Ducted Fan Vehicles
- Thread starter Antony
- Start date
Ducted fans needs to be combined with contra-grav. Remember that contra-grav negates about 1 percent of the gravitional vector of a planet. So a 700kg vehicle needs 7 kilos of thrust to lift. However, the 700kg will still affect the thrust to mass ratio when it comes to speed and accelleration.
far-trader
SOC-14 10K
I know what you mean
I tried out all of it back in the day, much of it I found didn't seem to quite work, like bits were missing (or I was missing seeing the bits). Reactive armor I recall being a real head scratcher.
So I'm sure I tried a ducted fan vehicle or two. Though I'm not sure exactly what you mean by the term. Do you mean a non-grav lift (aka air-cushion) vehicle? Or a S/VTOL aircraft? Or do you mean using Turbo (ducted fan) engines for thrust?
I can't recall problems with any of them. I wonder if I found a work around? Maybe increased lift due to the wing-in-ground type effect? Borrowed from the rules for WIG air-craft in the book? Or just the right mix of lighweight materials and such? I'd look at my old stuff but I'm not sure where it is, or even if it still is. Pack rat that I am it probably is around here somewhere but it'd take a long hunt as disorganized as my filing system is.
epicenter00
SOC-13
I remember reading a few times that some of the vehicles/equipment in TNE supplements that GDW put out used a "simplified" version of FF&S they used in-house so the results wouldn't exactly be the same as the those you'd get using FF&S.
That's about the time I tossed the FFS book (I'd already started calling it "For #*$@!'s Sake" before then).
It's pretty damning when the guys who wrote the rules don't use their own rules.
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On Topic:
I recall having a similar problem, Anthony, before I gave up on FFS. I was trying to design some 2300-style hovertanks for a lower-tech world that didn't have contra-grav.
Not that I doubt your word but I've never heard that before and would be rather surprised if it were true. GDW worked really hard on FF&S and was rather proud of what it achieved, even if it was immensely difficult to use.
I hit the wall when I started trying to figure out how to account for the total mass of a ship to calculate Gs of acceleration as it burns fuel and loses mass . . .
far-trader
SOC-14 10K
Rather than go looking for my stuff I figured I'd check the BARD pages, specifically the VERA archive:
http://www.downport.com/bard/bard/bardvera.html
Scroll down a bit and you'll find 3 hovercraft vehicles (4500 - Other Vehicles) that might suit you and offer insights into the designing of same.
You could also check out the yahoo TNE group:
http://games.groups.yahoo.com/group/Traveller_TNE/
Bound to be a few designs and help around there.
http://www.downport.com/bard/bard/bardvera.html
Scroll down a bit and you'll find 3 hovercraft vehicles (4500 - Other Vehicles) that might suit you and offer insights into the designing of same.
You could also check out the yahoo TNE group:
http://games.groups.yahoo.com/group/Traveller_TNE/
Bound to be a few designs and help around there.
No these are not hovercraft. The ducted fan vehicles in FF&S1 is a lift agency (in theory) in section 10 on page 75. Unlike CG lfters this is supposed to produce lift and thrust. It does not use CG lifters for which it is supposed to be an alternate tech (and which is found in the real world)
It is essentially like a hovercraft but does not use skirts. It is available from TL8. Unlike hovercrat though its calculations are based on the mass of the vehicle which appears to be part of the problem.
I have been through Vera and could find no examples of ducted fan lift vehicles only hovercraft. Hovercraft I can do.
Incidently my website
www.skaran.net
is covered with equipment designed using FF&S1 (It is Gurps Vehicles which terrifies me)
It is essentially like a hovercraft but does not use skirts. It is available from TL8. Unlike hovercrat though its calculations are based on the mass of the vehicle which appears to be part of the problem.
I have been through Vera and could find no examples of ducted fan lift vehicles only hovercraft. Hovercraft I can do.
Incidently my website
www.skaran.net
is covered with equipment designed using FF&S1 (It is Gurps Vehicles which terrifies me)
far-trader
SOC-14 10K
Ah, those Ducted Fans (I had a vague recollection of them, from the errata page).
I think I went with afterburners on MHD turbines for the early versions.
See post on next page for updated specs.
(I had a vague recollection of them, from the errata page).I think I went with afterburners on MHD turbines for the early versions.
See post on next page for updated specs.
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ThunderChilde
SOC-13
Meh, the house design tool is a rumour I heard way long time ago, no idea if there was any merit to it. FF&S any mark terrifies me as a dyslexic, way to much maths for sensible usage. For heavens sake, I have to run most equations three times and if two agree, thats what I roll with. I might have to go four or five times sometimes, or walk away before violence happens.
FF&S led to death of several calculators, the book itself got ripped up and nearly burned in a rage event.
Gurps vehicle, ah yes, no worse really, lesson learned, I only tinkered with it.
P.S. ONe the main reasons I ran screaming over the hill from TNE, and left Traveller till recently.
FF&S led to death of several calculators, the book itself got ripped up and nearly burned in a rage event.
Gurps vehicle, ah yes, no worse really, lesson learned, I only tinkered with it.
P.S. ONe the main reasons I ran screaming over the hill from TNE, and left Traveller till recently.
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far-trader
SOC-14 10K
Actually it's even better than I posted earlier (if I've got it right). I'd forgotten Ducted Fans had their own rule/capability for afterburn built in (page 76). So...
TL8 MHD Turbine powered Afterburn Ducted Fan unit for NOE use:
+0.6MW MHD Turbine is 1m3 and 1tonne costing MCr0.01
fuel consumption/hour is 0.4m3 at 0.4tonnes in Afterburn mode
0.6tonnes thrust Ducted Fan is 0.3m3 and 0.3tonnes costing MCr0.3
0.9tonnes thrust in Afterburn mode
1.8tonnes thrust in NOE Afterburn mode
Total per unit specs in NOE Afterburn mode are:
1.8tonnes thrust, 1.7tonnes mass, 1.7m3 and MCr0.31 including 1 hour of fuel.
Net thrust (not including craft, payload, and extra duration) is 0.1tonnes per unit.
So it should fly, with enough units (a big enough craft).
For flying out of NOE I'd work out some stub wings for a little lift at speed. Not sure if S/VTOL isn't a better deal at TL8 but at least it looks like it can be done. Interested in seeing your design when you get it worked up Antony
TL8 MHD Turbine powered Afterburn Ducted Fan unit for NOE use:
+0.6MW MHD Turbine is 1m3 and 1tonne costing MCr0.01
fuel consumption/hour is 0.4m3 at 0.4tonnes in Afterburn mode
0.6tonnes thrust Ducted Fan is 0.3m3 and 0.3tonnes costing MCr0.3
0.9tonnes thrust in Afterburn mode
1.8tonnes thrust in NOE Afterburn mode
Total per unit specs in NOE Afterburn mode are:
1.8tonnes thrust, 1.7tonnes mass, 1.7m3 and MCr0.31 including 1 hour of fuel.
Net thrust (not including craft, payload, and extra duration) is 0.1tonnes per unit.
So it should fly, with enough units (a big enough craft).
For flying out of NOE I'd work out some stub wings for a little lift at speed. Not sure if S/VTOL isn't a better deal at TL8 but at least it looks like it can be done. Interested in seeing your design when you get it worked up Antony
far-trader
SOC-14 10K
I've since given it a short look and while it sounds technically possible it looks practically pointless, at TL8. The margin (0.1tonnes thrust over unit mass) looks just too tight to build most practical vehicles. But I didn't play with it long.
Well I managed to get one together at TL9 (a TL8 version would likely be similar enough to work also) using the rules as written the TL9 craft can run for 1 hour and more fuel and it cannot lift its own mass. It has a top speed of around 33kph so no not terribly practical especially as it is on afterburners all the time.
The problems I see are based on the thrust rating of the ducted fan, at TL8/9 it produces the same thrust as a TL8 propeller. The other problem is the poor power output of FF&S1 power plants. You might get a better result using the existing powerplants by using the propeller design rules for the power plant which effectively halves the volume and mass of the power plant (effectively doubling the MW output and hence available thrust for a given size) This would make sense to me given that the fans are mounted through the vehicle hull not really in the interior as such.
Antoher possibility, especially if used in combination with the propeller power plant rules is to use the chemical engine stats from FF&S2 which seem to be more efficient and also have access to the size efficiency improvements missing in FF&S1
What do you think?
The problems I see are based on the thrust rating of the ducted fan, at TL8/9 it produces the same thrust as a TL8 propeller. The other problem is the poor power output of FF&S1 power plants. You might get a better result using the existing powerplants by using the propeller design rules for the power plant which effectively halves the volume and mass of the power plant (effectively doubling the MW output and hence available thrust for a given size) This would make sense to me given that the fans are mounted through the vehicle hull not really in the interior as such.
Antoher possibility, especially if used in combination with the propeller power plant rules is to use the chemical engine stats from FF&S2 which seem to be more efficient and also have access to the size efficiency improvements missing in FF&S1
What do you think?
ducted fans are propellers with shrouds that allow it to avoid mach speed issues at the tips and allow an increase in efficiency due to better lift distribution along individual blades.
I might use this:
http://www.sfrpg.org.uk/phpBB3/viewtopic.php?f=31&t=869
but allow for a step up in efficiency and allow flow speed at 3/4r to equal mach 1 instead of limiting it by mach 1 at the tip. Therefore allow max flow through the actuation disk of a ducted fan to be mach 1.6667 ( assuming there is enough thrust to break the sound barrier, which I doubt )
Prop efficiency takes a nose dive when the tip breaks the sound barrier and all that energy goes into noise. The TU-95 is hugely noisy. Ducted fans are a solution ( the shrouds do add mass and drag though ).
FFS1's handling of a lot of things like this is crap.
I might use this:
http://www.sfrpg.org.uk/phpBB3/viewtopic.php?f=31&t=869
but allow for a step up in efficiency and allow flow speed at 3/4r to equal mach 1 instead of limiting it by mach 1 at the tip. Therefore allow max flow through the actuation disk of a ducted fan to be mach 1.6667 ( assuming there is enough thrust to break the sound barrier, which I doubt )
Prop efficiency takes a nose dive when the tip breaks the sound barrier and all that energy goes into noise. The TU-95 is hugely noisy. Ducted fans are a solution ( the shrouds do add mass and drag though ).
FFS1's handling of a lot of things like this is crap.
Skysled class ducted fan skimmer
The Skysled is an open-topped vehicle designed to fly NOE. Like other vehicles of this type it is a heavy consumer of fuel.
Tech Level: 8
Chassis Type: Simple
Size: 42 cubic meters (3 displacement tons)
Mass: 22.4402 tons empty/29.24362 tons loaded
Price: 4,247,608 Cr (Prototype), 3,822,847 Cr. (Production)
Power: 15.8Mw MHD turbine supplying 15.6Mw to ducted fans generating 29.24362 tons of lift and 0.97819 tons of thrust in normal NOEflight. A total of 15.6 tons of lift produced (insufficient for non NOE flight) otherwise. Using built in afterburners ducted fans generate 29.24362 tons of lift and 8.77819 tons of thrust in normal NOE flight. A total of 23.4 tons of lift produced (generally insufficient for non NOE flight) otherwise. 0.018Mw excess power produced by MHD turbine.
Maintenance: 7
Controls: Enhanced electronic, TL8 flight avionics, TL8 terrain following avionics, 2xmodel/8 flight computers (one powered)
Communications: TL8 300km Radio
Sensors: 2xHeadlights, 3xRunning Lights
ECM: None
Life Support: Heat, light
Cargo: 83.42 kg (0.33367 cubic meters)
Crew: 1 (Driver)
Passengers: 3 (in adequate seats)
Speed: 97 kph maximum (400 kph on after burners), 73 kph cruise (300 kph on after burners), 120 kph safe NOE speed
Travel Mode: 291(1200 Afterburner)/291(720 Afterburner)
Combat Move: 13(17 Afterburner) NOE only
Maximum Acceleration: 0.0326G (0.2926 Afterburner)
Fuel Capacity: 6,320 liters hydrocarbon distillate for MHD turbine with ducted fans
Fuel Consumption/Endurance: 3,160 liters/hour (endurance of 2 hours), 6,320 liters/hour (endurance of 1 hour using afterburner)
Notes: The fuel tanks are equipped to carry oxygen in the event an atmosphere can not supply this to the power plant. This effectively halves the total fuel capacity. Personnel on board would need to provide their own life support systems in this case.
In theory with a very light load (ie driver, no cargo and fuel down to no more than 859.8 liters, and under afterburner the craft could leave NOE flight for around 8 minutes of flight with an average maximum speed of 43 kph.
Only construction rule modification made to enable ducted fan designs to be viable was to treat the power plant the same as one mounted on an aircraft, effectively halving the mass and volume of the plant.
Combat Statistics:
Configuration: Open Topped HF: [1]
Suspension: Ducted Fan HS: [1]
HR: [1]
Deck: Open
Belly: 1
The Skysled is an open-topped vehicle designed to fly NOE. Like other vehicles of this type it is a heavy consumer of fuel.
Tech Level: 8
Chassis Type: Simple
Size: 42 cubic meters (3 displacement tons)
Mass: 22.4402 tons empty/29.24362 tons loaded
Price: 4,247,608 Cr (Prototype), 3,822,847 Cr. (Production)
Power: 15.8Mw MHD turbine supplying 15.6Mw to ducted fans generating 29.24362 tons of lift and 0.97819 tons of thrust in normal NOEflight. A total of 15.6 tons of lift produced (insufficient for non NOE flight) otherwise. Using built in afterburners ducted fans generate 29.24362 tons of lift and 8.77819 tons of thrust in normal NOE flight. A total of 23.4 tons of lift produced (generally insufficient for non NOE flight) otherwise. 0.018Mw excess power produced by MHD turbine.
Maintenance: 7
Controls: Enhanced electronic, TL8 flight avionics, TL8 terrain following avionics, 2xmodel/8 flight computers (one powered)
Communications: TL8 300km Radio
Sensors: 2xHeadlights, 3xRunning Lights
ECM: None
Life Support: Heat, light
Cargo: 83.42 kg (0.33367 cubic meters)
Crew: 1 (Driver)
Passengers: 3 (in adequate seats)
Speed: 97 kph maximum (400 kph on after burners), 73 kph cruise (300 kph on after burners), 120 kph safe NOE speed
Travel Mode: 291(1200 Afterburner)/291(720 Afterburner)
Combat Move: 13(17 Afterburner) NOE only
Maximum Acceleration: 0.0326G (0.2926 Afterburner)
Fuel Capacity: 6,320 liters hydrocarbon distillate for MHD turbine with ducted fans
Fuel Consumption/Endurance: 3,160 liters/hour (endurance of 2 hours), 6,320 liters/hour (endurance of 1 hour using afterburner)
Notes: The fuel tanks are equipped to carry oxygen in the event an atmosphere can not supply this to the power plant. This effectively halves the total fuel capacity. Personnel on board would need to provide their own life support systems in this case.
In theory with a very light load (ie driver, no cargo and fuel down to no more than 859.8 liters, and under afterburner the craft could leave NOE flight for around 8 minutes of flight with an average maximum speed of 43 kph.
Only construction rule modification made to enable ducted fan designs to be viable was to treat the power plant the same as one mounted on an aircraft, effectively halving the mass and volume of the plant.
Combat Statistics:
Configuration: Open Topped HF: [1]
Suspension: Ducted Fan HS: [1]
HR: [1]
Deck: Open
Belly: 1
