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Re: 1/4 Scale Charlesworth ASK13

Posted: 24 Oct 2019, 11:02
by Peter Balcombe
Moving on to the tail feathers, I spent a quiet day yesterday attaching the fin, rudder & tailplane ribs to their respective spars using Cyano, ensuring alignment using a straight strip of balsa clipped between TE of end ribs for Rudder & Elevator.

Although the plan calls for TE from lengths of rectangular balsa, tapered to TE profile, then skinned with 1.5mm Balsa each side to match skinning elsewhere on each part, I decided to amend the process a little.
I firstly attached a strip of 0.4mm ply to the end of each rib underside to form a TE core, which would better define a sanded edge.
I then applied 1/16" balsa cap strips each side of this on the rudder (as there was very little rib contact, even after widening the TE strip from 9mm to 1/2") & similarly on the elevators after first glueing 1/16" balsa infill on top of the ply strip between each rib & sanding to profile before adding the top 1/16" cap strip.

The photos below show the components at this stage, apart from adding the top 1/16" balsa cap strip to the elevators. You should just be able to see the ply line at the TE after sanding the infill.

At present, I am building the RH elevator as standard. At some point, the trim tab will be released & either the removed piece hinged, else replaced with solid balsa item.
The various tips will be balsa blocks to be added later.
The Rudder LE also needs to have a tapered 1/2" balsa piece fitted to the front of the current 1/8" laser cut item - the whole then shaped into a semicircular LE.

Re: 1/4 Scale Charlesworth ASK13

Posted: 09 Nov 2019, 11:51
by Peter Balcombe
Progress has been made on the tail feathers over the past couple of weeks.
The fin has been completed and fitted to the fuselage, as has the tailplane - after getting the rake angle of the elevator hinge spar correct.
(The elevator hinges pivot at the rear face of the tapered elevator LE, so the tailplane hinge spar needs to be raked to suit the elevator taper angle in order to get a uniform gap between tailplane & elevator LE.

The tailplane is mounted using 2 pins at the lower rear, which slide into small brackets. The front of the tailplane rests on a bed and is secured using a single bolt into a captive nut.

The elevator has had its trim tab hinge spar added, so the tab space can now be removed & a solid balsa item fitted. The tab is pin hinged, but no details are included on the plan as to how this is intended to be operated (else fixed in position?). The Charlesworth Olympia 2b has a link back to the tailplane to give opposite tab movement wrt the elevator, but nothing is shown on the ASK13 plan.

The rudder horn has been fitted & a start made on adding the skinned areas.

Meanwhile, back on the fuselage, MPX connectors have been fitted at the wing root to connect the wing servos. The connectors are actually mounted on an internal part of the fuselage root structure which recesses the connectors slightly. ( The wing connectors can be pushed back into wing root pockets, so connectors/cabling are tidied away for storage).

Re: 1/4 Scale Charlesworth ASK13

Posted: 12 Nov 2019, 17:30
by Peter Balcombe
Today's job has been to revise the elevator horn/pushrod attachment method to ease rigging in due course.
The following method was used successfully on a Charlesworth Olympia 2b and allows the tailplane to be easily placed in position without any need for coupling up the elevator pushrod.

A 16SWG cross pin is soldered into the elevator horn as shown below and this is arranged to be able to drop into a slot in an upright pivoting arm, actuated as normal from a long pushrod down the fuselage.
The pivoting arm is made from 4 strips of epoxy board, epoxied together as shown. The outer strips have a crosswise slot cut at the top to receive the elevator horn cross-pin, whilst one of the inner strips has a forward projection for the pushrod clevis. The other inner strip is just a spacer to give sufficient gap between the outers to easily accept the elevator horn.
The slots in the outer strips needs to be a good sliding fit on the 16SWG cross pin to avoid elevator connection slop.
I find that if the slot is initially cut with a hacksaw blade, a rectangular needle file makes the slot width just right.

On the ASK13, the protruding 1/4" wide bottom keel strip make a good base to which a couple of side plates can be epoxied.
The pics below show the assembled arm, installation in the fuselage and the elevator horn cross pin.
(Note that the fuselage attachment point will be reinforced with balsa blocks in due course.)

Re: 1/4 Scale Charlesworth ASK13

Posted: 17 Nov 2019, 10:35
by Peter Balcombe
Further progress has been made to install the Rudder & Elevator servos on a tray in the fuselage, plus make up the elevator push rod from a length of thick walled carbon tube as shown below.
The rudder has also been hung and now just needs a few rib cap strips to complete.
The elevator has also progressed to install the hinge plates, and then the rib capping once the trim tab aperture had been cut out.
The plan appears to show a solid tab, but I cut off the tab area from the built-up structure & faced the LE prior to sanding a curved LE as shown.

Although the Charlesworth plan shows a hinged tab, it doesn't mention any method of tab control.
The full size K13 has a longish horn mounted on the top of the inboard end of the tab, with a push rod connecting this horn to a bellcrank under the rear of the tailplane within the fuselage opening. The bell-crank is operated by trim levers in each cockpit. The push rod passes the inboard end of the elevator & disappears into the fuselage opening near the elevator connection.
For our purposes, the forward end of the push rod can be fixed to the bottom rear of the tailplane to make rigging easy. The trim tab should then appear to work as an anti-servo tab as on the Charlesworth Olympia 2b.

The rudder servo will connect to an intermediate rudder bar to achieve the correct C/L same connection spacing as on the rudder horn.

Re: 1/4 Scale Charlesworth ASK13

Posted: 17 Nov 2019, 11:58
by Peter Balcombe
The 2 pics below show the full size elevator trim tab & pushrod for info.

Re: 1/4 Scale Charlesworth ASK13

Posted: 20 Nov 2019, 19:05
by Peter Balcombe
The elevator trim tab now has a (longish) horn fitted and has been hinged - although the outer hinge pin can be removed to remove the tab for covering etc.
Talking of which, the next job here is to cover the structure before the elevator is fixed to the tailplane

Re: 1/4 Scale Charlesworth ASK13

Posted: 27 Nov 2019, 11:02
by Peter Balcombe
A couple of bits of rework have been done on the fuselage servo installation & wheel mounting.
I decided that having a remote rudder crank behind the servo area was going to make any maintenance tasks very difficult once the turtledeck had been completed, restricting access to the front only (unless you have a removeable turtledeck section above the wing joiner area).
An extended rudder servo arm has thus been bolted to a servo disc & the servo raised slightly to ensure that the C/L wires pass above the elevator pushrod.

The 2nd issue was that with the mainwheel now available, the space between the wheel pant sides was going to be insufficient to get the wheel in once I had fitted the two 20G aluminium axle supports. Thus the wheel pant had to be removed, a couple of mm taken off the sides of the fuselage former slot & everything put together again :(
However, once done (and the inside of the new wheel pant re-glassed) there is ample space.

With the wheel installation sorted, the hardwood skid rear mount and aft balsa fairing have been fitted & roughly shaped.
The skid has also been cut from 1/8" Spruce sheet and the hardwood forward skid mount made & fitted.

Re: 1/4 Scale Charlesworth ASK13

Posted: 01 Dec 2019, 11:44
by Peter Balcombe
The tail feathers have now been covered with natural Solartex and the elevator assembly attached to the tailplane as shown below.
A short piece of piano wire goes from the trim tab horn to the underside of the tailplane between the elevator horn and RH tailplane locating pin, just forward of the elevator hinge spar (where a full depth balsa block was installed to fix the tailplane locating pins).
A couple of small bends on the wire allows the wire to clear the elevator during full movement.
The result causes the trim tab to act as an anti-servo tab.

Meanwhile, up forward - a couple of 0.8mm ply turtle deck sections have been fitted plus the outstanding side sections to finish the skinning apart from the final front turtledeck section over the servos & a bit of fairing around the rear of the root rib once the angled ends have been finally fixed.

Re: 1/4 Scale Charlesworth ASK13

Posted: 01 Dec 2019, 12:49
by RobbieB
Peter, why would you want an anti-servo tab on a servo operated control surface?

Set up as that, the servo is trying to move the elevator up and the tab is trying to push it down again. Anti-servo tabs are designed to put some 'feel' into the stick with a pilot on the other end of it, not a servo. It's just making the servo work harder.

Re: 1/4 Scale Charlesworth ASK13

Posted: 01 Dec 2019, 13:20
by Peter Balcombe
That is just the way it happens to work with the push rod fixed to the tailplane in order to make rigging easier (the tailplane comes off complete with trim tab pushrod attached & happens to work in a similar way to the elevator tab on the Charlesworth Oly2b - its just that on that model the tab pushrod goes from a horn on the bottom of the tab to a horn on the top of the tailplane).

On the full size ASK13, the elevator trim tab pushrod connects to a bellcrank inside the fuselage just below the elevator half connection, which in turn is operated from the trim levers in both cockpits.
The trim tab on a K13 is not just a trim tab it is also an anti-servo tab.
In trim mode the tab moves the opposite way to the elevator. ie if trimmed forward (nose heavy) then the tab will move UP which forces the elevator down.
In Anti servo mode as you move the elevator the tab moves the same way as the elevator, which increases the load on the stick the further the stick is away from the elevator neutral position
Viewed from outside, the trim bellcrank moves the same way as the elevator with zero deflection of both elevator and trim tab happening at about the same point. The trim effect is to move the zero deflection of the trim tab point to either elevator 1/3 up or 1/3 down.

Hope this makes sense, but I happen to have used the anti-servo mode on the model in order to simplify rigging.