HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Dec 02, 2010, 01:44 AM
Master of the Wind
G Norsworthy's Avatar
United States, CA, San Jose
Joined Sep 2008
1,189 Posts
A simple tow wrap does not increase shear strength. Only +/-45 degree fibers do that properly.

See pic for what I had in mind, the glass wrap may be easier since I am already wrapping the sock around the joiner box plus a little.

Mark, thanks again how lucky I am to have 3 world class experts on my team. I think I have all the tricks I need to finish this one off.

Joe, what a journey from the little homework assignment I got at the ISR, and long before that looking at the DS19 as a replacement for the MH32. Every one gets better, and I think this will be by far the best of all. You must come fly with us again when it is finished.
G Norsworthy is online now Find More Posts by G Norsworthy
Reply With Quote
Sign up now
to remove ads between posts
Old Dec 02, 2010, 10:18 AM
Registered User
Cambridge, MA USA
Joined May 2001
1,743 Posts
I was just looking back over the thread. Is the center spar just 1 layer of the 14 x 0.06" rods? That seems a bit thin for an airplane this size. Or are you stacking them in various lengths to get taper?

On a 3-panel wing, the sparcap loads at the center are 3-4 times bigger than at the joiner, so the center spar really wants a severe taper. If the center spar is not tapered, all the bend will be close to the center, so the wing will look more like a V rather than a U. And of course it will be weaker.
markdrela is offline Find More Posts by markdrela
Reply With Quote
Old Dec 02, 2010, 02:35 PM
Master of the Wind
G Norsworthy's Avatar
United States, CA, San Jose
Joined Sep 2008
1,189 Posts
So far the center is just the one layer of rods, but there is a solid carbon joiner replacing the shear web for about 3" each side of the centerline and 11.4 oz of carbon cloth skin continuous over the center joint for the middle 20" or so. (I've pulled this trick off before) I've done this wing before sparless with carbon skins and in the one I blew up the failure mode was 45 degrees through the cutout for the flap servo, probably after the stab failed. The spar is mainly there to bridge that weak point. I will also be lining the servo cavity with carbon cloth. Based on experience with polyhedral planes with glass skins, the skin is probably almost enough to carry all the load on this plane.

That said before I close up the other side of the spar I can relieve the shear web and add another layer of carbon sticks part of the way out. This will address the bending shape but will still not be continuous across the joint. For this I am relying on the skin and the permanent carbon joiner.

In my experience with the thicker skins that are required for dent resistance the wings don't bend that much. I'm not sure how much the spar is being loaded compared to the skins. The bigger Supra we build hardly bends at all on the launch.
G Norsworthy is online now Find More Posts by G Norsworthy
Reply With Quote
Old Dec 03, 2010, 01:11 AM
Master of the Wind
G Norsworthy's Avatar
United States, CA, San Jose
Joined Sep 2008
1,189 Posts
Here is a graph from the JW layup spreadsheet that shows a sparless construction with carbon skins. The spreadsheet shows a uni skin while ours is bias, so there is some loss, but then we also have a spar that is capable of taking the total by itself. Together we should have a pretty bulletproof wing, assuming I design hinges and linkages that will take it.

Behind schedule but will try to sneak off to paint the mylars tomorrow morning and get ready to bag the tails tomorrow night.
G Norsworthy is online now Find More Posts by G Norsworthy
Reply With Quote
Old Dec 08, 2010, 01:12 AM
Master of the Wind
G Norsworthy's Avatar
United States, CA, San Jose
Joined Sep 2008
1,189 Posts
Tails are out of the bag and the word is good. Have to wait for later in the week to pick them up.

Center spars are ready for the wrap.

Stole a bit of time today and was able to cut the shear webs for the tips. The last 1/3 or so is just embedded in the foam. I figured once we get out past the size of a DLG wing we can build it like a DLG wing, with a bit more skin. More cut and fit than I would like but going better than I expected. One spar is glued top and bottom. I think I have a roll of kevlar thread somewhere hidden in this mess to wrap the ends of the spars where the joiner ends.
G Norsworthy is online now Find More Posts by G Norsworthy
Reply With Quote
Old Dec 08, 2010, 01:23 AM
Master of the Wind
G Norsworthy's Avatar
United States, CA, San Jose
Joined Sep 2008
1,189 Posts
Tails ready for trim and a bit of LE work. Really liking the Super Fil over epoxy and microballoons.
G Norsworthy is online now Find More Posts by G Norsworthy
Reply With Quote
Old Dec 09, 2010, 01:15 AM
Master of the Wind
G Norsworthy's Avatar
United States, CA, San Jose
Joined Sep 2008
1,189 Posts
Tip spar came out a little thick. Had to pop the cap, cut it back, replace the shim smaller this time, and glue it with epoxy not fairing compound. Best to err on the thin side since we have to fill a bit anyway.
G Norsworthy is online now Find More Posts by G Norsworthy
Reply With Quote
Old Dec 09, 2010, 08:49 PM
Master of the Wind
G Norsworthy's Avatar
United States, CA, San Jose
Joined Sep 2008
1,189 Posts
OK it was slow and I stole the better part of a day to spend with multiple spreadsheets, formulas, etc. The important data point I found was the fuse wt off the previous models, which makes

Fuse wt + 0.3*wing wt = 4.5lbs + 2lbs = 6.5 lbs. Now our F is down to 182 lbs at 56G.

BTW to hit that 150mph = 67 m/s we need 67m/s/9.81 m/s2 or about 7 seconds of straight down dive plus a little more to account for the atmosphere. Standard procedure is to crack the flap after losing visual to limit the velocity, though it does not always work that way.

Yes it will bend more in the center but given the carbon sock, the kevlar wrap around the joiners, the spar, the embedded carbon joiner and the 11.4 oz of carbon over the center joint I'm sure this one is not going to go pop through the servo cutouts. I might even add one more piece of carbon uni over the center joint to be certain.

Should have the 4 spars ready to sock by tomorrow night.
G Norsworthy is online now Find More Posts by G Norsworthy
Reply With Quote
Old Dec 10, 2010, 01:32 AM
Master of the Wind
G Norsworthy's Avatar
United States, CA, San Jose
Joined Sep 2008
1,189 Posts
kevlar wrap

Found some kevlar thread that I have been lugging around for 10 years. It was damp so I put it in the oven for a few hours. Kevlar has a reputation for picking up water. 1/2" wide wrap over both ends of the joiner box and the solid embedded joiner at the center. Got the second tip spar in the fixture. Tomorrow we go to learn how to wrap the sock.
G Norsworthy is online now Find More Posts by G Norsworthy
Reply With Quote
Old Dec 10, 2010, 01:52 PM
Master of the Wind
G Norsworthy's Avatar
United States, CA, San Jose
Joined Sep 2008
1,189 Posts
Spent a few hours with this spreadsheet.

http://www.rcgroups.com/forums/showthread.php?t=1213427

Quite a useful tool once you figure it out. The biggest advantage is it will mix the spar and skin calculations and give you a final answer taking both into account. The most important trick to know is to use "darts" for the step downs in the cloth.

I filled it out using the closest available cloth from the list and the dimensions from the spar. Generic IM matched the properties of Graphlite closest. Neglecting the glass skin coat which is cosmetic, it looks like this wing will take 76G before it fails. Not sure what other part of the structure is in danger before that point. The fuse has carbon strips top and bottom on either side of the seam, and carbon disser in the tail boom. The stab is made just like a DLG wing but 2/3 the size. Via 2 different sources the nylon bolts should take about 300 lbs each x 4. The most important thing from here on is to build it without any defects.
G Norsworthy is online now Find More Posts by G Norsworthy
Reply With Quote
Old Dec 10, 2010, 06:37 PM
Master of the Wind
G Norsworthy's Avatar
United States, CA, San Jose
Joined Sep 2008
1,189 Posts
I'm up to almost $1000 on this plane. Some of it is re-usable like servos, mylars, RDS, templates. Does not include things I already had or scammed like epoxy, various cloth odds and ends, paint, graphlite. I don't see spending any more unless I need to buy some epoxy rollers. This should about cover it.
G Norsworthy is online now Find More Posts by G Norsworthy
Reply With Quote
Old Dec 12, 2010, 01:59 AM
Master of the Wind
G Norsworthy's Avatar
United States, CA, San Jose
Joined Sep 2008
1,189 Posts
3 out of 4 spars in the bag. Here are a few shots of the process.

Cut the pocket in the fin for the wiper. What you end up cutting to match the drawing looks scary deep. I lined it with 1.5 oz glass on a bias using 30 minute epoxy which is thicker and a lot stickier than laminating resin. It also goes off a lot faster. The skin was pretty dry and a little soft during the process but the glass on the inside of the pocket should do a lot to stiffen that up. I will put another layer in if it looks in any way weak. Next would be the wiper side, which will be interesting.

Took the car body scissors to the fuse. I was a bit nervous about this until I saw how Mike chopped up that big scale fuse. After that it looks like no big deal. I proposed leaving the tail long and making it smaller but my esteemed designer said that it would not handle the same so we go with the recommendation. I drew it based on the TVC and independently exported the side view into CAD and they both came up with the same number, so it must be right. The fat fuse is an optical illusion but I held it up against the Pike Perfect and it is indeed longer. Starting to look like an airplane.
G Norsworthy is online now Find More Posts by G Norsworthy
Reply With Quote
Old Dec 12, 2010, 08:57 PM
Master of the Wind
G Norsworthy's Avatar
United States, CA, San Jose
Joined Sep 2008
1,189 Posts
Close enough to keep the motivation up. Won't often see this.
G Norsworthy is online now Find More Posts by G Norsworthy
Reply With Quote
Old Dec 13, 2010, 12:41 PM
Throw it like you hate it
RCPC's Avatar
United States, CA, Castro Valley
Joined Apr 2007
3,086 Posts
nice picture, Greg. did you dress up for that?
paul
RCPC is offline Find More Posts by RCPC
RCG Plus Member
Reply With Quote
Old Dec 13, 2010, 12:43 PM
Registered User
TrekBiker's Avatar
United States, CA, Diamond Springs
Joined Mar 2004
556 Posts
Greg,

Can you tell us the thinking behind the shorter tail moment? Are you going to place the wing back behind the stock LE opening on the GJ fuse like on previous projects or is the nose section going to be the stock 19 inches?

Steve
TrekBiker is offline Find More Posts by TrekBiker
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion XC racer #8 in a series G Norsworthy Cross Country Soaring 185 Oct 01, 2014 02:52 AM
Discussion XC#9 in a series, Giant Supra and other possible wings G Norsworthy Cross Country Soaring 96 Apr 23, 2011 08:14 PM
Discussion Getting Started in XC - Planes, tips, advice aeajr Cross Country Soaring 42 Sep 02, 2010 07:45 AM
Discussion Giant RC DC-10 Turbine Powered Crash trev0006 Fuel Plane Talk 2 May 01, 2010 08:42 PM
FS: Giant WOODIE. Saggitta XC ronrange Aircraft - Sailplanes (FS/W) 5 May 17, 2005 01:17 PM