Wheels -v-Skids

[Vfrpilotpb]

Goood Morning Rotorheads,

Apart from the ground handling benefit, what advanage or disadvantage is there from fitting Helis with retractable wheels, when they seem to be an added weight and technical complication compared with Skids, and, which do you consider the most safe and practical option, Wheels or Skids?

:)

[Redbeard]

give me wheels anyday over those crazy cheap skids

don't have to be retractable.. flying the old lady lynx, we don't have those retractable type

:rolleyes:

[200psi]

Can't be too much of a technical complication otherwise the plank drivers wouldn't be able to work out how the lever works. Up and down wheels have been around for a long time I don't think there is anything too complicated about it.

Wheels come with oleos makes landings softer when done right, saves your butt when done wrong or when the go meter stops ticking over.

When tucked away reduces drag with all the flow on benefit that entails.

Speed brake when too hot.

With park brake on is very secure and stable on slopes, rigs and the like.

Makes OEI landings less exciting at the bottom. Or the ride of your life if they don't come down.

Maintain directional control thru differential braking when the T/R stops doing its thing.

Bumpy when flat spotted after poor use of differential braking or after leaving park brake on during run on landing.

Inflated to very high pressure (200psi
:D ) so will hurt ones toe when kicked.

[Nick Lappos]

200psi said most of it very well and very tersely (Lu, take a lesson!), let me add:

For the S-76, the retractable wheels gain you 6 knots at best range speed, enough to save the extra weight of the gear (about 90 pounds)on every full tank of gas.

Wheels are better for slope and rough field landings, as it is easier to find stable solutions for landing with 3 points on the same plane (wheels), rather than two parallel lines on that plane (skids).

Skids have advantages, such as cheaper to design and build, easier to maintain, lighter.

Generally, skids are not as safe as wheels, because in most landing and ground handling cases skids do not help the situation a bit, where wheels contribute positively. :cool:

[Devil 49]

Wheels are great if the surface you're putting them on is firm.
Skids spread the weight a little (surprisingly little) more on unimproved surfaces. Skid gear can allow you to find a level landing point if the surface is really rough. Skids more prone to catch on obstructions. No brakes to worry about.

[Nick Lappos]

Devil 49 said:
Skid gear can allow you to find a level landing point if the surface is really rough.

Nick sez:
Nope! On rough ground, it is usually hard to find stability with skids, unless the ground is also soft, where the skids can sink in a bit. That is because the skids form two parallel lines that are in one flat plane, and they must retain that relationship even on rough ground, where such planes don't exist. Usually, skids end up with one or both balancing or teetering on firm rough ground, because the long skid's straight line can't conform to the rough or rocky ground, so much of the skid doesn't touch. A wheeled helo can almost always find stability with the three wheels all touching firmly even on the roughest ground. Three wheels simply find their own plane and allow stable touchdowns anywhere, albeit with a sloped aircraft.

I have heard of marketing hype that discusses how much better skids are on rough terrain, and that is simply untrue. The US Army, with 7,000 helicopters in its inventory, and missions all over the world no longer will buy a skidded helo.

Devil 49 is right, skids don't conform to the surface, and the touchdown pressure on the ground is actually higher than wheels (more tendency to sink in and create dynamic rollover problems in skids). The touchdown pressure of the typical Bell 212/412 is about 170 psi. The typical tire pressure of a wheeled helo is 125 to 140 psi (the S-76 is the exception, at 165 psi for its tiny wheels). The psi of the landing gear directly measures the sinkability on soft terrain. That's why the HUMMER has a tire pressure adjustment system, and can go down to 10 psi if needed on mus or sand.

[Gainesy]

...that's why milking stools have three legs, not four. Why don't they do that for bar stools? :D

[elpirata]

Skids are for Kids !!

[Lu Zuckerman]

Every helicopter that I ever maintained had conventional wheeled landing gear. The only exception was the HTL-1 (Bell-47) that came with wheels and we changed those for floats when we went aboard ship. In many cases when landing on a small flight deck with the ship rolling while breaking ice the pilots had to land athwartship. This made the ground handling of the helicopter extremely dangerous and many times we almost lost it over the side. This particular helicopter (HO3-S) had tricycle landing gear and there were no direct acting brakes other than the parking brakes so the instant it landed we had to attach tiedowns from the landing gear to the deck. Another major problem with this landing gear setup was the possibility of getting into ground resonance during start up as the helicopter would be moving on the shock struts and the three blade system would go out of balance during start up. The problem of movement during landing was somewhat solved by placing a latticework of heavy lines across the deck. This however caused another problem and that was moving the helicopter to make room for the next one to come in for a landing. The other one was the HTL-1 on floats. To facilitate ground handling of this helicopter we used a hydraulic jacking system mounted on a dolly. The dolly had small wheels and these too would get caught up in the latticework of the lines.

The egg crate concept came a bit later and this was even worse as the helicopter could not be moved once the wheels were inside the individual boxes of the egg crate.

The Canadian Navy eventually solved the problem when they invented the beartrap system. A system similar to the beartrap was installed on the DD-963 destroyer series to facilitate both landing of the helicopter by winchdown and then translating the trapped helicopter into the hanger.

So it boils down to what works best for the application. Regarding the US Military not buying skid mounted helicopters I believe they are still purchasing the latest models of the AH1 series with skids. I think it could have been better stated that any new contract build helicopters would incorporate conventional wheeled landing gear. The last three major contracts for Army helicopters include the Apache, The Blackhawk and the Comanche and all of them have conventional landing gear.

[Nick Lappos]

Too bad Lu can't read.

The statement was "The US Army, with 7,000 helicopters in its inventory, and missions all over the world no longer will buy a skidded helo."

The AH-1 W/Z that Lu refers to is being bought by the US Marines.

The ground resonance Lu refers to is quelled by the oleos, which don't care if they are mounted on wheels or skids.

[Lu Zuckerman]

To: Nick I believe that you might be a bit wrong on what the oleos do and can’t do. If the oleos are not correctly inflated they can set up a resonant system that will allow the helicopter to move on the oleos and if during start up the three bladed system will be out of balance until it comes up to speed and centrifugal forces build up. This same situation can exist with properly inflated struts coupled with an external excitation source. A similar situation can develop if a damper is out of tune and this could result in ground resonance or even air resonance. The case I was describing the helicopter was aligned with the lateral axis of the ship. Because the ship was an icebreaker it would be rolling excessively to the left and then to the right. If it were actually be breaking the ice while rolling, the ship would also have an excitation from the bow to the stern. This combined rolling and pitching motion would cause the helicopter to rock on the struts. As the rotor system built up speed the blades would be displaced in such a way as to cause a severe imbalance. Because of the very high CG of the helicopter the rocking and pitching motion and the rocking on the struts would couple up with the imbalance of the rotor system. Another problem was that the dampers had cold soaked over night and their timing was off a bit. This problem would solve itself as soon as leading and lagging would take place but until that time the blades may not be in the same place due to the inertial loads created during startup. During this period the pilots would have to be prepared to lift off as soon as the rotors came up to speed or, sure as hell there would be a very major problem on the flight deck.

We had a similar problem with the float mounted Bell. When the helicopter was being started the flight mechanic would have to hold the blade tip in his fingertips in order to keep the blades at there mid point of teeter. The same rocking and rolling motion would apply to this helicopter on floats as it would rock back and forth and at the same time, it was bouncing on the floats. If this wasn’t done and the blades were free to teeter during start up the blade disc would whip so fast and so hard as to tip the helicopter over

[TeeS]

Approaching nine years of non-stop EMS work, so a fair proportion of real rough ground work - give me skids every time please!! Quite right that three wheels might be more stable once settled - however as you are lowering yourself gently among the surrounding boulders the wheels have a charming habit of finding the lowest spots to settle into while the aircraft skin is likely to find the highest pointy rock. Skids let you feel the 'average high spots'and if it does not feel OK you just have another go!

Also wheels sink, i've found no better combination than skids and anti-sink plates.

[Nick Lappos]

Good points, Tees, although some really nice belly clearance is also part of the right mix. 12 inches of clearance is tight, and 18+ inches is about right for rocky work. Often, wheeled helos are skimpy on belly clearance, probably a bias toward paved ramp activities worked into their assumed mission needs,

Regarding sinking, anti-sink plates on skids work very well, as do bear pads on wheels (just don't retract them!!)

[200psi]

Nick

Our tyre pressure is around the 195psi mark, is there differing pressures between the A/A+/A++/B/C model range.

Lu you must live in a 'what if' world of poor planetary alignment. Improper oleo pressures, damper alignment and ice bergs crikey why make a simple question into an unecessary diatribe. Take some oestrogen and have a good lie down. I believe we have maintenance procedures to keep things humming along.

[heedm]

One more place where wheels prevail is when you have to taxi a 21,000 lb. helicopter near Cessna 172's, R22's, people, buildings, etc. If we had to hover up to the in ground tanks, we'd be breaking things.

As far as rocks and belly clearance, we have a crew member lie down and look underneath helicopter just prior to setting down to ensure clearance. Best of both worlds.


Matthew.

[Thud_and_Blunder]

Have operated both configurations, and find it's horses for courses. The Chinook certainly wouldn't be comfortable during a running landing at 60kts on skids; the Wessex could never have been towed into our cunningly-camouflaged field hides on skids; we couldn't have shut-down at half the Jebel Akhdar (Oman) landing sites if the footprint had been as large as a wheeled heli, and the same goes here in the Borneo jungle (Blackhawk restricted to large LPs only - should've bought Seahawk :D) while B212 lands lever-fully-down on the tiniest pinnacle or arete.

Overall, unless it's for jungle - give me wheels any day. Even if the Chinook are only inflated to 88psi...

[thechopper]

To LU,
how many float-mounted Bell 47's have you experienced rolling over on start-up?

[collective bias]

Personally I've had to dive on the front of a B206 skid to prevent it toppling off the back of the truck. Wheels don't have that prob.
Wheels are easier to forget to select down. A guy in OZ even managed to cancel the 200ft warning before removing the aerials on the underside. Twice.
Skids bend. Once someone lands on uneven terrain or with the aircraft weight in the middle of the skid there is a really good chance it will stay bent in the middle. This generates stress and stress makes cracks and cracks make....
It also appears that the result of uneven load distribution through a skid would stress the airframe.
Another thought.
Why has no-one designed a manually retractable skid gear for a light turbine? Something to fold away and clean up the drag.
Race ya to the patent shop...
:D

[Fool on the Hill]

Imust admit that for operations I prefer retractable undercarriage but we also carry a crewman at all times. For training though I have to go for skids with a low belly. This increases the "1 foot bubble". the upshot of this is to make landing much more difficult for a student. They tend to slide of the bubble and overcontrol but when they do get it right you know that they can actually land a helicopter and not just plonk it on the oleos from 2-3 feet. :)

[Devil 49]

In spite of learned and persuasive argument, I'll take skids. They have a slight advantage in landing surface selection, but are quicker if the surface is a consideration. Like horseshoes and hand grenades, close is good enough for skids. I can locate within a foot on approach with no delay, and if it's softer than expected or not level, a quick slide forward will frequently get me level and stable.

[Lu Zuckerman]

To: the chopper

At the time I was working aboard the icebreaker in Greenland our two sister ships both US Navy were operating Bell HTL-5s. The HTL-5 had spring loaded teeter stops that kept the blades in the neutral teeter position until sufficient rotor speed was built up and the stops would disengage allowing the pilot to operate his cyclic. Our HTL-1s did not have this provision. Shortly before our deployment Bell issued a mod order requiring that the springs be removed from the centrifugal clutch. With the springs removed the clutch would immediately engage when the engine started to turn and in a fraction of a second the clutch would be fully engaged and the rotor would be turning over at engine speed minus the gear reduction.

That meant that our pilots and me the mechanic had no experience aboard ship with the helicopter in this modified configuration. The first few times we started we were not breaking ice and the ships’ flight deck was very stable. We did encounter the bouncing due to the turning frequency of the ships’ screws but there was no rocking. With a minimal wind speed the rotor would maintain somewhat of a median position which did not cause any problems during run up.

However when we started breaking ice and the ship was rolling left and right and pitching and heaving at the same time the helicopter would really bounce on the floats and it would also roll quite a bit on the floats. At this same time the blades would be moving all over the place. When the engine was started the blade would immediately start rotating at a high rate of speed. If the blades were teetered too far the physical action would be to move them to their neutral teeter position and this could result in a physical force that would cause the helicopter to roll over. It only took one time for us to realize that the blades had to be maintained in the neutral teeter position during start up. The Navy did not experience this phenomenon due to the spring loaded teeter stops.

To show how fast the blades rotated at start up if you did not pull your hand back after having the blade snatched from between your fingers the second blade hit your hand. Once again, it only took one time to learn the lesson. Or as they say, it doesn’t take me long to learn how to check out a hot horseshoe.

To answer your question about how many Bell 47s on floats rolled over during start up the answer is none but only because we learned from the experience. It was close but it didn't roll over although it could have.

[ 26 August 2001: Message edited by: Lu Zuckerman ]

[ 26 August 2001: Message edited by: Lu Zuckerman ]

[The Nr Fairy]

Nick :

To be fair to Lu, he did say "US Military", not "US Army".

Fair enough ?

[Thud_and_Blunder]

NR Fairy,

Actually, no - not fair enough. Lu is a bloke who's paid thousands to check details, yet he managed to put his own interpretation on Nick's message by changing 'Army' to 'military'. He tried to make an invalid point based on a factual misrepresentation. Unacceptable.

[Lu Zuckerman]

Thud_And_Blunder

I understood what Nick stated about the US Army with their 7000 plus helicopters not placing a contract for helicopters on skids. The point I made was that it should have referenced the release of a new build contract and not just they were not buying skid-equipped helicopters. The three major contracts released by the Army were the Apache, Blackhawk and the Comanche, all of which have wheeled landing gear. I believe that during both the Apache and Blackhawk programs the Army was still purchasing Bell Cobras either for their use of for the National Guard or, for foreign military sales. The Marines did continue to purchase variants of the Cobra as Nick had indicated.

Here is a related trivia question: What was the last contract released to Bell from the military to build a helicopter from the ground up?

[helmet fire]

Give me skids for operating to jungle platforms and training, but wheels for nearly everything else, especially one that has not been mentioned - dust landings. Not really an option on skids. Wheels definitely for ship landings. The smaller the machine, the more practical are skids. I didn't think you could go past the non retractable gear on the UH-60 for being able to take punishment - something like 10G capable before requiring a heavy landing inspection (I am really stretching the memory here, can you help Nick?)

Lu: you were saying that: >>As the rotor system built up speed the blades would be displaced in such a way as to cause a severe imbalance<<
and: >> If the oleos are not correctly inflated they can set up a resonant system that will allow the helicopter to move on the oleos and if during start up the three bladed system will be out of balance until it comes up to speed and centrifugal forces build up<<.

I thought that the rotor system was always in (or near to) static balance, and was irrespective of revolution speed (RRPM). Vibrations on the other hand are significantly affected by factors such as airspeed, loading, and in particular, RRPM. The effect of RRPM was because resonance is the manifestation of a harmonic, and a harmonic is excited or damped by relative natural frequencies which are determined (in part) by revolution frequency (RPM). That is why when encountering ground resonance, the thing the pilot can change is RRPM to try and avoid it (he cant change other fixed factors such as the shaft mass/lengths/lead lag dampers/oleos, etc), or he can attempt take off to eliminate the effect of the landing gear frequency excitation. Remember that oleos are present on skid type machines and also make them susceptible to ground resonance when improperly maintained.

Lastly, we used to hold the blades of B205 & B212 during start up when windy to reduce the possibility of blade sail and subsequent mast bump during low RRPM states. Never thought of it for ground resonance, how did it help?

[Roofus]

Hi peeps!

I reckon alot depends on personal preference & what you're doing with the Heli.
In the Navy & on the North Sea, wheels were essential! Some of my deck landings would have resulted in a very bad back if I'd had skids! :D
I now fly Police & have to say that I believe skids are the way to go! Alot of the landings we do are no-where near a prepared surface, as such I like the fact that the skids instantly transmit (through me seat) what's happening underneath.
I'm no boffin, so I don't know the facts & figures but I've never sunk yet with skids but have sunk with wheels. I accept the arguement about bear feet (thingies) on wheels alleviating that problem, but then they're hanging down creating drag etc anyway.
But hey, each to their own! :D

[MightyGem]

Hi Roofus, don't get too complacent. We had a lynx land on a slop at an exercise location in Germany many years ago. When the crew returned the downhill skid had sunk putting the aircraft past the limits for sloping ground. It took a long time to dig out under the uphill skid to put it back in limits!
:)

[4Rvibes]

Mighty Gem,
What about the London HEMS machine (AS365)which landed on the top of a public park hill only to be found at the bottom of said hill when the crew returned to it with the patient. The brake accumulator does bleed off after a wile you know. Skids don't have that problem. :rolleyes:

[Lu Zuckerman]

To: helmet fire

There were actually two different problems described and both problems had a common thread. That thread was the movement of the ship during the breaking of ice. Under the icebreaking condition the ship was made to heel left and right by shifting water ballast and at the same time water was pumped forward and aft. This imparted a rolling motion. If you can imagine a disc that is spinning and then loses momentum and it starts to roll on its’ edges until it finally stops. It is this final rolling motion that that best describes the action of the ship. This motion is further exacerbated by the vertical movement of the aft end of the ship (where the flight deck is located) caused by the screws and the major vibration imparted during the ice breaking process.

In the first instance the helicopter is mounted on tricycle landing gear and it is disposed over the lateral axis of the flight deck. The movement of the ship causes the helicopter to pitch and roll on the oleo struts and some sideward movement on the tires (tyres). When the rotor is brought up to speed the blades will due to inertia hang back on the dampers. With the blades not being in a 120-degree relationship with each other the system will be out of balance. The design of this helicopter S-51 (HO3-S) placed the cg very high. This imbalance would further exacerbate the rolling motion caused by the ship and the helicopter could possibly go into ground resonance. That is why I stated that the pilots had to be prepared to lift off as soon as rotor rpm had built up.

In the case of the Bell HTL-1 the helicopter could be aligned with either axis of the ship. Under icebreaking conditions the helicopter would bounce on the floats and would also shift position on the deck caused by the constantly changing side loads on the floats. It did not move from one position to another, it just moved from side to side as the floats rolled in relation to the flight deck.

Ground resonance although not a major problem was still possible. The first time we fired the helicopter up under icebreaking conditions the blade was free to teeter. With the springs removed from the centrifugal clutch as soon as the engine started the rotor would start rotating. The first time under these conditions the blades were at their maximum teeter angle and when they started to rotate they tried to position themselves at the neutral teeter position and the forces generated almost tipped the helicopter over. After that, we held the blades in the mid position during start up. Mast bumping was not a problem with this rotor system as they had Sprague cables that limited the rotor movement in relation to the teeter axis.

[MightyGem]

Obviously forgot the chocks then.

[VLift]

"oleos" will contribute to ground resonance. It's a constant consideration on the 269 and has been since 64' when the U.S Army started buying them.

If the Thrust Control Rod was not down in it's proper position in a CH-47 with non-proportional ECLs before going to flight with the ECLs, and a strut was not properly serviced, you could get a real ride till the blades got in sync.

A wheeled aircraft in rough enough terrain can be like a table in a restaurant with one short foot extension. Hard to stuff enough napkins under the wheel.

Skid gear, on the other hand, tend to sit on the high points, when there are enough of them.

Give me wheels to taxi around the airport.

[Vfrpilotpb]

Hey Roofus,

was that your thingy in the Daily Mail today?
Sorry, had a bad day!

:D

[Guinevere]

It would appear that wheels have the majority vote, however what is the preferred configuration, nose or tai-wheel and why?

For my part, a tail wheel wins every time if you are in a hurry and don't want to mince about in a LZ.

[64av8or]

To echo Elipatra, skids are for kids and wheels are for real!!
Resonance is a sensation to be enjoyed, just like pain! :D

[Harry (Snapper) Organs]

My five cents - I prefer wheels. Better on rocky ground, and allow flexibility for running landings when OEI. The tailwheel config is the only config I have been exposed to, but it is great for fast approach and landing using aerodynamic braking with the tailwheel pinned (mil tac ops). Oleos with a long stroke can absorb vertical impacts and help save your back at the bottom of an auto. I suppose skids are a fair bit lighter though, which is better for smaller helicopters.

[Arm out the window]

Skids don't go flat that often though!

[Thomas coupling]

TeeS: agreed, skidded are the best for emergency work. Our terrain lends itself to skids for the foll reasons:

massive ground clearance to take all our extra belly pod equipment. Less chance of smacking it!

Skids find an even datum after settling in sand (beach) unlike wheels where one of them might decide to dig down deeper!!

Better for a more stable line of contact while emplaning/deplaning, whereas a single point of contact on one wheel makes life a little harder to judge!

No worries re ground resonance!

Harder to pick up the helo to store in the hangar with wheels.

Smack a skid (hard) and you've still got a reasonable chance of securing a landing later on, damage one of the wheels and you've possibly got a major incident on your hands??

Apart from that very little in it....sorry NL. :D

[Nick Lappos]

Vlift said:
"oleos" will contribute to ground resonance. It's a constant consideration on the 269 and has been since 64' when the U.S Army started buying them.

Nick sez:
Gosh, vlift, the oleos prevent ground resonance! If you think they cause it, we'd just remove them!! Please don't try that, you won't get one complete rotor engagement before the parts made terrible noises and scattered across the ramp.

[Flight Safety]

Nick, Vlift is correct about the 269, although perhaps he should have said "improperly serviced oleos".

Here's a link to an NTSB report on the destruction of a Schweizer 300C (based on the 269) due to ground resonance, that had improper pressures in the skid dampers.
http://www.ntsb.gov/ntsb/brief.asp?ev_id=20001207X03924&key=1

[Thud_and_Blunder]

Just thought of another advantage for skids:

Ever imagined 3 abseilers per side trying to balance on one wheel?

[Nick Lappos]

The point is that oleos do not CAUSE ground resonance! They are specifically used to prevent ground resonance, so if you are dumb enough to allow them to go mis-serviced, you might get ground resonance.

THe little boy was standing on the corner shouting "No Elephants!" The man asked him why, so he said, "I want to chase the elephants away." The man said, "But there are no elephants anywhere close to here!" to which the boy responded, "See, it works!" ;)

[Roofus]

Lot's of interesting stuff being written here! But surely there is no right answer. 'Each to their own' as they say.

I do know one thing....wheels wouldn't have helped, the way the skids did, in my little mishap! :D

[Lu Zuckerman]

To: Nick Lappos

What you said about properly serviced oleo struts preventing ground resonance is not always true. In the icebreaker illustration I provided above the struts were properly serviced and they were doing what they were supposed to do when exposed to the externally applied loads caused by the rolling motion of the ship. The helicopter in question was an S-51, which has a very high CG, and it is mounted on tricycle landing gear. Any externally applied load will cause the helicopter to rock/roll on the struts and even though the wheels are up to pressure there is a rolling motion reacted by the tires. The rotor system has independent flapping and lag hinges similar to the heads on the CH-47. As the rotor is brought up to speed the blades will hang back and not being equally disposed at 120-degrees there will be an imbalance in the rotor system until it is brought up to speed. It was during this transitionary period that the out of balance rotor system and the movement of the helicopter on the struts would interact and exacerbate the situation. Because of this we could not keep the helicopter tied down and the only thing keeping it in place were the chocks on the three wheels. If the condition did not worsen then the pilot would keep it on the deck until released by the ships Captain. If the condition did worsen the pilot would immediately lift off to break contact with the rolling deck.

Elephants can be chased away using the method you described but penguins can not be chased from you mind. For the rest of the long weekend try not to think of penguins.

[Nick Lappos]

Lu said:
(Nick)What you said about properly serviced oleo struts preventing ground resonance is not always true. ......... Any externally applied load will cause the helicopter to rock/roll on the struts and even though the wheels are up to pressure there is a rolling motion reacted by the tires. .......Because of this we could not keep the helicopter tied down and the only thing keeping it in place were the chocks on the three wheels...

Nick sez:
Few things are ALWAYS true (except gravity.) But the belief that oleos cause ground resonance is ALWAYS incorrect, and also the belief that your scenario has something to do with oleos is mistaken.

The aircraft as a system relies on all the ways it receives forces externally to quell its dynamic response. We have had this go-around before, Lu about dynamic (oscillatory) behavior, so I will only write this once, regardless of how many ways you work it around in the interminable posts to come on this subject.

Your shipboard example proves my point, because you had the aircraft tied down. The tiedowns change the oscillatory response of the whole system, and make ground resonance more likely. All Navy folks know this, we even stencil it on the side of the aircraft next to the tie down rings!

The oleos PREVENT ground resonance, virtually ALL the time, that's why they are used. They are really shock absorbers, just like a car's (which prevent the car from bouncing uncontrollably when a bump is hit). Of course if the oleo is broken or impropoerly serviced it won't do its job - if you are improperly serviced, you won't do your job either.

IF THE AIRCRAFT IS TIED DOWN, ground resonance might occur. This has NOTHING to do with oleos, Lu, it has to do with a crew preventing the oleos from doing their job.

Gosh, I wish you could stay on topic, and not use unserviced parts or tied down scenarios to confuse the group. Of course, I wish I'd win the lottery so I could buy my own S-76, but that's a pipe dream, too. ;)

[Lu Zuckerman]

To: Nick Lappos

Because the helicopter was moving on the struts due to the pitching, heaving and rolling motion of the flight deck we could not tie the helicopter down to the deck. As I stated in a previous post it doesn’t take me long to check out a hot horseshoe (Learning by experience). Originally we kept the helicopters tied down until they were ready to lift off but the one time we did it and the ship was rolling and pitching and heaving we almost lost the helicopter when the pilot was forced to lift off. Luckily, I was able to release one of the tie downs and my assistant mechanic hit the cable release on the other and the pilot was able to free himself from the moving deck. He came up hard when the cable extended to its’ limits and if he tried to move up or sideways any further he would have crashed on the flight deck.

[tacr2man]

Hi, what are pro's and cons of wheels ala 222 versus skids ala 206 , having never operated a wheeled undercarriage on a heli ? :confused:

[Matari]

tacr2man:

Not sure you'll get any better response than the three pages already posted on this thread. Between Mr. Lappos, Mr. Zukerman and the rest, you've got a lot to digest here already!

[JohnDixson]

Just two observations from early Blackhawk/S-70 days:

1. The Army had done considerable study work prior to letting the UTTAS Request for Proposal out, and had concluded that for a helicopter of that size, wheels were the better solution. A Col Bud Patnode was in charge of this work, and he relayed that the discussions often became heated with the " if its on the Huey, its perfect" community.
2. Qualification testing of that aircraft recognized that if one has tires and struts maintained by humans, they will inevitably become improperly serviced at some point. Therefore, mechanical stability ( ground resonance ) testing was done at various CG's and Weights with a matrix of mis-serviced tires and struts. My recollection was that there was no tendency to self induce ground resonance except at full aft CG somewhere about 50% airborne, and with the cyclic almost full aft, just producing light droop stop contact ( brakes had to be on, and all in all, this is a pretty unusual state to be in ) . One had to wait a half minute or so before the ship would start off at 2/3P. ( this was on level concrete, a condition considered more conducive to ground resonance than softer ground ).

Thanks,
John Dixson

[ivakontrol]

........and I thought wheels v skids was all to do with the weight of the machine.:confused:

[TeeS]

Wheels in Summer!

http://i51.photobucket.com/albums/f369/TeeS12/Sunken109.jpg

Winter should be fun then!

TeeS

[Matari]

As long as we're on the subject, one thing I've always wondered: why are the Lynx rear wheels aligned "toe-out"?

I assume it makes for more stable shipboard ops...no sliding on deck etc.

But what about ground handling? Is there a pilot-activated electrical / mechanical device to re-align the wheels straight-parallel for ground taxi, etc?

[Flying Bull]

Hi Matari,

the Navy Lynx wheels are turned that way by a mechanical device by man.
The nose wheel can be castored to 90 degrees, allowing the Lynx to turn on the deck around the harpune securing it to the deck.
So starting/landing into wind is possible without turning the ship.


ucugXX6p43Y



look about 1min10
Running landing is still possible - evenso some rubber stays on the tarmac.

Greetings Flying Bull

P.S.
If you fly with wheeled helicopters, you might have to put the wheels on hard ground to prevent sinking in
http://cdn.fotocommunity.com/photos/13023069.jpg
http://www.fotocommunity.de/pc/pc/extra/egallery/pcat/367917/display/13023069

[Matari]

Flying Bull:

Impressive!

Thanks,
Matari

[CGWRA]

You wouldn't want wheels anywhere I've flown so far.

[jessie13]

From a maintainers view, skids - very little maintenance required but a bugger to tow the aircraft. Wheels - easy to tow aircraft but a lot of maintenance required! Just reading the responses so far and maintaining that perfect strut pressure can take a lot of effort. Dealing with punctures in the field can be fun. Replacing tail wheel lock pins because the pilot forgot to unlock during taxi can be stressful. Bleeding breaks, servicing struts, and pumping up tyres - boring. Undercarriage retraction and emergency blown down tests - exciting. Mixing up the pressure line for the brake and undercarriage jack on a Sea King sponson - spectacular!