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Cantilever wings and 4130 fuselage questions?

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Victor Bravo

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The Pelican wing is 17% thick, and brings with it all the benefits/problems that come with that much extra thickness (more camber and more lift, lower stall speed, lower minimum horsepower, lighter spar weight, slightly reduced cruise speed, slightly more profile drag, etc.).

The Facet Opal wing looks like it is either a symmetrical airfoil or very nearly so, which brings with it a different group of benefits/problems (lower pitching moment, requiring less reflex, higher cruise speeds, higher stall speeds, minimum power is greater, lower profile drag, etc.)

No engineering degree or formal aero education documents hanging on my wall, but I'm still pretty sure the Pelican is by far the better choice for low power / electric power and low speeds compared to the Opal.
 

rotax618

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The phenomenon alluded to in post 68 could be the problem I have observed in my “lifting body” models at slow speeds, when the chord of the control surface is small relative to the chord of the wing. The control surface appears to be in a ‘dead’ zone behind a wide chord wing. If you take note of other successful low aspect ratio aircraft ie. Rowe’s UFOs and Verhees Delta you will see they have very wide control surfaces. The only way to avoid the problem is to use their method an put up with heavy controls or use Junkers elevons, or an extra ‘trim’ surface like on the later Arup ad Dyke delta.
 

lr27

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I'll bet there are other ways. Some kind of strake or vortex generator comes to mind.
 

pictsidhe

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I'll bet there are other ways. Some kind of strake or vortex generator comes to mind.
They just help with flow attachment.
The problem with elevators on short fat flying wing is that back stick reduces the max Cl of the wing. There isn't really a way to deal with it other than with fkying exoerience. Swept wings with higher AR can use inboard elevators that move the other way and raise the wing Cl at back stick.
 

lr27

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I think he was talking about another phenomenon too, but I could be wrong. I imagine the boundary layer on the back of an Arup is pretty thick. Hence, possibly, the flipper like, outboard horizontal stabs on the V-173. Those are supposed to help with induced drag, too, I think, though I'm not sure if they work unless you put the c.g. back to a dangerous place, where it's just great as long as you don't stall! But that could be only with higher aspect ratios. It's all so complicated....
 

rotax618

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Rowe’s UFOs and the Verhees Deltas fly just fine, and at the speeds we are considering larger control surfaces are no deal breaker. It is interesting never the less if you look at the development of the Umbrella Plane, started out with conventional ailerons and flaps which turned int Junkers ailerons in the later version.
 

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billyvray

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I was only talking about the loss of CL when making a quick pull up on the stick, with a slight corresponding mush before taking on the new angle of attack. Nothing about controllability.
In flight, at speed, not next to a giant point of reference (i.e. the ground) it may not even be notable. This was from one of the most experienced pilots of such craft out there (Milt H.).
He originally tried Junkers style surfaces first, but said he didn't like the handling and complexity...
anywhoooo, not saying it won't work just pointing out a characteristic to be aware of. nothing bad. Carryon

I think he was talking about another phenomenon too, but I could be wrong. I imagine the boundary layer on the back of an Arup is pretty thick. Hence, possibly, the flipper like, outboard horizontal stabs on the V-173. Those are supposed to help with induced drag, too, I think, though I'm not sure if they work unless you put the c.g. back to a dangerous place, where it's just great as long as you don't stall! But that could be only with higher aspect ratios. It's all so complicated....
 

RJW

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Just wondering if the aero difficulties of a plank are worth the lighter weight. Would something like the attached be that much more difficult to build and weigh that much more?

The attached is a quick conglomeration of parts to illustrate a very light, low aspect ratio ultralightish concept similar to what the OP asked about. Wing area of 120ft^2 and AR of 3.3. If made from aluminum with a one-piece spar, a sheet metal d-cell, and Dacron, the entire wing would weigh only about 50 pounds. It has a slightly modified GA30-618 airfoil. Tail feathers would be built similarly to the wing. I drew the fuse the way it is because I like a central welded structure that everything else bolts to. It could of course be made any way one wants.

Again, since the OP wants a tractor, wondering if sticking a conventional tail on a stubby wing might end up being less work in the long run than all the work and worry that would go into a plank.

Rob
LAR 1.jpgLAR 2.jpg
 

Victor Bravo

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RJW that looks pretty cool, very similar to the concept of the VJ-1 Viera from Europe. That would be a perfect contender in our awesomely epic "Motorcycle of the Air" discussion. I re-read the OP and I didn't see him say that a tractor was necessary, other than mentioning an Airbike as something he wanted to study.
 

FoamandTape

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ok, been going back and forward now for the last few days! I keep wanting to try the plank but cant seem to stack its benefits vs a more traditional route. This is probably more my issue for not laying out the mission of this build! I think the highest priorities in this order will be what I shoot for. I really like RJW's drawing, its very close to what I'm looking for.

1) Small-ish. Reduced size means less materials for construction.

2) some what crash resistant, I want to fly this one more often than my previous crafts. Having an engine out is inevitable.

3) puller- this has more to do with putting the 2nd heaviest component out in front, I dont want to full stop into a wall and have the engine behind me!

4) Main spar not inline with torso- In the event of a crash into a not so moveable object I really dont want to be sitting in front of the main spar, its probably going to be the 3rd heaviest thing that will need to dissipate its energy somewhere!

5) operate from semi rough fields- this has me going against any pusher plank wings as most designs would seem to have a prop strike with the ground on a too abrupt rotation (and also stuff kicked up from the LG damaging the prop)

6) simple-ish to construct, I'm ok with welding this up as it doesn't seem to have too many downsides.

7) light weight (with a projected span of 18'-20'ft I want it to be complete at about 120lbs or less)

I think I may go back to a low wing approach, I'm still tempted to build the plank but as some have mentioned abrupt elevator changes can be a bit slow to translate into changes in the airplanes attitude (for the longer chord ones anyhow) I remember this as always a thing with the more under powered rc plank planes. I really dont want to go through the hassle of making yet another plane I may not be satisfied with the performance! I really want to scud run with this next plane so having solid 3 axis control is up there for being comfortable down low.

So I've tinkered with this rendition next, Lots of things will change as not all the 4130 has been added, Its a mix of 1/2 .035 and 3/8 .028 the total weight of the fuse is just shy under 15lbs! so not too terrible, I may opt to leave it not covered and just fly it as is.

The wings however are my main concern, I cannot seem to settle on doing them a certain way as I dont see very many cloth covered cantilever wings. This is pushing me to cover them in aluminum (which I have zero XP with) or doing something stupid like coroplast! Which I'm seriously considering. The nice thing is the wing will be built as one peice so the interface to the fuselage can be pretty easy to change out should I decide to scrap the first set of wings for a newer design. the current renderings are 8.5x 3/4 inch poplar spar with a aluminum 1/8th web plate bolted onto one side with 1 inch "L" stock on all four edges to pop rivet the skin to. This seems like it should be ok to build and now I can disregard the diagonal bracing inside the wings (is this anti drag struts??) The blue parts are just foam form lowes. Not drawn yet is the 1 inch strips of 1/16 aluminum I plan to cap each rib with, this will also serve as another pop rivet location for the coroplast, itll also hold the trailing edge piece of AL on.

does anyone have any resources for bending AL tubing and possibly what thickness I should use for the tail? I may jus bend that and cover that more traditionally for this build! I just have no exp with any of that! Howd they do it for the legal eagle or airbike?
 

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Victor Bravo

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Well, I have to admit that "the kids are all right" in this case. Peter's rationale and design philosophy, his thought process, and the parameters he used to make those decisions all sit well with me. He has laid out a strong and clear case for the low wing conventional tailed layout, and what he said is correct. The aircraft will be slightly heavier and more complex than the Pelican, but much more crashworthy.

Peter make sure you look closely at the Ivanov ZJ Viera ultralight https://abpic.co.uk/pictures/model/Interplane ZJ-Viera . This would give you some very good ideas and how Marek Ivanov solved certain conflicts or design issues.

For whatever it is worth, my vote would be to build the fuselage as a narrow box from sheet metal. This is easy enough for someone to do the engineering on, figure out the thicknesses of the parts, etc. You will be able to have the parts cut on a CNC router or water-jet to speed up construction greatly. And the alkuminum is predicatable in the event of a hard landing. One narrow box wold allow you to mount the engine, mount the wing, tail, mou nt the main wheel, and mount the seat all to one assembly. Leave the center wheel under the pilot, that adds protection directly in front of your spine and the family jewels in a hard landing, and still gives you the lightest and best performing aircraft.

The wing caan also be sheet aluminum, or if you just have to make it out of composite you can do that.
 

ScaleBirdsScott

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If he sticks around here too long suddenly he'll have built another all-aluminum beast and there won't be a lick of foam or tape in sight!

Not that there's anything wrong with all-aluminum beasts in my book.

For a fabric-covered cantilever wing there are examples out there. The common aspect to most of them is that you still tend to see a structural D-box leading edge or otherwise need a spar that is able to handle the torque. A Grumman/BD style tube spar would have you there, simple too. But heavy. Otherwise a wood or aluminum leading edge is probably in your future.

One thought is to mimic what Titan does in their Tornado and T-51, and it fits right along with the phoam motif: hotwire out a solid leading edge from foam, wrap a piece of thin aluminum sheet around with glue (If my memory serves they do this by literally pressing the cut leading edge and a sheet of aluminum into the negative remnant of the airfoil, which makes it also rather easy to clamp everything and wait for the bond to cure) That all has to get mounted to a spar one way or another, but then the trailing edge could be done in a traditional fabric-covered way, a bunch of lightweight foam/alum/plywood type of ribs, and some wire or tube drag bracing, and Bob's yer Auntie.
 

RJW

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Reply to VB: Yes the drawing I made was inspired by the ZJ Viera. That plane is very simple—very impressive. I wanted something similar but made from steel and aluminum. I also wanted something a bit bigger. The ZJ Viera is very tiny. Empty it weighs only 170 pounds!

@ Peter: The route you are headed seems fine to me. But I suggest resisting the urge to cover the wings with aluminum. It’s just too heavy. A plane with 120ft^2 of wing requires about 250ft^2 of covering. If you use .016in aluminum the covering alone will weigh about 60 pounds. Seems to me the lightest configuration is either an enclosed D-cell and parallel ribs (either partial sheet at the root and tip aft of the spar or angled ribs at root and tip to keep things parallel) with fabric covering, or a partial D-cell with angled ribs and fabric like on the Ercoupe.

Attached is another version of the reasonably low AR concept with tapered wings and the same area as the earlier attachment. This wing might end up a little lighter and work a little better than the earlier one but more time to build. The span on this is getting kind of long at 24 feet. Also attached is the concept on which the low AR drawings are based. It has 30 feet of span and only about 112ft^2 of wing—probably too long for a one-piece wing and too fast/heavy for Pt103.

Oh, and definitely give the mono-wheel gear some thought. It’s very simple and can use a big squishy tire for rough fields. Look up the videos on the ZJ Viera to see how easy it is to drive a mono-wheel around on the ground.

Rob
LAR 3.jpgEx 5.jpg
 

erkki67

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FoamandTape, your bird looks great indeed, somehow I like those dimensions.

A few years back I was interested at the ZJ-Viera, but the price tag was scared the hell out of me.

Fritz came up with some highly interessting designs, a low wing that comes close to yours with two exceptions, his designs are of sit on top and a normal layout, nor LAR as yours.

B24AE458-0220-41DC-A634-F80ED56EDD27.jpeg

Both plane concepts looks viable for me, so either your LAR concept, or Fritz’s sit on top concept.

If money would not be holding me back that much, I’d had already several planes at work. :gig:

Rki
 

cptcliffhanger

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peter,

Digging the design goals and priorities! also the 3D model.. I learned an neat trick from a guy that you might get a kick out of.. he would mock up his steal truss type designs (not unlike your fuselage) with toothpicks and hot glue.. this shows you right away if you have properly closed out the structure and that it is properly braced. if it twists and bends easily there's a missing triangle somewhere and it becomes obvious where you need to hot glue another. I know with FEA and other digital tools it's not completely necessary but there's nothing like making stuff with your hands and understanding the load paths.

S
 

Highflight

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I can say from personal experience a single wheel is a nuisance for ground handling and taxi, I prefer two or three wheels. It looks like you are now heading in the direction of creating a smaller, U/L along appearance of the Fly Baby. Lots potential for replacing traditional wood fabrication with composites and aluminum in the FB construction. My choice of covering would be Oratex, not sure why you are considering coroplast except possibly cost. Many recumbent bike fairings have been constructed from the coroplast, I can't speak to it's suitability for aircraft use. I assume you are intending on using it with the corrugation running span wise.
 
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