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I noticed a small item on the rear side of the nose wheel in multiple images of the Sukhoi PAK-FA, shown below. The item in question appears to be a grille wrapping around the back of the tires and I cannot think of any reason to put something like this on an aircraft's landing gear. Does anyone know what function it serves?

Image credit Dmitry Zherdin. Obtained via Wikimedia Commons. Image credit Alex Beltyukov. Obtained via Wikimedia Commons.

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    $\begingroup$ Pretty sure its a debris deflector, so that the aircraft doesn't throw up things into the intakes. $\endgroup$ – Ron Beyer Dec 12 '16 at 22:30
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    $\begingroup$ @RonBeyer Interesting, do other Russian fighters have them as well? I understand the Russian practice is to build aircraft to withstand the battlefield and FOD at the airfield, but had never noticed one of these before. $\endgroup$ – mishaturnbull Dec 12 '16 at 22:40
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    $\begingroup$ I'm not sure about Russian fighters, but it is pretty common on a lot of different aircraft. $\endgroup$ – Ron Beyer Dec 12 '16 at 22:46
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    $\begingroup$ "Especially design for rough field operations the single wheel sturdy nose gear features a mud guard/ FOD screen with downward facing deflectors louvers guiding all debris away from the large air intakes. It pivots around the wheel axis and is connected to the nose gear leg by two struts." Source. @RonBeyer is right. $\endgroup$ – mins Dec 12 '16 at 22:57
  • $\begingroup$ Looks like he forgot to feed the meter and the parking police booted it! $\endgroup$ – FreeMan Dec 13 '16 at 15:31
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It is a mud guard/FOD deflector, which is found in almost all Russian combat aircraft operating from land bases.

This is basically a reflection of the Russian philosophy of aircraft operations:

The fact is that most Russian fighters and attack aircraft were built to operate in pretty horrific conditions, ones that would chew up and destroy their western counterparts. Features that allowed them to do this usually included twin tire nose gear and a mud and debris catcher located behind the nose wheels.

The nose debris deflector prevents debris being ingested by the air intakes (which are to the rear of nose wheel) and damage to the airframe. According to ausairpower.net, it also has:

Alternate intakes for the propulsion system, as seen on earlier Flankers.

for rough field operations, similar to Mi-29. The image below shows the add-ons.

PAK-FA

Detail of inlet and lower fuselage area (Sukhoi); image from ausairpower.net

The FOD deflector is similar to that of the Su-27's, as shown below:

Su-27 nose landing gear

Su-27 nose landing gear, from another answer; originally from maybach300c.blogspot.com

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  • $\begingroup$ This sounds like a very cheap and easy solution. Why would American jets not implement this also? $\endgroup$ – David says Reinstate Monica Dec 13 '16 at 15:39
  • $\begingroup$ @DavidGrinberg It goes back to core philosophy. American fighters are designed to operate from generally well-cared, paved runways and bases... so there's an assumption that most of the time the American fighters would have relatively ideal conditions. The Russians take the opposite approach and design for horrible conditions, expecting their fighters to operate from country roads, unpaved impromptu runways, fields, basically anywhere anytime. Which is better? Well that depends on your projected operating conditions... $\endgroup$ – SnakeDoc Dec 13 '16 at 19:32
  • $\begingroup$ @SnakeDoc right, but it seems like that extra piece on the wheel is a very small price to pay such that you can get the best of both worlds $\endgroup$ – David says Reinstate Monica Dec 13 '16 at 20:01
  • $\begingroup$ @DavidGrinberg Russian fighters have a lot more than just the wheel FOD deflector that enables them to operate in rough conditions. They have deflectors covering intakes to prevent FOD ingestion, don't hang ordnance as low on the body as American fighters (risk of damage or strike FOD on runway at takeoff/landing), size and shape of the aircraft, weight, dual nosegear wheels/tires in some cases, etc. So, it's the entire design philosophy that enables Russian fighters to operate in the conditions they are designed for. American fighters simply are not designed with the same environment in mind. $\endgroup$ – SnakeDoc Dec 13 '16 at 20:11
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It's basically a mud deflector. Prevents or reduces rocks, mud, or other FOD that the nose wheel kicks up from getting airborne and either smashing into the airframe or being ingested by the engine. You will notice that most Russian fighters have this feature on the nose landing gear per their philosophy of war and the substandard conditions found at Russian airbases.

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