Blender modeling IV: Main gear

Yes I planned to do wings as next.Wings modeling is already in progress but not done yet (less free time at home last week). Fortunately I had some spare time in my job so I decided to do some modeling there as well (don't tell my boss ;) ) in parallel. Main wheel assembly seemed to be a good choice. I downloaded a service manual for DG 1001M where pretty detailed drawing of the main gear is and stared modeling. And here is the result...

Colors were applied just for better separation of parts. The spring differs a little bit. Original has a more rectangular like profile comparing to the circular I have used. I'm aiming to animate compresion of the spring so the rectangular profile would be a problem then. Also I do intend to use normal maps for texturing so some more details will be added.

Next (hopefully) the wings will be done :)

-Joe

Blender modeling III: Tail

I did continue with the tail area. Modeled horizontal and vertical stabilizer. Moving control surfaces.

And here all together with some mterials applied...

Nex I want to do wings.

-Joe

Blender modeling II: Canopy

Main parts of the canopy are glass and frame. It was quite hard to model the frame (visible from inside) with proportions that will match ones that can be seen on varios pictures. I decided to model the frame in one part together with piece of glass that is not translucent (white) to ease up later texturing.

Canopy frame with part of glass.

It took me three attempts to get about proper proportions. For now I'm not adding any bevels to fine out edges or similar. There are still some details to add.

This is how looks the whole canopy

And some teaser here as well ;)

There are some parts of the cockpit I made before I "oficially" started the project.

-Joe

Blender modeling I: Fuselage

The x-plane's plane maker supports exporting all parts to *.obj format so one can use them later to create more detailed replacements. However I found the mesh density not sufficient for further fine modeling. So I decided to create the fuselage from scratch. Prepared high resolution top and side view pics (from a  pdf downloaded from the DG's homepage). Blender base unit equals to 1 m so scaling and positioning of the background images was easy. To double check and comparsion I put original plane maker parts in other layer.

I decided to use 36 verticies for a fuselage section (compared to 16 from the plane maker). Sections spread is 0,2 m in most cases. Result looks as following:

Scaling the sections by X and Y axes however results in model that follows just max dimensions in the given view. Resulting section shape is more less elliptical. From looking at dozens of photos :) I found the DG1001 fuselage in cockpit area is not narrowing towards the bottom so steep as I get by simple scaling. Looking at several photos I figured out how it should  be approximately...

And here it is. The fuselage...

Next I'll continue with canopy. Some more serious modeling :)

Flight model

Finally! I managed to set the flight model to match the speed polar with acceptable accuracy. What it is acceptable? Well the L/D ratio of the flight model follows the speed polar with max 2.5% error. It means, for example if desired L/D = 43 @ 79 km/h then my flight model is in range +/-1 so the L/D equals say 42. For given speed of 79 km/h the glider should sink about 0.51 m/s. With L/D = 42 it will sink about 0.52 m/s. For now I'm fully satisfied with the result.
All tuning I performed with load of 490 kg (wing load = 28 kg/m2). X-plane flight model calculations seem to do a good job as I found the flight model matches the speed polar also for wing load = 42.8 kg/m2.
Here is the acheived flight model speed polar vs. real life* speed polar for wing load 28kg/m2

Speed polar 28 kg/m2

Center of Gravity II / Airfoil tuning

Last time I came to some wrong conclusions about force position relationship with airfoil shape/type. Moving the wing so that its 25% of chord will match approximately plane's CoG did not help much. Due the wing's shape and x-plane's internal calculations other than lift (induced drag etc) I still had to do some guessing on exact distance to shift the wing, including moment coef. Thus I did a little research and found something (http://wright.nasa.gov/airplane/ac.html). In general ALL airfoils for subsonic speeds are considered to have their liftforce at 25% plus a moment the airfoil produces. It is called Aerodynamic Center. And this is exaclty what x-plane expects user to enter. So I moved the wing back to its original position and continued with tuning the lift, drag and moment characteristics of the airfoil.

Based on wing area, desired speed and sink for every 5 km/h step of the speed polar range I calculated desired lift and drag coeficients I want the x-plane to end up. Then I started adding/reducing lift and drag coeficients of the airfoil based on actual results I got from stable glide at given speed. However this is still too much time consuming and I didn't reach my desired accuracy this way so far. As there are not all internal calculations of x-plane's flight model known (at least for me) I cant use exact math here. But I would be satisfied with some approximation of the unknown making difference between wing's lift and drag coefs vs. x-plane's lift and drag coefs. I assume that these differencies will be always same (approximately) at same angle of attack representing the unknown x-plane flight model calculation. I will play with these differences whether as percentages or constant numbers and hopefully get some expected results :)

DG 1001M video portrait

 Currently I'm deep in process of airfoil characteristics tuning to achieve proper speeds as plotted by polar diagram. DG company treats all data related to the HQK51 airfoil as classified so I did not succeeded with asking them for help. I thought that only airfoil shape itself is being kept as secret however found that  Cl, Cd, Cm characteristics are secret as well. Though most probably I would not use them direclty the data would give me a clue. Now I have to figure the data by reverse engineering along with trial-error method. So its a bit time consuming.

In the mean time here is a nice video portrait of the real DG 1001M. What a beauty...

X-plane 10 demo is out!

Well, that maight change a lot in my further development of the DG 1001M.

From X-Plane Wiki

Wondering what's changed from Version 9 to Version 10? The biggest new features are:

• a brand new system for auto-generating plausible scenery for the entire world,
• a new, highly-detailed cloud and weather rendering system,
• a flight model with improved accuracy and even greater power,
• a completely redone ATC and AI Aircraft system, and
• the ability to more fully utilize multi-core CPUs for enhanced realism.


Center of gravity

I was in process of tuning the glider's flight model to follow speed polar of the real one. However I noticed that model is quite much pitching up. I had to push hard forward to get the nose down. Definitely was something wrong with the balance. I did open the plane maker to double check the CoG position and wings position. Everything seemed to be OK. Somewhere over the x-plne forums I found that x-plane calculates resulting lift forces at 25% of wing's chord for any airfoil. Actually this can be visualized within the x-plane by pressing "/" key.

Clearly it is at 1/4 of the chord lenght


Gliders usually have laminar airfoils that may have resulting force at about 50% of the chord. That means the CoG (defined as in real DG1001M) is too much off of the resulting lift force in the X-plane. Thus a large moment is produced and the aircraft tends to pitch up.

So how to solve this problem?
A) Solution might be to simply change the CoG position in the plane maker. However that breakes designed balance for ground operation as the CoG moves towards the main wheel.
B) Move the wings so that chord's 25% (1/4) will match desired position of the CoG. Then just hide the wings and replace them by ones imported as misc. object that will not be taken into flight model calculation.
C) Calculate airfoil's moment correction.

I'll go for B). This sulution seems to be most accurate at given circumstances

B) solution applied

Edit:
As I found later, there is no need to move the lift force (wings). I misunderstood some things here. So the solution is C). Explanation is here.

Plane Maker model

Following exact dimensions obtained from official DG home page I created a base model in the Plane maker tool. This model will x-plane use for flight model calculations. Also it will be used as a reference for detailed model I'm going to create in Blender. That one then replces visually the simple model from plane maker.