Posts: 7024
Joined: 12/7/2001 From: Andover,
MN, USA Status: offline
Things have been kinda quiet lately, so I'm going to give a little update on what I've been working on.
I've been using skinned hinges on my surfaces for about the past year and a half. The aileron hinges have been working great, but my elevator hinges have not been quite as good. I was getting some some soft fiberglass elevator hinges, that weren't holding up all that well.
I decided to move to a little stiffer material for my elevator hinges, and went with 1" wide 1.4 oz Kevlar tape. I knew that I would probably get a slight edge around the tape, so I decided to use 2 oz fiberglass over the Kevlar to hopefully smooth out the transition.
I recently watched a (long but informative) DVD from Phil Barnes on how he lays up composite sailplanes, and it really helped me out. I cut out some properly sized mylars, and layed up the 2 oz fiber glass on the mylar. After I squeegeed most of the resin out, I wetted out the Kevlar tape on top of the fiberglass over the hinge line of the of the elevators. I continued to squeeze resin out until it was almost dry. I sandwiched the stab between the mylars and threw it in the bag.
It basically took overnight for the resin to dry completely (Its been awefully cold up here). I believe I used too much vacumm on the first stab I tried (about 18 oz of mercury) and the stab warped slightly. The second stab I did, I ran at about 10 oz and it came out perfect. I trimmed off the excess glass, and sanded to a razor sharp LE and TE. I embedded my torque rods, and filled in with resin/micro balloons.
The results were extremely good. I got a very slight transisiton bump were the kevlar transitioned into the glass (really not bad at all). The hinge line seems extremely STRONG, and the weight came out better than I expected. The weight of the V-tail ready to go came in at 1.6 oz. With a little primer and paint, it will still be lighter than the average composite tail.
Heres a couple pictures. I can elaborate if you have questions.
After the torque rods were installed, and filler around them 1.6 oz.
Really not sure If I can cut down on weight or not. If anything, I'm considering going with heavier balsa. Although the stab seems plenty strong enough, it does have a slight amount of flex.
Posts: 7024
Joined: 12/7/2001 From: Andover,
MN, USA Status: offline
From what I've heard, laying up over foam will necessitate extra resin, and be extremely "Dent Prone" .
Also, I would have a tough time embedding 1/64" ply stiffners into the edges of foam. I think the stiffners are extremely important in the tails integrity.
Posts: 896
Joined: 4/24/2002 From: Arvada,
CO, USA Status: offline
Dave,
I'm thinkin' you could use 1/4" balsa instead of 3/16". By the time you got done sanding & tapering, the extra weight wouldn't amount to a hill of beans ... the airfoil would be less of a flat plate, therefore less draggy when you deflected the elevators ... and you could taper it so it had more thickness & strength at the root, where it does the most good.
Another thought: For my tails I make a sandwich using 2 layers of very light 1/8" balsa with fiberglass cloth in between. This reduces warpage & saves me the trouble of having to inset the 1/64" ply at the edges. But it might also represent a weight saving, since 1/64" ply does have some heft to it. I wouldn't know since I don't have a cool scale like yours.
Posts: 7024
Joined: 12/7/2001 From: Andover,
MN, USA Status: offline
You would be suprised at how much you can taper a 3/16" slab and still have room for the 4/40 torque rods. I have not had an issue with the strength, primarily since I use a little heavier glass (2oz) on top and bottom. I may give the 1/4" a try though, I guess I always thought thinner was better.
As to the 1/64 ply, The laser cutter cuts it out perfectly for me, I just have to cut the groove in the tail. Lately I've been using a small dremel cutting wheel mounted in my drill press. I usually will cut out 2-3 of them at once when I get the height set properly. This works very well, and is fast to boot.
The scale came from my place of employment. We closed down a Facility in St Paul and no longer had a use for it. I expressed interest and it was given to me. It is a postal scale from Neopost. It works extremely well for light things (2 lbs and under), but can't handle much more than that. I primarily use it for weighing epoxies before mixing. Not sure what it cost, but I would guess that it was $100+ range.
Posts: 932
Joined: 3/2/2002 From: LITTLE ROCK,
AR, USA Status: offline
I used to work for a scale company. Your looking at somewhere in the range of $125 (+/-) the power adapter for the average small capacity scale. I can still get them. Not postal scales, real, calibrated, accurate to .1 gram scales. The price is set by how much you want to weigh and what resolution you want. just FYI.
< Message edited by 2fast4u -- 2/6/2004 3:38:50 PM >
The DVD Set is long (about 5 hours) and although extremely informative, it can get boring.
Most of the info is for Sailplanes, but there is enough good stuff there that applies to racing planes that made it worth it to me. It might make sense to split the cost with a couple friends. I believe the 2 DVDS were about $55.
Posts: 1731
Joined: 1/3/2002 From: Indianapolis, IN, USA Status: offline
DHG, Staples office supply has a similar digital scale for $35. I can't recall the brand but it weighs up to 5 lbs and can read in either grams or lbs and ozs to .1oz. I have one I've been using about a year. I have compared it to my lab precision beam scale and it checks within one gram throughout it's range. It's the cheapest digital I have found for general rc use. basmntdweller
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Posts: 7024
Joined: 12/7/2001 From: Andover,
MN, USA Status: offline
The stiffners are inserted roughly 1/4" deep ALL the way around the stab.
I have a small dremel circular razor saw blade that I chuck up in the drill press or router table (either work fine, the drill press is easier). Set the height of the blade so that it hits the center of the stab. Turn on the drill press and work the stab around the blade making sure to keep the stab flat all the way around.
I have to do one later today or tommorrow. I can take some pictures if you'd like?
Dave
< Message edited by daven -- 2/8/2004 8:39:07 AM >
Posts: 61
Joined: 8/15/2002 From: Goodyear,
AZ, USA Status: offline
I cant seem to get the pic to up load I will try to describe it. It is a 1.5 x 2.5 x 1/4 in ply plate that has a #11 blade screwd to it with ply spacers to bring the blade to the center of the stab.
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"Semi" Composite Tail - 
