combatpigg

My Feedback: (3)

I'm in a holding pattern with a couple of projects, so I thought this would be a good time to cut some foam before the rats eat it this winter. I've always wanted to build a fast wing with a .40.

I took some measurements off a ME-163 and am basing this design on that. What I ended up with is about 46 inches of span, 12 inches root chord and 6 inches at the tips. The fuselage will be 'glass over blue foam, permanently glued to the wing. The foam plug will be demolished after the laminating is cured. If done correctly, this plane should turn out pretty light....maybe in the low 3 pound range? The killer is the elevon servo weight and weight of the torque rods. I am not sure if 4-40 rods would be up to the task? I wonder if composite torque rods have been tried on such a thin wing as this?

This wing will end up just a little over 1 inch thick. I've read that 3/32" sheeting should be used for Nelson .40s..I'm sure there are several opinions about that. I've followed a few build threads in the pylon forum and am open to all suggestions.

Here's what we have so far.........

MJD

My Feedback: (1)

Cool.

My $0.02? As follows:

- forget torque rods and bury a servo in each wing with CF pushrods and make fairings for them. IOW, to heck with the hidden-everything thing, lose the torque rod worries and go for k-i-s-s. I tweaked some arrow shafts recently with thoughts of actuating something, but predictably they suck as torsion members since they are made from primarily longitudinal fibers - you can twist them by hand.

- use 3/32" balsa and forget how much less it would have weighed with 1/16". You be glad when the wings don't break, and you'll also never know if the 1/16" would have been enough but who cares. Are you putting a light glass topcoat on the wing or what's up in that department?

Whittle away!

MJD

combatpigg

My Feedback: (3)

Yeah, it's hard to imagine a light, trustworthy, tubular torque rod. The most punishment some of this stuff will get in normal use is from vibration and mild flutter. Hard to beat wire from point A to B.
You just put a whammy on me to use 3/32" sheet. The cupboards are full of 1/16"...of course I'm out of 3/32". If I was to use 1/16" now, the karma has been set up for an "ElFoldo", even if it had a titanium spar.

Now, I hear some Chowderhead around here uses lightply for spars on his Q40s.....can you believe that?

Mike Connor

My Feedback: (5)

The 3/32 is only 1/2 oz per sq ft heavier then the 1/16 and you only need it on top. However, look what we do to our deltas with only partial 1/16" sheeting and two spars. We can't break them... in the air. From what you are describing, I would think it would come out 3 lbs or les RTF.

MJD

My Feedback: (1)

I was going to suggest a couple of arrow shafts in there.. ;-)

My Doddgers are 3/32" top, 1/16" bottom. On this thing I'd imagine you'd want to think about similar negative and positive gees, unlike pylon racing, so I'd be tempted to go thick top and bottom. I bet 1/16" with light glass under and over would be a contender, although maybe a little too high tech?

MJD

combatpigg

My Feedback: (3)

This plane will likely only see the "speed pattern" with only positive pullouts from dives. The only other stresses might come from bad takeoffs and landings.

Now it's time to get some materials and scrounge a vacuum pump and pressure switch.

The lay ups I've studied end up weighing a pound, but these are wings that are prepped for landing gear.

combatpigg

My Feedback: (3)

None of the composite wing threads show prepping the cores for elevons. The elevons on the wing I'm building will be full span [except for the wingtips] and will have about 1.5" of chord.
The ailerons on a Q-40 are more like trim tabs, whereas these elevons will be shouldering more of a load.
The biggest fear is building a wing with flimsy, fluttering flaps.
I think the entire TE on these cores should be removed and replaced with solid balsa...

any thoughts about this?

MJD

My Feedback: (1)

You mean - a balsa TE cap on the wing plus aileron stock? I'd say that was mandatory, unless you do a *****in' job on foam core elevons and they don't twist. Decent C grain TE stock can be pretty light and stiff. In addition, I would supply push 'n' pull to those somewhere towards 35-40% span if possible, rather than putting the torsional forces on them at one end.

MJD

combatpigg

My Feedback: (3)

Well, the closest thing I've seen to what I'm building is that .60 sized ME-163. I don't know if RR would be so kind to razor saw the TE of his plane open so we could take a look in there? [:-]

I'm also wondering if having a hard edge on the wing core that runs full span will effect the way the sheeting layup turns out? Will there be a ridge formed during the vacuum proccess?

Today I try to piece together the vac pump. There is a list of parts that would make Rube Goldberg proud.

iron eagel

CP,
I have tried using composite torque rods a couple of times and they were a dismal failure. Flutter and very elastic response was a constant issue with them due to how they are made. Perhaps if ones were available that were bi-directionally spiral wound around a longitudinal core it would be worth a shot.
As far as the solid TE I would think that that is a must given what you want to do.
Using the 1/16 balsa over a foam core with a bit of carbon added to the foam may be something you may want to try to stiffen your wing a bit...

combatpigg

My Feedback: (3)

IE, that's what I think too, but I'd still like to knife into Rocket Robs ME-163 to see how it's done

iron eagel

You know you could try something I just did...
Because I don't think attacking the one with a knife, or razor saw is an option.
It's a lot of work (a bit of a pain), I haven't tried them yet, other than to twist and flex them to see how strong they were.

I built up a balsa frame for the ailerons the same way you would build a wing, LE with ribs and a solid, tapered trailing edge. made from 1/8X 3/16 stock that had a 1/16 CF rod CA'd to it.
I sheathed the bottom of the aileron with 1/32 balsa...
Then from the top side I covered all the interior surfaces with carbon fiber veil applied with dope, which covered all interior surfaces.
I left the top untouched so the it could also be sheathed after, to insure the top sheathing would bond to the leading edge, ribs and TE.
Top sheathing was then applied, and the entire aileron was wrapped in two layers of veil applied with dope.
It is very stiff, and very lightweight, but took two nights to build each one.

combatpigg

My Feedback: (3)

IE, you did a good job of describing the whole works.....wow! I'll bet it's superior to a solid balsa slab, but as you say it comes at a price. I'm not sure I need to take it that far yet. I flew the piped Nelson on a home made DD clone a couple years ago with just plain balsa elevons covered with Monokote. I'll bet it was doing close to 190 mph, it was night and day faster than the same plane that was clocked at 177 with a K&B 6.5 that I modified per Glen Dye. Anyway, I did run into flutter with the pushrods at the inboard end of the flaps. I moved the linkage out to 40% span and that took care of that, but to be honest all I got out of that engine was maybe 10 more flights before it was toast. So I'm not sure how long naked balsa would last, balsa does get worn out with mild flutter and stress.

iron eagel

The price is the time...
If only I had a laser cutter, cutting every thing took the bulk of the time...
Heck, why not just try some veil on the balsa ailerons?
That goes quick, and it will really stiffen the balsa on its on!
The ailerons I did had a 2.5 inch cord, and I was trying to save some serious weight.
Just that nasty smell you have to do outside, or the wife complains.

MJD

My Feedback: (1)

I've stiffened up a few things now, using CF veil and a top coat of silkspan applied with nitrate. Works well and is no big deal to do.

MJD

daven

My Feedback: (1)

Another idea for your torque rods is aluminum tube in a tube. Drill and JB weld a 4/40 bolt through each end at 90 degree angles. Its roughly somewhere around 1/4" diameter. Bruce at www.bigbruceracing.com has been doing this for several years and it works well, and is light. Others are using bent welding rod with a wheel collar and a 4/40 bolt at the center.

I would definately go with wing sheeting, I think 1/16" would be ok if it was glassed properly under and over the skins, you haven't mentioned what your power will be, other than a .40, could make a big difference, but I assume your thinking something pretty hot.

I also would use solid trailing edge stock, just because it would be easier than sheeting, cutting free, and capping the foam. I never seem to get a perfectly sanded transition there for some reason doing it that way.

Good Luck, looks like a fun project.

combatpigg

My Feedback: (3)

IE, the scale you are working at makes built up flaps practical. Here, the chord of the elevon is only 1.5", so by the time I build something up in that space the LE and TE would be almost touching. I like the idea of CV over solid slab elevons. Is the weave tight enough to give a paintable surface?

Dave, if all goes well I'll have a Nelson FAI RTR someday. My old one is toast and I bought up the last P/L sets PS had......but those liners are .040" smaller than my case. So to make things right, Dave is searching for a compatible case to the new liners and all should be well someday. So this plane might get a dose of fearsome power, if not I'll go with the Jett. That is probably wiser anyway, get the bugs worked out then go for the "max power load" later.

The aluminum torque tubes are probably doweled, too?

iron eagel

I have gotten some very nice finishes using dope over carbon fiber veil.
Using the veil is very much like using tissue, except that you have to use it over a solid surface and you do not shrink it.
You lay it over the surface you want to cover, and laminate it to the surface using no gloss clear dope, thinned about 50/50. When it is wet by the dope it lays down over the wood and conforms very nicely. After that one or two of clear coats will fill both the wood grain and the weave, I do not bother to sand the carbon fiber until after the second coat and then only very lightly to remove the fuzz. By the time you lay on your third coat you have what feels like a piece of plastic, I then spray on a final coat of color (sometimes more depending on the color used). The first three coats of dope is applied by brush, one caution on the first and coat do not try to brush over an area more than once, it will pull the fibers and even lift them and drag them over the surface. The reason for this is the dope breaks down the adhesive used to make the veil and the fibers float in the dope, and then bind to each other and the wood as the dope dries out.
The whole process is very similar to using plain old tissue but much stronger, and it paints up much nicer than tissue and gives you a real slick surface without a lot of work. The stuff sands very easily, you can sand right through it. If you do sand through it no big deal, lay on a patch and sand it it will blend right in, with little effort. The real plus to the whole process is being able to really take balsa to an extreme strength.

daven

My Feedback: (1)

CP the aluminum tubes are not doweled. If you consider the force acting on the tube, its structually nearly perfect. The load is at the strength of the tube.

The sleeve that goes around the tube is barely larger than the tube that applies the force. Go to one of those K&S tube kiosks at the hobby store and start matching up tubes and sleeves and you will know what I mean. I've done a few, and it does work well.

combatpigg

My Feedback: (3)

Dave, there's nothing I'd like more than to hear that concealed elevon linkage is doable on a 200 mph plane this size. I'm sure you realize that they have to carry the combined load that an elevator/aileron set up has on it. I've got to give this a try. The bolt heads will take up valuable space, so they will need to be grinded down. I guess Bruce uses JB weld at the extreme ends of the torque tubes to surround the threads of the 4-40 bolts?
I met him a few years ago out here.....he seems to be operating at a different speed than most of us.

vicman

My Feedback: (10)

Dave,
I looked at Bruce's site to see what you are talking about but didn't find anything. Would you mind posting a picture?

combatpigg

My Feedback: (3)

I wonder if the K&S aluminum tubing is seamless? I could machine a "heavy wall" torque tube out of round stock that is a slip fit in a K&S tube bearing.

daven

My Feedback: (1)

It is seamless, and K&S has tubing that is just every so slightly larger that makes the linkage tight. Once the outer tube is secured, there is virtually no slop possible.

Sorry Vic, packing has already started, camera mia for now

HighPlains

My Feedback: (1)

Go as big as possible on the torque tube diameter.
Double the tube that transfer the torque, by glueing a second tube inside.
Put plugs inside the points of tranfer (at both ends of the tube) to prevent collapse where torque tube is pierced by arms.

combatpigg

My Feedback: (3)

HP, that sounds like good advice.
I'm still a little bit leery of #4-40 arms, even if they are a high grade. I'll have to see what kind of bending force they'll take. Usually I use #6-32 for .40 sized projects.