abufletcher

TFF, there are indeed things that need to be specified and changed around. The mislabeling on the plans is probably the result of "copy and paste" in CAD. Deciding where to place servos is an important part of the design of any model...and it's very frustrating when plans don't even suggest where the radio gear might go. In this case, Chris has put a lot of effort into locating the servos so that fully detailed cockpits are possible.

But working out the linkages can be just as difficult and often requires a good bit of mechanical creativity. Tom seems to have worked out one solution. I'd like to have a straight link from the rudder servo arm to one of the rudder bellcranks.

abufletcher

For the moment, I'll focus on linkage between the rudder servo and the pair of bellcranks that transfer this movement to the cables. It sure seems to me like the RC car guys must have something that functions almost exactly like this for steering. In terms of commercially available parts (which would be nice in terms of a kit), these car turnbuckles with a clevis on each end might make for a good, no-slop (and adjustable) connection between the bellcranks. Heli-style ball links might also prove useful.

http://www3.towerhobbies.com/cgi-bin...?&I=LXFUG8&P=7

Below is a photo of Tom's solution. Personally, as I mentioned above, I'll like to be able to have a direct link from the servo arm to one of he bellcrank.

The other issue is the direction of the servo arm travel. There are two possibilities: 1) with the arm at 90 degrees to the servo, as with Tom's solution or 2) with the arm lined up with the servo, which might be better for a direct link to the bellcrank. I've already checked and there is room for the arm to move in this direction.

Finally, note that the servo can be "lowered" to whatever height might be best by placing blocks "under" the current mounting beams. This might turn out to be important.

abufletcher

This looks promising:

http://www3.towerhobbies.com/cgi-bin...?&I=LXRUH4&P=7

CTDavies

On the mockup I did it was possible to mount the servos after the fuse structure was completed. I personaly would hate having to build in servos in to a model without being able to remove them again later. Maybe everything needs to be fudge around a bit and the slack eliminated that happens when everything is just pegged together. I'll re-check my mockup but the goal is to have a model with removable hardware.
Tom's solution for the rudder linkage is pretty much what I also had in mind. I was going to work this out in more detail using the mockup but then through lack of time it must have got lost in the cracks somewhere. Working this kind of stuff out on a real model is much more revealing than in CAD anyway . I had already noticed the mislabelling of that servo and have corrected it. Copy and paste functions do sometimes lead to complacency.
To get back to that joint between the two fuse structures; I'd try adding some 6mm balsa strips between the formers on the front section to glue the longerons of the rear part on to. That way the pronounced curvature should be easy to maintain. Keep up the good work, guys.

abufletcher

A bit of fishing around in the parts draw and I think I've got the rudder linkage licked! First, I worked with the kit's GRP bellcranks but then happened to find a commercial set I had around and those looked better (bigger) for what I had in mind. I, first, inserted a short length of 5mm brass tube and then a slightly taller 4mm brass tube. A 3M bolt fit inside that perfectly. So now instead of connecting in the middle it connects on the outside of the bellcrank arm. This arm is longer than the kit bellcrank arm so I can add a clevis for the cable on an inner hole.

The servo is reversed from its position on the plans and the servo arm is aligned with it There's no restriction on the movement. The servo is perfect at its present height.

BTW, on the kit's GRP bellcrank, I recommend making them a bit larger and adding a curved area to the inside angle (as on most commercial bellcranks).

abufletcher

That's good to hear. But try as I might, I can't find a way to get the inverted mounted servo (with the arm on it) out through the top of the model. It's no fair taking off the arm since it wouldn't be possible to get at that screw with the sides and bottom closed. And this doesn't even take into account how we'd remove the screws.

BTW, I'd prefer to use one of the car-style "tie-rods" ("turnbuckle") I linked to above instead of the length of fully threaded 2-56 rod I have on there now. Because the ends are reversed-threaded, turning it would adjust the distance between the bellcrank arms for perfect motion. I find myself looking at the car and heli parts more and more these days!

abufletcher

OK. That's settled. There WILL be a bottom hatch for access to the elevator and rudder servos! Whew! The first four photos show the steps for getting the servo into place. A little careful cutting and I might be able to simplify this. The last photo suggest this area under the tank might be a good place to stow the receiver and battery.

It might be wise to think about this now and cut some holes for the servo wires (for example the ones for the wing servos). Actually that's a whole other thing to ponder on. Since the wings will be removable, clearly we need to be connecting the servo wires at the field so we'll need access to this area under the floor boards.

abufletcher

I created the world's shortest ball-joint linkage so now the rudder linkage is complete. However, I would like to get one of the car-type turnbuckle rods to use between the two bellcranks in order to make precision adjustment possible without having to take a clevis off.

Also, I filed some notches in the hardwood beams to allow clearance or the wires and a notch for servo arm clearance in former F4a and recessed a bit of the two main support pieces so that now I can slip the servos in with the servo arms attached. So I think I can now glue these parts onto the frame.

So HEADS UP future CI modelers.

abufletcher

All the fuselage servos are now installed..and a very neat installation it is too. Hats off to Chris! [sm=thumbs_up.gif][sm=shades_smile.gif]

In the last photo, I've just laid the old version of the engine mount compartment. I now have the parts for the kit's reengineered mount with the 2 degrees of right thrust, burt haven't yet glued it together.

GianFrancesco

A very neat servo installation indeed; only a question: why non a real working "rudder bar" instead of the two connected together bellcranks ?
Gianfrancesco

abufletcher

You know, I just asked that very same question in German on the German builder's build thread! Why not indeed! That's exactly what I'm doing on my DrI build and I don't really see any reason why it wouldn't work here AND be simpler. And simpler is always better! Plus it would be SCALE! [8D]

abufletcher

As it stands in the last photo, with the three servos (130g) in place, this unit weighs exactly 500g. Short of switching to lite ply for more of the parts (a questionable idea) I don't see much opportunity to lighten the structure. I could have saved maybe 30g by cutting lightening holes in the lite ply floor boards but that's hardly a worthwhile savings for the additional strength it provides.

I do wonder, given the incredible strength of the unit as it is (because of the interlocking formers on the two keel pieces), whether we need the traditional fuse doubler. We'd need the part of it in the nose area but I don't see what purpose it serves from about F4 back.

GianFrancesco

I agree with You that the simple is always better; even if not always I am able to find the simplest way!
It would be intersting to follow the thread (in German) of your german friend; where can I find it?
May be that my "Erinnerung" (forty years old) of the German language allow me to understand at least the sense of the phrases!

GianFrancesco

gefunden: http://www.rc-network.de/

abufletcher

Herzlich Willkommen! Now you can also see how bad my German has become!

Chris, I've been thinking (instead of sleeping). Just what structural functions does the ply doubler have? One job, and maybe the main job, on traditionally built WWI models was to provide strength along the length of the forward fuselage. In particular it provided support to the high stress area on the bottom of the fuse, just behind the UC. It was supposed to keep the model from "breaking its back" on a hard landing. But with your innovative new design technique of building on the twin keens with interlocking parts, you have in effect, provided the model with two strong internal spines, which are more than sufficient to take landing loads.

Another function of the ply doubler is to provide rigidity to what, on most WWI models, was usually a pretty light and flimsy balsa frame. It was the solid "box" onto which the engine was bolted. It kept the frame from twisting. But once again the twin keels and interlocking parts do most of this work.

Think back to the original design concept of the Albatros B and C series aircraft. Why were they skinned with ply? Was this just to save fabric (he asks rhetorically ). No. The skin actually replaced the need to have the traditionally wire-braced fuselage common at the time. In short, the ply skin prevented the fuselage from twisting! I don't see why we can't let the ply skin our our model do the same thing.

Do we really need this ply doubler when we are going to cover the sides, top and bottom of the entire fuselage with aircraft grade 0.8mm (1/32") ply sheeting?

Now, of course, on the current design, the doubler also does a few other odd jobs, such as providing an additional support for the UC beams. and guide holes for the brass wing tube. But those functions could be dealt with in other (lighter) ways.

The combined weight of the two ply doublers is only 72g. That may not seem like much, but I think we really do need to start looking for places to save weight on the fuselage. The interlocking design is heavy compared to a traditionally built WWI fuselage. But it's also very strong. It seems to me that we can rely on that strength and therefore save some weight in aspects of the construction. In short, the current ply doubler seems somewhat redundant.

abufletcher

Here's a link directly to the beginning of Tom's thread:

http://www.rc-network.de/forum/showthread.php?t=168193

abufletcher

The ply skins will add around another 200-250g.

TFF

Does the kit come with ply covering or is it a detail you have to furnish? I would say if the weight is in front of the trailing edge of the wing leave it, but if the doubler is thick may be half the thickness and along with the skin you would be covering both angles of the problem.

CTDavies

I see the fuselage doubler as a joiner between the l/g and cabane strut rails. An ideal situation would be where the l/g rail is at the bottom of a former and the cabane strut rail at the top of it. I think it's like this on the Pup, but not on the CI, at least at the front struts. An alternative would be an angled former but that brings a lot of other problems with it especially when space is limited because you're trying to conseal your servos and want to keep your cockpit clear of any radio equipment. Still, the loads from the top wing want to come crashing down on a hard landing which in extreme cases would snap the former. So the former needs to be stiffened lateraly (think of I-Beams). So the doubler really has two functions; it stiffens the formers and joins the strut rails. I hope this explains it.

abufletcher

Thanks, Chris, I hadn't thought "in that direction." Let me ponder that a while. TFF, yes, the kit comes with beautifully pre-cut overlapping panels (as on the original). There's a photo on the first page of this thread. But you may be on the right track about the two ply layers together.

geezeraviation

My Feedback: (3)

I suppose redundancy is the key here. Not having the benefit of having seen the complete plans and how things are laid out Chris's reasoning seems sound when considering loads during the less than perfect landings that often occor.
Doc

abufletcher

In terms of the vertical loads, the rear cabane strut beam is well supported by former F7, which once the ply skins are on will be rock-solid. The ply doubler doesn't add much there since it doesn't come in contact with the beam. All it does is help stabilize the F7 uprights. But the regular ply skins would do that just as well (in essence acting as cross-bracing). Support for the forward beam is more of a problem since it's not located above a former, so there definitely has to be something there.

abufletcher

BTW, I should start thinking seriously about detailing both cockpits at this point BEFORE it's all enclosed!

abufletcher

It's beginning to look more like a boat than a plane! I added the "datum line" piece to the side of the formers. This does an excellent job of making the whole structure more rigid, but this is really just temporary since the ply skin does that job. But this keeps everything straight and lined up in the meantime. Also it's entirely scale (as are the shape and location of all of these formers). Unfortunately, the ply doublers are NOT scale so that sort of cancels out the effect. [:@]

The ply doublers do fit nicely on the brass tubes and both ends are almost perfect. I do have a bit of a gap between the top of the doublers and the datum line that shouldn't be there. I used a length of 1m x 3mm hardwood I had instead of the ply the plans suggest (but that has to be cut from scape from the kit parts). I had to widen the cutouts in the former by about 1mm and thought I had that all figured out. For example, I left the bottom of the cutouts on the formers how it was, assuming that that like should precisely mate with the doubler. The doubler look right on the plans. So I don't know. May the slots on the formers are a bit higher up than shown on the plans.

Nieuport nut

My Feedback: (10)

Why is this being sheeted with 1/32" ply? Surely 1/64 would be quite adequate - lighter and closer to scale, (2mm?)?

Martin