Foam Rib Wing Contruction
02-03-2009, 08:24 PM
#1
Thread Starter
Foam Rib Wing Contruction
I’m building an Extra 200 from 3 view drawings that I downloaded from the Extra site, for the wings I decided to use foam rib method of construction that will be shown in this thread. I first learned this method while building a Laser 200 from Wayne Urley plans some 20 years ago. Back then I built two jigging platforms from ¾” plywood, each platform measures 21”X48” . I made mine so that they can be bolted together, I cut the wing sockets while bolted together so that everything is straight.
I cut the rib blanks from ½” blue foam board, pink stuff works just as well. The blanks are cut larger than needed and trimmed while in the jig. The rib blanks are held in place with parting strips nailed down to platform. I normally tack glue the foam to the strip just to make sure nothing moves while sanding.
I cut the rib blanks from ½” blue foam board, pink stuff works just as well. The blanks are cut larger than needed and trimmed while in the jig. The rib blanks are held in place with parting strips nailed down to platform. I normally tack glue the foam to the strip just to make sure nothing moves while sanding.
02-03-2009, 08:30 PM
#2
Thread Starter
RE: Foam Rib Wing Contruction
Once all the rib blanks are in place I trim the leading and trailing edges straight with hot wire bow. Once trimmed, I add ½” thick foam to edges as shown in the photo. I find this makes finishing the leading edge easier and provides for much greater gluing surface for both edges.
I use 3M 77 spray glue to hold edges on, doesn't effect the hot wire cutting, important point!
I use 3M 77 spray glue to hold edges on, doesn't effect the hot wire cutting, important point!
02-03-2009, 08:37 PM
#4
Thread Starter
RE: Foam Rib Wing Contruction
For the wing tube sockets I cut both wings together while the wing jigs are bolted together. You can see a similar template in the previous photo that I’m using to trim the trailing edge. The template is 1/8” plywood with a 1 9/16” hole, this provides a nice snug fit for the 1 ½” wing tube socket.
Here the sockets are glued into the foam with Gorilla Glue, exopy works also.
Here the sockets are glued into the foam with Gorilla Glue, exopy works also.
02-03-2009, 08:48 PM
#5
Thread Starter
RE: Foam Rib Wing Contruction
I use Formica for the airfoil templates. I had to buy a 4’X8’ sheet at Lowes but I believe it’s worth the cost, I tried other material in the past such as aluminum sheet and aircraft plywood, nothing works as good as Formica.
In my case I’m using scaled down airfoils from a 35% Hurley Extra, the plane will be 33% scale and about 98” wingspan. I simply reduced the drawings to correct size rather than layout new airfoils.
I prefer the two template method because I find it easier to hold the templates in position, waste more Formica but hey I got a 4”X8’ sheet! There is quite a bit of force on the template keeping the wire in contact while moving slowly. If the template moves, most likely you will be starting over.
In my case I’m using scaled down airfoils from a 35% Hurley Extra, the plane will be 33% scale and about 98” wingspan. I simply reduced the drawings to correct size rather than layout new airfoils.
I prefer the two template method because I find it easier to hold the templates in position, waste more Formica but hey I got a 4”X8’ sheet! There is quite a bit of force on the template keeping the wire in contact while moving slowly. If the template moves, most likely you will be starting over.
02-03-2009, 09:01 PM
#6
Thread Starter
RE: Foam Rib Wing Contruction
My darling wife and I cut the foam, she takes the short side while I lead the cutting from the longer side. I call out numbers from the template as cutting progresses. On these wings I called out a four count between each of the numbers on the template, 1-2-3-4 –2-1-2-3-4-3-1 etc. This worked very well because the numbers were spaced about a inch apart on the root of the wing and possibly took 15 seconds to cut between each of the numbers. On several occasions in the past she got ahead of me, not this time
02-03-2009, 09:21 PM
#9
Thread Starter
RE: Foam Rib Wing Contruction
I thought I would share some photos of the rest of the project. I need to order some 3/32" balsa for sheeting, let's see what Lone Star has to say, I was happy to hear they are back in business.
02-04-2009, 12:20 PM
#11
Thread Starter
RE: Foam Rib Wing Contruction
In my case there is no washout, both templates are set at zero. Normally wouldn't expect much washout in a aerobatic plane since stalling is ocassionally a good thing. On heavy weight scale models the wing tips are normally turned down about 3 degrees, that way the wing stalls closes to the fuselage preventing tip stall. In this case, the wing tip templates are adjusted to desired washout angle and cut in the same manner.
The centerline of the airfoil is shown on the attached drawing, I measure from the workbench top to this this line to ensure the wing templates are set level to the world. I do the same at the tip. If design included washout, the tip would be lower at leading edge than the trailing edge. I hope this makes sense?
The centerline of the airfoil is shown on the attached drawing, I measure from the workbench top to this this line to ensure the wing templates are set level to the world. I do the same at the tip. If design included washout, the tip would be lower at leading edge than the trailing edge. I hope this makes sense?
02-04-2009, 12:52 PM
#12
RE: Foam Rib Wing Contruction
Most Excellent! What will you sheet with? I assume the torsional properties will be the same for a solid wing, and what weight savings will you have.
02-04-2009, 05:54 PM
#14
Thread Starter
RE: Foam Rib Wing Contruction
ORIGINAL: TFF
Most Excellent! What will you sheet with? I assume the torsional properties will be the same for a solid wing, and what weight savings will you have.
Most Excellent! What will you sheet with? I assume the torsional properties will be the same for a solid wing, and what weight savings will you have.
02-04-2009, 06:03 PM
#15
Thread Starter
RE: Foam Rib Wing Contruction
The 1/4" spruce main spars are jointed to the wing tube socket with a mixture of epoxy and milled fiberglass, the gap was less than 1/16". The remainder of the joints are glued with Gorilla Glue. At this point I'm ready for sheeting however the LHS was out of 3/32"X 48" balsa. I seen that Lone Star is back in business so I placed an order last night, I hope their quality remains the same as it was prior to the fire.
02-08-2009, 05:53 PM
#16
Thread Starter
RE: Foam Rib Wing Contruction
I found enough 3/32" sheeting under my bench to sheet the top so here we go. I decided to add a 1/4" balsa spar ahead of the main spar just to keep the sheeting from sagging. The 4+ inch span between the ribs is just a little too far in my opinion, I'll sacrifice the weight for durability.
At the main spar I mask off half of the spar with tape, once the sheeting in position, I will remove the tape before the glue sets which will leave a clean surface for gluing the cap strips.
In the front of the wing you'll see three stops, I will use a 1" diameter alumunium bar to weight down the leading edge. The stops are set so the tangent point is right above the edge of the wing.
At the main spar I mask off half of the spar with tape, once the sheeting in position, I will remove the tape before the glue sets which will leave a clean surface for gluing the cap strips.
In the front of the wing you'll see three stops, I will use a 1" diameter alumunium bar to weight down the leading edge. The stops are set so the tangent point is right above the edge of the wing.
02-08-2009, 06:05 PM
#17
Thread Starter
RE: Foam Rib Wing Contruction
Here the sheeting is in place and weighted down. I had to give the sheeting a couple sprays of ammonia and water to get it to bend.
This is the first time I tried the method of weighting the leading edge with round bar, I recently read about this method on FG site. If I recall correctly, the author learned of the method from Robert Godfrey. I'm pleased so far.
On my previous wings I pinned the balsa down, that was time consuming.
This is the first time I tried the method of weighting the leading edge with round bar, I recently read about this method on FG site. If I recall correctly, the author learned of the method from Robert Godfrey. I'm pleased so far.
On my previous wings I pinned the balsa down, that was time consuming.
02-09-2009, 11:31 AM
#18
Thread Starter
RE: Foam Rib Wing Contruction
Here the trailing edge sheeting is added, then the section near the fuselage and the cap strips. The lower airfoil is now ready to be cut. I will sheet the left wing before we do so. The left wing cradle will be used to support the right wing while sheeting the bottom of the wing, likewise for the left wing.
02-09-2009, 07:11 PM
#19
Thread Starter
RE: Foam Rib Wing Contruction
Here's a comparison of the template for the upper airfoil cut and the same template cut for the lower cut. Since this is a one only build, there was no need to make seperate templates for future use. I find it better to use the two piece templates because it easier to clamp the templates in position.
02-09-2009, 07:58 PM
#20
Thread Starter
RE: Foam Rib Wing Contruction
Here's the right wing cut from the jig. Once the left is cut I'll lay the right wing in the left cradle and the left wing in the right cradle while spars, shear webs and sheeting are applied.
02-09-2009, 10:58 PM
#23
Thread Starter
RE: Foam Rib Wing Contruction
Construction has already began. The two rear 1/4" balsa spars form the aileron cutout. The spars are spaced at 1" to allow for 1/2" trailing and leading edges, both edges will be beveled. Basically I will remove the aileron by cuting at the rear of the front spar, then remove the 1" section of sheeting to the front of the rear spar. The edges will be drilled and beveled prior to gluing each to the spar. I will add filler where the control horn dowel is located before gluing the bottom sheeting on. A couple of caps on the ends and that will pretty much finish the ailerons. If this doesn't make sense, a few photos when I get there will clear things up.
02-12-2009, 01:19 PM
#25
Thread Starter
RE: Foam Rib Wing Contruction
I think generally the foam rib wings are lighter than foam core wings, at least that is my experience. The final weight is truely effected by the balsa wood selection, in my case the balsa for the tops of the wings came from my storage rack, and as one might expect the pieces were a little heavier than necessary ( That's why they were in the rack!) and I just had enough to do the job so there was no selection. I ordered extra for the rest of the build so I should be able to select some lighter pieces for the bottom.
Consider blue foam is 2 pounds per cubic foot and expanded bead polystrene is 1 pound per cubic foot, but the foam rib wing has only 10% by volume of foam, or 20% of the foam by weight.
Consider blue foam is 2 pounds per cubic foot and expanded bead polystrene is 1 pound per cubic foot, but the foam rib wing has only 10% by volume of foam, or 20% of the foam by weight.