Several propulsion types
Actually we have only one, which doesn't fit well. Very probably, that propulsions are going to differ between different bodies (just like it is between light and heavy bodies), so i propose two kinds:
- helicopter-like prop engine, whose kind is currently used only in ultimate scav mod for their helicopters. Heavy (at least) bodies could have even quadro-copter design. Wings (if present, should be essential for osprey-like design) should allow to gain speed higher than for amfibias.
- jet design. No comments. One specific proposal is to place horizontal engines as good known pair above body (not embedded to).
- plasma jet. Same as previous, but additionally requiring research for either plasma flamers or plasma cannon. If plasma weapon is so dangerous there, than using of this tech for jet should give great improvement for vtols.
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Any kind of propulsion is like to have some wings, useful for regular flight. But also, just like found in one design proposal for jet-specific body, it could have some weapon pilons. Their number should depend on body weight (1 for light, 4 for that super-heavy with 2 turret slots). These pilons may have some restriction for weapon weight and even its rotation (e.g., ideal for bombs).
Weapon, mounted on body, is expected to have may be not infinite ammo, but at least higher than on pilon. It should be able to use some super-heavy kinds like plasma-cannon, but probably requiring full-size wings unarmored (or it may be even impossible to take-off).
Speed dependency
Currently higher weight reduces speed, just like for ground-based units. But it is obvious, that real effect is opposing - it needs higher speed to hold self in air. Also this should affect maneurability (both rotation and acceleration).
About take-off
If load is too high for vertical takeoff, than it may need previous horizontal acceleration, eccentially with help of vertical engines (just like today real-life vtols do in such cases).
Air friction
Body geometry is more like to define air friction, which i see best for bug, collective light and heavy, nexus medium one and super-heavy 2-turret bodies and worse for project's heavy and collective medium bodies.
Fuel level property
Hehe! If ammo is so much limited, why not to limit fuel too? May be not for current vtol implementation, but when all proposals are implemented, resulting units are expected to be so overpowered, that limited fuel may be necessary for balance. Heavy bombers or assaulters should waste fuel much faster, than scout with some machineguns or assault gun.
Implementation of some weapons
- Cluster bombs are usually placed in special container with good aerodynamic form. Heavy anti-armor bombs may are either single big bomb or (for lighter than plasmite) or lancer-like installation, like anti-tank missiles, used on helicopters (anti-armor bombs).
New weapons
- Radar (if will return ever) is like one, used on airbus-based scout/monitoring/command unit. And btw..... command module would be very great for vtols, because ground-based one can't target air targets. But even if will - it is useless with them. And about radar: since vtols are operating usually on quite big height, they could have much wider radar range, like usual tower, placed on mountain with same height.
- External tanks may be used to increase fuel amount - imho, must have for monitoring/patrol units.
- Engineering stuff. Vor ground trucks it is useful only for engineer works. But for air units it could have another good usage: transporting of units (only by one , of course). Very useful if you have some very slow ground mammoth, which is barely working and/or just needs quick retreat (if some big air squad searches specially for it). Don't mentioning of course, using of it to build non-producing structures on hardly available places (sometimes they have only one square, and thus there is no place even for single cyborg engineer to work after dropping).
* Repairing vtol - same difference (can't be used against structures). Should land/mount on/lock unit in order to repair it, still capable to transport it at the same time. Why needs mounting - it would be super trick, repairing unit flying around it
. Though mounting of repairing unit on flying combat unit may be funny too 
.* Even if take-off with locked ground unit is impossible, this aggregate should at least have higher speed due to reducing of weight by vtol vertical engines and gaining ground engine work by vtol horizontal engines.
* Pilons may be used as well as body slots for additional tools, increasing build or repairing speed.
- Fuel-supply tool. Since units have limited fuel, refueling in air is essentially expected (of course, no even hope for rearming on air
).Not related to VTOL
- Plasma technique may be used in generator as MGD-generators technology
- May be (not sure)... using of plasma for better bullet and projectile acceleration in machineguns and cannons (e.g., because it is easier than previous proposed tech).
- Plasma shells for all cannons kinds, including mortars (at least mortars) and rockets warheads. With proper design blast radius should be smaller with higher damage, comparing to current plasma cannon, since warheads are expected to focus plasma at least in first moment after activation.
- Completely unrelated: what about laser and plasma fortresses?
