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Nov 08, 2009, 06:00 AM
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My method for KFm wings

I will use my Nifty as the example...for one method
Cutting cant be easier all straight lines for the wing layers.. I decided to put the top and bottom KF steps at 45%, again keeping it simple..
Main/centre layer 32 x 16.. 1 off
outer layers 32 x 7 1/4.. 2 off
Spars Balsa 1/4x3/4 x 32.. 2 off
marking up..
Put a line 1.5" from the front on both sides of the main panel and one side of each of the 2 layers/steps. this is where you will spread the uhu to laminate the layers together to form the leading edge...
On the two layers/steps also put a line 3/4 from the rear edge.. this is where the spar will be stuck
On the main panel put a line across at the rear of the step position..put another line 3/4 in front of that one..repeat on the other side.

one side at a time...spread UHU por along the LE and the spar positions on the main panel..
Spread uhu along one surface of one spar.
Spread uhu along one of the layers at LE and spar positions.
the first fix - the spar
By now the spar coating and the main layer coatings will be dry, so on a flat surface push the spar in position, then rub it down hard to fix it.
more glue
Spread uhu on the top of the spar and wait for it to dry.
the second fix - layer 1, the top
The top layer can now be fixed...with care position the layer first onto the spar, and rub down hard, it is important the layer must be fixed firmly to the spar and not be able to pull starting from the centre push the LE down to meet the main panel, work outwards, and firmly fix the two layers together..

Important notes
Do your laminating on a flat hard surface.. I use a glass table top..

The push down and fixing should always start at the centre of the wing and with the top layer.. for V wings and deltas this is at the nose..use two hands and work out from the centre evenly and at the end you will have a warp free laminated wing... when the first lamination is made some very slight curvature of the section occurs, with a KFm4 this will be reduced slightly, when the other sides lamination is made.. But it never all goes. dont worry, the wing will still fly well

Turn over and repeat...what youve got should look like the brown sections in the above picture

Shape and tape...

Shape the LE to a nice profile either symetrical or semi symetrical depending if KFm4 or KFm2

use 2" tape to cover the LE..TE.. and steps locations...It is quite practical to cover the complete wing, it makes for extra strength and stiffness..And double the tape at stress points like the prop cut out corners

Also cover the ailerons fully, for better stiffness

do not leave the tape off

On smaller models you can make the section using 3 layers of 6mm depron, no spars are required and the structure is good..
An example build is here..

method two ... now used the most...
Forget the balsa spars... there is no real need for deep KF steps.. 6mm high steps are ideal on most small models.. that's up to about a 48" span and 8-10" chord..
Simply laminate layers directly..
Then use a pallet strapping sandwich along the foam where the spars would normally fit.. or where its possible to place the straps..
crossing straps is fine, double parallel lines are good , the strapping even works with dihedral as it bends easily at the V..
see my latest PP1 model for examples..
Last edited by davereap; Apr 01, 2015 at 02:21 AM.
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Oct 07, 2013, 02:06 AM
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The second method is to simply use direct laminations of the foam , leave out the balsa spars
Put a CF spar into the main layer and trap it between the KF outer layers..

on very small wings no spar is needed.. Ive used EPP like this on 23" span wings, no spar and its flexible but not noticed in flight

Ive now been using pallet strapping instead of spars.. this works a treat... simply stick the strapping to the top and bottom wing surfaces to make a foam sandwich.. as strapping is so cheap I now use this method all the time..
Last edited by davereap; Apr 01, 2015 at 02:24 AM.

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