Wheeled Gear layout

[Spaced]

I was wondering what are the considerations given to the different gear layouts on wheeled helos.
What are the advantages of a tricycle over the tail dragger style, and vice versa.
Is one better for unpaved rough surfaces?
Is one easier to manouver?
Thanx in advance for the replies.

[sycamore]

Taildraggers are for real men, nosewheels are for cissies, and skids are for those who can`t really land anyway!!!!


Take-Cover----Incoming!!!!:oh:

[NickLappos]

sycamore,

You ask a very good question, one we go through each time we lay out a new helicopter. Here are some thoughts:

Tailwheels are great for utility and combat aircraft where the tail is protected against contact by the wheel, which absorbs a beating while landing. The tail cone has to be beefed up to take the load, and the wheel weight is very aft, a place all helicopter designers hate, since aft cg occurs so easily and is cured with difficulty. Tailwheels also require more deck space, so they are less convenient for ships and offshore decks. They also are dynamically unstable on running landings, so they require slightly more footwork to prevent groundlooping (but are usually equipped with a lock so this is a small issue). Quick tactical landings are easier with a tail wheel, since the aircraft can be landed while still flaring, a real asset in a hot landing zone.

Nose wheels have the virtues of smaller deck footprint, somewhat easier taxi handling and generally lighter overall aircraft weight, since the gear load path from the wheel to the transmission (the natural backbone of any helicopter) is naturally shorter and smaller, thus lighter.

Note the Black Hawk has a tail wheel, and the Sea Hawk, its naval twin, tucked in close to compromise between the two layouts.

[sycamore]

Thanks Nick, it was a rather flippant retort, but I blame it on late night Californian Red.!!
As you have gone nearly there, just a few additional comments.
All Naval helos(except trainers) will have wheels to facilitate deck operations, as they also have better coeff. of friction,as theres no way you can jack-up a skidded cab on a heaving deck and manhandle it around.
Also the u/c on naval helos is designed to to absorb a high sink-rate,to a positive landing , whereas I think skids would just splay, very few have dampers,and so you would not get a positive landing.
Tail-wheel helos also have their problems too, especially when flaring into a tac. landing , as you lower the lever you realise the parking brake is ON.Makes the eyes water!!

[Lu Zuckerman]

To: sycamore

as theres no way you can jack-up a skidded cab on a heaving deck and manhandle it around.

We had a Bell on floats and in order to park it on the pitching and heaving flight deck we had to put a special jacking unit under the cross tubes. It was difficult enough to maneuver the jacking unit but when we were moving the helicopter it could take as many as six men to position the helicopter and then the jacks were lowered and we tied the helo down to the deck with ratchet tie downs.

The other helicopter was a tricycle model and it only had parking brakes, which were not very effective. Most of the landings were athwart ship and were difficult because of ships rigging and a large hoist, which were quite close to the landing helicopter. With the deck pitching and heaving we had to get the ratchet tiedowns and chocks in place to keep the helo from going over the side. It was too dangerous to try to move the helicopter from the landing spot to the parking spot.


:E :E

[Thud_and_Blunder]

Nobody so far has mentioned the benefits of a wheel at each corner - Ka32, S55/Whirlwind and Chinook all seem to flourish on the layout. All capable of spot-turns on the ground virtually within one aircraft length. Running landings at 60 kts wouldn't be much fun with any other layout. Mind you, nose-up-slope landings in a Whirlwind without any nosewheel brakes were a sure way of making sure you achieved the appropriate disc-level attitude...

Oh, and as regards skids - anyone who's tried putting a Blackhawk onto a Borneo jungle pad will know how much better the B212 undercarriage was for that particular task!:ok:

[NickLappos]

Thud,
Those four corner wheels are convenient, agreed, but the turning circle is the same for almost any wheeled helo. It is determined by how you used the cyclic and brakes, mostly, not the gear pattern. I can turn an S-76 or a Black Hawk within its rotor disk with no special technique.

The four corner wheels are little used now because the crashworthy requirements make it pretty inefficient to have more than 3 wheels, since the requirements ask that one wheel take a large percentage of the crash force (by imposing a roll angle at touchdown).

[Thud_and_Blunder]

Nick,

Your point should've been obvious to me - ta for observing it so tactfully. As soon as I'd posted it I remembered seeing RN Sea Kings and Wessex spot-turning on deck - must remember to pause before hitting send.

There are one or 2 Chinook drivers around who know all about knocking 1 or more undercarriage legs off when arriving on board (or in the desert) - good to know the airworthiness people don't just sit on their shinies.

Still like leaving skid-marks (:ooh: ) wherever I go...

[Spaced]

Thanx for the informative responses guys.
Thud good point about the bed post layout, Id forgotten about those.

Nick, if I could pick your brain a little more, does the forward movement of the tail wheel in the Sea hawk, aside from easier shipboard handling offer any other advantages/disadvantages?

Due to the dynamic instability of the tail dragger config, are there restrictions in the POH on TO/running on speed?