Making Aircraft Lighter

[JohnF]

How feasible would it be to make an aircraft that had no undercarriage?

 

For landing and takeoff it would make use of an undercarriage assembly that ran along the runway independent of any permanent connection to the aircraft.

 

When the plane took off the undercarriage would be left behind ready for the next plane to land and make use of it. The undercarriage would then take the plane to the gate for passengers to disembark etc.

 

It would save quite a bit of weight in an aircraft.

[Cap'n Refsmmat]

There have been several experimental aircraft with an undercarriage that was released as soon as the aircraft took off. I'm not quite sure if they reused the undercarriage, but it did save wait. The aircraft then landed on retractable skis.

 

The problem with a scheme with undercarriages mounted in the runway is that you have to make the system standardized and capable of handling the varying weights of aircraft. If you need to handle the new A380, you'd have to upgrade your whole undercarriage system. It would save weight in aircraft at the cost of complexity of the airport systems.

[insane_alien]

there are other ways to reduce weight than removing the advantages of retractable undercarriage systems. one example is, don't paint them. this reduces the weight by quite a bit. you can always look at using lighter fluids in the hydraulics. ways of making the various alloy lighter. using a wireless control system would cut out the need for a LOT of cabling in the aircraft.

 

this can all be done now and doesn't add the complexities of training pilots to land on a platform that they can't even see. also, how would this hold up in foul weather, planes move around a lot then. and emergency landings suddenly become a lot more dangerous.

 

and as capn said, they would need to be able to be used on everything from a cessna to the A380.

 

not an easy thing to do.

[JohnF]

It would save weight in aircraft at the cost of complexity of the airport systems.

 

Clearly it would cost more. But if there was a method of leaving the aircraft at the gate or in a hangar without the undercarriage staying with the aircraft then each airport should only need 3 or 4 units for each aircraft type; plus any emergency requirement that was deemed necessary.

 

Initially you would introduce it for a new type of plane, carrying lots more passengers on very selected routes. The undercarriage would have to be free moving rather than using rails etc. so that the runway didn't need to be changed. If you had 8 aircraft flying between two airports then you may only need 6 undercarriage units, provided by the aircraft manufacturer or airline.

 

Eventually as new aircraft were designed to use the system they would either make use of existing undercarriage designs or introduce a new one. You could end up with just 6 undercarriage sizes that would accommodate all aircraft designed to make use of them.

 

It would have to be an evolutionary process however it came about.

 

The thing is, does the aircraft need landing gear at any other time. If it's going to make an emergency landing in a field for example, where there would be no undercarriage waiting, would it really make any difference that it had to land on its belly?

 

How would passengers feel about such aircraft?

[JohnF]

there are other ways to reduce weight than removing the advantages of retractable undercarriage systems. one example is, don't paint them. this reduces the weight by quite a bit. you can always look at using lighter fluids in the hydraulics. ways of making the various alloy lighter. using a wireless control system would cut out the need for a LOT of cabling in the aircraft.

 

this can all be done now and doesn't add the complexities of training pilots to land on a platform that they can't even see. also, how would this hold up in foul weather, planes move around a lot then. and emergency landings suddenly become a lot more dangerous.

 

and as capn said, they would need to be able to be used on everything from a cessna to the A380.

 

not an easy thing to do.

 

I would expect the pilot to land the aircraft as he does now. The undercarriage would just accelerate up to, and maintain speed and position with the aircraft as it touched down.

 

As for emergency landings. You just don't tell the undercarriage it's an emergency so it doesn't panic

[Cap'n Refsmmat]

I see what you mean.

 

But, one problem. How does the aircraft land? Does it rendezvous with the landing gear upon landing?

[Cap'n Refsmmat]

Ah, didn't see that post.

 

It's still a difficult maneuver to manage. You're introducing the possibility that the undercarriage might not connect properly, and you also have to manage to make a set of wheels capable of accelerating to 180mph and maneuver rapidly to dock with an aircraft. It'd need its own radar system and all that.

[swansont]

I would expect the pilot to land the aircraft as he does now. The undercarriage would just accelerate up to, and maintain speed and position with the aircraft as it touched down.

 

As for emergency landings. You just don't tell the undercarriage it's an emergency so it doesn't panic

 

And if it's an emergency landing not at a runway at a big commercial airport?

 

It seems like you've added some of the fun of mid-air refueling to the landing.

[JohnF]

I see what you mean.

 

But, one problem. How does the aircraft land? Does it rendezvous with the landing gear upon landing?

 

I would expect that the plane would make a normal approach. The landing gear would be waiting at the end of the runway and start to accelerate as the plane came in. The pilot would land as though he had normal undercarriage. He can't see the wheels anyway. From the pilots point of view he's just landing on the runway.

 

From an engineering point of view it makes sense because it is more efficient. However, could such an undercarriage be made to both achieve the speed required and maintain position with the aircraft, plus all the other problems that would need to be overcome?

 

If, on the other hand, passengers would find such an arrangement unacceptable then it's no good to start with.

[Cap'n Refsmmat]

As swansont said, you're making it as risky as mid-air refueling. If you miss the landing gear (or it misses you), you're in for a fun ride. I'm guessing the reliability of that system couldn't match the reliability of just having wheels.

[JohnF]

And if it's an emergency landing not at a runway at a big commercial airport?

 

It seems like you've added some of the fun of mid-air refueling to the landing.

 

That's a very valid point and may well be all that's required to knock such an idea on its head. But there are aircraft out there at the moment that can only land on certain runways, so it's a risk that is not considered too great even now.

 

What other advantages could be achieved without including the undercarriage in an aircraft?

 

The wing space used could carry more fuel. The fuselage could carry more cargo. Could the belly of the plane be made more able to withstand an emergency landing without undercarriage. That alone would be an advantage for landing in a field where undercarriage may be useless anyway.

[JohnF]

Let's forget the undercarriage altogether

 

We have a big tunnel with a fan at the end providing sufficient air throughput to maintain flight. The aircraft flies in to the tunnel until its relative speed with the tunnel is zero; though still flying through the air stream created by the fan.

 

Jacks etc. move out from the tunnel to fix the aircraft in place whilst the aircraft engines and tunnel fan are shut down.

 

For take off the process is reversed but the fan at the front is lowered away whilst a fan at the back, where the aircraft entered, is raised in to place to suck the air through the tunnel to create lift.

 

No wheels required

[Klaynos]

That would take ENOURMOSE amounts of energy compared to a normal landing...

 

Not to mention the difficulties of flying into a tunnel...

[JohnF]

That would take ENOURMOSE amounts of energy compared to a normal landing...

 

Not to mention the difficulties of flying into a tunnel...

 

But I bet it would be very exciting.

[Pangloss]

I'd try it!

[swansont]

Let's forget the undercarriage altogether

 

We have a big tunnel with a fan at the end providing sufficient air throughput to maintain flight. The aircraft flies in to the tunnel until its relative speed with the tunnel is zero; though still flying through the air stream created by the fan.

 

Jacks etc. move out from the tunnel to fix the aircraft in place whilst the aircraft engines and tunnel fan are shut down.

 

For take off the process is reversed but the fan at the front is lowered away whilst a fan at the back, where the aircraft entered, is raised in to place to suck the air through the tunnel to create lift.

 

No wheels required

 

And your turnaround time for the next aircraft is going to be less than the ~3 minutes from landing on a runway?

[JohnF]

And your turnaround time for the next aircraft is going to be less than the ~3 minutes from landing on a runway?

 

Hey, never mind the expense. We'll have one for every gate.

 

Checked what the biggest wind tunnel is; it's at NASA's Ames Research Center and is 80 feet by 100 feet so perhaps the shared undercarriage is better until one of you totaly crushes the idea.

 

By the way, it's a bit harsh comparing it to mid-air refueling.

 

Two vehicles maintaining a relative position in an unstable three dimensional space, whilst keeping local pitch, roll and yaw under control, and dangling a long fuel pipe to make contact with a small target. And trying to decide whether it will be smoked salmon of venison for lunch.

 

Don't think that's much like three vehicles maintaining a two dimensional position on a hard and stable surface with another fast moving object.

 

But I could be wrong; I've never flown an aircraft.

[Sisyphus]

Just weigh the pros and cons:

 

PROS:

*minor reduction in weight for aircraft

 

CONS:

*hideously expensive upgrades to all airports, everywhere

*aircraft that can't land anywhere without said upgrade

*one more major thing which can (and must not) go wrong in takeoffs and landings

 

I don't think it's worth it.

[Klaynos]

What this first reminded me of.

 

http://www.fanderson.org.uk/epguides/tbirdseg1.html#Episode%20One

 

Thunderbirds first ever episode.

[JohnF]

What this first reminded me of.

 

http://www.fanderson.org.uk/epguides/tbirdseg1.html#Episode%20One

 

Thunderbirds first ever episode.

 

Good episode that. See, it does work

 

What made me think about it was that my seven year old son did a number of drawings showing how vehicles moved. He explained each one to me in great detail. He came to a drawing with an aeroplane and explained how you could tell it was flying because there were no wheels to see. Then he turned the page and showed me the wheels and explained how the aircraft landed on them. If he'd been a bit older I'd have probably got him to put his idea on here, so I did it instead. He may have got the idea from Thunderbirds though as we have all the episodes and he's watched them all.

 

Sisyphus:

PROS:

*minor reduction in weight for aircraft

Would require a proper assessment by an aircraft designer to evaluate this. It may be minor or it may be significant. I have no figures, do you?

 

CONS:

*hideously expensive upgrades to all airports, everywhere

Introducing new road vehicles to airports?

 

*aircraft that can't land anywhere without said upgrade

No upgrade, just new aircraft at selected routes; see post 4. There's no need to take the wheels off an aircraft that has them.

 

*one more major thing which can (and must not) go wrong in takeoffs and landings

Valid point. Better cancel fly by wire then. This would come under risk analysis and would probably have some redundancy built in. Rather than three undercarriage units waiting for the aircraft there would be a fourth, backup unit too.

 

I don't think it's worth it.

But then are any of us on here qualified evaluate it?

 

It all depends on how much is saved in aircraft manufacture, running and maintenance costs against costs to build remote undercarriage, maintain and operate them. This will give an idea of how much can be spent in development. Then a risk analysis is required to determine if the system will have any effect on aircraft and passenger losses. As per post 11 it may afford an opportunity to increase the aircraft strength. For example, it may be possible to build an aircraft that can stay afloat indefinitely since there would be no openings for the undercarriage.

 

It would be better to think about the technical hurdles that have to be overcome.

Accelerating the undercarriage units up to 180 knots in sufficient time; would a pre-runway would be needed?

Maintaining position with the aircraft at speed; is radio used or an optical system?

Could a fast moving undercarriage make adjustments at the same rate wind sheer and gusting could shift the aircrafts position?

[cessna7686]

This is an interesting idea, but realistically I don't think it could ever work out. My first thought is that the public's reaction to flying on a plane that has no landing gear would be pretty negative. Even if it was proven safe there are already so many people who are scared of flying that I think the public wouldn't accept it. People have mentioned emergency landings on here and how it might be better to not have a landing gear when landing in a field, but what about the times when aircraft can perform an emergency landing on an open stretch of highway. This probably wouldn't happen with a plane like the A380 but it has happened for smaller aircraft. In that case it would defenitely be safer and more cost effective to land with the gears down. One benefit I could see is that it has the potential to reduce turn around time at the gate since it would eliminate the break cooling requirements for the airlines, but that would probably only effect smaller aircraft which have less passengers to load.

[John Cuthber]

Strictly speaking I'm not sure we are talking about "aircraft that can't land anywhere without said upgrade"

We are talking about aircracft that can land at any big airport once.

I understand that, in an emergency, it is possible to land big aircraft "safely" without the undercarriage. You get the airport to lay down a big mat of fire- fighting foam and skid to a halt in that.

I don't see this idea catching on anytime soon.

[Klaynos]

Surely if this was feasible in situations where one gear does not come down they would currently have a similar system?

[GutZ]

You could just...you know find different material to use....

[insane_alien]

You could just...you know find different material to use....

 

this is currently the main focus. lighter materials. its a far easier challenge than removing very necessary bits.

 

other areas being researched are more efficient engines, designs with less drag(blended body/wing designs) and a couple of others.