X-Plane/Developing/PlaneMaker

Attachments, gear and sanity.
In X-Plane there are 2 groups of moving items that you can attach stuff to, control surfaces and gear.

Attachment in x-plane means that the ANGULAR CHANGES usually applied around the origin point of a moving item are also applied around the origin point of the attached object.

So if you keep in your head that we are tracking angular changes, then most things follow on from there. Weapons have the added advantage that the attachment point can be easily moved, allowing the origin point for movement to be different to the origin point for the geometry of the object.

To attach a misc body(V8) or weapon (V7 and V8) just use the supplied selector/drop box that is in the editing screen.

NB Attached objects can be placed anywhere, they track angular changes with no actual contact required.

Control surfaces
Almost everything hinges or pivots around the x axis, which normally runs from left to right. The only difference is the rudder which pivots around the y axis, which normally runs from bottom to top. The control surfaces or attached bodies can appear at any angle or position, the changes are still applied around the origin point, which may have been rolled, yawed, or pitched.

These control surfaces don't know anything about the wing or fuselage angles or movement, their origins are linked to the origin of the body they are attached too, changing the origin or position of the body does not change the origin of the control surface relative to that body, so the control has no idea that things have moved, it is still attached to the same body in the same way.

Move a control surface and the attached object moves.

You can have to have a cord ratio of zero and the attached item will still move.

Gear, leave your sanity at the door!
Just when I though that things were simple, I started playing with gear. Remember this! This is the KEY! Gear legs move only around the x and z axis, between 0 and 180 degrees. 'movement' around the y axis is done with smoke and mirrors. They actually move the strut around the z axis and adjust the x axis.

The norm for gear is to pivot around the x axis and the leg follows the z axis which is offset down 90 degrees. The attached item is placed along this z axis. So the attached object points down the gear strut and it follows the movement of the strut.

So What I am saying here is that when we move our stuff forward (lon) through to 180 degrees things work as you expect.

Struts that move in any other direction have their origin rotated and so they pivot around the repositioned x axis, and still only to a max of 180 degrees, any more than 180 or less than 0 and the origin is re-adjusted, which means that as the strut and attachment move through 0 or 180 it flips around the z axis 180 degrees.

Wheels and Wheel Nacelles try and track some of this movement while looking normal in the extended position, and looking weird in the retracted position. I have noticed that some nacelles on some gear positions seemed to break a few of these rules, but I suspect that it is a bug.

Wheels and Nacelles track the end of the strut, attachments track the origin of the strut, so wheels and nacelles can move up and down, attachments can't.

You can get a pseudo y axis movement by using a combination of lon and lat gear settings. (lon 0/90 lat 90/90)

Piston Engines
In X-Plane, all piston engines are treated as turbo-supercharged engines. They develop Maximum Power (as entered in the Plane Maker field) up to Critical Altitude.


 * Turbo-supercharged engines can be simulated by entering the appropriate critical altitude. However, while X-Plane appears to model the demand of air by the engine so that boost pressure tends to drop when RPMs are increased, the increased amount of exhaust gases that would normally increase pressure seems not to be simulated.
 * Normally aspirated engines can be simulated by entering a critical altitude of 0 ft.
 * Engines with mechanically-driven centrifugal superchargers (as used in most Warbirds) have to be approximated by selecting a critical altitude and maximum power combination the real engine was capable of. Below critical altitude, the simulated engine will develop a bit too much power since the power loss due to throttling back is not considered.
 * Single-speed superchargers can be simulated relatively accurately.
 * Two-speed (or three-speed) superchargers are difficult to simulate correctly because they have two (or three) different combinations of critical altitude and maximum power. Select the high critical altitude/low maximum power combination to get the top speed at best altitude correct, or select the low critical altitude/high maximum power combination to get speed at sea level and take-off performance correct. Or select anything between for a compromise.

Tuning for Realistic Speed
When tuning for realistic speed, make sure


 * If Max Forwards Throttle is set to 1.0, Redline should be equal to Top of Green Arc, or the engine will not develop full power.
 * Transmission Losses for most engines that are built with a gearbox as default are 0. That's the way they are rated.
 * Make sure the propeller tip speed is in the correct range and you get a propeller efficiency of at least 80% in level flight.
 * Check if the Gear Ratio is correct. Some engines have different versions with different ratios, and if the propeller tips go supersonic, efficiency will drop.
 * Check if the Prop Radius is correct. It affects propeller tip speed just like the gear ratio.
 * Make sure that Propeller Design Speed is in the desired top speed range.
 * Make sure that Propeller Design RPM is top of green arc divided by gear ratio.

Summary
In general terms attachments only track angular changes to the nominated items, flaps, rudders etc. around the x axis. (rudders rotate around the y axis)

Gear/strut origins are are being manipulated (badly) to do what they do, and these extra/hidden angular changes are being applied to your attached items.

(I believe that X-Plane's messing with gear/struts causes problems in many aircraft and the bouncing effects may be fixed by angling the rear strut at 0 or slightly forward. That the positioning of gear above and below the CG and at some rearward angles, is seen by X-Plane that you may want a 'tail sitter' style aircraft and it may try and make that happen.)

Links

 * Plane Maker 7.30 -- a Tutorial - Tracy Walker


 * Polished Aluminum Skins Tutorial - Tracy Walker


 * Airfoil Listing &mdash; List of airfoils