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Old Nov 12, 2008, 07:50 AM
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Ashford. Kent. England
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weather flyable today but a bit breezy...
so out for a quick go with the octagon...
I am still using the little blue motor on this 29 1/2" version and its flying well, no problems but I think the COG wants to be 25% as per the nutball..I am flying with the COG back a bit, and when I put it inverted it climbs by itself and returns to a normal upright flying position..
Normal flying OK... similar to the NB which is expected, but it also seems slightly less stable..this could be because its a fair bit lighter than my big NB..but it rolls faster and loops smaller...so I am not certain...
It was floating well and could be harriered ok in the breeze, but it was also getting knocked about quite a lot..The little blue motor copes well with all general flying but it hasnt enough power for vertical go..
So next I am going to try the heavier/bigger motor plus a bigger battery to get the COG forward a bit more and give it a bit more weight to help in the poor conditions we normally fly in here

this is the little blue motor
http://robotbirds.com/catalog/produc...oducts_id=1787

I will get some video soon if this weather holds good
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Last edited by davereap; Nov 13, 2008 at 03:31 AM.
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Old Nov 13, 2008, 03:26 AM
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Ashford. Kent. England
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installed a larger motor and esc AUW previously 15.25oz now 17.25oz depending on battery this can be up to 18.5oz.... the more forward COG of 25% is now easily obtainable and is recommended, at least as a starting point....

this is the bigger pink motor..
http://www.overlander.co.uk/product....id=82&pid=2581
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Old Nov 13, 2008, 07:33 AM
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Ashford. Kent. England
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I have now flown the more powerfull version and, without doubt it is my best yet...
I think its because it is lighter by 4-5oz than my big NB and so it has a better power:weight ratio

heres the video

The octagon or 8ball - a Nutball version KFm2 (3 min 34 sec)
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Last edited by davereap; Nov 14, 2008 at 02:02 PM.
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Old Nov 14, 2008, 03:46 PM
Onward through the fog.
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Bohol Philippines
Joined Aug 2008
1,566 Posts
Nice vid Dave,
You make it look so easy.

Well the head gasket on the car blew on the way back from Tagbilaran so the car is in the shop and we're house bound for a bit. I'm also caught up in the middle of some honey-do's. The 8-ball, Nutball variant is ready to go but not sure when I can get out to the school. Wanted to go this weekend. Maybe we can take a tricycle. I have a carpenter here working on my boat at the moment too. Just a busy time and weather isn't cooperating either.

Same problem you had but at least here it's warm rain.

Steve.
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Old Nov 14, 2008, 03:49 PM
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Ashford. Kent. England
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Glad you liked the video..this sized rudder verson has turned out to be a great flyer..I think even better than my big nutball...I think the better power:weight ratio has everything to do with it
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Last edited by davereap; Nov 19, 2008 at 06:28 AM.
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Old Nov 14, 2008, 03:55 PM
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Ashford. Kent. England
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CONSTRUCTION NOTES
.... for the 6mm depron version
The build is identical for the normal round nutball shape

1.... draw up the octagon shape, using a series of parallel lines ...note a 12" set of lines will give you a 29.5" flat octagon and is a good size..
Cut one complete octagon for the main skin, and one half octagon for the top skin..Or cut one circle and one half circle
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Old Nov 14, 2008, 04:01 PM
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Ashford. Kent. England
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2.... cut a balsa spar 1/2 x 1/4...this is to be glued at the 50% step position
cut a depron spar ...(width not critical)...1.5" wide this goes between the skins at about the 30% position

each spar has three parts as seen in pic 2 ...the end sections are tapered from about half their length from 1/4 down to 0 thickness..

pic 3 shows the tips cut and glued and the spars also glued to the bottom skin

each tip is raised by 3" the joints were chamfered to about the correct angle, they were then glued with uhu-por ,, a cool melt glue gun was used running along the joints top and bottom to fill any gaps and strengthen the joint

the cool melt was also used to strengthen the spar joins.
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Last edited by davereap; Nov 14, 2008 at 04:09 PM.
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Old Nov 14, 2008, 04:22 PM
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Ashford. Kent. England
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the last main part..the top skin can now be fitted..

first the centre section ...then each of the tips... the tips will need some triming to get the edges champhered and because theres a slight curve the edges will need to be shaped a little bit to acheive a good fit..
fit dry first

Then apply uhu-por in about a 1.25" width arround the edges where the two skins will be joined ...and also use the uhu on the top of the balsa and depron spars

important note always laminate putting the rear edge down first onto the balsa spar..work forward to the depron spar then to the leading edges..
also work from the center first and go outwards with your pressure
Do your laminating on a flat surface...I use a glass topped table ..this is where you get a flat wing..or build in warps if you are not carefull

Another run arround with the cool melt gun is now the job..fill any gaps and put a thin layer along all seams
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Old Nov 14, 2008, 04:33 PM
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Ashford. Kent. England
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Engine mount

cut a slot through both layers to accept your mount, stick or tube type, glue the mount in using the cool melt gun..filling the slot....remember to cut for any side thrust and, when you glue, angle the mount down for the down thrust..

To reinforce the mount cut a 3" width 6mm depron for below, and a 3" width 6mm depron for the top..the depron goes from the leading edge back to the 50% step
Laminate these on using the uhu-por
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Last edited by davereap; May 05, 2009 at 04:14 AM.
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Old Nov 14, 2008, 04:46 PM
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Ashford. Kent. England
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Tail and Rudder

note the tail fin takes a lot of stress...so

Fix the tail fin in place with a couple of small side supports using epoxy..
Also fit a length of 2mm CF rod down its leading edge.. this goes through the wing and into a hard balsa underspline or block, which is also epoxied in place..My 1/2 x1/4 hard underspline ran from the trailing edge forward to the 50% step location
The CF rod is taped to the fin using 2" colored packing tape..

Reinforce, stiffen and strengthen the fin with a complete layer of the colored packing tape...similarly cover the rudder and use the tape as a hinge.
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Old Nov 14, 2008, 04:49 PM
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Ashford. Kent. England
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Taping it up

Elevator and Rudder

cover both sides with packing tape..this realy stiffens it up..put more tape top and bottom along the trailing edge of the wing... use more tape to hinge the elevator


Tape decor and reinforcing
Use the 2" wide tape..(zagi type of idea...available from staples in the UK)
tape top and botom of the leading edges, then all seam joints, even though they were glued..then another strip on top of, and below, the KF strip..It realy does add a lot of strength for only a bit of weight
You can cover the whole airframe if you like but it will add about 1.5-2oz .
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Last edited by davereap; May 05, 2009 at 04:18 AM.
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Old Nov 14, 2008, 05:01 PM
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Ashford. Kent. England
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Radio fixing

The servos are surface mounted with double sided sticky tape then glued with the cool melt adhesive... they wont come off without taking the depron as well..

The remainder of the gear is fixed on using velcro strips and tiedowns as seen in the last pic above ..
.sorry about its patchy nature but it was made by chopping up the first prop in slot version which had turned out no good. you can see the repairs where I removed the servos and filled in the prop slot holes etc


motor see post 77 prop 9x5gws 11.1v lipo

video
The octagon or 8ball - a Nutball version KFm2 (3 min 34 sec)
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Last edited by davereap; Nov 14, 2008 at 05:11 PM.
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Old Nov 14, 2008, 05:16 PM
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Ashford. Kent. England
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Wheels
two strips of velcro on the 2"wide depron lower reinforcing strip hold a removable trike UC in place

build here... http://www.rcgroups.com/forums/showp...16&postcount=2

Alternativly you can use the two wheeled version if you like...
But for the two wheeled version you will need to fit a spline fuz underneath the main wing

my choice is for the trike version..
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Last edited by davereap; Jan 11, 2009 at 09:26 AM.
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Old Nov 17, 2008, 11:42 AM
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gladwin,mi,usa
Joined Sep 2000
35 Posts
I'm about to try building this plane and was wondering if the kf wing design was just used on the center section and not the dihedral wing tips, would that signifantly change the flight characteristics? It would seem to save a fair bit of weight (foam, glue, and tape) and also be a lot easier to build since you wouldn't have to fit the tips.Also, I'm not real familiar with the kf wing design, but I did read where the thickness should be about 7%-9% of the chord. Do they figure that on the total chord(29" in this case) or just back to the step(14.5" in this case). Based on this design there is a 3/4" thickness on the wing at the step. This may sound basic but I'm a little confused. I have built and flown a 20" Dia NB but I wanted something bigger and heavier to handle the wind. Thanks for the help.
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Old Nov 18, 2008, 09:56 AM
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Ashford. Kent. England
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I havnt tried just using the KF on just the centre section, but used on the whole wing it does add a lot of stiffness...Try it, you can always add the tip sections later on..
For the step depth, I have been using a 1/4 thick balsa spar then glueing the depron on top..so the total step depth is about 12mm...(if you build with 6mm depron or 9mm if youve used a 3mm top skin)..this is the same all across the centre section ..from there the balsa gets tapered down to zero stopping 1 1/4" in from the edges so you can glue the layers together...personally I would use all 6mm depron of FFfoam whatever..the thinner depron does not save a significant ammount of weight..
Not accurate to the reccomendations on the KF thread, but it works, and you can see from the video that it will glide quite well..
In my different trials using the KF step, I have gone down as low as a 4% step depth, and the thing (the KF step) still does good...so I dont worry too much, I just dont get the tips with too thick a section...10% of the chord max..I always keep the step at a constant depth, even on tapered wings...so the ratio of step depth to chord can be half as much at the centre compared to the tips..
I would recommend going onto the tips as well, but this is for strength more than for performance..with the step you can handle the plane by the tips...without? you will just have to try....even a NutBall with no step goes well..
dont forget the tape reinforcing ...this again makes the whole thing a lot stronger for only a bit of extra weight....

for comparisons..
.
29.5" octagon video....
The octagon or 8ball - a Nutball version KFm2 (3 min 34 sec)
flying at 17.5oz
32" nutball video....
Nutball RC 32" KFm2 (6 min 2 sec)
loads of tape decor .. flying at 22oz .... 4ozsqft
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Last edited by davereap; May 05, 2009 at 04:22 AM.
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