Help! Need a Bit of Technical Input - DC-3 Landing Gear vs. A380

[V2-OMG!]

Hi - our photography/research class was given an assignment. We are supposed to take a photo of something old and something new, then write a paragraph about each.

My photos are landing gear - a DC-3 and A380.

There are so many knowledgeable people here. Could I please have some input as to how the DC-3 landing gear compares to the A380?
It does not have to be technically exhaustive, but any input re: design features and operational specs like back-up deployment etc. would enhance this project.

Thank-you.

[Old Fella]

As the saying goes "A picture is worth a thousand words". The comparison should be obvious, especially to an aviation geek and aviation magazine editor !!!

[V2-OMG!]

Wind-up? Who has time for a wind-up?

I am just trying to make a decent request for help.

[etudiant]

There is a plethora of stuff available online on both topics.
A Bing search provides photos, texts and links to multiple sites and technical details, way more than is needed to write a paragraph.
So what is the help that you are requesting? Is it personal anecdotes or details of operating experience with these products?

[John Farley]

The DC3 undercarriage design was typical of a 1930s design and relatively simple. The A380 being very heavy could potentially damage runway surfaces unless its weight was distributed over the runway surface. Hence multiple wheels were needed.

[Metro man]

IIRC The DC3 undercarriage was held up by hydraulic pressure and would extend in the event of a loss.

[MarkerInbound]

The hydraulic system in a DC-3 is a simple 900-1000psi system. There is a system pressure gauge and a "gear down line" pressure gauge. The landing gear lever is simply a ~18 inch extension from the landing gear selector valve and is located below and behind the First Officer's left arm rest. There is no modern symbolic tire at the end of the gear level as is found on modern airplanes. As stated above the gear is held up solely by trapped hydraulic pressure. On some aircraft it could become necessary to re-retracted the landing gear if gear down pressure started building over time. In the event of a loss of hydraulics the landing gear will free fall when the trapped pressure is released.


The gear is held down in the down position by trapped hydraulic pressure and a mechanical safety latch which holds the gear linkage to the aft end of the wheel well when the gear is extended and the safety latch is engaged. The safety latch is controlled by a short lever on the floor just inboard of the Captain's seat. So retracting and extending the landing gear is a multi-step process. To retract the gear you first rotate a clip at the end of the safety latch lever 90 degrees forward so it is no longer holding the safety latch lever to the floor. You then raise the safety latch lever to a 45 degree position from the floor. The safety latch lever also controls a dog and shoe on the landing gear selector valve so now you can raise the landing gear lever to retract the landing gear. When climb power is set you move the landing gear lever to the "OFF" position. When the landing gear lever is moved to OFF the safety latch lever drops to a ~20 degree position off the floor.


Extending the gear is the reverse. Move the landing gear lever to the down position. When the gear down line pressure and the system pressure gauges match and you have a green light return the gear lever to the OFF position. You can look out the window to confirm that landing gear is down. You then push the gear safety latch lever down flush with the floor and flip the clip up over the end to hold it down.


There is a lever on the bottom of the throttle quadrant that when moved aft raises a yoke or collar off a pin on the shaft that the tailwheel rotates around and allows the tailwheel to swivel freely. In the forward position the yoke will drop and catch the pin when the tailwheel is straight and lock it in position.


I know nothing about Airbus landing gear systems.

[Vinnie Boombatz]

Airbus A380 Specs - Modern Airliners (http://modernairliners.com/airbus-a380/airbus-a380-specs)

"The 22-wheel Goodrich landing gear consists of two under-wing struts each with four wheels, two central under-fuselage struts each with six wheels and a twin nose wheel. Each landing gear supports about 167 tonnes. Messier-Dowty supplies the nose landing gear with 350bar hydraulic pressure and Messier-Bugatti the braking and steering systems. Smiths Aerospace supplies the landing gear extension and retraction system. The load on the airport runways and aprons are of similar magnitude to that of a 747. "

"Maximum Take-off Weight 560,000 kg (1,234,600 lb)
Maximum Landing Weight 386,000 kg (850,984 lb)"

http://www.sandv.com/downloads/0811obse.pdf

"The six-wheel landing gear system weighs approximately 12,000 pounds, and its size exceeds 25 feet when fully extended."

http://faculty.dwc.edu/sadraey/Chapter%209.%20Landing%20Gear%20Design.pdf

"In general, the landing gear weight is about 3% to 5% of the aircraft take-off weight."


https://en.wikipedia.org/wiki/Airbus_A380

https://en.wikipedia.org/wiki/File:Airbus_A380_Fahrwerk.jpg

Ref 216 in the Wikipedia article is now here:

https://www.flightglobal.com/news/articles/flight-test-airbus-a380-209189/

A380 data from Airbus:

http://www.airbus.com/fileadmin/media_gallery/files/tech_data/AC/Airbus-AC-A380-Dec2014.pdf

Airbus A380-800F Wide-Bodied Freighter - Aerospace Technology (http://www.aerospace-technology.com/projects/airbus_a380/)

"Goodrich has been contracted to supply the two six-wheel under-fuselage landing gear and the two four-wheeled wing-mounted landing gear. The wing-mounted landing gear is slightly forward of the fuselage-mounted gear. The wheels on the main landing gear are fitted with carbon brakes.

The twin wheel nose landing gear is supplied by Messier-Dowty. The steering control is via the nose gear and via the rear axle of the fuselage landing gear. The gear allows u-turn manoeuvres on a 60m-wide runway."

Machinery Features Articledetailaspxarticleid=3903 | Machinery (http://www.machinery.co.uk/machinery-features/a380-landing-gear/3903/)

"Messier-Dowty, Bidos, France has delivered the first test A380 nose landing gear to Airbus UK, Filton. At 4.8 m tall when fully extended, it is the largest landing gear ever supplied by Messier-Dowty to Airbus "

DC-1 DC-2 DC-3 C-47 Dakota Aircraft (http://www.dc3history.org/dc3.htm)

"Max. gross weight: From 25,000 lbs (11,340 kg) to 36,800 lbs (16,692 kg)

Height: DST & Std. 16 ft, I I in (5.16 m)"

The A380 nose gear is slightly shorter (36 cm) than the max height of the whole DC-3.

The total landing gear weight for the A380 is probably greater than the max gross weight of the whole DC-3. Note that the 12,000 lbs quoted above is for a single 6-wheel body element of the full landing gear.

The max gross weight of the A380 is about 33.5 times that of the DC-3.

The DC-3 Hangar on douglasdc3.com DC3 C47 C-47 (http://www.douglasdc3.com/index.html)

DC3specs - The Business of Funding and Flying a Plane (http://www.douglasdc3.com/dc3specs/dc3specs.htm)

"Height 16ft 11½in "

tech (http://www.douglasdc3.com/tech/tech.htm)

dc3tec (http://www.douglasdc3.com/dc3tec/dc3tec.htm)

http://www.eliteflightservices.com/pdf/GTM-14-050130-LGearBrakes.pdf

[Greek God]

IIRC the DC3 gear didnt fully retract so in the event of a gear up landing the tyres would still rotate.

[pattern_is_full]

....and probably more importantly, would prevent the aircraft weight from settling on, and damaging, the nacelles. Pick it up, dust it off, and start all over again.

What's probably most newsworthy about the comparative technology is how little it changed, in the gross details, over 70 years. Hydraulic folding things, with angled stabilizing struts, and changes in orientation to accomodate fitting into different parts of the aircraft. The one major conceptual change is that the A380 main gear can steer a bit, to accomodate the long wheelbase.

[stilton]

Still find it odd that AB elected for a bogie design that trails forward.


This is a very unforgiving configuration on landing.

[V2-OMG!]

Thanks to those who didn't think this was a "wind-up."

The fact is - I do edit a small vintage aviation rag - but know little about aviation. They gave me the position (I am not paid for it) because I have an ability to compile information, then deliver it in a way that is enjoyable (hopefully) to the professional and layperson alike.

I have a question: were the DC-3 tires filled with air or nitrogen?

[V2-OMG!]

So what is the help that you are requesting? Is it personal anecdotes or details of operating experience with these products?

etudiant, some anecdotes or operational details would certainly add interest. If you have any, please share!

[Metro man]

The DC3 needed to be landed on the main wheels first, three point landings could be done but could easily break its back.

The tailwheel could be locked to assist in directional control.

[Capt Claret]

How bloody sad that a question can't be asked and answered without the smart arse assumptions.

I commend you OMG for keeping your cool and not biting back.

[Avtrician]

As I recall, the DC3 tyres were filled with air. They wernt heavily stressed on take offs and landings so no high temperatures to worry about. Also, when they were designed, I dont think nitrogen was so easy to come by, but there was lots of air.. :)

[MarkerInbound]

....and probably more importantly, would prevent the aircraft weight from settling on, and damaging, the nacelles. Pick it up, dust it off, and start all over again.

The props would be folded back and if that happened under power it's an engine change. I remember a conversation with an old mechanic who said from maintenance's perspective it would be best to land gear up with the props windmilling. Then two tips would be folded back and they would have to run out the crankshaft but if it passed the test the engine would be considered good. If the prop was feathered the landing force could be transmitted along the cord of the prop and rip the engine off the firewall.

[Sailvi767]

It was my understanding that they always used 80% nitrogen when filling DC3 tires.

[peekay4]

Filling tires with > 95% nitrogen is only required for aircraft with a maximum takeoff weight of over 75,000 lbs. (Per 14 CFR 25.733).

That's because heat from the extreme braking energy on heavier aircraft could cause the tire to release volatile gasses. These gasses could cause the tire to violently explode when combined with oxygen inside the tire at high temperatures.

So on heavier aircraft it is important to remove the oxygen from the tires, replacing it with an inert gas (such as nitrogen).

DC-3 with MTOW of around 26,000 lbs: regular air ok (78% nitrogen, 21% oxygen).

A380 with MTOW of about 1,200,000 lbs: dry nitrogen or other inert gasses (must be < 5% oxygen)

[Derfred]

Still find it odd that AB elected for a bogie design that trails forward.

This is a very unforgiving configuration on landing.

That is a myth.

[stilton]

Fourteen years on the 767 now and I can assure you its no myth.


Have you operated an aircraft with a landing gear of this design ?

[Old Fella]

CC, if your comment was aimed at me you may like to have another look at the heading of my post. I asked if it was a Wind up, no more or less.

[Yonosoy Marinero]

Fourteen years on the 767 now and I can assure you its no myth.

Right. Blame the tools...
:}

[Chris Scott]

Quote from MarkerInbound (my emphasis):
"The gear is held down in the down position by trapped hydraulic pressure and a mechanical safety latch which holds the gear linkage to the aft end of the wheel well when the gear is extended and the safety latch is engaged. The safety latch is controlled by a short lever on the floor just inboard of the Captain's seat. So retracting and extending the landing gear is a multi-step process. To retract the gear you first rotate a clip at the end of the safety latch lever 90 degrees forward so it is no longer holding the safety latch lever to the floor. You then raise the safety latch lever to a 45 degree position from the floor. The safety latch lever also controls a dog and shoe on the landing gear selector valve so now you can raise the landing gear lever to retract the landing gear. When climb power is set you move the landing gear lever to the "OFF" position. When the landing gear lever is moved to OFF the safety latch lever drops to a ~20 degree position off the floor."

That's a very neat description, if I may say so! Rather better than I was given in my type conversion. For young aviators: very important to raise the safety latch fully, as it's fairly stiff and quite a long reach from the right-hand seat, positioned as it is on the floor under the skipper's right elbow. The landing-gear lever (behind and below the co-pilot's left elbow, as MI writes) consists of an aluminium tube over a foot long and about an inch in diameter, usually fitted with a rubber hand-grip on the free end. My second P2 flight of a C-47 Dakota on the line was a heavily-laden night take-off (0430 hrs). The combination of my failing to raise the safety latch enough, followed by a degree of desperation on my part, and a L/G lever that had a circumferential fatigue crack near its pivot point led to a very interesting result...

[Tu.114]

A short question on the side, if I may.

When a fresh tire is taken from the store and installed on a rim, it is obviously initially filled with ambient air at atmospheric pressure. How is the air flushed out and replaced with pure nitrogen? Is it inflated, deflated and again inflated until mathematically only minuscule traces of oxygen are left; will simply pressurizing it to the required value with pure nitrogen do, or are there any other methods used?

[D-OCHO]

The main reason for the Nitrogen is that Nitrogen molecules are bigger then all the molecules that make up regular air. (Yes including O2 and H2O)
Fill a tire with Nitrogen and it will stay pressurized longer then when you fill it with regular air.
This is especially handy in the low pressure situations that aircraft are in when flying. You will still have pressure in you tires before landing.

[Chris Scott]

Hi Tu.114,
"When a fresh tire is taken from the store and installed on a rim, it is obviously initially filled with ambient air at atmospheric pressure. How is the air flushed out and replaced with pure nitrogen? Is it inflated, deflated and again inflated until mathematically only minuscule traces of oxygen are left; will simply pressurizing it to the required value with pure nitrogen do, or are there any other methods used?"

Now why didn't I ever think of that? In expectation of being corrected by someone who does it, however, I think your second idea might suffice, because of the high tyre pressures used in the kind of a/c we are talking about. To take a fairly modest example, 180 psi, that's roughly 12 times ambient if the inflation is being done at sea-level. After inflation, once the temperature has returned to ambient and the desired 180 psi (differential above ambient) is achieved, I reckon the mass of nitrogen inside would be about 13 times the 0 psi mass. As ambient air is only about 20% oxygen, that would suggest that the oxygen content would now only represent about 1.5% of the gas content of the tyre.

In the case of a car tyre at, say, 30 psi, I reckon the mass of nitrogen would be only about 3 times the 0 psi figure. But the higher percentage of oxygen remaining is probably not a problem in that application (see below).

Quote from D-OCHO:
"The main reason for the Nitrogen is that Nitrogen molecules are bigger then all the molecules that make up regular air. (Yes including O2 and H2O)
Fill a tire with Nitrogen and it will stay pressurized longer then when you fill it with regular air."

I'm sure you're right about the lower leak rate, but my understanding is that the main reason is to prevent the kind of oxygen-fuelled tyre explosion that brought down a Swissair Caravelle shortly after take-off from Geneva in about 1966. IIRC, before take-off in fog the a/c had taxied at a high power setting along the length of the runway, using continuous braking, in an attempt to raise the RVR to the minimum requirement for take-off. But there are many other causes of overheating tyres.

[tdracer]

The main reason for the Nitrogen is that Nitrogen molecules are bigger then all the molecules that make up regular air. (Yes including O2 and H2O)
Fill a tire with Nitrogen and it will stay pressurized longer then when you fill it with regular air.
This is especially handy in the low pressure situations that aircraft are in when flying. You will still have pressure in you tires before landing.

This is definitely a myth. The O2 molecule (molecular weight 32) is actually larger than the N2 molecule (molecular weigh 28). This one is right up there with the myth that if you fill your tires with nitrogen, the pressure won't increase when they get hot (I've heard that one a lot in the racing world, apparently they think that nitrogen doesn't conform to the ideal gas law) :ugh:

[peekay4]

Tu.114 & Chris: I believe you are right, new aircraft tires are simply inflated using nitrogen initially.

tdracer: You're conflating molecular weight and molecular size (kinetic diameter). N2 weighs less than O2, but N2 is (very slightly) larger in size than O2.

However, I agree that the effect on leak loss is likely negligible for all intents and purposes.

For racing, using nitrogen can indeed reduce pressure fluctuations.

If you fill tires with regular air then you're subject to whatever humidity level is in the ambient air at the time. On humid days this can result in a lot of water vapor in the tires.

At race speeds, the tire's internal temperature can rise to more than 100 C, the boiling point of water. This causes the water vapors to expand rapidly and the tire pressure can increase significantly. Hence the use of dry nitrogen instead of regular air.

[Chu Chu]

Not sure why water vapor would expand greatly at 100 Celsius, but any liquid water that had condensed in the tire surely would vaporize and expand hundreds of times. Also, water tends to condense in air compressors and get into air lines, so the fill air could have a lot more water than the ambient air. (It could also have less.)

Another advantage of nitrogen is that it reduces oxidation. Not just the explosive kind, but the gradual kind that causes rubber to deteriorate over time. How big a factor that is in overall tire life, I don't know.

[tdracer]

but any liquid water that had condensed in the tire surely would vaporize and expand hundreds of timesThanks Chu Chu - that is the essence of numerous arguments I've had with fellow racers. There is essentially no difference between DRY air and DRY nitrogen. If you pick up a tank of compressed gas from the local compressed gas vendor, it is almost certainly 'dry' since that is part of their bottling process - nitrogen is popular because it's readily available as a byproduct of producing bottled O2. And even when you throw H20 into the mix, it only comes into play if there is enough moisture that it changes state - in which case of course the effect can be huge (which is rarely the case). The funny part is I've watched guys spray 'soapy water' all over the bead and rim to help seat the bead when mounting tires, then brag about how using nitrogen will prevent the tire pressure from changing as the tires heated. :ugh:Oh, and unlike aircraft tires which are inflated to around 200 psi, we typically ran around one bar pressure - in which case whatever was inside the tire prior to beading was a significant percentage of the total. :ugh:


Peekay, I talked to a chemist buddy, and at least according to him, unless the Oxygen was "ionized" (missing electrons), the O2 molecule would 'act' larger than the N2 molecule when it came to passing through other materials. N2 and O2 are basically symmetrical molecules so their molecular weight does closely relate to their size (H2O, being highly asymmetric, does act much differently than what it's molecular weight would suggest).

[peekay4]

And even when you throw H20 into the mix, it only comes into play if there is enough moisture that it changes state
I don't think so.

Per Dalton's law, the total pressure for moist air is the sum of (dry air partial pressure) + (water vapor partial pressure)

The individual partial pressures can be calculated from the gas law in molar form:

pV = (m/M) R T

where m is the mass and M is the molecular weight and R is the ideal gas constant.

In other words, the rise or fall of the partial pressure relates to the inverse of the gas molecular weight. Or, equivalently, proportional to R/M, which is the specific gas constant.

Water vapor has a molecular weight of 18.02 g/mol. Dry air = 28.96 g/mol.

Water vapor's specific gas constant is 461.5 J/(Kg K), dry air = 287 J/(Kg K).

So we can see, given the same rise or fall in temperature, the water vapor partial pressure will change (461.5/287) = 1.6 times faster than the partial pressure of air.

Typical "dry air" sources available track side still has a lot of moisture in it.

Oh, and unlike aircraft tires which are inflated to around 200 psi, we typically ran around one bar pressure - in which case whatever was inside the tire prior to beading was a significant percentage of the total.

For racing applications, the air in the tires are typically removed (towards but above vacuum) before nitrogen is added, to achieve better than 95% Nitrogen, same as in aviation.

[tdracer]

Typical "dry air" sources available track side still has a lot of moisture in it.
For racing applications, the air in the tires are typically removed (towards but above vacuum) before nitrogen is added, to achieve better than 95% Nitrogen, same as in aviation. Pretty severe thread drift here, but even on a really hot day with 100% humidity, you're only looking at ~1% water vapor content - so 1.6 times 1% at one bar means that my H2O vapor saturated air hot tire will increase in pressure about a tenth of a psi or so more than if I used absolutely dry nitrogen. Pretty much in the mud.

Granted, my racing was amateur, not professional, but I never, ever saw "air removed" from tires after beading prior to inflation (and I'm talking hundreds, if not thousands, of tire mountings). I did however, on a regular basis, see soapy water used as a lube to seat the bead. Some of us used a water-free compound to lube the bead to allow it to seat (the stuff I used was called "Tire Snot") but we were not in the majority (although we did tend to run up front). Most of the time, the pressure required to set the bead was higher than the running pressure so they simply bleed the tire down to something close to the desired running pressure. On occasion, the tire valve was removed and all pressure allowed to escape, then the valve installed and the tire inflated to the desired pressure.
Not only did I never see a vacuum used to evacuate the tire, I never even saw the needed equipment to do it. And again, my point has always been there is no meaningful difference between dry air, and nitrogen when it comes to how tire pressure behaves. Racers use nitrogen because it's cheap and readily available, not because it's better than dry air.

[Chu Chu]

Peekay,

I have to say that I don't get it. pV = (m/M) R T gives you the pressure at a given temperature, not the change in pressure. If you had two identical flasks, and filled one with water vapor and one with dry air, the pressure in the first would be higher. No surprise there -- water is less dense, and therefore a given mass has to be compressed more to fit a given volume.

But (m/M) in your equation doesn't change with temperature. R, of course, is also constant, and the volume of a tire (V) we can also assume is constant. So if you double the absolute temperature (T) in your equation, pressure (p) has to double as well -- none of the other numbers change. And that's true whatever the value of (m/M) is.

It is true that neither water vapor nor air is an ideal gas, and they probably do expand at somewhat different rates. But it isn't as simple as a ratio of molecular weights, and I'm virtually positive the difference is much less profound.

[peekay4]

The ratio in pressure between the two flasks will be the same. But the absolute amount of rise or fall in pressure within each flask will not be the same.

It's basically a simple linear equation, y = mx + b. If you have two lines at two different slopes (assuming same intercept), then at any given x the ratio of y between the two lines will remain the same, but obviously one would rise/fall faster than the other. Here (m/M) is the slope aka derivative or rate of change.

But in general I would agree with you guys that if there's liquid water -- due to condensation or sloppiness -- then that would be the dominant factor, barring extreme temperature & humidity conditions.

[Tu.114]

ChrisScott, thank You, that makes sense. Filling the tire from its air-filled initial state and thereby diluting the 1/5 of oxygen with massive amounts of nitrogen will reduce its amount below what is required to sustain a combustion.

[V2-OMG!]

Hey! I studied this thread, made some notes, wrote my piece, it was published, and what do you know - I ran into an Emirates A380 Captain who had read it and complimented me for "nailing the A380 landing gear."

I stood there smiling and thinking.....wait til the Ppruners hear about this! Thank-you! Thank-you! Thank-you!

p.s. I'm am not paid for these literary jaunts, but if I were, I'd buy you all a beer.