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Post by ironhold on Feb 4, 2017 2:57:21 GMT
I've been trying to work on a science fiction series, and for the last little while a design for a combat unit has been in and out of my mind.
The base chassis is a diamond shape. The rear-most point and the two side points have ducted fans that can rotate to a limited degree; let's say they can rotate 20 degrees either way from vertical so that they can provide a limited amount of propulsion in addition to lift. I may or may not say that there's a large, more traditional series of hover fans underneath.
The front part of the diamond is the operator's compartment. It's elevated somewhat from the rest of the chassis (say a few inches) in order to make room for twin machine guns underneath and two directional thrusters on the sides.
In the middle is a large weapons turret that sits on a box-like structure. The turret assembly consists of a laser cannon (say about 60mm to 80mm if it was a ballistic cannon), an operator, and the doodads for it to function.
The "gimmick" for the design is that the box-like structure is actually a mount. The vehicle can deploy and retract the structure and laser cannon, at which point the weapon functions as if it was a fixed emplacement. Once the structure is deployed, panels move off to the side, allowing what's beneath to deploy. What's beneath? Three other weapons systems. In the middle of the space is a rack containing heat-seeking missiles. To the side are a pair of automated machine gun turrets whose pivot mounts are to the front of the newly-formed opening; this allows them to sweep the rear and side arcs, plus provide limited anti-aircraft support.
What I'm worried about is the hypothetical weight distribution issue. With the laser turret in place, that puts all of the weight on the center of the chassis, where it'll be supported by the main fans in the middle. But once the assembly is deployed, that's going to shift the center of balance forward, where I don't have a support fan of any sort envisioned because of the front weapons assembly.
Would there be a distribution issue enough to worry about if this was realistic?
Thanks.
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Post by ponytail61 on Feb 4, 2017 4:12:48 GMT
You need a power supply for the laser and a munitions storage for the other weapons. They could be on a rail type system underneath/behind. As the weight of weapons shifts the balance forward the power supply and munitions could slide rearward and balance out
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Post by the light works on Feb 4, 2017 6:48:53 GMT
You might want to take a look at the Hammer's Slammers series by David drake before committing completely. wikipedia pageHe used hovercraft as his primary vehicles. my primary comment on your design would be if you have effective energy weapons, why are you wasting space and weight on kinetic weapons? |
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Post by ironhold on Feb 4, 2017 7:25:29 GMT
You might want to take a look at the Hammer's Slammers series by David drake before committing completely. wikipedia pageHe used hovercraft as his primary vehicles. my primary comment on your design would be if you have effective energy weapons, why are you wasting space and weight on kinetic weapons? Trying to think from the hypothetical perspective of a toy manufacturer. If the "laser" and its electronics are confined to the box, the machine guns can simply be represented by molded plastic. |
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Post by the light works on Feb 4, 2017 8:23:38 GMT
You might want to take a look at the Hammer's Slammers series by David drake before committing completely. wikipedia pageHe used hovercraft as his primary vehicles. my primary comment on your design would be if you have effective energy weapons, why are you wasting space and weight on kinetic weapons? Trying to think from the hypothetical perspective of a toy manufacturer. If the "laser" and its electronics are confined to the box, the machine guns can simply be represented by molded plastic. and I'm thinking from the perspective of a military vehicle designer. the standard weapon of Hammer's Slammers was the powergun, which was essentially an energy weapon that used ammunition. the tanks mounted a 20cm main gun and a 2cm tribarrel gatling gun. this served the purpose of an anti-everything cannon, and a rapid fire gun which could be used for any non-armored target including either locally controlled or remote controlled antiaircraft/missile defense purposes. the only kinetic armament was antipersonnel defensive strips mounted along the edge of the turret, in case any infantry were stupid enough to think they could take down a tank. anything that was outside line of sight was a job for rocket artillery. |
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Post by silverdragon on Feb 4, 2017 11:19:05 GMT
A Diamond-shaped hovercraft hull will not 'fly'.
[experience]
The shape of the hull must not have sharp points in it, corners must be rounded, otherwise, the skirt will not produce "predictable" lift when deployed.
Check out the shape of the skirt on any hovercraft, even square corners are rounded, there is good reason....
If this has any effect on how you design your craft, then I hope this helps.
By the way, this only affects the skirt, not the shape of the superstructure above it.
Your Hull and skirt sit below the superstructure.....
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Post by ironhold on Feb 4, 2017 15:43:31 GMT
I'm thinking that the central skirt will be enclosed *within* the shape, allowing for a more rounded design; the points are where the directional fans will be mounted.
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Post by GTCGreg on Feb 4, 2017 15:47:28 GMT
It's your story, just build the craft out of unobtanimum. It's super strong, ultra light weight and available wherever science fiction novels are sold.
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Post by Cybermortis on Feb 4, 2017 17:08:09 GMT
Computer controlled vectored fans would be capable of compensating for the sift in weight if the turret is removed. I'm leaving out exactly how the crew is meant to remove the turret, or the advisability of weighing down a vehicle who's primary asset is speed and mobility with such a thing as standard.
A mixture of 'lasers' and ballistic/explosive weapons actually makes sense. Lasers can't fire over things, and in say heavy rain, mist or smoke a laser beam will be scattered and absorbed reducing its range and power. Something that is far less of an issue for ballistic weapons, which can also be used for indirect fire without having to expose the vehicle.
Added to this is that armours developed to deal with energy weapons would not do so well against kinetic weapons.
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Post by rmc on Feb 4, 2017 18:40:54 GMT
Have to admit I understood immediately what was being described with the triple fan layout with the 20 degree tilt rotor idea. But, man! Just try and find a hovercraft image that depicts something like that. All I can find are traditional hovercrafts where they move forward with a pusher fan. Or, some sort of ground effect vehicle, again using a pusher fan. Or we get into the whole Moller flying car where the tilt rotors work more like a group of helicopters tied together. www.renegadehovercraft.com/images/gall_big_pic20.jpgthefutureofthings.com/upload/items_icons/UH-19XRW-Hoverwing_large.jpgwww.technovelgy.com/graphics/content08/moller-skycar.jpgSo I am starting to feel as though maybe a hovercraft near ground level attempting to use a tilt rotor arrangement to move forward may not really be workable. While near ground level the air cushion created apparently requires you to use a pusher propel system of some sort in order to get going forward. Once leaving the ground-effect zone, you are then allowed to employ something like the Moller tilt rotors to move forward. Trying to tilt rotor while still in the ground effect zone will likely only create a bunch of bounce back forces in waves making the whole craft pitch and tilt in a series of unwanted waves. Very unstable. I am further wondering if even a computer control system could work out all those ground effect forces and stabilize it for you. Just a thought. Hoping someone finds some sort of picture proving the tilt rotor arrangement at ground effect works. I am totally willing to bite the bullet on this concern of mine, if I am wrong! Thanks again! EDIT: Unless of course you are not really making a traditional 'hovercraft' and have intended from the get go to make another type of flying 'car'. Then you are leaving the ground effect zone to move forward and my concerns are just silly as usual.  |
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Post by GTCGreg on Feb 4, 2017 19:41:53 GMT
So I am starting to feel as though maybe a hovercraft near ground level attempting to use a tilt rotor arrangement to move forward may not really be workable. But isn't that how the Harrier fighter jet works as it transitions form VTOL to horizontal movement? While it doesn't have tilt rotors, the same thrusters rotate from vertical lift to horizontal thrust. I see no reason why you couldn't use the same type system on a hovercraft. Forget rotors. Just use three small, or even large for that matter, jet engines with moveable thrust deflectors like on the Harrier. You could even design them to provide sideways movement. I would think the design would be rather simple. Mount the three jet engines vertically with a gimbal mounted nozzle on the bottom. You could then point the nozzle in any direction. |
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Post by Cybermortis on Feb 4, 2017 20:06:41 GMT
Large modern hovercraft usually use two engines, one for lift and one for propulsion. However smaller designs use a single engine for both.
Given the context, A futuristic military vehicle, you'd probably be looking at a single engine that directs airflow though computer controlled ducts for both lift and direction. This would potentially give you an astonishing agility, including the ability to go sideways, all at full speed.
That said my personal opinion is that the dropable turret would not be workable even with fictional technology. Even a futuristic hovercraft would be restricted by the amount of weight it could carry, and no designer or military force is going to add a second weapon array that can't be used unless you remove the first.
A more realistic design would be to have a universal turret ring onto which weapon arrays or other equipment could be placed quickly and easily. This would result in a very versatile vehicle, and remove stability issues as the distribution of weight for each 'turret' could be set into the control system allowing the computer to adjust the ducts to compensate.
Observation; Heat seeking missiles are not normally used in the ground to ground role. That is not to say that a futuristic missile might not be capable of tracking heat, indeed it seems likely that multirole missiles are likely to be developed in the future; That is capable of being fired at both land and air targets without any modification. Such multirole missiles are unlikely to use only a single tracking system.
Such a missile system would allow a missile armed vehicle to provide air, antitank and antistructure support all at once.
Chemical lasers might be practical for a vehicle. Although there would be a limited number of shots, it might be possible to recycle the chemical cells in the field using nothing more than a power supply. This would drastically simplify logistics.
Machine guns are not a great choice for air support, especially not if you have access to high powered lasers. Lasers would be a much better choice as you don't have to lead a target, and if computer controlled and coupled with a sensor array might even be capable of either shooting down or damaging the tracking systems of missiles aimed at the vehicle.
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Post by wvengineer on Feb 4, 2017 21:13:28 GMT
if you are using high powered projectile weapons, then you will run into issues with recoil. Whenever you shoot, Mr. Newton will take over with the whole action-reaction thingy and without firm ground contact to push against, all the reaction energy will go into the craft. All of today's military hovercrafts only have small arms on them. Note that a 50 cal machine gun is still considered small arms. If you are going to have more powerful weapons, recoil will quickly push your craft out of position and into trouble.
I agree on the drop able turret thing as being impractical. With a craft like this, weight is a major factor. A retractable turret will involve a lot more equipment for the additional movement system. That weight will have to come at a cost elsewhere. Extra ammo capacity, fuel capacity, performance, etc. Something will have to suffer because of it. Additionally, you have a lot of unusable volume. the cavity that the turret is retracted into means that you looks space for fuel, cargo, ammo, etc.
A more practical idea may be that the center turret is a modular design where the weapon payload can be easily swapped out back at base for different packages (projectile cannon, laser, sensor suite, etc) based on the mission profile.
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Post by wvengineer on Feb 4, 2017 21:29:03 GMT
You may want to look at the M-44 Hammerhead aka "Firewalker" from Mass Effect 2. It is a good, reasonable design. masseffect.wikia.com/wiki/M-44_Hammerheadunusualsuspex.deviantart.com/art/M-44-Hammerhead-ortho-435301950It uses rockets for ammo, so there is no recoil issue, although they never mention ammo supply. The tri-rotor (two smaller ones in front a large rear one) setup provides good stability, keeping the center of gravity within the triangle of the engines. It also has poor armor which you would expect from a aircraft. |
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Post by rmc on Feb 4, 2017 22:45:24 GMT
So I am starting to feel as though maybe a hovercraft near ground level attempting to use a tilt rotor arrangement to move forward may not really be workable. But isn't that how the Harrier fighter jet works as it transitions form VTOL to horizontal movement? While it doesn't have tilt rotors, the same thrusters rotate from vertical lift to horizontal thrust. I see no reason why you couldn't use the same type system on a hovercraft. Forget rotors. Just use three small, or even large for that matter, jet engines with moveable thrust deflectors like on the Harrier. You could even design them to provide sideways movement. I would think the design would be rather simple. Mount the three jet engines vertically with a gimbal mounted nozzle on the bottom. You could then point the nozzle in any direction. I did mention aircraft similar to the Harrier. That was what I was talking about with regard to the Moller design. But, what that class of aircraft are missing that allow them to operate using a tilt rotor configuration instead to get going forward is the skirt or in this case "diamond-shaped" platform that reflects and contains some of the air pressure to produce the air cushion. When you have that sort of enclosed skirt or platform the tilt-rotors are apparently not used. Instead the air-cushion is created and then some sort of forward-driving upright fan or jet is employed. Or, if you want to have tilting jets or tilt-rotors, just like the Moller design or the Harrier type, you have no enclosing "diamond-shaped" platform. |
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Post by ironhold on Feb 4, 2017 23:00:31 GMT
For the fans, I was thinking "central hover skirt in the middle for lift, three directional fans in a triangle pattern around the chassis". The triangle fans would be what turns it left and right or makes it go forward. What gave me the idea is this unit here: www.yojoe.com/vehicles/87/vindicator/ . It's a lot smaller than the unit I'm envisioning, but because it's small the design does spec all three fans as being both lift *and* propulsion. The rear wouldn't quite work as such since the rear-firing lasers can potentially restrict the angle of movement of the tail fan, but otherwise it's what it is. The package text does indeed list it as a "hovercraft" rather than a flying car, so that's what I'm looking at.  The "two vehicles in one" bit, by the by, is due to the fact that it comes with a smaller, collapsible ground vehicle that mounts beneath the main chassis (hence no central lift fan). The vehicle can be deployed and used to scout ahead, or it can park itself inside of the "Future Fortress" you can make from bits of the other vehicles in that assortment and serve as a fixed sensor emplacement:  Admittedly, this is also where I got the idea from for the removable turret assembly / fixed emplacement, as another vehicle in the assortment - a combat truck, www.yojoe.com/vehicles/87/eliminator/ , - *does* have a removable turret assembly; once it deploys, a missile rack elevates up in its place. |
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Post by Cybermortis on Feb 5, 2017 0:20:58 GMT
Having multiple engines for a hovering vehicle is a really bad idea, especially if it is a combat vehicle relying on them for stability. If one of the engines gets damaged when you are in motion the vehicle is going to cartwheel across the landscape.
If you look at successful VTOL craft, helicopters and the Harrier specifically, you'll note that they only use one engine. The Russian version of the Harrier uses two engines, one for vertical lift and the second for forward flight, and has one of the worst safety records of any aircraft in service. The French VTOL Mirage project used several engines to provide lift, and proved that if just one of the engines produced slightly less thrust than the others the result was scattering said aircraft across the runway. Now computer controls *might* be able to compensate minor errors, but would not be able to do anything should one engine fail - which in combat you HAVE to assume is going to happen. Especially since more lift engines adds to the size of the vehicle and increases the chances of a hit damaging the motive system.
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Post by GTCGreg on Feb 5, 2017 1:06:49 GMT
Having multiple engines for a hovering vehicle is a really bad idea, especially if it is a combat vehicle relying on them for stability. If one of the engines gets damaged when you are in motion the vehicle is going to cartwheel across the landscape. If you look at successful VTOL craft, helicopters and the Harrier specifically, you'll note that they only use one engine. The Russian version of the Harrier uses two engines, one for vertical lift and the second for forward flight, and has one of the worst safety records of any aircraft in service. The French VTOL Mirage project used several engines to provide lift, and proved that if just one of the engines produced slightly less thrust than the others the result was scattering said aircraft across the runway. Now computer controls *might* be able to compensate minor errors, but would not be able to do anything should one engine fail - which in combat you HAVE to assume is going to happen. Especially since more lift engines adds to the size of the vehicle and increases the chances of a hit damaging the motive system. Probably true on a three rotor craft, but look at the 4 and six rotor drones. They can keep flying if one motor goes out. On a 3 rotor hovercraft, it may be less complicated to have one large engine driving a generator and then use three electric motors to run the rotors. |
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Post by the light works on Feb 5, 2017 1:57:20 GMT
the powergun was david drake's solution to the laser energy problem - although he also invented the compact fusion "bottle" reactor to provide enough power to lift his beasts. I think he had a slight ability to deflect his main fans, and most of their propulsion was created by tilting the entire beast and spilling air out of the skirts. - he worked on the "strategic application of brute force" principle.
one factor to remember is the "because I said I can" principle. I still kind of think you are building an elephant. (elephant: a mouse built to government specifications) but that may the culture in the society you are creating. in one of my stories, an ambulance is built around a harrier engine, and carries a minigun under its chin.
addendum: one thing to think about is whether this thing is going to be limited to air cushion, or can lift to ground effect mode.
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Post by wvengineer on Feb 5, 2017 21:51:45 GMT
Having multiple engines for a hovering vehicle is a really bad idea, especially if it is a combat vehicle relying on them for stability. If one of the engines gets damaged when you are in motion the vehicle is going to cartwheel across the landscape. If you look at successful VTOL craft, helicopters and the Harrier specifically, you'll note that they only use one engine. The Russian version of the Harrier uses two engines, one for vertical lift and the second for forward flight, and has one of the worst safety records of any aircraft in service. The French VTOL Mirage project used several engines to provide lift, and proved that if just one of the engines produced slightly less thrust than the others the result was scattering said aircraft across the runway. Now computer controls *might* be able to compensate minor errors, but would not be able to do anything should one engine fail - which in combat you HAVE to assume is going to happen. Especially since more lift engines adds to the size of the vehicle and increases the chances of a hit damaging the motive system. I can't see a vehicle like this being effective as a direct combat vehicle. Weight is the enemy for a hovercraft like this. That means this will have to be very light on the armor. More armor mean it needs larger engines, making it an easier target to hit. It also reduces speed and maneuverability. Without heavy armor, it is dead meat in a full on combat situation. I see something like this being more of a fast attack craft. Something for hit and run missions. Almost a hovercraft version of a WWII PT boat. Get in quickly, fire your payload, and get out as fast as possible before the enemy can bring their main defenses to bare. Recon and intel is another option for a platform like this. ***** Once concern I would have is noise. Making a craft hover like this take a LOT of airflow. Between the air flow and then engines to drive that air flow, that is going to make a lot of noise and give the enemy plenty of warning that it is coming. That will limit what it can do for stealth and recon. You can't idle the engine(s) to cut down on noise without severely limiting the reasons it exists. |
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