PLAN Zubr Large Air Cushion Landing Craft

SamuraiBlue said:

There is one small problem to your logic. 0.4 psi may not sound big with a 1" pipe but when you need to exert that same amount of pressure evenly through two or more 15 m diameter fans then it becomes a big problem.
That is about 618,110Kg of air needed to be displaced per second.
I wonder how strong that fans requires to be and how much fuel it would take to run it?

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Sigh, since I work in metric and talk in imperial, its gonna be a pain... but here goes

pressure required 2.74 Pa.. lets say 3 Pa

Lets assume that the hover craft hovers 0.3 m for leakage. 57m X 25.6 = a perimeter of 165.2 m; with a height of 0.3 that is a leakage area of 49.56 m2, say 50 m2

Bernoulli's Equation... no height change, dp = 1/2*rho*V2

dp = 3 Pa
Rho = 1.225 kg/m3 @ sea level (literally)
therefore V = 2.21 m/s leakage

Q = Volume lost = 2.21 m/s X 50 m2 = 110.5 m3/s

Assume 50% rotor efficiency, Eff.

P (power) = (dp X Q) / Eff

P = 663 W

Now this is theoretical; no waves, flat surface, no rough losses... so lets say reality will be like 10X more energy so 6.6 kW? or ~2hp ? the Zubr can fly up to around 2 m on an air cushion.. so the fan is definitely much bigger and safety/failure backup..

The Zubr, have 5x gas turbine, 11,836 HP each, 2 is for levitation, i suppose one duty, one standby. gas turbine to electicity... around 25% efficiency, ~3000 HP; mechanical efficiency is like.. 70% and typical design safety is 200-300% so around 700-1000 HP is used for levitating the craft.

point in case is only that it doesn't take a very big fan to levitate a hovercraft;

Some 15 years ago, I worked on a school project for a 2 person hover craft, the whole thing with forward propulsion was on a 2 hp motor and it easily went 10-20 km/hr. fun days

Lezt said:

Sigh, since I work in metric and talk in imperial, its gonna be a pain... but here goes

pressure required 2.74 Pa.. lets say 3 Pa

Lets assume that the hover craft hovers 0.3 m for leakage. 57m X 25.6 = a perimeter of 165.2 m; with a height of 0.3 that is a leakage area of 49.56 m2, say 50 m2

Bernoulli's Equation... no height change, dp = 1/2*rho*V2

dp = 3 Pa
Rho = 1.225 kg/m3 @ sea level (literally)
therefore V = 2.21 m/s leakage

Q = Volume lost = 2.21 m/s X 50 m2 = 110.5 m3/s

Assume 50% rotor efficiency, Eff.

P (power) = (dp X Q) / Eff

P = 663 W

Now this is theoretical; no waves, flat surface, no rough losses... so lets say reality will be like 10X more energy so 6.6 kW? or ~2hp ? the Zubr can fly up to around 2 m on an air cushion.. so the fan is definitely much bigger and safety/failure backup..

The Zubr, have 5x gas turbine, 11,836 HP each, 2 is for levitation, i suppose one duty, one standby. gas turbine to electicity... around 25% efficiency, ~3000 HP; mechanical efficiency is like.. 70% and typical design safety is 200-300% so around 700-1000 HP is used for levitating the craft.

point in case is only that it doesn't take a very big fan to levitate a hovercraft;

Some 15 years ago, I worked on a school project for a 2 person hover craft, the whole thing with forward propulsion was on a 2 hp motor and it easily went 10-20 km/hr. fun days

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I thought it's not 3 Pa but 3000 Pa unless I missed something

kwaigonegin said:

I thought it's not 3 Pa but 3000 Pa unless I missed something

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You are right! lol, it was a long day,

so, V = 69.9 m/s say 70 m/s

Q = 3500 m3/s

= 21 MW
= 15,645 hp

thats more like it.

Just what we thought

asif iqbal said:

Just what we thought

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Yes, and it makes perfect sense for the PLAN too.

Looks like they will build at least two of vessels to carry them...maybe more.

Which makes me wonder how many of the Zubrs the PLAN is planning to have.

I bet they end up with more than the four.

So we can confirm 3 commissioned and 1 under construction?

kwaigonegin said:

I thought it's not 3 Pa but 3000 Pa unless I missed something

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Doubt you'll be able to lift anything with such lower output.
Remember the earth's average

So.... @navyreco has done a good write up on the new ship on the site... however I'm curious, where the hell is the 5000 ton displacement of 868 from?

At over 60,000 tons, the MLP dwarfs vessel 868 and its reported displacement of around 5,000 tons.

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Over on CDF they say it's 50,000 tons displacement full... and given the ship itself has dimensions of 175m x 35m (via google earth and also the CGI) it isn't impossible.
This is the proof: Huangpu Wenchong (the shipyard which did the conversion) posting about recent projects done, and refers to a "semi submersible vessel conversion project" for the military, of the 50,000 ton class.

The CGI picture (while not entirely reliable) itself lists a 30,000 ton displacement.


So I have to caution that the 5000 ton displacement is waaaaaayyyyyyy off. If the 5000 ton number is taken from china defence blog, it should be noted that they have since rectified it to 50,000 tons. Unfortunately they have not changed the rest of their entry; after all the USN's MLP class displaces over 60,000 tons full rather than 34,500 tons.


If one can read Chinese, the CGI also says it can carry 2 type 726 LCACs in place of a Zubr. I'm not sure if the CGI is reliable, but other CGIs of similar types have turned out to be quite accurate. Unfortunately the picture is of too low resolution for me to make out much else apart from what i've already stated.
Overall I think @navyreco, you are jumping to a rather rapid conclusion. The ship has been delivered to the Chinese navy, but it is multirole by nature. So I wouldn't necessarily assume that it will only ever accommodate a single Zubr on a barren deck... and it's probably a little early to assess just how similar 868 is to the Montford class MLP, as further modifications to the hull could occur (possibly removable modules, I myself suspect). I also wonder if 868 may only be the first of a converted testbed to precede a more dedicated, larger class of MLP type ship derived from semi submersible.


Also, at the bottom of the article:

By 2025, the PLAN is expected to have a fleet of 4x 40,000 tons Type 075 LHD, 4x 20,000 tons Type 071 LPD, several LSDs and sevel of these "vessel 868" follow ons...

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071 is 25,000 tons full load.
Also not sure where four 075s came from; I'd think maybe one or two at most in service by 2025. Possibly four by 2030.

The 5,000 ton displacement almost has to be a typo from an original web site that has propagated through to NavyReco's site.

One more zero and you have the 50,000 tons.

Probably as simple as that IMHJO.

Jeff Head said:

The 5,000 ton displacement almost has to be a typo from an original web site that has propagated through to NavyReco's site.

One more zero and you have the 50,000 tons.

Probably as simple as that IMHJO.

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Yes, I think so -- unfortunately that has led NavyReco to a few (IMHO) awkward and arguably unlikely conclusions about 868's capability and potential capability.

I also want to add that 868 is not merely a civilian semi submersible ship painted grey -- there was a conversion process the shipyard went through to militarize it. The most visible part we see is the shipping container like module placed transversely in front of the main superstructure, but there were likely other modifications too, internally. And like I said in my last post, I wouldn't be surprised if we see further modifications to 868 in due time.