yak 55 32" hobby craft foamboard build - Page 4 - RC Groups
Shop our Airplanes Products Drone Products Sales
Thread Tools
Sep 27, 2017, 04:28 AM
Registered User
Quote:
Originally Posted by Extreme Sports
I assume your 2mm spar is just a 2mm rod? If that is the case it adds nothing but weight, unless your structure is such that the combined effect of the spar and the wind is stiff - the rod on its own is not very stiff.

You'd be better off with a strip of CF bonded to the top or bottom wing surfaces (in effect creating an I beam), or using a 5mm CF rod (the rod on its own provides the stiffness).
Yes its a round solid cf roll which is hot glued into a channel on the wing it is adding some strength but not enough. I have crashed this thing numerous times and yet to break the wings, im sure without it the wings would have creased long ago in the middle (there has been one crease on the edge just beyond where the spar reaches)

anyway ill go for a carbon strip isntead on the next build.

I think i have improved the elevator issue though, it looks that when i removed the paper its also removed some of the glue holding the spar in so i reglued the spar which reduced the twisting, and then layered scotch tape which brought back the original strengtch that the tape has, it still twists on one side, hopefully when i take it back out i will see less elevator flutter. IM guess this is why im finding that im lacking elevator authority compared to ailerons
Sign up now
to remove ads between posts
Sep 27, 2017, 09:41 AM
Registered User
Extreme Sports's Avatar
There are two things a spar needs to do:
1) Keep the wing from breaking - by the sounds of things your CF rod does that
2) Keep the wings relatively rigid - ideally in both the bending and flexing planes. A 2mm CF rod definitely won't do that, but 2 rods or flat strips glued to the surface of the wing should do a better job.

Be interested to hear back how noticeable the rigidity improvement is on your next build.
Sep 27, 2017, 09:58 AM
Registered User
I had an idea.... why not give the wing a KF airfoil. i just came across a video (for a CAX 88 3D plane) which used the KF airfoil. No spar.

The extra foam would stiffen up the wing, could take half an hour to do.

Wouldnt effect balance either as its just infront of the CG
Sep 27, 2017, 11:12 AM
Registered User
Extreme Sports's Avatar
Yup, that would work and is one of the reasons KFm wings are popular - provides a stiff construction without necessarily needing as spar (at this size).

The trade off is you will add about 40% of the wing weight. What I would do is take the paper off the 40% sheet as then the weight addition is minimal. But do the KFM properly - main wing, thin foamboard strip as a spacer, then the 40% sheet...not just two sheets of foamboard glued one on top of the other.
Sep 27, 2017, 03:25 PM
Kimbers Keeper.
BHOFM's Avatar
You still need a spar. Trust me, I've been there.!
Sep 27, 2017, 03:42 PM
Mike's Ma Maaaaaaaaan
PaulB's Avatar



Good fun watching the developments

Sep 27, 2017, 04:07 PM
Kimbers Keeper.
BHOFM's Avatar
OK, I went to the first post and looked at your plane, parts, First, the flat parts, wing, fuselage, stabilizer need to be one piece. Or actually two, a left and right side, hot glued down the middle.
Then cut the fuselage in half down the thrust line. When you have the two wing halves done,
add the spar, or KFM. A 3D plane to fly good needs a symmetrical wing. You need a KFM on
both sides. And I would think this would do away with the need for a spar as such. I would
add a strip of filament tape top and bottom. The KFM will need to be three pieces, the center
across the seam and the add the ends to finish them out. This may not be necessary if you
foam sheets are big enough, mine are not.

Notch the fuselage halves to fit over the KFM sections and glue them to the wing section,
keeping the 90` to the wing. Add a bead of glue down each side of the seam.

Now are you completely confused and ready to start a stamp collection???

OK, I have thrown together a set of plans for a Yak 55. I am going to build one and lay out all the
part so you have a better view of the idea.

These are small prints of the plans I will post later if you want them.



Last edited by BHOFM; Sep 27, 2017 at 04:32 PM.
Sep 27, 2017, 04:19 PM
Registered User
Quote:
Originally Posted by BHOFM
OK, I went to the first post and looked at your plane, parts, First, the flat parts, wing, fuselage, stabilizer need to be one piece. Or actually two, a left and right side, hot glued down the middle.
Then cut the fuselage in half down the thrust line. When you have the two wing halves done,
add the spar, or KFM. A 3D plane to fly good needs a symmetrical wing. You need a KFM on
both sides. And I would think this would do away with the need for a spar as such. I would
add a strip of filament tape top and bottom. The KFM will need to be three pieces, the center
across the seam and the add the ends to finish them out. This may not be necessary if you
foam sheets are big enough, mine are not.

Notch the fuselage halves to fit over the KFM sections and glue them to the wing section,
keeping the 90` to the wing. Add a bead of glue down each side of the seam.

Now are you completely confused and ready to start a stamp collection???
Too much work for what this plane is.

There is a carbon rod in the wing although its half the diameter that it shouild be. I got the idea for the wing after seeing video of the COX 88 3d plane that someelse designed and sells plans for on there website, they dont use a spar on there wing. the wing is single peice of dollar tree foamboard and then 2 smaller pieces glued ontop.

The extra peices will run the entire length of the wing from tip to the fuselage. this will add quite a lot of strength ontop of the already installed spar.

The problem im having with this plane is its not as stable as it should be even in fairly moderate paced flight, which i think is partly due to te wait and partly due to control surfaces fluttering (the elevator for one definatly was before i reinforced it). In winds its quite a handfull (but what do you expect from a foamie) in a breeze its a bit of a balancing act watching for sudden roll twitches. Doing harriers is also a massive balancing act constantly correcting wing rock..

anyway its really beatup now, i nosed it in today flying in far too much wind, broke a prop and the seems between the wing and front side pices gave way and also crumpled on one side.

its repairable so ill try the extra wing peices see how it flies it its a big improvement ill rebuilt it with the spare foamboard sheets ive got. If not ill move onto something else more capable with extra weight (i think the FT 3D might do better having a proper airfoil with a wooden wing spar)
Sep 27, 2017, 05:45 PM
Kimbers Keeper.
BHOFM's Avatar
If the KFM doesn't span the center of the wing, it adds no strength at all.

I am going ahead with my build. Here are all the parts I need, plus a bit
of scrap to fill in the ends of the KFM sections.
Sep 27, 2017, 05:52 PM
Registered User
Quote:
Originally Posted by BHOFM
If the KFM doesn't span the center of the wing, it adds no strength at all.

I am going ahead with my build. Here are all the parts I need, plus a bit
of scrap to fill in the ends of the KFM sections.
Somehow i never saw the pictures you posted earlier, looks interesting.
850
What size of foamboard is needed? im limited by A1 size if using the hobbycraft foamboard,.
Sep 27, 2017, 06:50 PM
Kimbers Keeper.
BHOFM's Avatar
They are 20X30 Readifoam. I think they call it 6mm. It does vary in thickness a bit. No big deal.

Do you have a 1X1' piece of the board you are using? Can you get a weight on it?

I should have a plane in an hour or so!

Going to fix something to eat so, maybe two hours?
Sep 27, 2017, 07:51 PM
Registered User
Quote:
Originally Posted by BHOFM
They are 20X30 Readifoam. I think they call it 6mm. It does vary in thickness a bit. No big deal.

Do you have a 1X1' piece of the board you are using? Can you get a weight on it?

I should have a plane in an hour or so!

Going to fix something to eat so, maybe two hours?
23.4 x 33.1 in is the size of the foamboard i have so would work. Will see if theres a piece that size, i measured the weight of the pieces that made up my yakk 55 and cant remember what it was, think it was 150g before being put together and electronics added.

Ok i found this from a quick google.

Quote:
240g for an A1 sheet which I calculate to be 0.31g/sq in, or about 55% heavier than DTFB.
Sep 27, 2017, 08:42 PM
Kimbers Keeper.
BHOFM's Avatar
Started on the electronics.

That board is really too heavy for planes. Don't know what to say.

Sep 27, 2017, 08:47 PM
Registered User
Quote:
Originally Posted by BHOFM
Started on the electronics.

That board is really too heavy for planes. Don't know what to say.

I found anothe rpost stated about 40% heavier, maybe too heavier for floaters but peole have used it succesffully , jsut needs a little more power sometimse and doesnt fly as slow. For the 3d profile planes, yes its too heavy Im currently looking at several other options XPS foam possibly, trouble is i dont want 20 pieces. I dont have the space to be keeping a box full of 1200mm long sheets of foamboard that will sit for a year.
Sep 27, 2017, 08:48 PM
Kimbers Keeper.
BHOFM's Avatar
I think your +55% is dead on. Bare air frame is 104g, no electronics, no firewall.



Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Cool Twisted Hobbys - 32" Crack Yak - Build Thread (Lots of new pics!) hercdriver7777 3D Foamies 6782 Sep 04, 2017 06:25 AM
Discussion Twisted Hobbies 36-Inch Crack Yak 55 Build ????? dereckbc Foamies (Kits) 1 May 10, 2016 05:32 PM
Build Log YAK Attack-Yak 55 Scratch build - 60cc payne9999 Giant Scale Airplanes 62 Nov 30, 2015 07:32 PM
Alert SOLD - Twisted Hobby 32Ē Crack Yak 55 Gold for Sale Billbor Atlanta Area RC 7 Apr 28, 2015 09:02 PM
Build Log Got parts from Hobby Lobby Yak 55, lets build a full fuse Yak 55 Lampatex Foamies (Scratchbuilt) 16 Jun 13, 2007 10:50 AM