daven

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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.

daven

My Feedback: (1)

The balsa stab is 3/16" thick contest balsa, with a 1/4" wide 1/64" thick ply stiffner inserted around the perimeter of the stab.

The stab before fiberglassing was exactly .5 oz.

After fiberglass and kevlar 1.1 oz.

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.

Darrinc

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Why not just layup directly to foam?

daven

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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.

Dave

DHG

My Feedback: (7)

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.

Hey, cool scale! Where'd you get it, & how much?

DHG

daven

My Feedback: (1)

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.

2fast4u

My Feedback: (5)

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.

Stand

You can find deals on scales on Ebay sometimes.

Good write up Dave! Where did you get the Phil Barnes DVD? I'd like to see it.

Regards,
Stan Douglas

daven

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Heres the website that I found that has the info.

http://www.paonline.com/hayman/video.htm

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.

basmntdweller

My Feedback: (9)

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

Per_N

Dave, What tools do you use in the balsa for inserting the ply stiffnes and how deep do you think is necessary? Do you make the stiffness all around ?

Regards Per

daven

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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

leeul

Here is what I made for sloting the stab.

Lee

leeul

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.

Per_N

Thanks Dave
I understand perfectly. I Think I have to bye a drill press for my dremel.
Of course, pictures are always nice.

Per

Per_N

Leeul, Somthing like this? This is a simple tool that I make for insert mylar hinges.

Per

leeul

Same idea, only I use the tail as the fence not a table as yours appears to work. Ill send the pic to dave (that I can do) and if I ask nice enough mabe he will post it for me. If it fails again.

Lee

daven

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Here are the pics that Lee sent. Looks like a similar arangement to what you are doing Per.

Dave

daven

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Per,

I took a couple pictures when I did my tail here tonight. The first shows the saw blade I chuck up. I tried to get just a close up of the bit, but it came out blurry.

The second shows the drill press height adjusted so that the blade is exactly in the center of the stab. It takes a little practice to get it right, so I like to do 2 or 3 at a time once I get it set up. The radius of the blade is very close to 1/4" so that is the depth of the stiffners that I use.

DMyer

My Feedback: (2)

Dave,


Great write up. I also have been using my drill press and demel saw for years for slotting edge stiffeners as well as all hinges(do them the same time... perfect everytime). One thing to note... I always set my drill press for it's highest speed prior to performing a slotting operation.


Dan

Stand

I use the drill press and razor saw cutting wheel method too, I have a jig that I made so that I can control the depth of the cut. I find it better than the exact-o blade because it doesn't try to follow the wood grain on harder balsa and it takes out about 1/64" of material.

This works perfectly for running 1/64" ply around the outer edges were as the exacto blade requires the slot to expand and it is difficult to get epoxy in the little slit. I don't slot hinges with it, I use the skinned hinges described by Dave; much cleaner.

Regards,

Stan D.
If you find one of those razor saw blades, get it. They are very valuable around the shop. I even used mine to trim a hard to reach place to cut a Koa hard wood plank in a floor I was installing.

Alabama Racer

Being very cheap, I make my own fiberglass material for hinges. I use 3oz fiberglass cloth, cut on the bias, put down some wax paper on a piece of glass & then brush or roll epoxy into the cloth. I like to use peel ply on the top surface so that it will have a textured surface for glue to grab when I glue it onto the wing/ailerons. I weigh it down & put it in my heat box to cure. Have not had any failures or cracks out of any thus far. Used calipers & it measures out to be about .010 thick. Vacuum bagging the material would be good also but I have not found it necessary to do so.
Brad

Per_N

Great! Thanks Dave
I guess the the stiffness make a lot difference? I have never tried it but I will sure do on my next project.

Per

Per_N

BWT Dave, I forgotten to ask how you make the profile for you stiffness? Are you just laying your tail on the ply and mark the profile with a pen and the offset the contour? (My best guess)

Per

daven

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Per,

I'm not sure I understand your question. Are you asking how I get the stiffners to the proper size?

I will email you a copy of the plans, and it will show you the proper size of the stiffners in relation to the tail. These plans have been updated over the set I had sent you before.

Dave