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Anyone knows what's the plate behind the wheel of the Pilatus Porter for?

enter image description here

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Looks like a sort of gravel kit.
Real gravel kits are used by jet powered aircraft to land on rough airfields.

In this case though, the engine is in front, so it is likely that it is only there to reduce the amount of dirt raised when landing/taking-off so to reduce the chances of damaging the aircraft.

From the official PC-6 Porter brochure via pc-6.com (PDF), they call this option a mudguard:

enter image description here
MUDGUARD

And according to a service bulletin (pilatus-aircraft.com; PDF) there were prone to fatigue:

Operators have reported failures of the mudguard supports and stone guard mounting yokes. The failures are caused by fatigue damage.

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    $\begingroup$ I would suspect that without those plates stones might hit the lowered flaps during landing rollout. $\endgroup$ – Peter Kämpf Aug 10 '18 at 10:37
  • $\begingroup$ Someone told me it could be used as a mechanical brake when landing on an upwards muddy runway, sticking the plates in the mud in order to stop the plane if it moves backwards ( due to the upslope). Does it make sense? $\endgroup$ – Flightfighter Aug 10 '18 at 12:06
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    $\begingroup$ @Flightfighter it could make sense, but I would not expect it to be below the center of the wheel when "at rest" like in the pic. look at the right wheel, you can see that the supporting arm has a bend to lower the plate over the ground, such a bend reduces the load it can carry if used as a brake. Plus, the structure does not look like it is made to carry any load at all. $\endgroup$ – Federico Aug 10 '18 at 12:09
  • $\begingroup$ Thank you buddies, it was kind of obvious but just wanted to be sure:) $\endgroup$ – Flightfighter Aug 10 '18 at 17:25
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Federico hit the nail on the head. It’s a gravel kit and works similar to the mud flaps on trucks. On rough airstrips, it prevents rocks, gravel and other FOD from striking the airframe and damaging it during the ground roll.

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    $\begingroup$ How does this add anything to the already existing answer? $\endgroup$ – Christian Aug 11 '18 at 11:54
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Actually - Federico didn’t exactly hit the nail “squarely on it’s head” The main function of these devices is to spread the load, ie reduce the weight per square unit by increasing the ground contact patch of the tyres. Many bush airstrips has a very loose / soggy sub-soil, and I’ve seen first-hand that a heavy bush-plane can sink through to it’s belly while sitting still or moving slowly when operating in unimproved jungle-airstrips in Asia or Africa. Think “snow-shoes” in the Arctic or wheel-penetration skies, like the ones I flew in Antarctica. If the “ground contact patch” of the tyre itself, starts to break the surface, it will sink down until the device touches the surface, whereupon the load is spread out to much larger area, and the aircraft doesn’t break through.

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  • $\begingroup$ If it is supposed to take some of the airplane weight, the skimpy tubing that fixes that plate to the landing gear should be a bit beefier, wouldn't you think? On the other hand, the plate is wider than a pure mudguard needs to be … $\endgroup$ – Peter Kämpf Feb 20 at 8:02
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    $\begingroup$ Do you have a source for this? $\endgroup$ – Bianfable Feb 20 at 10:35

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