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Mud, Sticky & Dangerous Mud

We have been so unlucky with this untimely and unseasonal weather in our little part of Southeast England. With greater issues of Brexit and Aerosol murders in the news, I am obliged to be distracted into writing about mud and how it can obfuscate safe flying practices. Sounds cryptic doesn't it.

The other day, after a lull in the rain, I went flying from our grass airfield at Damyns Hall. The aircraft was the Pipistrel Sinus, a superbly smooth motor glider fitted with an 80 hp Rotax engine and a featherable composite propellor during gliding flight.

Checks completed, we started taxiing over the very damp grass, about 3 inches long now, because it had grown a bit in the 3 days that it was warmer than 13C and then gathered the rain during the next three days. The tail dragger was not at all difficult to steer, but I felt the main wheels stick in the mud, not with its weight but due to the sticky nature of the wet soil and grass.

We went downslope on the runway and as we turned onto the the taxiway and holding point of 03, I felt that the brakes were not required to stop. All power checks done with the toe brakes on, we applied power, but could not move forward. 3 attempts at moving by rocking the aircraft with intermittent application of full power were not successful.

In the event, we switched the motor off and got out of the aircraft and turned it around by lifting the tail and pushing on the door sills. We moved the aircraft so that one tyre (not fully inflated) was resting on the runway marker made of flat stone to reduce braking resistance of the mud.

Once restarted, we performed all predeparture checks and started the take off roll. To my surprise, it felt that the mud monster was grabbing the main wheels to stop us from accelerating to take off speed. The classic technique that the pilot owner used was to raise the tail slightly to lower the angle of attack, but this reduced the propellor clearance from the mud monster. I was about to grab the joy stick and keep it from going forward further to prevent a prop-strike and nose over.

After a normal flight, the landing was uneventful. The taxiing was done with plenty of power with the stick held fully back as normal.

Lessons learnt:-

  • Always walk and inspect the taxiway and runway after a few days of heavy rain.

  • Be prepared for sticky mud to collect in the wheel pants. You can remove the wheel pants and be prepared for

  • This mud can get thrown forwards and rearwards and may hit the propeller blades as well as the elevator and fuselage sides.

  • Allow the engine to warm up to correct operating temperatures before applying full power, which may be required just to start moving forward.

  • Ensure that you do not allow the tail to rise and the prop to strike the ground while taxiing under high power settings.

  • Do not use brakes as they will help dig the nose into the ground, especially after landing.

  • If any antennas are fitted under the aircraft belly, check and clear any mud after flight as they may be damaged, or dried and caked mud on the antenna will affect the radio and transponder emissions.

  • Be prepared to protect the propeller from striking the ground if the wheel catch in the mud on take off acceleration and landing deceleration.

  • Be prepared to accept a much longer take off roll, with the 3 point attitude, rather than lifting the tailwheel.

  • Ensure that the propeller is set to fully fine, especially on a variable or constant speed propeller.

  • Warn the pilot if you think he is unaware of the effects of taxiing on soft ground ( he may not be used to it)

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