# Is there a good reason why modern airliners can't have conventional landing gears (vs. tricycle landing gears)?

By "good reason", I mean a reason that we definitely cannot overcome with reasonable changes in aircraft design, control laws or procedures.

As possible benefits of this I see a much smaller (= lighter) tail landing-gear than the nose landing-gear. Also, an opportunity to reduce tail-strike margins (=increase incidence, reduce landing speed). And of course there is all that space at the front of the fuselage that is freed for other uses (systems, cargo, stairs,...?)

One drawback is of course passenger comfort. But passengers already experience high pitch angles during climb, and we could imagine to have the tail of the aircraft raised up (on a stand?) for boarding/deboarding. Also the APU has be moved (but I don't think this is impossible).

• – Federico Jul 17 '15 at 8:40
• I suspect you would find out one reason when trying to keep straight whilst braking hard on a rain-soaked runway. – Martin James Jul 17 '15 at 8:42
• @MartinJames, How about differential braking (+ the rudder) ? This is possible with electronic control logics on modern airliners. – Eric Leibenguth Jul 17 '15 at 8:47
• I would also make the comment that it seems to me (as an enthusiast only) that conventional landing gears would refer to tricycle, since the vast majority of aircraft (at least commercial) are that style vs tail dragger. – CGCampbell Jul 17 '15 at 11:33
• @CGCampbell: Conventional landing gear came first. When tricycle landing gear was first introduced, its acceptance was slower than it might have been, because tail wheel aircraft were considered superior for rough, unpaved runways - which describes many more airports then than today. What you suggest makes some sense except by trying to rename the configuration you are mucking around with tradition. Pilots learn early what 'conventional' and 'tricycle' means with regard to landing gear. Since this nomenclature is clear for pilots, what problem exactly are you trying to solve? – Skip Miller Jul 18 '15 at 13:52

Short answer: Yes. Not one, but several. A taildragger configuration for modern airliners comes with several disadvantages:

• Visibility during taxiing is much worse.

Visibility while taxiing is a safety-relevant issue (Picture source)

• Braking hard will result in a headstand. And with today's landing speeds, braking hard is needed if you want to fly from standard length runways. Carrier-borne aircraft were the first to feel this consequence of increasing landing speeds, so they converted first to tricycle gears.

That is what is colloquially called a "headstand" (Picture source)

• Loading and unloading will become more complicated. The current way of sliding containers manually on a flat deck would need to be replaced by internal winches pulling the containers up the ramp to the door.
• Drag during ground roll is much higher as long as tail lift is not sufficient to get the tail up. Take-off distances would also become longer.

In short, it comes down to minimizing field lengths and increasing safety.

Who says there are no taildragger airliners? (Picture source)

• @EricLeibenguth: All your points are valid. My preference is, however, for the most simple solution: Eyeball Mk I and glass. Cameras can get smudged, cables can break, connectors can corrode, electricity can fail. Also, the jacking-up at the ramp needs either ground equipment, or needs to be carried with the aircraft, reducing the weight advantage of a taildragger gear. The less external devices you need, the better. This is less of an issue in the first world, but if you operate in Africa or SE Asia, it certainly is. Drag: The taildragger has a net disadvantage that cannot be discussed away. – Peter Kämpf Jul 17 '15 at 13:51
• @J...: no. It will tip because of the torque of the braking, which exists only if the force is applied away from the center of mass. If the braking has no torque, it won't tip. – njzk2 Jul 17 '15 at 14:48
• @njzk2: No, you can use wheel brakes with a taildragger, just not as hard as with a tricycle gear. – jamesqf Jul 17 '15 at 18:52
• @DavidRicherby: You're right, but I couldn't resist. But still: The downward angle straight ahead is -20°, and pitching the fuselage up like the MD-11 above reduces this to -8°. Given that the pilot now sits much higher, he cannot see the ground for the next 80 - 100 m ahead of him (compared to maybe 20 m with a tricycle gear). This is still significant. – Peter Kämpf Jul 17 '15 at 20:44
• Here's more info on that tipped back Gemini Cargo plane, including more pictures. – Johnny Jul 17 '15 at 20:50

I don't think there is a reason they can't have conventional landing gear (tail wheel). But there are simply many advantages to tricycle landing gear:

• Aircraft with tricycle landing gear is directionally stable and therefore easier to control especially with cross-wind.
• Aircraft with tricycle landing gear has level attitude on the ground, which provides:
• Good visibility during taxiing and take-off and landing runs. Many tail-draggers have no forward visibility during taxiing!
• Since the main gear is aft of centre of gravity, aircraft with tricycle landing gear are less prone to bouncing on touch-down.

Conventional gear has less drag when it is non-retractable, but airliners all have retractable landing gear. The only other advantage is lower weight (the tail-wheel is lighter than nose-wheel), but that difference is not worth all the disadvantages for airliners.

Other answers have given all the good reasons you need, but there is one more that should not be discounted:

In a plane with conventional landing gear, when on the ground, the fuselage is standing at a angle to the ground that is not insignificant.

This means that passengers will have to walk uphill when boarding from the rear door or downhill when boarding from the front door. Same issue when disembarking, of course.

You can try this if you get the chance to visit a DC-3, of which quite a few are still flying with passengers (although the large majority are effectively run as museum pieces, many are still airworthy). A (hypothetical) modern airliner would probably be longer than the DC-3, and the effect hence presumably less pronounced, but still very real.

The effect of the difficulties of such a sloping aisle would be longer turn-around times (and short turn-arounds are the holy grail of low-cost operators), which would have to be offset by equal savings generated by the conventional landing gear.

• Not just longer turnaround times, but also safety issues. If a passenger slips and falls you would get a cascade effect that could injure several other pax. Rollaboards, especially spinners with their four free-spinning casters, would compound the effect. – Jamie Hanrahan Jul 17 '15 at 13:51
• @JamieHanrahan, the "cascade effect" I thought of was the lawsuits filed by passengers, especially in the US. Also, is Rollaboards a rolling suitcase? – FreeMan Jul 17 '15 at 13:55
• "Rollaboard" refers to a rolling bag that's small enough to be a carry-on. – Jamie Hanrahan Jul 17 '15 at 13:59
• @RickBrant Ah it's not rolla-board, it's roll-aboard! – yo' Sep 19 '17 at 21:32
• "rollaboard" has 107,000 Google hits, "roll-aboard" has 38,000. I agree that "roll-aboard" makes more sense. (I don't believe anybody wrote "rolla-board".) – Jamie Hanrahan Sep 20 '17 at 9:52

No-one has mentioned jet blast so far.

When a jet liner is starting up, taxiing and accelerating along the runway prior to rotation, its exhaust gases are directed to the rear.

If they were angled downwards, as would be the case with a tail-wheel configuration, the jet blast would rip up the runway and be deflected back at the aircraft itself. This could cause untold damage.

• Jetblast from C-5 engines has very literally "ripped up" tarmac in a few unfortunate instances, so with the right (wrong) combination of factors, I could see things getting beyond "damage" and fully into "ripping up." – Ralph J Jul 17 '15 at 19:08
• – David Richerby Jul 17 '15 at 21:23
• I think this is a very good point. Not only for the runway's sake, but also for performance: Prior to rotation, a whole component of the thrust vector is perpendicular to the trajectory, and is therefore plainly wasted. – Eric Leibenguth Jul 18 '15 at 9:43
• @FreeMan Durnit. Thanks for letting me know. For this one, the new URL is NL B734 Damaged During Engine Run Up (photos) (with title so people can find it next time the URL changes). – David Richerby Sep 19 '17 at 19:26
• @EricLeibenguth Speaking of engines, thanks to the nose wheel steering, jets can commonly taxi on one engine only, which has a fuel benefit, especially on busy airports will longish takeoff queues. – yo' Sep 19 '17 at 21:33

One of the reasons tricycle gears are popular are the fact that they help give plenty of propeller clearance. However, turbofans are by design normally smaller in diameter (They will accelerate a smaller volume of air to a higher velocity in comparison). Hence this is less of a concern. This would also imply that jet engines aligned with the aircraft body would be blasting the runway quite powerfully at full thrust, which would accelerate wear.

• How the plane is trimmed is independent of the type of the gear. It depends on how far the centre of lift is from the centre of gravity. Tail-draggers have wings further forward, since their main gear is ahead of CoG, but the trim can remain the same and the longer tail gives the elevator more leverage making it more efficient. – Jan Hudec Jul 17 '15 at 12:38
• @JanHudec Indeed, I was overthinking this; you are correct. – Thunderstrike Jul 18 '15 at 7:53

Once, all airliners were built as taildraggers. The most important reasons none are conventionally geared these days is simple. A taildragger has its center of gravity located behind the main wheels. Therefore, it is insanely easy to groundloop it. This is because taildraggers are not inherently directionally stable. This was not usually a problem when the pilot was ALWAYS expecting the tail to wander to either side on takeoff or landing roll. If a pilot got distracted or lazy and the tail wandered a bit too far and he was late correcting with rudder, then the plane would swing around in a wild unstoppable loop and often dig in a wingtip, which was not only embarrassing but often damaged the plane. The tricycle gear stopped all that. The new nosegear planes went where the pilot pointed them and stayed there pretty much automatically. The center of gravity was now in front of the main gear and so the groundloop became a thing of the past. Conventional gear is lighter, and allows shorter takeoffs since the plane naturally sits tail low by design, but the instability issue means that its just a no brainer that large powerful airliners will never again be designed with tailwheels...ever.

• All airliners were once taildraggers sounds like you're saying that, for example, the A380 was once a taildragger. Also, your statement on directional stability, while true for landings, is false for takeoffs. – Federico Feb 28 '16 at 7:28

It is perhaps worth looking at where the main (load-bearing) gear is located on today's airliners - bearing directly on the wing root, which is the structurally strongest part of the aircraft - and where it would be located on a taildragger conversion, considerably further forward.

Taildragger aircraft are universally built with a very forward CG, with both the wing and engines being moved forward to suit. This happened to be practical with piston-driven propellers, which mainly needed forward-facing mountings and were very heavy relative to the rest of the aircraft. The main gear was mounted forward of the CG, and often bearing directly on a wing spar which in turn supported the engines.

Imagine doing the same with an MD-80 pattern airliner, with both the engines and wing root towards the rear of the fuselage. It's then easy to see why tricycle gear is a natural fit for a modern design.

Every answer has some key points as to why airliners today SHOULDN'T have conventional landing gear... but it could be done despite the angle of the aircraft while on the ground (for loading/unloading cargo/passengers) or the drag, or the forward visibility while taxiing, or prop clearance (which wouldn't matter if we're talking about modern jet airliner designs)...

Putting aside safety concerns (prop clearance, stability, etc.) Comfort, loading and unloading concerns, practicality, expenses... Only focusing on why a modern airliner can't have a conventional landing gear... there is no physical reason, to my knowledge, as to why a modern airliner can't be configured as a tail-dragger.

The biggest reason why a modern airliner SHOULDN'T be configured this way... (which is a completely different question than why it CAN'T) would have to be the fact that the jet engines would need to be inline with the fuselage which means that until the tail of the aircraft generates enough lift to raise the tail (making the aircraft level with the ground) the jet engines thrust would be directed towards the ground and with jet engines becoming more and more powerful, this could cause a lot of damage to airport infrastructure and the aircraft itself and would put ground crews in an even more "danger close" proximity to the jet blast...

I'd also venture to say that it may become pretty unstable before it could reach rotation speeds (V1), and I have to wonder how the jet engines would effect the rest of the aircraft when they are spooled up to full power while the tail is still on the ground... I can imagine the engines wanting to stress the engine mounts to the point of some sort of failure whether the engines detach completely or twist the frame of the wings and/or fuselage, maybe even make the aircraft jump off of the ground or even flipping it over and in any case... causing the aircraft to become incapable of sustaining stable flight.

These factors, and more, make a conventional gear configuration completely invalid for a modern airliner. It could be done with enough capital for research and development that would have to change every preexisting design concept to date... reinventing the modern airliner to be something entirely different all together if it were to ever see flight while maintaining the standards and requirements (safety, performance, efficiency, production and operating costs... etc.) that our existing airliners must meet before being put on the market while being cost effective.