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Jul 09, 2009, 04:26 AM
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davereap's Avatar
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Build Log

A simple build Plank with KFm section.. with WOW! factor.. Called the "Nifty"

Rather than have the build spread out in the main KF thread, I decided to repost it all here
What was just a maybe idea built very quickly and flew so well I have to plug it like mad...dont miss out, its simple to build and WOW is the best way to describe how it goes...superb

edit wow its ugly as well

heres how it started
Ive just been looking at whats in the shops and came across this design in epp... My first thought was an easy KFm4 build, cant get much simpler 600 span 300 chord is the size and the pic tells the rest

The 600x300 is the 24" version... but the first Nifty built was a 32" version
Last edited by davereap; Apr 30, 2017 at 04:53 PM.
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Jul 09, 2009, 04:37 AM
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With a supply of 6mm depron I got cutting.
At my location small light planes are not the best, so I decided to go up a size ..from 600 span to 800.
800 is a good size and coresponds to the width of my sheets.. keep it simple .. the 32" span gave a 16" chord and an aspect ratio of 2..
Hence it designation as a KFm4-AR2-Plank

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..measurements in inches
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.......shown in red use balsa not depron..the balsa makes much stronger wing
Rough FUZ 3 x shape as drawing
wing tips 2 off, are near triangles 17" long x 6 1/4" high..but with a front squared edge 3/4 deep..check the picture first

EDIT there is a revised build .. It is easier and very simple..... directly laminate all the foam layers... and using pallet strapping instead of balsa spars, glue the strapping top and bottom of the wing making a strapping/foam/strapping sandwich...its a strong wing.... .. the rest is much the same..

If you want, for more strength, the main layer and its elevons can be doubled , then you can use a cloth hinge fitted between the layers..
Last edited by davereap; Jul 13, 2015 at 12:08 AM.
Jul 09, 2009, 04:45 AM
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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 7 1/4" ..this is the rear of the step position..put another line 3/4 in front of that one..repeat on the other side.
On the main panel cut off a 3" strip from the back for the elevons
one side at a time...spread UHU por along the LE and the spar positions on the main panel..
Spread uhu along one side of one spar.
Spread uhu along one of the layers at LE and spar positions.
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.
Spread uhu on the top of the spar and wait for it to dry.
The top layer can now be fixed...with care position the layer first onto the spar, and rub down hard, now starting from the centre push the LE down to meet the main panel, work outwards, and firmly fix the two layers together..

Turn over and repeat...what youve got should look like the brown sections in the above picture
Last edited by davereap; Jul 09, 2009 at 07:12 AM.
Jul 09, 2009, 04:46 AM
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Take your 3 rough cut FUZ parts and laminate together.. then fix them nicely central and squre under the wing. uhu will do the job ok.

The square stick for the motor mount is epoxied centrally on to the top front on the fuz blocks..shown in red pic3 two posts back... now make sure you can fit the motor mount to the front of the stick. Fill at the sides of the stick with more depron then add a further pair of side cheeks to the fuz ....see pic 5
Put the motor in place and do some carving on the fuz to get the shape you want..pic1

Shape the LE of the wing to a nice symetrical profile..

Thats the main build done... glue on and shape the tip fins, fit the elevons, and importantly you should add reinforcing tape as and where shown in the pictures..
The tape reinforcing uses the 2" wide colored packing tape.. this adds strength and damage resistance to the model and I think its a must use...
Fit the radio gear, again as per the pics and you will be OK

Important edit
The COG location should be at 20% for the first flight, with about 3mm up on the elevons.. launch at moderate power and it will go hands off..power up trim out and enjoy.
My impression is the COG can go back slightly for improved performance..
as the cog goes back you might need to reduce the elevator movements.. and use loads of expo to keep it sweet..
Last edited by davereap; May 26, 2012 at 03:16 AM.
Jul 09, 2009, 07:25 AM
“There’s no place like Foam”
gpw's Avatar
Love those Planks!!! .... We used to make them from Ace Foam Wings , with .049s... Not the most stable platform, but lots of FUN !!!!! The bigger the fins , the more it flies like a wheelbarrow... some experimentation is indicated...
Latest blog entry: Lost plans
Jul 09, 2009, 07:28 AM
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Try now with the KFm4 will be amazed... guaranteed

The KFm4 section has made this wing so good I dont beleive it myself..

These are hands off stable yet highly manouverable the best of everything..
Good safe glide, fast rolls etc...

And best of all its as simple as they come..

This the 24" 3mm depron version
24 inch Nifty the KFm4 plank - 1 (3 min 30 sec)

24 inch Nifty the KFm4 plank video 2 (2 min 46 sec)
Last edited by davereap; Aug 03, 2009 at 03:10 AM.
Jul 09, 2009, 07:34 AM
“There’s no place like Foam”
gpw's Avatar
We most certainly will !!!! Thanks !!!
Latest blog entry: Lost plans
Jul 09, 2009, 08:04 AM
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Gear and plane specs for the 32" version

2x 9gm servos
30A ESC ( bigger than actually needed )
corona 2.4Gb 4ch REC
1250 3 cell rhino lipo
9x5 gws prop
This motor..
Which gives 24oz thrust at 150W approx..
The plane weighs in at 15 1/4oz AUW which gives a wing loading of 4.3oz sqft

results... five grins...oh boy does it go

New motor added.. The cheepo bell, the 2208-21.. use a cut down 9x5.. cut to 7.5x5 and 3 another 2000 revs and about the same static thrusts..hovers on half power

Specs on a 24" are
2x5gm servos.... corona 4ch 2.4G rec
BW motor... 8x4 GWS prop
18A ESC... 1250 3 cell lipo
AUW...10.5oz area 2sqft
Last edited by davereap; Aug 03, 2009 at 03:15 AM.
Jul 09, 2009, 11:16 AM
D'oh.. Dumb Left Thumb
dekan's Avatar
Well done Dave... saves paying £25 or about $40US... Just what my FB is looking for...
He almost bought the Epp kit, but he's a bit "financially challenged" at the moment
Ok for the B&Q foam and lots parcel tape..
Jul 09, 2009, 11:28 AM
Out the Window
High Flyin''s Avatar
Dave....great looking design!

Since you have built several NutBalls, how does this one fly in comparison to the NutBall?
Are you using EPP on this one? How thick is the foam you are using?

Looking forward to the video!

Jul 09, 2009, 11:34 AM
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Dickeroo's Avatar
Originally Posted by davereap
Try now with the KFm4 will be amazed... guaranteed

The KFm4 section has made this wing so good I dont beleive it myself..

These are hands off stable yet highly manouverable the best of everything..
Good glide fast rolls etc...

And best of all its as simple as they come..

I will get video as soon as the wind dies down

Dave... I'm grinning from ear to ear. It just amazes me how the KFm4 airfoil can offer so much with so little cost and time to build. And, provide the strength that the wing needs without adding additional support. It's almost too good to be true. Another terrific thing is that the KFm concept allows for a wide range of experimentation. And, that's part of the fun of RC flying. Congratulations on a great experiment.
Jul 09, 2009, 12:47 PM
Looking forward to a vidio on this one dave,it,s as easy as the nutball to build and by the sound of it just as much fun.Goes to the top of my list with the stinger by Bogard.Just happen to have a couple of 1200X800 grey depron sheet waiting to be cut.

Last edited by jclassic1; Jul 09, 2009 at 01:10 PM.
Jul 09, 2009, 01:28 PM
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high flyin'.. all 6mm depron foam.... comparison with the nutball...difficult, they are two very different planes and each will cover different aspects of flight better.. I would say have both, as they are complimentary... the best I can say is I felt totaly confident with the planks flight, right from the start, and this makes you able to push your limits... my only other plane ever to do this was the 38" KFm4 superfly clone, and the plank' flight is more like that one, than the nutball

dekan.. I am still visiting my B&Q but they wont get me any of their foam
The robotbirds kit is £25 plus post, so not too expensive, I will let you work out the cost of mine, but I suspect its less than £5

Dick.. what ever did we do before we got your airfoil... from GPW's post, earlier versions of similar planks were a bit on the unstable side... this one is just the opposite, going precisely where you want with no problem, slow and fast. Yet I can manouver it as tight as I want..unbelievably good

jclassic1.. much easier to build than the KFm4 Nutball ..all straight lines.. no dihedral to allow for.. everything just square

edit here is some more info
Last edited by davereap; Aug 23, 2010 at 08:47 AM.
Jul 09, 2009, 01:53 PM
Dave ,I haven,t got any balsa for the spars so do you think that a strip of depron will do.I may have to add a carbon spar behind the top step.

Jul 09, 2009, 02:04 PM
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I would say treat yourself to a 1/4" x3" hard balsa plank and cut the 3/4" strips from that..Its far cheaper than adding a CF spar ... do not use just depron, its too flexy and doesnt add the strength that you will get from the balsa.. A CF tube or rod will do the job, but 2 balsa spars will only cost 60p..Better to wait till youve got the balsa.. dave

heres a video ..the flight was made with the cog at can see with the trim set for this cog power up causes a climb and eventually a loop... A second flight with the cog at 20% had the trim reduced and power up causing only a slight climb..At 20% its is still easy to fly but will loop or come round from a vertical bank so quick you will almost miss it.
This is the first video where the plank got its name Nifty.
The 32" 6mm depron version
A simple build KFm4-AR2-plank...The "Nifty" (5 min 20 sec)
Last edited by davereap; Aug 03, 2009 at 03:11 AM.

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