1/4 Scale Charlesworth ASK13

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Peter Balcombe
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Re: 1/4 Scale Charlesworth ASK13

Post by Peter Balcombe » 01 Dec 2019, 13:20

Robbie,
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.
Peter

John Vella
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Re: 1/4 Scale Charlesworth ASK13

Post by John Vella » 01 Dec 2019, 13:50

RobbieB wrote:
01 Dec 2019, 12:49
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.
Robbie, the reason for doing it is because it imitates the movement of the full size K13. On my Charlesworth K8 as the tailplane is normally left rigged the push rod comes from a quadrant on the fuselage under the tailplane. The tab movement thus follows the full elevator travel in a scale antibalance fashion. This scale setup has worked well for many years. In the event of derigging one mini lock nut on the end of the push rod is undone. Regards John.

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Cliff Evans
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Re: 1/4 Scale Charlesworth ASK13

Post by Cliff Evans » 01 Dec 2019, 15:48

Works well on the Cliff Charlesworth Oly as well!

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RobbieB
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Re: 1/4 Scale Charlesworth ASK13

Post by RobbieB » 01 Dec 2019, 20:49

I'm very familiar with the operation and principle of Flettner-type trim tabs in all their guises - numerous years experience with them on big ship's rudders was my first introduction and experience with those boys.

My point is, why introduce something into a model, purely in the interest of scale that is not in the best interest of a servo doing its best to operate the control surface - it's a servo, not a human. It serves(no pun intended) no useful purpose other than scale fidelity and will have a detrimental effect on the servos performance and power consumption.

Scale versus logistics? In this case, for me, logistics wins hands down - all cons and no pros.

I now await my lashing from the Scale Police with baited breath...........................

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Peter Balcombe
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Re: 1/4 Scale Charlesworth ASK13

Post by Peter Balcombe » 01 Dec 2019, 21:18

Robbie,
As I said earlier, the trim tab operation happens to be scale, but was chosen to simplify model rigging - slot the tailplane on without any need for separate elevator or tab linkage connection :D
(Same form of operation on the original Charlesworth Olympia 2b plan & my VV400 flies very well with a standard analogue servo).
Peter

John Vella
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Re: 1/4 Scale Charlesworth ASK13

Post by John Vella » 01 Dec 2019, 23:04

Robbie, if you look at the pics of my K8 you can see that the Flettner Tab system is quite a noticeable feature. I am modelling a scale glider and the extra load on the elevator system is minimal and my servo and double battery system is well able to cope . PS the elevator loads on the full-size are rather light, and the system was put in to deal with ham fisted abinitio pilots. Regards John.
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Peter Balcombe
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Re: 1/4 Scale Charlesworth ASK13

Post by Peter Balcombe » 05 Dec 2019, 10:41

Moving back to the wings, I have have progressed the LH wing top surface around the brake box & covered the D box to the start of the last bay.
Next job is to tackle the root end which tapers down towards the next rib.
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Jilles
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Re: 1/4 Scale Charlesworth ASK13

Post by Jilles » 07 Dec 2019, 23:41

Hi Peter. nice touch that scale like operating trim tab. However it is working the wrong way. When set to a certain setting the trim tab should move the opposite way to the elevator movement. If the elevator moves up the trim tab moves down relative to the elevator and the other way around
All Schleicher models from K6CR to ASK13 had this feature except those with the all flying tail plane like K6E
If the glider needs down trim the elevator needs a down thrust that is achieved by the trim tab going up.
I did experiment this on a full scale K8, by keeping the stick(elevator) in a fixed(blocked) position. One can then control pitch by the trim tab only. but moving the trim lever forward resulted in nose up and they other way around.

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Peter Balcombe
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Re: 1/4 Scale Charlesworth ASK13

Post by Peter Balcombe » 08 Dec 2019, 09:32

D box & root end skinning now complete on the LH wing, with aileron still to be cut out, LE, tip and all rib cap strips to be fitted.
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Geoff Pearce
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Re: 1/4 Scale Charlesworth ASK13

Post by Geoff Pearce » 08 Dec 2019, 10:47

Looking very nice Peter,l

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