Texturing I: The engine

For several reasons I decided to texture the engine before I move to the cockpit modeling. I never did texturing of 3D model before so I was expecting a lot of learning. Also wanted to check how my way of modeling affects texturing. For example I found that repetitive parts is better to duplicate by Alt+Enter in the blender so later only one instance is required to be textured. All duplicates are automatically textured at the same time. It took me lot of trial and errors to figure out how things are working. One has to switch his mind from technical, modeling thinking to more artistic way :). My goal was to use just 512x512 texture while level of details will be still good. To acheive this I could not simply unwrap all the parts and paint them. I had to think how to reuse particular areas of the texture. With combination of specular and normal map pretty satisfying results were acheived.

      

Some things may still change as I learn some new techniques in future. But for now I'm quite satisfied with the result. I prepared one "trailer" video displaying the textured engine using dramatic soundrack ]:-). Enjoy!

   -Joe

Blender Mdelling VIII: Engine pt. 3

The engine unit is getting close to finish. Though there are still some minor details to be added, it already looks great. I successfully applied main animations related to the engine extension. Most challenging was a properller-stopper assembly. I wanted to make it fully working as in real thing. It is a very little detail however the final result adds a lot to the realism of the whole model. The spring in that assembly is also fully animated. It means it extends/compresses as the lever catches the "pad". I found it very hard to notice, so it is probably just for making me feel better about it :) . FPS are still very good. Just couple less then default X-Plane's ASK21. So no need to worry about over-animating.


Applied animations:
 Engine unit extension
 Doors opening
 Working Propeller-stopper
 Propeller rotation
 Muffler disconnecting

I started to intensively work on the finalization of the DG 1001 M . It means I work on it almost on daily basis. Goal is to deliver one nice X-mas present :). But can't promise anything yet. At least you may be looking for more often updates ;)

See you soon!
-Joe

Blender Modeling VIII: Engine pt.2

Thanks to DG1001M service manual I managed to model the engine unit frame quite precisely. Though it took its time to read all the detail drawings and get all pieces one by one assembled into one big picture.

 

Then I continued adding various sub-assemblies onto it. Interesting one is a propeller-stopper. It blocks propeller from rotating while engine is retracted or in process of extension/retraction. Sure I will animate this later :). I really enjoy getting the things to work as in real. (Part attached to a fuselage are not displayed on the pic)






Another interesting part to model was the propeller. I started with low poly model which did't look good enough for me in closer look so I decided to go for more polys to achieve this...

Finally I was curious to see how it will perform in the xpl. Here is a short clip showing extension of the engine and start up...

And the whole engine as it looks currently:

 Next I will continue adding hoses (hm, how could it work without them :D ), screws and other details to finalize the whole engine assembly.

-Joe

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...

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.

DG 1001M

Considering documentation materials available and attractiveness I decided to model DG 1001M. It is a self-launching two seat modern nice looking glider. Self-launching means it can taxi and take off completely alone. No need for towing plane or winch to get airborne. Though still possible.

My aim is to model the glider as close as possible. Considering

- accurate flight model based on speed polar
- configurable features (center of gravity, weights using, watter balast)
- flight computer
- check procedures