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Old Aug 28, 2014, 12:37 PM
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Don Stackhouse's Avatar
United States, OH, Bradford
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Lincoln, good to hear you're working on it again.

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Originally Posted by lincoln View Post
Sit down Don, you'll be shocked.
I am, at least a little.

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After buying a house and moving, and a whole bunch of other stuff, I'm working on my Chrysalis again, though it looks like I'll have to break off and get something else ready for this weekend's RES contest. I probably wouldn't have to do that if not for my modifications, which I'm guessing will take more than half the time of the build. I think they're good mods, but they definitely affect the tradeoff between building time and performance. For instance, I wanted to make a two piece wing to keep the mass inboard, but I really couldn't fit something thick enough to take the load in between the upper cap doubler and the lower cap.
The added mass in the joints for the 3-piece wing is pretty negligible. Part of that is because the loads out there are far less than the loads at the center section that you would have to deal with on a two-piece wing. A typical 2-piece arrangement is likely to come out heavier.

On the 3-meter Chrysalis we do use a 2-piece wing, but I managed to get around the weight penalty by finding a way to make the joiners contribute to the overall bending strength of the wing, allowing me to lighten the spar enough to counteract the weight of the joiner system.

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So I'm going with the 3 piece. I've put up with too many one piece 2 meter wings. (And now I sort of inherited a model with a one piece 100 inch wing!) I'm building the conventional tail,
Yuck...

Seriously though, the two types are essentially identical in handling and stability, but the V is lighter and more durable in service.

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and dropped the basswood from the horizontal stab.
Uh-oh...

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I had an exceptional piece of wood for it, but I ended up putting in a little carbon and some bias glass.
Might be OK, but will not be any lighter.

Part of the reason for the basswood was to keep the stiffness properties of the stab different from that of the elevator, so they would not have the same natural frequencies (same reason why a lot of WW II era planes used sheet metal covering on tails, with fabric-covered control surfaces, to avoid flutter).

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So probably I'm back up to a similar weight,
If you're lucky...

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though I suspect it's stiffer. I also put some bias glass on the spoilers,
Not needed, and makes the spoilers harder to adjust.

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and used very light wood for the rudder and elevator, with bias glass to make up for it. I used to have a hlg Chrysalis with very light wood for the elevator, which was fine in the air but prone to hangar rash.
That means that your rudder and elevator will be more durable, but will now transfer those impact loads to the control horns and control linkages. Watch out for problems with the horn attachments, the horns themselves (watch the material around the pushrod holes), pushrods and their supports, and stripped servo gears. The higher weight in the control surfaces also worsens the likelihood and potential severity of flutter.

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Other mods under consideration are the archaic pull strings for the spoilers, which I've used before,
Friction problems, and can suck open on launch, which is why we decided not to go that route.

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and I'm thinking about using balsa for the tip section spar caps, or making them smaller. Any reason not to do this? If I'm not mistaken, the load at the inner end of the tip is something like 1/5 of the load at the center of the wing. I guess I might need to put a bit of reinforcement where the joiners are, but it seems like the moment of inertia in roll and yaw would be lower.
OK to do, but don't go too light with the balsa, shoot for about 8-10 lb. We did not go with balsa for these in the kit because sure as fate, someone would get them mixed up and end up with balsa spars on the inboard wing panels, which would be very bad, even with carbon added to the inboard spar caps.

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Just to be difficult, I'm also thinking of making a little tiller on the bottom of the rudder, that would go through a small hole in the elevator and be activated from underneath, so that the horns etc. are hiding behind the fuselage.
A fairly complex building task, but should look nice. Aerodynamic effects should be pretty minor, but overall a plus.

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I noticed that my pushrod housings aren't in very straight, at least in the visible areas up front where they aren't hidden by the top sheeting. I guess I'll have to readjust or at least check the friction.
One trick with 1/32" music wire pushrods is to "precurve" them to the same shape as the casings, so if there's a (long, gentle) bend in the casing, there's a matching bend in the wire at that location. Properly done, it can have a dramatic effect on friction. Doesn't work as effectively on flex cables, but can have some benefit.

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As suggested, I put some .014" precured carbon on the spars. Not precut, though. I found it to be a bit of a pain, since the glue seeped out a bit, and the carbon was slightly oversized the way I cut it. Also, I decided to sand down the caps to .125" rather than sanding the rib notches. Quite annoying, but obviously my own fault. Maybe next time I'll just (just?!?) get some 1/2 X 1/8 Osage Orange for spars. ;-)

Anyway, I just measured the joiners and they are about 4.08" long. Is that on the short side?
I'm not sure. We did have a batch of joiners that came in on the short end of tolerances around that time, but I don't recall the exact dimensions (the memory is the first thing that goes, and I forget what goes after that...). I have a call in to Joe to verify. We did increase the length of the joiners after that, enough that they would have to be cut off a little, so everyone could be sure they had at least enough. Not sure what you have, but I will find out.

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Also, are they supposed to be 3/16" diameter? I think mine are about .004" smaller than that, though if I was to swear to it I'd have to find a better caliper than the one I used.
NO. They are 0.180" diameter.

[quote]My kit was postmarked in July of 2011. Any other gotchas? If you need to send me something, please PM me for my current address.{/quote]

I will check on the joiner length issue, not sure where yours fall in that situation. Please email me your address through our website, I don't use the PM system on RC Groups, I've had problems with it in the past.

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P.S. I continue to be impressed with the kit, though as a former EZB builder I've replaced a few pieces.
The inevitable problem of making airplanes out of pieces of trees. We are very picky with our suppliers. We specify densities for all of our wood, giving them a 2 pound range to work within. When we get a new suppliers, we specify what we want, they send us what they think that is, and then we typically end up sending a third of the order back because it's out of spec. After that, they know we're serious. There's only one vendor we never had to do that with, but then they had a fire and went out of business.

However, we are at the mercy of what they send us, and they, in turn, are at the mercy of the raw logs that come here from Ecuador. Model airplane wood has always been only a tiny part of the market for balsa (a lot of it these days is used as sandwich core material in fiberglass wind turbine blades), so our little community has very little leverage. Sometimes we have to take the best we can get, or else shut down production.

Be careful though, about replacing wood. Yes, in some cases there might be some that's harder than we would like because that's the best we could get, but in some cases it's hard because that piece needs to be hard.

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P.P.S. Suggest you could offer a second set of plans along with it for a few extra bucks to avoid having to cut up the good ones. I made copies and have the original ones hanging on the wall of my workshop to check while I'm working. I also made a shrunk copy of the instructions to peruse when I'm not in the shop.
Those plans are surprisingly expensive to print, but we do sell replacements on occasion. Email Joe to purchase spare copies.
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Last edited by Don Stackhouse; Aug 28, 2014 at 12:46 PM.
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Old Aug 28, 2014, 03:49 PM
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United States, MA, Waltham
Joined Dec 2001
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Quote:
Originally Posted by Don Stackhouse View Post
Lincoln, good to hear you're working on it again.

Seriously though, the two types are essentially identical in handling and stability, but the V is lighter and more durable in service.
Yes but I want to use one of my really simple radios. It's only RES, after all. I don't really like bells and whistles.
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Uh-oh...

Might be OK, but will not be any lighter.

Part of the reason for the basswood was to keep the stiffness properties of the stab different from that of the elevator, so they would not have the same natural frequencies (same reason why a lot of WW II era planes used sheet metal covering on tails, with fabric-covered control surfaces, to avoid flutter).

If you're lucky...
You're such a pessimist. 19g so far, and quite stiff. Needs a bit of sanding and then some sanding sealer on the unglassed parts. Remember, this is a nice piece of wood! The price in my time is probably excessive, though. Unfortunately, it's really hard to get carbon dust out of wood, so it looks funny. The air won't care, and people will be able to tell it's one of mine. They're shocked by a Supra I have with only one little blemish on the wing.
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Not needed, and makes the spoilers harder to adjust.
I hate warped spoilers and I'm not sure how they're going to be harder to adjust.
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That means that your rudder and elevator will be more durable, but will now transfer those impact loads to the control horns and control linkages. Watch out for problems with the horn attachments, the horns themselves (watch the material around the pushrod holes), pushrods and their supports, and stripped servo gears.

The higher weight in the control surfaces also worsens the likelihood and potential severity of flutter.
I hadn't thought about those impact loads, though if you're talking about loads from the weight of the surfaces, the elevator weighs about 12.5 g with extra glass hanging off of it, and the rudder 4.6. A bit heavier than I'd hoped, but not so bad, I think. One could add 4 or 5 grams to the elevator with one of the heavier flavors of Monokote, which I won't use. Obviously if the surfaces hit something, they'll transmit more load before breaking. Still less likely to break linkages and such than the control surfaces I've had on a number of other models.

As a former EZB builder, I am about airplanes what cyclists would call a "weight weenie" if it was about bicycles. At least sometimes.
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Friction problems, and can suck open on launch, which is why we decided not to go that route.
I've had some pretty good experience with string activated spoilers. Spider Wire is pretty slippery, although before that, dial cord was fine. As for sucking open on launch, that's what the tiny magnets sitting on adjustable steel screws are for. (Round head if the magnets are too strong.)
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OK to do, but don't go too light with the balsa, shoot for about 8-10 lb. We did not go with balsa for these in the kit because sure as fate, someone would get them mixed up and end up with balsa spars on the inboard wing panels, which would be very bad, even with carbon added to the inboard spar caps.
Of course I won't, unless I scarf on something heavier on the inner end. You've got a good point about the spars, plus that's one less additional item for you to keep track of. The other thing is that shear webs stuck to the side of balsa (or balsa shear webs stuck to the side of something else) can fail across the grain. I'll have to do something about that, I guess.
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One trick with 1/32" music wire pushrods is to "precurve" them to the same shape as the casings, so if there's a (long, gentle) bend in the casing, there's a matching bend in the wire at that location. Properly done, it can have a dramatic effect on friction. Doesn't work as effectively on flex cables, but can have some benefit.
These curves are too short for that trick, unfortunately. Maybe it's just some kind of warping and I can pull them straight somehow.
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I'm not sure. We did have a batch of joiners that came in on the short end of tolerances around that time, but I don't recall the exact dimensions (the memory is the first thing that goes, and I forget what goes after that...). I have a call in to Joe to verify. We did increase the length of the joiners after that, enough that they would have to be cut off a little, so everyone could be sure they had at least enough. Not sure what you have, but I will find out.
Thanks for checking into the joiner issue. I sent my address through your site.
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NO. They are 0.180" diameter.
The inevitable problem of making airplanes out of pieces of trees. snip
We specify densities for all of our wood.....

However, we are at the mercy of what they send us,......

Be careful though, about replacing wood. ......

[/QUOTE]
I hear you about the wood. If you start measuring the stiffness AND the density, it gets even worse, to the point where 99 percent of the wood I have would be unsuitable, at least for an EZB. I had one truly exceptional piece, but it's gone.

I understand that different wood weights are suitable for different uses.

Again, I was actually impressed with the wood that came with the kit. I could have used every piece of it and ended up with a very nice model. I just like to muck around with that stuff. Maybe this time I won't have to put any lead or a larger battery pack in the nose.

Thanks for all the info!
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Old Aug 28, 2014, 03:57 PM
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P.S. Speaking of "added mass", the wing of the Chrysalis has "added mass" of on the rough order of 4 ounces of air. Something I picked up long ago in an engineering class, with respect to water. There, the added mass of the fluid influenced by the wing or other object is really significant. For instance, if you have something with a fat shape bobbing up and down in water, the added mass of the water moving with it will lower the frequency of the bobbing. I'm not sure how this plays out with flutter in air.
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