XC racer #8 in a series - Page 3 - RC Groups
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Jul 14, 2009, 02:31 PM
Master of the Wind
G Norsworthy's Avatar

Bagging the tips


The tip layup is 3 layers of 1.2 oz glass on the bias out to the tip, 4 layers from the poly joint to 42 inches out, 1 layer of 6 oz uni glass 22 inches out, and a patch of 6 oz uni glass at 90 degrees over the brass tube. All this glass was cut and stacked with the corners marked to ensure it matches. I remember buying balanced weave, and there are enough layers that it should not matter, but better to be safe.

The 1.2 is all wet out in one step, then dried with a paper towel and hard roller. Next the uni layers are put on, wet out, dried, and checked with a squeegee to make sure all the excess is out. Roll extra epoxy on the LE and root ribs. Stack it all together and put in the bag. We used paper towels top and bottom for bleeder cloth this time.
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Jul 14, 2009, 02:45 PM
Master of the Wind
G Norsworthy's Avatar

Tips, continued


The bag is carefully positioned over the bottom bed on a flat table. Pull out most of the air with the vacuum and then stack magazines and weight, evenly distributed. We lost the photographer so what is not shown is two people pushing down in addition to the weight for the final draw. Once it is under vacuum you can let go. Two days under vacuum and one in the hot box then we can peel.

Also shown is the hatch mold. About 10 layers of 1.2 scrap, oriented as found. No time to paint the mold so we will paint after cutting them to shape.

The US Composites 2:1 does cure but it takes a while and some heat. It is not as hard as the MGS and probably not the best choice for DLG but for thick layups like this it works fine.

Next we go back to the center section and tails for trimming, and some cosmetic work on the fuse seam.

Anybody know an elegant way to hold the wings together at the poly joint without tape?
Jul 14, 2009, 02:48 PM
Master of the Wind
G Norsworthy's Avatar
I found some wicked strong magnets. I may try to embed an opposed pair in the ply root ribs.
Jul 14, 2009, 04:03 PM
Registered User

Est Weight


Do you have an estimated weight of the tips using this layup?
Jul 14, 2009, 11:30 PM
Master of the Wind
G Norsworthy's Avatar
The E374 plane has something similar and is labeled 10.5, but the tip is shorter and I didn't know about rolling out the glass with paper towels.

We mixed 12 oz of resin per tip and didn't use it all.

I guess the right answer is I will take them to work and weigh them, probably Monday.
Jul 15, 2009, 10:32 AM
Master of the Wind
G Norsworthy's Avatar

Weight so far, airfoils


The JW layup spreadsheet is telling me 33 oz per half. This comes to 66 or 4.125 lbs for the wing. Throw in the ply root ribs and joiners, and we round up to 5 lbs out of my 11 lb budget. The fuse is 15 oz plus a little filler on the seam, make it an even pound. This takes me to 6. A pound of lead in the nose is customary. I like to leave 1/2 to 1 lb for repairs and come out at 10. This means I have 3 pounds left for the tails, radio, and wing mount. I'll have everything but the tips trimmed out by tonight so we can start to get some real weights by tomorrow.

Attached is an overlay plot of RG15, MH32, DS19, and AG23. Not too far off, especially considering wire cut and bagged wings.
Jul 17, 2009, 02:49 PM
Master of the Wind
G Norsworthy's Avatar

Center section, tails cont


The center section and tails are out of the bag. They look very good, better than any large wings I have made to date. The LE of the center section is trimmed with car body scissors and wet sanded to shape. The ends are cut off with scissors and a knife, finished with wet permagrit sander. We managed not to fill the joiner tube with epoxy. The TE is cut close to the line with car body scissors, very easy since it is mostly uni, then wet sanded with the permagrit. I'll check the LE with templates after the tips are sanded. There may be one round of fill and sand, or they may be fine the way they are. White electrical tape is the easiest but JW told me the bump at the edge is not good for the flow. I didn't want to say anything until they were out but the black is flat Krylon rattle can and came out pretty good. Not really flat since it backs up against waxed mylar, but releases well, covers well, and seems durable.

The tails are treated more or less in the same fashion. The fin needed some LE work as the kevlar did not conform all the way forward. If you are really careful and the foam is well epoxied, you can hit the kevlar with fast CA and wet sand immediately. Otherwise use epoxy and wait. Wet sanding with kevlar is much better than dry sanding. The stab came out almost perfect with almost no LE work.

Find the hinge lines and slit the skin on the open side. Use a new blade on the kevlar skin or it makes a mess. On the fin, open it up enough to expose the foam triangle. Now use a curved permagrit to pick/grind out the foam. Cut the skin back to the facing, ca and wet sand, and you have a prefaced hinge ready to use.

On the elevator, slit the hinge and start bending it back, cutting on the wood as it is exposed. At some point it will make a loud crack as the insert releases from the facing, or the wood cracks. Now you can peel out the insert and finish out the hinge line.

Twe rounds of fill and wet sand with epoxy and microballoons then spot putty on the fuse seam. This is not absolutely necessary, but this one looks good and I want to take it all the way.

Next we move on to the tips, and fitting the tails and center section to the fuse. Weights Monday.
Jul 17, 2009, 04:42 PM
yyz
yyz
Registered User
yyz's Avatar

The more things change, the more they stay the same...


Quote:
Originally Posted by G Norsworthy
<snip> Not too far off, especially considering wire cut and bagged wings.
Wow, not much visible difference at all....

Does any part of your wing (eg, tips) even come close to the low Re where Mark Drela suggests that the MH32 "starts falling apart" and wasn't that a major part of his effort on the Aegea sections?

Also, weren't the MH32 and RG15 originally pylon racing airfoils?

Greg, would have fully expected you to have both cruising and thermaling polars in that diagram

It's looking great. Love the red skunk stripe down the fuselage, by the way....

Mike
Last edited by yyz; Jul 23, 2009 at 05:56 PM.
Jul 18, 2009, 01:39 AM
Master of the Wind
G Norsworthy's Avatar

Tips, assembly


The Re range was considered in the design as follows: Root at 80 mph is 904,000, tip at 22 mph per John Ellias SBXC testing 22 mph 93,000. The previous version of this plane had a DS21/DS19 combo per JW but I had not learned from Anker not to subtract the skin thickness, plus the foam cutting left a bit to be desired. I think either combo is a viable plane but I went with the good Dr's foils because they were purpose designed for no camber change. The polars are in one of the older XC threads and I did compare them to the MH32, which according to my notes has a narrower drag bucket. I also noted that the AG24 looked similar to the RG15 at 200K but better at 100K. Plus we are not flying the AG24 at the tip but AG27 optimized for the chord.

#4 had an "MH32" if you could call it that by the time you subtract the spar bump and the distorted TE. I thought it flew a bit slow but it didn't last long in competition. I went with the max spar min skin approach and the plane had no finger dent resistance, and we blew the ailerons off it at 1400m. Still flew on the rudder.

Got the tips out of the bag tonight. 21.6 and 21.7 oz so we are consistant. Rest of the weights should follow when I have access to the good scale on Monday.

The fuse mold is not perfect, but it sure beats starting over.

Thanks again to dbaya for the tools and labor. From here on it is all back in my garage awaiting assembly.
Jul 18, 2009, 03:09 AM
Registered User
Nice work Greg - looking forward to hearing the flight reports.

Tom
Jul 18, 2009, 07:53 AM
Registered User
dbaya's Avatar
Greg,

Thanks for letting me work with you on this project! What a huge plane. It looks great assembled.

Dom
Jul 18, 2009, 10:58 AM
yyz
yyz
Registered User
yyz's Avatar
Amen to that! Looks great w/ the T-tail. Nice work, Greg. Beautiful.



Quote:
Originally Posted by dbaya
Greg,

Thanks for letting me work with you on this project! What a huge plane. It looks great assembled.

Dom
Jul 19, 2009, 12:50 AM
Master of the Wind
G Norsworthy's Avatar

Tails, dihedral joint


Next we will glue on the rudder and mount the stab. Rough up the paint on the side of the fin where it is glued to the subfin on the fuse. Round the bottom of the fin where it touches the bottom of the fuse. We will be glueing the fin to the fuse here. In this case the kevlar fuzz is fine since it gives some nice surface area to glue on. Rough up the joiner tape where it will touch the fin. Remember we used poly sheet to get a nice smooth finish on the joiner tape. Finally rough up the inside of the subfin. We used peel ply so it doesn't take much.

At this point I had to run out and buy another clamp because one was not enough. Set up a dry run of the fin clamped to the fuse with some foam rubber to spread the load and protect the paint. Check the alignment, it should be fine as long as the the two subfin sides are free as the clamps are tightened. Now take it back apart, cover the surfaces with 30 minute epoxy, and put it back together with clamps and tape. Let the California sun do its work for a while. Once the glue is cured, take it apart and peel the masking tape.
Jul 19, 2009, 01:00 AM
Master of the Wind
G Norsworthy's Avatar

dihedral joints


These stupid things never match no matter how careful you are fitting them to the raw cores. For lack of better tools I matched them with a Dremel and permagrit sander. Not half bad. I reached the limit of how much rib I want to grind off before compromising the joiner. When I get the resin back we will try a little saran wrap and tape trick to match these up. I want a joint I don't have to tape.

A word about the US Composites 2:1 slow system. In a hot garage or out in the sun the tip area where all the fibers are 45 degrees the wing feels a little floppy. Not a disaster as there is not much stress out here and it feels great in torsion. This is after 8h in a hotbox at 120F. I need to call them Monday and see what it will take to harden this stuff up. Once the wing cools it stiffens up again but California Valley is quite warm at times. I don't remember this happening with MGS or stinky 13:1 Shell. The thicker laminates like the center section and the double layer of kevlar on the nose feel fine.
Jul 19, 2009, 01:09 AM
Master of the Wind
G Norsworthy's Avatar

Stab mount


Use the foam cutting template to make a rough outline of where to cut the vertical grain wood for the stab mount. Cut and sand as needed to seat the stab on top of the fin.

Mark the locations of the through holes in the stab for the mounting bolts. Drill a pilot hole and make sure it lines up reasonably well. Now drill the through holes. Line up the stab to the fin using the shadow of the foam joint. Mark the location of the holes on the fin using a pencil. Drill a pilot hole then the tap hole through the carbon plates embedded in the top of the fin. Tap the holes in the fin then CA and tap again. Countersink the top of the stab, add CA, and cut out the kevlar fuzz with a sharp blade. If everything went right, bolt the stab onto the fin. I will try to get ahold of an incidence meter to rig this, as it is impossible to tell by eye where the T-tail is. I'll hold off on the fillet for either the wing or the stab until after it is trimmed in case it needs adjustment. There is plenty of meat left in the wood on top of the fin in case it needs to be cut down.
Last edited by G Norsworthy; Jul 19, 2009 at 01:13 AM. Reason: forgot pics


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