Thinking about our next wood glider kit.. Ludion

[Wayne]

Just thinking out loud and wanted get some feedback from you for a possible future kit from Aloft.

I have a soft spot for vintage designs and was hunting around for inspiration. Found this Le Ludion designed by JL Orain published in the French magazine 'Radio Commande' back in 1981.

This one caught my eye for a few reasons: it has some good lines, it is an early VTPR plane. And let's face it, twisty wings are always attractive. Overall it is a pretty simple structure, so should be an easy build.

And let's face it, I'm a sucker for a well rounded balsa fuselage.

Love the inverted launch:

They later modified the wing and fuselage a bit for an improved wing linkage setup, much closer to the setup like the CR Turbo. They also moved the wing back for better CG and changed the airfoil to an E193 instead of the original E374.

They reported some encouraging performance and suggested its use as a multi axis acro trainer that could fly in very light conditions.

What do you guys think of it?

Rough idea would be to complete the design as it is missing a number of details. Build it full size (75" wing span) and see how she does. Thinking of sheeting the D box area and cap stripping the ribs. Don't know.. It will make the plane more durable and more attractive, but more complex and adds weight.

See attached magazine articles if you are bored. (pdf format).

 

[Konrad]

YES!!!

No cap strips they do nothing other than add weight and time to the build. With proper covering technique the covering will add all the lateral support that the aft part of the rib needs. Also with proper covering technique the film will not curl the TE. I go into this here.

And I love the idea of using the Eppler code, none of this hyper critical optimized sales crap.

 

[Wayne]

What do you think about the size?

I kind of want to experience it as close to original as possible, but at the same time am thinking closer to a 50 inch span would be better. We aren't hefting full size radio gear and Nicad battery packs anymore. But then I picture this thing flying at Sunset... That big size would be sweet.

 

[Konrad]

The best thing one can do to improve glider performance is spread the distance between the wing tips. As I think your balsa stock comes in 36 inch lengths I would use that as the main manufacturing constraint. So wing span would be 36 x 2 plus fuse width and wing tip blocks (if used). I'd avoid the 50" stuff based on the performance of the Bridi kits.

 

[Doc James Hammond]

The "Dodger" in French - good name.

Looks like a really nice model, except possibly I might do away with that dihedral. It doesn't need it if it is to fulfill its purpose as an "aileron trainer" - albeit with no ailerons.

Like the man says - if it looks good...

Doc.

 

[Konrad]

The "Dodger" in French - good name.

Looks like a really nice model, except possibly I might do away with that dihedral. It doesn't need it if it is to fulfill its purpose as an "aileron trainer" - albeit with no ailerons.

Like the man says - if it looks good...

Doc.

+1

LE sweep should be more than enough effective dihedral.

 

[Mauiboy]

Looks really cool.
CR turbos and contenders were fun ships to fly. This twisty wing looks

 

[jure]

The "Dodger" in French - good name ...
Doc.

<OFF Topic alert>
Dodger you said ? here is mine:

 

[Wayne]

From past experience Wingeron performance sweet spot seems to be right around the 50" wing span. Full stick lengths and the wing tips and center fuselage pretty much should hit that 75" span.

 

[Wayne]

Started playing around in the CAD for the wing design. Just getting to know the software, lots of fine tuning to do still. I currently have 2° dihedral:

Looks like about the right amount of angle to give a little stability and cancel out the wing taper. I thought their plan called for 2 degrees, but looking back I see they spec out 4cm per die. Agree, that is a lot.
Here I have bottom aligned the ribs and picked the angle up to 4 degrees. Think bottom aligning will make the wing a little easier to build..

I'd like to try it will some extra angle in the wing then I would normally use as we do want the rudder to have a good bit of authority. I really do not want to alter the plane away from the original deign too much.

This is using the suggested E193 airfoil (10.22%). It is an interesting choice:

Basic structure currently:

Will double up some of the ribs with joiners.

This is mostly just mucking around at this point. Single airfoil, no twist. Leading edge joiner will be attached to the leading edge stock.

 

[Mauiboy]

Wayne , that looks like a fun build.
Looking good

 

[Konrad]

Since you are asking for input. I don't like holes in the ribs. With monolithic grained materials (not plywood) the loss of strength is much greater than the loss of mass when adding holes. So for any given weight the rib would be much stronger without the holes. This is because it is very easy to split the grain where the holes cut through the grain. So if looking to loose weight it is much better to go down in material thickness than the cut holes into the rib.

Going down in material size will benefit in material cost, laser cut time and in all likelihood be stronger!

 

[Konrad]

From past experience Wingeron performance sweet spot seems to be right around the 50" wing span. Full stick lengths and the wing tips and center fuselage pretty much should hit that 75" span.

I thought this (50") had more to do with the servos of the time. As I recall the 50" span was as a result of the 24" wide foam block we got as core material. If you are thinking of wing penetration and drag most of the limitations of old on the larger span can be addressed with today's carbon, ballast and servos.

 

[Hank GB Z]

Signing up to follow along. Looks cool.

Hank

 

[Wayne]

A good point - I have yet to decide on things like the lightening holes. I do like the looks of them.

We may well make the ribs from plywood, if so, lightening holes. I'm also debating adding half ribs between the existing 19 ribs.

Here is the current state of design:

I have added 1 degree of wing twist. Thoughts? My thought process was that this will be a low lift low level acro plane, that bit of washout could help avoid a nasty tip stall when working the airfoil hard. With no other methods to control tip stall, I think this is a fair trade. It is not going to be a fast plane with this airfoil and low weight, so don't think I'm leaving a lot of performance on the bench. Actually think it may allow a little more confidence if the plane does not want to bite the pilot when pushed hard. Thoughts? (I think 1 degree would be easy to pull out with the covering should it suck..)

Wing span - From my experience simple wingerons start too loose their "fun factor" when they go beyond 50" span. But that is based on the desire for a sporty plane that impresses with roll rate and some return in speed. You may well be right bout the 24" foam blank to avoid too much foam waste. LOL For now I'm sticking with the 1.8 meter span for the prototype.

So to summarize the aerodynamic changes made so far are less dihedral and 1 degree of washout. I still need to confirm the planform, I did some rough measurements from the plans. Rafael is going to start putting the Fuselage into CAD for me. The project would come to a halt if I had to do that step.

What do you guys think, built up tail like in the drawing, or balsa plank with lightening holes?

 

[Wayne]

With half ribs and holes modified.

We now have 27 ribs per side. LOL

 

[Konrad]

I like the stab as drawn, but I'd bring it down to the fuselage. It is up on the fin to give the bellcrank some leverage. Again old style servos. Mounted to the fuse it need not move. (AKA pitcheron (SP)).

I thought this was going to be "D" tube. If "D" and I like "D" tube wings there is no need for the half ribs.

Generally I don't like holed planks too much grain not adding strength to the structure.

 

[Doc James Hammond]

What is the envisaged 'slot' for this plane Wayne? What do you want it to do?

Light model aerobatics?
VTPR?
Just general flying on the slope, with a bit of aerobatics?
Light lift performer for calm evenings etc?

Cheers,

Doc.

 

[Hank GB Z]

Wayne,

As you embark on this venture remember “A camel is a Horse designed by a committee.”

Don’t make a camel. Go make your horse.

Hank

 

[Wayne]

I'm enjoying sharing this with the community. While I have my hand in a number of designs, and arm twisting with our manufacturers, this is my first crack at building a new wood kit for the slope. I'm having fun with it. I have not produced a glider design for many decades.

Konrad- I really like the lifted tail, I'm a fan of the ASW-17 look and have always had good performance from them. But yes, it does add to the complexity and weight. We will see how that fleshes out. Current plan is to skip using an internal bell-crank for the prototype. Down and dirty.

D-box - No, the original plane was not a D-box, and I'm not a fan of sheeting process. Also, wingerons tend to have issues around the front pins, if boxed it really makes repairs harder. For now, it is a pretty simple wing. I like that. I may box the main spar for a few ribs, still debating the structures for ease of construction. The original plane was a boxed spar for most of the span. If using plywood, I think the box is overkill. If using balsa, then box is a good thing. Heck, I don't even know what I'm going to use for a spar pass through just yet. We got in some pretty cool mandrel wrapped pultruded rods. We also have some smaller mandrel tubes. Or can use the good old steel joiner with brass sleeves.

Doc - Yes, for me this plane checks off a number of interests. I do think this was an early VTPR type, a good 20 years before VTPR definition came into being. Light weight, low wind, low energy ACRO beach plane.

Is this a cutting edge plane? Nope. Am I having fun with it? Yep!