combatpigg

My Feedback: (3)

How far would you carry the torque rod into the flap?

The inboard end of the flap could [would] be glued to the torque rod....I wonder if I could get away with setting the torque rod bolt 4-5 inches in [spanwise] on a 16 inch span flap?

vicman

My Feedback: (10)

Nice stationary [8D]

How is this an improvement over potting music wire in epoxy and cabosil?

HighPlains

My Feedback: (1)

I had a mechanical engineering buddy do the calculations on one of these about 17 or 18 years ago. I was building a F1 with the entire trailing edge as a camber changing flap, with a target speed above 175 He agreed that a double tube should be the way to go, as having double the thickness raises the buckling strength by about a factor of 4. Having the increased diameter also improves the moment or torque arm thus lowering the stress.

If the tube is less twisty than the elevon, then having multiple tangs out of it should decrease the chances for flutter. But then glass and carbon on the surface can do that too. Hell, if stiff enough, you don't need hinges, just bushings at both ends of the control surface and 4 or 5 tangs into the surface.

Music wire has 90% of it's mass internally where it has little resistance to twisting because it has no moment arm. Try twisting a beer can in half before you open it. Unless you introduce a local distortion to the surface, it will not break. And it is rather soft Al because it is formulated to be deep drawn.

I agree that the 6-32 would be better for arms. Less likely to fatigue.

iron eagel

Interesting...

combatpigg

My Feedback: (3)

Thanks HP, more good food for thought. A pair of tangs made from 4-40 Grade8s into the flaps... and 6-32s for the inner arms should be enough for my conscience to reconcile.
I never did consider the double wall tubing being a 4 factor improvement.........hooray!

Vic, music wire is tough stuff but pretty whippy. Especially if you make the torque rods long enough to reach 1/3 span on the elevons. They [ 1/8" MW] works OK for Q-40 ailerons because there isn't much surface area or flight load on them...they're just trim tabs to bank the plane with. Elevons are taxed more.

I've got to explore the aluminum torque tube possibilities with smaller planes now. A pair of 2-56 torque rods in a 1/2A plane is a significant amount of weight.

HighPlains

My Feedback: (1)

Not the same thing as torquing the tube. That only doubles. But it is important, because most failures have to buckle first. Which is why 3/32 is about twice as strong as 1/16 balsa for skins. Compression failures of skins are usually started as a localized buckling failure that allow the skin to pull away from the core.

daven

My Feedback: (1)

great picture CP, and even better stationary.

the best spot for the tang will always be in the center of the surface.

best of luck.

D

combatpigg

My Feedback: (3)

Here's some progress, lots of time consuming details. I picked up some thin wall 1/4" tubing and some heavy wall tubing that is a slip fit inside the thin wall tubing. Perfect.
Sizing things up, #4-40 high strength bolts look like the best choice. Crossdrilling the shaft for larger hardware would weaken the shaft too much. I carried the torque axles into each wing panel about 40%. The hex heads of the bolts are ground down to look like nail heads, for clearance. I did not fill the inner part of the tube with anything where the bolt passes through. I made special "nuts" out of aluminum roundstock to fasten the bolts to the axle. There are 2 heavy duty hinges per wing panel outboard of the tube axles.

The spars are 1/8" hard balsa [full depth] with a layer of .007" carbon laminate on each side. I just used medium CA to laminate the spars, then used Gorilla Glue to glue the spars into the foam slots. The slots were done free hand with a razor saw. Lightweight Spackle is used to fill imperfections. The spars should taper to reduce local stress where they end, but I'll do that on the next wing.

Now I'm about ready to throw in some cloth reenforcement in the center section and skin the wing

combatpigg

My Feedback: (3)

hinged and flapped

Mike Connor

My Feedback: (5)

You do good work cp. I may cut some elevon stock and fill the center gap between the elevons on mine like you did. Mine would not have been so wide but my first cut was wrong and didn't have another long piece.

combatpigg

My Feedback: (3)

Thanks Mike, you do good work too.

I got my vacuum pump going last night. I couldn't get a perfect seal, so the pump cycled between 10-13 inches all night. I set a box fan next to the pump which helped.
The wing turned out heavier then I would like but it is strong. I didn't do as much glassing under the skins as most pylon wing builds I've seen. I did put some C/F in there, vertically and horizontally. As it stands, this plane will end up weighing in the 3 3/4 pound range. There is about 52-54 inches of span here. The wing ended up about 1 1/8" thick.

daven

My Feedback: (1)

coming along nicely, looks very good.

iron eagel

Looking good!

combatpigg

My Feedback: (3)

Thanks guys.

There has to be a way to lose 6-8 ozs here. I've cored out white foam combat panels, but what a chore. There was 3 lengthwise tunnels per wing panel, so 6 individual tunnels per plane. We dropped a hot music wire through a guide to pilot holes through the 2 foot long panel, then traced a pattern to hog out neat holes. Everything had to be plumb to get the pilot rod to drop straight through.
I probably went overboard with the spars and glass underlayment here, but not sure. I put 3/4 oz cloth over the TE area and over the spars. There are 2 spars to support the big cut-out for the elevon servos.
It took 4 ozs of resin to do the entire lay up. I went with 3/32" skins, not contest grade but what I would call medium light SIG balsa.
The torque rod system could be lighter if a few inches were trimmed from it and if thin wall was used for the inner tube.

combatpigg

My Feedback: (3)

4 hours later we have a cowl....there's no way I'd make one of these for someone else unless it could be vacuformed.
This one was formed out of blue foam, the rough cuts are done on a bandsaw and some rough chaping can be done....but the next step is to 3M77 it to the firewall, now finish shaping it with 60 and 120 grit.
Now tape it as smooth as you can with clear packing tape. It takes a bunch of little patches to get around compound curves. Don't sweat little wrinkles, just tape over them again.
Next step is to cut up some squares of 4 oz cloth, mist with 3M77 and start laying over the mold.
Cut off a latex glove finger and smear with medium CA, then sand the rough spots down.
Repeat with another layer of 2 oz cloth, sand and trim the overlap at the firewall with a razorsaw, just don't cut into the plane.
Now you're ready to break it loose, it takes some work, hope you did a good job installing the firewall.
Grind the end of a hacksaw blade to a point and use it as a digging tool to remove the foam. Once you get to the barrier tape, it peels away cleanly from the glass.
At this point I like to make all the holes to suit the engine and get the part cleaned up enough to apply the final layer of cloth with epoxy resin. Paint the inside of the cowl with resin, too.
The CA method can leave dry spots, so those can always be hit with thin CA.

smoknrv4

My Feedback: (11)

Man, what a project, this plane looks like a real blast! I'm just contemplating making a fiberglass cowl for my shrike, so thanks a bunch for the info on the last post, very helpful, now is there an alternative to using Medium ca, just because of the toxicity of the stuff, just curious, this will be a first time for me, its one thing I havn't tried yet.

combatpigg

My Feedback: (3)

I only use CA because I'm not patient. It has to be Tower brand Medium, it is just the right thickness and I have only used Tower. It doesn't take much to soak the fibers and drys rock hard. You could do the whole cowl with 3 layers of 4 oz cloth and your laminating epoxy of choice. For cowls, Pic Epoxy works good and fully cures in 2 hours. I'll use it for the final layer for this cowl.

BTW, when I say "lightly mist the cloth", I mean to say, lay the cloth pieces out on the floor and give each piece as quick a shot as you can from 2 feet above...let the spray be almost un-noticeable. If you go overboard, the cloth wont absorb the resin fully.

When you wrap the mold with the pieces of cloth, limit the amount of overlapping. Too much overlapping creates a lumpy mess. The idea is to sand between each coat and to knock down the high spots. There will always be a little touch up needed with Bondo at the end, but not enough to fill a thimble.

RocketRob

My Feedback: (1)

CP, Hinge looks very well executed!
But what if the wing flexes, might it bind on the linear hinge?

combatpigg

My Feedback: (3)

Rob, it very well could bind...I greased them with moly-lube. We'll see. The wing is pretty stiff which is a plus, but I'm going to build the next one 6 ozs lighter. The next one should only weigh 14 ozs with working flaps.

iron eagel

CP,
Nice job on the cowl! I love the way it just barley wraps around the engine.
Boy does that clean up the aerodynamics of a glow engine...
With the cowl and fuse on it, that is one evil looking bird.
Despite the weight I think it will be a real performer!

Besides it seems you may already have a few ideas of how you may be able to lighten up the next one a bit.
Things I come up with are like:
Do a truss rather than solid fuselage. (more work)
Built up tail feathers. (again more work)
Loosing some of the foam core. (you already described the joy of that)
Perhaps using a much lighter glass under the foam.
Sealing the balsa surface before doing the external glass on the wing. (this would keep excess epoxy from soaking the balsa, when you bag you sometimes have the epoxy driven deep into the balsa)
I am not sure about trimming the torque rods down too much, you will have a better feel for that once you wrung this one out a bit.
I can not wait to hear how this one performs!

combatpigg

My Feedback: (3)

IE, I feel the same way about the wing, more work but worth it if the plane is to be an all around great flyer. I would have liked to move the engine back further into the wing but the elevon servos created a log jam...the only solution would have to been moving the fuel tank aft of the servos and I'm not experienced with a suction feed tank that far away. If I switch to a bladder tank, then that would work fine. It could still be done.

combatpigg

My Feedback: (3)

Here she is RTF.
Weighs 4 lbs 2 ozs....[]
It needs a AA cell pack in the extreme rear to balance.
I'm going to fly it at what looks like 15% CG, but I'll bring some lead along to fine tune the glide.

smoknrv4

My Feedback: (11)

Looks Sweet CP, nice job, looking forward to the maiden flight report!

daven

My Feedback: (1)

looks very good, but how are you going to land without the head taking the brunt of the landing?

combatpigg

My Feedback: (3)

It flys, it looks pretty cool in a flying wing kind of way. It's fairly fast like you would expect, but not a bullet so far.
The first launch with a 11x6 went chin first into the dirt, the model was just too nose heavy. After changing the prop and adding an oz of lead, it flew after a belly scraping takeoff and flew OK with quite a lot of up trim. The landing was like a sack of potatoes and it broke the engine mount.
After changing the mount and adding another oz of lead to the aft end [now we're up to 4 lbs 4 ozs total] it was launched again with a 11x6 and the launch was OK, it didn't dip so low. Now the plane isn't needing as much up trim. The glide and landing was much better, pretty good. So far the CG has been moved the thickness of my fingers, about a 1/2 inch. It is that critical.
Next flight was with a 10x7 and the launch was a little bit hairy. The difference in speed was pretty good, now it's starting to get with the program. The flight didn't last very long, 4 ozs just isn't going to cut it. After this flight I noticed that the firewall is loosening up. This plane needs work, but it should be interesting to see what can be done.
I see potential, but that is all I see so far.
The Jett .46 is really nice, it's a step up from my old Webra .50. I'd like to feed it with 8 ozs of fuel. The whole plane will have to be re-done. I'm really tempted to hog out the wing and recover it. The other detail would be to move the engine back, this will eliminate the need for lead. If I can get the weight down enough, then a 9x8 prop would be feasable for hand launching. I don't have a thrust calculator, but I know that you take a huge hit going from 10 inches to 9 inches. I can't see this thing clearing the hay unless it goes on a diet.

BTW, this plane now flys with NO UP-TRIM or REFLEX . The need for reflex, or special airfoils is a MYTH.....as long as the wingloading is kept below a certain point. The CG could even be move aft some more, but right now it's pretty close. I've always subscribed to the old school thinking that your fingers are good enough to check CGs, but for this plane it wasn't good enough. If this plane was a pound lighter, then the CG wouldn't be nearly as critical.
Well anyway, the encouraging thing was to see no up trim needed, to see a glimmer of speed and to get enough "data" today so I can retreat and reload.