top of the fin and replace with the correct shape. This will give a final shape which is much closer to scale and increase the tail volume at the same time. This is illustrated in the image attached.
A check of my scale drawings shows the full size Dart 17 fuselage length from nose to rudder post to be 7.0 metres as near as I can make out. At 1:3.5 scale this equates to 1.40 metres (which is pretty much the length of my 1:3.5 model by CW). The glass fuselage is 1.255m which scales up to 6.275m, 0.725m short or 0.145m at 1:5 scale. As I intend to add a further 23mm to the rear of the fin this will make the finished fuselage length 1.485m which equates to 122mm shorter than scale.
Now I suspect that the fuselage has probably been shortened by this amount in order to cut down the amount of lead that is required to balance the model. I know that in my CW Dart the majority of the nose cone is either lead or filler which makes it a bit of a lump.
However I am not sugesting in any way that a Dart built to the plan and unmodified will not fly well. All of Pats aeroplanes fly well. It is just my tendency to be finiky that leads me to make these proposed modifications.
Brian. :)
Attachments
Proposed extensions to fin.
Proposed extensions to fin.

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Barry_Cole
Posts: 1389
Joined: 10 Mar 2015, 09:30
Location: Hampshire UK

Re: 1/5 Scale Slingsby T51 Dart 17.

Post by Barry_Cole »

Pat's ??

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B Sharp
Posts: 723
Joined: 19 Mar 2015, 17:18
Location: Perthshire

Re: 1/5 Scale Slingsby T51 Dart 17.

Post by B Sharp »

Yes Barry. This fuselage dates back to West Mendip Sailplanes (Pat Teakle) as I have flown a couple from that era. Granted that these are now produced under the ownership of our own Cliff Evans. Can anyone correct me on this?
Brian. :D

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B Sharp
Posts: 723
Joined: 19 Mar 2015, 17:18
Location: Perthshire

Re: 1/5 Scale Slingsby T51 Dart 17.

Post by B Sharp »

Before I do any work on the modifications to the fin/rudder area I need to get the equipment bay sorted out. I need to be able to locate a servo and pushrod so a servo/Rx tray has to be installed. However before that I have to install the wheel well and axel supports. These were made out of ply and were glassed into place.
The servo tray is also made of ply and fitted just above the wheel well once again glassed in place. All very easy-peasy.
Brian. :)
Attachments
Wheel Bay.
Wheel Bay.
Axel supports.
Axel supports.
Servo/Rx tray in place.
Servo/Rx tray in place.
Dart 14.jpg

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B Sharp
Posts: 723
Joined: 19 Mar 2015, 17:18
Location: Perthshire

Re: 1/5 Scale Slingsby T51 Dart 17.

Post by B Sharp »

Having sorted out the wheel and servo arrangements at the front end its now back to the tail end again.
This afternoon I have built the tailplane halves. Due to the shorter than expected tail moment arm I have increased the area by 10% to retain the stability factor. You can see that the blanks have a very simple structure which mirrors the construction used by CW in his plans. I will leave these to set up solid for 24 hours before sanding them to section tomorrow.
I also constructed the all-moving-tailplane horn using epoxy board and brass tubing.
Brian. :)
Attachments
Tailplane blanks ready for sanding to section.
Tailplane blanks ready for sanding to section.
Tailplane crank.
Tailplane crank.

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B Sharp
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Joined: 19 Mar 2015, 17:18
Location: Perthshire

Re: 1/5 Scale Slingsby T51 Dart 17.

Post by B Sharp »

The tailplane is now finish sanded and weighs in at only 1.4oz or 42 gm with which I am very pleased.
The fin was carefully drilled and the actuation slot formed. The slot allows for a little more up elevator than down. The elevator crank fitted in perfectly and the tailplane now sits neatly in place.
The next task will be to manufacture and fit the pushrod before finally fixing the crank into place.
Brian. :)
Attachments
The finished tailplane.
The finished tailplane.
The fin drilled and slotted and with the crank in place.
The fin drilled and slotted and with the crank in place.
Tailplane fitted and sitting pretty.
Tailplane fitted and sitting pretty.

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B Sharp
Posts: 723
Joined: 19 Mar 2015, 17:18
Location: Perthshire

Re: 1/5 Scale Slingsby T51 Dart 17.

Post by B Sharp »

A nice 6mm carbon fibre tube has been formed into a pushrod with clevises at both ends and the tailplane crank swivel tube has been glued in place. The tailplane now sits absolutely square with a long baton sitting across the wing seat.
The fin extension pieces have been manufactured out of ½ inch balsa sheet (stiff but light) the front edged of which has been grooved to allow the balsa to sit inside the moulding by 6mm. I cut the top off the fin and a balsa substitute will take its place.
This has increased the width of the fin considerably and the height by about 30mm.
The next job will be to “pretty up” the whole assembly.
Brian. :)
Attachments
The fin extension components.
The fin extension components.
The components dry-fitted to the fin.
The components dry-fitted to the fin.

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B Sharp
Posts: 723
Joined: 19 Mar 2015, 17:18
Location: Perthshire

Re: 1/5 Scale Slingsby T51 Dart 17.

Post by B Sharp »

I have now just about finished with the tail end of the Dart. The fin extensions were glued into place and a 5mm strip of 1/64 ply attached each side to form shrouds for the rudder hinge line. After sanding I skimmed the fin with a very thin coat of filler and sanded it all back to smooth. I was pleased to find that this only added 30gm (1 oz) to the total weight of the fuselage.
The rudder was constructed and after final sanding it weighed in at 14gm (0.4 oz)
Yes, I have made a whole pile of extra work for myself by reconstructing the fin/rudder area, and yes, the plane would probably have flown absolutely fine without the modifications. However I’m happier that the whole of the tail is much closer to the scale outline.
The only work still to be done is to attach tailplane root ribs onto the side of the fin which will help support the tailplane pivot tube and tidy up the fin/tailplane junction.
Brian. :)
Attachments
The modified fin after final sanding.
The modified fin after final sanding.
The rudder.
The rudder.
Fin and rudder together.
Fin and rudder together.

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B Sharp
Posts: 723
Joined: 19 Mar 2015, 17:18
Location: Perthshire

Re: 1/5 Scale Slingsby T51 Dart 17.

Post by B Sharp »

A wet afternoon has allowed me to get on with the tail end of the Dart. I have now attached the stub roots for the tailplane and applied a little filler to fair them into the fin. Image #2 below shows the complete fin, tailplane and rudder assembly. I have only the hinges and horn to fit to the rudder before these are ready to cover.
Brian. :)
Attachments
Stub roots for the tailplanes.
Stub roots for the tailplanes.
The finished tail assembly.
The finished tail assembly.

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B Sharp
Posts: 723
Joined: 19 Mar 2015, 17:18
Location: Perthshire

Re: 1/5 Scale Slingsby T51 Dart 17.

Post by B Sharp »

Having now finished the tail end the next job is the wing centre section. The plans show this centre section protruding out from the fuselage sides slightly and being attached to the fuselage with 4 x 4mm bolts. The implication being that the assembly stays bolted to the fuselage semi-permanently and the wing halves attach to that.
Once again I can’t leave things alone and I have planned to attach this assembly to the fuselage with a single dowel peg to the rear and with a metal flange/wooden block and two bolts at the front, accessed through the cockpit. This will mean that I don’t have four bolt heads visible from the top.
The laser-cut ribs for the assembly fit together very quickly and accurately. My only comment is that there are 2 x F1 ribs which have to be glued together to locate in the centre. A single F1 rib made of 3mm ply would have been more sensible.
The whole construction is absolutely straight forward with the exception of the trailing edge. Here the plans show a 1/32 plywood trailing edge which butts up against the rear of the ribs and is held in place by the balsa sheeting above and below. I have to say that I have never seen this form of construction before. After a bit of thought I constructed a TE component from the ply laminated with an oversized piece if 1/16 balsa sheet on the underside. I made extensions to the rib up-stands to support the TE in the correct position whilst gluing the sheeting to the underside of the ribs. Once the top sheeting is in place this should stabilise the TE.
Brian. :)
Attachments
The partially built centre section.
The partially built centre section.
Detail of trailing edge construction.
Detail of trailing edge construction.

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