This is a post on a wing I am building, some of the methods are slightly different from others I have seen posted from Randy Etken and Dave Norman, I have stolen selfishly from their posts. This is the 5th wing that I have built using a vacuum bag and the 4th I have painted on mylar. This wing I am trying to get the wing to come out at 1 pound (16oz.) or less (without servos). My previous wings have been too heavy. In order to reduce weight I will use contest grade weight balsa, minimize the amount of paint and epoxy I use. The wing tips will be foam cored and balsa covered.
To start I prepare the sheeting, I ordered contest grade balsa from a local hobby store but after several weeks of waiting they informed me they could only get me 36” long material . I took the balsa in 36” but decided not to use it, rather I weighed it to determine what weight I would expect. I then went to the hobby store and found I could match the weight per sq. inch of the contest grade if I was very selective.
Here is a picture preparing the training edge of the balsa so the top and bottom sheet will taper to nothing .
< Message edited by wkevinm -- 1/13/2008 4:56:13 PM >
Here the cores are prepared and have a 1/8” light plywood spar that was routed into the cores after they were joined. This idea from Ed Smith and has worked well, I do not use any carbon with the spar and have not had any wing failures (on 3 earlier planes) using this method. The spar is glued into the routed slot with polyurethane glue. I fly in the Canadian district with a Nelson engine and a detuned muffler.
The sheeting was bonded to the cores using epoxy (West 105 / 206 hardner). I used a total of 1.5 oz by weight of epoxy for this. The epoxy was spread onto the sheeting and had a dull finish, this was as thin as I could get it. In the past I had used more epoxy than this and feel there was a weight saving (0.5 oz). Next I glued the LE to the sheeted cores with polyurethane, taped till the glue dried.
Next I routed the ailerons. In this case and the last wing I use a slightly different method and find the ailerons to move freely and at the same time very strong. I use .005” fiberglasssheeting on a 45 degree angle. Since this material is so thin I have found there is no special preparation for it. I also only route out the top sheet and through the core to the layer of 0.5oz carbon mat mentioned earlier. Later I will cut a 1/16” slot relieving the bottom sheeting, very simple and effective. The width is ¼” The wings are routed with my dremel against an angle iron straight edge. I finish the routing with a ¼” chisel.
The wing hardpoints are put in ¾” maple dowel for the LE and a 1/16” plywood plate embedded in the sheeting for the TE hold-downs.
Carbon mat 0.5oz. is cut for the TE of the wing (1/2” wide ) and for the area that will seat against the fuse. This forms a hard surface and will spread the contact point caused by the edge of the fuse wing saddle.
Note there is no glass at the center section of the wing. I have built without this in the last 2 wings and have not had any failure from this, a crash that has occured (due to pilot brain freeze around #1) and subsequent forensic examination shows the wing center remained in tact while the rest of the wing failed due to a hard hit with tera firma.
This shows the .005” fiberglasssheeting that will be used for the skin hinge. This has been cut on a 45 degree angle from the weave for added strength.
This shows the routed slot for the aileron with the torque rods installed. I preinstall the torque rods using collars with 4-40 allen head cap screws for the drive end.
In the past I have had trouble laying the 0.58oz glass cloth flat onto the epoxied mylar. This time I made a rack out of aluminum to help apply the cloth with as few wrinkles as possible.
< Message edited by wkevinm -- 1/13/2008 4:15:33 PM >
This shows the mylar ready to be epoxied. The mylar is painted on the top surface of the wing only. I weighed the mylar before and after painting. I had added 0.5 oz for the paint. I may have been too stingy and it may be a bit transparent, but I won’t know till it is done. I mixed up 2.5 oz of epoxy by weight (3 portions of West 105 with 206 hardner) and had .5oz left over.
I have clamped the TE to ensure is remains straight and does not deform. I have always clamped the TE by hanging it over the foam, this time I clamped it to the foam to try and hold the shape.
< Message edited by wkevinm -- 1/13/2008 4:24:30 PM >
Here are some weights and measures of the wing to date; Wing airfoil – MH17, span 52" Target weight 16oz without servo. Canadian pylon rules rules wing thickness – 11.25% of chord Wing area 500 sq. inches Used 1.6oz of epoxy to glue sheeting to cores. Wing weight wing skinned, no tips – no LE – 10.1oz. Wing weight with LE and wing tips primed - -12.3oz Painted mylar with 0.6oz of paint – Klasskote Weight of glass cloth (0.58 oz / square yd.) therefore approx 0.5oz. Epoxy weight used for glassing wing – 2 oz.
Estimated total weight = 15.4 oz I will know tomorrow (Jan 13, 2008)
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Joined: 9/20/2007 From: Raleigh,
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i would suggest you use some of the construction techniques used on DLG's (discuss launch gliders) Instead of getting the wing to be 16 ounces, they get their whole craft under 16. Try taking a foam wing with a single carbon spar that is visible on both the top and bottom of the wing, and then coat this in a single layer of fiber glass. It will be much stronger and lighter than you think. To loose even more weight, you can then melt out the foam from inside it with acetone. (if wont hurt the fiberglass at all.) Then finally sand the fiberglass to make it smooth, and don't even bother with covering it.
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Seeker wing build - 
