How to stealth a hybrid airship?

[Scott Kenny]

This thought spun out of the discussion of the completely bullshit "TR-6 Telos". I do not want any discussion of the concept as described by ATS and the rest of the fruitloops. This is strictly as an example large hybrid airship that needs to be stealthy, as an effective super long duration penetrating ISR asset.

Spoiler: Above Top Secret's idea of what it looks like. Spoilered for size.

Okay, it's a ~45deg swept wing of ludicrous size. ~520ft wingspan and ~220ft length. Also, those wings look to put the aerodynamic center of lift well aft of the center of mass. Guesstimated gas volume of 1-1.5mil cubic feet of helium, which means a buoyancy/lifting force of about 70-105klbs.

But here's my real question:

The gas cells in a helium LTA need to be aluminized to reduce the escape rate. Which means you need significant RAM on the wings to prevent returns off the interior gas cells. This RAM also needs to be flexible, as the gas cells expand and contract with temperature and pressure differentials.

How do you make significant RAM/RAS that is still flexible enough to allow for gas cell expansion at altitude?

Also, would the wing chord be long enough to effectively stealth against low frequency radars used for long range search?

 

[quellish]

This thought spun out of the discussion of the completely bullshit "TR-6 Telos". I do not want any discussion of the concept as described by ATS and the rest of the fruitloops. This is strictly as an example large hybrid airship that needs to be stealthy, as an effective super long duration penetrating ISR asset.

Spoiler: Above Top Secret's idea of what it looks like. Spoilered for size.

Okay, it's a ~45deg swept wing of ludicrous size. ~520ft wingspan and ~220ft length. Also, those wings look to put the aerodynamic center of lift well aft of the center of mass. Guesstimated gas volume of 1-1.5mil cubic feet of helium, which means a buoyancy/lifting force of about 70-105klbs.

But here's my real question:

The gas cells in a helium LTA need to be aluminized to reduce the escape rate. Which means you need significant RAM on the wings to prevent returns off the interior gas cells. This RAM also needs to be flexible, as the gas cells expand and contract with temperature and pressure differentials.

How do you make significant RAM/RAS that is still flexible enough to allow for gas cell expansion at altitude?

Also, would the wing chord be long enough to effectively stealth against low frequency radars used for long range search?

You would need to solve the shaping problems first. The shape is going to change over time, how do you make every possible relevant iteration of that shape retain reduced observables?

If for some reason it turns concave you have a big problem.

 

[_Del_]

If you have a rubber envelope and introduce carbon black, you've created a crude RAM. Bad news is it needs to be quite thick depending on the wavelength. Back to good news, there is little behind the RAM than a gas-filled cavity, potentially shaped keel, and more envelope.

At a high enough altitude, you might get away with just keeping the bottom flat to make geometry favourable.

Difficult, maybe not impossible.

 

[quellish]

Back to good news, there is little behind the RAM than a gas-filled cavity, potentially shaped keel, and more envelope.

Why would that be good news?

 

[_Del_]

Why would that be good news?

Because at least a portion of that gets bent around by passing through different media unlikely to return to the emitter.

 

[quellish]

Because at least a portion of that gets bent around by passing through different media unlikely to return to the emitter.

So the RF energy has to transition free space, then "RAM", and then helium (and then the reverse). Each of those will be an abrupt transition that produces diffraction effects. This is what "passing through different media" does. It is not beneficial to lowering RCS.

The RAM will also be less effective without a ground plane. A reflective ground plane also has the advantage of letting the RF pass through the RAM multiple times, increasing effectiveness.

The revolution in low observables of the mid 1970s was based on shaping to reflect MORE energy, but reflecting it in a direction away from the receiver. This is still how low observables works today. You can always reflect more energy than you can possibly absorb.

Alan Brown provides an explanation:

View: https://youtu.be/vJ3iuU4Y4Bs?si=Pf3KIVtA0WdIrJoV


Covering things in RAM was how RCS reduction was done before that, and was not nearly as effective.

 

[Dilandu]

How do you make significant RAM/RAS that is still flexible enough to allow for gas cell expansion at altitude?

Simple; you made a zeppelin. An inflatable gas bags inside the rigid frame surrounded by non-infatable outer skin.

 

[quellish]

Simple; you made a zeppelin. An inflatable gas bags inside the rigid frame surrounded by non-infatable outer skin.

So stuff an F-117 full of balloons.

 

[paralay]

According to the manufacturer, the use of the "Cape" makes it possible to reduce the probability of detecting a tank by 2-3 times with infrared homing heads, and in all radar ranges the visibility of a combat vehicle is reduced to six or more times. In the radio-thermal range, a tank with a "Cape" on the operator's screen or in the homing head almost merges with the background. This is achieved by using aprons at the front and rear of the tank, as well as elongated side screens from the Cape kit. The aiming range of some models of ATGM anti-tank guided missiles with radar and thermal guidance is also being reduced.

 

[Dilandu]

So stuff an F-117 full of balloons.

Basically the idea is to made outer skin radar-reflective & stealthy-formed, so it would have low RCS. Theoretically, it's possible. On practice, it would likely be a great headache, since outer skin must be rigid enough to maintain constant straight or curved lines. Still... airships are big, and individual facetes could be therefore made of large size, suitable for any radar wave.

 

[Ronny]

If the air ship can stay stationary then they will just become invisible to pulse doppler radar

 

[Foo Fighter]

Which is the speed at where a return is classified as 'background'. Birds etc?

 

[djfawcett]

I sat in a stealth surveillance and attack airship briefing some years ago that was attended by a couple of generals and numerous lower ranks as well as corporate types. I never have been in a briefing where there was so much snickering and at times outright laughter by generals and whoever else that could not maintain their composure. It was such a ridiculous concept at the time that the poor presenters had to run and hide once complete. I have no doubt today that a stealth hybrid airship would meet the same reception.

With that being said, it is fun academic study if one can figure out how to get the adversaries to eye patches on both eyes - LOL.

 

[_Del_]

So the RF energy has to transition free space, then "RAM", and then helium (and then the reverse).

Whatever structure you plan on needs a flat bottom.

One would need to find the critical angle from whatever frequency/wavelength based on the refractive index of the specific envelope and the helium to really work the RCS reduction of internal bits and bobs. If we provide n values for the refractive index for helium and a notional envelope for a given wavelength, we can figure out the critical angle.

Critical angle will be = arcsin of n[sub]RAM[/sub]/n[sub]He[/sub]


The angle of refraction cannot exceed 90°. If it exceeds the critical angle, the energy will simply reflect off the surface. In the case of the a flat-bottomed airship, that means it's reflecting away from the emitter at an angle equal to the angle of incidence.

You could probably use Nickel Chromium mesh for structure and layer it into the envelope like they did for Project FIRST to provide rigidity. Then size the gaps in mesh such that you have a simple flat reflector on the bottom of the craft.

 

[Hydroman]

Is periodic mowing and edging part of the maintenance cycle? I think I did hear the Tank Commander say Mucho Grassy Ass...

 

[Scott Kenny]

Which is the speed at where a return is classified as 'background'. Birds etc?

Depends on radar system, but IIRC they usually gate out and do not show anything going under 100mph. (exception for airport approach radars)

 

[Foo Fighter]

I am guessing that is how the Cessna got to Red Square.

 

[Elysium]

 

[Justo Miranda]

Hi

 

[publiusr]

Just get an airship and put aerogel wisps on it to make it look like a cloud…or Jean Jacket

The Cumulo-zeppelin

 

[aim9xray]

Just paint "Goodyear" on the side and you're good to go. If you get caught, just ask where the football game is.

 

[Orionblamblam]

I've seen a fair number of vids showing soldiers running across snowy fields covered in thermal "capes" meant to hide them from IR camera-equipped drones. On IR, the capes are certainly less visible than the unequipped solider... but on IR, their *footprints* in the snow stand out. The vids all end with the cape-equipped soldiers getting blown to smithereens.

 

[martinbayer]

Precisely define "hybrid airship" in engineering terms.

 

[paralay]

I've seen a fair number of vids showing soldiers running across snowy fields covered in thermal "capes" meant to hide them from IR camera-equipped drones. On IR, the capes are certainly less visible than the unequipped solider... but on IR, their *footprints* in the snow stand out. The vids all end with the cape-equipped soldiers getting blown to smithereens.

This is also true for low-profile aircraft.
In this case, we are talking about the radar stealth of flexible shells

 

[Orionblamblam]

This is also true for low-profile aircraft.
In this case, we are talking about the radar stealth of flexible shells

Low-profile aircraft typically have some advantage in speed. This means not only do they have a chance to run away, they also have a chance to slip by detection because they're in view for such a brief time.

A soldier, a tank, a blimp, an airship... these are all *slow.* They linger on sensors. You get a chance to do more than go "hey, what was that blip," you get a chance to focus in on them and send the murderbots.

 

[riggerrob]

...... The gas cells in a helium LTA need to be aluminized to reduce the escape rate. Which means you need significant RAM on the wings to prevent returns off the interior gas cells. This RAM also needs to be flexible, as the gas cells expand and contract with temperature and pressure differentials.
....

Yes, preventing those tiny hydrogen atoms from escaping is a challenge.
But may I suggest that finding another sealant will allow radar waves to blow completely through the gas-filled hull? Then the challenge is to find more low-reflectivity materials to build the hull.
If you still need rigid beams, then look at the compressed air beams built by that Swiss company: Prospective Concepts). Surely if you wrap those beams in Kevlar or Dyneema or High Modulus Aramid, you can reduce reflections.
They you only have to worry about radar reflecting from the crew, engines and other metal bits.

 

[quellish]

Then the challenge is to find more low-reflectivity materials to build the hull.

If you want to get operationally relevant degrees of signature reduction you want the most reflective materials you can get.

Reflect the signal in a direction other than back to the radar.

 

[sublight_]

Wasn't there some patent drawings on here where the outer shape was radar translucent and the inner structure was diamond shaped to reflect radar away?