The Tupolev Gullwing was made by the Russian military to be an
 amphibious boat/sled used to pick up cosmonauts downed in Siberia
 after their spaceflights..."What packs 365 horsepower, incorporates a
 pair of gullwing doors, and can transport a 630-pound payload at more
 than 90 mph across the Siberian tundra? It could only be the Tupolev
 N007, one of the oddest and most remarkable pieces of formerly secret
  Soviet machinery to be flushed out by the blossoming of a Western
 market economy.

 Though background information is sometimes contradictory, the Tupolev
 N007 appears to have been developed back in 1961 by Andrei Tupolev,
 the father of Soviet aviation, as a rescue vehicle for cosmonauts who
 fell back to earth on the wastelands of the western U.S.S.R. Small
 enough to be carried in the belly of a Soviet cargo helicopter, the
 N007 could cross ice, snow, lakes and swamps with impunity--just the
 vehicle to lift the spirits of any cosmonaut stranded in a hostile,
 trackless territory.

 http://tinyurl.com/25wxyry

 Dale Callaway Via Reeves Callaway


 Interesting air boat. Unfortunately, the journalists on the webpage
 throw in too much imagination. There is nothing in the design that
 would indicate "ground effect" or "hover" capability. There are no
 wings, therefore no ground effect lift (look up ikranoplan). I don't
 see a skirt, or indication of any ducted fans, no "hover" capability.
  It's a very cool vehicle just the same. C. Smith

 Thanks for the post, Dale. This is intriguing!

 And, Craig: your instinct is right :)

 When I saw the picture, it just strike me that I _should_ have seen
 this thing before!

 And, so it was. That thing is a Tupolev A-3, buoyant airsled, built
 for arctic conditions. A couple of those was bought to Canada and
 Finland for trials. Tupolev site states that production run was about
 700.

 There is no airdam or air-cushion effect. It is just a sled with prop
 on it. And what comes to "N007" marking, "top secret" and
 cosmonauts... :D that fella bought this for a couple of bucks, and
 seemed to get 186.000 USD from it on an auction recently :D Well
 Done! A healthy dose of poetic license seems to go a long way! :D :D

 Those type of crafts are used eg. here in Finnish archipelago at
 autumn and spring, when sea is either just frosted or melted to
 pieces. Boats are not useful then, and you cannot drive a car or snow
 tractor there either. So the concept is similar to Florida swamp
 airboats, but these ones are optimized for snow, ice and ice boulder
 conditions. Here's a recent version of this concept:
 http://www.airboats.fi/ (could be lighter and better with 2x13B-MSP
 with interlinking PSRU)


 And here's the Tupolev site quote: "In the 70-s- 80-s the A-3
 airsleigh of the second generation was built and operated
 successfully. The main distinguishing feature of the machine is the
 housing made in the shape of the boat-ski and aircraft engine of 350
 HP. This provided high amphibian characteristics of the airsleigh.
 During forty years more than 700 machines were operated by
 communication workers, geologists and frontier guards. The airsleighs
 were sold to Canada, Finland, Hungary."
 http://www.tupolev.ru/English/Show.asp?SectionID=79

 Cheers! Petri in Finland

By the way, that "Arctic airboat" proto seems to need some aircraft
engineering touch. Impression from their videos is that their air
suspension seems to work wonderfully, but prop assembly is not utilizing
any ducted fan/shrouded prop effect.
http://www.airboats.fi/videogallery/?show=2
Thrust from 500 hp engine should be awesome, but it seemingly isn't.

There was one very illustrating quote about ducted fan design on
eng-tips.com:

"The inlet lip radius has a huge static thrust effect; does the duct
converge,diverge or is it straight? Those also have an effect. Optimum
blade number, chord, angle of attack of the blades, and the tolerance
between the blade tip and the shroud all have major effects. The there's
compressibility effects as the tips get over 0.80 Mach.

It's a b**ch to design one of these s****rs."

http://www.eng-tips.com/viewthread.cfm?qid=58711&page=1

If this is done right, it's likely that just a 250 hp p-port renesis
with a good shrouded prop can do the work of 500 hp V-8 with
non-optimized free prop. And, btw, I don't think that they can drive
that V-8 at 400-500hp more than 5 mins...

The complexity of shrouded prop design could be relieved a bit by using
a "blisk". I just got back from Amsterdam Marine Equipment Trade Show,
and run into this there:
http://www.vandervelden-marinesystems.com/rudders.cfm?pk=497&lang=en

It's a bow thruster where cavitation noise is killed by eliminating the
gap between tunnel and prop blade. The downside could be that bearings
eat too much of mechanical efficiency if used as main propulsor.

But... perhaps it could be made to work as well with a central hub,
making that blisk shroud as a light aerodynamic seal. That still leaves
the problem of maintaining the shroud-blisk clearance under vibration
and gyroscopic loads - but if it is solvable on conventional fans, why
not in this case?

Cheers,
Petri

Here is some stuff I have on ducted fans.

Paul Lamar