Ground taxy

[zudhir]

What is best method to ground taxy - using differential braking or by using tail rotor thrust?

[eivissa]

In general:
-Tail rotor thrust for turning (Nosewheel must be unlocked first)
-Cyclic centered
-Collective for moving forward

[Helipilot1982]

Its a balance of differential braking, a small amount of pedal, collective and cyclic inputs. If you use only tail rotor thrust (ie pedal) for turning the you run the risk of putting too much stress on the tail section - not good (especially for the 139 drivers!!)

[Geoffersincornwall]

The 139 tail section is good for a 45 knot crosswind and I'm pretty sure that the flight loads involved far exceed that experienced when ground taxiing. If there were any doubts about that then EASA would have required an amendment to the RFM limitations. Let's not get carried away with one event that is now well documented and not representative of a serviceable airframe.

The 139 is unusual insofar as the RFM required the pilot to avoid the use of in-turn cyclic and not to apply cyclic laterally except to deal with a crosswind.

G.

[Savoia]

What is best method to ground taxy ...

Like this .. ? Perhaps not.

93cF_3wQacE

Check out the wheel shimmy at 6:41

[Darkhorse30]

In most Russian helicopters (Mils) there are no differential brakes, no toe brakes. Ground taxy is done with cyclic slightly forward of neutral, tail rotor thrust for turning and fine maneuvering, and collective as needed. The brakes are applied through a bicycle lever just forward of the cyclic grip. It works very well and with a little practice you can maneuver without applying brakes.

It's a very simple system. Western helo manufacturers should look into this. They (Russians) use only one master cylinder for the brake system.

[hihover]

It will depend on the type of helicopter and on how much weight you take on the rotor head. In general, I would say that tail rotor thrust is normally adequate, certainly for the types I have flown (109, 139, Puma).

TM

[Aser]

Savoia (http://www.pprune.org/members/330391-savoia) what's wrong with that taxi? I can't see the relation to the "shimmy" :confused:

[Savoia]

Slightly quick, perhaps? I'm not sure if there are a specific set of ingredients which contribute towards wheel shimmy on the 139 but speed might be one of them.

[Geoffersincornwall]

It's all part of living with a nose wheel (or a tail wheel). Not unusual and a feature of many a wheeled undercarriage.

G

[Aser]

Savoia, I had the same incident because I went over a taxiway light and I was between 10-15 knots.

[Fareastdriver]

In all my time on Pumas and S76s, 1971-2007 I always preferred to taxi on the wheelbrakes wherever possible. This had to be assisted by tail rotor effort some of the time so the ratio was about 80/20.
The S76 was easy on either the brakes or nosewheel but the Puma got harder on the tail rotor over the years because of the extra weight it was carrying on the nosewheel because of higher weights and longer noses. An empty 332L has over 40 per cent of its weight on the nosewheel.
Initial flying of the Puma was in the military and in line astern behind another one watching the pylon twist as it lifted a heavy load tends to make you respect what the boom assembly has to put up with. Over the aircraft's life the pylon joint has had doubling and then trebling plates added on.
The tail rotor has a lot of work to do so I would give it a rest during taxiing.

My opinion for what it's worth.

[MightyGem]

Western helo manufacturers should look into this.
Westlands did. For the Lynx Mk9.

[Shawn Coyle]

Anyone care to try to describe how to three-wheel taxi a CH-46??? One of the more challenging exercises for new CH-46 pilots.

[Jack Carson]

Shawn,
It is pretty straight forward. The first rule is keep the pedals centered. Attempting to use the pedals may cause the flap stops to be contacted. Raise the collective slightly while adding forward cyclic. One instructor told me to rock the aircraft fore and aft with the cyclic. This will get the aircraft moving. With the cyclic slightly forward the aircraft can be steered using lateral cyclic. I hope this helps. My experience in the Boeing is limited. Hopefully, an experienced tandem pilot can add additional information. :8

[teej5536]

My ground taxi experience is limited to AS332L2, and EC225LP. I endeavor to use diff braking as much as possible, as use of the pedals can cause significant roll in the opposite direction of the turn, due to high tail rotor position. On our undulating ramp/taxiway to the main, this can quickly start to look like static rollover material. Furthermore - in the winter when we encounter ice on the taxiway, the pedal is not as helpful as it leads to lateral skidding.
A sticky nose wheel can encourage the use of extra pedal but, as it was said earlier, the tail has a lot of work to do so I avoid it as much as possible.

A slight digression, but something I mentioned: Static rollover in ground taxi. If when taxiing the aircraft does roll, and the inside wheel begins to lift/the sensation of pitch begins -as the aircraft pivots around the axis subtended between the nose wheel and the outside wheel- immediate opposite pedal will stop the rolling. eg. turning right, aircraft rolls left: apply left pedal, lower lever.

[teej5536]

I agree savoia. He was taxiing quickly, and may have been a little light on the wheels as he tried to straighten out from the turn? It looked like their was some significant lean to the left as he turned the corner then as the aircraft sprung back the shimmy started.
Only time I've had nose wheel shimmy was taxiing too quickly, and too light on the wheels as I touched down with a little run on speed (maybe 10knots).
Aser: what you describe is fair enough. However I think Savoia's point was the way in which this wheel shimmy was induced (perhaps hurried taxiing); not to say that all shimmy is a result of bad taxi technique.

[Thud_and_Blunder]

No Chinook pilots here? Nothing quite like the look on the students face when you first demo the cyclic position set-up prior to 2-wheel taxying. The analogy of the collective as a hand-brake also used to take some folk a while to get used to - they'd forget the teaching and a part of their mind would rebel against increasing power/lift to stop.

Mind you, after about 20 minutes most studes had mastered the art of the reverse 2-wheel taxy 90-degree turn into a parking slot.

[Shawn Coyle]

I wasn't going to try to explain how to three wheel taxi a CH-46. Too much fun to watch an ab-initio helicopter test pilot student try it. Two wheel taxiing was equally as much fun.
And then try to get them to write about it!!!