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Where to put CF to reduce elevator flex ?

Old 08-18-2019, 03:41 PM
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solentlife
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Default Where to put CF to reduce elevator flex ?

Some may have followed my Hawker Hunter Profile scratchbuild thread and flights.

On increasing power - I have reason to believe that elevator flex is making turns more difficult than they should.

The elevators have a serious taper to them to allow a single servo / wire joiner setup. This makes the outer tips far larger than the inner root where the horn and wire joiner are mounted.

Here's the elevator as now ... you can see the wire joiner and the horn. Also the amount of taper.



Now where would best line be for putting CF to reduce that flex ? A ... B ..... or C ?



Serious question ... and may help others with similar ?
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Old 08-19-2019, 01:20 AM
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quorneng
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Solentlife
Sir Sydney Camm would be turning in his grave at the shape of that elevator on a Hunter!

IMHO it will depend to a degree on what shape CF you intend to put in.
If a tube (good in torsion for it weight) then A but placed parallel to, or even at, the hinge line and fixed rigidly to the horn.. Ultimately how much twist will depend on strength of the glue joint foam to CF.
If the CF is strips then C is likely to be the better option but it will not resist twist to anything like the capability of the CF.
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Old 08-19-2019, 09:17 AM
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As can be appreciated - the shape is dictated by not wanting to have two servos ... straightening the hinge line allowed me to use a joiner and single servo.

The real Hunter of course has split stab / elevators - but the elevators are parallel chord and swept back .... being a sub-sonic flyer.

Another has suggested PVA / Paper combo to stiffen the foam ... instead of paper - I would use light dress material ....

At present still considering replies. The problem seems to be really one of when I push her at speed with 4S .... so maybe simplest remedy is to revert to 3S ??

I also wonder if the high mounted tailplane may be 'moving' in total .... it may benefit from having a triangular gusset glued in either side of stab ?
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Old 08-19-2019, 11:35 AM
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I've just added support pieces under the stab and its a world of difference. The stab is now more stable and I hope will help cure the tail problem.



Snoopy is back in his 'seat' ...



And she's ready to try again ... (I haven't added CF ... I know I know ... )



Many thanks to all replies - they all got me thinking and trying to solve it ..
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