Intake fans atop a flying saucer

[Spacescifi]

 

The idea of a flying saucer is not new, but I wanted to know if having intake fans on the roof of the saucer is viable to suck up sufficient air for the cluster of rocket engines in the rear? Or do intake fans only work best when they are opposite the thrust hitting the forward air headon?

(Note the intake fans)

(Those port openings could easily be air intake fans).

Engine used is nuclear lightbulb rocketry, with liquid hydrogen as launch fuel, and a tank of liquid methane for vacuum flight. Also air breathing capable due to reactor and air intakes.

 

 

Edited September 25, 2019 by Spacescifi

[Guest]

Intakes should be pointed into the airflow. Otherwise, Conada effect will reduce their effectiveness greatly, even at subsonic speeds. Basically, if air flows sideways over the intake at high speeds, it can't be sucked in.

On the other hand, if you're using a lifting engine separate from forward propulsion, a top-mounted intake is all right. All real saucers used this configuration (not that they worked particularly well, but they did work).

Edited September 26, 2019 by Guest

[Superfluous J]

As a side note, do not use the Millennium Falcon or the cover of any science fiction novel as a reference for what is reasonable in real life.

[Spacescifi]

15 minutes ago, Dragon01 said:

Intakes should be pointed into the airflow. Otherwise, Conada effect will reduce their effectiveness greatly, even at subsonic speeds. Basically, if air flows sideways over the intake at high speeds, it can't be sucked in.

On the other hand, if you're using a lifting engine separate from forward propulsion, a top-mounted intake is all right. All real saucers used this configuration (not that they worked particularly well, but they did work).

 

Thanks. I thought there had to be good reason why aircraft only use roof fans for VTOL.

Now I know.

Thanks to the knowledge of you and others, I now can create a scifi saucer SSTO that could reasonabbly fly.

Currently the idea is a thick 'pancake' saucer, with a row of rocket nozzles covering the back, and now I know that the 'corners' of the front of the saucer would be where the air intake fans would have to go, as the front nose would just be hull.

 

It would mostly be propellant and crew going up, with smaller SSTO's docking with it in orbit to offload needed gear and antimatter fuel for long haul spaceflight.

We do not need antimatter to reach orbit. A nuclear lightbulb with LH can do it. Liquid metallic methane is another option though... a scifi option for launch fuel.

10 minutes ago, 5thHorseman said:

As a side note, do not use the Millennium Falcon or the cover of any science fiction novel as a reference for what is reasonable in real life.

Indeed.

 

https://m.youtube.com/watch?v=jWsfzt0_PLE

 

 

Edited September 26, 2019 by Spacescifi

[sevenperforce]

4 hours ago, Spacescifi said:

The idea of a flying saucer is not new, but I wanted to know if having intake fans on the roof of the saucer is viable to suck up sufficient air for the cluster of rocket engines in the rear? Or do intake fans only work best when they are opposite the thrust hitting the forward air headon?

The amount of thrust that can be provided by a fan scales as a function of the area of the fan.

Intake fans work best when they are facing the airstream. Their efficiency, however, drops rapidly with Mach number. Once you are above Mach 1.5 you are better off relying on ram effect.

4 hours ago, Spacescifi said:

Engine used is nuclear lightbulb rocketry, with liquid hydrogen as launch fuel, and a tank of liquid methane for vacuum flight. Also air breathing capable due to reactor and air intakes.

You've got it flipped. You want to use methane as your launch fuel because it is denser and will provide better T/W; you want to use liquid hydrogen to finish your ascent and provide all your burns in vacuum.

An ideal nuclear SSTO would lift off pushing water or hydrazine through the engine, transition to RP-1 once well in motion, transition to methane during the final boost out of the atmosphere, and finish the flight on hydrogen. That way you have constant volumetric flow but a mass flow that decreases as your need for thrust decreases, and a specific impulse that increases as it becomes more important. Of course the tankage for this is stupidly difficult so that wouldn't work well for those reasons.

Another good option is to have a constant-flow liquid-hydrogen NTR with a LOX afterburner and drop tanks for the LOX. At liftoff, you inject LOX into the engine bell downstream of the throat to boost your thrust tremendously and to prevent overexpansion and flow separation. This gives you a higher T/W ratio than what is standard for NTRs. You decrease the LOX flow as you ascend to match the desired expansion ratio, and then you eventually drop your LOX tanks (they will have a high ballistic coefficient and can be chuted down into the ocean for reuse) and proceed to orbit on hydrogen alone.

[sevenperforce]

3 hours ago, Spacescifi said:

I thought there had to be good reason why aircraft only use roof fans for VTOL.

Now I know.

Thanks to the knowledge of you and others, I now can create a scifi saucer SSTO that could reasonabbly fly.

Currently the idea is a thick 'pancake' saucer, with a row of rocket nozzles covering the back, and now I know that the 'corners' of the front of the saucer would be where the air intake fans would have to go, as the front nose would just be hull.

A rather large challenge for SSTOs is always going to be re-entry and landing. How do you get back down? How do you land? Using a very large VTOL intake fan is a large weight penalty, but if it obviates the need for wings, wheels, or landing burn propellant, then maybe it's a good trade-off. If that same intake fan can be used to force air through rocket ducts to add thrust at liftoff and reduce the need for bigger/heavier engines, all the better.

But remember that an intake fan, even one pointing into the airstream, is only going to be useful from Mach 0 to Mach 2 or so (it's useful beyond, but only marginally). And you need to make Mach 25 to hit orbit. Simply using a ducted rocket engine is going to give you many of the same advantages and a much greater useful envelope.

Why make it a saucer? Is there some particular purpose, like volume concerns?

[kerbiloid]

Yes, the top fans are required.

Spoiler

 

P.S.
And it's a shame that such Kerbal thing is still not in stock. Or at least in mods.

Edited September 26, 2019 by kerbiloid

[Spacescifi]

2 hours ago, sevenperforce said:

The amount of thrust that can be provided by a fan scales as a function of the area of the fan.

Intake fans work best when they are facing the airstream. Their efficiency, however, drops rapidly with Mach number. Once you are above Mach 1.5 you are better off relying on ram effect.

You've got it flipped. You want to use methane as your launch fuel because it is denser and will provide better T/W; you want to use liquid hydrogen to finish your ascent and provide all your burns in vacuum.

An ideal nuclear SSTO would lift off pushing water or hydrazine through the engine, transition to RP-1 once well in motion, transition to methane during the final boost out of the atmosphere, and finish the flight on hydrogen. That way you have constant volumetric flow but a mass flow that decreases as your need for thrust decreases, and a specific impulse that increases as it becomes more important. Of course the tankage for this is stupidly difficult so that wouldn't work well for those reasons.

Another good option is to have a constant-flow liquid-hydrogen NTR with a LOX afterburner and drop tanks for the LOX. At liftoff, you inject LOX into the engine bell downstream of the throat to boost your thrust tremendously and to prevent overexpansion and flow separation. This gives you a higher T/W ratio than what is standard for NTRs. You decrease the LOX flow as you ascend to match the desired expansion ratio, and then you eventually drop your LOX tanks (they will have a high ballistic coefficient and can be chuted down into the ocean for reuse) and proceed to orbit on hydrogen alone.

 

Rocketry is really complex when you weigh the balance of thrust vs how long your propellant will actually last.

LH would be fine to use as you say, but I would only keep just enough to use it all up, since if this is an interplantary trip (the moon), it will be vaping away in the tank the whole time anyway.

Metallic liquid methane would be a great scifi thrust propellant though, inasmuch it would be more dense compared to the less dense liquid methane.

1 hour ago, sevenperforce said:

A rather large challenge for SSTOs is always going to be re-entry and landing. How do you get back down? How do you land? Using a very large VTOL intake fan is a large weight penalty, but if it obviates the need for wings, wheels, or landing burn propellant, then maybe it's a good trade-off. If that same intake fan can be used to force air through rocket ducts to add thrust at liftoff and reduce the need for bigger/heavier engines, all the better.

But remember that an intake fan, even one pointing into the airstream, is only going to be useful from Mach 0 to Mach 2 or so (it's useful beyond, but only marginally). And you need to make Mach 25 to hit orbit. Simply using a ducted rocket engine is going to give you many of the same advantages and a much greater useful envelope.

Why make it a saucer? Is there some particular purpose, like volume concerns?

 

I am all for simpler designs, popular scifi art tends to mislead, so blame my choice of intake fans on that and minimal knowledge of them. Use nuclear lightbulb to augment the ducted airflow for thrust.

I would be fine with intake ducts, is'nt that what a ramjet is anyway? Or maybe a scram jet? No... it's simpy what it sounds like... an open duct way leading to the nuclear lightbulb chamber no?

At any rate I know project pluto had an intake duct, but also fan blades if I recall correctly. But it was not designed for space orbit anyway. 

Why saucers? Star Trek fever I guess, and I love the look.

In spite of their drag, or perhaps because of it they do offer some benefits:

Reentry can be slowed faster by entering belly first. More drag. In order to avoid those expensive heat tiles I could pull an Elon Musk idea and design the hull to 'sweat' to cool. Basically it pumps water or some cool liquid within the outer hull and sprays it outside to cool the hull of the vessel as it reenters the atmosphere.

And it looks cool for scifi stories. But do not get me wrong. If I do a saucer, it had better be functional.

 

[kerbiloid]

33 minutes ago, Spacescifi said:

Reentry can be slowed faster by entering belly first.

With 20 g overloads inside.

Any reentry craft should glide, and disc is not the best option.

33 minutes ago, Spacescifi said:

In order to avoid those expensive heat tiles I could pull an Elon Musk idea and design the hull to 'sweat' to cool.

This idea is called "ablation" and is older than Elon Musk's grandfather.

A secret tip: usually you don't need to deliver the water, but just keep the ablator covering the hull from outside.

Edited September 26, 2019 by kerbiloid

[wumpus]

14 hours ago, 5thHorseman said:

As a side note, do not use the Millennium Falcon or the cover of any science fiction novel as a reference for what is reasonable in real life.

But is using the Moller Sky car any better?

[kerbiloid]

48 minutes ago, wumpus said:

But is using the Moller Sky car any better?

Without the Moller's car you can't win Tatooine races and become a space pilot.

[Nuke]

vertical intake fans are fine for ground operations. but you are better off closing them when your main engines starts giving you enough speed to get lift.

[sevenperforce]

39 minutes ago, Nuke said:

vertical intake fans are fine for ground operations. but you are better off closing them when your main engines starts giving you enough speed to get lift.

Better to have horizontal intake fans that can be ducted downward for ground operations, lift off that way, and then reorient the duct for forward acceleration once airborne. 

[wumpus]

17 hours ago, kerbiloid said:

This idea is called "ablation" and is older than Elon Musk's grandfather.

A secret tip: usually you don't need to deliver the water, but just keep the ablator covering the hull from outside.

I know the Apollo spacecraft used ablation and I think Mercury (and  Vostok) did as well.  Oddly enough, white oak makes a pretty good ablator on its own.

I'm curious of the earliest use of such ablation (older than Elon Musk's grandad?).  Perhaps the lubrication of steam engines?  Lubrication of cannon or rifles, especially high volume things like gattling guns and Maxim guns?

[magnemoe]

12 hours ago, wumpus said:

But is using the Moller Sky car any better?

Moller Sky car or something like it is possible to build and get to hover. It just don't works well, you get issues like getting it to be stable and able to fly forward at reasonable speed. For practical use having an short range and not being loader than an bear bomber is also useful 
 

[kerbiloid]

5 hours ago, wumpus said:

I'm curious of the earliest use of such ablation (older than Elon Musk's grandad?).  Perhaps the lubrication of steam engines?  Lubrication of cannon or rifles, especially high volume things like gattling guns and Maxim guns?

Humans sweat when it's hot, and the evaporation cools them, taking heat away. So, the idea itself is pretty old.
And the shower protection is used in metallurgy for 1-2 centuries.

But I mean that the ablation is used in all reentry vehicles since 1950s, and it's definitely is older than Musk.
Spreading coolant from inside the hull through holes has its advantages and disadvantages, and doesn't differ radically from the coolant covering the hull from outside.

When the ablator is outside, you don't need pumps and pipes, and you still can refuel the heat protection cover between the flight,
Say, VA of TKS was spending the resin filler as ablator, but the matrix made of silicon composite stayed unchanged even for a millimeter, and could be reloaded with the resin up to 10 times. (Unlike Apollo's single-use honeycomb)

So, the ablator spreading just makes it easier to reload the ablator for big crafts.
On another side, when the ablator is an outside cover, you can just replace its sections for maintenance and drop unreliable ones.
And it protects the inner volume from the thermal flow with its thermal capacity and resistance, while the internal coolant tank doesn't.
And it's an additional rad protection which you anyway need for a crewed craft.

Edited September 27, 2019 by kerbiloid

[Spacescifi]

23 hours ago, kerbiloid said:

With 20 g overloads inside.

Any reentry craft should glide, and disc is not the best option.

 

If a disc glided nose first that may provide optimum slow down while not giving too much g-force.

Really, it seems that there really is no one size fits all vehicle for space travel, unlike in scifi.

A saucer may be more optimal in a thinner atmosphere like mars to help slow reentry faster.

Really though, I think spaceship class types of the future could be named after what planet they are rated for reentry for.

A spacecraft rated for Earth reentry is Terra class, while one rated for Mars reentry is Martian class and so on.

 

Orbital ships would be optimized as well. Space travel really does not seem to favor jack of all trades crafts.

Edited September 27, 2019 by Spacescifi
Class

[DDE]

On 9/26/2019 at 1:57 AM, Spacescifi said:

(Those port openings could easily be air intake fans).

Those wholes on the Falcon are canonically escape pod silos.

[Nuke]

On 9/26/2019 at 11:47 AM, sevenperforce said:

Better to have horizontal intake fans that can be ducted downward for ground operations, lift off that way, and then reorient the duct for forward acceleration once airborne. 

its a matter of what is heavier/costs more/more robust. a ductd fan powered by a brushless motor for example is incredibly simple. so simple its better to have different ones for vertical and horizontal flight. you can optimize the fan blades for hover or cruise. using the same fan for both usually means having controllable blade pitch which adds weight and complexity to the system. not to mention the structural and mechanical components for mounting fan that can be rotated. granted this is specific to an electric hybrid system. if you are driving the fans mechanically through a shaft you add a whole lot of weight and complexity where it might pay off to reduce the number of fans in use. 

[sevenperforce]

5 hours ago, Nuke said:

its a matter of what is heavier/costs more/more robust. a ductd fan powered by a brushless motor for example is incredibly simple. so simple its better to have different ones for vertical and horizontal flight. you can optimize the fan blades for hover or cruise. using the same fan for both usually means having controllable blade pitch which adds weight and complexity to the system. 

No, just duct the flow downward like the F-35.

[Nuke]

4 hours ago, sevenperforce said:

No, just duct the flow downward like the F-35.

i thought the f35 had a separate vertical lift fan that was driven directly off the engine shaft in concert with an exhaust nozzle that can down vector. essentially 2 points of thrust down the center line. its a pretty clever configuration i think. 

Edited September 29, 2019 by Nuke

[sevenperforce]

8 minutes ago, Nuke said:

i thought the f35 had a separate vertical lift fan that was driven directly off the engine shaft in concert with an exhaust nozzle that can down vector. essentially 2 points of thrust down the center line. its a pretty clever configuration i think. 

Right, down vector. You can point the exhaust nozzle down and you could also use a moveable panel to duct a driver fan down.

Fan and rocket engine both either gimbaled or ducted down for liftoff, then realigned inline for horizontal flight.