Skids or Wheels

[anchorhold]

Here is a question from a fixed wing pilot.

This question relates to the AW109 in Air Ambulence operations in the UK.

Why do they have retractable wheels and not skids, as they prequently land on soft areas such as parks, fields, beaches, snow and playing fields. There are two reasons for asking this, is that landing three tonnes of helicopter on what are small wheels, it strikes me that on soft ground the helicopter could sink far enough to deform the wheel bay doors and cuase all sorts of havoc with the landing gear. My second point os landing on wheels as opposed to skids on unknown areas it could be all too easy to place an whel on an old well, drain, etc.. My thinking is that wheels are more convenient for pulling the helicopter out of the hanger, yet ploice EC335 helicopters managa ground handlers on skids.

This leads me onto another question, in the event of a double engine failure, during a forced landing would you land wheels up or down on a AW109. I have seen from the left hand seat an EC335 do a simulated double engine failure and landing, it was quite impressedm but I am less confident as what would happen in a AW109m whells up or otherwise.

Finally from an anti collision perspective, on the AW109, do the landing lights retract with the gear?

[ShyTorque]

There's no hard and fast rule, but generally speaking, utility aircraft are often better on skids. Passenger aircraft, especially where the helicopter has to taxi close to people or structures etc. are better on wheels, to avoid excessive downwash issues.

Having flown both, though, landing "off helipad" on wheels isn't as much of a problem as you seem to think. It's not a matter of just plonking the aircraft down and hoping for the best, a good pilot will "feel" his/her way down as each wheel makes ground contact and reposition if unhappy. Slope limits are usually more of an issue.

On the A109, at least on the ones still in production, have landing/taxi lights built into the undercarriage sponsons, so they aren't affected by undercarriage retraction. They also have a steerable search light under the nose. For those who do require skids, Leonardo (Agusta Westland) fairly recently announced a skidded version known as the Trekker. I've not seen one yet, though.

Edit: As for landing wheels up....are you serious? The landing gear absorbs energy....and is fitted with brakes

[Nescafe]

The most authoritative position on this issue is that ‘skids are for kids.’

😉

[maeroda]

Ehm.....

Very busy commercial traffic airports normally deny entrance to skids helicopters due to FOD that could be trowed in the direction of parked aircrafts by the main rotor wash.
This is true for NON Hems helicopters.

On the other hand, multi purpose helicopters with wheels could be equipped with bear paw mobile skids for winter/rainy season, in this case gear retraction would be impossible.

Landing lights are deployable regardless of landing gear position.

[gulliBell]

.. is that landing three tonnes of helicopter on what are small wheels..

...landing on wheels as opposed to skids..

...in the event of a double engine failure, during a forced landing would you land wheels up or down on a AW109...


1. I sank to the axles on asphalt whilst re-fuelling at an airport in a S76, so yeah, you need to be mindful of that.

2. wheels (3 points in contact with the ground), tends to be more stable compared to skids with off-site landings at unprepared HLS.

3. you always land wheels down, whether 1, 2 or no engines are working. Unless you had a landing gear extend unsafe in which case you hover whilst ground support pulls the gear into place and pins them. If one of the MLG refuse to extend you can land gently on the belly with gear retracted.

[gulliBell]

..Landing lights are deployable regardless of landing gear position.

Not quite. The landing light on a S76 is bolted to the right MLG strut with an electrical interlock to ensure it's off with gear retracted. The landing light only works with the gear down. The S76 also has a pilot controllable search light that can be used with the gear up or down. Typically however pilots will have both the landing light and search light on for night take-off and landing, so when the gear goes up you still have use of the search light.

[SilsoeSid]

The most authoritative position on this issue is that ‘skids are for kids.’
😉

... and 'wheels are for w-anchors'

:ok:

[Bell_ringer]

wheels are for transport, skids are for fun :E
Runways are for Beauty queens ;)

[JohnDixson]

Some background on this subject, as applied to one user community, arising from the US Army UTTAS design requirements ( short version ):

In 1969, the Army initiated studies aimed at a UH-1 replacement. It should be remembered that the UH-1 started out as a med-evac machine, but which morphed into a combat assault vehicle due to Vietnam requirements. The Army used UH-1 accident and combat data to form the new requirements. For the landing gear, the crashworthy requirements arising from the accident/combat data decided the issue in favor of wheeled gear. A secondary operational issue in favor of the wheeled gear was that wheels alleviated the need to always hover a fairly heavy machine into its parking position, etc..

As I said, this is one segment of the user community who must address a demanding operational environment.

[VeeAny]

I'll show my hand as I am directly involved with the AW109 HEMS operation in the UK.

The 109 has no more issues in the HEMS role than any other aircraft in relation to skids or wheels in unprepared landing sites.

We occasionally have to reposition in boggy fields due to the wheels sinking, no more than we've seen skidded helicopters having to reposition on uneven rocky surfaces or unable to land on some slopes. Bear Paws are available, we've never felt it necessary to install them though.

I am not aware of even brake pipe damage (the most likely thing to break in my mind) as a result of HEMS landings in an AW109, the company flight safety system has no mention of any occurrence of incidents like this.

I would suggest that if an AW109 HEMS aircraft got bogged down so deeply that damage was caused to the aircraft, that a skidded aircraft would probably have not wanted to land in the same site either.

The taxi and landing lights as others have said are in the fixed portion of the Sponsons.

A steerable light is standard, 2 on the newer model are available as a factory fit.

One of the aircraft is hangared about 1/4 of a mile from the spot it sits on during the day and towing it is not an issue.

Wheels definitely get selected down for every landing , no matter 2,1 or no engines running.

The AW factory pilots used to demonstrate engine off landings to the ground years ago, I believe full EOLs are now only done in the sim even at the factory, but I may be wrong.

If the wheels don't come down for any reason (there are two hydraulic systems that operate the wheels just in case), it is possible to land the aircraft on it's belly and it has been done before, I know for certain in the older models without sponsons, which I think are less stable in roll in a wheels up scenario as they are narrower at the point they contact the ground.

[ShyTorque]

Not quite. The landing light on a S76 is bolted to the right MLG strut with an electrical interlock to ensure it's off with gear retracted. The landing light only works with the gear down. The S76 also has a pilot controllable search light that can be used with the gear up or down. Typically however pilots will have both the landing light and search light on for night take-off and landing, so when the gear goes up you still have use of the search light.

The OP wanted answers with regard to the AW109, though....

Finally from an anti collision perspective, on the AW109, do the landing lights retract with the gear?

[Sir Korsky]

as previously mentioned, wheeled aircraft are far more ramp friendly. Skidded aircraft can cause a ramp tornado when positioning at busy FBOs.

[gulliBell]

The OP wanted answers with regard to the AW109, though....

I was replying to the comment by @maeroda, not the OP.

[Saint Jack]

Some helicopters, the Bell 222 comes to mind, seem to have retractable wheels purely for aesthetic purposes, generally driven by the marketing department.


Some observations of both systems:


Skids: cheap, lightweight, low maintenance,
Wheels: expensive, heavy, moderate maintenance.


Also, at some time the retractable wheels WILL fail to extend, either through forgetfulness or mechanical issues. This is why some operators have stand-by provisions to receive a helicopter with wheels that won't come down, usually old tyres (tires) or similar to gently land on. In these cases it is worth remembering that it isn't the landing that does the damage, rather it's the protrusions, particularly antennas and WSPS deflectors that get pushed up into the lower structure causing substantial damage.


Skid-equipped helicopters are not immune from similar issues, I've personally seen two such helicopters with fractured rear cross tubes and I can assure you that this causes similar damage to a wheels-up landing, but perhaps not so extensive.

[BOBAKAT]

I fly both and both have pro and cons. WHEELS : Funny to taxiing on wheels...and landing only nose wheels in mountain side ;) More easy to land on sea carrier in bad wheather (small or Xsmall , big one same same..) Easy to autorotation on hard runway.. on smooth surface looke like sand, better skids....
Maintenance and weights...Cheaper on skids and you can't miss to low gear...lol

[anchorhold]

VeeAny.......

In the AW109, in the event of a double engine failure, upon making a forced landing, what would your forward speed be upon making contact with the ground?

I am assuming 'bear paws' are like snow shoes, but how to you fix them on?

Finally, assuming the AW109 has FADEC, in that case if while in the hover at 100 ft AGL, an engine fails, how long does it take to the live engine to deveop full power and is there a height loss?

[MightyGem]

is that landing three tonnes of helicopter on what are small wheels, it strikes me that on soft ground the helicopter could sink far enough to deform the wheel bay doors and cuase all sorts of havoc with the landing gear.
We had a Lynx(skids) land on sloping ground, which turned out to be quite soft. The downhill skid sank in to the ground, putting the aircraft out of sloping ground limits. Some considerable time digging under the uphill skid to get back in limits.

[ShyTorque]

Finally, assuming the AW109 has FADEC, in that case if while in the hover at 100 ft AGL, an engine fails, how long does it take to the live engine to deveop full power and is there a height loss? Yes, there would be a height loss, how much depending on the ambient density altitude, wind velocity, the all up mass of the aircraft and of course the reaction of the pilot (which would, or should be, to immediately lower the nose, gain airspeed and fly away).

The later A109 series aircraft are quite well off for engine power, compared to most other helicopters of that size but hovering for prolonged periods at 100 ft agl is something that most A109 pilots don't routinely need to do. The manufacturer provides details of "profiles" that afford Class A performance for departure and landing and public transport operations should be carried out with those in mind.

[handysnaks]

I am assuming 'bear paws' are like snow shoes, but how to you fix them on?

Is there any fixing other than harry black, jubilee clips or a ty-wrap? :)

[jayteeto]

Bear paws are pretty much essential for our HEMS operations. Our neighbours use wheels, we use skids. On the moors, they often struggle for a good site, we don’t. In winter, if you retract muddy, wet wheels, you risk them freezing in the up position. I am praying our lot don’t go for the 5 tonne wheeled market option.
That said, you gain 5-10 knots without the drag......

[maeroda]

My two cents:

having flown HEMS in mountains/onshore and Oil&Gas as well with Aw139, B412 and BK117, I can tell operational wise they're both effective for an array of reasons.
Skids are more durable as wheels do get consumed by use, wheels get flat, in mountain the tripod landing gear gives more stability on rough terrain, in swampy landings you may want skids instead of wheels, wheeled landing gear is more prone to failures to retract or extend (ECL issues to be addressed with proper training during OPC's and LPC's), on snow doesn't really matter because both systems use removable snow skids (mandatory on all Hems winter contracts), on drill ships you may want wheels because the net is often installed on the decks and skids get entangled, having to haul in and out airports wheels are better as you can taxi without hovering for the time taken to commercial aircrafts to clear the taxiways with heavy departing traffic, the belly is usually higher on skids helicopter so antennas and drain pipes are more protected from intercepting the ground....

Cheers