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4 sheet 80" wing build thread

evranch

Well-known member
#1
I was supposed to be doing more important things today, but I was outside all day already. And it's cold and dark. So I started my 80" wing build (too bad these never got names?) https://www.flitetest.com/articles/four-sheet-no-waste-flying-wing

The template is drawn up and cut. Unfortunately I'm running low on white, so I used my last two white sheets for the template, and the wing is going to be black.
One thing that is immediately obvious is this is going to be a big boi with very low wing loading as this plan gets mirrored for each wing. 4 sheets wide.

Drawing out this plan was quite enjoyable. It reminded me of the pre-internet (and foamboard) days when you would get plans in a magazine or a book and draw them on poster board - the layout was very well thought out and measurements easy to transfer with only one spot requiring alignment on the fly (and this is only because he used a 1-1/4" ruler to cheat and mark his out). Easier than taping and tracing a tiled plan, in fact. Kudos to dharkless for professional plans and a great job of using all the foam. IMG_20200107_223929.jpg
Tomorrow the real building begins.
 

evranch

Well-known member
#3
Sounds like as good a name as any for it, rather than just the 4 sheet 80" wing.

First wing completed. It's very lightweight for its size. Glue over-smear and tape joints really are obvious on black foam, which is unfortunate due to the number of butt joints in this project. Otherwise, I've always liked the look of black foam. IMG_20200108_212542.jpg
Unfortunately, the front spar tipped over a bit in the rush to get the long glue joints stuck together. This resulted in a slightly lower profile and the trailing edge sticking a bit back of the aileron joint. It did tip evenly from end to end. I'm not sure how to keep this from happening again.
IMG_20200108_212603.jpg
IMG_20200108_212624.jpg
I'm going to build the second wing before I trim anything. If it comes out the same or similar, I'll just trim the TE flush with the aileron and mate them up. If the spars stand significantly more proud, I might just remake the first wing. There isn't all that much work to build one of these, just looooong glue joints.
 

evranch

Well-known member
#5
Planning on using a 350W Pichler Boost 25 980kV I have sitting on the bench swinging a 10x6 or 11x5.5 prop.
Going to run it on 3s, will probably maiden with a 2200 up in the nose and then see if I can balance it with one of my big 7700 lipos somewhere in the middle. Dharkless flew his with 5400 mAh so I think it should work out without folding up.

I'm planning to skip on the gear and hand launch it, maybe ditch the two side pods in favour of simple runners to land in the snow. Or, I could free up the main fuselage for FPV and autopilot gear by putting a series pair of 3s cells in the two side pods to spread out the weight, and go 6s?

All depends whether this turns into a practical FPV cruising platform or not once I get it in the air.
 

evranch

Well-known member
#6
Ok, so the second wing was an exact duplicate of the first, despite my efforts to get the spar to stand up straighter. Works for me - I attached the two. It has about 5" of dihedral which was the recommended amount.

The halves are supposed to mate on the bottom, possibly requiring lower surface trimming. Instead, mine did not touch on the lower surface and I had to trim the upper surface. This is quite a bit trickier but worked out in the end with a couple gaps filled with glue.

It quickly became apparent as I started to search for somewhere to photograph it that this is my biggest bird ever. I'm not sure how it's going to get into the air. I was hoping to do a discus type toss from a wingtip, but that's not going to happen. Fortunately it will have an underhung center fuselage, and I could give it a throw from that and then get on the throttle.

Either that or the overhead toss from that video I linked in the Spear thread. Maybe I'll give my Spear a couple practice tosses before I risk that move on a maiden.

IMG_20200109_233201.jpg
 

evranch

Well-known member
#7
I was considering splitting these 30" long elevons right in half, so they can be driven by four 9gr servos, and possibly to allow crow braking for yaw control in the future. Any input on whether this is a good idea as opposed to just using a larger servo (which I don't have any of in stock, by the way)?
 

BATTLEAXE

Well-known member
#8
I was considering splitting these 30" long elevons right in half, so they can be driven by four 9gr servos, and possibly to allow crow braking for yaw control in the future. Any input on whether this is a good idea as opposed to just using a larger servo (which I don't have any of in stock, by the way)?
I know slopers use crow braking. They could also be programed to split as your hi/low rates, and if thats all you have it will work. Although wings do tend to slow down nice for landing just below stall as well. I say go for it
 

evranch

Well-known member
#9
I noticed that about the Spear. Is this a characteristic of wings in general? You can haul up elevator all day at low speed and it doesn't either flip over or drop the nose, it just gently floats down in a nice attitude for landing and slows way down.

The main plan I had for crow was to mix it on the rudder stick so that I can increase drag on one or the other wing and pull the nose around. Apparently this is how some full scale wings do their yaw control.

Doing some research on yaw stability in wings I'm not sure about the central stabs at all. It looks like the main function of wingtip stabs is to act with the wing sweepback as a kite tail more than a true stabiliser, dragging the wing back to center if it gets twisted off of the direction of travel. Being so close to the centerline and the CG, the center stabs can't really do this. But I can always cut them off and move them to the wingtips.

There is also mention of washout improving yaw stability, and I've read that FT style wings end up with washout built in as a consequence of the design. Maybe it will fly great, only one way to find out.
 

BATTLEAXE

Well-known member
#10
The main plan I had for crow was to mix it on the rudder stick so that I can increase drag on one or the other wing and pull the nose around. Apparently this is how some full scale wings do their yaw control.
From what I have seen this works only if the exposed flaps are on both the bottom and the top to evenly create drag so the wing won't pitch up or down. The B2 stealth bomber uses this for yaw control.

I noticed that about the Spear. Is this a characteristic of wings in general? You can haul up elevator all day at low speed and it doesn't either flip over or drop the nose, it just gently floats down in a nice attitude for landing and slows way down.
Really you can do this in most planes of any design, wings just happen to be more stable. I was blown away when I first figured it out
 

evranch

Well-known member
#11
Elevons split and servos mounted. Long extensions soldered on, made out of the internals of some scrap ethernet cable.
Running well with Y-cables as I only have 4ch receivers available now. Slightly more throw on the outer surfaces due to the geometry. If I put an autopilot in it I can use SBUS but otherwise the servos will just work as pairs.

Nothing left but the power pod and stabilizers to figure out now. The stock FT pod is too narrow for the battery I want to fly, so I'm going to have to draw up a slightly wider one.
IMG_20200110_191856.jpg
 
#12
Heres mine. i used colored tape for color but also to reinforce. i put 2 paint stirrers in the middle for spars. they are sticking up and down like the original spars are. I am thinking the same thing 4 9 gram servos. I haven't decided if im going to use flaperons or go with crow, but either would work and allow me to use 4 9 gram servos instead of 2 larger ones. I made the lower part of the fins with 4 pieces instead and i just plan to land on them. maybe i will put some paint stirrers for skid plates??? I plan to build a motor pod that is centered on the back, and then i am almost thinking about a pod like the ft arrow for the center on top. havent figured out what motor i want yet. as of now im sitting at 652 grams.
80 inch wing.jpg
 

evranch

Well-known member
#13
Heres mine. i used colored tape for color but also to reinforce. i put 2 paint stirrers in the middle for spars. they are sticking up and down like the original spars are. I am thinking the same thing 4 9 gram servos. I haven't decided if im going to use flaperons or go with crow, but either would work and allow me to use 4 9 gram servos instead of 2 larger ones. I made the lower part of the fins with 4 pieces instead and i just plan to land on them. maybe i will put some paint stirrers for skid plates??? I plan to build a motor pod that is centered on the back, and then i am almost thinking about a pod like the ft arrow for the center on top. havent figured out what motor i want yet. as of now im sitting at 652 grams.
Looks good! I didn't do any wooden spars, I'm interested in seeing how well the foam holds up at this scale.
You're following basically the same path as me, I'm planning to land on those lower fin skids as well. That's why I put my servos on the top of the wing, as opposed to the original build where they are on the bottom. Usually for skid plates I use the very thin dollar store cutting board, it is light and incredibly durable.

I haven't made any progress on mine since I've been dealing with farm issues in the cold and it steals my motivation for design and engineering. I'm still planning one main fuselage with the motor on the rear, but am not sure if I want to follow the original socketed design or do something different. I need to be able to get the batteries out somehow!

I just weighed mine and I'm at 570g without the stabs. Tape weighs a surprising amount on a large wing. I think I'm going to try the Minwax process on this one for snow-proofing.
 

evranch

Well-known member
#14
So YouTube just threw this video at me randomly with the Scout on floats in the snow:

I'm surprised how well the floats fly off the snow. And how well the plane launches off the ramp, lol... I should have tried that with my overweight Maja. Maybe instead of the 2 side pods, a pair of pontoons? I've never seen a delta wing with floats before, but it definitely would be a way to get it up to speed without having to throw it. I wonder if it could balance on the Simple Cub floats or if they are too short.
 

BATTLEAXE

Well-known member
#15
So YouTube just threw this video at me randomly with the Scout on floats in the snow:

I'm surprised how well the floats fly off the snow. And how well the plane launches off the ramp, lol... I should have tried that with my overweight Maja. Maybe instead of the 2 side pods, a pair of pontoons? I've never seen a delta wing with floats before, but it definitely would be a way to get it up to speed without having to throw it. I wonder if it could balance on the Simple Cub floats or if they are too short.
I have a set of simple cub floats and a set upscaled to 130% for the Kitfox. would you like some measurements to get an idea of the scale you are looking for?
 

evranch

Well-known member
#16
I have a set of simple cub floats and a set upscaled to 130% for the Kitfox. would you like some measurements to get an idea of the scale you are looking for?
Yes please, that would be helpful. I'm guessing that I would need to go with at least the 130% to keep this thing from pitching over one way or the other, maybe even to 200% and doubled foam.
 

BATTLEAXE

Well-known member
#17
Floats at 100% - overall length 22"
- nose to step 11.5"

Floats at 130% - overall length 28.5"
- nose to step 15"

If you went 200% the floats would be 44" long and over 6" wide. Kinda overkill and will be heavy. They are built pretty solid as it is. I think you might be good at a maximum of 130%. It's not like you have a nose or tail like a traditional fuselage, at 200% you would be all floats and not much wing lol.

Remember you want the step to be just behind the CG so the airframe has a chance to rotate on take off. Let me know how the measurements work out
 

evranch

Well-known member
#18
Oh wow, these floats are huge. They look so much smaller in the video, I think I assumed the plane was a mini. Sometimes it's hard to tell scale in a video.

I think the original 100% floats are probably adequate as the wing chord is only 20" at its widest point (the center). So the floats will cover the entire span, and the step might even be a bit far back as the CG is fairly forward on the wing. Worst case it just doesn't rotate, I guess.

How tall are the floats then? I probably won't have any issues clearing the prop from the snow.
 

BATTLEAXE

Well-known member
#19
Oh wow, these floats are huge. They look so much smaller in the video, I think I assumed the plane was a mini. Sometimes it's hard to tell scale in a video.

I think the original 100% floats are probably adequate as the wing chord is only 20" at its widest point (the center). So the floats will cover the entire span, and the step might even be a bit far back as the CG is fairly forward on the wing. Worst case it just doesn't rotate, I guess.

How tall are the floats then? I probably won't have any issues clearing the prop from the snow.
The floats are around 2.5 - 3" tall at the step. You will want a bit more clearance then that though. As it rotates nose up the TE of the wing tips will drop since they are behind the CG, If I was you I would want to have them up on struts another 2 - 3" for clearence. Since you are running off snow there will be some sink. I am really interested to see how well this works, I could make another big Goblin and put it on floats as well
 
#20
i slapped an old detrum 3720 650kv swinging a 13x6 in it. I had it from a dynam su-26m. went ahead and put the motor on the nose just cause all of my wings are pushers so far, and the nose had a bit more meat to glue too. Also went with the crow mix. Maidened today, and all went well. it balanced with a 4s 2200 right behind the spar. I need to make a box for the motor mount to glue to. just chopping the tip of the nose off wasnt enough. when i landed the motor and mount folded down. Wind was around 6=8mph. launched by hand wasnt to awkward. Crow braking was awesome it came to a complete stop. I could of just grabbed it out of the air.

Another reason i went with the prop in the front was i thought i could slap on some landing gear later and make it a tail dragger... I rolled and flipped it, even flew inverted fine. Cool build, i will add a camera to it next just to see how stable it is up there. seemed pretty stable from the ground.